Flow properties of molten ethylene–vinyl acetate copolymer and melt fracture

In an investigation of the behavior and formation mechanism of melt fracture the flow properties of molten ethylene–vinyl acetate (EVA) copolymer in the region of high shear rate were measured with a capillary-type rheometer. EVA copolymer differs slightly in flow curve from low-density polyethylene (LDPE); it seems, however, that the difference is due to the difference in molecular weight distribution (MWD) rather than to the materials themselves. The fluidity of molten EVA copolymer having a narrow MWD is equivalent to that of LDPE having a broad MWD and, generally, EVA copolymer has a higher fluidity than LDPE. It is expected that the fluidity increases with incorporation of vinyl acetate at the same MWD and the same M?_w. The critical shear rate increases with melt index and temperature. It cannot be found that the materials themselves and the MWD directly influence the critical point of melt fracture formation when the melt index is taken as a parameter. The critical viscosity (η_c) at which melt fracture forms decreases in an almost straight line with an increase of melt index. It was found from the studies of end correction and behavior of melt fracture formation that melt fracture occurs at the inlet of the die, and it is supposed that the melt fracture formation is caused by the elastic turbulence in the flow pattern due to a failure of recoverable shear strain at the die inlet.     

Studies on the polyblends of poly(vinyl chloride) with various methacrylate copolymers,melt rheological properties. II

Studies have been made on the melt rheological properties of poly(vinyl chloride) (PVC) with copolymers of methyl methacrylate (MMA) and methyl acrylate (MA), ethyl acrylate (EA), butyl acrylate (BA), and 2-ethyl hexyl acrylate (EHA) at a blending ratio of 80:20. Effect of blend composition on shear stress–shear rate, melt viscosity, melt elasticity, and extrudate distortion have been studied. A significant decrease in the melt viscosity is observed on incorporation of low T_g, acrylate copolymers such as those with BA and EHA, thereby reducing the processing temperature. First normal stress and die swell ratio also decreases with an increase in the side chains of acrylate copolymer. PVC blended with P(MMA-co-BA) and P(MMA-co-EHA) is sensitive to both temperature and shear stress.     

聚氯乙烯／丁腈橡胶共混体系的流变性能

本文研究了聚氯乙烯／丁腈橡胶共混体系的流变性能,并对用流变法测聚氯乙烯的相对凝胶废作了初步探讨。结果表明,该体系的流动符合假塑性流体的流动规律,表观粘度随剪切速度的增大而降低,熔体的粘流活化能具有剪切速率依赖性,弹性效应使溶体挤出胀大,胀大经胺剪切速率和温度的影响。     

Melt flow behavior of blends from poly(vinyl chloride) and epoxidized natural rubber

Blends from poly(vinyl chloride) (PVC) and epoxidized natural rubber (ENR) were prepared in a Brabender plasticorder by the melt blending technique. The melt flow behavior of these blends with respect to blend ratio and temperature has been examined using a melt flow indexer and capillary rheometer. ENR decreases the Brabender torque, increases the melt flow index (MFI), and decreases the melt viscosity of PVC in the blends. Arrhenius plots were used to study the effect of temperature on melt flow index (MFI) and viscosity. Moreover, the flow behavior index (n′) obtained from capillary rheometer data was found to be dependent on temperature and blend ratio.     

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     

Rheological and viscoelastic behavior of dynamically vulcanized poly(vinyl chloride)–epoxidized natural‐rubber thermoplastic elastomers

Dynamically vulcanized poly(vinyl chloride)–epoxidized natural‐rubber thermoplastic elastomers (PVC–ENR TPEs) were prepared using a semi‐EV vulcanization system. The compounds were melt‐mixed, and the rheological behavior was evaluated. The effect of curatives concentration on the rheological behavior using the shear dependence of viscosity and the activation energy for viscous flow was evaluated. Viscoelastic behavior was also investigated with the Monsanto MDR 2000. The parameters studied include the elastic modulus at maximum torque, the loss peak at maximum torque, and their ratio (tan δ). The data obtained were correlated with the material properties, such as hardness and resilience. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2886–2893, 1999     

Effect of polymerization conditions on the melt rheological properties of vinyl chloride–vinyl acetate copolymers

Mathematical models have been developed which predict the composition, molecular weight, and melt rheological properties for vinyl chloride/vinyl acetate copolymers of inherent viscosity range 0.4–0.7 dL/g and bound vinyl acetate levels of 3.8–17.4%. The effect of polymer long chain branching on the viscous/elastic moduli ratio is discussed as well as the comparison of Tinius–Olsen melt index measurements vs. mechanical spectrometer results. The reactivity ratio for vinyl chloride/vinyl acetate comonomer pairs was remeasured and found to be significantly different from literature values.     

