The effect of SEBS on interfacial tension and rheological properties of LDPE/PS blend

The effects of SEBS as a compatibilizer on the interfacial tension and rheological properties of LDPE/PS blend have been studied. Interfacial tension was measured by the breaking thread method. The measured interfacial tension of the LDPE/PS blend was 8.26 dyn/cm. It decreased rapidly with SEBS contents to 1 wt % and then leveled off to a saturation value, 3.6 dyn/cm. Dynamic oscillatory shear, elongational viscosity, and recovery after elongation were measured as the rheological properties. Storage modulus at low frequencies decreased with SEBS contents to 1 wt %. More addition of SEBS, however, increased the storage modulus at low frequencies. Similar behaviors could be observed in elongation viscosity and recovery after elongation. Hardening of elongational viscosity and recovery after elongation were reduced with 1 wt % SEBS, and they enhanced again with more SEBS contents. This means that there is a critical concentration of SEBS that acts as a compatibilizer and reduces the interfacial tension. More SEBS than the critical concentration saturates the interface and increases the elasticity of the LDPE/PS blend, while maintaining the interfacial tension between LDPE and PS constant. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 905–911, 2005     

Measurements and modeling of PS/supercritical CO2 solution viscosities

This paper presents a technology to determine the melt viscosity of a PS/super-critical CO₂ solution using a linear capillary tube die mounted on a foaming extruder. CO₂ was injected into the extrusion barrel and the content of CO₂ was varied in the range of O to 4 wt% using a positive displacement pump. Single-phase PS/CO₂ solutions were formed using a microcellular extrusion system and phase separation was prevented by maintaining a high pressure in the capillary tube die. By measuring the pressure drop through the die, the viscosity of PS/CO₂ solutions was determined. The experimental results indicate that the PS/CO₂ solution viscosity is a senstive function of shear rate, temperature, pressure, and CO₂ content. A theoretical model based on the generalized Cross-Carreau model was proposed to describe the shear-thinning behavior of PS/CO₂ solutions at various shear rates. The zero-shear viscosity was modeled using a generalized Arrhenius equation to accommo-date the effects of temperature, pressure, and CO₂ content. Finally, the solubility of CO₂ has been estimated by monitoring the pressure drop and the absolute pressure in the capillary die.     

Measurement and prediction of LDPE/CO2 solution viscosity

When CO₂ is dissolved into a polymer, the viscosity of the polymer is drastically reduced. In this paper, the melt viscosities of low‐density polyethylene (LDPE)/supercritical CO₂ solutions were measured with a capillary rheometer equipped at a foaming extruder, where CO₂ was injected into a middle of its barrel and dissolved into the molten LDPE. The viscosity measurements were performed by varying the content of CO₂ in the range of 0 to 5.0 wt% and temperature in the range of 150°C to 175°C, while monitoring the dissolved CO₂ concentration on‐line by Near Infrared spectroscopy. Pressures in the capillary tube were maintained higher than an equilibrium saturation pressure so as to prevent foaming in the tube and to realize single‐phase polymer/CO₂ solutions. By measuring the pressure drop and flow rate of polymer running through the tube, the melt viscosities were calculated. The experimental results indicated that the viscosity of LDPE/CO₂ solution was reduced to 30% of the neat polymer by dissolving CO₂ up to 5.0 wt% at temperature 150°C. A mathematical model was proposed to predict viscosity reduction owing to CO₂ dissolution. The model was developed by combining the Cross‐Carreau model with Doolittle's equation in terms of the free volume concept. With the Sanchez‐Lacombe equation of state and the solubility data measured by a magnetic suspension balance, the free volume fractions of LDPE/CO₂ solutions were calculated to accommodate the effects of temperature, pressure and CO₂ content. The developed model can successfully predict the viscosity of LDPE/CO₂ solutions from PVT data of the neat polymer and CO₂ solubility data.     

CO2-环烷烃/芳香烃界面张力的测定与估算

CO₂驱油技术是利用CO₂采出被束缚在地层中的剩余油,提高采收率,同时实现CO₂掩埋。由于CO₂可降低原油的界面张力,CO₂-原油系统的界面张力数据是CO₂采油技术的重要基础数据。本研究采用悬滴法,选取原油系统中环烷烃和芳香烃典型代表,测定了40~120℃,0.27~14.70 MPa下,CO₂-环戊烷/环己烷/环辛烷/ 甲苯/乙苯/乙基环己烷六个二元体系的界面张力。分析了压力、温度、碳原子数及烷烃分子结构对界面张力的影响。结果表明,界面张力与压力呈线性关系;较低压力下,界面张力随温度的升高而降低,在较高压力下则呈现相反趋势;CO₂-形态结构相同组分的界面张力随着碳数的增加而增大;分子间作用力对界面张力存在一定的影响。通过分析多种因素的影响,总结现有的CO₂-原油(正构烷烃、环烷烃、芳香烃)实验数据,提出关联方程,将表面张力关联为温度、压力、碳原子数和偏心因子的函数,相关系数(R² )为0.958,均方根误差(RMSE)及平均相对偏差(AARD)分别为1.12和11.01%。     

