Some Factors Affecting the Interfacial Interaction at Thermomechanical Pulp Fiber and Polypropylene Interphase

Abstract

This dissertation focused on some selected factors that influence the interfacial interactions at the interphase between wood based materials and thermoplastic surfaces. Several treatments were applied to enhance interfacial properties. In general, interfacial properties were altered by physical and chemical surface modification. Study of the interfacial interactions between wood fiber surfaces as a reinforced material and thermoplastics as a matrix material is important to understand fundamentals of wood fiber-plastic composites (WPC). This study represents fundamental research to define treatment effects on surfaces of wood pulp fibers and polypropylene (PP) film. Two thermosets, ion implantations, and maleic anhydride (MA) grafting were used to increase interfacial adhesion between wood based materials and PP. Thermoset resins were applied at three levels to fiber handsheets and PP film laminates. The surface treatment increased shear and tensile strength properties and PP crystallinity ( ) as determined by differential scanning calorimetry (DSC). The ion implantation method using oxygen and argon as ion sources proved to be one of the most effective treatments to improve interfacial bonding between thermomechanical pulp (TMP) fibers and PP film. Oxygen plasma treatment was more effective than argon to increase tensile strength due to the electron donor and accepter mechanism generated by magnetic fields between two electrodes. The MA grafting effect also improved the tensile strength of TMP fiber handsheets and PP film laminates fabricated with a 50/50 weight fraction. A brittle failure was observed by scanning electron microscopy (SEM) at the fracture surface of tensile specimens made from TMP fiber handsheets and PP film laminates (TPL). It was found by using extraction with CH2Cl2 and H2O as solvents that the PP nucleation ability on fiber surfaces was extremely reduced due to the removal of deposit materials from the surface. Thus, the extractives on the wood/non-wood fiber surface played a potential role for surface induced nuclei and lamella deposits for the PP melts. In conclusion, the surface treatments of ion implantations, thermoset treatment, and MA modification enhanced interfacial strength of TPL. Electron interaction and mechanical interlocking in the wood fiber handsheet improved interfacial interactions between wood-based materials and PP.