Beiträe zur künstlichen bewitterung von PVC

The concentration dependences of particle size of the dispersed phase on rheological properties of the components were investigated by scanning electron microscopy for blends of polypropylene and ethylene-propylene elastomers obtained by melt mixing. At very low concentrations the minority component is dispersed the more finely the lower its viscosity is. With increasing concentration of the dispersed phase the size of its particles in the given matrix increases the more quickly the lower the viscosity of the dispersed phase is. With increasing viscosity of the matrix the particle size of the minority phase decreases at all compositions of the blend. The results obtained were interpreted as a result of dynamic equilibrium between the break up and coalescence of particles in flow. At elastomer concentrations higher than 15% the differences between impact strength values of the blends are determined by the size of inclusions of the elastomeric modifier. Dispersions finer than the optimal one with respect to impact strength can be reached only with the polypropylene matrix possessing high viscosity.     

Dilatometric investigation of deformation mechanisms in polystyrene-polyethylene block copolymer blends: correlation between Poisson ratio and adhesion

To gain more insight into the deformation behaviour of blends containing polystyrene (PS), low density polyethylene(IdPE) and a PSPE block copolymer, tensile tests have been performed with simultaneous volume measurements. Assuming that shearing does not give rise to volume changes, it is shown that, after yielding, crazing is the only deformation mechanism of blends with a low PE and PSPE block copolymer content. Shearing becomes important at relatively high copolymer concentrations. This is explained by the formation of a semi-continuous low-modulus phase. The decrease of the Poisson ratio with PE content in PSPE blends, as opposed to an increase if some block copolymer has been added to these blends, shows that the Poisson ratio is very sensitive to adhesion between the components. Toughness of PSPE blends is discussed in terms of concentrations of craze nuclei. Too few craze nuclei give rise to brittle failure: the resulting low number of crazes cannot take over much of the deformation of the matrix. Too many craze nuclei cause brittle failure because chances are high that some of the high number of crazes formed will combine to produce a fatal crack. Therefore high toughness is only obtained at intermediate craze nuclei concentrations. The concentration of craze nuclei is shown to be dependent on the number of dispersed particles and the adhesion between these particles and the matrix.     

Effect of the dispersed phase fraction on particle size in blends with high viscosity ratio

It has been reported that for polymer blends with high viscosity ratio (>1), the size of the dispersed particles decreases with increasing volume fraction of the dispersed phase. In order to explain this effect, an equation was derived for the affine deformation of an imaginary plane of the dispersed phase in stratified two‐phase steady, simple, shear flow. The model predicts that for viscosity ratio >1, the deformation rate increases with volume fraction of the dispersed phase, and the shear stress also increases, leading to an increase of the breakup time. Therefore, the total deformation of the dispersed phase, before breakup, increases with increase of volume fraction, resulting in a decrease of the size of the dispersed phase particles. Accordingly, one can expect that in industrial mixers, the particle size of the blends should decrease as the volume fraction increases, if coalescence is suppressed. Experiments were carried out in a Haake batch mixer, using polyethylene/polyamide‐6 blends compatibilized by adding maleic anhydride grafted polyethylene. Particle size decreased up to 20 wt% polyamide‐6, at 100, 150, and 200 RPM, and increased between 20 and 30 wt%. The decrease of the particle size is mainly due to increased deformation of the dispersed phase. The increase of the particle size above 20 wt% is due to coalescence at high fractions.     

Extrusion of PE/PS blends with supercritical carbon dioxide

The effects of dissolved supercritical carbon dioxide on the viscosity and morphological properties were investigated for polyethylene/polystyrene blends in a twin-screw extruder. The viscosities of the blend/CO₂ solutions were measured using a wedge die mounted on the extruder. A considerable reduction of viscosity was found when CO₂ was dissolved in the blend. It was observed that the dissolution of CO₂ into PE/PS blends, regardless of the CO₂ content used, led to decreased shear thinning behavior resulting in an increase of the power law index from 0.29 to 0.34. The cell structures of foamed PE/PS blends showed a typical dependence of pressure and CO₂ concentration, with higher operating pressures and CO₂ content leading to a smaller cell size. Also, it was noted that the size of the dispersed PS phase in the PE/PS phase blends decreased by increasing the CO₂ concentration, and that the dispersed PS phase domains were highly elongated in the direction normal to the cell radius.     

