Increase In Complex Viscosity Research Articles

Influence of Carbon Nanoparticles on Thermal, Mechanical and Rheological Properties of Polypropylene Nanocomposites Modified with Vinyl Trimethoxysilane

SummaryIn the present study, masterbatch of polypropylene and graphene nanocomposite was obtained by in situ polymerization. Afterwards, this masterbatch was diluted in commercial PP matrix previously treated with dicumyl peroxide (DCP) and vinyl trimethoxysilane (VTMS), originating grafted and reinforced filaments. Then, this material was crosslinked in water at 90 °C through condensation of hydroxyl groups derived from grafted PP chains. These materials were evaluated according to their thermal, mechanical and rheological properties. The results showed that it was possible to graft and crosslink PP, however, crosslinking was hindered by the presence of graphene sheets in the polymer matrix. In non‐reinforced crosslinked polymer, an increase in complex viscosity was observed, showing that actually occurred crosslinking. Furthermore, the grafted sample has lower molecular weight compared to the commercial PP. The crosslinked sample reduced its Newtonian plateau.

Thermoplastic Vulcanizate Based on Poly(lactic acid) and Acrylic Rubber Blended with Ethylene Ionomer

ABSTRACTA new thermoplastic vulcanizate (TPV) was developed by meltblending of poly(lactic acid) (PLA), acrylic rubber (ACM), and ethylene-methacrylic acid with sodium ions (EMAA-Na). The PLA/ACM/EMAA-Na blend showed low-yield strength, low modulus, and excellent strain recovery. It also demonstrated an increase in complex viscosity and decrease in melting temperature due to the interfacial reaction between the PLA and the ACM phases. The Fourier transform infrared spectroscopy results indicate that EMAA-Na can interact with both PLA and ACM, and that the Na+ ions act as a catalyst for the interfacial reaction between PLA and ACM, while PLA does not react with ACM without EMAA-Na. Moreover, the tensile strength at break of the PLA/ACM/EMAA-Na blend was observed to be extremely improved by the addition of hexamethylenediaminecarbamate (HMDC) due to the increasing of the cross-link density inside the rubber phase. The morphology of the PLA/ACM/EMAA-Na blend with HMDC was finer than that of PLA/ACM/EMAA-Na without HMDC. From the results, it is suggested that the interfacial reaction between the PLA and the ACM phases, the cross-linking in the ACM phase, and the finer morphology improved the mechanical properties of the blend.

Production of refractory chamotte particle-reinforced geopolymer composite

Geopolymer resins are obtained by alkaline activation of aluminosilicate sources where raw calcined clays are one of the suitable potentialities. Besides the fact that chemical composition has an essential effect on final properties of the geopolymer binder, the type of filler strongly affected resulting properties of such granular composite. However, very few comparative studies have been done on detail description of composite systems: binder - granular filler, in relation to aggregate gradation design and rheology properties of the mixture. The aim of this work is to develop and describe granular composite concerning workability of the mixture and kinetics of geopolymerization/polycondensation through flow behaviour. The rheological measurements indicated that initial viscosities of the mixtures and their evolution are different for various proportions of the filler. Moreover, it was demonstrated that increase in complex viscosity responds to the creation of chemical bonds and the formation of structural network. Finally, a correlation of the mechanism of geopolymer formation was carried out by differential scanning calorimetry (DSC).

