Effects of stick–slip transition on polymer melt apparent shear viscosity measurement

A twin-bore capillary rheometer is used for the apparent shear viscosity measurement of commercial polyolefin melts based on Ostwald-de Waele model. The effects of stick–slip transition of linear low-density polyethylene (LLDPE) and high-density polyethylene (HDPE) are investigated. The maximum error of apparent shear viscosity calculated by corrected shear rate is 23% when the stick–slip transition occurs. Based on the entanglement‑disentanglement theory, a schematic diagram for shear stress curve containing stick–slip transition is presented to illustrate polymer melt flow in capillary. In this study, the critical stress at the beginning of stick–slip transition at 220 °C is 23.01 kPa higher than that at 190 °C, and why it increases with increasing temperature is discussed with a molecular mechanism in combination with entropy elasticity and entanglement‑disentanglement theory. Through the analysis of ULDPE, PS, EVA, and K-Resin, it can be found that short branches or side groups are helpful to avoid the stick–slip transition. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48230.     

Research on the rheological and flow characteristics of a supramolecular gel in fractures

Loss circulation is one of the major concerns in drilling and well construction. An effective way to control drilling fluid loss and strengthen the wellbore is to plug fractures and holes with loss circulation materials. In this work, a hydrophobic association supramolecular hydrogel GP-A developed by n-dodecylacrylamide, methacrylamide and 2-acrylamide-2-methylpropylsulfonic acid was proposed as a potential lost circulation material for malignant drilling fluid loss. The results show that the initial decomposition temperature of GP-A was 172°C, and the flow characteristics conform to the Herschel-Bulkley model with yield stress. Microstructural analysis shows that GP-A gel with a 3D spatial network, and hydrogen bonds between branched chains form a dynamically recoverable structure. Based on POLYFLOW, the Phan Thien–Tanner model with viscoelastic parameters was used to simulate the viscoelastic flow characteristics of the fluid in fractures. The higher the concentration is, the greater K, and the higher the inlet driving pressure, while the nonlinear relationship between the driving pressure and the gel slug length is evident. The introduction of supramolecular gel polymer as a loss circulation material is an innovative research topic, which provides a new method to simulate the flow of polymer fluid in fractures.     

Viscoelastic rheology in the melting and crystallization domain: Application to polypropylene copolymers

The purpose of this article was to study the relationship between the rheological properties and the crystallization or melting of two polypropylene‐based copolymers used in the welding of the coating of offshore pipelines. The materials microstructure was studied via X‐ray diffraction, scanning electron microscopy, and optical microscopy. Differential scanning calorimetry was used to determine the crystallization and melting properties at different cooling and heating rates. Dynamic rheological analysis was used to define the rheological properties in the molten and in the transition zone from the molten to solid state and inversely. Both experiments (DSC and rheology) were performed under non‐isothermal conditions to allow complete accessibility to the transition zone. Crystallization and melting are both complex processes in which coexist amorphous and crystalline phases in the sample. A correlation between the rheological properties and crystallization was proposed. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44690.     

Correlating ultra-toughening of bio-based polyamide 410 with melt rheological and solid state relaxation dynamics by gelation rheology approach

The sol–gel or viscous-elastic transitions of the bio-based polyamide 410/POE-g-MA (polyethylene-co-octene copolymer grafted with maleic anhydride) blends have been systematically discussed in the framework of melt rheology as assessed on a parallel plate rheometer set-up in small amplitude oscillatory shear mode and solid state dynamic mechanical relaxation measurements. The viscous response dominated enhancement in elastic moduli of the blends that was characterized by the phase transitions across the composition range of 10–15 wt% of POE-g-MA. A direct correlation between the gel point (estimated from the cross-over of frequency-independent loss tangent curves) and the ultra-toughness (maximized to an extent of ~15-fold increase in notched Izod impact strength) could be established vis-a-vis its corroboration from the morphology of the impact-failed surfaces. The extent of maleic anhydride (−MA) content induced phase interaction with polyamide 410 via the formation of a polyamide-co-(polyoctene-co-ethylene) type copolymer linkage in solid-state and its subsequent impact on solid-state damping was analyzed. The study establishes qualitative correlation between ultra-toughening of polyamide 410 to that parameters based on relaxation dynamics measurements using melt rheology and solid-state dynamic responses conforming to the principles of gelation rheology.     

