Composition PVAC dispersion

Figure 5 Development of major phase composition of c/p dispersions in bidestilled water or concrete pore solution (POW). (A) c/PVAc in POW (B) c/PVAc in Bidest (C) c/PVA in POW (D)...

Poly (vinyl alcohol-co-vinyl acetate) polymers are surface active species which can be used to stabilise latex and oil in water dispersions. In order to understand the properties of these materials, it is necessary that their sequence distributions are well characterised. A number of NMR studies on the microstructure of PVA/PVAc copolymers have been made [51-53] (see also chapter 3). Moritani and Fujiwara [51], for example, have used proton and carbon-13 NMR spectroscopy to extract dyad distributions for a range of copolymers with different degrees of deacetylation. Samples were prepared using one of three routes direct saponification of PVAc alcoholyis of PVAc using sodium methoxide and reacetylation of PVA. From the polymer composition and the dyad distribution, the parameter rj was calculated for each polymer as follows ... 

B) Polymer-cement concrete is a modified concrete in which a part of the cement binder is replaced by organic polymer. It is produced by incorporating a monomer, prepolymer, or dispersed polymer latex into a cement-concrete mixture. The process technology used is similar to that of conventional concrete and has the advantage that it can be cast in place for field applications. Most of the polymer-cement-concrete composites are based on different kinds of lattices obtained especially by emulsion polymerization. The lattices are aqueous emulsions containing polymer particles such as SBR, NBR, PVAc, copolyesters of AA-MAA, and PAA-PMAA-SBR. The compatibility of SBR, PVAc, and acrylic lattices with Portland cement produces particular characteristics that led to wide use of this component as polymer-concrete composites. 

Poly(vinyl alcohol) has also been shown to provide mechanically adaptive properties to composite films comprised of a PVOH electrospun mat and a PVAc or EO-EPI matrix. Films made from such composites exhibited controlled response to hydration that resulted in a two fold decrease of the storage modulus which, in the case of the PVAc composite, was fully reversible. Expanding on this concept and in a similar motif to the aforementioned CNC composites, Korley and coworkers have recently showcased the potential use of montmorillonite in mechanically adaptive composite materials. Montmorillonite is a layered silicate with high aspect ratio and surface area and is often used in polymer composites to mechanically reinforce the resulting material, while its dispersibility and tunable surface chemistiy make its use particularly attractive. In this case, the incorporation of montmorillonite in the PVOH fibrous filler resulted in enhanced moduli when the polymer matrix consisted of EO-EPI, as opposed to the limited enhancement observed in the case of a PVAc matrix. Nonetheless, both composites showed mechanically switching properties upon hydration, with the weight fraction of montmorillonite affecting the mechanical contrast as well as the response time. ... 

The dispersion of fibers in polymer latex to prepare composite has been reported for poly(6-hydroxyoctanoate) (PHO) [101, 102], polyvinylchloride (PVC) [103], waterborne epoxy [104] and polyvinyl acetate (PVAc) [94]. Most of the works focus on the use of non-polar, non-water-sensitive polymers, while keeping an aqueous media for the processing of the films to preserve the dispersion of the nanoparticles. In their pioneering work, Favier et al [94] adopted the technique of solvent casting using a synthetic latex obtained by the copolymerization between styrene (35 wt%) and butyl-acrylate (65 wt%) (poly(S-co-BuA)). Nanowhiskers were dispersed in the latex and evaporated. The nanocomposite films were obtained by water evaporation and particle coalescence at room temperature, that is at a temperature higher than Tg of poly(S-co-BuA), around 0 C. 

Zardalidis et al. [53] investigated the molecular dynamics of PEO/PVAc blends as a function of composition, temperature and pressure. For blends with a high PVAc content, all short-range correlations were dominated by the PVAc component. The fact that an invariant frequency dispersion was observed for different blend compositions under isochronal conditions suggested a covariance of the width of the distribution with stmctural relaxation time, as found in other glassforming liquids. 

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