The reaction of polyvinyl alcohol with montmorillonite

Abstract

The interaction of montmorillonite with low concentrations (1-5 %) of completely hydrolysed polyvinyl alcohol (PVA) has been investigated. As there was no release of cations from the clay on adding PVA it is concluded that the exchangeable cations, in particular divalent cations, are not directly involved in the bonding of PVA to montmorillonite. This is consistent with an earlier hypothesis (Emerson 1960) that PVA is hydrogen-bonded to the clay. Efforts to inhibit the formation of these bonds by the addition of various low molecular weight polyhydroxy compounds were not successful. The linkage of PVA to Na-montmorillonite was strongly influenced by the order of addition of small amounts of sodium chloride. Adding salt after the PVA increased the viscosity of the clay suspensions far more than adding salt first. This difference in bonding was also reflected in the swelling behaviour of flakes prepared by filtering and drying the suspensions. It appears that in the presence of salt, the clay crystals come together before many clay PVA bonds are formed, resulting in smaller flocs and looser links due to the unabsorbed segments of the polymer chains. This sensitivity of PVA to salt is in contrast to that of anionic polymers, where the presence of a Stern layer of cations improved the efficiency of bonding. The effective bonding of PVA to the clay is considered to be by OH . . . O bonds along single chains to the clay oxygens. The basal (001) spacing observed on X-ray examination of complexes formed at higher PVA concentrations arises from the crossing of two chains, attached to adjacent silicate sheets.