Effect of the mixing conditions on the phase structure of PP/PS blends

The effect of the rate and time of mixing in a batch mixer on the phase structure of polypropylene/polystyrene (PP/PS) blends with various rheological properties of the components was studied. Regions with substantially different average sizes of the dispersed particles were found in the studied blends. Differences between the average size of the particles in individual regions of the samples persist in all blends and mixing conditions under study. No dependence of the average particle size on the rate of mixing has been obtained for the PP/PS (75/25) blends. On the other hand, decrease of the average particle size with increasing rate of mixing has been found for the PP/PS (95/5) blend. These results are discussed as a consequence of the competition between the breakup and coalescence of the dispersed particles. © 1996 John Wiley & Sons, Inc.     

Effect of mixing protocol on compatibilized polymer blend morphology

We investigated the effect of mixing protocol on the morphology of compatibilized polymer blends made with premade compatibilizer and reactively formed in‐situ compatibilizer in a custom‐built miniature mixer Alberta Polymer Asymmetric Minimixer (APAM). The compatibilized blends show a finer morphology than uncompatibilized blends if the polymers are mixed together in the dry state and then fed into the mixer. It is found that premelting one polymer, and premixing polymers and compatibilizer, both greatly affect the compatibilized blends' morphology. The effects are complex since the dispersed phase particle size and distribution of the compatibilized blends may be smaller or larger when compared with the uncompatibilized system, depending on the material's physical and chemical properties; for example, diblock molecular weight or the preference of copolymer to migrate to a particular phase can change the final morphology. Good mobility of the copolymer to reach the interface is crucial to obtain a finer morphology. Micelles are observed when a high molecular weight diblock copolymer P(S‐b‐MMA) is used for a PS/PMMA blend. Because of its enhanced mobility, no micelles are found for a low molecular weight diblock copolymer P(S‐b‐MMA) in a PS/PMMA blend. For PS/PE/P(S‐b‐E) blends, finer morphology is obtained when P(S‐b‐E) is first precompounded with PS. Because the block copolymer prefers the PE phase, if the P(S‐b‐E) block copolymer is compounded with PE first, some remains inside the PE phase and does not compatibilize the interface. In the case of reactive blend PSOX/PEMA, premelting and holding the polymers at high temperature for 5 min decreases final dispersed phase particle size; however, premelting and holding for 10 min coarsens the morphology. POLYM. ENG. SCI. 46:691–702, 2006. © 2006 Society of Plastics Engineers.     

调节聚苯乙烯树脂粒度分布的研究

研究了悬浮法聚苯乙烯粒度分布的两种调节方法：改变分散剂用量和改变反应初期分散相粘度。结果表明，分散剂用量增加，树脂粒径减小；分散相粘度增大，树脂粒径增大。     

Proposed Fracture Theory of a Dispersion-Strengthened Glass Matrix

A fracture theory is proposed for a composite system based on a continuous glass matrix. It is hypothesized that hard crystalline dispersions within the glass matrix will limit the size of Griffith flaws and strengthen the composite. Quantitative relations are derived for the effect of a dispersed phase on composite strength. At low volume fractions of the dispersed phase, the average flaw size is statistically reduced independent of the size of the dispersed particles. At high volume fractions of the dispersed phase, the average flaw size is governed by the average distance between particles dispersed in the matrix. The strength of a composite should, therefore, be a function of the volume fraction of the dispersed phase at low volume fractions and dependent on both the volume fraction and particle size of the dispersed phase at high volume fractions. For verification of the theory, cross-bending strengths were measured on a sodium borosilicate glass containing varying volume fractions of spheroidized alumina over a range of particle sizes. The average distance between dispersed particles ranged from approximately 15 to 500μ. Good agreement with theory was found. Values of glass surface energy calculated from the experimental data agree well with literature data.     

