退火温度和时间对PET高卷速拉伸变形丝熔化与结晶行为的影响

本文用DSC和密度法研究了高卷速拉伸变形丝(DTY)的熔化与结晶行为。定量地测定了不同温度迟火5分钟急冷后的试样,在DSC曲线上出现的各转变峰温和热焓随退火温度变化的规律,找到了DSC测定的熔化热焓和密度法测定的结晶度之间的对应关系。从试样在熔化峰温退火→冷却结晶→再扫描和在熔化峰温→继续扫描两种方式在DSC曲线上所表现的熔化与结晶行为,探讨了试样在熔融状态退火冷却结晶后再扫描出现双熔化峰的原因,继而研究了试样在熔化峰温的退火时间对结晶完善程制的影响。     

乙烯-辛烯共聚物/淀粉共混体系的非等温结晶动力学

通过差示扫描量热仪(DSC)研究了乙烯-辛烯共聚物/淀粉共混体系的非等温结晶动力学,用Jeziorny和Ozawa方程描述了结晶动力学过程.共混物的结晶温度和结晶焓强烈依赖于淀粉含量和冷却速率.结果表明,随着冷却速率的增加,每个试样的结晶放热曲线均变宽,并向低温区移动.当温度一定高时,所有试样均具有较快的结晶速率. Jeniorzy方程可以较好地描述POE/淀粉共混物的非等温结晶模式,而Ozawa方程对于POE/淀粉共混体系不太适合.     

半晶聚对苯二甲酸乙二酯中的受限非晶相

当半晶聚对苯二甲酸乙二酯 (PET)的结晶度 (Xwc)处于一定范围内时 ,其物理老化后在差示扫描量热(DSC)曲线上的玻璃化转变区有吸热双峰出现 .通过对此吸热双峰分别与完全非晶试样和具有相当高Xwc 的半晶试样物理老化后在DSC曲线上出现的吸热单峰的比较 ,表明半晶PET中存在两种性质极为不同的非晶区 ,即自由非晶区和受限非晶区 .动态力学热分析 (DMTA)曲线上显示的损耗正切 (tanδ)双峰进一步证实了这两种不同非晶区的存在 .这两种不同非晶区的产生是由于试样中晶粒对非晶相中高分子链段活动性的不同限制作用所致 .研究发现 ,对于由冷结晶得到的半晶试样来说 ,出现两种不同非晶区所需的Xwc 上下限都随结晶温度 (Tc)的升高而增高 .还发现 ,在物理老化过程中 ,虽然非晶相的总量基本保持不变 ,但部分自由非晶区却逐渐转变为受限非晶区 .上述实验结果很好地符合Struik的“扩展玻璃化转变”模型 .     

热处理对尼龙1010固态结晶和玻璃态热松驰的影响

本文用DSC首先论证淬火尼龙1010试样在DSC曲线上出现的放热峰是冷结晶峰,然后研究淬火尼龙1010在不同热处理条件下,冷结晶峰和玻璃态热松驰峰的变化规律。实验结果表明,等温结晶时间较短,试样的固态结晶速率较快;等温结晶时间较长,固态结晶速率较慢,这可能与在Tg区域等温所形成的新氢键有关。当升高等温温度时,固态结晶速率加快。在低于Tg的不同温度退火,玻璃态热松弛峰的峰高及热焓在281K达最大值,进而确定对玻璃态热松驰影响最敏感的温度区间是277～284K。     

β晶相聚丙烯的研究——Ⅲ. 乙丙嵌段共聚物

乙丙嵌段共聚物中的丙烯链段在β晶型成核剂存在下,可在20—140℃结晶成高纯度的β晶型。研究了结晶温度对试样中β晶型的相对含量及试样熔融行为的影响。发现依赖于结晶温度、形成了二类β晶型。在20—100℃淬火形成的β晶型、熔融后会重结晶成稳定的β晶型,在高于100℃结晶则形成稳定的β晶型。研究了β晶型试样的力学性质,发现其屈服强度低于而抗冲强度高于α晶型试样。     

硅灰石填充聚丙烯复合材料性能的研究

本文研究了硅灰石填充聚丙烯(含乙烯22％)复合材料的热学、广角X-射线衍射和动态力学性质。复合材料中β晶含量随硅灰石含量增高而增加。试样的熔融及结晶行为表明,所有硅灰石填充试样均含有α和β两种晶型,4个结晶熔融转变;而未填充试样只有a晶型,2个结晶熔化转变。在DSC曲线上,β晶在升温过程中转变成α晶型。硅灰石填料对聚丙烯动态力学性能的影响表明,硅灰石起到了增强剂和β晶成核剂的双重作用,填料硅灰石已进入聚丙烯的结晶相。     

尼龙1010在加热扫描中结构重组的研究

用DSC观察了经不同热处理的尼龙1010的热历史和结构重组的再现过程。合理地解释了DSC曲线上吸热和放热峰的性质,提出预熔结晶峰表征再结晶集合的观点。确定了对结晶完善敏感的热处理温度范围。为尼龙1010的加工和应用提供了部分理论依据。     