Microencapsulation of 1-methylimidazole using solid epoxy resin: study on microcapsule residence time and properties of the system

In this study for the first time 1-methylimidazole was microencapsulated successfully by solid epoxy resin using solvent evaporation method. Fourier transform infrared spectroscopy, scanning electron microscopy, thermal gravimetric and differential scanning calorimetry were used for characterization of microcapsule and epoxy resin/microcapsule systems. The results revealed that although the solid epoxy shell was in contact with imidazole curing agent for a long time, it still remained as a thermoplastic. The chain length of the solid epoxy resin was grown in anionic polymerization process which led to an increase in the melting temperature from 64 to 78 °C. On the other hand, all epoxy functional groups of the shell did not participate in the curing reaction of resin with core curing agent of the microcapsule. The results showed that by increasing the residence time of the microcapsules, the number of epoxy groups of liquid epoxy decreased slightly but the rate of complex viscosity increase or the rate of curing reaction was increased and the cured epoxy system exhibited a single-phase morphology. On the other hand, in the presence of microcapsules the curing reaction of epoxy resin was successfully carried out and the curing temperature and the onset of viscosity increase or gel time at 120 °C were not more or less affected by sufficiently long contact time of epoxy and microcapsule.

The effect of pH and modified maize starches on texture, rheological properties and meltability of acid casein processed cheese analogues

The objective of this study was to investigate the influence of pH on texture, rheological properties and meltability of processed cheese analogues obtained using acid casein (AC) at 11, 12 or 13 % concentration or using 10 % AC with 1, 2 or 3 % acetylated distarch adipate (ADA) or hydroxypropyl distarch phosphate (HDP). Hardness, adhesiveness, cohesiveness and viscosity increased with protein or starch concentration. The increase in complex viscosity (η*) was greater for samples contained ADA than HDP. In general, starch-containing cheese analogues exhibited more viscous properties (tan δ > 1) in higher pH values (6.0–7.0) and more elastic properties (tan δ < 1) in lower pH values (4.5–5.5). All processed cheese analogues obtained at pH 5.0–7.0 presented good melting characteristics. These various characteristics analysed in the present study may ensure the valuable information for obtaining cheeses with proper textural/rheological properties and meltability.

Rheological and mechanical properties of polyamide 6 modified by electron-beam initiated mediation process

Abstract Polyamide (PA6) has been modified by electron-beam initiated mediator process to improve drawbacks of PA6. Glycidyl methacrylate (GMA) was chosen as a reactive mediator for modification process of PA6. The mixture of the PA6 and GMA was prepared by using a twin-screw extruder, and then the mixture was exposed to electron-beam irradiation at various doses at room temperature. The modified PA6 were characterized by observing rheological and mechanical properties and compared virgin PA6. Thermal properties, water absorption, and gel fraction were also investigated. Tight gel was not found even when PA6 was irradiated at 200 kGy. Complex viscosity and storage modulus of PA6 were remarkably increased by electron-beam irradiation with medium of GMA. Maximum increase in complex viscosity was 75 times higher than virgin PA6 at 0.1 rad/s when it was irradiated at 200 kGy with the GMA. Mechanical properties were also improved without scarifying of processability. The reaction mechanisms for the mediation process with the reactive mediator of GMA were estimated to elucidate the cause of significantly enhanced rheological and mechanical properties without loss of thermoplasticity.

Study on ternary low density polyethylene/linear low density polyethylene/thermoplastic starch blend films.

In this work, low-density polyethylene/linear low-density polyethylene/thermoplastic starch (LDPE/LLDPE/TPS) films are prepared with the aim of obtaining environmentally friendly materials containing high TPS content with required packaging properties. Blending of LDPE/LLDPE (70/30 wt/wt) with 5-20 wt% of TPS and 3 wt% of PE-grafted maleic anhydride (PE-g-MA) is performed in a twin-screw extruder, followed by the blowing process. Differential scanning calorimetric results indicate starch has more pronounced effect on crystallization of LLDPE than LDPE. Scanning electron micrograph shows a fairly good dispersion of TPS in PE matrices. Fourier transfer infrared spectra confirm compatibility between polymers using PE-g-MA as the compatibilizer. Storage modulus, loss modulus and complex viscosity increase with incorporation of starch. Tensile strength and elongation-at-break decrease from 18 to 10.5 MPa and 340 to 200%, respectively when TPS increases from 5 to 20%. However, the required mechanical properties for packaging applications are attained when 15 wt% starch is added, as specified in ASTM D4635. Finally 12% increase in water uptake is achieved with inclusion of 15 wt% starch.

