Rheological properties of poly(methyl methacrylate)/rigid ladderlike polyphenylsilsesquioxane blends

A series of poly(methyl methacrylate) (PMMA) blends with rigid ladderlike polyphenylsilsesquioxane (PPSQ) were prepared at weight ratios of 100/0, 95/5, 90/10, 85/15, and 80/20 by solution casting and then hot‐pressing. Their rheological properties have been studied under both dynamic shear and uniaxial elongation conditions. Their rheological properties depend on the compositions. The storage modulus, G′, loss modulus, G″, and dynamic shear viscosity, η*, of the PMMA/PPSQ 95/5 blend were slightly lower than those of pure PMMA. However, the values of G′, G″, and η* for the other PMMA/PPSQ blends are higher than those of PMMA. The G′ values increase with an increase in PPSQ content from 5% through 15% PPSQ at low frequencies and then drop as the PPSQ content increases to 20%. Uniaxial elongational viscosity (η_E) data demonstrate that PMMA/PPSQ blends exhibit slightly weaker (5% PPSQ) and much weaker (10% PPSQ) strain‐hardening than PMMA. In contrast, the PMMA/PPSQ 85/15 blend shows strain‐softening. Neither strain‐hardening nor strain‐softening was observed in the 80/20 blend. The special rheological properties for the 95/5 blend is probably due to a decrease in PMMA entanglements brought by the specific PMMA–PPSQ interactions. Rheological properties of PMMA/PPSQ blends with higher PPSQ content (≥10%) are mainly affected by formation of hard PPSQ particles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 352–359, 2007     

Photochemical aging and processability of life‐time‐controlled polystyrene/high‐impact polystyrene blends

This work investigated the influence of the addition of acetophenone and benzophenone (2.5 and 5%) on the photodegradability of polystyrene/high‐impact polystyrene blends (50/50 w/w) prepared by sheet extrusion, aiming to improve their decomposition during exposure to a natural environment. The modified materials were submitted to photodegradation under controlled conditions, and the extent of degradation was monitored by suitable characterization techniques, such as infrared and ultraviolet–visible spectroscopy, viscosimetry, and measurements of the mechanical properties. The processability of the modified blends was also studied by capillary and oscillatory rheometry. Evidence for the formation of hydroperoxides and carbonyl groups, the occurrence of chain scission, and the loss of mechanical properties was achieved, being greater for samples with benzophenone. It was also observed that for the same ketone level, benzophenone caused greater changes in the mechanical properties, and this was in agreement with the decrease in the molecular weight observed. Thus, the addition of this type of chemical compound could enhance the photodegradability of polystyrene/high‐impact polystyrene blends without a significant effect on their processability and mechanical performance. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Relationship between branch length and the compatibilizing effect of polypropylene‐g‐polystyrene graft copolymer on polypropylene/polystyrene blends

Three polypropylene‐g‐polystyrene (PP‐g‐PS) graft copolymers with the same branch density but different branch lengths were evaluated as compatibilizing agents for PP/PS blends. The morphological and rheological results revealed that the addition of PP‐g‐PS graft copolymers significantly reduced the PS particle size and enhanced the interfacial adhesion between PP and PS phases. Furthermore, it is verified that the branch length of PP‐g‐PS graft copolymer had opposite effects on its compatibilizing effect: on one hand, increasing the branch length could improve the compatibilizing effect of graft copolymer on PP/PS blends, demonstrated by the reduction of PS particle size and the enhancement of interfacial adhesion; on the other hand, increasing the branch length would increase the melt viscosity of PP‐g‐PS graft copolymer, which prevented it from migrating effectively to the interface of blend components. Additionally, the crystallization and melting behaviors of PP and PP/PS blends were compared. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40126.     

Thermal and structural properties of blends of isotactic with atactic polystyrene

