高分子聚合物松弛行为及模型的研究进展

高分子聚合物材料作为一种使用频率高且应用范围广的材料,其松弛行为对于其加工制品的精度具有重要的影响,且高分子化学合成的结果会最终影响高分子聚合物的松弛行为。由此总结了高分子聚合物松弛行为的特点,整理了其力学松弛及模型、松弛时间的研究进展。并由此提出现阶段高分子聚合物的松弛行为研究的局限性,并指出未来的研究方向。     

EPDM闭孔发泡材料压缩应力松弛行为分析

闭孔发泡材料的应力松弛过程包含分子链段的应力松弛和因气体扩散而导致气体压力下降所引起的松弛两方面内容。本文根据菲克扩散定律,利用分离变量法和边界条件推出气体扩散对应力松弛的影响,在此基础上,结合未发泡材料应力松弛的研究成果,建立了闭孔发泡材料的应力松弛模型,采用该模型拟进一步研究EPDM橡胶发泡材料的应力松弛行为。     

Maxwell与Kelvin两个模型的计算

<正> 高分子的应力松弛与蠕变性质理论上可以用Maxwell与Kelvin两模型来描绘,Maxwell模型模拟了定形变时应力松弛过程,而Kelvin模型则反应了定应力时具有粘弹性质的高分子的蠕变行为,应用这两个模型可以对高聚物的粘弹行为进行理论计算,这些计算不仅有助对应力松弛与蠕变过程本质的深刻了解,对实验研究工作也很有实际意义。     

国外橡胶期刊目录精选

<正>采用原始分子链网络模型预测高分子材料的应力松弛行为459填充补强材料的橡胶的粘弹性形变反应模型464     

橡胶胶料的动态力学应力松弛研究

一、引言应力松弛被公认为是评估密封用橡胶胶料的最合适方法,在许多应用场合,例如发动机和流体动力学应用方面,经常出现动态承载下的密封问题,为了研究这些条件下的密封能力,应该在压缩条件发生变化的情况下即动态压缩条件下进行应力松弛测量,按这种方法测定的应力松弛被称做“动态力学应力松弛”,“振动松弛”或“动态应力松弛”,本文将采用最后一种命名.     

高分子材料记忆效应形成的理论基础及其影响因素

<正> 高分子材料的记忆效应,是指高分子材料的下述特殊的应力应变行为。对已经赋形的高分子材料在高弹态下施加应力,并人为的将该应力以材料应变的形式冻结在高分子链内,而在高分子材料后来的使用过程中,给予适当的条件使冻结的应力释放出来,那么高分子材料也将随之形变而恢复原始的赋形。这种恢复原始赋形的特殊的应力应变行为,称之为高分子材料的记忆效应。     

用动态粘弹试验测定丁腈-26硫化胶热氧老化动力学参数

高分子弹性体受热与氧作用,会导致分子链的断裂或交联。Tobolsky采用间断和连续应力松弛对弹性体的热氧老化交联和降解过程进行了详细的研究。用应力松弛试验研究弹性体的热氧老化,除了化学引起松弛外,分子链滑移引起的物理松弛也必然掺入过程中,致使过程变得复杂了。     

各向异性导电胶应力松弛力学行为

对固化后的各向异性导电胶（ACF）,利用动态力学分析仪进行了单频和多频温度扫描试验,确定了ACF的玻璃化转变温度,得到玻璃化转变温度与频率的关系式.在不同温度和应变下进行了应力松弛实验,实验发现：在一定（25、80、120℃）的温度下,随着应变值的增加,初始应力和在任一时刻的松弛应力都增加;随着温度的提高,应力松弛的松弛率在增加,并且在不同应变下的松弛曲线变得接近;当温度达到玻璃化转变温度附近时,ACF的应力松弛曲线与应变无关.并进行了湿热老化对ACF应力松弛力学行为的实验研究.     

气炮加载下PBXs替代材料中的应力波幅衰减特性

利用白糖、环氧树脂E–51、乙二酸、增塑剂、固化促进剂等通过配方形成的高聚物粘结炸药(PBXs)替代材料,通过一级轻气炮实验,研究了材料在一级轻气炮加载条件下的应力波传播特性,研究发现应力波幅衰减服从指数衰减规律。计算出冲击波波速约为1 500 m/s,波长约为1.5×10^–3 m,通过和白糖颗粒直径的比较分析了应力波幅衰减的机理主要来自于粘结剂的粘性和颗粒滑移与破碎的能量耗散。将PBXs替代材料处理为黏弹性材料,利用Maxwell模型来表征材料在气炮加载下的应力应变关系,并在此基础上研究了材料松弛时间特性。研究发现,随着应变率的增加,PBXs替代材料的松弛时间反而减少,并且呈现出明显的幂率关系,在准静态条件下的松弛时间的应变率相关性在气炮加载下依然存在,从细观尺度下材料微结构运动特征给出了这种相关性的机理解释。     

