Die-swell Ratio Research Articles

High temperature-size exclusion chromatography with triple detection to assess the molecular architecture of low-density polyethylene: Insight into branching and processability correlations.

In this study, three commercially available low-density polyethylene (LDPE) polymers produced via a tubular reactor process, with varying melt flow rates at 190°C/2.16kg (4.0, 1.9, and 0.75g/10min), have been selected and subjected to high temperature-size exclusion chromatography (SEC) analysis coupled with an infrared-5 (IR-5), viscometer (VISCO), and multiangle laser light-scattering detectors. The molecular weight (MW), MW distribution, short-chain branching (SCB), and long-chain branching parameters were investigated. It was found that MW obtained by the universal technique (∼1.57-1.7 times) and multiangle laser light-scattering detection technique is (∼1.43-1.55 times) higher than that of the conventional calibration technique, which could be attributed to structural complexity associated with LDPEs which is not clearly understood by conventional SEC mode alone. The bulk SCB per 1000 total carbon atoms estimated by IR-5 detection was found to range from 16.50 to 17.80. On the other hand, long chain branching frequency per 1000 total carbon atoms obtained by online VISCO and multiangle laser light-scattering detection ranged from 0.46 to 0.54 and 0.65 to 0.94, respectively. Further, the significance of long chain branching parameters on the polymer processing behavior was studied in correlation with rheological property (Die swell ratio).

Experimental and Numerical Investigation of the Die Swell in 3D Printing Processes

Fused deposition modelling is one of the most widely used additive manufacturing techniques and the diffusion of 3D printers has increased in popularity even further in recent times. Since high precision is required in 3D printing, a good control over the extrusion process is necessary. In this regard, a crucial phenomenon to be accounted for is the die or extrudate swell, i.e., the enlargement of the cross-section of the strand when coming out of the printer nozzle. While this phenomenon has been studied in large scale extruders, it has not yet been investigated in depth for 3D printing processes. In this work, the die swell phenomenon observed in a printed PLA filament is studied by experiments and fluid dynamic simulations. A novel, easy-to-use, accurate and fast procedure for measuring the value of the die swell ratio during the printing process is developed, accounting for typical errors related to a non-constant strand diameter and possible oscillations of the filament with respect to the extrusion direction. As the printing velocity is increased, a linearly increasing swelling ratio is observed at low printing speeds. The trend flattens at moderate speed values. A sudden increase is found at high printing velocities. The swelling ratio measured with the proposed technique is compared with the results of multi-mode viscoelastic simulations at different temperatures. A fair agreement between the experimental measurements and the numerical predictions is found for printing velocities that are typically employed in commercial 3D printers, supporting the reliability of the developed procedure.

Online characterization of ambient temperature influence on die swell behavior of rubber compound

In this study, the influence of the ambient temperature in the range of 20–60 °C on the die swell behavior of rubber compound were studied by a capillary rheometer with new designed external heating device. The results demonstrated that the die swell ratio (B) increased rapidly in the initial phase and reached a stable value after a certain time. The time dependence of B was then calculated based on the experimental data using Burger's model. In addition, it can be found that B was proportional to the ambient temperature of the extrudate, since the relaxation time decreased obviously with increasing ambient temperature. At the constant time of 130 min, B in the range of 20–60 °C were 1.393, 1.405, 1.420, 1.425 and 1.438 mm, respectively. Furthermore, an equation was established to describe the relationship among the B, test time and ambient temperature. The calculated value was consistent with experimental data, which was 1.447 and 1.449 mm, respectively. While the equation was not applicable when the ambient temperature lay above 70 °C due to the decreased interaction between rubber and carbon black. It was also found that the contraction effect played a significant role on the behavior of die swell. B of the extrudate under 60 °C and 70 °C was reduced by 1.5% and 1.2%, respectively.

Effects of Wood Flour (WF) Pretreatment and the Addition of a Toughening Agent on the Properties of FDM 3D-Printed WF/Poly(lactic acid) Biocomposites.

In order to improve the properties of wood flour (WF)/poly(lactic acid) (PLA) 3D-printed composites, WF was treated with a silane coupling agent (KH550) and acetic anhydride (Ac2O), respectively. The effects of WF modification and the addition of acrylicester resin (ACR) as a toughening agent on the flowability of WF/PLA composite filament and the mechanical, thermal, dynamic mechanical thermal and water absorption properties of fused deposition modeling (FDM) 3D-printed WF/PLA specimens were investigated. The results indicated that the melt index (MI) of the specimens decreased after WF pretreatment or the addition of ACR, while the die swell ratio increased; KH550-modified WF/PLA had greater tensile strength, tensile modulus and impact strength, while Ac2O-modified WF/PLA had greater tensile modulus, flexural strength, flexural modulus and impact strength than unmodified WF/PLA; after the addition of ACR, all the strengths and moduli of WF/PLA could be improved; after WF pretreatment or the addition of ACR, the thermal decomposition temperature, storage modulus and glass transition temperature of WF/PLA were all increased, and water absorption was reduced.

