Thermal property and flame retardancy comparisons based on particle size and size distribution of clays in ethylene vinyl acetate (EVA) adhesive sheets for cross-laminated timber (CLT)

Abstract

Cross-laminated timber (CLT) is widely used as a building material, and recent interest in this material has increased rapidly due to environmental problems. For instance, the phenol resorcinol formaldehyde (PRF) used as an adhesive in CLT can release toxic gases during a fire, resulting in adverse health effects. These properties cause concern regarding the use of CLT as a building material and restrict its use. In this study, the effects of the particle size and size distribution of clays on the thermal properties and flame retardancy of composites were investigated. Ethylene vinyl acetate (EVA)/clay adhesive sheets were prepared to substitute for the PRF that is used to cohere the timber in CLT. To increase the dispersibility of clay inside the EVA matrix, the clays were organically treated using cetyltrimethylammonium bromide (CTAB), and the interlayer spacing was determined via X-ray diffraction. In addition, the EVA/clay adhesive sheets presented a broad peak due to their good dispersion. As the clay contents increasingly degraded, the thermal properties, such as the degradation temperature and final residue, of the EVA/clay adhesive sheets enhanced. However, the adhesive sheets showed continuous improvement only for a specific particle size and size distribution due to the difference in the degree of organic treatment. The results from cone calorimetry showed a decrease in the heat release rate (HRR) as the clay content increased. With respect to the flame retardancy of EVA/clay adhesive sheets, clay with a large particle size is more effective than clay with a small particle size, while the size distribution does not have a strong influence.