A free-volume-based approach to modeling thermoset cure behavior

The free-volume theory for the temperature dependence of transport properties of glass-forming polymers is extended to obtain their relationship to the extent of cure. This treatment centers on the unifying role of molecular mobility and yields a model which connects extent of reaction, viscosity, diffusivity, ionic conductivity and dipole relaxation time. The temporal dependence of these properties is expressed by coupling the extended free-volume model with a relationship for the rate of cure, which included diffusional limitations. Analyses based on this model are applied to the observed behavior of a model epoxy-amine resin system. The intrinsic kinetics of this model system are shown to be first order. It is shown that diffusional limitations strongly affected the progress of the reaction in the final stages of cure. The diffusion-modified rate expression predictions agree with extent of reaction versus time data over the range of experimental temperatures. The temporal dependence of viscous behavior of the curing resin is measured. The extended free-volume model accurately describes the evolution of resin viscosity during cure. The dielectric behavior is similarly characterized and is in close agreement with the predictions of the general free-volume expression. The results of this study indicate that the free-volume theory modified to account for molecular weight effects allows prediction of resin properties with a two-parameter model. The results show that a power-law relationship exists between viscosity and ionic conductivity. This result suggests that electrical properties may be used for on-line measurement of resin viscosity during cure.     

[Bmim]FeCl_4离子液体的物理性质

研究了自制[Bmim]FeCl4离子液体的电导率、黏度与温度的关系,并与文献数据进行了对比.结果表明,采用落球法和旋转法都能准确地测量[Bmim]FeCl4离子液体的黏度;与Andrade方程相比,VTF方程能更好地拟合[Bmim]FeCl4离子液体的黏度和温度的关系,其相关系数达0.999 9.采用不同电导率仪测量的[Bmim]FeCl4离子液体的电导率有较大差别;相比Arrhenius方程而言,VTF方程能更好地拟合电导率与温度的关系;随着温度的变化,电导率与黏度的关系符合Walden规则,其相关系数达到0.99以上.     

The effect of stoichiometry on chain segment and ion mobility in partially polymerized epoxy systems

The temperature dependence of steady-shear viscosity and ionic conductivity were measured for a series of unreacted mixtures and partially cured, ungelled samples of diglycidyl ether of bisphenol-A (DGEBA) and an amine cross-linking agent, diamino diphenyl sulfone (DDS). Six stoichiometric ratios of epoxide groups to amine hydrogens were examined. Free volume expressions were used to model the temperature dependence of the conductivity and viscosity for the unreacted DGEBA-DDS mixtures. In addition, these expressions were combined to successfully correlate changes in viscosity and conductivity during the DGEBA-DDS polymerization prior to gelation. It also was demonstrated that the change in weight average molecular weight during polymerization could be interpreted from the dielectric data. Through studying variations in the stoichiometry, it was possible to examine the effects of changes in chemical structure and ion concentration on the fitted parameters in the free volume models. The inherent ion transport factor (ζ₀) was found to be inversely proportional to the concentration of ions in the test samples. The fractional free volume for segmental motion (B) was found to increase with an increase in the glass transition temperature and to be a function of the rigidity of the polymer. ©1995 John Wiley & Sons, Inc.     

Melt flow behavior of polypropylene composites filled with multi-walled carbon nanotubes during extrusion

Polypropylene (PP) composites filled with multi-walled carbon nanotubes (MWCNTs) were prepared using a twin-screw extruder. The melt flow properties of the composites were measured with a capillary rheometer in a temperature range from 180 to 230 °C and at various apparent shear rates varying from 100 to 4000 s⁻¹. The results showed that the melt shear stress increased almost linearly while the melt shear viscosity decreased almost linearly with increasing shear rates in a bi-logarithmic coordinate system. The melt shear flow followed the power law relationship and the dependence of the melt shear viscosity on temperature obeyed the Arrhenius equation. The relationship between the melt shear viscosity and the MWCNT weight fraction was roughly linear under the investigated range of temperature or shear rate.     

