Rheology and microstructure of functionalized polymer‐modified asphalt

Viscoelastic and morphological properties of functionalized‐polymer‐modified asphalt, FPMA, have been described as function of number of epoxy groups presented in the functionalized polymer. At low temperatures, simple viscoelastic models can predict the elastic response of FPMA at short times and its viscous behavior at long times. The increase of epoxy groups yielded an increase on activation energy for viscous deformation of FPMA, and so, on its resistance to irreversible deformations under strain cycles. From ambient to higher temperatures, emulsion model can predict rheological properties of FPMA because they behave as viscoelastic emulsions. Modification of relaxation spectrum for FPMA due to the presence of a polymer network was not as strong as in normal PMA, thus, the rheological behavior of FPMA was found similar to systems having weak networks. However, the network became stronger as the number of epoxy groups was increased. This trend was verified by morphology of FPMA. Emulsion‐like structure was observed for all FPMA but differentiating each other by the polymer particle size. It was also observed that increase on epoxy groups, polymer particle size in the FPMA decreased, and higher stability at 180°C of FPMA was observed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Diffusion of chloride ions in polymer‐mortar composites

In recent years, the rapid deterioration of various reinforced concrete structures has been a widely recognized problem in the world. Penetration of chloride ions into the concrete structures was found to be the major cause of premature corrosion of reinforcing steel and to promote their deterioration. The present articles deals with the resistance to chloride penetration of polymer‐mortar, which are often used as low‐cost promising materials for preventing or repairing various reinforced concrete structures. To gain more knowledge on the efficiency of polymer‐mortar, four mortar mixtures: one specimen with Portland cement (control sample) and three mixtures with 2.5, 5, and 7.5 wt % of the replacement of cement by polyethylene terephthalate (PET) were tested for chloride ion permeability under immersion in 5% sodium chloride solution. Their chloride ion penetration behavior is discussed by applying Fick's second law. In conclusion, the chloride ion penetration depth and apparent chloride ion diffusion coefficient of the polymer‐mortar composites are smaller than those of unmodified mortar. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Novel polymer‐ceramic composites for protection against ballistic fragments

For the first time, internally reinforced aggregate polymer ceramic composites were evaluated against fragment simulating projectiles (FSPs) of various calibers to investigate their ballistic impact response. Samples were prepared by mechanically mixing B₄C and cBN over a range of ratios and combinations with either thermosetting phenolic or epoxy resin and aramid pulp. Dry mixtures were then molded in a closed die using a heated platen press. The resulting tiles were then mounted as “strike faces” to an aramid backing material using an epoxy resin. Backed targets were tested in a fully instrumented firing range against 5.56 mm FSPs to test ballistic limit. A further series of tests using 7.62, 12.5, and 20 mm FSPs was conducted to examine round deformation across a range of fragments calibers. Round deformations were measured after impact and plotted against shot velocity. It was found that the polymer ceramic composite materials were effective round deformers and, like sintered ceramic strike faces, demonstrated improved ballistic performance at an equivalent areal density and impressive multihit capability. POLYM. COMPOS., 2012. © 2013 Society of Plastics Engineers     

Rheological study on high‐density polyethylene/organoclay composites

Maleic anhydride‐grafted polyethylene (MAPE) is investigated as a compatibilizer of polyethylene/organoclay nanocomposite. With MAPE help, partial exfoliation of the organoclay occurs in the nanocomposites with the melt compounding method for organoclay loading up to 8.0 wt%. Investigation of the rheological behaviors shows that at high frequencies or shear rates, the viscosity is essentially unaffected by the presence of organoclay; however, at low frequencies or shear rates, viscoelastic behavior alters dramatically, and this is attributed to the presence of anisotropic stacks of randomly oriented organoclay sheets and the formation of network structures. The important observations are firstly the initial stress overshooting observed in steady shear. At low shear rates, stress is much greater at the initial stage than the stress at the steady state; however, it can be eliminated by preshear at low shear rates, which means that preshearing can effectively break down the network structures and align the organoclay. Second, the normalized stress at the overshoot point is a function of the critical strain unit. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Polypropylene‐organoclay nanocomposite: Preparation,microstructure, and mechanical properties

