共查询到20条相似文献,搜索用时 15 毫秒
1.
Wenwei Zhao Yukio Yamamoto Seiichi Tagawa 《Journal of polymer science. Part A, Polymer chemistry》1998,36(17):3089-3095
Radiation effects on the formation of conjugated double bonds in the thermal degradation of poly(vinyl chloride) (PVC) and poly(vinyl alcohol) (PVA) were investigated. Thin films of PVC and PVA were either irradiated with γ-rays at ambient temperature (pre-irradiation) and then subjected to thermal treatment, or irradiated at elevated temperatures (in situ irradiation). An extensive enhancement of the thermal degradation was observed for the pre-irradiation of the PVC films, which was more effective than the effect of the in situ irradiation at the same absorption dose. For the PVA degradation, however, the effect of the in situ irradiation was larger than that of the pre-irradiation. The results were explained and related mechanisms were discussed based on radiation-induced chemical reactions and their individual contributions to the thermal degradation behaviors of the two polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3089–3095, 1998 相似文献
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We show that the mechanical properties of nano-sized electrospun poly(vinyl alcohol) fibers can be modified using broad-energy ion beam implantation. The elastic moduli were determined using atomic force microscopy multi-point mechanical bending tests on individual fibers before and after treatment. With a dose of 8.0 × 1015 ions/cm2 of nitrogen ion we observed 30% increases in fiber elastic modulus with a simultaneous fiber diameter reduction. Two additional doses of nitrogen ion as well as a 8.0 × 1015 ions/cm2 of helium ion treatment showed that this stiffness improvement effect was dependent on ion dosage and ion species. The surface morphological features of the fiber mat were shown to be unaltered due to the ion beam treatment. Key chemical modifications via nitrogen ion treatment were the introduction of the functional groups amine and amide. These groups are important in promoting cell compatibility on polymer surfaces. 相似文献
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To improve the drawability of poly(vinyl alcohol) (PVA) thermal products, poly(ethylene oxide) (PEO), a special resin with good flexibility, excellent lubricity, and compatibility with many resins, was applied, and the Fourier transform infrared spectroscopy, dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and wide‐angle X‐ray diffraction (WXRD) were adopted to study the hydrogen bonds, water states, thermal properties, crystal structure, and nonisothermal crystallization of modified PVA. It was found that PEO formed strong hydrogen bonds with water and PVA, thus weakened the intra‐ and inter‐hydrogen bonds of PVA, changed the aggregation states of PVA chains, and decreased its melting point and crystallinity. Moreover, the interactions among PVA, water, and PEO retarded the water evaporation and made more water remain in the system to plasticize PVA. The existence of PEO also slowed down the melt crystallization process of PVA, however, increased the nucleation points of system, thus made more and smaller spherulites formed. The weakened crystallization capability of PVA and the lubrication of PEO made PVA chains to have more mobility under the outside force and obtain high mechanical properties. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1946–1954, 2010 相似文献
5.
Influence of electron beam irradiation on physicochemical properties of poly(trimethylene carbonate)
Joanna JozwiakowskaRadoslaw A. Wach Bozena RokitaPiotr Ulanski Sameer P. NalawadeDirk W. Grijpma Jan FeijenJanusz M. Rosiak 《Polymer Degradation and Stability》2011,96(8):1430-1437
Electron beam (EB) irradiation of poly(trimethylene carbonate) (PTMC), an amorphous, biodegradable polymer used in the field of biomaterials, results in predominant cross-linking and finally in the formation of gel fraction, thus enabling modification of physicochemical properties of this material without significant changes in its chemical structure. PTMC films (Mw: 167-553 kg mol−1) were irradiated with different doses using an electron accelerator. Irradiation with a standard sterilization dose of 25 kGy caused neither significant changes in the chemical composition of the polymer nor significant deterioration of its mechanical properties. Changes in viscosity-, number-, weight-, and z-average molecular weights of PTMC for doses lower than the gelation dose (Dg) as well as gel-sol analysis and swelling tests for doses above Dg indicate domination of cross-linking over degradation. EB irradiation can be considered as an effective tool for increasing the average molecular weight of PTMC and sterilization of PTMC-based biomaterials. 相似文献
6.
Carlos M. Nunez Anthony L. Andrady Rong K. Guo Jesse N. Baskir David R. Morgan 《Journal of polymer science. Part A, Polymer chemistry》1998,36(12):2111-2117
Hybrid blends of poly(amidoamine) PAMAM dendrimers with two linear high polymers, poly(vinyl chloride), PVC, and poly(vinyl acetate), PVAc, are reported. The interaction between the blend components was studied using dynamic mechanical analysis, xenon nuclear magnetic resonance (NMR) spectroscopy, and tensile property measurements. The data suggest a much higher degree of interaction between components of PVAc-containing blends compared to those containing PVC. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2111–2117, 1998 相似文献
7.
