Improved interfacial compatibility between unsaturated polyester resin and rice straw fibers after non-washing treatment with Ca(OH)₂

The agricultural industry produces a substantial volume of rice straw (RS) annually, highlighting the importance of recycling RS for sustainable materials. However, the poor interfacial compatibility between RS and polymers often leads to drawbacks in their composites, such as water-swelling and limited tensile strength. Here, we propose a novel approach using Ca(OH)₂ that offers several distinct advantages: enhancement of interfacial compatibility, elimination of the need for water washing, and formation of calcified hybrid particles on fiber surfaces by capturing CO₂ from the atmosphere. The non-washing calcified rice straw (NCRS) fibers were used to fabricate composites with unsaturated polyester resin (UPR), resulting in NCRS/UPR composites exhibiting significant enhancements in water resistance and mechanical properties compared to RS/UPR composites. The NCRS/UPR composites achieved a water absorption rate below 25 %, thickness swelling rate below 10 %, and tensile strength of 19.9 MPa. This work comprehensively explored the mechanism underlying these achievements through experimental studies. Findings suggest that CaCO₃ particles involving with released lignin act as an interfacial bridge between RS fiber surface and UPR, resulting in significantly improved properties. This approach demonstrates promising prospects as a simple and eco-friendly methodology for manufacturing RS-based composite materials.