Gel‐spinning of partially saponificated poly(vinyl alcohol)

DMSO/water (80/20 volume ratio) solutions of commercial poly(vinyl alcohol)s (a‐PVA₉₉, a‐PVA₈₈) with degrees of saponification of 99.3 and 88 mol % were gel‐spun into methanol (−20 and −70°C). The dry filaments obtained were drawn at 200°C (a‐PVA₉₉) and 150–180°C (a‐PVA₈₈). The maximum draw ratio and Young's modulus were 26 and 34 GPa for a‐PVA₉₉ and 21 and 24 GPa for a‐PVA₈₈ (drawing temperature: 160°C). So, at first, the dry filaments obtained for a‐PVA₈₈ were drawn at 150–180°C until 10 times their original length. Moreover, the predrawn a‐PVA₈₈ filaments were perfectly saponificated under fixing at the both ends and then the filaments were redrawn at 200°C. The maximum draw ratio and Young's modulus for the filaments (a‐PVA_88→99) predrawn at 150°C were 28 and 39 GPa, respectively. The a‐PVA_88→99 filaments had two melting peaks (228 and 236°C). © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2872–2876, 2000     

Properties of syndiotacticity-rich poly(vinyl alcohol) thin film in water. I. Effect of the load on the extension of untreated thin film in water

The effect of the load on the extension of untreated thin film of syndiotacticity-rich poly(vinyl alcohol) (PVA_VTFA) derived from vinyl trifluoroacetate was examined in water. The untreated thin film obeys Hooke's law under a certain constant load at 25°C. Young's modulus of untreated PVA_VTFA film in water at 25°C was about 4.8 × 10^?4 GPa. The maximum elongation of PVA_VTFA film in water at 25°C is achieved for a short time under high load, whereas not under low load. The expansion of PVA_VTFA thin film by the elevation of temperature of water occurs mildly in the range of temperature of 45–55°C under low load, whereas not under high load. The temperature at break T_b is in the range of 70–90°C and increasing load roughly tends to decreasing T_b. The elongation at break decreased with the increase in load.     

Blends of aliphatic polyesters. IV. Morphology,swelling behavior,and surface and bulk properties of blends from hydrophobic poly(L-lactide) and hydrophilic poly(vinyl alcohol)

Blend films were prepared from hydrophobic poly(L -lactide) (PLLA) and hydrophilic poly(vinyl alcohol) (PVA) with different PLLA contents [X_PLLA (w/w) = PLLA/(PVA + PLLA)] by solution casting and melt quenching. Their morphology, swelling behavior, and surface and bulk properties were investigated. Polarizing optical microscopy, scanning electron microscopy, differential scanning calorimetry, X-ray diffractometry, and tensile testing revealed that PLLA and PVA were phase separated in these blend films and the PLLA-rich and PVA-rich phases both formed a continuous domain in the blend film of X_PLLA = 0.5. The water absorption of the blend films was higher for the blend films of low X_PLLA values when compared at the same immersion time, and it was larger than expected from those of nonblended PLLA and PVA films. The dynamic contact angles of the blend films were linearly increased with an increase in X_PLLA. The tensile strength and Young's modulus of the dry blend films decreased with a rise in X_PLLA, but this dependence was reversed because of the large decreases in tensile strength and Young's modulus for the blend films having high X_PLLA values after immersion in water. The elongation at break was higher for the wet blend film than for the dry blend film when compared at the same X_PLLA and that of the dry and wet blend films decreased with an increase in X_PLLA. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2151–2160, 2001     

Preparation of high-strength poly(vinyl alcohol) fibers by crosslinking wet spinning

High-strength poly(vinyl alcohol) (PVA) fiber was obtained by the crosslinking wet-spinning technique, which is an improved technique of the conventional non-crosslinked type wet-spinning of PVA. High tensile strength as well as high Young's modulus was achieved by introduction of the borate ion-aided crosslinks during the coagulation process. The drawability of the as-spun fiber greatly depends on the fiber thickness. The thinner the fiber, the higher the drawability. Since thinner fiber is subject to a very high shear rate on extrusion, the crosslinks introduced are believed to maintain topological memory of the oriented chains, which have a low density of entanglements. This allows drawing the fiber to a higher draw ratio. The strength and Young's modulus of the resultant highly drawn PVA fiber were achieved to be 22 g/d (2.3 GPa) and 430 g/d (50 GPa), respectively. The mechanism of the spinning was discussed and the spinning condition was carefully examined in order to optimize the final mechanical properties of the PVA fibers.     