The dynamic performance of a shear thickening fluid viscous damper

This paper presents a study of the rheological properties of shear thickening fluids (STF) and the performance of a viscous damper filled with an STF by performing a cyclic loading test. In the rheological test, the STF samples were prepared by blending nanoscale fumed silica powder with polypropylene glycol fluid in different weight fractions. Using a strain-controlled rheometer with a cone and plate tool, both steady and oscillatory state experiments were performed and the rheological properties of the STF were observed. Experimental results showed an abrupt increase in complex viscosity beyond a critical dynamic shear strain rate . In this study, a hydraulic steel tube was filled with an STF to develop an innovative passive damper device. The STF-filled damper performance test showed that the area and shape of hysteresis loops can vary with different loading conditions. The analytical models studied and a numerical approach showed that STF-filled dampers are potentially useful in practical engineering applications.

Effect of OMMT on Morphology and Property of PTT/ASA Blends

Nanocomposites of poly(trimethylene-terephthalate)/poly(acrylonitrile-styrene-acrylate)/organic montmorillonite(PTT/ASA/OMMT) were prepared by means of melt-blending intercalation. The effect of OMMT contents on the phase morphology, crystallization behavior, rheological- and mechanicalproperties were investigated. The results show that the size of dispersed phases decreases with increasing OMMT content. The crystallization peak shifts to high temperature and melting peak moves to low temperature owing to the heterogeneous nucleation of OMMT. The exfoliated OMMT is located in the PTT matrix and at interface of PTT/ASA phases The rheological measurements show that the elastic modulus and complex viscosity increase with increasing OMMT content. The interfacial modulus and interfacial layer thickness predicted by Palierne and Gramspacher-Meissner models are enhanced by introduction of OMMT. The tensile strength and notched impact strength of blends increase with increasing OMMT content.

Investigations on clay dispersion in polypropylene/clay nanocomposites using rheological and microscopic analysis

ABSTRACTMorphology assessment plays an important role as the ultimate properties of the processed nanocomposites mainly depend upon the morphology. This study focuses on the evaluation of polypropylene/clay nanocomposite structure using rheological and transmission electron microscopic investigation. Melt processing of nanocomposite was carried out on a co‐rotating twin screw extruder. Maleic anhydride grafted polypropylene (PP‐g‐MA) was used as a compatibilizer to facilitate better mixing of clay in polypropylene. The effect of compatibilizer to clay ratio on dispersion was analyzed through rheological data. An increase in complex viscosity and storage modulus with increase in compatibilizer content is observed at lower frequency region. Shifting of crossover frequencies to a lower value also indicate better exfoliation. Improved exfoliated morphology was also corroborated by Cole–Cole and inverse loss tangent plots. Transmission electron microscopy (TEM) micrograph based unique statistical image analysis was carried out using ImageJ software. A compatibilizer to clay content of 2 : 1 was found to be the optimum composition which was further supported by dielectric and mechanical properties. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4464–4473, 2013

Flow Characteristics and Dynamic Behavior of Polyamide 6/Acrylonitile Butadiene Styrene (PA6/ABS) Blends

The objective of this research was to investigate the effect of incorporation of maleic anhydride grafted acrylonitrile-butadiene-styrene (ABS-g-MAH) on rheological properties of PA6/ABS blends. Flow properties of the blends were examined by dynamic and capillary rheometers. The dynamic rheological analyses showed an increase in complex viscosity with the incorporation of a compatibilizer. The reduction of tan δ peaks showed enhanced interfacial interaction between PA6 and ABS phase, which resulted in the enhancement of melt strength. The power law index analysis showed that 1.5 wt.% resulted in minimum n and maximum K value for the blends while still retaining the pseudoplastics behavior necessary for plastics processing and prediction for the end use performance of the PA6/ABS blends.

