非晶态粉体玻璃化转变温度的测量方法与装置

为了研究非晶态高分子粉体玻璃化转变与结块特性,需要建立一种实用有效的玻璃化转变温度的测定方法。基于非晶态高分子粉体的体膨胀系数在玻璃化转变时发生突变的原理,采用热膨胀计技术,提出了一种用膨胀计测量非晶态高分子粉体玻璃化转变温度的新方法——膨胀计法,并建立了相应的测量装置。以聚苯乙烯为例,详细介绍了用该方法进行测量及数据处理的过程,并考察了测量结果的有效性。以谷物及含水淀粉体为例,考察了该方法在食品粉体玻璃化转变温度测量中的应用。结果表明,膨胀计法测量非晶态高分子粉体玻璃化转变温度,实用、有效,为非晶态高分子粉体的玻璃化转变温度测量提供了一种新途径。     

Interaction of epoxy resins with water: the depression of glass transition temperature

The depression of T_g in a number of epoxy-water systems has been investigated calorimetrically. Except where an unbalanced reaction stoichiometry was used, experimental results are in good agreement with theoretical predictions based on equations developed for the composition dependent T_g in polymer diluent-systems. Thermal analysis also demonstrates a complex thermal behaviour on rescanning of samples, attributed to diluent diffusing out of the sample. The importance of this behaviour in the context of solvent-induced physical ageing of epoxy resin composites is discussed.     

Effect of post-cure on the glass transition temperature and mechanical properties of epoxy adhesives

The effects of post-curing and cure temperature on the glass transition temperature, T _g, and the mechanical properties of epoxy adhesives were studied. T _g was measured by a dynamic mechanical analysis apparatus developed in-house and the mechanical properties of the adhesives (yield strength, Young’s modulus and failure strain) were measured by a tensile machine. The relationships between T _g and mechanical performance under various post-cure conditions were investigated. The curing process was the same for all tests, consisting of an initial stage performed at different temperatures followed by cooling at room temperature. Three sets of specimens were considered, sharing the same initial cure process, but with a different post-curing procedure. In the first set, the specimens were only subjected to a curing process; in the second set, the specimens were subjected to a curing process followed by a post-cure performed at a temperature below the T _g of the fully cured network, T _g∞; and in the third set, the specimens were subjected to a curing process followed by a post-cure performed at a temperature above the T _g∞. When post-cured at a temperature above T _g∞, the mechanical and physical properties tend to have a constant value for any cure temperature.     

粉末涂料的玻璃化温度

重点讨论了粉末涂料玻璃化温度、玻璃化转变理论,并对玻璃化温度与粉末涂料稳定性、熔融黏度、热应力、分子量、化学结构和聚合物的关系做了全面的阐述。     

The role of network architecture on the glass transition temperature of epoxy resins

A series of epoxy networks were synthesized in which the molecular weight between crosslinks (M_c) and crosslink functionality were controlled independent of the network chain backbone composition. The glass transition temperature (T_g) of these networks was found to increase as M_c decreased. However, the rate at which T_g increased depended on crosslink functionality. The dependency of M_c on T_g is well described by two models, one based on the concept of network free volume while the other model is based on the principle of corresponding states. Initially, neither model could quantitatively predict the effect of crosslink functionality in our networks. However, our tests indicated that both the glass transition and the rubbery moduli of our networks were dependent on M_c and crosslink functionality, while the glassy state moduli were independent of these structural variables. The effect of crosslink functionality on the rubbery modulus of a network has been addressed by the front factor in rubber elasticity theory. Incorporation of this factor into the glass transition temperature models allowed for a quantitative prediction of T_g as a function of M_c and crosslink functionality. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 387–395, 1997     

Unexpected partial crystallization of an amorphous polyamide as induced by combined temperature and humidity

