Melt Shear Flow Research Articles

3D printing boron nitride nanosheets filled thermoplastic polyurethane composites with enhanced mechanical and thermal conductive properties

The rapid development of high-power integrated electronic devices for 5 G system has created an urgent requirement for thermally conductive and electrically insulating materials, which has attracted significant research interest, especially for the engineering materials with mechanical flexibility and anisotropic thermal conductivity. In this study, exfoliated hexagonal boron nitride nanosheets (BNNSs) were incorporated in thermoplastic polyurethane (TPU) with varying contents of 10, 20 and 30 wt% through the solution-melt compounding. Then samples for testing were fabricated from the composites by 3D printing, and their thermal conductivity and tensile properties were evaluated to explore the structure-activity relationship. Results showed that the effects of melt squeezing and shear flow occurred during in 3D printing process were dominant in enabling the orientation of BNNSs within the TPU matrix, which was found to be more dependent on the ratio ( dn/h ) of nozzle diameter dn to layer thickness h and less dependent on the printing speed v . Such in-plane orientation of BNNSs combined with the rastering structure of the deposited strands in the warps and wefts and the low density of inner voids were helpful to improve the mechanical and thermal conductive performance of printed BNNS/TPU composites, demonstrating a much better retention of tensile strength and greatly increased thermal conductivity than those of molded samples via hot compression. In addition, the performance of printed composites was also beneficial from the size effect of BNNSs, which could not be achieved without nano exfoliation. As a result, the tensile strength and elongation at failure of the BNNS/TPU composites with 30 wt% loading were 106.2% and 116% higher than those of printed BN/TPU composites, respectively. In addition, anisotropic thermal conductivity of printed BNNS/TPU in the printing direction and thickness direction increases from 1.51 to 1.80 Wm −1 K −1 and from 1.26 to 1.30 Wm −1 K −1 , representing increases of 19.21% and 3.17%, respectively.

On the Feasibility of Printing 3D Composite Objects Based on Polypropylene/Multi-walled Carbon Nanotubes

In this paper, the feasibility of 3D printing polypropylene/ multi-walled carbon nanotube (PP/MWCNT) composites by fused deposition modeling. First, the rheological behavior of PP with 0.3, 0.5 and 1 wt.% of MWCNT was investigated in order to determine the printability in terms of melt shear viscosity and flow activation energy. Second, the filament extrusion process was optimized by the trial-and-error method in order to obtain round and constant filaments. Finally, tensile specimens were printed and tested in order to determine the mechanical properties at various printing direction. Experimental results show that the PP/MWCNT composite filaments with MWCNT loading up to 1 wt.% have good printability characteristics and can be successfully 3D printed with good mechanical performance.

Melt shear flow behavior of flame-retardant polypropylene composites filled with microencapsulated red phosphorus

Melt shear flow behavior and melt shear viscosity are important characterization of processing properties for polymeric materials. The effects of microencapsulated red phosphorus (MRP) content and experimental conditions on the melt shear flow behavior of the polypropylene (PP) composites were investigated using a torque rheometer. It was found that the melt shear viscosity, the torque, and energy consumption at balance state of the composites increased nonlinearly with increasing MRP weight fraction while decreased slightly with increasing temperature, the maximum torque increased with increasing the roller speed, and the dependence of the melt shear viscosity and the energy consumption at balance state on temperature roughly obeyed the Arrhenius equation. These findings would provide useful data for processing these flame-retardant PP composites.

Melt Flow and Flexural Properties of Polypropylene Composites Reinforced with Graphene Nano-Platelets

Abstract The effects of graphene nano-platelets (GNPs) content on melt flow behavior and flexural properties of reinforced polypropylene (PP) composites were investigated. The results showed that both the flexural modulus and strength at room temperature increased when GNPs weight fraction was lower than 0.4 wt.%, and then decreased with increasing GNPs weight fraction. During the melt flow of the PP composites in capillary extrusion within temperatures ranging from 180 to 230 °C and in apparent shear rates varying from 100 to 4 000 s−1, the melt shear flow followed the power law relationship, and the dependence of the melt shear viscosity on temperature obeyed the Arrhenius equation. The correlation between the melt shear viscosity and GNPs weight fraction was approximately linear under the given test conditions.

