Phase inversion and viscoelastic properties of phase-separated polymer blends

Summary The morphologies and viscoelastic properties of the phase-separated poly(styrene-co-maleic anhydride)/poly(methyl methacrylate) bends have been investigated using TEM and rotational rheometry. Various rheological criteria based on the viscoelastic properties of the blends have been used to evaluate the phase inversion. By correlating the rheological results to data from morphological analysis by TEM, it is found that the maximum of the storage modulus and the viscosity at low shear rate are most suitable for determining the phase-inversion composition of the present phase-separated polymer blends. While the data from the maximum of the shear viscosity at high shear rate and from the shear-thinning extent proposed by Ziegler et al. slightly deviate from that from TEM micrograph, which indicates that shear-induced structure lie. Moreover, the prediction using various rheological models, as the viscosity ratio of the two coexisting phases is substituted for that of the pure components, is in nearly good agreement with that from TEM observation.     

Relation between the viscoelastic and flammability properties of polymer nanocomposites

Previous work has shown that the formation of a network structure of nanoparticles within a polymer matrix can significantly reduce nanocomposite flammability and that viscoelastic properties could be utilized to predict their flammability reduction. The present work extends this type of investigation to the study of clay and carbon nanotube nanocomposites. In particular, we study PS/clay, PS/MWNT, PMMA/clay, and PMMA/SWNT nanocomposites. At a clay level of about 10% by mass, the network structure is formed for the PS and the PMMA clay nanocomposites; it requires a level of about 0.5% with the SWNT and 2% with the MWNT. These samples showed significantly reduced mass loss rates of PS and PMMA. However, the solid residues collected from radiative gasification tests of PS/clay and PMMA/clay showed many small cracks, despite the network formation within the initial sample. This is in contrast to the smooth, continuous residues (no cracks or openings) for PS/MWNT and PMMA/SWNT nanocomposites. The cracks in the clay samples are probably formed due to weaker network at elevated temperatures due to weaker bridging interaction between clay platelets as compared to stronger network resulting from dense entanglement and bridging of carbon nanotubes.     

聚合物熔体动态黏弹特性微尺度效应实验研究

针对聚合物熔体在微流道内,因拉伸/压缩作用导致的黏弹特性受物理尺度影响的问题,通过动态剪切流动实验系统研究了四种聚合物材料的黏弹特性,以及黏弹特性随物理尺度的变化规律。结果表明,在角频率1~100 rad/s的范围内,聚酰胺、聚氨酯、聚乳酸均表现出耗能模量大于储能模量的黏性占优特征,聚丙烯在高频区时表现出弹性占优特征。储能模量与耗能模量均随着物理特征尺度的减小而降低。物理特征尺度从1000 μm减小到250 μm的变化过程中,聚氨酯、聚酰胺和聚丙烯三种熔体的弹性效应对微尺度变化的敏感性比黏性效应强烈,储能模量变化率与耗能模量变化率的差值分别为5.8%、4.2%和2.6%。聚乳酸熔体的黏性效应对微尺度变化的敏感性与弹性效应基本一致,其储能模量变化率与耗能模量变化率的差值为-0.3%。材料分子链特征的差异导致储能模量与耗能模量随物理特征尺度减小的变化率不同。熔体黏弹特性对微尺度变化敏感性的强弱依次为聚氨酯、聚酰胺、聚丙烯和聚乳酸,其黏弹性特征参量的变化率分别为28.6%、22.6%、20.6%和19.45%。     

Dynamic mechanical properties of polymer melts: The dependence of viscoelastic properties on molecular weight distribution

An investigation of the dynamic mechanical properties of several molten polymers was performed using the Maxwell Orthogonal Rheometer. Relaxation spectra derived from experimental data for the terminal region of viscoelastic response indicate that as molecular weight distribution broadens, terminal relaxation phenomena associated with molecular disentanglement and translation extend over a corresponding wider frequency range. The same data indicate that a true maximum relaxation time beyond which no elastic response is observed exists for the materials studied. Moreover, the maximum relaxation time corresponds to the reciprocal of the frequency where the dynamic viscosity deviates from its zero-shear value. Thus an estimate of the time necessary for complete elastic recovery in polymer melts is readily obtained experimentally.     

