Correlation of capillary entrance pressure drops with normal stress data

The pressure loss at the entrance of a capillary tube was studied as a means of characterizing viscoelastic fluids. Measurements of four polymer solutions were made and correlated with an equation of the form where D is the shear rate and where H_ch and λ_ch are a characteristic stress and a characteristic time, respectively, determined independently from viscosity and normal stress measurements. Various theoretical analyses of capillary entrance flow are also compared.     

End corrections in the capillary flow of polystyrene melts

The origin of the discrepancy between the Bagley method and the modified method suggested by Han in obtaining the end correction data is traced to the effect of a deviatoric stress contribution in the pressure measurement at the capillary wall. The end correction factors for polystyrene melt were obtained by the Bagley method. The effects of temperature, die entry angle, contraction ratio or reservoir diameter-to-die diameter ratio are discussed.     

Wall slip and melt-fracture of polystyrene melts in capillary flow

We investigated slip and unstable flow phenomena of polystyrene melts in capillaries from the view of the effects of temperature and molecular weight by using three polystyrene samples with different molecular weights (M_w = 192,000, M_w = 258,000, and M_w = 321,000). The slip velocities are estimated by the Mooney method and the modified Mooney method. We found that the slip velocity increases and the critical slip stress above which a slip starts to occur decreases with the temperature. We also observed the melt-fracture at above a critical melt-fracture stress higher than . We found that the onset of melt fracture is affected by the extensional stress near the entry region to the capillary in the barrel and the melt-fracture tends to easily occur with increase of the molecular weight, but is not sensitive to the temperature.     

Excess pressure losses in capillary flows

Accurate determinations of excess pressure losses at the entry and exit of capillary flows are essential for rheological characterization of fluids by capillary viscometry. A modification of Bagley's end correction method is presented which accounts for the effects of slight variations in the diameters of the tubes of varying length used in the evaluations. The method was applied to capillary flows of dilute aqueous Polyox solutions using the three homologues WSR 301, Coagulant and FRA of Polyox. The excess pressure losses were found to increase with increase in the apparent shear rate, polymer concentration and tube diameter.     

Correlation of normal stresses in polystyrene melts and its implications

It is found that the principal normal stress difference, N₁, in commercial polystyrene melts is a unique function of shear stress σ₁₂, independent of temperature and molecular weight, An empirical expression representing this relationship is developed. The functional dependence reported does not represent data for narrow molecular weight distribution polystyrenes, generally significantly overpredicting N₁ values. The basis for this behavior is discussed. The implications of the N₁ ? σ₁₂ relationship to some rheological and processing problems are described.     

Environmental stress cracking in impact polystyrene

Environmental stress cracking (ESC) measurements for various impact polystyrenes were performed using a constant load technique with the specimens in contact with a 50/50 solution of cotton seed oil and oleic acid. It was shown that ESC in impact polystyrene is controlled by the transport of the aggressive liquid through a pre-established dry craze structure where capillary pressure is the driving force. At moderate stress levels just above the critical stress for environmental cracking, there is an apparent incubation time for the dry craze formation. The craze incubation time is strongly influenced by thermal stresses induced by the gel particles. As a consequence, ESC is two-stage process involving both an incubation time and actual crack growth. Control of the craze structure to maximize fibril content is essential for good ESC resistance. The craze fibril content can be altered by variables such as gel particle size, matrix molecular weight, plasticizer content, and rubber content.     

Chain-scission and yellowing in high impact polystyrene

Different grades of impact-modified polystyrene were studied by viscometry, tensile impact test and colour change upon exposure to polychromatic irradiation at 55°C in air. The samples underwent extensive reduction in intrinsic viscosity [η] and tensile impact strength, and yellowed upon polychromatic irradiation (λ ≥ 290 nm). Chain-scission during photo-oxidative degradation was also studied under conditions where evolution of volatiles was negligible. Tristimulus values were calculated for unirradiated and irradiated samples. The rate of oxidative degradation was maximum in the sample possessing higher unsaturation content.     

