Binders for exterior coatings exhibiting low soiling tendency

Elastomeric coatings protect building facades and flat roofs from moisture and weather exposure. As a drawback, these coatings are prone to dirt-pickup due to the low glass transition temperature of the used polymeric binders. Strategies to overcome this enhanced soiling tendency are discussed, and the results of laboratory and outdoor soiling tests are compared. A novel method for the assessment of wet soiling tendency is presented.     

High temperature silylation of glass capillary columns

This paper describes the results of a study on the deactivation of the surface of glass capillary columns by high temperature silylation (HTS). The different steps, leaching, washing, dehydration and HTS were optimized. A practical procedure yielding a high percentage of very good columns is given. The influence of leaching and HTS on the temperature stability and coating efficiency of capillary columns coated with OV-1 was studied. The inertness of the glass surface after HTS is demonstrated by several examples.     

A generalized theory for the glass transition temperature of crosslinked and uncrosslinked polymers

A generalized theory for the glass transition temperature of crosslinked and uncrosslinked polymers has been developed, which takes into account the influences of end groups, branching, and crosslinking, and their functionality distribution. DiBenedetto's theory was found to correctly characterize the influence of crosslinks on the glass temperature. Normalized to constant crosslink functionality, the crosslink constant is a universal parameter suggesting that the entropic theory of glasses is applicable to crosslinked systems. Data on linear polymers and networks from the crosslinking of polymer chains, vinyl/divinyl-copolymers and step-growth polymers, such as polyurethanes, amine-cured epoxies, or inorganic glasses, are presented.     

Loss of water during heat treatment of acid leached glass and fused silica capillary columns

A study was carried out on the effects of acid leaching of capillary column wall materials. Leaching experiments with glass and fused silica were performed under static and dynamic conditions; moreover, the influence of the temperature was investigated. The amount of water released during different temperature programs was measured with a microwave plasma detector. Different leaching conditions and column wall materials cause considerable variations in water production. These results probably explain the disappointing deactivation efficiency obtained for fused silica and dynamically leached soft glass if HMDS is used. Evidence was found for an increase in surface area due to acid leaching.     

Thermal transformations of selected transition metals oxyhydroxides

We investigated the features of the glass transition relaxation of two room temperature ionic liquids using DSC. An important observation was that the heat capacity jump, that is the signature of the glass transition relaxation, shows a particularly strong value in this type of new and promising materials, candidates for a range of applications. This suggests a high degree of molecular mobility in the supercooled liquid state. The study of the influence of the heating rate on the temperature location of the glass transition signal, allowed the determination of the activation energy at the glass transition temperature, and the calculation of the fragility index of these two ionic glass-formers. It was concluded that this kind of materials belong to the class of relatively strong glass-forming systems. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal analysis of mechanochemically activated glass

Thermal analysis (TG, DTG, DTA, DSC) has been used to study the influence of mechanochemical activation of glass making batch on its melting and obtained glass crystallization. It revealed, that long time (12 h) mechanical treatment accelerates the glass batch melting and also improving network homogeneity influence the internal structure of the obtained glass. Refinement of the glass, at the beginning reduces temperature and increases degree of crystallization as a result of nucleating action of the increasing surface area of grains. However long time activation lowers the crystallization ability of glass and increases crystallization temperature. This is attributed to the deformation of the structure surface layer and surface energy increase, hampering the crystals nuclei formation.     

