Thermal degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)

The degradation kinetics of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate), a member of the Nodax family of polymers, were investigated using transient constant shear rate and dynamic time sweep rheological tests. The rate of chain scission at several times and temperatures was correlated with viscosity data and verified using molecular weight determination of the degraded samples. The experimental results show that the molecular weight and the viscosity of Nodax decrease with time over the range of temperatures that were studied (155–175°C). The degradation kinetics, which exhibited first‐order behavior, were determined as a function of the flow history and thermal history. An apparent activation energy of 189 ± 5 kJ/mol for thermal degradation was found by modeling variations in the rate with temperature using an Arrhenius law model. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 66–74, 2005     

Rheological characterization of shear‐induced structural formation in the solutions of poly(vinyl alcohol) in dimethyl sulfoxide

Gelation behavior of the solutions of poly(vinyl alcohol) (PVA), whose syndiotactic diad content was 52% and weight‐average molecular weight of PVA ranged from 89,000 to 186,000, in dimethyl sulfoxide (DMSO) was investigated in terms of shear rate, concentration, and molecular weight of the polymer. To trace time‐dependent gelation behavior, a programmed time sweep experiment was carried out by repeating the following procedure 3 times; 10 min of measurement followed by 5 min relaxation. All of the PVA solutions in DMSO exhibited time‐dependent rheological responses, particularly under low shear rate of 2 rad/s, indicative of the formation of physical structures. At high shear rate of 200 rad/s the rheological responses were independent of time. Referring to Winter's view on gelation, a weak shear produced a soft gel structure whereas a strong shear produced an irreversible strong gel. Gelation was more affected by molecular weight than by concentration over the period of shearing. At low frequency, relaxation time was increased with time, and then leveled off after prolonged shearing. At high frequency, however, little change of relaxation time was noticed. They can be interpreted as a consequence of formation of three‐dimensional gel structure through the polar interactions by hydroxyl groups whose strength was dependent on shearing conditions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 465–471, 2006     

Rheological Behavior of Wastewater Sludge Following Cationic Polyelectrolyte Flocculation

The rheological characteristics of the wastewater sludge were investigated by using a Haake Rheostress RS 75 rheometer. The shear creep compliance experiments and the dynamic viscosity measurements were conducted. The shear creep compliance experiments indicate the addition of polymer coagulants to the sludge samples will form more rigid structures. The elastic solid-like behaviors were always observed in the samples with polymers. The Voigt model was successfully employed in modeling the viscoelastic retardation behavior of sludge samples in the shear creep compliance tests. Moreover, the dynamic viscosity curves of the sludge samples with/without polymer could be described by the power law model of Ostwald and de Waele at the medium shear rates, ca. 100–300 s^?1. Consequently, addition of polymer to the sludge tends to extend the applicable ranges of the shear rates for the power law model as well as to decrease the power law index.     

Viscoelastic properties of a 60 mol% para-hydroxybenzoic acid/40 mol% poly(ethylene terephthalate) liquid crystalline copolyester. II: Effect of shear history

Temperature sweeps of dynamic viscoelastic properties have shown that phydroxybenzoic acid (PHB)-based liquid crystalline polyesters, specifically in this case those copolymerized with poly(ethylene terephthalate) (PET), can be subjected to considerable supercooling if initial heating curves are compared to subsequent cooling curves, indicating that this type of material can be in quite different states even at the same temperature, depending on thermal history. Utilizing this supercooling behavior, viscoelastic properties of a 60 mol% PHB/40 mol% PET material produced by Unitika were monitored before and, particularly, after large-scale shear deformation to determine how potential structure changes induced by the shear are reflected in viscoelastic properties immediately, and with time. According to dynamic viscoelastic temperature sweep data four quite different initial states were employed including conditions with, as well as largely free of, crystallites. However, in all cases, post-shear monitoring showed decreased G′ and G″ values with almost no evidence of return towards initial values within approximately 25 min. These results, in addition to furthering somewhat the fundamental understanding of the flow and relaxation properties of liquid crystalline polymers, may be useful in polymer processing, where large-scale shear deformations employed in forming processes appear to be capable of changing considerably the subsequent behavior of such materials.     

Rheological properties of progesterone microemulsions: Influence of xanthan and chitosan biopolymer concentration

In this preformulations study, rheological properties of microemulsions with progesterone (1%) were studied to analyze the effect of xanthan and chitosan at different concentrations (0.5–3%). Steady shear and oscillatory rheological properties were analyzed using a controlled stress rheometer. Steady shear data were satisfactorily adjusted to the Carreau model. For all preparations, shear‐thinning behavior was observed. Zero shear viscosity (η₀) increased with the biopolymer concentration. The results from dynamic experiments showed the behavior of all preparations with xanthan gum and those of chitosan to be characteristic of weak gels and liquid‐like solutions, respectively. The correlation between dynamic and steady‐shear properties (extended Cox‐Merz rule) was satisfactory for the two polymers. The recovery analysis of microemulsions with xanthan showed a total recovery percentage of 90% for the highest concentrations of this polymer. However, microemulsions with chitosan showed practically no recovery. Progesterone release was greater for the microemulsions with chitosan. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Rheological behavior of noncompatibilized and compatibilized PP/PET blends with SEBS‐g‐MA

The rheological behaviors of noncompatibilized and compatibilized polypropylene/polyethylene terephthalate blends (80/20) in relation with their morphology were studied at two constant levels using maleic anhydride‐modified styrene‐ethylene‐butylene‐styrene polymer. By scanning electron microscopy of cryofractured surfaces, the morphology of the blends was examined after etching. The frequency sweep and step strain experiments were carried out for the blends. The frequency sweep results indicated that increasing the compatibilizer causes behavioral changes of the rheological properties, which could be related to the aggregation of the dispersed particles with rubbery shell. Also, the frequency sweep and step strain experiments in linear region, after cessation of simple steady shear flow with various preshear rates (higher shear stress values than G′_p), were done on compatibilized blend. The results showed that the morphology characteristics, defined by the aggregation of the dispersed particles based on rheological experimental data, were destroyed and replaced by an alignment in the flow direction for present imposed shear rates. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Wetting kinetics of polymer solutions and force‐based contact angles

The effect of the shear thinning behavior and elasticity of polymer solutions on the dynamic contact angles are investigated. Under dynamic conditions, the contact angle of a liquid on a solid surface changes significantly with the substrate velocity from its equilibrium value. The dynamic contact angles for polyethylene oxide (PEO) solutions of two molecular weights 3 × 10⁵ and 4 × 10⁶ have been measured using a polyethylene terephthalate (PET) plate. The three‐parameter Ellis model to fit the rheological data to obtain shear thinning power n, characteristic shear stress, and the zero‐shear viscosity is used. The theory indicates that dynamic contact angles follow power law in this instance instead of showing Newtonian behavior with zero‐shear viscosity when the shear thinning effects are considered. The elastic effect becomes important at larger polymer concentrations that reduces the dependence on capillary number, that is, reduces n keeping with the experiments. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2533–2541, 2016     

Influence of ageing on rheology of SBR/sulfur‐modified asphalts

The effect of short‐term and long‐term oxidative ageing on the rheological, physical properties, the morphology, and thermodynamic behavior of the styrene‐butadiene rubber (SBR)‐ and SBR/sulfur‐modified asphalts is studied respectively. The dynamic rheological tests show the two major effects of ageing on the rheological behavior of the asphalt binders. Ageing prompts the degradation of polymer and increases the viscous behavior of the binders, on the other, ageing improves the elastic behavior of the binders due to the changed asphalt components, the final rheological behavior of the aged binders depends on the combined effect. The SBR/sulfur‐modified asphalt is more susceptible to ageing and dynamic shear due to the structural instability and show a viscous behavior with increasing the sulfur level after ageing. Under the influence of repeated shear force, the high‐temperature property of the SBR/sulfur‐modified asphalts declines. The morphology observation shows the compatibility between polymer and asphalt is improved with further ageing especially for the SBR/sulfur‐modified asphalt. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Rheological Behavior of Wastewater Sludge Following Cationic Polyelectrolyte Flocculation

The rheological characteristics of the wastewater sludge were investigated by using a Haake Rheostress RS 75 rheometer. The shear creep compliance experiments and the dynamic viscosity measurements were conducted. The shear creep compliance experiments indicate the addition of polymer coagulants to the sludge samples will form more rigid structures. The elastic solid-like behaviors were always observed in the samples with polymers. The Voigt model was successfully employed in modeling the viscoelastic retardation behavior of sludge samples in the shear creep compliance tests. Moreover, the dynamic viscosity curves of the sludge samples with/without polymer could be described by the power law model of Ostwald and de Waele at the medium shear rates, ca. 100-300 s^-1. Consequently, addition of polymer to the sludge tends to extend the applicable ranges of the shear rates for the power law model as well as to decrease the power law index.     

Dynamic stress/strain response of the interphase in polymer matrix composites

The interphases of various sized E‐glass‐fiber/epoxy‐amine systems were tested at displacement rates in the range of 230 to 2450 fxm/sec using a new experimental technique (dynamic micro‐debonding technique). The fiber systems include unsized, epoxy‐amine compatible sized, and epoxy‐amine incompatible sized glass fibers. A data reduction scheme was developed to relate the force vs. displacement response obtained from the dynamic micro‐debonding technique to interphase shear stress/strain response. The stress/strain curves and interphase shear modulus values were obtained from these composite systems under average shear strain rates (ASSR) in the range of 215–3278 (1/s). The results showed that the magnitude of the interphase shear modulus was sizing and strain rate dependent. In all cases, the shear modulus was found to be more compliant than the bulk matrix. The two sized fiber systems exhibited the highest strain rate sensitivity, with modulus increasing about threefold over the range studied. In addition, the rate dependent behavior of the model interphase materials were determined using the dynamic mechanical analysis (DMA) technique. The model interphase materials closely resemble the interphase that forms on unsized and compatible sized fibers. Master curves relating the flexural storage modulus to strain rate were constructed based on the time‐temperature superposition principle from DMA frequency sweep measurements. The DMA measured results are consistent with the dynamic micro‐debonding test results, providing confidence in the test method as a reliable technique for characterizing the high strain rate properties of the interphase in composites.     

Dynamic and capillary rheology of LDPE‐EVA–based thermoplastic elastomer: Effect of silica nanofiller

The effect of pristine silica nanoparticles on the dynamic and capillary rheology of a model LDPE‐EVA thermoplastic elastomeric system is explored in this paper. The pristine silica nanoparticles were melt‐blended with the LDPE‐EVA system at 1.5, 3, and 5 wt% loadings, respectively, by varying the sequence of addition. In one of the compositions, coupling agent bis‐[3‐(triethoxysilyl)propyl] tetrasulphide (Si‐69) was used to improve the interaction of hydrophilic silica particles with polymer matrix. Results obtained reveal that the viscoelastic behavior of such composites is influenced remarkably by loadings of silica, variation of sequence, and addition of Si‐69. Upon addition of coupling agent, G′ value increases especially at higher strain levels due to increased polymer‐filler interactions. All systems with various loading of nanosilica represent an increase in elastic response with increasing frequency. Both the unfilled and filled blends exhibit rheological behavior of non‐Newtonian fluids. But interestingly, the viscoelastic response varies markedly with the temperature. The dynamic and steady shear rheological properties register a good correlation in regard to the viscous vs. elastic response of such systems. Finally, the rheological behavior is correlated with morphology of the present system processed at various shear rates. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Rheological behavior of polypropylene nanocomposites with tailored polymer/multiwall carbon nanotubes interface

Maleic anhydride grafted polypropylene (MA‐g‐PP) or polypropylene (PP) was noncovalently coated onto acid functionalized multiwall carbon nanotube (f‐MWNT) through solution mixing. These coated f‐MWNTs and pristine MWNT (p‐MWNT) were melt microcompounded with neat PP to form PP/f‐MWNT and PP/p‐MWNT nanocomposites at 0.1–1 wt% MWNT concentration. Complex viscosity and tan δ (ratio of loss modulus to storage modulus) behavior of these systems were studied using dynamic frequency sweep test, while relaxation time, activation energy, and melt homogeneity were also calculated and compared. Among the three types of samples, PP/f‐MWNT masterbatch‐based nanocomposite demonstrated not only the presence of interphase but also good processability. As a consequence, increase of both the crystallization rate in the presence of shear and the melt elasticity during annealing were found only in the masterbatch‐based samples but not in the PP/p‐MWNT. The mechanism of such increased melt elasticity was attributed to the formation of the space‐spanning network, which is consistent with the Cole–Cole plot showing similar behavior to the branched polymers in the literature. This has implications in polymer processing due to suggested changes in the balance between melt strength and polymer flow. Nanocomposite rheological behavior has also been correlated with the mechanical properties. POLYM. ENG. SCI., 59:1763–1777, 2019. © 2019 Society of Plastics Engineers     

Nonlinear rheological behavior of a novel oil displacing agent

In this work, the shear and elongational rheologies have been investigated for a newly developed oil displacing agent, polymeric surfactant‐PSf. It was found that the PSf solutions exhibited Newtonian, shear‐thinning, and shear‐thickening behavior, respectively, depending on the polymer concentration and shear rate, and Cox–Merz rule was not applicable to these systems. The first normal stress difference (N₁) versus shear rate plots for PSf were complicated, which varied with the composition of the solutions. The uniaxial elongation in capillary breakup experimental results indicated that Exponential model could be used to fit the experimental data of the PSf solutions at lower polymer concentrations. In addition, it was found that PSf was more effective in improving shear viscosity than partially hydrolyzed polyacrylamide, but not in the case of elongational viscosity. The experimental results indicated that the microstructural mechanisms are responsible for the rheological behavior of the polymers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40813.     

Effect of polymer matrix on the rheology of hydroxyapatite‐filled polyethylene composites

The effect of matrix polymer and filler content on the rheological behavior of hydroxyapatite‐filled injection molding grade high‐density polyethylene (HDPE) has been studied. Studies of the flow curves revealed that the matrix and the composite exhibit three distinct regions in the flow curve, namely, a pseudoplastic region at low to moderate shear rates, a plateau and a second pseudoplastic region at high shear rates. The shear stress corresponding to the plateau (τ_c) is dependent on both the filler concentration and the melt temperature. Addition of HA in the HDPE matrix increases the value of τ_c and decreases compressibility of the melt. An increase in temperature also raises the value of τ_c. From the nature of flow curves it is concluded that the matrix polymer largely decides the rheology of the composite.     

Influence of the morphological structure of carbon nanotubes on the viscoelasticity of PMMA‐based nanocomposites

The rheological behavior of polymeric nanocomposites provides major determination for their processability. In this work, three carbon nanotubes (CNTs) with varied geometries were adopted as nanofiller and then were introduced into poly(methyl methacrylate) (PMMA) matrix with different loadings (0.07–1.0 wt %). The different preparation routine led to varied CNTs dispersion states, on which the shear viscosity and the compressibility of their melts were proved to be sensitive. The technology for the preparation of their nanocomposites played a crucial role in controlling their rheological behavior. With melting blended bare CNTs, the dynamic shear viscosity of PMMA/CNTs increased with the increase of CNTs content, accompanied by aggregated CNTs in which no polymer matrix was entrapped. With the help of surface modification and pre‐mixing, well dispersed CNTs were obtained and a rather low aggregation rate ca. 0.029% was revealed. The well dispersed CNTs with an organic layer which was constructed by small molecules and presented lower viscosity. Such CNTs led to no remarkable clusters within polymer host and played the role of lubricant with an increased‐mobility layer, which can be reflected from the weighted relaxation time spectra. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46444.     

Dynamically vulcanized blends of polypropylene and ethylene octene copolymer: Influence of various coagents on thermal and rheological characteristics

The present study focuses on the influence of the three structurally different coagents, namely triallyl cyanurate (TAC), trimethylol propane triacrylate (TMPTA) and N,N′‐m‐phenylene dimaleimide (MPDM) on the thermal and rheological properties of thermoplastic vulcanizates (TPVs) based on the polypropylene (PP) and ethylene octene copolymer (EOC). Depending on the structure and reactivity, different coagents show different behaviors. All the TPV compositions were made by melt mixing method in a Haake Rheomix at 180°C. Rheological properties have also been evaluated at the same temperature. Viscoelastic properties of the TPVs were analyzed by a dynamic oscillatory rheometer in the melt state in a Rubber Process Analyzer (RPA 2000). Morphologically, TPVs consist of dense crosslinked rubber domains dispersed in a continuous thermoplastic matrix. The crosslinked rubber particles have a tendency to form agglomerates and build local clusters which undergo disintegration by shearing. A variety of rheological characteristics such as Payne effect, shear rate sensitivity, modulus recovery and dynamics of relaxation were studied by performing strain sweep, frequency sweep and stress relaxation tests. Among the various coagents taken for investigation, MPDM‐based TPVs show improved dynamic functions (complex modulus and complex viscosity) and lower rate of stress relaxation over TAC, TMPTA and the control sample without any coagent. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and characterization of suspension terpolymer of N‐cyclohexylmaleimide,methyl methacrylate,and styrene

N‐cyclohexylmaleimide (ChMI) and styrene (St) were polymerized with methyl methacrylate (MMA) at different St feed content by suspension polymerization method. The glass transition temperatures (T_g) of the terpolymers were detected by torsional braid analysis (TBA). Two transition peaks in TBA curves of the terpolymers with a high St content illustrated that these terpolymers have a heterogeneous chain structure and the phase separation occurred. The lower transition temperature, T_g1, was assigned to the random St‐MMA components, and the higher transition temperature, T_g2, was assigned to the St‐ChMI units‐rich segments. Thermogravimetric analyses (TGA) revealed that all the terpolymers showed a two‐step degradation process. The tensile strength of the terpolymers decrease with increasing St content while the impact strength tended to increase slightly. The rheological behavior of the terpolymers was also detected. The result illustrated that the terpolymers showed rheological behavior similar to that of pseudoplastic liquid. The apparent shear viscosity decreased with the increasing of St content. All terpolymers have a higher value of flow n than the poly(MMA‐co‐ChMI). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 918–922, 2006     

Adjustable Twin‐Slit Rheometer for Shear Viscosity Measurement of Extruded Complex Starchy Melts

An online rheometer with an innovative system of height‐adjustable and independently temperature‐controlled slits was designed to measure the shear viscosity of extruded wheat bran fiber‐containing starchy materials. The range of melt pressures and temperatures, obtained with a die, could be covered by the rheometer. A close ingredient thermomechanical history in the extruder was achieved both with the die and the rheometer, while covering an apparent shear rate from 5 to 30 s^–1. Although minor technical problems remained, first rheological data were obtained and showed a pseudoplastic flow behavior for all recipes. The flow curves were fitted by a power law model. Wheat bran fiber addition influenced both the K‐ and n‐values, leading to more shear‐thinning melt behavior and an increase in true shear viscosity. Only a limited effect on these values was found in these preliminary experiments when further increasing the fiber content.     

Morphology and rheology relationships of epoxy/core‐shell particle blends

The morphological and rheological behaviors of toughened epoxy resins modified with core‐shell rubber particles (CSR) were studied. These rubber particles were based on a poly (butadiene‐co‐styrene) core and a crosslinked poly (methyl methacrylate) shell. The effect of functionalized groups was performed on two types of CSR particles: first, those containing carboxyl‐functionalized groups (CSf), and second, particles containing no carboxyl‐functionalized groups (CSnf) in the PMMA‐shell. For these blends, the correlations between the morphology, particle dispersion state and their rheological behaviors before curing were investigated. Preliminary work using TEM micrographs indicated that the blends modified with CSf and CSnf exhibited the same particle size but differed with respect to the dispersion state. Rheological behavior of these blends was assessed in steady shear flow and dynamic viscoelastic experiments. Yield viscosity near‐zero shear rate occurred in the DGEBA/CSf blend presenting non‐Newtonian behavior at the particle volume fraction of 20% vol. The rheological behavior was clearly related to the state of particle dispersion and analyzed taking into account interactions between the particles‐particles and the particles‐matrix. The Williams‐Landel‐Ferry (WLF) shift procedure was used to construct modulus master curves G′ and G″ from the elastic solid state to molten polymers. A secondary plateau existed at low frequencies and was related to the presence of interactions leading to a physical network‐type structure. The deviation between theoretical G′ (Paleirne's model) and experimental G′ values was evaluated and exhibited high elasticity at the terminal zone, which correlated well with available literature.     

Melt rheology of poly(lactic acid): Consequences of blending chain architectures

The rheology of blends of linear and branched poly(lactic acid) (PLA) architectures is comprehensively investigated. Measurement of the melt rheological properties of PLA is complicated by degradation effects but the addition of 0.35 wt% tris(nonylphenyl) phosphite (TNPP) provides excellent stabilization over a range of temperatures. Master curves of dynamic viscosity constructed using time‐temperature superposition show significant dispersion for unstabilized samples; this behavior is accompanied by a loss of molecular weight. TNPP stabilized samples show excellent superposition throughout the entire frequency range and minimal loss in molecular weight. For the linear architecture, the Cox‐Merz rule is valid for a large range of shear rates and frequencies. The branched architecture deviates from the Cox‐Merz equality and blends show intermediate behavior. Both the zero shear viscosity and the elasticity (as measured by the recoverable shear compliance) Increase with increasing branched content. The viscosities of both the unstabilized samples and the TNPP stabilized samples roughly obey a log additivity mixing rule. The recoverable shear compliance is monotonic in blend composition and a mixing rule for this property is also presented. For the linear chain, the compliance is independent of temperature but this behavior is apparently lost for the branched and blended materials. Tensile and thermal properties of the blends are also measured and found to be roughly equal within the statistical error of the experiments. The results suggest that excellent control over rheological behavior of PLA is possible through blending chain architectures without compromising mechanical properties.