Influence of molecular weight distribution on the linear viscoelastic properties of polymer blends

Literature data for the dynamic viscoelastic properties of binary blends of nearly monodisperse polybutadienes, polystyrenes, and poly(methyl methacrylate)s was analyzed using logarithmic plots of dynamic storage modulus G′ versus loss modulus G″, based on a recent theoretical study by Han and John.²⁸ It has been found that for binary blends of monodisperse polymers with molecular weights M much greater than the entanglement molecular weight M_e, the value of G′ in log G′ ? log G″ plots becomes independent of molecular weight, increases sharply as small amounts of a high-molecular-weight component are added to a low-molecular-weight component, and passes through a maximum G′_max at a critical blend composition (?₂)_max, and that G′_max becomes larger and (?₂)_max becomes smaller as the ratio of component molecular weights increases. However, as the molecular weight distribution of the constituent components becomes broader, the effect of blend composition on G′ in log G′ ? log G″ plots becomes less pronounced. This observation has enabled us to explain why log G′ ? log G″ plots of binary blends of commercial polymers, namely, blends of two low-density polyethylenes, blends of poly(?-caprolactone) and poly(styrene-co-acrylonitrile), and blends of poly(methyl methacrylate) and poly(vinylidene fluoride), all having broad molecular weight distributions, give rise to values of G′ between those of the constituent components. When one of the constituent components has molecular weight smaller than M_e, while the other has molecular weight larger, and as small amounts of the high-molecular-weight component are added to the low-molecular-weight component, log G′ ? log G″ plots of binary blends give rise to values of G′ larger than those of the constituent components at low values of G″, but approaches the value of G′ for the low-molecular-weight component as the value of G″ is increased. However as the amount of the high-molecular-weight component is increased above a certain critical composition, binary blends give rise to values of G′ close to that of the high-molecular-weight component at all values of G″. The experimentally observed dependence of G′ on blend composition in log G′ ? log G″ plots is favorably compared to the theoretical prediction of a blending law proposed by Montfort and co-workers.^14,15     

Dependence of viscoelastic properties on segregation degree of components in interpenetrating polymer networks

The temperature dependences of elastic moduli, loss moduli, and mechanical loss angle tangent were investigated for the interpenetrating polymer networks: polyurethane–polyurethane acrylate by the method of dynamic mechanical spectroscopy (DMS). The segregation degree of components due to phase separation have been calculated from the parameters of relaxation maxima. An essential change was found in the segregation degree of components with the curing sequence of individual networks being changed. It was shown that, with the conditions and sequence of IPN formation changed, the phase separation degree can be fixed at a particular stage, i.e., the structures with a different segregation degree of components are obtainable. For the IPNs under investigation the variation of elastic moduli of the composites proved possible by fixing the separation degree of components.     

Evaluation of thermal and viscoelastic properties of asphalt binders by compounding with polymer modifiers

A series of potentially useful asphalt blends containing polyethylene with different extents of polarity as modifiers have been prepared and characterized for asphalt pavement. The results of differential scanning calorimetry (DSC) studies show that poly(ethylene‐graft‐maleic anhydride) (MPE) exhibit more interaction with asphalt phase than low density polyethylene (LDPE) and high density polyethylene (HDPE) due to more dispersion of the amorphous content of MPE into the asphalt matrix. The phase distributions of micrographs from scanning electron microscopy (SEM) confirm that polyethylene modifiers with different extents of polarity in asphalt blends results in dispersion of polymer additive into the asphalt phase and affect the certain degree of the phase separation of asphalt blends. From rheological studies, most of asphalt blends exhibit superior performance at higher temperature with increasing the contents of modifiers such as reducing Newtonian flow response, enhancing rutting resistance as well as frequency of loading and improving creep resistance than tank asphalt. POLYM. COMPOS., 31:1738–1744, 2010. © 2010 Society of Plastics Engineers.     

Measurement of dynamic viscoelastic properties of polymer melts and liquids by the modified rheovibron

A new technique is presented which permits the quantitative characterization of the dynamic viscoelastic properties of polymer melts and liquids. A new sample holding system with oscillatory shear platen and modification of the amplifier and oscillating unit made it possible to measure rheological properties of the viscous liquids using the Rheovibron. The dynamic shear modulus, viscosity, and internal friction of acrylic dope, and silicone fluids are obtained by using the new procedure and developed mathematical expressions. This technique will be useful in studies on the rheological properties characterization of polymer melts and liquids in conjunction with process parameters.     

