Lower Newtonian viscosities of polystyrene

A falling coaxial cylinder viscometer was used to measure the melt flow behaviour of a commercial polystyrene with Mw 260,000. The shear stress region extended down to 0.6 × 10⁴ dynes/cm² and shear rates were as low as 3 × 10^?2 sec^?1 at 186°C. The shear rate-shear stress plots were linear at low shear stresses with slopes (differential viscosities) of 3.3 × 10⁵ poises at total shear less than 120 units and decreasing differential viscosity with higher total shear. The flow curves at relatively low total shear were initially dilatant and became pseudoplastic with increasing shear stress. The inflection point represents a Newtonian apparent viscosity, which agrees fairly well with literature values for polystyrenes of the same Mw. Newtonian apparent viscosity is characteristic of a point value of shear stress and shear rate and is not necessarily a plateau region. Observation of a Newtonian region with decreasing shear stress or shear rate does not prove that this flow regime persists unchanged to zero values of the experimental parameter. The existence and magnitude of the Newtonian apparent viscosity reflects shear history of the polymer as well as its constitution and molecular weight distribution.     

Rheological properties of molten poly(ethylene terephthalate)

The complete steady-state flow properties of molten poly(ethylene terephthalate) for shear stresses ≦4.14 × 10⁶ dynes/cm² were determined. A single, complete master curve had been constructed in earlier work by Gregory and Watson; the curve interrelates the shear stress, shear rate, temperature, and molecular weight (inherent viscosity) by using a temperature superposition scheme from the literature and a similar molecular weight superposition scheme. Equations in agreement with theory and with other published experimental data were derived from the master curve. Results presented here make possible the direct calculation of the melt viscosity of poly(ethylene terephthalate) at shear stresses ≦4.14 × 10⁶ dynes/cm². The effects of a unit temperature change and/or a unit change in inherent viscosity (I. V.) on the melt viscosity were determined. For poly(ethylene terephthalate) with a 0.6 I. V., a 0.0025 change in I. V. accounts for about the same change in melt viscosity as a 1°C change in temperature.     

Structure‐property relationships of blends of polycarbonate

Three grades of bisphenol‐A polycarbonate—high molecular weight linear, high molecular weight branched and low molecular weight linear—and their blends have been studied by GPC, DMTA, DSC, rheometry and impact measurements. The molecular weight distribution of the blends agred with that predicted from the component's distributions, indicating that no transesterification reactions had occurred during melt blending. The T_g of the blends varied with blend composition according to the Fox equation and was related to the reciprocal molecular weight predicted by the Flory‐Fox equation. The low shear rate viscosity of the blends agreed with a logarithmic rule of mixtures and showed power‐law dependence on the weight average molecular weight. At higher shear rates, shear thinning was observed. The steady shear viscosity correlated well with the dynamic viscosity, as suggested by the Cox‐Merz relation. The stress relaxation behavior of the melt was very sensitive to the blend composition and molecular weight and correlated well with the real modulus. Temperature studies of the dart impact energy showed that only the low molecular weight polymer underwent a brittle‐duetile transition at ea ?30°C and that all the blends were tough at room temperature. The enhanced stress triaxiality inherent in the notched lzod test caused the impact strenght at room temperature to decrease almost linealy with blend composition.     

Interrelationship of strength and flow characteristics of polystyrene

This study investigated the interrelationship between strength and flow characteristics of general-purpose polystyrene (GPPS) used in injection molding applications. The ease of flow was chosen as a measure of processability and was evaluated using the melt flow rate and capillary rheometer techniques. Of the different strength tests that were examined, flexural and notched tensile strength tests were most effective in differentiating between commercial grades of high and low molecular weight GPPS. While characterizing strength of injection molded specimens, the degree of molecular orientation was taken into consideration. For unplasticized resins, increasing the weight average molecular weight by about 100,000 enhanced the flexural strength by 10%, but also increased the viscosity at low shear rates (10 to 100 s^?1). The increase in molecular weight had virtually no effect on viscosity at the highest shear rates (up to 10,000 s^?1). Plasticized resins displayed a 6% loss in flexural strength as well as a significant reduction in viscosity (throughout the shear rate range) as compared with the unplasticized resins. As expected, the improvement in strength achieved by increasing molecular weight leads to a simultaneous increase in the viscosity, i.e., a deterioration of processability. In addition, our study indicates that for samples without preferential molecular orientation, narrowing the molecular weight distribution significantly improves the balance of strength and melt flow rate properties.     

