Effect of vibration on rheology of polymer melt

In this article, under shearing vibration and pressure vibration, the rheological behavior of HDPE, ABS, and PS melts and the mechanical properties of molded parts are studied. The experimental results show that, under the vibration condition, the apparent viscosity of the polymer melt decreases with an increasing of the vibration frequency and amplitude applied. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1587–1592, 2002     

Self-compatibilization of polymer blends via novel solid-state shear extrusion pulverization

The mechanochemistry of a novel economical solid-state shear extrusion (SSSE) pulverization is investigated. SSSE compatibilizes incompatible blends in situ; the process has great potential in recycling of post-consumer plastic waste (PCPW). It is proposed that SSSE causes this self-compatibilization of blends by rupturing polymer chains and allowing them to recombine with their neighboring chains. When this recombination involves dissimilar chains at an interface between powder particles, block copolymers are formed, and if the chain transfer reactions are possible, graft copolymers are formed. These copolymers at the interfaces in the phase-separated, incompatible blend lower the interfacial tension and increase the adhesion at the interfaces, thus compatibilizing the blend. Our nuclear magnetic resonance (NMR) and rheology studies reveal the formation of long chain branches (LCBs) in an linear low-density polyethylene (LLDPE), which is equivalent to the formation of graft copolymers in blends. With NMR, an increase from ∼ 0.2 to ∼ 2.0 of the number of LCBs per 1000 carbon atoms is observed due to pulverization of the LLDPE. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1179–1187, 1997     

Improving melt strength of polypropylene by minimal branching and blending

Branched polypropylenes (PPb) with markedly improved melt strength were produced without significantly affecting the processability of the original PP. A two-step process of functionalization with MA and crosslinking with m-XDA was used, both by batch mixing and by extrusion. Branching degrees of ~0.06 LCB/1000 monomer units or smaller were obtained. All PPbs display clear and significant strain hardening, being the PPb obtained by extrusion the one that shows the largest melt strength. This polymer has a zero-shear-rate viscosity slightly smaller than that of PP while its strain-hardening index is about 10 times higher. Moreover, the nonlinear behavior of PP at elongation begins at a time similar to its terminal relaxation time or larger, while the ratio of these times reduces significantly with branching. PP/PPb blends were prepared to extend the range of obtainable melt strength in PP. They display rheological behavior between those of the mixed polymers with slight positive deviation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 137, 48845.     

Improving the mechanical properties of polypropylene via melt vibration

The effect of melt vibration on the mechanical properties of polypropylene prepared by low-frequency vibration-assisted injection molding (VAIM) has been investigated. With the application of melt vibration technology, the mechanical properties of polypropylene are improved. The yield strength increases with the increment of the vibration frequency, and a peak stands at a special frequency for VAIM; the elongation at break decreases first and then increases with increasing vibration frequency, and a valley stands at a special frequency. The tensile properties increase sharply at an enlarged vibration pressure amplitude with sharply decreased elongation at break. The Young's modulus and impact strength also increase with the vibration frequency and pressure vibration amplitude. When it is prepared at 59.4 MPa and 0.7 Hz, the maximal yield strength is approximately 40 MPa versus 33.7 MPa for a conventional sample; an 18.7% increase in the tensile strength is produced. Self-reinforcing and self-toughening polypropylene molded parts have been found to be prepared at a high vibration frequency or at a large pressure vibration amplitude. Scanning electron micrographs have shown that, in the vibration field, the enhancement of the mechanical properties is attributable to more pronounced spherulite orientation and increased crystallinity in comparison with conventional injection moldings. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

In‐process rheological monitoring of extrusion‐based polymer processes

Since rheology is very sensitive to the structure and macromolecular conformation of polymer systems, rheological measurements performed in situ during extrusion are attractive for monitoring the process. After introducing the concepts of in‐process monitoring during extrusion operations, the benefits of rheology for assessing filler dispersion in polymer composites, morphology development in polymer blends or the extent of chemical reaction in reactive extrusion are briefly reviewed. Then, in‐process rheological tools are reviewed. For each device, the information conveyed is detailed. © 2020 Society of Industrial Chemistry     

Improving flame retardancy and melt processability of polyethersulfone using low molecular weight additives