High‐tensile‐strength polyvinyl alcohol films prepared from freeze/thaw cycled gels

The mechanical properties and molecular structure of a poly(vinyl alcohol) (PVA) film, which was obtained by eliminating water from a PVA hydrogel using repeated freeze/thaw cycles, were investigated by tensile tests, thermal analysis, and X‐ray diffraction measurements. The mechanical properties of PVA with 99.9% saponification were measured as a function of the number of freeze/thaw cycles performed. The tensile strength and Young's modulus increased and the elongation at break decreased with increasing freeze/thaw cycles. The tensile strength and Young's modulus of PVA films obtained after seven freeze/thaw cycles were as high as 255 MPa and 13.5 GPa after annealing at 130°C. Thermal analysis and X‐ray diffraction measurements revealed that this is because of a high crystallinity and a large crystallite size. A good relationship between the tensile strength and the glass transition temperature was obtained, regardless of the degree of saponification and annealing conditions. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40578.     

Effect of copper sulfate pentahydrate on the structure and properties of poly(vinyl alcohol)/graphene oxide composite films

Poly(vinyl alcohol) (PVA)/graphene oxide (GO)/copper sulfate pentahydrate (CuSO₄·5H₂O) composite films were prepared by the solution casting method, and the effect of CuSO₄·5H₂O on the structure and properties of the PVA/GO composites was investigated. Fourier transform infrared (FTIR) analysis proved the crosslinking interaction between CuSO₄·5H₂O and the ? OH group of PVA. The crystallinity of the composite films increased first and then decreased. For the composite films, the tensile strength, Young's modulus, and yield stress values improved with increasing CuSO₄·5H₂O, whereas the elongation at break decreased compared with that of the neat PVA/GO composite film. The thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG) patterns of the PVA/GO/CuSO₄·5H₂O composite films showed that the thermal stability decreased; this was consistent with the TGA–FTIR analysis. A remarkable improvement in the oxygen‐barrier properties was achieved. The oxygen permeability coefficient was reduced by 60% compared to that of the neat PVA/GO composite film. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44135.     

Preparation of poly(vinyl alcohol) films with promising physical properties in comparison with commercial polyethylene film

Poly(vinyl alcohol) (PVA) films with different thicknesses (0.08, 0.2, 0.23, 0.42 mm) were prepared by a casting technique. The transmission and the absorption of the PVA films were measured as functions of the wavelengths. PVA film with a thickness of 0.42 mm showed zero transmission in the wavelength range of 190–350 nm. The transmission spectrum of a commercial polyethylene film with a thickness of 0.21 mm was compared to the transmission spectrum of PVA film with a thickness of 0.42 mm. A correlation was found between the two transmission spectra in the region 190–350 nm and a 20% increase in the transmission of the PVA film in comparison with the transmission of commercial polyethylene in the region 350–1500 nm. The near‐infrared region of the transmission of commercial polyethylene was increased by 15% with respect to the transmission of the PVA film. The stress–strain measurements were done for PVA and commercial polyethylene films. The Young's modulus and the strength at break for PVA films are higher by two orders of magnitude than those for commercial polyethylene film. The strain at break for commercial polyethylene is 17% lower than that for PVA film. Radiation effects on the optical properties of PVA and commercial polyethylene films were investigated. The PVA and commercial polyethylene films were irradiated with a xeon arc lamp at 3.5–5 W/cm². The optical properties for PVA and commercial polyethylene films were studied after irradiation. The obtained results showed that PVA film with a thickness of 0.42 mm gave promising properties which could be used in technological applications. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1219–1226, 2002     

