硫化体系对天然橡胶耐热空气老化性能的影响

研究了硫化体系(CV、EV和SEV)对炭黑填充天然橡胶胶料耐100℃热空气老化性能的影响,并采用化学探测法测试了NR硫化胶老化后交联密度和交联键类型的变化。结果表明,100℃热空气老化后,CV硫化胶力学性能和交联密度均发生明显劣化;EV硫化胶表现出优异的耐100℃热空气老化性能,其力学性能和交联密度变化幅度均明显低于CV硫化胶;SEV硫化胶耐100℃热空气老化性能与CV硫化胶接近。CV硫化胶以多硫键为主,单硫键含量非常低,100℃热空气老化后多硫键含量下降,单硫键含量升高,双硫键基本保持不变;EV硫化胶以单硫键为主,多硫键含量很低,100℃热空气老化后单硫键含量增大,多硫键含量减小,双硫键变化不大;SEV硫化胶中双硫键含量最高,单硫键和多硫键含量基本相同,100℃热空气老化后多硫键含量和双硫键含量均下降,单硫键含量增大。     

硫化时间对绿色轮胎胎面胶交联网络结构与性能的影响

针对以溶聚丁苯橡胶(SSBR)/顺丁橡胶(BR)并用胶为主体材料的绿色轮胎胎面胶,研究在不同硫化时间下未填充白炭黑的SSBR/BR并用胶(简称未填充白炭黑体系胶料)及填充白炭黑的SSBR/BR并用胶(简称填充白炭黑体系胶料)形成的交联网络结构与性能变化。结果表明:对于未填充白炭黑体系胶料,随着硫化时间的延长,硫化胶的交联密度略有降低,硬度、定伸应力、拉伸强度和回弹值等变化不大,撕裂强度提高,拉断伸长率和耐伸张疲劳性能降低;对于填充白炭黑体系胶料,随着硫化时间的延长,硫化胶的填料网络结构化程度逐渐提高,交联密度略有增大,键能较低的多硫键减少,键能较高的单硫和双硫键增多,硫化胶的拉伸强度、回弹值、耐伸张疲劳性能和耐磨性能基本不变,生热和滚动阻力降低;未填充及填充白炭黑体系硫化胶的耐老化性能均随硫化时间的延长而逐渐提高,这表明以SSBR/BR并用胶为主体材料的胎面胶即使在高温下硫化较长时间,仍具有较好的性能。     

偶联剂Si69对炭黑补强NR硫化胶性能的影响

研究了偶联剂Ｓｉ６９用量对炭黑补强ＮＲ胶料硫化特性、硫化胶物理性能和热氧老化性能的影响,并用傅立叶变换红外光谱（ＦＴＩＲ）研究了硫化胶在拉伸疲劳过程中结构的变化。结果表明,当Ｓｉ６９的用量为炭黑用量的１／１０左右时,硫化胶的拉伸强度和３００％定伸应力具有最大值,且耐老化性能最好。胶料中加入Ｓｉ６９,使体系中的多硫键数量增多,从而改善了体系的交联键类型和硫化胶性能。在拉伸疲劳过程中,随着疲劳过程的进行,多硫键数量减少,而单硫键数量增多,再次证明硫化胶具有自愈合能力。     

ACM橡胶二段硫化交联网络结构的研究

研究了二段硫化温度和时间对聚丙烯酸酯 (ACM)橡胶交联网络结构的影响 ,结果表明 ,随着二段硫化时间延长 ,表观交联密度 (Vr)出现峰值 ,压缩永久变形值下降 ;随着二段硫化温度升高 ,Vr峰值所对应的二段硫化时间缩短。压缩永久变形值下降 ,当二段硫化条件为 190℃× 4h时 ,ACM硫化胶既可取得较低的压缩永久变形值 ,又可获得良好的物理机械性能。说明在二段硫化过程中 ,ACM硫化胶不仅发生脱氯交联反应 ,同时还存在着多硫键向单硫键、双硫键和碳—碳键的交联结构转变过程以及交联键断裂的老化过程     

