轮胎胶料挤出流动中粘弹特性分析

考察了洞口胶、缓冲胶和翻胎胎面胶胶料在毛细管挤出流动中的粘弹性行为及机理。结果表明,在温度为90℃和表观剪切速率为1－10^3s^-1的操作条件下,3种胶料的剪切滚动均服从幂律,且非牛顿指数值相差不大;入口压力降和挤出膨胀比均随表观剪切速率的增大而呈非线性函数形式增大,且洞口胶的挤出膨胀比最大,缓冲胶最小;而缓冲胶的入口压力降最大,洞口胶最小。应用挤出膨胀方程估算的试样剪切弹性模量与壁面剪切应力呈线性函数关系,其预测值与文献值相当接近。     

Linear viscoelasticity of discotic mesophases

The small-amplitude oscillatory capillary Poiseuille flow of uniaxial incompressible discotic nematic liquid crystals, representative of discotic mesophases, is characterized using analytical, computational, and scaling methods. Linear viscoelastic material functions are calculated and discussed in terms of fundamental anisotropic viscoelastic processes. The role of orientation to generate flow and store elastic energy is discussed. Viscoelastic behavior is found only at frequencies of similar magnitude to the single orientation relaxation time. In the terminal small-frequency zone the storage modulus scale as G^′∼ω², and the loss modulus as G^″∼ω, typical of viscous fluids. Comparisons between steady and oscillatory Poiseuille flow shows that the Cox-Merz rule is not obeyed, but that as expected the steady and complex viscosities in the terminal zone are identical. A remarkable and useful correspondence between the stored elastic energy under steady flow and the storage modulus G^′ has been discovered.     

Blends of syndiotactic polystyrene with SEBS triblock copolymers

Blending of styrene-b-(ethylene-co-1-butene)-b-styrene (SEBS) triblock copolymers with syndiotactic polystyrene (PSsyn) has been performed in a Brabender mixer above the higher glass transition temperature of the triblock copolymer but below the PSsyn melting point. The large excess of the triblock copolymer over the homopolymer as well as the significant amount of plasticized amorphous PSsyn phase allowed the easy processing under the used temperature conditions with good interface compatibility. The consequent interfacial adhesion between the amorphous PS phase and the unmelted PSsyn crystallites affects both the final morphology of the blend as well as its dynamic behavior. Indeed, such solid particles act as reinforcing point of the overall blend structure, as evidenced by scanning electron microscopy. Moreover, they contribute to a T_g increase in the order of 20 °C with respect to pure SEBS and to an appreciable conservation of mechanical properties at temperatures higher than the T_g of the PS blocks of SEBS. The mechanical and thermal behavior of the synthesized blends has been studied and tentatively correlated to the molecular weight ratio between PSsyn and the PS blocks of SEBS.     

Linear viscoelasticity and structure of polypropylene-montmorillonite nanocomposites

Polypropylene (PP)/clay composites were prepared by melt mixing in a thermoplastic mixer using a polypropylene grafted with maleic anhydride (PPg) as the compatibilizer. Concentrations of an organophilic montmorillonite (MMT) between 2 and 15 wt% and concentration ratios of PPg/clay between 1:3 and 3:1 were employed to investigate the relationship between the structural characteristics of the hybrids and their rheological properties. The structure was analyzed with electron microscopy, X-ray diffraction and melt rheology. Thermogravimetric analysis and infrared spectroscopy were also used. The clay interlayer spacing increases after mixing with PP while the addition of PPg only facilitates the partial exfoliation of the clay platelets without changing that spacing. When clay loadings of 8 wt% or larger were used, an important fraction of the original clay particles was found to remain unmodified. The dynamic moduli show little effect of the presence of the inorganic material when no compatibilizer is added or the amount of PPg or clay is too small. As the extent of exfoliation increases, the linear viscoelastic behavior of the composites gradually changes with time while in the molten state, mainly at low frequencies. Evidence of solid-like behavior appears as the concentration of clay increases, for a given PPg/clay or PP/PPg concentration, or as the PPg concentration increases (for a given clay concentration). The concentrations of PPg and clay that induce percolation were observed to have an inverse relation. Evidence of regions with large concentration of MMT was obtained in the annealed samples of composites with solid-like rheological behavior. Additionally, infrared spectra of these materials suggest the simultaneous occurrence of chemical reactions between the PPg and the surfactant or products derived from its thermal decomposition during the annealing process.     

