Polyurethane foam

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An assortment of polyurethane foam products for cushioning and insulation Polyurethane Products.png
An assortment of polyurethane foam products for cushioning and insulation

Polyurethane foam is a solid polymeric foam based on polyurethane chemistry. As a specialist synthetic material with highly diverse applications, polyurethane foams are primarily used for thermal insulation and as a cushioning material in mattresses, upholstered furniture or as seating in vehicles. Its low density and poor thermal conductivity combined with its mechanical properties make them excellent thermal and sound insulators, as well as structural and comfortable materials.

Contents

Polyurethane foams are thermosetting polymers. They cannot be melted and reshaped after initially formed, because the chemical bonds between the molecules in the material are very strong and are not broken down by heating. Once cured and cooled, the material maintains its shape and properties [1] .

Classification of polyurethane foams

Polyurethane foams are the most widely used representatives of thermoset foams. Depending on their cellular structure, they can be classified as open or closed-cell foams. Looking at mechanical properties, there are two main types of polyurethane foam; flexible (soft) and rigid (hard) foams. [2] Generally speaking, flexible polyurethane foams have an open-cell structure where the pores are interconnected, smaller in size and irregularly shaped; contrary to rigid polyurethane foams that have a closed-cell structure, where the pores are not interconnected. [3] The market share between these two types is largely equal. [4]

There are various processing technologies in the production of polyurethane foams. Depending on the properties of the end application, the two most often used at large scale production are moulding and slabstock (block) foaming. [5] Next to these, other prominent types include cavity-filling foam (e.g. car fillings used for acoustic insulation); and spray foam (e.g. roof thermal insulation). These are known as semi-flexible foams behind appropriate overlays. [6]

Flexible polyurethane foam

The so-called flexible polyurethane foam is produced from the reaction of polyols and isocyanates, a process pioneered in 1937. [7] flexible polyurethane foam allows for some compression and resilience that provides a cushioning effect. Because of this property, it is often used in furniture, bedding, automotive seating, athletic equipment, packaging, footwear and carpets. [7]

Rigid polyurethane foams

Rigid polyurethane foam has many desirable properties which has enabled increased use in various applications, some of which are quite demanding. [8] [9] These properties include low thermal conduction making it useful as an insulator. It also has low density compared to metals and other materials and also good dimensional stability. [10] A metal will expand on heating whereas rigid PU foam does not. They have excellent strength to weight ratios. [11] Like many applications, there has been a trend to make rigid PU foam from renewable raw materials in place of the usual polyols. [12] [13] [14]

They are used in vehicles, planes and buildings in structural applications. [15] They have also been used in fire-retardant applications. [16]

Space shuttles

Polyurethane foam has been widely used to insulate fuel tanks on Space Shuttles. However, it requires a perfect application, as any air pocket, dirt or an uncovered tiny spot can knock it off due to extreme conditions of liftoff. [17] Those conditions include violent vibrations, air friction and abrupt changes in temperature and pressure. For a perfect application of the foam there have been two obstacles: limitations related to wearing protective suits and masks by workers and inability to test for cracks before launch, such testing is done only by naked eye. [17] The loss of foam caused the Space Shuttle Columbia disaster. According to the Columbia accident report, NASA officials found foam loss in over 80% of the 79 missions for which they have pictures. [17]

By 2009 researchers created a superior polyimide foam to insulate the reusable cryogenic propellant tanks of Space Shuttles. [18]

Related Research Articles

<span class="mw-page-title-main">Polyurethane</span> Polymer composed of a chain of organic units joined by carbamate (urethane) links

Polyurethane refers to 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 term does not refer to the 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 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.

