基于α-PVA/s-PVA/NaCl共混体系的薄膜制备和表征

以两种等规度不同的聚乙烯醇（PVA）为原料,水作溶剂,加入不同含量的氯化钠（NaCl）,在室温干燥、水洗、再干燥后制成无规聚乙烯醇（a-PVA）／间规聚乙烯醇（s-PvA）共混薄膜。采用差示扫描量热仪（DSC）、傅立叶红外光谱仪（FT-IR）、力学性能测试以及热失重分析（TG）等方法对薄膜进行表征。结果显示,随NaG和s-PVA的含量变化,共混膜的吸收峰和熔点规律变化,并在3％（w）NaC1时获得最佳拉伸强度和弹性模量,分别为47．54MPa与1．95GPa。共混膜的热性能随着s-PVA含量增加而提高,s-PVA所占比例从0提高到40％时,相应地薄膜的熔点从231.4℃增至239.8℃。     

Effect of addition of saccharose on gelation of aqueous poly(vinyl alcohol) solutions

The properties of poly(vinyl alcohol) (PVA) hydrogels containing saccharose were examined. The effect of the addition of saccharose to atactic PVA (α-PVA) gels on their melting temperatures was larger than that for syndiotacticity-rich PVA (s-PVA) gels and the melting temperature was above 100°C for α-PVA gels with saccharose contents of 60 wt %. However, the fusion enthalpy (ΔH) of the α-PVA gels was at most 100 kJ/mol. The release of solvent (water/saccharose) from gels in air decreased with an increase in the saccharose content and the equilibrium was achieved after standing for 20 days for the α-PVA and s-PVA gels with saccharose contents above 40 and 20 wt %, respectively. © 1995 John Wiley & Sons, Inc.     

Gels of syndiotacticity-rich poly(vinyl alcohol)–water/dimethyl sulfoxide or – water/ethylene glycol solutions

Gels of syndiotacticity-rich poly(vinyl alcohol) (s-PVA) in mixed solvents of water/dimethyl sulfoxide (DMSO) or water/ethylene glycol (EG) were made by chilling at the temperatures of 0–70°C from those solutions with the polymer concentrations below 10g/dL. The melting points of the gels were measured warming the gel from the gelling temperature (T_gel) at a constant heating rate. The apparent enthalpy of fusion of a junction of gel, ΔH was estimated from the relation between the apparent melting temperature and the polymer concentration. The s-PVA gels made from the mixtures of the water/lower contents of DMSO or EG had a minimum at lower T_gel and a maximum ΔH at a higher T_gel. On the other hand, the s-PVA gels made from the mixtures of the water/higher contents of them had nearly a maximum ΔH at a higher T_gel. From those results, it was considered that the former gels received a high thermal history while the latter gels received only slight thermal history.     

Gelation of poly(vinyl alcohol)/phenol/water solutions and gel spinning

The light transmittance of the gels of poly(vinyl alcohol) (PVA)/phenol/water solutions was examined for the entire range of phenol/water content. Excellent transparency was found for the gels with phenol contents of 70–95 vol %. In full consideration of the results for the transparency and melting temperature of the gels and the viscosity and gelation ability of solutions, the PVA solutions of 75 vol % phenol content were selected for the gel spinning. The maximum dynamic moduli of drawn filaments at 25°C (room temperature) were 42 GPa (15x) for atactic PVA and 45 GPa (14x) for syndiotacticity-rich PVA. © 1995 John Wiley & Sons, Inc.     

High modulus polypropylene fibers. II. Influence of fiber preparation upon structure and morphology

