机械剪切对天然橡胶分子量及其性能的影响

通过机械剪切力作用改变天然橡胶(SCRWF)的分子量及其分布,采用凝胶渗透色谱法测试发现,SCRWF在处理后的相对分子量和分布的变化明显,比较分析不同胶样塑性初值(P_0)、塑性保持率(PRI)、门尼粘度和应力松弛时间等生胶性能,对硫化胶的热稳定性、力学性能,及加工性能进行分析。结果表明,随着机械剪切力作用增加,天然橡胶分子量减小,其单峰趋势明显,生胶质量受其影响变化较大,对热稳定性有影响,且硫化胶的力学性能下降。RPA分析表明,在应变扫描中,随着应变的增加,机械剪切力作用增加的胶样的损耗因子(tanδ)线性增加而弹性模量(G′)线性减小;频率扫描中,随着频率增加,机械剪切力作用增加的胶样损耗因子(tanδ)线性减小而弹性模量(G′)线性增加。     

天然橡胶分子链双键中引入环氧基对其性能的影响

天然橡胶在乳液状态下与过氧乙酸反应，在主分子链双键中引入环氧基团，可显著提高分子极性，但其高强伸性能基本保持不变；玻璃化温度上升，冲击弹性下降，耐油性、气密性、粘合性显著改善。     

天然橡胶与软聚氯乙烯的粘合 Ⅰ.天然橡胶-甲基丙烯酸甲酯-醋酸乙烯酯共聚体系

本文是研究天然橡胶与软聚氯乙烯的粘合问题,目的在于以廉价易得的聚氯乙烯塑料部分地代替来源不足的天然橡胶,以敷当前生产上的需要。聚氯乙烯系一种热塑性树脂,具有类似橡胶的机械强韧性、耐磨性和耐腐性。另外,从经济观点来看,聚氯乙烯要比天然橡胶便宜,而且在我国已开始大规模的生产,将来成本还要继续下降。但是,聚氯乙烯的弹性毕竟要比橡胶差,而且它的玻璃化温度较高,使用     

测定零切变速度下特性粘数的简便方法

引言高分子溶液的特性粘数是一个十分重要的物理量。它和大分子的化学结构、分子量和大分子在溶液中的形态、尺寸大小等重要特性有关。特性粘数和分子量之间的联系更被广泛地利用于测定分子量。因此,如何准确而又简便地测定特性粘数值一向被人们所重视。无数实验事实表明,高分子溶液并非牛顿流体。特性粘数随切变速度的增加而下降,其下降量的大小随分子链刚硬程度、溶剂性能良好程度和分子量的增     

炭黑N134在不同橡胶基体中的分散及其混炼工艺调控

以炭黑N134作为填料,对比了异戊橡胶、丁苯橡胶及仿生橡胶3种体系下混炼工艺对硫化胶性能的影响,并针对仿生橡胶体系炭黑分散度低的问题,对混炼工艺进一步优化,从而提高分散度和动静态性能.结果表明,在所研究的密炼时间范围内,随着密炼时间的延长,异戊橡胶体系和丁苯橡胶体系的分散等级由原本的1级左右提升至6级以上.但延长密炼时间并未明显提升仿生橡胶体系的炭黑分散度.针对该问题引入塑炼和包辊工艺,仿生橡胶炭黑分散性明显提高.随炭黑分散等级的增加, 3种橡胶体系的伸张疲劳性能均得到了较大改善.其中仿生橡胶生胶经塑炼后,门尼黏度和重均分子量均明显下降,表明塑炼对于增强胶料的加工性能有明显作用.相同炭黑混炼时间下,随着塑炼时间的延长,硫化胶佩恩效应也增强,这主要是由于炭黑分散程度的提高使得炭黑与橡胶基体的有效接触面积增加,进而在一定程度上增加了界面结合胶的含量.     

硼酰化钴在橡胶与镀锌钢丝粘合中的应用研究

研究硼酰化钴的用量变化对丁苯橡胶／天然橡胶与镀锌钢丝粘合的影响,通过表面分析对其粘合机理进行了研究。研究表明：硼酰化钴对丁苯橡胶／天然橡胶与镀锌钢丝粘合的粘合增强作用十分明显。硼酰化钴添加2phr左右,粘合性能最佳,同时硫化胶的物理性能得到改善。X-射线光电子能谱分析表明,粘合物镀锌钢丝界面中存在ZnO、ZnS、CoS2,说明粘合时发生了Zn的硫化反应,硼酰化钴中的钴向钢丝表面迁移,继而在锌层中扩散,提高了ZnO和ZnS晶格的缺陷浓度,这两种行为的共同作用,使橡胶与镀锌钢丝的粘合强度显著提高。     

