Effects of water on drawability,structure, and mechanical properties of poly(vinyl alcohol) melt‐spun fibers

Poly(vinyl alcohol) (PVA) melt‐spun fibers with circular cross‐section and uniform structure, which could support high stretching, were prepared by using water as plasticizer. The effects of water content on drawability, crystallization structure, and mechanical properties of the fibers were studied. The results showed that the maximum draw ratio of PVA fibers decreased with the increase of water content due to the intensive evaporation of excessive water in PVA fibers at high drawing temperature. Hot drying could remove partially the water content in PVA as‐spun fibers, thus reducing the defects caused by the rapid evaporation of water and enhancing the drawability of PVA fibers at high drawing temperature. The decreased water content also improved the orientation and crystallization structure of PVA, thus producing a corresponding enhancement in the mechanical properties of the fibers. When PVA as‐spun fibers with 5 wt % water were drawn at 180 °C, the maximum draw ratio of 11 was obtained and the corresponding tensile strength and modulus reached ～0.9 GPa and 24 GPa, respectively. Further drawing these fibers at 215 °C and thermal treating them at 220 °C for 1.5 min, drawing ratio of 16 times, tensile strength of 1.9 GPa, and modulus of 39.5 GPa were achieved. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45436.     

Structure evolution of melt‐spun poly(vinyl alcohol) fibers during hot‐drawing

The drawability of melt‐spun poly(vinyl alcohol) (PVA) fibers and its structure evolution during hot‐drawing process were studied by differential scanning calorimetry (DSC), two dimensional X‐ray diffraction (2‐D WAXD) and dynamic mechanical analysis (DMA). The results showed that the water content of PVA fibers should be controlled before hot‐drawing and the proper drying condition was drying at 200°C for 3 min. PVA fibers with excellent mechanical properties could be obtained by drawing at 200°C and 100 mm/min. The melt point and crystallinity of PVA fibers increased with the draw ratio increasing. The 2‐D WAXD patterns of PVA fibers changed from circular scattering pattern to sharp diffraction point, confirming the change of PVA fibers from random orientation to high degree orientation. Accordingly, the tensile strength of PVA fibers enhanced by hot‐drawing, reaching 1.85 GPa when the draw ratio was 16. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Improvement of the water resistance of atactic poly(vinyl alcohol) nanowebs by a heat treatment

Nanoscale materials can be rationally designed to exhibit significantly changed physical, chemical, and biological properties because of the extremely small dimensions. Therefore, atactic poly(vinyl alcohol) (a‐PVA) nanowebs by an electrospinning technique have very high water solubility because of their nanoscale in comparison with microscale materials such as fibers and films. In this study, a‐PVA nanowebs were prepared via electrospinning under suitable conditions to form PVA webs with uniform nanofibers (fiber average diameter = 200 ± 50 nm), not a bead or bead‐and‐string morphology. Furthermore, to improve the water resistance of the water‐soluble a‐PVA nanowebs, the PVA nanowebs were heat‐treated at various heat‐treatment temperatures. The melting temperature of the heat‐treated PVA nanowebs shifted toward a lower temperature with an increase in the heat‐treatment temperature, and this indicated that micronetwork domains formed. Moreover, with the exception of a PVA nanoweb treated at an excessive heat‐treatment temperature, the heat‐treated PVA nanowebs showed higher crystalline and mechanical properties than a pure PVA nanoweb. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Studies on fibers spun from poly(vinyl alcohol‐b‐acrylonitrile) emulsions prepared by ultrasonic technique. II. Properties of the fibers

The moisture content of poly(vinyl alcohol‐b‐acrylonitrile) fibers decreases with an increasing hydrophobic AN content and crystallinity of the fibers; however, the copolymer fiber with 26.94% AN, drawn × 5, and heat‐treated at 200°C has a moisture content value slightly lower than that of commercial PVA fiber, but much higher than that of commercial PAN fiber. The block copolymer fibers have a water‐retention value higher than that of commercial PVA fiber, owing to the presence of voids in these fibers, and have a stronger wicking ability than that of commercial PVA, PAN fibers, and wool and cotton mainly due to the grooved surface and bulk porous morphology of the fibers. The tensile strength of the copolymer fibers with an appropriate AN content are lower than that of commercial PVA fiber, but higher than that of commercial PAN fiber and much higher than that of wool and cotton. The melting temperatures of the copolymer fibers increase with increasing heat‐treatment temperature. The copolymer fibers possess a lower peak cyclizing temperature than that of the PAN fiber and have a higher thermal stability than that of both PVA and PAN fibers. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 989–994, 2001     

