Rotational Moulding of Poly-lactic Acid

This paper is aimed to study the effect of poly(lactic acid) (PLA) grade and granulometry on the processability by rotational molding. Two different grades of PLA were considered: besides different viscosities, the grades are also characterized by different quenchability, defined as the capability of forming an amorphous structure with the slow cooling rates typical of rotational molding. Three different granulometries were considered: coarser, as received pellets, intermediate size pellets produced by extrusion, and finer powders. Besides the different dimensions, the intermediate pellets also experienced a supplementary extrusion step above melting, which induces degradation of the material. For all grades and granulometries, void free prototypes were obtained, which is indicative of a very efficient sintering process. As a consequence, the modulus of the prototypes was found to be unaffected by the PLA grade or granulometry. In contrast, the strength and ductility were shown to be more significantly dependent on quenchability than on viscosity. Also, previous thermal treatments of particles were shown to significantly decrease the strength and ductility of prototypes, as a consequence of the thermal degradation induced by heating above melting.