Blends of isotactic polystyrene (iPS) with non-crystallizable atactic polystyrene (aPS) were studied by differential scanning calorimetry and small angle X-ray scattering. The iPS/aPS blends, prepared by solution casting, were found to be miscible in the melt over the entire composition range. Both quenched amorphous and semicrystalline blends exhibit a single, composition-dependent glass transition temperature, depressed from that of either of the homopolymer components. Addition of aPS causes a decrease in crystallinity and in the rigid amorphous fraction, and suppression of the reorganization/recrystallization of iPS during thermal scanning: only one melting peak is observed for blends with larger aPS content. Formation and devitrification of the rigid amorphous fraction of iPS are also affected by aPS addition. The annealing peak, which is due to the relaxation of rigid amorphous fraction in parallel with melting of a tiny amount of crystals, is retarded with an increase of the composition of aPS, resulting in the slow devitrification of RAF in parallel with the melting of large amount of crystals. X-ray scattering shows that the long period in the iPS/aPS blends is greater than in the iPS homopolymer, and long period increases slightly as aPS content increases. Comparison of the volume fraction of phase 1 with the volume fraction crystallinity from DSC suggests that more and more amorphous phase is rejected outside the lamellar stacks as aPS content increases. The effect of aPS addition is to reduce the confinement of the amorphous phase chains. The cooperativity length, ξ_A, which is calculated from thermal analysis of the T_g region, increases with aPS addition. The interlamellar and extra-lamellar amorphous chains both contribute to the glass transition relaxation process.     

PC/ABS共混物的流变性能

采用熔融共混的方法,制备了不同配比的聚碳酸酯(PC)/丙烯腈-丁二烯-苯乙烯(ABS)共混物。采用毛细管流变仪研究了PC/ABS共混物的流变行为。结果表明:PC/ABS共混物熔体的流变行为呈假塑性流体的特征,表观黏度随剪切速率的增加而减小,随温度的升高而降低,随ABS含量的增加而减小;随着ABS含量的增加,共混物表观黏度对温度的敏感性降低,对剪切速率的敏感性增加;加入相容剂使PC/ABS共混物更易加工成型。     

Form birefringence and turbidity of polystyrene/poly(methyl methacrylate) blends in slit dies and planar contractions

The birefringence and turbidity of a polystyrene/poly(methyl methacrylate) (PMMA) blend, with the concentration of the PMMA dispersed phase ranging up to 1%, were measured in both a slit channel with a constant cross section and a planar hyperbolic contraction/expansion (8:1:8). The measurements were performed by the attachment of a modular rheo‐optical die to a twin‐screw extruder. The optical arrangement had a red light‐emitting diode as the source and two photoresistors, with one of them measuring the turbidity and the other one measuring the transmitted intensity between cross‐polarizers. The experimental procedure consisted of the stopping of the extruder feeding, while the screw rotation was kept constant. Because the form birefringence could be associated with the shape of the droplets, these measurements were used to infer information about the PMMA droplet deformation and breakup. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44066.     

Rheological studies of the poly(styrene-co-acrylonitrile) and poly(vinyl chloride-co-vinyl acetate) blends

The rheological studies of the poly(vinyl chloride-co-vinyl acetate) and poly(styrene-co-vinyl acetate) and poly(styrene-co-acrylonitrile) blends were performed by a Brabender Rheotron at three different temperatures and also at different shear rates. Flow curves of the blends at different temperatures were drawn. The flow behavior index and, also, zero-shear viscosity of the blends at different temperatures were determined. From the flow curves, it has been found that as shear stress increases, melt viscosity decreases at all temperatures, indicating that pseudoplastic behavior and experimental values lies above the line of the log-additivity value and below the line of the additivity rule of mixture. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2577–2583, 1998     

Dynamic rheological properties of high‐density polyethylene/polystyrene blends extruded in the presence of ultrasonic oscillations

The linear rheological properties of high‐density polyethylene (HDPE), polystyrene (PS), and HDPE/PS (80/20) blends were used to characterize their structural development during extrusion in the presence of ultrasonic oscillations. The master curves of the storage shear modulus (G′) and loss shear modulus (G″) at 200°C for HDPE, PS, and HDPE/PS (80/20) blends were constructed with time–temperature superposition, and their zero shear viscosity was determined from Cole–Cole plots of the out‐of‐phase viscous component of the dynamic complex viscosity (η″) versus the dynamic shear viscosity. The experimental results showed that ultrasonic oscillations during extrusion reduced G′ and G″ as well as the zero shear viscosity of HDPE and PS because of their mechanochemical degradation in the presence of ultrasonic oscillations; this was confirmed by molecular weight measurements. Ultrasonic oscillations increased the slopes of log G′ versus log G″ for HDPE and PS in the low‐frequency terminal zone because of the increase in their molecular weight distributions. The slopes of log G′ versus log G″ for HDPE/PS (80/20) blends and an emulsion model were used to characterize the ultrasonic enhancement of the compatibility of the blends. The results showed that ultrasonic oscillations could reduce the interfacial tension and enhance the compatibility of the blends, and this was consistent with our previous work. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3153–3158, 2004     