尼龙1010结晶与熔融行为的研究

用DSC研究了降温速率R对尼龙10 10结晶与熔融的影响,以及室温(RT)和液氮(LN)骤冷退火样品的熔融.降温时结晶温度随R增大线性降低;T_g以上可完成结晶时结晶度相同;结晶起始温度>181℃生成的晶体有三个熔融峰,对应于环状和放射状球晶的转化与熔融;在181℃和T_g间结晶,无放射球晶转化峰;T_g下有结晶放热峰样品加热时有冷结晶发生.RT未退火样品三个熔融峰,退火温度T_α≥180℃样品两个峰,结晶度C∝T_a;LN未退火样品单一熔融峰,T_a>160℃双峰,T_a≤160℃三峰,低温峰温与C均∝T.     

冷拉伸无定形聚酯纤维的形态研究

本文用差示扫描量热法与X光衍射法相结合,研究涤纶无定形纤维在室温下拉伸后,超分子结构形态的变化。由于采用非晶样品,在一定条件下避免了晶区的出现,肯定了在T_g附近的DSC的宽放热峰包是取向结晶的贡献。它可能是“第三相”的部分热行为。     

结晶对等规立构聚甲基丙烯酸甲酯辐射消旋和辐射裂解的影响

本文通过核磁氢谱、DSC和分子量测定,研究了结晶对等规立构聚甲基丙烯酸甲酯辐射消旋和辐射裂解的影响.分子量测定的结果表明,等规立构聚甲基丙烯酸甲酯结晶后,其辐射裂解反应减弱,裂解G值减小将近一半.核磁氢谱测定辐照试样的空间立构变化结果为:随着辐照剂量的增加,等规立构逐渐变为无规立构和间规立构,其变化规律相似于非晶试样.结果还表明,晶区的消旋反应比裂解反应更为显著.DSC测得的试样熔点,随着辐照剂量的增加而急剧下降,由Flory结晶熔化理论计算得晶区的辐射破坏G值为8.8.该值远大于聚乙烯晶区的破坏G值.     

Role of thermal history on the thermal behavior of poly(<Emphasis Type="Italic">L</Emphasis>-lactic acid) studied by DSC and optical microscopy

Summary The thermal behavior of poly(L-lactic acid) (PLLA) was studied with differential scanning calorimetry (DSC) and polarized optical microscopy. For amorphous PLLA samples, double cold crystallisation peaks were observed in the DSC traces during heating process, being strongly dependent on heating rates. The observation was discussed based on the assumption that the quenched PLLA sample presented some remaining metastable or a precrystalline phase. A small exothermal peak was observed before the main melting peak at low heating rates. The probable reason was discussed through melt-recrystallisation mechanism. Influence of thermal history on the cold crystallisation and melting behavior was also performed on heating process for PLLA samples.     

聚丙烯-聚乙烯嵌段共聚物和相应共混物的热分析

用DSC研究了预期为聚丙烯-聚乙烯两嵌段共聚物(PP-PE)和相应共混物(PP+PE)在热学性能上的差异。经用不同分子量的PP和PE及其共混物进行试验后发现,由于PP和PE在结晶时出现过冷的难易不同。在共混物降温热分析曲线上,当降温速率较快时仅出现一个放热峰,而降温速率较慢时出现PP和PE各自的结晶放热峰,从而解释了文献中的不同结果。并发现共混物的PP和PE熔融、结晶温度均较组分相同的嵌段共聚物的相应温度为高;嵌段共聚物中PP和PE的△H_f值均低于均聚物的△H_f值,而PE的值降低尤甚。我们认为这与嵌段间的共价键限制嵌段活动和结晶过程有关,从而确认DSC热分析可以作为识别是否为嵌段共聚物的一种方法. 本工作的结果表明,所研究的PP-PE试样具有嵌段结构。     

THERMAL ANALYSIS OF POLYPROPYLENE-b-POLYETHYLENE DIBLOCK COPOLYMERS AND CORRESPONDING BLENDS

Difference in thermal behavior of presumed polypropylene-b-polyethylene block copolymers(PP-PE) and corresponding PP+PE blends was studied. Different views in the literature were unified in our observation that faster cooling rate yielded only one exothermal peak for the blends, while slower cooling rates revealed both PP and PE exothermal peaks. Further details on when a single or double exothermal peaks would appear are discussed. Melting and crystallization temperatures for both PP and PE in blends were found to be a few degrees higher than for PP and PE in block copolymers. Thus, thermal analysis can be used to identify PP-PE block copolymers. These phenomena and the lower △H_f-values of PP and PE in block copolymers than the △H_f-values of pure homo-PP and -PE (for PE even more so) are explained in terms of restricted block movement due to covalent bond between blocks and of crystallization processes in block copolymers. The presence of block structure in the PP-PE samples studied is inferred.     

Effects of experimental sample mass on the calorimetric study of thermoset resins

It is known that experimental parameters may affect peak characteristics in DSC studies. Kinetic parameters calculated from isothermal and dynamic runs, can also be affected by the choice of experimental conditions.The sample mass can affect the determination of reaction parameters because of the heat transport and the self-insulating properties of large masses.In the curing process of thermoset resins like unsaturated polyester crosslinked by styrene, the exothermal heat results from the reaction advance but it also produces an autocatalytic process that induces an increase in the reaction rate. The sample mass, in this kind of experiments, can influence the determination of reaction parameters not only through the effect of heat transport or thermal lag on the calorimetric results but also through the action that the sample mass exerts on the exothermal heat, and consequently, on the autocatalytic process.In this paper we intend to present the results obtained in the study of the curing kinetics of thermoset resins by DSC technique using different sample masses. We will point out that the reaction heat determined by dynamic measurement was found to be independent of the sample mass. We have obtained differences in the kinetic parameters like the reaction order, activation energy and preexponential factor when the sample mass was changed.The research reported was supported by CICYT under Grant no. MAT89-377-C02-02.     

Nucleation and crystallization of WO3 from pure and Pb2+ doped NaF fluxes

DTA runs and flux growth experiments have shown that the crystallization temperatures of WO₃ from NaF flux are in the range of 1020–1090°C. Addition of Pb²⁺ influences the crystal growth and the crystallization temperatures are altered (within this range). A thermal effect giving rise to an exothermal DTA peak was observed above the crystallization temperature. This peak occurs at a higher temperature when lead ions are present. We propose an explanation based on pre-crystallization clustering and on the number of nucleation sites on the surface of the platinum crucible.     

Modulated temperature DSC measurements relating to the cold crystallization process of poly(ethylene terephtalate)

The modulated temperature differential scanning calorimetric method (MT-DSC) yields three temperature dependent signals, an underlying heat capacity curve from the underlying heat flow rate (corresponding to the conventional DSC signal), and a complex heat capacity curve with a real part (storage heat capacity) and an imaginary part (loss heat capacity). These curves have been measured in the cold crystallization region for poly(ethylene terephtalate) with a modified Perkin-Elmer DSC-7. The underlying curve shows the well known large exothermic crystallization peak. The storage heat capacity shows a step change which reproduces the change in heat capacity during crystallization. This curve may be used as baseline, to separate the crystallization heat flow rate from the underlying heat flow rate curve. The loss heat capacity curve exhibits a small exothermic peak at the temperature of the step change of the storage curve. It could be caused by changes of the molecular mobility during crystallization.Dedicated to Professor Wunderlich on the occasion of his 65th birthday     

Local control over phase transitions in microgel assemblies

Poly( N-isopropylacrylamide) microgels were coassembled with Au nanoparticles into disordered glassy phases and irradiated with a tightly focused laser (lambda = 532 nm) to study crystallization dynamics following a localized photothermal annealing process. The degree of crystallization produced by the annealing process is dependent upon heat flux into the sample at the site of irradiation, the length of irradiation time, and the temperature of the surrounding bulk assembly that functions as a quenching bath. Control over these sample conditions provides a method by which to probe the dynamics of crystallization over a set of microgel concentrations. The mobility, and thus the crystallization, of particles is shown to be frustrated as the microgel concentration is increased. This is in contrast with equilibrium experiments that have shown an increase in particle mobility with microgel concentration that is manifest as an increase in the freezing transition of the bulk assembly with increasing packing density.     

Transport properties and microstructure changes of talc characterized by emanation thermal analysis

Thermal behavior of talc samples (from locality Puebla de Lillo, Spain) were characterized by emanation thermal analysis (ETA), DTA and TG. The ETA, based on the measurement of radon release rate from samples, revealed a closing up of surface micro-cracks and annealing of microstructure irregularities of the talc samples on heating in the range 200–500°C. For ground talc sample a crystallization of non-crystalline phase formed by grinding, into orthorhombic enstatite was characterized as a decrease of radon mobility in the range 785–825°C and by a DTA exothermal effect with the maximum at 830°C. ETA results characterized the microstructure development of the talc samples on heating and served to evaluate their radon mobility and transport properties on heating and cooling. Transport properties of the talc samples were evaluated by using ETA experimental data measured during heating to 600 and 1300°C, respectively, and subsequent cooling to room temperature.     

Effect of β-nucleation on crystallization of photodegraded polypropylene

The work deals with crystallization of photodegraded polypropylene containing various amounts of β-nucleating agent based on N,N′-dicyclohexylnaphthalene-2,6-dicarboxamide. Compression-moulded samples were irradiated by UV-light, melted and subsequently non-isothermally crystallized. The results showed that the crystallization temperature decreased with increasing irradiation time. The irradiation caused the splitting of crystallization exotherms into two peaks indicating two crystallization mechanisms. The presence of β-nucleating agent in the material suppressed the peak splitting; the higher was the amount of nucleating agent in the sample, the later was the splitting observed.