Modelling the influence of moisture on the mechanical behaviour of crosslinked polyurethane adhesives

Abstract

Crosslinked polymers are typically viscoelastic in nature and show non-linear behaviour due to large deformation. The mechanical behaviour of these polymers is influenced by moisture diffusion because of the hygroscopic properties of the material. The crosslinked polymers are formed by the shorter and longer chain length distribution. The shorter chains tend to break/debond from the network with an increase in the deformation thus leading to the softening of the material. In this paper, the crosslinked polymer mechanical behaviour is modelled with a micro-mechanical polymer network model that considers the softening of the elastomer. The network evolution concept used in the micro-mechanical model formulation considers the shorter and longer chain length distribution allowing the softening of material. The moisture diffusion in the material is anomalous behaviour, therefore, the Langmuir-type diffusion model is used to model the moisture diffusion in the crosslinked polymer. The influence of moisture on the mechanical behaviour is modelled by coupling the micro-mechanical network model with the diffusion model. The coupled diffusion and deformation model uses the moisture-dependent mechanical parameter to compute the local parameter for the evaluation of the mechanical behaviour with inhomogeneous moisture distribution. In this paper, crosslinked polyurethane adhesives are used in the numerical investigation of ageing under the influence of moisture with the coupled material model. The experimental investigation for tensile and diffusion behaviours is investigated for different humid conditions at an isothermal condition of 60◦C.