Poly(vinyl alcohol)/CaCO3‐diacid nanocomposite: Investigation of physical and wetting properties and application in heavy metal adsorption

Poly(vinyl alcohol) (PVA) nanocomposite and modified CaCO₃ nanoparticles (NPs) were fabricated by ultrasound agitation method with particle content altering from 3, 5, and 8 wt %. The CaCO₃ surface was successfully treated by 10 wt % of bioactive dicarboxylic acid (DA). The influences of loading modified NPs on the thermal, mechanical, adsorption, contact angle, and physical properties of the poly(vinyl alcohol) nanocomposite films were thoroughly studied. The results showed that incorporation of modified CaCO₃ into the PVA matrix had better performance than the pure PVA. Meanwhile, tensile strength, Young's modulus, and thermal stability are enhanced from 33.36 MPa, 1.26 GPs, and 242.918C (neat PVA) to 81.7 MPa, 4.81 GPa, and 312.95 °C (PVA/CaCO₃‐DA NC 5 wt %), respectively. Also, the adsorption capacity of the PVA/CaCO₃‐DA NCs 5 and 8 wt % revealed that the NC films could act as an appropriate absorbent for the removal of Cd(II) ions with maximum adsorption capacity of about 20.70 and 25.19 mg g^?1 for Cd(II), respectively. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45414.     

High strength poly(vinyl alcohol) films obtained by drying and then stretching freeze/thaw cycled gel

The mechanical properties of stretched poly(vinyl alcohol) (PVA), which is formed by stretching a film prepared from a freeze/thaw cycled gel, were investigated as a function of the stretching ratio. The tensile strength and Young's modulus of 800% stretched PVA annealed at 130°C were 3.4 and 119 GPa, respectively. These values were much higher than those for a PVA film prepared without freeze/thaw cycling. For a film stretched more than 600% before annealing, two melting peaks, assignable to folded and extended chain crystals, were observed around 220°C and 230°C, respectively. This indicates that a shish‐kebab structure is formed as the stretching ratio increases. After annealing at 130°C, the folded‐chain crystal transformed to an extended‐chain crystal if an extended‐chain crystal was present in the stretched film before annealing. High tensile strength and Young's modulus after annealing were due to the formation of extended‐chain crystal. Therefore, the presence of extended‐chain crystal for annealing is important to provide good mechanical properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41318.     

Structure and properties of syndiotacticity‐rich poly(vinyl alcohol) prepared through saponification of drawn poly(vinyl trifluoroacetate) with gaseous ammonia

The structure and properties of syndiotacticity‐rich poly(vinyl alcohol) (s‐PVA) prepared through the saponification of drawn poly(vinyl trifluoroacetate) (PVTFAc) with gaseous ammonia were studied. The PVTFAc samples with s‐diad % of 59 and 64 were used. The s‐PVAs had low densities and showed X‐ray diagrams similar to the fiber diagram of PVA with indistinct 100, 101, 101¯, and 200 plane reflections and without the plane reflections seen at the equator of a typical fiber diagram, such as 001, 201, and 002. The s‐PVAs had melting points comparable to those of saponified and heat‐drawn samples, indicating a PVA with the typical fiber structure as seen in the X‐ray diagram of a sample. The intensity of the 916 cm⁻¹ band in the infrared spectrum related to syndiotactic diads decreased with drawing, suggesting an increase in the crystallinity. Crystals with more defects are thought to be produced in saponification. The s‐PVA films drawn 16 times and saponified had a Young's modulus and strength at break of 22 and 1.5 GPa for the sample from S‐59 and 14 and 1.2 GPa for the sample from S‐64, respectively. The crystallization‐sensitive band of 1145 cm⁻¹ in the infrared spectra of the saponified samples was weak. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 467–474, 2001     

