Effects of graphite content on the morphology and barrier properties of poly(vinylidene fluoride) composites

• Published in: Polymer (Guilford) 1999-10, Vol.40 (22), p.6023-6029
• Main Authors: Busick, Deanna N., Spontak, Richard J., Balik, C.Maurice
• Format: Article
• Language: English
• Subjects: Applied sciences; Composites; Diffusion; Exact sciences and technology; Forms of application and semi-finished materials; Graphite; Poly(vinylidene fluoride); Polymer industry, paints, wood; Technology of polymers
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/S0032-3861(98)00826-X

We have performed a series of morphology and CO 2-probe diffusion analyses to ascertain the existence and composition dependence of voids in graphite/poly(vinylidene fluoride) composites both above and below the graphite percolation threshold, as determined from electrical conductivity measurements. Sorption data indicate that, with increasing graphite loading: (i) the diffusivity of CO 2 in the composite material decreases; and (ii) the volume fraction of voids in the material increases. Differential scanning calorimetry reveals that polymer crystals nucleate heterogeneously on graphite particles and that samples containing graphite have higher degrees of crystallinity than the neat polymer. Crystallinity effects appear to dominate barrier properties at low graphite loadings, while porosity effects dominate at high graphite loadings. Our results strongly suggest that, although voids in these composites are probably associated with relatively poor adhesion along graphite/polymer interfaces, the voids are also discrete (i.e. they do not form a continuous network, even if the graphite particles do).