The influence of drawing on the limiting draw ratio upon formation of the morphological structure of fibers spun from binary polypropylene (PP) blends was studied. Fibers were spun from a fiber‐grade CR‐polymer and from the blends of a fiber‐grade CR‐polymer with a molding‐grade polymer in the composition range of 10–50 wt % added. As‐spun fibers were immediately moderately and additionally highly drawn at the temperature of 145°C. The structure and morphology of these fibers were investigated by small‐angle X‐ray scattering, wide‐angle X‐ray scattering, differential scanning calorimetry, scanning electron microscopy, density, birefringence, and sound velocity measurements. It was shown that continuously moderately drawn fibers are suitable precursors for the production of high tenacity PP fibers of very high modulus, because of so called oriented “smectic” structure present in these fibers. With drawing at elevated temperature, the initial metastable structure of low crystallinity was disrupted and a c‐axis orientation of monoclinic crystalline modification was developed. Hot drawing increased the size of crystallites and crystallinity degree, the orientation of crystalline domains, and average orientation of the macromolecular chains and resulted in extensive fibrillation and void formation. It was found that the blend composition has some influence on the structure of discontinuously highly drawn fibers. With increasing the content of the molding‐grade polymer in the blend, the size of crystalline and amorphous domains, density and crystallinity, as well as amorphous orientation decreased. Relationship has been established between the mechanical properties, crystallinity, and orientation of PP fibers. It was confirmed that by blending the fiber‐grade CR‐polymer by a small percentage of the molding‐grade polymer, maximization of elastic modulus is achieved, mainly because of higher orientation of amorphous domains. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1067–1082, 2006     

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     

Properties of syndiotactic-rich poly(vinyl alcohol) thin film in water. VII. Elastic behavior of swollen film in water through heating/cooling or cooling/heating cycles

The thermoelastic behavior for highly swollen films of syndiotactic-rich poly(vinyl alcohol) (s-PVA) was ascertained under loads in water through heating/cooling or cooling/heating cycles (in the range of 25–70°C). The s-PVA films kept at the high temperature of 70°C behaved as a perfect elastomer through the cooling/heating cycle and had very low Young's modulus, 2–3.5 × 10⁶ dyn/cm². When highly swollen s-PVA films were kept at lower temperatures below about 50°C for a long time, microcrystals were formed or propagated in the s-PVA films and plastic deformation occurred in addition to elastic deformation through heating process. The microcrystalline growth and propagation at lower temperatures were supported by an increase in Young's modulus and a decrease in the molecular weight between junctions.     

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     

Ultradrawing of blend films of ethylene-dimethyl-aminoethyl methacrylate copolymer and ultra-high molecular weight polyethylene prepared by gelation/crystallization from solutions

Copolymer ethylene-dimethyl-aminoethyl methacrylate (EDAM) with 3.9% DAM side groups and ultra-high molecular weight polyethylene (UHMWPE) were blended in decalin solvent. The hot homogenized solution was poured into an aluminum tray to form gels and the decalin was allowed to evaporate from the resultant gels under ambient condition. Surprisingly, the resultant dry blend films could be elongated to more than 200-fold (λ=200) even for the blend film with 90% EDAM content (9/1 composition), although the maximum draw ratio of EDAM homopolymer films was 1.6-fold (λ=1.6). The mechanism of the great drawability was dependent upon the content of EDAM. The drawability for the 9/1 composite films was attributed to large crystal lamellae of UHMWPE ensuring crystal transition from a folded to a fibrous type. Accordingly, EDAM chains were independent of ultradrawing of UHMWPE and kept a random orientation under ultra-drawing process. The storage (Young's) modulus was 10 GPa at 20 °C. In contrast, EDAM chains within the 1/1 composite films were oriented drastically together with UHMWPE crystallites. The modulus of the 1/1 composition at 20 °C reached 68 GPa, which was higher than the value (40 GPa) of polypropylene films with λ=100. Such considerable difference of modulus due to EDAM content was analyzed in relation to the gelation/crystallization from solutions.     

Water stability of syndiotactic poly(vinyl alcohol)/iodine complex film

The desorption behavior of iodine in syndiotactic poly(vinyl alcohol) (s-PVA) with a syndiotactic diad content of 63.1% iodine film in water was investigated in relation to the solubility of s-PVA in water. Despite a low number-average degree of polymerization of 900, the degree of solubility of s-PVA film in water at 80°C was limited to about 10%, whereas atactic poly(vinyl alcohol) (a-PVA) film was completely soluble at a lower temperature, 50°C. The degree of iodine desorption of s-PVA/iodine film at a high temperature decreased remarkably compared with that of a-PVA/iodine film. The fastness of iodine of the drawn s-PVA/iodine film was far superior to that of the undrawn film. Over a draw ratio of 5, the iodine desorption was suppressed significantly with increasing drawing temperature rather than the draw ratio. In addition, the iodine desorption of postdrawn s-PVA/iodine film was lower than that of predrawn s-PVA/iodine film. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 108–113, 2001     

