尼龙6动态黏弹性研究

利用熔融指数仪模拟尼龙6的加工工艺,通过改变挤出温度和挤出压力,使尼龙6熔融塑化挤出成丝状样条,热拉伸后所得纤维状样品采用动态力学分析仪测定其储能模量(E')、损耗模量(E")及损耗因子(tanδ)与温度和压力的关系。结果表明:在一定压力下,不同加工温度对尼龙6的储能模量、损耗模量无线性影响,然而加工温度越高,其损耗因子越大;同一加工温度下,储能模量、损耗模量与加工压力的线性关系不明显,而损耗因子对加工压力不敏感,几乎无变化。     

抗滴落阻燃聚丙烯动态粘弹性能及其纺丝温度研究

在聚丙烯／蒙脱土(PP／MMT)纳米复合材料的基础上添加受阻胺型阻燃剂制备抗滴落阻燃聚丙烯切片并纺丝。动态粘弹性测试表明,加入质量分数为1％的阻燃剂就极大的增加PP／MMT纳米复合材料在低频下的储能模量,抗滴落阻燃聚丙烯的类固态流体行为更加明显。随着蒙脱土含量的增加,抗滴落阻燃聚丙烯纤维内部的网络结构逐渐完善,对纺丝温度的影响也逐渐加大,需要适当降低纺丝温度,以适应网络结构,达到可纺性要求。     

聚阴离子纤维素(PAC)与羟丙基甲基纤维素(HPMC)混合体系动态粘弹性研究

考察了溶液浓度对PAC以及PAC/HPMC水溶液动态粘弹性的影响。结果表明,溶液储能模量(G’),耗能模量(G")均随溶液浓度的增大而增大,但储能模量随频率增大的幅度大于耗能模量随频率增大的幅度;溶液的损耗角正切(tanδ)值随浓度增大而逐渐减小;G’~f与G"~f两曲线交点随溶液浓度增大向低频方向移动;由于PAC与HPMC分子间存在氢键作用,因此,与纯PAC溶液相比,相同浓度下PAC/HPMC水溶液的G’~f与G"~f交点对应的频率更高;ω=0相对应的初始tanδ值比同浓度下纯PAC溶液更高。     

涤纶工业丝动态粘弹性的研究

采用动态热机械分析仪分析纺丝温度对涤纶工业丝动态粘弹性的影响,研究了纤维储能模量(E')、损耗模量(E″)及损耗因子(Tanδ)的温度依赖性。结果表明:纺丝温度300℃,涤纶工业丝初生纤维取向及结晶几率低,链段运动能力强,经后拉伸可有效提高纤维强度;在玻璃化转变温度范围内,E',E″及Tanδ均出现极大值,随温度升高,E'及E″下降,在120℃左右E'和E″再次升高,140℃左右则趋于平衡。     

Dynamic viscoelasticity and phenomenological model of electrorheological elastomers

Electrorheological elastomers (EREs) present a tunable viscoelasticity with the application of an electric field. For their application, it is necessary to investigate the viscoelasticity of the EREs under various loading conditions and establish an accurate constitutive model. In this study, anisotropic silicone‐rubber‐based EREs with 30 vol % TiO₂–urea core–shell particles were prepared under an orientation electric field. We evaluated their viscoelasticities by testing their shear stress–shear strain hysteresis loops under various electric fields, frequencies, and strain amplitudes. On the basis of the experimental data, a nonlinear, revised Bouc–Wen phenomenological model was established, and the parameters in the model were identified. The results indicate that the revised model could accurately describe the viscoelastic properties of the EREs within a low frequency. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45407.     

