结晶及拉伸取向对聚对苯二甲酸乙二酯纤维分子运动的影响

用声频共振法在 100—430°K温度范围内研究了结晶及拉伸取向对 PET纤维分子运动的影响。在研究的温度范围内PET出现两个转变,243°K(β_c),354—383°K(α_a)。拉 伸使α_a转变显著移向高温,而β_c转变基本上不随拉伸比改变,这说明PET纤维的拉伸主要改变了非晶区分子链间的相互作用。 根据高柳的力学模型及建议的方法从α_a及β_c转变的损耗模量峯值计算了PET的“结晶度”,说明用密度法测得的结晶度反映了晶区与晶区缺陷部分的总和。     

拉伸温度对α’-型聚乳酸结构与性能的影响

α’-晶型聚乳酸(PLA)膜被制备和单轴拉伸.通过凝胶渗透色谱仪(GPC)、全反射红外光谱(ATR-IR)、差示扫描量热仪(DSC),X射线衍射(XRD)及Raman光谱等测试技术研究了拉伸温度梯度变化对α’-晶型PLA膜的分子量及其分布、分子链构象、结晶度、晶型转变和取向行为的影响.在恒定拉伸速度与应变下,拉伸温度对PLA膜的应力-应变曲线,特别是屈服强度、拉伸模量产生了较大的影响,其值随拉伸温度的增加而降低.GPC测试结果表明,在不同的温度下拉伸后,PLA会发生一定程度的降解,分子量降低;ATR-IR,XRD,DSC和Raman光谱测试结果表明,在不同的温度下拉伸后α’-型PLA没有发生晶型的转变,即没有由α’-晶体转变为α-或β-晶体.结果表明PLA的结晶度、分子链取向程度强烈依赖于拉伸温度:当拉伸温度低于100℃时,α’-型PLA膜的结晶度与沿着拉伸方向的变形程度随拉伸温度的增加而增加,分子链的高度取向诱导了PLA结晶;当拉伸温度超过100℃后,PLA的分子链沿着拉伸方向上的有序度与结晶度将降低.     

β型聚丙烯注塑件的分层结构与力学性能

用X-射线衍射仪研究了不加和加成核剂形成不同晶型的三种聚丙烯注塑件的分层结晶结构,获得各层结晶度和β晶型含量(k_β)随皮芯距离的分布规律,测定了试件弯曲、拉伸和冲击性能。发现,纯等规聚丙烯试件主要含α晶型,皮层的结晶度和k_β低于芯层。加有α成核剂的试件仅含有α晶型,皮层的结晶度也低于芯层。加有β成核剂的试件主要含β晶型,皮层的结晶度和k_β值高于芯层。纯聚丙烯试件和β型为主的试件的分层结构中存在α晶和β晶间的转变。与α型聚丙烯相比,β型聚丙烯有较低的屈服强度,却有较高的抗张强度,显示很高的拉伸韧性和延展性,可明显提高室温以及玻璃化温度以下的低温抗冲击性能。     

不同后处理条件下聚萘二甲酸乙二酯纤维的结构变化

对不同纺速下制得的聚萘二甲酸乙二酯 (PEN)初生纤维进行了冷拉伸、定长热处理和热拉伸等后处理 .通过WAXS、DSC等测试研究了纤维中结构变化与后处理条件之间的关系 .结果表明 ,较低纺速下所制得的无定形初生纤维在低于Tg 温度下的冷拉伸时发生了应力诱导结晶 ,纤维中生成了α晶体 .同样的初生纤维在定长热处理过程中直至 2 0 0℃仍保持无定形结构 .这些结果说明施加应力相对于升高温度对于α晶体的生成更为重要 .而热拉伸样品中结晶结构的形成与初生纤维的结构有很大关系 ,低纺速下无定形初生纤维在热拉伸后形成α晶体 ,而高纺速下主要含有 β晶体的初生纤维经热拉伸后 β晶体会部分转变为α晶体 ,且 β晶转变为α晶的难易程度取决于初生纤维中 β晶的完善程度 ,初生纤维中 β晶越完善 ,热拉伸时 β晶体越不易转变为α晶体     

