甲基丙烯酸锌增强弹性体的相态研究 II.硫化胶料(英文)

利用扫描电子显微镜(SEM)和透视电子显微镜(TEM)研究了甲基丙烯酸锌增强多种弹性体(包括BR,SBR,EPDM,NBR,EPM,POE和HNBR)的微观相态结构。发现在各体系的硫化胶料中均存在两类基本分散结构:纳米分散结构和微米分散结构。其中纳米增强结构是在胶料过氧化物交联过程中由ZDMA原位聚合生成的;而微米结构就是残余的ZDMA颗粒。这两种结构的尺寸及相对含量因不同的复合体系而不同。对于BR和SBR体系,其微米分散结构较其他体系更多,且纳米分散结构的尺寸相对略小。而在EPDM,NBR,EPM,POE,HNBR中,微米分散结构较少,且纳米分散结构的尺寸相对较大。还研究了ZDMA颗粒的原生尺寸对硫化胶料的相态结构的影响,发现在POE体系,较大的ZDMA原生尺寸将造成其硫化胶料中微米分散结构的大量增多;而EPDM,EPM,NBR,HNBR胶料的相态则对ZDMA原生尺寸的变化不敏感。硫化胶料的微观相态的差异必将对其物理机械性能产生直接的影响。     

Interfacial crystallization and its mechanism in in-situ dynamically vulcanized iPP/POE blends

The effect of in-situ crosslinking of poly (ethylene-co-octene) (POE) rubber phase on the interfacial crystallization of isotactic polypropylene (iPP) in dynamically vulcanized iPP/POE blends was studied. The results showed that in situ crosslinking of POE obviously increased the interfacial crystallization of iPP in the dynamically vulcanized blends, comparing with that of pure iPP and the unvulcanized blend. The interfacial crystallization of iPP was further increased with the increase in crosslink degree. After annealing, the obvious interfacial crystallization was still obtained in the blend with high crosslink degree. Based on the fluctuation assisted nucleation mechanism in solution blended iPP/polyolefin block copolymer (OBC) blends, we proposed for the first time the interfacial crystallization mechanism in dynamically vulcanized blends: the oriented chains of iPP formed by concentration fluctuation at the interface during phase separation or shearing stress during melt mixing can be maintained because of the in situ crosslinking of POE phase, resulting in the enhancement of nucleation density at the iPP/POE interface. Our study proposes a new interfacial crystallization mechanism, and provides guidance for the preparation of high performance thermoplastic vulcanizates (TPVs) product by tailoring the interfacial crystallization of TPVs.     

Behaviour of the spin-spin relaxation time for natural rubber vulcanizates under large deformation

The spin-spin relaxation time, T₂, for DCP-cured natural rubber with various crosslink densities, v_e, has been measured under various deformation. T₂ is separated into two components: one is the long T₂ component, T_2L, for the mobility of amorphous network chains, the other is the short one, T_2S, for that of the strain-induced crystalline chains. T_2L decreased exponentially with increasing extension ratio,α, and the decreasing rate was more remarkable with increasing v_e. The α and v_e dependence of T_2L has been quantitatively explained by the equation experimentally derived by Nishi et al.T_2L under various extension increased and became almost constant with increasing temperature, while the corrected fraction of T_2S, T_2S (%), gradually decreased. The apparent melting point, T_m, at which the corrected T_2S (%) was zero under various deformation was determined. The α dependence of T_m, has been discussed by using Flory's equation.     

Effect of carbon black addition and its phase selective distribution on the stress relaxation behavior of filled thermoplastic vulcanizates

