To improve the interfacial bonding of sisal fiber-reinforced polylactide biocomposites, polylactide (PLA) and sisal fibers (SF) were melt-blended to fabricate bio-based composites via in situ reactive interfacial compatibilization with addition of a commercial grade epoxy-functionalized oligomer Joncryl ADR^@-4368 (ADR). The FTIR (Fourier Transform infrared spectroscopy) analysis and SEM (scanning electron microscope) characterization demonstrated that the PLA molecular chain was bonded to the fiber surface and the epoxy-functionalized oligomer played a hinge-like role between the sisal fibers and the PLA matrix, which resulted in improved interfacial adhesion between the fibers and the PLA matrix. The interfacial reaction and microstructures of composites were further investigated by thermal and rheological analyses, which indicated that the mobility of the PLA molecular chain in composites was restricted because of the introduction of the ADR oligomer, which in turn reflected the improved interfacial interaction between SF and the PLA matrix. These results were further justified with the calculation of activation energies of glass transition relaxation (∆E_a) by dynamic mechanical analysis. The mechanical properties of PLA/SF composites were simultaneously reinforced and toughened with the addition of ADR oligomer. The interfacial interaction and structure–properties relationship of the composites are the key points of this study.

Low-polymerization degree polylactide was grafted onto sisal fiber surface on the basis of the principle of lactide coordinative ring-opening polymerization. The effects of surface treatment on the thermal properties of sisal fibers were investigated. Sisal fiber reinforced polylactide composites were prepared by melt blending, and the impacts of surface treatment and annealing treatment on thermal properties and crystallization of the composites were studied. Results demonstrated that thermal stability of composites decreased with the addition of sisal fibers, among which lactide-grafted sisal fiber reinforced polylactide (PLA/SF-g-LA) composites decreased the most. The crystallinity of composites increased with the addition of sisal fibers compared with neat polylactide. Transcrystallinity appeared in PLA around the sisal fibers with the addition of sisal fibers. The glass transition temperature, crystallinity and crystal perfection of neat polylactide and composites were improved with annealing treatment.

Hybrid sisal fibers (HSFs) were made by mixing untreated sisal fibers (USFs) with alkali treated sisal fibers (ASFs), and blended with PLA matrix to make PLA/HSFs composite. It was found that the reinforced effect of HSFs was better than that of ASFs. Impact strength and crystallinity of PLA/HSFs had obvious improvements. β crystal of PLA was found from the XRD graph of PLA/HSFs, which may lead to an enhance in the impact strength and thermal stability.

The in situ reactive interfacial compatibilization and properties of polylactide/sisal fiber biocomposites made via melt blending with an epoxy-functionalized terpolymer elastomer, ethylene/methyl acrylate/glycidyl methacrylate (EGMA), were investigated. Scanning electron microscopy results showed that the introduction of EGMA improved the interfacial adhesion between the sisal fibers (SF) and matrix, which was ascribed to the improved interfacial compatibilization between the polylactide and fibers via in situ reaction with EGMA during the melt-blending processing. It was also observed that the EGMA tends to weld on the surface of the fibers, which is called a self-weld fiber structure. The interfacial reaction and microstructure of the composites were further investigated by FTIR characterization, and thermal and rheological analyses. The results demonstrated that the mobility of the polylactide molecular chain was restricted due to the enhanced interfacial interaction of the composites. The addition of EGMA improved the toughness of the polylactide/sisal fiber composites without much decline in the tensile strength. Polylactide/sisal fiber composites with a good stiffness-toughness balance were obtained.

Sisal fibers were pretreated by alkali and alkylation, and then mixed with polylactic acid to make sisal fiber-reinforced polylactic acid composites, respectively. The architecture and aspect ratio of sisal fibers before and after mixing, the micro-morphology of fracture surface, and the properties of composites were investigated. The results showed that surface treatment greatly impacted the fiber fracture behavior. Shearing fracture occurred to the untreated sisal fibers and alkali-treated sisal fibers, which led to a sharp reduction in the length of the fiber, while the shear-tear facture occurred to the alkylation-treated sisal fibers and resulted in obvious decrease in both length and diameter of alkylation-treated sisal fibers. The fiber aspect ratio of sisal fibers was affected first by the pretreatment method, then by the processing temperature, and the sisal fiber content. Furthermore, the mechanical properties of reinforcing fibers and sisal fiber-reinforced polylactic acid composites were influenced fundamentally by the pretreatment method.