The effect of a calcium stearate (CaSt₂) additive on the melt processability and flame retardancy of polyethersulfone (PES) was studied. Measurements of the viscosity of PES and its composites showed a marked decrease in viscosity with increase in the fraction of CaSt₂ additive. About 40% reduction in viscosity of PES was achieved with addition of 5 wt % CaSt₂. By decreasing the viscosity, the CaSt₂ additive enabled the melt extrusion of PES at lower temperatures up to 90 °C below that of conventional melt processing. The flammability was also investigated using a Pyrolysis Combustion Flow Calorimeter (PCFC). The CaSt₂ additive resulted in tremendous improvement in the flame retardancy of PES as evident in the reduction of the heat release capacity (HRC) of the composites by up to 37%. Moreover, the peak of heat release rate (pHRR) of PES in the composites was up to 84% lower than in the neat polymer. The remarkable improvement in flame retardancy of PES was demonstrated to be related to the rapid charring of the composites and the in situ formation of calcium carbonate/calcium oxide upon decomposition of CaSt₂. The CaSt₂ additive was also found to enhance the flame retardancy of thermoplastics including polyamide‐6 and polypropylene (PP). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43525.     

聚合物球型螺杆电磁动态低温塑化挤出过程

为了研究振动场作用下聚合物低温塑化成型过程,研制了一套球型螺杆电磁激振挤出装置,建立了振动场作用下聚合物低温塑化成型的物理模型,深入分析了振动场作用下聚合物低温塑化机理,然后从振动耗散能、聚合物变形能、摩擦热、剪切热等方面分析了聚合物塑化的能量来源,并通过数学推导得出了能量输送密度的数学表达式。最后使用球型螺杆电磁激振实验台和低密度聚乙烯(LDPE)进行实验和理论计算,实验结果与理论计算结果符合很好,并得出结论:振动场的引入可以降低聚合物的成型温度40℃以上、可以节约单位质量物料成型能耗47%以上,同时可以提高制品力学强度。本研究将会为聚合低温成型工艺和成型设备的研究提供可靠的理论基础。     

Influence of the die configuration on the gross melt fracture of linear polyethylene

In this study, capillary extrusion experiments and rupture visualization experiments were carried out with a combined die configuration where two different dies were attached in a capillary rheometer. We observed that the gross melt fracture (GMF) and rupture of the melt occurred simultaneously when the diameter of the die located at the upstream position was larger than that of the die located downstream. However, when the location of the dies were interchanged, that is, the diameter of the upstream die was smaller than that of the downstream die, the upstream rupture did not accompany GMF up to a certain extent of shear rate. From these observations, we present a new theory on the origin of GMF. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

High-density polyethylene reinforced by low loadings of electrochemically exfoliated graphene via melt recirculation approach

The purpose of the paper is to demonstrate the effectiveness of high-aspect ratio electrochemically exfoliated graphene (EEG) as a filler in high-density polyethylene (HDPE); we use an industrially viable polymer processing technique (melt blending with melt recirculation) to ensure excellent dispersion and reinforcement at low loadings. The effects of nanofiller loading were evaluated for two different HDPE grades with two different melt flow indices (MFI) based on crystallization, tensile, and rheological properties. The findings indicate improvements in mechanical properties (tensile modulus and tensile strength) for all HDPE/EEG nanocomposite samples; however, the reinforcement was more pronounced at 0.2 wt% loading, indicating a transition from excellent dispersion at lower loadings to aggregated at higher loadings. The low and high MFI HDPE/EEG nanocomposites at 0.2 wt% EEG loading displayed an improvement of 31% and 40% in tensile modulus and 19% and 33% in tensile strength, respectively. The improved mechanical response with higher MFI nanocomposites is likely due to enhanced dispersion associated with the lower melt viscosity. Similarly, the rheological results also showed maximum increase in storage and loss modulus at a loading of 0.2 wt% EEG. In conclusion, EEG can be an effective filler if proper dispersion is achieved, which is challenging at high loadings.     

Simulation of polymer melt processing

Polymer melt processing requires an integration of fluid mechanics and heat transfer, with unique issues regarding boundary conditions, phase change, stability and sensitivity, and melt rheology. Simulation has been useful in industrial melt processing applications. This brief overview is a personal perspective on some of the issues that arise and how they have been addressed. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

含氟弹性体对LLDPE熔体流变性能的影响

通过改变含氟弹性体(PPA)的含量,研究了PPA对线型低密度聚乙烯(LLDPE)熔体流变行为的影响.研究发现,将PPA加入到LLDPE中,熔体的挤出压力、挤出胀大比均减小,发生鲨鱼皮畸变和挤出压力振荡等不稳定流动现象时的临界剪切速率提高,扩大了加工范围;足量的PPA甚至可完全消除鲨鱼皮畸变现象.     

