Three-dimensional finite element analysis of polymer rotational extrusion

A three-dimensional finite element approach has been employed to model steady, creeping, isothermal helical flows and to study the effect of an imposed rotational field in a wire coating process and a tube extrusion process. It has been shown that the rotational field can affect process characteristics with an underlying viscous character, such as the velocity profile, pressure drop, viscous extrudate swelling, material pathlines, and deformation field. Significant pressure drop reduction may be achieved with implications on the process productivity, pressure drop reduction being most prevalent at low power-law indices because of the increased nonlinearity in the shear-thinning viscosity function. Extrudate swelling has been shown to be affected by the rotational field owing to the shear-thinning nature of polymeric materials. Finally, it has been shown that significant material deformation may result from the imposition of the rotational field.     

Hydrostatic extrusion of polypropylene and properties of extrudates

The solid-state extrusion of polypropylene by hydrostatic pressure has been investigated at four different temperatures: 25, 50, 75, and 100°C. The pressure to effect extrusion was found to be essentially a linear function of the extrusion ratio at each temperature, while the magnitude of the extrusion pressure, for any given extrusion ratio, decreased appreciably with increasing temperature. With increase in extrusion-ratio, the polypropylene extrudates became increasingly transparent. After passing through the extrusion dies; the Sample showed some elastic recovery. The amount of this recovery decreased with increasing extrusion ratio, X-Ray diffraction measurements taken before and after extrusion showed reduction in sharpness of the crystalline Peaks. Differential, scanning calorimetric measurements, on the other hand, indicate that the relative heat of fusion of the extrudates increases with the extrusion ratio at each extrusion temperature. It also increases with extrusion temperature for a given ratio. Tensile stress-strain tests were made at various hydrostatic pressure levels on the extrudates obtained at 25°C and the extrusion ratio of 2.8. Unlike on the virgin sample of polypropylene, ho yield maximum was observed on the extrudate sample at all pressures investigated. However, the effects of pressure on the relative increase in the yield stress-and the modulus of the extrudate are comparable to those of original, unoriented samples.     

Morphological investigation of cellulose acetate/cellulose nanocrystal composites obtained by melt extrusion

Composites were prepared from cellulose acetate (CA) and cellulose nanocrystals (CNC) by melt extrusion using two methods for the introduction of CNC: direct mixing and predispersion in CA solution. CNC were isolated using hydrochloric acid to increase thermal stability allowing the composites to be processed above 150 °C. The effect of CNC dispersion on the composites morphology, thermal, and mechanical properties was investigated. Field emission scanning electron microscopy and transmission electron microscopy results indicated that the predispersion method allows better CNC dispersion and distribution when compared to the direct mixture method. In addition, predispersion promotes preferential CNC orientation in relation to the injection flow. The predispersion method also showed a 14% Young's modulus increase in composites containing 15 wt % CNC while no significant change was observed when using the direct mixing. The results obtained in this work show that, to achieve the percolation threshold, nanoparticle distribution is as important as their content. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44201.     

Thermal and mechanical degradation during polymer extrusion processing

Polymer processing often activates material degradation, which affects to some extent the performance or the life cycle of the obtained products. Polymer degradation is usually evidenced by molecular weight variations as consequence of exposure to high processing temperature and to relevant mechanical stresses. The degrading effects of melt extrusion under different thermo‐mechanical conditions on polymethyl‐methacrylate and polystyrene are investigated. Materials were processed at different temperatures and rates in a single screw extruder and in a capillary rheometer. Processed and as‐received materials were analysed by Gel permeation chromatography, solution viscosity, and melt rheology. Evaluations of molecular weight and rheological behavior changes after processing, as compared with as‐received materials, evidenced the extent of degradation in the different conditions. Experimental analysis was accompanied by finite elements simulation of the polymer flow and heat transmission within the extruder. This allowed an estimation of the expected shear stresses and temperatures distributions, thus indicating potentially critical situations. It was found that the materials processed at the highest rates in extruder presented lowest molecular weight reductions. This was attributed to the shorter residence time in the extruder and to the possibility of wall slip phenomena, which likely reduce the actual shear stress and viscous dissipation in the fast processing conditions. POLYM. ENG. SCI., 47:1813–1819, 2007. © 2007 Society of Plastics Engineers     

Plasma treatment of polyacrylonitrile/vinyl acetate films obtained by the extrusion process

This work presents a study of superficial properties of polyacrylonitrile (PAN) films obtained by extrusion process. This innovative material was submitted to microwave plasma treatment generated at low pressure. The contact angle was measured with and without treatment in nitrogen and argon plasma, by the pendant drop technique. The work of adhesion was calculated by the Young–Dupré equation. The surface energy was calculated by the harmonic and geometric average methods, through the technique of two liquids proposed by Fowkes and Wu. The results showed an increase on the surface wetting, for films of plasma treat under nitrogen and argon, which indicated a modification in the surface of the PAN polymeric film.     

