Degradation of EPDM and FPM elastomers irradiated at very high dose rates in mixed gamma and neutron fields

Elastomers are widely used in radioactive environments, where ionizing radiations induce a deterioration of their properties due to degradative phenomena occurring in the polymer structure. Their radiation resistance is usually assessed using γ‐rays and relatively low dose rates, but in actual applications, they are often exposed to mixed radiation fields and higher dose rates. Ethylene propylene diene monomer (EPDM) is known for its excellent resistance to γ‐rays but absorbs a larger dose by neutron interactions than fluoroelastomer (FPM). In this work, EPDM and FPM were irradiated in mixed neutron and gamma fields, using high dose rates (from 22 to 700 kGy h^?1) and total absorbed doses between 0.2 and 3.5 MGy. The effects of irradiation were assessed by swelling tests, differential scanning calorimetry analysis and dynamic mechanical thermal analysis, and tensile tests. The results show that, even if irradiations were carried out in air, degradation took place under nonoxidative conditions owing to the high dose rates employed. Under such conditions, crosslinking is the dominant radiation‐induced reaction in both elastomers. Moreover, material degradation seems to be influenced mostly by the total absorbed dose and not by the type of radiation. Contrary to what observed at the lower dose rates employed with γ‐rays, major dose rate effects are not observed. POLYM. ENG. SCI., 59:2522–2532, 2019. © 2019 Society of Plastics Engineers     

Cold Plasma Modification Effects on the Water Flow through Sintered UHMWPE Membranes

Natural rubber latex and various concentration of natural antioxidant were blended in different ratios and irradiated at various absorbed doses by gamma rays from Co-60 source at room temperature. The aqueous extraction of Diospyros peregrina was used as natural antioxidant. It was found that the addition of different concentration of natural antioxidant into natural rubber latex improve the aging property of the film. Decreasing in tensile strength of rubber film with 10 phr natural antioxidant and 15 kGy radiation dose after 24 hours aging at 100°C was 9.34% compared to 13.89% for film without natural antioxidant. The tensile strength, tear resistance and modulus at 500% elongation of the rubber film were found to be optimum at 15 kGy radiation dose and with 10 phr natural antioxidant. Elongation at break, permanent set and swelling ratio decreases with the increasing absorbed radiation dose as well as the concentration of the natural antioxidant.     

Radiation processing of ethylene‐propylene rubber

The effects of ionizing radiation on ethylene‐propylene copolymer were evaluated over the range of total γ doses up to 500 kGy. The influence of the irradiation dose was investigated by oxygen uptake and thermal analysis. Four testing temperatures (170, 180, 190, and 200°C) and two heating rates between 2.9 and 5.9 K/min were selected for oxygen uptake measurements and thermal analysis, respectively. The competition between crosslinking and scission was examined on the basis of kinetic parameters of postirradiation oxidation. The influence of the momentary concentration of hydrocarbon free radicals is discussed in regard to the contribution of the antagonistic processes of crosslinking and oxidative degradation. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 298–303, 2000     

Free radical activity in gamma‐irradiated polyethylene film,drawn tape and ultra‐high‐modulus fibres determined by grafting performance

Grafting rates of gaseous butadiene to a range of morphological forms of gamma‐irradiated polyethylene, including ultra‐high‐modulus fibres (UHMPE), have been measured in order to determine the availability of active free radicals over time at various temperatures. Blank experiments on unirradiated samples showed that monomer diffusion is not rate‐controlling with film and natural draw ratio tapes, but is likely to be a major factor in the control of grafting rates in UHMPE fibres. Grafting rates from monomer loss/time experiments with irradiated samples indicate that grafting is always in competition with free radical self‐annihilation, the extent being influenced by temperature, dose and morphology, including prior sample annealing. At lower temperatures, graft‐active radicals are produced over long periods of time, eg close to linear grafting rates were monitored over 20 hours for PE tape at 0 °C (50 kGy) and for gel‐spun UHMPE at 40 °C (100 kGy). At higher temperatures, grafting rates steadily decrease with time. Grafting rates are almost independent of irradiation dose in the early stages, however, the dose has an increasing positive influence as the reaction proceeds. At any given temperature and irradiation dose, the rates decrease in the series undrawn film; natural draw ratio tape; high draw ratio gel‐spun fibre; high draw ratio melt‐spun fibre. An analogy is drawn between these results and the optimum conditions required for improving the creep properties of PE tape and UHMPE fibres by acetylene‐sensitized irradiation crosslinking. Copyright © 2005 Society of Chemical Industry     

