Residual water in polyvinyl alcohol

Abstract

The state of sorbed water molecules in the matrix of polyvinyl alcohol is investigated via the meth ods of static sorption, DSC, TGA, IR Fourier spectroscopy, 1 H NMR spectroscopy, and quantum chemical simulation. It is shown that the sorption of water by polyvinyl alcohol characterized by an S shaped isotherm is described by the double sorption model. It is established that the low diffusion coefficients and extremely low rates of desorption processes observed in the range of low activities are determined by a shift of the equi librium toward the formation of hydrogen bonded complexes of water molecules with hydroxy groups of the polymer. A mechanism for the behavior of residual water in hydrophilic polymers is suggested. It implies that differences between polymers are determined only by the quantity of residual water immobilized in "traps" and the energy of hydrogen bond formation.

Free Volume and Water Sorption by Cellulose Esters

“…It is interesting to note that the transition from S-shaped to concave isotherms is also observed for cellulose hydrate, but during its thermal annealing, which is due to disequilibrium of the initial state of the sorbent and relaxation of excess free volume during annealing [ 9 ]. For cellulose esters, this effect is observed against the background of free volumeconstancy ( Table 3 ).…”

“…The molecular weight of cellulose acetates was determined viscosimetrically using solutions of CA in acetone and the Mark–Kuhn–Hauvinck equation [η] = 1.6 × 10 −4 M η 0.82 [ 22 ]. The glass transition temperature of CA samples was determined by DSC [ 9 ]. The measurements were carried out on a NETZCN DSC 204 F1 Phoenix (Netzsch, Selb, Germany) in the temperature range from 293 to 520 K. All experiments were performed on sample weights not less than 15 mg.…”

“…Among currently developed models [ 1 , 2 , 3 , 4 , 5 , 6 ] for the description of sorption and solubility of water in polymeric sorbents, the concept of van Krevelen group contributions [ 7 , 8 ] based on notionsonhydrate numbers of functional groups of monomer links of macromolecular chains is widely used. The efficiency of this approach was demonstrated by describing the sorption properties of polyvinyl alcohol (PVA) [ 9 ], aliphatic and aromatic polyamides [ 10 , 11 ], elastomers [ 11 ], polyacrylates [ 12 , 13 ], polyurethanes [ 14 ], chitin and chitosan [ 15 , 16 ], naturally and artificially aged polyolefins [ 17 ], etc.…”

“…In [ 9 , 10 , 18 ], it was proposed to use this approach for the determination of structural and morphological features of sorbent structure: crystallinity degree, availability of functional groups of monomer links, content of hydrophilic polymers in mixed compositions and grafted systems [ 19 ], and estimation of osmotic pressure in swollen polymers [ 1 ]. In [ 20 ], an attempt was made to extend this concept to other polar sorbates, in particular, sulfur dioxide, carbon dioxide, and saturated hydrocarbons.…”