The viscoelastic properties of a halogen-free polymer composition, for cable products

The viscoelastic properties of a halogen-free polymer composition for cable products have been investigated. The influence of temperature parameters, shear rate on the die-swell ratio of the polymer composition has been determined; the dependence of the melt density on a temperature was investigated. The polymer matrix is a mixture of polyolefins (linear low density polyethylene; polyolefin elastomer and maleic anhydride modified linear low density polyethylene) as a flame retardant filler for the polymer composition is trihydrate alumina. The content of flame retardant filler in the polymer composition is 60 %. The polymer composition was manufactured on the compounding line of X-Compound, Switzerland. The investigation of both melt density and die-swell ratio of the polymer composition has been conducted with help of capillary viscometer type IIRT-AM. To determine the density of the melt the ratio of capillary length to diameter L/D=8/2 was used. The results of the study of the dependence of the melt density of the polymer matrix from a temperature of 150–190 °C at different loads showed that this parameter decreases from 789 to 744 kg/m3 and for polymer composition from 1309 to 1268 kg/m3. The die-swell ratio in the case of an increase of the shear rate at temperatures of 150–190°C for the polymer matrix increases from 1,102 to 1,520, and for the polymer composition decreases from 1,056 to 1,018. The investigation results of the dependence of both die-swell ratio of the polymer matrix and the polymer composition on the ratio of the length of the forming tool to the diameter indicates that the die-swell ratio for the polymer matrix was reduced from 1,296 to 1,152, and for the polymer composition from 1,045 to 1,01. It was established that the viscoelastic properties of the halogen-free polymer composition are significantly influenced by: processing temperature, shear rate, melt density, the ratio of the length of the forming tool to the diameter. The research results give a possibility for a reasonable approach for the determination of technological parameters of an insulation, sheathing of power cables and optical cables of microtube construction. It will also allow to quickly adjust the geometrical parameters of the forming tool of cable heads.

Solvent evaporation induced fabrication of porous polycaprolactone scaffold via low-temperature 3D printing for regeneration medicine researches

Liquid deposition modeling (LDM) is an evolving three-dimensional (3D) printing approach that mainly utilizes polymer solutions to enable the fabrication of biomedical scaffolds under mild conditions. A deep understanding of the rheological properties of polymer printing inks and the features of yielded scaffolds are critical for a successful LDM based fabrication of biomedical scaffolds. In this work, polymer printing inks comprised of Poly(epsilon-caprolactone) (PCL), sodium chloride (NaCl), and trichloromethane (CHCl3) were prepared. The rheological properties, including extrudability (shear stress, viscosity, and shear-thinning) and self-supporting ability (viscosity) of all printing inks were analyzed. Then printing performance was evaluated by measuring the die-swell ratio, 2D, and 3D printing fidelities. Finally, a series of porous PCL scaffolds were fabricated using printing inks comprised of different feed ratios (20:80, 40:60, 50:50, 60:40, and 80:20) of NaCl to PCL, and the porosity, mechanical properties, degradation behaviors, and biocompatibility were discussed. The results suggested that the printing ink formulation is greatly affected the printing performances. The increasing NaCl content in printing inks reduced shear force for extrusion, enhanced the shear-thinning behavior, increased the curing time. The dropping temperature and solvent evaporation both enhanced the self-supporting ability of the printing inks and solvent evaporation is a critical factor for the curing of the printing inks. The further evaluation demonstrated that the obtained fabricated porous PCL scaffolds were endowed with good biocompatibility and controllable porosity, mechanical features, and in vitro degradation behavior related to the NaCl content in the printing inks. This study built a fabricating method of porous polymer scaffolds by 3D printing at low temperatures for regeneration medicine researches.

Melt rheology and extrudate swell properties of talc filled polyethylene compounds

An experimental study of high-density polyethylene (HDPE) composites filled with talc (0–15 wt.%) was carried out to investigate the rheological properties. The apparent melt viscosity, melt density, and die-swell ratio (B) of the composites were measured at constant shear stress and constant shear rate by using a melt flow indexer and capillary rheometer. The experimental conditions were set to a temperature range from 190 to 220 °C for both apparatuses whereas a load range from 5 to 12.16 kg was selected for melt flow indexer and shear rate range from 1 to 10000 s−1 for capillary rheometer. The initial study showed that the talc particulates did not influence the melt viscosity compared with the neat HDPE but decreased the elasticity of the polymer system. The HDPE/talc systems obeyed power-law model in shear stress–shear rate variations and were shear thinning, meanwhile, the die-swell increased with an increased wall shear rate and shear stress. The melt density of the composites increased linearly with an increase of the filler weight fraction and decreased with the increase of the testing temperature. The talc-HDPE composites showed compressible in the molten state.

