Concrete Jacking Experts Crystal Lake

Concrete Jacking Experts Crystal Lake

Driveway Leveling Crystal Lake

You'll find their technique fascinating. This visual proof can give you a clear idea of what to expect. Let's explore the potential changes on the horizon and how they might affect you in the long run.

Residential Driveway Leveling

  1. No-Dig Concrete Repair
  2. Polyjacking Services
  3. Foundation Repair
  4. Concrete Slab Stabilization
  5. Concrete Crack Repair
  6. Cracked Driveway Repair
  7. Fast Dry Concrete Lifting
  8. Sinking Slab Correction
  9. Local Concrete Leveling Services
  10. Concrete Raising Contractors
  11. Backyard Patio Repair
  12. Concrete Raising Reviews
  13. Concrete Floor Repair
  14. Concrete Sinking
  15. Mudjacking
  16. Concrete Leveling
  17. Concrete Patching Services
  18. Fix Uneven Driveway Crystal Lake
  19. Concrete Grinding
You won't be waiting around for days to see results. Learn more about Concrete Jacking Experts Crystal Lake here
Heavy rains can erode soil, while droughts can cause it to shrink. Learn more about Expert Concrete Lifting Services in Crystal Lake, Illinois here. It's not merely about the visual appeal; it's a safety concern too. Quality workmanship is a hallmark of Acme's service.
As you dig deeper, you'll discover that the Smart Lift system represents just the beginning of a surge in high-tech solutions coming your way. But how exactly do they achieve these remarkable transformations, and what makes their method stand out from traditional repair techniques? This traditional technique involves pumping a mixture of water, soil, and cement beneath settled concrete to raise it.
They'll set a date to begin work, always aiming to minimize disruption to your daily routine. This speed doesn't compromise its strength; in fact, it ensures a stronger bond with the existing concrete, enhancing its stability and longevity. They appreciated not only the high-quality work but also the way our team took the time to explain the process, ensuring they understood every step. Slabjacking

This quality prevents additional sinking and reduces the risk of future repairs. Driveway Leveling Crystal Lake Well, it's simple. This approach not only saves you money but also time, as repair work is typically completed much faster than full replacements. They understand the stress that comes with repair projects and strive to make the process as smooth as possible. Concrete Pressure Grouting After securing your investment with Acme Concrete's repair services, it's crucial to embrace maintenance practices that'll prolong the durability of your concrete.

Next, we drill small, strategically placed holes into the sunken slab. With every repair, they're not just fixing a crack or leveling a slab; they're enhancing the visual harmony of the surroundings. This proactive approach ensures you're not caught off guard by the cost and can budget accordingly for your concrete repair needs. The entire process is quick, often completed in just a few hours, and the disruption to your property is minimal.

Sensors embedded within concrete will monitor its health in real-time, alerting you to potential issues before they become major problems. The polyurethane foam used in this process is lighter on the environment, requiring less material and reducing the overall carbon footprint of your repair project. Acme Concrete's advanced repair system enhances safety by addressing potential hazards before they escalate. In most cases, the entire process is completed in just a few hours, minimizing disruption to your daily routine.

Acme Concrete's pricing structure takes into account the severity of the concrete damage, the square footage of the area needing repair, and any special considerations unique to your project. However, when you look at the long-term financial impact, the picture changes. Firstly, downtime is a critical factor for any business. You're kept in the loop throughout the entire process, with clear communication on timelines and any necessary adjustments.

Citations and other links

Top Rated Concrete Lifting Crystal Lake

Many homeowners face the challenge of aging concrete, which can significantly impact the safety and aesthetics of their property. You're not just fixing your concrete issues; you're doing so in a way that's mindful of the planet's health. These before and after snapshots not only highlight the aesthetic improvement but also underscore the importance of safety and accessibility enhancements provided by our concrete raising services. After our team worked their magic, he was amazed at the seamless finish. 'I wish I'd called Acme sooner. This can exacerbate the initial problem, leading to a vicious cycle of repairs.

Understanding the cause of sunken concrete is the first step towards finding a lasting solution and restoring your property's beauty and safety. You might wonder how it works. Most jobs can be completed in just a few hours, meaning you won't have to navigate around a lengthy construction site at your home. It's a win-win situation for both you and the planet.

Instead of replacing the entire slab, which can be both expensive and time-consuming, concrete raising offers a quicker, more affordable solution. Acme prides itself on fair pricing and top-notch service, so you can expect a competitive quote without any hidden fees. Opting for Acme Concrete's system not only serves your immediate needs but also plays a part in fostering a strong, vibrant community. They're professional, friendly, and extremely efficient.'These testimonials highlight just a fraction of the positive feedback Acme Concrete receives regularly. Settled Concrete Solutions

This is where Acme Concrete Raising & Repair steps in, offering a solution that not only enhances the beauty of Crystal Lake but also prioritizes your safety. This method stands out for its quick application and curing time, allowing you to address uneven concrete surfaces without significant downtime. Homeowners across Crystal Lake are enjoying smoother driveways, revitalized sidewalks, and sturdy patios, thanks to Acme's innovative approach. This means no odd color patches or visible signs of intervention.

Top Rated Concrete Lifting Crystal Lake
Concrete Lifting Contractor Near Me Crystal Lake

Concrete Lifting Contractor Near Me Crystal Lake

This system isn't about patchwork that screams “repair”; it's about a seamless integration that makes your concrete appear as good as new.

Chicagoland Concrete Solutions

  1. Helical Piers
  2. No-Dig Concrete Repair
  3. Polyjacking Services
  4. Foundation Repair
  5. Concrete Slab Stabilization
  6. Concrete Crack Repair
  7. Cracked Driveway Repair
  8. Fast Dry Concrete Lifting
  9. Sinking Slab Correction
  10. Local Concrete Leveling Services
  11. Concrete Raising Contractors
  12. Backyard Patio Repair
  13. Concrete Raising Reviews
  14. Concrete Repair Estimate Crystal Lake
  15. Chicagoland Concrete Solutions
  16. Concrete Lifting Near Me
  17. Porch Leveling
  18. Concrete Pressure Grouting
  19. Crystal Lake Foundation Contractors
  20. Precision Concrete Leveling
Having explored the challenges of aging concrete, let's now look at how Acme Concrete's innovative repairs offer a sustainable solution for Crystal Lake homeowners. Looking ahead, the future of concrete raising appears increasingly promising thanks to innovative technologies like the Smart Lift system.

Driveway Leveling Crystal Lake

  1. Fast Dry Concrete Lifting
  2. Sinking Slab Correction
  3. Local Concrete Leveling Services
  4. Concrete Raising Contractors
  5. Backyard Patio Repair
  6. Concrete Raising Reviews
  7. Patio Leveling
  8. Residential Concrete Services
  9. Residential Driveway Leveling
  10. Concrete Repair Estimate Crystal Lake
  11. Chicagoland Concrete Solutions
  12. Concrete Lifting Near Me
  13. Porch Leveling
  14. Concrete Pressure Grouting
  15. Crystal Lake Foundation Contractors
  16. Precision Concrete Leveling
  17. Concrete Floor Repair
By choosing their innovative repair services, you're making a smart financial decision that benefits your wallet both immediately and in the long term.

The integration of digital tools and IoT (Internet of Things) into concrete raising will enable real-time monitoring of conditions, predicting potential issues before they become problems. Concrete Repair Estimate Crystal Lake It's quick and minimally invasive. What sets Acme apart is their commitment to using environmentally friendly materials in their repairs.

The result?

Uneven Concrete Repair

  1. Foam Jacking
  2. Concrete Joint Sealing
  3. Concrete Leveling Companies
  4. Subgrade Stabilization
  5. Polyurethane Concrete Lifting
  6. Sidewalk Trip Hazard Fix
  7. Void Filling
  8. Affordable Slab Lifting Crystal Lake
  9. Driveway Settling Solutions
  10. Concrete Support Injection
  11. Sunken Concrete
  12. Driveway Void Repair
  13. Garage Apron Repair
  14. Slab Leveling Solutions
  15. Concrete Void Filling
  16. Quick Concrete Lifting Service
  17. Driveway Repair
  18. Garage Floor Lifting
  19. Crystal Lake Mudjacking Company
  20. Concrete Surface Repair
For residents of Crystal Lake, embracing the Smart Lift system offers a significant upgrade in addressing uneven concrete with minimal disruption and lasting results. They don't just patch problems; they provide lasting solutions.

Firstly, you've got the local coffee shop on Main Street, whose uneven front walkway posed a trip hazard for customers. Let's dive into how the Smart Lift System raises your concrete with its innovative process. This technique isn't only efficient but also cost-effective, saving you from the hassle and expense of complete slab replacement.

Concrete Jacking Near Me Crystal Lake

You'll be amazed at how quickly and quietly the process unfolds, often in mere hours. It requires a comprehensive approach that not only fixes the damage but also strengthens the structure against future wear. You're not just saving money on the initial service; you're also minimizing disruption to your home or business. With Acme Concrete, you're investing in a safer tomorrow, today. Once the lifting is done, the drilled holes are filled and sealed, making them barely noticeable.

When you choose us, you're opting for a team that's committed to excellence at every turn.

Slabjacking

  • Crystal Lake Foundation Contractors
  • Precision Concrete Leveling
  • Concrete Floor Repair
  • Concrete Sinking
  • Mudjacking
  • Concrete Leveling
  • Concrete Patching Services
  • Fix Uneven Driveway Crystal Lake
  • Concrete Grinding
  • Concrete Raising Experts
  • Water-Resistant Foam Injection
  • Garage Slab Settlement
  • Local Concrete Repair Crystal Lake
  • Sustainable Concrete Repair
  • Concrete Contractors Crystal Lake
  • Concrete Lifting Specialists
  • Interior Floor Lifting
Having seen the impressive results of modern concrete raising techniques, it's crucial you select a contractor who's not only skilled but also well-versed in these advanced methods. In most cases, the areas are ready to use the same day. The foam cures quickly, meaning you won't have to wait days to use your walkway again.