Flow properties of ABS (acrylonitrile–butadiene–styrene) terpolymer

ABS (acrylonitrile–butadiene–styrene) terpolymer is a two-phase thermoplastic with SAN (styrene–acrylonitrile) copolymer constituting the continuous phase (matrix). The flow properties of ABS with varying molecular parameters were studied using a capillary viscometer at the shear rate range encountered in its processing. The viscosity-average molecular weights (M_v) of matrix SAN with 26% acrylonitrile content are in the range of 90,000 to 150,000, and M_v of poly-butadiene-are in the range of 150,000 to 170,000. The weight-average molecular weight of the matrix SAN is the main controlling factor for the flow properties of ABS at low shear rate, while the molecular weight distribution of the matrix SAN becomes increasingly important with the increase of shear rate. The presence of SAN grafted polybutadiene increases the melt viscosity of ABS by 40–60% over comparable free SAN copolymer and also decreases the activation energy at constant shear stress to 24–25 kcal/mole from the 33–36 kcal/mole for free SAN. The die swell of ABS and SAN can be correlated with the dynamic shear modulus G′, and the melt fracture of ABS and SAN starts at G′ equal to 3.6 × 10⁶ dynes/cm².     

Observation of melt fracture of polypropylene resins in capillary flow

Melt fracture, shear viscosity, extensional viscosity, and die swell of two polypropylene resins were studied using a capillary rheometer. A modified Bagley plot with consideration of pressure effects on melt viscosity and end effect was used. From the true wall shear stress the shear viscosity was calculated. Extensional viscosity was calculated from the end effect. Both shear and extensional viscosities of different molecular weights and temperatures correlated well under the time-temperature Williams-Landel-Ferry (WLF) superposition. Die swell increased when shear stress increased, and was higher for shorter dies at a given shear rate. When shear rates increased the extrudate staged from smooth to gross melt fracture with regular patterns (spurt), and then turned into irregular shapes. In the regular stage the wavelength of extrudates was measured, and corresponding frequency was calculated. The frequency increased when molecular weight decreased and when melt temperature increased. The shift factor based on shear viscosity also brought frequency data of different molecular weights and temperatures into master curves. The frequency decreased slightly when die lengths increased from L/R=10 to 60. A small maximum was observed when shear rates increased.     

聚烯烃弹性体的结构与熔体黏度关系的研究

采用凝胶渗透色谱仪和核磁共振仪表征了一系列聚烯烃弹性体（POE）样品的结构,并用毛细管流变仪考察了其挤出稳定性、剪切依赖性和黏温依赖性,分析了熔体黏度与聚合物结构的关系。结果表明,随着剪切速率的提高,高相对分子质量的POE熔体易出现不稳定流动,挤出物表面发生畸变;相对分子质量越大、温度越低、共聚单体含越高,发生不稳定流动的临界剪切速率c越低;POE的剪切黏度很大程度上受相对分子质量的影响,与共聚单体的含量关系不大;不同相对分子质量及组成的POE熔体的黏流活化能相近,约为2.8×10^4 J/mol。基于Carreau、Cross和Arrhenius等方程,分别建立了关联熔体零切黏度与聚合物重均相对分子质量和温度关系的半经验式、关联熔体表观黏度与零切黏度和剪切速率关系的半经验式;两式可用于预测POE熔体的黏度,其适用范围为温度为130~190 ℃,剪切速率为10~2 000 s-1,重均相对分子质量（Mw）为4.2×10^4~1.24×10^5 g/mol。     