Melt die-swell behavior of polyoxymethylene blended with ethylene-vinyl acetate copolymer and high-density polyethylene

The influence of extrusion conditions (temperature ranging from 170 to 220 °C, loads varying from 1.2 to 12.5 kg) and high-density polyethylene (HDPE) content on swelling behavior of polyoxymethylene (POM)/ethylene-vinyl acetate copolymer (EVA)/HDPE blend melts was examined. It was found the melt die-swell ratio of the blends decreased approximately linearly with rise in temperature, while it increased as a quadratic function with increasing shear rate or shear stress. The melt die-swell ratio increased with increasing HDPE weight fraction under constant test temperature, and the effect of temperature on the sensitivity of the melt die-swell ratio to the HDPE weight fraction was insignificant, while the effect of load on the melt die-swell ratio was significant. The correlation between the melt die-swell ratio of the blends and the HDPE weight fraction followed a quadratic relation. The melt extrudate swell behavior mechanisms of the blends during the die extrusion flow are discussed.

Study on die swell of cellulose diacetate spinning dope at the exit of regular triangular orifice

Chemical fibers are typically spun with a spinneret, whose cross-sectional shape may be round, cross, trilobal, etc. On the contrary, cellulose diacetate (CDA) fibers used as cigarette tows are commonly spun with a regular triangular prism spinneret having a regular triangular cross-section because the cross-section of the spun cigarette tow is Y-shape owing to acetone solvent evaporation in the spinning column and the filter efficiency of the cigarette tow can reach the maximum value. However, previously CDA tows or fibers produced with such a regular triangular orifice were seldom reported. Many parameters influence the CDA tow spinning process with die swell being one of the most important factors. In this study, a model of a die swell was developed using rheological knowledge and second-type surface integrals. In order to confirm the validity of the model, the die swell of a CDA spinning dope at the exit of a regular triangular orifice was determined with a travelling microscope. Further, each parameter of die swell was studied. The apparent viscosity of the CDA spinning dopes was determined for different mass concentrations and temperatures with respect to shear rate and storage modulus and loss modulus with different mass concentrations and temperatures versus angular frequency were measured with a Physica MCR101 rheoviscometer. In addition, the flow rate was measured with a metering pump attached to the spinneret, and pressure drop was calculated from the above parameters. The results demonstrated that the die-swell ratio decreased when the dope temperatures were increased, but increasing trends were observed with dope concentrations and shearing rate. The experimental die-swell ratios were in good agreement with the calculated model results with less than ±6 % deviation. Therefore, this study can provide support for related CDA tows spinning studies.

Numerical Investigation and Experimental Observation of Extrudate Swell for Viscoelastic Polymer Melts

Abstract In the present research die swell phenomenon is investigated for the viscoelastic polymer melts both experimentally and by developing a mathematical model in a circular die for high impact polystyrenes (HIPS), high density polyethylene (HDPE), low density polyethylene (LDPE) and linear low density polyethylene (LLDPE). Die swell is generally attributed to the fluid stress field when the fluid flows in a die. The Leonov-like equations as a conformational model are solved simultaneously with dynamic equation of momentum transfer to predict the stress field for a viscoelastic fluid in a circular die. The average molecular weight, the polymer relaxation time and the polymer mobility tensors are determined using the experimental measurements of shear viscosity. Then, based on those data, a model is developed. The results predicted by the model for flow stress field are then used to calculate die swell ratio by Tanner’s analytical model. Die swell ratio is also found out experimentally using a capillary rheometer for the samples. Comparison of the die swell results predicted by the model and measured experimentally show very good agreement for the polymers.

Melt Rheological Properties of LLDPE/PP Blends Compatibilized by Cross-Linked LLDPE/PP Blends (LLDPE-PP)

A novel linear low-density polyethylene (LLDPE)/polypropylene (PP) blends were prepared by melt blending with moderate cross-linked LLDPE/PP blend (LLDPE–PP) as compatibilizer, the rheological properties associated with the morphological structure of the LLDPE/PP/LLDPE-PP blends were studied by SEM, capillary rheometer, HAAKE torque rheometer and melt fiow rate instrument. The results showed that adding LLDPE-PP in the blends improved compatibility between LLDPE and PP phases, made the pseudo plastic behavior of the melt decrease and the melt viscosity and the balance torque increase slightly. Moreover, in the range of high shear rate, the die-swell ratio of the blends decreased with increasing LLDPE-PP content.