With years of hands-on experience, we've honed our skills to provide not just quick fixes, but long-lasting solutions that stand the test of time. This could involve repair, resurfacing, or sometimes a combination of techniques aimed at extending the life of your concrete without the need for a complete replacement.

Uneven Concrete Repair

  • Concrete Surface Repair
  • Slab Foundation Repair
  • Level Concrete Surfaces
  • Concrete Lifting
  • Illinois Concrete Repair
  • Crystal Lake Concrete Experts
  • Concrete Driveway Maintenance
  • Helical Piers
  • No-Dig Concrete Repair
  • Polyjacking Services
  • Foundation Repair
  • Concrete Slab Stabilization
  • Concrete Crack Repair
  • Cracked Driveway Repair
  • Fast Dry Concrete Lifting
  • Sinking Slab Correction
  • Local Concrete Leveling Services
During the inspection, we'll assess the extent of the damage and determine the best course of action. Moreover, the Smart Lift System is kinder to the environment.

Settled Concrete Solutions

  • Concrete Raising Contractors
  • Backyard Patio Repair
  • Concrete Raising Reviews
  • Concrete Pressure Grouting
  • Crystal Lake Foundation Contractors
  • Precision Concrete Leveling
  • Concrete Floor Repair
  • Concrete Sinking
  • Mudjacking
  • Concrete Leveling
  • Concrete Patching Services
  • Fix Uneven Driveway Crystal Lake
  • Concrete Grinding
  • Concrete Raising Experts
  • Water-Resistant Foam Injection
  • Garage Slab Settlement


Your satisfaction drives us, and these successful projects are a testament to our dedication. Unlike traditional methods that often involve digging up and replacing entire sections, Acme's system focuses on precision lifting and stabilization. Acme's Smart Lift System ensures your commercial spaces look their best, contributing to a positive image of your business. The root of the problem often lies beneath the surface.

Concrete Jacking Near Me Crystal Lake
Patio Lifting Services Crystal Lake
Patio Lifting Services Crystal Lake

Then there's Mike, who'd been tripping over his uneven driveway for months. So, if you're facing sinking concrete, Acme's Smart Lift could be the smart solution you're looking for. Next, we use the latest technology to lift and stabilize your sunken concrete. After Acme's intervention, not only was the driveway raised to its original level, but the homeowner saved a significant amount over complete replacement costs. Unlike traditional mudjacking, which uses a heavier material that can further strain the already weak soil beneath your concrete, polyurethane foam is lightweight.
You've probably seen sidewalks or driveways marred by cracks, uneven sections, and discoloration, detracting from a home's curb appeal. Reviews and testimonials can be a goldmine of information, revealing not just the quality of work but also the company's reliability and customer service. You'll appreciate that polyurethane foam sets and cures much faster than the mix used in mudjacking, allowing you to use the treated areas sooner-often within hours.

Precision Concrete Leveling

  1. Sunken Concrete
  2. Driveway Void Repair
  3. Garage Apron Repair
  4. Slab Leveling Solutions
  5. Concrete Void Filling
  6. Quick Concrete Lifting Service
  7. Driveway Repair
  8. Garage Floor Lifting
  9. Crystal Lake Mudjacking Company
  10. Concrete Surface Repair
  11. Slab Foundation Repair
  12. Level Concrete Surfaces
  13. Concrete Lifting
  14. Illinois Concrete Repair
  15. Crystal Lake Concrete Experts
  16. Concrete Driveway Maintenance
  17. Helical Piers
After the assessment, you'll receive a detailed proposal that outlines the scope of work, the timeline, and the cost.
Addressing walkway repairs promptly can save you money in the long run, preventing more extensive and costly damage.

Precision Concrete Leveling

  1. Concrete Raising Contractors
  2. Backyard Patio Repair
  3. Concrete Raising Reviews
  4. Concrete Crack Injection
  5. Concrete Foundation Settlement
  6. Structural Slab Lifting
  7. Concrete Expansion Joint Repair
  8. Patio Leveling
  9. Residential Concrete Services
  10. Residential Driveway Leveling
  11. Concrete Repair Estimate Crystal Lake
  12. Chicagoland Concrete Solutions
  13. Concrete Lifting Near Me
  14. Porch Leveling
  15. Concrete Pressure Grouting
You'll see cracked, sunken slabs turn into seamless, stable paths. They use state-of-the-art equipment and the latest techniques to ensure the job is done right the first time. They're constantly exposed to water and chemicals, contributing to deterioration. Read more about Concrete Jacking Experts Crystal Lake here
This cutting-edge method offers a plethora of benefits, from minimal disruption to the environment to extended longevity of the concrete surfaces.

Crystal Lake Foundation Contractors

  • Void Filling
  • Affordable Slab Lifting Crystal Lake
  • Driveway Settling Solutions
  • Concrete Support Injection
  • Sunken Concrete
  • Driveway Void Repair
  • Garage Apron Repair
  • Slab Leveling Solutions
  • Concrete Void Filling
  • Quick Concrete Lifting Service
  • Driveway Repair
  • Garage Floor Lifting
  • Crystal Lake Mudjacking Company
  • Concrete Surface Repair
  • Slab Foundation Repair
  • Level Concrete Surfaces
  • Concrete Lifting
  • Illinois Concrete Repair
  • Crystal Lake Concrete Experts
  • Concrete Driveway Maintenance
Acme Concrete's unmatched expertise in the industry sets them apart as the go-to for Crystal Lake's repair needs.

Concrete Foundation Settlement

  1. Concrete Joint Sealing
  2. Concrete Leveling Companies
  3. Subgrade Stabilization
  4. Polyurethane Concrete Lifting
  5. Sidewalk Trip Hazard Fix
  6. Void Filling
  7. Affordable Slab Lifting Crystal Lake
  8. Driveway Settling Solutions
  9. Concrete Support Injection
  10. Sunken Concrete
  11. Driveway Void Repair
  12. Garage Apron Repair
  13. Slab Leveling Solutions
  14. Concrete Void Filling
  15. Quick Concrete Lifting Service
  16. Driveway Repair
  17. Garage Floor Lifting
  18. Crystal Lake Mudjacking Company
As we explore how Acme Concrete transforms troubled slabs into stable surfaces, you'll find compelling reasons to consider this method for your own needs. When it comes to concrete repair, driveways, walkways, and patios are among the most frequently serviced areas.

Concrete Leveling and Raising Crystal Lake

Our team of experts conducts thorough inspections to identify potential hazards before they become bigger issues. That's why we're committed to providing Crystal Lake with services that don't just look good but significantly reduce the risk of trips and falls. Traditional repair methods, like slab replacement or mudjacking, can be invasive, time-consuming, and not always long-lasting. Moreover, the industry's focus on sustainability is driving the development of green concrete repair materials. This rapid turnaround minimizes downtime for businesses and inconvenience for homeowners, making it a more practical choice for busy lives.
It's perfect for a wide range of commercial applications, from warehouse floors to parking lots, sidewalks, and more. When you choose Acme Concrete, you're not just getting a service; you're getting peace of mind, knowing you've entrusted your property to the best in the business. It's about making informed decisions that reflect your values and the kind of world you want to live in. Let's help you say goodbye to those safety concerns and hello to a beautified space.
First, you'll need to get in touch with their team. Beyond enhancing safety, the advanced repair system dramatically improves the aesthetic appeal of your concrete surfaces. If you've noticed sinking driveways, walkways, or patios around your home, you're witnessing a common issue that affects many properties. Not only does it save you money, but it also significantly reduces the time involved in making your concrete surfaces safe and appealing again.
With Acme, you're just a few steps away from restoring your concrete and peace of mind. You're probably wondering how they manage this feat and what sets them apart from the competition. The materials used are less harmful to the environment, helping you reduce your carbon footprint while maintaining the aesthetics and safety of your property. Stay with us to uncover the intricacies of this process and the remarkable transformations that have convinced locals of its merits. Structural Slab Lifting

Explore Concrete Jacking Experts Crystal Lake here Concrete Foundation Settlement

Structural Slab Lifting

  • Concrete Sinking
  • Mudjacking
  • Concrete Leveling
  • Concrete Patching Services
  • Fix Uneven Driveway Crystal Lake
  • Concrete Grinding
  • Concrete Raising Experts
  • Water-Resistant Foam Injection
  • Garage Slab Settlement
  • Local Concrete Repair Crystal Lake
  • Sustainable Concrete Repair
  • Concrete Contractors Crystal Lake
  • Concrete Lifting Specialists
  • Interior Floor Lifting
  • Foam Jacking
  • Concrete Joint Sealing
  • Concrete Leveling Companies
  • Subgrade Stabilization
  • Polyurethane Concrete Lifting
  • Sidewalk Trip Hazard Fix
Concrete Leveling and Raising Crystal Lake
Polyurethane synthesis: the urethane groups −NH−(C=O)−O− link the molecular units, resulting in a polymer consisting of an alternating chain of two monomers.
A kitchen sponge made of polyurethane foam

Polyurethane (/ËŒpÉ’liˈjÊŠÉ™rəˌθeɪn, -jʊəˈrÉ›θeɪn/;[1] often abbreviated PUR and PU) is a class of polymers composed of organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane does not refer to a single type of polymer but a group of polymers. Unlike polyethylene and polystyrene, polyurethanes can be produced from a wide range of starting materials, resulting in various polymers within the same group. This chemical variety produces polyurethanes with different chemical structures leading to many different applications. These include rigid and flexible foams, and coatings, adhesives, electrical potting compounds, and fibers such as spandex and polyurethane laminate (PUL). Foams are the largest application accounting for 67% of all polyurethane produced in 2016.[2]

A polyurethane is typically produced by reacting a polymeric isocyanate with a polyol.[3] Since a polyurethane contains two types of monomers, which polymerize one after the other, they are classed as alternating copolymers. Both the isocyanates and polyols used to make a polyurethane contain two or more functional groups per molecule.

