过氧化物预硫化天然胶乳硫化过程胶乳胶膜的热分析

用热重法-微商热重法(TG—DTG)和差热分祈(DTA)研究了用过氧化物预硫化胶乳过程中，硫化时间不同时胶乳胶膜热氧降解的过程。结果表明，过氧化物预硫化胶乳胶膜的起始降解温度、DTG峰顶温度和DTG峰的终止温度、起始放热温度和DTA峰顶温度均随硫化过程发生变化。     

月桂酸铵对浓缩天然胶乳贮存稳定性及硫化胶性能的影响

浓缩天然胶乳(简称浓缩胶乳)是制备天然胶乳制品的重要原材料,在其贮存过程中添加月桂酸铵作为稳定剂来提高胶乳稳定性.月桂酸铵对浓缩胶乳贮存稳定性及硫化胶性能有显著影响,进而影响其制品的性能.本研究通过对浓缩胶乳贮存过程中的机械稳定性(MST)和挥发脂肪酸(VAF)值变化情况进行分析,并对其硫化胶膜交联密度、力学性能和热稳定性能进行测试表征,研究月桂酸铵对浓缩胶乳贮存稳定性及硫化胶性能的影响.结果表明,加入月桂酸铵后,浓缩胶乳Zeta电位绝对值明显增加,乳胶粒子粒径变小,胶乳稳定性增强;月桂酸铵含量为0.050％～0.075％(质量分数,下同)时,浓缩胶乳的机械稳定性显著提高,MST值达到国家标准所需的最短贮存时间(20 d);月桂酸铵导致浓缩胶乳硫化速率降低,在相同预硫化时间下,加入月桂酸铵的浓缩胶乳硫化胶交联密度较低,硫化胶膜力学性能和热性能也下降.     

微波辐射凝固天然橡胶硫化胶热降解动力学的研究

采用热分析法(TA)研究了微波辐射凝固天然橡胶(NR-m)和自然微生物凝固天然橡胶(NR-n)的硫化胶在氮气气氛中的热降解行为,为探索微波凝固天然胶乳这种新加工工艺提供了科学依据.采用Achar法和CoatsRedfern's法求出NR-m和NR-n硫化胶热降解反应中的机理函数,确定热降解反应中可能遵循的动力学机理,并得到了各步反应中的平均表观活化能Ea以及频率因子A等动力学参数.     

膨胀型阻燃剂对硫化天然胶乳胶膜力学性能和阻燃性能的影响

以聚磷酸铵(APP)、季戊四醇(PER)和三聚氰铵(MEL)组成膨胀型阻燃体系(IFR),考察阻燃剂配比及用量对硫化天然胶乳力学性能和阻燃性能的影响,并通过热重分析仪分析其热稳定性、扫描电镜(SEM)分析阻燃剂在胶乳中的分散效果。结果表明,添加PER和MEL的硫化胶膜力学性能很好,但阻燃性能较差;添加APP和IFR的硫化胶膜力学性能较差,但是阻燃性能很好;SEM观察发现APP与橡胶相容性差;热失重分析可知,改性的硫化胶膜比未改性的硫化胶膜的阻燃性好,且IFR改性硫化胶膜的阻燃效果是最好。     

天然胶乳与丁苯胶乳并用胶乳的性能研究

研究了停放时间、并用比对天然胶乳与丁苯胶乳并用胶乳胶体性能的影响,并测试了天然胶乳与丁苯胶乳共混胶乳胶膜的物理机械性能;用差示扫描量热仪(DSC)和热重分析(TG-DTG)法,分析表征并用胶乳的热性能.结果表明:随着停放时间的延长,并用胶乳的黏度显著下降,表面张力下降幅度不明显;随着天然胶乳在并用胶乳中比重的增加,表面张力随之增加;随天然胶乳用量的增加,并用胶乳胶膜力学性能逐步提高.     

BCT-2/NH3复合保存剂对浓缩天然胶乳保存效果及性能的影响

采用水溶性杀菌剂BCT-2与NH3复配作为浓缩天然胶乳的保存剂,研究了复合保存剂对浓缩天然胶乳保存效果,预硫化胶乳粘度、成膜特性,硫化胶膜的干燥特性及物理力学性能的影响。结果表明,在BCT-2用量为0.05%(质量分数)、NH3用量为0.35%(质量分数)时,BCT-2/NH3复合保存剂对浓缩天然胶乳有很好的保存效果,在保存180天后,挥发脂肪酸值(VFA NO.)、机械稳定度(MST)均符合GB/T 8289-2008标准的要求,尤其是VFA NO.仅为0.03,远低于国标0.08;预硫化胶乳停放5天后粘度变化不大,且成膜特性良好,胶膜干燥时间短,干燥速率常数为9.04×103 min-1;与用NH3+TT/ZnO作保存剂时相比,硫化胶膜的拉伸强度变化不大,但撕裂强度达到了53.72kN/m,提高了9.55kN/m。     