单轴拉伸对聚偏二氟乙烯薄膜压电响应性能的影响

采用溶液涂覆成膜工艺制备聚偏二氟乙烯(PVDF)薄膜，对其进行单轴拉伸制得不同拉伸比(R=3, 5, 7)的PVDF薄膜.研究了不同拉伸比对薄膜化学结构、结晶行为、铁电性能及压电响应性能的影响，实现了对PVDF结晶相的本征压电响应性能的增强.单轴拉伸使PVDF结晶度提高，同时促使其结晶相由α相向β相转变；拉伸比越大，极性β相相对含量越高，当拉伸比为7时，薄膜β相的相对含量最高达到85.12%，此时薄膜的电输出性能最佳：外加电场为200 MV/m时，其剩余极化强度为2.69μC/cm~2；应变为5%时，其平均闭路电流密度为58.92 nA/cm~2，平均开路电压为89.70 mV.     

着色剂对锦纶-6结构性质影响

用差示扫描量热法(DSC)和X—射线衍射法,研究了着色剂对锦纶—6(PA—6)热性能和晶态结构的影响。结果表明,可溶性染料影响着色PA—6的熔点,促进PA—6晶态结构中γ晶态的成长。拉伸着色PA—6,总结晶指数不变,(γ+h)晶态中h部分转变为α晶态。松弛热处理能使着色PA—6中无定型结构直接转变为α晶态结构,h晶态全部转化为α晶态,因此热处理的PA—6α晶态和总结晶指数明显增加。     

红外光谱法测定尼龙-6纤维的晶型与取向

原理尼龙-6纤维为多晶高聚物,有α-型与γ-型之分。在卷绕丝中含有较多的无定形部分,其结晶部分主要是不稳定的γ-型结构。拉伸中由于温度及外力的作用,大分子沿着拉伸方向取向。与此同时,晶体逐渐向序列更加规整方向进行,即由γ→α。这种微观结构     

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。     

等规聚丙烯β晶型向α晶型的相转变行为研究进展

等规聚丙烯(iPP)是典型的多晶型半结晶性聚合物,其常见晶型有单斜(α),三方(β),三斜(γ)以及四方或双四方(e),其中稳定性最好的α晶型和处于亚稳态的β晶型工业和经济价值较大,因此二者之间的相转变行为得到了人们的广泛关注.本文综述了近年来β→α-iPP生长相转变的研究进展.在高临界温度(141°C)和低临界温度(100°C)区间内,β-iPP生长速率高于α-iPP,而温度高于141°C,或低于100°C,由于α-iPP在动力学上占优势,β-iPP会发生向α-iPP的生长转变.但由于α-iPP是热力学上最稳定的晶型,β-iPP熔融重结晶过程也会发生β→α-iPP相转变.此外,拉伸形变过程中也会发生β→α-iPP相转变,广泛用于制备聚丙烯气体交换膜、过滤膜或锂电池隔膜等.目前对变形过程中的β→α-iPP相转变机理还存在争议,本文也对2种主要的机理进行了介绍,并对聚丙烯晶型转变行为的研究方向进行了展望.     

聚丙烯β相结晶的研究

本文研究了冷却速率、结晶温度和熔体温度等因素对聚丙烯β相结晶得到的试样的熔融行为的影响。发现β晶型熔融峰的面积随冷却速率的降低或结晶温度的升高而增加。在低于300℃的温度下,熔体温度对聚丙烯的β相结晶无影响。300℃以上的高温破坏了聚丙烯β相结晶的晶核,冷却结晶时不再生成β相晶体。测定了α相及β相球晶在123—140℃的温度范围内线性增长速率,发现在140℃以下,β球晶的增长速率大于α球晶。研究了β相结晶动力学,发现聚丙烯β相结晶不符合Avrami方程,而要用不完全球晶结晶的动力学理论来描述。     

Changes of the Molecular Mobility of Poly(<Emphasis Type="Italic">ε</Emphasis>-caprolactone) upon Drawing,Studied by Dielectric Relaxation Spectroscopy