Monitoring of the shrinkage during the photopolymerization of acrylates using hyphenated photorheometry/near‐infrared spectroscopy

This article describes a new method for the quantitative determination and time‐resolved monitoring of the polymerization shrinkage during ultraviolet (UV) photopolymerization. It is based on rheometry using a modified oscillating rheometer. Shrinkage is determined from the decrease of the gap between the rheometer plates. Moreover, near‐infrared (NIR) spectra can be recorded directly in the rheometer, which allows continuous determination of the conversion at any time of a shrinkage measurement. As both shrinkage and conversion data come from the same experiment, shrinkage can be analyzed in dependence on the current conversion achieved during UV irradiation, which enables direct investigation of correlations between both parameters. Hyphenated photorheometry/FT‐NIR spectroscopy was used for the determination of the polymerization shrinkage of pure acrylate monomers and oligomers as well as acrylate‐based formulations. Quantitative shrinkage values were found to be in excellent correlation with data that were determined by an independent method (via buoyancy measurements) and data from literature. Furthermore, the effect of ambient and irradiation conditions or the content of nanoparticles on the degree of shrinkage was studied. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 729–739     

Bulk Viscosity and the Relation between Transport Coefficients

Abstract

The longitudinal and bulk viscosity of the fluid Argon is calculated using its relation with self diffusion coefficient. This relation was derived by developing the relation between coherent and incoherent scattering functions. The results obtained are compared with recent simulation data of bulk viscosity. A good agreement is achieved for a wide range of temperatures at the triple point density. Our results successfully explain the increase in bulk viscosity with decrease in temperature near the triple point. The validity of the relation between diffusion and longitudinal viscosity is also tested for liquid metals. The results obtained for liquid metals of the longitudinal viscosity, at their melting points, are not found to be in agreement with experimental results. A relation between thermal conductivity and self-diffusion coefficient is proposed.     

质子型离子液体N,N-二甲基乙醇胺丙酸盐的密度、粘度及电导率

在283.15-333.15 K温度范围内, 测量了质子型离子液体N,N-二甲基乙醇胺丙酸盐(DMEOAP)的密度、粘度及电导率. 讨论了温度对密度、粘度和电导率等物理化学参数的影响. 通过经验和半经验方程得到了该离子液体的热膨胀系数、分子体积、标准摩尔熵及晶格能等热力学性质参数. 由电导率和密度计算出了该离子液体的摩尔电导率. 利用Vogel-Fulcher-Tamman (VFT)方程, 将测量的动力粘度和电导率对温度拟合, 得到了动力粘度和电导率随温度变化方程式.并通过Walden规则, 建立了粘度与摩尔电导率之间的联系.     

Chemorheology relations for epoxy-amine crosslinking

The goal of this study is to elucidate the relationship between the mechanism of bond formation, resulting structure, and the viscosity during the step polymerization of a thermoset. The system chosen for this work consists of a bifunctional epoxy, diglycidyl ether of bisphenol A, cured with a tetrafunctional amine, diaminodiphenyl sulfone. Steady shear and dynamic viscosity are measured as a function of extent of reaction throughout the epoxy-amine cure. Branching theory is used to relate the extent of reaction (i.e., conversion of epoxy groups) to certain structural parameters, including the weight-average molecular weight. The combination of the viscosity-conversion data with the branching theory enables the correlation between changes in rheological properties and network structure during polymerization. The steady shear viscosity rise is modeled as the product of a structure-dependent friction factor and weight-average molecular weight. The structural significance of the point in cure when the dynamic storage and loss modulus are equal (i.e., tan δ = 1) is also explored.     

含氰基离子液体的合成、表征及流变性质研究

摘要合成、 表征了一系列新的含氰基咪唑类离子液体. 测定了该离子液体的密度、 熔点及溶解性等物理性质, 研究了其在稳态、 瞬态和动态条件下的流变行为. 结果表明, 当剪切速率在0.1～50 s^-1范围内时, 其粘度不随剪切速率的变化而变化, 但随温度升高而降低, 粘流活化能随取代基长度变化呈现规律性变化. 对于1-丁基-3-氰乙基咪唑六氟磷酸盐离子液体, 维持剪切速率不变时, 其剪切应力和粘度均不随时间变化, 且随着温度的升高而降低; 在动态条件下, 在线性粘弹区, 复合粘度和损耗模量G″ 随温度升高而降低. 关键词     

Correlation between chain segment and ion mobility in an epoxy resin system. A free volume analysis

Steady shear viscosity and ionic conductivity have been measured for nine commercial diglycidyl ether of bisphenol-A (DGEBA) epoxy resins with molecular weights ranging from 340 to 14,200. The temperature dependence of viscosity and ionic conductivity was modeled using free volume viscosity and ionic conductivity relationships, which correlate the fractional free volume required for polymer chain segment motion (B) and the fractional free volume required for ion motion (B′) with polymer structure. The fractional free volume required for polymer chain segment mobility was observed to increase systematically with the molecular weight of the resins. The fractional free volume required for ion mobility did not vary for the resin series. A stoichiometric mixture of a low molecular weight DGEBA resin and a 4,4′-diaminodiphenyl sulfone cross-linker was partially polymerized to extents of reaction ranging from 0% to 49%. The fractional free volume required for polymer segment mobility for these partially polymerized samples was consistent with results for the neat resins. © 1993 John Wiley & Sons, Inc.     

