Effect of the Alkali Pretreatment on the Structure and Properties of Bamboo-Based Porous Molding Materials

The development of novel materials from biomass is a potential alternative to replace traditional petrochemical resources. In accordance with the "Bamboo Substitute Plastic" initiative, bamboo-based lightweight porous materials are a class of foam materials fully prepared from biomass resources with a lightweight and high-strength structure. However, issues such as excessive lignin content and uneven pore structure distribution within these materials hinder their application. This study utilized bamboo powder as a raw material to prepare lightweight, porous molding materials through a hydrothermal grinding process. The influence of different concentrations of alkaline pretreatment was investigated. The fabricated molding material had a density of 0.36-0.49 g/cm³ at 80 °C and 0.32-0.38 g/cm³ at 105 °C. Samples dried at 80 °C had a water absorption of 161% to 304%, while those dried at 105 °C had a water absorption of 223% to 305%. The wet swelling was characterized by volume expansion from 6.2% to 7.7%. The surface of the molding materials became increasingly homogeneous without any cracks due to the alkali pretreatment. FTIR data showed that more surface hydroxyl groups were observed after alkaline pretreatment, and some carbonyl groups in the hemicellulose structure were removed; meanwhile, the crystallinity index after alkaline pretreatment was higher than that of untreated bamboo. The alkali solution was proposed to remove part of the lignin and improve the fibrillation degree of the bamboo fibers. The highest tensile strength of the samples was 9.63 MPa, while the highest compressive strength obtained was 0.92 MPa under the alkali treatment. With lightweight and fully degradable properties, the bamboo-based porous molding materials have promising application prospects in environmental protection, construction, packaging, and related fields.