Shear field in the mold cavity of multimelt multi‐injection molding revealed by the morphology distribution of a model polymer blend

The morphology distribution of a model polymer blend, polystyrene (PS)/polyethylene (PE), molded by multimelt multi‐injection molding (MMMIM) process was studied by scanning electronic microscopy and polarizing light microscopy. An unusual double skin/core morphology was observed. The minor phase, PS, showed highly deformed morphology in both the skin layer near the mold wall and the core layer near the skin/core layer's interface. Meanwhile, in the regions that highly deformed PS phase showed, highly ordered cylindritic crystal structures of PE are also formed. As we all know the driving force and the basic prerequisite to deform the dispersed droplet and form the oriented crystal structure is the shear field. So an attempt was made to correlate the dispersed phase morphology, crystalline morphologies, and shear rate. The shear rate, estimated via the capillary number, across the thickness of the parts molded by MMMIM was bimodal. Even if the coalescence and relaxation of the dispersed phase during and after mold filling cannot be ignored, both the highly dispersed PS domains and the highly ordered crystal structure of PE showed in the regions with the maximum calculated shear rate, which is consistent with the generally accepted theories that strong shear flow is favorable to the formation of the oriented structures. POLYM. ENG. SCI., 54:2345–2353, 2014. © 2013 Society of Plastics Engineers     

Crystalline crosslinked microparticles from immiscible blends of polyethylene and polystyrene

Crystalline crosslinked polyethylene microparticles with size distribution averages ranging from 0.374 to 0.944 μm were prepared from immiscible PS and PE blends in the melt phase for microgel applications. The particles were crosslinked either concurrently while blending using dicumyl peroxide or post blending via electron-beam irradiation. The effects of varying the processing temperature, blend duration, and block copolymer compatibilizer content on the particle morphology were studied and it was found that only a decrease in processing temperatures (increase in continuous-to-dispersed phase viscosity ratio) resulted in finer particles for the range of variables tested. The chemical composition of the isolated particles was determined using infrared and nuclear magnetic resonance spectroscopy while the particle morphology was investigated using electron microscopy image analysis in conjunction with thermogravimetric analysis. It was determined that particles produced with and without the block copolymer contained a small amount of PS even after meticulous extraction with a PS solvent (THF). However, the exact location of PS on the PE particles remains obscure.     

The effect of mixing time on the morphology of immiscible polymer blends

The effect of mixing time on the morphology, with the viscosity ratio and composition as parameters in the mixing process, was studied for two immiscible binary polyblend systems, polyamide/polyethersulfone (PA/PES) and poly(butylene terephthalate)/polystyrene (PBT/PS), by selective dissolution followed by macroscopic and microscopic observations. At a short mixing time, the morphology of each phase depends not only on the composition, but also on the viscosity difference of two phases, shown by the results of PA/PES blends with a viscosity ratio of 0.03. The lower viscous phase (PA) forms particles, fibrils, and layers successively with its increasing content and becomes a continuous one at low concentrations as the minor phase, while the high viscous phase (PES) appears mainly in the form of particles and directly becomes a continuous one at high concentrations. With increasing mixing time, the effect of the viscosity ratio becomes less and the morphology is determined mainly by the volume fraction of each phase. Particles are the final morphology of the minor phase. Only at a viscosity ratio of unity is the morphological development of two phases (PBT and PS) with mixing time the same, and any one of these two components is in the form of particles when it is the minor phase. At the composition near 50/50, fibrillar or continuous structure may coexist for both phases. The composition range of co-phase continuity is decided not only by the viscosity ratio but also by the mixing time. With increasing mixing time, this range becomes narrower and finally occurs at volume fraction of 50/50, no longer affected by the viscosity ratio. © 1996 John Wiley & Sons, Inc.     

Melt blending of linear low-density polyethylene and polystyrene in a Haake internal mixer. II. Morphology-processing relationships

A measure of the effective shear rate range for dispersive mixing in the Haake mixer has been developed, which is more representative of shearing conditions than that currently used. In addition, the effects of processing conditions, composition, and compatibilizer on linear low-density polyethylene and polystyrene (LLDPE/PS) blend morphology were studied. Fiber/stratified morphologies form with blends when the minor phase has low viscosity and is present at its higher concentration. The influence of the viscosity ratio on phase size was found to be a minor effect for mixtures having a low fraction of the dispersed phase (20% PS). The effect of shear intensity, however, was found to be more important at a low composition of the dispersed phase or in compatibilized blends. During Haake blending, an optimal time for adding compatibilizer to stabilize phase morphology was found to be when the final morphology of an incompatible blend had developed. Further studies have concluded that the addition of styrene–ethylene/butylene–styrene (SEBS) stabilized the blend morphology of LLDPE/PS more efficiently than styrene–ethylene/propylene (SEP) on different blending conditions and compositions. At high temperatures, the addition of SEP to a LLDPE/PS blend did not modify the dispersed phase size. On the other hand, SEBS stabilized the dispersion so that the final domain size is independent of composition. © 1995 John Wiley & Sons, Inc.     