The influence of molecular weight on the melt rheology of polypropylene

Melt viscosity and melt elasticity data were obtained over a broad range of temperatures and shear rates on a series of four polypropylenes of different molecular weight but approximately the same molecular weight distribution. The superposition technique was used with both temperature and molecular weight to shift flow curves for all four materials at three temperatures each along the shear rate axis to generate a master flow curve at a given temperature and molecular weight. For polypropylenes of this type, and molecular weight distribution shift, factors which can be used to extend the useful range of experimentally obtained flow data were determined. The dependency of apparent viscosity on weight average molecular weight at shear stresses as high as 10⁶ dynes/cm² is shown. The dependency of melt elasticity on molecular weight and temperature is discussed.     

Preparation of long‐chain branched poly(ethylene terephthalate): Molecular entanglement structure and toughening mechanism

Poly(ethylene terephthalate) (PET) was long‐chain branched (LCB) by ring‐opening reaction with both pyromellitic dianhydride and tetrahydrophthalic acid diglycidyl ester as chain extenders through reactive melt processing. It was found that with the increase of chain extenders dosage, the intrinsic viscosity of PET increased and melt index decreased greatly, while both the tensile strength and impact strength of PET were remarkably improved. The elastic modulus (G′) and viscous modulus (G″) were enhanced by chain branching. Compared with PET, the complex viscosities of LCB‐PET were much higher at full frequency range, and obvious shear thinning was presented. The Cole–Cole curve deviated from the semicircular shape and the curve end was inclined to upward in high viscosity region, indicating the formation of the multiple hierarchical structures. The molecular weight of the branch (M_B) was much greater than critical entanglement molecular weight (M _e), which essentially confirmed the existence of LCB structure and fairly strong molecular entanglement in the LCB‐PET molecular chain. When subjected to external force, the entanglement point, acting as physical crosslinking point between the molecules, was in favor of increasing the molecular interaction, reducing the molecular slippage, and bearing a large deformation. POLYM. ENG. SCI., 59:1190–1198 2019. © 2019 Society of Plastics Engineers     

A model relating the elastic properties of high-density polyethylene melts to the molecular weight distribution

An earlier model relating the variation of the steady-shear melt viscosity of high-density polyethylene to the molecular weight distribution is applied toward predicting the steady-shear elastic compliance, the first normal stress difference, and relaxation spectrum as a function of shear rate from the molecular weight distribution. The model envisions the cutting off of longer relaxation times as the shear rate is raised such that at any shear rate ${\rm \dot \gamma }$ the molecular weights and their corresponding maximum relaxation times τ_m are partitioned into two classes; the relaxation times are partitioned into operative and inoperative states, depending on whether they are less than or greater than τ_c, the maximum relaxation time allowed at ${\rm \dot \gamma }$. Equations relating molecular weight and relaxation time to the steady-shear elastic compliance and viscosity are assumed valid at nonzero shear rates, except for the partitioning effect of shear rate. The shear rate dependence of the first normal stress difference and the steady-shear viscosity for polyethylene melts is successfully predicted over the range covered by the cone-and-plate viscometer. The assumed proportionality constant between τ_c and 1/${\rm \dot \gamma }$ was determined to be 1.7. Using this relation, the maximum relaxation time at 190°C for a polyethylene molecule of molecular weight M is given by τ_m = 1.4 × 10^?19 (M)^3.33. Reasonable agreement has been obtained between the experimentally determined relaxation spectrum of a polyethylene melt and that predicted from the molecular weight distribution. The agreement is best at the longest relaxation times.     

