Preparation of ketoprofen‐loaded high‐molecular‐weight poly(vinyl alcohol) gels

High‐molecular‐weight atactic poly(vinyl alcohol) (a‐PVA) gels loaded with (R,S)‐2‐(3‐benzoylphenyl)propionic acid (ketoprofen) were prepared from 5, 6, 7, and 8 g/dL solutions of a‐PVA with a number‐average degree of polymerization of 4000 in an ethylene glycol/water mixture with an aging method to identify the effect of the initial polymer concentration on the swelling behavior, morphology, and thermal properties of a‐PVA gels. Then, the release behavior of ketoprofen from a‐PVA gels was investigated. As the polymer concentration decreased, the ability for network formation decreased, and the degree of swelling of the a‐PVA gels increased. In addition, the enthalpy increased with an increase in the a‐PVA concentration, but the melting temperatures of the gels prepared at different initial polymer concentrations were the same; this indicated that tighter gel networks would be formed by a higher polymer chain density. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of gel spinning accompanied with cross‐linking using boric acid on the structure and properties of high‐molecular‐weight poly(vinyl alcohol) fiber

To enhance the thermal stability of poly(vinyl alcohol) (PVA) fiber, the fiber was prepared from the gel spinning of high molecular weight (HMW) PVA by using dimethyl sulfoxide/water (8/2, v/v) as a solvent, accompanied with the cross‐link by boric acid (B‐PVA). In addition, the structure and properties of the B‐PVA fiber were compared with those of the HMW PVA fiber obtained by using the same spinning system without cross‐linking (NB‐PVA). Through a series of experiments, it turned out that cross‐linking actualized by an optimum amount of boric acid (0.3 wt % based on PVA) and zone drawing caused significant changes in the properties of HMW PVA gel fiber. That is, cross‐linking increased thermal degradation temperatures at each degradation step and amounts of final residues, resulting in improving thermal properties of the PVA fiber. On the contrary, it was found that in the case of the B‐PVA fiber, some broadening of the original PVA unit cell occurred, which was identified by the peak shift to lower angle in X‐ray diffractogram. The tensile strength and Young's modulus of B‐PVA fiber with draw ratio of 15 are 23.1 and 308.3 g/d, respectively. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of heat treatment on tensile properties of high‐strength poly(vinyl alcohol) fibers

The tensile properties of high‐strength poly(vinyl alcohol) (PVA) fibers after heat treatment in air, water, and engine oil were studied. The results show that heat treatment in air, water, and engine oil have a different influence on the tensile properties of high‐strength PVA fibers. After heat treatment in air, the fibers possess excellent heat stability of the tensile properties. But in water, especially in hot water, the tenacity, Young's modulus, and specific work of rupture of the fibers decrease, while the elongation at break of the fibers increases. Similarly, engine oil has a significant influence on the tensile properties of the fibers. When the temperature of engine oil is above 120°C, the tensile properties of the fibers decrease drastically. We also discuss the influence of heat, water, and engine oil on the tensile properties of high‐strength PVA fibers in relation to the structure of the fibers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 237–242, 2000     

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     

Preparation of ultrahigh molecular weight syndiotactic poly(vinyl alcohol) microfibrillar fibers by low‐temperature solution polymerization of vinyl pivalate in tertiary butyl alcohol and saponification

Vinyl pivalate (VPi) was solution polymerized in tertiary butyl alcohol (TBA) and in dimethyl sulfoxide (DMSO) with a low chain transfer constant using a low temperature initiator, 2,2′‐azobis(2,4‐ dimethylvaleronitrile) (ADMVN). The effects of polymerization temperature and initiator concentration were investigated in terms of polymerization behavior and molecular structures of poly(vinyl pivalate) (PVPi) and its saponification product poly(vinyl alcohol) (PVA). TBA was absolutely superior to DMSO in increasing the syndiotacticity and molecular weight of PVA. In contrast, TBA was inferior to DMSO in causing conversion to polymer, indicating that the initiation rate of VPi production in TBA was lower than that in DMSO. These effects could be explained by a kinetic order of ADMVN concentration, calculated by the initial rate method. Low‐temperature solution polymerization of VPi in TBA or DMSO by adopting ADMVN proved to be successful in obtaining PVA of ultrahigh molecular weight [maximum number‐average degree of polymerization (P_n): 13,500–17,000] and of high yield (ultimate conversion of VPi into PVPi: 55–83%). In the case of bulk polymerization of VPi at the same conditions, maximum P_n and conversion were 14,500–17,500 and 22–36%, respectively. The P_n and syndiotactic diad content were much higher and the degree of branching was lower with PVA prepared from PVPi polymerized at lower temperatures in TBA. Moreover, PVA from the TBA system was fibrous, with a high degree of orientation of the crystallites, indicating the syndiotactic nature of TBA polymerization. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1992–2003, 2002     

