一种阻燃抗静电聚丙烯的流变性能

采用毛细管流变仪和旋转流变仪分别研究了溴系阻燃剂、炭黑填充对聚丙烯熔体高剪切挤出畸变和动态黏弹特性的影响。发现低含量下随填充量的提高,发生挤出畸变的临界剪切速率提高,扩大了加工窗口。动态流变试验表明树脂中添加更多炭黑后剪切变稀时的复数黏度、储能模量和损耗模量都增大,但损耗因子下降。进一步用缠结模型和Cross模型定量分析表明,填料吸附高分子链段而减少其壁面吸附,减轻挤出畸变,进而提高临界剪切速率;粒子分布网络提高了平台模量和缠结密度,缩短了松弛时间,恢复更快而减小挤出胀大比。复合材料中添加3.5%（质量）炭黑后形成逾渗网络,表现为高零切黏度和长松弛时间,发生“类液-类固”转变;同时材料表面电阻下降明显,此时黏弹逾渗点与导电逾渗点基本一致。     

Rheological characterization of styrene acrylonitrile copolymers

The relationship between copolymer composition, molecular weight distribution, and rheological properties of random styrene acrylonitrile copolymers synthesized by radical polymerization in bulk was investigated. From differential scanning calorimetry analysis, glass transition temperature was obtained and increases with the acrylonitrile content. The knowledge of the glass transition is a key factor to compare the different copolymers in an iso‐free volume condition for melt rheology. Owing to time temperature superposition, a large frequencies window ranging from the terminal zone until the glassy plateau can be obtained. Thus, the mechanical spectroscopy was used to estimate the rubbery plateau modulus and the Newtonian viscosity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1316–1321, 2000     

Influence of Residual Water in a Glass on Its Rheological and Relaxation Properties (by the Example of a 5Na2O · 95B2O3Glass)

Glasses of the 5Na₂O · 95B₂O₃(mol %) composition synthesized at a temperature of 1100°C for 180 and 20 min are studied. The temperature dependences of the viscosity and the thermal expansion of glasses are obtained. The thermal expansion coefficients and glass transition temperatures of the studied glasses are determined, and the parameters of structural relaxation (the constant characterizing the width of the spectrum of relaxation times, the relaxation modulus equal to the ratio of the viscosity to the relaxation time, and the relaxation time at zero reciprocal temperature) are calculated from the dilatometric curves measured at temperatures close to the glass transition range. The water content in the studied glasses is estimated by comparing the obtained dependence of the viscosity on the water content with the data available in the literature for glasses of a similar composition. The assumption is made that the structural relaxation time in sodium borate glass decreases with an increase in the water content.     

Is the structural relaxation of glasses controlled by equilibrium shear viscosity?

Knowledge of relaxation processes is fundamental in glass science and technology because relaxation is intrinsically related to vitrification, tempering as well as to annealing and several applications of glasses. However, there are conflicting reports—summarized here for different glasses—on whether the structural relaxation time of glass can be calculated using the Maxwell equation, which relates relaxation time with shear viscosity and shear modulus. Hence, this study aimed to verify whether these two relaxation times are comparable. The structural relaxation kinetics of a lead metasilicate glass were studied by measuring the refractive index variation over time at temperatures between 5 and 25 K below the fictive temperature, which was initially set 5 K below the glass-transition temperature. Equilibrium shear viscosity was measured above and below the glass-transition range, expanding the current knowledge by one order of magnitude. The Kohlrausch equation described very well the experimental structural relaxation kinetics throughout the investigated temperature range and the Kohlrausch exponent increased with temperature, in agreement with studies on other glasses. The experimental average structural relaxation times were much longer than the values computed from isostructural viscosity, as expected. Still, they were less than one order of magnitude higher than the average relaxation time computed through the Maxwell equation, which relies on equilibrium shear viscosity. Thus, these results demonstrate that the structural relaxation process is not controlled by isostructural viscosity and that equilibrium shear viscosity only provides a lower boundary for structural relaxation kinetics.     

