Polyurethane urea elastomer

Last updated

The polyurethane urea elastomer (PUU), or poly (urethane urea) elastomer, is a flexible polymeric material that is composed of linkages made out of polyurethane and polyurea compounds. Due to its hyperelastic properties, it is capable of bouncing back high-speed ballistic projectiles as if the material had “hardened” upon impact. PUUs were developed by researchers from the U.S. Army Research Laboratory (ARL) and the Army’s Institute for Soldier Nanotechnology at the Massachusetts Institute of Technology (MIT) to potentially replace polyethylene materials in body armor and other protective gear, such as combat helmets, face shields, and ballistic vests. [1]

Contents

Composition

In general, PUUs are composed of both hard and soft segments that each play a role in the material’s physical properties. The soft segments consist of two types of chemical compounds, long-chain polyols and diisocyanates, that react and connect together with urethane linkages. On the other hand, the short-chain diamines react with the diisocyanates to form the hard segments that are held together with urea linkages. The mechanical properties of the PUU largely depend on the specific diisocyanates, long-chain polyols, and short-chain diamines in play, because how these components interact determines how well the soft and hard segments of the elastomers both crystallize and undergo microphase separation. As a result, variations in this molecular arrangement of chemical compounds have been shown to greatly affect the elastomer’s morphology and the macroscopic, mechanical properties that it exhibits. [2] [3]

Hyperelastic behavior

In 2017, researchers from the Army Research Laboratory and MIT reported that PUUs are capable of demonstrating hyperelastic properties, meaning that the material becomes extremely hardened upon being deformed within a very short time. As a result, the material may withstand ballistic impacts at exceptionally high speeds. [4]

For the study, the researchers investigated the performance of different PUU variants where 4,4’-dicyclohexylmethane diisocyanate (HMDI) was chosen as the diisocyanate compound, diethyltoluenediamine (DETA) was chosen as the short-chain diamine compound, and poly(tetramethyleneoxide) (PTMO) was chosen as the long-chain polyol compound. Despite consisting of the same chemical compounds with the same stoichiometric ratio of 2:1:1 of [HDMI]:[DETA]:[PTMO], the samples differed regarding the molecular weight of their respective PTMO component, namely 650 g/mol (10,400 oz/lbmol), 1,000 g/mol (16,000 oz/lbmol), and 2,000 g/mol (32,000 oz/lbmol), for the soft segments of the elastomers. [5]

Each of the three samples were subjected to a laser-induced projectile impact test (LIPIT), which tested the dynamic response of the material by using a pulsed laser to shoot it with microparticles made of silica at speeds ranging from 200 to 800 m/s (660 to 2,620 ft/s). [5] [6] The researchers found that the sample with the 650 g/mol (10,400 oz/lbmol) PTMO was the most rigid variant with the particle exhibiting a shallow penetration of about 4 μm (0.00016 in) upon impact despite travelling at 790 m/s (2,600 ft/s) before rebounding at 195 m/s (640 ft/s). In contrast, the sample with the 2,000 g/mol (32,000 oz/lbmol) PTMO displayed a deeper penetration of about 9 μm (0.00035 in), but had a slower particle rebound of 80 m/s (260 ft/s), making it the most rubber-like among the PUU samples. The strain-rates associated with these impacts were on the order of 2.0 x 10^8/s for the former and 8.1 x 10^7/s for the latter. [5]

However, all three PUU variants demonstrated rebound capabilities with no signs of post-mortem damage after impact from the microparticles. In contrast, when the LIPIT was performed on a ductile, glassy polycarbonate at similar speeds to that of the 650 g/mol (10,400 oz/lbmol) PTMO PUU variant, the polycarbonate displayed predominant deformation upon impact, despite its high fracture toughness and ballistic strength. [5] [7] According to the researchers, the effectiveness of the PUUs may come from how the molecules “resonate” similar to chain-mail upon impact with each oscillations at specific frequencies dissipate the absorbed energy. In comparison, the polycarbonate lacked the broad range of relaxation times, a characteristic that reflects how efficiently the molecules in the polymer chains respond to an external impulse, that PUUs are known to have. [7] As a result, the researchers concluded that even the most rubber-like variant of the PUU, specifically the 2,000 g/mol (32,000 oz/lbmol) PTMO sample, demonstrated greater robustness and dynamic stiffening than the glassy polycarbonate. [5]

