Durability of flax-basalt hybrid composites for marine applications

The aim of the present work is to evaluate the influence of external layers of mat basalt on the durability behaviour and performances of flax/epoxy laminates. To this scope, long-term aging tests were performed to evaluate the durability of the two different laminates in critical environmental conditions. In particular, Flax composites were constituted by ten layers of bidirectional flax fabric whereas hybrid laminates (i.e. Flax-Basalt) were produced by replacing four external layers of bidirectional flax with four layers of basalt mat. Both laminates had a total average thickness equal to 3 mm. The samples were exposed to critical environmental conditions following the ASTM B 117 standard. The salt fog had a chemical composition of 5% NaCl solution (pH between 6.5 and 7.2). In the climatic chamber, the samples were aged continuously with a temperature of 35°C. Every 2 weeks some samples were mechanically tested until a whole period of 2 months. The removed samples, wished and dried, were preserved in a sealed plastic storage bag with silica gel desiccant to ensure no further corrosion evolution during storage. Three point bending tests, dynamic mechanical tests (DMTA) and Charpy impact tests were performed according to ASTM D 790, ASTM D 4065 and ISO 179 standards, respectively. Moreover, five samples of both laminates were removed periodically, dried with a lint free cloth, and weighed with the aim to evaluate the water absorption. The experimental results showed that aging resistance of Flax composites can be improved by using basalt layers as outer laminae thus evidencing that hybridization with basalt fibres is a practical approach for enhancing mechanical properties and durability of natural fibre composites.