Suitable charcoal loadings improving heat-resistance and mechanical properties of epoxy resins composites

Abstract: Wood-plastics composite (WPC) is a new kind of composite material, booming at home and abroad in recent years. It includes 2 types: one is the composite produced directly using extrusion and injection methods based on biomass materials such as wood powder, bamboo powder and hemp fiber; the other is based on carbonized biomass materials, which is fabricated by carbonizing biomass materials at high temperature and then compounding with polymer. The former has been studied in detail, but the latter is scarce. So in this paper, we prepared the charcoal/epoxy composites using compressing method. The effects of charcoal content on the mechanical properties and the heat resistance of charcoal/epoxy composites were investigated using scanning electron microscope (SEM), material testing machines, dynamical thermal mechanical analyzer (DMA) and Vicat softening temperature (VST) measuring instrument. The epoxy, diluents and curing agent at weight ratio of 3:2:5 were used to yield charcoal/epoxy composites. The weight fraction of charcoal in composite was set to 5%, 10%, 20%, 30% and 40%, and the curing temperature and curing time were 100℃ and 3 h, respectively. The results showed that the charcoal in composites, acting as physical cross-link, could improve the mechanical properties of epoxy resins. The flexural strength of composites increased from 10.1 to 38.2 MPa as charcoal loading increased from 0 to 10%, but it started to reduce when charcoal loading exceeded 10%. Like flexural strength, the impact strength of composites also increased from 8.7 to 20.5 kJ/m2 within 10% charcoal loading. However, the flexural modulus of composites increased with charcoal loading increasing till 30%. At high charcoal content, due to the poor wetting properties of charcoal, the mechanical properties of composites began to decrease. The DMA results confirmed that the glass transition temperature of epoxy resins was elevated from 37.5℃ to 60.5℃ as charcoal loading increased from 0 to 10%, indicating strong interaction between epoxy and charcoal. When charcoal loading exceeded 10%, the glass transition temperature started to decline, but it was still higher than that of net epoxy resins. The addition of charcoal improved the heat resistance of epoxy composites, and the VST of charcoal/epoxy composites increased linearly with the increasing of charcoal loading. The 10% charcoal made the VST of epoxy resins increase from 81.2℃ to 126.6℃. Further elevating the charcoal loading caused the VST of composites to exceed 200℃. The results indicate that the charcoal/epoxy composites have better mechanical properties and heat resistance with the charcoal loading of 10%.