天然橡胶的粘弹性质Ⅲ——本体粘度与粘均分子量之间的关系

关于非晶态高分子化合物的本体粘度依赖于分子量的关系,过去曾有不少工作,但对天然橡胶的数据尚付缺如。 本工作的目的,卽在阐明了天然橡胶本体的非牛顿粘流特性贝及粘流与塑流的互相转变之后,对天然橡胶的本体粘度与粘均分子量之间的关系进行了研究,借所订定的关系式卽可应用机械方法来测定天然橡胶本体的粘均分子量。     

分子量分布对双烯类聚合物粘弹性能的影响—Ⅰ.分子量分布对顺-1,-4聚丁二烯粘弹性能的影响

本文采用沉淀分级和溶液混合的方法制备分子量相近但分子量分布不同的顺-1,4-聚丁二烯样品,通过凝胶渗透色谱(GPC)和应力松弛的方法,研究分子量分布宽度对生胶粘弹性能的影响,并考察低分子量级份对缠结网络密度的作用和高分子量级份对生胶粘弹性能的影响。结果表明,聚合物本体的稳流切变粘度对分子量分布最为敏感。随分子量分布的变宽,低分子量级份增多,缠结网络密度变小,当高分子量级份增加时,生胶的弹性记忆效应加强。     

流变学法研究部分水解聚丙烯酰胺/Cr(III)交联反应I.浓度的影响

采用流变学法系统地考察了部分水解聚丙烯酰胺（HPAM）/Cr(III)交联体系的 反应动力学。HPAM溶液的粘性模量G”大于弹性模量G’,且其数值随时间不发生变 化,体系为粘性溶液。而HPAM/Cr(III)体系的G’和G”的数值都随时间变化,G” 在反应开始阶段大于G’,当反应进行一段时间后,G’超过G”占据主要地位,体 系成为弹性体系。交联过程可分为三个阶段：第一上升阶段,平缓上升阶段和第二 上升阶段。利用G’～ t曲线可以推测反应机理。实验发现成胶速率随反应物HPAM 和Cr(III)的浓度的增加而增加,而成胶时间缩短。在羧基浓度过量的情况下,交 联反应对Cr(III)浓度的反应级数是1。凝胶的有效弹性交联密度随聚合物浓度的增 加而增,且随凝胶反应的进行而增加。凝胶的交联点间的平均分子量随Cr(III)浓 度的增加和交联反应的进行而下降。     

流变学法研究部分水解聚丙烯酰胺/Cr(III)交联反应I.浓度的影响

采用流变学法系统地考察了部分水解聚丙烯酰胺（HPAM）/Cr(III)交联体系的 反应动力学。HPAM溶液的粘性模量G”大于弹性模量G’,且其数值随时间不发生变 化,体系为粘性溶液。而HPAM/Cr(III)体系的G’和G”的数值都随时间变化,G” 在反应开始阶段大于G’,当反应进行一段时间后,G’超过G”占据主要地位,体 系成为弹性体系。交联过程可分为三个阶段：第一上升阶段,平缓上升阶段和第二 上升阶段。利用G’～ t曲线可以推测反应机理。实验发现成胶速率随反应物HPAM 和Cr(III)的浓度的增加而增加,而成胶时间缩短。在羧基浓度过量的情况下,交 联反应对Cr(III)浓度的反应级数是1。凝胶的有效弹性交联密度随聚合物浓度的增 加而增,且随凝胶反应的进行而增加。凝胶的交联点间的平均分子量随Cr(III)浓 度的增加和交联反应的进行而下降。     

Analysis of wax solubility of rubber vulcanizates using wax solution in toluene and molten wax

Wax is commonly used as an antidegradant for rubber materials by formation of an impervious barrier. Wax solubilities in natural rubber (NR), styrene–butadiene rubber (SBR), and butadiene rubber (BR) vulcanizates were measured using wax solution in toluene and molten wax. Wax solubilities using molten wax were much higher than those using wax solution in toluene. The wax solubility of NR vulcanizate was higher than those of SBR and BR. Parameters influencing wax solubility were the solvent swell, rubber fraction and filler type as well as the rubber type. Molecular weight distribution of the dissolved wax was different from that of the raw wax; the dissolved waxes with lower molecular weights were relatively higher than the raw ones. We believe that wax solubility and molecular weight distribution of the dissolved wax can be widely used for determining the wax type and content.     

