Biodegradability of microcrystalline cellulose/poly(lactic acid)-graftedmaleic anhydride/poly(lactic acid) composites

Abstract

This research aimed to prepare microcrystalline cellulose (MCC)/PLA composite films in which MCC was obtained from acid hydrolysis of cotton fabric (CT-MCC) by hydrochloric acid. In addition, maleic anhydride – grafted-polylactic acid (PLA-g-MA) was synthesized and used as a compatibilizer. The optimum conditions for PLA-g-MA synthesis were investigated in terms of reaction time and temperature. The results showed that the optimum conditions for synthesis PLA-g-MA was that PLA was dissolved in THF and using BPO as an initiator under nitrogen atmosphere at 85 ºC until 3 h. NMR, FT-IR, TGA, DSC, and SEM were used to characterize chemical structure and properties of PLA-g-MA. After that, the CT-MCC/PLA composites were prepared at various ratios (0, 10, 20, 30, and 40 wt%) while the amount of PLA-g-MA was fixed at 5 wt% based on MCC content by using a twin screw extruder and a compression molding, respectively. The mechanical properties, fractured surface, water absorption, thermal properties, and biodegradability of the composites were investigated. The results showed that the elongation at break of all composites increased with increasing CT-MCC loading. The composite films consisted of PLA-g-MA showed better mechanical properties than the uncompatibilized films. In particular, the 10%wt CT-MCC/5%PLA-g-MA/PLA composite films exhibited the highest tensile strength. These results were confirmed and in good agreement with the results from SEM analysis. Better adhesion and dispersion of the CT-MCC/PLA-g-MA/PLA composite films was observed. Moreover, uncompatibilized composite films exhibited higher water absorption than neat PLA, while the compatibilized composites showed lower water absorption than the uncompatibilized composite films. This is due to the hydrophobic surface of the formation of covalent bonds between the functional groups of maleic anhydride and the hydroxyl groups at the surfaces of CT-MCC. Finally, the biodegradability of the films was evaluated under (1) enzymatic degradation using lipase and cellulase and (2) controlled composting condition according to the waste water treatment system condition. The composite films can be degraded under both conditions, especially the biodegradation rate was increased after 4 days in enzymatic condition, and 4 weeks in the waste water treatment system condition. After degradation for 7 days, the %weight loss of 40%CT-MCC/PLA composite films under cellulase solution, lipase solution, and activated sludge system was 4%, 3%, and 1.74%, respectively.