The influence of the processing temperature on gamma curing of epoxy resins for the production of advanced composites

Gamma radiation curing of an epoxy monomer, in the presence of an iodonium salt, as initiator, is studied. Systems have been polymerized at the same irradiation dose and dose rate and at different processing temperatures. The experimental results show that all the irradiated materials exhibit a latent reactivity, undergoing toward an increase of crosslinking density if they are thermally cured after irradiation. The results indicate that the processing temperature affects both the crosslinking density after irradiation and the sensibility to the post-irradiation thermal treatment.     

Crease recovery properties of cotton fabrics modified by urea resins under the effect of gamma irradiation

Cotton fabrics initially dyed with reactive dyes were treated with dimethylol dihydroxy ethylene urea (DMDHEU) resin in order to improve the crease recovery properties. As a comparison, the treatment with DMDHEU was carried out by the conventional thermal curing and gamma irradiation. The effect of treatments on the colour properties, crease recovery, mechanical and thermal properties was studied. It was found that the finishing of cotton fabrics with gamma irradiation affords better crease recovery values at low doses without affecting the colour intensity and the physical properties than the finishing by thermal curing. However, the finishing with higher doses of gamma radiation affects the mechanical properties of cotton fabrics. On the other hand, it was found that the thermal properties were improved with increasing dose.     

Degradation of poly(bisphenol-a-epichlorohydrin) by gamma irradiation

In this study, radiation stability of poly(bisphenol-a-epichlorohydrin) (PBEH) was studied via gamma irradiations at two different dose rates of 1540 and 82.8 Gy/h, in order to understand the possible use of PBEH in radioactive waste management as a solidifying agent. The total dose of irradiation was up to 2150 kGy. Degradation nature was tested by studying the changes in mechanical and thermal properties with the change of dose rate and total dose of irradiation. Tensile strength at yield was increased first then decreased when irradiated, while toughness decreased. The half value dose (HVD) of elongation was found as 29 kGy at dose rate of 1540 Gy/h. The non-irradiated PBEH was transparent, and the color changed to yellow with irradiation. Mechanical tests showed that PBEH has high radiation stability although there were some structural changes. It was seen that PBEH is a candidate polymer to be used in the immobilization of radioactive waste regarding radiation stability.     

电子束固化环氧树脂的物理特征及其分析

分析了环氧树脂电子束辐射固化的物理特征 ,电子束辐射固化过程受活性中心扩散控制 ,整个固化区域由片层状结构组成 .与电子能量沉积分布相对应 ,环氧树脂辐射固化度的最高值是在一定深度而不是在辐射表面出现 .对电子束辐射环氧树脂体系的固化过程进行了模型解释 ,固化区域大小主要由电子的能量传递范围和浓度决定 ,反应活性中心的扩散作用影响较弱     

Radiation curing of methacryloyloxyalkyl carbonates

The results of studying the radiation curing of methacryloyloxyalkyl carbonates (MC), a new type of oligomer, are presented. These oligomers are notable for their high rates of radiation curing. The radiation yield G(–M) is 2 × 10⁵ for MC and 2 × 10⁴ for triethylene glycol dimethyacrylate. The polymerization rate of MC appeared to be proportional, independent of the conversion degree, to the irradiation dose rate in the power of 0.9–1.0 (for dose rates ranging from 0.4 to 15 rad/s). In regard to the temperature dependence of the polymerization rate of MC for small conversion degrees, two temperature regions with different values of effective activation energy (18–20 kcal/mol and 2 kcal/mol, respectively) were observed. When an irradiated MC sample is being unfrozen, its polymerization occus in the region of devitrification (220–240°K). As distinct from mass polymerization, in the polymerization of MC solutions in acetone and benzol the mobility of growing chains increases so that the bimolecular termination becomes possible and the limiting conversion of double bonds is derived. Rather small irradiation doses necessary for curing MC and the proportionality of the radiation-induced polymerization rate to the dose rate make these oligomers valuable for various industrial applications.     

Thermal curing and photocuring of a DGEBA modified with multiarm star poly(glycidol)-b-poly(ε-caprolactone) polymers of different arm lengths

The influence of two multiarm star polymers, hyperbranched poly(glycidol)-b-poly(ε-caprolactone) of different arm lengths, on the thermal curing and the photocuring of a diglycidyl ether of bisphenol A epoxy resin (DGEBA) is studied. Star polymer with short arms PCL-10 decelerates more the thermal curing than the polymer with long arms PCL-30 because the latter is less solubilized in the epoxy matrix and its effect on the polymerization of the resin and the thermal–mechanical properties is less important. The kinetic triplet corresponding to the thermal curing of the different formulations has been determined. In the analysis of the photocuring process, we have also found that short-arm star PCL-10 is better solubilized in the epoxy matrix and its effect on the photocuring kinetics is more significant than that of the long-arm star. The effect of both polymers on the thermal–mechanical properties of the cured thermosets is less important due to the lower solubility at the relatively low photocuring temperatures.     