Probing the viscoelastic properties of brominated isobutylene‐co‐p‐methylstyrene rubber/tackifier blends using a rubber process analyzer

The viscoelastic behavior of brominated isobutylene‐co‐p‐methylstyrene (BIMS) rubber/hydrocarbon resin blends and BIMS/phenol formaldehyde resin blends was studied with the use of a rubber process analyzer. Dynamic mechanical analysis and scanning electron microscopy were used to evaluate the compatibility between the BIMS/tackifier blends. Strain sweep tests at temperature below the softening point of the tackifiers showed the formation of resin–resin networks in the incompatible BIMS/phenolic resin blends. However, resin–resin network was not prominent in the case of the compatible BIMS/hydrocarbon resin blends. Frequency sweep tests were performed at the strain amplitude within the linear region at several temperatures and the variations of shear storage modulus, G′ and complex viscosity, η* against frequency were recorded. The tackifying resins modified the viscoelastic properties of the BIMS rubber by reducing the storage modulus at lower frequency and by increasing the storage modulus at higher frequencies. However, this action was found to be highly dependent on (a) rubber‐tackifier compatibility, (b) blend proportions, and (c) test temperature. Furthermore, stress relaxation measurements of the BIMS/tackifier blends at temperature below the softening point of the tackifiers showed longer period of relaxation for the incompatible BIMS/phenolic resin blends. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Relationship between molecular structure and zero‐shear viscosity of polymers

The relationship between molecular structure and zero‐shear viscosity of polymers was studied. In this study we propose a new equation, which is based on Berry and Fox's equation. This new equation is constructed from some molecular parameters, such as mean square length and average molecular weight of statistical skeletal unit, characteristic ratio, entanglement molecular weight, glass‐transition temperature, free volume fraction at glass‐transition temperature, and thermal expansion coefficient of free volume. It is proposed that some of these molecular parameters could be predicted by group contribution methods, except for the free volume parameters. We also propose new empirical relations between free volume parameters and molecular structures of polymers, which make it possible for free volume parameters to be obtained from molecular structure. Using these relationships, it is possible that the zero‐shear viscosity and its temperature dependence are obtainable from the molecular structure of polymers. We applied this formula to some polymers, including both amorphous and semicrystalline polymers. Comparison between the measured and calculated zero‐shear viscosity showed quite good agreement. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1609–1618, 2001     

Viscoelastic properties of reactive and non‐reactive blends of ethylene‐methyl acrylate copolymers with styrene‐maleic anhydride copolymer

The effects of compatibilizing reactions on the viscoelastic properties and morphology of ethylene‐methyl acrylate copolymers were studied. Potentially reactive blends of styrene‐maleic anhydride copolymer (SMAH) and a terpolymer of ethylene/methyl acrylate/glycidyl methacrylate (E‐MA‐GMA) were compared with a non‐reactive blend of SMAH and an ethylene/methyl acrylate (E‐MA) copolymer with similar rheological properties. Melt mixing was carried out in a batch mixer and in a co‐rotating twin screw extruder. The morphology of the reactive blends showed smaller domain sizes than the non‐reactive blends, and the viscoelastic properties of the blends were very different. The storage and loss moduli and the complex viscosity of the reactive blends were greater than those of non‐reactive blends. The reactive blends had a higher zero shear viscosity, plateau modulus and mean relaxation time than their non‐reactive counterparts, indicating a higher degree of melt elasticity. The melt elasticity was maximum at 25% functionalized ethylene‐methyl acrylate concentration.     

Maxwell equation and classical theories of glass transition as a basis for direct calculation of viscosity at glass transition temperture

The main relaxation theories of glass transition (Leontovich-Mandelstam and Volkenstein-Ptitsyn) variously formulate the kinetic criteria of glass transition. Both of the approaches are shown to be equivalent in physical sense and provide a single expression that connects the rate of change of a melt temperature and the structure relaxtion time. The theory characterizes the width of a temperature band δT _g in which the glass transition occurs. The values of δT _g can either be obtained from the experiment or be accepted to conform to the value of a temperature step under the change of viscosity by an order of magnitude (direct method for finding by the Volkenstein-Ptitsyn theory). Using the Maxwell equation, a new equation for the calculation of the viscosity for viscoelastic relaxation was suggested, which is based on a shear modulus of glass and the cooling rate. The theory was verified basing on the published data for oxide glass. The average difference between the calculated and measured values of lgη upon glass transition comprises 0 ± 0.30. These results correspond to the cooling rate of 3 K/min and log(η, Pa s) = 12.76 ± 0.26 (for all glass considered). It is shown that the most probable cooling rate which provides the viscosity upon glass transition of ～1012 Pa s is close to 20 K/min (oxide melts). The theory predetermines the dependence of viscosity upon glass transition on the nature of a glass-forming liquid. The disadvantages of other approaches to the problem under consideration are demonstrated.     