Characteristics and Bond Performance of Wood Adhesive Made from Natural Rubber Latex and Alkaline Pretreatment Lignin

The aim of this study was to characterize an aqueous polymer isocyanate (API) type adhesive made from natural rubber latex (NRL) and lignin as base polymers, and to evaluate bond performance of the adhesive as laminated wood adhesive. The base polymers of the adhesive were prepared by blending NRL, polyvinyl alcohol (PVA), and lignin isolated from black liquor of alkaline pretreatment of oil palm empty fruit bunch (OPEFB) and sugarcane bagasse (SB) with compositions of 25/25/0, 25/20/5, 25/15/10, 25/10/15, 25/5/20, and 25/0/25 (w/w/w). The isocyanate crosslinker was added at the level of 15% of the weight of base polymer. The glass transition temperature (Tg), heat degradation, and the homogenity of the adhesive blend were analyzed. The adhesive was used for producing laminated wood (20×8 cm²). Results showed that the addition of lignin in the base polymer blends of API adhesive did not significantly affect the Tg of the adhesives. However, it affected the thermal decomposition and bond performance of the adhesives. There were more residues and less homogenous adhesive solution due to the addition of lignin in the base polyemr blends of API adhesives. The addition of lignin in the base polymer blends caused significant decrease in bond performance of the adhesive applied in glue laminated wood.     

The Study on Pervaporation Behaviors of Dilute Organic Solution Through PDMS/PTFE Composite Membrane

As an energy-efficient alternative to distillation, pervaporation has been widely combined with fermentation to remove organic compounds from their dilute solutions in a fermentation broth. In this work, the organic permselective composite membrane is prepared by coating polydimethylsiloxane (PDMS) cross-linked with n-heptane on the substrate of polytetrafluoroethylene(PTFE) membrane. The separation behavior is studied in different dilute organic solutions, which include acetone dilute solution, butanone dilute solution, cyclohexanone dilute solution, ethanol dilute solution, isopropanol dilute solution, n-butyl alcohol dilute solution, acetic acid dilute solution, and ethyl acetate dilute solution. Most of these solutions are main reaction products or by-products from fermentation process. The effects of solubility of organics in the membrane, molecular weight, and polarity of the organics on the pervaporation performance are investigated. The effects of operating temperature and organic concentration in the feed solutions on the performance of composite membrane are studied as well. The experimental results show that molecular volume has less influence than solubility and molecular polarity for these organic solvent. The selectivity of PDMS membrane to ethyl acetate is relative high due to good solubility and diffusion of ethyl acetate molecules in polymer.     

Elaboration of adhesive composites using osonized isoprene rubber for glueing resins

Modification of isoprene rubber was performed using ozonation to improve the adhesive characteristics of its glue composites. Rubber ozonation for 1 h was shown to considerably increase the adhesive durability of those glue combinations. Using 0.1% (w/w) aniline as an amino-containing modified admixture in glue composites on the basis of SKI-3 ozonized rubber additionally allows increasing the durability rates of adherence.     

Effect of modification with rubber on properties and process of curing of epoxy–rubber adhesive compositions

The effect of SKN-30KTRA low molecular weight rubber on the elastic and strength properties of adhesive compositions made with epoxy-rubber composition, is shown. The data on the effect of rubber on curing of adhesive compositions are presented.     

Effects of acid rain on soil humic compounds

The modifications induced by acid rain on the solubility, molecular configuration and molecular weight distribution of humic (HA) and fulvic (FA) acids were studied. A natural soil was subjected to simulated acid rain until a soil pH of 4 was obtained; HA and FA acids were then extracted and characterised. The results obtained were compared both with those of natural soil and with those of a soil subjected to acid rain. Elute analysis indicates the continuous release of soluble organic compounds as a consequence of acid rain simulation, although no relationship was found with the process of soil acidification. The yields of HA and FA show that HA values are the same while FA amount is higher in the natural soil; in acid soils their water solubility increases. The molecular weight distribution shows that HA consist of a mixture of compounds of different molecular weights; they are molecules for the most part larger than 100 kDa and their distribution is not changed by soil acidification. FA can be considered to form a much more homogeneous system; in natural soil, the molecules are larger than 50 kDa, while in acidified soil they are for the most part smaller than 3 kDa.     

