Model products were needed to elucidate structure–property relationships in a starch graft polymer research program. Simultaneous irradiation of amylose and acrylamide in oxygen-free, dilute aqueous solutions gave graft polymers with maximum add-on of about 16%. The graft polymers were separated from homopolymer and subfractionated by incremental additions of nonsolvent (methyl or ethyl alcohol) to irradiated aqueous reaction media. The graft polymers were fairly homogeneous in graft content. Effects were determined of ratios of monomer to substrate, dose rate, and total dose on yield, graft content, intrinsic viscosity, and homopolymer characteristics. Under some conditions, crosslinks probably formed between graft side chains. Large differences in solution properties of a synthetic mixture of separately irradiated amylose and acrylamide and an irradiated solution of amylose and acrylamide indicated that grafting had occurred. Further evidence for true grafting was based on the action of a selective precipitant, n-butyl alcohol, on graft polymer solutions. 相似文献
Dielectric properties of various coals and aqueous NaOH solutions were determined to study thermochemical coal desulphurization by microwave irradiation. Aqueous NaOH solutions were used as media for irradiation. The coal samples were placed in a rectangular cavity and irradiated with 2450 MHz microwaves, resulting in 70–80% desulphurization efficiency. 相似文献
Summary The modifications in PET induced by swift heavy ion irradiation are analyzed. PET membrane of 15 μm was irradiated by Cl9+ ions of 100 MeV at TIFR Mumbai. The changes due to exposure to high-energy ions were investigated by Fourier Transform Infrared
(FTIR) and Ultraviolet/ Visible absorption (UV/VIS) spectroscopies, X-Ray diffraction technique, dynamic mechanical analysis
and by the gas permeation. A significant loss of crystallinity is observed by the XRD data. Particle size or grain size calculated
using Scherrer formula indicates measurable change in particle size of irradiated samples. The polymer chain scissions and
structure degradations are expected to occur for irradiated samples. Optical properties of the films were changed due to irradiation
that could be clearly seen in the absorption and FTIR spectra. Gas permeation through these membranes before and after irradiation
using hydrogen and carbon dioxide gases shows that permeability for both gases increased after irradiation but permeability
for hydrogen is higher than carbon dioxide due to its small molecular size. 相似文献
The stability of linear polyacrylamides (PAAM) under thermal and irradiation conditions were investigated. The study showed that PAAm is stable under fluorescent lights and does not release any detectable acrylamide (AAM) in hot aqueous solution at 95 °C. Hydrolysis of side-chain amide groups to acid groups was observed during the thermal aqueous degradation. Under UV irradiation, small levels of released AAm were observed; however they are generally below 50 parts per million repeat monomer units in the polymer. A drop in viscosity is also observed. This indicates that the acrylamide released is due to chain scission, not a unzipping of the polymer chain. Methods of purifying a linear PAAM are also discussed. 相似文献
The reaction of poly(vinyl chloride) containing N-methyl-N-carboxymethyl dithiocarbamate (PSDC) with metal ions in a heterogeneous system and the effects of γ-irradiation on the reactivity were studied. Slurried PSDC has an affinity for a number of metal ions in aqueous solutions. On the basis of analyses for nitrogen and sulfur and on infrared spectra, a possible chelating structure for PSDC was deduced. The gaseous products evolved during the gamma radiolysis of PSDC under vacuum were measured. Although the dithiocarbamate group bonded to the main chain gave some protection against the dehydrochlorination of poly(vinyl chloride) component, a small amount of the carboxymethyl group was decomposed. It was found that with γ-irradiation doses up to 30 Mrad, only about 1 mole-% out of 17.6 mole-% of N-methyl-N-carboxymethyl dithiocarbamate in the polymer was decomposed. It was shown that the reactivity of the irradiated PSDC in water toward metal ions was almost the same as that before irradiation. 相似文献
The effect of polymer density, processing conditions (quenching of annealing), degree of crystallinity, size of crystallite and mobility of polymer chains on the photo-and radiation-induced degradation and the polymer stability have been studied by UV, FTIR spectroscopic, viscosity and mechanical property measurements. Four kinds of annealed or quenched polyethylene (PE) films varying densities were used to the studies. Polystyrene (PSt) films were used to investigate the effect of chain mobility on polymer degradation. The following results were obtained.
1. In linear low density (LLD) PE, greater amounts of crosslinking (irradiated in vacuum) and chain scission (irradiated in air) were noticed than in mediun density (MD) PE and high density (HD) PE samples.
2. Polyene formation is favored in the case of the irradiation in vacuum for LLDPE.
3. Polymer stability evaluated by mechanical property such as elongation at break (%) is superior in LLDPE to MDPE and HDPE for annealed and quenched samples.
