Water transport in cement-in-polymer dispersions at variable temperature studied by magnetic resonance imaging

The hydration of recently developed cement-in-polymer dispersions (c/p) containing 30% and 40% poly (vinyl acetate) [PVAc] and 30% poly(vinyl alcohol) [PVA] was monitored on-line at various temperatures using ¹H Single Point Imaging (SPI). The physical changes undergone by the materials as well as the complex manner in which the absorption process takes place and the evolution of the spin density were characterized and were found to be strongly dependent on the nature and amount of polymer and on the temperature. Based on the results obtained we propose a simple mathematical model which can be used to characterize the behaviour of the c/p dispersions exposed to hydration at variable temperature.     

Characterization of strong polyelectrolyte hydrogels based on poly(vinyl alcohol)

Maleic anhydride (MA) was grafted onto both partially and fully hydrolyzed poly(vinyl alcohol) (PVA) in the presence of an initiator. Strong polyelectrolyte polymers were prepared by sulfonation of PVA–MA grafts. The sulfonation was completed by reaction of hydroxyl groups of PVA–MA grafts with two different sulfonating reagents (chlorosulfonic acid and pyridine sulfonic acid). The sulfonation degree was evaluated by acid–base titration and ¹H NMR analysis. The solution behaviour of the prepared grafts was evaluated from viscosity measurements. Four kinds of water‐insoluble PVA–MA and PVA–MA‐SO₃H hydrogels were prepared by heat treatment, physical gelation and chemical crosslinking with different weight ratios of N,N‐methylene bisacrylamide (MBA) crosslinker. The swelling parameters were measured for all prepared gels in deionized water and aqueous solutions at different pH values from 2 to 12 having constant ionic strength (I = 0.1). All gels exhibit a different swelling behaviour upon environmental pH changes. Copyright © 2004 Society of Chemical Industry     

Phase structure in the blend of atactic poly(vinyl alcohol) with atactic poly(vinyl alcohol‐block‐vinyl acetate)

An almost fully saponified atactic poly(vinyl alcohol) and an atactic poly(vinyl alcohol‐block‐vinyl acetate) of which degree of saponification is 89 mol % were blended by a solution casting method. The phase structure of the blend film was analyzed by optical microscopy, ¹³C‐NMR, and differential scanning calorimetry. The most remarkable structure of the blend was composed of cylindrical domains penetrating the film. The swelling behavior of the blend films was also investigated in the dimethylsulfoxide and water mixed solvents to find differences in solubility and diffusion behavior between the matrix and the domain. The cylindrical domains could be selectively dissolved away in water and the film became porous. We tried to change the size of the cylindrical domain with various film preparation conditions. This aimed to turn the film into the useful filter membrane. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1807–1815, 2002     

Physicochemical characterization of hydrogels based on polyvinyl alcohol–vinyl acetate blends

Hydrogels made of polyvinyl alcohol–vinyl acetate and its blends with water soluble polymer were studied in terms of swelling behavior, microstructure, and dynamic mechanical properties. Hydrogels prepared by blending polyvinyl alcohol–vinyl acetate with either polyacrylic acid or poly(4‐vinyl pyridine) exhibited a strong pH dependency. When poly(vinyl pyrrolidone) was used for blending, an unusual pH dependency was observed. An increase in the equilibrium water content in all systems resulted in an increase in the freezable water as determined by DSC. Critical point drying led to a striated surface on polyacrylic acid–polyvinyl alcohol–vinyl acetate hydrogels, whereas a porous structure was observed on the freeze‐dried poly(vinyl pyrrolidone)–polyvinyl alcohol–vinyl acetate gels. Hydrogels with elevated storage modulus were obtained when either polyvinyl alcohol–vinyl acetate alone or polyacrylic acid–polyvinyl alcohol–vinyl acetate blends were thermally treated at high temperatures (i.e., 150°C). Low storage modulus was observed for both poly(vinyl pyrrolidone) and poly(4‐vinyl pyridine)‐containing hydrogels. Temperature dependency of storage modulus from 20 to 60°C was observed only for poly(4‐vinyl pyridine)–polyvinyl alcohol–vinyl acetate hydrogels. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3578–3590, 2001     

Development of a nonaqueous solvent system for poly(vinyl alcohol) and its characterization