Thermal and mechanical properties of silane‐grafted water crosslinked polyethylene

The effects of linear low density polyethylene (LLDPE) grafting with vinyltrimethoxysilane by different types and contents of peroxide were studied. When grafting silane onto LLDPE, with 0.10 phr of Dicumyl peroxide (DCP) or 0.05 phr content of 2,5‐Dimethyl‐2,5‐di (tert‐butyl‐peroxy)‐hexane (DHBP), it was found that the grafting effect was improved; however, as Di(2‐tert‐butylperoxypropyl ‐(2))‐benzene (DIPP) or excess DHBP was used, LLDPE was supposed to cause self‐crosslinking, which reduced the grafting effect of silane and was invalid in the processing of extrusion. In this study, vinyl trimethoxysilane (VTMS) was grafted onto various polyethylenes (HDPE, LLDPE, and LDPE) using DCP as an initiator in a twin screw extruder. The grafted polyethylenes were able to crosslink utilizing water as the crosslinking agent. The effects of varied crosslinking time on the mechanical properties of the crosslinked polyethylenes were studied. It was found that the HDPE and LLDPE were apt to crosslink during the grafting process and thus decreased the grafting ratio. Multiple melting behavior was observed for crosslinked LDPE and LLDPE. Mechanical and thermal properties of the crosslinked PE are much better than that of uncrosslinked PE. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2383–2391, 2005     

Gamma radiation effect of polymethylvinylphenylsiloxane rubbers under different temperatures

The gamma radiation effect on polymethylvinylphenylsiloxane (PMVPS) rubbers is investigated by irradiation exposure of PMVPS rubbers to a maximum dose of 200 kGy in the temperature range 28–110 °C. Compared with unirradiated PMVPS rubber, the elongation at break of irradiated PMVPS rubber decreases while its elastic modulus increases with the increase of absorbed dose or radiation temperature. DSC, ATR‐FTIR, XPS, and ¹H‐NMR indicate that slight degradation and oxidation reaction occur during the irradiation of PMVPS. Solvent swelling and gel fraction study confirms that the crosslinking density of PMVPS rubbers increases gradually with increasing absorbed dose or radiation temperature. Therefore, radiation‐induced crosslinking of PMVPS is dominant reactions for the chosen dose or temperature range. Furthermore, synergistic effect exists in the high‐temperature radiation process for PMVPS rubbers. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45404.     

Accelerated electron effects on EVA based compound

The major effects induced by accelerated electron irradiation on EVA based polymeric compound were evaluated for various doses up to 240 kGy. Some main characteristics (gel fraction, density, elongation at break, and tensile strength) were investigated. Oxygen uptake and thermal analysis methods (TG, DTG, and DTA) were applied for determination of oxidation resistance of radiation processed EVA samples. It was established that a 30 kGy exposure dose promotes maximum crosslinking. At this dose the density and tensile strength reach maximum values, which are maintained for higher doses up to 240 kGy. On the other hand, the thermooxidative stability exhibits a sharp decrease as the absorbed dose rises from 0 to 30 kGy and has a constant value for the absorbed dose range 30–240 kGy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 613–617, 2005     

Influence of electron beam radiation on mechanical and thermal properties of styrene‐butadiene‐styrene block copolymer

Electron beam crosslinking of elastomers is a special type of crosslinking technique that has gained importance over conventional chemical crosslinking method, because the former process is fast, pollution free, and simple. The technique involves the impingement of high‐energy electrons generated from electron accelerators and the subsequent production of free radicals on target elastomers. These radicals result in crosslinking of elastomers via radical–radical coupling. In the process, some chain scission may also take place. In this work, a high‐vinyl (～ 50%) styrene‐butadiene‐styrene (S‐B‐S) block copolymer was used as the base polymer. An attempt was made to see the effect of electron beam radiation on the mechanical and thermal properties of the block copolymer. Radiation doses were varied from 25 to 300 kGy. Mechanical properties like tensile strength, elongation at break, modulus at different elongations, hardness, tear strength, crosslink density, and crosslink to chain scission of the irradiated samples were studied and compared with those of unirradiated ones. In this S‐B‐S block copolymer, a relatively low‐radiation dose was found effective in improving the level of mechanical properties. Differential scanning calorimeter and dynamic mechanical analyzer were used to study the thermal characteristics of the irradiated polymer. Influence of a stabilizer at different concentrations on the properties of S‐B‐S at varied radiation doses were also focused on. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The structural changes in butyl and halogenated butyl elastomers during gamma irradiation