Preparation and properties of keratin–poly(vinyl alcohol) blend fiber

Keratin–poly(vinyl alcohol) (PVA) blend fibers containing 13–46 wt % of –SSONa⁺ (S‐sulfo) keratin were prepared by the wet‐spinning technique. They were formed by dehydration of an aqueous solution of S‐sulfo keratin and PVA (spinning dope) in a coagulation bath of sodium sulfate–saturated solution and subsequently drawn. Keratin–PVA fibers showed higher tenacity than that of wool, presumably originating from the high mechanical strength of the PVA component. The heat treatment at about 200°C improved the waterproof characteristics such as shrinkage of keratin–PVA fibers more conspicuously than did PVA fibers. That is, after heat treatment at 195°C for 10 min, keratin–PVA blend fiber shrank 20% in water at 60°C, whereas PVA fiber shrank 56%. Differential thermal analysis suggested the crosslinking of disulfide bonds between keratin molecules during the heat treatment, whereas the additional crystallization of PVA component was not observed. Adsorption of heavy metal and toxic gas to keratin–PVA fibers was also investigated. Keratin–PVA fiber was found to adsorb Ag⁺ and formaldehyde gas more efficiently than PVA. Thus, blends of keratin and PVA were advantageous for both polymer fibers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 756–762, 2004     

Improvement of hot water resistance of poly(vinyl alcohol) hydrogel by acetalization and irradiation techniques

In order to improve the heat stability of poly(vinyl alcohol) (PVA) hydrogel, acetalized PVA was irradiated with electron beam irradiation. The acetalization was strongly affected by PVA water content. There is an optimum water content of 20–30% for acetalization of PVA. The PVA gave maximum tensile strength at a dose of 100 kGy before or after acetalization. The PVA hydrogel maintained tensile strength of 10 MPa, even after 90 min boiling (98°C) in water or autoclave sterilization (121°C). It was confirmed that irradiation after, or before, acetalization is effective for enhancing heat resistance of a PVA hydrogel. The hydrogel is transparent, soft, has high tensile strength, and high hot water resistance. © 1995 John Wiley & Sons, Inc.     

Crosslinked PVA nanofibers reinforced with cellulose nanocrystals: Water interactions and thermomechanical properties

Acid‐catalyzed vapor phase esterification with maleic anhydride was used to improve the integrity and thermo‐mechanical properties of fiber webs based on poly(vinyl alcohol), PVA. The fibers were produced by electrospinning PVA from aqueous dispersions containing cellulose nanocrystals (CNCs). The effect of esterification and CNC loading on the structure and solvent resistance of the electrospun fibers was investigated. Chemical characterization of the fibers (FTIR, NMR) indicated the formation of ester bonds between hydroxyl groups belonging to neighboring molecules. Thermomechanical properties after chemical modification were analyzed using thermal gravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis. An 80% improvement in the ultimate strength was achieved for CNC‐loaded, crosslinked PVA fiber webs measured at 90% air relative humidity. Besides the ultra‐high surface area, the composite PVA fiber webs were water resistant and presented excellent mechanical properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40334.     

High‐strength regenerated cellulose fibers spun from 1‐butyl‐3‐methylimidazolium chloride solutions

High‐performance regenerated cellulose fibers were prepared from cellulose/1‐butyl‐3‐methylimidazolium chloride (BMIMCl) solutions via dry‐jet wet spinning. The spinnability of the solution was initially evaluated using the maximum winding speed of the solution spinning line under various ambient temperatures and relative humidities in the air gap. The subsequent spinning trials were conducted under various air gap conditions in a water coagulation bath. It was found that low temperature and low relative humidity in the air gap were important to obtain fibers with high tensile strength at a high draw ratio. From a 10 wt % cellulose/BMIMCl solution, regenerated fibers with tensile strength up to 886 MPa were prepared below 22 °C and relative humidity of 50%. High strengthening was also strongly linked with the fixation effect on fibers during washing and drying processes. Furthermore, an effective attempt to prepare higher performance fibers was conducted from a higher polymer concentration solution using a high molecular weight dissolving pulp. Eventually, fibers with a tensile strength of ～1 GPa and Young's modulus over 35 GPa were prepared. These tensile properties were ranked at the highest level for regenerated cellulose fibers prepared by an ionic liquid–based process. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45551.     

