Investigation of ultrasonic welding for joining polylactic acid based bio-degradable packaging product

Abstract

There is a successful formula for biodegradable materials for packaging applications. Joining the developed biodegradable materials is important for sustainable packaging applications. Among the different types of joining methods available for polymer-based materials, ultrasonic welding is popular among manufacturers due to variety of reasons. It is a cost-effective, eco-friendly and time-saving joining method which does not require additional parts or materials, like bonding materials and mechanical fasteners used in adhesive and mechanical joining. However, there is a lack of literature evidence on assessing the joining performance of ultrasonic welding of biodegradable materials. Therefore, this study aims to investigate the possibility of applying ultrasonic welding for joining bio-degradable packaging sheets. The biodegradable packaging material sheets were developed in the laboratory using the solvent casting technique. The samples were prepared using ‘Ceiba Pentandra’ as reinforcement fibre and PLA as a matrix polymer to develop sheets of PLA-Ceiba Pentandra fibre composites. Both these raw materials of the composite are biodegradable in the environment. A semi-automatic ultrasonic welding machine(20 kHz) was used to join the PLA/natural fibre composite samples. The strength of the ultrasonically welded specimens was tested by conducting tensile strength tests with the help of a universal tensile strength machine. The design of experiments (Taguchi method) and variance analysis (ANOVA) were used for the experimentation and analysis process. The parameters influencing the joining strength are the composition of fibre and PLA, welding time, holding pressure, and amplitude. These parameters were changed to see the variation in the output parameters of the joint strength and energy consumption. Using ANOVA, the optimum set of parameter levels were found to maximize the strength of the joints. The optimum parameter levels are; 0.5% of fibre/PLA composites, a holding pressure of 2.5 bar, a welding time of 1.5 Seconds and an amplitude of 75 μm. Fibre percentage and welding time significantly affect the welding strength and contribute to the tensile strength by 40.1% and 34.1%, respectively. Pressure and amplitude have a minor effect on the welding strength, contributing to the tensile strength by 10.3% and 11.5%, respectively. Time and amplitudes significantly affect the energy used to make the bonds by 87.2% and 10.3%, respectively. Fibre percentage and pressure have a minor effect on energy usage, contributing to the total energy by only 0.5% and 1.9%, respectively. The results were validated using a confirmation test, which compared the calculated results with the experimented results