Mechanical properties and morphology of flax fiber reinforced melamine-formaldehyde composites

The mechanical performance of natural fiber reinforced polymers is often limited owing to a weak fiber-matrix interface. In contrast, melamine-formaldehyde (MF) resins are well known to have a strong adhesion to most cellulose containing materials. In this paper, nonwoven flax fiber mat reinforced and particulate filled MF composites processed by compression molding are studied and compared to a similar MF composite reinforced with glass fibers. Using flax instead of glass fibers has a somewhat negative effect on tensile performance. However, the difference is relatively small, and if density and material cost are taken into account, flax fibers become competitive. Tensile damage is quantified from the stiffness reduction during cyclic straining. Compared to glass fibers, flax fibers generate a material with a considerably lower damage rate. From scanning electron microscopy (SEM, it Is found that microcracking takes place mainly in the fiber cell walls and not at the fiber-matrix interface. This suggests that the fiber-matrix adhesion is high. The materials are also compared using dynamic mechanical thermal analysis (DMTA) and water absorption measurements.