Melt Processing Conditions Research Articles

Effect of melt‐processing conditions on the electrical conductivity and microwave absorbing properties of composites based on clean scrap poly(vinylidene fluoride/ethylene vinyl acetate copolymer and graphene nanoplatelets

AbstractClean scrap polyvinylidene fluoride (rPVDF) from industrial reject was compounded with ethylene vinyl acetate (EVA) copolymer and graphene nanoplatelets (GNP) to produce low cost and scalable conductive composites. The effect of the melt processing conditions (temperature, time, and rotor speed) on the electrical conductivity and microwave absorbing (MWA) properties was investigated. All systems presented co‐continuous morphology indicated by scanning electron microscopy (SEM) and selective extraction experiments. The preferential localization of GNP in the EVA phase was evidenced by selective extraction and thermogravimetric analysis (TGA). Higher conductivity value was observed for the composite processed at 210°C for 3 min at a rotor speed of 200 rpm. The MWA performance of monolayer and bilayer composite structures with 2 mm thickness was investigated in terms of minimum reflection loss (RL) and effective absorption bandwidth (EAB). The bilayer system provided the best MWA response with RL = − 43.1 dB (>99.99% of EM attenuation) when prepared at 190°C for 3 min at a rotor speed of 200 rpm. The ecological and environmental importance of finding new applications for plastic waste, and the low cost of the materials and processing make this composite an interesting candidate for MWA purpose.Highlights Promising application of clean scrap polyvinylidene fluoride (PVDF) in microwave absorbing materials; Conductivity and absorbing performance are affected by processing conditions; Co‐continuous structure of rPVDF/EVA blend influenced by graphene nanoplatelets (GNP); Selective localization of GNP in EVA phase; Outstanding microwave absorption properties achieved with bi‐layer structure.

Carbon fibers from bitumen-derived asphaltenes: Strategies for optimizing melt spinnability and improving mechanical properties

The demand for low-cost carbon fibers with exceptional mechanical properties continues to grow across various industries. Bitumen-derived asphaltenes have emerged as a promising alternative to polyacrylonitrile (PAN), yet asphaltenes are a complex mixture of compounds, and the fundamental understanding of which asphaltenes are melt spinnable is not clearly understood. In this study, we utilized three distinct types of asphaltenes, each exhibiting notably distinct thermal softening temperatures (Ts) and aromaticity. The optimal melt processing conditions of asphaltenes were determined by dynamic rheology tests. Moreover, we introduced a novel strategy to facilitate the melt spinning of non-spinnable samples by preparing 100 % asphaltene blends with a low Ts asphaltene at different weight fractions. By this means, we achieved continuous melt spinning of precursor fibers. After careful selection of the stabilization and carbonization conditions, uniform carbon fibers were obtained from asphaltenes, which had the highest tensile strength (∼570 MPa) and modulus (∼60 GPa) values, comparable to isotropic pitch-based carbon fibers. Further post-processing of the as-spun fiber resulted in a significant increase in tensile properties, ∼1.1 GPa for strength and ∼91 GPa for modulus. Overall, this study identified spinnable asphaltene precursor characteristics and fiber post-processing methods for achieving low-cost, high-quality carbon fibers from asphaltenes.

Polyphenylene sulfide for high-rate composite manufacturing: Impacts of processing parameters on chain architecture, rheology, and crystallinity

High performance semi-crystalline thermoplastics necessitate high temperature processing to form useful structures, but the effects of repeated exposure to these extreme environments on key polymer properties are not well understood. This work investigates the influence of degradation-driven structural changes resulting from exposure to standard melt processing conditions in oxygen rich environments on the rheological properties, crystallization behavior, and crystal structure of polyphenylene sulfide (PPS). Melt processing temperatures (300°C, 320°C, and 340°C) and hold times (up to 60 min) are varied to probe the effects of thermal exposure on polymer properties. Extended melt-state exposure causes an increase in PPS melt viscosity due to the formation of complex branched/crosslinked structures where increasing temperature causes this process to occur more rapidly. Dynamic isothermal rheology of PPS displays a 70x increase in the complex viscosity at 10 rad/s after 60 minutes at 340°C. Frequency sweep rheological experiments reveal a notable deviation from linearity (terminal slope = 2) with slopes as low as 0.14 after thermal exposure. Stress recovery experiments indicate thermally processed PPS requires more time to relax stress under an applied strain. Imperfections along the polymer backbone in the form of branches/crosslinks decrease overall crystallinity and reduce lamellar thickness, with no changes to the unit cell structure. For semi-crystalline high performance thermoplastic matrix composites relying on high degrees of crystallinity to provide solvent resistance and strength, these results have serious implications for the need to tightly control melt processing steps and understand the final material state. Furthermore, viscoelastic properties of post-processed PPS polymers should be considered for recycling and reuse strategies.