In this study, it is presented for the first time, the characterization of an amorphous polyamide after having been subjected to humid thermal conditions such as those typically applied in the industrial sterilization of packaged foods. From a fundamental point of view, it was fortuitously found that the combination of heat and moisture, with and without the assistance of pressure, was capable of inducing some crystallization in the otherwise amorphous polymer. Characterization of the crystallization process was carried out by differential scanning calorimetry, Fourier transform infrared, and simultaneous time‐resolved small and wide angle X‐ray scattering synchrotron experiments. The crystallization of the polymer began as characterized by wide angle X‐ray scattering and differential scanning calorimetry in the presence of humidity at ～90°C and extended up to 120°C under autoclave conditions, and it is thought to be the result of heated moisture being able to disrupt the intense amide groups self‐association. Thus, the thermally activated molecular structure is thought to become plasticized by the combined presence of heat and water which, in turn, provoke sufficient segmental molecular mobility in the system to promote some degree of lateral order. Propertywise, the resulting consequences of this behavior are an increase in the barrier properties to oxygen and a reduction in water sorption. From an applied view point, it is suggested that this unexpected behavior could make this polymer of significant interest in retortable food packaging applications. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1216–1223, 2006     

The effect of citrate esters as plasticizers on the thermal and mechanical properties of poly(methyl methacrylate)

Plasticizers play a key role in the formulation of polymers and in determining their physical properties and processability. This study examines the effects of citrate esters, triethylcitrate, and triacetine as plasticizers on the thermal and mechanical properties of poly(methyl methacrylate). The samples were characterized by differential scanning calorimetry, dynamical mechanical analysis, and mechanical testing under different plasticizer contents. Both citrate esters proved to be effective as plasticizers, DSC data for the triacetine additive fits with Fox equation. Microstructure and relaxation properties were studied by dynamic mechanical analysis where loss modulus shows clearly that absorbed plasticizer shifts the α‐transition to lower temperature and β‐relaxations associated to ester side groups are unchanged even up to 30 wt % plasticizer. Mechanical properties were evaluated with an Instron testing machine. Both additives produced (1) an initial plasticization, with a decrease in tensile strength and modulus; (2) an antiplasticization, reflected as an increase in tensile strength; and modulus and (3) a final plasticization, with a notable decrease in tensile strength and modulus and an increase in elongation where a 35 wt % of triethylcitrate added to the poly(methyl methacrylate) increased in 200% its elongation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

丁羟胶玻璃化温度的模拟计算

丁羟胶的玻璃化转变温度(Tg)预测对丁羟推进剂的贮存、运输和使用具有重要的参考意义。根据丁羟胶的主要性质搭建合理的无定形端羟基聚丁二烯(HTPB)结构模型,选用COMPASS力场、在恒温恒压(NPT)系综下,采用分子动力学(MD)方法模拟计算HTPB在不同温度时的比体积。研究结果表明,比体积与温度的关系曲线斜率在Tg处会发生转折;模拟计算得到的Tg为208.00K,采用差示扫描量热(DSC)法实测得到的Tg为194.86K,两种结果在误差允许范围内基本一致,表明MD法可以用来预测丁羟胶的Tg。     

温度调制热分析技术对预吸热峰的研究

以快速的冷却速率冷却熔体获得的金属玻璃通常远离平衡状态。如果在适当温度经过合适时间退火后,在热流曲线上玻璃转变温度之前会产生明显的预吸热峰。使用常规差示扫描量热法(DSC)和温度调制差示扫描量热法(TMDSC)对Pd₄₀Ni₁₀Cu₃₀P₂₀和Au₄₉Ag_5.5Pd_2.3Cu_26.9Si_16.3两种金属玻璃进行研究。结果表明,预吸热峰从玻璃态到过冷液态是一个连续演变过程,当预吸热峰出现在玻璃转变温度之下时,预吸热峰向高温移动过程中对玻璃化转变过程没有影响。然而,当预吸热峰出现在玻璃化转变温度以上时,玻璃转变开始温度会随着预吸热峰值的增加而增加,因此金属玻璃的动力学稳定性得到了提高。实验结果对理解预吸热峰从玻璃态到过冷液态过程中的稳定变化具有重要意义。     

Direct measurement of the carbon dioxide-induced glass transition depression in a family of substituted polycarbonates