核磁共振法表征硫黄用量对天然橡胶交联密度及结构的影响

用核磁共振(NMR)法测定了硫黄用量及硫化温度对天然橡胶(NR)硫化胶交联结构的影响,并与传统的平衡溶胀法进行了对比.结果表明,用NMR法可以测定硫化胶的总交联密度、未硫化胶的物理交联密度和由于交联反应产生的化学交联密度;NR硫化胶的总交联密度和化学交联密度随硫黄用量的增加而呈线性增加;随着硫黄用量的增加.交联密度增加,NR硫化胶的纵向弛豫时间和横向弛豫时间下降;NR硫化胶的交联密度越大,弛豫时间对温度的依赖性越小;NMR法可以清晰展示NR/硫黄/促进剂NS硫化体系的硫化过程中橡胶交联点间的相对分子质量、化学交联密度及橡胶大分子连到橡胶交联网络上的演变过程.     

高温和低温聚合的SBR硫化胶的交联密度、动态力学行为和微观结构的研究

以硫磺、二硫化巯基苯并噻唑(MBTS)和四甲基二硫化秋兰姆(TMTD)为硫化剂,选用5种不同的硫化体系,制备出高温及低温丁苯橡胶(SBR)硫化胶。通过苯溶胀及应力-应变分析测定了硫化胶的交联密度。利用硫醇-胺化学探测仪,测定了硫磺硫化胶的交联键的类型,研究了硫化胶及生胶(未交联)的动态力学性能和热稳定性。利用拉曼(Raman)光谱测定了丁二烯的微观结构及总不饱和度。讨论了硫化胶的交联密度及交联键类型对其性能的影响。     

热氧老化对氯丁橡胶化学结构及性能的影响

对氯丁橡胶（CR）硫化胶进行热氧老化试验,研究100 ℃下老化时间对CR硫化胶化学结构、交联密度、溶胶质量分数和相对分子质量分布、氯质量分数、拉伸性能的影响。结果表明,在热氧老化过程中,CR硫化胶的橡胶分子链发生氧化反应,化学结构发生明显变化。在老化初期,CR硫化胶的交联密度增大,溶胶质量分数和相对分子质量减小,橡胶分子链以交联为主;老化时间超过192 h后,CR硫化胶的交联密度减小,溶胶质量分数、相对分子质量及其分布指数增大,橡胶分子链氧化断裂增多;在老化过程中,交联及脱氯使CR硫化胶结构化越来越严重,导致CR硫化胶的拉伸性能明显降低。     

用校准曲线法测定EPDM硫化胶的交联密度及交联键结构

根据“每消耗3mol二硫化四甲基秋兰姆（TMTD）分子产生1mol交联键”理论,建立了EPDM纯胶和炭黑N326（50phr)增强EPDM体系的化学交联密度－溶胀因子校准曲线,以此测定了硫黄硫化EPDM的交联密度和交联键类型,TMTD硫化EPDM的交联键类型,用溶胀法测定了EPDM／TMTD的纯胶体系和炭黑增强体系的总交联密度,结果表明,溶胀法测得的交联密度要比由TMTD质量摩尔浓度计算得到的值小。     

老化对NR硫化胶的影响

研究了热空气老化和真空老化对ＮＲ硫化胶结构和性能的影响,采用化学探测剂脱硫的方法测定了老化过程中ＮＲ硫化胶交联密度及交联键分布变化的情况,同时测定了硫化胶的力学性能和动态性能随时间变化的情况。结果显示,热空气老化使硫化胶的交联密度增加,但力学性能损失严重,原因是主链氧化断裂。真空老化使ＮＲ硫化胶交联密度略微降低,但力学性能保持良好,类似于硫化返原。热空气老化使ＮＲ硫化胶的动态性能改善,而真空老化后     

抗硫化返原剂SR534与PK900在NR中的对比研究

研究了抗硫化返原剂SR534和PK900在天然橡胶(NR)中采用普通硫黄硫化体系时胶料的硫化特性、力学性能、耐压缩疲劳温升、耐磨耗、耐屈挠龟裂和动态力学性能的对比,并采用平衡溶胀法和化学探测剂法测定了胶料硫化至t90、30min、60min时非多硫键交联密度.当硫化温度为160℃和抗硫化返原剂用量为2份时,硫化曲线和非多硫键交联密度显示含SR534胶料在过硫化阶段生成的C-C交联键多于PK900,抗返原作用更为明显.SR534和PK900都明显提高了硫化至60min时硫化胶的交联密度、力学性能、耐压缩疲劳温升和耐磨耗性能,60℃时的tanδ值较低有利于降低轮胎的滚动阻力.     

