The presence of well dispersed montmorillonite (MMT) clay in glass mat thermoplastic (GMT) grade isotactic polypropylene (iPP) results in significant increases in the melt viscosity at low shear rates, and this is shown to reduce the rate of impregnation of glass fibre mats in model experiments [1]. Satisfactory impregnation has nevertheless been obtained with iPP/MMT under conditions comparable to those used in industrial processing, and the flexural modulus of consolidated specimens prepared from the modified GMT has been found to show much greater increases than expected from the measured increases in the matrix stiffness on MMT addition. By using a combination of etching and optical and atomic force microscopy it has been demonstrated that the MMT is relatively homogeneously distributed within the matrix, i.e. that there is little filtering by the fibre bed, and that its presence significantly influences relaxation of the glass mat during impregnation, leading to modified through-thickness glass fibre distributions in the consolidated specimens. Thus, depending on the initial lay-up and overall glass fibre content, the bending modulus and strength of the consolidated specimens may either increase or decrease with increasing matrix MMT content, whereas the tensile properties are more consistent with the predictions of simple micromechanical models based on the assumption of a uniform glass fibre distribution. Results from fractographic analyses are used to show that the presence of matrix rich layers at the specimen surfaces may also lead to premature crack initiation and effective failure in flexion and under impact.  

 [1] Houphouët-Boigny, C., Plummer, C.J.G., Wakeman, M.D., Månson, J.-A.E., “Glass fiber reinforced thermoplastic nanocomposites” Journal of Thermoplastic Composite Materials.2008; 21: 103-118.

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