Synergistic enhancement of crystallization and mechanical performance of polypropylene random copolymer by strong shear and β‐nucleating agent

AbstractInvestigation of microstructure and properties is critical for the development and application of polymer materials. Polypropylene random copolymer (PPR) and β‐nucleated PPR are widely used in water pipe production. The effect of melt shear flow on the crystalline structure and mechanical properties of PPR containing β‐nucleating agent needs in‐depth understanding. In this paper, we demonstrated the preparation of PPR and PPR containing 0.1 wt% calcium pimelate (Ca‐Pim) samples by conventional injection molding (CIM) and oscillation shear injection molding (OSIM). The multilayer structures and morphologies of the samples were characterized by SEM, two‐dimensional X‐ray scattering and DSC. The mechanical properties and the microstructures of samples prepared by these two injection molding methods were compared. Compared with samples prepared by CIM, the stronger shear provided by OSIM induced the formation of a thicker layer of a shish‐kebab structure and a higher content of γ crystals, and dramatically suppressed the β‐nucleating effect of Ca‐Pim. The OSIM samples have more shish‐kebab structures and higher crystallinities than CIM samples and therefore the former exhibit better rigidity than the latter. The β crystals in the core layer and the thicker layer of shish‐kebab structure endow OSIM‐PPR/0.1 wt% Ca‐Pim with excellent impact toughness. © 2017 Society of Chemical Industry

Effects of MWCNTs Size on Melt Flow Properties of Polypropylene Composites During Capillary Extrusion

The influence of multi-walled carbon nanotubes (MWCNTs) size including average diameter and length-diameter ratio on the melt flow behavior of polypropylene composites were investigated by means of a capillary rheometer in a temperature ranging from 190 to 230 °C and under apparent shear rates varying from 100 to 4000 s−1. It was found that the melt shear flow approximately obeyed the power law; the values of the melt shear viscosity increased with an increase of the filler weight fraction, while decreased with increasing the average diameter of the MWCNTs; the dependence of the melt shear viscosity on temperature roughly obeyed the Arrhenius equation; the relationship between the melt shear viscosity and the MWCNTs weight fraction was almost linear; the sensitivity of the melt apparent shear viscosity to the MWCNTs weight fraction was weakened with increasing the MWCNTs average diameter.

Compatibility, steady and dynamic rheological behaviors of polylactide/poly(ethylene glycol) blends

ABSTRACTUnderstanding the rheological behavior of plasticized polylactide (PLA) contributed to the optimization of processing conditions and revealed the microstructure–property relationships. In this study, the morphological, thermal, steady and dynamic rheological properties of the PLA/poly(ethylene glycol) (PEG) blends were investigated by scanning electron microscope, differential scanning calorimeter, and capillary and dynamic rheometers, respectively. The results illuminated that the melt shear flow basically fitted the power law, whereas the temperature dependence of the apparent shear viscosity (ηa) or complex viscosity (η*) followed the Arrhenius equation. Both the neat PLA and PLA/PEG blends exhibited shear‐thinning behavior. Because the incorporation of PEG reduced the intermolecular forces and improved the mobility of the PLA chains, the ηa, η*, and storage and loss moduli of the PLA/PEG blends decreased. The PEG content (WPEG) ranged from 0 to 10 wt %, both ηa and η* decreased significantly. However, the decrements of ηa and η* became unremarkable when WPEG exceeded 10 wt %. The reason was attributed to the occurrence of phase separation, which resulted in the decrease in the plasticization and lubrication efficiencies. This study demonstrated that the addition of the right amount of PEG obviously improved the flow properties of PLA. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 42919.

Melt flow behavior of polypropylene composites filled with multi-walled carbon nanotubes during extrusion

Polypropylene (PP) composites filled with multi-walled carbon nanotubes (MWCNTs) were prepared using a twin-screw extruder. The melt flow properties of the composites were measured with a capillary rheometer in a temperature range from 180 to 230 °C and at various apparent shear rates varying from 100 to 4000 s−1. The results showed that the melt shear stress increased almost linearly while the melt shear viscosity decreased almost linearly with increasing shear rates in a bi-logarithmic coordinate system. The melt shear flow followed the power law relationship and the dependence of the melt shear viscosity on temperature obeyed the Arrhenius equation. The relationship between the melt shear viscosity and the MWCNT weight fraction was roughly linear under the investigated range of temperature or shear rate.