Solubility of poly(vinyl alcohol) (PVA) in water prevents the preparation of various derivatives through homogeneous techniques as most of the derivatives thus formed are insoluble in aqueous medium. There are a number of solvents that can swell PVA under hot conditions but cannot dissolve PVA. In the present study, N,N‐dimethyl acetamide (DMAc) has been identified as solvent in which PVA can be dissolved in the presence of an equimolar amount of lithium chloride (LiCl). ¹H nuclear magnetic resonance (¹H‐NMR), ¹³C‐NMR, infrared (IR), and X‐ray diffraction (XRD) studies have been carried out to characterize the regenerated poly(vinyl alcohol) (RPVA). DMAc–LiCl is found to be a true solvent system for dissolution of PVA. An attempt has also been made to prepare poly(vinyl acetate) from this solution of PVA by a homogeneous technique. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 663–669, 1999     

Synthesis of copolymeric acrylamide/potassium acrylate hydrogels blended with poly(vinyl alcohol): Effect of crosslinking and the amount of poly(vinyl alcohol) on swelling behavior

A novel series of copolymeric acrylamide/potassium acrylate superabsorbents, blended with poly(vinyl alcohol), have been synthesized by using N, N′‐methylenebisacrylamide as a crosslinker and potassium persulphate (K₂S₂O₈) as an initiator. Swelling behavior of these hydrogels in water was investigated; and on the basis of swelling properties, the diffusional behavior of water into these hydrogel systems was analyzed. It was observed that with the increase of amount of poly(vinyl alcohol) or crosslinking, the swelling of the hydrogels decreased. The hydrogel synthesized by addition of 5% poly(vinyl alcohol) and 0.25% crosslinking showed maximum swelling of 54445%. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1927–1931, 2005     

Solid state NMR and LVSEM studies on the hardening of latex modified tile mortar systems

Construction mortars contain a broad variety of both inorganic and organic additives beside the cement powder. Here we present a study of tile mortar systems based on portland cement, quartz, methyl cellulose and different latex additives. As known, the methyl cellulose stabilizes the freshly prepared cement paste, the latex additive enhances final hydrophobicity, flexibility and adhesion. Measurements were performed by solid state nuclear magnetic resonance (NMR) and low voltage scanning electron microscopy (LVSEM) to probe the influence of the latex additives on the hydration, hardening and the final tile mortar properties. While solid state NMR enables monitoring of the bulk composition, scanning electron microscopy affords visualization of particles and textures with respect to their shape and the distribution of the different phases.

Within the alkaline cement paste, the poly(vinyl acetate) (VAc)-based latex dispersions stabilized by poly(vinyl alcohol) (PVA) were found to be relatively stable against hydrolysis. The influence of the combined organic additives methyl cellulose, poly(vinyl alcohol) and latexes stabilized by poly(vinyl alcohol) on the final silicate structure of the cement hydration products is small. But even small amounts of additives result in an increased ratio of ettringite to monosulfate within the final hydrated tile mortar as monitored by ²⁷Al NMR. The latex was found to be adsorbed to the inorganic surfaces, acting as glue to the inorganic components. For similar latex water interfaces built up by poly(vinyl alcohol), a variation in the latex polymer composition results in modified organic textures. In addition to the networks of the inorganic cement and of the latex, there is a weak network build up by thin polymer fibers, most probably originating from poly(vinyl alcohol). Besides the weak network, polymer fibers form well-ordered textures covering inorganic crystals such as portlandite.     

Pervaporation dehydration of water/ethanol/ethyl acetate mixtures using poly(vinyl alcohol)–silica hybrid membranes

The novel organic–inorganic hybrid membranes were prepared from poly(vinyl alcohol) (PVA) and vinyltriethoxysilane (VTES). They were characterized using Fourier transform infrared (FTIR), X‐ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), thermogravimetric analysis (TGA), and contact angle metering. The as‐prepared membranes are formed at a molecular scale at a low VTES content. Aggregations in the surface of the as‐prepared membranes were clearly evident above 18.43 wt % VTES loading. The introduction of VTES into the PVA matrix resulted in a decrease in the crystalline and an increase in compactness and thermal stability of the as‐prepared membranes. Silica hybridization reduced the swelling of the as‐prepared membranes in water/ethanol/ethyl acetate mixtures, decreased the permeation flux, and remarkably enhanced water permselectivity in pervaporation dehydration of ethanol/ethyl acetate aqueous solution. The hybrid membrane with 24.04 wt % VTES has the highest separation factor of 1079 and permeation flux of 540 g m^?2 h^?1. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Swelling behavior of semi‐interpenetrating polymer network hydrogels composed of poly(vinyl alcohol) and poly(acrylamide‐co‐sodium methacrylate)