Determination of structural changes of dispersed clay platelets in a polymer blend during solid-state rheological property measurement by small-angle X-ray scattering

The poly(ethylene terephthalate)/thermotropic liquid crystal polymer (weight ratio 80:20) blend composites with two different weight percentages of nanoclay were prepared using a twin-screw extruder. The frequency sweep experiments at a constant strain and different temperatures were carried out by a dynamic mechanical analyzer. The temperature sweep experiments of unmodified and nanoclay modified blends were conducted to find out the variation of flexural storage and tan δ values as a function of temperature. Results showed that the modulus of the blend increases after composite formation with nanoclay and the variation of frequencies during temperature sweep experiments do not affect the glass transition temperature values. The small-angle X-ray scattering studies showed that the degree of anisotropy and mean orientation angles of clay platelets in blend matrix were altered significantly after frequency and temperature sweep tests.     

类水滑石对纳米凹凸棒土悬浮液流变性的影响

采用液相共沉淀方法,按n(Mg)∶n(Al)∶n(Fe)一定配比制得Mg-Al-Fe类水滑石(Mg-Al-Fe-HTlc),添加到凹土水悬浮液体系,研究其对流变性的影响。结果表明,单纯凹土水悬浮液体系当含量大于2%后为塑性非牛顿型流体,有一定的屈服值,凹土含量小于2%时,剪切速率与剪切应力有良好的线性关系,为牛顿型流体。由于带负电荷的凹土和带正电荷的Mg-Al-Fe-HTlc之间的静电相互作用,随着胶土比增加,同样剪切速率下的剪切应力呈现增大、减小然后再增大的变化趋势。     

Bulk density of polymer solid granules in vane cylinder

Polymer granules are conveyed and plasticized using an innovational vane extruder composed of several vane plasticizing and conveying units (VPCUs). This study developed a mathematic model to analyze the bulk density of polymer granules in a VPCU, as well as conducted an experiment to investigate the effects of device geometry, polymer properties, and operating conditions on the model. By comparing the theoretical model data with the experiment data, the proposed model of bulk density is found to be aligned with actual conditions, thus providing a basis for device and process optimization. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 842‐850, 2013     

A rheological study on kinetics of poly(butylene terephthalate) melt intercalation

A multilayered sample with alternatively superposed poly(butylene terephthalate) (PBT) and nonpolar polymer/clay sheets was elaborately prepared to investigate the whole hybridization process of polar polymer. The kinetics of PBT melt intercalation was studied by a rheological approach. The whole intercalation process was demonstrated by the changes of the low‐frequencies viscoelastic response with annealing time. The results of the apparent diffusivities and the calculated activation energy indicate that the PBT/clay hybrid formation presents a molecular weight dependence, which may result from the enhancement of interactions between polar groups on PBT chains and the silicate surface. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1865–1871, 2006     

Investigations of cell immobilization in alginate: rheological and electrostatic extrusion studies

In this study, the process of electrostatic extrusion as a method for cell immobilization was investigated. We have assessed the effects of concentrations of yeast cells (as a model cell type) and Na alginate on the size of the resulting microbeads and attempted to rationalize the obtained findings by rheological characterization of the cell–alginate suspensions. Under the investigated conditions, microbeads, 50–600 µm in diameter, were produced and the increase in both alginate and cell concentrations resulted in larger microbeads with their sizes having higher standard deviations. Rheological characterization revealed non‐Newtonian, pseudoplastic behavior of cell–alginate suspensions with higher viscosities at higher alginate concentrations. However, the presence of cells even at high concentrations (5 × 10⁸ and 1 × 10⁹ cells mL^?1) did not significantly affect the rheological properties of the Na alginate solution. Finally, we have investigated the kinetics of alginate gelation with respect to the quantity of Ca²⁺ ions and the presence of cells. The molar ratio of α‐L ‐guluronic acid units to Ca²⁺ ions of 4:1 provided complete crosslinking. The presence of cells decreased the rate of network formation as well as the strength of the obtained Ca alginate hydrogel. Copyright © 2006 Society of Chemical Industry     

Effects of chemical modification of wood flour on the rheological properties of high‐density polyethylene blends

Chemical modification of lignocellulosic fibers can improve interfacial adhesion and dimensionally stabilize the resulting plastic composites. This study examined the rheological properties of wood flour/high density polyethylene (HDPE) melts after poplar wood flour was modified with glutaraldehyde (GA, mainly cell wall cross‐linking) and 1,3‐dimethylol‐4,5‐dihydroxyethyleneurea (DMDHEU, mainly poly‐condensation). Results show improvement in both the dispersibility of treated wood flour in the HDPE and its interfacial compatibility. Treatment with GA decreased melt viscosity, moduli, and shear stress as evidenced by rheometry. However, the modifying effects of DMDHEU were not observed, which was mainly due to reduced HDPE content. This study indicates that chemical modification of wood flour is a promising approach to improve the processability of highly filled wood thermoplastic composites via extrusion/injection molding processing. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41200.     

