Gallic Acid as a Potential Substitution for Phenol in Phenol-Formaldehyde Resin for Biocomposite Matrices

This project explores the production of new resins using gallic acid (GA) as a substitute for phenol in phenol-formaldehyde (PF) resin. A special curing schedule was made tailored to the limitations of the equipment used. Phenol was substituted with GA at various contents until the optimum ratio has been reached, which in this present study is 31% of gallic acid. The effects of co-reaction of GA and phenol with formaldehyde on mechanical, thermal, chemical and morphological properties were investigated. Test specimens were prepared by synthesising the pre-polymer at certain processing conditions and curing it in the autoclave. From the flexural test, addition of GA showed improvement in the flexural modulus and strength. The thermal properties of PF resin and GA resin were investigated by Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA) and Thermogravimetry Analysis (TGA). From the DSC result, no residual exotherm can be seen below 150 ℃ which indicates that the resin is suitable for use in natural fibre composites. Glass transition temperature (Tg) from DMA suggest that substitution of phenol with GA in production of resol resin has increased the glass transition temperature while TGA results showed that increasing GA substitution level in the compound resulted in increasing weight loss at lower temperature, and hence lower thermal stability. Based on Scanning Electron Microscopy (SEM) analysis, the flexural fracture surfaces for PF and GA resin displays no bubbles and voids present in the resin. It shows that the cure cycle proved to be successful in producing bubble-free specimens. In this study, Group Interaction Modelling (GIM) was also used to predict the Tg of the resin, which compares very well with the experimental work. Following the successful production of resin, nettle fibre was added as a reinforcing agent in producing the biocomposites. It shows that up to certain amount of nettle fibres, which is in this study 15 wt% of nettle fibres, the mechanical properties of the resin improved substantially. However, in composite systems, we can see particles and holes where fibres have pulled out upon fracture are clearly visible in the SEM images, which indicates poor interaction between fibre-matrix

Effect of ammonium polyphosphate on flame retardancy, thermal stability and mechanical properties of alkali treated kenaf fiber filled PLA biocomposites

In present research polylactic acid (PLA) biocomposites were prepared from PLA and kenaf fiber using dry blending, twin screw extrusion and compression molding techniques. PLA was blended with kenaf core fiber, polyethylene glycol (PEG) and ammonium polyphosphate (APP). Kenaf fiber was treated with 3%, 6% and 9% NaOH solution separately. Both raw and treated kenaf along with 10, 15 and 20 phr APP was utilized during composite preparation. The effects of APP content and alkali treatment on flammability, thermal and mechanical properties of kenaf fiber filled PLA biocomposites were investigated. APP is shown to be very effective in improving flame retardancy properties according to limiting oxygen index measurement due to increased char residue at high temperatures. However addition of APP decreased the compatibility between PLA and kenaf fiber, resulting in significant reduction of the mechanical properties of PLA biocomposites. Thermogravimetric analysis (TGA) showed that NaOH treatment improved the thermal stability of PLA biocomposites and decreased carbonaceous char formation

PLA/Kenaf/APP biocomposites: effect of alkali treatment and ammonium polyphosphate (APP) on dynamic mechanical and morphological properties

Kenaf-filled polylactic acid (PLA) biocomposites were prepared using dry blending, twin screw extrusion and compression molding. PLA was blended with raw and alkali treated kenaf, polyethylene glycol and ammonium polyphosphate (APP). Dynamic mechanical properties of biocomposites were investigated by dynamic mechanical analysis. Storage modulus of composites decreased, while magnitude of damping peaks increased with increase in APP content. The T g of composites shifted to lower values with APP addition. Alkali treatment improved interfacial adhesion between PLA and kenaf. SEM analysis indicates good dispersion of APP in PLA matrix, however interfacial adhesion between PLA and matrix decreased with increasing APP content