Interpenetrating polymer network (IPN) hydrogels based on poly(vinyl alcohol) (PVA) and poly(acrylamide‐co‐sodium methacrylate) poly(AAm‐co‐SMA) were prepared by the semi IPN method. These IPN hydrogels were prepared by polymerizing aqueous solution of acrylamide and sodium methacrylate, using ammonium persulphate/N,N,N¹,N¹‐tetramethylethylenediamine (APS/TMEDA) initiating system and N,N¹‐methylene‐bisacrylamide (MBA) as a crosslinker in the presence of a host polymer, poly(vinyl alcohol). The influence of reaction conditions, such as the concentration of PVA, sodium methacrylate, crosslinker, initiator, and reaction temperature, on the swelling behavior of these IPNs was investigated in detail. The results showed that the IPN hydrogels exhibited different swelling behavior as the reaction conditions varied. To verify the structural difference in the IPN hydrogels, scanning electron microscopy (SEM) was used to identify the morphological changes in the IPN as the concentration of crosslinker varied. In addition to MBA, two other crosslinkers were also employed in the preparation of IPNs to illustrate the difference in their swelling phenomena. The swelling kinetics, equilibrium water content, and water transport mechanism of all the IPN hydrogels were investigated. IPN hydrogels being ionic in nature, the swelling behavior was significantly affected by environmental conditions, such as temperature, ionic strength, and pH of the swelling medium. Further, their swelling behavior was also examined in different physiological bio‐fluids. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 302–314, 2005     

Self‐association through hydrogen bonding and sequence distribution in poly(vinyl acetate‐co‐vinyl alcohol) copolymers

Correlation between hydrogen‐bonding self‐association and sequence distribution in poly(vinyl acetate‐co‐vinyl alcohol) copolymers (ACA) with different degrees of basic hydrolysis and sequence distributions has been studied by thermal analysis and NMR spectroscopy. ¹³C NMR spectroscopy has also been used to elucidate the blocky nature, branching, and tacticity of the copolymers. Thermal analytical studies indicate that hydrogen bonding distribution in block alcohol and vinyl acetate copolymers strongly depend on the sequence distribution wherein hydroxyl–hydroxyl self‐association is preferred. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 123–133, 1999     

Influence of the molecular structure of poly(vinyl alcohol) on the ultrasonic absorption

The properties of poly(vinyl alcohol) are essentially determined by the content of residual acetate groups. In this paper the influence of the molecular structure on the ultrasonic absorption is studied. As structure parameters, the residual acetate content and the ¹³C n.m.r. microstructure parameters are determined. Some commercial and laboratory products prepared by different methods are investigated. Broad ultrasonic absorption spectra are obtained. The theory of normal mode relaxation of the Rouse-Zimm type can be applied. For products with higher acetate contents, notable discrepancies between normal mode losses and measured absorption occur. The influence of acetate content and block structure on ultrasonic absorption is demonstrated but the absorption behaviour cannot only be explained by both parameters in all cases.     

Characterization of Poly(Vinyl Alcohol) and Poly(Vinyl Pyrrolidone) Co-polymer Blend Hydrogel Prepared by Application of Gamma Radiation

Hydrogel is prepared from a poly(vinyl pyrrolidone) (PVP) and poly(vinyl alcohol) (PVA) blend solution by gamma radiation with a ₆₀Co λ source at room temperature. Properties of the prepared hydrogel, such as gel fraction, gel strength swelling ratio, equilibrium water content, and water absorption in room temperature, were investigated. Blending hydrogel with PVP and PVA obviously increased the gel strength and decreased the swelling ratio of hydrogel. It was observed that the gel fraction increased while the swelling ratio and water content decreased with increased radiation dose, but gel strength increased up to a certain radiation dose and then decreased. The percentage of water absorption at room temperature increased with time but after a certain time it became steady and decreased with radiation dose.     

