聚乙烯－葡萄糖氧化酶膜的制备和性能研究

聚乙烯－葡萄糖氧化酶膜的制备和性能研究朱如瑾，殷弘浩，刘永盛，黄家湛（成都高分子材料国家重点实验室成都科技大学高分子研究所成都６１００６５）关键词聚乙烯，等离子体，固定化酶，葡萄糖氧化酶固定化酶是６０年代发展起来的生物工程技术Ｉ‘］．酶的固定化方法主...     

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Monomer dependence of radiation graft polymerization. V. Poly(ethylene-g-4-vinylpyridine)

The radiation-initiated graft polymerization of 4-vinylpyridine to high-density polyethylene has been studied under diffusion-free conditions by the mutual irradiation technique. The reaction rate is 1/2 order in radiation intensity over the range 0.00076–0.011 Mrad/hr. The reaction rate is first order in monomer at 0.00076 Mrad/hr, over the complete range of monomer concentrations; at 0.021 Mrad/hr, up to 60 vol % monomer; and at 0.21 Mrad/hr, up to 50 vol % monomer.     

Graft polymerization of arcylamide onto LLDPE film by electron beam pre-irradiation in air or argon. I. Influence of dose,grafting temperature,and monomer concentration

Linear low density polyethylene (LLDPE) film was irradiated by electron beam in air or argon prior to grafting in aqueous solutions of acrylamide containing 0.05% of Mohr's salt. The grafting kinetics was studied with pre-irradiation doses in the range of 2.5–25 Mrad and in the temperature range of 40–70°C. Grafting rates and final degrees of grafting were higher for LLDPE pre-irradiated in air than for LLDPE pre-irradiated in argon. The overall activation energies for the grafting reaction were dose-dependent. Above 5 Mrad, the overall activation energies were higher for LLDPE pre-irradiated in argon which is interpreted as being due to crosslinking of the LLDPE. © 1995 John Wiley & Sons, Inc.     

Surface studies of ultra‐high molecular weight polyethylene irradiated with high‐energy pulsed electron beams in air

Ultra‐high molecular weight polyethylene (UHMWPE) was irradiated in air with high‐energy (9 MeV), pulsed electron beams to doses ranging from 2.5 to 100 Mrad and subsequently heat treated at 120°C for a time period of 120 min. Surface characterization of the target side of irradiated UHMWPE samples was carried out both before and after the heat treatment by means of attenuated total reflection Fourier‐transform infrared (FTIR/ATR) spectroscopy and microhardness measurement. The obtained results provided further evidence supporting our earlier observation (Tretinnikov, O. N.; Ogata, S.; Ikada, Y. Polymer 1998, 39, 6115) that thermal decomposition of hydroperoxides formed upon irradiation of UHMWPE with high‐energy, pulsed electron beams in air leads to surface crosslinking, and the subsequent surface hardening of the irradiated polymer. Importantly, we found that this phenomenon has the highest contribution to the surface hardness enhancement of the polymer when the radiation dose is in the range of 10–30 Mrad. In addition, we found that this irradiation and subsequent heat treatment of UHMWPE in air does not lead to formation of carbonyl‐containing products unless the radiation dose exceeds 20 Mrad. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1503–1512, 1999     

Starch and amylose degradation by 60Co γ-irradiation

The effects of γ-irradiation (0.02–4.0 Mrad absorbed dose and 1.2 Mrad/hr dose rate) on depolymerization and selected physical properties of corn starch and amylose (both dry solid and solution forms) were investigated under conditions used to make graft polymers. Radiation introduces an alkali-sensitive structure, most likely β-alkoxycarbonyl, having a G value of 2.8. A dimethyl sulfoxide (DMSO)-acetic acid-water solvent for intrinsic viscosity was developed that degraded irradiated amylose less than did aqueous 90% DMSO. The G (scission) value of 1.3 for solid amylose irradiated at 0°C under nitrogen is lower than most literature values for either amylose or other polysaccharides. The protection of amylose against irradiation degradation in water by additions of DMSO is noteworthy. The G (scission) for amylose irradiated in 99.8% DMSO is 2.3; whereas, in water it is 30.     

γ-irradiation of polypropylene in vacuum and in air

Polypropylene films were irradiated with ⁶⁰Co γ-rays in vacuum or in air and stored in air. Just after irradiation, the concentration of carbonyl group of the sample irradiated in air only increased with dose. The concentrations of both samples increased with storage time. The more the absorbed doses, the higher the increasing rates. The increasing rate of the concentration of carbonyl group during irradiation in air was higher than those during storage in air. Just after irradiation, the tensile strengths and the elongations of the both samples somewhat increased with dose at the doses less than 5 Mrad, but decreased at doses more than 13 Mrad. The tensile strength and the elongation of the sample irradiated in air decreased with storage time. Those of the sample irradiated in vacuum also decreased with storage time but the decreasing rates were much smaller than those in the sample irradiated in air. The gel fractions of the samples irradiated in vacuum and annealed in vacuum were somewhat higher than those irradiated in vacuum and not annealed. To elucidate high oxidation rate in the sample irradiated in air during and after irradiation, reaction mechanisms were discussed. To clarify the difference of mechanical properties between the samples irradiated in vacuum and in air, the effect of crosslink was considered, together with the oxidation.     

