Mechanical and thermal properties of steel slag/stone-wood plastic composites reinforced with calcium sulfate whisker

Abstract

The development of steel slag/stone-wood plastic composites reinforced with calcium sulfate whisker is beneficial for reducing costs in the stone-wood plastic industry and promoting the resource utilization of industrial waste. Steel slag powder (SSP) composited with calcium sulfate whisker (CSW) was investigated as a replacement for a portion of talc powder (TP) in the creation of calcium sulfate whisker-reinforced steel slag/stone-wood plastic composites (CSW-SSP/SPCs). The reinforcement effect and thermal stability mechanism of CSW within these composites were examined by assessing their mechanical properties, mineral composition, structural composition, thermal stability, crystallinity, and microstructure. The results showed that the tensile strength, flexural strength, and impact strength of CSW-SSP/SPCs were increased by 28.13%, 25.02%, and 45.55%, respectively, which were significantly better than those of the pure TP sample. The SSP composited with CSW effectively replaced part of the TP, where CSW significantly reinforced the composites through its bridging, micro-filling, and synergistic effects with the SSP. Meanwhile, the MgO, Al2O3, and Fe2O3 in the SSP crosslinked with the carbon layer skeleton and residual materials to form a more stable carbon layer, which inhibited the combustion reaction and further enhanced the thermal stability and retarded the thermal degradation process.

1. Introduction

The growing resource shortage has driven the search for alternative sources and solutions for resource conservation and emission reduction. As a major by-product of the iron and steel industry, the annual output of steel slag reaches hundreds of millions of tons, but its comprehensive utilization rate has long been lower than 30%, and the large amount of stockpiling triggers environmental problems such as land encroachment and heavy metal leaching [1]. Under the dual-carbon goal, it becomes particularly important to explore and optimize new technologies and resource utilization paths for steel slag treatment. By replacing traditional raw materials, steel slag not only significantly reduces natural resource extraction, energy consumption, and carbon emissions throughout the life cycle, but also promotes the efficient use of resources, minimizes waste, and facilitates the development of a circular economy model. Steel slag is rich in various metal oxides (e.g., CaO, Fe2O3, MgO, and Al2O3) and has unique advantages such as abrasion resistance and heat resistance, which holds great potential for resource utilization [2]. Although there have been studies exploring the application of steel slag in cementitious materials [3], road base layers [4] and ceramic aggregates [5], after the implementation of the GB 175—2023, the dosage of steel slag in traditional building materials has been strictly limited, forcing researchers to turn to the field of polymer composites to seek breakthroughs.

Stone-wood plastic composites (SPCs), a popular modern building material, are typically produced by mixing and extruding talc powder (TP), wood powder, and polymer resin through a specialized process. These composites combine the benefits of stone, wood, and plastic, offering the easy moldability of thermoplastics, the hardness of stone, and the secondary processability of wood. They also possess advantages such as insect resistance, aging resistance, corrosion resistance, abrasion resistance, low water absorption, and reusability, making them widely applicable in construction and home decoration. Traditionally, TP is used as a filler in SPCs due to its excellent lubricating properties, which facilitate smooth processing [6]. However, the mining process of the natural resource TP produces a large number of tailings, and the average annual price increase of 18%, seriously restricts the sustainable development of the industry [7]. Previous studies have shown that when steel slag powder (SSP) is directly used to replace TP, it can reduce the production cost, but the enhancement of the tensile strength and impact toughness of the composite material is not obvious, and the reinforcing properties of steel slag are not fully reflected. This is mainly attributed to the high surface energy of SSP and the significant interfacial energy barriers between SSP and nonpolar matrices such as polyethylene, resulting in inefficient stress transfer [8].