Mechanical Behaviour of 3d Braided Natural Fibre Fabric Reinforced Biodegradable Composites

Abstract

Synthetic fibre reinforced composites (such as glass, carbon and kevlar) have high specific strength and modulus and popularly used in the applications of automotive, aerospace and wind energy sectors. These composites are non-degradable and their disposal after the end use is a significant problem. Hence the research in the development of more sustainable and renewable natural fibre filled bio-composites is extremely topical. In this study, to fabricate the biodegradable composites flax fibre is used as filler material and polylactic acid (PLA) polymer is used as matrix material. Flax fibre braided yarn is prepared by solid braiding method, followed by this the plain woven fabric is prepared using a handloom machine. Before the preparation of the composite laminates, PLA and natural fibre braided yarn fabric (NFBF) sheets are prepared by solution casting method. Film stacking method and hot press compression molding methods are used to prepare the composites with the different weight fraction of fibre. In this work, influence of NFBF reinforcement in PLA resin on mechanical properties, thermal buckling, water absorption, biodegradability, wear, fracture toughness, mechanical buckling and free vibration characteristics are investigated. Initially, geometrical and tensile properties of the prepared braided yarn and woven fabric are studied. Mechanical properties of the composites are characterised experimentally in the warp and weft directions of the composite surface plies. The NFBF/PLA composites results are compared with the pristine PLA results. It is observed that the mechanical properties of the composites are improved with the reinforcement of NFBF compared to pure PLA. Warp direction loaded composites showed higher mechanical properties compared to weft direction loaded composites. The NFBF/PLA composites are compared with the other natural fibre PLA composites results reported in literature and it is noticed that the NFBF/PLA composites have moderate tensile strength, higher flexural and impact strengths. Thermal properties (flammability, DSC, TGA, HDT and thermal deflection) of the NFBF/PLA composites are determined experimentally. Thermal deflection behaviour of pure PLA and NFBF/PLA composites are carried out on an in house built experimental set up at different temperature loading conditions. Effect of NFBF reinforcement, its weight percentage, loading direction (warp and weft) of the iii composites and nature of temperature load change on deflection behaviour of the PLA and NFBF/PLA composites are studied. Results revealed that, burning rate of the NFBF/PLA composites is reduced compared to pure PLA. Meanwhile, enthalpy (ΔHm), percentage crystallinity (Χc), thermal stability and HDT are enhanced for the NFBF reinforced PLA composites over pure PLA. Thermal deflection of the composites is reduced compared to pristine PLA and it further decreased with the increase in fibre content. Due to higher modulus and strength associated with the NFBF/PLA composites. Similarly, the warp direction loaded composites showed higher reduction in deflection compared to pure PLA and weft direction loaded composites. The reinforcement of NFBF improved the thermal resistance property and this result for the reduction in thermal deflection peak temperature for different heating cases. Reinforcement also enhanced the thermal sustainability of the composites. Influence of environmental conditions on NFBF/PLA composites are analysed by performing water absorption and soil incubation tests. Water absorption, thickness swelling, flexural tests are performed in different loading directions (warp and weft) of the composites. Similarly, biodegradation study is carried out in a compost soil medium at different incubation time periods (0, 15, 30, 60, 90 days). Biodegradation study is analysed based on weight loss measurement, change in FTIR spectra and reduction in tensile strength. Results revealed that water absorption and thickness swelling are increased with the reinforcement of NFBF, the weft direction loaded composite showed higher water absorption and thickness swelling values. Warp direction loaded composites showed maximum flexural strength and modulus. These values are decreased after water absorption. The NFBF reinforcement also enhanced the biodegradability of the NFBF/PLA composites compared to neat PLA. Tensile properties are decreased with the increase in the incubation time. Biodegradability analysis revealed that NFBF reinforcement enhanced the resistance against degradation than other types of reinforcement. It is due to the high fibre aspect ratio associated with short fibre reinforcement that increases the interaction with water molecules, whereas it is low for braided reinforcement. iv Friction co-efficient and wear rate of the composites are analysed using pin-on-disc tribometer under dry contact sliding condition and various operating conditions (velocity and load) for a fixed sliding distance of 3000 m. The reinforcement of NFBF with the PLA reduced the polymer film generation and improved the surface roughness significantly. Wear rate of the composites are decreased drastically compared to pure PLA. Also, fracture toughness study is performed on single-edge- notched-bend (SENB) specimens using three point bending method. It is found that plane-strain fracture toughness (KIC) and strain energy release rate (GIC) values of the PLA composites are higher than pure PLA for NFBF35 reinforcement. KIC values of the NFBF reinforced PLA composites are much high compared to similar natural fibre composites reported in literature. This is attributed to high resistance offered by the interweaving yarns of the braided fabric hence more energy is required to begin crack propagation compared to other typical forms of reinforcement. Influence of mechanical edge load on free vibration frequencies of NFBF/PLA beam is studied experimentally. Initially, the buckling load of the beam is calculated. Then variation of natural frequencies with and without compression loads is analysed. Buckling strength of the PLA beam is enhanced by NFBF reinforcement. Increase in the axial load results in reduction in the frequencies and the effect is very significant for the lowest frequency for the loads around the buckling load. Furthermore, the lowest frequency increase is very significantly for the loads higher than critical load due to the increase in geometric stiffness.