Water based esterification of cellulose nanofibrils for compounding with PLA

Abstract

The incorporation of cellulose nanofibrils (CNFs) into bio-based polymeric systems has been investigated as a method of improving the properties of the bio-based polymers while maintaining bio-based nature of the resulting composite. However, the hydrophobic polymer and hydrophilic CNFs are often incompatible. In this study a water-based catalyzed esterification of CNFs was attempted using lactic acid. The unmodified and modified CNFs were both used to make cast films without a polymer matrix to evaluate the effectiveness of the modification, and to compound with poly(lactic acid) (PLA) to produce injection molded composites. Films were made from lactic acid (LA)-grafted CNFs and ungrafted CNFs by vacuum filtration and were characterized for functional, thermal and mechanical properties. FTIR spectra of the modified samples revealed the presence of carbonyl peaks at 1720 cm-1 , an indication that the esterification reaction was successful. Comparable dynamic mechanical properties were observed in the LA-grafted and ungrafted CNF, but a decrease in tensile strength was observed. In addition, both samples displayed similar levels of thermal stability. PLA composites containing modified CNFs appeared to exhibit better dispersion and improved transparency compared with PLA composites containing unmodified CNFs. Therefore, esterification of CNFs in aqueous medium may provide an environmentally benign way of modifying the surface chemistry of CNFs resulting in enhanced compatibility with PLA, potentially leading to improvement in the properties of PLA as a packaging material.