Thermal-mechanical Characterization of bio-based epoxy adhesive modified with cotton and epoxidised soybean oil

This study aims to leverage the environmentally friendly characteristics of bio-based epoxy resin and natural modifiers while reducing dependence on synthetic materials. To achieve this, the bio-based GreenPoxy resin was modified with natural modifiers, and the resulting thermal and mechanical properties were evaluated. Milled cotton fibers and epoxidized soybean oil (ESO) were incorporated as natural reinforcement and plasticizer, respectively. Cotton content was varied from 0 to 15 wt%, while ESO content was fixed at 20 wt% based on prior studies indicating optimal toughening performance. Thermal analysis revealed that ESO addition slightly enhances the thermal stability of GreenPoxy by 4.9%, whereas cotton reduces it by 1.3%. Cotton modified GreenPoxy showed lower thermal degradation temperature and a reduced weight loss rate. In terms of mechanical performance, cotton addition in GreenPoxy resulted in significant improvement in impact strength, with a 20.8% increase, followed by ESO addition with 12.8% increase. The highest impact strength improvement of 23% was achieved in GreenPoxy with a combination of 5 wt% cotton and 20 wt% ESO. Conversely, the tensile strength of GreenPoxy decreased slightly by 3.4% with cotton addition and more significantly by 19.6% with ESO addition. Increasing cotton content further reduced tensile strength, reaching a 32.8% decrease compared to neat GreenPoxy. These results revealed that the combined use of low cotton content and ESO effectively enhances impact resistance while maintaining an acceptable level of thermal and tensile performance, improving the suitability of the modified composite for engineering applications where high impact strength is critical.