Investigating the Thermal and Mechanical Performance of Polylactic Acid (PLA) Reinforced with cellulose, wood fibers and Copolymer

Abstract

Polylactic Acid, a sugar based biodegradable polymer possesses attractive properties that makes it a candidate for sustainable applications. However, other properties limiting an application like low thermal stability, reduced mechanical performance and moisture sensitivity compared to polypropylene, polyethylene and polystyrene. In the current study, properties of PLA were improved by compounding and hot pressing it with different natural commercial and readily available fibers of Kraft cellulose, wood fiber, viscouse Lyocell® and Cordenka® in mass proportions of 10%, 20% and 30% relative to the matrix PLA with 10% of an additional copolymer. Charpy impact strength, tensile strength, thermal properties and morphology were investigated and compared for all composites and their possible applications. It was found that Charpy impact strength reduced with increase in fiber content with highest impact of (63 kJ/m2) at 10% viscouse fiber loading. A high tensile strength of 67 MPa was obtained from 30% Lyocell fiber in the composite which was 4 MPa and 10 MPa higher than that of Kraft cellulose at the 30% fiber loading and pure PLA respectively. Modulus of elasticity reached a maximum value of 6 GPa at 30 % loading of Kraft cellulose. Addition of copolymer showed reduced stiffness for all the composites due to impregnation of the active sites instead of bonding hence did not improve the fiber-matrix interaction. Detailed analysis showed better fiber-matrix interface, fiber pullout and the active role played by fibers in absorbing energy thus enhancing the mechanical properties. Water absorption on the other hand showed prolonged water uptake. Thermal analysis for composite without copolymer revealed a stable crystal structure whereas those with copolymer showed different melting peaks indicative of the presence of different phases in the structure. The results obtained shows that the properties of PLA can be enhanced by addition of natural fibers in cellulosic form. This will reduce the cost of these composites and will open up an avenue in which biodegradable composites can be utilized in applications to replace the components made from non-degradable polymers.