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.     

Study of viscoelastic properties of nanocomposites of SiO2–acrylonitrile–butadiene–styrene

Nanocomposites of acrylonitrile–butadiene–styrene (ABS) and nanosilica with different nanoparticle sizes and various loadings are prepared. Rheological experiments such as frequency sweep, strain sweep, and rotational test are performed to investigate the influence of nanoparticle loading and size on the viscoelastic properties of the nanocomposites. The results show that nanocomposites with higher filler loading and smaller particle size have both higher storage and loss moduli. Moreover, the results indicate that the storage modulus is more sensitive than loss modulus to filler loading and nanoparticle size. The smaller nanoparticles and higher filler loadings lead to the enhancement of nanoparticle surface area so that the viscoelastic properties are intensified through increase of polymer chain adsorption on nanoparticle, and creation of a network structure in the nanocomposites. The network structure causes changes to the rheological behavior of the nanocomposite such as solid‐like behavior in the low‐frequency region and reduction of the Newtonian region. The scanning electron microscopy micrographs revealed that the particle aggregates increase with particle size reduction and increasing nanoparticle content. We also used a nonlinear optimization to obtain the parameters of a multimode Maxwell model for low nanofiller content ABS/SiO₂ nanocomposites and found the relaxation times of the polymer chains increased with increasing nanoparticle content. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of epoxy resin contents on the rheological properties of epoxy‐asphalt blends

Epoxy‐asphalt and its mixture have been proposed for the long span orthotropic steel deck bridges because it shows excellent heat resistance, free from bleeding, low temperature cracking resistance, and aggregate scattering resistance. In this study, the effects of epoxy resin contents on rheological properties of epoxy‐asphalt binders were studied using dynamic shear rheometer. Experimental results indicated that the improvement of the viscoelastic performance of asphalt binder is noticeable at high temperatures, at which the elasticity is increased (higher G* and lower δ) for epoxy‐asphalt with increase in epoxy resin contents. The viscous behavior of the asphalt also increased when epoxy resin is added. Creep test results indicated that epoxy‐asphalt binder can not only resist deformation at elevated temperatures but recover satisfactorily from strain. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Evaluation of typical rheological models fitting for polycarbonate squeeze flow

High viscous polycarbonate melt exhibits some special rheological characters different from generalized Newtonian fluid during squeezing. It is necessary to evaluate whether the typical rheological models are suitable for polycarbonate squeeze. To avoid the difficult of measuring the inner melt rheological behavior directly, this study presents a method of measuring the compressing force applied on the upper disc of the rheometer to reveal the melt rheology indirectly. The finite difference method (FDM) was employed to discretize the governing equations and constitutive equations established on cylinder coordinate system and to simulate the compressing force. The experiments were carried out under four temperatures and three compressing velocities to test the validations of Leonov, Phan‐Thien–Tanner (PTT), eXtended Pom‐Pom (XPP), and Cross Williams‐Landel‐Ferry (Cross‐WLF) models. The experimental results show the unique character of compressing force evolution as ‘steep—steady—steep—steady’ pattern. Comparison between experiments and simulations reveals that both viscoelastic and viscous models can predict the two steady regions correctly, but only viscoelastic models can simulate the steep increase and decrease of the compressing force. Among the evaluated viscoelastic models, XPP is the most suitable to describe polycarbonate melt compression flow. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42279.     

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.     

Rheology of Cream-like Emulsions Prepared with Soybean Milk and Low Trans Vegetable Fat

The objective of this work was to study the effect of fat globule size and fat content on the rheological behavior of oil-in-water emulsions prepared with soybean milk, sunflower oil and low trans vegetable fat (LTF). Emulsions were prepared with 40 % w/w lipid phase (containing different proportions of LTF) and three different homogenization methods were used in order to obtain different globule sizes. Emulsions were subjected to controlled magnetic shaking until an increase in thickness. Partial coalescence was observed in all systems containing solid fat, which gave a rheopectic behavior and an increase in the viscoelastic parameters of the emulsions. Smaller particle sizes required higher shaking times to produce an increase in thickness, even though this did not lead to different final values of the viscoelastic parameters. The highest partial coalescence degree was observed at 50 % LTF in lipid phase, but the highest final viscoelastic parameters after shaking were observed at 100 % LTF in the lipid phase. The rheological behavior of these emulsions indicates that they could be a potential vegetable substitute for traditional dairy creams.     

