Expanding the Bounds of Bioplastics
Enhanced Processing Properties
An employee produces injection-molded articles from bioplastics in a pilot plant of the Fraunhofer Institute for Applied Polymer Research (IAP) in Schwarzheide near Berlin, Germany.
“WACKER identified this trend early on and its VINNEX® range now offers a product line that significantly improves the processing of bioplastics such as biopolyesters and starches,” explains WACKER manager Dr. Marcus Pfaadt. The additive system based on poly(vinyl acetate) makes it possible to combine various biopolyesters, thus selectively influencing the properties of the created polymer blend. “This opens up a broad, customizable product range for bio-based plastic blends,” stresses Pfaadt. Even adding three or four percent of VINNEX® to the polymer blend is enough to significantly increase the material properties and the ease of processing of the blend.
The biopolyesters that are currently readily available and can replace plastics produced from petrochemicals include polylactic acid (PLA), which is generally manufactured from corn starch, and polybutylene succinate (PBS), which can be partially manufactured from renewable raw materials via an intermediate stage involving succinic acid. Key applications for WACKER’s additives include injection-molded products, plastic packaging or combinations of plastics and paper such as cardboard box coatings or the moisture-barrier lining as a in paper cups.
Bioplastics undergoing blown-film extrusion at the Fraunhofer Institute for Applied Polymer Research (left): an employee adjusts the air supply in order to stabilize the bubble (above). As before, a polylactic acid/VINNEX® compound is being processed here.
The poly(vinyl acetate)-based additive VINNEX® 2526 enables, for example, PLA-based blown and cast films to be optimally processed. The additive improves the melt strength, and thereby also the bubble stability during extrusion. It also enables the process temperature to be reduced by about 10 °C.
Even Better Printability
“By minimizing the ‘necking,’ i.e. the constriction of the melt film that is often observed in PLA and PBS, the improved melt strength results in optimal thickness distribution,” says Karl Weber, WACKER technical service manager, who has led the development of additives for bioplastics. Another benefit: the otherwise good printability of the PLA or PBS biopolyesters is also further increased by using VINNEX®. VINNEX® also makes it possible to combine different biopolyesters with one another or with starch, and prevents post-crystallization effects.