Morphology and barrier properties of solvent cast composites of thermoplastic biopolymers and purified cellulose fibers

This paper shows and discusses the morphology, thermal and transport properties of solvent cast biocomposites of poly(lactic acid) (PLA), polyhydroxybutyrate-co-valerate (PHBV) and polycaprolactones (PCL) containing purified alfa micro-cellulose fibers as a function of filler content. The SEM, optical microscopy and Raman imaging results indicate that a good dispersion of the fibers in the matrix was achieved for the three biopolymers. However, detrimental fiber agglomeration was clearly observed to take place for samples with fiber contents in excess of 5 wt%. The heat of fusion (related to crystallinity) of the semicrystalline PCL and PHBV biopolymers was seen to decrease, particularly in low fiber content biocomposites, but it seemed to increase slightly in the highly amorphous PLA biocomposites. In accordance with the morphology data, water and d-limonene direct permeability were seen to decrease to a significant extent in the biocomposites with low fiber contents. The permeability reduction was mostly related to a decrease in diffusivity but solubility was also found to be favorable. The main conclusion from this work is that purified cellulose fibers can also be used to enhance the barrier properties of thermoplastic biopolyesters of interest in, for instance, packaging and membrane applications.