Biocomposites of Poly(Lactic Acid) and Microcrystalline Cellulose: 2 Influence of the Coupling Agent on Thermomechanical and 3 Absorption Characteristics

In this study, poly(lactic acid) (PLA) and micro- 6 crystalline cellulose (MCC)-based green biocomposites were 7 developed using a solution casting technique. Essentially, the 8 bonding between PLA and MCC is quite feeble; therefore, the 9 current study is conducted to strengthen the bonding by 10 incorporating a coupling agent, thereby enhancing the overall 11 quality of the biocomposites. Thus, the present study aimed to 12 examine the influence of combined coupling agents maleic 13 anhydride (MAH) and maleic acid (MA) (MAH−MA) on the 14 properties of polylactic acid (PLA)/microcrystalline cellulose 15 (MCC) biocomposites. The investigation also encompassed an 16 examination of the impact of MCC loading (2, 3, and 5% w/w) 17 into a PLA matrix. The Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) examination 18 revealed the interfacial interaction and adhesion among MCC, PLA, and coupling agents and the formation of biocomposites. The 19 incorporation of MAH−MA led to improved mechanical properties of the PLA/MCC biocomposites. Furthermore, the 20 incorporation of MAH−MA into the PLA/3 wt % MCC composite exhibited enhancements in both the tensile strength and tensile 21 modulus, accompanied by a reduced elongation at break. In addition, it is worth noting that the thermogravimetric analysis (TGA) 22 curve of the PLA composite with 3% w/w of MCC and MAH−MA displayed a significant decrease in weight beyond a temperature 23 threshold of 492.65 °C. The water absorption demonstrates that the incorporation of MAH−MA into the PLA/MCC composite led 24 to advantageous water barrier characteristics. The observed improvements were attributed to the efficient dispersion of MCC at the 25 most favorable amount of coupling agents, along with the chemical interactions involving grafting and esterification between MCC 26 and the MAH−MA coupling agent. Furthermore, the incorporation of MAH−MA into the PLA/3% (w/w) MCC composite 27 exhibited enhancements in both the tensile strength and tensile modulus, accompanied by a reduction in the elongation percentage 28 at break. The experimental results about water absorption demonstrate that the incorporation of MAH−MA into the PLA/MCC 29 composite led to advantageous water barrier characteristics. These improvements were attributed to good MCC dispersion and the 30 chemical interactions involving grafting and esterification between the MCC and the MAH−MA coupling agent.