Melt Flow Behavior in Capillary Extrusion of Nanosized Calcium Carbonate Filled PLLA/PCL Bio-Composites

Nanosized calcium carbonate (nano-CaCO3) filled poly-l-lactide (PLLA)/polycaprolactone (PCL) bio-composites were prepared by using a twin-screw extruder. The melt flow behavior of the composites, including the entry pressure drop, melt shear flow curves and melt shear viscosity were measured through a capillary rheometer operated at a temperature range of 170–200 °C and shear rates varying from 50 to 103 s−1. The melt shear flow roughly followed the power law, while the effect of temperature on the melt shear viscosity might be estimated by using the Arrhenius equation. Moreover, the relationship between the PCL weight fraction and the melt shear viscosity for the PLLA/PCL/nano-CaCO3 composite was described by a quadratic equation.

Morphology control of nanofillers in poly (phenylene sulfide): A novel method to realize the exfoliation of nanoclay by SiO2 via melt shear flow

We for the first time report a novel method to achieve the morphology control of two kinds of dimensional different nanofillers, the platelike nanoclay and globelike SiO2, by using their “filler to filler” interaction in poly (phenylene sulfide) (PPS). The strong interaction between layered nanoclay and rigid SiO2 is obtained by their different response to shear flow in PPS melt processing. As a result, the exfoliation structure of nanoclay and well-dispersed nano-SiO2 are realized simultaneously. With this successful morphology control, the reinforcement effect of nanofillers in PPS is improved with very little addition. Moreover, with the restriction of exfoliated clay and nano-SiO2 particles, the mobility of PPS molecular chains is confined, leading to the significant change in crystalline behaviors of PPS.

Melt flow behavior in capillary extrusion of nanosized calcium carbonate‐filled poly(L‐lactic acid) biocomposites

AbstractNanosized calcium carbonate (nano‐CaCO3)‐filled poly‐L‐lactide (PLLA) biocomposites were compounded by using a twin‐screw extruder. The melt flow behavior of the composites, including their entry pressure drop, melt shear flow curves, and melt shear viscosity were measured through a capillary rheometer operated at a temperature range of 170–200°C and shear rates of 50–103 s−1. The entry pressure drop showed a nonlinear increase with increasing shear stress and reached a minimum for the filler weight fraction of 2% owing to the “bearing effect” of the nanometer particles in the polymer matrix melt. The melt shear flow roughly followed the power law, while the effect of temperature on the melt shear viscosity was estimated by using the Arrhenius equation. Hence, adding a small amount of nano‐CaCO3 into the PLLA could improve the melt flow behavior of the composite. POLYM. ENG. SCI., 52:1839–1844, 2012. © 2012 Society of Plastics Engineers

Effects of melt structure on shear-induced β-cylindrites of isotactic polypropylene

The effects of melt structure and shear flow on the polymorphic nature of β-cylindrites were investigated by means of wide angle X-ray diffraction (WAXD), small angle X-ray scattering (SAXS), polarized light microscopy (PLM), differential scanning calorimeter (DSC), and Scanning Electron Microscope (SEM). The temperature-resolved SAXS/WAXD experiments indicate that the NMP (near melting point) melting process (the annealing temperature between Tm “the nominal melting temperatures” and Tm0 “the equilibrium melting temperature”) erases the polymer crystalline structure of unit lattice, however, the lamellar structures of iPP can survive in this melt for long time, even annealing (partially melting) temperature above the Tm. We call this incomplete relaxed melt (include survived lamellar structures) as “ordered melt”. The observations from SAXS experiments of ordered melt suggest that between 167 and 180 °C, the long period (L) increases from 29.2 to 48.9 nm (Strobl method) and the lamellar thickness (dc) increases from 9.2 to 12.9 nm with increasing Tm∗. The long period and lamellar thickness changed slightly with increasing melting time. In order to study the effect of ordered structures in NMP melt on crystals structure after shear flow, the shear-induced specimens were prepared by extruding the near melting point (NMP) ordered melt of iPP through capillary die. It was found that, even only very low shear stress (σw = 0.020 MPa) have been applied to ordered melt, the shear-induced β-cylindrites can be observed. Length and number of the β-cylindrites decreases with increasing temperature of ordered melt (Tm∗ = 177–190 °C), and the content of β-iPP remained almost invariant when Tm∗ was set from 177 to 180 °C, however, as Tm∗ was above 180 °C, the β-iPP content obviously decreased. According to the results of shear-induced β-cylindrites from ordered melt, here we proposed the formation process of β-cylindrites, it is suggested that the survived lamellar structures may remain in the NMP ordered melt which can act as shear-precursor during the course of recooling and initiate the shear-induced crystallization. The structures (the size and density of survived lamellar structures) of ordered melt strongly influence by partially melting temperature.