Extrudate swell behavior of polypropylene composites filled with microencapsulated red phosphorus

The microencapsulated red phosphorus (MRP) filled polypropylene (PP) composites were prepared using a twin-screw extruder. The effects of load and temperature on the extrudate swell behavior of the PP/MRP composite melts were investigated by means of a melt flow indexer. The test temperatures and loads were varied from 180 to 205°C and from 2.16 to 12.5 kg, respectively. The results showed that the die-swell ratio (B) of the composite melts increased roughly linearly with increasing load while decreased slightly with a rise of test temperature. The sensitivity of the die-swell ratio of the composite melts to load was significant. When the test temperature or load was constant, the values of the B of the composite melts decreased slightly with increasing MRP weight fraction. The findings can provide useful information for processing of these composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Melt extrudate swell behavior of POM/EVA/HDPE/nano-CaCO3 composites

Abstract Polyformaldehyde (POM)/ethylene-vinyl acetate copolymer (EVA)/high-density polyethylene (HDPE) composites filled with nanometer calcium carbonate (nano-CaCO3) were prepared using a twin-screw extruder. The effects of load and temperature on the melt extrudate swell behavior of the composites were investigated, by using a melt flow rate instrument under experimental conditions, with temperatures ranging from 170°C to 220°C and loads varying from 1.2 kg to 12.5 kg. The results showed that the melt die-swell ratio (B) of the composites decreased linearly with a rise of temperature as the load was fixed, while it increased nonlinearly with increase in the melt volume flow rate (MVR) and load, when the test temperature was constant; they also showed that B is a quadratic function of shear rate or shear stress. The value of B increased nonlinearly with an increase of the HDPE weight fraction (ϕ) as the temperature was constant, and the temperature sensitivity of B to ϕ was insignificant, while the effect of load was significant. The correlation between B and ϕ obeyed a quadratic equation.

Effect of Die-Swell Ratio on Polyacrylonitrile As-Spun Fiber Formation

In this paper, the effect of die-swell ratio on the microstructure and properties of as-spun fibers was systematically analyzed by electron microprobe analysis (EMPA) and the measurement of die-swell ratio, boiling-water shrinkage, porosity and mechanical properties. The formation mechanism of the spin orientation and skin-core structure were revealed. It was shown that with different die-swell ratio, the spinodal decomposition speed and the orientation degree between the outer and inner of as-spun fibers is different, which leads to a difference of denseness and hardness between the outer and inner, thus the skin-core and porous structures are formed. A small die-swell ratio leads to an enhanced spin orientation, a reduced skin-core difference and a more compact and homogeneous microstructure. As a result, the breaking tenacity of as-spun fibers and resultant precursors all increased.

Evaluation on extrudate swell and melt fracture of polypropylene/kaolin composites at high shear stress

Kaolin-filled PP composites were compounded using a heated two-roll mill prior to extrusion process in order to improve the rheological properties of the samples. The extrudate swell and flow instability (melt fracture) behavior of kaolin-filled PP composite melts were investigated using a constant rate type of capillary rheometer at high extrusion rates and test temperatures varied from 165°C to 220°C. The extrudate swell studies demonstrate that the die swell ratio decreases with an increase in the processing temperature and filler loading at fixed shear stress. Nonetheless, the study on the effect of shear stress and shear rate showed that the die swell ratio (B) of the melts decreases linearly with increasing apparent shear stresses and shear rates for both systems, unfilled and filled PP only up to one point above the critical shear rate (1.8 × 10 s-1). The B values remained almost constant when the shear rate is greater than 1.8 × 10 s -1 at a constant temperature. Kaolin-filled PP composites exhibit a characteristic of flow instability and extrudate distortions upon exiting from extrusion dies at low filler loading and at low processing temperature of 165°C. This type of defect is characterized by highly rough, fractured, and distorted extrudate surface. It was also found that decreasing the shear stress improved the surface appearance of all samples. Finally, the melt fracture tended to be suppressed when a capillary die with a high L/D ratio, which is 10 was used.