Global production in 2019 was 25 million metric tonnes,[4] accounting for about 6% of all polymers produced in that year.

History

[edit]
Otto Bayer in 1952 demonstrating his creation

Otto Bayer and his coworkers at IG Farben in Leverkusen, Germany, first made polyurethanes in 1937.[5][6] The new polymers had some advantages over existing plastics that were made by polymerizing olefins or by polycondensation, and were not covered by patents obtained by Wallace Carothers on polyesters.[7] Early work focused on the production of fibers and flexible foams and PUs were applied on a limited scale as aircraft coating during World War II.[7] Polyisocyanates became commercially available in 1952, and production of flexible polyurethane foam began in 1954 by combining toluene diisocyanate (TDI) and polyester polyols. These materials were also used to produce rigid foams, gum rubber, and elastomers. Linear fibers were produced from hexamethylene diisocyanate (HDI) and 1,4-Butanediol (BDO).

DuPont introduced polyethers, specifically poly(tetramethylene ether) glycol, in 1956. BASF and Dow Chemical introduced polyalkylene glycols in 1957. Polyether polyols were cheaper, easier to handle and more water-resistant than polyester polyols. Union Carbide and Mobay, a U.S. Monsanto/Bayer joint venture, also began making polyurethane chemicals.[7] In 1960 more than 45,000 metric tons of flexible polyurethane foams were produced. The availability of chlorofluoroalkane blowing agents, inexpensive polyether polyols, and methylene diphenyl diisocyanate (MDI) allowed polyurethane rigid foams to be used as high-performance insulation materials. In 1967, urethane-modified polyisocyanurate rigid foams were introduced, offering even better thermal stability and flammability resistance. During the 1960s, automotive interior safety components, such as instrument and door panels, were produced by back-filling thermoplastic skins with semi-rigid foam.

In 1969, Bayer exhibited an all-plastic car in Düsseldorf, Germany. Parts of this car, such as the fascia and body panels, were manufactured using a new process called reaction injection molding (RIM), in which the reactants were mixed and then injected into a mold. The addition of fillers, such as milled glass, mica, and processed mineral fibers, gave rise to reinforced RIM (RRIM), which provided improvements in flexural modulus (stiffness), reduction in coefficient of thermal expansion and better thermal stability. This technology was used to make the first plastic-body automobile in the United States, the Pontiac Fiero, in 1983. Further increases in stiffness were obtained by incorporating pre-placed glass mats into the RIM mold cavity, also known broadly as resin injection molding, or structural RIM.

Starting in the early 1980s, water-blown microcellular flexible foams were used to mold gaskets for automotive panels and air-filter seals, replacing PVC polymers. Polyurethane foams are used in many automotive applications including seating, head and arm rests, and headliners.

Polyurethane foam (including foam rubber) is sometimes made using small amounts of blowing agents to give less dense foam, better cushioning/energy absorption or thermal insulation. In the early 1990s, because of their impact on ozone depletion, the Montreal Protocol restricted the use of many chlorine-containing blowing agents, such as trichlorofluoromethane (CFC-11). By the late 1990s, blowing agents such as carbon dioxide, pentane, 1,1,1,2-tetrafluoroethane (HFC-134a) and 1,1,1,3,3-pentafluoropropane (HFC-245fa) were widely used in North America and the EU, although chlorinated blowing agents remained in use in many developing countries. Later, HFC-134a was also banned due to high ODP and GWP readings, and HFC-141B was introduced in early 2000s as an alternate blowing agent in developing nations.[8]

Chemistry

[edit]

Polyurethanes are produced by reacting diisocyanates with polyols,[9][10][11][12][13][14] often in the presence of a catalyst, or upon exposure to ultraviolet radiation.[15] Common catalysts include tertiary amines, such as DABCO, DMDEE, or metallic soaps, such as dibutyltin dilaurate. The stoichiometry of the starting materials must be carefully controlled as excess isocyanate can trimerise, leading to the formation of rigid polyisocyanurates. The polymer usually has a highly crosslinked molecular structure, resulting in a thermosetting material which does not melt on heating; although some thermoplastic polyurethanes are also produced.

 
Carbon dioxide gas and urea links formed by reacting water and isocyanate

The most common application of polyurethane is as solid foams, which requires the presence of a gas, or blowing agent, during the polymerization step. This is commonly achieved by adding small amounts of water, which reacts with isocyanates to form CO2 gas and an amine, via an unstable carbamic acid group. The amine produced can also react with isocyanates to form urea groups, and as such the polymer will contain both these and urethane linkers. The urea is not very soluble in the reaction mixture and tends to form separate "hard segment" phases consisting mostly of polyurea. The concentration and organization of these polyurea phases can have a significant impact on the properties of the foam.[16]

The type of foam produced can be controlled by regulating the amount of blowing agent and also by the addition of various surfactants which change the rheology of the polymerising mixture. Foams can be either "closed-cell", where most of the original bubbles or cells remain intact, or "open-cell", where the bubbles have broken but the edges of the bubbles are stiff enough to retain their shape, in extreme cases reticulated foams can be formed. Open-cell foams feel soft and allow air to flow through, so they are comfortable when used in seat cushions or mattresses. Closed-cell foams are used as rigid thermal insulation. High-density microcellular foams can be formed without the addition of blowing agents by mechanically frothing the polyol prior to use. These are tough elastomeric materials used in covering car steering wheels or shoe soles.

The properties of a polyurethane are greatly influenced by the types of isocyanates and polyols used to make it. Long, flexible segments, contributed by the polyol, give soft, elastic polymer. High amounts of crosslinking give tough or rigid polymers. Long chains and low crosslinking give a polymer that is very stretchy, short chains with many crosslinks produce a hard polymer while long chains and intermediate crosslinking give a polymer useful for making foam. The choices available for the isocyanates and polyols, in addition to other additives and processing conditions allow polyurethanes to have the very wide range of properties that make them such widely used polymers.

Raw materials

[edit]

The main ingredients to make a polyurethane are di- and tri-isocyanates and polyols. Other materials are added to aid processing the polymer or to modify the properties of the polymer. PU foam formulation sometimes have water added too.

Isocyanates

[edit]

Isocyanates used to make polyurethane have two or more isocyanate groups on each molecule. The most commonly used isocyanates are the aromatic diisocyanates, toluene diisocyanate (TDI) and methylene diphenyl diisocyanate, (MDI). These aromatic isocyanates are more reactive than aliphatic isocyanates.

TDI and MDI are generally less expensive and more reactive than other isocyanates. Industrial grade TDI and MDI are mixtures of isomers and MDI often contains polymeric materials. They are used to make flexible foam (for example slabstock foam for mattresses or molded foams for car seats),[17] rigid foam (for example insulating foam in refrigerators) elastomers (shoe soles, for example), and so on. The isocyanates may be modified by partially reacting them with polyols or introducing some other materials to reduce volatility (and hence toxicity) of the isocyanates, decrease their freezing points to make handling easier or to improve the properties of the final polymers.

MDI isomers and polymer
MDI isomers and polymer

Aliphatic and cycloaliphatic isocyanates are used in smaller quantities, most often in coatings and other applications where color and transparency are important since polyurethanes made with aromatic isocyanates tend to darken on exposure to light.[page needed][18] The most important aliphatic and cycloaliphatic isocyanates are 1,6-hexamethylene diisocyanate (HDI), 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophorone diisocyanate, IPDI), and 4,4′-diisocyanato dicyclohexylmethane (H12MDI or hydrogenated MDI). Other more specialized isocyanates include Tetramethylxylylene diisocyanate (TMXDI).

Polyols

[edit]

Polyols are polymers in their own right and have on average two or more hydroxyl groups per molecule. They can be converted to polyether polyols by co-polymerizing ethylene oxide and propylene oxide with a suitable polyol precursor.[19] Polyester polyols are made by the polycondensation of multifunctional carboxylic acids and polyhydroxyl compounds. They can be further classified according to their end use. Higher molecular weight polyols (molecular weights from 2,000 to 10,000) are used to make more flexible polyurethanes while lower molecular weight polyols make more rigid products.

Polyols for flexible applications use low functionality initiators such as dipropylene glycol (f = 2), glycerine (f = 3), or a sorbitol/water solution (f = 2.75).[20] Polyols for rigid applications use higher functionality initiators such as sucrose (f = 8), sorbitol (f = 6), toluenediamine (f = 4), and Mannich bases (f = 4). Propylene oxide and/or ethylene oxide is added to the initiators until the desired molecular weight is achieved. The order of addition and the amounts of each oxide affect many polyol properties, such as compatibility, water-solubility, and reactivity. Polyols made with only propylene oxide are terminated with secondary hydroxyl groups and are less reactive than polyols capped with ethylene oxide, which contain primary hydroxyl groups. Incorporating carbon dioxide into the polyol structure is being researched by multiple companies.

