Alkali absorption and durability studies on CFRP laminated composites

Fiber Reinforced Plastics (FRP) are widely used in marine, aeronautical, automotive, space applications due to their corrosive resistance and low cost to performance. The main aim of this research was to examine the impact of alkali absorption and durability in the Carbon/Epoxy, Carbon/Vinylester, and Carbon/Isopolyester composites immersed in 13.59 pH alkaline solutions for a maximum of 25 days at 27°C (room temperature) and 65°C. Epoxy, vinyl-ester and Isoployester resin are selected as a matrix material and Poly-acrylonitrile-based Carbon fiber of 200 gsm fabrics is chosen as reinforcement and hand lay-up process is used for fabrication in the ratio of 35: 65 respectively and cured at room temperature with applied pressure using hydraulic press for 24 hrs. Solution of alkali was prepared and specimens were subjected to alkali solution. The moisture absorption was calculated on the basis of rate of moisture for every 5days interval and rate of diffusion coefficient (m2/sec) were calculated. Similarly durability studies (UTS, ILSS and FS) are conducted at 27°C and 65°C. Characterization of the fractured area was done using a scanning microscope. The obtained result rate of moisture absorption in case of neat casting and CFRP specimen shows the maximum alkali absorption in Iso-polyester / carbon whereas the minimum absorption was shown in vinyl ester/carbon specimens at RT and at 65°C over a period of 25days. At room temperature and 65°C the diffusion coefficient (D) was found and identified higher value for Iso-polyester/carbon and low for vinyl ester/carbon this is because Iso-polyester are distributed along the main chain, which makes easily available for reaction but in vinylesters the ester functional groups acts as a shield by methyl groups which restrict the easy absorption. Reduce in percentage in mechanical properties is due to Alkali absorption in terms of reduced degradation values in UTS, Flexural Strength and ILSS samples, carbon / epoxy showed supremacy over vinylester / carbon and iso-polyester / carbon. Scanning electron microscopy images show the embrittlement and micro-cracks on surface due to exposure to the alkali environments, matrix bonded to fiber are hardly identified as the temperature increases.