Effect of degumming on the tensile properties of silkworm (Bombyx mori) silk fiber

Forcibly reeled silkworm (Bombyx mori) silk was used to study how exposure to a degumming treatment (boiling in distilled water for 30 min) affects tensile properties. Because forcibly reeled and naturally spun fibers exhibit comparable mechanical behavior, the results can be generalized to material obtained conventionally from cocoons. The effects of degumming include: a decrease in the initial elastic modulus, a decrease in the stress at the proportional limit (yield strength), a change in the qualitative shape of force‐displacement curves, and significant qualitative and quantitative variability in force‐displacement data from samples subjected to nominally identical degumming histories. Immersion in water at room temperature or heating in air at 100°C for 30 min are both qualitatively equivalent to a 30‐min degumming treatment in boiling water, in terms of the effect on silk tensile properties. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1431–1437, 2002; DOI 10.1002/app.10366     

Influence of tension on the oxidative stabilization process of polyacrylonitrile fibers

Polyacrylonitrile fibers were heat‐treated in air, and a series of stretching experiments were conducted in different temperature zones. The effects of tension on the microstructure of the heat‐treated fibers and the tensile strength of the resultant carbon fibers were investigated. The results show the variations in morphological characteristics affected by stretching were different as stabilization proceeded. A possible mechanism of tension on cyclization and, thus, stabilization was elucidated. During stabilization, tension at low temperatures led to a great increase in the tensile strength of the carbon fibers, whereas tension at high temperatures resulted in only small improvement in the tensile strength of the carbon fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1029–1034, 2005     

Crosslinked poly(vinyl alcohol) and starch composite films: Study of their physicomechanical,thermal, and swelling properties

Crosslinked poly(vinyl alcohol) was blended with 10, 20, 40, and 50 wt % starch by a solution‐casting process. The solution‐cast films were dried, and then their physicomechanical properties including tensile strength, tensile elongation, tensile modulus, tear strength and density, and burst strength and density were tested. Thermal analysis was performed by differential scanning calorimetry. A moisture analysis of the PVA/starch films was performed and their moisture content determined. Also investigated were the films'resistance to solubility in water, 5% acetic acid, 50% ethanol, and sunflower oil and their swelling characteristics in 50% ethanol and sunflower oil. The prepared PVA/starch blends showed significant improvement in tensile modulus and in resistance to solubility in water, 5% acetic acid, and 50% ethanol. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1127–1132, 2007     

Improvement of tensile properties of ramie yarns by applying a winding machine with heat treatment

A winding machine with heat treatment was newly developed to strengthen ramie yarns. During the treatment process, ramie yarn in normal or wet state was wound on a winding machine and passed continuously through a heater at 100 and 150°C, respectively, with different winding speeds and tensions. Higher tensile strength and stiffness of ramie yarn was achieved after heat treatment on wet yarn and winding speed had a significant influence on the tensile properties of yarns. However, a little decline in tensile strength was found for ramie yarns after heat treatment in normal state. This implies that the water‐swollened structure of ramie yarn during the heat treatment is crucial in strengthening yarns. In the case of heat treatment on wet yarns, the effect of winding tension on the tensile properties of yarns was studied. It was found that the tensile strengths and Young's moduli of ramie yarns first increased and then reached equilibrium as the winding tension was increased. The crystallinity calculated from X‐ray diffraction diagrams showed a slight decrease in heat‐treated ramie yarns whereas the crystalline orientation factors had no appreciable change. It was considered that the improved effect was related to the more oriented molecular chains in amorphous region and optimized yarn structure. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Water‐resistant modification of poly(vinyl alcohol)/polyamidoxime chelating fibers prepared by emulsion spinning and their adsorption properties

The poly(vinyl alcohol)/polyacrylonitrile (PVA/PAN) precursor fiber prepared by emulsion spinning was separately crosslinked with dimethyloldihydroxyethyleneurea (DMDHEU), formaldehyde (FA), and both DMDHEU and FA for preparing PVA/polyamidoxime (PAO) chelating fibers with elevated water‐resistance. Effects of different crosslinking systems on the properties of the composite amidoxime chelating fibers have been investigated. Results show that FA treatment can effectively increase the water‐resistance of composite fiber, but would dramatically decrease the adsorption properties of composite fiber. Conversely, DMDHEU treatment has inferior effects on the water‐resistance of the composite fiber, but would impressively increase the adsorption properties of composite fiber. The composite fiber treated with both DMDHEU and FA could reach good overall performances (water contact angle: 94.83°; soft point in hot water: 116 °C; breaking strength in dry condition: 441.80 MPa; the maximum adsorption capacities of precious ions: 1207.66 and 653.59 mg Ag g^?1). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44965.     