Gamma irradiation degradation/modification of 5-ethylidene 2-norbornene (ENB)-based ethylene propylene diene rubber (EPDM) depending on ENB content of EPDM and type/content of peroxides used in vulcanization

In this study, the radiation degradation/modification of the vulcanized EPDM and the effects of dose rate, peroxide type/content in vulcanization system and ENB content of EPDM were studied to investigate the change in the extend of the modification/degradation of the mechanical properties of vulcanized EPDM via gamma irradiation. In addition, thermal, dynamic mechanical, ATR-FTIR, TGA, TGA-FTIR tests were carried out to understand the change of properties of vulcanized EPDM via irradiation.Samples were irradiated with two different dose rates of 1280 and 64.6 Gy/h. Total dose of irradiation was up to 184 kGy. The FTIR spectral analysis showed structural changes of EPDM via irradiation. It was observed that the dose rate changed the mechanical properties with different extends. The change of ENB content of EPDM and peroxide type and content in vulcanization system affect extend of the modification/degradation of the EPDM's properties.     

含共引发剂的环氧树脂电子束固化特性

对引发剂组成、含量不同的环氧树脂体系进行了低吸收剂量及高吸收剂量的电子束辐射固化,通过对不同样品辐射过程中的温度特性和辐射后的凝胶含量、内耗tanδ及动态模量变化趋势的研究,得到共引发剂对环氧树脂辐射固化的影响规律.在相同的树脂含量及吸收剂量下,共引发剂的加入可以提高环氧树脂体系的凝胶含量,但其提高幅度并不随着共引发剂含量的增多而增大,而是存在一个最佳值.随着碘盐引发剂含量的增加,共引发剂对体系凝胶含量的提高幅度减小.在辐射过程中,环氧树脂体系的温度会出现一个峰值,共引发剂对峰值温度和辐射后体系的玻璃化转变温度的影响与对凝胶含量的影响类似.碘盐引发剂含量较低时,加入共引发剂的体系的常温及高温模量与未加体系相比没有明显变化;碘盐引发剂含量较高时,加入共引发剂的体系的常温模量比未加体系有所上升,而高温模量则变化不大.     

三官能度甲基丙烯酰氧基单体的合成与性能研究

用甲基丙烯酰氯分别与二乙醇胺和三乙醇胺反应合成了两种三官能度甲基丙烯酰氧基单体.以实时红外光谱(RT-IR)法研究了两种单体的光聚合动力学性质,考察了不同单体、不同引发剂和引发剂浓度、不同光强对聚合性能的影响,并采用动态力学分析仪(DMA)测试了光固化后材料的力学性能.结果表明,随着引发剂浓度的增大,单体转化率、最大反应速率都增大,随着光强的增大,单体转化率、最大反应速率都降低.与二苯甲酮(BP)相比,2-羟基-2-甲基-1-苯基丙酮(1173)对两种单体具有较好的引发效果.两种单体加入三缩四乙二醇双甲基丙烯酸酯(SR209)中后,对体系光固化后的产物力学性能有不同影响.     

Hydrothermal ageing of radiation cured epoxy resin-polyether sulfone blends as matrices for structural composites

The hydrothermal ageing of epoxy-thermoplastic blends, used as matrices for carbon fibre composites, cured by electron beam, has been studied. Two different thermoplastic percentages have been adopted. A suitable choice of both curing process and formulation parameters allows to carry out irradiation at mild temperature with several advantages, coming from a “non thermal” process, for both the final properties of the materials and the environment. Nevertheless the occurring of vitrification phenomena needs the use of a short thermal treatment after irradiation on the already solid materials, in order to complete the cure reactions. Radiation cured epoxy based matrices have been subjected to a thermal and moisture absorption ageing treatment and its influence on the thermal and mechanical properties has been investigated through dynamic mechanical thermal analysis and fracture toughness tests. The results have been interpreted on the basis of the different curing degree reached by the investigated systems and in the light of their morphological structures. Plasticization, thermal curing and degradation reactions occur in different extent depending on the kind of the material. In particular, for fracture properties, a better resistance to ageing is shown by the system at higher thermoplastic concentration.     