Rheometric study of the gelation and fusion processes of poly(vinyl chloride‐co‐vinyl acetate) plastisols with different commercial plasticizers

Evolution of the complex viscosity of pastes of PVC‐VA (vinyl chloride‐vinyl acetate copolymer) plasticized with different commercial plasticizers has been studied. Knowledge of the rheological behavior of the formulations allows for better understanding of the gelation and fusion processes. Twenty commercial plasticizers of different types and with different functional groups have been studied and are grouped into five families: phthalate esters with linear chains, phthalate esters with branched chains, adipates (normal and polymeric), citrates, and rest of the plasticizers (carboxylates, alkylsulfonates, and pentaerythritol ester derivatives). Interesting relationships among the observed rheologies and the nature and molecular weight of the plasticizer have been observed. The evolution of the complex viscosity with temperature—at the temperatures where the blowing agents normally used in PVC plastisol foaming processes generate the main amount of gas—has been newly discussed with regard to the chemical structure and molecular weight of all of the plasticizers used. It was found that several different dynamic processes must be synchronized in order to understand the relationships among the chemical structure, plasticization, plasticizer compatibility, rheological properties, and foaming process of such materials. J. VINYL ADDIT. TECHNOL., 2012. © 2012 Society of Plastics Engineers     

Synthesis and rheological properties of poly(styrene-co-butyl methacrylate) as an ink vehicle

Poly(styrene-co-butylmethacrylate) as an ink vehicle was synthesized using free radical polymerization. The molecular weights and monomer ratios in copolymers were determined. According to the results, the molecular weight could be controlled by the addition of a chain transfer agent and the copolymer ratio was nearly the same as the mole ratio of the monomer feed. The effect of the copolymer ratio on the rheological property was also studied. The polymer melt resembled a very viscous Newtonian fluid at a rate above the critical shear rate. Also, it is possible to synthesize a copolymer whose activation energy value is independent of the shear rate. The viscosity and melt behavior of the copolymer can be controlled with proper blending.     

Melt rheological and thermodynamic properties of polyethylene homopolymers and poly(ethylene/α-olefin) copolymers with respect to molecular composition and structure

Various types of polyethylene homopolymers and copolymers, including linear high-density polyethylene (HDPE), branched low-density polyethylene (BLDPE), poly(ethylene vinyl acetate) copolymer (EVA), heterogeneous linear poly(ethylene/α-olefin) copolymer (het-LEAO) or commonly known as linear low-density polyethylene, homogeneous linear poly(ethylene/α-olefin) copolymer (hom-LEAO), and homogeneous branched poly(ethylene/α-olefin) copolymer (hom-BEAO), were evaluated for their melt rheological and thermodynamic properties with emphasis on their molecular structure. Short-chain branching (SCB) mainly controls the density, but it has little effect on the melt rheological properties. Long-chain branching (LCB) has little effect on the density and thermodynamic properties, but it has drastic effects on the melt rheological properties. LCB increases the pseudo-plasticity and the flow activation energy for both the polyethylene homopolymer and copolymer. Compared at a same melt index and a similar density, hom-LEAO has the highest viscosity in processing among all polymers due to its linear molecular structure and very narrow molecular weight distribution. Small amounts of LCB in hom-BEAO very effectively reduce the average viscosity and also improve the flow stability. Both hom-LEAO and hom-BEAO, unlike het-LEAO, have thermodynamic properties similar to BLDPE. © 1996 John Wiley & Sons, Inc.     

黄原酸酯调控的氯乙烯的可逆-加成断裂链转移聚合

以三种不同结构的黄原酸酯为调控剂,进行氯乙烯（VC）溶液和细乳液可逆加成-断裂链转移（RAFT）聚合,发现O-乙基黄原酸丙酸乙酯对VC聚合的调控效果良好,氯乙烯RAFT细乳液聚合速率明显大于溶液聚合,VC聚合12 h转化率大于90%,但聚氯乙烯（PVC）的分子量分布宽于溶液聚合产物。核磁共振和紫外可见吸收光谱分析证明合成的PVC具有黄原酸酯基端基结构,结构缺陷少。含黄原酸酯基PVC可进一步调控VC及醋酸乙烯酯聚合,进行扩链或得到嵌段共聚物。结合聚合动力学,说明黄原酸酯调控的氯乙烯聚合具有活性特征。     

Rheological properties of partially hydrolyzed ethylene–vinyl acetate copolymers

Studies have been made of steady-shear and dynamic viscosities for melts of two ethylene–vinyl acetate copolymers and their partially hydrolyzed derivatives using a Weissenberg rheogoniometer over the temperature range of 123–150°C with some tests at 160°C. The flow activation energy of all samples studied was essentially independent of shear stress. The introduction of hydroxyl groups in controlled concentrations, however, produced a complicated flow behavior. At low concentrations, there is a marked increase in Newtonian viscosity, flow activation energy, and shear dependence of viscosity. In contrast to previous reports, a further increase in all three functions was not observed with increasing vinyl alcohol concentration. Dynamic viscosities, in contrast, show monotonic increases with increasing hydroxyl group content, as do activation energies derived from the temperature dependence of the dynamic viscosity. These data may result from an increased chain cohesion due to hydrogen bonding of hydroxyl groups.     

