Polylactic acid/wood-based in situ polymerized densified composite material

Abstract

To develop an advanced wood bio-composite, an economical and energy-efficient manufacturing strategy is showcased in this study. Wood slabs were delignified and impregnated with a simple modifying precursor of lactic acid oligomers. The impregnated wood samples were in situ polymerized and densified with heat and pressure, turning the wood into a functionalized densified material. The modified material was confirmed by observing the nano and micro-structure with a scanning electron microscope (SEM) and performing chemical analysis using thermogravimetric analysis (TGA). Mechanical property such as modulus of rupture (flexural strength) was measured using an Instron universal testing machine and a water resistance study was conducted using a tensiometer to measure contact angle and surface water absorption. SEM images showed wood lumens thickened and collapsed, with a filled-in sub-structure, leading to a compact multi-layered assembly. The functionalized densified material had better surface wear resistance and excellent mechanical performance (flexural strength was approximately 150% higher than that of the original wood and surface hardness was enhanced). The water absorption rate of the functionalized densified samples reduced significantly compared to the original wood which in turn enhanced the surface water repellency. This was due to the reduction of hydrophilic groups as well as the clogging of the pores (pits) on the wood surface. Such enhanced performance makes the functionalized densified wood composite a promising candidate for advanced structural and engineering applications.