Cure state detection for pre-cured carbon-fibre epoxy prepreg (CFC) using Temperature-Modulated Differential Scanning Calorimetry (TMDSC)

Carbon-fibre prepregs have found widespread use in lightweight applications. They are based on a carbon-fibre fabric impregnated with reactive epoxy resin. Prepreg materials are generally pre-cured so that they have a higher molecular weight than typical resins in order to reduce resin flow, which facilitates storage and later processing properties.The measurements were carried out using commercially available materials and follow the published DMA investigations of the same material [1]. TMDSC was used to find the correlation between curing conditions, the degree of cure and glass transition temperature. TMDSC has the advantage over standard DSC that it enables better determination of the glass transition temperature, which is often accompanied by an exothermic curing reaction, and thus overshadowed. The influence of the amplitude of temperature modulation was tested in preliminary experiments. For non-cured material a glass transition temperature of approximately 0 °C was determined; whereas for the totally cured material it was approximately 230 °C. The changes in degree of cure, temperature of actual glass transition and post-reaction are given as a function of curing time at 180 °C. The correlation between actual glass transition temperature and degree of cure is derived.     

Effect of Na‐ionomer on dynamic rheological,dynamic mechanical and creep properties of acrylonitrile styrene acrylate (ASA)/Na+1 poly (ethylene‐co‐methacrylic acid) ionomer blend

A special class of engineered copolymers, called ionomers, comprising both electrically neutral repeating units and a fraction of ionized units was melt blended to weather resistant acrylonitrile/styrene/acrylate (ASA) terpolymer for improved electrical conductivity, heat sealing ability, direct adhesion to several polymers, glass and metals without affecting the aesthetics and colorability of ASA. The similar chemical nature of one of the components of each blended materials viz. acrylate rubber in ASA and acrylic acid of Na‐ionomer in addition to the presence of ionic crosslinking within Na‐ionomer, polar acrylonitrile group in ASA affects chain dynamics as compared to neat polymers. In this context, dynamic rheological properties, DMA properties, creep behavior and DSC of the newly developed ASA/Na‐ionomer blends were analyzed. Based on Na‐ionomer content, the blend system either forms “mushroom” or “brush” type conformation and formation of ionic crosslinking in “brush regime” leads to three tiers Caylay tree conformation. The different chain topology resulted into characteristic loss modulous (G″) curve during stress relaxation process. The chain conformation as well as ionic crosslinking and ion–dipole interaction between the blend components also affected DSC endotherm peak and glass transition temperature. The tan δ peak temperature from DMA also revealed the similar observation. The creep compliance of the blends was dependent on Na‐ionomer content and with temperature. The Findley model analysis of creep compliance suggested that the creep compliance was depended on Na‐ionomer content and ionic crosslinking controlled the creep. The findings can be utilized to design weather resistant smart polymer using suitable filler system. Copyright © 2014 John Wiley & Sons, Ltd.     

氮丙啶交联剂的交联性能及固化动力学研究

合成了一种氯丙啶交联剂，并以丙烯酸树脂乳液为模型化合物对交联剂的交联性能及固化动力学进行了研究。结果表明：在丙烯酸树脂乳液中加入适量的氯丙啶交联剂，可使胶膜的力学性能及耐水碱性，耐溶剂性都得到很大的提高；但交联对玻璃化转变温度的影响较小。用程序升温DSC（差示扫描量热法）方法对固化反应动力学进行了研究，计算出固化反应的活化能。     

木糖醇玻璃焓松弛的量热分析

为了考察木糖醇的玻璃化转变和焓松弛行为,寻求碳链长度对线性多元醇玻璃化转变和焓松弛行为的影响,利用差示扫描量热(DSC)技术测定了不同降温速率下木糖醇在玻璃化转变温度(Tg)前后的比热容(Cp),通过曲线拟合获得了TNM(Tool-Narayanaswamy-Moynihan)模型参数,并和其他多元醇类已有研究结果进行对照.结果表明,尽管TNM模型可以很好地重现不同降温速率体系的实验比热容数据,但模型参数并不是材料常数,而是和热历史有关,不同的降温速率对应不同的模型参数.指前因子(A)、非线性参数(x)和非指数参数(β)均随着降温速率的增加而降低,松弛活化焓(△h*)的变化趋势刚好相反.几种线性多元醇玻璃化转变和TNM模型参数的对照表明,玻璃化转变温度,松弛活化焓和动力学脆度(m)都随着烷基碳链长度的增加而增加.虽然非线性参数、非指数参数随碳链长度的增加有降低的趋势,但木糖醇展现出反常变化的情形.     

