Influence of Carbon Black and Silica Filler on the Rheological and Mechanical Properties of Natural Rubber Compound

Rubber compounds are reinforced with fillers such as carbon black and silica. In general, filled rubber compounds shows smooth rheological behavior and mechanical properties. Variation in rheological behavior and mechanical properties was studied in terms of the filler composition using natural rubber compounds filled with both carbon black and silica CB/Si = 0/60, 20/40, 30/30, 40/20 and 60/0 phr (parts per hundred rubber is parts of any non-rubbery material per hundred parts of raw gum elastomer (rubbery material)). The rheological behaviour can be showed in measurement of Mooney viscosity and cure time. The Mooney viscosity of rubber compounds increase with the increasing the carbon black in the compounds. The compound filled with CB/Si of 30/30 and 60/0 showed abnormal rheological behaviour in which the cure time decreased suddenly and the increased at certain ratio during the measurement. The mechanical properties such as hardness, abrasion resistance and tensile stress at 300% elongation were studied. In the hardness and abrasion resistance measurement, the higher ratio CB/Si decrease contribution of silica, which resulting smaller of hardness value. Ratio CB/Si 40/20 gives an optimum filler blended. It is also clearly understood that higher abrasion resistance mainly due to the lower hardness value under the same condition. The tensile stress at 300% elongation of rubber compound increased with the increasing carbon black filler.     

Injectable poloxamer/graphene oxide hydrogels with well‐controlled mechanical and rheological properties

Although significant progress has been made in the design and application of injectable hydrogels for biomedical applications, concurrent control of rheological and mechanical properties of injectable hydrogels has remained as an open challenge to the researchers. In this work, we introduce and put into practice a photo‐curable poloxamer (also known as Pluronic)/graphene oxide (Plu/GO) injectable hydrogel with well‐controlled rheological and mechanical properties. Acrylate group was anchored to hydrogel structure to endow photo‐crosslinking ability through decelerating degradation rate of poloxamer hydrogels after injection. It was found that the modified Plu remains stable in biological media for a long‐term period without significant weight loss. Rheological properties of hydrogels were also carried out as essential prerequisite for an ideal injectability via frequency sweep, flow curve, recovery, and yield stress before and after modification, signifying shear‐thinning behavior of Plu/GO hydrogels with high recoverability. The viscosity of shear‐thinning‐like hydrogels dropped at higher shear stress, which facilitated injection process. Moreover, mechanical behavior of Plu was optimized by manipulating the content of Plu, degree of modification with reactive precursor, curing, and particularly incorporation of GO without deteriorating effects on rheological behavior of Plu.     

Design of PP/EPDM/NBR TPVs with tunable mechanical properties via regulating the core-shell structure

In this work, polypropylene (PP)/ethylene-propylene-diene monomer (EPDM)/butadiene acrylonitrile rubber (NBR) TPVs with different EPDM/NBR ratios were prepared by the core-shell dynamic vulcanization. The relationship between the core-shell structure and mechanical properties of the TPVs were thoroughly investigated. The formation of core-shell structure by adding NBR is conducive to the mechanical properties of the TPVs. The ratio of EPDM to NBR has an important effect on the structure and performances of the final products, and there is a critical ratio for this effect change. Transmission electron microscope (TEM), tensile test, reprocessing test, ageing test, rheological behavior test and stress relaxation were used to characterize the morphology and properties of the TPVs in detail. It was found that when the ratio of EPDM/NBR was 2:4, the tensile strength increased by ~14% compared with PP/EPDM TPV without NBR. Meanwhile, the reprocessing properties, rheological characteristics and instantaneous tensile deformation, etc. all exhibited sudden changes at this critical ratio.     

Effect of thermo-mechanical cycles on the physico-chemical properties of poly(lactic acid)

Polylactic acid (PLA) has now become an economically viable commodity plastic in many industries. This raises the question of recyclability of industrial production waste and some packaging wastes as well. The evolution of rheological and mechanical properties of polymer with the number of recycling cycles up to seven was investigated. For PLA, only the tensile modulus remains constant with the thermo-mechanical cycles. In contrast, stress and strain at break, rheological factors and the modulus and hardness probed by nanoindentation decrease for PLA. This dramatic effect is ascribed to a large decrease in the molecular weight due to several different complex degradation processes which are discussed. The effect of two stabilizers is also assessed.     