Correlation between entry pressure losses and elongation viscosity of polyethylene melts

The correlation between the entry pressure drop and elongation viscosity during entry converging flow of polymer melts was discussed in this article. The entry pressure drop during extrusion of a low density polyethylene (LDPE) melt and a linear low density polyethylene (LLDPE) melt was measured by means of a capillary rheometer under test conditions with temperature of 170 °C and shear rate varying from 10 to 300 s⁻¹. The results showed that the entry pressure drop increased nonlinearly with an increase of the shear stain rate, and the variation of entry pressure drop of the two melts was close to each other. The melt elongation viscosity of the two resins was estimated using Cogswell equation from the measured entry pressure drop data, and the predictions were compared with the melt extension viscosity measured by using a melt spinning technique published in literature. It was found that the melt extension viscosity from entry converging flow was slightly lower than that from melt spinning technique under the same temperature and extension strain rate.     

内胎胶挤出流动中第一法向应力差的预测

用毛细管流变仪考察了内胎胶挤出口型膨胀行为。基于实测的挤出胀大比数据,借助相关的公式估算了试样的第一法向应力差（Ｎ１）,并与几个熟知公式的预测结果进行了比较。结果表明,预测的Ｎ１与用Ｂａｇｌｅｙ等和Ｇｒａｅｓｓｌｅｙ等提出的公式的计算值较为接近。     

Polybutadiene content and microstructure in high impact polystyrene

The polybutadiene (PB) content and its microstructure in different grades of high impact polystyrene (HIPS) has been studied by various spectroscopic techniques. PB is characterized by deformation bands in FTIR spectroscopy at 994, 967, 912, and 729 cm⁻¹. FT-Raman was used for higher constant resolution over the range of wave numbers. It provides reasonable signal to noise ratios in near IR excited Raman. Proton and ¹³C-NMR spectroscopy was utilized for the determination of polybutadiene content in HIPS and tacticity, and reactivity ratios. © 1996 John Wiley & Sons, Inc.     

高光泽高抗冲聚苯乙烯的结构与性能

利用激光粒径分析仪、动态力学分析仪和气相色谱-液相质谱联用仪等分析了高光泽高抗冲聚苯乙烯(HIPS)和普通HIPS的结构和性能。结果表明:两个高光泽HIPS(HIPS A和HIPS B)试样在力学性能上的表现各有侧重。高光泽HIPS的溶胀指数与普通HIPS(HIPS C)相近,为11.0左右,表明三个试样的交联程度相近。相对于高顺式聚丁二烯橡胶改性的HIPS,高光泽HIPS中苯乙烯与橡胶的接枝点数量多,光泽度提高了约三倍,橡胶相平均粒径为1.0μm左右且分布较窄,凝胶质量分数大于22.0%,低相对分子质量组分的质量分数为2.1%～2.9%,但硬脂酸锌添加量大。HIPS A,HIPS B,HIPS C中的增塑剂含量逐渐增加。     

Anomalous first normal stress difference behavior of polymer nanocomposites and liquid crystalline polymer composites

The first normal stress difference (N₁) behavior of polymer nanocomposites and liquid crystalline polymer (LCP) composites is a measure of elasticity and is affected by shear stress as a result of morphological alterations at the molecular and nanostructure levels. In this study, the steady shear rheological behaviors of polylactide (PLA) and nanographite platelet (NGP) bionanocomposites containing 1, 2, 3, and 5 wt% nanofiller were investigated. The shear rheological properties of glass fiber‐filled LCPs (filler aspect ratio > 100) were also examined. One of the objectives of this study was to obtain a correlation between N₁, filler contents, and shear stress/rate of the measurements. The results suggest that N₁ in PLA/NGP bionanocomposites is dependent on the level of filler loading as well as the shear rate beyond a critical value. For the LCP systems, N₁ is positive for the unfilled and negative for the glass fiber‐filled LCPs, respectively. A novel rectangular hyperbola model was successfully developed and utilized to fit the N₁ data of the neat PLA and PLA/NGP composites as well as the unfilled LCPs. The anomalous N₁ behavior of PLA/NGP and LCP composites was also thoroughly discussed in this study. POLYM. ENG. SCI., 54:1300–1312, 2014. © 2013 Society of Plastics Engineers     

Viscosities and normal stress coefficients of high impact polystyrene-mineral oil mixtures

Measured melt viscosities and primary normal stress coefficients are presented for a well-characterized, rubbermodified polystyrene as a function of shear rate and mineral oil diluent concentration. The logarithmic blending relationship accurately predicts the observed data. Melt relaxation times and shear compliance data are also calculated. The compliance numbers are consistent with molecular models based on a simple dumbbell (appropriately modified for rubber and mineral oil addition).     

