丁苯橡胶在热空气和海水中老化性能的比较

对丁苯橡胶在热空气和海水中进行了加速老化试验,比较了老化前后其性能的变化,得出了该橡胶的性能变化与老化时间的函数关系,并建立了100%定伸应力和撕裂强度与硬度的关联关系。结果表明,在整个老化期间,丁苯橡胶的100%定伸应力和硬度逐渐增大,撕裂强度逐渐减小。在相同的温度下,老化初期在海水中丁苯橡胶的性能变化比在空气中的快,而老化后期在空气中的性能变化比在海水中快。丁苯橡胶的100%定伸应力和撕裂强度与硬度呈线性关系,说明通过硬度的变化监测丁苯橡胶力学性能的变化是可行的。     

丁苯橡胶热空气老化性能变化之间的相关性

通过热空气老化试验,建立了丁苯橡胶(SBR)热空气老化拉伸性能变化率与邵尔A硬度变化值之间的相关性。结果表明,在热空气老化过程中,无论是普通硫化体系还是有效硫化体系,SBR硫化胶老化后的邵尔A硬度变化值随老化时间的延长而呈指数趋势增加,且老化后扯断伸长率变化率与邵尔A硬度变化值之间呈线性关系;在普通硫化体系下,硫化胶表现为老化后扯断伸长率变化率和拉伸强度变化率随老化时间的延长而呈指数趋势下降,而老化后拉伸强度变化率与邵尔A硬度变化值之间以及拉伸强度变化率与扯断伸长率变化率之间呈线性关系。     

VARTM用环氧树脂固化工艺的研究

对3种配方的真空辅助传递模塑(VARTM)工艺用环氧树脂,采用动态升温DSC实验,升温速率分别为5、10和15℃/min,引入Kissinger理论,确定了树脂体系的表观活化能分别为4.32kJ/mol、5.57kJ/mol和3.49kJ/mol;利用外推法,确定了参考固化工艺温度。     

氯丁橡胶耐热氧老化性能的快速评价

采用热重/差示扫描量热同步分析仪考察了氯丁橡胶硫化胶的耐热氧老化性能,得到氧化反应的表观活化能、反应速率常数(K_T)和氧化诱导期(t_i),并与热空气老化箱试验结果进行对比。结果表明,K_T和t_i可表征硫化胶的耐热氧老化性能,所得结果与热空气老化箱试验结果一致。提高二苯胺类防老剂与对苯二胺类防老剂用量,有利于改善硫化胶的耐热氧老化性能。     

超细六硝基茋的热分解性能

为了解超细六硝基茋(HNS)的热分解性能,通过DSC-TG实验研究HNS-Ⅳ的热分解过程,用Kissinger法和Ozawa法计算了HNS-Ⅳ热分解反应动力学参数.结果表明,HNS-Ⅳ的热稳定性与HNS-Ⅱ相当.Kissinger法和Ozawa法得到的HNS-Ⅳ分解表观活化能分别为221.4 kJ/mol和220.3 kJ/mol,比静态气氛下HNS-Ⅱ热分解反应的表观活化能减小27 kJ/mol.     

苯并环丁烯封端的聚酰亚胺树脂的流变行为研究

用旋转流变仪研究了苯并环丁烯封端的聚酰亚胺树脂体系固化过程中的化学流变行为,用动态和静态两种方法分析了其固化过程,发现存在三个固化阶段,用Arrhenius方程确定了固化前的表观物理粘流活化能为195.9kJ/mol.并用Roller法确定固化反应过程中表现化学粘流活化能和表现固化反应活化能,分别为148.2kJ/mol和161.2kJ/mol.结果表明,在整个固化成型工艺温度范围内,苯并环丁烯封端的聚酰亚胺树脂的粘度特性符合Roller模型方程,通过该模型可较好地预测该树脂在固化过程中的粘度特性.     

新型防老剂555PD用于丁苯橡胶SBR1500防老化

用热空气老化的方法考察了防老剂555PD不同加入量对丁苯橡胶SBR1500的热空气老化防护性能及物理机械性能的影响。并与防老剂PPDB进行了对比研究。实验结果表明,防老剂555PD热空气防老化性能优于PPDB,对丁苯橡胶物理机械性能没有明显影响,用于丁苯橡胶SBR1500可降低生产成本,具有一定的经济效益。     

水热处理对含油污泥热解特性及动力学影响

利用热重分析仪研究了水热处理对含油污泥（OS）热解特性的影响,并使用Kissinger-Akahira-Sunose(KAS)和Ozawa-Flynn-Wall (FWO)的方法对其热解动力学进行了分析,确定了经过不同水热温度处理后的含油污泥在不同热解阶段的表观活化能,考察了水热处理及其水热温度对含油污泥热解特性及动力学参数的影响。热分析的结果表明：水热处理使得含油污泥在热解不同阶段的终止温度向较低温度区间移动,在相同的转化率下经过水热处理后的OS在不同热解阶段的表观活化能均低于原样。随着水热反应温度从160℃增加到240℃,根据FWO法估算的OS在热解第一阶段的平均表观活化能从75.20kJ/mol增加到78.28kJ/mol,热解第二阶段的平均表观活化能从151.04kJ/mol降低到144.18kJ/mol,热解第三阶段的平均活化能从171.12kJ/mol增加到了192.59kJ/mol。     

某种聚硫密封剂的老化寿命计算模型

文章讨论了某种聚硫密封剂的老化反应过程,并进行高温老化实验,采用断裂伸长率对聚硫密封剂的,运用动力学经验公式和Arrhenius公式对实验结果进行线性拟合,外推计算了聚硫密封剂老化反应的活化能以及常温下的老化寿命.结果显示,聚硫密封剂老化反应的活化能为78.783kJ/mol,老化寿命为35.8年.     