Rheological properties and thermal transitions in millable polyurethane fluoroelastomers

A series of segmented polyurethane fluoroelastomers based on dimethylol‐terminated perfluoropolyethers (PFPEs), aliphatic diisocyanates and allyl functionality is presented. Depending on the type of diisocyanate monomer used, it was found that quite different prepolymer molecular weights were achieved. Thermal analysis by differential scanning calorimetry showed formation of polyphasic copolymers, either amorphous or semi‐crystalline depending on the monomer structure. Rheological measurements showed that much higher zero‐shear viscosity, a shorter Newtonian plateau and more marked shear thinning behaviour were achieved with polyurethanes based on hexamethylene diisocyanate (HDI) or H₁₂‐MDI monomers. Isothermal viscosity curves were fitted with either three‐ or two‐parameter empirical models, and relaxation times of the structures were estimated at the temperature of 120 °C. Copyright © 2004 Society of Chemical Industry     

基于流变特性探讨聚芳砜酰胺纺丝液的稳定性

利用旋转流变仪研究了聚芳砜酰胺(PSA)纺丝液的稳态和动态流变行为,结果表明:以二甲基乙酰胺(DMAc)为溶剂的聚芳砜酰胺溶液表现出典型的聚合物浓溶液流变特性,在低剪切速率区表现为牛顿流体特性,而随着剪切速率的增大,呈现出切力变稀行为,纺丝液的零切黏度、松弛时间随PSA特性黏度的增大而增大,非牛顿特性增强;证明了PSA纺丝溶液在测试温度范围内处于均质溶液状态,在进一步的动态温度扫描分析中,没有发现溶液的凝胶化转变现象,说明在试验温度范围内,PSA纺丝液处于均质稳定状态。     

Stress Relaxation Modulus of a Commercial Glass

The stress relaxation modulus in compression of a container glass was investigated over a wide range of strain, time, modulus, and temperature. The glass is a linear viscoelastic liquid up to 2% strain, and the modulus is a smooth function of time, with no pseudorubbery plateau apparent down to a modulus of 10° dynes/cm². The data cover 4 decades in time and a range of almost 100°C above the glass transition, T ₀ =536°C. Within experimental error, changes in temperature simply shift the modulus-vs-time curve along the time axis without altering its shape. This behavior implies that the same mechanism controls both the bulk and shear spectra. The shift factors fit the WLF equation well with values for the parameters c₁ and c₂ of 16.7±0.2 and 345±5°C, respectively. Data from the literature for silicate glasses agree with these parameters.     

Viscoelastic properties of poly(ethylene-co-styrene) copolymers

The viscoelastic properties of narrowly distributed linear poly(ethylene-co-styrene) copolymers with different mole fractions of styrene (x_S = 0–20.5 mol %) and molecular weights (M_w = 64–214 kg/mol) were analyzed in the molten state at different temperatures by means of oscillatory rheometry. Analyzing the thermorheological properties of the polymers, we found that the time temperature superposition principle is fulfilled. The corresponding shift factors follow up to 16.5 mol % of styrene units the Arrhenius behavior of neat polyethylene. For a styrene content of about 20 mol %, the polymers no longer crystallize and a transition from Arrhenius to WLF behavior of pure polystyrene was observed. The zero shear viscosity, η₀, of the polymers was derived from the mastercurves. The determination of the plateau modulus by the well-known tan δ-min criterion is not possible due to the beginning crystallization in the corresponding temperature range. An approximate calculation of this value is based on the characteristic relaxation time λ_x = 1/ω_x, corresponding to the crossover of G′ and G′. Indeed, the characteristic modulus G_px calculated as η₀/λ_x is a good approximation for the plateau modulus G_p. The viscosity–molecular weight and relaxation time–molecular weight scaling relations were established for three copolymers with different molecular weights and nearly the same styrene content. For both material parameters, the scaling exponent is around 3.4, confirming the linear architecture of the investigated polymers. The mixing rules describing the change of such material parameters like zero shear viscosity or plateau modulus independent of styrene content are of logarithmic linear character using the weight fraction of styrene units instead of the mole fraction. The relations found allow the prediction of melt state properties for polymers with arbitrary styrene content. In the future, when catalysts with sufficient activity for the synthesis of high styrene content copolymers are available, these predictions will have to be checked. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:209–215, 1997     

Rheological property and curing behavior of poly(amide-co-imide)/multi-walled carbon nanotube composites

