Liquid Composite Molding of Multiphase Composites Using Resin with Nanofibrillated Cellulose : Distribution of Particles and Effect on Composite Properties

Abstract: Two objectives have served as the basis for the present work. The first objective was to experimentally verify the output of a Monte Carlo-based model on particle deposition in porous structures (i.e. fiber preform) during the resin transfer molding (RTM) process. This model is expected to have a positive impact on process optimization and reduce costs by enabling theoretical prediction of how particles are deposited when nanoparticle filled resin is used in RTM. The second objective was to produce a multiphase composite where the epoxy (EP) matrix makes use of the mechanical enhancement that cellulose nanofibres (CNF) can impart when incorporated into the liquid phase of the used polymer matrix. The study was conducted by production of the CNF-filled EP matrix, and by using this to produce multiphase composites out of glass- as well as carbon fibers. The RTM was carried out in collaboration with CSI Composite Solutions and Innovations Oy (Vilppula, Finland). Characterization techniques, including Raman spectroscopy, optical and electron microscopy were used to investigate the microstructure and for assessment of the CNF distribution in the produced composites. These observations were qualitatively compared with the output from the proposed model to evaluate its applicability. EP/CNF nanocomposites (i.e. the consolidated resin) were evaluated by tensile test to investigate the influence of CNF on the mechanical properties of epoxy. Three-point bending tests (ISO 14125) was performed on the multiphase composite to evaluate the impact of CNF-inclusion in the matrix. Obtained results indicate that the model is consistent with the process by which the CNF are deposited in RTM, as both the model and experiment show that the CNF are accumulated in the upper layers (injection side) of the preform. However, work remains to be done for the model to fully comply with specific aspects of the used reinforcement in RTM (e.g. pore size and geometry of the used fiber reinforcement), and thus predict the correct deposition profile and penetration depth of the CNF. The mechanical tests showed that the incorporation of CNF in the epoxy provides a composite with enhanced performance relative a reference without the CNF. The percentage change relative the reference composite was up to 22 % in flexural strength and 25 % in flexural modulus. It is suggested that the increase in mechanical performance is a result of CNF accumulation due to filtering in the fiber preform.