Recycled poly(lactic acid)–based 3D printed sustainable biocomposites: a comparative study with injection molding

Abstract

With the objective of giving a new economic life to postindustrial waste poly(lactic acid) (PLA), biocomposites based on recycled PLA were manufactured using conventional melt blending, and the strands produced were successfully used for three-dimensional (3D) printing of American Society for Testing and Materials (ASTM) samples by means of the fused deposition molding (FDM) method. This article further discusses the processing advantages and challenges associated with void formation, anisotropic behavior, and the quality of the 3D printed (3DP) samples in comparison with injection-molded (IM) counterparts. The blends were manufactured containing 30 wt % of recycled PLA in a matrix of virgin PLA. Similarly, blends were also prepared with addition of an epoxy-based chain extender (CE) and as well as with the CE and a reinforcing phase of microcrystalline cellulose (MCC). One of the limitations of recycled PLA in FDM-based 3D printing is its high melt flow due to the reduced molecular weight after recycling, which results in excessive material flow during extrusion, and hence limits its application in FDM-based 3D printing. Consequently, the main effect of the CE, Joncryl, was to control the Melt Flow Index (MFI) of the biocomposites containing the recycled PLA. The addition of CE also resulted in improvement of the impact strength of 3DP samples. In general, the CE in combination with the natural fibers (MCC) allowed the incorporation of postindustrial PLA. Data suggest that more recycled PLA may be incorporated by using this blend combination. In general, owing to the void formation, 3DP samples presented lower values of density (lightweight) and mechanical properties as compared with IM samples. However, the tensile strength, modulus and Izod impact strength of 3DP biocomposites were increased by up to 88%, 127%, and 11%, respectively, by the addition of 5 wt % MCC, as compared with 3DP samples based on postindustrial PLA without additives.