Antioxidant,antifungal, water binding,and mechanical properties of poly(vinyl alcohol) film incorporated with essential oil as a potential wound dressing material

In this study, the properties of poly (vinyl alcohol) (PVA) films incorporated with Zataria multiflora essential oil (ZMO) as a potential antioxidant/antibacterial material was investigated. PVA films were prepared from PVA solutions (2% w/v) containing different concentrations of ZMO. Water solubility, moisture absorption, water swelling, and water vapor permeability for pure PVA films were 57 ± 1.1, 99 ± 3.2%, 337 ± 8%, and 0.453 ± 0.015 g mm/m² h, respectively. Incorporation of ZMO into PVA films caused a significant decrease in water swelling and moisture absorption and increase in solubility and water vapor permeability. Tensile strength, elastic modulus, and elongation at break for pure PVA films were 13.5 ± 0.61 MPa, 15.2 ± 0.8 MPa, and 216 ± 4%, respectively. Incorporation of ZMO into the PVA films caused a significant decrease in tensile strength and elastic modulus and increase in elongation at break of the films. Pure PVA film showed UV‐visible light absorbance ranging from 280 to 440 nm with maximum absorbance at 320 nm. Addition of ZMO caused a significant increase in light absorbance and opacity. PVA films exhibited no antioxidant and antifungal activities, whereas PVA/ZMO films exhibited excellent antioxidant and antifungal properties. Although the bioactivity PVA films were improved by the addition of ZMO, however, the mechanical properties and water binding capacity of the films were weaken slightly. Thus, ZMO emulsified in the ethanol not compatible with PVA matrix and more suitable emulsifier was needed in order to obtain strong film with higher mechanical properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40937.     

Preparation of poly (vinyl alcohol)/gelatin composites via in-situ thermal/mechanochemical degradation of collagen fibers during melt extrusion: effect of extrusion temperature

By in-situ degradation of collagen fibers into gelatin under the thermal/mechanochemical effects of the extruder, PVA/gelatin composites were successfully prepared using PVA and collagen fibers derived from cattle hide limed split wastes as raw materials. The effect of extrusion temperature on the degradation of collagen fibers and the thermal processability and mechanical properties of the composites were studied. The results showed that the controllable degradation of collagen fibers in extruder could be realized by adjusting the extrusion temperature. Particularly, high extrusion temperature promoted the generation of low-molecular-weight gelatin and the esterification between the hydroxyl of PVA and the carboxyl of gelatin, as well as the hydrogen bonding between O-H, C = O, N-H in gelatin and water or O-H in PVA, thus endowing gelatin with the good compatibility with PVA, and significantly increasing the content of non-freezable bound water in system. Ascribing to the plasticization of the gelatin with lower molecular weight and more non-freezable bound water, PVA/gelatin composites exhibited the improved thermal processability and the decreased mechanical properties with the increase of extrusion temperature. Even so, the tensile strength and Young’s modulus of the composite obtained at 175 °C still above 40 MPa and 1.0 GPa respectively, satisfying some practical applications.     

PVA凝胶纺丝工艺对纤维结构与性能的影响

讨论了聚乙烯醇（ＰＶＡ）凝胶纺丝过程中的凝固浴、初生冻胶丝的溶剂萃取和干燥收缩以及干冻胶丝超拉伸、热定型等工艺条件对ＰＶＡ纤维结构和性能的影响，并制备出拉伸强度和模量分别为１１．３和４３０ｃＮ／ｄｔｅｘ的高强高模ＰＶＡ纤维。     

Mechanically Robust Nanofibrous Xerogel Membrane for One‐Pass Removal of Trace Water in Oil