不同来源胶原肽对光老化皮肤成纤维细胞的影响研究

比较研究了海蜇、牛骨和鳕鱼皮3种不同来源胶原肽对光老化皮肤成纤维细胞的修复作用。发现3种胶原肽均可显著提高光老化细胞的细胞增殖活性,经紫外照射后,人皮肤成纤维细胞Ⅰ型、Ⅲ型胶原蛋白及透明质酸合成量明显降低,表现为差异性极显著(P0.01),同时细胞内抗氧化酶系T-SOD、CAT和GSH-Px的抗氧化酶活力也都降低。当加入3种胶原肽后,光老化细胞的Ⅰ型、Ⅲ型胶原蛋白及透明质酸合成量与细胞内T-SOD、CAT和GSH-Px酶活力均有所增加,且改善光老化细胞内抗氧化酶活力与增加细胞胶原分泌效果较好的是海蜇胶原肽。     

Viscoelastic properties of young and old human dermis: A proposed molecular mechanism for elastic energy storage in collagen and elastin

We have studied the strain‐rate dependency of the viscoelastic mechanical properties of human dermis from young (23‐year‐old) and old (87‐year‐old) donors using incremental stress–strain measurements. The elastic spring constant for elastic fibers was found to be strain‐rate and age dependent, whereas that for collagen was only age dependent. Fibril lengths were observed to decrease with increased strain rates and age for both elastic and collagen fibers; however, the large decrease in collagen fibril viscosity was hypothesized to be a result of thixotropy that results when neighboring collagen fibrils slide by each other. It is concluded that the elastic spring constant measured for elastic fibers may be higher than previously reported and is consistent with stretching of α‐helical segments of elastin into a more extended conformation during the initial part of the elastic stress–strain curve. The decrease in the elastic spring constant with increased age observed is consistent with disruption of the elastic fibers and loss of α‐helical structure. The pH dependency of the elastic modulus reported previously for collagen suggests that charge–charge interactions within and between collagen molecules are involved in energy storage during stretching. Elastic energy storage is consistent with the stretching of charged pairs located in flexible regions of the collagen molecule. Shear thinning, or thixotropy of skin, is hypothesized to reflect breakage of bonds that occur between collagen fibrils. It is hypothesized that both collagen and elastin are complex macromolecules that are hybrids of flexible and rigid regions. The flexible regions reversibly store elastic energy during stretching by breakage of secondary bonds. After stretching, the flexible regions become extended and transfer stress to the rigid regions of these molecules. This prevents premature mechanical failure of collagen and elastic fibers in the dermis. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1978–1985, 2002     

Dynamic viscoelasticity of PUF under small strain and prediction of dynamic viscoelasticity in a wide frequency range

The dynamic viscoelasticity of polyurethane fiber (PUF) under small strain was studied with dynamic mechanical analysis and differential scanning calorimetry, and its viscoelasticity was predicted in a wide frequency range. The results revealed that the loss factor (tan δ) was about 0.05 and the phase angle (δ) was 2.86°, very close to the δ of a perfect elastomer in the range from −100°C to −80°C. The master curves superimposed by time-temperature superposition (TTS), the frequency range of the storage modulus master curve spanned 17 orders of magnitude from 10⁻⁷ Hz to 10¹⁰ Hz, and the loss modulus master curve spanned 13 orders of magnitude from 10⁻³ Hz to 10¹⁰ Hz. The apparent activation energy of the soft segment relaxation decreased with increasing temperature in the range from −70 to −26°C. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47070.     

Preparation and viscoelasticity of anisotropic polyurethane composites filled with TiO2 particles

An anisotropic structure arranged by fillers is an effective method to make composites possess special properties, but the conventional particle-reinforced polyurethane (PU) composites usually have an isotropic 0-3 structure. In this study, a precipitation method was used to synthesize TiO₂ particles. The particles were dispersed in a PU matrix, and the structures were observed by scanning electron microscopy. The results indicate that in the presence of an applied electric field, 1-3-like composites with TiO₂ particles in an oriented arrangement were prepared, while 0-3 PU composites were prepared without an electric field. Dynamic viscoelasticity test results show that the PU-TiO₂ composites with a 1-3-like structure have a higher storage and loss modulus. The creep properties of these two kinds of PU composites were measured and further fitted with a Findley power law and Weibull model. It was found that the creep resistance and recovery properties of the PU composites were enhanced by the anisotropic structures of the filler particles in the matrix. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47450.     