The effect of materials' rheology on process energy consumption and melt thermal quality in polymer extrusion

Polymer extrusion is an important but an energy intensive method of processing polymeric materials. The rapid increase in demand of polymeric products has forced manufactures to rethink their processing efficiencies to manufacture good quality products with low-unit-cost. Here, analyzing the operational conditions has become a key strategy to achieve both energy and thermal efficiencies simultaneously. This study aims to explore the effects of polymers' rheology on the energy consumption and melt thermal quality (ie, a thermally homogeneous melt flow in both radial and axil directions) of extruders. Six commodity grades of polymers (LDPE, LLDPE, PP, PET, PS, and PMMA) were processed at different conditions in two types of continuous screw extruders. Total power, motor power, and melt temperature profiles were analyzed in an industrial scale single-screw extruder. Moreover, the active power (AP), mass throughput, torque, and power factor were measured in a laboratory scale twin-screw extruder. The results confirmed that the specific energy consumption for both single and twin screw extruders tends to decrease with the processing speed. However, this action deteriorates the thermal stability of the melt regardless the nature of the polymer. Rheological characterization results showed that the viscosity of LDPE and PS exhibited a normal shear thinning behavior. However, PMMA presented a shear thickening behavior at moderate-to-high shear rates, indicating the possible formation of entanglements. Overall, the findings of this work confirm that the materials' rheology has an appreciable correlation with the energy consumption in polymer extrusion and also most of the findings are in agreement with the previously reported investigations. Therefore, further research should be useful for identifying possible correlations between key process parameters and hence to further understand the processing behavior for wide range of machines, polymers, and operating conditions.     

Facile dispersion of exfoliated graphene/PLA nanocomposites via in situ polycondensation with a melt extrusion process and its rheological studies

This work attempted to improve the dispersion of graphene by coating poly(lactic acid) pellets with a masterbatch before melt processing. An in situ polycondensation reaction of lactic acid oligomer was utilized to prepare the masterbatch (MB) of exfoliated graphene (GR). MB dispersed composites of poly(lactic acid) (PLA) were fabricated by melt extrusion of MB‐coated PLA. One normal coated composite without MB coating (PLA‐M‐0.2GR) was fabricated for comparing properties. X‐ray diffraction, Raman spectroscopy, and morphological studies revealed better compatibility, dispersion, and interaction of GR for the diluted‐MB composite compared to the normal coated composite. The thermal stability, crystallization properties, and mechanical properties of the composites were examined, and the effect of short PLA chains in diluted‐MB composites was observed. The melt rheology nature of the composites was examined. Cole–Cole plots and Han plots suggested a uniform distribution of graphene. The sample PLA‐MB‐0.05GR showed improved modulus and elongation at break. It also showed better dispersion of GR, comparable thermal stability, good miscibility, good chain mobility, and high activation energy. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46476.     

Geometrical dependence of viscosity of polymethylmethacrylate melt in capillary flow

The shear viscosity of polymethylmethacrylate (PMMA) melt is particularly investigated by using a twin‐bore capillary rheometer at four temperatures of 210, 225, 240, and 255°C with different capillary dies. Experimental results show that the geometrical dependence of shear viscosity is significantly dependent on melt pressure as well as melt temperature. The measured shear viscosity increases with the decrease of die diameter at lower temperatures (210 and 225°C) but decreases with the decrease of die diameter at higher temperatures (240 and 255°C). Based on the deviation of shear viscosity curves and Mooney method, negative slip velocity is obtained at low temperatures and positive slip velocity is obtained at high temperatures, respectively. Geometrical dependence and pressure sensitivity of shear viscosity as well as temperature effect are emphasized for this viscosity deviation. Moreover, shear viscosity curve at 210°C deviates from the power law model above a critical pressure and then becomes less thinning. Mechanisms of the negative slip velocity at low temperatures are explored through Doolittle viscosity model and Barus equation, in which the pressure drop is used to obtain the pressure coefficient by curve fitting. Dependence of pressure coefficient on melt temperature suggests that the pressure sensitivity of shear viscosity is significantly affected by temperature. Geometrical dependence of shear viscosity can be somewhat weakened by increasing melt temperature. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3384–3394, 2013