SURFACE MODIFICATION | SCRATCH AND WEAR
thermal stability. Its high melt viscosity and low melt strength make melt processing difficult. It also suffers from a low rate of crystallisation, with post-crystallisation being the reason that PLA articles typically become progressively more brittle. By contrast, PBS has mechanical properties
more similar to polyolefins. Unlike PLA, it is a flexible, tough material of high tensile strength. By virtue of its comparatively high degree of crystallin- ity, PBS has high heat resistance. However, it also tends to post-crystallise. Four additives were studied - Vinnex 2504 and
Above:
Bioplastics have been a target for bulk and surface property modification at Wacker
polarities tuned precisely to biodegradable polyesters. The resulting compatibility makes them highly effective. The company also supplies its Genioplast Pellet range of silicone-based additives for thermoplastics compounding. These act as processing aids by reducing friction, which enhances the polymer’s properties.
Combined benefits The company’s researchers set out to study how a combination of both additive systems might affect the processing and material properties of biode- gradable polyesters. The project focused on polylactic acid (PLA) and calcium carbonate-filled polybutylene succinate (PBS), which made it possible to look into the additives’ effects on both filled and unfilled polymer systems. Two standard commercial grades of polyester
were used as polymer matrixes - Ingeo Biopolymer 4043 D (PLA) from Nature Works and BioPBS FZ 91 PM (PBS) from PTT MCC Biochem. Both are semi-crystalline, made from renewable raw materials and have been optimised by the manu- facturers for the production of plastic film. PLA is known as a rigid, high-tensile material, which is extremely brittle and fragile and has poor
2525, and Genioplast Pellet S and Pellet P Plus. Vinnex 2504, a vinyl acetate-ethylene copolymer, is a powder grade primarily used by compounders to incorporate soft segments into a polymer matrix. Vinnex 2525 is a pellet format polyvinyl acetate homopolymer. When used as a processing aid, it improves flow, increases the melt strength, and reduces post-crystallisation by semi crystalline polyesters. Genioplast Pellet P plus is a food contact approved grade, while the Pellet S grade is primarily aimed at technical applications. There are no other significant differences in the properties of these two grades. The biopolyesters used in the screening were compounded on a ZE-25 co-rotating twin-screw extruder from KraussMaffei. The compounds were then pelletised and processed into test specimens – including injection-moulded test panels, flow spirals, blown film and compression moulded panels – which were tested and assessed in accordance with industry standards. The non-addi- tive biodegradable polyesters served as references and were processed in the same way. The modified compounds were produced by incorporating either a Vinnex grade on its own or a combination of Vinnex and Genioplast Pellet into the polyesters. The PLA-based compounds were all unfilled, while the PBS based counterparts contained 15% calcium carbonate.
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HIGH ELECTRICAL CONDUCTIBILITY COMPOUNDS FOR VINYLS WITH VERSATILITY
YOUR TAILOR SAFETY SOLUTION
IMAGE: WACKER
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