Fiber spinning from the nematic melt. VI. Flow instabilities in the 30:70 copolyester of hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid

The rheological behavior and fiber spinning are investigated for the Celanese liquid crystal copolyester 30 mol% p-hydroxybenzoic acid and 70 mol% 2-hydroxy-6-naphthoic acid (designated as 30HBA/70HNA) with inherent viscosity 7.8 dL/g. Shear thinning viscosity, and yield stress are observed at low shear stress, which probably results from the existence of crystallites in the melt. The crystal-nematic melting point of the copolymer, as measured by differential scanning calorimetry, is around 309°C. Extrudates are collected at four different temperatures ranging from 315 to 345°C. Melt fracture and die swell are observed above 335°C at low shear stress. A wide-angle x-ray diffraction (WAXS) study of an annealed sample indicates that the abnormal phenomenon may be due to crystallites arising from blocky units of HNA. Fiber spinning is performed at high shear rate at 325 and 335°C. Flow is stable under these conditions. The spin draw ratio is the ratio of take-up velocity to the velocity of extrudate existing from the capillary. The initial modulus reaches a maximum at a fairly low spin draw ratio. Instron and wide-angle x-ray (WAXS) studies show that the mechanical properties and orientation are poor for the fiber spun near the crystal-nematic melting point. Also, thermal history is found to affect the rheological behavior. Heat treatment offibers, particularly those which are well oriented, brings an improvement of mechanical properties.     

Development of a novel compression tester and rheo-mechanical properties of wet-mass powder. I--Effect of kneading time on the rheo-mechanical properties

In our previous paper [Watano S., et al., Chem. Phram. Bull., 49(1), 64-68, (2001)], a compaction tester was developed to quantitatively evaluate the water dispersion condition of wet kneaded masses prepared by a paddle type kneader. It was also demonstrated that the physical properties of pellets prepared by extrusion granulation after the kneading could be well predicted by the vertical pressure transmission obtained through the compaction tester. However, in this compression tester, the vertical pressure transmission was just obtained and rheological and mechanical properties (so called rheo-mechanical properties) of wet mass-powder that should be the most important to determine the deformation process were not well studied. In this study, a novel compression tester, which can measure both vertical and radial pressure transmissions, has been developed. Based on the compression test, mechanical property (Young's modulus) and rheological property (effective internal friction) of wet mass powder prepared by different kneading times were quantitatively investigated. Granules (pellets) were then obtained through the extrusion granulation and fluidized bed drying, and the physical properties (strength and disintegration time) of the obtained pellet were evaluated. The relationship between the granule (pellet) physical properties and the mechanical and rheological (rheo-mechanical) properties was analyzed.     

Thermoplastic elastomer based on epoxidized natural rubber/thermoplastic polyurethane blends: influence of blending technique

Epoxidized natural rubber (ENR) and thermoplastic polyurethane (TPU) blends were prepared by simple blend and dynamic vulcanization. The main objective was to prepare a low‐hardness TPU material with good damping and elastic and mechanical properties. It was found that the incorporation of ENR into the blend shows a reduction in Young's modulus, hardness (i.e. <70 Shore A), damping properties (i.e. tan δ < 0.3), and tension set (i.e. <20%) compared with the pure TPU. This indicates the formation of softer TPU materials with superior damping and elastomeric properties. However, incorporation of ENR sacrificed mechanical properties in terms of tensile strength and elongation at break, but these still remain in the range of applicability for industrial uses. It was also found that dynamic vulcanization caused enhancement of mechanical properties, relaxation, damping, rheological properties, and elasticity of the blends. Temperature scanning stress relaxation measurements revealed an improvement in stress relaxation properties and thermal resistance of the dynamically cured ENR/TPU blend. Copyright © 2011 John Wiley & Sons, Ltd.     