Effect of gamma-irradiation on the acidic properties of Na-Y zeolites

Na-Y zeolite samples were subjected to different doses of γ-irradiation ranging between (10–160 Mrad). The effect of this treatment on the surface acidity was investigated via temperature programmed desorption (TPD) of pyridine and ammonia.The results obtained revealed that γ-irradiation brought about a considerable decrease in the concentration of acidic sites to an extent proportional to the dose employed up to 80 Mrad. A dose as high as 160 Mrad was sufficient to expell completely the labile and moderately bound acidic centres (Bronsted type). These results have been attributed to the stimulation effect of the departure of structural water brought about by γ-irradiation. However, γ-irradiation was found to exert undetectable effect on the Lewis acidity of the investigated zeolites.     

Effect of Gamma-Radiation on the Molecular-Topological Structure of Polyethylene

The molecular-topological structure of powdered high-density polyethylene (PE) after its compression under an optimized pressure and γ-radiolysis was first analyzed. A semicrystalline structure composed of one amorphous block and three crystalline modifications was formed with different rates and different melting onset temperatures in unirradiated PE and in PE irradiated to a dose of 5.5 Mrad. This structure was retained to 242 Mrad; after such a dose, the amorphous block completely disappeared. The net crystallinity of PE at a dose of 5.5 Mrad reached a minimum value but was close to 100 wt % in the initial state or after irradiation to 242 Mrad.     

Radiation-Induced Grafting of Ethyl Vinyl Ether onto Polyvinyl Chloride)

The radiation-induced graft polymerization of ethyl vinyl ether (EVE) onto polyvinyl chloride) (PVC) was studied under a variety of conditions. Graft copolymer and homopoly(EVE) were formed in all cases. The presence of water reduced overall polymerization rates, percentage grafting, and homopoly(EVE) molecular weights. With “superdry” EVE, grafting reached 29% at a total dose of 6.9 Mrad. Grafting to PVC films was less efficient than grafting to PVC powder. Application of a relatively poor swelling agent for PVC resulted in an increase in the efficiency of grafting. From a comparison of studies of radiation-induced EVE homopolymerization and the present work, it was concluded that dry and superdry EVE are grafted to PVC by a cationic mechanism and wet EVE is grafted mainly by a free-radical mechanism.     

Thermal expansion of irradiated polyethylene from 10 to 340 K

The coefficient of thermal expansion of γ-irradiated polyethylene has been measured from 10 to 340 K by using the three-terminal capacitance technique. The samples are irradiated to 500 Mrad in steps of 100 Mrad in air at room temperature with γ-rays from a Co⁶⁰ source at a dose rate of 0.3 Mrad/h. The crystallinity of the sample is measured by x-ray diffraction. The crystallinity is found to decrease with radiation dose. The thermal expansion coefficient is found to be constant with radiation doses from 10 to 110 K and decreases with doses from 110 to 340 K. © Wiley & Sons, Inc.     

Radiation-induced grafting of hexafluoroacetone to polyethylene

Although hexafluoroacetone is not polymerized by ionizing radiation, it is shown that γ-irradiation of hexafluoroacetone dissolved in polyethylene films produces a graft with a G value of 500 and, therefore, a kinetic chain length of 200. The effects of dose rate (0.021–3.55 Mrad/hr), temperature (21–53°C), and pressure (1.5–6.2 atm) on the graft rates have been measured. Also the effect of temperature (21–53°C) on the postirradiation grafting reaction and on the physical properties of the grafted films have been investigated. Together with solubility, diffusivity, infrared, and EPR data, the results lead to the following mechanism: The first step represents production of secondary alkyl radicals in the polyethylene by irradiation of the polymer–monomer system. The second step involves the linkage of the monomer to the radical site to form the alkoxy radical. Since it cannot add to another monomer unit, this radical abstracts a hydrogen atom from an adjacent polyethylene chain in the third step. Radical R· can then continue the kinetic chain. Radical combination and radical–impurity reactions terminate the chain. The graft may be unique in that it is the only one we have found in which a pendant group containing only one monomer unit is attached by a chain reaction. At dose rates up to 0.215 Mrad/hr, the grafting was linear with time and proportional to the 0.73 power of the dose rate at 21°C and to the 0.81 power at 53°C. The reaction is insensitive to increases in dose rate above 0.215 Mrad/hr where diffusivity measurements show the reaction to be diffusion-controlled. The rate of reaction increased 10% when the temperature was increased from 21 to 53°C. While there was significant postirradiation grafting reaction at 21°C, there was none at 53°C. The results do not fit the equations of reaction-controlled steady-state graft-polymerization kinetics. The deviations arise from an observed increase in monomer solubility in the film with increasing graft combined with low diffusivity of the monomer in polyethylene, and the presence of a radical-scavenging impurity which terminates the kinetic chain with the appearance of a relatively stable radical. EPR data suggests that the impurity is a trace of oxygen which may be produced radiolytically.