Capillary breakup extensional rheometry of associative and hydrolyzed polyacrylamide polymers for oil recovery applications

High molecular weight polymers used for heavy oil recovery exhibit viscoelasticity that can influence the oil recovery during chemical enhanced oil recovery. Different polymers having similar molecular weight and shear rheology may have different elongation flow behavior depending on their extensional properties. Displacing slugs are more likely to stretch than shear in tortuous porous media. Therefore, it is critical to seek an analytical tool that can characterize extensional parameters to improve polymer selection criteria. This article focuses on the extensional characterization of two polymers (hydrolyzed polyacrylamide and associative polymer) having identical shear behavior using capillary breakup extensional rheometer to explain their different porous media behavior. Maximum extensional viscosity at the critical Deborah number and Deborah number in porous media classified the associative polymer as the one having high elastic‐limit. Extensional characterization results were complemented by significantly higher pressure drop, marginally increased oil recovery of associative polymer in porous media. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46253.     

Effect of SiO2 on rheology,morphology, thermal,and mechanical properties of high thermal stable epoxy foam

A series of highly thermostable epoxy foams with diglycidyl ether of bisphenol‐A and bisphenol‐S epoxy resin (DGEBA/DGEBS), 4,4′‐diaminodiphenyl sulfone (DDS) as curing agent have been successfully prepared through a two‐step process. Dynamic and steady shear rheological measurements of the DGEBA/DGEBS/DDS reacting mixture are performed. The results indicate all samples present an extremely rapid increase in viscosities after a critical time. The gel time measured by the crossover of tan δ is independent of frequency. The influence of SiO₂ content on morphology, thermal, and mechanical properties of epoxy foams has also been investigated. Due to the heterogeneous nucleation of SiO₂, the pore morphology with a bimodal size distribution is observed when the content of SiO₂ is above 5 wt %. Dynamic mechanical analysis (DMA) reveals that pure epoxy foam possesses a high glass transition temperature (206°C). The maximum of specific compressive strength can be up to 0.0253 MPa m³ kg^?1 at around 1.0 wt % SiO₂. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40068.     

Natural Giesekus fluids: Shear and extensional behavior of food gum solutions in the semidilute regime

The shear and extensional behavior of two aqueous gum solutions, namely (1) 1–20 g/L guar gum (Torres et al., Food Hydrocolloids. 2014;40:85–95) and (2) κ/ι‐hybrid carrageenan solutions (5–20 g/L), are shown to exhibit Giesekus‐fluid behavior when in the semidilute regime. In this regime, a common set of Giesekus fluid parameters described both shear and extensional behavior. A new analytical result describing the extension of a Giesekus fluid in the filament stretching geometry is presented. This also gave reasonable predictions of the Trouton ratio. Higher concentration guar solutions, in the entangled regime, yielded different Giesekus fluid parameters for extension to those for simple shear. The extensional data for all concentrations of both gums collapsed to a common functional form, similar to that reported for cake batters (Chesterton et al., J Food Eng. 2011;105(2):332–342); the limits of the new filament thinning expression provide insight into this behavior. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3902–3915, 2014     

Insights into the synergistic mechanism of reactive aliphatic soft chains and nano-silica on toughening epoxy resins with improved mechanical properties and low viscosity

Toughening epoxy resin (EP) without sacrificing strength, modulus, and processing performance is always a harsh task. Here, a series of epoxy systems containing soft butyl glycidyl ether (BGE) and rigid nano-silica (nano-SiO₂) were prepared. Micro-phase separation structures derived from the self-assembly effect of BGE can be observed in atomic force microscopy images by controlling the total amount of BGE and nano-SiO₂ at 2 wt% for the EP_C:Si-m:n (m + n = 4) systems. Due to the synergistic effect of self-assembly effect of BGE and the rigid effect of well dispersed nano-SiO₂, EP_C:Si-2:2 system exhibited improvement of tensile strength of 59.3% (92.63 MPa), tensile modulus of 24.8% (3.52 GPa), elongation at break of 78.6% (4.84%), and glass transition temperature of 2.4% (138.4°C) compared with Pure EP system. Besides, due to the low loading of nano-SiO₂ (≤2 wt%) and the dilution effect of BGE, the viscosity of all the toughening systems is lower than 600 mPa·s, which can provide this toughening system with superior processing performance for large production of composites by automotive manufacturing methods such as vacuum assistant resin infusion technology.     

