Rheological behavior of partially hydrolyzed poly(vinyl acetate-co-ethylene)

The rheological behavior of partially hydrolyzed poly(vinyl acetate-co-ethylene) (VAE) was investigated, using a Rheometrics Dynamic Mechanical Spectrometer. For the investigation, measurements of storage modulus (G′), loss modulus (G″) and loss tangent (tan δ) of the materials were recorded as functions of temperature at a fixed frequency (i.e., using temperature scans) and, also, as functions of frequency at a fixed temperature (i.e., using frequency scans). For the hydrolysis, three different grades of copolymer (containing 34, 47, 62 mol% of vinyl acetate) were used to yield poly(vinyl acetate-co-ethylene-co-vinyl alcohol) (VAEOH) with varying amounts of hydroxyl group. For comparison purposes, the viscoelastic properties of blends of VAE copolymer with poly(vinyl alcohol) (PVOH), having varying blend compositions, were also measured. The blends were prepared by first mixing a solution of VAE copolymer, which was dissolved in a toluene/dichloroethane mixed solvent, and an aqueous solution of PVOH, and then freeze drying the mixture to a constant weight. Also measured were the glass transition temperature (T_g) of the VAE copolymers and the T_g and melting point (T_m) of the VAEOH terpolymers, using a DuPont Thermal Analyzer equipped with a 910 DSC Module. It has been found that (1) introduction of hydroxyl group into the backbone of the amorphous VAE copolymer has made the resulting VAEOH terpolymer semicrystalline; (2) the T_m, T_g, G′, and the complex viscosity (η^*) of the VAEOH terpolymers increase with increasing amounts of hydroxyl group; (3) the physical blending of PVOH with VAE copolymer has not affected the T_g of the VAE copolymer; (4) the G′ and η^* of the VAE/PVOH blends are found to increase with the amount of PVOH in the blend. The use of logarithmic plots of G′ versus G″ has been found to be very useful for discerning the differences in the structure of the materials tested.     

Measurement and simple equation models of the specific heats of neat and glycerol‐plasticized poly(vinyl alcohol)

The specific heats (C_sp) of neat and glycerol‐plasticized poly(vinyl alcohol) (PVOH) were studied by differential scanning calorimetry at 330–530 K. Glycerol‐plasticized poly(vinyl alcohol) was prepared by a melt‐blending method. The outcomes were modeled into mathematical functions. Incorporation of glycerol increased the specific heat of PVOH. Glycerol provided internal lubrication to the PVOH system, giving a smoother and lower‐amplitude melting curve. As a result, glycerol‐plasticized PVOH had a lower melting‐temperature range than neat PVOH. However, higher energy was required to increase the temperature of glycerol‐plasticized PVOH. The modeling functions showed a best fits regression range of 0.967–0.999. Neat PVOH and glycerol‐plasticized PVOH required 1166.05 J/g and 2113.09 J/g, respectively, to increase the temperature from 330 to 530 K. J. VINYL ADDIT. TECHNOL., 18:198–203, 2012. © 2012 Society of Plastics Engineers     

Effect of citric acid,PVOH, and starch ratio on the properties of cross-linked poly(vinyl alcohol)/starch adhesives

The properties of tapioca starch adhesives were improved by cross-linking and the cross-linked adhesive compared with pure tapioca starch and poly(vinyl alcohol) adhesives. The effect of starch ratio, type of PVOH, and adding citric acid were important factors on the cross-linked adhesives. Wood adhesives made from cross-linked PVOH/starch were prepared by PVOH and tapioca starch, using hexamethoxymethyl melamine (HMMM) and citric acid (CA) as a cross-linking agent and catalyst, respectively. The effect of CA, PVOH/starch ratio, and type of PVOH such as medium (M PVOH) and high molecular weight (H PVOH) were investigated. The condition of the cross-linking reaction was 175?°C for 15?min. The structural properties of cross-linked adhesive were investigated by FT-IR spectroscopy. The results were confirmed in terms of thermal properties with a differential scanning calorimeter (DSC) and the shear strength of the adhesive. The cross-linked adhesive resulted in the increase of T _g and showed good blend compatibility with all of the cross-linked adhesives. The adhesive strength significantly increased when using CA as a catalyst in the cross-linking reaction. The optimum contents of the cross-linked PVOH/starch adhesives were 1:1.8 for M PVOH and 1:0.5 for H PVOH.     