聚苯乙烯微球制备过程中界面张力的影响因素

系统考察了聚苯乙烯(PS)微球制备过程中十二烷基硫酸钠浓度、离子强度对于界面张力的影响.研究结果表明,十二烷基硫酸钠水溶液与苯乙烯的界面张力随十二烷基硫酸钠浓度的增加,先降低再升高,然后趋于平衡.离子强度与苯乙烯/H2O界面张力之间也存在同样的变化关系.根据离子强度对乳液的影响,选择了最佳的离子浓度,采用膜二次射流法制备乳液,然后将乳液加热聚合制备出大小均一的PS微球,粒径约为200 nm.     

Dynamic interfacial tension in melts of fibre-forming polymer blends

The dynamic interfacial tension was determined in melts of fibre-forming polymer blends: PPr-HDPE, PPr-LDPE, P4MP1-HDPE, P4MP1-PPr, PCA-PPr, PCA-HDPE, PCA-LDPE. It was determined by the method of capillary decomposition of liquid polymer jets. Translated from Khimicheskie Volokna, No. 1, pp. 19–22, January–February, 1998.     

PS/LDPE/ESI 共混体系的性能研究

采用ESI24作为增容剂,系统考察了ESI24添加量5%和10%两类增容体系中ESI24对PS/LDPE共混体系的增容作用。实验结果表明,LDPE含量的增加使体系的冲击性能得到了较大提高,当LDPE含量介于40%～60%时,增容体系的综合力学性能最佳。固定LDPE的添加量为50%,对比相容剂ESI24和SEBS的增容效果,表明ESI24对PS/LDPE共混体系的增容效果远比SEBS的好,而且ESI24可以在较大的添加量条件下,大幅度地改善增容体系的综合力学性能。     

Adsorption of 2-phenylethyl alcohol on silica aerogel from saturated solution in supercritical CO2

Adsorption of 2-phenylethyl alcohol (PEA) from supercritical CO₂ onto silica aerogel was investigated. A monolayer to multilayer adsorption isotherm was observed, measured at 15.0 MPa and 323.2 K, from the PEA-unsaturated to PEA-saturated supercritical CO₂, indicating the potential utility of the solute-saturated supercritical adsorption (SSA)_. The amount of PEA adsorbed on the silica aerogel with SSA at different temperatures and pressures was measured, and the release of PEA from the aerogel at 303.2 K was also evaluated. A theoretical model for the SSA equilibrium was developed with the assistance of the adsorption isotherms of pure CO₂ onto the silica and considering a three-phase binary system, where the two-dimensional van der Waals equation of state and the three-dimensional Stryjek–Vera modification of the Peng–Robinson equation of state were used respectively to describe the adsorbed phase and the bulk phases (vapor phase and liquid phase). Results showed that the model was capable of describing the adsorption behavior of the system with an average absolute relative deviation of 3.3%.     

聚苯乙烯/CO2的在线流变行为研究

通过在线流变实验研究分析了聚苯乙烯/CO2溶液的流变行为,并由实验推导出了不同工艺条件下零剪切黏度η0以及非牛顿指数n的计算公式。同时采用超声波探测系统测量了不同温度条件下PS/CO2溶液的临界压力。     

超临界CO2制备NaCl/PS微孔泡沫复合材料

利用超临界流体发泡技术制备了氯化钠(NaCl)颗粒填充聚苯乙烯(PS)的微孔泡沫复合材料。通过扫描电子显微镜(SEM)观察了材料的断面形态,并分析了氯化钠的粒径、含量及超临界CO2的饱和温度对微孔泡沫复合材料的泡孔形态的影响。结果表明:含有NaCl颗粒的微孔PS泡沫与纯PS泡沫在泡孔的形状和泡孔的尺寸等方面有所不同,纯PS微孔泡沫材料的泡孔分布较均匀、形状呈椭圆形,而添加了NaCl的PS微孔泡沫出现了大、小泡孔并存的泡孔结构。     

LDPE/PS就地相容化研究

在熔融状态下，利用Friedel-crafts烷基化反应就地增容低密度聚乙烯（LDPE）／聚苯乙烯（PS）合金，考察了催化剂品种及其用量、温度、时间等对接枝反应及合金性能的影响。结果显示，无水三氯化铝为一有效催化剂，能实现大分子间的接枝反应，形成LDPE-g-PS，其用量增大时可使体系产生凝胶；升高温度、延长反应时间都不利于接枝百分比的提高；增容后的LDPE／PS合金，其性能得到显著改善。     