We present a method for the direct measurement of the glass transition temperature of compressed gas–polymer systems. The technique utilizes a Setaram C80D microcalorimeter equipped with high-pressure cells. Pressurizing the cells and running in scanning mode allows direct determination of the glass transition temperature. To validate the method, T_g measurements of the CO₂–poly(methyl methacrylate) system as a function of gas phase pressure were made. The results compare favorably with literature values. However, the effects of foaming appear to interfere with T_g measurement at the highest gas pressures. The CO₂-induced T_g depression of a series of polycarbonates was also measured. The magnitude of the T_g depression increases with decreasing glass transition temperature, reflecting an increase in intrinsic chain mobility, as evidenced by the glass transition temperature. The data correlate well with the Chow model. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1441–1449, 1998     

Deformation-induced bonding of polymer films below the glass transition temperature

Bonding between polymers through interdiffusion of macromolecules is a well-known mechanism of polymer adhesion. A new polymer bonding mechanism in the solid state, taking place at ambient temperatures well below the glass transition value (T_g), has been recently reported; in this mechanism, bulk plastic compression of polymer films held in contact led to adhesion over timescales of the order of a fraction of a second. In this study, we prepared various blends of plasticized polymer films with desirable ductility from amorphous and semicrystalline powders of hydroxypropyl methylcellulose and polyvinyl alcohol derivatives; then, we observed the bonding of these polymers at ambient temperatures, up to 80 K below T_g, purely through mechanical deformation. The deformation-induced bonding of the polymer films studied in this work led to interfacial fracture toughnesses in the range of 1.0–21.0 J/m² when bulk plastic strains between 3% and 30% were imposed across the films. Scanning electron microscopy observation of the debonded interfaces also confirmed that bonding was caused by deformation-induced macromolecular mobilization and interpenetration. These results expand the range of applicability of sub-T_g, solid-state, deformation-induced bonding processes.     

Effects of four isocyanates and four plasticizers on the thermomechanical and tensile properties of hydroxyl-terminated polybutadiene elastomers and the effect of solid particle filling

The aim of this study is to analyze effect of four different isocyanates and four different plasticizers in hydroxyl-terminated polybutadiene (HTPB) based elastomers by quantitative analysis of the shape of the loss factor (tan δ), tensile strength, deformation frequency shift of the maximum temperatures of loss moduli G" and of tan δ. The first part of the study shows intensities of the tan δ curves with the four isocyanates follow the order HDI > IPDI > H12MDI > Desmodur™ E305. By molecular modeling of the isocyanates and the corresponding polyurethane parts the influence of molecular geometry on tan δ are discussed. The second part of the study analyzes HTPB-IPDI elastomers with the four different plasticizers DOA, DOS, DOZ, and IDP. The IDP provides lowest T_g at about −83°C, while the others provide at about −78°C. In the third part, aluminum (Al-18 μm) and ammonium perchlorate (AP-200 μm) are added to HTPB-IPDI+DOA to analyze the effect of particle size, wt% content and particle type on the shape and intensity of the tan δ curves. From the frequency shift of the two maximum temperatures one receives activation energies Eaf. Their average values without and with plasticizer are with tan δ 178 and 165 kJ/mol and with G" 274 and 248 kJ/mol, respectively.     

The influence of iodide on glass transition temperature of high-pressure nuclear waste glasses

The glass transition temperature (T_g) is a key parameter to investigate for application in nuclear waste immobilization in borosilicate glasses. T_g for several glasses containing iodine (I) has been measured in order to determine the I effect on T_g. Two series of glass composition (ISG and NH) containing up to 2.5 mol% I and synthesized under high pressure (0.5 to 1.5 GPa) have been investigated using differential scanning calorimetry (DSC). The I local environment in glasses has been determined using X-ray photoelectron spectroscopy and revealed that I is dissolved under its iodide form (I⁻). Results show that T_g is decreased with the I addition in the glass in agreement with previous results. We also observed that this T_g decrease is a strong function of glass composition. For NH, 2.5 mol% I induces a decrease of 24°C in T_g, whereas for ISG, 1.2 mol% decreases the T_g by 64°C. We interpret this difference as the result of the I dissolution mechanism and its effect on the polymerization of the boron network. The I dissolution in ISG is accompanied by a depolymerization of the boron network, whereas it is the opposite in NH. Although ISG corresponds to a standardized glass, for the particular case of I immobilization it appears less adequate than NH considering that the decrease in T_g for NH is small in comparison to ISG.     

