Abstract: Polylactic acid (PLA) possesses good mechanical and biodegradability properties which make it a suitable material for polymer composites whereas brittleness and high costs limit its utilization in various applications. The reinforcement of natural fibres with biopolymers has been formed to be an efficient technique to develop composites having the ability to be fully biodegradable. This study concerns with the incorporation of various percentages of untreated and alkali-treated Coir Fibres (CF) and pineapple leaf fibres (PALF) in PLA biocomposites and characterizations of flexural, morphological and dynamic mechanical properties. Flexural properties showed that the treated C1P1 hybrid composites (C1P1A) displayed highest flexural strength (35.81 MPa) and modulus (5.28 GPa) among all hybrid biocomposites. Scanning Electron Microscopy (SEM) revealed a behaviour of fibre-matrix adhesion in untreated treated biocomposites. SEM observation revealed good dispersion of the fillers in PLA. Dynamic mechanical analysis revealed that C1P1A showed highest glass transition temperature ( Tg ) and storage modulus ( E ′) while untreated C3P7 displayed the least Tg and E ?. Overall findings showed that alkali-treated hybrid biocomposites (CF/PALF/PLA) especially C1P1A have improved flexural properties, dynamic and morphological properties over untreated biocomposites. Success of these findings will provide attracting consideration of these hybrid biocomposites for various lightweight uses in a broad selection of industrial applications such as biomedical sectors, automobile, construction, electronics equipment, and hardware tools. 

Key words: Coir fibres, Pineapple leaf fibres, Biocomposites Polylactic acid Mechanical properties, Dynamic mechanical properties