Dielectric relaxation spectroscopy (DRS) of poly(ε-caprolactone) with different draw ratios showed that the mobility of polymer chains in the amorphous part decreases as the draw ratio increases.The activation energy of the α process,which corresponds to the dynamic glass transition,increases upon drawing.The enlarged gap between the activation energies of the αprocess and the β process results in a change of continuity at the crossover between the high temperature a process and the α and β processes.At low drawing ratios the a process connects with the βprocess,while at the highest drawing ratio in our measurements,the a process is continuous with the a process.This is consistent with X-ray diffraction results that indicate that upon drawing the polymer chains in the amorphous part align and densify upon drawing.As the draw ratio increases,the α relaxation broadens and decreases its intensity,indicating an increasing heterogeneity.We observed slope changes in the α traces,when the temperature decreases below that at which τα ≈ 1 s.This may indicate the glass transition from the ‘rubbery’ state to the non-equilibrium glassy state.     

Study of nucleation induced structure modification in isotactic polypropylene by DMTA and solid state NMR

Isotactic polypropylene (iPP) modified by heterogeneous nucleation and molten state drawing was investigated using the DMTA and NMR methods. The nucleation was realized by specific α and β nucleating agents, 1,3,2,4-bis(3,4-dimetylobenzylideno) sorbitol (Millad 3988, Miliken) leading to the creation of the α phase, and N,N′-dicyklohexylo-2,6-naftaleno dikarboxy amid (NJ100) as the β phase promoter. The processing induced modification was performed by molten state drawing during an extrusion in the range between the die exit and the calibration unit. An increase of the glass transition temperature of iPP was found to be drawing independent for the β-nucleated samples, and dependent in the case of the α-iPP. Changes in the macromolecular mobility, depending on the α/β iPP structure and molten state drawing, was found by NMR lineshape and second moment measurements.     

Studies on the β-crystalline form of isotactic polypropylene

A study has been made of the mechanical, thermal, and morpholigical characteristics of melt-crystallized isotactic polypropylene containing high levels of the β or pseudohexagonal crystalline form. Different levels of β-form crystallinity were produced in the polymer by blending in low levels of quinacridone dye nucleating agent. Microscopical studies of the crystallization process revealed that both α-form (monoclinic), and β-form spherulites nucleated on the dye particles, with α-spherulite growth commencing at a higher temperature. These observations were able to qualitatively explain the dependence of β-form level on both the nucleant concentration and its state of dispersion in the polymer. Improving the dispersion of the nucleant was found to reduce the level of β-form crystallinity if the nucleant concentration exceeded an optimum level. A new procedure for quantifying the volume fraction of β spherulites in a sample was developed which utilized the technique of selective solvent extraction. From volume-fraction, x-ray, and density data, the pure α and β crystal densities were obtained. Dynamic mechanical measurements-obtained on unoriented specimens containing varying levels of β-form crystallinity showed an increase in the magnitude of the damping in the post-T_g region with increasing β content. High levels of the β form lead to lower values of the modulus and yield stress, and higher values of the elongation at break and impact strength.     

High-temperature phases of poly(p-xylylene)

The crystal structure of poly(p-xylylene), as polymerized, is the α form. This transforms irreversibly to the β from by annealing or drawing. To clarify the mechanism of this transition, structural changes of the α and β crystals were examined with a high-temperature stage in the electron microscope. Two high-temperature phases, β₁ and β₂, were found and their structures were analyzed. In these structures lattice distortions due to rotational and translational motions of chains are in troduced, especially in the β₂ form. The α → β transition is induced through such a disordered phase. The statistical arrangement of a molecule in the β-form unit cell results from freezing the disorder in the high-temperature phases.     

THE EFFECT OF HOT DRAWN ON THE PHYSICAL AGING OF ATACTIC POLYSTYRENE

The physical aging behavior of atactic polystyrene (aPS) films achievedunder different drawing conditions has been studied by optical birefringence and modulatedifferential scanning calorimeter (m.d.s.c.). The results show that on annealing at specifictemperature below glass transition temperatue (T_g), the enthalpy relaxation (△H) and T_gdecrease with increasing of birefringence (△n). On the other hand, the effect of moleculardraw ratio (MDR) is confusing: △H and T_g decrease with increasing of MDR in the earlystage of aging, but the MDR's effect become unobvious with the development of aging.It may be concluded that the ordered domain generated by the drawing below or aboveglass transition temperature will affect the development of physical aging behavior. Theviewpoint of cohesional entanglement is used to account for the above observations.     