Effects of miscibility on probe tack of natural-rubber-based pressure-sensitive adhesives

Natural rubber (NR) was blended in various ratios with 29 kinds of tackifier resins, which were prepared from rosin, terpenes, and petroleum. Miscibilities of all the blend systems were illustrated as phase diagrams in our previous articles. From these blend systems, we selected 7 systems having typical phase diagrams [completely miscible, completely immiscible, and lower critical solution temperature (LCST) types] and carried out measurements of probe tack. Probe tack values were measured at various rates of separation and temperatures to obtain master curves. In the case of miscible pressure sensitive adhesives (PSAs) at the condition of measurement, the peak position in the master curve of probe tack shifted to the lower velocity (higher temperature) as the tackifier content increased. On the contrary, immiscible PSAs had much smaller probe tack values than miscible ones and did not give manifest shift of peaks. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 771–776, 1998     

Linear viscoelasticity and stress growth in blood

This note complements a previous publication where we used first order kinetics to describe biofluid behavior, especially blood, in the cases of simple shear flow, hysteresis and yield stress. Here, we extend the model and consider the viscoelastic properties of blood. Specifically, we look at small amplitude oscillatory flow and stress growth. Successful comparisons of model predictions with blood data are produced.     

Toughening and compatibilization of polyphenylene sulfide/nylon 66 blends with SEBS and maleic anhydride grafted SEBS triblock copolymers

In this study, styrene‐b‐ethylene/butylene‐b‐styrene triblock copolymer (SEBS) and maleic anhydride grafted SEBS (SEBS‐g‐MA) were used as compatibilizers for the blends of polyphenylene sulfide/nylon 66 (PPS/PA66). The mechanical properties, including impact and tensile properties and morphology of the blends, were investigated by mechanical properties measurements and scanning electron microscopy. Impact measurements indicated that the impact strength of the blends increases slowly with elastomer (SEBS and SEBS‐g‐MA) content upto 20 wt %; thereafter, it increases sharply with increasing elastomer content. The impact energy of the elastomer‐compatibilized PPS/PA66 blends exceeded that of pure nylon 66, implying that the nylon 66 can be further toughened by the incorporation of brittle PPS minor phase in the presence of SEBS or SEBS‐g‐MA. The compatibilization efficiency of SEBS‐g‐MA for nylon‐rich PPS/PA66 was found to be higher than SEBS due to the in situ forming SEBS interphase between PPS and nylon 66. The correlation between the impact property and morphology of the SEBS‐g‐MA compatibilized PPS/PA66 blends is discussed. The excellent impact strength of the nylon‐rich blends resulted from shield yielding of the matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

SBS and SEBS block copolymers as impact modifiers for polypropylene compounds

Blends of polypropylene (PP) and thermoplastic elastomers (TPE), namely SBS (styrene‐butadiene‐styrene) and SEBS (styrene‐ethylene/1‐butene‐styrene) block copolymers, were prepared to evaluate the effectiveness of the TPE type as an impact modifier for PP and influence of the concentration of elastomer on the polymer properties. Polypropylene homopolymer (PP‐H) and ethylene–propylene random copolymer (PP‐R) were evaluated as the PP matrix. Results showed that TPEs had a nucleating effect that caused the PP crystallization temperature to increase, with SBS being more effective than SEBS. Microstructure characterization tests showed that in most cases PP/SEBS blends showed the smallest rubber droplets regardless of the matrix used. It was seen that SEBS is a more effective toughening agent for PP than SBS. At 0°C the Izod impact strength of the PP‐H/SEBS 30% b/w blend was twofold higher than the SBS strength, with the PP‐R/SEBS 30% b/w blend showing no break. A similar behavior on tensile properties and flexural modulus were observed in both PP/TPE blends. Yield stress and tensile strength decreased and elongation at break increased by expanding the dispersed elastomeric phase in the PP matrix. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 254–263, 2005     

Linear viscoelasticity of polymer blends with co-continuous morphology

The co-continuous morphology of polymer blends has received much attention not only because of its potential promotion of mechanical or electrical properties of polymer blends, but also due to its importance in phase separation by spinodal decomposition. Compared to the recent advances in the characterization of co-continuous structure, the rheology of co-continuous blends has not been understood clearly. In this work, a rheological model is suggested to correlate the linear viscoelasticity and the structural information of co-continuous blends. The dynamic modulus of co-continuous blends is composed of the contribution from components and the interface. The interfacial contribution, which is most important in the rheology of blends, is calculated from a simplified co-continuous structure. This model has been compared satisfactorily with available experimental results, which proves a reasonable connection between the co-continuous structure and linear viscoelasticity of blends.     