M. van Gurp G. van Ginkel Y. K. Levine 《Journal of Polymer Science.Polymer Physics》1988,26(8):1613-1625
The symmetry of the orientational distribution function of dye molecules in stretched PVA films is studied using polarized fluorescence. The different symmetries are monitored by a simple experimental technique in which angle-resolved fluorescence depolarization ratios are measured. A uniaxial distribution of rhodamine 6G molecules is obtained on stretching the film at temperatures above 60°C. In contrast a biaxial distribution of trypaflavine molecules is found for stretch temperatures in the 50–115°C range. It is suggested that the hydrogen bonding between the PVA chains, and between the dye molecules and the PVA chains, influences the symmetry of the distribution upon stretching. 相似文献
8.
M.I. Abdullin R.F. Gataullin K.S. Minsker A.A. Kefelil S.D. Razumovskii G.E. Zaikov 《European Polymer Journal》1978,14(10):811-816
The influence of ozone on the kinetics and mechanisms of poly(vinyl chloride) degradation has been studied. The rate constants for reaction of ozone with saturated and unsaturated units of macromolecules have been measured. The products of the reaction of ozone with double bonds are inactive and do not influence the subsequent thermal dehydrochlorination of the polymer. The products of reaction of ozone with saturated units greatly increase dehydrochlorination. 相似文献
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Kunio Nakamura 《Journal of Polymer Science.Polymer Physics》1975,13(1):137-149
The complex compliance in extension of gels of poly(vinyl chloride) (PVC) in di(2-ethylhexyl) phthalate (DOP) and in tricresyl phosphate (TCP) was measured over the frequency range from 0.6 to 0.006 cps and the temperature range from ?66 to 65°C: the weight fractions of DOP and TCP in the gels were 0.32, 0.40, 0.49, and 0.59. Measurements were carried out in an apparatus using forced low-frequency longitudinal osillations. Data for the gels could not be combined by the method of reduced variables, since there were gradual changes with decreasing temperature, attributable to an increase in crystallinity. Application of the reduction method of Ninomiya and Ferry for solutions of crystalline polymers was found to be successful. The apparent melting temperatures (T′m) were obtained from the temperature dependence of the vertical shift factors. An apparent heat of fusion of ca. 120 cal/mole of monomer unit was found. This melting range was in agreement with that of secondary crystallinity in plasticized PVC reported in calorimetric studies by Juijn. With decreasing temperature, two phenomena occurred in the temperature range from Tg + ca. 80°C to Tg: the vitrification of a concentrated amorphous solution and the slight crystallization of the polymeric component. The larger the difference between Tg and T′m the broader the primary dispersion zone on the frequency scale. This broadening effect was explained as due to the difference in dependence of Tg and T′m on plasticizer concentration, without any need to consider any specific interaction between plasticizer and PVC. 相似文献
11.
Kunio Mori Yoshiro Nakamura 《Journal of polymer science. Part A, Polymer chemistry》1971,9(3):639-650
PVC was crosslinked by immersing PVC–dithiol blends in ethylenediamine at 30°C. Properties of the products depended on the chain length and chemical structure of the crosslinkage and on the molecular weight of the polymer chain between crosslinks Mc. Crosslinking by the agent of soft structure and long molecular chain resulted in high tensile strength at break and impact strength and low brittle temperature. The use of the crosslinking agent of short molecular chain gave high yield strength, Young's modulus, and heat distortion temperature. The relation of Mc and the chemical structure of the crosslinks to the properties of the crosslinked rigid polymer was discussed in regard to the crosslinking effect and plasticizing effect. 相似文献
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《International Journal of Radiation Applications and Instrumentation. Part C. Radiation Physics and Chemistry》1989,33(5):461-464
Effects of electron beam (EB) irradiation on poly(butylene adipate)diol (PBAD) were studied by means of GPC, DSC, and X-ray diffractometry. Below 5 Mrad, chain scission predominantly occurs, while above 10 Mrad, crosslinking and chain scission take place in parallel. Structure of EB-irradiated PBAD is mainly characterized by the main reactions, degradation and crosslinking. Crystallinity of PBAD increased by EB irradiation. This phenomenon was explained by reorganization due to high molecular mobility of EB-irradiated PBAD. But, increment of crystallinity decreased with increasing dose because of formation of crosslinking, excessive degradation and thermal effect of EB. As the result, the crystallinity of EB-irradiated PBAD with a high dose becomes lower than that of original PBAD by thermal treatment. 相似文献
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Tsutomu Nakagawa Makoto Okawara 《Journal of polymer science. Part A, Polymer chemistry》1968,6(7):1795-1807
Retardation of discoloration of poly(vinyl chloride) with diimide was studied in dimethylformamide at 130°C. with the use of p-toluenesulfonylhydrazide (PSH) as a source of diimide. A process was proposed that involved prolonging the induction periods of discoloration by inhibiting the development of conjugated polyene structure. The optimum proportion of PSH was one fourth of the poly(vinyl chloride), the best results. Furthermore, poly(vinyl chloride) discolored by thermal degradation in o-dichlorobenzene or gamma-ray irradiation under vacuum was decolorized in solution at 130°C. by addition of PSH. The decolorized poly(vinyl chloride) thus obtained was thermally stable compared with that obtained by oxidative methods. 相似文献
16.