Physical aging effects on high temperature relaxations of poly(DTH carbonate) and poly(DTO carbonate) monitored by TSPC and TSDC

Thermal stimulated polarization and depolarization experiments with blocking electrodes are performed on two tyrosine-derived polycarbonates: poly(DTH carbonate) and poly(DTO carbonate). Aging effects are studied in a high temperature range that involved the contribution of the glass transition relaxation peak and the charge redistribution peak originated by the conduction through the sample and the presence of blocking electrodes. A reliable new models are used to described these high temperature relaxations and the results are presented as a function of aging times, polarization conditions and changing structure. For each sample the glass transition temperature, the parameter related with the shape of the glass transition peak and the contribution between the two modeled peaks, are found to be constant and independent of aging time. The variations in shape and temperature position of the maximum of the charge redistribution peak show logarithmic time dependence with aging time. These results are compared to the ones previously reported on a particular tyrosine-derived polyarylate, and the analysis suggests that structural differences in mobility and flexibility of the polymeric chains originate the observed variations. The examination of the experimental data indicates that charge redistribution and glass transition peaks share the same origin, and that the conduction aging effects are triggered by the onset of the glass transition.     

骨胶原清本润肌润体露治疗皮肤瘙痒症的临床疗效和安全性研究

本研究主要评价外用蒽菲优生骨胶原清本润肌润体露产品治疗皮肤瘙痒症的临床疗效和安全性研究,采用CallegariS.P.A.SOFT5.5检测皮肤的pH、皮肤油脂含量及皮肤含水量,用问卷量表方式比较治疗前、后受试者与皮肤干燥相关的症状以及前后疗效评价等方法。     

Studies of triblock copolymer-tackifying resin interactions by viscoelasticity and adhesive performance

—One of the most important applications for styrene-diene triblock copolymers is in the area of pressure-sensitive adhesives (PSA). Tackifiers, amorphous resins with molecular weights in the 500-2000 range, are added to elastomers to make them tacky and thus create a pressure-sensitive adhesive. In this work, various levels of a C₅ aliphatic resin (Escorez 1310LC) were blended into an elastomeric styrene-isoprene triblock copolymer (Shell's Kraton 1107) and viscoelastic studies and tack measurements of these polymer-resin blends were carried out. The function of the resin is to reduce the plateau modulus of the polymer and raise the Tg of the matrix phase. There is some evidence from the thermomechanical properties that two phases exist in the elastomer region, although this point is certainly not proven. However, it seems that there is none or a very minimal amount of resin intruding into the polystyrene domains. Assuming a simple and highly idealized model, a one-to-one correspondence between energy dissipation measured viscoelastically and debonding resistance measured by industry tests was obtained when the adhesives fulfill the Dahlquist criterion. In essence, it was found that PSA performance in several industry tests was linearly correlated with the logarithm of loss modulus at the reduced frequency corresponding to the speed of the debonding test.     

Relationship between viscoelasticity and scratch morphology of coating films

In order to make clear the relationship between viscoelasticity of coating film and its scratch resistance, a number of clear coatings were examined by surface observation and measurements of their mechanical properties.

The scratches can be classified into two types by means of optical microscopic observation with attached polarizing filter, scraped fracture-type and plastic deformation-type. The ratios of the damaged areas to the whole observed areas were determined by image analysis as a measure of scratch resistance.

The comparison between the relaxation spectrum of the coatings and the ratio of the scratched area showed that the degree of surface damage caused by a scratch tester which simulated car washing machine correlated with the storage modulus of the coatings G_sr, at a relaxation time of 1 s. Moreover, the degree of plastic deformation by scratches depended also on S_pls, the minimum strain which could cause plastic deformation in the film.     

淀粉粉体对水系泡沫稳定性及扩张粘弹性质的影响(英文)

Surface dilational rheological behavior and foam stability of starch/surfactant mixed solutions were studied at differ-ent starch concentrations and constant surfactant concentration. The results show that dilational viscoelasticity modulus, dilational elasticity modulus and dilational viscosity modulus increase with the concentration of starch particles. Foam stability increases with dilational viscoelasticity. Foam strength also increases with starch concentra-tion. Starch particles play a positive effect on foam stability and dilational viscoelasticity and the effect becomes more significant as drainage proceeds. Film pictures indicate that the film with 20%(by mass) starch particles is thicker than that without starch. Starch particles gather in Plateau border and resist drainage, making the foam more stable. ? 2014 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. Al rights reserved.     