Poly(ethylene glycol)-interpenetrated genipin-crosslinked chitosan hydrogels: Structure,pH responsiveness,gelation kinetics,and rheology

In the development of pH-responsive chitosan-based hydrogels, achieving reproducible porosity and swelling behavior is essential for the design of hydrogel networks. Herein, we enhance the level of control in hydrogel microarchitecture by incorporating poly(ethylene glycol) (PEG) into the chitosan–genipin matrix. Hydrogels, varied in composition, were synthesized under mild conditions (37°C, 1 atm, 24 hr), yielding microporous structures with a pore diameter ranging from 11 to 57 μm and an average cross-sectional porosity of approximately 40–64%. Compared to chitosan–genipin hydrogels without PEG, presence of PEG in concentrations up to 1.9 mM generated the same effect as would increase in genipin content, yielding structures with a smaller pore diameter, a lower swelling degree in pH 2 buffer and a higher elastic modulus. Considering cost effectiveness and scale-up, reducing genipin content by the addition of PEG is favorable. Importantly, hydrogel samples containing higher concentrations of PEG (2.9 mM and above) showed a sudden increase in the swelling degree accompanied with a decrease in the elastic modulus. Findings showcase the potential variation in the composition of these hydrogels has in yielding scaffolds with significantly different physico-chemical behaviors.     

Polyethylene terephthalate/low density polyethylene/titanium dioxide blend nanocomposites: Morphology,crystallinity, rheology,and transport properties

Physical features of polyethylene terephthalate (PET)/low density polyethylene (LDPE) immiscible blends, rich in PET, with and without titanium dioxide (TiO₂) nanoparticles are studied. These materials are of industrial interest, because they can be obtained by recycling PET bottles containing TiO₂ with their corresponding polyethylene made caps. Their potential application in packaging is investigated. Droplet-matrix morphology is observed by scanning electron microscopy; coalescence occurs during compression molding. Transmission electron microscopy results show that TiO₂ nanoparticles are located at the interface between PET and LDPE, forming a physical barrier that favors development of smaller droplets. Thermal analysis results are compatible with the morphology of the blends and the location of the TiO₂ nanoparticles. Viscosity obtained by extrusion continuous flow and oscillatory flow measurements in the linear regime show that some of the blends have viscoplastic behavior. Permeability results reveal that 80PET/20LDPE/TiO₂ blend nanocomposite shows a balanced barrier character to both oxygen and water vapor. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46986.     

Melt rheology and interfacial properties of binary and ternary blends of PS,EOC, and SEBS

This works systematically investigates the interfacial properties of the binary and the ternary blends based on polystyrene (PS), ethylene octene copolymer (EOC), and styrene–ethylene–butylene–styrene (SEBS) by analyzing the melt linear rheological behavior of the blends and neat components. Moreover, the relationship between rheology, phase morphology, and mechanical properties of PS/EOC ternary blends with various quantities of SEBS were studied. The surface shear modulus (β) and interfacial tension values obtained by Palierne model indicated that the EOC/SEBS blend has the best interfacial properties, while the lowest interaction was found for PS/EOC blend. Based on the Palierne model and Harkin's spreading coefficients a core–shell type morphology with EOC phase encapsulated by the SEBS shell dispersed in the PS matrix was determined for the ternary blends. Scanning electron microscopy results revealed that both fibrillar and droplet forms of dispersed phase could be developed during the blending of PS and EOC in presence of SEBS. The extent of fibrillar morphology and interfacial interactions in PS/EOC/SEBS ternary blends was dependent on the SEBS content. The improvement of the mechanical properties of PS/EOC blends in the presence of SEBS was evidenced by the tensile and impact resistance experiments. The tensile strength reinforcement was more pronounced for the ternary blends with more fibrillar dispersed phase. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48791.     

Linear‐nonlinear dichotomy of the rheological response of particle‐filled polymers

Novel nanoparticles, polymer‐particle coupling agents, and functionalized polymers are being developed to enhance the performance of particle‐reinforced polymer systems such as advanced rubber compounds for automobile tires. Understanding the complex rheological behavior of rubber is critical to providing insights into both processability and end‐use properties. One unique aspect of the rheology of filled elastomers is that the incorporation of particles introduces a hysteretic softening (Payne effect) at small dynamic strains. This study demonstrates that this nonlinear viscoelastic behavior needs to be considered when attempting to correlate steady shear response (Mooney viscosity) to oscillatory shear measurements from test equipment such as the Rubber Process Analyzer (RPA). While a wide array of unfilled gum elastomers show good correlation between Mooney viscosity and dynamic torque from the RPA at all of the strain amplitudes used, rubber compounds containing silica and carbon black particles only exhibit good agreement between the two measures of processability when the oscillatory strain amplitude is high enough to sufficiently break up the filler network. Other features of the filler network and its influence on nonlinear rheology are considered in this investigation, including the effects of polymer–filler interactions on filler flocculation and the use of Fourier transform rheometry to illustrate the “linear‐nonlinear dichotomy” of the Payne effect. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40818.     

Flow characteristics of three enhanced oil recovery polymers in porous media

This article presents an experimental study aiming to explore the relationship among rheological properties, flow characteristics in porous media, and enhanced oil recovery (EOR) performance of three typical EOR polymers. The results suggest that xanthan gum exhibits a very pronounced shear‐thinning behavior, which is probably also the reason explaining its moderate adsorption extent within porous media (thickness of adsorbed layer, e = 3.1 μm). The advanced viscoelastic properties coupled with the less adsorption extent compared to the hydrophobically modified copolymer (HMSPAM) allow xanthan gum to establish a “piston‐like” displacement pattern and lead up to 49.4% original oil in place (OOIP) of the cumulative oil recovery during polymer flooding. Regarding HMSPAM, the significant permeability reduction of the porous media induced by multilayer adsorption (e = 5.6 μm) results in much higher drive forces (ΔP) in the extended waterflooding stage, which further raises the cumulative oil recovery by 18.5% OOIP. In general, xanthan gum and HMSPAM totally produced 84% OOIP which is 15% higher than the extensively used EOR polymer, hydrolyzed polyacrylamide (HPAM), under the same experimental conditions. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41598.     

Rheological behavior and morphology of poly(lactic acid)/low-density polyethylene blends based on virgin and recycled polymers: Compatibilization with natural surfactants

Blends based on poly(lactic acid) and low-density polyethylene were compatibilized exploiting an innovative strategy involving the introduction of different mixtures of two sustainable liquid surfactants characterized by dissimilar hydrophilic–lipophilic ratios. The compatibilization method was first applied on blends made of virgin polymers, aiming at assessing the surfactant mixture inducing a more significant morphology refinement. Besides, to verify the effectiveness of the selected compatibilizers on recycled materials, the same process was carried out on blends based on reprocessed polymers. Interestingly, the compatibilization caused a significant microstructure modification, with a decrease of 54% of the mean size of the dispersed particles, in the case of virgin polymers-based blends, with a consequent increase of 19% of the dynamic elastic modulus. On the other hand, in the case of reprocessed polymers-based blends, a different compatibilizer efficiency was observed, as the noncompatibilized blend showed amore regular microstructure compared to the compatibilized counterpart.     

Dependence of rheological behaviors of polymeric composites on the morphological structure of carbonaceous nanoparticles

Carbonaceous nanoparticles (CNPs), including carbon black, carbon nanotubes, and graphene nanopiece, were selected as nanoadditives for investigating the rheological behavior dependence of their polymer‐based composites on morphological and interfacial structure. Polypropylene (PP) was adopted as matrix and a series of contents of CNPs were used for sample compounding. With identical concentration, the morphological structure of CNPs was emphasized as the dominant effect affecting the shear viscosity and the compressibility of PP/CNPs melts. The viscosity dependence on the CNPs contents and physical structure, such as particle size, aspect ratio, and specific area, was fully discussed in this work. The newly‐introduced inner voids, induced around the interface region between matrix and CNPs during physical mixing, were contributive to the rheological deviation, which was further reflected from the melt compressibility. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46416.     

Influence of pH and protei thermal treatment on the rheology of pea protein-stabilized oil-in-water emulsions

The influence of emulsion pH and previous thermal treatment of the protein on the rheological behavior of pea protein-stabilized emulsions has been studied. Oil-in-water emulsions with 65% weight oil and 6% weight pea protein isolate were prepared. Emulsion pH was varied between 3.5 and 7.0. In addition to this, the protein aqueous phase was submitted to different previous thermal treatments by modifying temperature from 25 to 90°C and heating time from 20 to 60 min. To study the influence of the above-mentioned variables, droplet size distribution and steady-state flow curves were determined, and linear viscoelastic measurements were carried out. An increase in the pH of the emulsion initially leads to an increase in emulsion viscosity and viscoelastic functions, as well as to a decrease in the mean droplet size, up to an emulsion pH close to the protein isoelectric point, where a singular rheological behavior is found. An increase in temperature or heating time on the protein aqueous phase yields higher values of steady-state viscosity and linear viscoelasticity functions, up to a complete denaturation of the protein.     

Tackling slip effects in the nonlinear flow properties of gellan fluid gels

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

Effect of dispersed phase on the morphology of in situ microfibrils and the viscoelastic properties of its composite via direct extrusion

A triangle arrayed triple‐screw extruder was used to prepare in situ polypropylene (PP) microfibrillar composites (MFCs) by direct extrusion, in which polyamide 6,6 (PA66) and poly(butylene terephthalate) (PBT) were used as dispersed phases while PP as matrix phase. The morphological evolution of the dispersed phase were investigated by SEM through taking samples along the extruder from different positions. The results showed that the fibrillating mechanism of PA66 was entirely different from that of PBT. Dynamic oscillatory shear rheological properties were used to analyze the effect of different types of in situ microfibrils on the rheological properties of MFCs. The obtained results showed that the storage modulus and complex viscosity of both PP/PA66 and PP/PBT MFCs were improved with increasing fibrillar aspect ratios. The loss tangent tan δ at low frequencies decreased with the increase of fibrillar aspect ratio. Moreover, the gel point concentration of PP/PA66 composite was lower than that of PP/PBT composite. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46286.     

Plasticizing effect of biodegradable dipropylene glycol bibenzoate and epoxidized linseed oil on diglycidyl ether of bisphenol A based epoxy resin

Major limitation for use of epoxy thermosets in engineering applications is its sudden brittle failure. In the present study dipropylene glycol dibenzoate (DPGDB) based plasticizer is used to modify diglycidyl ether of bisphenol A (DEGEBA) based epoxy resin system via simple blending technique. Bio-based epoxidized linseed oil was also used to modify epoxy resin system and compared with DPGDB modified resin. For DPGDB modified resin storage modulus and loss modulus of the epoxy system modified with 10% plasticizer increased by 7.54% and 12.24%, respectively. The primary mechanism responsible for such behavior is improved crosslinking density. With 5% plasticizer loading, flexural strength increased by 21%. There was an improvement of 312.74% in strain at failure for 10% plasticizer loading, while preserving its mechanical strength. It was found that DPGDB based modification was better than epoxidized linseed oil modification.     

H3PO4-induced micellization of styrene-ethylene oxide block copolymers in toluene solutions

In toluene/dimethoxyethane (80/20)_v solution, copolymers containing 11, 33, and 51 mol% of oxyethylene residues and having a fixed PS-segment molecular weight of ~60,000 g/mol, are dissolved molecularly. Doping with 10, 20, and 50 mol% of H₃PO₄ based on the oxyethylene content, induces varying degrees, of micellization in the respective block copolymer solutions. Light scattering and viscometry were used to evaluate the relationship between block-copolymer composition and the state of aggregation for solutions of styrene/ethylene oxide block copolymers as a function of solution concentration and level of doping with phosphoric acid. Specifically, diffusion coefficients, hydrodynamic radii, and critical micelle concentration were evaluated by dynamic light scattering. Radii of gyration were obtained by complementary static light scattering measurements. In all three block copolymers, complete micellization is realized at the 50 mol% H₃PO₄ doping level. At the 20 mol% H₃PO₄ doping level, complete micellization is induced with the copolymers containing 11 and 33 mol% of oxyethylene residues.