Challenges in biopolymer processing

Biopolymers introduce new challenges in processing related to the chemical/ physical properties of the processed material and to final product attributes 

The following examples review process issues relating to biopolymers. They deal mainly with poly-L-lactic acid (PLLA) processing, because it is the most widely studied biomaterial. 

Harris and Lee (2008) studied the increase of crystallinity of injection molded poly(lactic acid) (PLA). The PLA was first dried and dry mixed with fillers. It was then melt extruded with a twin screw extruder in a temperature range of 160-190 °C with a screw speed of 230 rpm. Extruded pellets were dried and injection molded at various mold temperatures. They found that material crystallinity was enhanced by addition of nucleating agents (about 2%), by annealing injection molded samples or by directly molding the material in a preheated mold. 

Jiang et al. (2008) prepared a composite material of poly(3-hydroxybutyrate- 

CO-3-hydroxy valerate) (PHBV) and cellulose by extrusion blending, using a co-rotating twin screw extruder with a temperature profile ranging from 160 to 145 °C. PHBV pellets were dried, dry mixed with a cellulose nanowhisker powder and extruded. The extrudate was cooled in a water bath and the final pellets were dried. This material did not have the same mechanical properties and the same cellulose dispersion as the analogous composite prepared with solvent casting process. It was necessary to add a compatibilizer to improve the dispersion. 

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