Rheological study of the SAN modified epoxy–DDM system: relationship between viscosity and viscoelastic phase separation

The rheological behavior and structural transitions in an epoxy–amine system and poly(styrene-acrylonitrile) SAN modified epoxy–amine systems were studied by, optical microscopy and rheometry. The SAN modified epoxy blends undergo viscoelastic phase separation. The concentration of SAN has a profound effect on viscoelastic phase separation and hence the rheological behavior of modified epoxy systems. The evolution of complex viscosity is closely related to viscoelastic phase separation. The increase in complex viscosity shifted to shorter times upon increasing the concentration of SAN due to viscoelastic phase separation. The complex viscosity profiles follow an exponential growth with phase separation at various cure temperatures. The relaxation time of viscosity growth depends on both the concentration of SAN and cure temperature. The relaxation time of viscosity growth can be described by the WLF equation.

Reactive extrusion of polypropylene/polystyrene blends with supercritical carbon dioxide

A reactive extrusion process for immiscible polypropylene/polystyrene (PP/PS) blends with peroxides and multifunctional agents in the presence of supercritical carbon dioxide (scCO2) was studied. The PP/PS blends were investigated by rheological measurement, scanning electron microscopy, thermal analyzer, and mechanical testers. The results show that the complex viscosity and the storage modulus of the blends increase with the addition of peroxides and multifunctional agents, which might represent the formation of copolymer during melt processing. From the morphology analysis of the blends, the size of the dispersed PS domain decreases significantly. Moreover, the analysis of the blends also reveals that the use of supercritical carbon dioxide leads to an increase of complex viscosity and a decrease of domain size. It was believed that the use of scCO2 improved the compatibility of the blends. The interfacial tensions of the PP/PS blends were predicted theoretically from the rheological data using the Choi and Schowalter model and the Palierne model. The values of the interfacial tension decreased as the compatibility of PP/PS blends was improved. From the results above, we strongly suggest that the use of supercritical carbon dioxide-assisted reactive extrusion is an effective way to improve the compatibility of the PP/PS blends.

A study on the effect of nano-ZnO on rheological and dynamic mechanical properties of polypropylene: Experiments and models

Three polypropylene (PP)/zinc oxide nanocomposites containing 5, 10 and 15wt.% nanoparticles were prepared through melt-blending. Compression molded samples for dynamic mechanical and morphological studies were prepared. The nano-ZnO particles were observed to be dispersed uniformly, but with a different level of coalescence, by means of scanning electron microscopy (SEM). The plots of experimental and theoretical storage moduli values at 20°C for various loadings of nanoparticles by wt.% Showed that the Einstein model had better agreement with experimental values while the Guth model deviated the most. Dynamic rheometry using a parallel plate rheometer showed that the rheological moduli of the nanocomposites increased with increase in nanofiller concentration; however this increase was greater in the high frequency region. There was an increase in complex viscosity of the nanocomposites with increasing the nanofiller concentration. Moreover, the rheological behavior of nanocomposites is more sensitive to nanoparticle concentration at low frequencies. All of the models used for prediction of melt viscosity underestimated the viscosity of nanocomposites, but the Einstein equation was the nearest to experimental values.

Estudo do reprocessamento de polietileno de baixa densidade (PEBD) reciclado do processamento de extrusão de filmes tubulares