Morphology development of PC/PE blends during compounding in a twin-screw extruder

The morphological development of a polycarbonate/polyethylene (PC/PE) blend in a twin-screw extruder was studied using a scanning electron microscope (SEM). The effects of extrusion temperature, viscosity ratio (the ratio of the viscosity of the dispersed phase to that of the matrix), and the screw configuration on the morphology of the PC/PE blend during the extrusion were discussed in detail. It was found that the morphology of the dispersed particles and the interfacial adhesion between the dispersed phase and matrix were both influenced by the extrusion temperature. The dispersed phase had a spheroidal shape and a small size during the high temperature processing, and an irregular shape and a large size when it was processed at low temperature. The PC phase with a lower viscosity was easier to disperse and also to coalesce. Therefore, the deformation of the low-viscosity dispersed phase during the processing was more intense than that of the high-viscosity dispersed phase. By comparing the effects of the different screw configurations on the morphology development of the PC/PE blend, it was found that the melting and breaking up of the dispersed phase were mainly affected in the initial blending stages by the number of the kneading blocks. While a kneading block with a 90 degree staggering angle was used, the size of the dispersed particles decreased and the long fibers were shortened, the large particles were drawn by the additional kneading zone. Finally, all of these structures were completely changed to the short fibers. POLYM. ENG. SCI., 47:14–25, 2007. © 2006 Society of Plastics Engineers     

聚苯乙烯共混聚丙烯树脂的熔融流变行为

文章研究了聚苯乙烯（ＰＳ）与聚丙烯（ＰＰ）共混物的熔融流变行为。采用索氏抽提法研究表明ＰＳ与ＰＰ产生了接技反应，ＰＳ用量在０～２０ｗｔ％范围内，１０ｗｔ％共混物接技量为最大，同时在ＰＰ中分散的ＰＳ粒径最小。随着ＰＳ含量的增加，减少了熔融粘度，组成－熔融粘度曲线在ＰＳ为１０ｗｔ％时略有所弯曲，通过接技反应，增大了ＰＰ粒子的范畴。     

The optical properties of two-phase polymer systems: Single scattering in monodisperse,non-absorbing systems

Two-phase polymer systems have achieved commercial importance due mainly to the improvement in impact strength brought about by the addition of dispersed rubber particles to a normally brittle glassy polymer. Rubber-reinforced polystyrene and ABS plastics are two familiar examples. An important drawback of this class of materials is their lack of transparency, caused by the scattering of light at the interface between the phases. The theory of light scattering by spherical particles indicates that the degree of scattering (turbidity) is a function of the amount of dispersed phase present, its particle size, the ratio of refractive indices of the phases, and the wavelength of light. Quantitative predictions of the effects of the above parameters on the transparency of two-phase systems can be made, providing answers to the questions “How close must the refractive indices be?” and “What size must the dispersed-phase particles be?” for a given level of transparency. Calculations for typical polymer pairs reveal that at a given dispersed-phase level, a maximum in turbidity is obtained roughly in the range of particle sizes thought to be necessary for good impact strength. Also, if the refractive indices are matched at a particular temperature, small particle sizes greatly increase the temperature range over which scattering is minimized.     

Development of phase morphology in incompatible polymer blends during mixing and its variation in extrusion

An experimental study of the development of phase morphology in incompatible polymer melt blends of polyethylene/polystyrene (PE/PS), polyethylene/polycarbonate (PE/PC), and polyethylene/nylon-6 (PE/N6) is presented. Different temperatures (180°C, 240°C) of mixing and polyethylene molecular- weight levels were used in the PE/PS studies. Little variation in the cross-sectional phase morphology of the PE/PS extrudates was observed with these variables, though the morphology became finer with increased shear rate/stress in capillary die flow. Variations in the longitudinal morphology are observed with continuous filaments of dispersed phase only arising when the dispersed phase has an equal or lower viscosity than the continuous phase. The PE/N6 and PE/PC, especially the former, give coarser morphologies when the N6 and PC are the continuous phases. This was attributed to larger inter-facial tensions. The effect of viscoelasticity was also discussed.     