Gelation of poly(vinyl alcohol)/ethylene glycol solutions and properties of gels

The melting temperature of the gels of the poly(vinyl alcohol) (PVA)/ethylene glycol (EG) system was measured. It was found that the temperature was independent of the thermal hysteresis. The apparent enthalpy of the fusion of the junction, ΔH, was 206 kJ/mol for a high molecular weight atactic PVA (HDP α-PVA), 172 kJ/mol for a low molecular weight syndiotacticity-rich PVA (LDP s-PVA), and 238 kJ/mol for an HDP s-PVA. The gels obtained by chilling at temperatures over 80°C or by gradual cooling are considered to have larger microcrystals. The Young's modulus of the HDP α-PVA drawn films were highest among the samples tested. The maximum and mean Young's moduli of the HDP α-PVA films drawn 15 times the original length were 37 and 26 GPa, respectively. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1283–1289, 1997     

Uniaxial tensile and structural properties of poly(vinyl alcohol) films: The influence of heating and film thickness

Poly(vinyl alcohol) as pure or composite materials is widely used in the food and textile industries, andbiomedical applications due to some important properties such as uniaxial tensile, biocompatibility, and noncarcinogenicity. Investigation of the influence of the film thickness and heating on the uniaxial tensile, spectroscopic, and surface properties of PVA films investigated in this study is quite important for improving the properties of such materials and their applicability in different conditions. In this study, with the influence of heating, a necking behavior was observed at around 2% for thin films and 4–9% strain for thicker PVA films for which a kind of transition point at around 1–2% strain was observed. The mechanical strength of PVA films, strain at break, and Young's modulus were enhanced greatly as the temperature increased from 80 to around 110 °C, and then most of them decreased. The degree of crystallinity increased linearly with the heat temperature from around 36–40%. Although PVA thin films obtained a very smooth surface structure after being heated at 80 °C, with increasing heat temperature, the surface roughness of both thin and thick PVA films increased and the PVA thin films obtained more degraded film surface. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44915.     

Properties of syndiotacticity-rich poly(vinyl alcohol) thin film in water. IV. Elastic behavior of untreated thin film by repeated elongation and contraction in water

The activation energy ΔE_a for diffusion of water molecules into untreated thin film of poly(vinyl alcohol) (PVA_VTFA) derived from vinyl trifluoroacetate was estimated as 30.3 kcal/mol from the temperature dependence of the initiation time of swelling. The degree of equilibrium swelling increases with the increase in temperature in the range of 10–70°C, passing through the constant range between 30 and 50°C. Under the forced, repeated elongation and contraction for swollen PVA_VTFA thin film in water, the perfect elastic behavior is kept up to higher elongation with the increase in temperature and especially up to about three times equilibrium swelling length at 70°C. Young's modulus of swollen PVA_VTFA thin film in water was 6.47 × 10⁶ to 1.60 × 10⁶ dyn/cm² at 25–70°C. The molecular weight between junctions M_c increased with the increase in temperature; M_c was nearly equal to about one-sixth of the molecular weight of raw polymer M at 25°C and about one-third of M at 70°C. The interaction parameter between PVA_VTFA and water X₁, was 0.493–0.497 at 25–70°C.     

Structure and properties of poly(vinyl alcohol)/κ‐carrageenan blends

Blends of a commercial atactic poly(vinyl alcohol) (a‐PVA) derived from vinyl acetate and κ‐carrageenan were prepared by mixing the aqueous solutions of both samples. Blend films prepared by casting were transparent. In the DSC curves of the blend films, the endothermic peaks shifted to lower temperature with an increase of the content of κ‐carrageenan. The Young's modulus and the strength at break increased with an increase of the content of a‐PVA. As the standing temperature of the blend solutions decreased, the gelation region increased also at high content of carrageenan. In the amorphous regions of blend films, a‐PVA and κ‐carrageenan were miscible. © 2001 Society of Chemical Industry     

A transdermal diltiazem hydrochloride delivery device using multi-walled carbon nanotube/poly(vinyl alcohol) composites