Preparation of syndiotacticity‐rich high molecular weight poly(vinyl alcohol)/iodine polarizing film with high water resistance

To enhance durability of poly(vinyl alcohol) (PVA)/iodine polarizing film under humid and warm atmospheres and to identify the effects of syndiotacticity on the polarizing efficiency (PE) and durability of PVA/iodine complex film, we prepared three high molecular weight (PVA)s with similar number‐average degree of polymerization (P_n) of 4000 and with different syndiotactic diad (s‐diad) contents of 53, 56, and 59%, respectively. It was found that syndiotacticity of PVA had a significant influence on the durability of PVA/iodine complex film in warm and humidity conditions (relative humidity of 80% and temperature of 50°C). That is, both desorption of iodine in PVA/iodine film and transmittance of film decreased with increasing syndiotacticity of PVA. In the case of PE, the values of over 99% were obtained at each optimum conditions. The change of PE (durability) of PVA/iodine complex films having P_n of 4000 and s‐diad contents of 56 and 59%, respectively, in warm and humidity conditions was almost zero, whereas those of PVA/iodine film with s‐diad content of 53% and with (P_n)s of 1700 and 4000 were about 60% and 50%, respectively, under same conditions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Development of high‐strength fibers from aliphatic polyketones by melt spinning and drawing

We have investigated the formation of high‐strength, high‐modulus fibers from four aliphatic polyketone resins. One resin was a perfectly alternating copolymer of ethylene and carbon monoxide, while the other three were terpolymers containing up to 6 mol % propylene. The mechanical properties were measured as a function of processing conditions, and the structures of the filaments were characterized using birefringence, WAXS, SAXS, SEM, and thermal analysis. Fibers formed from all resins develop very high molecular orientations and a microfibrillar structure. Fibers having room temperature tenacities as high as 10 gpd (～1.1 GPa) were obtained. Tensile moduli reached values as high as 120 gpd (～13 GPa). The melting point of the fibers was primarily dependent on the composition of the resin, while the maximum strength and modulus were largely determined by the maximum draw ratio achieved. The maximum draw ratio achieved in the present experiments was greater for the terpolymers than for the copolymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1794–1815, 2001     

Syndiotacticity‐rich ultrahigh molecular‐weight poly(vinyl alcohol) film. I. Determination of optimum polymer concentration by zone‐drawing method in film preparation

A new method using a simple zone‐drawing technique has been suggested for determining the optimum initial concentration of a polymer solution that has suitable macromolecular entanglements. This method was developed to replace the incorrect inherent viscosity‐measuring method for syndiotacticity‐rich (syndiotactic diad content of 63.4%) ultrahigh molecular‐weight (number‐average degree of polymerization of 12,300) (UHMW) poly(vinyl alcohol) (PVA) solution. Syndiotacticity‐rich UHMW PVA films were prepared from dimethyl sulfoxide (DMSO) solutions with different initial concentrations: of 0.1, 0.2, 0.3, 0.4, and 0.5 g/dL. In order to investigate the drawing behavior of the syndiotacticity‐rich UHMW PVA films with different solution concentrations, the films were drawn under various zone‐drawing conditions. Through a series of experiments, it was discovered that the initial concentration of PVA solution in DMSO caused significant changes in the draw ratio of the syndiotacticity‐rich UHMW PVA film. That is, the one‐step and maximum zone draw ratios of the film at an initial concentration of 0.3 g/dL exhibited its maximum values and gradually decreased at higher or lower concentrations. Thus, it was disclosed that the initial concentration of 0.3 g/dL is the optimum polymer concentration to produce a maximum draw ratio in this work. Based on the above results, it may be concluded that the optimum concentration of the initial PVA solution can be determined directly by measuring the zone draw ratio. The draw ratio, birefringence, crystallinity, degree of crystal orientation, tensile strength, and tensile modulus of the maximum drawn PVA film were 32.9, 0.0449, 0.61, 0.991, 1.91, and 46.2 GPa, respectively. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 123–134, 2000     