Influence of diblock addition on tack in a polyacrylic triblock copolymer/tackifier system measured using a probe tack test

The influence of diblock copolymer addition on the tack properties of a polyacrylic triblock copolymer/tackifier system was investigated. For this purpose, poly(methyl methacrylate)‐block‐poly(n‐butyl acrylate)‐block‐poly(methyl methacrylate) triblock copolymer (MAM) and a 1/1 blend with a diblock copolymer consisting of the same components (MA) were used as base polymers, and a tackifier was added in amounts ranging from 10 to 30 wt %. The temperature dependence of tack was measured by a probe tack test. The tack of MAM/MA at room temperature was significantly higher than that of MAM, and the improvement of MAM/MA upon the addition of the tackifier was higher than that of MAM. The peeling process at the probe/adhesive interface during the probe tack test was observed using a high‐speed microscope. It was found that for MAM/MA, cavitation was caused in the entire adhesive layer, and peeling initiation was delayed by the absorption of strain energy due to deformation of the adhesive layer. In contrast, for MAM, peeling progressed linearly from the edge to the center of the probe. The greater flexibility of the soft block chain in the diblock copolymer resulted in improved interfacial adhesion. ¹H pulse nuclear magnetic resonance analysis showed that the addition of the tackifier improved the cohesive strength of the adhesive. Adhesion strength is affected by two factors: the development of interfacial adhesion and cohesive strength. In the MAM/MA/tackifier system, the presence of MA and the tackifier improved the interfacial adhesion and cohesive strength, respectively. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Melt viscoelasticity of polyethylene terephthalate resins for low density extrusion foaming

The rheological properties of conventional polyethylene terephthalate (PET) resins are not particularly suitable for low density extrusion foaming with physical blowing agents; as a result, chemically modified resins through chain extension/branching reactions are often used. Such resins have overall higher melt viscosity and higher melt strength/melt “elasticity” than unmodified materials. In this work, following a review of the prior art on PET chemical modification, an unmodified and a chemically modified resin were selected and characterized for their melt viscoelastic properties including shear and dynamic complex viscosity over a broad shear rate/frequency range, storage and loss modulus, and die swell. Certain rheological models were found to provide better fits of the entire viscosity curve for the unmodified vs. the modified resin. Foamed extrudates having variable densities (from about 1.2 to 0.2 g/cc), were prepared by carbon dioxide injection in monolayer flat sheet extrusion equipment. Foams with increasingly lower density, below 0.5 g/cc, were obtained by increasing gas pressure only in the case of the chemically modified resin. The effects of variables such as concentration of the physical blowing agent, resin rheology, resin thermal properties and choice of process conditions are related to product characteristics including density, cell size and crystallinity.     

用反应挤出法合成苯乙烯-异戊二烯嵌段共聚物

以同向紧密啮合双螺杆挤出机为反应器,有机锂为引发剂,采用混合单体加料方式,本体法一步合成了苯乙烯-异戊二烯嵌段共聚物。核磁共振谱图和透射电子显微照片均表明该共聚物具有纳米级多嵌段结构,其物理机械性能受异戊二烯质量分数的影响。     

CO2与环氧丙烷共聚物的反应挤出

采用双螺杆挤出机对CO_2与环氧丙烷共聚物(聚碳酸亚丙酯多元醇)、异氰酸酯和扩链剂1,4-丁二醇进行反应挤出,从而提高共聚物的相对分子质量。通过单螺杆挤出机,用偶联剂对共聚物进行处理使其力学性能达到吹塑要求。结果表明,异氰酸酯指数为1.3,扩链剂羟基用量与体系总羟基量的摩尔比为0.6,双螺杆挤出机挤出温度为120℃,螺杆转速为30 r/min,偶联剂质量分数为0.2%,反应挤出的共聚物可以进行稳定的吹塑实验。     

反应挤出合成S/B嵌段共聚物的研究

以同向紧啮合双螺杆挤出机为反应器、有机锂为引发剂,采用混合单体加料方式,本体法一步合成了苯乙烯-丁二烯嵌段共聚物。^1H-NMR图谱表明该丁苯共聚物的结构以嵌段为主,无规链段为辅。其力学性能则体现出受丁二烯质量分数的影响。     