Dynamic Properties of Di(cyclopentadienecarboxylic Acid) Dimethyl Esters.

Di(cyclopentadienecarboxylic acid) dimethyl ester (DCPDME) is a potential dynamic covalent system. When such molecules are used as dynamic crosslinkers in polymers, understanding the reversibility of cyclopentadiene dimerization is crucial to determine optimal melt processing conditions. To this end, we synthesized DCPDME, which consists of three regioisomers with different physicochemical properties, which were investigated by isolating them and further characterizing them using 1H NMR, FTIR and DSC. There have been many attempts to improve the synthesis process to increase the reaction yield and purity of isomer 3, and this goal remains a challenge today. In this work, we show that pure isomers 1 and 2 irreversibly convert to the more stable DCPDME isomer 3 at temperatures between 120 and 140 °C in N2. This shows that isolation of the pure isomer 3 from the DCPDME isomer mixture is not necessary. The DCPDME isomer 3 is reversibly cleaved to the monomeric cyclopentadienecarboxylic acid methyl ester (CPME), as confirmed with GC-MS and the resulting mass spectrum. The conversion of DCPDME isomers 1 and 2 to isomer 3 was confirmed by heating the synthesized mixture of DCPDME isomers at 135 °C for 5 min in N2, producing an almost pure isomer 3 which increased its synthesis yield by 35%.

Hot melt processing strategy to modify eucommia ulmoides gum by click reaction

AbstractUnder the condition of hot melt processing, the modification of eucommia ulmoides gum (EUG) by mercapto compounds, n‐Octyl mercaptan (OM), and isooctyl mercaptoacetate (IOMA) was realized by the click reaction of thiol‐ene. The 1H‐NMR results confirmed that the grafting rate of mercapto compounds was 2.28%–5.30% and 1.68%–3.85% when OM and IOMA reacted with EUG in thiol‐ene click reaction under hot melt processing conditions. The DSC results showed that the crystallinity of EUG‐OM was higher than that of EUG when the amount of grafted compound OM ranged from 0.86 to 1.39 mol%. When IOMA‐modified EUG products change from partially crystalline to amorphous, the critical value of IOMA is 2.15 mol%. With the grafting rate of mercapto compounds increasing, T10, T50, and T90 of mercapto modified EUG has decreased to some extent, the ML, MH, and the difference of MH and ML also decrease at the same time. Compared with unmodified EUG vulcanizate, the hardness and tensile strength of a mercapto compound modified EUG vulcanizate decrease, while the elongation at break significantly increases. The stress‐strain curve of a mercapto compound modified EUG vulcanizate confirmed the transition from rigid crystalline materials to elastomers. This property change should be attributed to the plasticizing effect caused by the crystallization property of the modified EUG. The chemical modification of EUG under solvent‐free conditions is environmentally friendly, and the product is uniform, which may be of great significance for practical industrialization.

Optimization of Cellulose Nanofiber Loading and Processing Conditions during Melt Extrusion of Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) Bionanocomposites.

This present study optimized the cellulose nanofiber (CNF) loading and melt processing conditions of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) P(HB-co-11% HHx) bionanocomposite fabrication in twin screw extruder by using the response surface methodology (RSM). A face-centered central composite design (CCD) was applied to statistically specify the important parameters, namely CNF loading (1-9 wt.%), rotational speed (20-60 rpm), and temperature (135-175 °C), on the mechanical properties of the P(HB-co-11% HHx) bionanocomposites. The developed model reveals that CNF loading and temperature were the dominating parameters that enhanced the mechanical properties of the P(HB-co-11% HHx)/CNF bionanocomposites. The optimal CNF loading, rotational speed, and temperature for P(HB-co-11% HHx) bionanocomposite fabrication were 1.5 wt.%, 20 rpm, and 160 °C, respectively. The predicted tensile strength, flexural strength, and flexural modulus for these optimum conditions were 22.96 MPa, 33.91 MPa, and 1.02 GPa, respectively, with maximum desirability of 0.929. P(HB-co-11% HHx)/CNF bionanocomposites exhibited improved tensile strength, flexural strength, and modulus by 17, 6, and 20%, respectively, as compared to the neat P(HB-co-11% HHx). While the crystallinity of P(HB-co-11% HHx)/CNF bionanocomposites increased by 17% under the optimal fabrication conditions, the thermal stability of the P(HB-co-11% HHx)/CNF bionanocomposites was not significantly different from neat P(HB-co-11% HHx).

Curly morphology of β’-crystals of poly(butylene-2,6-naphthalate)

Crystallization of PBN at high temperature leads to growth of highly non-isometric β’-crystals, with their long and short dimensions being several µm and 10–20 nm, respectively. In the needle-like or lamellar crystals, molecular segments/stems are oriented parallel to their short dimension, as concluded from polarized-light optical microscopy (POM). In the early stage, the growth of β’-crystals is straight while in the later stages, when exceeding a critical length, distinct bending and circular growth occurs. These features cause an unusual appearance of the semicrystalline structure when viewed by POM. The spherulitic growth is uneven in the various directions of space, the spherulite surface appears frayed due to missing space-filling and reduced branching, and the finally curly crystal morphology yields a spotty decoration. The analysis of the morphology of β’-crystals of PBN is expected yielding an improved understanding of structure–property-relations, as these crystals may form at specific melt-processing conditions.

Impact of Melt Processing Conditions on the Degradation of Polylactic Acid.

To reduce the degradation of polylactic acid (PLA) during processing, which reduces the molecular weight of PLA and its properties, prior studies have recommended low processing temperatures. In contrast, this work investigated the impact of four factors affecting shear heating (extruder type, screw configuration, screw speed, and feed rate) on the degradation of PLA. The polylactic acid was processed using a quad screw extruder (QSE) and a comparable twin screw extruder (TSE), two screw configurations, higher screw speeds, and several feed rates. The processed PLA was characterized by its rheological, thermal, and material composition properties. In both screw configurations, the QSE (which has a greater free volume) produced 3–4 °C increases in melt temperature when the screw speed was increased from 400 rpm to 1000 rpm, whereas the temperature rise was 24–25 °C in the TSE. PLA processed at low screw speeds, however, exhibited greater reductions in molecular weight—i.e., 9% in the QSE and 7% in the TSE. Screw configurations with fewer kneading blocks, and higher feed rates in the QSE, reduced degradation of PLA. At lower processing temperatures, it was found that an increase in melt temperature and shear rate did not significantly contribute to the degradation of PLA. Reducing the residence time during processing minimized the degradation of PLA in a molten state.

The Use of Branching Agents in the Synthesis of PBAT.

Biodegradable polyesters represent an advanced alternative to polyolefin plastics in various applications. Polybutylene adipate terephthalate (PBAT) can compete with polyolefins in terms of their mechanical characteristics and melt processing conditions. The properties of PBAT depend on the molecular weight, dispersity, and architecture of the copolymer. Long-chain branching (LCB) of the PBAT backbone is an efficient method for the improvement of the copolymer characteristics. In the present work, we studied branching agents (BAs) 1–7 of different structures in the two-stage polycondensation of 1,4-butanediol, dimethyl terephthalate, and adipic acid and investigated the composition and melt rheology of the copolymers. According to the results of the research, 1,1,1-tris(hydroxymethyl)ethane 2 and 3-hydroxy-2-(hydroxymethyl)-2-methylpropanoic acid 5 outperformed glycerol 1 as BAs in terms of shear thinning behavior and viscoelasticity.

Extrusion and Injection Molding of Poly(3-Hydroxybutyrate-co-3-Hydroxyhexanoate) (PHBHHx): Influence of Processing Conditions on Mechanical Properties and Microstructure.

Biobased and biodegradable polyhydroxyalkanoates (PHAs) have great potential as sustainable packaging materials. However, improvements in their processing and mechanical properties are necessary. In this work, the influence of melt processing conditions on the mechanical properties and microstructure of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) is examined using a full factorial design of experiments (DoE) approach. We have found that strict control over processing temperature, mold temperature, screw speed, and cooling time leads to highly increased elongation at break values, mainly under influence of higher mold temperatures at 80 °C. Increased elongation of the moldings is attributed to relaxation and decreased orientation of the polymer chains together with a homogeneous microstructure at slower cooling rates. Based on the statistically substantiated models to determine the optimal processing conditions and their effects on microstructure variation and mechanical properties of PHBHHx samples, we conclude that optimizing the processing of this biopolymer can improve the applicability of the material and extend its scope in the realm of flexible packaging applications.

Durability of nanolayer Ti–Al–O–N hard coatings under simulated polycarbonate melt processing conditions

To protect forming tools and components from abrasion, adhesion and corrosion, the application of thin hard coatings by physical vapor deposition is state-of-the-art. The use of a hybrid coating technology, consisting of high power pulse magnetron sputtering (HPPMS) and direct current Magnetron Sputtering (dcMS), allows a combination of the advantageous properties of both. HPPMS coatings for examples show a dense morphology, high hardness and smooth surface. Using dcMS, higher deposition rates can be achieved, resulting in a higher economic efficiently. Within the scope of this work, a novel multilayer coating concept of the material system Ti–Al–O–N was developed. The coatings were deposited using an industrial coating unit. Cold work steel X42Cr13 was used as substrate material. The coatings consist of a metallic titanium bond coat and a nitride TiN/AlN nanolayer as an interlayer. The nanolayer coating architecture leads to a dense, compact and fine crystalline morphology with smooth surfaces. Finally, an oxynitride toplayer with two different oxygen contents was applied. In order to investigate the coating durability relevant for polycarbonate melt processing, electrochemical impedance spectroscopy and linear sweep voltammetry were carried out in borate buffer, NaClO4 and benzoic acid electrolyte. An increased oxygen content in the oxynitride toplayer led to a decreased interfacial current density.

The Effect of SEBS/Halloysite Masterbatch Obtained in Different Extrusion Conditions on the Properties of Hybrid Polypropylene/Glass Fiber Composites for Auto Parts.

Masterbatches from a linear poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) and halloysite nanotubes (HNT-QM) were obtained in different conditions of temperature and shear using two co-rotating twin-screw extruders. The influence of screw configuration and melt processing conditions on the morpho-structural, thermal and mechanical properties of masterbatches at macro and nanoscale was studied. A good dispersion of halloysite nanotubes and better thermal stability and tensile and nanomechanical properties were obtained at a lower temperature profile and higher screw speed. The effect of masterbatches, the best and worst alternatives, on the properties of a polypropylene (PP)–glass fiber (GF) composite was also evaluated. Double hardness, tensile strength and modulus and four times higher impact strength were obtained for PP/GF composites containing masterbatches compared to pristine PP. However, the masterbatch with the best properties led further to enhanced mechanical properties of the PP/GF composite. A clear difference between the effects of the two masterbatches was obtained by nanoindentation and nanoscratch tests. These analyses proved to be useful for the design of polymer composites for automotive parts, such as bumpers or door panels. This study demonstrated that setting-up the correct processing conditions is very important to obtain the desired properties for automotive applications.

The 3D/4D Printing Defects and Their Influence on the Functional Behavior of the Achieved Items from Renewable Compounds. (I)

The paper is part of a series in which the influence of the manufacturing defects on the functional behavior in biodegradation medium of some items obtained, both by 3D printing and by classical procedure (pressing), from an originaly renwable matrials based on polylatic acid will be presented. The first results regarding the correlation of the defects appeared at manufacturing into plates with the biodegradation behavior in an Aspergillus Niger(A.niger) medium, studied by SEM microscopy, are presented. These results demonstrated that the development of the A. Niger microorganism is related manly to the defects appeared at the melt processing of renewable polymeric material into finished product. A notable role in controlling the appearance of the manufacturing defects belongs both to the melt rheological properties which are responsible for the continuous or discontinuous flow and to the technical performance of the used equipement, 3D printer or classic hydraulic press. If the polymeric material melt has too high viscosity than the continuous flow is not possible and so the overlapped melt fronts are created which generate the voids formation, sometimes joined by small nano and/or micrometric channels. The rheological properties of the melts depend both on the material formulation and the seleted melt processing conditions.

Process-Property Relationships for Melt-Spun Poly(lactic acid) Yarn.

Poly(lactic acid) (PLA) is an attractive biomaterial due to its biocompatibility, biodegradability, and fiber-forming ability. However, the polymer is highly susceptible to both hydrolytic and thermal degradation during processing. Melt processing conditions typically involve high temperature and shear, whereas to prevent premature degradation, PLA needs to be processed under the mildest conditions that still yield the desired yarn properties. Thus, there is a need to determine the optimum processing conditions to achieve the desired properties of extruded PLA yarn. This study focuses on the effect of melt-spinning process parameters on the mechanical and physicochemical properties of the resulting PLA yarn and to derive their process–property relationships. The study compares the effect of process parameters like melt temperature, throughput through the spinneret, take-up speed at the wind-up roller, draw ratio, and drawing temperature on the yarn properties such as the yarn size (linear mass density), tenacity, elongation at break, crystallinity, and molecular weight. Depending on the combination of process parameters, the resulting PLA yarn had a yarn size ranging from 6.2 to 101.6 tex, tenacity ranging from 2.5 to 34.1 gf/tex, elongation at break ranging from 4 to 480%, and degree of crystallinity ranging from 14.6 to 62.2%. Certain combinations of processing parameters resulted in higher process-induced degradation, as evident from the reduction in molecular weight, ranging from 7.6% reduction to 20.5% reduction. Findings from this study increase our understanding on how different process parameters can be utilized to achieve the desired properties of the as-spun and drawn PLA yarn while controlling process-induced premature degradation.

In situ dual crosslinking strategy to improve the physico-chemical properties of thermoplastic starch

This study is focused on enhancing the stability of mechanical and chemical properties of thermoplastic starch (TPS) by dual crosslinking strategy through melt processing conditions. The dually crosslinked TPS was prepared by in situ reaction of starch, glycerol, and epichlorohydrin (ECH), resulting in both noncovalent and covalent bond formation. The TPS was characterized by tensile testing, dynamic mechanical analysis (DMTA), rheology, and solubility in water. A substantial increase in tensile strength, Young's modulus, insoluble portion, and stability in water for dually crosslinked TPS was observed in comparison with conventional TPS. The rheology results indicated that the ECH induced the formation of 3D networks and significantly limited the chain mobility of the melted TPS, resulting in an extended relaxation process, which was also verified by DMTA. The suggested strategy avoids any chemical modification pretreatment of starch for introducing covalent bonds into TPS before one-step mixing using the melt processing technique.

Viscoelastic Behavior and Thermal Stability of Poly(Lactic Acid) Bio‐Composite Filled with Micro‐Graphite

AbstractPoly(lactic acid) or PLA bio‐composite is prepared by filling with micro‐graphite via solution blending. The micro‐graphite loading is varied from 0–15 wt%. The objectives of this research are to investigate the influence of micro‐graphite loading on PLA bio‐composite, on the viscoelasticity and thermal stability. The viscoelasticity behavior exhibits a considerable dependence on the melt properties of the PLA/micro‐graphite bio‐composites on the percentage micro‐graphite. The complex viscosity |η*|, storage modulus (G’), and loss modulus (G″) tend to improve with increasing micro‐graphite loading. Thermogravimetric analyses indicate that the micro‐graphite slightly stabilizes the PLA. The decomposition reaction is shifted to a higher temperature in the range 7–9 °C. This reaction leads to the loss of volatile byproducts, which occur at temperatures higher than 310 °C. It means far from the melt processing conditions. The differential scanning calorimetry thermogram shows that the glass transition temperature (Tg) and the melting temperature are close to that of neat PLA with changes only around 2–4 °C.