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     

Investigation of stress relaxation behavior of carbon‐containing shape memory epoxy composites

A series of shape memory epoxy composites reinforced by varied carbon‐black (CB) contents were prepared. Stress relaxation tests were preformed to characterize the viscoelastic behavior of the specimens at different temperatures. An empirical rheological model was used to simulate the impacts of the temperature and CB content on the viscoelastic behavior of the materials. The results show that the additive of CB particles can significantly improve the stiffness and decrease viscoelastic properties of shape memory epoxy. In addition, parameter analyses in the theoretical simulation present a further understanding about the impact of the additives on the properties of SMPs. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Optimization of compression molding of stand‐alone microlenses: Simulation and experimental results

Hot compression molding is a promising method to fabricate polymer stand‐alone microlenses. A reliable theoretical as well as statistical analysis is required for the optimization of the process to minimize the residual stresses and to predict the amount of springback to achieve a better replication of the mold profile. This article in this context focuses on the finite element simulation (FES), optimization as well as experimental validation of hot compression molding of polymer stand‐alone microlenses. Three steps such as molding, cooling, and demolding, under different molding parameters, were analyzed using ABAQUS/standard solver and the results were compared with experimental results. Compression test and compression relaxation test have been conducted at different temperatures and strain rates to characterize the rheological behavior of material. Two material models, linear viscoelastic and hyperelastic–viscoelastic models, were developed and used for compression test simulations. Hyperelastic–viscoelastic model is found to predict the material behavior in low strain rates better and, thus, is used for the simulation of actual lens compression molding. Good agreement is found between the FES‐predicted curve and the lens profile molded at different molding temperatures. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

System identification and modeling of viscoelastic behavior from capillary melt rheological data

An investigation was conducted to identify and characterize the relaxation spectrum of polymer melts from transient capillary rheological data. System identification techniques using an iterative prediction‐error minimization (PEM) method were applied to isolate the viscoelastic melt response from the apparatus dynamics. Parameters for linear time invariant (LTI) models of varying complexity were estimated using capillary rheology data across a range of temperatures and shear rates using the principle of time‐temperature superposition. Melt capillary rheology data for polystyrene was found to exhibit viscoleastic behavior. Subsequently, three viscoelastic constitutive models were then implemented and their model coefficients directly fit using optimization techniques. The implemented methods provided useful relaxation behavior from melt capillary rheology data while also explaining much of the residual error in the purely viscous response as traditionally fit to the Cross‐WLF model. POLYM. ENG. SCI., 54:2824–2838, 2014. © 2014 Society of Plastics Engineers     

Effects of addition of functionalized SEBS on rheological,mechanical, and tribological properties of polyamide 6 nanocomposites

The effects of the addition of styrene‐ethylene/butylene‐styrene copolymer (SEBS) with various functionalized groups on the rheological, mechanical, and tribological properties on polyamide 6 nanocomposite filled with layered silicate (PA6/Clay) were investigated. Four types of SEBS: unmodified SEBS (SEBS), maleic anhydride grafted SEBS (SEBS‐g‐MA), amine group grafted SEBS (SEBS‐g‐NH₂), and carboxyl group grafted SEBS (SEBS‐g‐COOH) were added with PA6/Clay nanocomposite to prepare various polymer blends. These polymer blends were extruded by a twin screw extruder and injection molded. Dynamic viscoelastic properties of these blends in the molten state and their tensile, impact, and tribological properties were evaluated. The viscoelastic properties were found to increase with the addition of SEBS and were highly influenced by the types of functionalized groups contained. Influence of the addition of SEBS on the mechanical properties of these systems differed for each mechanical property. Although the tensile properties decreased with SEBS, Izod impact properties improved with the addition of various functionalized SEBS. These mechanical properties and viscoelastic properties correlated closely with the size of dispersed SEBS particles and interparticle distance. The tribological properties also improved with the addition of SEBS, and the influence of the amount added was higher than the type of SEBS used. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Rheological characterization of UV‐curable epoxy systems: Effects of o‐Boehmite nanofillers and a hyperbranched polymeric modifier

An organo‐modified Boehmite (o‐Boehmite) was used to prepare nanocomposite UV‐curing coatings, based on a cycloaliphatic epoxy resin (3,4‐epoxycyclohexylmethyl‐3′,4′‐epoxycyclohexane carboxylate). A hyperbranched polymer (HBP) based on highly branched polyester, was also added to the resin, with the aim to modify its reactivity, such as a possible route to increase the toughness of the resin. Different amounts of the nanofiller and the HBP, ranging from 5 up to 20 wt % of resin, were dispersed into the resin in the presence of triarylsulfonium hexafluoroantimonate, as a photoinitiator for the UV curing of the resin. The rheological behavior of the formulations produced was studied as function of the shear rate and of the content of each filler using a cone and plate rheometer. A general increase in viscosity was observed with increasing the volume fraction of each filler and a moderate pseudoplastic behavior was observed when o‐Boehmite filler was added. A non‐Newtonian behavior was observed with the incorporation of the HBP. The viscosity of the epoxy/boehmite resin mixtures was analyzed as function of the nanofiller volume fraction. In the case of epoxy/hyperbranched resin mixtures, the Cross equation was used to predict the viscosity of each formulation as a function of the shear rate and an appropriate relationship to predict the viscosity of each formulation as a function of the filler volume fraction, was determined. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Opposing effects of nanoclay on viscoelastic response of reactive phenoxy/poly (trimethylene terephthalate) blends: Clay‐induced transreactions versus percolated network formation

The role of nanofillers in reactive blends, which are compatibilized via interchange/exchange reactions, in particular transesterification reactions, is still a challenge. In this study, effects of clay on viscoelastic response of reactive melt intercalated phenoxy/poly (trimethylene terephthalate) blends are investigated. Using rheological plots, it was found that at low clay contents, clay‐induced transreactions could cause an unexpectedly enhanced viscous response. But higher clay contents lead to an enhancement in elastic behavior by inducing the formation of a percolated network. The observed opposing effects of clay particles on viscoelastic response were further examined by stress relaxation analysis, which verified the enhanced viscous response at low clay contents. The effect of interaction between the silicate layers and the blend matrix is also probed by using two different organo‐modifiers. Viscoelastic behavior of samples was also studied by dynamic mechanical analysis, and the results corroborated our findings from rheological measurements. Based on loss modulus data, the improved dynamic homogeneity of nanocomposites is attributed to the enhanced transreactions and stronger hydrogen bonds between the blend components. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Thermal and mechanical properties of a hydroxyl‐functional dendritic hyperbranched polymer and trifunctional epoxy resin blends

Curing characteristics of blends of a hydroxyl‐functionalized dendritic hyperbranched polymer (HBP) and a triglycidyl p‐amino phenol (TGAP) epoxy resin have been studied. THe HBP strongly enhances the curing rate owing to the catalytic effect of the hydroxyl groups. THe thermal and dynamic viscoelastic behavior of the blends of various compositions (HBP content 0–20%) have been examined and compared to the neat TGAP matrix. THe glass transition temperature (T_g) gradually decreases with increase in HBP concentration. The blends show a higher impact strength compared to neat TGAP. Scanning electron microscopy analysis indicates a single‐phase morphology.     

Thermomechanical and morphological properties of epoxy resins modified with functionalized hyperbranched polyester

Thermomechanical and morphological properties of blends of epoxy monomers and hydroxyl and epoxy functionalized hyperbranched polyesters have been studied. Different properties of the blends were found by changing the cure cycles (a precure step followed by a postcure at higher temperature). All the blends showed phase separation with a particulate morphology. Through the addition of the hydroxyl‐ended modifiers, rather than the epoxy‐ended, an increase of the viscosity and of the reactivity of the uncured blends was obtained. The blends containing the epoxy functionalized polymer showed some liquid–liquid transitions in the rheological traces, probably because of the phase separation phenomena. POLYM. ENG. SCI., 46:1502–1511, 2006. © 2006 Society of Plastics Engineers     

High‐Temperature Creep Behavior of SiOC Glass‐Ceramics: Influence of Network Carbon Versus Segregated Carbon

Three silicon oxycarbide samples with different carbon contents are analyzed in the present study with respect to their high‐temperature creep behavior. The tests were performed in compression at 1100°C, 1200°C, and 1300°C; in this temperature range the mechanism of creep relies on viscoelastic flow within the samples and has been modeled with the Jeffreys viscoelastic model. After the release of the applied mechanical stress, a viscoelastic recovery behavior was observed in all samples. The creep behavior of the investigated samples indicates two rheological contributions in SiOC: (i) a high viscous answer, coming from the silica‐rich network, and (ii) an elastic response from the segregated carbon phase within the samples. Furthermore, two distinct effects of the carbon phase on the HT creep behavior of SiOC were identified and are discussed in the present paper: the effect of the carbon presence within the SiOC network (the “carbidic” carbon), which induces a significant increase in the viscosity and a strong decrease in the activation energy for creep, as compared to vitreous silica; and the influence of the segregated carbon phase (the “free” carbon), which has been shown to affect the viscosity and the activation energy of creep and dominates the creep behavior in phase‐separated silicon oxycarbides.     