Influences of polymer matrix melt viscosity and molecular weight on MWCNT agglomerate dispersion

In order to study the influence of melt viscosity and molecular weight on nanotube dispersion and electrical volume resistivity, three different polycarbonates (PCs) varying in molecular weight were melt compounded with 1 wt% multiwalled carbon nanotubes (MWCNTs, Baytubes^® 150 HP) using a small-scale compounder. The experiments were performed at constant melt temperature but at varying mixing speeds, thereby applying different magnitudes of shear stress. Light transmission microscopy was used to access the state of agglomerate dispersion, and electrical resistivities of the composites were measured on pressed plates. The results indicate that with increasing matrix viscosity the agglomerate dispersion gets better when using constant mixing conditions but worse considering comparable shear stress values. To study the effect of molecular weight, in a second set of experiments melt temperatures were adjusted so that all PCs had similar viscosity and mixing was performed at constant mixing speed. As investigated on two viscosity levels, the composites based on the low molecular weight matrix showed smaller sized un-dispersed primary agglomerates as compared to composites with higher molecular weight matrices, highlighting the role of matrix infiltration into primary nanotube agglomerates as the first step of dispersion. The resistivity values of composites prepared using low viscosity matrices were lower than those of composites from high viscosity matrix.     

Concentrated solution and melt rheology of poly(vinylidene fluoride)

The concentrated solution and melt rheology of poly(vinylidene fluoride) [PVDF] were studied by using a falling needle solution viscometer, a Brookfield viscometer, and a Kayeness capillary rheometer. It was found that the concentrated solution (15 wt% in N-dimethyl acetamide) rheology exhibited a different behavior for various grades of PVDF produced by different types of polymerization. While Newtonian behavior was found in one type of PVDF, shear thinning was found in another type. The power law model was used to describe the general solution behavior of these materials. Zero shear rate viscosity correlated well with the molecular weight (M_w) of the material. Melt viscosity of PVDF exhibited continuous shear thinning behavior throughout the whole range of shear rates. The data were best fitted by a second-degree polynomial curve. Correlations were established between the molecular weight, molecular weight distribution, and the parameters of the polynomial curve. These correlations are useful for the prediction of various grades of PVDF designated for specific engineering applications. The correlations obtained from solution provided better and more accurate correlations to M_w parameters than those of melt rheology.     

Effects of Molecular Weight and Thermal Treatment on Wear Behavior of Polyamide 6

Abstract

A series of polyamide 6 (PA 6) samples varying in their molecular weight (between 10000 and 50000) were annealed for 6 h in vacuum at various temperature (between 100 and 220°C) in order to create different morphological structures. The samples have been characterized with respect of their density, melting and crystallinity (from DSC), thermal expansion coefficient, humidity, predomination α- or γ-crystalline modification (from IR), shear melt viscosity and their tribological behaviour (the specific wear rate W_s ). It is found that density increases with increasing annealing temperature T_a but decrease with the rise of molecular weight (m.w.). The thermal expansion coefficient is more sensitive to T_a than to m.w. Contrary, shear-viscosity increases from 35 MPa for PA 6 with a m.w. of 10000 to 7200 MPa for samples with a m.w. of 50000. Concerning wear behavior it is concluded that the observed tendency for a decrease of W_s with an increase of T_a , particularly for samples with low m.w. is attributed to the formation of a more stable physical structure during annealed. This well defined tendency (except samples annealing at highest T_a ) is related to the observed drastic increase of shear melt viscosity with an increase of m.w.     

Adhesive Evaluation for New Forms of LARCTM-TPI

LARC^TM-TPI is a linear aromatic polyimide that was developed at NASA Langley Research Center in the 1970's and subsequently licensed to Mitsui Toatsu Chemicals, Inc., (MTC) in Japan. This company has made it easier to process for use in application as a structural adhesive or as a composite matrix resin. The present forms that exist are (1) high melt viscosity or Low Flow Grade (LFG); (2) medium melt viscosity or Medium Flow Grade (MFG); and (3) low melt viscosity or High Flow Grade (HFG). As expected, the low melt viscosity material is the easiest to process but has poor toughness; the high melt viscosity material is very tough but is more difficult to process. Because of these two extreme situations we have worked closely with MTC to develop an optimized system. This work has resulted in the medium melt viscosity material as well as two other modified or blended medium-flow variations.