Poly(amide-co-imide) (PAI)/multi-walled carbon nanotube (MWCNTs) composites were prepared by using solution mixing with ultrasonication excitation in order to investigate effects of MWCNTs on rheological properties and thermal curing behavior. Steady shear viscosity of the composite showed bell shaped curves with three characteristic patterns: shear thickening, shear thinning, and Newtonian plateau behavior. Both storage modulus and complex viscosity were increased due to higher molecular interaction than that of the pure PAI resin. Especially, hydrogen peroxide treated MWCNT/PAI composites had the highest storage modulus and complex viscosity. Glass transition temperature of the PAI/MWCNT composite was increased with increasing MWCNT content and thermal curing time since the mobility of PAI molecules was reduced as more constraints were generated in PAI molecular chains. It was found that thermal curing conditions of PAI/MWCNT composites are determined by considering effects of weight fraction and surface modification of MWCNTs on internal structure and thermal properties.     

Ultraviolet‐induced chain extension of poly(ethylene terephthalate) based on radical reaction with the aid of trimethylolpropane triacrylate and glycidyl methacrylate during extrusion

In order to improve the processing properties of poly(ethylene terephthalate) (PET), carbon–carbon double bonds were end‐capped onto the chain end of PET by reacting with glycidyl methacrylate (GMA) and then the product was reacted with trimethylolpropane triacrylate (TMPTA) based on a free radical reaction initiated by ultraviolet light to form long‐chain branching structures. The reaction was demonstrated by intrinsic viscosity measurements, carboxyl content analysis, Fourier transform infrared spectroscopy and size exclusion chromatography. Then the rheological and thermal properties of PET were investigated with various TMPTA and GMA contents. Chain extended PET displayed higher complex viscosity than pristine PET and pronounced shear‐thinning behavior. Moreover, the relaxation time spectrum revealed that the modified PET displayed a longer relaxation time during the relaxation process, which was attributed to the higher degree of entanglements resulting from long‐chain branching. Besides, its crystallization temperature and melt temperature shifted to lower temperatures, and the glass transition temperature shifted to higher temperature, indicating that the thermal properties of the modified PET had also been improved. Thus this method can be used to improve the overall properties of PET. © 2020 Society of Chemical Industry     

Charge density effects on polyelectrolyte dynamic rheology

The dynamic rheological properties of an uncharged polymer and charged polyelectrolytes were evaluated in salt‐free water at various concentrations above the entanglement concentration. A poly(acrylic acid) homopolymer was used as the uncharged polymer and was ionized to anionic poly(acrylic acid‐co‐sodium acrylate) at five levels of ionization (0.05, 0.10, 0.15, 0.30, and 0.50). The polymers exhibited a terminal region at a low frequency and a plateau region at a high frequency. The dynamic data for the nonionic parent and all charged polymers could be reduced to a master curve, which indicated a similar distribution of relaxation times for the nonionic and charged polymers. The shear modulus, relaxation time, and zero shear viscosity properties exhibited a concentration and charge density dependence. Higher power‐law exponents for the rheological properties were noted for the nonionic polymer versus the charged derivatives. The number of mechanically active entanglements per number of chains increased with the polymer concentration and charge density. The total number of mechanically active entanglements per number of chains that occurred because of imposing a charge to the nonionic parent did not change with increased concentration, and this indicated a different entanglement mechanism for charged polymers in comparison with their nonionic parent. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Viscoelastic properties of a styrene-isoprene-styrene triblock copolymer and its blends with polyisoprene homopolymer and styrene-isoprene diblock copolymer

The effects of added polyisoprene homopolymer (PI) and polyisoprene-blockstyrene diblock copolymer (SI) on the viscoelastic properties of a polystyrene-block-polyisoprene-block-polystyrene triblock copolymer (SIS) having a spherical domain morphology have been examined. The former two species are used to model the effects of imperfections in structures that result from triblock copolymers missing, respectively, two or one polystyrene end blocks. The results indicate that the loss modulus and tangent delta in the plateau region can be dominated by imperfections in the copolymer structure. The interpretation of viscoelastic data in the rubbery plateau region as an indication of interface structure in block copolymers is therefore greatly complicated. Small angle X-ray scattering (SAXS) and rheological tests were also used to determine the order-disorder transition temperature for an SIS triblock copolymer and its blend with an SI diblock. The SAXS data are consistent with Han's rheological criteria for determining the order-disorder transition temperature. However, the complex viscosity does exhibit Newtonian behavior for low rates at the highest temperatures, even though the domain morphology persists. Stress relaxation and dynamic modulus data at high temperatures clearly show a secondary “rubbery” plateau at long times, and we offer a qualitative explanation for this feature based on a proposed relaxation mechanism.     

