A Comparison of the Effect of Silk Fibroin Nanoparticles and Microfibers on the Reprocessing and Biodegradability of PLA/PCL Blends

Abstract

In this research, the effect of reprocessing on the properties of poly(lactic acid)/poly(e-caprolactone) (PLA/PCL) blends reinforced with silk nanoparticles (NP) and silk microfibers (SF) was investigated. In this regard, the multiple extrusion process was applied to the PLA/PCL based composites and their morphology, thermal stability, intrinsic viscosity, water absorption, mass loss, barrier, and mechanical properties were studied and compared. The results of atomic force microscopy showed that silk nanoparticles were mainly located in the PLA matrix and partially at the phase interphase with a thickness of layers around 80 nm. The scanning electron microscopy results illustrated a good dispersion of NPs in the blend and poor adhesion between SFs and the polymer matrix. The thermogravimetric analysis results showed that the presence of bio-fillers stabilized the thermal properties of composites and decreased the thermo-mechanical degradation of recycled materials. Furthermore, the addition of NPs and SFs improved the barrier properties of materials and led to a decrease in the value of water absorption and mass loss of PCL/PCL composites. The results of microhardness and impact tests also demonstrated that the mechanical properties of neat PLA/PCL blends are deteriorated by increasing the number of reprocessing cycles; however, the incorporation of both NPs and SFs improved the mechanical performance of recycled PLA/PCL composites. The results suggest that the use of silk fillers represents a cost-effective and environmentally friendly way of improving the properties of reprocessed PLA-based plastic.