Composites from maleated polyolefin-grafted wood particles produced via reactive extrusion

This study examined the concept of using a reactive extrusion process to develop a new, formaldehyde-free binding system for wood composite products. The surfaces of wood particles were modified by grafting maleated polyethylene (MAPE) and maleated polypropylene (MAPP) compounds through a continuous reactive extrusion process. MAPE content was varied to study the effect of material composition on grafting efficiency, while extruder barrel temperatures and rotational screw speeds were varied to evaluate the effects of processing conditions on the modification of wood particles. Polymer molecular weight effects were followed using MAPP with different molecular weights. Efficiency of the modification was assessed using FTIR. 13C NMR and XPS surface analysis techniques, along with a titrimetric analysis to verify the esterification reaction between the wood particles and maleated polyolefins. Composite panels were made from wood particles modified with MAPE and MAPP binding agents under two different manufacturing methods. Specific contrasts of (i) base resin type, PE vs. PP, (ii) molecular weight/maleic anhydride content in MAPP binding agents, and (iii) the manufacturing methods (reactive extrusion vs. hot press) were investigated to determine the effects of these factors on the physico-mechanical properties of the composites. Finally, a response surface method using a Box-Behnken design was constructed to statistically model and optimize the material compositions-processing conditions-mechanical property relationships of formaldehyde-free wood composite panels.; FTIR, 13C NMR, XPS and titration data confirmed the grafting of maleated polyolefins onto wood particles through an esterification reaction, while the level of grafting of MAPE onto wood particles was determined to be a function of the MAPE concentration. However, there was no significant difference in grafting efficiency at different extrusion processing conditions; rather all of the conditions resulted in adequate grafting. Similarly, there was no difference in grafting efficiency with molecular weight of MAPP. Reactive extrusion was found to be a suitable technique for the modification of wood particles with maleated polyolefins for all of the material compositions and processing conditions studied. Mechanical property test results indicated that most composite panels met or even exceeded the standard requirements for particleboard of medium density. While extruding the particles before panel pressing gave better internal bond (IB) strength, superior bending properties were obtained through compression molding alone. (Abstract shortened by UMI.)...