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1.
    
Mold temperature is one of the key factors affecting the morphology and quality of plastic parts. This article explores the melt flow phenomena in a vario‐thermal mold cavity. A coupled numerical method, considering the conjugate heat transfer between the mold and melt, is developed for the melt flow simulation. Mold temperature variations and melt flow phenomena for short shot injection in an electrical heated mold cavity are numerically studied and verified by experiments. The results indicate that the melt flow length and cavity filling ratio increase significantly with the elongation of the preheating time before injection. Melt filling ratio increased nearly linearly with the increasing of electric heating time. The smaller the injection pressure is, the bigger the relative filling ratio increment is. Therefore, polymer melt can flow much longer or the mold cavity can be filled up with a smaller injection pressure when the cavity is preheated. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45193.  相似文献   

2.
    
The nonlinear stress relaxation behavior after a step shear strain of star-shaped SSBR/silica compounds containing 21 vol% filler of various surface areas was measured and simulated using constitutive equations. A styrene-butadiene rubber (SBR) gum and SBR filled with silica having BET surface areas of 55, 135, 160, and 195 m2/g were used. Relaxation modulus behavior of the filled compounds was found to be dependent on surface area. Specifically, stress relaxation tests indicated that an increase in surface area led to increase in values of relaxation moduli in both the linear and nonlinear regimes. The time-dependent relaxation modulus exhibited a plateau at long times of relaxation in compounds containing silica of high surface area. Additionally, good time-strain superpositions were achieved for all samples at intermediate times of relaxation, and the strain-dependent damping function decreased with filler surface area. The constitutive equations proposed by Leonov and Simhambhatla and Leonov, modified to include multimodal relaxation of the particle network, were used to predict the time evolution of the relaxation modulus in the nonlinear regime for all samples. The simulations provided good results for the SBR gum for all tested strain levels. Also, in the compounds filled with silica, both models satisfactorily described the experimental observation in the nonlinear regime at low strain levels. However, at higher strain levels, due to a possible slip effect, the simulations overpredicted measured values of the relaxation moduli, thus leading to only qualitative predictions of the observed behavior. It is also possible that neither model accurately captured the floc rupture kinetics of these complex rubber compounds.  相似文献   

3.
    
The dynamic rheological behaviors at 210, 230, and 250 °C are measured by small amplitude oscillatory shear on a rotational rheometer for a polypropylene(PP)/ ethylene‐propylene‐diene monomer(EPDM) block copolymer/ high density polyethylene (HDPE)/blend. The scanning electron microscope (SEM) photomicrographs show the blend has a droplet/matrix, semi‐co‐continuous, co‐continuous morphology respectively at different weight ratios. The Cole–Cole (G″ vs. G′) data of the blends can be fitted by the simplified Palierne's model only for very narrow weight ratios. A physical scheme is proposed that the dispersed droplets are enclosed by EPDM, thus an equivalent dispersed phase is made up of “expanded” EPDM. With this physical scheme the G″ vs. G′ data of the HDPE‐rich blends at 210 °C can be fitted well by Palierne's model. Also with the physical scheme the G″ vs. G′ data of the PP‐rich blends at three temperatures can be fitted well by G–M's model with G* of interface equals to zero. This means the proposed physical scheme is reasonable. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43709.  相似文献   

4.
    
High viscous polycarbonate melt exhibits some special rheological characters different from generalized Newtonian fluid during squeezing. It is necessary to evaluate whether the typical rheological models are suitable for polycarbonate squeeze. To avoid the difficult of measuring the inner melt rheological behavior directly, this study presents a method of measuring the compressing force applied on the upper disc of the rheometer to reveal the melt rheology indirectly. The finite difference method (FDM) was employed to discretize the governing equations and constitutive equations established on cylinder coordinate system and to simulate the compressing force. The experiments were carried out under four temperatures and three compressing velocities to test the validations of Leonov, Phan‐Thien–Tanner (PTT), eXtended Pom‐Pom (XPP), and Cross Williams‐Landel‐Ferry (Cross‐WLF) models. The experimental results show the unique character of compressing force evolution as ‘steep—steady—steep—steady’ pattern. Comparison between experiments and simulations reveals that both viscoelastic and viscous models can predict the two steady regions correctly, but only viscoelastic models can simulate the steep increase and decrease of the compressing force. Among the evaluated viscoelastic models, XPP is the most suitable to describe polycarbonate melt compression flow. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42279.  相似文献   

5.
    