超临界二氧化碳/乙醇共发泡制备聚砜泡沫制品

以超临界二氧化碳(scCO_2)和乙醇为共发泡剂,通过釜压发泡的方法制备特种工程塑料聚砜(PSU)珠粒泡沫制品。研究了乙醇含量、发泡温度、饱和压力对PSU泡沫材料的泡孔结构和珠粒粘接的影响,阐明了共溶剂发泡与泡沫材料泡孔结构的关系。结果表明,乙醇的引入增加了scCO_2在PSU基体中的溶解度,降低了PSU的发泡温度(最低发泡温度为150℃),拓宽了PSU的发泡温度窗口,增大了泡孔尺寸和膨胀倍率。当乙醇含量为33. 9%,发泡温度为180℃,饱和压力为8 MPa时,PSU珠粒泡沫的平均孔径可达86. 0μm,膨胀倍率可达10. 9倍,泡孔密度为9. 4×10~5个/cm~3,其泡沫制品珠粒间粘接良好,力学性能优良,压缩强度可达7. 2 MPa。     

The effect of barium titanate ceramic loading on the stress relaxation behavior of barium titanate-silicone elastomer composites

The stress relaxation behavior of barium titanate (BTO)-elastomer (Ecoflex) composites, as used in large strain sensors, is studied using the generalized Maxwell-Wiechert model. In this article, we examine the stress relaxation behavior of ceramic polymer composites by conducting stress relaxation tests on samples prepared with varying the particle loading by 0, 10, 20, 30, and 40 wt% of 100 and 200 nm BTO ceramic particles embedded in a Ecoflex silicone-based hyperelastic elastomer. The influence of BTO on the Maxwell-Wiechert model parameters was studied through the stress relaxation results. While a pristine Ecoflex silicone elastomer is predominantly a hyperelastic material, the addition of BTO made the composite behave as a visco-hyperelastic material. However, this behavior was shown to have a negligible effect on the electrical sensing performance of the large strain sensor.     

Electrical conductivity and optical properties of a new quaternized polysulfone

Quaternized polysulfone with triphenylphosphonium pendant groups was investigated, as to its optical and electronic properties. Optical properties were analyzed by refractivity and transmission spectra. To obtain the optical parameters, the approach proposed by Tauc for amorphous semiconductors has been used, because of the similarity of the absorption edges. Values of pseudogap energy and Urbach energy of 3.89 eV and 168 meV, respectively, were obtained. The dielectric properties and AC-conductivity were also studied as a function of temperature and frequency. Decrease in the dielectric constant was observed with the increase in frequency and decrease in temperature. Also, quaternized polysulfone films were characterized by two relaxation processes, γ and β relaxation, which appear at different temperatures, depending on the pendant group. The frequency–temperature-dependent conductivity showed that conductivity increases with frequency and also that the quaternized polysulfones possess typical semiconducting properties. All parameters have been found as slightly influenced by the polymer chain structure.     

On the nonlinear characterization of the long term behavior of polymeric materials

In the linear viscoelastic range the long term behavior of viscoelastic materials—such as polymers—can be described by using exponential series with a limited number of terms for the approximation of the relaxation modulus or of the creep compliance. This procedure can be extended to the nonlinear viscoelastic range by multiplying the linear parameters of the material by certain nonlinearity factors, which depend upon the level of the applied loading. Application of this method to stress relaxation data of several polymers has shown that nonlinearity factors can be approximated as linear functions of the applied constant strain. From creep tests, on the other hand, one can observe that the immediate strain response to the suddenly applied stress is linear elastic even in the nonlinear viscoelastic range of the investigated polymer. The computation of the linear viscoelastic material parameters as well as of the nonlinearity factors is conducted numerically by using least squares techniques. Good agreement between computed results and experimental data can be observed in the presented examples.     

Mechanical relaxation in polycarbonate–polysulfone blends

Lexan polycarbonate and polysulfone P-1700 were blended to various weight percentages by dissolution in methylene chloride. The blended material was reclaimed in the form of evaporated thin films which were dried, ground, and molded. Low-frequency mechanical relaxation tests were run on specimens machined from this material as a function of composition and thermal treatment. In addition to the β-peak, a second peak, β′, was resolved in unannealed 75 wt/o P-1700 specimens. These results are presented and a possible interpretation is discussed and compared with previously proposed mechanisms.     

