A line of specialty elastomers is being added to polyolefins to create rigid thermoplastic olefins (TPO), soft thermoplastic elastomers (TPE), and transparent compounds or polymer blends for applications that require improved toughness, impact strength, flexibility, elasticity, clarity, reduced stress whitening, or weight reductions. ExxonMobil Chemical’s Vistamaxx is being applied as a minority blend partner by compounders and dry-blending converters to create materials seeing use in flexible hoses/tubing, adhesives, containers, and semi-rigid/rigid food-contact packages. The company positions the compounds as an alternative to polyvinyl chloride (PVC). Vistamaxx was initially focused on applications in nonwoven films, but the company is now anticipating broader markets, including blowmolded and injection molded goods.
Vistamaxx reportedly exhibits excellent compatibility with polyethylene (PE) and polypropylene (PP), acting in some cases as a partial substitute for a variety of polymers, including styrene block copolymers and polyisobutylene, leading to reduced costs and improved performance.
The material’s elastic properties, which result from a predominantly amorphous ethylene propylene matrix with a network of fine, well-dispersed isostatic PP crystallites, allow for compounds with flexibility and impact resistance, while remaining clear in PP random copolymer and homopolymer blends.
ExxonMobil says compounds become more flexible as Vistamaxx levels increase, while tensile strength drops steeply with the addition of the elastomer due to a reduction in the blend’s crystallinity. If elastomer content exceeds 30%, elongation at break increases steeply with the creation of a co-continuous phase. Low Vistamaxx concentrations have little effect on initial PP hardness.
Adding Vistamaxx to random copolymer or homopolymer PPs can improve impact strength down to -20°C (-4°F). In terms of thermal properties at concentrations below 30%, compounds will act like PPs, while in compounds with elastomer levels above 30%, stickiness is observed in materials aged above 100°C (212°F). As elastomer levels increase, the Vicat softening point goes lower. Low haze-level compounds can be produced when Vistamaxx is added to random copolymers, although ExxonMobil notes that thorough mixing of dry blends during processing or melt blending is needed to optimize transparency. Tests have shown that when mixed in above 30%, Vistamaxx can reduce or eliminate stress whitening in homopolymers. In styrene ethylbutylene styrene (SEBS), Vistamaxx elastomers can increase tensile and tear strength by up to 45%.—[email protected]
ExxonMobil Chemical Co., Houston, TX, U.S.A.; +1 281-870-6607; www.exxonmobil.com