Properties of soy protein isolate/poly(vinyl alcohol) blend “green” films: Compatibility,mechanical properties,and thermal stability

Blend films from nature soy protein isolates (SPI) and synthetical poly(vinyl alcohol) (PVA) compatibilized by glycerol were successfully fabricated by a solution‐casting method in this study. Properties of compatibility, mechanical properties, and thermal stability of SPI/PVA films were investigated based on the effect of the PVA concentration. XRD tests confirm that the SPI/PVA films were partially crystalline materials with peaks of 2θ = 20°. And, the addition of glycerol will insert the crystalline structure and destroy the blend microstructure of SPI/PVA. Differential scanning calorimetry (DSC) tests show that SPI/PVA blend polymers have a single glass transition temperature (T_g) between 80 and 115.0°C, which indicate that SPI and PVA have good compatibility. The tension tests show that SPI/PVA films exhibit both higher tensile strength (σ_b) and percentage elongation at break point (P.E.B.). Thermogravimetric analysis (TGA) and water solubility tests show that SPI/PVA blend polymer has more stable stability than pure SPI. All the results reflect that SPI/PVA/glycerol blend film provides a convenient and promising way to prepare soy protein plastics for practical application. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Oxidative aging of thermoplastic polyimide films

Two linear polyimides were subjected to accelerated isothermal aging at temperatures between 300 and 400°C. Losses in toughness correlated well with changes in glass transition temperature (T_g) of the films, but not with weight loss. Both materials have extrapolated lifetimes of 100,000 h near their T_g's. © 1995 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Thermal,mechanical, and surface characterization of starch–poly(vinyl alcohol) blends and borax‐crosslinked films

Starch–poly(vinyl alcohol) (PVA) blends with different compositions were prepared and crosslinked with borax by in situ and posttreatment methods. Various amounts of glycerol and poly(ethylene glycol) with a molecular weight of 400 were added to the formulations as plasticizers. The pure starch–PVA blends and the crosslinked blends were subjected to differential scanning calorimetry, thermogravimetry, and X‐ray photoelectron spectroscopic studies. Broido and Coats–Redfern equations were used to calculate the thermal decomposition kinetic parameters. The tensile strengths and elongation percentages of the films were also evaluated. The results suggested that the glass‐transition temperature (T_g) and the melting temperature strongly depended on the plasticizer concentration. The enthalpy relaxation phenomenon was dependent on the starch content in the pure blend. The crosslinked films showed higher stability and lower T_g's than pure PVA and starch–PVA blends, respectively. High‐resolution X‐ray photoelectron spectroscopy provided a method of differentiating the presence of various carbons associated with different environments in the films. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1313–1322, 2005     

Role of Chain Entanglements in the Electrospinning of Wheat Protein-Poly(Vinyl Alcohol) Blends

The aim of this investigation was to determine if the rapid solvent removal evaporation that occurs during electrospinning enabled the gluten protein and poly(vinyl alcohol) (PVOH) chains to remain at least partially entangled in the final product. Natural and synthetic biopolymer blends are known to phase separate in the melt. Differential scanning calorimetry (DSC) was used to test our hypothesis, which we achieved by systematically comparing the thermal profiles of the nonwoven fibrous sheets comprising: 1) 100% commercial wheat gluten, 2) 100% PVOH, and 3) the (75/25) wheat gluten/PVOH blend. The DSC scans of the two PVOH-containing, nonwoven fibrous sheets exhibited differences in the characteristics and positions of the melting peaks (T_m) of the PVOH crystalline phase, while the DSC scans of the nonwoven fibrous sheets comprising either 100% commercial wheat gluten or the wheat gluten/PVOH blend yielded neither a measurable glass transition temperature (T_g) nor a T_m. Energy dispersive spectroscopy (EDS) was used to compare the elemental compositions of the individual fibers with the compositions of the spherical domains found in the nonwoven fibrous mats. These scans revealed that the mineral matter found in commercial wheat gluten (roughly 1% by weight) had phase-separated from the bulk gluten protein as a result of electrospinning.     