Membranes with high strength and elasticity are of great demand in patch therapy. Similar membranes have been developed by combining carboxy-functionalized multiwalled carbon nanotube (c-MWCNT) with different poly(vinyl alcohol) (PVA) as potential diltiazem delivery device through aqueous mixing. High molecular weight PVA (PVA_H) produced stronger interaction with c-MWCNT than low molecular weight PVA (PVA_L) preferably at low concentration. Positive changes in favor of PVA_H in infrared and solid state ¹³C nuclear magnetic resonance spectroscopy, wide angle X-ray scattering, thermal stability, morphology and dry and wet mechanical properties clearly demonstrate that. Fibrillar c-MWCNT array at 1 wt.% in PVA_H (PVA_H/1) has drastically improved PVA crystalline cell dimension, tensile strength (201%) and elongation (196%) than neat PVA_H whereas the similar improvement is much less (100% and 185%) in PVA_L (PVA_L/1) due to globular morphology. Instead, c-MWCNT performed better at 0.5 wt.% in PVA_L (PVA_L/0.5). The kinetic data reflects better encapsulation and slower release by PVA_H (5.87%) than PVA_L (10.17%) due to greater interfacial interaction.     

Enhancing interfacial adhesion performance by using poly(vinyl alcohol) in (low‐density polyethylene)/(natural rubber)/(water hyacinth fiber) composites

The effects of (a) the chemical modification of water hyacinth fiber by poly(vinyl alcohol) (WHF‐_PVA) and (b) loading on the properties of low‐density polyethylene (LDPE)/(natural rubber (NR))/(water hyacinth fiber (WHF)) composites were studied. Mechanical properties, water absorption behavior, morphology, and thermal properties were examined; X‐ray diffraction and infrared spectroscopic analysis were done. The results indicated that LDPE/NR/WHF‐_PVA composites had higher values of tensile strength, Young's modulus, melting temperature, and water absorption resistance but lower elongation at break than LDPE/NR/WHF composites. The LDPE/NR/WHF‐_PVA composites had better interfacial adhesion between the matrix and the fibers than LDPE/NR/WHF composites, as shown by SEM results. The LDPE/NR/WHF‐_PVA composites exhibited lower interparticle spacing than LDPE/NR/WHF composites, a feature which enhanced the interparticle interaction between the water hyacinth fibers and the LDPE/NR matrix. J. VINYL ADDIT. TECHNOL., 19:47–54, 2013. © 2012 Society of Plastics Engineers     

Properties of polyamide 6,10/poly(vinyl alcohol) blends and impact on oxygen barrier performance

The oxygen transmission rate, average volume of free‐volume cavities (V_f) and fractional free volume (F_v) of polyamide 6,10 (PA610)/poly(vinyl alcohol) (PVA) (i.e. PA610_xPVA⁰⁵_y, PA610_xPVA⁰⁸_y and PA610_xPVA¹⁴_y) blend films reduced to minimum values when their PVA contents reached corresponding optimal values. Oxygen transmission rate, V_f and F_v values obtained for optimal PA610_xPVA^z_y blown films were reduced considerably with decreasing PVA degrees of polymerization. The oxygen transmission rate of the optimal bio‐based PA610₈₀PVA⁰⁵₂₀ blown film was only 2.4 cm³ (m²·day·atm)^?1, which is about the same as that of the most often used high‐barrier polymer, ethylene–vinyl alcohol copolymer. Experimental findings from dynamic mechanical analysis, differential scanning calorimetry, wide‐angle X‐ray diffraction and Fourier transform infrared spectroscopy of the PA610_xPVA^z_y blends indicate that PA610 and PVA in the blends are miscible to some extent at the molecular level when the PVA contents are less than or equal to the corresponding optimal values. The considerably enhanced oxygen barrier properties of the PA610_xPVA^z_y blend films with optimized compositions are attributed to the significantly reduced local free‐volume characteristics. © 2017 Society of Chemical Industry     

Characteristics and sensing behavior of electrochemically codeposited polypyrrole–poly(vinyl alcohol) thin film exposed to ethanol vapors

