Incorporation of poly(glycidylmethacrylate) grafted bacterial cellulose nanowhiskers in poly(lactic acid) nanocomposites: Improved barrier and mechanical properties

Abstract

Poly(glycidyl methacrylate) (PGMA) was grafted onto bacterial cellulose nanowhiskers (BCNW) by means of a redox-initiated free radical copolymerization reaction. The incorporation of PGMA chains decreased the thermal stability and crystallinity of BCNW. The neat and the PGMA-grafted BCNW were subsequently incorporated as fillers into the PLA matrix. PGMA grafting improved both matrix-filler adhesion and the dispersion of cellulose nanocrystals. However, the dispersion of the nanofiller was still not completely optimized and loadings higher than 3wt.% resulted in increased agglomeration. The incorporation of both neat and PGMA-grafted BCNW significantly reduced the oxygen permeability of PLA for low relative humidity conditions. However, due to the moisture sensitivity of cellulose, smaller improvements were attained when increasing the water activity. The detrimental effect of moisture on the oxygen permeability of nanocomposites was limited by the grafting copolymerization since PGMA-grafted BCNW seemed to present a more hydrophobic behavior. Furthermore, increased elastic modulus and tensile strength were observed for all the nanocomposites, especially when the concentration of nanocrystals was around the percolation threshold, i.e. 3wt.%, but only nanocomposites containing PGMA-grafted BCNW preserved the ductility of neat PLA.