A series of polypropylene (PP) nanocomposites containing 2, 4, and 6 wt % of an organophilic montmorillonite clay was prepared via direct melt mixing in the presence of maleic anhydride grafted polypropylene (PP‐g‐MAH) as compatibilizing agent. Microstructure characterization was performed by X‐ray diffraction analysis. Nanocomposites exhibited a 15 and 22% enhancement in tensile modulus and impact strength, respectively. The heat deflection temperature of PP nanocomposites was 36°C greater than for pure PP. Thermal and mechanical properties of nanocomposites were compared to properties of traditional PP‐talc and PP‐glass fiber composites. The results showed that the properties of nanocomposites improved compared to ordinary polypropylene composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The impact of chaotic advection on the microstructure of polymer‐modified bitumen

Owing to the high viscosity of the materials involved, mixing is often a critical step when processing polymer‐modified bitumen (PMB), directly influencing the microstructure and the stability of final products. We provide experimental evidence suggesting that laminar chaotic advection may prove a valuable strategy for obtaining a homogeneous and finely interdispersed polymer‐bitumen mixture in affordable time. As a case study, we investigate the mixing performance of a lab‐scale flat‐bottomed cylindrical vessel stirred by a radial impeller, either located symmetrically or eccentrically with respect to the vessel axis. The same geometries with a flat‐disk impeller are also considered for comparison. The Mix‐Norm is used in combination with image analysis as an objective measure of mixing performance. Results of mixing performance are independently validated by rheological tests. The experiments pinpoint kinematic chaos as the fundamental transport mechanism enhancing both the dispersion process and the microstructural quality of the resulting PMBs mixture. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1870–1879, 2014     

Effects of organoclay modification on microstructure and properties of polypropylene–organoclay nanocomposites

We prepared polypropylene nanocomposites based on a modified organoclay with isobutyl trimethoxysilane to investigate the effects of such modifications of organoclay on the microstructure and properties of the nanocomposite. The organoclay was preliminarily intercalated with distearyldimethylammonium bromide via an ion exchange before being grafted with silane. The morphology of the polypropylene–organoclay nanocomposites was characterized by wide‐angle X‐ray diffraction analyses and transmission electron microscopy. The modification of the edges of clay platelets with organic silane resulted in a more uniform dispersion of nonagglomerated tactoids, which consisted of several intercalated clay platelets. However, the unmodified organoclay led to a mixed morphology with both agglomerated and nonagglomerated tactoids. The grafting of the clay edges with organic silane also affected the linear viscoelastic properties of the nanocomposites in the melt state, which was shown to be sensitive to the interaction between the edges of clay platelets as well as to the interaction of the polymer with the platelet edges. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1752–1759, 2006     

Manipulating the conductivity of carbon‐black‐filled immiscible polymer composites by insulating nanoparticles

The conductivity of an immiscible polymer blend system, microfibrillar conductive poly(ethylene terephthalate) (PET)/polyethylene (PE) composite (MCPC) containing carbon black (CB), was changed by the addition of insulating CaCO₃ nanoparticles. In MCPC, the PET forms microfibrils during processing and PE forms the matrix. The CB particles are selectively localized in the PET microfibrils. When the insulating CaCO₃ nanoparticles are added, they substitute for some of the conductive CB particles and obstruct the electron paths. As a result, the resistivity of the MCPC can be tailored depending on the insulating filler content. The resistivity‐insulating filler content curve displays a sluggish postpercolation region (the region immediately following the percolation region and in front of the equilibrium flat of the resistivity‐filler content curve), suggesting that the MCPC in the postpercolation region possesses an enhanced manufacturing reproducibility and a widened processing window. These features are of crucial importance in making sensor materials. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008.     