Geometry dependence of the elongation behavior of a polypropylene melt through a micro die

A series of rheological experiments was performed for a polypropylene (PP) melt to explore its elongation behavior through a capillary die. Using an advanced twin-bore capillary rheometer with dies measuring 1.0, 0.5, and 0.25 mm in diameter, the experiments were performed at 210, 220, and 230 °C. The results indicated that the temperature of the PP melt had a significant effect on its extensional viscosity. The different decreases in the extensional viscosity values in the tested dies revealed the geometry dependence of the extensional viscosity. In the case of PP in the 0.25 mm die at 210 °C, the extensional viscosity values under different extensional strain rates were much higher than those in the other dies. Only in the 1.0 mm die did the relationship between the extensional viscosity of PP and its temperature obey the Arrhenius equation due to the larger die size which related to a slight size effect on its elongation behavior. The calculated deviations of the extensional viscosity in the tested dies demonstrated that the increasing pressure applied to the PP melt in the micro channel was related to the geometry dependence of the elongation behavior of the PP melt. The change in the extensional viscosity eventually relied on the interaction of the die geometry, the temperature, and the extensional stress of the PP melt.     

聚醚酯嵌段共聚物熔体的流变性能

采用毛细管流变仪测定了组成比、聚醚分子量、熔融时间和熔融温度对嵌段聚醚酯熔体表观粘度的影响．结果发现在所研究的温度和切变速率范围内,该结构聚醚酯熔体为假塑性非牛顿流体,其粘度随聚酯段含量的增加而增加,随熔融时间增加而降低,随聚醚分子量的增大而增大．聚醚酯的零切粘度可由Ｓｐｅｎｃｅｒ Ｄｉｌｌｏｎ 公式外推得到,零切粘度对温度的依赖关系服从Ａｎｄｒａｄｅ 公式．     

Natural rubber/styrene-butadiene rubber blends prepared by solution mixing: Influence of vulcanization temperature using a Semi-EV sulfur curing system on the microstructural properties

Blends of natural rubber (NR) and styrene-butadiene rubber (SBR) were prepared by solution mixing and vulcanized with sulfur and accelerator in a Semi-EV system at 433 K and 443 K in order to study the vulcanization kinetic and the influence of vulcanization temperature on final structure of the blends. The vulcanization kinetic studied through the variation in rheometer curves was analyzed using the Ding and Leonov model, which takes into account the reversion effect during the cure process. The average free nanohole volume and the fractional free volume of samples with different NR/SBR ratio were estimated using positron annihilation lifetime spectroscopy (PALS). Also, the crosslink density was determined by means of swelling tests in a solvent. For all the compounds, a correlation between the free nanohole volume and the delta torque obtained from the respective rheometer curves was established.     

Properties of a carbon filled cyclic olefin copolymer

This article investigates electrical conductivity and rheological aspects of cyclic olefin copolymer (COC) composites containing both carbon fiber (CF) and carbon black (CB) at various concentrations. The different formulations of carbon filled COC were compression molded in such a manner that the formed circular sheets exhibited preferred in‐plane filler orientation. Through‐plane and in‐plane conductivity were measured by 2‐probe and 4‐probe methods, respectively, while an ARES rheometer in dynamic mode was employed to measure the storage modulus and complex viscosity. It was found that formulations with CF:CB ratios around 3 and where the CB content was close or below its critical percolation concentration resulted in higher electrical conductivity while maintaining the viscosity of the composite at a level acceptable for polymer processing machinery. For those composites containing both fillers, collaborative associations between the CB and CF fillers were found in the established percolating network structure, producing measured conductivities which exceeded the estimated values by the additive rule by up to sixfold. An empirical expression to handle hybrid filler systems is proposed in this work based on the standard percolation model. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1808–1820, 2007     

Phase separation during fast (RIM) poly-urethane polymerization

Phase separation dynamics during a reaction injection molding process of an elastomeric polyurethane was studied via FT-IR and rheology. 4, 4′ methylenediphenyl isocyanate and 1, 4 butanediol were mixed with 50 wt% of a 2000 molecular weight poly(proplyene oxide)polyol catalyzed by dibutyltin dilaurate. A small reaction injection molding machine was used to impingement mix the chemicals and inject these directly into a Fourier transform infrared spectrometer or into a rheometer. The reaction conversion was followed by the isocyanate absorbance and the development of inter-urethane hydrogen bonding was related to phase separation dynamics. Isothermal dynamic mechanical modulus build-up during reaction was monitored by a thin gap parallel plate geometry subjected to small amplitude oscillation. An optimum reaction temperature was found, below which phase separation prematurely cuts off high molecular weight build up. Above this temperature phase separation is too slow and incomplete; modulus values are lower. Increasing catalyst reduces this optimum temperature.     