A phenomenological description of the non-linear viscoelastic properties of polymer melts and concentrated solutions

The non-linear stress response of molten polymers and concentrated solutions to an applied strain is formulated in terms of a material response function. The response function is considered to depend explicitly on the resulting stress history and it is shown how many of the non-linear features of these systems can be described both qualitatively and quantitatively. The particular equations used involve one non-linear term in addition to the usual linear response terms. Finally the non-linear equation is interpreted in terms of a plausible model process.     

ABS高分子附聚工艺的开发

为了使生产的ABS树脂有足够高的抗冲击强度,要求聚丁二烯胶乳的粒径要足够大。通过高分子附聚工艺,生产出大粒径聚丁二烯胶乳,考察了附聚过程中的工艺条件对高分子附聚效果的影响。通过试验确定了ABS高分子附聚试验的工艺,经高分子附聚所得到的聚丁二烯胶乳粒径呈单峰分布,小粒径胶乳较少,无大颗粒产生;该胶乳经接枝、凝聚及掺混后所得ABS树脂,抗冲击强度高于公司同类产品。     

Crystallization behavior of PBT/ABS polymer blends

Poly(butylene terephthalate) (PBT) crystallization behavior is modified by blending it with acrylonitrile‐butadiene‐styrene copolymers (ABS). The effects of ABS on melting and crystallization of PBT/ABS blends have been examined. Most ABS copolymers of different rubber content and styrene/acrylonitrile ratios studied showed little effect on the melting behavior of PBT crystalline phase. However, ABS copolymer with high acrylonitrile content had a significant effect on the crystallization behavior of the PBT/ABS blends. The nucleation rate of the PBT crystalline phase decreased due to the presence of the high acrylonitrile content ABS, whereas the spherulitic growth rate increased significantly. These phenomena are attributed to changes in nucleation and growth mechanisms of PBT crystalline phase promoted by ABS. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 423–430, 1999     

The viscoelastic relaxation of cross-linked polymer networks

Summary Theoretical interpretations of the viscoelastic relaxation behavior of cross-linked elastomers are discussed. The dangling chain retracing mechanisms of deGennes and Pearson-Helfand, which assume that the stress contribution of a dangling chain decreases as it assumes successively lower entropy configurations, are replaced by an alternative relaxation mechanism, based on the hopping model of hindered diffusion.     

Effect of viscoelastic properties of the base polymer on extrusion foaming with thermally expandable microcapsules

Thermally expandable microcapsules (MCs) are applicable to the foam processing of polypropylene (PP). The purpose of this study is to clarify the influence of processing conditions, such as temperature, shear rate and resin selection, on the behavior of thermally expandable MCs in PP. In this study, MC was added to several types of PP and extrusion foaming was performed. The average diameter of the MCs after processing was calculated to characterize the expansion of PP including MCs. Two types of molecular architecture, homo- and impact-PP, were examined in this study. The expansion behavior could be summarized by the shear viscosity at the extrusion die. Irrespective of the molecular architecture, data were summarized on one curve on a plane that expressed the relation between the shear viscosity and average MC diameter. Shear viscosity is thus an effective parameter to examine base resin selection for MC foaming. POLYM. ENG. SCI., 60:558–562, 2020. © 2020 Society of Plastics Engineers     

Effect of fiber orientation on viscoelastic properties of polymer matrix composites subjected to thermal cycles

Fibers in polymer composites can be designed in various orientations for their usage in service life. Various fiber orientated polymer composites, which are used in aeroplane and aerospace applications, are frequently subjected to thermal cycles because of the changes in body temperatures at a range of −60 to 150°C during flights. It is an important subject to investigate the visco‐elastic properties of the thermal cycled polymer composite materials which have various fiber orientations during service life. Continuous fiber reinforced composites with a various fiber orientations are subjected to 1,000 thermal cycles between the temperatures of 0 and 100°C. Dynamic mechanic thermal analysis (DMTA) experiments are carried out by TA Q800 type equipment. The changes in glass transition temperature (T_g), storage modulus (E′), loss modulus (E′′) and loss factor (tan δ) are inspected as a function of thermal cycles for different fiber orientations. It was observed that thermal and dynamic mechanical properties of the polymer composites were remarkably changed by thermal cycles. It was also determined that the composites with [45°/−45°]_s fiber orientation presented the lowest dynamic mechanical properties. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

PC/ABS阻燃合金材料的研制

采用双螺杆熔融挤出加工工艺,以聚碳酸酯(PC)和丙烯腈-丁二烯-苯乙烯共聚物(ABS)为基础树脂,研究了阻燃剂、相容剂及抗氧剂等对PC/ABS阻燃合金材料综合性能的影响.结果表明,PC/ABS阻燃合金材料的简支梁缺口冲击强度随着阻燃剂用量的增加而下降,拉伸强度、弯曲强度、弯曲模量随着阻燃剂含量的增加而增加.当阻燃剂、相容剂质量分数分别为18%,2.0%～3.0%时,该材料使用性能最佳.     