Die-swell behavior of PP/Al(OH) 3/Mg(OH) 2 flame retardant composite melts

Die-swell is an important parameter related to the melt elasticity during extrusion of polymeric melts, and the degree of swell is usually expressed by die-swell ratio ( B). The die-swell ratio for polypropylene (PP) composites filled with aluminum hydroxide (Al(OH) 3) and magnesium hydroxide (Mg(OH) 2) was measured by means of a capillary rheometer under experimental conditions of temperature ranging from 180 to 200 °C and apparent shear rate varying from 10 1 to 10 3 s −1, to identify the effects of the extrusion conditions as well as the filler particle content and size on the melt die-swell ratio. The results of the experiments indicated that B of the composite melts increased linearly with increase of shear stress and apparent shear rate, and this rate of increase reduced gradually with further increase of the apparent shear rate. However, the B of the composite melts decreased with a rise of the test temperature when the apparent shear rate was fixed. When the apparent shear rate and temperature were constant, the B of the composite melts decreased linearly with an increase of the filler concentration, and increased approximately linearly with increase of the particle size of the flame retardant.

Effect of Co-Monomer Content on Rheological Property of Sawdust/ABS Composites

Effect of co-monomer content in Acrylonitrile-Butadiene-Styrene copolymer (ABS) on the rheological property of sawdust reinforced ABS composites was investigated using capillary die rheometer. Three grades of commercial ABS resin were used. Sawdust from Para rubber tree treated with N-2(aminoethyl) 3-aminopropyl trimethoxy silane was blended with ABS by melt blending process using twin-screw extruder. From the results, shear thinning behavior was found for all of composites in the same shear rate ranges for testing that were investigated. At the low shear rate, the composites which contain higher acrylonitrile content, showed higher viscosity. At high shear rate, the viscosity of each co-monomer dependent composites tends to come close to each other on the curves. In this study, Carreau’s model was used for curve fitting and those parameters were also determined. Die swell ratio of the composites tended to increase at the initial ranges of shear rate of 10-500 s-1, and then the swelling ratio value decreased dramatically once the shear rate were further applied. The molecular weight has more effects than comonomer content on the die swell behavior i.e., at the same molecular weight, composites with higher butadiene content show higher swelling ratio.

Study of Metallocene-Catalyzed Linear Low-Density Polyethylene Solid-State Extrusion: Processing and Mechanical Properties

The effect of extrusion temperature and extrusion drawing ratio (EDR) on the die swell ratio (DSR) and mechanical properties of metallocene-catalyzed linear low-density polyethylene (m-LLDPE) was examined with the application of solid-state extrusion (SSE). Scanning electron microscopy (SEM) was employed to characterize the microstructure and morphology of the extrudates. Extruded from a convergence-divergence die, compared with samples obtained by melt-state extrusion (MSE), the DSR decreases for SSE samples prepared at low extrusion temperature and high EDR. Mechanically strong SSE samples were also obtained at low extrusion temperatures and high EDR. Mechanically strong SSE samples were also obtained at low extrusion temperatures and high EDR. SEM indicates that the microstructures of the MSE samples consist primarily of ring-banded spherulites; the microstructure of the SSE samples was microfibers oriented along the direction of extrusion. The highly oriented microfibers contribute to the improved mechanical strength of the SSE samples.

Effects of Extrusion Conditions on Melt Viscoelasticity during Capillary Flow of Low-Density Polyethylene

The melt viscoelastic properties of a low-density polyethylene (LDPE) are measured, at temperatures varying from 140°C to 170°C and in a wide range of extrusion rates by means of a capillary rheometer, to identify the influence of extrusion conditions (such as temperature, die diameter, and flow rate) on the melt viscoelastic behavior. The results show that the entry pressure drop (▵Pen) and the melt extension stress are a quadric function of extrusion rate (V), and it decreases with an increase in die diameter (d). Similarly, the die-swell ratio (B) increases nonlinearly with increasing V and shear stress at the channel wall. The dependence of B on temperature corresponds approximately with the Arrhenius expression. Under these experimental conditions, the ▵Pen and B increase roughly as an exponential function with an increase in the channel contraction ratio.

Effects of extrusion conditions on die-swell behavior of polypropylene/diatomite composite melts

Die-swell is an important parameter for characterization of elastic properties during extrusion of polymeric melts, and the degree of swell is usually expressed by die-swell ratio ( B). The swell ratio for polypropylene composites filled with diatomite with different particle sizes (volume fraction of 10%) was measured by means of a melt flow rate instrument to investigate the effects of die geometry and extrusion conditions on the die-swell behavior of the composite melts with temperature varying from 210 to 230 °C and load varying from 5 to 12.5 kg. The results showed that B of the composites increased nonlinearly with increase of shear stress and shear rate, while it decreased linearly with rise of temperature. When load and temperature were constant, B increased nonlinearly with increase of the die diameter, whereas it reduced nonlinearly with increase of the die length/diameter ratio.