Rheological Behavior and Mechanical Properties of Blends of Poly(vinyl chloride) with CP-POSS

In this work, a polyhedral oligomeric silsesquioxane which contains 3-chloropropyl groups (CP-POSS) was synthesized. The rheological behavior of CP-POSS/PVC blends was investigated by torque rheometer and capillary rheometer. Mechanical properties were investigated by electronic material tester. Influences of blending composition, shear rate and shear stress on melt apparent viscosity and non-Newtonian index (n) were discussed. The results show that the plastic time decreases and melt viscosity increases with increasing content of CP-POSS. CP-POSS has a good compatibility with PVC. The blend has the best impact strength when the content of CP-POSS is 7 wt%. The CP-POSS can be used as a processing aid and impact-resistant aid for PVC.     

Melt rheology of vinyl chloride-vinyl acetate copolymers

Melt flow behavior of vinylchloride-vinyl acetate copolymers is measured and expressed as melt viscosity, shear rate and shear stress—information useful to the plastics engineer in formulation, design, and processing. Copolymer of comparable I.V. to homopolymer PVC requires less energy to process. Good compounding techniques are required to realize the potential of ultra-clear profile extrudates.     

不同特性粘数PBT切片的流变性能研究

采用毛细管流变仪研究了5种不同特性粘数的聚对苯二甲酸丁二醇酯(PBT)的流变性能,计算得到了PBT的非牛顿指数和粘流活化能。结果发现:不同特性粘数的PBT熔体能够达到的最大剪切速率不同,随着特性粘数的增大,PBT熔体的非牛顿指数逐渐减小,粘流活化能先是逐渐减小,然后又变大。     

Effects of molecular weight distribution and branching on rheological properties of polyolefin melts

The objective of this work was to determine the relationships among molecular and melt parameters of polyolefins. The polyolefins studied are polypropylene, poly-1-butene, poly-1-hexene, poly-1-dodecene, these have regularly spaced short-chain branches. Conclusions from previous work, as well as some new data, on polyethylene are given. As the molecular weight increases, the critical shear rate decreases but the melt viscosity and non-Newtonian ratio increase. As the molecular weight distribution broadens, the critical shear rate decreases, whereas the normal forces and the non-Newtonian ratio increase. Increasing the number of short-chain branches increases the energy of activation and the melt viscosity but decreases the non-Newtonian ratio. As the length of the short-chain branches increases, the non-Newtonian ratio increases, but the melt viscosity, critical shear rate, and energy of activation decrease. Increasing the number of long-chain branches decreases the non-Newtonian ratio, but the normal forces and the melt viscosity increase. Such information allows the polymer chemist to design a polyolefin molecule having the critical melt properties required for a given production technique.     

氯乙烯/丙烯酸酯二元及多元共聚物的研究进展

介绍了氯乙烯/丙烯酸酯多元共聚物、聚氯乙烯树脂/丙烯酸酯/顺丁烯二酰亚胺接枝共聚物、聚氯乙烯树脂/N-取代马来酸胺/丙烯酸酯接枝共聚树脂、氯乙烯/乙酸乙烯/丙烯酸羟丙酯共聚物、氯乙烯/乙酸乙烯/丙烯酸丁酯共聚乳液、聚丙烯酸酯-氯乙烯接枝共聚物、氯乙烯/乙烯/丙烯酸羟乙酯共聚涂料树脂、氯乙烯/丙烯酸甲酯共聚乳液的特点、生产工艺及其性能和用途.     

Rheological effects of the incorporation of chlorinated polyethylene compatibilizers in a HDPE/PVC blend

Small‐amplitude oscillatory measurements, creep and recoil experiments, capillary extrusion flow and shrinkage measurements have been performed to elucidate the effect of block and random chlorinated polyethylene (CPE) on the rheological properties of a ternary high density polyethylene (HDPE)/ poly(vinyl chloride) (PVC)/CPE system. It is observed that the storage modulus, the complex viscosity and the steady stale viscosity at low shear rates decrease when a small amount of CPE is incorporated to 50/50 (wt.) HDPE/PVC binary blend. However, at high shear rates, in experiments performed in extrusion flow, the trend is reversed, and the incorporation of CPE to the binary blend increases viscosity. The high melt elasticity of HOPE is severely reduced when this polymer is mixed with PVC, but when CPE is included as a third component, elastic recovery is considerably increased. All these rheological results, which are independent of type (block or random) of CPE used, are explained considering the morphological changes produced by CPE and during extrusion flow.     

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     

Studies on miscibility of blends of poly (ethylene acrylic acid) and ethylene‐co‐vinyl acetate by melt rheology

Rheological behavior of blends of poly (ethylene‐acrylic acid) (EAA) and ethylene vinyl acetate (EVA) copolymer have been carried out at various temperatures, namely, 100, 110, and 120°C, and different shear rates from 61.33 to 613.30 s^?1 using a Monsanto Processability Tester. The melt viscosity of the blends shows synergism during processing. The activation energy of the blends is in the range 20.7–44.6 kJ/mol. Highest activation energy was observed for the blends containing 40–60% of EVA by weight. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1947–1954, 2005