bioplastics | Materials
Figure 1: High heat PLA performance characteristics
Like conventional PLA, de Bie says these high heat
PLAs can be processed on existing injection moulding equipment, with appropriate adjustments to tempera- ture settings and process. PLLA and PDLA homopoly- mers - and PLA compounds - are hygroscopic materials and can absorb up to 0.3 – 0.4% of moisture. Moisture causes hydrolyis of the PLA homopolymer during high temperature processing, resulting in a loss of mechani- cal properties in the fi nal part. Therefore, it is impor- tant to reduce the moisture content before processing by pre-drying in a desiccant hot air dryer to levels of less than 250 ppm. Purac recommends drying to less than 50 ppm if possible. Optimum heat performance and injection moulding
cycle times are achieved when processed at relatively high mould temperatures (approximately 100°C). Sprues and low shear hot runners can be used for processing PLA. Purac does not produce commercial PLA polymers
but is able to supply samples of PLLA, PDLA and PLA compounded blends for product evaluation purposes. The company says it has a number of supply partners able to deliver commercial quantities using its Puralact monomers. De Bie says the company is already working with some key development partners to develop applications and that moulders can play a key part in the development chain. “Injection moulders are in the unique position that
they can offer their customers a strong product benefi t whilst moving to sustainable PLA themselves. Those injection moulders who are ahead of their competitors and already work with PLA can offer this to their customers, enabling them to offer bio-based, recyclable articles with a reduced CO2
footprint to their end-con-
sumers. In this way, injection moulders are now in an excellent position to be among the fi rst to offer brand owners a switch to bio-based plastic,” says de Bie.
www.purac.com
Figure 2: Puralact lactide monomers: building blocks used to make PDLA and PLLA homopolymers
38 INJECTION WORLD | April 2013
Source: Purac
Figure 3: The new PLAs can close the performance gap Source: Purac
www.injectionworld.com
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