Fiber medicine

The impact resistance of the new rubber material surpasses that of fiberglass reinforced plastic

Schematic illustration at the molecular level of SIS and i-SIS. 1 credit

Thermoplastic elastomers (TPEs, sometimes called thermoplastic rubbers) are a chemically bonded combination of several polymers (“copolymer”) – usually a plastic and a rubber – that have both thermoplastic and elastomeric properties. The thermoplastic property is useful in injection molding, while the elastomeric property gives the object the ability to stretch and return almost to its original shape. These materials are ubiquitous, for example, in vehicle interiors and exteriors. The best known TPEs include “styrenic block polymers”, which contain molecular blocks of polystyrene, which is hard, and polydiene, which is rubbery. Two prominent examples are polystyrene-b-polyisoprene-b-polystyrene (SIS) and polystyrene-b-polybutadiene-b-polystyrene (SBS). Styrenic block polymers were developed by the Shell Chemical Company in the 1960s and have since been developed by many researchers in academia and industry. While the annual global market for TPEs based on styrenic block polymers is worth billions of dollars, elastomers with improved mechanical properties, including toughness, also remain in high demand.

To improve the mechanical properties of styrenic block polymers, Nagoya University and Zeon Corporation recently announced an industry-friendly synthesis of chemically modified SIS such as hydrogen-bonded SIS (h-SIS) and “functionalized SIS ionically” (i-SIS) – which is SIS with positive ions such as sodium bound in it. The “cation” has one (monovalent) electron removed from the outer shell. Preliminary measurements have shown that i-SIS has an extremely high tensile strength of 480 MJ/m3, which is the highest value of any thermoplastic rubber material known to us.

Although preliminary tensile testing is useful for studying common mechanical properties of materials, it does not reveal all mechanical characteristics of materials, especially impact strength which is of crucial importance in practical applications. Additionally, the measurement of impact strength is also important for understanding the mechanism by which desirable mechanical properties arise in the material, and therefore how they can be achieved.

The impact resistance of the new rubber material surpasses that of fiberglass reinforced plastic

Configuration for impact testing. 1 credit

This study by Nagoya University and Zeon Corporation is the first to evaluate the impact resistance of new elastomeric materials based on i-SIS and compare them to the impact resistance of a typical high-strength material based on fiberglass reinforced plastic. (GFRP), which has a tensile strength of 330 MPa. Drop weight impact tests have demonstrated that i-SIS with monovalent or divalent cations is 3 or 4 times more impact resistant than chemically unmodified SIS; additionally, i-SIS with divalent cations is found to be 1.2 times more impact resistant than typical high strength GFRP. Overall, i-SIS, especially with divalent ions, has proven to be very impact resistant, even though inorganic fillers – a typical additive for polymer hardening – are not incorporated into the polymer and the molecular structure of the polymer is not chemically crossed. bound.

The impact resistance of the new rubber material surpasses that of fiberglass reinforced plastic

Photographs of SIS, i-SIS and GFRP, and impact resistance of each sample compared to that of SIS. 1 credit

Manufacturers of automobiles and other vehicles are constantly looking for lighter materials that also resist damage. Since i-SIS can be synthesized on an industrial scale, it has great potential to become a next-generation elastomeric material to be used not only in automotive interior and exterior parts, but also for automotive bodies, and even exterior panels of automobiles, trains, and other vehicles that require high-impact structural materials and easy fabrication. These research achievements will also contribute to the development of lightweight vehicles and the establishment of a carbon-free society.

The paper was published in ACS Omega.

Elastic polymer that is both rigid and resistant, solves a long-standing dilemma

More information:
Takato Kajita et al, High impact resistant block polymer based thermoplastic elastomers with an ionically functionalized rubber phase, ACS Omega (2021). DOI: 10.1021/acsomega.1c05609

Provided by Nagoya University

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