Ionizing radiation induces various changes in the molecular structure of elastomers; consequently, the macroscopic properties of the irradiated elastomers will be modified. The newly formed products and the alteration of the initial chemical structure are the result of free-radical reactions which provide the crosslinking and/or the depolymerization of the tested materials and destructive simultaneous processes involving diffused aggressive agents. This paper describes the behavior of butyl and chlorinated and brominated butyl elastomers under the action of gamma radiation for total doses up to 0.5 MGy. The experimental data provided by several procedures emphasize a complex chemistry circumstance consisting of the simultaneous crosslinking and scission of the macromolecular chains and consecutive processes involving free radicals. Evaluation of the studied changes was via gel content, oxidation level, unsaturation, and halogen distribution as dependent on the total radiation dose. The mechanism of the degradation and a relationship between the crosslinking/scission ratio and the absorbed dose are discussed. © 1996 John Wiley & Sons, Inc.     

Thermal behavior of gamma‐irradiated amorphous poly (ethylene terephthalate) films

Poly (ethylene terephthalate) (PET) was irradiated in air by gamma rays at dose rate of 28 kGy/h for doses up to 3500 kGy. The influences of gamma irradiation on the glass transition and degree of crystallinity were investigated by differential scanning calorimetry. For amorphous PET, the observed glass transition temperature T_g and step of heat capacity ΔC_p decreased with absorbed dose. These decreases were attributed to a predominant chain scission process. The glass transition temperature may be useful as an indicator of radiation to the PET. The results also showed that such chain scission increases in mobility lead to a greater crystallizability. POLYM. ENG. SCI. 46:1374–1377, 2006. © 2006 Society of Plastics Engineers     

Free radicals in gamma-irradiated polyamide 6 from the point of view of chemical ESR-dating

Polyamide 6 was irradiated with gamma rays in air at room temperature with a radiation dose of 17 kGy. The arising composite spectrum indicates the presence of two types of free radicals. The ratio of spectral lines was measured for the time period of 45 days. As the rate constants of decay of individual types of free radicals are different, the intensity ratio of lines of the composite spectrum significantly changes in the course of decay. It has been pointed out that this temporal dependence of the line ratio can be used for determining the time interval between the radiation impact and the measurement of ESR spectrum. The possibilities of using this information for the purpose of retrospective chronodosimetry are discussed.     

Radiation‐induced grafting of styrene onto poly(tetrafluoroethylene) (PTFE) films. I. Effect of grafting conditions and properties of the grafted films

Radiation‐induced grafting of styrene onto poly(tetrafluoroethylene) (PTFE) films was studied by a simultaneous irradiation technique. Grafting was carried out using γ‐radiation from a ⁶⁰Co source at dose rates of 1.32–15.0 kGy h⁻¹ at room temperature. The effects of type of diluent, dose rate, irradiation dose, and the initial monomer concentration in the grafting solution on the degree of grafting were investigated. The degree of grafting was found to be strongly dependent upon the grafting conditions. The dependence of the initial rate of grafting on the dose rate and the initial monomer concentration in the grafting solution was found to be in the order of 0.6 and 1.7, respectively. The chemical structure and the crystallinity of the grafted PTFE films were studied by means of Fourier‐transform infrared, (FTIR), electron spectroscopy for chemical analysis (ESCA) and X‐ray diffractometry (XRD). © 2000 Society of Chemical Industry     

Features of the Structure and Properties of Radiation Vulcanizates Based on Blends of Polybutadiene and Ethylene‐Propylene Diene Rubber

