materials development | Compounding bioplastics
are colourless and highly transparent. The biodegrada- bility of the biopolymer is unaffected.
Pfaadt also said that Vinnex powders enable increased fi ller content without sacrifi cing perfor- mance. “Depending on the grade used, up to 30% of fi ller content can be added to the blend without severely impacting physical properties,” he claimed. In addition, Vinnex can be used to improve the
processing behaviour of PLA, Pfaadt added. It improves fi lm sealing properties, enhances impact strength, improves melt strength, and provides a very stable bubble.
Graph shows the effect on modulus of an Ingeo PLA from NatureWorks by the addition of two different Proviplast compounds from Proviron. Proviplast C1215 contains ATBC plasticizer, Proviplast C2215 contains a new molecule
Acrylic property enhancers
Dow Plastics Additives highlights three Paraloid additives it has developed to improve PLA properties. The fi rst is Paraloid BPM 515, an acrylic impact modifi er that improves the impact resistance of clear thermofor- med sheets, preventing shattering during cutting and punching. The product works at addition levels as low as 2%, maintaining product clarity. Dow says that Paraloid BPM 515 has “excellent” stability, and so retains its properties even after recycling.
Paraloid BPM 520 is another impact modifi er, but is optimised for injection moulding compounds of PLA and PLA blends (PLA/PC for example). Dow says that it imparts an “exceptional” combination of impact strength (even at low temperatures), very good colourability, and smooth surface fi nish.
The third additive, Paraloid BPMS 260, is a high
The properties of Natureworks Ingeo PLA can be adjusted using Wacker’s Vinnex 2505
applications and have a greater effect on processing properties, such as the necking and fl exibility of rigid fi lms. Both types improve the tack to paper and the sealing properties. The binder is compatible with many biopolymers, including PLA, PHA and PBS (polybutylene succinate), and different grades can be combined with one or more biopolyesters (some of which are normally incompatible with each other: PLA and PBS for example) and fi llers. “Depending on the composition and Vinnex content, polymer blends have higher impact strengths, are more fl exible or have a higher melting strength than conven- tional biopolymers,” Wacker says. Speaking at the NatureWorks conference, Marcus
Pfaadt, Wacker’s senior manager for business develop- ment, said that PLA and PVAc are miscible, as is evidenced by the fact that blends show only one glass transition temperature, which is lower than that of pure PLA. With 20% of Vinnex 2525 in Ingeo 4043D, for example, the Tg is lowered by approx. 4°C. The blends
24 COMPOUNDING WORLD | June 2014
molecular weight acrylic copolymer that increases melt strength during fi lm and sheet extrusion, blown fi lm extrusion, or calendering.
“This additive enables high line speeds, reduces equipment diffi culties, and provides lower costs,” says a representative. Once again, addition levels as low as 2% signifi cantly increase melt elasticity. Thanks to its effect based on chain entanglements, excellent batch to batch repeatability is said to be observed, which Dow says provides an advantage over reactive technologies. All three additives conform to European and US requirements for food contact applications.
Montanic acid soaps Clariant cites its Licomont CaV 102, a calcium soap of montanic acid, as an alternative to amide waxes currently used as processing aids for PLA in injection moulding applications. Beate Treffl er, head of technical marketing for waxes in Clariant’s Additives Business Unit, says that drawbacks with amide wax include poor crystallization behaviour and instability under high shear. This can lead to poor printability and mould deposits, which cause problems especially in complex
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