Rheological Properties of Hot-Melt Adhesives: A Model for Describing the Effects of Resin Content

The complex shear modulus of a series of EVA/resin blends has been measured in a broad range of frequencies and temperatures. The variations of the viscoelastic parameters (plateau modulus, limiting compliance, zero-shear viscosity) have been studied as a function of resin content. The addition of small compatible molecules to the polymer has two effects: a topological effect due to the swelling of the entanglement network and a thermodynamic effect due to the increase of the glass transition temperature. It is possible to play on both effects to get the wanted elastic and viscous behavior, as far as process and adhesive properties are concerned. As a consequence, a viscoelastic model is given, allowing one to calculate in a wide range of frequencies (or times) the behavior of these bases of hot melt adhesives, given the composition of the blend and its temperature.     

A comparison of Newtonian and viscoelastic constitutive models for dry spinning of polymer fibers

A comparison is made of the predictions of one‐dimensional mathematical model simulations of dry spinning based on Newtonian and viscoelastic constitutive equations for the spin dope. The viscoelastic model is based upon a modified Giesekus constitutive equation with a temperature and composition‐dependent relaxation time. The simulation algorithm includes the effects of the glass transition on the expected solution viscosity and relaxation time behavior along the spinline. Predictions of axial velocity, tensile stress, and composition profiles for the two cases suggest the role of viscoelasticity in the locking‐in behavior associated with fiber solidification along the spinline. The effects of model parameters and processing conditions are also discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2136–2145, 2003     

Rheological Behavior and Structure of a Commercial Esterquat Surfactant Aqueous System

Aqueous dispersions of a commercial esterquat‐type surfactant widely used in fabric softeners were rheologically characterized. While at 4 wt % esterquat concentration, a Newtonian response was observed; non‐Newtonian (Sisko) flow behavior and viscoelastic properties were found at 12 wt % and higher concentrations. The onset of nonlinear viscoelasticity in oscillatory shear provided interesting information on the strength of quiescent surfactant aggregates. Mechanical spectra corresponded to the plateau zone and the onset of the transition zone. The plateau modulus and the characteristic slopes of the relaxation spectra depended on the strength of the interactions among the aggregates. Start‐up at the inception of the shear experiments were carried out to obtain information on the time‐dependent shear behavior. Cryo‐SEM micrographs demonstrated the occurrence of a dispersion of vesicles embedded into a bilayer matrix.     

Viscosity of glass‐forming systems

As one of the most important properties of glass‐forming liquids, viscosity has drawn significant attention in both glass manufacturing and fundamental research. We review the recent scientific progress in viscosity of glass‐forming systems, including both the liquid and glassy states. After the Vogel‐Fulcher‐Tammann (VFT) equation was introduced, many more efforts have been made to develop more accurate models to describe the temperature dependence of viscosity. In addition to the VFT equation, we also discuss three other viscosity models, viz., the Adam‐Gibbs, Avramov‐Milchev, and Mauro‐Yue‐Ellison‐Gupta‐Allan models. We compare the four viscosity models in terms of their theoretical underpinnings and ability to fit measured viscosity curves. The concept of fragility and the universality of the high‐temperature viscosity limit are also discussed. Temperature‐dependent constraint theory is introduced in detail as a powerful tool for predicting the composition dependence of viscosity. Some examples of the application of this approach to predict the glass transition temperature and fragility of various glass systems are shown. Topological constraint theory is not only of scientific interest, but also has important industrial applicability. We also discuss the thermal history dependence of viscosity in the glassy state. Some phenomenological models are briefly reviewed, while the main focus is given to the modified Mauro‐Allan‐Potuzak model, which can accurately predict the nonequilibrium viscosity as a function of temperature, thermal history, and composition. The correlation of viscosity with elasticity is described in terms of the shoving model. Some theoretical implications of the various viscosity models are discussed, including the concepts of the Kauzmann paradox and the ideal glass transition. Some of the evidence against the existence of these phenomena are discussed. We also review the link between glass relaxation and viscosity, that is, emphasizing that the viscosity equations presented in this review can also be used to model different types of relaxation effects based on the Maxwell relation.