4. Segmental motion of polymer chain also affects the polymer stability
The resistivity of insulating materials for electrostatic, ion chamber dosimeters must be very high and must remain so after exposure to ionizing radiation. Low dielectric polarization and good fabrication characteristics make hydrocarbon polymers most suitable, but both the conductivity during irradiation and its decay afterward vary greatly even for the same type of polymer, probably depending on impurities. Amorphous, styrene-based polymers and copolymers polymerized in aqueous emulsion and initiated with K2S2O8 were found to have much more rapid decay of conductivity after irradiation than pure polystyrene or other nonpolar polymers. The synthesis method incorporates sulfate groups on the polymer chain ends and leaves emulsifier residues distributed throughout the polymer as was demonstrated by various analytical procedures. To identify the trapping species a synthesis program was carried out varying selected ingredients in the polymerization recipe. It was found that the postirradiation conductivity was not dependent on the chemical nature of the emulsifier residues. On the other hand, the decay time of conductivity after irradiation did depend on the polar groups incorporated in the polymer chain. It was concluded that effective charge carrier traps were constituted of a polar second phase highly dispersed through the polymer by association with polar groups incorporated on the polymer chain. 相似文献
The large dosage irradiation effect on polyethylene in air was examined by the method of double irradition. Polyethylene was first irradiated with γ-rays to a dosage of a few hundred Mrad in air at 298°K. The formed radicals were destroyed, and the polymer, changed chemically and morphologically, was irradiated again in vacuo at 77°K with a dose of 12.7 Mrad. The thermal decay of radicals produced in polyethylene by the second irrdiation was investigated. The results were compared with the sample not exposed to the first irradiation. The results were also compared with previous data of polyethylene irradiated in vacuo to a great extent and then treated in the same manner as that in the present experiment. The results show that scission of the polymer chain by oxidation makes the radical decay faster. Simultaneously, crosslinks formed in polyethylene irradiated in air to a great extent slow down the radical decay. Almost the same number of double bonds was formed in polyethylene irradiated in air as in polyethylene irradiated in vacuo. These double bonds react with alkyl radicals to form allyl radicals. 相似文献
Hydroxypropylcellulose (HPC) hydrogel being a material of natural origin, combines the properties of a polymer, which make up the network, with biodegradability. In this report the effects of high energy radiation on the ether of cellulose‐HPC are presented. The polymer irradiated in its solid state or in dilute aqueous solution underwent mainly degradation, induced by the cleavage of glycosidic bonds in its main chain. Irradiation of HPC in aqueous solutions at moderate concentrations resulted in the formation of hydrogels. Chemical cross‐links bond the chains of polymer, turning it to an insoluble macroscopic gel. We have found that in addition to concentration, dosage and dose rate can affect the results of irradiation. Electron beam irradiation gave higher gel fraction, up to 90%, than gamma irradiation, which has a maximum gel fraction of 65%. Swelling of the cross‐linked hydrogels was related to the density of cross‐links and was the highest at low irradiation doses. HPC hydrogels displayed thermally reversible character in their swelling. The volume of gel underwent continuous deswelling with an increase of the solution temperature, with the deswelling rate increasing rapidly over 40°C. At elevated temperatures the hydrogel collapsed, lost its transparency and changed color to translucent white. This transition was fully reversible when the gel was placed in the medium of low temperature. The hydrogel demonstrated superior mechanical properties. Despite of the stable three‐dimensional cross‐linked network, the gels underwent biodegradation under controlled conditions when enzyme was used. 相似文献
Summary: The effect of electron‐beam (EB) irradiation on interfacial adhesion in bioflour (rice‐husk flour, RHF)‐filled poly(propylene) (PP) biocomposites in which either only the RHF had been EB irradiated or the whole biocomposite had been EB irradiated was examined at different EB‐irradiation doses. The tensile strengths of PP–RHF biocomposites with EB‐irradiated RHF and EB‐irradiated PP and PP–RHF biocomposites were slightly higher than those of the nonirradiated samples. The improved interfacial adhesion of PP–RHF biocomposites with EB radiated RHF and the EB‐irradiated PP–RHF biocomposites compared with the nonirradiated samples was confirmed by the morphological characteristics. In addition, the thermal stability of EB‐treated biocomposites was slightly higher than those of nonirradiated samples at the irradiation doses of 2 and 5 Mrad. However, at the high irradiation dose (30 Mrad), the tensile strengths of the biocomposites were slightly decreased by main‐chain scission (degradation) of PP and RHF. Attenuated total reflectance FT‐IR and X‐ray‐photoelectron‐spectroscopy findings confirmed this result by showing that that EB irradiation changed the functional groups of RHF, PP, and the biocomposites and improved the surface characteristics of the biocomposites. The thermal characteristics of the EB‐irradiated PP and biocomposites were investigated using differential scanning calorimetry. From the results, we concluded that use of low‐dose EB radiation increases the interfacial adhesion between matrix polymer and biofiller.
Lexan polycarbonate films were irradiated by UV radiation at wavelength $ \lambda $ = 250 nm under different time exposures of 1, 2, 4, 6 and 7 h. Structural, optical and mechanical modifications were studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), UV–Visible spectroscopy, impedance analysis, tensile testing and rheometry methods. The crystallite size and percentage of crystallinity were found to decrease upon irradiation as was studied by XRD. It indicated that polymer was moving towards more disordered state after irradiation corroborating DSC results. FTIR Study showed the carbonate linkage is the radiation-sensitive linkage and benzene ring does not undergo any change after irradiation. SEM results showed the formation of pores after irradiation. The atomic force microscopy measurements revealed that the average roughness of the film increased after being irradiated. The glass transition temperature was observed to decrease after irradiation as revealed by DSC measurement. UV–Visible spectra showed decrease in optical band gap after irradiation due to chain scission in the Lexan polycarbonate. Plot of AC conductivity versus log (f) displayed a sharp increase in conductivity at higher frequencies and dielectric constant/loss was observed to change with the irradiation time. The mechanical properties and average molecular weight of Lexan polycarbonate decreased after irradiation, while the average number of chain scissions per original polymer molecule increased with increase in time of exposure. 相似文献