Melt rheology of organoclay and fumed silica nanocomposites

The objective of the present work is to investigate, from the open literature, the recent developments in the rheology of silica and organoclay nanocomposites. In particular, this paper focuses on general trends of the linear viscoelastic behaviour of such nanocomposites. Hence, the variations of the equilibrium shear modulus and critical strain (limit of linearity), which depend on power laws of the volume fraction of particles, are discussed as filler fractal structure. In the third section, the strong nonlinearity behaviour (Payne effect) of filled polymers has been discussed in terms of filler nature. Typically two mechanisms arise to depict the linear solid-like behaviour and the Payne effect: particle–particle interactions is the dominant mechanism in fumed silica nanocomposites whereas particle–polymer interaction is the dominant one in colloidal silica nanocomposites at identical filler concentrations. However, these interactions are balanced in each nanocomposite systems by the silica surface treatments (chain grafting, silane modification) and the molecular weight of the matrix. Finally, we aim to unify the main findings of the literature on this subject, at least from a qualitative point of view.We finally report on the thixotropy and modulus recovery after a large deformation in steady and dynamic shear conditions. Following this, the nonlinear rheological properties of nanocomposite materials have been discussed. The discussion is particularly focused on the effect of flow history (transient shear experiments) on the orientation–disorientation of clay platelets. Actually, the linear and nonlinear rheological properties are consistent with a network structure of a weakly agglomerated tactoids. As far as exfoliated clay nanocomposites are concerned, the inter-particle interaction is the dominant effect in the nonlinearity effect.     

Rheological investigations on the flow behavior of polymer‐microsized iron powder composites

With respect to the fabrication of metal parts carrying surface relief microstructures using composite reaction molding as a rapid prototyping variant of micrometal injection molding, the influence of microsized iron powder on the viscosity of different unsaturated polyester resins applied as polymer binder has been investigated systematically. The initial binder viscosity determines the viscosity of the composite and hence the accessible critical filler load. A further dilution of the unsaturated polyester resin with styrene allows a significant increase of the filler load at constant shear rate and temperature from 36 up to 57 vol% iron content. A successful estimation of the critical filler load using different established empirical models initially developed for ceramic‐filled solutions or dispersions is possible. A pronounced flow activation energy increase at high iron loads was also observed. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Dynamic and capillary shear rheology of natural fiber‐reinforced composites

An extended dynamic and capillary rheological study of molten flax and sisal polypropylene (PP) composites was performed. Fiber concentration varied from 20 to 50 wt% and shear rate from 0.1 rad s^?1 to 10,000 s^#142;?1. Maleic anhydride‐grafted‐PP was used as compatibilizer; it strongly reduces PP and composite viscosity. Composites are yield‐stress shear‐thinning fluids with solid‐like behavior being more pronounced at high fiber content. Composites do not obey Cox–Merz rule, which was explained by different macrostructures of the molten composites in parallel plates and capillary die geometries: random fiber orientation versus strong alignment in the flow direction, respectively. Theories describing the viscosity of suspensions of solid particles were applied to the composites studied and rheological parameters and maximal packing fiber volume fraction were calculated. POLYM. ENG. SCI., 53:2582–2593, 2013. ©2013 Society of Plastics Engineers.     

Physicomechanical properties of irradiated SBR latex polymer‐modified cement mortar composites

This study investigated the effect of styrene–butadiene‐rubber (SBR) latex/cement ratio as well as γ‐irradiation dose on physicomechanical properties of cement mortar. Specimens were prepared with a different SBR/cement mass ratio of 2.5, 5, 10, 15, and 20. Two curing methods were used: wet cure and dry cure. The best specimens were irradiated to doses of 10, 30, and 50 kGy. The compressive strength, total porosity, and bulk density were studied. The result indicated that the compressive strength, total porosity, and the bulk densities of the composites decrease with increase in the polymer cement ratios. In addition, it was observed that the compressive strength of irradiated polymer‐modified cement mortar composites was improved with the increase in the γ‐irradiation dose, and the compressive strength of mix‐cured samples was higher than those wet‐cured samples at any irradiation dose. X‐ray diffraction, thermogravimetric analysis, acid attack, and microstructure of SBR‐modified cement mortar were characterized. J. VINYL ADDIT. TECHNOL., 26:144–154, 2020. © 2019 Society of Plastics Engineers     