Microstructure and mechanical properties of hydroxyapatite obtained by gel-casting process

In the present work, well-shaped HAp green bodies were obtained by the gel-casting process with 50 vol.% slurry. After drying, the microstructure and pore distribution of the green body were investigated. The density, compressive strength and flexural strength of the green body were 1.621 g/cm³, 32.6 ± 3.2 MPa and 13.8 ± 1.0 MPa, respectively. After pressureless sintering at the range of 1100–1300 °C for 2 h, the relative density of the final product ranges from 71.8 to 97.1% th. The maximum value of flexural strength, elastic modulus, hardness and fracture toughness were 84.6 ± 12.6 MPa, 138 ± 7 GPa, 4.45 ± 0.18 GPa and 0.95 ± 0.13 MPa m^1/2, respectively. SEM images show a compact and uniform microstructure; the average grain size was found by using the linear intercept method. XRD and FTIR determined the phase and the radical preserved after sintering.     

Mechanical behaviour modelling of a nanostructured polyamide blends obtained by reactive extrusion process

The aim of the present work was to study the effect of the composition and operating conditions on the properties of nanostructured polyamide blends obtained by reactive extrusion. The ultimate objective consisted in optimizing the high impact energy of these materials using an experimental design based on the D-optimality and rotatability criteria. A thermodynamic approach of relaxation phenomena called distribution of nonlinear relaxations (DNLR) was proposed to account for the nonlinear mechanical behaviour of the obtained polyamide blends for different compositions and extrusion conditions. Five parameters of the DNLR law have thus been modelled as functions of these operating conditions using quadratic polynomial relations.The accuracy of this modelling was evaluated by establishing some comparison between the experimental data and the predictive results and by performing statistical tests.     

Well-ordered polymer nano-fibers with self-cleaning property by disturbing crystallization process

Bionic self-cleaning surfaces with well-ordered polymer nano-fibers are firstly fabricated by disturbing crystallization during one-step coating-curing process. Orderly thin (100 nm) and long (5–10 μm) polymer nano-fibers with a certain direction are fabricated by external macroscopic force (F_blow) interference introduced by H₂ gas flow, leading to superior superhydrophobicity with a water contact angle (WCA) of 170° and a water sliding angle (WSA) of 0-1°. In contrast, nano-wires and nano-bridges (1–8 μm in length/10-80 nm in width) are generated by “spinning/stretching” under internal microscopic force (F_T) interference due to significant temperature difference in the non-uniform cooling medium. The findings provide a novel theoretical basis for controllable polymer “bionic lotus” surface and will further promote practical application in many engineering fields such as drag-reduction and anti-icing.     

Numerical simulation of polymer foaming process in extrusion flow

Computer simulations of polymer foaming processes in extrusion flow have been carried out in order to improve current understanding of viscoelasticity and bubble growth effects on die-swelling in the production of polymer foam. The linear and non-linear viscoelastic materials functions of a commercial low density polyethylene (LDPE) melt have been extracted by fitting its rheometric data with constitutive models including a simple viscoelastic model (SVM), the exponential Phan-Thien–Tanner (EPTT) model and the double convected pom–pom (DCPP) model. Simulations of LDPE melt under extrusion flow without foaming show that the predictions of the die-swell by the SVM are in reasonably good agreement with the results obtained from the EPTT and DCPP models. By comparison of the simulation results of LDPE foaming in extrusion flow using the Bird–Carreau model and the SVM, a cooperative effect of polymer viscoelasticity and bubble growth on the die-swell has been quantified. The numerical results also show that the density of polymeric foam decreases significantly with the increasing concentration of foaming agent, and that the combination of the SVM and bubble growth model can account for some essential physics of polymer foaming process in extrusion flow.     