间甲钴黏合体系在轮胎骨架材料中的黏合机理研究

为验证与进一步探索黏合树脂及钴盐对轮胎与镀铜钢丝帘线的增黏作用机理,选取传统黏合树脂R80与2种新型黏合树脂HT1005和H620,通过对2种新型黏合树脂的结构分析、橡胶硫化特性、静态T抽出测试与力学性能测试,并设计了一种新的黏合层强度测试方法与黏合层表征方法,进行机理探索,得出如下结论:含有羟基的极性黏合树脂在橡胶硫化时,会由于与非极性天然橡胶的极性差异产生的热力学不相容从而产生自动相分离,向橡胶与镀铜钢丝的界面层进行迁移汇集,且极性越高迁移能力越强,产生一个介于橡胶与镀铜钢丝之间的树脂富集层.因为黏合树脂交联反应温度为140℃左右,会在天然橡胶硫化反应时发生同步交联反应,黏合树脂形成的网络模量高于橡胶硫化网络,会增强镀铜钢丝与橡胶之间的黏合层强度,并形成一个镀铜钢丝与橡胶之间的模量过渡层,进一步增强黏合层.且极性越强,树脂网络交联程度与橡胶硫化网络交联程度越接近,增黏效果越好;钴盐会活化橡胶中的S,使更多的S迁移到镀铜钢丝表面从生成更多硫化亚铜键,增强黏合.     

Characterization of natural rubber concerning its components and molecular weight in Taraxacum kok-saghyz Rodin using pyrolysis gas chromatography-mass spectrometry

Taraxacum kok-saghyz Rodin (TKS) has abundant natural rubber in its root and the molecular weight of its natural rubber is higher than that in Hevea brasiliensis. Thus, TKS is an excellent alternative for the commercial production of natural rubber. The content and molecular weight of natural rubber are two qualitative indicators. Efficient determination for both indicators is still a challenge. In this study, we developed a method to simultaneously determine the content and molecular weight of natural rubber in TKS with pyrolysis－gas chromatography-mass spectrometry. The content of natural rubber was quantified by internal standard method. We optimized the pyrolysis temperature and chromatographic method during content determination. The limits of detection and quantification were 0.47 and 1.56 μg, respectively. In addition, the arachidonic acid methyl ester, an unsaturated fatty acid proposed from the α-end group of natural rubber, was quantified to obtain the number of natural rubber polymers. Based on the content and the polymer number, we also quantified the molecular weight of natural rubber. Thus, the content and molecular weight of natural rubber were simultaneously determined in TKS. Our study provides a new perspective for the high throughput analysis of natural rubber.     

Preparation of Meltable Aromatic Polyimides and Their Adhesive Properties

A series of molecular-weight-controlled aromatic polyimides based on 4,4′-oxydiphthalic anhydride (ODPA), 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6FAPB) and 3,3′-diaminodiphenylsulfone (3,3′-DDS) were synthesized in the presence of phthalic anhydride (PA) as an end-capping agent. The effect of molecular weight on the solubility, melt viscosity, thermal and mechanical properties of the polyimides was investigated. Experimental results demonstrated that the polyimides exhibit good solubility in most polar aprotic solvents and in some common organic solvents, such as DMSO and THF. Homogeneous and stable polyimide solutions with solid contents as high as 40–45 wt% were prepared. High-quality polyimide films were obtained by casting the polyimide solutions onto glass plates and baking them at a relatively low temperature. The polyimide films exhibited outstanding thermal and mechanical properties. The rheological behavior of the polyimides depends on their molecular weight. The adhesive properties of polyimide films bonded to stainless steel at different temperatures were evaluated by the lap shear strength (LSS) test. The polyimides with moderate molecular weight exhibited better adhesive properties. The LSS of polyimide films at ambient and elevated temperatures increased with increasing bonding temperature, which is attributed to the better flow and wetting of the polymer melts during the bonding process.     

Diffusion and permeability of aldehydes into blends of natural rubber and chemically modified low molecular weight natural rubber

Low molecular weight natural rubber (LMWNR) obtained from natural rubber (NR) by depolymerization of natural rubber latex (NRL) was modified by epoxidation to 35% epoxide level to yield epoxidized low molecular weight natural rubber (ELMWNR). The ELMWNR was in turn modified in a solution of thioglycollic acid (TGA) (0.5 mol phr) to yield a product of 20% conversion of its initial LMWNR epoxide. Blends of NR with LMWNR, ELMWNR and epoxidized low molecular weight natural rubber thioglycollic acid (ELWMNR‐TGA) adduct were made. The mixes were vulcanized at 150°C for 20 min before determining the system parameters (n and k), the sorption (S), diffusion (D) and permeability (P) of the vulcanizates in acetaldehyde and formaldehyde solutions at three different temperatures (25, 40 and 60°C) for a period of 90 days. The sorption, diffusion and permeability of the vulcanizates were found to be temperature dependent. The vulcanizates containing ELMWNR were found not to be easily penetrated by both acetaldehyde and formaldehyde when compared with base mix A that is vulcanizates with only NR. The reaction system was found not to be spontaneous but dependent on the activation energies. Copyright © 2005 John Wiley & Sons, Ltd.