Modification of gel-drawn poly(vinyl alcohol) fibers with formaldehyde

Poly(vinyl alcohol) fibers which were drawn from dried gels were chemically treated with formaldehyde to induce crosslinking in the amorphous phase. The room temperature storage modulus decreased early in the treatment, to an almost constant value of 50–60% of the initial modulus of the fiber. This behavior was independent of the concentration of formaldehyde used. The modulus at low temperature was also reduced, and no T_g peak could be seen in heavily treated fibers. The modulus above the original T_g, 70°C, was much less affected. The crystallinity determined by DSC fell by one third as the room temperature modulus decreased, and X-ray diffraction indicated a reduction in the crystal length along the chain direction at the same time. Thus, under the conditions of treatment used, the loss of properties due to destruction of crystals outweighs the stiffening and reduced water sensitivity of the crosslinked amorphous phase.     

Fabrication of oriented electrospun cellulose nanocrystals–polystyrene composite fibers on a rotating drum

Nitrobenzene (CNC-1), trifluoromethyl benzene (CNC-2) modified and polystyrene-grafted (CNC-g) cellulose nanocrystals in polystyrene (PS)-N,N dimethylformamide (DMF) solutions were electrospun and collected as stretched and aligned fibers on a rotating drum. Scanning electron microscope pictures showed significant alignment in the case of unmodified and nitrobenzene-modified CNC-1/PS nanocomposite fibers once the linear speed of rotor reached to 15 m s⁻¹. Fiber diameter decrease was more strong with rotor speed increase in the case of trifluoromethyl benzene modified (CNC-2) and polystyrene-grafted (CNC-g) cellulose nanocrystals/PS systems. Dynamic mechanical analysis including storage and elastic modulus of electrospun-oriented fibers were performed on surface-modified and polymer-grafted CNC/PS samples. According to α transition peak, the increase in the glass-transition temperature with filler concentration was the highest in polymer-grafted CNC-g/PS composite fibers. It was due to the interpenetration of grafted polymer brushes and free polymer chains in continuous phase and resulted in restrictions of motions of polymer chains in the PS matrix. The elastic moduli of nitrobenzene (CNC-1) and trifluoromethyl benzene (CNC-2)-modified CNC-filled PS composite fibers agreed well with percolation model, which indicates the CNC–CNC interactions and network formation with an increase in concentration. Magnitude of the elastic modulus of polymer grafted CNC-g at 0.33 vol % in PS was significantly higher than the prediction from percolation theory. It was due the immobilized polymer chains around CNC-g particles. However, grafted polymer chains, at higher CNC concentrations acted like stickers among CNC particles and caused CNC agglomerates with entrapped free polystyrene from the matrix, thus caused a decrease in the elastic modulus. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48942.     

Physicochemical evaluation of nanocomposite hydrogels with covalently incorporated poly(vinyl alcohol) functionalized graphene oxide

To avoid the negative effect of graphene oxide (GO) nanosheets aggregation in aqueous solutions on physicochemical properties of GO incorporated nanocomposite hydrogels, poly(vinyl alcohol)-functionalized GO (GO-es-PVA) are synthesized and are used for preparation of nanocomposite hydrogels. By graft copolymerization of GO-es-PVA with poly(AA-co-AAm) chains, the nanocomposite hydrogel samples with covalently incorporated GO-es-PVA are achieved. FTIR spectroscopy, XRD analysis, and SEM and EDAX techniques confirm successful synthesis process. It is clear that GO-es-PVA content has significant effect on physicochemical properties of nanocomposite hydrogels, such as improvement of the water uptake properties, porosity, and gel strength. The hydrogel sample with 1:80 mass ratio of GO-es-PVA/AAm has the best physicochemical properties due to the optimum amount of GO-es-PVA, which gives the hydrogel proper viscoelasticity as well as fine porosity and water uptake rate. Interpenetration of PVA chains into the polymeric networks makes the movement of the polymer chains easier, which leads to softer polymeric networks. This phenomenon is called plasticizing effect. The plasticizing nature of PVA and its high hydrophilicity are the main reasons for the fine physicochemical properties. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48025.     