The long term mechanical behavior of thermoplastic vulcanizates (TPV) based on polypropylene (PP) and ethylene propylene diene terpolymer (EPDM) and different types and concentrations of carbon black (CB) has been characterized by means of stress relaxation experiments. Evaluation of the relaxation curves was carried out using the two‐component model allowing a division of the initial stress into different stress components which are caused by different networks available in TPV. The discussion focussed on the background of the stress components, which are originated by the CB addition, the non‐relaxing stress components σ, and σ, as well as the relaxing stress components Δσ^{CB(polymer‐layer)} and Δσ^CB(network). It was found that the concentration and type of CB as well as the phase specific CB distribution strongly affect the non‐relaxing and relaxing stress components. Up to a CB concentration of 9% in the EPDM phase the composite behaves as a thermo‐rheologically simple material because the impact of CB addition on the α‐relaxation of the crystalline PP phase is still negligible. A master curve was created by the horizontal shift of the relaxing stress curves Δσ^Comp(t) to a reference curve. At higher local CB loadings the additional relaxation processes induced by CB addition overlap with the α‐relaxation, thus, no master curve could be made in that case. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Investigation of the degradation properties of low molecular weight natural rubber blends in oven,oxygen, ozone,water, and some organic solvents

Studies into how heat, oxygen, ozone, water, and some organic solvents affect the physico‐mechanical properties of vulcanizates prepared from blends of natural rubber (NR) and low molecular weight natural rubber (LMWNR) were investigated. Various ratios of NR and LMWNR (100:0, 95:5, 90:10, 80:20, 50:50, 25:75 10:90, 5:95, and 0:100 w/w) were mixed and labeled as mixes A to I. The physico‐mechanical properties of all the vulcanizates before and after ageing in oven, oxygen, ozone, and water were measured and compared while the resistance of the vulcanizate in toluene, carbon tetrachloride, acetone, ethanol, cyclohexane, mineral oil, and brake fluid were determined in terms of swelling and solubility measurements. From the unaged results, mix A with 100% NR has the best physico‐mechanical properties. After degradation, mix C with 10% LMWNR showed the best ageing resistant. Similarly, mix D with 20% LMWNR showed more resistance in most of the solvents used, and this was closely followed by mix C. The results generally have proven that LMWNR is capable of improving the ageing properties and solvent resistance of NR. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

填充剂表面改性对硫化胶磨耗性能及形态的影响

研究了13种表面改性剂对白炭黑填充天然橡胶／顺丁橡胶（NR／BR）硫化胶磨耗性能及其形态的影响，结果表明，改性剂改变了白炭黑和橡胶的结合形式，进而影响硫化胶的耐磨性，其耐磨性的优劣顺序为：硅烷类偶联剂＞表面活性剂＞钛酸酯类偶联剂，SEM照片对硫化胶磨面的形态分析起到了宏观力学性能和微观的结构分析所达不到的作用，硫化胶的耐磨性越差，其磨纹表面的凸棱越粗。     

硫化橡胶贮存和老化寿命的预测方法

从交联网的微观结构模型出发,用统计力学和老化反应动力学相结合的方法,求得了硫化橡胶的老化时间同某些力学性能间的定量表达式,提出了四种确定老化时间系数和老化反应速率常数的简易新方法。以加速老化法研究了丁腈硫化橡胶在70—110℃,0—100天范围内老化时间与力学性能间的关系,确定了五种不同温度下的老化时间系数和老化速率常数等分子参数值。     

Studies of the network structure of rubber vulcanizates by cryoscopic methods: 2

The freezing point depression, ΔT, of swollen DCP-, TT- and sulphur-cured natural rubber in benzene was observed. The dependence of the parameter, a_H, introduced by Kuhn, was not affected by the type of structure of crosslink sites. It was found from the comparison of the experimental results and scaling law that a_H can reflect not only the difference in three-dimensional structure of network between a degraded and an undegraded rubber vulcanizates but also the difference in degraded network structures between rubber samples with various conditions of degradation.     

Studies of the network structure of rubber vulcanizates by a cryoscopic method: 1

The freezing-point depression, ΔT, of swollen dicumene peroxide cured natural rubber in benzene has been measured. The parameter a_H, introduced by Kuhn, which varies inversely as ΔT, should be regarded as an indication of the depression. The anomalous depression is considered to occur due to a non-frozen benzene area formed on the surrounding network chains. From comparison of the scaling law and the experimental results, it was clear that a_H can reflect not only the quantity corresponding to network chain density determined by conventional methods but also the difference in three-dimensional network structure between degraded and undegraded rubber vulcanizates.