Effect of Joule heating on efficiency and performance for microchip-based and capillary-based electrophoretic separation systems: a closer look

An attempt is made to revisit the main theoretical considerations concerning temperature effects ("Joule heating") in electro-driven separation systems, in particular lab-on-a-chip systems. Measurements of efficiencies in microfabricated devices under different Joule heating conditions are evaluated and compared to both theoretical models and measurements performed on conventional capillary systems. The widely accepted notion that planar microdevices are less susceptible to Joule heating effects is largely confirmed. The heat dissipation from a nonthermostatically controlled glass microdevice was found to be comparable to that from a liquid-cooled-fused silica capillary. Using typically dimensioned glass and glass/silicon microdevices, the experimental results indicate that 5-10 times higher electric field strengths can be applied than on conventional capillaries, before detrimental effects on the separation efficiency occur. The main influence of Joule heating on efficiency is via the establishment of a radial temperature profile across the lumen of the capillary or channel. An overall temperature increase of the buffer solution has only little influence on the quality of the separation. Still, active temperature control (cooling, thermostatting) can help prevent boiling of the buffer and increase the reproducibility of the results.     

Method of determination of dielectric relaxation characteristics of plasticized polystyrenes on the basis of calorimetric glass temperature

The dielectric loss measurements of different polystyrenes (fractions and blends) with different molecular weights (M _n 2000–125000 g/mol) were carried out in the frequency range 10^–2–10⁶ Hz and the temperature range of the glass process (60°–135°C, depending on the molecular weight). The measurements of the pure fractions showed that the half-width of the glass relaxation process of the different polystyrenes can be correlated by a straight line, if they are plotted versus the relaxation frequency maxima of the glass process, regardless of the difference in both their molecular weight and glass transition temperature. Moreover, the fine structure of the shape of the glass process of polystyrenes with different molecular weights was found to be the same when the glass process appears at the same relaxation frequency range. The addition of oligostyrenes or low molecular <10% wt additives to the high molecular weight polystyrene did not influence the shape of the glass process. The calorimetric glass transition temperature of polystyrene was found to be only dependent on the number average molecular weight as well as on the number of end groups, but not on the molecular weight distribution. The obtained experimental results were correlated to develop a method for the estimation of the dielectric relaxation characteristics (relaxation frequency as well as the shape parameters) of the glass process of plasticized polystyrenes based on the calorimetric glass transition temperature. A method for the analysis of the dielectric relaxation curves of mixtures of label and polymer is suggested.     

Effect of a reactive diluent on the curing and dynamomechanical properties of an epoxy-diamine system

Differential scanning calorimetry was used to study the influence of an epoxy reactive diluent, vinylcyclohexane dioxide, on the curing reaction of a polymeric system composed of diglycidyl ether of bisphenol A (n=0) and 1,2-diaminecyclohexane (DCH). Heat evolution and glass transition temperature, were measured in terms of the added diluent percentage. Experimental results show that both the curing degree and the glass transition temperature of the polymeric system decrease with an increase in the diluent percentage. Dynamic mechanical analysis of several samples also showed that T _g decreases with the increase of diluent percentage, thus corroborating DSC measurements.     