Multivariable fuzzy decoupling control of the polymer electromagnetism dynamic extrusion process

The plastic electromagnetism dynamic extruder has gained wide applications because of its novel structure and fine engineering performance. In the polymer processing, melt temperature and melt pressure control is crucial to the quality of the extruded product. A new multivariable fuzzy decoupling control algorithm of melt temperature and melt pressure for the novel extruder is introduced in the transfer function matrix system, which is obtained through the experimental data with system identification. To verify the application of the proposed control algorithm, the multivariable closed‐loop fuzzy decoupling system is implemented on programmable computer controller. Experimental results show melt temperature and melt pressure can be successful individually controlled by the heater power and the screw speed. The good system performance verifies the control strategy's validity. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

板材级ABS的产品性能及挤出成型工艺研究

对比并分析了国内市场常用板材级ABS树脂与通用级ABS树脂的性能特点,介绍了挤出板材的工艺流程和工艺条件,并对ABS板材挤出成型工艺的影响参数及控制要点进行了讨论,分析探讨了AgS板材从粒料干燥到板材冷却定型的各种工艺参数、影响因素及其控制要点,归纳总结了挤出成型ABS板材的各种质量缺陷、产生原因及其相应的对策措施。     

Observation for mechanical property variations of single polymer particles

Monodisperse polymer particles were prepared via conventional microsuspension polymerization or one‐step seeded polymerization, using 1,6‐hexanedioldiacrylate or its mixture with ethylene glycol dimethacrylate (EGDMA) as crosslinking monomer and poly(methyl methacrylate) synthesized by soap‐free polymerization as seed particles. For the study, the effects of the ratio of the absorbed monomer or monomer mixture to the seed polymer particles (swelling ratio), the ratio of EGDMA in absorbed monomer mixture, the dosage of initiator, polymer particle structure, and the electroless Ni plating on the mechanical properties of polymer particles, such as recovery rate, K‐values, breaking strength, and breaking displacement were investigated using micro compression test. It was observed that monomer swelling ratio influenced only on breaking strength, whereas EGDMA ratio in monomer mixture, dosage of initiator, polymer structure and electroless Ni plating did on both K‐values and breaking strength. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Controlling the structure of a porous polymer by coupling supercritical CO2 and single screw extrusion process

A study on the extrusion of Eudragit E100 was carried out using supercritical carbon dioxide (scCO₂) as plasticizer and foaming agent. ScCO₂ modifies the rheological properties of the material in the barrel of the extruder and acts as a blowing agent during the relaxation when flowing through the die. For experiments, a single‐screw extruder was modified to be able to inject scCO₂ within the extruded material. The aim is to determine a correlation between operating conditions and foam structure. The effect of three parameters was studied: the temperature in the die and in the metering zone, the screw speed, and the volumetric flow rate of CO₂. An increase in temperature enhances the expansion rate and the average pore diameter and appears to be the most significant parameter. The effect of CO₂ concentration is significant at small concentrations only: the higher the CO₂ concentration, the lower the pore density and the higher both the pore diameter and the expansion rate. The effect of the screw speed is tricky because a variation of this speed involves a decrease of CO₂ weight ratio. This study shows that the structure of the extrudates does not evolve with a coupling of screw speed increase and a subsequent CO₂ weight ratio decrease. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

振动力场强化聚合物反应挤出过程的研究

介绍了将电磁场引起的机械振动力场引入聚合物反应挤出过程的作用和基本作用原理。引入振动力场可以对挤出机内的物理和化学反应产生积极影响，改善聚合物熔体的粘弹性，提高聚合物混炼和动态硫化效果。该方法可用于提高动态硫化EPDM／PP热塑性弹性体的质量。     

Compatibility studies on some polymer blend systems by electrical and mechanical techniques

Systematic electrical and mechanical studies were carried out on natural rubber (NR) blended with different types of synthetic rubber such as styrene‐butadiene rubber (SBR), polybutadiene rubber (BR), and ethylene‐propylene‐diene monomer (EPDM) as nonpolar rubbers and nitrile‐butadiene rubber (NBR) and chloroprene rubber (CR) as polar rubbers. The NR/SBR, NR/BR, NR/EPDM, NR/NBR, and NR/CR blends were prepared with different ratios (100/0, 75/25, 50/50, 25/75, and 0/100). The permittivity (ε′) and dielectric loss (ε″) of these blends were measured over a wide range of frequencies (100 Hz–100 kHz) and at room temperature (∼ 27°C). The compatibility results obtained from the dielectric measurements were comparable with those obtained from the calculation of the heat of mixing. These results were confirmed by scanning electron microscopy and showed that NR/SBR and NR/BR blends were compatible while NR/EPDM, NR/NBR, and NR/CR blends were incompatible. To overcome the problem of phase separation (incompatibility) between NR and EPDM, NBR, or CR, a third component such as SBR or poly(vinyl chloride) (PVC) was added as a compatibilizing agent to these blends. The experimental data of dielectric and mechanical measurements showed that the addition of either SBR or PVC could improve the compatibility of such blends to some extent. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 60–71, 2001     