Graft polyols (also called filled polyols or polymer polyols) contain finely dispersed styrene–acrylonitrile, acrylonitrile, or polyurea (PHD) polymer solids chemically grafted to a high molecular weight polyether backbone. They are used to increase the load-bearing properties of low-density high-resiliency (HR) foam, as well as add toughness to microcellular foams and cast elastomers. Initiators such as ethylenediamine and triethanolamine are used to make low molecular weight rigid foam polyols that have built-in catalytic activity due to the presence of nitrogen atoms in the backbone. A special class of polyether polyols, poly(tetramethylene ether) glycols, which are made by polymerizing tetrahydrofuran, are used in high performance coating, wetting and elastomer applications.

Conventional polyester polyols are based on virgin raw materials and are manufactured by the direct polyesterification of high-purity diacids and glycols, such as adipic acid and 1,4-butanediol. Polyester polyols are usually more expensive and more viscous than polyether polyols, but they make polyurethanes with better solvent, abrasion, and cut resistance. Other polyester polyols are based on reclaimed raw materials. They are manufactured by transesterification (glycolysis) of recycled poly(ethyleneterephthalate) (PET) or dimethylterephthalate (DMT) distillation bottoms with glycols such as diethylene glycol. These low molecular weight, aromatic polyester polyols are used in rigid foam, and bring low cost and excellent flammability characteristics to polyisocyanurate (PIR) boardstock and polyurethane spray foam insulation.

Specialty polyols include polycarbonate polyols, polycaprolactone polyols, polybutadiene polyols, and polysulfide polyols. The materials are used in elastomer, sealant, and adhesive applications that require superior weatherability, and resistance to chemical and environmental attack. Natural oil polyols derived from castor oil and other vegetable oils are used to make elastomers, flexible bunstock, and flexible molded foam.

Co-polymerizing chlorotrifluoroethylene or tetrafluoroethylene with vinyl ethers containing hydroxyalkyl vinyl ether produces fluorinated (FEVE) polyols. Two-component fluorinated polyurethanes prepared by reacting FEVE fluorinated polyols with polyisocyanate have been used to make ambient cure paints and coatings. Since fluorinated polyurethanes contain a high percentage of fluorine–carbon bonds, which are the strongest bonds among all chemical bonds, fluorinated polyurethanes exhibit resistance to UV, acids, alkali, salts, chemicals, solvents, weathering, corrosion, fungi and microbial attack. These have been used for high performance coatings and paints.[21]

Phosphorus-containing polyols are available that become chemically bonded to the polyurethane matrix for the use as flame retardants. This covalent linkage prevents migration and leaching of the organophosphorus compound.

Bio-derived materials

[edit]

Interest in sustainable "green" products raised interest in polyols derived from vegetable oils,[22][23][24] fatty acids,[25] lignin, sorbitol,[26] etc. These are mostly contributing to polyol part. There are attempts made to prepare isocyanate part using bio-derived material. However, as far as commercialization is concern, polyol part is more targeted being easy and required in more quantity than isocyanate part. Various oils used in the preparation polyols for polyurethanes include soybean oil, cottonseed oil, neem seed oil, algae oil,[27][28] and castor oil. Vegetable oils are functionalized in various ways and modified to polyetheramides, polyethers, alkyds, etc. Renewable sources used to prepare polyols may be fatty acids or dimer fatty acids.[29] Some biobased and isocyanate-free polyurethanes exploit the reaction between polyamines and cyclic carbonates to produce polyhydroxyurethanes.[30]

Chain extenders and cross linkers

[edit]

Chain extenders (f = 2) and cross linkers (f ≥ 3) are low molecular weight hydroxyl and amine terminated compounds that play an important role in the polymer morphology of polyurethane fibers, elastomers, adhesives, and certain integral skin and microcellular foams.

The elastomeric properties of these materials are derived from the phase separation of the hard and soft copolymer segments of the polymer, such that the urethane hard segment domains serve as cross-links between the amorphous polyether (or polyester) soft segment domains. This phase separation occurs because the mainly nonpolar, low melting soft segments are incompatible with the polar, high melting hard segments. The soft segments, which are formed from high molecular weight polyols, are mobile and are normally present in coiled formation, while the hard segments, which are formed from the isocyanate and chain extenders, are stiff and immobile. As the hard segments are covalently coupled to the soft segments, they inhibit plastic flow of the polymer chains, thus creating elastomeric resiliency. Upon mechanical deformation, a portion of the soft segments are stressed by uncoiling, and the hard segments become aligned in the stress direction. This reorientation of the hard segments and consequent powerful hydrogen bonding contributes to high tensile strength, elongation, and tear resistance values.[12][31][32][33][34] The choice of chain extender also determines flexural, heat, and chemical resistance properties.

The most important chain extenders are ethylene glycol, 1,4-butanediol (1,4-BDO or BDO), 1,6-hexanediol, cyclohexane dimethanol and hydroquinone bis(2-hydroxyethyl) ether (HQEE). All of these glycols form polyurethanes that phase separate well and form well defined hard segment domains, and are melt processable. They are all suitable for thermoplastic polyurethanes with the exception of ethylene glycol, since its derived bis-phenyl urethane undergoes unfavorable degradation at high hard segment levels.[10] Diethanolamine and triethanolamine are used in flex molded foams to build firmness and add catalytic activity. Diethyltoluenediamine is used extensively in RIM, and in polyurethane and polyurea elastomer formulations.

Table of chain extenders and cross linkers[35]
Compound type Molecule Mol.
mass
Density
(g/cm3)
Melting
pt (°C)
Boiling
pt (°C)
Hydroxyl compounds – difunctional molecules Ethylene glycol 62.1 1.110 −13.4 197.4
Diethylene glycol 106.1 1.111 −8.7 245.5
Triethylene glycol 150.2 1.120 −7.2 287.8
Tetraethylene glycol 194.2 1.123 −9.4 325.6
Propylene glycol 76.1 1.032 Supercools 187.4
Dipropylene glycol 134.2 1.022 Supercools 232.2
Tripropylene glycol 192.3 1.110 Supercools 265.1
1,3-Propanediol 76.1 1.060 −28 210
1,3-Butanediol 92.1 1.005 207.5
1,4-Butanediol 92.1 1.017 20.1 235
Neopentyl glycol 104.2 130 206
1,6-Hexanediol 118.2 1.017 43 250
1,4-Cyclohexanedimethanol
HQEE
Ethanolamine 61.1 1.018 10.3 170
Diethanolamine 105.1 1.097 28 271
Methyldiethanolamine 119.1 1.043 −21 242
Phenyldiethanolamine 181.2 58 228
Hydroxyl compounds – trifunctional molecules Glycerol 92.1 1.261 18.0 290
Trimethylolpropane
1,2,6-Hexanetriol
Triethanolamine 149.2 1.124 21
Hydroxyl compounds – tetrafunctional molecules Pentaerythritol 136.2 260.5
N,N,N′,N′-Tetrakis
(2-hydroxypropyl)
ethylenediamine
Amine compounds – difunctional molecules Diethyltoluenediamine 178.3 1.022 308
Dimethylthiotoluenediamine 214.0 1.208

Catalysts

[edit]

Polyurethane catalysts can be classified into two broad categories, basic and acidic amine. Tertiary amine catalysts function by enhancing the nucleophilicity of the diol component. Alkyl tin carboxylates, oxides and mercaptides oxides function as mild Lewis acids in accelerating the formation of polyurethane. As bases, traditional amine catalysts include triethylenediamine (TEDA, also called DABCO, 1,4-diazabicyclo[2.2.2]octane), dimethylcyclohexylamine (DMCHA), dimethylethanolamine (DMEA), Dimethylaminoethoxyethanol and bis-(2-dimethylaminoethyl)ether, a blowing catalyst also called A-99. A typical Lewis acidic catalyst is dibutyltin dilaurate. The process is highly sensitive to the nature of the catalyst and is also known to be autocatalytic.[36]

Another class of catalysts was published in a study in May 2024. In this study, polyurethane synthesis was investigated in the presence of acid catalysts, namely dimethylphosphite (DMHP), methanesulfonic acid (MSA), and trifluoromethanesulfonic acid (TFMSA). The thermodynamic profile was examined and described in detail through computational tools, showing that TFMSA had the best catalytic properties. The study aimed to open the door to a new class of catalysts.[37]

Factors affecting catalyst selection include balancing three reactions: urethane (polyol+isocyanate, or gel) formation, the urea (water+isocyanate, or "blow") formation, or the isocyanate trimerization reaction (e.g., using potassium acetate, to form isocyanurate rings). A variety of specialized catalysts have been developed.[38][39][40]

Surfactants

[edit]

Surfactants are used to modify the characteristics of both foam and non-foam polyurethane polymers. They take the form of polydimethylsiloxane-polyoxyalkylene block copolymers, silicone oils, nonylphenol ethoxylates, and other organic compounds. In foams, they are used to emulsify the liquid components, regulate cell size, and stabilize the cell structure to prevent collapse and sub-surface voids.[41] In non-foam applications they are used as air release and antifoaming agents, as wetting agents, and are used to eliminate surface defects such as pin holes, orange peel, and sink marks.

Production

[edit]

Polyurethanes are produced by mixing two or more liquid streams. The polyol stream contains catalysts, surfactants, blowing agents (when making polyurethane foam insulation) and so on. The two components are referred to as a polyurethane system, or simply a system. The isocyanate is commonly referred to in North America as the 'A-side' or just the 'iso'. The blend of polyols and other additives is commonly referred to as the 'B-side' or as the 'poly'.[citation needed] This mixture might also be called a 'resin' or 'resin blend'. In Europe the meanings for 'A-side' and 'B-side' are reversed.[citation needed] Resin blend additives may include chain extenders, cross linkers, surfactants, flame retardants, blowing agents, pigments, and fillers. Polyurethane can be made in a variety of densities and hardnesses by varying the isocyanate, polyol or additives.