胆固醇与β-环糊精包合物热稳定性及热动力学研究

采用非等温热重法研究了 β 环糊精和胆固醇包合物的热分解反应动力学。实验结果表明 ,β 环糊精和胆固醇包合物热分解反应级数大于 1,用Ozawa(1)法和Reich法求得热分解反应的平均表观活化能分别为 78 6 9kJ/mol、86 82kJ/mol。较低的表观活化能说明包合物的热稳定性与 β 环糊精和胆固醇之间的匹配性有关     

空气中PE-LD与PE-LD-g-HEA的非等温热分解行为研究

采用固相接枝法制备了丙烯酸-2-羟乙酯（HEA）接枝低密度聚乙烯（PE-LD）共聚物（PE-LD-g-HEA）,通过X射线衍射仪、傅里叶红外光谱仪分析了不同温度处理下PE-LD、PE-LD-g-HEA的结构变化,并用热重分析法研究了二者的热分解动力学。结果表明,热处理时PE-LD-g-HEA较PE-LD的结晶度变化小,主链断裂缓慢,热稳定性提高;Kissinger法和Crane法计算了PE-LD表观活化能为88.63 kJ/mol、指前因子1.17×106 s-1、反应级数为0.88,接枝产物的表观活化能为217.35 kJ/mol、指前因子5.92×1015 s-1、反应级数为0.95,Ozawa法计算的表观活化能值与Kissinger法相相近。     

Aging of EPDM rubber

The effect of oxidative and thermal aging of EPDM raw rubber and rubber vulcanizate on gelation, network structure, and techical properties has been studied over a wide range of temperatures and times of aging. Three grades of EPDM having different types of diene have been considered. The kinetics of aging of both raw rubber and vulcanizates has also been reported. Different network structures have been produced due to different reactivity of temonomers. Cross-link density, cross-link efficiency, polysulfidic linkage, zinc sulfide sulfur, combined sulfur, free sulfur, and sulfur inefficiency change with aging time and temperature. The number of polysulfidic cross-links decreases continuously with increase in time or temperature of aging. There is no definite trend in other structural features. It is quite evident that postcuring reactions as well as destruction of cross-links are taking place in the aging process. The predominance of the former or latter depends on the structure of the diene. Tensile and tear strength of the compounds decreases or increases with time or temperature of aging. At high temperature, it always decreases with time. Changes in these properties can be approximately correlated with changes in structure only at high temperature. At lower temperature, relations between network structure and technical properties are complicated owing to the competing reactions discussed above. In general, retention of properties of ENB-EPDM vulcanizate is the best. The properties after aging do not exclusively depend on the network structure, nature of cross-link, rank of sulfur, or pendant or cyclic sulfide. The backbone structure is important in all these cases. Changes are less drastic on aging in nitrogen, but a similar trend is found. Raw EPDM rubber forms a gel, which increases with temperature of aging. The activation energy for gelation has been found to be 98 kJ/mol, similar to the oxidation of diene-containing rubbers. The activation energy for desulfurization of various grades of EPDM vulcanizates is 60–85 kJ/mol. The activation energy for fracture calculated from aging data is, however, 30–36 kJ/mol from tensile measurement and 32–46 kJ/mol from tear strength measurement.     

橡胶型乙烯－醋酸乙烯共聚物配方及老化性能研究

研究了橡胶型乙烯－醋酸乙烯共聚物（ＥＶＭ）的配方及热氧老化性能。试验结果表明：ＥＶＭ具有优异的热空气老化性能，经１７５℃×７２ｈ老化后仍有很高的拉伸强度和扯断伸长率保持率；需采用过氧化物进行硫化，同时并用适量的三烯丙基异氰脲酸酯可以显著改善ＥＶＭ的压缩永久变形性能；它是一种典型非自补强性橡胶．需加入适量的补强填充剂；聚酯增塑剂可以在一定程度上降低ＥＶＭ的硬度，而对老化性能影响不大；防老剂ＲＤ可赋予胶料更优良的热空气老化性能和耐水解性能。     