Structure‐rheology responses of polylactide/calcium carbonate composites

Polylactide (PLA) and calcium carbonate (CaCO₃) were melt blended using a twin‐screw extruder. The morphology of PLA/CaCO₃ composites was observed by scanning electronic microscopy. The linear and nonlinear shear rheological behaviors of PLA/CaCO₃ melts were investigated by an advanced rheology expended system. The results show that the CaCO₃ particles are evenly dispersed in the PLA matrix. The incorporation of low CaCO₃ content (<20%) causes the reduction of the storage moduli, loss moduli, and dynamic viscosities whereas high CaCO₃ content (>30%) leads to the increase of the storage moduli, loss moduli, and dynamic viscosities. The composites with high CaCO₃ content show pseudo‐solid‐like behaviors at low frequency. High CaCO₃ content also results in a significant increase of flow activation energy and a dramatic decrease of flow index n, which is in consistent with the more serious shear‐thinning tendency of high‐filled PLA composites melts. The particular rheological responses might be attributed to the formation and destruction of the percolating network. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Nematic–isotropic transition in polymer‐confined and polymer‐free liquid crystal mixtures

Depending on the processing conditions in liquid crystal (LC) display manufacturing, LC/polymer composite films may exhibit unusual properties with respect to the compositional and phase behavior of the LC constituents. In particular, we have observed extraordinary large shifts of phase transition temperatures in LC/polymer composites, which can not be explained by preferential solvation or adsorption. Therefore, the influence of real manufacturing conditions such as thermal stress, storage in vacuum, and UV irradiation on the nematic–isotropic (n–i) transition temperatures of commercial nematic mixtures was investigated. Shifts of the clearing temperature of up to 88 K, presumably due to partial evaporation or UV degradation, were observed. Furthermore, we found that annealing may lead to the replacement of the nematic phase by the smectic A phase at room temperature in both LC/polymer composites and pure LC samples. Among the tested commercial LC blends, the mixtures E7, MLC‐6650, and L101 showed the smallest stress effects. Practical consequences of our results are discussed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Recycling of poly(ethylene terephthalate) as polymer‐polymer composites

Microfibrillar reinforced composites (MFC) comprising an isotropic matrix from a lower melting polymer reinforced by microfibrils of a higher melting polymer were manufactured under industrially relevant conditions and processed via injection molding. Low density polyethylene (LDPE) (matrix) and recycled poly(ethylene terephthalate) (PET) (reinforcing material) from bottles were melt blended (in 30/70 and 50/50 PET/LDPE wt ratio) and extruded, followed by continuous drawing, pelletizing and injection molding of dogbone samples. Samples of each stage of MFC manufacturing and processing were characterized by means of scanning electron microscopy (SEM), wide‐angle X‐ray scattering (WAXS), dynamic mechanical thermal analysis (DMTA), and mechanical testing. SEM and WAXS showed that the extruded blend is isotropic but becomes highly oriented after drawing, being converted into a polymer‐polymer composite upon injection molding at temperatures below the melting temperature of PET. This MFC is characterized by an isotropic LDPE matrix reinforced by randomly distributed PET microfibrils, as concluded from the WAXS patterns and SEM observations. The MFC dogbone samples show impressive mechanical properties—the elastic modulus is about 10 times higher than that of LDPE and about three times higher than reinforced LDPE with glass spheres, approaching the modulus of LDPE reinforced with 30 wt% short‐glass fibers (GF). The tensile strength is at least two times higher than that of LDPE or of reinforced LDPE with glass spheres, approaching that of reinforced LDPE with 30 wt% GF. The impact strength of LDPE increases by 50% after reinforcement with PET. It is concluded that: (i) the MFC approach can be applied in industrially relevant conditions using various blend partners, and (ii) the MFC concept represents an attractive alternative for recycling of PET as well as other polymers.     