Health and safety

[edit]

Fully reacted polyurethane polymer is chemically inert.[42] No exposure limits have been established in the U.S. by OSHA (Occupational Safety and Health Administration) or ACGIH (American Conference of Governmental Industrial Hygienists). It is not regulated by OSHA for carcinogenicity.

Open-flame test. Top: untreated polyurethane foam burns vigorously. Bottom: with fire-retardant treatment.

Polyurethanes are combustible.[43] Decomposition from fire can produce significant amounts of carbon monoxide and hydrogen cyanide, in addition to nitrogen oxides, isocyanates, and other toxic products.[44] Due to the flammability of the material, it has to be treated with flame retardants (at least in case of furniture), almost all of which are considered harmful.[45][46] California later issued Technical Bulletin 117 2013 which allowed most polyurethane foam to pass flammability tests without the use of flame retardants. Green Science Policy Institute states: "Although the new standard can be met without flame retardants, it does NOT ban their use. Consumers who wish to reduce household exposure to flame retardants can look for a TB117-2013 tag on furniture, and verify with retailers that products do not contain flame retardants."[47]

Liquid resin blends and isocyanates may contain hazardous or regulated components. Isocyanates are known skin and respiratory sensitizers. Additionally, amines, glycols, and phosphate present in spray polyurethane foams present risks.[48]

Exposure to chemicals that may be emitted during or after application of polyurethane spray foam (such as isocyanates) are harmful to human health and therefore special precautions are required during and after this process.[49]

In the United States, additional health and safety information can be found through organizations such as the Polyurethane Manufacturers Association (PMA) and the Center for the Polyurethanes Industry (CPI), as well as from polyurethane system and raw material manufacturers. Regulatory information can be found in the Code of Federal Regulations Title 21 (Food and Drugs) and Title 40 (Protection of the Environment). In Europe, health and safety information is available from ISOPA,[50] the European Diisocyanate and Polyol Producers Association.

Manufacturing

[edit]

The methods of manufacturing polyurethane finished goods range from small, hand pour piece-part operations to large, high-volume bunstock and boardstock production lines. Regardless of the end-product, the manufacturing principle is the same: to meter the liquid isocyanate and resin blend at a specified stoichiometric ratio, mix them together until a homogeneous blend is obtained, dispense the reacting liquid into a mold or on to a surface, wait until it cures, then demold the finished part.

Dispensing equipment

[edit]

Although the capital outlay can be high, it is desirable to use a meter-mix or dispense unit for even low-volume production operations that require a steady output of finished parts. Dispense equipment consists of material holding (day) tanks, metering pumps, a mix head, and a control unit. Often, a conditioning or heater–chiller unit is added to control material temperature in order to improve mix efficiency, cure rate, and to reduce process variability. Choice of dispense equipment components depends on shot size, throughput, material characteristics such as viscosity and filler content, and process control. Material day tanks may be single to hundreds of gallons in size and may be supplied directly from drums, IBCs (intermediate bulk containers, such as caged IBC totes), or bulk storage tanks. They may incorporate level sensors, conditioning jackets, and mixers. Pumps can be sized to meter in single grams per second up to hundreds of pounds per minute. They can be rotary, gear, or piston pumps, or can be specially hardened lance pumps to meter liquids containing highly abrasive fillers such as chopped or hammer-milled glass fiber and wollastonite.[citation needed]

The pumps can drive low-pressure (10 to 30 bar, 1 to 3 MPa) or high-pressure (125 to 250 bar, 12.5 to 25.0 MPa) dispense systems. Mix heads can be simple static mix tubes, rotary-element mixers, low-pressure dynamic mixers, or high-pressure hydraulically actuated direct impingement mixers. Control units may have basic on/off and dispense/stop switches, and analogue pressure and temperature gauges, or may be computer-controlled with flow meters to electronically calibrate mix ratio, digital temperature and level sensors, and a full suite of statistical process control software. Add-ons to dispense equipment include nucleation or gas injection units, and third or fourth stream capability for adding pigments or metering in supplemental additive packages.

Tooling

[edit]

Distinct from pour-in-place, bun and boardstock, and coating applications, the production of piece parts requires tooling to contain and form the reacting liquid. The choice of mold-making material is dependent on the expected number of uses to end-of-life (EOL), molding pressure, flexibility, and heat transfer characteristics.

RTV silicone is used for tooling that has an EOL in the thousands of parts. It is typically used for molding rigid foam parts, where the ability to stretch and peel the mold around undercuts is needed. The heat transfer characteristic of RTV silicone tooling is poor. High-performance, flexible polyurethane elastomers are also used in this way.

Epoxy, metal-filled epoxy, and metal-coated epoxy is used for tooling that has an EOL in the tens of thousands of parts. It is typically used for molding flexible foam cushions and seating, integral skin and microcellular foam padding, and shallow-draft RIM bezels and fascia. The heat transfer characteristic of epoxy tooling is fair; the heat transfer characteristic of metal-filled and metal-coated epoxy is good. Copper tubing can be incorporated into the body of the tool, allowing hot water to circulate and heat the mold surface.

Aluminum is used for tooling that has an EOL in the hundreds of thousands of parts. It is typically used for molding microcellular foam gasketing and cast elastomer parts, and is milled or extruded into shape.

Mirror-finish stainless steel is used for tooling that imparts a glossy appearance to the finished part. The heat transfer characteristic of metal tooling is excellent.

Finally, molded or milled polypropylene is used to create low-volume tooling for molded gasket applications. Instead of many expensive metal molds, low-cost plastic tooling can be formed from a single metal master, which also allows greater design flexibility. The heat transfer characteristic of polypropylene tooling is poor, which must be taken into consideration during the formulation process.

Applications

[edit]

In 2007, the global consumption of polyurethane raw materials was above 12 million metric tons, and the average annual growth rate was about 5%.[51] Revenues generated with PUR on the global market are expected to rise to approximately US$75 billion by 2022.[52] As they are such an important class of materials, research is constantly taking place and papers published.[53]

Degradation and environmental fate

[edit]

Effects of visible light

[edit]
Polyurethane foam made with an aromatic isocyanate, which has been exposed to UV light. Readily apparent is the discoloration that occurs over time.

Polyurethanes, especially those made using aromatic isocyanates, contain chromophores that interact with light. This is of particular interest in the area of polyurethane coatings, where light stability is a critical factor and is the main reason that aliphatic isocyanates are used in making polyurethane coatings. When PU foam, which is made using aromatic isocyanates, is exposed to visible light, it discolors, turning from off-white to yellow to reddish brown. It has been generally accepted that apart from yellowing, visible light has little effect on foam properties.[54][55] This is especially the case if the yellowing happens on the outer portions of a large foam, as the deterioration of properties in the outer portion has little effect on the overall bulk properties of the foam itself.

It has been reported that exposure to visible light can affect the variability of some physical property test results.[56]

Higher-energy UV radiation promotes chemical reactions in foam, some of which are detrimental to the foam structure.[57]

Hydrolysis and biodegradation

[edit]

Polyurethanes may degrade due to hydrolysis. This is a common problem with shoes left in a closet, and reacting with moisture in the air.[58]

Microbial degradation of polyurethane is believed to be due to the action of esterase, urethanase, hydrolase and protease enzymes.[59] The process is slow as most microbes have difficulty moving beyond the surface of the polymer. Susceptibility to fungi is higher due to their release of extracellular enzymes, which are better able to permeate the polymer matrix. Two species of the Ecuadorian fungus Pestalotiopsis are capable of biodegrading polyurethane in aerobic and anaerobic conditions such as found at the bottom of landfills.[60][61] Degradation of polyurethane items at museums has been reported.[62] Polyester-type polyurethanes are more easily biodegraded by fungus than polyether-type.[63]

See also

[edit]
  • Botanol, a material with higher plant-based content
  • Passive fire protection
  • Penetrant (mechanical, electrical, or structural)
  • Polyaspartic
  • Polyurethane dispersion
  • Thermoplastic polyurethanes
  • Thermoset polymer matrix

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[edit]
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  60. ^ Russell, J. R.; Huang, J.; Anand, P.; Kucera, K.; Sandoval, A. G.; Dantzler, K. W.; Hickman, D.; Jee, J.; Kimovec, F. M.; Koppstein, D.; Marks, D. H.; Mittermiller, P. A.; Nunez, S. J.; Santiago, M.; Townes, M. A.; Vishnevetsky, M.; Williams, N. E.; Vargas, M. P. N.; Boulanger, L.-A.; Bascom-Slack, C.; Strobel, S. A. (2011). "Biodegradation of Polyester Polyurethane by Endophytic Fungi". Applied and Environmental Microbiology. 77 (17): 6076–84. Bibcode:2011ApEnM..77.6076R. doi:10.1128/AEM.00521-11. PMC 3165411. PMID 21764951.
  61. ^ "Could Plastic-Eating Mushrooms Solve mankind's Plastic Problem?". Sciencemint. 2021-04-14. Archived from the original on 2021-07-09. Retrieved 2021-07-02.
  62. ^ Cappitelli, F.; Sorlini, C. (2007). "Microorganisms Attack Synthetic Polymers in Items Representing Our Cultural Heritage". Applied and Environmental Microbiology. 74 (3): 564–9. Bibcode:2008ApEnM..74..564C. doi:10.1128/AEM.01768-07. PMC 2227722. PMID 18065627.
  63. ^ Tokiwa, Yutaka; Calabia, Buenaventurada P.; Ugwu, Charles U.; Aiba, Seiichi (2009). "Biodegradability of Plastics". International Journal of Molecular Sciences. 10 (9): 3722–42. doi:10.3390/ijms10093722. PMC 2769161. PMID 19865515.
[edit]
  • Center for the Polyurethanes Industry: information for EH&S issues related to polyurethanes developments
  • Polyurethane synthesis, Polymer Science Learning Center, University of Southern Mississippi
  • Polyurethane Foam Association: Industry information, educational materials and resources related to flexible polyurethane foam
  • PU Europe: European PU insulation industry association (formerly BING): European voice for the national trade associations representing the polyurethane insulation industry
  • ISOPA: European Diisocyanate & Polyol Producers Association: ISOPA represents the manufacturers in Europe of aromatic diisocyanates and polyols

