Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Chemical Engineering

First Advisor

John R. Collier


Mechanical properties of polypropylene (PP)/wood fiber composites depend not only on the properties of each primary component but also on a complex interaction of several factors such as fiber loading and size, characteristics of fiber-polymer matrix interface, and the processing conditions. Both sequential and simultaneous composites are formulated in this research. First, sequential composites are made by compounding wood fibers with PP in the presence of maleated polypropylene (MPP) as a coupling agent in a twin-screw extruder. A small amount of MPP (1 wt%) present in these sequential composites can increase the tensile strength of the composites significantly. The tensile strength and Young's modulus increase with fiber content up to 50 wt% while the elongation exhibits a logarithmic decrease with increasing fiber loading. Both shear and elongational viscosities of sequential composites increase with fiber loading and show higher shear thinning and strain thinning behavior with increasing fiber loading. Secondly, simultaneous composites are produced by in-line maleation and compounding of wood fibers with PP, maleic anhydride, and initiator in the same extruder. Similar tensile properties are observed for the simultaneous composites as the sequential composites. The effects of maleic anhydride and initiators are evaluated. Compared to virgin PP, simultaneous composite shows an initial shear viscosity decrease and then increase in shear viscosity with wood fiber content. Maleation of PP cause succinic anhydride groups to be grafted onto the PP backbone, accompanied by the degradation of PP. The succinic anhydride grafting level increases with increasing initiator and maleic anhydride concentration up to a certain level. The shear viscosity of MPP is lower than that of virgin PP but higher than that of PP/initiator sample. It is also shown that the shear viscosities increase with the initial concentration of maleic anhydride and the succinic anhydride grafting level; whereas the elongational viscosity of MPP is lower than that of virgin PP and decreases with increasing succinic anhydride grafting level. The surface energy, especially polar surface energy, of MPP can be increased significantly by contacting with water at either room temperature or the boiling point of water.