四溴双酚A环氧树脂/二氨基二苯砜固化过程的研究

用高分子材料动态力学谱仪 (TBA)、示差扫描量热仪 (DSC)等方法研究了二氨基二苯砜 (DDS)固化四溴双酚A环氧树脂 (TBBPAER)的固化过程 ,讨论了固化时间、固化剂用量及固化剂的种类等因素对固化物玻璃化转变温度 (Tg)的影响。实验结果表明 ,随着固化时间的延长 ,固化产物的玻璃化转变温度逐渐升高 ,并且在固化初始阶段为一个值 ,到固化中间阶段变为两个值 ,最后到固化末期又为一个值 ,显示出固化产物的结构有所不同 ;适当增加固化剂的用量未超过理论用量的 2 0 %之前 ,可有效地提高固化产物的玻璃化转变温度Tg值 ;选择不同的固化剂 ,可获得具有不同玻璃化转变温度Tg值的固化产物。     

阻燃韧性不饱和聚酯树脂的粘弹性研究

对用己二酸-二溴新戊二醇-丙二醇-顺酐合成的阻燃韧性不饱和聚酯树脂进行了动态力学测试及分析，确定了该树脂的玻璃化转变温度(Tg)，分析了温度对模量、内耗和玻璃化转变温度的影响，同时对其他影响因素进行了讨论。     

乙烯-醋酸乙烯酯弹性体的制备和研究

制备乙烯-醋酸乙烯酯(EVA)共聚物弹性体,研究溶剂引发剂选择及不同反应乙烯压力对EVA弹性体分子结构、固含量、玻璃化转变温度(Tg)、分子量和特性粘数[η]的影响。研究表明,链转移常数低的小分子醇类宜作为反应溶剂;适量引发剂可提高EVA弹性体醋酸乙烯酯(VAc)含量(w)和分子量;反应压力提高,EVA分子结构亚甲基质子峰向高磁场移动,产物固含量增加,玻璃化转变温度(Tg)和特性粘数[η]降低。     

有机硅丙烯酸乳液的混拼研究

研究了不同比例的高玻璃化转变温度(Tg)硅丙乳液和低Tg硅丙乳液混拼对底材的渗透性、乳液的最低成膜温度(MFT)和涂料性能的影响。     

聚苯乙烯合成及玻璃化转变特性研究

通过使用乌式黏度计和差示扫描量热仪,分别测定了聚苯乙烯的特性黏度[η]和玻璃化转变温度(Tg),并通过实验数据的回归,得到了其数均相对分子质量(Mn)与Tg的关系。为聚苯乙烯的简易制备和Tg测试提供了一种实用方法。     

不同反应压力下乙烯-乙酸乙烯酯树脂的制备及研究

在不同反应乙烯压力下制备乙烯-乙酸乙烯酯(EVA)共聚物,研究不同反应乙烯压力对EVA分子结构、树脂固含量、玻璃化转变温度(Tg)和特性粘数[η]的影响,并用热裂解法对EVA和乙烯-乙烯醇共聚物(EVOH)进行分析。研究表明,随着反应压力的升高,EVA分子结构中的亚甲基质子峰开始向高磁场移动,树脂固含量逐渐增加,玻璃化转变温度(Tg)和特性粘数[η]逐渐降低,并且1.533 min处的峰是EVA分子中乙酸酯基团的热裂解特征峰。     

氰酸酯/联苯型环氧树脂共混体系的DSC研究

采用非等温差示扫描量热法对氰酸酯/联苯型环氧树脂共混体系的固化反应动力学、特征温度、转化率和玻璃化转变温度(Tg)进行了研究。共混体系的表观活化能随着联苯型环氧树脂量的增加而降低,质量比为80/20树脂体系的表观活化能为88.6k J·mol~(-1),高于80/20氰酸酯/双酚A型环氧树脂体系的表观活化能。当固化程度接近完全时,80/20共混体系的Tg为249.2℃,比80/20氰酸酯/双酚A型环氧树脂体系的Tg值高出24.3℃。催化剂的加入能使共混体系的表观活化能下降约20k J·mol~(-1),反应特征温度降低约100℃,同时对Tg影响较小。     

PPO/EP复合材料的玻璃化转变温度及其测试方法

介绍了玻璃化转变温度(Tg)的内涵及其主要测试方法;以聚苯醚/环氧树脂(PPO/EP)为研究对象,分别采用DSC法和DMA法测定其Tg值,并讨论了两种测试方法的异同。结果表明:两种测试方法的测试条件、测试精度及影响测试结果的因素是不同的。在给出某一种高聚物的Tg时须注明测试方法和条件。     

玻璃化转变温度测试方法对测试结果的影响

以玻纤增强尼龙66、高密度聚乙烯为样品,分别采用差示扫描量热法和热膨胀法测试了样品的玻璃化转变温度(Tg)。结果表明,材料的Tg随测试方法、测试条件的不同而变化,采用不同的测试方法所得的Tg结果之间不具有可比性,在说明某种材料的Tg时,应注明所采用的测试方法和测试条件。     