Polybutadiene rubber (BR) was blended with ethylene‐propylene diene (EPDM) rubber on rubber mill with different weight ratios (100/0‐70/30‐50/50‐30/70‐0‐100), then application of gamma rays at different irradiation doses from 25 up to 150 kGy to induce crosslinking. Mechanical, physio‐chemical, and characterization of prepared blends are to be followed up as functions of the blend composition and the radiation absorbed dose. Mechanical properties like tensile strength (TS), elongation at break (E_b), and tensile modulus (M₁₀₀) were increased with increasing content of EPDM in blend composition. On the other hand, TS and M₁₀₀ increased with radiation dose, whereas the value of E_b decreased with radiation dose. Physico‐chemical properties like gel fraction and volume fraction of rubber in swollen gel (V_r) increased with increasing the content of EPDM rubber in blend formulation while the swelling ratio and soluble fraction decreased with increasing content of EPDM. On the other hand, the V_r increased with radiation dose, whereas the values of soluble fraction and selling ratio (Q) decreased with radiation dose. Fourier transforms‐infrared measurements confirmed the compatibility between BR and EPDM rubber moieties in the blend matrix. J. VINYL ADDIT. TECHNOL., 25:E64–E72, 2019. © 2018 Society of Plastics Engineers     

Radiation‐induced grafting of pentamethyl hindered amine light stabilizer 1,2,2,6,6‐pentamethyl‐4‐piperidinyl methacrylate onto polypropylene

The γ‐radiation‐induced grafting of 1,2,2,6,6‐pentamethyl‐4‐piperidinyl methacrylate (PMPM) onto polypropylene (PP) was investigated with a simultaneous irradiation technique. The effects of the solvent, dose, monomer concentration, and photoinitiator on the grafting were investigated. The grafting was easier in a benzene solution than in chloroform and acetone solutions. The grafting percentage first increased almost linearly with the irradiation dose until 20 kGy and then increased slowly or remained constant. The grafting percentage increased with the monomer concentration until 1.1 mol/L. The grafting percentage was higher when the proper amount of benzophenone was added. The grafted samples were characterized with Fourier transform infrared spectroscopy and thermogravimetric analysis. Carbonyl groups were found on grafted PP samples, and the carbonyl index increased with the grafting percentage. Thermogravimetric analyses proved the existence of grafted materials on PP, and grafted PMPM thermally decomposed at a lower temperature than PP. The radiation resistance of PP with grafted PMPM was better than that of pristine PP. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2157–2164, 2005     

纤维素辐照改性及其应用

辐照技术利用电离辐射诱发物理化学反应(例如交联、聚合、接枝、降解等)对材料进行加工或改性,与常规加工方法相比,具有节能、无环境污染等特点。将辐照技术应用于纤维素改性过程近年已成为非动力核技术应用领域研究的热点之一。本工作对目前纤维素的辐照技术及其基本反应机理进行了概述,其中包括纤维素膜材料、纤维素水凝胶、纤维素微晶/纳米材料,并对纤维素辐照改性过程的辐照环境,包括溶剂、敏化剂、温度、辐照剂量、环境氛围、结晶度等进行了总结。     

Parameters affecting the free‐radical melt grafting of maleic anhydride onto linear low‐density polyethylene in an internal mixer

Our main objective of this study was to study the parameters affecting the free‐radical melt grafting of maleic anhydride (MA) onto linear low‐density polyethylene (LLDPE) with dicumyl peroxide (DCP) in an internal mixer. The degree of grafting (DG) was measured with titrometry and Fourier transform infrared spectroscopy. The extent of chain‐branching/crosslinking was evaluated with gel content and melt flow index measurements. The flow behavior and melt viscoelastic properties of the grafted samples were measured by using rheometric mechanical spectrometry. Feeding order, DCP and MA concentration, reaction temperature, rotor speed, and grade of LLDPE were among parameters studied. The results show that the reactant concentration (MA and DCP) played a major role in the determination of the grafting yield and the extent of the chain‐branching/crosslinking as competitive side reactions. The order of feeding also had an appreciable effect on the DG and the side reactions. Increasing the rotor speed increased the grafting yield and reduced side reactions by means of intensification of the mixing of reactants into the polyethylene (PE) melt. Chain‐branching dominated the side reactions for lower molecular weight PE, whereas for higher molecular weight PE, chain‐branching led to crosslinking and gel formation. The results of the melt viscoelastic measurements on the grafted samples provided great insight into the understanding of the role of influential parameters on the extent of side reactions and resulting changes in the molecular structure of the grafted samples. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 141–149, 2006     

Radiation synthesis of a thermo-pH responsive binary graft copolymer (PP-g-DMAEMA)-g-NIPAAm by a two step method