Gelation of poly(vinyl alcohol) solutions at low temperatures (20 to −78°C) and properties of gels

The flow points of atactic poly(vinyl alcohol) (a-PVA) gels with H₂O/dimethyl sulfoxide (DMSO) = 90/10 (v/v) chilled at 20 to ?78°C for 24 h depended on the chilling temperature and were 0–30°C for gels with the initial polymer concentrations (C_i) of 2–5 g/dL, whereas those for H₂O/DMSO = 50/50 chilled at 0 to ?78°C were independent of the chilling temperature and were 70–75°C. Syneresis occurred after eight cycles of freezing (?24°C) and thawing (20°C) for a-PVA hydrogels at concentrations above C_i = 4 g/dL and two such cycles for syndiotacticity-rich PVA (s-PVA) hydrogels at concentrations above C_i = 1 g/dL. The extent of syneresis per one cycle for s-PVA hydrogels was higher than that for a-PVA hydrogels at the initial cycles. In the a-PVA hydrogels with an initial polymer concentration of ca. 30 g/dL, syneresis was expected not to occur even after 20 cycles. If all the free water in the gels is assumed to have transuded by syneresis after 20 cycles, the residual water is bound water and is estimated to be six water molecules per one vinyl alcohol monomer unit. © 1994 John Wiley & Sons, Inc.     

Ultra-high modulus isotactic polypropylene. I. The influence of orientation drawing and initial morphology on the structure and properties of oriented samples

The influence of a number of factors (temperature–speed regime and the quantity of draw stages, molecular weight of a polymer, etc.) on the deformability of initial isotropic IPP and on mechanical characteristics of highly-oriented samples, obtained in the process of a two-stages isothermal orientation drawing, was studied. It was shown that the maximum achievable values of elastic modulus and draw ratio depended not only on the molecular weight of a polymer and the sizes of spherulites, constituting initial IPP, but on the structural organization of inner-and interspherulite regions. Upon physical aging of initial isotropic films, irreversible structural changes take place, which result in the formation of microvoids while being drawn and in the reduction of mechanical properties of obtained material. An extremal dependence of elastic modulus and draw ratio of maximum drawn IPP samples on draw speed was discovered. A structural model, which is supposed to possesstie molecules with various degrees of tautness in amorphous layers, was proposed. Higher effectiveness of two-stage drawing in comparison with one-stage drawing was established. The optimum temperature–speed regime of orientation drawing, which permits the reception of highly oriented, ultra-high modulus IPP with maximum high mechanical characteristics (elastic modulus ～ 30–35 GPa and tensile strength ～ 1,1 GPa), was determined.     

Melting,regelling, and remelting of poly(vinyl alcohol) hydrogels

The melting behaviors of hydrogels of syndiotacticity-rich poly(vinyl alcohol) (s-PVA), derived from vinyl trifluoroacetate, during heating at various rates of rising temperature were examined. For the hydrogels with the polymer concentrations above 5 g/dL chilled at the temperatures of 0 ∼ 40°C, the melting temperature increased with a decrease in the rate of rising temperature. During rising temperature at lower rates, the phase separation with spinodal decomposition progressed even in gels and the microcrystals, which play an important role as the junction points, propagated to thermally more stable size. The small, broad exothermic peaks during rising temperature of s-PVA hydrogels in DSC thermograms was found at the temperature ranges of 10 ∼ 30 and 45 ∼ 60°C. © 1996 John Wiley & Sons, Inc.     