硬段含量对水性聚氨酯性能的影响

以聚酯多元醇和异佛尔酮二异氰酸酯(IPDI)为主要原料，引入亲水单体二羟甲基丙酸(DMPA)，按不同配比合成了系列聚氨酯乳液。考察了硬段含量对乳液粒径、表观黏度、膜吸水性、硬度、力学性能的影响，并通过动态力学性能测试(DMA)研究了软段和硬段的玻璃化转变温度。结果表明：提高-NCP/-0H物质的量之比、DMPA用量均使聚氨酯中软段的玻璃化温度Tg(s)降低，硬段的玻璃化温度Tg(h)升高，△T值增加，软硬段相分离程度增加。随乙二胺用量的增加，会使软段玻璃化转变温度Tg(s)移向高温，软硬段相分离程度降低；硬段含量提高，胶膜硬度增加，拉伸强度增加，胶膜耐水性降低。     

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。     

Glass transition and the flowability and caking of powders containing amorphous lactose

Many powders contain amorphous components, such as amorphous lactose in milk powders, which when given sufficient conditions of temperature and water content, will mobilise as a high viscosity flow making the particles sticky. This can lead to increased cohesiveness, powder caking and increased adhesion to surfaces. The transition from the glassy state is established by increasing the powder temperature to above its glass transition temperature which can be measured using differential scanning calorimetry. Exposing milk powder to over 10-20 °C above the lactose glass transition makes the powder more sticky, rendering it a lot more cohesive and also increases its adhesion to a stainless steel surface. This glass transition induced stickiness is time-dependent. Over time, crystallisation can take place converting the amorphous lactose into crystalline lactose. Furthermore, the caking behaviour of powders depends on the amount of component present in the amorphous state. Finally, this work presents an approach for applying the measured relationship between the glass transition and water content for predicting caking problems with powders containing amorphous components.     

Influence of glycerol and water content on the structure and properties of extruded starch plastic sheets during aging

The properties of starch plastic sheets were investigated by stress—strain measurements in relation with starch crystallinity. Granular potato starch was plasticized with different amounts of glycerol and water by extrusion. The materials were amorphous directly after processing. During aging above the glass transition temperature at various humidities single helical (V and E-type) and double helical (B-type) crystallinity was formed. The rate of crystallization is a function of water and glycerol content. The amorphous rubbery materials were soft and weak with high elongations. During aging the materials became less flexible with higher elastic modulus and tensile stress. The changes are related to changes in water content and glass transition temperature and to changes in B-type crystallinity. The changes in stress—strain properties are explained by the formation of helical structures and crystals, which results in a reinforcement of the starch network by physical crosslinking. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1411–1422, 1997     

Comparing the caking behaviours of skim milk powder, amorphous maltodextrin and crystalline common salt

This work examined and compared the caking behaviour of three physically and chemically different food powders. The food powders studied were maltodextrin DE21 which is an amorphous powder, common salt which consists of crystalline NaCl, and skim milk powder (SMP) which contains a mixture of components including 51% lactose. The three powders were all exposed to high relative humidities (76% or 100%) over a 1-week period and to a humidity cycle to investigate their caking behaviour and interpret their caking mechanisms. The humidity cycle consisted of 2-day exposure to a high relative humidity (RH) followed by 2-day exposure to low RH of 11% and finally 2-day exposure to the original high RH. At the end of each day, cake strength was measured using a force displacement tester and cake water content was also measured. All three powders sorbed much water when exposed to high relative humidities; however, their cake strengths were very different. Cake strength was influenced by glass transition and the ability of the powders to form sinter bridges. All three powders had similar water content profiles during the humidity cycle with water gain at high RH and loss at low RH. The cake strength profile of the amorphous maltodextrin powder and amorphous SMP were different even though the maltodextrin and lactose glass transition temperatures were reduced below the powder temperature during exposure to high RH. The cake strength of maltodextrin decreased during low RH exposure while it increased for SMP. The cake strength profile of the SMP was similar to the crystalline NaCl. The paper presents an interpretation of the caking mechanisms behind the caking behaviour of each powder.     

膨胀防火涂料阻燃性能与乳液玻璃化温度研究

研究了乳液的玻璃化温度对防火涂料阻燃性能的影响。试验发现：不同玻璃化温度的不同类型乳液制备的防火涂料，阻燃性能不同，玻璃化温度越低其阻燃性能越好；玻璃化温度相近的防火涂料，阻燃性能相近；不同玻璃化温度的同一类型乳液防火涂料，阻燃性能不同。乳液玻璃化温度对防火涂料的阻燃性能有关键作用。     