Morphological evolution and mechanical property enhancement of natural rubber/polypropylene blend through compatibilization by nanoclay

Nanocomposites of natural rubber (NR)/polypropylene (PP) (80/20 wt %) blends filled with 5 phr pristine clay were prepared by melt‐mixing process. Effects of clay incorporation technique via conventional melt‐mixing (CV) and masterbatch mixing (MB) methods on nanostructure and properties of the blend nanocomposites were investigated. The XRD, SAXS, WAXD, and TEM results showed that the clays in the NR/PP blend nanocomposites were presented in different states of dispersion and were locally existed at the interface between NR and PP as well as dispersed in the NR matrix. The presence of clay caused unique morphological evolution such as fine fibrillar PP domains. The tensile strength was improved over the unfilled NR/PP blends by 53% and 224%, and the storage modulus at 25 °C was increased by 78% and 120% for the NR/PP/clay nanocomposites prepared by CV and MB methods, respectively. Significant improvement in both properties was particularly obtained from the MB method due to finer dispersion fibrillar PP phase in the NR matrix and stronger interfacial adhesion between NR and PP fibers, as suggested from DMA. The oil resistance of blend nanocomposites was also improved over that of the unfilled NR/PP blend, and this property was further progressed by the masterbatch mixing method. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44574.     

Mechanical properties of pitch-coal extrudates during the carbonization process

Combined thermogravimetric and thermomechanical measurements are used to investigate the carbonization of coal-pitch extrudates. Changes in mass and dimensions are measured as a function of temperature. Qualitative dynamic measurements help to elucidate the mechanical properties of interacting coal-pitch systems during the carbonization step.     

Morphological and electromechanical studies of fibers coated with electrically conductive polymer

Electrically conductive fibers have been prepared by polymerization of pyrrole on surfaces of commercial polymer fibers. Thickness and morphology of the conducting thin film on the surface of the fibers were examined by scanning probe microscopy, indicating a strong dependence of the substrate's nature, in addition to the processing conditions. Electromechanical property was investigated by an electromechanical testing system, showing that a smooth and uniform coating and the matched mechanical properties will lead to a satisfied performance of conductive fiber sensors. The difference in the behavior of two types of composite fibers was investigated by scanning electron microscopy in situ observations. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1844–1854, 2005     

Investigation for surface morphology and mechanical property variations of single polymer particles

Monodisperse polymer particles were prepared via one‐step seeded polymerization using polystyrene, poly(methyl methacrylate), or styrene/methyl methacrylate copolymer [poly(ST‐co‐MMA)] as seed particles and 1,6‐hexanedioldiacrylate or divinylbenzene as crosslinking monomer. For the study, the effects of the combination of seed polymer and crosslinking monomer, the ratio of the absorbed monomer to the seed polymer particles (swelling ratio: S/R), and the seeded polymerization rate on the variation of surface morphology and mechanical properties of polymer particles, such as recovery rate, K‐values, breaking strength, and breaking displacement were investigated by using microcompression test. It was observed that the surface morphology could be controlled by changing polymerization rate or combination of seed polymer and crosslinking monomer, and it had a great influence on mechanical properties, especially the breaking strength. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2350–2360, 2007     

Formation and peculiarities of heterogeneity in polyethylene samples obtained by extrusion

Three-layer structure was observed in the polyethylene strips obtained under definite conditions of extrusion, with the high degree of orientation of the core layer being most remarkable. The wide-and small-angle X-ray investigation of the different layers of the strips and the pole figures analysis were performed. In the outer layers a texture is formed. Crystalline structure formed in the core is characterized by almost regular cylindrical arrangement of a and b axes around the extrusion direction. The c axes direction almost coincides with the extrusion direction. In the core of the extruded strand, lamellae are arranged in parallel stacks. The angle value between the normal to the lamellae surface direction and the extrusion direction is about 30°.