Optimisation of interfacial properties for tensile strength by plasma polymerisation

Plasma polymerisation was used to coat E glass fibres with an acrylic acid/1,7-octadiene copolymer at varying concentrations of acrylic acid. These fibres were then used to produce unidirectional composite panels. By so doing it was possible to produce composites with varying degrees of adhesion between fibre and matrix. The panels were then prepared into test pieces and tested in tension.It was found that stress, strain and energy absorbed to failure were higher in specimens produced from plasma polymer coated fibres than from uncoated controls. Tensile strength and energy absorbed in failure were dependent on the concentration of acrylic acid in the monomer flow used to coat the fibres but strain to failure and modulus were not. The presence of a plasma polymer coating increased the longitudinal tensile strength by 20%. By tailoring the composition of the coating to create the optimal degree of fibre–matrix bonding the tensile strength was increased by a further 30%. This optimal degree of bonding was obtained at an intermediate level of interfacial adhesion which was less than the maximum achievable. It was also observed that the plasma polymer coating can change the failure mechanisms and fracture behaviour of the composite.