Influence of interfacial interactions on the properties of PVC cellulosic fiber composites

The surface properties at the interface between thermoplastic and cellulosic fibers strongly influence the mechanical properties of plastic/cellulosic fiber composites. This paper examines the role of surface acid-base properties of plasticized WC and cellulosic fibers on the mechanical properties of the composites. The acid-base surface characteristics of cellulosic fibers were modified by treating the fibers with gamma-aminopropyltriethoxysilane (A-1100), dichlorodiethylsilane. phthalic anhydride, and maleated polypropylene. The empirical acid (K-A) and base (K-D) characteristics (i.e., electron donor/acceptor abilities) of untreated and treated fibers, as well as plasticized PVC, were determined using inverse gas chromatography (IGC) technique, These parameters were used to yield information on the acid-base pair interactions that were correlated with the tensile and notched Izod impact properties of the composites. Acid-base pair interactions have been found to be a valuable parameter in the design of surface modification strategies intended to optimize the tensile strength of the composites. By tailoring the acid-base characteristics of cellulosic fibers and plasticized WC, a composite with equal tensile strength and greater modulus than unfilled WC was developed. However, the acid-base factors did not correlate with tensile modulus, the elongation at break, and the notched Izod impact property of PVC/newsprint fiber composites. Aminosilane has been observed to be a suitable adhesion promoter for PVC/wood composites improving significantly the tensile strength of the composites. Other treatments (dichlorodiethylsilane, phtalic anhydride, and maleated polypropylene) were found to be ineffective, giving similar strengths compared to the composites with untreated cellulosic fibers. FTIR spectroscopy results suggested that aminosilane was effective because treated cellulosic fibers can react with PVC to form chemical bonds. The resulting bond between PVC and cellulosic fibers accounts for the effectiveness of aminosilane, when compared with other coupling agents.