The microwave radiation effect on the polymerization of styrene

Styrene was cured by microwave radiation at two different powers: 300 and 500 W. The temperature profile of the sample during the microwave curing process was determined to select a suitable temperature for comparison with the conventional method of cure. The results indicate a similar comparable temperature of about 80°C irrespective of the microwave power used. The percentage conversion of the cure was followed by Fourier transform infrared (FTIR) spectroscopy. The thermal polymerization at 79(±1)°C displayed a gradual increase in the rate of reaction at the gel effect from about 30 to 50% conversion of the reaction. The microwave cure at 300 and 500 W displayed a large and sharp gel effect from about 20 to 69 and 64% conversion of the reaction, respectively. The limiting conversion decreased with increase in microwave power which was also observed in the polymerization of methyl methacrylate (MMA). Based on similarity in temperature and reaction conditions, the 500 W cure was found to show a reaction rate enhancement of 190% and the 300 W cure 120%. A comparison of microwave induced reactions with thermal methods, therefore, must also specify the microwave power used. © 1996 John Wiley & Sons, Inc.     

Role of additives in wood–polymer composites. Relationship to analogous radiation grafting and curing processes

Wood polymer composites (WPC) were prepared by impregnating an Australian softwood, Pinus radiata with methyl methacrylate which subsequently underwent in situ polymerisation utilising either γ radiation or the catalyst–accelerator method. Novel additives including thermal initiator, crosslinking agents, an inclusion compound and oxygen scavenger were incorporated to improve the polymer loading and properties of the resulting WPC. Polymer loadings of WPC obtained utilising the accelerator–catalyst method corresponded well with those obtained using γ radiation with 20 kGy radiation dose. The mechanistic significance of the current work in analogous radiation grafting and curing processes is discussed.     

Effect of gamma irradiation on linear low density polyethylene/magnesium hydroxide/sepiolite composite

Radiation crosslinking is generally used to improve the thermo-mechanical properties of the composites. A study has been carried out to investigate the effect of gamma radiation on the thermo-mechanical properties of linear low density polyethylene containing magnesium hydroxide (MH) and sepiolite (SP) as non-halogenated flame retardant additives. The developed composites are irradiated at different doses upto maximum of 150 kGy. Infrared spectra of the irradiated composites reveal the reduction in the intensity of O-H band with increase in the absorbed doses, thus indicates a distinct structural change in MH at higher doses. The thermogravimetric analysis results of unirradiated and composites irradiated at low doses (≤75 kGy) show two steps weight loss, which is changed to single step at higher doses with lower thermal stability. The melting temperature (T_m) and crystallization temperature (T_c) of irradiated composites are lowered with irradiation whereas Vicat softening temperature (VST) is increased. The increasing trend in gel content with increase in the absorbed dose confirms the presence of crosslinked network. The mechanical properties, results show significant improvement in the modulus of irradiated composites. The results also confirm that MH gradually loses its OH functionality with irradiation.     

Mechanical and thermal properties of irradiated films based on Tilapia (Oreochromis niloticus) proteins

Proteins are considered potential material in natural films as alternative to traditional packaging. When gamma radiation is applied to protein film forming solution it resulted in an improvement in mechanical properties of whey protein films. The objective of this work was the characterization of mechanical and thermal properties of irradiated films based on muscle proteins from Nile Tilapia (Oreochromis niloticus). The films were prepared according to a casting technique with two levels of plasticizer: 25% and 45% glycerol and irradiated in electron accelerator type Radiation Dynamics, 0.550 MeV at dose range from 0 to 200 kGy. Thermal properties and mechanical properties were determined using a differential scanning calorimeter and a texture analyzer, respectively. Radiation from electron beam caused a slightly increase on its tensile strength characteristic at 100 kGy, while elongation value at this dose had no reduction.     

Thermal expansion of irradiated polytetrafluoroethylene

The thermal expansion coefficient of gamma-irradiated Polytetrafluoroethylene (PTFE) has been measured in the temperature range 80–340 K by using a three-terminal capacitance technique. The samples are irradiated in air at room temperature with gamma rays from a Co⁶⁰ source at a dose rate of 0.26 Mrad/h. The change in crystallinity is measured by an x-ray technique. The expansion coefficient is found to increase with radiation dose below 140 K owing to the predominant effect of degradation. Above 140 K, the expansion coefficient is found to decrease with radiation dose because of the enhanced crystallinity. The temperatures of the two first-order phase transitions are also found to shift to lower temperatures owing to degradation of PTFE.     