Synthesis,characterization, and properties of poly(vinyl acetate)‐ and poly(vinyl alcohol)‐grafted chitosan

Graft copolymers of chitosan and vinyl acetate were synthesized by free radical technique using cerium (IV) as the initiator. Under controlled conditions, as much as 92% grafting with a grafting yield of 30–40% could be achieved. Chitosan‐g‐poly(vinyl alcohol) copolymers were derived by the alkaline hydrolysis of the chitosan‐g‐poly(vinyl acetate) precursor. Thermogravimetric, FTIR, and X‐ray diffraction analyses of chitosan and the copolymers confirmed the grafting reaction between chitosan and vinyl acetate and also the subsequent hydrolysis. Both the copolymers possessed very good film‐forming properties. Grafting resulted in a significant increase in mechanical strength of both the copolymers in the dry condition. Chitosan‐g‐poly(vinyl acetate) (CH‐PVAc) proved more hydrophobic than did pure chitosan, whereas chitosan‐g‐poly(vinyl alcohol) (CH‐PVOH) exhibited enhanced hydrophilicity as evident from their swelling characteristics and contact angle measurements. The enhanced swelling of CH‐PVOH was ascribed to the presence of the pendant poly(vinyl alcohol) group. At pH 1.98, the CH‐PVAc copolymer films showed greater stability than do pure chitosan films, which is highly beneficial for specific biomedical applications. Both the copolymers showed lower glass transition temperature than do pure chitosan. Grafting did not affect the overall thermal stability, and the differential thermogram substantiated the grafting. The investigations indicate that the synthetic–natural hybrid copolymers having desirable mechanical properties and tailored hydrophilic/hydrophobic characteristics are realizable. These polymers could be exploited for varied biomedical applications. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1852–1859, 2007     

Miscible blends from plasticized poly(vinyl chloride) and epoxidized natural rubber

Miscible blends from plasticized poly(vinyl chloride), and epoxidized natural rubber having 50 mol% epoxidation level were prepared in a Brabender Plasticorder by the melt-mixing technique. Changes in Brabender torque and temperature, density, dynamic mechanical properties, and differential scanning calorimetry of the samples were examined as a function of blend composition. The plasticized poly(vinyl chloride)/epoxidized natural rubber blends behaved as a compatible system at all composition ranges as evident from their single glass-rubber transition temperature (T_g) obtained from dynamic mechanical analysis as well as from differential scanning calorimetry. Profound changes in the nature of the glass-rubber transition were noted with respect to blend composition. The T_g-width values of blends lie between those of plasticized poly(vinyl chloride) and epoxidized natural rubber.     

Physical and mechanical properties of highly plasticized pectin/starch films

Blends of citrus pectin and high amylose starch plasticized with glycerine were investigated to determine the effect of compositional variables on film properties. Several films with representative compositions were made from sugar beet and almond pectin, and tested for comparison. The films were cast from water onto glass plates, dried, and removed. Mechanical analysis was done using a Rheometrics RSA II solids analyzer. Increasing the glycerine concentration led to decreases in static modulus, dynamic modulus, and tensile strength, but to increases in elongation. Increasing levels of starch in the blend lowered the effect of glycerine on mechanical properties. Oxygen permeability of the films was extremely low. Sugar-beet pectin and almond pectin gave films with mechanical properties comparable to those made with citrus pectin. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Thermal analysis of poly(phenylene sulfide) polymers. I: Thermal characterization of PPS polymers of different molecular weights

Thermal properties of Fortron®

1 ®Registered trademark of Hoechst Celanese Corporation.

poly(phenylene sulfide) (PPS) polymers of different molecular weights were studied by DSC. Crystallization studies revealed that the ability of these polymers to crystallize decreases with increasing molecular weight. The Avrami equation poorly describes the isothermal crystallization of PPS. Lamellar crystallization was observed for the lowest molecular weight sample. For the other, higher molecular weight polymers the Avrami exponent is always between 2 and 3, suggesting development of distorted spherulites with heterogeneous nucleation. The temperature dependence of the solid and melt heat capacities have been determined. The solid specific heat capacity did not exhibit a molecular weight dependence. The heat capacity increase at the glass transition, T_g, has been calculated to be 28.1 J°C^?1 mole^?1. The equilibrium melting point of PPS has been estimated to be 348.5°C using the Hoffman–Weeks method. The T_g of PPS increases with molecular weight. The T_g of the highest molecular weight evaluated is 92.5°C. A DMA relaxation peak corresponding to the onset of the phenylene ring rotation occurs at ?92°C. Only the highest molecular weight could be quenched to a completely amorphous state.     

