LIGHTWEIGHT APPROACH TO SMC COMPOSITES: NANOCELLULOSE COATED GLASS FIBER FABRIC
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The focus of this study is to investigate how to lightweight SMC composites for automotive applications without compromising their performance. This is accomplished by replacing, at least partially, the heaviest materials such as the glass fibers (GF) or calcium carbonate (CaCO3) with nanocellulose or nanoclays. In addition, the chopped glass fibers are replaced by glass fabric in order to better control the location and orientation of the glass fiber reinforcement and thus engineer the mechanical properties. Unsaturated polyester resin (UPR) is used as the resin, and a pilot scale sheet molding compounds (SMC) is used to make the SMC. The composites are made by stacking plies of SMC layers in a mold, after appropriate conditioning of the SMC, and compression molding. The properties of interest are the tensile and flexural modulus and strength according to the corresponding ASTM standards and the density of the composites. The void content is also determined using acid digestion and scanning electron microscopy. The main goal is to replace traditional chopped glass fibers (GF) used in SMC with unidirectional glass fabric coated with cellulose nanocrystals (CNC). The reasoning is to enhance properties with a better UPR/GF interface and controlled fiber orientation while reducing density. The glass fiber fabric is coated with nanocellulose using a scalable spraying technique that leads to homogeneous coatings. The four different glass fiber fabrics that were used in this study vary in CNC coating amount. To understand the effect of the nanocellulose, the glass fiber content of all composite formulations was kept constant at about 30 vol%. In addition, to determine the mechanical properties of the composites, the viscosity was verified for all formulations to ensure processability using the SMC pilot line. SEM micrographs show the quality of the CNC coating on the glass fiber fabric. Water uptake of all composites was also determined. The expected results address design, processing, and testing challenges, and successes and failures. The question to be addressed is whether CNC coated fabric is significantly advantageous for SMC compared to randomly oriented, chopped GF.