过氧化物预硫化天然橡胶/丝素蛋白抗菌复合材料的制备与性能研究

采用三元混合体系溶解丝素蛋白,纯化后与过氧化物预硫化天然橡胶复合,得到了具有抗菌性能的天然橡胶/丝素蛋白(PVNR/SF)复合材料,并对胶乳和胶膜的相关性能分别进行测试分析。结果表明,SF的加入保持了天然胶乳的稳定性。在干燥制成胶膜后,与基体材料有很好的相容性,并且可以在一定程度上起到补强的作用,SF使天然橡胶获得良好的抗菌性能的同时,对基体的热稳定、粘弹等性能没有很大的影响。另外,通过红外光谱我们可以推测SF在胶膜中的抗菌性能与酰胺I结构有关。     

微生物凝固天然橡胶的性能

采用从胶乳中分离、筛选出来的菌种凝固天然胶乳,制备微生物凝固天然橡胶(NR-m)。研究了NR-m的理化性能、热氧降解性能、硫化特性和硫化胶力学性能,并与酸凝固天然橡胶(NR-a)进行了对比。结果表明:与NR-a相比,NR-m的P0和灰分含量高,而挥发物含量、杂质含量、PRI、氮含量低,数均分子量(Mn)大,分子量分布(MWD)窄;混炼胶的最大扭矩值(MH)高,t10和t90短,硫化速率指数(Vc)大;硫化胶力学性能好,老化前、后性能变化较大;NR热氧降解可分为两个阶段,NR-m热氧降解的特征温度T0、TP和Tf均比NR-a低。     

过氧化物硫化三元乙丙橡胶的高温硫化过程模拟

通过橡胶加工分析仪探讨了采用2种一级唯象动力学方程模拟过氧化物高温硫化三元乙丙橡胶(EPDM)的可行性。结果表明,该模型与实测曲线之间具有良好的相关性,随着硫化温度的升高,过氧化物硫化EPDM橡胶的交联反应程度和断链反应程度均增大,反应速率加快。当温度低于195℃时,交联反应的活化能与断链反应的活化能基本相等;当高于195℃时,交联反应的活化能降低,而断链反应活化能的大小依赖于温度变化。并且发现高温硫化EPDM硫化胶拉伸储能模量(E’)的频率依赖性明显增强,硫化时间长短也会影响分子链的松弛行为。     

月桂酸钠对天然胶乳与丁苯胶乳并用胶乳性能的影响

研究了月桂酸钠的不同用量对天然胶乳与丁苯胶乳并用胶乳胶体性能与胶膜的物理机械性能的影响.结果表明:随着月桂酸钠在并用胶乳中用量的增加,并用胶乳的黏度下降,表面张力的变化不大;月桂酸钠在并用胶乳中的用量为0.2％,NRL/SBRL为90/10时,并用胶乳胶膜的物理机械性能最好.     

Adsorption-desorption of ondansetron on latex particles

Ondansetron is a carbazol with antiemetic properties. It is used primarily to control nausea and vomiting caused by cytotoxic chemotherapy and radiotherapy, as well as for treatment of postoperative vomiting in gynecological surgery. Ondansetron has a shelf life of about 3 hr; hence, it is a matter of great interest to determine the ideal adsorption-desorption conditions for this drug on latex particles for designs of formulations (oral suspensions) containing polymers with the aim of delivering different drugs in a prolonged and controlled fashion. Time, pH, electrolytes, and concentration of the active principal at which maximal adsorption occurred were determined. Desorption of the drug from latex polymer particles was studied in different media. The results obtained suggest that this polymer is suitable as carrier of drug for obtained formulations of controlled release. The findings suggest that pH is the principal factor influencing the release of the ondansetron from Aquateric®. The greatest release of drug occurs at acid pH, approximately 70% in the first hour; for the basic medium, the release is about 6%     

Parametric characterizations in superparamagnetic latex

The effect of synthesis parameters on the production of superparamagnetic latex, which are magnetite nanoparticles covered with a poly(methyl methacrylate) layer, were studied. The synthesis method was based on the developed route of emulsifier-free emulsion polymerization. Under this study, effects of the monomer and initiator concentrations, the amount of magnetic sol, the stirring rate and the adding rate of the magnetic sol on the properties of synthesized latexes were investigated. The characterizations were performed by a high resolution transmission electron microscopy, a dynamic light scattering, a vibrating sample magnetometer and a gel permeation chromatography. The results showed that the monomer concentration was found to be the most effective parameter on latex stability. As the initiator amount and the stirring rate increased, saturation magnetization and average molecular weight decreased due to the reactions occurring between surfaces of magnetite nanoparticles and initiator fragments. On increasing amount of magnetic sol, the saturation magnetization and polymer molecular weight increased but the size of nanospheres was unchanged because of the ions in magnetic sol. It was seen that the desired size and magnetic properties of the latex could be obtained since the parameters were found to have substantial impact on their properties.     