 

Polyurethane synthesis: the urethane groups −NH−(C=O)−O− link the molecular units, resulting in a polymer consisting of an alternating chain of two monomers.
A kitchen sponge made of polyurethane foam

Polyurethane (/ËŒpÉ’liˈjÊŠÉ™rəˌθeɪn, -jʊəˈrÉ›θeɪn/;[1] often abbreviated PUR and PU) is a class of polymers composed of organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane does not refer to a single type of polymer but a group of polymers. Unlike polyethylene and polystyrene, polyurethanes can be produced from a wide range of starting materials, resulting in various polymers within the same group. This chemical variety produces polyurethanes with different chemical structures leading to many different applications. These include rigid and flexible foams, and coatings, adhesives, electrical potting compounds, and fibers such as spandex and polyurethane laminate (PUL). Foams are the largest application accounting for 67% of all polyurethane produced in 2016.[2]

A polyurethane is typically produced by reacting a polymeric isocyanate with a polyol.[3] Since a polyurethane contains two types of monomers, which polymerize one after the other, they are classed as alternating copolymers. Both the isocyanates and polyols used to make a polyurethane contain two or more functional groups per molecule.

Global production in 2019 was 25 million metric tonnes,[4] accounting for about 6% of all polymers produced in that year.

History

[edit]
Otto Bayer in 1952 demonstrating his creation

Otto Bayer and his coworkers at IG Farben in Leverkusen, Germany, first made polyurethanes in 1937.[5][6] The new polymers had some advantages over existing plastics that were made by polymerizing olefins or by polycondensation, and were not covered by patents obtained by Wallace Carothers on polyesters.[7] Early work focused on the production of fibers and flexible foams and PUs were applied on a limited scale as aircraft coating during World War II.[7] Polyisocyanates became commercially available in 1952, and production of flexible polyurethane foam began in 1954 by combining toluene diisocyanate (TDI) and polyester polyols. These materials were also used to produce rigid foams, gum rubber, and elastomers. Linear fibers were produced from hexamethylene diisocyanate (HDI) and 1,4-Butanediol (BDO).

DuPont introduced polyethers, specifically poly(tetramethylene ether) glycol, in 1956. BASF and Dow Chemical introduced polyalkylene glycols in 1957. Polyether polyols were cheaper, easier to handle and more water-resistant than polyester polyols. Union Carbide and Mobay, a U.S. Monsanto/Bayer joint venture, also began making polyurethane chemicals.[7] In 1960 more than 45,000 metric tons of flexible polyurethane foams were produced. The availability of chlorofluoroalkane blowing agents, inexpensive polyether polyols, and methylene diphenyl diisocyanate (MDI) allowed polyurethane rigid foams to be used as high-performance insulation materials. In 1967, urethane-modified polyisocyanurate rigid foams were introduced, offering even better thermal stability and flammability resistance. During the 1960s, automotive interior safety components, such as instrument and door panels, were produced by back-filling thermoplastic skins with semi-rigid foam.

In 1969, Bayer exhibited an all-plastic car in Düsseldorf, Germany. Parts of this car, such as the fascia and body panels, were manufactured using a new process called reaction injection molding (RIM), in which the reactants were mixed and then injected into a mold. The addition of fillers, such as milled glass, mica, and processed mineral fibers, gave rise to reinforced RIM (RRIM), which provided improvements in flexural modulus (stiffness), reduction in coefficient of thermal expansion and better thermal stability. This technology was used to make the first plastic-body automobile in the United States, the Pontiac Fiero, in 1983. Further increases in stiffness were obtained by incorporating pre-placed glass mats into the RIM mold cavity, also known broadly as resin injection molding, or structural RIM.

Starting in the early 1980s, water-blown microcellular flexible foams were used to mold gaskets for automotive panels and air-filter seals, replacing PVC polymers. Polyurethane foams are used in many automotive applications including seating, head and arm rests, and headliners.

Polyurethane foam (including foam rubber) is sometimes made using small amounts of blowing agents to give less dense foam, better cushioning/energy absorption or thermal insulation. In the early 1990s, because of their impact on ozone depletion, the Montreal Protocol restricted the use of many chlorine-containing blowing agents, such as trichlorofluoromethane (CFC-11). By the late 1990s, blowing agents such as carbon dioxide, pentane, 1,1,1,2-tetrafluoroethane (HFC-134a) and 1,1,1,3,3-pentafluoropropane (HFC-245fa) were widely used in North America and the EU, although chlorinated blowing agents remained in use in many developing countries. Later, HFC-134a was also banned due to high ODP and GWP readings, and HFC-141B was introduced in early 2000s as an alternate blowing agent in developing nations.[8]

Chemistry

[edit]

Polyurethanes are produced by reacting diisocyanates with polyols,[9][10][11][12][13][14] often in the presence of a catalyst, or upon exposure to ultraviolet radiation.[15] Common catalysts include tertiary amines, such as DABCO, DMDEE, or metallic soaps, such as dibutyltin dilaurate. The stoichiometry of the starting materials must be carefully controlled as excess isocyanate can trimerise, leading to the formation of rigid polyisocyanurates. The polymer usually has a highly crosslinked molecular structure, resulting in a thermosetting material which does not melt on heating; although some thermoplastic polyurethanes are also produced.

 
Carbon dioxide gas and urea links formed by reacting water and isocyanate

The most common application of polyurethane is as solid foams, which requires the presence of a gas, or blowing agent, during the polymerization step. This is commonly achieved by adding small amounts of water, which reacts with isocyanates to form CO2 gas and an amine, via an unstable carbamic acid group. The amine produced can also react with isocyanates to form urea groups, and as such the polymer will contain both these and urethane linkers. The urea is not very soluble in the reaction mixture and tends to form separate "hard segment" phases consisting mostly of polyurea. The concentration and organization of these polyurea phases can have a significant impact on the properties of the foam.[16]

The type of foam produced can be controlled by regulating the amount of blowing agent and also by the addition of various surfactants which change the rheology of the polymerising mixture. Foams can be either "closed-cell", where most of the original bubbles or cells remain intact, or "open-cell", where the bubbles have broken but the edges of the bubbles are stiff enough to retain their shape, in extreme cases reticulated foams can be formed. Open-cell foams feel soft and allow air to flow through, so they are comfortable when used in seat cushions or mattresses. Closed-cell foams are used as rigid thermal insulation. High-density microcellular foams can be formed without the addition of blowing agents by mechanically frothing the polyol prior to use. These are tough elastomeric materials used in covering car steering wheels or shoe soles.

The properties of a polyurethane are greatly influenced by the types of isocyanates and polyols used to make it. Long, flexible segments, contributed by the polyol, give soft, elastic polymer. High amounts of crosslinking give tough or rigid polymers. Long chains and low crosslinking give a polymer that is very stretchy, short chains with many crosslinks produce a hard polymer while long chains and intermediate crosslinking give a polymer useful for making foam. The choices available for the isocyanates and polyols, in addition to other additives and processing conditions allow polyurethanes to have the very wide range of properties that make them such widely used polymers.

Raw materials

[edit]

The main ingredients to make a polyurethane are di- and tri-isocyanates and polyols. Other materials are added to aid processing the polymer or to modify the properties of the polymer. PU foam formulation sometimes have water added too.

Isocyanates

[edit]

Isocyanates used to make polyurethane have two or more isocyanate groups on each molecule. The most commonly used isocyanates are the aromatic diisocyanates, toluene diisocyanate (TDI) and methylene diphenyl diisocyanate, (MDI). These aromatic isocyanates are more reactive than aliphatic isocyanates.

TDI and MDI are generally less expensive and more reactive than other isocyanates. Industrial grade TDI and MDI are mixtures of isomers and MDI often contains polymeric materials. They are used to make flexible foam (for example slabstock foam for mattresses or molded foams for car seats),[17] rigid foam (for example insulating foam in refrigerators) elastomers (shoe soles, for example), and so on. The isocyanates may be modified by partially reacting them with polyols or introducing some other materials to reduce volatility (and hence toxicity) of the isocyanates, decrease their freezing points to make handling easier or to improve the properties of the final polymers.

MDI isomers and polymer
MDI isomers and polymer

Aliphatic and cycloaliphatic isocyanates are used in smaller quantities, most often in coatings and other applications where color and transparency are important since polyurethanes made with aromatic isocyanates tend to darken on exposure to light.[page needed][18] The most important aliphatic and cycloaliphatic isocyanates are 1,6-hexamethylene diisocyanate (HDI), 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophorone diisocyanate, IPDI), and 4,4′-diisocyanato dicyclohexylmethane (H12MDI or hydrogenated MDI). Other more specialized isocyanates include Tetramethylxylylene diisocyanate (TMXDI).

Polyols

[edit]

Polyols are polymers in their own right and have on average two or more hydroxyl groups per molecule. They can be converted to polyether polyols by co-polymerizing ethylene oxide and propylene oxide with a suitable polyol precursor.[19] Polyester polyols are made by the polycondensation of multifunctional carboxylic acids and polyhydroxyl compounds. They can be further classified according to their end use. Higher molecular weight polyols (molecular weights from 2,000 to 10,000) are used to make more flexible polyurethanes while lower molecular weight polyols make more rigid products.

