Degradation Of Polymer Composites Research Articles

The influence of UV radiation on the properties of GFRP laminates in underwater conditions

Degradation of polymer composites is a significant problem in many engineering aspects. Due to the interaction of various degradation factors during the exploitation of composites, a synergistic effect of destruction is observed. The article describes the phenomena occurring in glass fiber reinforced polyester laminates under the influence of ultraviolet radiation (UV) in an aquatic environment. The laminates were exposed to UV-A, UV-B and UV-C radiation for 1000 h in free-air and underwater conditions. During the test, the materials were immersed at stable depth of 1 mm and 10 mm, respectively. The three-point bending tests performed on the samples after being exposed to UV showed an increase in the flexural strength of the composites. Simultaneously, degradation of the outer surface layer was observed. The degradation removed the thin resin film from the surface which resulted in a direct exposure of the reinforcing fibers to the environment. The transformations taking place in the deeper layers of the composite increased the mechanical strength due to the additional cross-linking reactions excited by the energy arising from the radiation. Moreover, the formation of polymer structures from free styrene remaining after the technological process and the occurrence of free radical reactions as a result of the cage effect was also observed.

An Alteration of the Time-Temperature Superposition Principle to Account for Environmental Degradation in Fibre Reinforced Plastics

The approach suggested in this analysis stems from basic material science laws and considers that any environmental degradation of polymer composites ultimately consists in chemical link and cohesion force alteration. Such alteration leads to the modification of material viscoelastic characteristics that can be measured through stress relaxation or creep. Then the analysis deals with the applicability of the time-temperature shift principle for prediction test in cases involving environmental degradation. It is demonstrated that the shift factor as determined from Arrhenius Law needs to incorporate an additional term to account for the variation of the activation energy of the chemical and physical degradation. The method leads to excellent prediction of the time and environment dependent material strength.