Water Absorption and Dimensional Stability of Polypropylene/Acetylated Wood Fiber

Influences of the wood fiber acetylation as well as the compatibilizer MAPP on water absorption, thickness swelling and dimensional stability of acetylated wood/ polypropylene composites (WPCs) were the main concerns of this research. Wood fibers were acetylated with acetic anhydride without using any catalyst to achieve weight percent gains (WPGs) of 4.5, 7.5 and 17.6%. The acetylated fibers were mixed with MAPP (0, 2, 3 and 5%) and matrix polymer polypropylene (PP) to prepare samples of the WPCs. The samples were made at 180°C with a hot press. Tests specimens were cut and soaked in the water for 1512 hours to determine the water absorption, the thickness swelling, the anti-swelling as well as the water repellent effects in the acetylated WPCs. The interfaces between acetylated wood fibers and the polypropylene were studied with a scanning electron microscope. Results revealed that acetylation of the wood fibers reduced significantly the water absorption and the thickness swelling in the WPCs. Addition of the MAPP decreased those properties as well. However, influence of the fiber acetylation was more effective than that of the MAPP. Electron microscopy of the interfaces showed reduction of micro-gaps in the WPCs and also improved interfaces between matrix polymer (PP) and the wood fiber. It was also revealed that the acetylated WPCs had smooth surfaces.