Summary  (PP-g-DMAEMA)-g-NIPAAm was synthesized using gamma radiation from a ⁶⁰Co source. Graft polymerization of N,N’-dimethylaminoethylmethacrylate (DMAEMA) onto polypropylene (PP) was accomplished in about 100 percent yield by the mutual irradiation technique at a dose of 10 kGy. Grafting of N-isopropylacrylamide (NIPAAm) onto PP-g-DMAEMA was carried out by the pre-irradiation method with doses from 20 to 100 kGy. The influence of temperature, reaction time, and monomer concentration on grafting yield was studied. Grafting processes were confirmed by infrared spectroscopy (FTIR-ATR). (PP-g-DMAEMA)-g-NIPAAm films were characterized by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The lower critical solution temperature (LCST) and critical pH point of the films were obtained by water contact angle and percent swelling measurements. The LCST was also determined by DSC. We report here hare a new binary graft copolymer which shows two LCST values, synthesized in two steps.     

Drug delivery system based on poly(ether‐block‐amide) and acrylic acid for controlled release of vancomycin

Poly(ether‐block‐amide) (PEBA) films were grafted with acrylic acid (AAc) by gamma radiation, using the oxidative pre‐irradiation technique. The effect of dose, monomer concentration, temperature, and reaction time on the graft percentage of AAc onto PEBA was studied. The modified material PEBA‐g‐AAc was characterized by Fourier infrared spectroscopy (FTIR), scanning electron microscopy, and water contact angle. It was found that PEBA films did not suffer degradation at low doses (<30 kGy) during the grafting process. Additionally, PEBA‐g‐AAc was proved as drug delivery system using vancomycin as drug model. The PEBA‐g‐AAc with 39 and 98% of AAc loaded 63 and 98 mg g^?1, respectively. The release profiles showed a sustained delivery by 48 h with a partial retention of drug, which depends of grafting percentage. The microbiological tests showed that PEBA‐g‐AAc was able to inhibit the growing of Staphylococcus aureus in three consecutive challenges. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45745.     

Optimization of Novel Human Acellular Dermal Dressing Sterilization for Routine Use in Clinical Practice

Gamma rays and electrons with kinetic energy up to 10 MeV are routinely used to sterilize biomaterials. To date, the effects of irradiation upon human acellular dermal matrices (hADMs) remain to be fully elucidated. The optimal irradiation dosage remains a critical parameter affecting the final product structure and, by extension, its therapeutic potential. ADM slides were prepared by various digestion methods. The influence of various doses of radiation sterilization using a high-energy electron beam on the structure of collagen, the formation of free radicals and immune responses to non-irradiated (native) and irradiated hADM was investigated. The study of the structure changes was carried out using the following methods: immunohistology, immunoblotting, and electron paramagnetic resonance (EPR) spectroscopy. It was shown that radiation sterilization did not change the architecture and three-dimensional structure of hADM; however, it significantly influenced the degradation of collagen fibers and induced the production of free radicals in a dose-dependent manner. More importantly, the observed effects did not disrupt the therapeutic potential of the new transplants. Therefore, radiation sterilization at a dose of 35kGy can ensure high sterility of the dressing while maintaining its therapeutic potential.     

Development of amidoxime functionalized silica by radiation‐induced grafting

A novel amidoxime‐based silica adsorbent was prepared by using radiation‐induced grafting technique. Grafting of acrylonitrile (AN) on silanized silica that was silanized by vinyltriethoxysilane (VTES) was carried out in solvent‐free system. The grafting of AN was increased with increasing the absorbed dose and monomer concentration in the mixture. Grafting of 748% of AN was achieved at 20 kGy dose. The nitrile groups of acrylonitrile grafted silica (AN‐g‐S) were chemically converted into amidoxime groups. The structure of AN‐g‐S and its corresponding products was investigated by FTIR, SEM, TGA, BET, and XRD analysis. FTIR and EDX analysis confirmed the grafting of AN onto silica surface. The changed morphology of SEM images shows the presence polyacrylonitrile layers on silica particles. The adsorption application of amidoxime‐grafted silica (AO‐g‐S) was studied against Cu²⁺. Its adsorption capacity is strongly depended on the pH of the solution and 172 (mg/g) of Cu²⁺ uptake was obtained at pH 5.0. The developed adsorbent has potential application to remove heavy metal ions from aqueous solutions. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45437.