Enhancing cationic ring‐opening photopolymerization of cycloaliphatic epoxides via dark cure and oxetanes

Due to the longevity of the cationic active centers, cationic ring‐opening photopolymerization can continue after illumination ceases. In addition, substantial reactivity enhancement for epoxides is realized through copolymerization with oxetanes. Here, the separate reactions of epoxide and oxetane moieties were resolved during illumination and subsequent dark cure via real‐time Raman spectroscopy. Using oxetane additives, reactivity and conversion of 3,4‐epoxycyclohexylmethyl‐3′,4′‐epoxycyclohexane carboxylate (EEC) were improved during illumination and subsequent dark cure through modulation of the initial formulation viscosity and selection of the oxetane secondary functional groups. The largest enhancement in reactivity occurred with secondary groups comprising either aliphatic chains with their flexibility or hydroxyls with their chain‐transfer capacity. In contrast, oxetanes containing UV‐absorbing phenyl rings reduced the initiation efficiency, and difunctional oxetanes suppressed overall conversion through additional crosslinking. Although bulk conversion was directly related to initial formulation viscosity, the impact of the oxetane secondary functional groups was greater. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1436–1445     

Isothermal cure kinetics of epoxy/phenol‐novolac resin blend system initiated by cationic latent thermal catalyst

The investigation of the cure kinetics of a diglycidyl ether of bisphenol A (DGEBA)/phenol‐novolac blend system with different phenolic contents initiated by a cationic latent thermal catalyst [N‐benzylpyrazinium hexafluoroantimonate (BPH)] was performed by means of the analysis of isothermal experiments using a differential scanning calorimetry (DSC). Latent properties were investigated by measuring the conversion as a function of curing temperature using a dynamic DSC method. The results indicated that the BPH in this system for cure is a significant thermal latent initiator and has good latent thermal properties. The cure reaction of the blend system using BPH as a curing agent was strongly dependent on the cure temperature and proceeded through an autocatalytic kinetic mechanism that was accelerated by the hydroxyl group produced through the reaction between DGEBA and BPH. At a specific conversion region, once vitrification took place, the cure reaction of the epoxy/phenol‐novolac/BPH blend system was controlled by a diffusion‐control cure reaction rather than by an autocatalytic reaction. The kinetic constants k₁ and k₂ and the cure activation energies E₁ and E₂ obtained by the Arrhenius temperature dependence equation of the epoxy/phenol‐novolac/BPH blend system were mainly discussed as increasing the content of the phenol‐novolac resin to the epoxy neat resin. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2945–2956, 2000     

Emanation investigation of the structure microheterogeneities of Fe-S,Co-S and Ni-S melts

Liquid-liquid structural transitions have been investigated by means of the emanation method in Fe?S, Co?S, Ni?S melts near the eutectic point. Both polythermal and isothermal conditions were used in the experiments. The superheating values were 0–300 ° above the melting temperature. In order to calculate the diffusion coefficient of²²⁰Rn in melts a model connecting the emanation level with the diffusion coefficient of radon was employed. Using the diffusion coefficient vs. viscosity relationship /the Stokes-Einstein relation/ the viscosity of melts as a function of the composition and temperature was obtained. Cluster-formation in sulphide melts was estimated theoretically, the particle number in a cluster as a function of the composition was determined, and a correlation was established between viscosity and particle number in clusters vs. composition.     

Epoxy – diamine thermoset/thermoplastic blends: thermoset reactions and rheological evolutions during curing

Isothermal rates of reaction during the cure of epoxy‐amine/thermoplastic blends were studied. Epoxy‐amine reaction induces a phase separation. Experimental results show that when TP concentration is higher than 30 wt% an increase of reaction rate is observed after phase separation. A modelling of the kinetics of each phase before and after phase separation, shows that in the epoxy‐amine rich phase, gelation occurs for a conversion close to 0.6. Rheological behaviour was studied during the cure. The viscosity was found greatly dependent of the morphology, the epoxy amine conversion and of the evolution of the phase composition. Modelling of the viscosity using simple relations gives a good fit of the experimental results during the cure.