Polypyrrole–poly(vinyl alcohol) (PPy–PVA) composite films were prepared electrochemically by means of codeposition at a constant potential. Their sensing behaviors to various ethanol-vapor concentrations were investigated. Increasing the molar fraction of PVA up to PPy_0.964PVA_0.036 showed an increase of the sensitivity of the composite sensors. However, the sensitivity decreased if further PVA was incorporated. The ethanol-sensing behaviors were also largely dependent upon the electropolymerization charge, ranging from 50 to 200 mC in this investigation. Higher sensitivity was measured from the composite film prepared with a lower electrical charge. For example, a sensitivity of 7.70 mΩ mg⁻¹ L, about 3.3 times the sensitivity of the pristine PPy sensor, was measured by the PPy_0.964PVA_0.036 composite film prepared at 50 mC. However, incorporating PVA into the conducting polymer was at the sacrifice of the response speed as well as the stability of the composite as it was under continuous exposure to ethanol vapor. An adsorption model based on the Langmuir isotherm was used to interpret the sensing behaviors and the equation derived from this model correlated well with the measured sensitivities. The sensing parameters including the adsorption equilibrium constant, K_m, and the resistance change caused by a pseudomonolayer, [m(r₁ − r₂)]/n, were determined and found to decrease with increasing polymerization charge. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2079–2087, 1999     

Effects of Plasticizing on Mechanical and Viscous Characteristics of Poly(vinyl alcohol): A Comparative Study between Glycerol and Diethanolamine

Although plasticizing materials by modification with small-molecular chemicals has been extensively utilized in the industrial community, processing poly(vinyl alcohol) (PVA) at high concentrations (C_PVA) or with a high degree of polymerization (DP) remains challenging. Optimization the plasticizing conditions is one means of addressing this issue. In this study, two types of frequently used plasticizers, glycerol (GLY) and diethanolamine (DEA), are chosen to plasticize PVA resin with a DP of 2400. Both PVA/plasticizer films possess excellent optical transmittance and mechanical ductility, whereas the films blended with DEA exhibit higher strength than the PVA/GLY films. The viscosity variation in the temperature (T_op)–C_PVA space is monitored by real-time viscous flow testing, demonstrating that DEA is more effective for reducing the viscosity of PVA, which should improve the processability, facilitating film-forming from concentrated solutions. Furthermore, density functional theory calculations and molecular dynamics simulations illustrate that the PVA/DEA system has a lower binding energy, longer hydrogen bond length, and higher isotropic diffusion coefficient, indicating a stable hydrogen bond network and homogenous dispersion of the plasticizer, leading to good solution fluidity and mechanical performance. This study is significant for guiding the design and manufacture of optically transparent, high-performance PVA films as polarizer precursor.     

Studies on the properties of poly(vinyl alcohol) film plasticized by urea/ethanolamine mixture

This study investigated the effects of urea/ethanolamine mixture (UE) on the crystallinity, thermal, and mechanical properties of poly(vinyl alcohol) (PVA) films. PVA films were prepared from solutions containing PVA, urea, ethanolamine, and water by casting and evaporating at 50°C for 12 h. The plasticization efficiency of UE was compared with that of glycerol (GL), the conventional plasticizer for PVA. The properties of PVA films plasticized by UE and GL, abbreviated to UE-plasticized PVA film and GL-plasticized PVA film, respectively, were investigated by Fourier-transform infrared spectroscopy, X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, and mechanical testing. It was proved that UE could form more stable hydrogen bonding with the hydroxyl group of PVA molecule and was more effective in breaking the hydrogen bonds between the hydroxyl groups. Thus, the crystallinity of UE-plasticized PVA films was lower than that of GL-plasticized PVA films. The melting temperatures of UE-plasticized PVA films were lower than those of GL-plasticized PVA films. It was found that UE-plasticized PVA film showed a higher degradation temperature compared with GL-plasticized PVA film. The degree of swelling of UE-plasticized PVA film was higher than that of GL-plasticized PVA film but solubility (S) of UE-plasticized PVA film was lower in aqueous solution. Furthermore, UE-plasticized PVA films show lower tensile strength and higher elongation at break (E) than those of GL-plasticized PVA films. The tensile strength, E, and Young's modulus of PVA film containing 30% UE mixture reached 50.78 MPa, 591.19% and 76.9 MPa, respectively. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012