These novel forms of LARC^TM-TPI have resulted in adhesives that can be melt processed at pressures as low as 0.01 MPa (15 psi) at temperatures between 343–371°C (650–700°F). Evaluation of adhesive performance has been accomplished using lap shear specimens and evaluating flow, wet out and shear strength. Initial strengths for these optimized materials range from 20.7–41.4 MPa (3000–6000 psi) at room temperature and 13.8–20.7 MPa (2000–3000 psi) at elevated test temperatures.     

Rheological and chemorheological studies of cyclic aryl ether ketone and aryl ether thioether ketone oligomers containing the 1,2-dibenzoylbenzene moiety

The melt stability, shear rate, and temperature dependence of steady-state shear viscosity of molten cyclic aryl ether ketone and thioether ketone oligomers containing the 1,2-dibenzoylbenzene moiety have been investigated. The isothermal chemorheology of the ring-opening polymerization of cyclic oligomers 4 and 9 in the presence of a nucleophilic initiator was also conducted. The cyclic aryl ether ketone oligomers are thermally stable in the melt, and their melt viscosity is several orders of magnitude lower than their high molecular weight linear counterparts. At a given temperature, the steady-state shear viscosity of the molten cyclics initially undergoes shear thinning as the shear rate increases, and once the shear rate is above 10 s⁻¹, the molten cyclic oligomers behave like Newtonian fluids. For the amorphous cyclic oligomers studied, the steady-state shear viscosity at 100 s⁻¹ at a given temperature only depends on their glass transition temperature. The cyclic aryl thioether ketone oligomers are thermally unstable in the melt and undergo ring-opening polymerization in the absence of an initiator to form high molecular weight linear polymers with a concomitant rapid increase in viscosity. The rate of change in viscosity increases with temperature and is promoted by the addition of a catalytic amount of elemental sulfur or a disulfide such as 2,2-dithiobis(benzothiazole). It is hypothesized that the ring-opening polymerization is initiated by the in situ generated thiyl radical(s) and proceeds via a free radical route. © 1996 John Wiley & Sons, Inc.     

Melt fracture,melt viscosities,and die swell of polypropylene resin in capillary flow

The melt fracture, shear viscosity, extensional viscosity, and die swell of a polypropylene resin were studied using a capillary rheometer and dies with a 0.05‐cm diameter and length/radius ratios of 10, 40, and 60. A temperature of 190°C and shear rates between 1 and 5000 s^?1 were used. A modified Bagley plot was used with consideration of pressure effects on both the melt viscosity and end effect. The shear viscosity was calculated from the true wall shear stress. When the true wall shear stress increased, the end effect increased and showed critical stresses at around 0.1 and 0.17 MPa. The extensional viscosity was calculated from the end effect and it showed a decreasing trend when the strain rate increased. Both the shear and extensional viscosities correlated well with another polypropylene reported previously. The die swell was higher for shorter dies and increased when shear stress increased. When the shear rates increased, the extrudate changed from smooth to gross melt fracture with regular patterns (spurt) and then turned into an irregular shape. In the regular stage the wavelength of the extrudates increased when the shear rate increased. The frequency of melt fracture was almost independent of the shear rate, but it decreased slightly when the die length increased. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1587–1594, 2003     

Effects of extrusion conditions on rheological behavior of acrylonitrile–butadiene–styrene terpolymer melt

The influence of temperatures and flow rates on the rheological behavior during extrusion of acrylonitrile–butadiene–styrene (ABS) terpolymer melt was investigated by using a Rosand capillary rheometer. It was found that the wall shear stress (τ_w) increased nonlinearly with increasing apparent shear rates and the slope of the curves changed suddenly at a shear rate of about 10³ s^?1, whereas the melt‐shear viscosity decreased quickly at a τ_w of about 200 kPa. When the temperature was fixed, the entry‐pressure drop and extensional stress increased nonlinearly with increasing τ_w, whereas it decreased with a rise of temperature at a constant level of τ_w. The relationship between the melt‐shear viscosity and temperature was consistent with an Arrhenius expression. The results showed that the effects of extrusion operation conditions on the rheological behavior of the ABS resin melt were significant and were attributable to the change of morphology of the rubber phase over a wide range of shear rates. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 606–611, 2002     