DSC法对阳离子染料可染共聚酯热性能的研究

利用差示扫描量热法(DSC)对阳离子染料可染共聚酯即高温高压型(CDP)及常压沸染型(ECDP)的熔融和结晶过程进行了研究。结果表明:无定形CDP的玻璃化转变温度(T_g)、冷结晶温度(T_(ch))高于PET,但其熔点(T_m)低于PET,无定形ECDP的T_g与T_m低于PET和CDP,且随第四单体聚乙二醇(PEG)的含量及相对分子质量((?)_n)的增加而降低,其结晶速率随PEG的(?)_n及含量的增加而增加。对于等温结晶的共聚酯,1,3-间苯二甲酸双羟乙酯-5-磺酸钠(SIPE)的引入及PEG含量的增加,共聚酯的熔融焓(△H_m)及T_m下降;当PEG含量相同时,随PEG (?)_n增加,ECDP的△H_m及T_m均增加。     

PVC及PMMA在CO_2环境中玻璃化转变特性的研究

对聚合物在CO2环境中的玻璃化转变特性进行了研究。利用蠕变柔量法,在自建的实验装置上,对聚氯乙烯和聚甲基丙烯酸甲酯在CO2环境中不同压力下的玻璃化转变温度进行了测定,并利用间接法测定了对应状态下聚合物中CO2的质量分数。结果表明,在CO2环境中2种材料的玻璃化转变温度显著降低。利用基于经典热力学与统计热力学理论构建的模型,对聚合物中不同的CO2质量分数对应的玻璃化转变温度值进行了计算,得到的计算结果与实验结果较吻合。     

Influence of material properties on the agglomeration of water-soluble amorphous particles

The viscosity and elasticity of particles influence their agglomeration behaviour. Such mechanical particle properties are determined by the supra-molecular and microscopic structure of the particles and process conditions such as temperature, humidity and strain rate or frequency.Most food powders are composed of amorphous water soluble substances. Accordingly spray dried dextrose syrup is used as a model substance for the current study.Such amorphous water-soluble substances show visco-elastic behaviour and depending on strain rate, temperature and moisture content, either the viscous or the elastic properties dominate their material behaviour. The viscous behaviour of a material can be characterised through its shear or its complex viscosity. The materials viscosity affects all types of agglomeration processes. The complex viscosity can be measured by Dynamic Mechanical Thermal Analysis (DMTA) while the shear viscosity is typically determined using a rotational viscometer. Alternatively it is possible to estimate the viscosity based on the difference between glass transition and process temperature.In the current study the glass transition temperature of spray dried dextrose syrup (DE21) is measured for different moisture contents and the obtained data are used for estimating the viscosity. In addition, the viscosity of the dextrose syrup powder at different temperature/moisture/frequency combinations is determined for higher viscosities by DMTA or measured for the lower viscosity range using a rotational viscometer. The obtained data are used to predict growth and pressure agglomeration processes such as fluid bed agglomeration and tabletting.     

Mechanical properties of thermoplastic waxy maize starch

The properties of thermoplastic amylopectin materials were investigated by stress-strain and relaxation measurements as a function of water content and crystallinity. Granular waxy maize starch was plasticized by extrusion with water and glycerol. The materials are amorphous after processing. The sharp fall in modulus at a water content of 10% is characteristic of a glass to rubber transition of an amorphous polymer. The materials are brittle below their glass transition temperature with a modulus of approximately 1000 MPa and an elongation of less than 20%. The amorphous rubbery materials are soft and weak with moduli of 0–10 MPa and tensile strengths of 0–2 MPa. The materials are viscoelastic, show plastic flow, and form a highly entangled polymer matrix, resulting in high values of elongation (500%), due to the high amylopectin molecular mass. Above glass transition temperature the amylopectin forms inter- and intramolecular double helices, crystallizing in a B-type crystal. The initial increase in modulus, tensile strength, and relaxation time is the result of the lower mobility of the amylopectin molecules and the reinforcement of the network by physical crosslinking. The drastic reduction of the elongation and the formation of cracks is the result of intramolecular crystallization. At crystalline junction zones the internal stress is increased and the interaction between molecules is reduced. © 1996 John Wiley & Sons, Inc.     

Effects of drying process for amorphous waxy maize starch on theophylline release from starch‐based tablets

Physical properties and theophylline‐release profiles of compressed tablets prepared with amorphous waxy maize starches dried using different methods were examined. A gelatinized waxy maize starch paste (10% solids in water) was either freeze‐dried or oven‐dried (40 or 105°C) until the moisture content reached to <5%. To form the tablets, the dried amorphous starch powders, either with or without theophylline (3 : 10, w/w), were remoistened to a water content of (17 ± 0.2)%, and compressed into tablets. The drying process applied to the amorphous starch powders affected both the compactness and swelling behavior of the tablets. Although no crystallinity was detected in all the starches tested, X‐ray diffraction patterns indicated that starch chains dried at the lower temperature (40°C) are allowed more time to re‐associate during the drying process than those dried at the higher temperature (105°C). The freeze‐dried starch powders formed tablets characterized by greater compactness and rigidity than was observed in the oven‐dried starch samples. The drug release of the tablets prepared with the starch dried at the higher temperature (105°C) occurred at a much slower rate than that of the tablets made with the starch dried at the lower temperature (40°C). The drug release characteristics of the freeze‐dried starch tablets were nearly identical to those of the tablets prepared with the starch dried at 105°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007