Thermoforming of Composites Made from Bamboo Fabric and Thermoplastic Polymers

Abstract

Petroleum-based thermoplastics have been seen as favourable materials in a vast range of applications, particularly in packaging. However, the use of these materials is facing great pressure to reduce pollutant emissions. This has driven packaging manufacturers to seek new solutions in producing renewable and environmentally friendly products such as recyclable and biodegradable packaging materials. In this study, bamboo fabric has been used to reinforce PP and PLA polymers to produce partially and fully biodegradable composites. Bamboo fabric has excellent mechanical properties which indicate that it may be a potential material for reinforcement in PP and PLA. An understanding of the behaviour of these sheet materials during forming is crucial in assessing their applicability to various products and uses. This thesis discusses the manufacturing of PP and PLA composites using bamboo fabrics for packaging applications. The composites have been manufactured using a compression moulding method. A statistical analysis based on Taguchi approach has been used to study the multivariable system involved in the process of compression moulding. This design of experiment has been used to investigate the effects of manufacturing parameters on mechanical properties of the composites. The effects of consolidation parameters on the mechanical properties, which were determined by performing mechanical tests as per ASTM standards, have been investigated. The tensile strengths and moduli of the composites were experimentally measured and compared to theoretical calculations. Finally, the thermal properties of the composites have been determined and reported. It has been noted that the crystallinity of the polymers can increase in the presence of bamboo fabric reinforcement. In order to explore the potential of the PP and PLA composite sheets in packaging applications, a comparative study of several functional properties of the composites was conducted. Physical properties, heat deflection temperature, impact resistance (drop weight impact test), recyclability and biodegradability are important functional properties for packaging. It has been shown that the energy absorption and maximum load of PLA composites improved significantly compared to those of the neat PLA. The effects of extrusion and injection moulding of PLA composites on mechanical and thermal properties are presented. The mechanical properties of the recycled materials have also been investigated using samples obtained by injection moulding. Tensile, flexural and impact tests were performed. DSC testing has revealed that the degree of crystallinity decreases after recycling. The biodegradability of PLA composites was investigated under two different conditions. PLA composites degraded rapidly under elevated temperature in laboratory composting conditions as compared to real composting conditions. Investigation on the thermoformability of the PP and PLA composites is also considered to be very important as the thermoforming process is one of the common methods to convert the composites into packaging products. In this study, the composite laminates were subjected to a series of single and double curvature forming experiments to investigate the effects of different test parameters on the occurrence of deformation characteristics during sheet forming of fabric reinforced materials. Fabric reinforced thermoplastics were chosen due to their ease of forming into complex shapes. Better anticipation of such defects facilitates the tooling design process, resulting in significant lead time reductions. Grid strain analysis (GSA) was also performed to investigate the strains that occur during the forming of complex components. Finally, the energy absorption characteristics were experimentally determined by subjecting the composite domes to quasi-static compressive and impact loadings.