Polyols for flexible applications use low functionality initiators such as dipropylene glycol (f = 2), glycerine (f = 3), or a sorbitol/water solution (f = 2.75).[20] Polyols for rigid applications use higher functionality initiators such as sucrose (f = 8), sorbitol (f = 6), toluenediamine (f = 4), and Mannich bases (f = 4). Propylene oxide and/or ethylene oxide is added to the initiators until the desired molecular weight is achieved. The order of addition and the amounts of each oxide affect many polyol properties, such as compatibility, water-solubility, and reactivity. Polyols made with only propylene oxide are terminated with secondary hydroxyl groups and are less reactive than polyols capped with ethylene oxide, which contain primary hydroxyl groups. Incorporating carbon dioxide into the polyol structure is being researched by multiple companies.

Graft polyols (also called filled polyols or polymer polyols) contain finely dispersed styrene–acrylonitrile, acrylonitrile, or polyurea (PHD) polymer solids chemically grafted to a high molecular weight polyether backbone. They are used to increase the load-bearing properties of low-density high-resiliency (HR) foam, as well as add toughness to microcellular foams and cast elastomers. Initiators such as ethylenediamine and triethanolamine are used to make low molecular weight rigid foam polyols that have built-in catalytic activity due to the presence of nitrogen atoms in the backbone. A special class of polyether polyols, poly(tetramethylene ether) glycols, which are made by polymerizing tetrahydrofuran, are used in high performance coating, wetting and elastomer applications.

Conventional polyester polyols are based on virgin raw materials and are manufactured by the direct polyesterification of high-purity diacids and glycols, such as adipic acid and 1,4-butanediol. Polyester polyols are usually more expensive and more viscous than polyether polyols, but they make polyurethanes with better solvent, abrasion, and cut resistance. Other polyester polyols are based on reclaimed raw materials. They are manufactured by transesterification (glycolysis) of recycled poly(ethyleneterephthalate) (PET) or dimethylterephthalate (DMT) distillation bottoms with glycols such as diethylene glycol. These low molecular weight, aromatic polyester polyols are used in rigid foam, and bring low cost and excellent flammability characteristics to polyisocyanurate (PIR) boardstock and polyurethane spray foam insulation.

Specialty polyols include polycarbonate polyols, polycaprolactone polyols, polybutadiene polyols, and polysulfide polyols. The materials are used in elastomer, sealant, and adhesive applications that require superior weatherability, and resistance to chemical and environmental attack. Natural oil polyols derived from castor oil and other vegetable oils are used to make elastomers, flexible bunstock, and flexible molded foam.

Co-polymerizing chlorotrifluoroethylene or tetrafluoroethylene with vinyl ethers containing hydroxyalkyl vinyl ether produces fluorinated (FEVE) polyols. Two-component fluorinated polyurethanes prepared by reacting FEVE fluorinated polyols with polyisocyanate have been used to make ambient cure paints and coatings. Since fluorinated polyurethanes contain a high percentage of fluorine–carbon bonds, which are the strongest bonds among all chemical bonds, fluorinated polyurethanes exhibit resistance to UV, acids, alkali, salts, chemicals, solvents, weathering, corrosion, fungi and microbial attack. These have been used for high performance coatings and paints.[21]

Phosphorus-containing polyols are available that become chemically bonded to the polyurethane matrix for the use as flame retardants. This covalent linkage prevents migration and leaching of the organophosphorus compound.

Bio-derived materials

[edit]

Interest in sustainable "green" products raised interest in polyols derived from vegetable oils,[22][23][24] fatty acids,[25] lignin, sorbitol,[26] etc. These are mostly contributing to polyol part. There are attempts made to prepare isocyanate part using bio-derived material. However, as far as commercialization is concern, polyol part is more targeted being easy and required in more quantity than isocyanate part. Various oils used in the preparation polyols for polyurethanes include soybean oil, cottonseed oil, neem seed oil, algae oil,[27][28] and castor oil. Vegetable oils are functionalized in various ways and modified to polyetheramides, polyethers, alkyds, etc. Renewable sources used to prepare polyols may be fatty acids or dimer fatty acids.[29] Some biobased and isocyanate-free polyurethanes exploit the reaction between polyamines and cyclic carbonates to produce polyhydroxyurethanes.[30]

Chain extenders and cross linkers

[edit]

Chain extenders (f = 2) and cross linkers (f ≥ 3) are low molecular weight hydroxyl and amine terminated compounds that play an important role in the polymer morphology of polyurethane fibers, elastomers, adhesives, and certain integral skin and microcellular foams.

The elastomeric properties of these materials are derived from the phase separation of the hard and soft copolymer segments of the polymer, such that the urethane hard segment domains serve as cross-links between the amorphous polyether (or polyester) soft segment domains. This phase separation occurs because the mainly nonpolar, low melting soft segments are incompatible with the polar, high melting hard segments. The soft segments, which are formed from high molecular weight polyols, are mobile and are normally present in coiled formation, while the hard segments, which are formed from the isocyanate and chain extenders, are stiff and immobile. As the hard segments are covalently coupled to the soft segments, they inhibit plastic flow of the polymer chains, thus creating elastomeric resiliency. Upon mechanical deformation, a portion of the soft segments are stressed by uncoiling, and the hard segments become aligned in the stress direction. This reorientation of the hard segments and consequent powerful hydrogen bonding contributes to high tensile strength, elongation, and tear resistance values.[12][31][32][33][34] The choice of chain extender also determines flexural, heat, and chemical resistance properties.

The most important chain extenders are ethylene glycol, 1,4-butanediol (1,4-BDO or BDO), 1,6-hexanediol, cyclohexane dimethanol and hydroquinone bis(2-hydroxyethyl) ether (HQEE). All of these glycols form polyurethanes that phase separate well and form well defined hard segment domains, and are melt processable. They are all suitable for thermoplastic polyurethanes with the exception of ethylene glycol, since its derived bis-phenyl urethane undergoes unfavorable degradation at high hard segment levels.[10] Diethanolamine and triethanolamine are used in flex molded foams to build firmness and add catalytic activity. Diethyltoluenediamine is used extensively in RIM, and in polyurethane and polyurea elastomer formulations.

Table of chain extenders and cross linkers[35]
Compound type Molecule Mol.
mass
Density
(g/cm3)
Melting
pt (°C)
Boiling
pt (°C)
Hydroxyl compounds – difunctional molecules Ethylene glycol 62.1 1.110 −13.4 197.4
Diethylene glycol 106.1 1.111 −8.7 245.5
Triethylene glycol 150.2 1.120 −7.2 287.8
Tetraethylene glycol 194.2 1.123 −9.4 325.6
Propylene glycol 76.1 1.032 Supercools 187.4
Dipropylene glycol 134.2 1.022 Supercools 232.2
Tripropylene glycol 192.3 1.110 Supercools 265.1
1,3-Propanediol 76.1 1.060 −28 210
1,3-Butanediol 92.1 1.005 207.5
1,4-Butanediol 92.1 1.017 20.1 235
Neopentyl glycol 104.2 130 206
1,6-Hexanediol 118.2 1.017 43 250
1,4-Cyclohexanedimethanol
HQEE
Ethanolamine 61.1 1.018 10.3 170
Diethanolamine 105.1 1.097 28 271
Methyldiethanolamine 119.1 1.043 −21 242
Phenyldiethanolamine 181.2 58 228
Hydroxyl compounds – trifunctional molecules Glycerol 92.1 1.261 18.0 290
Trimethylolpropane
1,2,6-Hexanetriol
Triethanolamine 149.2 1.124 21
Hydroxyl compounds – tetrafunctional molecules Pentaerythritol 136.2 260.5
N,N,N′,N′-Tetrakis
(2-hydroxypropyl)
ethylenediamine
Amine compounds – difunctional molecules Diethyltoluenediamine 178.3 1.022 308
Dimethylthiotoluenediamine 214.0 1.208

Catalysts

[edit]

Polyurethane catalysts can be classified into two broad categories, basic and acidic amine. Tertiary amine catalysts function by enhancing the nucleophilicity of the diol component. Alkyl tin carboxylates, oxides and mercaptides oxides function as mild Lewis acids in accelerating the formation of polyurethane. As bases, traditional amine catalysts include triethylenediamine (TEDA, also called DABCO, 1,4-diazabicyclo[2.2.2]octane), dimethylcyclohexylamine (DMCHA), dimethylethanolamine (DMEA), Dimethylaminoethoxyethanol and bis-(2-dimethylaminoethyl)ether, a blowing catalyst also called A-99. A typical Lewis acidic catalyst is dibutyltin dilaurate. The process is highly sensitive to the nature of the catalyst and is also known to be autocatalytic.[36]

Another class of catalysts was published in a study in May 2024. In this study, polyurethane synthesis was investigated in the presence of acid catalysts, namely dimethylphosphite (DMHP), methanesulfonic acid (MSA), and trifluoromethanesulfonic acid (TFMSA). The thermodynamic profile was examined and described in detail through computational tools, showing that TFMSA had the best catalytic properties. The study aimed to open the door to a new class of catalysts.[37]

Factors affecting catalyst selection include balancing three reactions: urethane (polyol+isocyanate, or gel) formation, the urea (water+isocyanate, or "blow") formation, or the isocyanate trimerization reaction (e.g., using potassium acetate, to form isocyanurate rings). A variety of specialized catalysts have been developed.[38][39][40]

Surfactants

[edit]

Surfactants are used to modify the characteristics of both foam and non-foam polyurethane polymers. They take the form of polydimethylsiloxane-polyoxyalkylene block copolymers, silicone oils, nonylphenol ethoxylates, and other organic compounds. In foams, they are used to emulsify the liquid components, regulate cell size, and stabilize the cell structure to prevent collapse and sub-surface voids.[41] In non-foam applications they are used as air release and antifoaming agents, as wetting agents, and are used to eliminate surface defects such as pin holes, orange peel, and sink marks.