Spreading dynamics of a functionalized polymer latex

Functionalized polymer nanoparticles are used as binders for inorganic materials in everyday technologies such as paper and coatings. However, the functionalization can give rise to two opposing effects: It can promote adhesion via specific interactions to the substrate, but a high degree of functionalization can also hamper spreading on substrates. Here, we studied the spreading kinetics of individual functionalized vinyl acetate-co-ethylene polymer nanoparticles on inorganic substrates by atomic force microscopy (AFM) imaging. We found that the kinetics underwent a transition from a fast initial regime to a slower regime. The transition was independent of functionalization of the particles but depended on the wettability of the substrate. Furthermore, the transition from the fast regime to the slow regime occurred at a size-dependent contact angle, leading to a h ～ a(3/2) scaling dependence between the height (h) and the width (a) of the spreading particles. Thereafter, spreading continued on a slower time scale. In the slow regime, the kinetics was blocked by a high degree of functionalization. We interpret the observations in terms of a nanoscale stick-slip transition occurring at interface stress around 6 kPa. We develop models that describe the scaling relations between the particle height and width on different substrates.     

The effect of latex on macrodefect-free cement

The effect of adding latex to macrodefect-free cement was studied. The porosity of the modified pastes was smaller than the normal macrodefect system but the pore size was not significantly changed. The traditional relationship between strength and flaw size in the cement system was found to be inadequate to explain the observed mechanical behaviour of the latex-modified systems. Scanning electron microscopy of the fracture surfaces of the normal and latex-modified pastes revealed that the use of different polymers resulted in different fracture paths through the cement composite. This was due to the difference in chemical nature of the polymer. The results demonstrated that the modulus (E) and fracture energy (R) terms in the traditional Griffith equation become limiting factors for strength determination in low-porosity cement systems.     

Effect of waste latex paint on concrete

Approximately 20% of paint sold in western countries does not get used for its intended purpose, and in time much of this left-over paint ends up in land-fill as part of the household waste collection, at a significant economic and environmental cost. In New Zealand, a comprehensive product stewardship campaign has been initiated to recover waste paint before it enters the waste stream, while the collaboration amongst a cohort of companies has contributed to utilising waste latex paint in concrete. The objective of this study was to investigate the effects of waste latex paint on concrete, with special focus on a low strength standard 20 MPa concrete mix. It is demonstrated that waste latex paint can improve the workability and durability of concrete, whilst achieving sufficient compressive strength. Phase analysis indicated that the addition of waste latex paint does not affect the concrete hydrates. It was established that concrete with 12 L/m³ of waste latex paint is suitable for use in low strength non-structural concrete.     

Interactions between aroma compounds and latex films: partition coefficients and influence on latex film formation

The potential of various latex grades to take up, retain and release different types of aroma compound has been explored. The latex grades used included two styrene–acrylate latices and two styrene–butadiene latices, of which one contained talc. The aroma compounds used were ethyl butyrate, 1‐hexanol, heptanal, 3‐octanone, α‐pinene and limonene dissolved in propylene glycol. It was shown that talc improves both the uptake of aroma compounds in the dispersion phase and the retention during the film formation process. However, the styrene–acrylate latex had a greater ability than the styrene–butadiene latex to hold the aroma compounds once the films were formed. These results have been compared to calculated solubility parameters. The uptake of 1‐hexanol and propylene glycol in the latex dispersions were higher than expected from the theoretical calculations, probably because of the amphiphilic nature of these molecules. In addition, the influence of aroma compounds on the film formation was evaluated. Copyright © 2005 John Wiley & Sons, Ltd.     

Investigating the rheological properties of native plant latex

Plant latex, the source of natural rubber, has been of interest to mankind for millennia, with much of the research on its rheological (flow) properties focused towards industrial application. However, little is known regarding the rheology of the native material as produced by the plant, a key factor in determining latex''s biological functions. In this study, we outline a method for rheological comparison between native latices that requires a minimum of preparatory steps. Our approach provides quantitative insights into the coagulation mechanisms of Euphorbia and Ficus latex allowing interpretation within a comparative evolutionary framework. Our findings reveal that in laboratory conditions both latices behave like non-Newtonian materials with the coagulation of Euphorbia latex being mediated by a slow evaporative process (more than 60 min), whereas Ficus appears to use additional biochemical components to increase the rate of coagulation (more than 30 min). Based on these results, we propose two different primary defensive roles for latex in these plants: the delivery of anti-herbivory compounds (Euphorbia) and rapid wound healing (Ficus).