Melt flow behavior in capillary extrusion of nanometer calcium carbonate filled PCL bio-composites

Nanosized calcium carbonate (nano-CaCO3) filled polycaprolactone (PCL) bio-composites were prepared by using a twin-screw extruder. The melt flow behavior of the composites, including the entry pressure drop, melt shear flow curves and melt shear viscosity, were measured through a capillary rheometer operated in a temperature range of 170∼200 °C and shear rates varying from 50 to 103 s−1. The entry pressure drop showed a non-linear increase with increasing shear stress when the filler weight fraction was less than 3%, while it decreased slightly with an increase of shear stress at a filler weight fraction of 4%. The melt shear flow roughly followed a power law, while the effect of temperature on the melt shear viscosity was estimated by using the Arrhenius equation. Moreover, the influence of the nano-CaCO3 on the melt shear viscosity of the PCL composite was not significant at low filler levels.

Melt shear viscosity of PP/Al(OH)3/Mg(OH)2 flame retardant composites at high extrusion rates

AbstractThe melt apparent shear viscosity (ηa) of 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 to 2 × 103 s−1, to identify the effects of the filler particle content and size on the melt viscosity. The results showed that the melt shear flow of the composites obeyed the power law and presented pseudoplastic behavior. The dependence of ηa on temperature was consistent with the Arrhenius equation. The sensitivity of ηa for the composite melts to temperature was greater than that of the unfilled PP, and weakened with increasing apparent shear rate. The ηa increased linearly with an increase of the weigh fraction of the flame retardant, especially in the low apparent shear rate region. The ηa of the composites decreased slightly with an increase of particle size of flame retardant. Moreover, the variation for the ηa with particle size of flame retardant was much less than with apparent shear rate under these test conditions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Studies on melt flow properties during capillary extrusion of PP/Al(OH) 3/Mg(OH) 2 flame retardant composites

The apparent melt shear viscosity of polypropylene (PP) composites filled with aluminium hydroxide (Al(OH) 3) and magnesium hydroxide (Mg(OH) 2) was measured by means of a melt flow rate instrument under experimental conditions of temperature ranging from 170 to 195 °C and load varying from 2.16 to 12.5 kg, to identify the effects of particle size and content. The results showed that the melt shear flow of the composites obeyed the power law under the experimental conditions, the dependence of the melt apparent shear viscosity ( η a) on temperature was consistent with the Arrhenius equation, and the sensitivity of the η a for the composite melts to temperature increased with addition of flame retardant. The η a of the composites decreased with increasing apparent shear rate. The η a increased with an increase of the content of flame retardant, but this rate of increase decreased with a rise of temperature or load. When the particle size of flame retardant was smaller than 5 μm, the η a of the composites increased with increase of particle size of flame retardant, and then reduced with a further increase of particle size of flame retardant.

Melt Rheology during Extrusion of Polypropylene Composites Filled with Diatomite Particles

The melt volume flow rate (MVR) is an important parameter for characterization of flow properties of polymer. The MVR of the polypropylene composites filled with diatomite particles was measured by means of a MVR instrument to investigate the effects of the filler content, particle size and extrusion conditions (temperature 210—230°C, load 5.0—12.5 kg) on the melt flow properties of the composite systems. The results showed that the MVR of the composites increased as a quadratic function with the increase of load, while decreased nonlinearly with the increase of filler particle diameter. The MVR was a linear function of temperature. The MVR decreased quickly when the filler volume fraction (φf) was <5%, and then reduced slightly with an increase of φf. In addition, the melt shear flow obeyed roughly power law under the experimental conditions, and the influence of particle size on the temperature sensitivity of the melt shear viscosity is insignificant at low filler concentration.