反应挤出合成苯乙烯/丁二烯多嵌段共聚物

研究了反应挤出多嵌段苯乙烯／丁二烯共聚物结构。^1H—NMR及FTIR表明,在四氧化锇与双氧水的共同作用下,多嵌段共聚物中丁二烯嵌段的双键全部氧化切断,而苯乙烯嵌段保持不变。降解所得聚苯乙烯碎片经多角度小角激光光散射检测联用GPC分析得知,共聚物降解前相对分子质量为单分布,而降解后碎片为双峰分布,其中相对分子质量较大的碎片是首先聚合的嵌段,较小的碎片是后面形成的嵌段。丁二烯进入体系参与聚合需要体系有足够的黏度,决定了首先聚合的苯乙烯嵌段大小。     

Linear viscoelasticity of polymer melts filled with nano-sized fillers

The linear dynamic rheology of polymer melts filled with nano-sized fillers is investigated in relation to a proposed two phase model. A common principle is disclosed for nanofilled polymers exhibiting either fluid- or solid-like behaviors with increasing filler volume fraction. The bulky polymer phase far away from the filler inclusions in the nanocomposites behaves the same as in the unfilled case while its contribution to the composite modulus is enlarged due to strain amplification effect. The filler forms aggregates together with polymer chains absorbed on the filler surface, which is termed as the “filler phase” in the proposed model. The dynamics of the “filler phase” slow down with increasing filler concentration. The applicability of the proposed two phase model is discussed in relation to the well-known structural inhomogeneity of nanofilled polymers as well as the strain amplification and the filler clustering effects.     

Linear viscoelasticity,extensional viscosity,and oxygen permeability of nanocomposites based on propylene copolymer and organoclay

Random propylene‐terpolymer (PEBC)/organophilic montmorillonite nanocomposites were prepared by melt mixing, using PEBC modified with maleic anhydride (PEBCg) as compatibilizer. Clay concentrations up to 8 wt %, compatibilizer/clay ratios up to 3:1 and concentrations of anhydride groups (AG) in PEBCg of 0.4 and 0.6 wt % were considered. The degree of exfoliation of the clay increases with PEBCg content and its concentration of AGs. The dynamic moduli allow estimating the percolation threshold of the nanofiller at 5.4 wt %, which yields an average of 11 silicate layers per tactoid at percolation, in agreement with the minimum thickness estimated from XRD data. The presence of exfoliated clay gives place to strain hardening and softening, depending on clay concentration and magnitude of the Hencky strain. The amount of exfoliated clay, however, plays a minor role in front of the content of AGs of the compatibilizer in regard with the oxygen permeability of the polymer. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45840.     

Infra-red dichroism investigation of molecular viscoelasticity using isotopically labelled block copolymers

Summary Infra-red dichroism has been used to measure the orientation of the different sequences of isotopically labelled block copolymers. We have determined the orientation from dichroic ratios of two bands of deuterated polystyrene, and compared in block copolymers the orientation of the central part of the chain with that of the ends. The relaxation of the ends is more rapid, than that of the center, which exhibits a plateau.     

Linear and networked blends and copolymers of polyimide

Preparation and characterization of blends and copolymers of a fluorinated polyimide with network constituents is reported. 4,4′‐Hexafluoroisopropylidene diphthalic anhydride and 4,4′‐diaminodiphenyl ether (6FDA–DDE) polyimide were used as the linear hosts and mellitic acid hexamethyl ester ‐ 4,4′‐diaminodiphenyl ether (MAHE–DDE) was employed as the network constituent for the blend and copolymer. Cast films of the polyimides were characterized by FTIR, XPS, DMA, and TGA. The multifunctional nature of MAHE facilitated crosslinking among the constituents. Both blends and copolymers showed significant improvement in the storage modulus and glass transition temperature relative to that observed for the 6FDA homopolymer. The occurrence of a single glass transition temperature for the blends suggests that they were at least partially miscible. Presence of low molecular weight species in the copolyimides, combined with steric hindrance to crosslinking, may have resulted in the existence of an optimum in the amount of the network components for improving the mechanical properties. Inclusion of network components is presented as a facile method for improving the desirable properties of polyimide. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3000–3008, 2006