Effect of alternating salt fog and dry conditions on the behavior of flax fiber reinforced epoxy composites
Topic(s) : Material and Structural Behavior - Simulation & Testing
Co-authors :
Vincenzo FIORE (ITALY), Luigi CALABRESE (ITALY), Carmelo SANFILIPPO (ITALY), Edoardo PROVERBIO , Antonino VALENZA (ITALY)Abstract :
Natural fiber reinforced composites have gained growing attention in recent years because they represent a promising option to bring together quite good mechanical performances along with sustainability. Nevertheless, some issues related to heterogeneity of natural fibers such as their great tendency to absorb moisture as well as their poor compatibility with polymeric matrices, limiting their widespread use in wet or humid environmental conditions. In such a context, aim of the present research work is to assess how the exposition to repeated salt spray fog-dry aging cycles can modify the physical and mechanical performances of epoxy composites reinforced with five layers of twill weave woven flax fabric (areal weight 318 g/m2) and manufactured via vacuum assisted resin infusion process. In particular, the whole aging campaign lasted 3 months (i.e., 12 weeks) consisting of three wet/dry cycles, each with duration of 4 weeks: i.e., 10 days of foggy environment (i.e., wet phase) followed by 18 days of drying (i.e., dry phase). In more detail, the wet phase was performed by exposing composites to salt-spay fog (i.e., 5 wt% NaCl solution) at 35°C and 100% R.H., by using a corrosion chamber (model CC1000IP by Ascott) in accordance to ASTM B 117 standard, while the dry phase was carried out by keeping them under controlled conditions (i.e., 22°C and 50% R.H). Quasi-static three-point bending tests were performed after 0, 5, 10 and 18 days of drying for each salt fog-dry cycle, by using an universal testing machine (model Z005 by Zwick-Roell), according to ASTM D790 standard. Furthermore, physical properties such as water absorption capacity, density and voids content have been evaluated by monitoring the weight and size of composite samples at regular time intervals during the entire aging campaign.
As quite predictable, the experimental results evidenced a progressive worsening of the composites' performances when exposed to repeated wet-dry phases, as shown by both water sorption-desorption curves and mechanical data. In particular, gradual increases in the maximum amounts of water absorbed and desorbed during the subsequent three wet-dry cycles were observed. This behavior can be mainly attributed to the progressive composite softening evidenced during the salt-fog aging phase, followed by a reversible performances recovery evidenced during the dry phase. More interestingly, both flexural properties (i.e., modulus and strength) at the end of wet phase of each cycle increases with increasing the cycle's number, despite the water uptake trend. This means that the flax fiber reinforced composites evidenced a growing capability to recover reversibly their mechanical performances with increasing the aging time, when exposed to repeated wet/dry cycles.
As quite predictable, the experimental results evidenced a progressive worsening of the composites' performances when exposed to repeated wet-dry phases, as shown by both water sorption-desorption curves and mechanical data. In particular, gradual increases in the maximum amounts of water absorbed and desorbed during the subsequent three wet-dry cycles were observed. This behavior can be mainly attributed to the progressive composite softening evidenced during the salt-fog aging phase, followed by a reversible performances recovery evidenced during the dry phase. More interestingly, both flexural properties (i.e., modulus and strength) at the end of wet phase of each cycle increases with increasing the cycle's number, despite the water uptake trend. This means that the flax fiber reinforced composites evidenced a growing capability to recover reversibly their mechanical performances with increasing the aging time, when exposed to repeated wet/dry cycles.