Mechanical and Rheological Behavior of Unvulcanized and Dynamically Vulcanized i-PP/EPDM Blends

The mechanical and rheological behavior of dynamically vulcanized PP/EPDM blends is examined and compared with those of unvulcanized blends. The effect of blend ratio and dynamic vulcanization of EPDM rubber on tensile properties and flow are investigated. The mechanical properties of the blends are strongly influenced by the blend ratio. With the increasing of EPDM content the value of yield stress in a solid state decreases with the elastomer volume fractions less than 0.45 for the unvulcanized blends. For the dynamically vulcanized blends the interval of EPDM content, at which the yield peak is seen, is rather limited below 0.25 elastomer volume fractions. It is shown that dynamic vulcanization changes the deformational behavior of PP/EPDM blends. The rheological properties of dynamically vulcanized blends depending on the ratio of the components may be similar to the properties of polymer composites containing the highly disperse structuring filler. The distinction between the rheological behavior of unvulcanized and dynamically vulcanized blends is related to differences of their structures and viscoelastic characteristics of unvulcanized and vulcanized EPDM phase.     

Effect of the C/O ratio in graphene oxide materials on the reinforcement of epoxy-based nanocomposites

The effect of the C/O ratio of graphene oxide materials on the reinforcement and rheological percolation of epoxy-based nanocomposites has been studied. As-prepared graphene oxide (GO) and thermally-reduced graphene oxide (TRGO) with higher C/O ratios were incorporated into an epoxy resin matrix at loadings from 0.5 to 5 wt %. Tensile testing revealed good reinforcement of the polymer up to optimal loadings of 1 wt %, whereas agglomeration of the flakes at higher loadings caused the mechanical properties of the composites to deteriorate. The level of reduction (C/O) of the graphene oxide filler was found to influence the mechanical and rheological properties of the epoxy composites. Higher oxygen contents were found to lead to stronger interfaces between graphene and epoxy, giving rise to higher effective Young's moduli of the filler and thus to superior mechanical properties of the composite. The effective modulus of the GO in the nanocomposites was found to be up to 170 GPa. Furthermore, rheological analysis showed that highly oxidized graphene flakes did not raise the viscosity of the epoxy resin significantly, facilitating the processing considerably, of great importance for the development of these functional polymeric materials. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 281–291     

Tailoring the interfacial assembly of colloidal particles by engineering the mechanical properties of the interface

Fluid interfaces can be used as a platform for promoting the direct and spontaneous self-assembly of colloidal particles, where the driving force is the reduction in interfacial energy. In addition, fluid interfaces allow fine-tuning of the particles ensemble by an external force, such as the presence of an imposed interfacial flow, or by engineering the interparticle interactions dictated by the interplay of interfacial forces. As a consequence, a wide-ranging set of interfacial structures can be achieved from liquid-like layers, which can flow under stress, to amorphous solids that are able to sustain static stress. Here, far from a comprehensive overview of the interfacial assembly of colloidal particles, different ways of tailoring it by rationally designing the rheological properties of the interface are provided, with a focus on experimental and theoretical methods and model systems that have been recently exploited. In particular, ligand-coated nanoparticles, with a strong emphasis on the effect of the ligands on the interfacial structure and the rheological properties, and soft nanogel particles, in which an environmental factor, such as the temperature, drives to different interfacial structures and mechanical responses will be further discussed.     

Investigation of the rheological and mechanical behavior of Polypropylene/ultra-high molecular weight polyethylene compounds related to new online process control

Ultra-high molecular weight polyethylene (UHMWPE) is a high performance material that has excellent wear and impact strength compared to other polymers. Due to its chemical structure and molecular mass, UHMWPE is difficult to handle on standard extrusion systems. In this paper, the compounding, rheological, and mechanical behavior of different Polypropylene (PP)/UHMWPE blends were investigated. Raw materials were blended on a co-rotating twin screw extruder. The shear and extensional viscosity of polymer blends were investigated using an inline rheometer. Mechanical and rheological properties were presented for various UHMWPE loadings, and correlations between mechanical and rheological data were examined.     

Thermally exfoliated graphene oxide reinforced stress responsive conductive nanocomposite hydrogel

Lightweight and flexible biosensors that can sustain mechanical deformation and can be adhered to human skin is an interesting field of study. In the current article, a systematic study on development of thermally exfoliated graphene oxide (TEGO)–reinforced poly(vinyl alcohol) (PVA)–based conductive hydrogel nanocomposites has been reported. The free‐standing hydrogels were synthesized using controlled and repetitive freeze‐thaw cycles. The samples were then studied for their mechanical as well as electrical properties. The hydrogels were characterized for their microstructural, chemical, and rheological properties to understand the observed macroscopic properties. Additionally, a study on the behavior of hydrogels immersed in phosphate‐buffered saline (PBS) was carried out to investigate their hydrolytic stability within simulated biological environment. Overall, the nanocomposite hydrogels demonstrated excellent static and dynamic mechanical performance, stability in PBS, considerable electrical conductivity, and significant electrical response to applied external stress, establishing their potential for use as flexible biosensors.     

