Thermal behavior and water absorption kinetics of polylactic acid/chitosan biocomposites

In this study, biodegradable polylactic acid (PLA)/chitosan (Cs) composites were produced via melt compounding and compression molding techniques. Various chitosan loadings of 2.5, 5, 7.5 and 10 parts per hundred parts of polymer (php) were incorporated into PLA and its effects on thermal, water absorption kinetics, tensile and morphological characteristics were investigated systematically. Thermal analysis indicated that an increase in chitosan loading of up to 10 php enhanced the crystallinity percentage ( χ c ) of neat PLA to an extent of 51%, yet reduced the thermal stability of the resulting biocomposites. The kinetic study results revealed that water absorption of PLA/Cs biocomposites approached the Fickian diffusion behavior. The maximum water uptake ( M sat ) increased with chitosan addition, which can be attributed to stronger water–filler interaction. This was correlated to higher diffusion ( D ), solubility ( S ) and permeability ( P ) coefficients, which suggested the acceleration in diffusion rate and better water permeation through the biocomposites. In addition, the tensile results of dry samples showed enhancement in tensile strength and tensile modulus by 2% and 14%, respectively, relative to neat PLA through the incorporation of 2.5 php of chitosan loading. However, the water-immersed biocomposites demonstrated deterioration in all tensile properties (tensile strength, tensile modulus, and elongation-at-break values) which signified hydrolytic polymer degradation. This was confirmed by the FESEM micrographs of the fractured surfaces which exhibited filler pulled-out phenomenon and cavity formation after 50 days of water immersion.