The interpretation of the strain-dependent Poisson's ratio in auxetic polyethylene

The strain-dependent behaviour characteristic of auxetic (i.e. having a negative Poisson's ratio) polymers has been modelled using a simple geometric model which consists of rectangular nodules interconnected by fibrils. Careful consideration of the correct form of the model to use depending on the experimental method employed to test samples of auxetic ultra high molecular weight polyethylene (UHMWPE) has resulted in very good agreement between the experimental and theoretical Poisson's ratios and total engineering strain ratios when the deformation is predominantly due to hinging of the fibrils. Auxetic UHMWPE has been processed to yield a very wide range of Poisson's ratios depending on its microstructural parameters (i.e. nodule shape and size, fibril length and the angle between the fibril and nodule). These can be predicted using the model, allowing the possibility of tailoring Poisson's ratio of the material.