PS/LDPE接枝共混物接枝率分析

用体积比为1的环己烷/丙酮混合溶剂对PS/LDPE接枝共混物进行选择性溶解分离,红外光谱法分析了不溶物中PS的含量,测得了接枝共混物的接枝率。     

Processing naproxen with supercritical CO2

Naproxen has been processed with supercritical fluids in order to improve the dissolution rate and bioavailability. Microparticles of naproxen have been obtained by a Rapid Expansion of Supercritical Solutions (RESS) process in which carbon dioxide has been used as a solvent and methanol as a cosolvent. The influence of extraction pressure (200–300 bar) and extraction temperature (60 °C and 100 °C) on the naproxen precipitation has also been investigated. In general, the morphology of the precipitated particles improved and particle size (PS) decreased in comparison to the raw material. Lower extraction pressure and higher extraction temperature led to a smaller particle size. On the other hand, a supercritical antisolvent (SAS) process has been applied due to the relative medium solubility values of naproxen in supercritical carbon dioxide, with precipitation obtained successfully in all cases. The initial concentration of the solution and the solvent effect has both been analysed. Morphologies and mean diameter ranges have been analysed by scanning electron microscopy (SEM) and the influence on crystallinity of both supercritical processes has been evaluated by X-ray diffraction (XRD) measurements.     

Interfacial tension in polymer melts. Part II: Effects of temperature and molecular weight on interfacial tension

Interfacial tension is one of the most important parameters that govern the morphology of polymer blends and the quality of adhesion between polymers. However, few data are available on interfacial tension due to experimental difficulties. A pendant drop apparatus was used for the determination of the interfacial tension for the polymer pair polypropylene/polystyrene (PP/PS). The effects of temperature and molecular weight were evaluated. The range of temperatures used was from 178° to 250°C, and the range of molecular weights used was from 1590 to 400,000. The interfacial tension decreased linearly with increasing temperature. With only one exception, higher molecular weight systems showed weaker dependence of interfacial tension on temperature than lower molecular weight systems. Also, polydisperse systems showed a stronger dependency on temperature than the monodisperse systems. The value of the interfacial tension, which increases with molecular weight, appears to level off at molecular weights above the entanglement chain length. For the polymer pair PP/PS, the dependency of the interfacial tension on the number average molecular weight appears to follow the well-known semi-empirical (?2/3) power rule over most of the range of molecular weights. Comparable correlations were obtained with values of the power between ?1/2 and ?1.0.     

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.     

纳米SiO_2/表面活性剂对油水界面张力的影响

以液体石蜡为油相,考察了疏水性纳米SiO_2对阴离子表面活性剂SDS、阳离子表面活性剂CTMAB与非离子表面活性剂OP-10的协同效应,以及Na Cl浓度对复配体系油水界面张力的影响。试验结果表明:纳米SiO_2与SDS和CTMAB之间具有良好的协同作用,且油水界面张力在400 s内变化明显,超过600 s后几乎不再变化;质量分数0.004%的纳米SiO_2与SDS和CTMAB复配后随着表面活性剂浓度升高(0.001 mol/L升至0.1 mol/L),协同效应越来越不明显,但表面活性剂浓度稀释至0.1 mmol/L后纳米颗粒分散稳定性差;随着NaCl浓度升高,与单一表面活性剂相比,SDS/SiO_2协同作用先增强后减弱,CTMAB/SiO_2协同作用持续减弱且200 s内界面张力变化幅度较大;纳米SiO_2与OP-10之间未观察到明显的协同作用,但OP-10分散稳定性强,即使在高矿化度也具有良好的分散能力。     