<span class="mw-page-title-main">Thermosetting polymer</span> Polymer obtained by irreversibly hardening (curing) a resin

In materials science, a thermosetting polymer, often called a thermoset, is a polymer that is obtained by irreversibly hardening ("curing") a soft solid or viscous liquid prepolymer (resin). Curing is induced by heat or suitable radiation and may be promoted by high pressure or mixing with a catalyst. Heat is not necessarily applied externally, and is often generated by the reaction of the resin with a curing agent. Curing results in chemical reactions that create extensive cross-linking between polymer chains to produce an infusible and insoluble polymer network.

<span class="mw-page-title-main">Memory foam</span> Component primarily utilized for making cushions or mattresses

Memory foam consists mainly of polyurethane with additional chemicals that increase its viscosity and density. It is often referred to as "viscoelastic" polyurethane foam, or low-resilience polyurethane foam (LRPu). The foam bubbles or ‘cells’ are open, effectively creating a matrix through which air can move. Higher-density memory foam softens in reaction to body heat, allowing it to mold to a warm body in a few minutes. Newer foams may recover their original shape more quickly.

In organic chemistry, a polyol is an organic compound containing multiple hydroxyl groups. The term "polyol" can have slightly different meanings depending on whether it is used in food science or polymer chemistry. Polyols containing two, three and four hydroxyl groups are diols, triols, and tetrols, respectively.

<span class="mw-page-title-main">Foam rubber</span> Rubber manufactured with a foaming agent

Foam rubber is rubber that has been made with a foaming agent so that its structure is an air-filled matrix. Commercial foam rubber is generally made of synthetic rubber, natural latex, or polyurethane. Latex foam rubber, used in mattresses, is well known for its endurance. Polyurethane is a thermosetting polymer that comes from combination of methyl di-isocyanate and polyethylene and some chemical additives.

<span class="mw-page-title-main">Polyisocyanurate</span> Type of plastic typically used for thermal insulation

Polyisocyanurate, also referred to as PIR, polyol, or ISO, is a thermoset plastic typically produced as a foam and used as rigid thermal insulation. The starting materials are similar to those used in polyurethane (PUR) except that the proportion of methylene diphenyl diisocyanate (MDI) is higher and a polyester-derived polyol is used in the reaction instead of a polyether polyol. The resulting chemical structure is significantly different, with the isocyanate groups on the MDI trimerising to form isocyanurate groups which the polyols link together, giving a complex polymeric structure.

A blowing agent is a substance which is capable of producing a cellular structure via a foaming process in a variety of materials that undergo hardening or phase transition, such as polymers, plastics, and metals. They are typically applied when the blown material is in a liquid stage. The cellular structure in a matrix reduces density, increasing thermal and acoustic insulation, while increasing relative stiffness of the original polymer.

<span class="mw-page-title-main">Building insulation material</span> Insulation material

Building insulation materials are the building materials that form the thermal envelope of a building or otherwise reduce heat transfer.

<span class="mw-page-title-main">Melamine resin</span> Hard, thermosetting plastic material often used in dinnerware

Melamine resin or melamine formaldehyde is a resin with melamine rings terminated with multiple hydroxyl groups derived from formaldehyde. This thermosetting plastic material is made from melamine and formaldehyde. In its butylated form, it is dissolved in n-butanol and xylene. It is then used to cross-link with alkyd, epoxy, acrylic, and polyester resins, used in surface coatings. There are many types, varying from very slow to very fast curing.

Reaction injection molding (RIM) is similar to injection molding except thermosetting polymers are used, which requires a curing reaction to occur within the mold.

Polybutylene (polybutene-1, poly(1-butene), PB-1) is a polyolefin or saturated polymer with the chemical formula (CH2CH(Et))n. Not be confused with polybutene, PB-1 is mainly used in piping.

<span class="mw-page-title-main">Spray foam</span> Building material

Spray foam is a chemical product created by a chemical reaction of two component parts, commonly referred to as side A and side B. Side A contains very reactive chemicals known as isocyanate. Side B contains a polyol, which reacts with isocyanates to make polyurethane, and a mixture of other chemicals, including catalysts, flame retardant, blowing agents and surfactants. These react when mixed with each other and expand up to 30-60 times its liquid volume after it is sprayed in place. This expansion makes it useful as a specialty packing material which forms to the shape of the product being packaged and produces a high thermal insulating value with virtually no air infiltration.

