Effect of Aluminum Hydroxide on Thermal and Mechanical Properties of Composites Derived from Pine Wood Flour and Waste Polyethylene

Effect of Aluminum Hydroxide on Thermal and Mechanical Properties of Composites Derived from Pine Wood Flour and Waste Polyethylene



Abstract

Background and Objective

With increasing environmental concerns arising from the accumulation of polymer waste and the scarcity of natural resources, the development of wood-polymer composites has attracted considerable attention as a sustainable alternative. These materials, utilizing both polymer and lignocellulosic wastes, possess the potential to replace conventional materials in various applications. However, their high flammability and certain mechanical limitations have challenged their widespread utilization. In this study, the effect of aluminum hydroxide addition as a flame retardant on the mechanical and thermal properties of composites based on recycled polyethylene and pine wood flour was investigated.

Materials and Methods

In this research, recycled polyethylene (at a fixed level of 50 wt%), pine wood flour (at a fixed level of 50 wt%), aluminum hydroxide at three levels (0, 5, and 10 wt%), and maleic anhydride-grafted polyethylene at a fixed level of 3 wt% were mixed using a twin-screw extruder, and standard test specimens were fabricated via injection molding. Mechanical properties including tensile strength and modulus, flexural strength and modulus, and notched impact resistance, as well as thermal and flammability properties, were measured according to ASTM standards.

Results

The results indicated that increasing aluminum hydroxide content led to a significant reduction in mechanical properties. At the 10 wt% level, tensile strength, tensile modulus, flexural strength, flexural modulus, and impact resistance decreased by approximately 15.12%, 12.93%, 14.21%, 23.69%, and 9.7%, respectively. This reduction is attributed to the weakening of interfacial adhesion, stress concentration development, and decreased matrix flexibility. Conversely, the thermal test results demonstrated a significant improvement in the flammability behavior of the composites. The limiting oxygen index (LOI) value increased from 19% in the control sample to 21.93% in the sample containing 10 wt% additive, indicating reduced flammability. Furthermore, the increased residual ash content in the TGA test confirmed the formation of a protective carbonaceous-mineral layer and enhanced thermal stability of the composite structure.

Conclusion

Overall, the results of this study demonstrate an inverse relationship between mechanical properties and thermal performance in the presence of aluminum hydroxide. In other words, although this additive improves fire resistance, it simultaneously causes a decline in mechanical properties. Therefore, determining the optimal additive content based on the final application requirements is essential. This study can serve as a basis for the design and optimization of wood-plastic composites with multi-functional performance.