Biodegradation dynamics of polymer–starch composites

The dynamics of starch biodegradation in polyethylene–starch (PE–S) composites was investigated by aerobic biodegradation methods and computer simulations, with the starch fraction p above and below the percolation threshold p_c. Two models for starch degradation were considered: (i) microbial invasion through the composite and (ii) macromolecular (enzyme) diffusion which results in the back‐diffusion of small molecules to the surface for further assimilation by microorganisms. The microbial‐invasion model was based on scanning electron microscopy (SEM) studies of PE–S composites that contained a 1–15‐micron distribution of starch particles. Following exposure to soil test conditions, micrographs of thin films clearly showed the colonization of microorganisms within channels of the matrix that were initially occupied by starch. The enzymatic diffusion was based on hydrolytic experiments of PE–S composites. Following exposure of a composite to a hydrolytic test condition, small molecules were produced. The starch accessed by microbes and enzymes was computed by simulating degradation of a monodisperse and polydisperse (starch grains of 1–10‐micron diameter) composite. Aerobic degradation studies in a biometer indicate that the starch accessibility. A follows a power‐law dependence with time A ∼ tⁿ, where the exponent n depends on the fractal dimension of the accessed starch clusters and pathways and approaches unity when p > p_c. Microbial invasion simulations indicate that the average power‐law exponent near p_c is approximately 0.5 and approaches 1.0 at p > pc, whereas the enzymatic diffusion simulations indicate that the average power‐law exponent near p_c is about 0.25 and approaches 0.5 at p > pc. The observed exponent for the aerobic degradation study suggests that for composites with a starch fraction less than and greater than p_c the starch is predominantly accessed by microbial invasion. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1643–1657, 2000     

Electrical conductivity and rheology of carbon‐filled liquid crystal polymer composites

One emerging market for electrically conductive resins is for bipolar plates for use in fuel cells. Adding carbon fillers to thermoplastic resins increases composite electrical conductivity and viscosity. Current technology often adds as much of a single type of carbon filler as possible to achieve the desired conductivity, while still allowing the carbon‐filled thermoplastic matrix material to be extruded and molded into a bipolar plate. In this study, varying amounts of two different types of carbon, one carbon black and one synthetic graphite, were added to Vectra A950RX liquid crystal polymer. The resulting single filler composites were then tested for electrical conductivity and rheological properties. The electrical conductivity followed that typically seen in polymer composites with a percolation threshold at 4 vol % for carbon black and at 15 vol % for synthetic graphite. Over the range of shear rates studied, the viscosity followed a shear‐thinning power law model with power‐law exponent (n ? 1) = ?0.5 for neat Vectra A950RX and (n ? 1) = ?0.7 for highly filled composite materials. Viscosity increased with increasing filler volume fraction for all shear rates. The viscosity–enhancement effect was more rapid for the composites containing carbon black when compared with those containing synthetic graphite. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2680–2688, 2006     

Probe dependency of polymer‐plasticizer and polymer‐polymer interaction parameters in inverse gas chromatography

Inverse gas chromatography has been widely used to determine the Flory–Huggins parameter, χ, between a plasticizer and a polymer, or between two polymers. Many studies showed that interaction parameters may be probe dependent. In a recent study it was proposed that, when a specific interaction occurred between two polymers, the probes had less interaction with the polymers, leading to a lower solubility parameter for polymer blends than the volume average of the components. An equation was derived to relate the probe dependency to the deviation of solubility parameter of polymer mixtures. Here this approach is applied to plasticized poly(vinyl chloride) (PVC) and a copolymer, and to poly(vinylidene fluoride)–poly(ethyl methacrylate) blends. For a PVC and epoxidized oil system the relative deviation of specific retention volume showed two trends, with saturated hydrocarbons as one group, and polar and aromatic probes as another group. For the poly(vinylidene fluoride)/poly(ethyl methacrylate) system the plot of retention volume deviation versus solubility parameter of probes also showed separate trends for n‐alkanes, esters, and alcohols. But the plot of ?₂?₃RT(χ₂₃/V₂) versus solubility parameter had better linearity for the systems studied. The slope of this plot was used as an indicator for miscibility. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Ionic polymer‐metal composites made from radiation grafted FEP‐g‐styrene‐SO3H membranes

Ionic polymer‐metal composites have been made from radiation grafted fluorinated ethylene propylene (FEP) membranes. Membranes have been synthesized by grafting of styrene on FEP films followed by sulfonation. These membranes were then used to fabricate IPMCs. Chemical plating of silver has been done to form the microelectrodes. Influence of degree of grafting on actuation, surface resistance, and tensile properties of the IPMC have been evaluated. It has been observed that on increasing the degree of grafting surface resistance, tensile strength, and elongation of IPMC decrease while degree of actuation and modulus increase. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008