Epoxy functionalized poly(lactide) reactive modifier for blown film applications

Epoxy functionalized poly(lactide) (EF‐PLA) was synthesized by reacting PLA with a multifunctional epoxy polymer (MEP) using reactive extrusion processing. These polymers can function as a rheology modifier for PLA and a compatibilizer for other biopolyesters in blown film and foam applications. Model compound studies show that the epoxy functional group on the MEP reacts selectively with the carboxylic acid chain‐ends of PLA at processing temperatures below 200°C. An EF‐PLA containing up to 10% MEP was prepared without gel formation and reactively extruded with neat PLA to obtain three different product formulations containing MEP (0.25, 0.5, and 1.0%). These products showed significantly enhanced rheological properties compared to what has been reported by other groups and is currently used in the PLA blown film industry, the blending of MEP with PLA in a single step. These benefits are a result of how the MEP gets distributed in the material, and can lead to improved properties even at lower MEP concentrations. Our new materials showed significant strain hardening rheological behavior demonstrating that they can be readily blown into films and foams. A statistical simulation was developed to provide a fundamental understanding of the reaction as well as provide information on the molecular weight characteristics and reactivity of the EF‐PLA. The EF‐PLA molecule shows good potential for use as a rheology modifier and compatibilizer. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42243.     

Rheological Properties of Hot-Melt Adhesives: A Model for Describing the Effects of Resin Content

The complex shear modulus of a series of EVA/resin blends has been measured in a broad range of frequencies and temperatures. The variations of the viscoelastic parameters (plateau modulus, limiting compliance, zero-shear viscosity) have been studied as a function of resin content. The addition of small compatible molecules to the polymer has two effects: a topological effect due to the swelling of the entanglement network and a thermodynamic effect due to the increase of the glass transition temperature. It is possible to play on both effects to get the wanted elastic and viscous behavior, as far as process and adhesive properties are concerned. As a consequence, a viscoelastic model is given, allowing one to calculate in a wide range of frequencies (or times) the behavior of these bases of hot melt adhesives, given the composition of the blend and its temperature.     

Modeling of the relationship between morphology and viscoelastic behavior of unidirectional fiber-reinforced polymers

A new approach is proposed to predict the relationship between geometric arrangement of fibers within the polymer matrix and viscoelastic behavior displayed by unidirectional fiber-reinforced polymers. Based on a quantitative morphology analysis of epoxy/glass fibers composites, a four-phase model taking into account the fiber spatial distribution is developed to rigorously express the reinforcement effect of the polymer matrix over a wide range of fibers and temperatures. Comparisons with other modelings and experiment illustrate the validity of the proposed approach. In addition, changes in the viscoelastic behavior of the epoxy matrix in composite materials resulting from a decrease in the crosslinking degree of such a kind of polymer are, subsequently, assessed through such an approach.     

Rheological properties of hydroxyl‐terminated and end‐capped aliphatic hyperbranched polyesters

The rheological behavior of two series of aliphatic hyperbranched (HB) polyesters, based on 2,2‐bis(hydroxymethyl)propionic acid (bis‐MPA) and di‐trimethylol propane (Di‐TMP) as a tetrafunctional core, was studied. The effect of the size (pseudo‐generation number, from second to eight) and structure on the melt rheological properties was investigated for a series of hydroxyl‐terminated HB polyesters. In addition, the influence of the nature and degree of modification of the terminal OH groups in a series of fourth‐generation polyesters end‐capped with short and long alkyl chains and some aryl groups on the rheological properties was analyzed. The time–temperature superposition procedure was applied for the construction of master curves and for the analysis of the rheological properties of HB polyesters. The data obtained from WLF analysis of the HB polyesters showed that the values of the thermal coefficient of expansion of free volume α_f and the fractional free volume at the glass transition temperature, f_g, increase with increasing size of the HB polyesters. It was shown that the modified HB polyesters exhibited lower T_g and T_G′=G″ temperatures, above which viscous became dominant over elastic behavior. From an analysis of the master curves of the modified HB polyesters, it was observed that with increasing degree of modification, both storage and loss modules and complex dynamic viscosity and apparent energy for viscoelastic relaxation decrease, because of reduced intermolecular hydrogen interactions. They do not exhibit a plateau of rubbery behavior, which confirms that no entanglements are present and that the molar masses are below the critical molar mass. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41479.