Effect of starch particles on foam stability and dilational viscoelasticity of aqueous-foam

Surface dilational rheological behavior and foam stability of starch/surfactant mixed solutions were studied at differ-ent starch concentrations and constant surfactant concentration. The results show ...     

Influence of crosslinking and plasticizing on the viscoelasticity of highly filled elastomers

Solid propellants, like all highly filled elastomers, exhibit a complex nonlinear viscoelastic behavior. The aim of this study was to establish the relationships between the structure and properties, which is needed to construct a robust constitutive law for these materials. An extensive design of experiments approach allowed us to quantify the influence of the curing agents and plasticizer molecules on the microstructure of the propellant and its viscoelastic properties. Swelling and gel permeation chromatography measurements described the microstructure of the propellant and prestrained dynamic mechanical analysis (PDMA) characterized the viscoelastic behavior. The curing agents reacted with polymer chain ends participating in the network, in the sol fraction, or in filler–binder links. Consequently, the polymer network was incomplete even in stoichiometric conditions, and a minimum of 10% of the polymer was free in the microstructure. In addition, preswelling the polymer with plasticizer molecules before curing modified the obtained network by decreasing the crosslink density in the binder and increasing it in the vicinity of the filler surface. This study provided new insight into the local deformation mechanisms controlling nonlinearity as measured by PDMA. The nonlinear behavior appeared between 0 and 1.7% prestrain in both the elastic and viscous parts of the behavior. The network reached its maximum extensibility in the elastic part and constrained the sol fraction in this extended mesh for the viscous part. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40392.     

Influence of hydrochloric acid concentration on the demineralization of cortical bone

Although demineralized bone matrix has been considered a successful grafting material, combining both osteoconductive and osteoinductive properties, conflicting results have been published in the literature regarding its bone-inducing abilities. This may be a consequence of following different demineralization procedures that naturally result in products with different properties.The present work examines the evaluation of the demineralization process of similar samples of human cortical bone using three different concentrations of hydrochloric acid solutions (0.6 M, 1.2 M and 2.4 M). Sample calcium content was determined (by Atomic Absorption Spectroscopy) at various immersion times, allowing the construction of the corresponding kinetic profiles. Phase and chemical composition were enabled by X-Ray Diffraction Spectroscopy and Fourier Transform Infrared Analysis, respectively. Structural modifications were followed by Light and Scanning Electron Microscopy and quantified by mercury porosimetry (in terms of porosity and pore size distribution).As expected, increasing the acid concentration led to an increase in the demineralization rate, but not in a proportional way. However, one of the most significant effects of the acid concentration was found on the sample structural features. In fact, a considerable increment in porosity was detected for the sample subjected to the highest hydrochloric acid concentration. Microscopic observations demonstrated that despite the structural deformation resultant from demineralization, the basic microstructure was preserved.     

Influence of fillers and bonding agents on the viscoelasticity of highly filled elastomers

Highly filled elastomers such as solid propellants exhibit a complex nonlinear viscoelastic behavior. This work aimed at determining the influence of binder–filler and filler–filler interactions on the microstructure and the viscoelastic properties of the propellant using a design of experiments method. The influences of the filler fraction and of the filler–binder bonding agents (FBBA) were measured by swelling experiments and prestrained dynamic mechanical analyses. The results showed that FBBA react on the filler surface and concentrate the curing agents in the vicinity of the fillers. The nonlinearity of the viscoelastic behavior originated from filler–filler interactions that created high stress zones between fillers and therefore constrained the movements of the macromolecules of the binder. Filler–binder interactions induced by the FBBA increased the filler effective volume as well as the heterogeneous stress distribution in the microstructure. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40664.     

Creep and strength retention of aramid fibers

Creep tests at ambient conditions have been carried out on Kevlar 49 and Technora yarns covering a wide stress spectrum (10–70% average breaking load) for a long period of time (up to a year). The results confirm that Kevlar 49 and Technora yarns show a nonlinear behavior at stresses below 40% of the breaking load and a linear behavior at stresses above 40%. The strength retention following creep for Kevlar 49 and Technora has also been examined. The results show a significant difference in the behavior of the two materials. Kevlar 49 appears to lose strength almost linearly with time, while Technora seems to lose strength much more rapidly. These results would have significant implications for design. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012