Reversible gelation of acrylonitrile–vinyl acetate copolymer solutions. II. Mechanical properties

Concentrated solutions of acrylonitrile polymers exhibit reversible gelation. The rate of gelation at 25°C. was determined for various solutions of an acrylonitrile copolymer containing 7.7% vinyl acetate in mixtures of dimethylacetamide (solvent) and water (nonsolvent) by measuring the shear modulus of the forming gel as a function of time. The mechanical properties were also measured on a series of gels formed by cooling solutions to ?78°C. It was found that both the rate of gelation at 25°C. and the modulus of gels formed at ?78°C. increase very rapidly as either the solids level of the solution of the water content of the solvent is increased. The gelation rate data wree correlated with the gel melting points of the gels. The results are discussed and compared with the analogous but limited data available for other systems.     

Crystallization and orientation behaviors in isotactic polystyrene and poly(2,6-dimethylphenylene oxide) blends

The crystallization and orientation behavior in the miscible iPS/PPO blends were studied aiming at producing oriented materials consisting of iPS crystals and amorphous PPO chains. Oriented films of iPS/PPO blends were prepared by drawing the melt-quenched blend films. The films were heat-treated under constraint at the drawing temperature so as to crystallize the molecular chains of iPS in the oriented state. The crystallinity and the crystal orientation in the drawn annealed films were studied by the wide-angle X-ray diffraction (WAXD), and the orientation behaviors of molecular chains were analyzed by polarized FTIR spectroscopy. WAXD diagrams show the presence of the highly oriented crystalline structure of iPS in the drawn annealed films of pure iPS and iPS/PPO=7/3 blend. The polarized FTIR spectra of drawn annealed films suggest that the molecular orientation of the amorphous chains of PPO and iPS is markedly relaxed by the heat treatment, although the orientation of iPS with 3₁ helical structure was retained during the oriented crystallization. It was concluded that the drawn annealed samples of the iPS/PPO=7/3 blend consist of highly oriented iPS crystals and nearly isotropic amorphous materials. The mechanical properties of the oriented iPS/PPO blends were measured not only in the stretching direction but also perpendicular to the stretching direction. It was shown that the ultimate strength in the perpendicular direction is 4-5 times higher in the drawn annealed film of iPS/PPO=7/3 blend than in the drawn annealed iPS. The improvement in the vertical strength in the blend is discussed in relation to the structural characteristics of the iPS/PPO blend.     

Thermal conductivity of ramie fiber drawn in water in low temperature

To understand the effect of extension of molecular chain in amorphous region in polymer fibers to thermal conductivity, the thermal conductivity, tensile modulus and crystal orientation angle of ramie fibers and those drawn by the stress of 17.4 kg/mm² (water treatment) in the water were investigated. The tensile modulus of ramie fiber in fiber direction increased from 61 to 130 GPa by drawing in the water. The crystal orientation angles of ramie fiber with and without water treatment were measured by X‐ray diffraction. The orientation degrees of ramie fibers without and with water treatment were estimated as 92.9 and 93.6%, respectively. Therefore, the tensile modulus increases two times as that of blank ramie by water treatment although crystal orientation angle does not change distinctly. The increasing of tensile modulus of ramie fiber by water treatment was explained by extension of the molecular chains in the amorphous region. Thermal conductivities of ramie fibers with and without water treatment were measured in the fiber direction in the temperature range from 10 to 150 K. Thermal conductivity of ramie fiber in the fiber direction increased by water treatment. The increasing ratio of thermal conductivity by water treatment agreed to that of sound velocity induced by increasing tensile modulus. Those results suggest that thermal conductivity of polymer fiber increase by the extension of molecular chains in the amorphous region. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2196–2202, 2006     

Blends containing liquid crystalline polymers: Preparation and properties of melt-drawn fibers,unidirectional prepregs,and composite laminates

This paper discusses the effect of melt drawing on the mechanical properties and morphology of liquid crystalline polymer (LCP) and thermoplastic polymer blends. Extruded fibers and films of LCP/polymer blends were melt drawn to develop uniaxial orientation of the dispersed LCP phase. The longitudinal modulus increased with increasing draw. The increase in modulus was due to higher aspect ratio of the LCP fibrils and improved molecular orientation of the LCP chains within the fibrils. Laminated composites were prepared using the extruded sheets as prepregs. The mechanical properties and the coefficient of thermal expansion (CTE) of the prepreg and the laminates agreed well with predictions from conventional composite lamination theories.