Study on crystalline phases and degree of crystallinity of the melt compounded PVA/MMT and PVA/PVP/MMT nanocomposites

Abstract

Polymer nanocomposite (PNC) films comprised poly(vinyl alcohol) (PVA) and also its blend with poly(vinylpyrrolidone) (PVP) (i.e., PVA/PVP = 75/25 wt/wt%) as host matrices loaded with different amounts of montmorillonite (MMT) nanoclay up to 10 wt% were prepared by melt compounded method. X-ray diffraction (XRD) patterns of these PNC films were recorded in the appropriate angular range of 2θ values 3.8°–26° for their crystalline phase structural characterization. In comparison to the broader-type single diffraction peak for the aqueous solution cast prepared pure PVA film and that of the PVA/PVP blend film which is attributed to the hydrogen bonded isotactic and syndiotactic PVA crystals, five sharp diffraction peaks of different intensities corresponding to the evolution of various crystallites in the melt compounded PVA and PVA/PVP blend films were observed. Further, these peaks intensities were found significantly affected by the amounts of loaded MMT in these polymer matrices-based nanocomposites. It was observed that the prominent crystalline phase of the pure PVA converted into alternative tactic phases in the PVA/MMT films with the variation of MMT concentration. The prime crystalline phase of the PVA/PVP/MMT nanocomposites underwent alternative crystal structures formation abruptly on the initial loading of the 1 wt% amount of MMT in the PVA/PVP blend matrix reflecting a substantial alteration in the direction and nature of hydrogen bonding within the PVA crystal structures, and less changes were found with the further increase of MMT concentration up to 10 wt%. The effect of MMT loading on the crystallite sizes, degree of crystallinity, and the exfoliated and intercalated MMT structures in these PNC materials were analyzed in detail.