Optimization of Ingredients in Polystyrene Waste-Based Adhesive for Wood-to-Wood Bonding Using Experimental Planning

Abstract

In this study, an adhesive was prepared using waste polystyrene foam for wood-to-wood bonding. The effects of natural rubber (NR) and methylene diphenyl diisocyanate (MDI) content on adhesion were investigated. NR modifies polystyrene, acting as a plasticizer to address its hardness and brittleness, while MDI functions as a curing agent for the adhesive system. Characteristics such as the viscosity and wettability of the liquid adhesive were determined. Differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) were employed to evaluate the properties and structure of the resulting adhesive films. The bonding ability between two wood plates using this adhesive was evaluated through tensile shear strength and impact strength. An experimental plan was devised to identify the optimal content of NR and MDI, providing the highest tensile shear strength and impact strength of the bond. The research revealed that the highest tensile shear strength achieved was 3.87 N/mm² at 16.468% NR and 7.882 phr MDI, while the highest impact strength reached 15.352 kJ/m² with NR and MDI contents of 16.079% and 7.620 phr, respectively. The experimental planning models demonstrated a good fit for predicting tensile shear strength and impact strength.