In situ compatibilized polymer blends of phenoxy and ABS

The combination of styrene-acrylonitrile-glycidyl methacrylate (SAG) reactive copolymer and sodium lauryl sulfonate catalyst is able to function as an effective in situ compatibilizer for the otherwise immiscible and incompatible polymer blends of phenoxy and acrylonitrile-butadiene-styrene (ABS). The copolymer formed from the reaction between phenoxy and SAG under melt blending conditions tends to reduce interfacial tension in the melt and results in finer morphological domains of the blends. The presence of this in situ formed compatibilizer also raises the interphase adhesion of the blends and results in significant improvements in mechanical properties. © 1994 John Wiley & Sons, Inc.     

Dynamic mechanical properties of polymer melts: The effect of molecular weight distribution on the temperature dependence of viscoelastic properties

An experimental investigation of the dynamic mechanical response of molten polymers was performed using the Maxwell Orthogonal Reheometer. One purpose of the study was to evaluate the effect of molecular weight distribution on the temperature dependence of viscoelastic properties. Data were obtained over a range of temperatures for both monodisperse and polydisperse materials which indicate that viscoelasticity is highly temperature dependent only for monodisperse polymers. On a molecular basis the reduction in temperature sensitivity for polydisperse materials logically can be attributed to the influence of the low molecular weight species present in a distribution on the relaxation spectrum. Since the relaxation spectrum largely determines all viscoelastic functions, the observations made from th dynamic data shown in this paper can be generalized to all viscoelastic experiments.     

The viscoelastic behavior of polymer/oligomer blends

The viscoelastic properties of poly(α-methyl styrene), its hexamer, and their athermal blends at various concentrations are studied. Master curves for the dynamic shear responses, G′ and G″, are successfully constructed for both the pure materials and the blends, indicating the validity of the time-temperature superposition principle for these systems. The temperature dependence of the shift factor follows the Vogel-Fulcher behavior over the temperature range studied, and the temperature dependence is slightly weaker for the blends. The rubbery plateau modulus scales with the polymer concentration as ; the terminal relaxation time scales with the polymer concentration as . The shape of the segmental dispersion appears unchanged by concentration, which differs from our calorimetric studies where mixtures show obviously temperature-broadened glass transitions and depressed enthalpy overshoots. The TNM (Tool-Narayanaswamy-Moynihan) model indicates that the change in the temperature dependence is not sufficient to account for the observed calorimetric broadening. We conclude that the temperature broadening of the glass transition for our blends is not due to a broadening of the dynamic spectrum or to changes in its temperature dependence. The possibility that the broadening is due to changes in the non-linearity parameter x in the TNM model is also considered. While the broadening could be due to a decreasing value of x, we found that this same decrease would lead to increasing enthalpy overshoots on heating, contrary to the experimental observations. The combination of the calorimetric results with the rheological measurements further indicates that the fundamental basis of the TNM-type of model of structural kinetics in glasses is potentially wrong.     

Thermal,mechanical, and diffusional properties of nylon 6/ABS polymer blends: Compatibilizer effect

The thermal, mechanical, and water absorption properties of blends of nylon 6 (PA6) and acrylonitrile‐butadiene‐styrene copolymer (ABS) with and without the compatibilizer maleic anhydride (MAH) were studied. Polymers were melt‐blended using a twin screw extruder, and injection molded into sheets. Tensile and impact properties, hardness, heat deflection resistance, and dimensional stability were enhanced by the incorporation of MAH. Synergistic effects were observed for tensile elongation and flexural properties. The melting temperature and the thermal stability were not significantly affected by the incorporation of MAH. The mechanical property enhancement by the introduction of compatibilizer was explained by the formation of a micro‐domain structure in the blends. The equilibrium water uptake increased with increasing concentration of PA6, and the diffusion coefficient was determined from the water transport kinetics at different temperatures. Activation energy was extracted from the temperature dependence of the diffusion coefficient. No compatibilizer effect was observed in the swelling behavior.