Effect of chemical modifications of the pineapple leaf fiber surfaces on the interfacial and mechanical properties of laminated biocomposites

Natural fiber reinforced renewable resource based laminated composites were prepared from biodegradable poly(lactic acid) (PLA) and untreated or surface-treated pineapple leaf fibers (PALF) by compression molding using the film stacking method. The objective of this study was to determine the effects of surface treatment of PALF on the performance of the fiber-reinforced composites. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) were used to aid in the analysis. The mechanical properties of the PLA laminated composites were improved significantly after chemical treatment. It was found that both silane- and alkali-treated fiber reinforced composites offered superior mechanical properties compared to untreated fiber reinforced composites. The effects of temperature on the viscoelastic properties of composites were studied by dynamic mechanical analysis (DMA). From the DMA results, incorporation of the PALF fibers resulted in a considerable increase of the storage modulus (stiffness) values. The heat defection temperature (HDT) of the PALF fiber reinforced PLA laminated composites was significantly higher than the HDT of the neat PLA resin. The differential scanning calorimeter (DSC) results suggest that surface treatment of PALF affects the crystallization properties of the PLA matrix. Additionally, scanning electron microscopy (SEM) was used to investigate the distribution of PLA within the fiber network. SEM photographs of fiber surface and fracture surfaces of composites clearly indicated the extent of fiber-matrix interface adhesion. It was found that the interfacial properties between the reinforcing PALF fibers and the surrounding matrix of the laminated composite are very important to the performance of the composite materials and PALF fibers are good candidates for the reinforcement fiber of high performance laminated biodegradable biocomposites.