Rheological and thermal properties of single‐site polyethylene blends

Branched polyethylenes, low‐density polyethylenes (LDPE1 and LDPE2) or long‐chain‐branched very low density polyethylenes (VLDPE2), were blended with very low density polyethylenes containing short branches (VLDPE1 and VLDPE3). The rheological and thermal measurements of the pure copolymers and their blends (VLDPE1–LDPE1, VLDPE1–LDPE2, VLDPE1–VLDPE2, and VLDPE2–VLDPE3) were taken by controlled stress rheometry and differential scanning calorimetry, respectively. The shear‐thinning effect became stronger with increasing long‐chain‐branched polymer compositions when it was correlated with the flow behavior index, and the extent of shear thinning was different for each blend set. Stronger shear thinning and a linear composition dependence of the zero‐shear viscosity were observed for the VLDPE1–LDPE1 and VLDPE1–LDPE2 blends. These blends followed the log additivity rule, and this indicated that they were miscible in the melt at all compositions. In contrast, a deviation from the log additivity rule was observed for the VLDPE1–VLDPE2 blend compositions with 50% or less VLDPE2 and for the VLDPE3–VLDPE2 blends with 50% or more VLDPE2. The thermal properties of the blends were consistent with the rheological properties. VLDPE1–LDPE1 and VLDPE1–LDPE2 showed that these blends were characteristic of a single‐component system at all compositions, whereas the phase separation (immiscibility) was detected only for VLDPE1–VLDPE2 blends with 50% or less VLDPE2 and for VLDPE3–VLDPE2 blends with 50% or more VLDPE2. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1549–1557, 2005     

Rheological and thermal properties of polypropylene blends based in a low molecular weight EVA

Blends of polypropylene (PP) and poly(ethylene-co-vinyl acetate) (EVA) having a PP/EVA viscosity ratio of 240 were prepared by melt mixing. EVA concentration varies from 2 to 26 wt%. All blends display two-phase structure with quasi-spherical EVA domains evenly distributed in the PP matrix. The diameter of the domains increases with EVA concentration from about 0.4 to 6 μm. Each component crystallizes separately. The melting temperature of PP phase is no noticeably affected by the presence of EVA while the crystallization one gradually increases by 4°C. The dynamic moduli of the blends are well predicted by the emulsion model of Palierne, revealing that the system PP/EVA has a very small interfacial tension. The thermal degradation behavior of the blends, determined by thermogravimetry, shows that the deacylation process in EVA is not affected by the presence of PP while the beginning of the degradation process of PP is increased by up to 20°C due to the presence of EVA. This effect goes along with an increment in the maximum degradation rate of PP.     

Melt rheology of compatibilized polystyrene/low density polyethylene blends

Investigations have been made on the melt rheological behaviors of compatibilized blends composed of polystyrene, low density polyethylene and hydrogenated (styrene‐butadiene‐styrene) triblock copolymer used as a compatibilizer. The experiments were carried out on a capillary rheometer. The effects of shear stress, temperature and blending ratio on the activation energy for viscous flow and melt viscosity of the blends are described. The study shows that the viscosity of the blends exhibits a maximum or minimum value at a certain blending ratio. The activation energy for viscous flow decreases with increasing LDPE content. Furthermore, the concept of equal‐viscosity temperature is presented and its role in the processing of the blend is discussed. In addition, the morphology of the extrudate sample of the blends was observed by scanning electron microscopy and the correlation between the morphology and the rheological properties is explored. © 1999 Society of Chemical Industry     

Rheological properties of recycled chlorinated polyethylene/natural rubber blends vulcanized by sulfur

Blends of elastomeric chlorinated polyethylene (CPE) and natural rubber (NR) with a blend composition ratio of 80/20 were prepared and recycled. Viscoelastic properties of the blends as a function of the recycling cycle were monitored. The results obtained revealed that, with an increase in the number of recycling cycles, a noticeable change in the viscoelastic properties of blends could be observed; that is, a decrease in the elastic contribution associated with a noticeable shift in the glass‐transition temperature of the NR phase of the blends was observed, implying a molecular change in the NR phase via a thermal chain‐scission mechanism. The influence of magnesium oxide (MgO) as an acid acceptor for CPE on the viscoelasticity of the blends was also investigated. Through a reduction of the amount of MgO, the molecular change was found to be more pronounced in NR than in CPE phases in a manner similar to the increase in the recycling cycles. An explanation of the changes in the viscoelastic properties of the blends with various MgO loadings and recycling cycles is proposed in terms of thermal degradation via a molecular chain‐scission mechanism taking place mainly in the NR phase. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Rheological and mechanical properties of compatibilized polystyrene/ethylene vinyl acetate blends