Simulations of evolution of cure‐induced stresses in a viscoelastic thermoset resin are presented. The phenomenology involves evolution of resin modulus with degree of cure and temperature, the development of stresses due to crosslink induced shrinkage, and the viscoelastic relaxation of these stresses. For the simulations, the detailed kinetic and chemo‐thermo‐rheological models for an epoxy‐amine thermoset resin system, described in Eom et al. (Polym. Eng. Sci. 2000, 40, 1281) are employed. The implementation of this model into the simulation is facilitated by multiphysics simulation strategies. The trends in simulated cure‐induced stresses obtained using the full‐fledged viscoelastic model are compared with those obtained from two other equivalent material models, one involving a constant elastic modulus, and the other involving a cure‐dependent (but time‐invariant) elastic modulus. It is observed that the viscoelastic model not only results in lower estimates of cure‐induced stresses, but also provides subtle details of the springback behavior. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013  相似文献   

6.
    
The large amplitude oscillatory shear (LAOS) and steady shear behavior of star-shaped SSBR/silica 60 phr (21 vol%) compounds with various filler surface areas was measured and simulated. An SBR gum and SBR compounds containing four different silicas with surface areas of 55, 135, 160, and 195 m2/g were utilized. Rheological behavior indicated clear correlation with surface area. LAOS tests showed an increase in dynamic moduli, shear stress, and higher order harmonic contributions with surface area. Elastic and viscous Lissajous figures showed significant distortion at intermediate and higher strain amplitudes. Additionally, ratios of third and fifth order stress harmonics to the first stress harmonic (I3/1 and I5/1 , respectively) showed a ''bump'' at intermediate strain amplitudes for the three highest surface area compounds. With regards to steady shear, all materials showed strong shear thinning behavior, and an increase in shear viscosity with surface area. The Cox-Merz rule was shown to be valid for the SBR gum but not for the filled compounds. However, the complex viscosity as a function of shear rate amplitude at various frequencies at high strain amplitudes and the steady shear viscosity as a function of shear rate coincided. This correlation, referred to as the Philippoff approach, has important ramifications for the rubber industry, providing quick data for predicting processing behavior. The Simhambhatla-Leonov model was successfully employed to simulate rheological behavior for the SBR gum and the lowest surface area silica compound, but the model yielded mixed results for the higher surface area silica compounds.  相似文献   

7.
    
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  相似文献   

8.
    
The creep behavior caused by the viscous mechanical effect of biodegradable polylactic acid (PLA-max) material is of great significance to its application. To better understand the creep properties of PLA-max materials processed by fused filament fabrication, the effects of printing parameters including printing angle and layer thickness on them are studied theoretically and experimentally. The experimental results show that within the range of loading stress and loading time, the creep deformation of the PLA-max material decreases with the increase of the printing angle or the decrease of the layer thickness. The experimental results are processed and analyzed, and a modified Burger model is proposed to quantitatively analyze the creep deformation of PLA-max. In this modified Burger model, the four parameters are functions of printing angle and stress level. The modified model can accurately calculate the creep deformation of the specimen at other printing angles, which provides an important reference for the design of functional structures with specific mechanical properties.  相似文献   

9.
    
Direct ink writing of soft materials is a very promising technology in 3D printing, and the rheological properties of inks are crucial for successful printing. In this paper, the effect of the rheological properties on the printing process of silicone rubber inks is studied to lay a foundation for the configurations of 3D printing process parameters. Also, the shape retention of the printing filaments is studied to provide a basis for the viscosity deployment of the inks. In addition, by studying the die swell ratio of nano-silica-reinforced silicone rubber inks at normal printing speed, it is found that the die-swell ratio is proportional to the ink's relaxation time. Finally, the influence of the configuration of the short-nozzle on the die swell is investigated, and the concave nozzle has a smaller extrusion swelling effect than the convex nozzle and the conical nozzle, providing new ideas for the adjustment of the filament diameter.  相似文献   

10.
    
The structure and rheological properties of binary blends of polycarbonate (PC) and polystyrene (PS) were investigated using various PS samples with different molecular weights, namely PS1k (Mw = 1,000), PS53k (Mw = 53,000), and PS240k (Mw = 240,000). The blends with PS53k and PS240k show phase-separated structures, whereas the blend with PS1k is miscible. The shear viscosity decreases greatly on addition of PS53k and PS240k, especially at high shear rates, which would be a great advantage at processing operations. Because the nonlinear response occurs in the small strain region for multilayered films of PC and PS240k, the origin of the significant viscosity drop for the phase-separated system is interfacial slippage at the phase boundary.  相似文献   

11.
    