ARL researchers have stated that the PUU’s primary benefit comes not from its extra strength but its fabric-like flexibility, which demonstrates its potential as a replacement material for the rigid ceramic and metal plates generally found in military battle armor. However, as of 2018, the PUU is still under development in the testing phase. [8]

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 is produced from a wide range of starting materials. 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">Petrochemical</span> Chemical product derived from petroleum

Petrochemicals are the chemical products obtained from petroleum by refining. Some chemical compounds made from petroleum are also obtained from other fossil fuels, such as coal or natural gas, or renewable sources such as maize, palm fruit or sugar cane.

<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">Carbamate</span> Chemical group (>N–C(=O)–O–)

In organic chemistry, a carbamate is a category of organic compounds with the general formula R2NC(O)OR and structure >N−C(=O)−O−, which are formally derived from carbamic acid. The term includes organic compounds, formally obtained by replacing one or more of the hydrogen atoms by other organic functional groups; as well as salts with the carbamate anion H2NCOO−.

<span class="mw-page-title-main">Polyurea</span> Class of elastomers

Polyurea is a type of elastomer that is derived from the reaction product of an isocyanate component and an amine component. The isocyanate can be aromatic or aliphatic in nature. It can be monomer, polymer, or any variant reaction of isocyanates, quasi-prepolymer or a prepolymer. The prepolymer, or quasi-prepolymer, can be made of an amine-terminated polymer resin, or a hydroxyl-terminated polymer resin.

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">Methylene diphenyl diisocyanate</span> Aromatic diisocyanate

Methylene diphenyl diisocyanate (MDI) is an aromatic diisocyanate. Three isomers are common, varying by the positions of the isocyanate groups around the rings: 2,2′-MDI, 2,4′-MDI, and 4,4′-MDI. The 4,4′ isomer is most widely used, and is also known as 4,4′-diphenylmethane diisocyanate. This isomer is also known as Pure MDI. MDI reacts with polyols in the manufacture of polyurethane. It is the most produced diisocyanate, accounting for 61.3% of the global market in the year 2000.

<span class="mw-page-title-main">Isosorbide</span> Chemical compound

Isosorbide is a bicyclic chemical compound from the group of diols and the oxygen-containing heterocycles, containing two fused furan rings. The starting material for isosorbide is D-sorbitol, which is obtained by catalytic hydrogenation of D-glucose, which is in turn produced by hydrolysis of starch. Isosorbide is discussed as a plant-based platform chemical from which biodegradable derivatives of various functionality can be obtained.

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

Polyisocyanurate, also referred to as PIR, polyiso, 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.

<span class="mw-page-title-main">Hot-melt adhesive</span> Glue applied by heating

Hot-melt adhesive (HMA), also known as hot glue, is a form of thermoplastic adhesive that is commonly sold as solid cylindrical sticks of various diameters designed to be applied using a hot glue gun. The gun uses a continuous-duty heating element to melt the plastic glue, which the user pushes through the gun either with a mechanical trigger mechanism on the gun, or with direct finger pressure. The glue squeezed out of the heated nozzle is initially hot enough to burn and even blister skin. The glue is sticky when hot, and solidifies in a few seconds to one minute. Hot-melt adhesives can also be applied by dipping or spraying, and are popular with hobbyists and crafters both for affixing and as an inexpensive alternative to resin casting.

FKM is a family of fluorocarbon-based fluoroelastomer materials defined by ASTM International standard D1418, and ISO standard 1629. It is commonly called fluorine rubber or fluoro-rubber. FKM is an abbreviation of Fluorine Kautschuk Material. All FKMs contain vinylidene fluoride as the common monomer, to which different other monomers are added for specific types and functionalities, fitting the desired application.

Thermoplastic polyurethane (TPU) is any of a class of polyurethane plastics with many properties, including elasticity, transparency, and resistance to oil, grease, and abrasion. Technically, they are thermoplastic elastomers consisting of linear segmented block copolymers composed of hard and soft segments.