A small-angle neutron scattering and rheology study of the composite of chitosan and gelatin

The composite chitosan/gelatin solutions and films formed from these solutions were studied by rheological measurements, SANS and tensile tests. The relationship between the inter-molecule interactions with microstructure, rheological behaviour of a solution and eventually the mechanical performance of formed films was established. It was found that the complex formed between chitosan and gelatin was mainly through hydrogen bond but the size of the structure was also affected by electrostatic repulsions. The local structure (correlation length) and the global structure (large inhomogeneous structure size) in the composite solutions were found to be highly correlated to each other. It was also found that the interactions between these two polymers in solution were closely related to the mechanical properties of the formed films. This work will enable one to design films with desired mechanical properties through the combination of different polymers at optimum weight ratios.     

Mechanical reinforcement of a supramolecular hydrogel comprising an artificial glyco-lipid through supramolecular copolymerization

Supramolecular copolymer hydrogels were prepared by mixing 1 and the additives 2-8, and their rheological properties were evaluated. It was found that additive 3 reinforced the mechanical strength of the resultant hydrogel most efficiently, increasing the yield stress of SCH 1+3 about fourfold. The optimal mixing between the glyco-lipid hydrogelator 1 and the additive 3 sufficiently enhanced the mechanical strength of the resultant SCH, which improved the handling of the SH on the large scale. These results indicate that supramolecular copolymerization can provide the supramolecular hydrogel with desired properties and/or functions.     

Poly(lactic acid)/coplasticized thermoplastic starch blend: Effect of plasticizer migration on rheological and mechanical properties

Polylactic acid (PLA) and thermoplastic starch (TPS) are known as bio‐based and biodegradable thermoplastic polymers that can be used in different applications owing to their inherent physical and mechanical properties. In order to reduce the higher costs of PLA and tuning its physical and mechanical properties suitable for short life packaging applications, blending of PLA with the TPS, more economical biodegradable polymer, has been considered in academic and industrial researches. However, melt blending of PLA with TPS without compatibilization process caused some drawbacks such as coarsening morphology and declining mechanical properties and ductility because of thermodynamic immiscibility, which may restrict its usage in packaging applications. Subsequently, our approach in this research is compatibilization of PLA/TPS blends by utilization of primary well tuning of TPS formulation with a combination of sorbitol and glycerol plasticizers. In this work, the wide composition range of melt mixed PLA/TPS blends was prepared using a laboratory twin screw extruder. The effects of microstructure on the rheological and mechanical properties of PLA/TPS blends were studied using different methods such as scanning electron microscopy (SEM) images, contact angle, oscillatory shear rheological measurements, and tensile and impact strength mechanical tests. The rheological and mechanical properties were interpreted according to the morphological features and considering the possibility of plasticizer migration from TPS to PLA phase during melt blending. Reduction in complex viscosity and storage modulus of PLA matrix samples indicates the improved melt processability of blends. Finally, in comparison with mechanical results reported in literature, our simple approach yielded the blends with elastic modulus and ductility comparable with those of chemically compatibilized PLA/TPS blends.     

Rheology of polyacrylate binders produced via catalytic chain transfer polymerization as an alternative to bitumen in road pavement materials

Catalytic chain transfer polymerization has been successfully used to produce a range of methyl acrylate (MA) and butyl acrylate (BA) synthetic polymers of specific, targeted molecular weights, with polydispersity index values in the range of 2–4.5. The rheological properties of a subgroup of these synthetic binders consisting of four MA homo-polymers and one MA–BA co-polymer were then determined by means of oscillatory testing using a dynamic shear rheometer (DSR). The rheological tests consisted of a combination of stress/strain amplitude and frequency sweeps using a standard 8 mm diameter parallel plate testing geometry. The rheological parameters of phase angle and complex, storage and loss moduli were then shifted to form master curves at a reference temperature of 25 °C and isochronal plots at 0.1, 1 and 10 Hz. The rheological properties of the synthetic polymers were also compared to those of standard road pavement bitumens. The results show that it is possible to produce a range of synthetic polyacrylates with different rheological responses by altering the reactant type, reactant concentration and polymerization conditions to match the rheological properties of road bitumens. All the polyacrylate binders showed a similar rheological profile with a unique viscoelastic response as represented by the phase angle master curves together with an upper limiting stiffness and intermediate temperature/frequency ‘plateau’ region as shown in the complex modulus master curves. The results of the rheological examination of the binders showed that the key material property that influenced the performance of the polyacrylates in these specific application tests was glass transition temperature rather than molecular weight. Over this range of investigated molecular weights, it is the ratio between the two polymers which determines the glass transition and as such determines the material properties. These findings suggest that such sustainably sourced polyacrylate binders may allow for a move from petrochemical feed stocks to be made and allow for targeted road pavement design based on local climates, offering improved mechanical robustness.     

