Forward extrusion of bulk wood containing polymethylmethacrylate: Effect of polymer content and die angle on the flow characteristics

In this study, the forward extrusion of non-pulverized bulk wood containing polymethylmethacrylate (PMMA) was investigated to obtain new fundamental insights regarding the plastic forming of bulk wood. In particular, we studied the effect of the polymer content and die angle (20°-120°) on the extrusion forces and flow of various types of bulk wood during extrusion. Plastic-impregnated wood (composite) specimens with high (49%) and low (27%) polymer content were obtained by impregnating wood with solutions containing different concentrations of methyl methacrylate (MMA). Before the impregnation, the wood was hydrophobized by acetylation to allow the MMA to penetrate into the cell walls. The load during extrusion for the 49% composite was lower than that for the 27% composite at all die angles. For both composites, the extrusion force increased with decreasing die angle for small die angles (20°-40°) because of the increase in friction force at the die wall surface. For the 27% composite, the extrusion force increased with increasing die angle beyond 40° due to the formation of dead zones and shear zones in the wood. Therefore, the optimal die angle that minimized the extrusion force was near 40°. In contrast, the extrusion force for the 49% composite exhibited no significant difference for die angles larger than 40° in spite of the formation of dead zones and shear zones. Chevron cracking appeared in the 49% composites, whereas no cracks and voids were formed in the 27% composites.