Deformation temperature and lamellar thickness dependency of Form I to Form III phase transition in syndiotactic polypropylene during tensile stretching

Phase transition from form Ⅰ to form Ⅲ in syndiotactic polypropylene crystallized at different conditions during tensile deformation at different temperatures was investigated by using in situ synchrotron wide angle X-ray diffraction technique. In all cases, the occurrence of this phase transition was observed. The onset strain of this transition was found to be crystalline thickness decided by crystallization temperature and drawing temperature dependent. The effect of drawing temperature on this phase transition is understood by the changes in mechanical properties with temperature. Moreover, crystalline thickness dependency of the phase transition reveals that this form Ⅰ to from Ⅲ phase transition occurs first in those lamellae with their normal along the stretching direction which have not experienced stress induced melting and recrystallization.     

淬火温度对聚偏氟乙烯形态结构的影响

用透射电子显微镜（ＴＥＭ）和傅里叶交换红外光谱（ＦＴＩＲ）等方法研究了结晶温度对聚偏氟乙烯（ＰＶＦ２）晶相结构的影响．结果表明，从ＰＶＦ２熔体高速淬火到较低温度等温结晶可直接生成β相结晶，临界淬火温度为３０℃．淬火温度在４０—７０℃时，α和β相共存．当淬火温度较高时（８０—１５０℃），生成α相结晶．在淬火温度高于１６５℃时，则得到ＰＶＦ２的γ相结晶．在临界温度以下淬火的ＰＶＦ２薄膜含有β相微晶，而高于临界淬火温度时则生成α相或γ相的片晶或球晶结构．     

全同立构聚丙烯的晶片形态

本文应用光学显微镜,扫描和透射电子显微镜从三种不同层次的结构水平上研究了α和β两种晶型的全同立构聚丙烯的球晶和晶片形态结构,特别是应用四氧化钌染色技术直接观察到两种不同晶型聚丙烯球晶中单独分离的晶片形态.结果表明,不同晶型聚丙烯球晶的形态是不同的,其所呈现的性质与其内部晶片结构的排列特征相对应.同时研究了两种晶型聚丙烯在熔体拉伸结晶条件下生成的晶片形态,倾向于相同的取向晶片结构.电子衍射数据证明了,β型聚丙烯在拉伸取向结晶时将转变为α晶型.     

尼龙1010的拉伸结晶行为及Brill转变

摘要 :本文通过示差扫描热分析,广角X射线衍射分析及二维广角X射线散射等手段研究和讨论了尼龙1010在不同的拉伸比率(λ)及拉伸温度（Td）下拉伸诱导的晶体转变及结晶取向行为。实验表明,在拉伸条件下,尼龙1010易于从α晶型向δˊ晶型转变,而拉伸比率的提高,有利于促进这种Brill转变。而在相同的拉伸比率下,随着拉伸温度的提高,发现了尼龙1010从δˊ晶型向α晶型的独特转变,而这种过程刚好与无拉伸状态下的尼龙1010晶型和温度的相互关系截然相反。二维广角X射线散射实验研究结果表明尼龙1010的晶体取向度主要和拉伸比有关,并且（002）的晶面间距随着拉伸比率的提高而增大,表明了长轴尺寸的增大对拉伸取向的依赖关系。     

拉伸热历史对取向聚对苯二甲酸乙二酯膜在热处理过程中收缩和伸长的影响

弄清取向非晶态聚合物在热处理过程中的收缩和伸长的变化规律,以及所对应的结构变化,有较大的实用意义和科学意义。 对于取向聚对苯二甲酸乙二酯的热收缩和热伸长已有很多研究,但对于拉伸热历史对取向PET在热处理过程中的尺寸变化的影响尚缺乏系统的研究。在热拉伸的过程中发生分子链的取向、热弛豫和结晶三个相互竞争的过程。因此,改变拉伸条件可以得到具有各种不同取向和结晶的PET试样。当非晶态PET膜片在80-105℃以较低