DSC and FTIR Analyses of The Curing Behavior of Epoxy/dicy/solvent Systems on Hermetic Specimens

The curing characteristics of adicyandiamide-cured epoxy system under the influence of solvents in a closed environment were studied by means of isothermal differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The DSC analyses revealed that the presence of solvent results in decreases in the curing exotherm, the initial curing rate, the glass transition temperature, the reaction rate and the reaction order of the epoxy resin. The greatest decreases were caused by the solvent with the highest boiling temperature. A change in temperature-dependent curing route due to the heat absorbed during solvent evaporation is responsible for the difference. The FTIR analyses confirmed that the composition of the cured resin is affected by the solvent, the curing temperature and the specimen configuration. As compared with those obtained from open systems, specimens produced in a closed environment have an enhanced curing exotherm, initial curing rate, glass transition temperature, reaction rate and reaction order because of the retention of volatile catalytic by-products. This revised version was published online in July 2006 with corrections to the Cover Date.     

热释电研究聚碳酸酯掺杂染料体系的玻璃化转变

采用热刺激电流 /松弛谱图分析法 (TSC/RMA)研究了聚碳酸酯掺杂染料体系 (TDAA/PC)的玻璃化转变 ,发现染料含量增加 ,体系的玻璃化转变温度 (Tg)随之降低 ,玻璃化转变的温度范围变宽 .在TDAA掺杂质量比达到 4wt%时 ,其玻璃化转变 (协同松弛 )延伸至 95℃ ,温度范围增加到 3 5℃ .在较大的温度范围内存在协同松弛 ,说明在低于Tg 数十度的温度时 ,染料发色体的极化松弛仍然主要受聚合物玻璃化转变的控制 .     

Determination of glass transition temperature,thermal expansion and,shrinkage of epoxy resins

On the basis of measurements of linear thermal expansion of hardened epoxy resins the influence of some modifiers on the thermal expansion of epoxy resin Epidian-5 has been examined. The glass transition temperatures of examined samples were determined.The paper presents also results of the examinations of changes in thermal and cure shrinkage for epoxy resins that occur under the influence of such modifiers as plasticizers and fillers.Five different compositions were examined. A simple and fast measuring method was applied, in which sample elongations vs temperature were determined with a cathetometer. Specific volume changes of liquid resins with temperature were measured with a quartz dilatometer and a cathetometer.     

Study of Dynamic Rheological,Dynamic Mechanical and Creep Properties of Acrylonitrile Styrene Acrylate (ASA)/Zn+2poly(ethylene-co-methacrylic acid) Ionomer Blend

A new class of blend system comprising weather resistant acrylonitrile/styrene/acrylate (ASA) terpolymer and Zn-ionomer was developed. Based on Zn-ionomer content, the blend system either forms ‘mushroom’ or ‘brush’ type conformation which affected dynamic rheology, DSC, DMA and creep properties differently. Formation of ionic crosslinkings by Zn-ionomer in ‘brush regime’ as well as limited ionic crosslinkings in ‘mushroom regime’ resulted in different nature molecular chain relaxation response. The DSC endotherm peak and glass transition temperature were also influenced by the type of conformation and ion-dipole interaction between the blend components. The tan δ from DMA study also reflected the similar trend. The creep deformation behavior of the blend was found to be dependent on highly deformable Zn-ionomer content and with temperature. The Findley model analysis suggests the ionic crosslinkings may be the possible reason for controlled creep deformation of the blend.     

用DSC测量葡萄糖溶液部分玻璃化转变温度的新方法

用差示扫描量热仪, 采用经过退火处理的连续扫描法, 以不同浓度(20%、45%)的葡萄糖溶液为研究对象, 研究了退火温度对Tgf(部分结晶的玻璃化转变温度)的影响, 给出了确定Tg′(部分玻璃化转变温度)的新方法. 研究发现, 不同退火温度下的Tgf不同. 在−50 ℃以上退火, Tgf随着退火温度的增大而减小; 在−50 ℃以下退火, Tgf随着退火温度的增大而增大, 都有很好的线性关系. 不同浓度的溶液具有相似的规律. 提出从Tgf确定Tg′的方法: Tgf在−50 ℃上下随退火温度变化线的交点所对应的部分结晶玻璃化转变温度即为Tg′. 使用该方法测得葡萄糖的Tg′为−55 ℃.