Application of the rheology of monodisperse and polydisperse polystyrenes to the analysis of injection molding behavior

Monodisperse and polydisperse polystyrenes of equal weight average molecular weight (M _w) are evaluated for melt flow behavior in an Instron capillary rheometer and for injection molding behavior in a 12 ounce in-line reciprocationg screw injection molding machine. The influence of molecular weight distribution on the shape of the flow curves is deconstrated over a wide range of shear rate and temperature. The influence is also reflected in injection molding behavior as defined by pressure to fill or flash the mold at a given melt temperature. Studies of capillary rheometer data for correlation with injection moling beghavior indicate poor agreement when low shear rate viscosity data are used. Good agrement is foun using high shear rate viscosity data in the range 10³ to 10⁴ sec^?1 Striking crossover points on melt rheology and injection colding area diagram curvs are found with the monodisperse and polydisperse polystyrenes of the same M These crossovers shift with melt temperature and make possible the determination of a “controlling shear rate” for the injection molding process. This is found to be 3500 sec^?1 for short shot and 6200 sec^?1 for flash with the ASTM test specimen mold used in this study.     

瓶级聚酯质量对流变及加工性能的影响研究

研究和分析了加工温度、特性黏数、摩尔质量及其分布、间苯二甲酸含量(IPA)、二甘醇(DEG)含量等因素对瓶级聚酯流变性及加工性能的影响。结果表明,在低剪切速率下,温度的升高使熔体的切力变稀现象逐渐减弱,当剪切速率达到8 000 s-1以上时,温度及剪切速率都几乎对熔体的表观黏度没有影响;摩尔质量越高,熔体黏度的切变速率依赖性越大,摩尔质量分布宽有利于成型加工条件的控制;在相同剪切速率下,熔体的剪切黏度随着IPA含量的增大而逐渐降低;DEG含量低的聚合物熔体在低剪切速率下出现非牛顿性流动的现象比DEG含量高的要明显得多。     

Studies on binary and ternary blends of polypropylene with SEBS,PS, and HDPE. I. Melt rheological behavior

Studies are reported on melt rheological behavior of some binary and ternary blends of polypropylene (PP) with one or two of the following polymers: styrene–b-ethylene butylene–b-styrene triblock copolymer (SEBS), polystyrene (PS), and high-density polyethylene (HDPE). Blend composition of the binary blends PP/X or ternary blends PP/X/Y were so chosen that the former represent addition of 10 wt % X to PP while the latter represent 10 wt % addition of X or Y to the PP/Y or PP/X blend of constant composition 90:10 by weight, X/Y being SEBS, PS, or HDPE. Measurements were made on a capillary rheometer using both temperature elevation and constant temperature methods to study the behaviors prior to flow and in the flow region. Flow behavior, measured at a constant temperature (200°C) and varying shear stress (from 1.0 to 5.0 × 10⁶ dyn/cm²) to evaluate melt viscosity and melt elasticity parameters, is discussed for its dependence on the nature of the blend. Extrudate distortion, studied as a function of shear stress to evaluate the critical shear stress for the onset of extrudate distortion, showed differences in the tendency for extrudate distortion or melt fracture of these different blends. Also discussed is the effect of melt viscosity and melt elasticity on extrudate distortion behavior at the critical condition, which showed a unique critical value of the ratio (melt elasticity parameter)^1/2 (melt viscosity) for all these blends. Blend morphologies before and after the flow through the capillary are investigated through scanning electron microscopy, and their correlations with rheological parameters of the melt are discussed.