透明高抗冲聚苯乙烯树脂研究进展

物理共混法、自由基共聚合法和阴离子聚合法是制备透明高抗冲聚苯乙烯(THIPS)树脂的主要方法.而自由基共聚合法又可分为乳液法、溶液法、本体-悬浮法和连续本体法等.综述了国内外在THIPS树脂领域中的研究进展及国内在THIPS中试及工业化进程中取得的成果,并讨论了增韧剂种类、聚合方法、相对分子质量和残留单体量等因素对TH...     

Determination of the first and second normal stress differences in the truncated-cone-and-plate apparatus

Summary The steady state radial pressure distribution in the truncated cone-and-plate (TCP) apparatus has been measured for a highly elastic polyisobutylene solution in cis-trans decalin (M_W=4300 kgmol^–1 M_W/M_n=2) at eight shear rates from 1 to 270 s^–1 and temperatures of 3.0, 20.0, 30.0 and 46.0° C. The slope of pressure, corrected for inertia by the classical formula, versus the logarithm of radius provides a combination of normal stress differences N₁+2N₂ with a typical experimental scatter of 1 % at all measured temperatures and shear rates. The plots of N₁+2N₂ versus shear rate can be shifted, without loss of accuracy, by means of the time-temperature superposition principle, the shift factors strictly adhering to a WLF equation. Extrapolated rim pressures, when corrected for elastic hole pressure with a theoretical equation, give values of the second normal stress difference with typically less than 10 % of experimental scatter. Contrary to previous analyses of the TCP apparatus, the center-hole pressure is found to give a useful estimate of the second normal stress difference, although there are insufficient data at present to perform the differentiation of a nonlinear function required in the analysis of the data. Instrument imperfections are reviewed briefly in the Appendix.     

Relationship between rheological properties and impact strength in high impact polystyrene

Two batches of a commercially available high-impact polystyrene having different impact strengths were investigated. The steady-shear flow properties, dynamic shear properties, and elongational flow properties of the two were measured. Transmission electron microscopy (TEM) was used to study the microstructure. It is suggested that melt rheology can be a sensitive tool in the characterization of final product properties of rubber-modified polymers: the zero-shear-rate viscosity and the dynamic storage modulus G′, at low frequencies, were experimentally shown to correlate directly with the impact strength, despite the fact that TEM revealed no gross differences in the morphology of the two batches.     

Factors influencing the impact strength of high impact polystyrene

The relationship between synthesis factors and the impact resistance of high impact polystyrene (HIPS) is investigated in the light of its morphology and dynamic mechanical properties. A decrease in polymerization temperature results in an increase in T_g, melt viscosity and molecular weight of the continuous polystyrene phase as characterized by gel permeation chromatography. The separated, occluded polystyrene phase however shows an invariant T_g suggesting that the grafting and/or crosslinking effect overweighs the molecular weight effect. The observed high impact strength has been correlated with the homogeneous 1-2 μ rubber particle size distribution, a comparatively sharp rubber T_g transition at lower temperature, and a much lower occluded polystyrene content in the dispersed phase.     

Flame retardancy and toughening of high impact polystyrene

Flame retardant high impact polystyrene (HIPS) was prepared by melt blending HIPS, nano‐modified aluminum trihydrate (nano‐CG‐ATH), red phosphorus masterbatch (RPM), and modified polyphenylene oxide (MPPO). Styrene‐butadiene‐styrene (SBS) was used as a toughener in this research. The effects of nano‐CG‐ATH, RPM, MPPO, and SBS on properties of HIPS composites were studied by combustion test, mechanical tests, and thermogravimetric analysis. The morphologies of fracture surfaces and char layers were characterized through scanning electron microscopy (SEM). The HIPS/nano‐CG‐ATH/RPM/MPPO (60/6/9/25) composite and its combustion residues at various temperatures were characterized by Fourier transform infrared (FTIR) spectra analysis. The results showed that the UL‐94 rating of the HIPS/nano‐CG‐ATH/RPM/MPPO (60/6/9/25) composite reached V‐0 and its char layer after flame test was integrated, but its impact strength was low. Addition of SBS improved its impact property and did not influence its thermal and flame retardant properties but lowered its tensile strength and flexural modulus to some extent. The FTIR spectra confirmed that the P O C group was present in the charred substance. POLYM. COMPOS., 28:551–559, 2007. © 2007 Society of Plastics Engineers