Abstract
A new type of reinforcement for unidirectional natural fiber composites has been developed, where a paper layer is assembled with a layer of unidirectional flax yarns. The paper layer chemically and mechanically bonds to the loose yarns to maintain their alignment and enables better manipulability of the reinforcement during stacking in the mold. Unfortunately, the paper layer adversely affects the permeability of the whole reinforcement to liquid resin and thus limits the impregnation quality of the final part. In this paper, a technique is adopted to increase the impregnation performance by modifying the architecture of the fibrous network in the paper layer. In particular, a method has been developed to replace a proportion of the Kraft fibers by short flax fibers in the paper layer, in an attempt to open the structure and increase the paper permeability. Permeability measurements show a major improvement in global reinforcement permeability. Basic mechanical properties of resulting composites were also analysed. Results show a slight decrease in modulus and strength when the paper layer is present. This is compensated by an important reduction in variability. Furthermore, increasing the flax proportion in the paper layer limits the loss of mechanical properties, while reducing variability even further.
Highlights
The resin transfer molding (RTM) process is typically used to produce large structural parts where the resin must flow long distances in the fibrous reinforcement [1]
The UD flax fibers were always oriented at 0 ̋ with respect to the length of the mold
The same tendencies were observed. These results indicate that at equal paper surface density, increasing were observed. These results indicate that at equal paper surface density, increasing flax flax fiber content and flax fiber length both help increase inter fiber porosity
Summary
The resin transfer molding (RTM) process is typically used to produce large structural parts where the resin must flow long distances in the fibrous reinforcement [1]. In this process, the reinforcement is placed in a rigid mold and the resin is injected to impregnate the fibers. For natural fibers applications where the design objective is to maximize mechanical properties, UD yarns are used instead of mats. In this case the yarns are aligned and stacked such that the stiffness and strength of the composite part are optimally distributed. The twist level must be limited to small values as it generally
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