Effects of Extrusion Rate, Temperature, and Die Diameter on Melt Flow Properties During Capillary Flow of Low-Density-Polyethylene

The melt flow properties of a low-density polyethylene were measured at test temperatures varying from 140 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, shear rate, and die diameter) on the melt flow behavior in the present paper. The results showed that the entry pressure drop increased nonlinearly with an increase of the piston speeds, and it decreased with an addition of the die diameter. The melt shear flow obeyed roughly the power law and the melt shear viscosity decreased approximately linearly with an increase of the true shear rates in a bi-logarithmic coordinate system. The dependence of the melt shear viscosity on temperature accorded approximately the Arrhenius expression. Under these experimental conditions, the entrance pressure drop increases as an exponential function with an addition of the channel contraction ratio.

Effects of Particle Size and Shear Rate on Melt Flow Properties During Capillary Extrusion of Glass Bead-Filled LDPE Composites

Abstract The melt flow properties of a low-density polyethylene (LDPE) filled with glass brads (GB) were measured at 150°C by means a capillary rheometer to identify the effects of the particle size and extrusion rate on the melt flow behavior in the present paper. The volume fraction of the glass beads was 8.4 %. The surface of the particles had been treated with a silane-coupling agent and the diameter range was from 4 μm to 180 μm. The results showed that the entry pressure drop was a component function of apparent shear rate and the melt shear flow approximately obeyed the power law. The melt shear viscosity decreased roughly linearly with an increase of the wall shear stress, and it varied slightly with an addition of the bead diameter under various shear stress levels. Namely, the influence of the bead size on the melt flow properties of the LDPE/GB composites was insignificant at lower concentration of the fine spheres. This might be attributed to the relatively weak interfacial adhesion between the particles and the matrix due to the smooth spherical surface of the beads.

Phase morphology and toughening mechanism of polyamide 6/EPDM- g-MA blends obtained via dynamic packing injection molding

One of the most important findings in polymer-toughening is known as the critical matrix ligament thickness ( τ c) theory, which is directly related to both rubber concentration and average size of particles. All these studies assume that rubber particles are spherical and randomly distributed in the matrix. Rubber particles may be stretched and oriented along the shear flow direction in real processing. In this paper the effect of stretched and oriented rubber particles on the impact strength of PA6/EPDM- g-MA blends have been studied via dynamic packing injection molding (DPIM). The impact strength of specimens obtained by DPIM was found substantially increase at all the blends investigated, compared with the one obtained via conventional injection molding. Particularly, more than 30 kJ m −2 increase of the impact strength was observed for specimens with a higher rubber content (more than 15 wt%). SEM results showed a remarkably decrease of rubber particle size and more uniform dispersion of the dynamic molded specimens. This can be attributed to the shear induced reaction at the interface between polyamide 6 and EPDM- g-MA during the packing stage. The rubber particles were found stretched along the melt shear flow direction when it is content above 15 wt%. A master curve can be also constructed by plotting the impact strength versus the inter-particle distance, indicating that Wu's criterion still works for blends with stretched and oriented rubber particles when the crack propagation direction is perpendicular to the orientation direction of rubber particles. The observed higher impact strength in dynamic specimens could be due to, in part, the enhanced flexural stiffness, which will absorb more energy during impact process when the fracture of IZOD bars is incomplete, but more importantly due to the existence of the stretched and oriented rubber particles, which are more efficient in slowing the velocity of crack propagation and thus cause higher impact resistance when the fracture propagation direction is perpendicular to the rubber oriented direction.

Melt Flow Properties During Capillary Extrusion of Linear Low-Density Polyethylene

The melt flow properties of a linear low-density polyethylene (LLDPE) were measured by means of a capillary rheometer under the experimental conditions of temperatures from 220° to 260°C and apparent shear rates varying from 12 to 120 s−1. The end pressure drop (ΔPend) was determined by employing the Bagley's plotting method. The results showed that ΔPend increased nonlinearly with increasing shear stress. The end pressure fluctuation phenomenon was observed at lower shear stress level, and several plateau regions were generated in the end pressure drop-shear stress curves, suggesting onset of the wall-slip phenomenon during die extrusion of the resin melt. The critical shear stress with onset end pressure fluctuation phenomenon increased with a rise of temperature. Furthermore, the melt shear flow did not strictly obey the power law. The melt shear viscosity decreased nonlinearly with increasing shear stress and with a rise of temperature, whereas the dependence of the melt shear viscosity on the test temperature accorded with a formula similar to the Arrhenius expression.