Streaming potential of microporous membranes made from homogeneously functionalized polysulfone

Microporous membranes were prepared from chemically modified polysulfone. The substitution of the polysulfone was performed in solution using reactions known from polymer modification such as halomethylation, aminomethylation, and lithiation. Membranes can be prepared directly from halomethylated polysulfones which are consecutively converted heterogeneously in a second step to the final functionalized form. Sometimes, two-step reactions are necessary to yield the polymers from which the membranes were cast. In those cases where the reactions change the charge of the polymer, the success of the reaction can be demonstrated by streaming potential measurements. The advantage of this analytical method lies in the fact that the intact membrane is investigated.     

Effect of Silica Nanoparticles on the Performance of Polysulfone Membranes for Olefin‐Paraffin Separation

The separations of ethylene/ethane and propylene/propane using polysulfone‐silica nanocomposite membranes were studied. Silica nanoparticles were prepared via sol‐gel method and the membranes by phase inversion. Characterization by Fourier transform spectroscopy and scanning electron microscopy indicated a good distribution of silica nanoparticles in the polymer matrix and also a good compatibility between the two phases. The performances of the prepared membranes in ethylene‐ethane and propylene‐propane separation were evaluated. The results showed the increments in gas permeability and selectivity by silica. Higher silica contents increased the solubility coefficient and reduced the diffusion coefficient of gases. The plasticization pressure of polysulfone was increased by incorporating the silica nanoparticles in polymer.     

Stress–relaxation in three-element and four-element mechanical models of viscoelastic materials

Three- and four-element mechanical analogues are commonly used to describe viscoelastic behavior in creep (deformation under constant force or stress) but not in stress relaxation (stress response after a suddenly imposed, constant strain). Mathematical models of the mechanical analogues in stress–relaxation are re-derived in this work, keeping notation familiar to polymer scientists. The relationship is shown to meet consistency tests and predicts, with very good accuracy, the behavior of a polyisobutylene sample in stress relaxation when the equation constants were derived from creep experiments. In experiments on an actual mechanical analog, the motion of the Voigt element is shown to exhibit a maximum stress. Implications for the interpretation of creep and stress–relaxation data on the same material are discussed. © 1993 John Wiley & Sons, Inc.     

磺化聚醚砜(SPES)/聚砜(PSF)共混超滤膜的研制

以磺化聚醚砜(SPES)和聚砜(PSF)为膜材料,用共混法制备了SPES/PSF超滤膜。采用均匀实验设计法,研究了SPES/PSF共混超滤膜的制膜工艺,并通过回归分析得到了水通量的模型方程。根据模型方程,作者进行了单因素影响模拟计算,考察共混比、聚合物总浓度、添加剂浓度等对水通量的影响。结果表明:根据最优配方所制备的SPES/PSF膜的水通量为93.1 L/(m2.h),对聚乙烯醇的截留率达93.37%。     

Crosslinked polysulfone obtained by Wittig‐Horner reaction in biphase system

Phase transfer catalyzed reactions are often more easily and cheaply performed than conventional method and they are therefore of particular interest. A polysulfone functionalized with phosphonate (2‐PSF) was prepared under phase transfer catalysis (PTC) conditions, and it was evaluated by spectrometric method (Fourier transform infrared spectroscopy, using potassium bromide (KBr) pellet). The phosphorus content of the modified polysulfone was determined, and it was used for the determination the fraction of repeating units functionalized with phosphonate groups. The modified polysulfone contains 1.40 mmol phosphonate/g polysulfone. Polysulfone functionalized with phosphonate groups and polysulfone functionalized with aldehyde groups (3‐PSF) were used in Wittig‐Horner reaction, to introduce double bonds on polymer and to obtain crosslinked polysulfone (4‐PSF). The reactions were performed using PTC method, solid‐liquid (potassium carbonate (K₂CO₃), tetrahydrofuran (THF), tetraethylammonium iodide (TEAI)) system. The structure of polysulfone functionalized with phosphonate groups and polysulfone functionalized with aldehyde group were confirmed by ¹H‐, ¹³C‐, and ³¹P‐nuclear magnetic resonance (NMR). The peak for phosphorus in PSF‐phosphonate appears in ³¹P NMR spectrum as a singlet at 25.712 ppm. The thermal properties of aldehyde, phosphonate, and crosslinked polysulfone were studied by thermogravimetric analysis (TG) and differential thermogravimetric analysis (DTG). Scanning electron microscopy images for polysulfone functionalized with phosphonate and crosslinked polysulfone are in concordance with nitrogen (N₂) adsorption‐desorption isotherms.POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers