Rheological study of mixing in molten polymers: 1-mixing of low viscous additives

A new mixing device has been designed and developed in order to investigate complex mixing situations encountered in polymer blends and formulations. This mixing device called here rheo-mixer has been adapted on a classical rheometer and calibrated in terms of shear/stress that both permanent and dynamic regimes may be quantitatively run. The ability of the mixer to bring interesting information about complex polymeric systems was demonstrated by following the process of incorporation of a miscible liquid or partially miscible into a high viscosity polymer. As examples, EVA/diethyl 2-hexyl phtalate, poly(ε-caprolactone)/ε-caprolactone, and EVA/ε-caprolactone systems were tested.It was demonstrated that the viscosity ratio is not the predominant parameter for mixing process control because the mixing is mainly controlled by the diffusion for these low viscosity ratio systems (λ<10⁻⁵) as miscible systems (EVA/DOP and PCL/ε-CL) and partially miscible systems (EVA/ε-CL) are concerned. Actually, the mixing efficiency of these fluids is poor because the shear migration diminishes the rate of mixing due to a decrease of the deformation in the high viscous media. The mixing by thick striation is only effective when the viscosity ratio becomes, by the diffusion process, typically higher than 10⁻³. Furthermore, the discussion based on the mutual diffusion coefficient agrees well with the experimental finding, at least qualitatively.     

Thermal processability and properties of highly filled poly(vinyl alcohol)/talc composite

Abstract

A highly filled PVA/talc composite was prepared through our invented thermal processing technology without using any coupling agent or compatibiliser. The results showed that compared with neat PVA, the melt temperature of the composite decreased and the degradation temperature increased, providing a big temperature window for thermal processing of PVA/talc composite. The composite melt exhibited shear thinning behaviour while its viscosity increased with increasing talc, still satisfied the requirement of thermal processing. The morphology analysis confirmed that talc was well dispersed in PVA, improving heat deflection temperature (HDT), tensile strength and modulus of PVA. When talc was 50 wt-%, the HDT, tensile strength and modulus of the composite were 115°C, 48 MPa, 1·23 GPa respectively, increased by 92, 16 and 150%, compared with PVA, and the elongation at break was 100% of the composite, confirming that the high filled PVA/talc composite was a novel PVA based material with excellent thermal and mechanical properties.     

Rheology and sedimentation velocity of alkaline suspensions of hematite particles at elevated temperature

This study aims to characterize the sedimentation velocity and the rheology of suspensions of hematite particles suspended in strongly alkaline media at 100 and 110 °C, as done for an alternative electrochemical process in development for iron production by direct electrode reduction of hematite. Considering the medium used in the process, i.e. 12% (v/v) suspension of hematite particles in 50% sodium hydroxide aqueous, the sedimentation velocity of hematite particle at 110 °C is 0.010 mm/s, which is very slow because the average size of the solid particles is around 10 μm and the significant collisions and interactions occuring between the particles in the concentrated suspension. Two geometries were used to characterize the rheological behavior of the apparent viscosity of the suspension of 12% (v/v) (i.e. 33 wt%) at 100 °C: a conventional Couette geometry and a helical ribbon mixer. The suspension was found shear thinning in the range of shear rate studied. The rheological behavior of the suspension can be described by a power-law model. The apparent viscosity of the hematite suspension estimated at a shear rate between 0.5 and 10 s⁻¹ is between 100 and 20 mPa s for the two geometries. The apparent viscosity calculated from the terminal velocity of 10 μm particles is of the same order of magnitude of the results obtained with the two rheometer configurations. The effect of the particle concentration on the sedimentation velocity and viscosity of the hematite suspensions was also studied.     

Shear thickening fluids in protective applications: A review

A thorough and critical review on Shear Thickening Fluids (STFs) is presented based on a literature survey. The rheological properties of STFs are discussed considering many factors affecting shear thickening behavior and the use of STFs in protective systems is reviewed. The main focus of this review is multi-phase STFs, relatively new to the literature (in the last five years). Multi-phase STFs include a second phase in suspensions and the influences of this additional phase on rheological behavior and protective applications are discussed extensively. Based on this extended review, STF do benefit protective applications, but the major contribution is not driven by the shear thickening behavior. Rather, STFs are responsible for the increase in friction along fabrics and enhanced fiber/yarn coupling in fabric based protective systems. As a result, of these effects, the load transfer is spread over a wider area and penetration depth is lowered in an impacted structure.     

Rheological and optical properties of polypropylene filled with synthetic silicates and calcium carbonate

The rheology of PP filled with three different types of fillers, namely synthetic sodium aluminium silicate (SSAS), aluminium silicate (AS) and calcium carbonate (CaCO₃), at concentrations up to 40% was studied. Variation of shear and extensional viscosity was evaluated for all the compositions. When filler loading was less than 20%, the shear viscosity at low shear rates was less than that of virgin PP. Flow curves are described by the Ellis model. The onset of non-Newtonian shear thinning behaviour is related to parameter η₁₀/τ_1/2. Although fillers are white, they imparted a yellowish tone at lower loadings. At higher loadings, this yellowing effect was masked, yielding a lower yellowness index.     

Rheology of pulp fibre suspensions: A critical review

This paper reviews past studies on the measurement of rheological properties of pulp fibre suspensions. Such suspensions are complex fluids important in the manufacture of many pulp-fibre based products, such as communication papers, hygiene products, packaging, as well as other fibre-based materials. Pulp suspensions play a role in other biomass conversion processes as well. This review focuses on key properties of fibre suspensions, such as regimes of behaviour based on inter-fibre contact, apparent yield stress, apparent viscosity, and viscoelasticity. Difficulties encountered in measurement of these properties due to flow regime changes, heterogeneous mass distribution, and formation of depletion layers at solid boundaries is discussed and methods to overcome them are reviewed.     

Rheology to understand and optimize processibility, structures and properties of starch polymeric materials

This paper reviews the state of the art in the field of the rheology of starch polymers, including specially designed rheometric techniques and complex rheology as influenced by different conditions. In terms of rheometric techniques, off-line extruder-type capillary/slit rheometers are commonly used but subsequent changes during measurement often occur as starch structures are highly sensitive to thermomechanical treatment. An in-line rheometer set-up with a double-channel die incorporated to the processing extruder is a direct and effective method to minimize the processing history change at different testing shear rates. In addition, pre-shearing, multipass, and mixer-type rheometers are also suitable for starch polymers. The rheological behavior of starch polymeric materials can be greatly impacted by their formulation (botanical source, plasticizer and additive type and content, and the structure related to blend or composite) and processing conditions (temperature, mechanical energy, etc.). Starch polymer melts exhibit shear-thinning and extension-thinning behaviors, and shows strong elastic properties. A wide range of rheological models, considering formulation and processing conditions, have been reviewed for different multiphase systems. The rheological behavior can also be related to the compatibility (blends, composites), expansion/foaming properties, film blowing properties, etc. The significance of processing rheology of starch polymers lies in characterizing the complex melting and flow behaviors, characterizing the viscoelastic properties, determining optimal processing method and conditions, and better controlling the quality of the final products.     

Synthesis,characterization and rheological properties of three different microstructures of water-soluble polymers prepared by solution polymerization

Three different structures were synthesized via solution free radical polymerization. Polyacrylamides hydrophobically modified with small amounts of two different N′N-dialkylacrylamides [N,N-dihexylacrylamide (DHAM) and N,N-dioctylacrylamide (DOAM)] and two different N-alkylacrylamides [N-dodecylacrylamide (DAM) and N-hexadecylacrylamide (HDAM)] have been synthesized using two linear hydrophobic initiators with 12 (ACVA₁₂) and 16 (ACVA₁₆) carbon atoms and two di-substituted hydrophobic initiator with two chains of 6 (ACVA_di6) and 8 (ACVA_di8) carbon atoms derived from 4′4-azobis(4-cyanopentanoic acid) (ACVA). The polymers obtained were telechelic, multisticker and combined. The initiators, monomers and polymers synthesized were characterized by ¹H NMR and light scattering (LS). The rheological properties of these three different associative polymers were investigated using steady-state experiments. The effect of location and structure (linear or di-substituted) of the hydrophobic groups upon the viscosity of the polymer in solution was studied.     

Rheology of crosslinked entangled polymers: Shear stiffening in oscillatory shear

Polyborosiloxane (PBS) was synthesized from boric acid and hydroxyl-terminated polydimethylsiloxane (PDMS). The oscillatory shear behavior of PBS formed by PDMS with different molecular weight was studied. The relaxation time of PBS was calculated by Doi-Edwards model. Finally, the shear-stiffening mechanism of reversibly crosslinked entangled polymer was obtained. Shear stiffening occurs at lower shear frequencies, which is mainly due to crosslinking bonds and friction between molecules hindering the movement of molecules. The increase in storage modulus at high frequencies is attributed to the resistance caused by entanglement in the stretching process of molecular chains. In addition, the molecular weight is greater and the degree of shear stiffening is higher. Such a conclusion is useful to further study the application of shear stiffening. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48421.     

Influence of polymerization procedure on polymer topology and other structural properties in highly branched polymers obtained by A2 + B3 approach

Computational studies were carried out to investigate the influence of polymerization procedure on the topology and various macromolecular characteristics of the highly branched polymers formed by the reaction of A₂ and B₃ type monomers through step-growth polymerization reactions. The influence of three different polymerization procedures on the properties of the polymers formed was investigated, namely, (i) slow addition of A₂ over B₃, (ii) slow addition of B₃ over A₂, and (iii) mixed A₂ + B₃. Topology, degree of branching, number and weight average molecular weights, and polydispersity index of the polymers were determined using Monte Carlo simulations, assuming different levels of cyclization ratios during the reactions. Interestingly model polymers obtained by the slow addition of B₃ over A₂ produced much higher degree of branching or truly hyperbranched polymers, when compared with the other two methods, which mainly resulted in linear growth with slight branching.     

A comparative study of the structure-property behavior of highly branched segmented poly(urethane urea) copolymers and their linear analogs

The solid-state structure-property behavior of highly branched segmented poly(urethane urea) (PUU) copolymers and their linear analog was investigated. A limited study of their solution rheological behavior was also undertaken. The linear PUUs were synthesized by the two-step prepolymer method, whereas the oligomeric A₂+B₃ methodology was utilized to synthesize the highly branched materials. The soft segments (SS) were either poly(tetramethylene oxide) (PTMO) or poly(propylene oxide) (PPO). All copolymers utilized in this study, with one exception, contained 28 wt% hard segment (HS) content. DMA, SAXS, and AFM studies indicated that the linear as well as the highly branched PUUs were microphase separated. The SS T_g of the highly branched PUUs was nearly identical to that of their respective linear analogs. However, the linear copolymers exhibited broader and less temperature sensitive rubbery plateaus, both attributed to one or both of two reasons. The first is better hydrogen bonding organization of the HS phase as well as greater HS lengths than in the highly branched analogs. The second parameter is that of a potentially higher chain entanglement for the linear systems relative to the branched analogs. Tapping-mode AFM phase images confirmed the microphase morphology indicated by SAXS and DMA. Ambient temperature strain-induced crystallization was observed in the PUU based on PTMO 2040 g/mol at a uniaxial strain of ca. 400%, irrespective of the chain architecture. Stress-strain, stress relaxation, and mechanical hysteresis of the highly branched copolymers were in general slightly poorer than that of their linear analogs. Ambient temperature solution viscosity of the highly branched materials in dimethyl formamide was substantially lower that that of the linear samples of nearly equal molecular weight.     

Dynamic mechanical behavior of highly filled polymers: Energy balances and damage

Dynamic tests using the Naval Weapons Center torsion–tension tester and end-bonded cylindrical propellant specimen were carried out to evaluate the effects of internal damage on propellants by subjecting samples to small tensile oscillations during low constantstrain rate tests. It is shown that microstructural damage in a propellant causes significant changes in mechanical properties. The mechanical property curves demonstrate that the response is markedly strain sensitive. So long as the maximum strain experienced by the sample during a test is not exceeded, the response of the propellant to small tensile oscillation during repeated strains below that maximum value remains relatively unchanged after the first initial dramatic change. The differences between mechanical energy balances of “undamaged” and “damaged” propellant samples were used to demonstrate microstructural damage and to estimate the extent of damage. For any one propellant, the total lost energy caused by microscopic failure of the propellant seems to be additive, constant, and independent of the mechanical path to failure.     

Polyhydroxyalkanoates: biodegradable polymers with a range of applications

Increased and accelerated global economic activities over the past century have led to interlinked problems that require urgent attention. The current patterns of production and consumption have raised serious concerns. In this context, greater emphasis has been put on the concept of sustainable economic systems that rely on technologies based on and supporting renewable sources of energy and materials. Average UK households produce around 3.2 million tonnes of packaging waste annually whereas 150 million tonnes of packaging waste is generated annually by industries in the UK. Hence, the development of biologically derived biodegradable polymers is one important element of the new economic development. Key among the biodegradable biopolymers is a class known as polyhydroxyalkanoates. Polyhydroxyalkanoates (PHAs) are a family of polyhydroxyesters of 3‐, 4‐, 5‐ and 6‐hydroxyalkanoic acids, produced by a variety of bacterial species under nutrient‐limiting conditions with excess carbon. These water‐insoluble storage polymers are biodegradable, exhibit thermoplastic properties and can be produced from renewable carbon sources. Thus, there has been considerable interest in the commercial exploitation of these biodegradable polyesters. In this review various applications of polyhydroxyalkanoates are discussed, covering areas such as medicine, agriculture, tissue engineering, nanocomposites, polymer blends and chiral synthesis. Overall this review shows that polyhydroxyalkanoates are a promising class of new emerging biopolymers. Copyright © 2007 Society of Chemical Industry     

Synthesis and applications of stimuli-responsive hyperbranched polymers

Benefiting from their responsiveness and adaptability, the stimuli-responsive polymers have been widely investigated and exploited in the various fields, such as environmental monitoring, electronics, photonics, controlled drug delivery, medical imaging and diagnostics. These potential applications have greatly promoted the development of advanced functional materials, and meanwhile set higher requirements for the smart materials in the aspects of the spatial structures, diverse linkages and variable functions. However, the linear functional polymers can not satisfy all the requirements of the multi-dimensional molecular design and acute sensitiveness due to the architectural limitation. Accordingly, stimuli-responsive hyperbranched polymers (HBPs) have been drawing more and more attention in recent years owing to their unique globular void-containing topological structure featured with a large number of terminal functional groups and branches, lower solution or melt viscosity, and better solubility. Therefore, design and synthesis of stimuli-responsive HBPs provide a robust tool for controlling the structure transition and creating the hierarchical sensitivity driven by different triggers. In this review, the developments and recent advances of preparation procedures, performance control and promising applications of various stimuli-responsive HBPs have been comprehensively summarized. Besides, the developing trend of stimuli-responsive HBPs is also discussed. It can be found that stimuli-responsive HBPs with different synthetic strategies and diverse performances have manifested more and more versatile applications.     

超支化聚合物合成方法与应用研究进展

介绍了超支化聚合物的合成方法:缩聚法、活性聚合法、离子聚合法、开环聚合、可逆加成链转移聚合法和自缩合基团转移聚合等新型合成方法;阐述了目前超支化聚合物在涂料、共混改性、聚合物膜、药物、纳米复合材料、聚电解质、超支化液晶等方面的应用进展;展望了该类聚合物今后的研究发展方向。     

Processing,properties and applications of highly porous geopolymers: A review

Geopolymers, possessing a semi-crystalline three-dimensional inorganic network generated by the dissolution and reaction of a solid alumino-silicate source with an activating solution, have attracted increasing attention from both academia and industry because of their unique and favorable characteristics. This review deals with the synthesis, characterization and potential applications of porous geopolymers, realized through different processing routes. Firstly, the processing approaches are divided into five categories: (i) Direct foaming, (ii) Replica method, (iii) Sacrificial filler method, (iv) Additive manufacturing, and (v) Other methods. Their microstructure, porosity and properties are compared and discussed in relation also to the different processing routes. This review highlights the fact that porous geopolymers are promising low-cost candidates for technologically significant applications such as catalyst supports or membranes, filtration of liquid or gases, adsorption and insulation. This review aims at summarizing the main published results and fostering further investigations into developing innovative ways to generate components with improved properties.     

Rheological properties of highly flowable mortar containing limestone filler-effect of powder content and W/C ratio

The effect of a limestone filler addition in superplasticized cement mortar was investigated. The mixtures considered in this study are highly fluid, yet stable mortars that can be used to proportion self-consolidating concrete (SCC). All the mixtures were proportioned with a fixed unit water content of 250 l and various water-cement ratios varying from 0.35 to 0.45. A limestone filler with a specific surface area of 480 m²/kg was used at different addition percentages.This paper reports test results leading to the recommendation of suitable powder contents that can be used to proportion mortar mixtures containing a limestone filler and achieving adequate rheological properties. Test results show that the effect of limestone filler is mainly affected by the W/C and the limestone filler content in use. For a given W/C, the addition of a limestone filler within a certain range did not affect fluidity. However, beyond a critical dosage, the incorporation of some limestone filler resulted in a substantial increase of the viscosity of mortar. An accurate model that can be used to predict the viscosity of such mixtures is proposed and validated on various mixtures.     

Flame retardants and heat release: review of data on individual polymers

This is part of a project considering whether flame retardants affect polymer heat release, a critical issue to assess whether adding flame retardants decreases fire hazard. The work investigated the following. (1) Fire properties affecting fire hazard, confirming that heat release rate is the key fire property most strongly influencing fire hazard. (2) Ways to assess heat release and whether full‐scale fire heat release rate can be predicted from small‐scale test results, confirming that cone calorimeter and Ohio State University data are adequate to predict full‐scale heat release. (3) Analysis of key 1988 NBS/NIST study comparing the fire hazard of flame retarded products versus non‐flame retarded products for the same application. This confirmed that the study demonstrated that flame retardants lower fire hazard and that the levels of additives in the flame retarded products used were not excessive. (4) Review of studies investigating effects of flame retardants on various polymeric systems. The overall conclusion is that flame retardants does indeed improve fire safety (when used appropriately) primarily because they decrease heat release. Part 2 of the project (separately) considers the key polymers that need to be potentially flame retarded and reviews recent studies on effects of flame retardants on heat released by such polymers. Copyright © 2014 John Wiley & Sons, Ltd.     

Sensors based on conductive polymers and their composites: a review

Conductive polymers (CPs) for sensors present numerous advantages such as high sensitivity, short response time, room temperature operation, and the possibility of tuning both chemical and physical properties by using different substituents. Therefore, sensors based on CPs and their composites have attracted much attention from researchers. The CPs used for sensors mainly consist of polyaniline, polypyrrole and poly(3,4‐ethylenedioxythiophene) etc. In this review, the fabrication, sensing performance, mechanism and perspectives of sensors based on CPs and their composites are thoroughly summarized. The CPs and their thin films were prepared under different polymerization conditions and used as various sensors. CP composites combine the advantages of CPs and other sensing materials such as carbonaceous materials, metal oxides, metals etc., and their sensors demonstrate a high sensing performance due to the synergistic effect of the components. Finally, the perspectives and development trends of sensors based on CPs and their composites are introduced. © 2019 Society of Chemical Industry     

Modification of polysiloxane polymers for biomedical applications: a review

This paper reviews methods of modifying polydimethylsiloxane (PDMS) polymers to improve their properties for biomedical applications. The modification methods are discussed under three different categories: bulk, surface and other modification techniques. Surface modification techniques include physical and chemical techniques to modify polymer surfaces. Bulk modification techniques include blending, copolymerization, interpenetrating polymer networks (IPNs) and functionalization. The third category includes less common modification techniques. © 2001 Society of Chemical Industry