Removal of sodium acetate in poly(vinyl alcohol) and its quantification by 1H NMR spectroscopy

A major impurity in poly (vinyl alcohol) (PVA) is sodium acetate which remains after its preparation by a base catalyzed hydrolysis of poly(vinyl acetate), and the amount of sodium acetate in commercial PVA samples may reach several percentages. To establish an optimal condition for the removal of sodium acetate, several washing parameters such as washing period, solvent polarity, and temperature were investigated in this study. Nuclear magnetic resonance (NMR) spectroscopy was successfully applied to determine the residual amounts of sodium acetate in the purified poly(vinyl alcohol). The relative integral value for the methyl peak of sodium acetate in PVA was converted to a relative mass value and finally to the sodium acetate content contained in PVA. The results showed that over 95% of sodium acetate in PVA was removed by a washing of PVA with distilled water within 2 h. When methanol was used as a washing solvent, a higher temperature than room temperature was required for an effective removal of sodium acetate. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis of poly(vinyl butyral)s in homogeneous phase and their thermal properties

The condensation reaction of butyraldehyde (BA) with poly(vinyl alcohol) (PVA) to give poly(vinyl butyral) (PVB) was studied in detail using N‐methyl‐2‐pyrrolidone (NMP) as solvent for PVA and PVBs. PVBs having various degrees of acetalization were obtained. The acetalization reaction under a variety of conditions gave at best a polymer with 97% acetalization. The extent of modification and the structure of the polymer, i.e., the ratio of acetal units from meso and racemic dyads of PVA, were determined by ¹H‐NMR. The acetalization degree was reflected in the solubility of PVB; all products were soluble in NMP. PVBs were characterized by IR spectroscopy and ¹H and ¹³C‐NMR. The glass transition temperatures of PVBs, determined by DSC, increased as vinyl alcohol units increased and displayed a positive departure from linearity. Thermal degradation of PVBs was studied using differential thermal analysis (DTA) and thermogravimetry (TGA) under dynamic conditions in nitrogen. The content of hydroxyl groups had an effect on the thermal stability of PVBs; the thermal stability of PVBs decreased as vinyl alcohol units increased. The apparent activation energy of the decomposition was determined by the Kissinger and Flynn–Wall methods, which agree well. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5007–5017, 2006     

Pervaporation of ethanol-water mixtures through poly(vinyl alcohol-g-acrylic acid) membranes prepared by use of Fenton's reagent in grafting

Ionic crosslinking of the ferric ions and the carboxylic groups in the poly(vinyl alcohol-g-acrylic acid) (poly(VA-g-AA)) membranes improves the size screening effect in the pervaporation of ethanol-water separation. In the grafting polymerization of acrylic acid monomer onto poly(vinyl alcohol) (PVA), ferric ions are remained in the polymer membranes as the Fenton's reagent(Fe²⁺-H₂O₂) is used to initiate the reaction. Completely reversed trends in terms of the degree of swelling, the pervaporation selectivity, and the flux of permeates are obtained depending on that the ferric ions are present or absent in the membranes. The degree of swelling decreases, the pervaporation selectivity increases, and the flux decreases as the grafting percentage increases for the membranes containing ferric ions. The degree of swelling and the flux of permeates increase but the pervaporation selectivity is reduced as the grafting percentage increases for the membranes which were washed with acid to remove ferric ions.     

Dispersion of graphene nanoplatelets in poly(vinyl acetate) latex and effect on adhesive bond strength

Graphene nanoplatelets (GNPs) were directly dispersed in poly(vinyl acetate) (PVAc) latex in concentrations from 0.05 up to 2 wt% (based on dry weight), without using additional surfactants or dispersants. Stable dispersions were obtained due to interaction of the GNPs with protective colloids (poly(vinyl alcohol) and hydroxyethylcellulose) originally present in the latex. This caused an increase in viscosity and accentuated the pseudoplastic behavior of the latex, as evidenced by rheological measurements. Cryo‐SEM imaging showed that individual nanoplatelets were present in the aqueous phase. The equilibrium contact angle for water on dry PVAc films increased by 13° upon incorporation of 0.1 wt% GNPs due to the nanofiller hydrophobicity. However, this increase was lower for higher loadings, probably due to the occurrence of GNP agglomeration. Bond strength measurements performed with an automated bonding evaluation system setup on veneer lap joints showed more than 50% shear strength increase with incorporation of only 0.1–0.3 wt% GNPs. At higher loadings the bond strength decreased, indicating less efficient nanofiller dispersion in the polymer matrix. Raman spectroscopy analysis confirmed that GNP agglomeration was more significant at higher loadings.     