Production

[edit]

Polyurethanes are produced by mixing two or more liquid streams. The polyol stream contains catalysts, surfactants, blowing agents (when making polyurethane foam insulation) and so on. The two components are referred to as a polyurethane system, or simply a system. The isocyanate is commonly referred to in North America as the 'A-side' or just the 'iso'. The blend of polyols and other additives is commonly referred to as the 'B-side' or as the 'poly'.[citation needed] This mixture might also be called a 'resin' or 'resin blend'. In Europe the meanings for 'A-side' and 'B-side' are reversed.[citation needed] Resin blend additives may include chain extenders, cross linkers, surfactants, flame retardants, blowing agents, pigments, and fillers. Polyurethane can be made in a variety of densities and hardnesses by varying the isocyanate, polyol or additives.

Health and safety

[edit]

Fully reacted polyurethane polymer is chemically inert.[42] No exposure limits have been established in the U.S. by OSHA (Occupational Safety and Health Administration) or ACGIH (American Conference of Governmental Industrial Hygienists). It is not regulated by OSHA for carcinogenicity.

Open-flame test. Top: untreated polyurethane foam burns vigorously. Bottom: with fire-retardant treatment.

Polyurethanes are combustible.[43] Decomposition from fire can produce significant amounts of carbon monoxide and hydrogen cyanide, in addition to nitrogen oxides, isocyanates, and other toxic products.[44] Due to the flammability of the material, it has to be treated with flame retardants (at least in case of furniture), almost all of which are considered harmful.[45][46] California later issued Technical Bulletin 117 2013 which allowed most polyurethane foam to pass flammability tests without the use of flame retardants. Green Science Policy Institute states: "Although the new standard can be met without flame retardants, it does NOT ban their use. Consumers who wish to reduce household exposure to flame retardants can look for a TB117-2013 tag on furniture, and verify with retailers that products do not contain flame retardants."[47]

Liquid resin blends and isocyanates may contain hazardous or regulated components. Isocyanates are known skin and respiratory sensitizers. Additionally, amines, glycols, and phosphate present in spray polyurethane foams present risks.[48]

Exposure to chemicals that may be emitted during or after application of polyurethane spray foam (such as isocyanates) are harmful to human health and therefore special precautions are required during and after this process.[49]

In the United States, additional health and safety information can be found through organizations such as the Polyurethane Manufacturers Association (PMA) and the Center for the Polyurethanes Industry (CPI), as well as from polyurethane system and raw material manufacturers. Regulatory information can be found in the Code of Federal Regulations Title 21 (Food and Drugs) and Title 40 (Protection of the Environment). In Europe, health and safety information is available from ISOPA,[50] the European Diisocyanate and Polyol Producers Association.

Manufacturing

[edit]

The methods of manufacturing polyurethane finished goods range from small, hand pour piece-part operations to large, high-volume bunstock and boardstock production lines. Regardless of the end-product, the manufacturing principle is the same: to meter the liquid isocyanate and resin blend at a specified stoichiometric ratio, mix them together until a homogeneous blend is obtained, dispense the reacting liquid into a mold or on to a surface, wait until it cures, then demold the finished part.

Dispensing equipment

[edit]

Although the capital outlay can be high, it is desirable to use a meter-mix or dispense unit for even low-volume production operations that require a steady output of finished parts. Dispense equipment consists of material holding (day) tanks, metering pumps, a mix head, and a control unit. Often, a conditioning or heater–chiller unit is added to control material temperature in order to improve mix efficiency, cure rate, and to reduce process variability. Choice of dispense equipment components depends on shot size, throughput, material characteristics such as viscosity and filler content, and process control. Material day tanks may be single to hundreds of gallons in size and may be supplied directly from drums, IBCs (intermediate bulk containers, such as caged IBC totes), or bulk storage tanks. They may incorporate level sensors, conditioning jackets, and mixers. Pumps can be sized to meter in single grams per second up to hundreds of pounds per minute. They can be rotary, gear, or piston pumps, or can be specially hardened lance pumps to meter liquids containing highly abrasive fillers such as chopped or hammer-milled glass fiber and wollastonite.[citation needed]

The pumps can drive low-pressure (10 to 30 bar, 1 to 3 MPa) or high-pressure (125 to 250 bar, 12.5 to 25.0 MPa) dispense systems. Mix heads can be simple static mix tubes, rotary-element mixers, low-pressure dynamic mixers, or high-pressure hydraulically actuated direct impingement mixers. Control units may have basic on/off and dispense/stop switches, and analogue pressure and temperature gauges, or may be computer-controlled with flow meters to electronically calibrate mix ratio, digital temperature and level sensors, and a full suite of statistical process control software. Add-ons to dispense equipment include nucleation or gas injection units, and third or fourth stream capability for adding pigments or metering in supplemental additive packages.

Tooling

[edit]

Distinct from pour-in-place, bun and boardstock, and coating applications, the production of piece parts requires tooling to contain and form the reacting liquid. The choice of mold-making material is dependent on the expected number of uses to end-of-life (EOL), molding pressure, flexibility, and heat transfer characteristics.

RTV silicone is used for tooling that has an EOL in the thousands of parts. It is typically used for molding rigid foam parts, where the ability to stretch and peel the mold around undercuts is needed. The heat transfer characteristic of RTV silicone tooling is poor. High-performance, flexible polyurethane elastomers are also used in this way.

Epoxy, metal-filled epoxy, and metal-coated epoxy is used for tooling that has an EOL in the tens of thousands of parts. It is typically used for molding flexible foam cushions and seating, integral skin and microcellular foam padding, and shallow-draft RIM bezels and fascia. The heat transfer characteristic of epoxy tooling is fair; the heat transfer characteristic of metal-filled and metal-coated epoxy is good. Copper tubing can be incorporated into the body of the tool, allowing hot water to circulate and heat the mold surface.

Aluminum is used for tooling that has an EOL in the hundreds of thousands of parts. It is typically used for molding microcellular foam gasketing and cast elastomer parts, and is milled or extruded into shape.

Mirror-finish stainless steel is used for tooling that imparts a glossy appearance to the finished part. The heat transfer characteristic of metal tooling is excellent.

Finally, molded or milled polypropylene is used to create low-volume tooling for molded gasket applications. Instead of many expensive metal molds, low-cost plastic tooling can be formed from a single metal master, which also allows greater design flexibility. The heat transfer characteristic of polypropylene tooling is poor, which must be taken into consideration during the formulation process.

Applications

[edit]

In 2007, the global consumption of polyurethane raw materials was above 12 million metric tons, and the average annual growth rate was about 5%.[51] Revenues generated with PUR on the global market are expected to rise to approximately US$75 billion by 2022.[52] As they are such an important class of materials, research is constantly taking place and papers published.[53]

Degradation and environmental fate

[edit]

Effects of visible light

[edit]
Polyurethane foam made with an aromatic isocyanate, which has been exposed to UV light. Readily apparent is the discoloration that occurs over time.

Polyurethanes, especially those made using aromatic isocyanates, contain chromophores that interact with light. This is of particular interest in the area of polyurethane coatings, where light stability is a critical factor and is the main reason that aliphatic isocyanates are used in making polyurethane coatings. When PU foam, which is made using aromatic isocyanates, is exposed to visible light, it discolors, turning from off-white to yellow to reddish brown. It has been generally accepted that apart from yellowing, visible light has little effect on foam properties.[54][55] This is especially the case if the yellowing happens on the outer portions of a large foam, as the deterioration of properties in the outer portion has little effect on the overall bulk properties of the foam itself.

It has been reported that exposure to visible light can affect the variability of some physical property test results.[56]

Higher-energy UV radiation promotes chemical reactions in foam, some of which are detrimental to the foam structure.[57]

Hydrolysis and biodegradation

[edit]

Polyurethanes may degrade due to hydrolysis. This is a common problem with shoes left in a closet, and reacting with moisture in the air.[58]

Microbial degradation of polyurethane is believed to be due to the action of esterase, urethanase, hydrolase and protease enzymes.[59] The process is slow as most microbes have difficulty moving beyond the surface of the polymer. Susceptibility to fungi is higher due to their release of extracellular enzymes, which are better able to permeate the polymer matrix. Two species of the Ecuadorian fungus Pestalotiopsis are capable of biodegrading polyurethane in aerobic and anaerobic conditions such as found at the bottom of landfills.[60][61] Degradation of polyurethane items at museums has been reported.[62] Polyester-type polyurethanes are more easily biodegraded by fungus than polyether-type.[63]

See also

[edit]
  • Botanol, a material with higher plant-based content
  • Passive fire protection
  • Penetrant (mechanical, electrical, or structural)
  • Polyaspartic
  • Polyurethane dispersion
  • Thermoplastic polyurethanes
  • Thermoset polymer matrix

References

[edit]
  1. ^ "polyurethane". Dictionary.com Unabridged (Online). n.d.
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[edit]
  • Center for the Polyurethanes Industry: information for EH&S issues related to polyurethanes developments
  • Polyurethane synthesis, Polymer Science Learning Center, University of Southern Mississippi
  • Polyurethane Foam Association: Industry information, educational materials and resources related to flexible polyurethane foam
  • PU Europe: European PU insulation industry association (formerly BING): European voice for the national trade associations representing the polyurethane insulation industry
  • ISOPA: European Diisocyanate & Polyol Producers Association: ISOPA represents the manufacturers in Europe of aromatic diisocyanates and polyols