Identifying Melt Processing Conditions for a Polyacrylonitrile Copolymer Plasticized with Water, Acetonitrile and their Mixtures

Abstract This paper discusses the feasibility of the melt spinning process of polyacrylonitrile (PAN) copolymer (acrylonitrile/methylacrylate 95.6/4.4 mol% ratio) plasticized with H2O acetonitrile (ACN) and their mixture. The objective is to use water only as a plasticizer to melt spin PAN under specific conditions (composition, temperature etc.). The melting point and rheological measurements have been conducted by differential scanning calorimetry (DSC) and a modified capillary rheometer, respectively, for this plasticized system. The DSC results show that the melting point of the PAN copolymer can be reduced from over 300°C to below 180°C, which is the temperature for the onset of degradation (cyclization and crosslinking) of PAN. Rheological results show that the PAN copolymer can be extruded with a reasonable viscosity at 15 to 20°C above its melting point, and also the stability and viscosity are strongly dependent on temperature and the plasticizer type and content. Furthermore, the results indicate that the most appropriate condition for PAN melt spinning is for the PAN/H2O mixture of 70/30 wt% ratio at a temperature of 180°C for which the copolymer sample can remain stable without significant degradation for around 120 min and maintain its viscosity in the range of around 600 Pa s.

Solidification processing of scrap Al-alloys containing high levels of Fe

The accumulation of iron in molten aluminium is one of the main concerns for the recycling and casting industries because it leads to the formation of undesirable Fe-rich intermetallic compounds which are detrimental to mechanical properties. Many methods have been developed in the past to reduce the iron accumulated in molten aluminium scrap, but they all suffer from poor efficiency. Hence, a more efficient method is urgently needed to mitigate the negative effect of high iron levels in the melt, thereby avoiding downgrading secondary aluminium to low quality products or the dilution with expensive primary aluminium. This contribution provides a study of the Fe-rich intermetallic compounds developed in aluminium casting alloys with high levels of Fe as a function of melt processing conditions. Results show that the formation of the Fe-compounds is not only dependent on the cooling rate and holding time before solidification, but more on the initial melt treatment as it enhances the nucleation and growth of the Fe-phases. Elemental addition of Mn leads to the formation of large and compact intermetallic particles, but at slow rate. Physical melt treatment by intensive high shearing produces a much faster nucleation and results in a fine dispersion of smaller iron containing intermetallic particles. The latter could be used either to increase the tolerance to iron contamination or to facilitate the iron removal process, providing huge benefits for the recyclability of scrap aluminium alloys as it would allow the transformation of low-grade feedstock into a low cost and small carbon footprint material for high quality castings.

The influence of dynamic rheological properties on carbon fiber-reinforced polyetherimide for large-scale extrusion-based additive manufacturing

Printing high-performance thermoplastics on large scale extrusion-based additive manufacturing platforms requires stability over a range of processing conditions. However, studies on the melt dynamics and processing conditions of these thermoplastics in big area additive manufacturing (BAAM) are limited. This study characterizes the dynamic rheological behavior of polyetherimide (PEI), a high-performance thermoplastic, as well as carbon fiber (CF)-reinforced PEI composites as a BAAM feedstock material. The viscoelastic properties, such as the storage and loss moduli and complex viscosity, are investigated in relation to the BAAM extrusion process. The results show that CF-PEI composites behave like a viscous liquid during BAAM extrusion. The addition of CF to PEI enhances the shear thinning effect and significantly increases the complex viscosity (2.5× increase for 20% CF, and 3× for 30% CF). The increased viscosity increases the torque on the extruder, which may be alleviated by increasing the material processing temperature.

Determination of melt processing conditions for high performance amorphous thermoplastics for large format additive manufacturing

As the application space for large-scale 3D printed components continues to grow, it is necessary to identify appropriate processing conditions for high-performance thermoplastics on large format Additive Manufacturing (LFAM) systems. This study compares the rheological behavior of a high-performance thermoplastic, polyphenylsulfone (PPSU), with that of a commonly used low-temperature polymer, acrylonitrile butadiene styrene (ABS), to identify suitable processing conditions for large format AM systems. The linear viscoelastic properties (complex viscosity, storage modulus, loss modulus, and tan delta) of these materials are evaluated as a function of temperature, angular frequency, and carbon fiber content. Over the range of frequencies of interest to LFAM (10–100 rad/s), ABS behaves more like an elastic solid whereas PPSU behaves more like a viscous liquid. The addition of 20–35% by weight of carbon fiber increased the shear thinning effect of both thermoplastics, showing a potential variation of 2–3 x over the range of expected LFAM extrusion shear rates (10–100 s−1).