In this study, a blend of polystyrene (PS)/ethylene vinyl acetate (EVA) (PS/EVA, 90 : 10 wt %) was compatibilized with three different block copolymers, in which their end blocks were compatible with either styrene or EVA. The compatibilized blends with different compositions were prepared using a twin‐screw extruder and injection molded into the required test specimens. Mechanical properties of the blends, such as tensile properties and Charpy impact strength, morphology of tensile fractured surfaces, rheological properties, and thermal properties, were investigated. The results show that the interaction between the dispersed and continuous phase can be improved by the addition of a compatibilizer. Appreciable improvement in the impact strength of the blend with 15 wt % of compatibilizer C (polystyrene‐block‐polybutadiene) was observed. Its mechanical properties are comparable to those of the commercial high‐impact polystyrene, STYRON 470. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2071–2082, 2004     

Rheological properties of citrus pectin dispersions and its blends with polyquaternium‐7 and colloidal particles

This article reports on the rheological behavior of a 5% (w/w) citrus pectin (CP) dispersion, its blends with polyquaternium‐7 (PQ) and also with 200 nm nanoparticles (NP) and 1.8 µm microparticles (MP) of CP. The viscous (G″) and elastic (G′) moduli of the CP dispersion were similar, whereas G′ was higher than G″ for PQ. The 1:20 (w/w) blend of CP and PQ enhanced the viscoelastic profile of CP and also decreased its cross‐over frequency. NP and MP were equally effective in enhancing the viscoelastic properties of CP. The best viscoelastic behavior was obtained with 1:20:0.4 (w/w) CP:PQ:(NP or MP) composition. The association of CP with PQ and/or MP or NP tended to change the behavior of CP and PQ dispersions from pseudoplastic to Newtonian. Cox‐Merz superposition was observed for CP:PQ and CP:(MP or NP). These findings contribute for modulation of the rheological properties of CP dispersions for specific applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40583.     

The study of polystyrene blends: The relationship of phases and structure in blends of polystyrene with ethylene–propylene diene monomer rubber and its grafted copolymer

Pressed films of blends of polystyrene (PS) with ethylene–propylene diene monomer rubber (EPDM) or grafted copolymer of styrene (St) onto EPDM (EPDM-g-St) rubber were examined by small-angle X-ray scattering (SAXS), and scanning electron microscope (SEM). Small-angle X-ray scattering from the relation of phase was analyzed using Porod's Law and led to value of interface layer on blends. The thickness of interface layer (σ_b) had a maximum value at 50/50 (PS–EPDM-g-St) on blends. The radius of gyration of dispersed phase (domain) and correlation distances a_c in blends of PS–EPDM-g-St were calculated using the data of SAXS. The morphology and structure of blends were investigated by SEM. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 805–810, 1998     

Compatibilization of polypropylene/polystyrene blends with poly(styrene-b-butadiene-b-styrene) block copolymer

The compatibilizing effect of the triblock copolymer poly(styrene-b-butadiene-b-styrene) (SBS) on the morphology and mechanical properties of immiscible polypropylene/polystyrene (PP/PS) blends were studied. Blends with three different weight ratios of PP and PS were prepared and three different concentrations of SBS were used for investigations of its compatibilizing effects. Scanning electron microscopy (SEM) showed that SBS reduced the diameter of the PS-dispersed particles as well as improved the adhesion between the matrix and the dispersed phase. Transmission electron microscopy (TEM) revealed that in the PP matrix dispersed particles were complex “honeycomblike” aggregates of PS particles enveloped and joined together with the SBS compatibilizer. Wide-angle X-ray diffraction (WAXD) analysis showed that the degree of crystallinity of PP/PS/SBS slightly exceeded the values given by the addition rule. At the same time, addition of SBS to pure PP and to PP/PS blends changed the orientation parameters A₁₁₀ and C significantly, indicating an obvious SBS influence on the crystallization process in the PP matrix. SBS interactions with PP and PS influenced the mechanical properties of the compatibilized PP/PS/SBS blends. Addition of SBS decreased the yield stress and the Young's modulus and improved the elongation at yield as well as the notched impact strength in comparison to the binary PP/PS blends. Some theoretical models for the determination of the Young's modulus of binary PP/PS blends were used for comparison with the experimental results. The experimental line was closest to the series model line. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 2625–2639, 1998     