Spinnability of polyacrylonitrile (PAN) solution was studied based on the spinning dynamics simulation and dry‐jet wet spinning experiments. The spinnability phenomenon was observed from the extruding and extending spinning experiments. The suitable conditions of normal extruding and extending of the PAN solution were obtained and the critical spinnability conditions were simulated. The experimental and simulation results showed that pressure drop through the spinneret was similar, while the temperature, velocity, and velocity gradient through the spinneret of PAN solution changed dramatically. It suggests that pressure drop can be chosen as one of the spinnability criterion for solution extruding and filaments forming during dry‐jet wet spinning. Furthermore, the effect of spinneret parameters and spinning conditions on spinnability was simulated. It shows that spinneret entrance angle, outlet channel length and width have impacts on the pressure drop and the die swell ratio, which suggests the spinneret design can be optimized to regulate the spinnability according to the simulation results. It is also found that some bad situations of spinnability such as sticking phenomenon can be avoided by decreasing spinning temperature or increasing mass flow rate to increase the pressure drop at a certain level under the premise of extruding smoothly. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46377.  相似文献   

12.
    
The three‐dimensional coextrusion flow of two polymer melts is solved over the die‐extrudate region using the finite element method. As elastic recovery is known to be the main source of extrudate swelling, a viscoelastic constitutive model (the Phan‐Thien‐Tanner or PTT model) is adopted to characterize the rheological behavior of the elastomers. A major challenge in the simulation of multilayer flow inside and outside the die is to update multiple moving surfaces (material interface and extrudate free surface) simultaneously. This difficulty is resolved by introducing a two‐step updating algorithm which decouples the iterations of the interface and the free surface. The effects of extrudate swelling and bending on interface deformation are investigated herein, together with the interface shape dependency on flow elasticity. The numerical method is also applied to an industrial profile and the simulation result is in quantitative agreement with the experimental coextrusion data. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43522.  相似文献   

13.
    
The relaxation behaviors of the binary immiscible blends reflected on the plots of the storage modulus and the imaginary part of complex viscosity were investigated using the Maxwell and the Palierne models. It was revealed that the peaks in the high‐ and low‐frequency regions on the complex viscosity imaginary part plot are owing to the relaxations of the blend and deformed dispersed droplets, respectively. Based on these two models, six emulsion parameters (interfacial tension, relaxation times and viscosities of two components, and dispersed phase volume fraction) were investigated in terms of their effects on the shape features of the plots of the imaginary part of complex viscosity and the Cole–Cole. The results showed that the viscosities of two components and dispersed phase volume fraction play key roles in the radii of the two circular arcs on the Cole–Cole plot. Furthermore, the two circular arcs are well separated in the case of lower interfacial tensions and dispersed phase viscosities, shorter matrix relaxation times, and higher matrix viscosities and dispersed phase volume fractions. The total relaxation time of the deformed dispersed droplets increases with increasing the viscosities of two components, especially with decreasing the interfacial tension. Three types of polymer blends were prepared and their dynamic frequency sweep testing results demonstrated the effectiveness of the corresponding predicted results. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39690.  相似文献   

14.
    
Residual wall thickness is an important indicator which aims at measuring the quality of water‐assisted injection molding (WAIM) parts. The changes of residual wall thickness around dimensional transitions and curved sections are particularly significant. Free interface of the water/melt two‐phase was tracked by volume of fluid (VOF) method. Computational fluid dynamics (CFD) method was used to simulate the residual wall thickness, and the results corresponded with that of experiments. The results showed that the penetration of water at the long straight sections was steady, and the distribution of the residual wall thickness was uniform. However, there was melt accumulation phenomenon at the dimensional transitions, and the distribution of the residual wall thickness wasn't uniform. Adding fillet at the dimensional transitions could improve the uniformity of the residual wall thickness distribution, and effectively reduce water fingering. Additionally, at the curved sections, the residual wall thickness of the outer wall was always greater than that of the inner wall, and the fluctuations of the residual wall thickness difference were small. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013  相似文献   

15.
    
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  相似文献   

16.
    