Compatibilizing effect of polyarylate-polystyrene block copolymer in polyarylate/polystyrene blends

The compatibilizing effect of polyarylate-polystyrene (PAR-PS) block copolymer prepared from macroazo initiator was examined in polyarylate/polystyrene blends from the view-points of morphology, density, and thermal, mechanical, and rheological properties. PARPS block copolymer enhanced the mutual dissolution of the homopolymers. Reduced dispersed-domain size and increased density showed the efficiency of the block copolymer as a compatibilizing agent. Results from mechanical and rheological properties could also be explained by the compatibilizing effect of PAR-PS block copolymer in the blends. © 1994 John Wiley & Sons, Inc.     

Enhanced mechanics in injection molded isotactic polypropylene/polypropylene random copolymer blends via introducing network-like crystal structure

The crystallization behavior, rheological behavior, mechanical properties and microstructures of injection molded isotactic polypropylene(i PP), polypropylene random copolymer(co-PP) and i PP/co-PP blends were investigated. Differential scanning calorimetry(DSC) and dynamic rheological analysis illustrated that i PP and co-PP were compatible in the blends and co-PP uniformly dispersed in the i PP phase. Polarizing optical microscope(POM) was adopted to observe the crystal size and morphology evolution. The results of mechanical properties and scanning electron microscopy(SEM) indicated that the crystal size of i PP in i PP/co-PP blends(10 wt% co-PP + 90 wt% i PP and 30 wt% co-PP + 70 wt% i PP) radically decreased after the incorporation of co-PP. During crystallization, the molecular chain segments of co-PP could penetrate i PP spherulites and form a network-like crystalline structure. The network-like crystal structure could effectively transmit stress and consume more energy to overcome intermolecular forces to resist stretching. In this way, the strength would improve to a certain degree. The impact fracture mechanism of i PP/co-PP blends is quasi ductile fracture by multiple crazes. Our work discovered that the blends containing 10 wt% and 30 wt% of co-PP exhibited prominent toughness and reinforcement.     

Effect of the method used for crystal structure formation on the rheological behavior of organocyclotetrasiloxane in the plastically crystalline state

The rheological properties of cis-cyclotetrasiloxane, cis-[PhSi(O)(OSiMe₃)]₄, in the plastically crystalline state were investigated. The yield stress and non-Newtonian character of the flow indicates that cis-[PhSi(O)(OSiMe₃)]₄ is a viscoplastic material with respect to its rheological behavior. The conditions of crystal structure formation determine the rheological properties of organocyclotetrasiloxane in the mesophase. The temperature and stress during capillary flow were shown to affect the size and orientation of crystallites formed upon cooling of extrudates.     

Polymer nanoparticles: their effect on rheological,thermal, and mechanical properties of linear low‐density polyethylene (LLDPE)

Rheological, thermal, and mechanical properties of polymer particle/LLDPE blends were studied in this paper. The blends were prepared individually by incorporating nanoparticles of polystyrene (nPS) of ～60 nm and polymethyl methacrylate (nPMMA) of ～50 nm with different wt% loading (i.e., 0.10–0.5%). It was shown from the experimental results that rheological, thermal and mechanical properties were increased as polymer particles blended with LLDPE. Blends with 0.25 wt% loading of nPS and 0.5 wt% loading of nPMMA exhibited better rheological, thermal, and mechanical properties compared with that of other wt% loadings. The improvements in properties were due to the close packing of LLDPE chains as recorded by improvement in crystallinity of LLDPE with addition of nPS and nPMMA as shown by SEM. Copyright © 2010 John Wiley & Sons, Ltd.