FUSION WELDING OF NATURAL FIBER BASED THERMOPLASTIC COMPOSITES

Abstract

The technological advancements in the field of materials and manufacturing has catalyzed the interest of research fraternity/innovators towards the conceptualization, design and development of sustainable products. Consequently, the products based on natural fiber reinforced composites (NFRCs), that address this concern have become an interesting alternative. In order to further enhance the commercialization of these products without compromising or violating the government policies, concerted efforts have become a necessity for the research fraternity. The distinct benefits offered by natural fiber based products, such as, biodegradability, easy availability and renewability, create an edge over synthetic fiber based products (specially their non- biodegradability which overshadow their other benefits). Therefore, the application spectrum of NFRCs has been continuously increasing in the industrial sectors, such as, automobile, aircraft and household products. As far as product development is concerned, the welding operation of subcomponents at various intermediate levels of manufacturing stages is inevitable. The welding processes are majorly categorized into mechanical, adhesive and fusion based processes. Ultrasonic welding, has proved to be a cost-efficient method as compared to other modes of joining, such as, adhesive joining and mechanical joining. In the present experimental investigation, the ultrasonic welding behavior of pure polymers (high density polyethylene (HDPE), recycled high density polyethylene (rHDPE) and poly lactic acid (PLA) and their composites reinforced with natural fibers (banana and aloe vera) at different fiber loading (5, 10, 20%) with/without energy directors (triangular energy director (TED), semi-circular energy director (SCED), cross energy director (CED) and flat energy director (FED)) is investigated. In addition, the effect of different processing routes (injection molding and 3D printing processes) on the mechanical performance of welded joints is also investigated. In the first phase, the optimum welding parameters (welding time, welding pressure and amplitude) for the welding of HDPE, rHDPE and PLA materials were obtained by using the Central Composite Design (CCD) philosophy of Response Surface Methodology (RSM) optimization technique. Thereafter, the injection molding molds were designed for fabricating the specimens with different energy director (TED, SCED, CED and FEDs) profiles. Then, the performance of pure HDPE, rHDPE and PLA materials with and without energy directors was analyzed. All the welded joints with CED profiles performed better than the TED and SCED in case of ultrasonic welding of HDPE, rHDPE and PLA adherends. The welded joints of HDPE and rHDPE materials with flat energy director (0.75 mm thickness) recorded highest load bearing capacity. In addition, PLA specimens with FED (0.5 mm thickness) recorded higher failure load bearing capacity. In the second phase, the effect of infill density, type of energy directors (triangular (TED), semicircular (SCED) and cross energy directors (CED)) and different levels of welding parameters has been investigated on the mechanical and thermal behavior of welded joints of adherends fabricated using Injection Molding and Fused Deposition Modelling (FDM) process. Presence of rasters and gap between them plays a pivotal role in overall heat generation at weld interface. All molded and 3D printed specimens having CED profile performed better than the specimens having TED and SCED profiles, welded at LLWP. At medium and higher levels of welding parameters, both printed/molded specimens with CED observed comparatively more degradation of joints due to higher concentration of energy at weld interface. In the third phase, ultrasonic welding behavior of short fibers (banana and aloe vera fibers) based HDPE, rHDPE and PLA thermoplastic composites (with and without energy directors) is experimentally investigated. The composite specimens for welding were fabricated (at 5, 10 and 20 % fiber loading) using extrusion injection molding (EIM) process. The effect of fiber loading, type of energy directors (TED, SCED and CED) and process parameters has been investigated on the mechanical and thermal behavior of the welded joints. Heat generated at the weld interface is mainly governed by the fiber attrition (higher at higher fiber loading); thermal conductivity of fibers (banana and aloe vera) and matrices (HDPE, rHDPE and PLA) as well as the dynamic mechanical properties of the developed composites. All the welded joints of composite adherends with 10% fiber loading depicted better load bearing capacity than the welded joints in composite adherends with 5% and 20% fiber loading. The welded joints of HDPE and rHDPE materials (at 10% banana fiber loading) with flat energy director (0.75 mm thickness) recorded highest load bearing capacity. In addition, the welded joints of PLA material (at 10% banana fiber loading) with FED (0.5 mm thickness) recorded higher failure load bearing capacity. TGA and DTG results established that the repeated thermal cycles (during fabrication of specimen and welding) do not affect the thermal characteristics of the welded specimen significantly in comparison to the unwelded samples.