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Towards improved properties of biodegradable polymers made from Sugar Cane, PLA

D. Reichert
In daily life, construction polymers play an important role. Most of products are not reusable for different reasons (cost, hygiene, ) so the need of an environment saving production and disposal is evident. To besides from the obvious task on saving resources and environment, there is also a growing economical interest in this issue. On of the most promising candidates for a thermoplastic construction polymer that can be manufactured from bio-renewable resources and is biodegradable is Polylactic acid (PLA), for which Corn starch (in the U.S.) or sugarcanes (rest of world) are the common feedstock.
Polylactic acid can be processed like most thermoplastics into fiber (for example using conventional melt spinning processes) and film. However, the low glass transition temperature prohibits many applications, like usage for coffee cups that will simply soften and flow away upon filling with hot drinks. One popular option to cope with this is the modification with other polymers, either conventional product or even enantiomers of PLA itself. For example, the melting temperature can be increased 40-50° C and the Heat Deflection temperature of PLLA can be increased from approximately 60° C to up to 190 ° C for by physically blending the polymer with PDLA (poly-D-lactide). PDLA and PLLA are known to form a highly regular stereocomplex with increased crystallinity. The maximum effect in temperature stability is achieved when a 50-50 blend is used, but even at lower concentrations of 3-10% of PDLA a substantial effect is achieved. In the latter case PDLA is used as a nucleating agent, thereby increasing the crystallization rate. Due to the higher crystallinity of this stereo-complex, the biodegradability will become slower. The interesting feature is that the polymer blend remains transparent, which is one to the desirable properties that must be kept upon modification.




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