NR硫化返原过程的动力学研究

采用依据ＮＲ硫黄硫化返原机理建立起来的硫化返原动力学模型,对普通硫黄硫化体系和半有效硫化体系的ＮＲ在不同温度下的硫化曲线进行了计算机非线性拟合,从而求出了各步反庆的速率常数,并进上步得到多硫键、双硫键和单硫键密度之和及交联密度随硫化时间变化的关系。结果表明：不同温度下两种体系采用该模型得到的模拟曲线与实际数据相吻合,求出的同一体系速率常数与硫化温度的关系符合Ａｒｒｈｅｎｉｕｓ方程。两种体系多硫键的     

天然橡胶硫化胶的热氧老化性研究

用热分析法(TGA、DSC)和裂解气相色谱-质谱分析(PGC-MS)研究了天然橡胶硫化胶的耐老化性能及其机理。结果表明,天然橡胶硫化胶的热氧老化初期力学性能和交联密度增加,热失重起始温度上升,随着老化过程的进行,降解效应占优势,硬度和交联密度下降,热氧稳定性变差。其热解机理可能是主链中键的断裂,产物主要是异戊二烯单体和1,4-二甲基-4-乙烯基环己烯。     

Reclamation of vulcanized rubbers by chemical degradation. V. Degradation of vulcanized synthetic isoprene rubber by the phenylhydrazine–ferrous chloride system

The changes of effective network chain density and soluble fraction were measured for gum vulcanizates of synthetic isoprene rubber (IR) during the degradation by the phenylhydrazine–ferrous chloride system. From the decrease of effective network chain density and the increase of soluble fraction, the network chain was concluded to undergo a severance reaction by the reagents in the following order of ease: polysulfide linkage > monosulfide linkage > carbon–carbon crosslink. Analysis of the relation of soluble fraction with decrease of effective network chain density according to the theory of Horikx indicated that the severance of crosslinks predominated over main-chain scission in the degradation of sulfur vulcanizate by the reagents. The experiments of the degradation of sulfur vulcanizate in sealed vessels in the absence of oxygen indicated that atmospheric oxygen is necessary for the degradation reaction.     

Influence of rubber composition on change of crosslink density of rubber vulcanizates with EV cure system by thermal aging

Variation of the crosslink density of a rubber vulcanizate depending on the rubber composition after the thermal aging was studied with single rubber, biblend, and triblend vulcanizates of natural rubber (NR), butadiene rubber (BR), and styrene‐butadiene rubber (SBR). The efficient vulcanization (EV) system was employed to minimize the influence of free sulfur in the vulcanizate on the change of the crosslink density. Thermal aging was performed at 40, 60, and 80°C for 20 days with 5‐day intervals. The crosslink densities of the vulcanizates after the thermal aging increase. For the single rubber vulcanizates, variation of the crosslink density by the thermal aging has the order: SBR > BR > NR. For the biblend vulcanizates, variations of the crosslink densities of the NR/SBR and SBR/BR blends are larger than that of NR/BR blend. Variation of the crosslink density of the vulcanizate increases by increasing the SBR content in the vulcanizate. Variation of the crosslink density of the rubber vulcanizate depending on the rubber composition was explained by miscibility of the blends, combination reaction of the pendent groups, and mobility of the pendent group. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1378–1384, 2000     

Reinforcement of EPDM by in situ prepared zinc dimethacrylate

The mechanical properties and crosslink density of peroxide‐cured ethylene‐propylene‐diene rubber (EPDM) reinforced with zinc dimethacrylate (ZDMA) were studied. ZDMA was in situ prepared in EPDM matrix through the neutralization reaction of zinc oxide (ZnO) and methacrylate acid (MAA). The effect of ZnO/MAA amount and molar ratio of ZnO/MAA on the properties of the EPDM vulcanizate were investigated in detail. The experimental results showed that EPDM can be greatly reinforced by ZDMA. The excess amount of ZnO considerably increases the tensile strength of the EPDM vulcanizate to reach as high as 37 MPa, whereas its elongation at break keeps over 350%. The process of in situ formation of ZDMA in the EPDM compound was verified by WAXD. Such vulcanizate contains both covalent crosslinks and ionic crosslinks. Crosslink density was determined by an equilibrium swelling method. Dependence of crosslink density on the amount and molar ratio of ZnO/MAA was studied and the extraordinary high tensile strength of the EPDM/ZDMA vulcanizate was related to ionic crosslink density. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1339–1345, 2002; DOI 10.1002/app.10112     

