Life Cycle Evaluation of Manufacturing and Mechanical Properties for Novel Natural Fibre Composites

Abstract

Life Cycle Assessment (LCA) is a method for evaluating the environmental impacts associated with all stages of a product’s life-cycle (production, use and disposal) by identifying, e.g., energy consumption and CO2 emissions. This work has been aiming for a life cycle assessment for the manufacturing of natural flax fibre roving reinforced composites. The research focused on the processing gate-to-gate (GtG) system boundaries through tests and analysis of the energy consumptions and carbon foot-prints based on real primary data. The working data was obtained from specialists and composite manufacturers using a monitoring computer, ecoinvent software, connected to the machine. Then, SimaPro 8 for LCA was used to produce the process tree and to determine the environmental impact of the production through auto indication. The overall LCA of the natural fibre composites production is reflected by using a limited number of stages on targeted energy consumptions within the “factory-door-in to factory-door-out”, which have been determined and assessed in the designed in-situ or in-line operation processes. The composite material is comprised of a flax roving, polylactic acid (PLA) and maleic anhydride polypropylene (MAPP). This matrix is commingled in the process for new composite material in the form of a flax/PLA and flax/MAPP tape according to the technical requirements by industry. The quality of the composite tape is dependent on the temperature and roving speed in manufacturing. The processing condition was optimised and it was found that the best processing rate was at a temperature of 170 0C and speed of 4.0 m/min. The results showed that flax/PLA and flax/MAPP mixed well as a matrix material for natural fibre composite. In contrast, the normal tri-axial glass fibre production is optimised with a speed of 1m/min using a standard roving glass fibre laminating machine. The composite flax/PLA tape, however, is about four times faster compared with the normal tri-axial manufacturing. The life cycle gate-to-gate results of the process showed that the energy consumption, to produce 1.0 kg of flax/PLA tape or flax/MAPP tape was 4.4 MJ, and the CO2 emissions were estimated at 0.63 kg. The energy consumption to produce a similar amount of glass fabrics for composites is about 23.8 MJ with CO2 emissions estimated to be at the level of 3.45 kg. Therefore, the process to manufacture flax/PLA tape can be produced considerably quicker than that of woven fibreglass fabrics for glass fibre composites. As an important part of the composites processes, moulding composites flax/PLA or flax/MAPP tape were primarily accounted and analysed. The suggested standard procedures, to perform the processing setup, were used throughout the work to avoid the dry region or non-impregnated fibres during the moulding process. The energy consumption and environmental impacts, of the compression moulding process for the composite flax/PLA tape, were evaluated and compared to the composite glass/PP. The results show that the electricity used for the compression moulding process varies between 17 MJ to 19 MJ for the composite flax/PLA tape and glass/PP. Still, the environmental impact of the composite glass/PP is largely superior to that of the composite flax/PLA tape. More detailed processing comparisons of composite flax/PLA were carried out regarding energy consumption and CO2 emissions, in a production of a car component, by using an eight layer-flax prepreg tape through a conventional hot press-moulding. The moulding data displayed showed that to produce a 250 mm x 250 mm sheet, estimated energy consumption was 17.1 MJ, and the CO2 emission was 2.6 kg. Meanwhile, the ultimate tensile strength achieved was between 57 MPa to 105 MPa and the flexural strength was between 10 MPa to 80 MPa. Production results portrayed that a tape composition with 60% volume fraction Flax and 40% volume fraction PLA resulted in better tensile properties than other volumetric ratios. The outcomes may support alternative options for some material applications and selections for the automotive industry such as boot trim, door insert, parcel shelf and truck interior. An effort was made to optimise the mechanical properties of composites flax/PLA and flax/MAPP, mainly, through calculations of the thickness using flexural modulus formula three-point bend. Based on the experiment results of the mechanical properties observed, the thickness of the natural fibre composites flax/PLA and flax/MAPP tape is 2.1 mm lower than for the composite, whereas glass unit directional (glass UD) fabric is 3.5 mm. This is primarily when focusing on the specific composite properties as a result of the low density of natural fibre. The flexural modulus of the composite tape is significantly lower than that of their counterpart composite materials glass/PP or glass UD fabric. The flexural modulus formula of natural fibre composite material and glass/PP or glass UD fabric were combined to find the require thickness need to add to the composite flax/PLA and flax/MAPP tape. The outcomes show that natural materials flax/PLA and flax/MAPP tape have breadth increased to 5 mm and to 8 mm respectively to be equivalent to the stiffness of composite glass unit directional fabric. Therefore, enhancing the thickness improved the mechanical properties, while other dimensions (length and width) stay the same, whilst increasing the energy consumption for the compression moulding. A life cycle gate-to-gate was used to compare material transformation, fibre into fabric and fibre into the composite tape, by a current production method using a tape machine and triaxial machine. This was followed by prepreg and compression moulding, into the component that can be used for automotive applications. The results of the life cycle process indicated that the negative effect on human health, of natural fibre composite tape, is lower than the synthetic fibre and is, therefore, an ecologically friendly alternative. However, because of limitations of the life cycle method, the results are only an interpretation and not the absolute truth, as some factors like the effect of heat loss and machine wear and tear were not included in the analysis. The evaluation of the manufacturing process shows different environmental effects. Therefore, the outcomes may support alternative options for some material productions and less environmental impact.