Although apparently simple, the polycondensation reaction leading to polyazomethine is difficult to control because of its equilibrium character, the conversion degree being influenced by a series of parameters. The reaction between a siloxanediamine, 1,3‐bis(3‐aminopropyl)tetramethyldisiloxane, and terephthalaldehyde was performed here in solution (in tetrahydrofuran) without by‐products removal and in absence of any catalyst or pH modifier. Different conditions (co‐monomers ratio, dilution, and temperature), considered as input parameters for the process modeling, were varied according to a pre‐established experimental program. The viscosity of the reaction mixture was chosen as output parameter, being monitored with a Haake Viscotester 7 Plus‐L. The process modeling was performed using a hybrid combination of artificial neural networks and differential evolution algorithm, the last one having the role of developing the neural model in an optimal form. The simulation results showed that the methodology provides accurate results, the model predictions being in close correlation with the experimental data. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42552.  相似文献   

17.
    
Gellan gum is a biopolymer widely used in the food, pharmaceutical, chemical, and agrochemical fields. Its ability to form a strong gel makes it possible to produce fluid gels. These materials present an apparent yield stress, but its value could be influenced by the wall-slip effect when performing the rheological measurements by which it is determined. In this work, the influence of the measuring surface and gap on flow behavior was first determined. The tests revealed the need to use geometries with rough surfaces, although the sample thickness using a parallel plate has no influence. Subsequently, the value of yield stress was obtained by means of creep tests (found to be 4.3 Pa), and, finally, the effect of wall slip on the dynamic viscoelastic behavior was assessed. There was an influence on the extension of the linear viscoelastic region, but not on the viscoelastic functions of the mechanical spectra. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46900.  相似文献   

18.
    
Comprehensive exploration of the viscoelastic properties of polyaniline–emeraldine base (PANI–EB) nanostructured films is presented from two viewpoints of experimental study associated with dynamic mechanical thermal analysis and thermogravimetric measurements and of computational simulations by molecular dynamics (MD) approach. The results are expressed in storage and loss modulus components (E′ and E″). The role of drying temperature, time, and residual solvent content were studied on the E′ and E″ of prepared PANI–EB films. Using the principle of time–temperature superposition, E′ and E″ at different temperatures and frequencies can be plotted on master curves. The relationship between the modulus components with the solvation level of PANI–EB film is also studied. MD simulation is applied to study the viscoelasticity of simulated PANI structures with different monomeric aniline chains. The temperature dependence of viscoelastic properties provides good information for fractional free volume, cavity size distribution, and activation energy of PANI structures. Simulation outcomes provide a fairly good compatibility with the experimental results. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41858.  相似文献   

19.
    
The operating windows of the solution casting of two polymeric liquids were evaluated experimentally. The experimental setup and procedure were the same as used previously for the casting of Newtonian fluids (Journal of Applied Polymer Science 2013, 129, 507–516). Aqueous carboxymethylcellulose/glycerol solutions exhibited pure shear‐thinning behavior at low polymer concentrations but became viscoelastic at high polymer concentrations, whereas polyacrylamide/glycerol solutions showed viscoelastic behavior over a wide range of concentrations. The shear‐thinning behavior, in conjunction with a low level of elasticity, of the casting solution was found to be useful in expanding the stable operating windows. However, an opposite effect on the operating windows was found for highly elastic solutions. The non‐Newtonian effect on the maximum stable casting speed was prominent only when the capillary number exceeded unity. Defects outside of the operating window were mostly similar to those observed in Newtonian solution casting. For highly concentrated solutions, a new rough surface defect was observed. This defect could be attributed to polymer chain entanglement, alignment, or breakup. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41411.  相似文献   

20.
    
In this study, the melt linear viscoelastic rheological properties of polyamide 6 (PA6)–acrylonitrile butadiene styrene terpolymer (ABS) immiscible blends were analyzed with the help of Coran and fractional Zener models (FZMs) to assess the microstructure of the blends. For this purpose, dynamic shear flow experiments and scanning electron microscopy investigations were performed. The nonzero value of the elastic modulus of the spring element (Ge) of the FZM for ABS‐rich blends was explained by the formation of a networklike structure because of the agglomeration of the rubber phases of the ABS matrix, whereas for the PA6‐rich blends with a high content of ABS, the interactions and/or interconnectivity of the ABS dispersed phase led to a nonzero value of Ge. The value of the fitting parameter of the Coran model (f) was near to 0.5 for the 50/50 blend; this was fully in agreement with the formed cocontinuous morphology for this blend composition. On the other hand, the f value for the blends with a matrix–droplet‐type morphology was near to zero for the PA6‐rich blends; this indicated the lower continuity of the ABS dispersed phase as a harder phase compared to the PA6 soft matrix, whereas the f value was near to 1 for ABS‐rich blends. This confirmed the formation of an interconnected networklike structure for this series of blends. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45423.  相似文献   

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