Silane coupling agents used for natural fiber/polymer
Natural fiber reinforced polymer composites (NFPCs) provide the customers with more alternatives in the material market due to their unique advantages. Poor fiber–matrix interfacial adhesion may, however, negatively affect the physical and mechanical properties of the resulting composites due to the surface incompatibility between hydrophilic natural fibers and non-polar polymers (thermoplastics and thermosets). A variety of silanes (mostly trialkoxysilanes) have been applied as coupling agents in the NFPCs to promote interfacial adhesion and improve the properties of composites. This paper reviews the recent progress in using silane coupling agents for NFPCs, summarizes the effective silane structures from the silane family, clarifies the interaction mechanisms between natural fibers and polymer matrices, and presents the effects of silane treatments on the mechanical and outdoor performance of the resulting composites.
To effectively couple the natural fibers and polymer matrices, the silane molecule should have bifunctional groups which may respectively react with the two phases thereby forming a bridge in between them. Silane coupling agents have a generic chemical structure R(4−n)Si(R′X)n (n = 1,2) where R is alkoxy, X represents an organofunctionality, and R′ is an alkyl bridge (or alkyl spacer) connecting the silicon atom and the organofunctionality.
The interaction mode between the silane-treated fiber and the polymer matrix is a crucial factor for the mechanical properties of the resulting NFPCs. Physical blending of the silane-treated fibers and the thermoplastic matrices enhances their mutual adherence via inter-molecular entanglement, or acid–base interactions (ABI). The interfacial shear strength (ISS) between jute fibers and PP,