Poly(vinyl alcohol) composite films with high percent elongation prepared from amylose‐fatty ammonium salt inclusion complexes

Amylose inclusion complexes prepared from cationic fatty ammonium salts and jet‐cooked high amylose starch were combined with poly(vinyl alcohol) (PVOH) to form glycerol‐plasticized films. For the octadecylammonium salt complexes, elongation was significantly higher than the PVOH control when the amount of complex incorporated was from 20% to 70%. For the dodecyl‐ and hexadecylammonium salt complexes, elongation was significantly higher than PVOH films for 20% to 40% incorporation of cationic complex. Tensile strength declined with increasing levels of amylose‐ammonium salt complex, and surface hydrophobicity (contact angle) was significantly higher than PVOH films. Microscopy showed no phase separation or phase inversion, suggesting intimate mixing due to ionic interactions between cationic ammonium salt complexes and the hydroxyl groups of PVOH. The high elongations of these films and increased water contact angles are marketable advantages, along with the lower cost and increased biodegradability of the starch‐based component. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44110.     

Head to head polymers

Blends of poly(-caprolactone) with either head-to-head or head-to-tail poly (vinyl chloride) were prepared by solvent casting in the form of films and their glass transition temperatures were determined by DSC analysis. The DSC scans of the blends of both poly(vinyl chloride) isomers were very similar. For blends containing 25% and 50% of poly(-caprolactone), a single transition step, a T_g, was observed, whereas for a blend containing 75% of poly (-caprolactone) three transition steps were observed, one glass transition and also a crystallization and a melting transition.Part 19: H. Kawaguchi, J. Muggee, Y. Sumida and O. Vogl, Polymer (London), in press     

Synthesis,miscibility, and properties of rodlike/flexible polymer composites via in-situ rod chain formation

Summary Flexible, soluble poly(amic diethyl ester) precursors of rodlike poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA) and poly(4,4-oxydiphenylene biphenyltetracarboximide) (BPDA-ODA), which are more stable than the respective poly(amic acid)s and are not in the equiliration with the constituent anhydride and amine monomers so that chemical exchange reactions are prevented in their solution blending, were synthesized. Homogeneous precursor/precursor solutions with various compositions were obtained in N-methyl-2-pyrrolidinone with appreciably high solid contents. The dried precursor blend films and resultive polyimide composite films thermally imidized were optically transparent, regardless of compositions and film process conditions. The composites showed single T_g behavior. Conclusively, rodlike BPDA-PDA/flexible BPDA-ODA molecular composites were achieved from the blend of the respective flexible poly(amic diethyl ester) precursors through conventional drying and imidization process. In addition, film properties of composites were characterized.     

Polymer Nanocomposites based on Modified ZrO2 NPs and Poly(vinyl alcohol)/Poly(vinyl pyrrolidone) Blend: Optical,Morphological, and Thermal Properties

Nanocomposite films were prepared successfully by simple solution casting method from the blend of poly(vinyl alcohol) and poly(vinyl pyrrolidone) as the polymer matrix and functionalized ZrO₂ nanoparticles as nanofiller. To prevent aggregation and improve the dispersion of nanoparticles into the matrix, ZrO₂ nanoparticles were functionalized with citric acid and ascorbic acid. Then, nanocomposites were fabricated by adding different contents of modified nanoparticles into the poly(vinyl alcohol)–poly(vinyl pyrrolidone) matrix. Thermal stability of the obtained nanocomposite films was improved in comparison to the pure blend. Furthermore, optical property of nanocomposites makes them a potential candidate for ultraviolet shielding material.     