Effect of curing agents on some properties of a polysulfide sealant

The effect of curing agents on the properties of a polysulfide sealant composition was investigated. Commercially used curing agents, namely, lead dioxide, manganese dioxide, and ammonium dichromate, were selected for this study. It was established that curing agents affect joint strengths, stress–strain properties, dynamic mechanical properties, and thermal stability of the sealant. Sealant cured with ammonium dichromate had highest shear bond strength, ultimate tensile strength, modulus, and thermal stability, whereas these properties were lowest for lead-dioxide-cured sealant. Peel bond strength and elongation at break were highest for lead-dioxide-cured sealant. The observed changes in properties were attributed to the difference in crosslink density of the cured sealant, produced by the curing agents. The curing agents have no appreciable effect on the fuel resistance of the polysulfide sealant.     

Interaction Between Fumed-Silica and Epoxidized Natural Rubber

Epoxidized natural rubber (ENR)/fumed silica vulcanizates were prepared by mechanical mixing method. Fumed silica content can affect mechanical properties of the composites, and ten parts per hundreds of rubber (phr) fumed silica lead to the best tensile strength. The interaction between ENR and fumed silica was characterized by Kraus equation, crosslink density (tested by NMR), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA) and scanning electron microscope (SEM). The results showed that the dispersion of silica in ENR was better than in natural rubber (NR), hydrogen bond was produced between ENR and fumed-silica in ENR/silica blends, and glass transition temperature of ENR/silica vulcanizate was higher than pure ENR vulcanizate. TGA and DMA confirmed that there was intense interaction between ENR and silica.     

三种微生物脱硫废乳胶及其填充天然橡胶的力学性能比较

利用三种微生物鞘氨醇单胞菌、脂环酸芽孢杆菌和酵母菌对废乳胶(WLR)进行了脱硫再生,考察了脱硫过程中微生物的生长情况以及脱硫前后WLR溶胀和交联密度的变化,并将WLR和脱硫WLR(DWLR)以不同份数填充到天然橡胶(NR)中,对比了DWLR/NR硫化胶和WLR/NR硫化胶的力学性能和交联密度。结果表明,利用鞘氨醇单胞菌脱硫的WLR溶胀值较高,交联密度较低。随着乳胶用量的增加,填充NR硫化胶的拉伸强度和交联密度逐渐降低,扯断生长率逐渐增加。DWLR/NR硫化胶的力学性能明显优于WLR/NR硫化胶,且鞘氨醇单胞菌脱硫的DWLR/NR的力学性能明显优于其它两种微生物脱硫的DWLR/NR硫化胶。     

NR/改性气相法白炭黑复合材料的性能研究

在改性气相法自炭黑填充NR胶料中加入粘合剂RH，研究粘合剂RH用量对胶料性能的影响，并与偶联剂Si69／气相法白炭黑胶料进行对比。结果表明，粘合剂RH的加入明显改善了硫化胶的物理性能，拉伸强度提高10％以上；粘合剂RH用量为4份时，硫化胶的综合物理性能最佳；有机改性剂M2改性气相法白炭黑参与了橡胶的共硫化，使硫化胶的交联密度增大；偶联剂Si69对硫化胶物理性能的改善效果不及粘合剂RH。     

防老剂对氯化聚乙烯橡胶性能的影响

研究不同防老剂对氯化聚乙烯橡胶(CM)性能的影响.结果表明:加入不同防老剂的CM胶料ML和MH减小,t10和t90延长,CM硫化胶的硬度、100％定伸应力和拉伸强度增大,拉断伸长率减小;交联密度随老化时间的延长而呈增大趋势.当防老剂RD用量为2份时,CM硫化胶的耐热氧老化性能最优.