Preparation of bamboo scraps/magnesium oxychloride lightweight composites with high water resistance by PVAc

In this paper, in order to continuously promote the carbon peak and neutrality targets, and accelerate the construction of the waste material recycling systems, a lightweight construction material was prepared by compounding magnesium oxychloride cement (MOC) inorganic cementitious material and waste bamboo scraps, and foaming them with hydrogen peroxide. However, the poor water resistance of MOC composites makes it difficult to meet the needs under special environmental conditions, which seriously affects their popularization and application range. To solve this problem, Polyvinyl acetate (PVAc) was used to enhance the water resistance. It was deduced that the hydrolysis products of PVAc combined with each other, under the effect of hydrogen bonding induction, can form a hydrated polymer protective film covering the exterior of MOC crystals, thus reducing the contact of water with the crystals. In addition, the protective film and the hydroxyl groups on the cellulose of bamboo scraps are interconnected by hydrogen bonding, which improves the bonding strength of MOC gelling particles to bamboo scraps. Moreover, the PVAc hydrolysis products were combined with water molecules, bamboo scraps, and phase 3 crystals in MOC by hydrogen bonding to form a gelling structure, which further improved the adhesive tightness of MOC gelling particles. These three aspects led to the increase of the softening coefficient of the modified material by approximately 14%, and a substantial increase of the water resistance. Furthermore, the addition of PVAc improved the foaming effect of the material and increased the porosity, leading to a further decrease of the density and strength of the foamed material. The study of the water resistance of this lightweight composite material effectively provides a theoretical support and technical reference for the application of water-resistant and energy-saving materials in the construction fields.