Thermoplastic foaming mechanism and Pb²⁺ adsorption of poly(vinyl alcohol)/shell powder porous composite

Abstract Combining the respective advantages of PVA and shell in wastewater treatment, poly(vinyl alcohol)/shell powder (PVA/SP) porous composite suitable for the removal of heavy metal ions from wastewater was prepared via thermoplastic foaming technology using water as both plasticizer and physical blowing agent. The effects of SP content on the thermoplastic foaming mechanism including interactions among components, water states and water evaporation behaviors, as well as cell structure and Pb²⁺ adsorption property of the porous composite were studied. The results showed that SP could form different hydrogen bonding or coordination interactions with water and PVA, making free water in system reduced and nonfreezing water increased, thus realizing the controllable foaming of water and avoiding the formation of the big cells caused by intensive evaporation of water. SP particles could also act as heterogeneous nucleating agents to effectively increase the number of heterogeneous nucleating points in the system, resulting in the formation of denser and more uniform cells. With the increase of SP content, the adsorption capacity of porous composite on Pb²⁺ increased, and reached the maximum at 10 wt%, that is, 31.1 mg/g, higher than that of pure SP powders, that is, 23.4 mg/g, ascribing to the good dispersion of SP in PVA matrix as well as the high hydrophilicity of PVA porous material.