星型低顺式聚丁二烯橡胶的合成及反应动力学研究

采用负离子溶液聚合的方法合成了树脂级低顺式聚丁二烯橡胶（LCBR）,并研究了其聚合反应动力学,考察了单体质量分数、温度、引发剂用量等对聚合过程的影响;求取了聚合动力学参数k;＂,表观增长活化能Ep＇为91．70kJ／mol;考察了影响LCBR胶液粘度的因素,结果表明,基础胶相对分子质量为3．50×10^4时,聚合物的胶液粘度为25mPa·s;基础胶相对分子质量为6．00×10^4时,聚合物的胶液粘度为35mPa·s。     

The degradation of guayule rubber and the effect of resin components on degradation at high temperature

Degradation of pure guayule rubber and rubber in the presence of stearic, oleic, linoleic, and linolenic acid, has been studied at high temperatures (from 150°C to 600°C) using thermogravimetric analysis (TGA). On-line mass spectrometric analysis of the products of decomposition has also been done to understand the mechanism of degradation. Degradation of rubber starts around 230°C in air and 330°C in nitrogen. Presence of acids changes the onset of degradation, because of low decomposition temperature of the acids. In the derivative curve, there is one T_max for degradation in nitrogen; two for rubber; and three for rubber containing acids are observed for degradation in air. The activation energy of degradation, as observed by isothermal kinetics, in the 1–10% weight loss region, is 225 kJ/mol in nitrogen and 167 kJ/mol in air. In the 10–100% region, however, the activation energy of degradation measured by the Freeman and Carroll method using dynamic thermogravimetry, is 239 kJ/mol in both nitrogen and air atmosphere. The main products of pyrolysis in inert atmosphere are propylene, propane, isobutylene, methyl butene, isoprene, 2,3-dimethyl cyclopentene, octene, 2,4-dimethylcyclohexene, dipentene, etc. Isoprene is found to be the most abundant. Fragments having m/e values of 136, 121, 107, 93, 79, and 53 are also produced in large quantities. The ratio of concentration of dipentene to isoprene increases marginally with temperature. The concentration of other fragments however increases drastically with temperature. The additives have no effect on the nature of products obtained. The conversion to different fragments depends upon the temperature of degradation and the stability of intermediate products. All smaller molecules are obtained from either dipentene or isoprene. A mechanism of formation of these products has been suggested.     

单向阀胶防老剂的选取

通过替换现有成熟单向阀胶料配方中防老剂的品种以解决气味问题,并进行拉伸强度、拉断伸长率、硬度(邵氏A)、永久变形、热空气老化、屈挠龟裂、臭氧老化测定,通过数据对比分析选取符合潜水帽单向阀性能要求和使用要求的防老剂。     

Thermal aging of polyethylene-co-methyl acrylate elastomer activation energies of physical and physicochemical mechanisms

This article deals with the thermal aging of a polyethylene-co-methyl acrylate elastomer. Six different activation energies have been determined corresponding to the following different mechanisms: surface oxidation, whole bulk oxidation in the case of heterogeneous oxidation, consumption of antioxidant, creep, and relaxation (compression set). Relaxation mechanism has been found to have the lowest activation energy (45 kJ/mol). Dominant chemical modification has been found to have the highest activation energy (119 kJ/mol). The case of heterogeneous oxidation is considered in details: a variation of the activation energy is obtained. The activation energy varies from a constant upper value related to homogeneous oxidation, to a lower value related to the so-called “total heterogeneous oxidation”. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2507–2515, 1997     

Degradation and life prediction of a natural rubber engine mount compound

To assess and predict the functional life of a natural rubber engine mount compound, the mechanical property changes were determined under accelerated aging conditions. The rubber was aged at temperatures ranging from 70 to 110°C for times ranging from 1 h to 5 weeks. Tensile and fatigue measurements were used to characterize the aging trends and mechanisms of the engine mount compound. With the time–temperature superposition approach, the activation energy was found to be about 98 kJ/mol for the elongation at break, 93 kJ/mol for the tensile strength, and 60 kJ/mol for the fatigue life. The tensile strength after aging for 13 weeks at 50°C was predicted to be 18.73 MPa, which was very close to the experimental value of 19.04 ± 2.25 MPa. With a 50% reduction in the tensile strength used as the failure criterion, it was predicted that the tensile strength of the engine mount compound would take 80 days to decrease by 50% at 70°C. At 23°C, it would last approximately 140 times (31 years) its lifetime at 70°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

助交联剂对过氧化物硫化HNBR性能的影响

考察了三羟甲基丙烷三甲基丙烯酸酯(SR350)、三羟甲基丙烷三丙烯酸酯(SR351)作为过氧化物的助交联剂对氢化丁腈橡胶(HNBR)的硫化特性、加工性能、物理机械性能及老化性能的影响,并采用无转子流化仪研究了2种助交联剂的硫化反应动力学。结果表明,添加助交联剂的胶料的门尼粘度下降,硫化程度都有所增加,压缩永久变形性能改善,并且老化后性能保持率变好。其中添加SR351的试样的硫化程度较高,加工性能和压缩永久形变更佳。而助交联剂的存在提高了硫化反应的活化能,加入SR350和SR351胶料的活化能分别为154.76kJ/mol和158.78kJ/mol,表明加入助交联剂的硫化反应速率对温度的依赖性更大。