Three‐dimensional thermorheological behavior of isotactic polypropylene across glass transition temperature

The aim of this work was to determine the three‐dimensional thermorheological behavior of isotactic polypropylene (i‐PP) in the region of its glass transition temperature (T_g) by a master curve. The i‐PP is a widespread polymer with a T_g ～ 0°C. Dynamic mechanical analysis (DMA) at varying frequencies and temperatures and bulk tests at varying temperatures and times are carried out to obtain the relaxation spectra. Traditionally, the combination of time and temperature is done for thermorheological simple material by the creation of a master curve based on the Arrhenius or William–Landel–Ferry (WLF) equation. This investigation shows that these equations do not fit the behavior across the glass transition of i‐PP. Instead, a new arc tangent function is derived. Additionally, it can be shown that the shifting factors differ from shear to bulk load. Therefore, the mode of mechanical stress seems to have an influence on the thermorheological behavior. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 877–880, 2004     

分子动力学模拟预测壳聚糖的玻璃化转变温度

为了预测壳聚糖的玻璃化转变温度,在COMPASS力场和恒温恒压（NPT）系综条件下,利用分子动力学模拟方法,在343～543 K温度范围内研究了壳聚糖的玻璃化转变行为,通过模拟体系在不同温度下的比体积、回转半径和能量参数,获得了壳聚糖的玻璃化转变温度(T_g)。研究结果表明,壳聚糖的比体积、回转半径、内能随温度有规律的变化并在T_g处发生转折。模拟计算得到的壳聚糖的T_g与实验方法获得的值基本相符,分子动力学方法可用于壳聚糖玻璃化转变温度的预测。其中,通过回转半径-温度曲线获得的T_g与实验值最相符,回转半径是影响玻璃化转变的一个重要因素,可用于预测聚合物的玻璃化转变温度。     

不同固化剂对环氧树脂玻璃化温度影响的分子动态模拟研究

提出了一个分子动态模拟方法研究环氧树脂玻璃化转变温度(Tg)随固化剂结构变化。首先,建立了固化环氧树脂的一些简单分子模型;然后是一个分子动态模拟(MD)被重复执行。用模拟得到的数据作V-T关系曲线,用曲线上的转折点确定Tg的值。该模拟值与计算值有很好的吻合,尽管与实验值有较大的偏差,固化剂对Tg的影响可以用MD模拟定性得到。所提出的方法对于开发具有提高固化效果的固化剂有潜在的意义。     

聚酯（PET）在超临界二氧化碳中溶胀玻璃化转变温度模型研究

在实验测得高压环境中PET玻璃化转变温度（您）的基础上，将所得实验数据与G—D，CHOW等理论模型计算的％值进行验算比较，发现两种模型均不能很好的描述高压条件下CO2对PET的溶胀行为。     

用玻璃化转变评价氟橡胶的低温性

针对普通氟橡胶耐低温性差的缺点,以低温性好的PL855、GLT两种牌号氟醚生胶为基体制备了氟醚硫化胶。阐述了用玻璃化转变评价氟橡胶低温性的原理,采用差示扫描量热仪测试了不同升温速率下氟醚生胶的玻璃化转变温度,采用动态热机械分析仪测试了不同频率下氟橡胶的玻璃化转变温度,根据所得数据计算玻璃化转变活化能。结果表明,PL855氟醚生胶的玻璃化转变温度和玻璃化转变活化能均比GLT氟醚生胶低,耐低温性更好;用两种氟醚生胶硫化而成的橡胶的耐低温性均比普通氟橡胶的耐低温性好,其中以PL855氟醚生胶制成的橡胶的耐低温性最好。该方法的评价结果与实际应用情况相符合。