Degradation of poly(carbonate urethane) by gamma irradiation

Poly(carbonate urethane) (PCU), is a valuable commercial engineering polymer. In order to understand the possible use of PCU in radioactive waste management as a solidifying agent or as a disposal container, radiation stability of the PCU is studied by Co-60 gamma irradiations at two different dose rates of 1540 and 82.8 Gy/h. The total dose of irradiation was up to 6.24 MGy. Degradation nature was tested by studying the changes in mechanical and thermal properties with rate and total dose of irradiation. Ultimate tensile strength and toughness first increased and then decreased with the irradiation dose. Half value dose (HVD) for elongation was 4010 kGy and for tensile strength 6010 kGy at the dose rate of 1540 Gy/h. The non-irradiated PCU transparent color changed to yellow and then brown with increased irradiation dose. The FTIR spectral analysis showed a random scission of polymer with irradiation. From the experimental observation, it was shown that PCU can be used for embedding radioactive waste for about 300 years.     

Characterization of irradiation-induced crosslink of epoxidised natural rubber/ethylene vinyl acetate (ENR-50/EVA) blend

The effect of irradiation on tensile, dynamic mechanical properties, thermal properties and morphology of ENR-50, EVA and ENR-50/EVA blend was investigated. All the samples were irradiated using a 3.0 MeV electron beam (EB) machine with doses ranging from 20 to 100 kGy. Results indicate that the gel fraction of ENR-50, EVA and ENR-50/EVA blend increases with irradiation dose. Concerning tensile properties, it can be seen that EB radiation increases the tensile strength of all the samples, increases the elongation at break of ENR-50 and ENR-50/EVA blend, reduces the elongation at break of EVA, increases M200 (modulus at 200% strain) of ENR-50 and EVA, while decreases M200 of the ENR-50/EVA blend. For dynamic mechanical studies, it was found that EB radiation increases the T_g of all the samples due to the effect of irradiation-induced crosslinking. The compatibility of ENR-50/EVA blend also found to be improving upon irradiation. In the case of thermal properties, it was detected that T_m, T_c and the degree of crystallinity of ENR-50/EVA blend increase with an increase in irradiation dose. This was due to the perfection in the crystal growth occurring upon radiation. Morphology changes play a major role in the changes of the properties of ENR-50/EVA blend. Finally, it can be concluded that ENR-50/EVA blend can be vulcanized by EB radiation.     

固化条件对聚合物分散液晶膜电光性能的影响

选用聚乙二醇二缩水甘油醚(EGDE)/季戊四醇缩水甘油醚(PERTGE)/1,8-二氨基-3,6-二氧杂辛烷(EDBEA)/向列相液晶(SLC1717)复合体系,在不同的固化条件下,通过热聚合诱导相分离方法制备了一系列电光性能不同的聚合物分散液晶(polymer dispersed liquid crystal,简称PDLC)膜.研究了固化温度和固化时间对制备的PDLC膜中聚合物网络的微观形貌和电光性能的影响.结果表明,随着固化温度的升高以及固化时间的缩短,PDLC膜的对比度、驱动电压和开态响应时间逐渐增大,而关态响应时间逐渐减小.在固化温度为363.2 K,固化时间为7 h时,所制备的PDLC膜具有较佳的电光性能.     

Curing behavior of epoxidized soybean oil with biobased dicarboxylic acids

In this study, we report the curing of ESO with biobased dicarboxylic acids (DCAs) with different carbon chain-lengths to synthesize fully sustainable polymers. Both non-isothermal and isothermal curing processes analysis indicated that the curing rate and activation energy decreased with increasing chain-length of DCAs. The optimum COOH/epoxy molar ratio is 0.7 for preparation of ESO/DCA cured product with maximum degree of crosslinking. Addition of 4-N, N-dimethylaminopyridine (DMAP) as a catalyst can efficiently accelerate the curing rate and reduce activation energy. We systemtically studied the effect of chain-length of DCAs on the physical properties of cured products, and found that with increase in chain-length of DCAs, the glass transition temperature of the cured ESO/DCA decreased, the tensile strength and Young's modulus increased while elongation at break decreased, due to the decreased crosslinking density resulted from the increased chain-length between crosslinking sites. All cured ESO/DCA showed excellent thermal stability with initial decomposition temperature of higher than 340 °C.     

Modifications of radiation detection response of PADC track detectors by photons

Photon induced modifications in polyalyldiglycol carbonate (PADC) track detectors have been studied in the dose range of 10¹–10⁶ Gy. It was found that some of the properties like bulk-etch rate, track-etch rate got enhanced at the dose of 10⁶ Gy. Activation energy for bulk-etching has been determined for different gamma doses. In order to correlate the high etch rate with the chemical modifications, UV–Vis, IR and ESR studies were carried out. These studies clearly give the indication that radiation damage results into radical formation through bond cleavage. TGA study was performed for understanding the thermal resistance of this detector. The results are presented and discussed.