Removal of trace water from oil is essential for a high‐performance fuel supply system. Trace water in fuel is a crucial contributor to frequent system maintenance and failure. In this work, an electrospun polyacrylic acid/polyvinyl alcohol (PAA/PVA) nanofibrous xerogel membrane (NFM) is prepared to remove trace water in oil. Based on the optimization of the weight ratio and the crosslinking conditions of PAA/PVA, the resultant NFM shows remarkable water‐retaining capacity (swelling ratio of 124.8 g/g) and rapid absorption property. The optimal membrane displays a small average pore size of 523.2 nm, high porosity of 79.6% as well as robust tensile strength of 8.1 MPa. Additionally, after just one pass through a single layer membrane (thickness of 35 ± 3 µm and areal density of 3.5 ± 0.5 g m^?2), the milky oil containing 1 wt% water is clarified and the water content reduced to 130 ppm. With extensive water being absorbed into the 3D network (different with the conventional separation mechanism) as well as good compatibility with oil, a multilayer pleated scheme may provide a practical methodology for enhancing fuel oil properties and performances.     

Preparation and characterization of chitosan/poly(vinyl alcohol) blend fibers

Chitosan and poly(vinyl alcohol) blend fibers were prepared by spinning their solution through a viscose‐type spinneret at 25°C into a coagulating bath containing aqueous NaOH and ethanol. The influence of coagulation solution composition on the spinning performance was discussed, and the intermolecular interactions of blend fibers were studied by infrared analysis (IR), X‐ray diffraction (XRD), and scanning electron micrograph (SEM) and by measurements of mechanical properties and water‐retention properties. The results demonstrated that the water‐retention properties and mechanical properties of the blend fibers increase due to the presence of PVA in the chitosan substract, and the mechanical strength of the blends is also related to PVA content and the degree of deacetylation of chitosan. The best mechanical strength values of the blend fibers, 1.82 cN/d (dry state) and 0.81 cN/d (wet state), were obtained when PVA content was 20 wt % and the degree of deacetylation of chitosan was 90.2%. The strength of the blend fibers, especially wet tenacity could be improved further by crosslinking with glutaraldehyde. The water‐retention values (WRV) of the blend fibers were between 170 and 241%, obviously higher than pure chitosan fiber (120%). The structure analysis indicated that there are strong interaction and good miscibility between chitosan and poly(vinyl alcohol) molecular resulted from intermolecular hydrogen bonds. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2558–2565, 2001     

Radiation‐induced crosslinking of ultra high molecular weight polyethylene fibers by means of electron beams

Crosslinking of ultra high molecular weight polyethylene fibers (UHMW‐PE fibers) is investigated by means of electron beam irradiation. The structure and mechanical properties of the fibers in different irradiation atmospheres are discussed. The results show that the gel fraction and crosslinking density increase with the increase of absorbed dose. The swelling ratio and average molecular weight of crosslinked net decrease with the increase of absorbed dose. The relation between s + s^?1 of the UHMW‐PE fibers and reciprocal irradiation dose 1/R is obtained. The tensile strength and failure elongation decrease with the increase of absorbed dose, and the tensile modulus increases with the increase of absorbed dose. The samples are irradiated in air, vacuum, and acetylene atmospheres, separately. The radiation effects, such as crosslinking fraction and mechanical properties of UHMW‐PE fibers, are the most significant in acetylene atmosphere in comparison with in air and in vacuum. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1761–1764, 2005     

Insert injection molding of high‐density polyethylene single‐polymer composites

A process for making high‐density polyethylene (HDPE) single‐polymer composites (SPCs) by insert injection molding was investigated. HDPE SPCs with relatively good tensile and interfacial properties were prepared within a short cycle time within a temperature range of 40°C. Melt‐spun HDPE fibers were made from the same resin as the matrix. The fibers were heat treated in silicone oil, with and without tension, to study the changes of fiber properties upon exposure to high temperature. HDPE SPCs containing about 30 wt% lab‐made HDPE fabric achieved a tensile strength of 50 MPa, 2.8 times that of neat HDPE. The peel strength of HDPE SPCs increased with increasing injection temperature and achieved a maximum value of 16.7 N/cm. Optical micrographs of polished transverse cross‐sections of the SPC samples showed that higher injection temperature is beneficial to the wetting and permeation properties of the matrix. Scanning electronic microscope photographs suggested good bonding and compatibility between the fibers and the matrix. POLYM. ENG. SCI., 55:2448–2456, 2015. © 2015 Society of Plastics Engineers