Influence of diblock copolymer on the morphology and properties of polystyrene/poly(dimethylsiloxane) blends

Blends of polystyrene (PS) and poly(dimethylsiloxane) (PDMS), with and without diblock copolymers (PS‐b‐PDMS), were prepared by melt mixing. The melt rheology behavior of the blends was studied with a capillary rheometer. The morphology of the blends was examined with scanning electron microscopy. The miscibility of the blends was studied with differential scanning calorimetry. The morphology of PS/PDMS blends was modified by the addition of PS‐b‐PDMS copolymers and investigated as a function of the molar mass of the diblock copolymers, viscosity ratios and the processing conditions. As investigated, the observed morphology of the melt‐blended PS/PDMS pair unambiguously supported the interfacial activity of the diblock copolymers. When a few percent of the diblock copolymers blended together with the PS and PDMS homopolymers, the phase size was reduced and the phase dispersion was firmly stabilized against coalescence. The compatibilizing efficiency of the copolymers was strongly dependent on its molar mass. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2747–2757, 2004     

Rheological properties of ethylcellulose latex

Because of their large specific surface area, aqueous‐based pseudolatex systems of ethylcellulose can absorb large amounts of drugs. In addition, the stability of polymeric particles in biological fluids delays the release of the drug as in controlled drug delivery systems. The aim of the present study was to characterize the rheological properties of latex particles as a measure of their colloidal stability. Here, we report the effect of three variables: pH, electrolyte concentration, and temperature. The rheograms clearly show that the polymer suspensions displayed Bingham plastic behavior. Internal structuring of the latex was greatest at acid and natural pH values, particularly at the highest ionic strength. In acid solutions, only temperature appeared to play a fundamental role; both the shear stress corresponding to the onset of nonlinear viscoelasticity and the elastic modulus at all frequencies were higher at 37°C than those at room temperature. This is assumed to be a consequence of deformation of the polymer particles upon heating. The effect of ionic strength was noticeable only at the natural pH (pH ? 6.5). At high concentrations of sodium chloride, the particles aggregated because of the decrease in double layer repulsion, and as a result, the latex became structured and its elastic modulus subsequently increased. Interestingly, when the temperature was increased further, this structure presumably broke, down, at least partially, and the storage modulus was reduced. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 847–851, 2006     

HTPB/液化MDI型聚氨酯与聚苯乙烯共混研究

用同步聚合法制备了一系列HTPB和液化MDI型聚氨酯与聚苯乙烯的混材料，运用FTIR，DSC，TG，SEM和拉力实验机对共物的反应进度、玻璃化转变温度，热稳定性，力学性能和微观形态进行考查，结果表明，共混体系在同步聚合过程中，PU的形成速率明显大于PS的聚合速率，共混材料具有比纯组分较好的热稳定性，其玻璃化温度高温段Tg2外移且程度不大，力学性能显示随着共混物中PS组成的减少材料的拉伸强度和硬度逐渐减小，断裂伸长率先增加后减小，冲击强度增大，共混材料的微观形态呈两相分离，相转变发生在PU／PS组成质量比在15：85到30：70之间。     

A unifying approach for melt rheology of linear polystyrene

Several studies of melt rheological properties of polystyrene have been conducted over the past 50 years. Several approaches, including empirical models, have been developed to understand the behavior of materials using simple equations. The existing melt rheology models are best suited for high‐molecular‐weight polymers whose T_g does not vary. In this work, a semiempirical viscosity equation has been derived, including the effect of T_g dependence on molecular weight, to describe the melt rheology of low‐molecular‐weight polymers. The equation is derived based on a combination of well‐known concepts, such as the effects of free volume and molecular dynamics on polymer rheology. This provides a better understanding of the rheological behavior in the low‐molecular‐weight regime with respect to temperature and molecular weight. Because of the industrial trend towards lower molecular weight materials for applications such as high solids coatings, this unifying approach, based on the free volume theory with a simple expression, is of extreme practical significance. This equation can predict the zero shear viscosity behavior for different molecular weights, including low‐molecular‐weight regions, and temperatures. Viscosity calculations using the empirical equation agree with published experimental data. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2597–2607, 2007