O mercado de reciclagem para os polímeros termoplásticos encontra-se atualmente em acentuada ascensão. Os materiais reciclados são vistos como materiais de propriedades inferiores em relação ao material virgem. O presente trabalho avaliou as características viscoelásticas e térmicas do polietileno de baixa densidade (PEBD) reciclado. As amostras foram reprocessadas até dez vezes em condições extremas de processamento (300 °C/80 rpm) em uma extrusora monorosca, a fim de avaliar modificações estruturais nas suas propriedades. Foram realizadas análises de reometria oscilatória de placas paralelas e calorimetria exploratória de varredura (DSC). A partir das análises de reometria oscilatória foram calculados espectros de relaxação e retardação pelo programa de regularização não-linear (NLREG) e através das análises de DSC no primeiro aquecimento foram calculados os parâmetros cinéticos pelos métodos de Avrami e Freeman-Carroll. Os resultados do estudo reológico demonstraram que as amostras reprocessadas acima de quatro vezes apresentaram aumento da viscosidade complexa e dos módulos de armazenamento e perda, além de fenômenos de relaxação e retardação mais largos. Entretanto, os termogramas de DSC e os parâmetros cinéticos de fusão demonstraram que o PEBD estudado manteve sua estabilidade térmica, independentemente da modificação de suas características viscoelásticas.

Effect of nano-CaCO 3 on rheological and dynamic mechanical properties of polypropylene: Experiments and models

Three polypropylene (PP)/calcium carbonate nanocomposites containing 5, 10 and 15 wt% nanoparticles were prepared through melt-blending. Compression molded samples for dynamic mechanical and morphological studies were prepared. The nano-CaCO 3 particles were observed to be dispersed uniformly, but with a different level of coalescence, by means of scanning electron microscopy (SEM). The plots of experimental and theoretical storage moduli at 20 °C for various loadings of nanoparticles by wt% Showed that the Einstein model had better agreement with experimental values while the Guth model deviated the most. Dynamic rheometry using a parallel plate rheometer showed that the rheological moduli of the nanocomposites increased with increase in nanofiller concentration; however this increase was greater in the high frequency region. There was an increase in complex viscosity of the nanocomposites with increasing nanofiller concentration. Moreover, the rheological behavior of nanocomposites is more sensitive to nanoparticle concentration at low frequencies All of the models used for prediction of melt viscosity underestimated the viscosity of nanocomposites, but the Roscope equation was the nearest to experimental values.

Dimer acid-based thermoplastic bio-polyamides: Reaction kinetics, properties and structure

New dimer acid-based-polyamides were synthesized with rapeseed oil-based dimer acid (DA) and 1,2-diaminoethane, 1,6-diaminohexane or 1,8-diaminooctane to form DAPAe, DAPAh and DAPAo, respectively. Effects of diamine chain lengths on kinetics evolution as well as on the thermal, physical and mechanical properties of the different polyamides synthesized were investigated. DAPAo was found to be the most reactive diamine because of its higher nucleophilic character. Differential scanning calorimetry (DSC) combined with X-ray diffraction revealed a low-order semi-crystalline structure for all polyamides. A tentative schema for the structural organization of these DAPA is proposed and shows a specific organization with local semi-crystalline segregation domains. DAPAe was found to possess the higher melting temperature likely due to higher crystal cohesion, which was confirmed by higher Young modulus in stress-strain experiments. Rheological data showed an increase of the glass transition temperature concomitantly with the increase of diamine chain length. They also revealed an increase of complex viscosity with the diamine chain length. Investigation of thermal stability showed that DAPAe degrades before DAPAh and DAPAo in connection with the number of methylene units per diamine.

Rheology and extrusion foaming of chain‐branched poly(lactic acid)

AbstractIn this study, the effect of macromolecular chain‐branching on poly(lactic acid) (PLA) rheology, crystallization, and extrusion foaming was investigated. Two PLA grades, an amorphous and a semi‐crystalline one, were branched using a multifunctional styrene‐acrylic‐epoxy copolymer. The branching of PLA and its foaming were achieved in one‐step extrusion process. Carbon dioxide (CO2), in concentration up to 9%, was used as expansion agent to obtain foams from the two PLA branched using chain‐extender contents up to 2%. The foams were investigated with respect to their shear and elongational behavior, crystallinity, morphology, and density. The addition of the chain‐extender led to an increase in complex viscosity, elasticity, elongational viscosity, and in the manifestation of the strain‐hardening phenomena. Low‐density foams were obtained at 5–9% CO2for semi‐crystalline PLA and only at 9% CO2in the case of the amorphous PLA. Differences in foaming behavior were attributed to crystallites formation during the foaming process. The rheological and structural changes associated with PLA chain‐extension lowered the achieved crystallinity but slightly improved the foamability at low CO2content. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers

Effect of different matrices and nanofillers on the rheological behavior of polymer‐clay nanocomposites

AbstractIn this work, a comprehensive study of the rheological behavior under shear and isothermal and nonisothermal elongational flow of low density polyethylene (LDPE) and ethylene‐vinyl acetate copolymer (EVA) based nanocomposites was reported to evaluate their “filmability”, that is, the ability of these material to be processed for film forming applications. The influence of two different kinds of organoclay – namely Cloisite 15A and Cloisite 30B – and their concentration was evaluated. The presence of filler clearly affects the rheological behavior in oscillatory state of polyolefin‐based nanocomposites but the increase of complex viscosity and the shear thinning are not dramatic. A larger strain‐hardening effect in isothermal elongational flow is shown by the nanocomposites compared to that of the pure matrix, particularly for EVA based nanocomposites. The melt strength measured under nonisothermal elongational flow increases in the presence of the nanofiller, while the drawability is only slightly lower than that measured for the neat matrix. Moreover, the rheological behavior under nonisothermal elongational flow of EVA‐based nanocomposites is similar for both nanoclays used. Differently, LDPE‐based nanocomposites show a strong dependence on the type of organoclay. Finally, the mechanical properties of the materials were measured by tensile tests. They revealed that the presence of the filler provokes, in all the cases, an increase of the rigidity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 344–355, 2010

Influence of coal thermoplastic properties on coking pressure generation: Part 2 – A study of binary coal blends and specific additives

A number of coal blends and pitch/coal blends were evaluated using rheometry, thermogravimetric analysis and microscopy to confirm and further elucidate the coking pressure mechanism previously proposed by Duffy et al. (2007) [1]. We confirm that blending a low rank, high fluidity, low coking pressure coal, with a high rank, low fluidity, high coking pressure coal can significantly reduce the coking pressure associated with the latter. Interestingly, blending does not necessarily result in a fluidity that is midway between that of the two coals; sometimes the fluidity of the blend is less than that of the low fluidity coal, especially when the coals are significantly different in rank. This occurs because the increase in complex viscosity ( η*) through resolidification of the low rank, high fluidity coal counteracts the reduction in η* resulting from softening of the high rank, low fluidity coal. It has also been confirmed that the η* of the resultant blend can be estimated from the η* of each component coal using a logarithmic additivity rule commonly employed for polymer blends. Polarised light microscopy has indicated that the degree of mixing between coals of different rank is minimal, with fusion restricted to the particle surface. It is therefore inappropriate to think of such a coal blend in the same way as a single coal, since each component coal behaves relatively independently. This limited fusion is important for understanding the coking pressure mechanism for blends. It is proposed here that the lower rank coal, which softens at lower temperature, is able to expand into the interparticle voids between the high rank coal that is yet to soften, and these voids can create channels for volatiles to traverse. Then, and importantly, when the high rank coal begins to expand, the pore structure developed in the resolidified structures of the low rank coal can facilitate removal of volatiles, while the resolidified material may also act as a suitable sorbent for volatile matter. This is considered to be the primary mechanism by which coal blending is able to alleviate coking pressure, and applies to addition of inert material also. Addition of a coal tar pitch was found to increase fluidity but also to extend the thermoplastic range to lower temperatures. This caused an increase in the swelling range, which was accompanied by a long plateau in η*, a feature which has previously been observed for certain high fluidity, high pressure coals. Elasticity and η* at the onset of expansion were also higher for both the pitch impregnated coals and the high pressure blends, which supports previous findings for singly charged high pressure coals, and confirms the potential use of such criteria for identifying potentially dangerous coals/blends.