<span class="mw-page-title-main">Polytetrahydrofuran</span> Chemical compound

Polytetrahydrofuran, also called poly(tetramethylene ether) glycol or poly(tetramethylene oxide), is a collection of chemical compounds with formula HO(CH2)4O(CH2)4)nOH or HO((CH2)4O-)n-H. The material is a mixture of polyether diols terminated with alcohol groups. It is produced by polymerization of tetrahydrofuran as well as 1,4-butanediol.

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.

Moisture-cure polyurethanes -- or polyurethane prepolymer -- are isocyanate-terminated prepolymers that are formulated to cure with ambient water. Cured PURs are segmented copolymer polyurethane-ureas exhibiting microphase-separated morphologies. One phase is derived from a typically flexible polyol that is generally referred to as the “soft phase”. Likewise the corresponding “hard phase” is born from the di- or polyisocyanates that through water reaction produce a highly crosslinked material with softening temperature well above room temperature.

Polyurethane dispersion, or PUD, is understood to be a polyurethane polymer resin dispersed in water, rather than a solvent, although some cosolvent maybe used. Its manufacture involves the synthesis of polyurethanes having carboxylic acid functionality or nonionic hydrophiles like PEG incorporated into, or pendant from, the polymer backbone. Two component polyurethane dispersions are also available.

Hydrogenated MDI (H12MDI or 4,4′-diisocyanato dicyclohexylmethane) is an organic compound in the class known as isocyanates. More specifically, it is an aliphatic diisocyanate. It is a water white liquid at room temperature and is manufactured in relatively small quantities. It is also known as 4,4'-methylenedi(cyclohexyl isocyanate) or methylene bis(4-cyclohexylisocyanate) and has the formula CH2[(C6H10)NCO]2.

<span class="mw-page-title-main">Diethyl toluene diamine</span> Chemical compound

Diethyl toluene diamine (DETDA) is a liquid aromatic organic molecule with formula C11H18N2. It is chemically an aromatic diamine and has the CAS Registry number of 68479-98-1. It has more than one isomer and the mixture of the two main isomers is given a different CAS number of 75389-89-8. It is often marketed as a less toxic version of 4,4'-methylenedianiline (MDA). It is also used to replace the more toxic 4,4'-methylenebis(2-chloroaniline) (MOCA). The toxicology is reasonably well understood.

References

  1. ↑ Owens, Katherine (October 23, 2017). "A new polyurethane-based material could mean self-hardening, almost impenetrable helmets". Defense Systems. Retrieved August 30, 2018.
  2. ↑ Hsieh, Alex; Orlicki, Joshua; Beyer, Rick (March 2009). "Molecular Design of Novel Poly(urethane-urea) Hybrids as Helmet Pads for Ballistic and Blast Trauma Mitigation". U.S. Army Research Laboratory. Archived from the original on November 28, 2012 – via Defense Technical Information Center.
  3. ↑ Hsieh, Alex; Sarva, Sai; Rice, Norman (September 2009). "Improved Dynamic Strain Hardening in Poly(Urethane Urea) Elastomers for Transparent Armor Applications". U.S. Army Research Laboratory.
  4. ↑ "PUUs Seem to be Propitious for Soldier and Vehicle Protection". AZO Materials. October 11, 2017. Retrieved August 30, 2018.
  5. 1 2 3 4 5 Veysset, David; Hsieh, Alex; Kooi, Steven; Nelson, Keith (June 27, 2017). "Molecular influence in high-strain-rate microparticle impact response of poly(urethane urea) elastomers". Polymer. 123: 30–38. doi:10.1016/j.polymer.2017.06.071. hdl: 1721.1/123990 . S2CID   136267170.
  6. ↑ Mraz, Stephen (November 20, 2017). "Army Investigates New, Tougher Materials for Helmets". Machine Design. Retrieved August 30, 2018.
  7. 1 2 "Army finds promise in durable material for future Soldier combat helmets". U.S. Army. October 11, 2017. Retrieved August 30, 2018.
  8. ↑ Keller, Jared (October 11, 2017). "The Army's Next Body Armor May Get Stronger The Harder It's Hit". Task & Purpose. Retrieved August 30, 2018.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.