Rheological behavior of a LDPE/PS/SBS blending melt

The dynamic rheological behaviors are measured by small amplitude oscillatory shear on a rotational rheometer for a low-density polyethylene (LDPE)/polystyrene (PS)/styrene–butadiene–styrene (SBS) block copolymer blend with the tool of cole–cole plot. The morphology of the blend is measured by scanning electron microscope (SEM) micrograph, the storage moduli–angular frequency (G′–ω) data are fit by the Palierne model, and the relaxation time spectrum is investigated. The storage modulus and loss modulus of the LDPE/PS/SBS blend at low frequency increase when the weight ratio LDPE/PS increases from 10/90, reaches a maximum of 30/70, and drops thereafter. The cole–cole plots of some blends (10/90/3, 70/30/3, 90/10/3 and 100/0/3) have only one main arc due to compatibilizing effect of the SBS, and those of other blends (0/100/3, 30/70/3 and 50/50/3) have a second arc or a long tail besides the main arc probably due to phase separation. The SEM micrographs of the LDPE/PS/SBS = 10/90/3, 30/70/3, 50/50/3 show sea-island, semi-co-continuous and co-continuous structure, respectively. G′–ω curve of two LDPE/PS/SBS = 30/70/3 and 50/50/3 blends shows a power law, and the power index is much lower than one (0.748 and 0.817), respectively, showing a co-continuous morphology also verified by the SEM micrographs. The experimental data of G′–ω curve of the LDPE/PS/SBS blends are fit by Palierne model, the deviation between the fit line and the experimental data increases gradually as the LDPE/PS weight ratio decreases from 90/10 to 10/90. For the LDPE/PS/SBS blends, the weighted relaxation spectra τH (τ)–τ show a main as well as a second arc or tail; the former corresponding to the relaxation of PS phase and the latter corresponding to that of LDPE phase. Due to the compatibilizing effect of SBS the relaxation time and spectrum strength of LDPE/PS = 50/50 (wt) blends are both increased.     

Evaluation of thermodynamic theories to predict interfacial tension between polystyrene and polypropylene melts

The commonly used thermodynamic theories (mean field theory and the square gradient theory) to predict interfacial tension between polymers have been modified. The results of these theoretical developments have not yet been fully tested and compared to experimental data. In this paper, experimental data for the effects of temperature, molecular weight, and molecular weight dispersity on interfacial tension for polypropylene/polystyrene polymer pairs are compared with the predictions of the new versions of the above theories. To evaluate these theories, it is necessary to know the Flory-Huggins interaction parameter for the polymer pairs studied. The relation correlating the Flory-Huggins interaction parameter to the Hildebrand solubility parameter was not suitable for evaluating the theoretical predictions of interfacial tension. Instead, the Flory Huggins interaction parameter was expressed as the sum of an enthalpic contribution, χ_H, and entropic contribution, χ_s. In the absence of reliable experimental values, a method was developed to evaluate the two contributions, based on interfacial tension data. The procedure provided an interaction parameter that is allowed to depend on molecular weight. When this approach was used, the predictions of only the new version of the square gradient theory were in good agreement with the experimental data for the influence of temperature and molecular weight on interfacial tension. However, the theory predicted the effect of polydispersity on interfacial tension only at high temperatures.     

Elastic behavior of LDPE/HEPE blend melts in capillary extrusion

The studies of the elastic behavior in the capillary flow of LDPE/HDPE blend melts were carried out at a test temperature range from 180 to 200°C and at an apparent shear rate of about 25–120 s⁻¹. The end‐pressure drop (ΔP_end) increased nonlinearly with increasing wall shear stress (τ_w) and achieved a minimum value at a weight fraction (ϕ_HD) of HDPE of 50%. The die‐swell ratio (B) increased basically linearly with increasing τ_w or ΔP_end and achieved a maximum value at ϕ_HD of 50%. With the addition of the die length–diameter ratio, the values of B were decreased linearly. At a low shear rate, the temperature sensitivity of the melt die‐swell was more significant than at a high shear rate. With increasing ϕ_HD, B increased when ϕ_HD < 50%, then decreased. B reached a maximum value at ϕ_HD of 50% and a fixed apparent shear rate. This phenomenon may be explained by using the theory of viscoelastic competition between components of polymer blend melts. Furthermore, the first normal stress difference (N₁) of the sample melts was estimated by using an equation published in a previous work. The results showed that B increased linearly with increasing N₁. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 759–765, 2000     

Measurement and prediction of diffusion coefficients of supercritical CO2 in molten polymers

The solubility and diffusivity of supercritical carbon dioxide (sc‐CO₂) in low‐density polyethylene (LDPE), high‐density polyethylene (HDPE), polypropylene (PP), ethylene‐ethylacrylate copolymer (EEA) and polystyrene (PS) were measured at temperatures from 150°C to 200°C and pressures up to 12 MPa by using the Magnetic Suspension Balance (MSB), a gravimetric technique for gas sorption measurements. The solubility of CO₂ in each polymer was expressed by Henry's constant. The interaction parameter between CO₂ and polymer could be obtained from the solubility data, and it was used to estimate the Pressure‐Volume‐Temperature relationship and the specific free volume of polymer/CO₂ mixtures. The diffusion coefficients were also measured by the MSB for each polymer. The resulting diffusion coefficients were correlated with the estimated free volume of polymer/CO₂ mixture. Combining Fujita's and Maeda and Paul's diffusion models, a model was newly developed in order to predict diffusion coefficients for the polymers studied. Polym. Eng. Sci. 44:1915–1924, 2004. © 2004 Society of Plastics Engineers.