<span class="mw-page-title-main">Rigid panel</span>

Rigid panel insulation, also referred to as continuous insulation, can be made from foam plastics such as polyurethane (PUR), polyisocyanurate (PIR), and polystyrene, or from fibrous materials such as fiberglass, rock and slag wool. Rigid panel continuous insulation is often used to provide a thermal break in the building envelope, thus reducing thermal bridging.

<span class="mw-page-title-main">Insulated pipe</span>

Insulated pipes are widely used for district heating and hot water supply. They consist of a steel pipe called "service pipe", a thermal insulation layer and an outer casing. The insulation bonds the service pipe and the casing together. The main purpose of such pipes is to maintain the temperature of the fluid inside the service pipes. Insulated pipes are commonly used for transport of hot water from district heating plants to district heating networks and for distribution of hot water inside district heating networks.

A thermoset polymer matrix is a synthetic polymer reinforcement where polymers act as binder or matrix to secure in place incorporated particulates, fibres or other reinforcements. They were first developed for structural applications, such as glass-reinforced plastic radar domes on aircraft and graphite-epoxy payload bay doors on the Space Shuttle.

In polymer chemistry, the term prepolymer or pre-polymer, refers to a monomer or system of monomers that have been reacted to an intermediate-molecular mass state. This material is capable of further polymerization by reactive groups to a fully cured, high-molecular-mass state. As such, mixtures of reactive polymers with un-reacted monomers may also be referred to as pre-polymers. The term "pre-polymer" and "polymer precursor" may be interchanged.

Biofoams are biological or biologically derived foams, making up lightweight and porous cellular solids. A relatively new term, its use in academia began in the 1980s in relation to the scum that formed on activated sludge plants.

Covalent adaptable networks (CANs) are a type of polymer material that closely resemble thermosetting polymers (thermosets). However, they are distinguished from thermosets by the incorporation of dynamic covalent chemistry into the polymer network. When a stimulus (for example heat, light, pH, ...) is applied to the material, these dynamic bonds become active and can be broken or exchanged with other pending functional groups, allowing the polymer network to change its topology. This introduces reshaping, (re)processing and recycling into thermoset-like materials.

Polyetheramines are a group of chemicals that are aliphatic organic species based on both ether and amine groups. They are produced by reacting either ethylene oxide or propylene oxide with polyols and then aminating them. There are a number of commercially available molecules with different CAS numbers and molecular weights. They often come with a prefix of M, D or T for monofunctional, difunctional and trifunctional respectively. D-230 would mean difunctional with a molecular weight of 230. A key use is for curing epoxy resins.