Effect of the tacticity of poly(methyl methacrylate) on the phase diagram of its ternary blends

Previously, isotactic and atactic poly(methyl methacrylates) (PMMAs) were found to be miscible with poly(vinyl phenol) (PVPh) and poly(hydroxy ether of bisphenol‐A) (phenoxy) because all the prepared films were transparent and showed composition‐dependent glass transition temperatures (T_g's). However, syndiotactic PMMA was immiscible with PVPh because most of the cast films had two T_g's. On the contrary, syndiotactic PMMA was still miscible with phenoxy. According to our preliminary results, PVPh and phenoxy are not miscible. Also to our knowledge, nobody has reported any results concerning the effect of the tacticity of PMMA on its ternary blend containing PVPh and phenoxy. The miscibility of a ternary blend consisting of PVPh, phenoxy, and tactic PMMA was thus investigated and reported in this article. Calorimetry was used as the principal tool to study miscibility. An approximate phase diagram of the ternary blends containing different tactic PMMA was established, probably for the first time, based on differential scanning calorimetry data. Immiscibility was found in most of the studied ternaries but a slight difference due to the effect of tacticity of PMMA was definitely observed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2720–2726, 2002     

NMR imaging of adhesive-bonded structures: the use of the T1 and T2 relaxation time information

—Nuclear magnetic resonance imaging (NMRI) is used to obtain cross-sectional images of three poly(vinyl alcohol) (PVOH) stabilized poly(vinyl acetate) (PVAc) emulsions in glass vials and in glue-lines between a wood block and a ceramic tile. From a series of T, and T₂ weighted images acquired with different repetition and echo times, pure T, and T₂ images of the emulsions are calculated. The T₁ relaxation times are between 0.83 and 1.04 s and the T₂ relaxation times between 15 and 26 ms for the emulsions. The relaxation information is used to compute a proton spin density image. Optimum pulse sequence parameters are determined to detect and to create a maximum intensity contrast for the signals of two different emulsions in a 200-300 μm glue-line.     

Effects of water content on the properties of starch/poly(ethylene–vinyl alcohol) blends

The physical properties of unmodified starch, poly(ethylene vinyl alcohol), glycerol, and water mixtures are reported. Thermal and melt-flow properties of the preprocessed, physically mixed materials were determined along with the tensile properties and morphology of injection-molded microtensile samples. Melt-flow properties were measured by a capillary rheometer, and the water content was varied from 4 to 18%. The morphology, rheology, and tensile properties are all highly related to the percentage of water present. A transition in the tensile properties and morphology of the blends was observed at approximately 11% moisture content. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Mechanical properties of vinyl alcohol—ethylene copolymers

The stress‐strain behavior of vinyl alcohol‐ethylene copolymers, with vinyl alcohol as main component, was studied. Films of the copolymer samples, either quenched or slowly cooled from the melt, were stretched at 23, 40 and 80°C. The two former temperatures are below the glass transition (T_g) and the latter is well above the T_g of the studied samples. The drawing process was carried out at different strain rates, and the influence of the stretching parameters (temperature, strain rate) as well as the thermal history and composition of the copolymer samples are discussed in relation to the corresponding homopolymers, poly(vinyl alcohol) and polyethylene. The copolymer with the highest vinyl alcohol content exhibited a critical strain rate, showing maximum values of Young's modulus at a deformation rate around 0.66/min.     

Preparation,characterization, electrical and antibacterial properties of sericin/poly(vinyl alcohol)/poly(vinyl pyrrolidone) composites

In this study, we focused on the fabrication of poly(vinyl alcohol) (PVA)/poly(vinyl pyrrolidone) (PVP)/sericin composites via a simple solution‐blending method. The composites were characterized by Fourier transform infrared (FTIR) spectroscopy, UV spectroscopy, X‐ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry, thermogravimetric analysis (TGA), and measurements of the conductivity, tensile strength, and antibacterial activity against Staphylococcus aureus. The results of FTIR and UV spectroscopy implied the occurrence of hydrogen bonding between sericin and the PVA/PVP blend. The structure and morphology, studied by XRD and SEM, revealed that the sericin particles were well dispersed and arranged in an orderly fashion in the blend. The glass‐transition temperature (T_g) of the composite was higher than that of the pure blend, and the T_g value shifted toward higher temperatures when the volume fraction of sericin increased. TGA indicated that sericin retarded the thermal degradation; this depended on the filler concentration. The mechanical and electrical properties, such as the tensile strength, alternating‐current electrical conductivity, dielectric constant, and dielectric loss of the composites, were higher than those of the pure blend, and these properties were enhanced when the concentration of sericin was increased up to 10 wt % filler content, whereas the elongation at break of the composite decreased with the addition of sericin particles. The antibacterial properties of the composite showed that sericin had a significant inhibitory effect against S. aureus. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43535.