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     

Properties of high‐speed spun high molecular weight poly(ethylene terephthalate) filaments

High‐speed spinning of high molecular weight poly(ethylene terephthalate) (PET) having an intrinsic viscosity of 0.98 dL/g was performed at the take‐up velocity range of 2.5–5.5 km/min. The structure of the as‐spun filaments was analyzed by density, birefringence, WAXS, DSC, boiling water shrinkage, and tensile properties. Stress‐induced crystallization takes place above 3 km/min, which is confirmed by the steep increase in density, the growth of the crystal size, melting point increase, and the decrease in boiling water shrinkage. The plot of crystallinity versus birefringence shows that crystallinity increases drastically after birefringence reaches the value of about 0.075. A comparison with the data of other researchers will clearly present the effects of molecular weight on the properties of PET filaments spun at high speed, for example, the take‐up velocity range of the steep increase in density for high molecular weight PET is lower than that for low molecular weight PET by about 1 km/min. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1283–1291, 1999     

Effect of syndiotacticity on the morphology of water-soluble low molecular weight poly(vinyl alcohol) by solution copolymerization of vinyl pivalate/vinyl acetate in tetrahydrofuran and saponification

Syndiotacticity-rich low molecular weight (LMW) poly(vinyl alcohol) (PVA) was synthesized by solution copolymerization of vinyl pivalate (VPi) and vinyl acetate (VAc) with various monomer ratios in tetrahydrofuran at low temperature using 2,2′-azobis(2,4-dimethylvaleronitrile) (ADMVN) as an initiator and successive saponification of copoly(VPi/VAc). Solution copolymerization of VPi and VAc by ADMVN and saponification produced water soluble syndiotacticity-rich LMW PVA with number-average degrees of polymerization (P_n)s of 220-520, syndiotactic diad (s-diad) contents of 55.5-61.3%, and with maximum conversions of VPi and VAc into copoly(VPi/VAc) of 70-80%. The effect of stereosequences of PVA was investigated in terms of morphology of water-soluble LMW PVA. Especially, to precisely identify the effect of syndiotacticity of LMW PVA on the change of morphology, we prepared various PVAs with similar P_n of 1200 and with different s-diad contents of 55.5-61.3%, respectively. The PVA with s-diad content of 61.1% revealed a well-defined fibrous morphology. Each fiber was composed of a number of microfibrils. As the s-diad content of PVA decreased, some morphological change was observed. The specimen with s-diad content of 59.9% formed a divided precipitate with microfibrillar structure. In contrast, in the case of PVA with s-diad content of 55.7%, irregular shaped particles were observed.     

高强度聚乙烯醇纤维结构与性能研究

继超高相对分子质量聚乙烯(UHMW-PE)纤维得到较快发展以来,有关高强度聚乙烯醇纤维的研究与开发也受到人们重视,介绍和讨论了高强度聚乙烯醇纤维的研究和开发现状,包括制备方法、纤维结构与性能、应用等方面的情况。     

Characterization of poly(L‐lactic acid) fibers produced by melt spinning

Biodegradable poly(L ‐lactic acid) (PLLA) fibers were processed by a two‐step melt‐spinning method (melt extrusion and hot draw) from PLLA with three different viscosity‐average molecular weights (494,600, 304,700, and 262,800). Before spinning, the polymer flakes were first milled into powders and dried under vacuum. Viscosity‐average molecular weight of PLLA following the fabrication process was monitored. Tensile properties of as‐spun and hot‐drawn fibers were investigated. Morphology of the PLLA fibers was viewed under a scanning electron microscope. Crystallinity of these fibers was assessed by thermogram analysis of differential scanning calorimetry. Results showed that the extent of decrease in the viscosity‐average molecular weight of PLLA dropped sharply by 13.1–19.5% during pulverization and by 39.0–69.0% during melt‐extrusion. The hot‐draw process in this study had a little effect on the viscosity‐average molecular weight of PLLA. Smoother fibers could be obtained for the die temperature at least 230°C for raw materials with higher crystallinity (more than 75%) and at least 220°C for raw materials with lower crystallinity (about 60%). The as‐spun fibers showed crystallinity of 16.5–22.8% and the value increased to 50.3–63.7% after hot draw. Tensile moduli of the as‐spun fibers were in the range of 1.2–2.4 GPa, which were raised to 3.6–5.4 GPa after hot draw. The final PLLA fibers with 110–160 μm diameters showed tensile strengths of 300–600 MPa. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 251–260, 2001     

Water stability of high‐molecular‐weight (HMW) syndiotacticity‐rich poly(vinyl alcohol) (PVA)/HMW atactic PVA/iodine complex blend films

To precisely identify the effect of blend ratios of syndiotacticity‐rich poly(vinyl alcohol) (s‐PVA)/atactic PVA (a‐PVA) on the water stability of s‐PVA/a‐PVA/iodine complex blend films, we prepared two PVAs with similar number‐averaged degrees of polymerization of 4000 and degrees of saponification of 99.9% and with different syndiotactic diad contents of 58.5 and 53.5%, respectively. The desorption behavior of iodine in s‐PVA/a‐PVA/iodine complex films in water was investigated in terms of the solubility of s‐PVA/a‐PVA blend films in water. The degree of solubility of s‐PVA/a‐PVA blend films with s‐PVA content over 50% in water at 70°C was limited to about 10–20%, whereas that of s‐PVA/a‐PVA blend films with s‐PVA content of 10% was 85% under the same conditions. The degree of iodine desorption of complex blend films decreased with increasing s‐PVA content. The degree of iodine desorption of s‐PVA/a‐PVA drawn film with s‐PVA content of 90% was limited to 7%, regardless of the soaking temperature from 30 to 70°C. The desorption of iodine in water was strongly affected by the dissolution of blends. Moreover, the stability of iodine in the drawn s‐PVA/a‐PVA/iodine blend films in hot water was far superior to that of the undrawn film. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1435–1439, 2004     

Highly crystalline and oriented high‐strength poly(ethylene terephthalate) fibers by using low molecular weight polymer

High‐strength poly(ethylene terephthalate) (PET) fibers were obtained using low molecular weight (LMW) polymervia horizontal isothermal bath (hIB), followed by postdrawing process. We investigated the unique formations of different precursors, which differentiated in its molecular orientation and crystalline structures from traditional high‐speed spinning PET fibers. Sharp increase in crystallinity was observed after drawing process even though the fibers showed almost no any crystallinity before the drawing. Properties of as‐spun and drawn hIB and control filaments at different process conditions were compared. As would be expected, performances of resulted treated undrawn and drawn fibers have dramatically improved with developing unique morphologies. Tenacities more than 8 g/d for as‐spun and 10 g/d for drawn treated fibers after just drawn at 1.279 draw ratio were observed. These performances are considerably higher than that of control fibers. An explanation of structural development of high‐strength fibers using LMW polymer spun with hIB is proposed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42747.     

Study on gel‐spinning process of ultra‐high molecular weight polyethylene

An ultra‐high molecular weight polyethylene (UHMW‐PE) fiber was prepared by gel spinning using general kerosene as the solvent and gasoline as the extraction solvent. The process of the phase separation of gel as‐spun, spun under various spinning conditions, was investigated. Its extracting and drying process were also studied. The results reveal that the gel as‐spun, spun under a lower spin draft and a lower spin quenching temperature, extracted in times and dried under free‐shrinkage, exhibits a good afterdrawability that eventually endows the fiber with excellent mechanical behaviors. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 670–675, 1999     

Preparation of water‐soluble syndiotacticity‐rich high molecular weight poly(vinyl alcohol) microfibrillar fibers using copolymerization of vinyl pivalate and vinyl acetate and saponification

Water‐soluble high molecular weight (HMW) syndiotactic poly(vinyl alcohol) (s‐PVA) microfibrillar fibers were prepared by the saponification with various conditions such as amount of alkali solution, saponification temperature, and saponification concentration from copoly(vinyl pivalate (VPi)/vinyl acetate (VAc)) copolymerized using various VPi/VAc feed ratios. To produce s‐PVA microbrillar fibers having various water‐soluble temperatures for many industrial applications, the intrinsic viscosities, syndiotactic diad (S‐diad) contents, and degrees of saponification (DS)s of PVAs were finely controlled to 1.2–3.6 dL/g, 56.3–58.3%, and 91.4–98.3%, respectively. Through a series of experiments, it was found that the amount of alkali may alter the structure of the saponified polymers, primarily the DS, and the structural variation changes viscosity. That is, intrinsic viscosity was sharply decreased as the amount of alkali solution was increased. DS was increased with an increase in the amount of alkali solution. S‐diad content was increased with an increase in the VPi content. HMW s‐PVA microfibrillar fibers having S‐diad content of 56.3–58.3% prepared by the saponification of copoly(VPi/VAc) were completely soluble in water at 100°C. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1482–1487, 2003     

Preparation of high‐molecular‐weight poly(vinyl alcohol) with high yield by solution polymerization of vinyl acetate in methanol using 4,4′‐azobis(4‐cyanovaleric acid)

Vinyl acetate (VAc) was solution‐polymerized at 40°C and 50°C using 4,4′‐azobis(4‐cyanovaleric acid) (ACVA) as an initiator and methanol as a solvent, and effects of polymerization temperature and initiator concentration were investigated in terms of conversion of VAc into poly (vinyl acetate) (PVAc), degree of branching (DB) for acetyl group of PVAc, and molecular weights of PVAc and resulting poly(vinyl alcohol) (PVA) obtained by saponifying with sodium hydroxide. Slower polymerization rate by adopting ACVA and lower viscosity by methanol proved to be efficient in obtaining linear high‐molecular‐weight (HMW) PVAc with high conversion and HMW PVA. PVA having maximum number–average degree of polymerization (P_n) of 4300 could be prepared by the saponification of PVAc having maximum P_n of 7900 polymerized using ACVA concentration of 2 × 10^?5 mol/mol of VAc at 40°C. Moreover, low DB of below 1 could be obtained in ACVA system, nevertheless of general polymerization temperatures of 40°C and 50°C. This suggests an easy way for producing HMW PVA with high yield by conventional solution polymerization without using special methods such as low‐temperature cooling or irradiation. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 4831–4834, 2006     

Role of molecular weight of atactic poly(vinyl alcohol) (PVA) in the structure and properties of PVA nanofabric prepared by electrospinning

Atactic poly(vinyl alcohols) (a‐PVAs) having number‐average degrees of polymerization [(P_n)s] of 1700 and 4000 were prepared by the solution polymerization of vinyl acetate, which was followed by the saponification of poly(vinyl acetate) to investigate the effects of molecular weights of a‐PVA on the characteristics of electrospun a‐PVA nanofabrics. A‐PVA nanofabrics were prepared by electrospinning with controlling the process parameters including the electrical field, conductivity, tip‐to‐collector distance, and solution concentration. Through a series of characterization experiments, we identified that the molecular weight of a‐PVA had a marked influence on the structure and properties of nanofabrics produced. That is, the higher the molecular weight of PVA, the superior the physical properties of PVA nanofabric. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1638–1646, 2004     

Lubrication of poly(vinyl alcohol) chain orientation by carbon nano‐chips in composite tapes

The extraordinary structural properties of graphene and carbon nanotube materials motivate the development of practical methods for their use in fabricating continuous, strong, and tough composite fibers. Poly(vinyl alcohol) (PVA)/carbon nano‐chip fiber (CNCF) composite tapes with 0.5 wt % loading show that Young's modulus, tensile strength, and toughness are increased by 585%, 653%, and 20%, respectively as compared to the control (PVA) tapes. Nano‐chips exfoliated from the CNCF during processing, lubricate polymer chain alignment, and orientation during drawing, where composite tapes could be drawn to higher draw ratios compared with the control tapes. As a result, the Herman's orientation factor (f) increased from 0.5 (control tape) to 0.8 (composite tape). Theoretical analysis shows ～ 16 vol % of the composite tapes consists of fully oriented PVA chains, which contributes to its exceptional mechanical performance. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013