Grafting and adsorption of poly(vinyl) alcohol in vinyl acetate emulsion polymerization

Poly(vinyl alcohol) is often used in vinyl acetate emulsion polymerization as a protective colloid, but its role is complex and controversial since it partakes in grafting reactions with the monomer, influencing process mechanisms, and affecting the colloidal properties of the latex. Furthermore, in industrial operations, the wide scatter of macromolecular properties of the commercial types of poly(vinyl alcohol) causes process irreproducibilities. In this work different types of polyvinyl alcohol were used to perform a series of polymerizations, and their kinetics were compared. A selective solubilization procedure was applied to separate the three fractions of poly(vinyl alcohol) in the final latex: free in the water phase, physically adsorbed onto the polymer particles and chemically grafted. These results were compared with those obtained from pure adsorption measurements of polyvinyl alcohol onto ‘emulsifier-free’ polyvinyl acetate dispersions. The rheological behavior of the different latexes was also compared, and the results were used to formulate an hypothesis on the interaction mechanisms acting in these systems.     

Preparation and characterization of colloidal dispersions of vinyl alcohol–vinyl acetate copolymers: application as stabilizers for vinyl chloride suspension polymerization

Well‐defined colloidal dispersions of vinyl alcohol–vinyl acetate copolymers (PVAs) with different degrees of hydrolysis (DH) were prepared by a coacervation technique. Colloidal particles in the size range 150–250 nm, with an acetate‐rich core and a hydrophilic PVA corona, were obtained using a combination of a hydrophobic PVA (PVA II) having an average DH ( ) value of 43 mol% with a ‘blocky’ hydrophilic PVA (PVA I) with a value of 72 mol%. The core–shell structure of these particles was demonstrated using ¹H NMR and using fluorescence‐labelled PVA I. The stabilization efficiency of PVA I and PVA II and their combination was examined for 1‐chlorobutane–water emulsions, as a ‘model solvent’ for vinyl chloride–water emulsions. Preliminary tests of vinyl chloride suspension polymerization confirmed the beneficial effect of PVA I and PVA II combinations as stabilizers on the granulometry and the porosity specifications of the poly(vinyl chloride) grains. Copyright © 2006 Society of Chemical Industry     

Characterization by solid-state NMR and selective dissolution techniques of anhydrous and hydrated CEM V cement pastes

The long term behaviour of cement based materials is strongly dependent on the paste microstructure and also on the internal chemistry. A CEM V blended cement containing pulverised fly ash (PFA) and blastfurnace slag (BFS) has been studied in order to understand hydration processes which influence the paste microstructure. Solid-state NMR spectroscopy with complementary X-ray diffraction analysis and selective dissolution techniques have been used for the characterization of the various phases (C₃S, C₂S, C₃A and C₄AF) of the clinker and additives and then for estimation of the degree of hydration of these same phases. Their quantification after simulation of experimental ²⁹Si and ²⁷Al MAS NMR spectra has allowed us to follow the hydration of recent (28 days) and old (10 years) samples that constitutes a basis of experimental data for the prediction of hydration model.     

Synthesis and characterization of conducting copolymers of poly(vinyl alcohol) with thiophene side‐groups and pyrrole

Graft copolymers of poly(vinyl alcohol) with thiophene side‐groups and pyrrole were synthesized by electrochemical polymerization methods. Poly(vinyl alcohol) with thiophene side‐groups (PVATh) was obtained from the reaction between poly(vinyl alcohol) (PVA) and thiophene‐3‐acetic acid. The syntheses of copolymers of PVATh and pyrrole were achieved electrochemically by using three different supporting electrolytes, p‐toluene sulfonic acid (PTSA), sodium dodecyl sulfate (SDS) and tetrabutylammonium tetrafluoroborate (TBAFB). Characterization of PVATh and graft copolymers was performed by a combination of techniques including cyclic voltammetry, scanning electron microscopy, thermal gravimetry, differential scanning calorimetry, size‐exclusion chromatography, ¹H NMR and FT‐IR. The conductivities were measured by the four‐probe technique. Copyright © 2004 Society of Chemical Industry