Increasing PVA Content Research Articles

Separation of liquid mixtures by using polymer membranes, V. Water‐alcohol separation by pervaporation through poly(vinyl alcohol)‐graft‐poly(styrene‐co‐maleic anhydride) membranes

AbstractGraft copolymerization of styrene‐maleic anhydride copolymer (ST‐co‐MA) onto poly(vinyl alcohol) (PVA) was carried out by a condensation‐coupling reaction through esterification. The ST‐co‐MA copolymer was obtained by the copolymerization of MA and ST in dimethyl sulfoxide (DMSO), using azoisobutyronitrile as initiator. The structure of the reaction products was confirmed by infrared analysis. The dependence of composition, viscosity and yield of the graft terpolymers on the concentration of the reactants are presented in detail. Mechanical properties of membranes with different compositions were measured over a wide range of composition. It was found that water was permeated through the membranes preferentially in all ranges of feed compositions. The permeation decreased and the selectivity increased with increasing ethanol concentration in the feed and with increasing PVA content in the membrane. The effect of the molecular size of the permeating species on both permeation and separation is also discussed.

Thermal behaviour and miscibility of poly(3-hydroxybutyrate)/poly(vinyl alcohol) blends

Thermal behaviour and miscibility of poly(3-hydroxybutyrate) (P(3HB)/poly(vinyl alcohol) (PVA) blend films prepared by casting have been analysed by d.s.c., n.m.r. and density measurements. Blends containing glycerine were also analysed by d.s.c. Melting temperature ( T m) of the P(3HB) crystalline phases decreased as PVA content increased, whereas T m of the PVA phase remained almost unchanged. The crystallinity of P(3HB) in the blends also decreased with increase of PVA content. These results indicated that the thermal behaviour of the P(3HB) phase was influenced by the existence of PVA. Glycerine had no effect on the thermal properties of the blend, except for depression of T m of the PVA phase. Miscibility in the amorphous phase of the blend has been analysed by density measurement. If P(3HB) is completely immiscible with PVA, the crystallinity of PVA can be estimated from the crystallinity of P(3HB) and the density of the sample. However, the crystallinities of the PVA phase estimated for some blend samples were greater than unity. This behaviour can be accounted for when these blends are partially miscible in the amorphous phase. In order to investigate the miscibility in detail, we have determined the 1H spin-lattice relaxation times in the laboratory frame ( T 1) and in the rotating frame ( T 1 ϱ ). Both T 1 and T 1 ϱ values for the P(3HB) and PVA phases tend to approach those of blend partners with increase of PVA content. That is to say, the increase of PVA content in a blend enhances the miscibility.

Separation of liquid mixtures by using polymer membranes. I. Water–alcohol separation by pervaporation through PVA‐g‐MMA/MA membrane

AbstractA membrane was designed for the separation of a water–alcohol mixture by pervaporation on the basis of the difference in hydrogen‐bonding interaction between two components of the membrane. Two kinds of poly(vinyl alcohol)‐g‐maleic anhydride/methyl methacrylate membrane were prepared by different methods: (1) A homogeneous membrane was formed by casting from dimethyl sulfoxide solution after purification. (2) A porous membrane was obtained directly by casting from the reaction solution, and then was purified. It is found that water was permeated through a homogeneous membrane preferentially in all ranges of feed compositions. Moreover, the flux was found to decrease with increasing PVA content in the membrane. The porous membrane after heat treatment has selective permeability for methanol. Pervaporation of water was investigated with respect to the feed concentration and also to the operating conditions. The effect of the molecular size of the permeating species on both permeation and separation is also discussed.

Molecular dynamics in bulk and plasticized poly(vinyl acetate): a spin-probe study

Poly(vinyl acetate) (PVA) in bulk and plasticized with di- n-butyl phthalate (DBP) over a wide composition range was spin-probed with the nitroxide radicals, 2,2-di- n-butyl-5,5-dimethyl-3-oxazolidinyl oxyl (DBOZ) and 2,2-di- n-nonyl-5,5-dimethyl-3-oxazolidinyl oxyl (DNOZ). The correlation times, τ c, for rotational diffusion of the probes over the temperature range 130–370 K were calculated from their electron spin resonance (e.s.r.) spectra by standard methods. Arrhenius plots of τ cfor all samples except pure DBP showed three distinct regimes: a high-temperature region of relatively high activation energy ( E a) in which E a −1 decreased linearly with increasing PVA content, a low temperature region of very low E a in the range 0–3 kJ mol −1, and an intermediate region of E a ca. 7 kJ mol −1 independent of composition. It was concluded that in the high-temperature region the probe responds to the glass-to-rubber relaxation of PVA and in the intermediate region to the γ or merged β, γ relaxation. In the low-temperature region it seems likely that a proportion of the probes can rotate freely in ‘holes’ or voids in the polymer, the remainder being immobilized within the glassy matrix. The values of E aa for rotation of DBOZ and DNOZ in pure bulk PVA were 69 and 56 kJ mol −1, respectively. It is tentatively suggested that this reversal of the order expected from the relative molecular volume of the two probes, is due to local plasticization by the long alkyl chains on DNOZ.