References

  1. ↑ EURO-MOULDERS (2023) 'What is polyurethane foam' https://euromoulders.org/polyurethane-in-automobiles/what-is-polyurethane-foam/
  2. ↑ Skleničková, Kateřina; Abbrent, Sabina; Halecký, Martin; Kočí, Vladimír; Beneš, Hynek (2022-01-17). "Biodegradability and ecotoxicity of polyurethane foams: A review". Critical Reviews in Environmental Science and Technology. 52 (2): 157–202. doi:10.1080/10643389.2020.1818496. ISSN   1064-3389.
  3. ↑ Huang, C.H.; Lou, C.W.; Chuang, Y. C.; Liu, C.F.; Yu, Z.C.; Lin, J.H. (2015). "Rigid/flexible polyurethane foam composite boards with addition of functional fillers: Acoustics evaluations" (PDF). Sains Malays. 44 (12): 1757–1763.
  4. ↑ Kemona, Aleksandra; Piotrowska, Małgorzata (2020-08-05). "Polyurethane Recycling and Disposal: Methods and Prospects". Polymers. 12 (8): 1752. doi: 10.3390/polym12081752 . ISSN   2073-4360. PMC   7464512 . PMID   32764494.
  5. ↑ "What is Polyurethane Foam? – Euromoulders" . Retrieved 2024-11-18.
  6. ↑ Ullmann's encyclopedia of industrial chemistry. 19: Vol. A. Alphabetically arranged articles Parkinsonism treatment to photoelectricity (5., completely rev. ed.). Weinheim: VCH Verl.-Ges. 1991. ISBN   978-0-89573-169-2.
  7. 1 2 "What Is Flexible Polyurethane Foam?". Polyurethane Foam Association. Retrieved 1 February 2023.
  8. ↑ McIntyre, A.; Anderton, G. E. (1979-02-01). "Fracture properties of a rigid polyurethane foam over a range of densities". Polymer. 20 (2): 247–253. doi:10.1016/0032-3861(79)90229-5. ISSN   0032-3861.
  9. ↑ Chen, W.; Lu, F.; Winfree, N. (2002-03-01). "High-strain-rate compressive behavior of a rigid polyurethane foam with various densities". Experimental Mechanics. 42 (1): 65–73. doi:10.1007/BF02411053. ISSN   1741-2765.
  10. ↑ Tu, Z. H; Shim, V. P. W; Lim, C. T (2001-12-01). "Plastic deformation modes in rigid polyurethane foam under static loading". International Journal of Solids and Structures. 38 (50): 9267–9279. doi:10.1016/S0020-7683(01)00213-X. ISSN   0020-7683.
  11. ↑ Thirumal, M.; Khastgir, Dipak; Singha, Nikhil K.; Manjunath, B. S.; Naik, Y. P. (2008-05-05). "Effect of foam density on the properties of water blown rigid polyurethane foam". Journal of Applied Polymer Science. 108 (3): 1810–1817. doi:10.1002/app.27712.
  12. ↑ Chian, K. S.; Gan, L. H. (1998-04-18). "Development of a rigid polyurethane foam from palm oil". Journal of Applied Polymer Science. 68 (3): 509–515. doi:10.1002/(SICI)1097-4628(19980418)68:3<509::AID-APP17>3.0.CO;2-P. ISSN   0021-8995.
  13. ↑ Hu, Yan Hong; Gao, Yun; Wang, De Ning; Hu, Chun Pu; Zu, Stella; Vanoverloop, Lieve; Randall, David (2002-04-18). "Rigid polyurethane foam prepared from a rape seed oil based polyol". Journal of Applied Polymer Science. 84 (3): 591–597. doi:10.1002/app.10311. ISSN   0021-8995.
  14. ↑ Guo, Andrew; Javni, Ivan; Petrovic, Zoran (2000-07-11). "Rigid polyurethane foams based on soybean oil". Journal of Applied Polymer Science. 77 (2): 467–473. doi:10.1002/(SICI)1097-4628(20000711)77:2<467::AID-APP25>3.0.CO;2-F. ISSN   0021-8995.
  15. ↑ Menges, G.; Knipschild, F. (August 1975). "Estimation of mechanical properties for rigid polyurethane foams". Polymer Engineering and Science. 15 (8): 623–627. doi:10.1002/pen.760150810. ISSN   0032-3888.
  16. ↑ Zhu, Menghe; Ma, Zhewen; Liu, Lei; Zhang, Jianzhong; Huo, Siqi; Song, Pingan (2022-06-10). "Recent advances in fire-retardant rigid polyurethane foam". Journal of Materials Science & Technology. 112: 315–328. doi:10.1016/j.jmst.2021.09.062. ISSN   1005-0302.
  17. 1 2 3 Michelle Tsai (13 August 2007). "Get Your Foam On". Slate . Retrieved 1 February 2023.
  18. ↑ "Insulating Foams Save Money, Increase Safety". NASA. 2009. Retrieved 1 February 2023.
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