Lanxess' Levapren 500 increases notch impact resistance of polylactide
Tuesday, July 2, 2013
Leverkusen, Germany - Levapren, the ethylene-vinyl acetate rubber (EVM) from specialty chemicals company LANXESS, is very effective in helping to reduce the brittleness of polylactide (PLA). The best results are achieved by Levapren 500 containing 50 to 60 percent vinyl acetate. EVM grades with this VA content are specialty products from LANXESS. This material from the pioneer of synthetic rubber might just help a promising, sustainable plastic gain greater market presence. “Polylactide is a very promising substance that can be obtained from a renewable raw material: lactic acid, the basic building block, can be produced by fermenting whey, for example, which in turn is a byproduct or waste product of cheese manufacturing,” says Herman Dikland, head of the Specialty Elastomers business line in the LANXESS High Performance Elastomers business unit. This polymer material thus is ideal in an age when sustainability is increasingly important – as confirmed by the overwhelming growth rates. “This material unquestionably rivals petroleum-based plastics in many respects. It can be processed in PET plants, for instance to make packaging materials.” One major disadvantage of polylactide, however, is its brittleness: the raw material's notch impact resistance values are in the region of 3 kJ/m2. However, by adding impact-resistant modifiers, this value can be increased significantly. Ethylene-vinyl acetate rubber products, such as Levapren, are suitable for this purpose, as shown in a study by a team of researchers headed by Piming Ma of the Polymer Technology Group in the Department of Chemical Engineering and Chemistry at Eindhoven University of Technology. “EVM grades with a vinyl acetate content of around 50 percent have proven to be the best modifiers,” Dikland explains. “The notch impact resistance of the polylactide increases by a factor of 20 just by adding 20 percent Levapren 500.” It jumps by a factor of 10 even when as little as 10 percent is added. Just five percent Levapren 500 makes the elongation at break rise tremendously, while tensile strength decreases only moderately. “It is difficult to determine why the notch impact resistance increases,” Dikland says, “but under a microscope we can see that Levapren 500 is distributed very evenly in the PLA matrix, making it more resilient. What's more, the rubber absorbs strong mechanical loads by forming small cavities in the Levapren domains.” According to the Eindhoven study, EVA rubber grades with significantly lower or higher VA percentages cannot do such a good job.