Ione Cendoya Daniel Lpez Angel Alegría Carmen Mijangos 《Journal of Polymer Science.Polymer Physics》2001,39(17):1968-1975
In this article we report on the investigation of the dynamics of poly(vinyl alcohol) (PVA) and PVA‐based composite films by means of dielectric spectroscopy and dynamic mechanical thermal analysis. Once the characterization of pure PVA was done, we studied the effect of a nanostructured magnetic filler (nanosized CoFe2O4 particles homogeneously dispersed within a sulfonated polystyrene matrix) on the dynamics of PVA. Our results suggest that the α‐relaxation process, corresponding to the glass transition of PVA, is affected by the filler. The glass‐transition temperature of PVA increases with filler content up to compositions of around 10 wt %, probably as a result of polymer–filler interactions that reduce the polymer chain mobility. For filler contents higher than 10 wt %, the glass‐transition temperature of PVA decreases as a result of the absorption of water that causes a plasticizing effect. The β‐ and γ‐relaxation processes of PVA are not affected by the filler as stated from both dynamic mechanical thermal analysis and dielectric spectroscopy. Nevertheless, both relaxation processes are greatly affected by the moisture content. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1968–1975, 2001 相似文献
17.
M.H. Casimiro A.G. Silva J.V. Pinto A.M. Ramos J. Vital L.M. Ferreira 《Radiation Physics and Chemistry》2012,81(9):1314-1318
Polymeric catalytic membranes bearing sulfonic acid functions have been prepared by mutual gamma irradiation at a 60Co source, of poly(vinyl alcohol) (PVA) membranes and methanesulfonic acid. The effect of various synthesis conditions on membranes' physical–chemical properties and catalytic activity in the esterification reaction between acetic acid and isoamyl alcohol to obtain isoamyl acetate (banana flavor), was evaluated. The membranes were characterized by ATR-FTIR, TPP, AFM and SEM. Water contact angle determinations were also performed. The obtained results showed that within the range of conditions studied the increase in sulfonic acid groups' content is accompanied by an enhancement in the membranes catalytic activity, while the increase in absorbed dose leads to a decrease in catalytic activity. 相似文献
18.
The optical and mechanical properties of poly(vinyl chloride) film were examined by observing both the stress and birefringence during stretching at constant rate, during relaxation at constant length and during a dynamic birefringence experiment. Experiments were also done by varying the temperature at constant length. The changes in birefringence are interpreted in terms of changes in negative distortional birefringence, changes in positive orientation birefringence, and possible reversible changes in birefringence with temperature arising from conformational changes in the polymer chain and changes in the contribution of birefringent crystals. 相似文献
19.
《European Polymer Journal》1987,23(5):361-365
The thermal properties of the poly(vinyl alcohol) pseudo-gel obtained by freezing have been investigated by differential scanning calorimetry in the temperature range 200–390 K. Determination of the enthalpies of melting and crystallization of the water contained within pseudo-gel allowed the classification of three different states of water viz. non-freezing, restrained and free water. It was also demonstrated by thermogravimetry that the water of pseudo-gel evaporated in three steps in the temperature range 340–420 K. The amount of non-freezing water was found to be constant, while those of restrained and free water were shown to depend on the thermal histories produced during the freezing. The size of ice crystals which formed in the gel was affected by the rate of freezing and it necessarily controlled the number of pseudo-crosslinks formed between poly(vinyl alcohol) molecules. A good relationship was observed between the amount of restrained water and the thermal stability of the gel. 相似文献