Influence of elasticity on dispersed‐phase droplet size in immiscible polymer blends in simple shearing flow

The influence of elasticity of the blend constituent components on the size and size distribution of dispersed‐phase droplets is investigated for blends of polystyrene and high density polyethylene in a simple shearing flow. The elasticities of the blend components are characterized by their first normal stress differences. The role played by the ratio of drop to matrix elasticity at fixed viscosity ratio was examined by using high molecular weight polymer melts, high density polyethylene and polystyrene, at temperatures at which the viscosity ratios roughly equaled each of three different values: 0.5, 1, and 2. The experiments were conducted by using a cone‐and‐plate rheometer, and the steady‐state number and volume‐mean averages of droplet diameters were determined by optical microscopy. After steady‐state shearing, the viscoelastic drops were larger than the Newtonian drops at the same shearing stress. From the steady‐state dispersed‐phase droplet diameters, the steady‐state capillary number, Ca, defined as the ratio of the viscous shearing stress over the interfacial tension stress, was calculated as a function of the ratio of the first normal stress differences in the droplet and matrix phases. For the blend systems with viscosity ratio 0.5, 1 and 2, the values of steady‐state capillary number were found to increase with the first normal stress difference ratio and followed a power law with scaling exponents between 1.7 and 1.9.     

有机纳米稀土光能转换剂与PE相容性及流变性的研究

利用透射电镜和扫描电镜对以2,2-二羟甲基丙酸等为配体制备的有机纳米稀土光能转换剂的形态、粒径以及分散情况进行了分析。通过对有机纳米稀土光能转换剂与PE共混体系的剪切应力、剪切速率、表观粘度、非牛顿指数、粘流活化能之间关系的分析,对共混体系的流变性能进行了研究。结果表明:制备的有机纳米稀土光能转换剂均匀分布在PE中,其粒径为100nm-150nm。随着有机纳米稀土光能转换剂含量的增加,其PE共混体系的表观粘度,粘流活化能均有所下降,且其流动性得到改善。     

Segregated structures in carbon black-containing immiscible polymer blends: HIPS/LLDPE systems

The structure/electrical resistivity relationship in CB-loaded immiscible HIPS/LLDPE blends was studied. Effects of CB content and location, dispersed polymer phase size and shape, dispersed phase viscosity, and processing procedures were examined. The elongated dispersed phase in CB-containing blends is essential for promoting conductivity in formulations prepared by melt mixing and compression molding. However, the same formulations proved highly resistive when injection-molded, due to orientation and excessive shearing. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1097–1106, 1997     

Electrostatic and electrosteric stabilization of aqueous suspensions of barite nanoparticles

Electrostatic and electrosteric stabilization of aqueous suspensions of barite nanoparticles were investigated. The state of dispersion was evaluated in terms of zeta potential, apparent viscosity and the mean particle size of solid phase in the solution. Zeta potential, apparent viscosity and the mean particle size as a function of pH were performed in absence of dispersant. The result showed that electrostatic stabilization of the aqueous suspension of barite nanoparticles can be accomplished in low acidic and high basic range of pH. In presence of sodium polyacrylate (PAA-Na) dispersant, the isoelectric point (IEP) of the barite nanoparticles was shifted to lower pH and the negative zeta potential was increased in a large range of pH above the (IEP). The optimum amount of PAA-Na dispersant is discussed in the light of zeta potential and viscosity. It is found that the adsorption of PAA is correlated to the net surface charge of the barite nanoparticles and the fraction of dissociated polymer at pH 4, 8.5 and 10. At pH 4, the state of dispersion was achieved at higher amount of electrolyte due to the low fraction of negatively charged dissociated polymer and the positively charge particles. At basic pH, the fraction of dissociated polymer was high and the surface charge of particle was highly negative, therefore, the lowest viscosity was obtained at a small amount of PAA. In addition, the optimum amount of polymer decreased with the increase in pH of the suspension.