Shear and elongational flow measurements on polystyrene melts reinforced with small particles were carried out. The influences of loading level, particle size and surface treatment on shear viscosity, principal normal stress difference, and elongational viscosity were discussed. These systems exhibited yield values for both shear and elongational flow. Experimental values for the ratio of the tensile to the shear yield stress give satisfactory agreement with the predictions of the von Mises yield criterion. The yield value appears to increase with decreasing particle size and may be varied with surface treatment. The principal normal stress difference at fixed shear stress decreases with volume loading of particulates. The results are interpreted in terms of a system forming a gel due to interparticle forces, which is disrupted by a critical distortional strain energy.

Experimental investigations of shear and elongational flow properties of polystyrene melts reinforced with calcium carbonate, titanium dioxide, and carbon black

The flow behavior of carbon black loaded styrene-butadiene (SBR)-cis-polybutadiene (BR) is investigated as a function of mixing and the location of carbon black. The blends consist of an 80:20 weight ratio of SBR and BR with the incorporation of 20 phr carbon black via three different schemes to control the location of carbon black in the individual rubber phases. These are: (A) free black mixing of the three components, (B) mixing of SBR-black masterbatch with BR, and (C) mixing of BR-black masterbatch with SBR. Dynamic Mechanical Analysis (DMA) was used to characterize carbon black distribution. The damping characteristics indicate that when carbon black is masterbatched into either one of the rubbers, it continues to remain incorporated in that particular rubber phase upon blending with the second rubber. The flow behavior is measured with an Instron capillary rheometer. The results indicate that the viscosity function of these blends is not sensitive to the mixing conditions. However, the elasticity is always, dependent on mixing. Elasticity is expressed as ΔPe/σ, where ΔPe is the entrance pressure drop from the Bagley plot and σ the shear stress. In general, ΔPe/σ of the blend decreases with increasing mixing.

Flow of carbon black loaded styrene‐butadiene (SBR)‐cis‐polybutadiene blends through capillary dies—influence of mixing and the location of carbon black

A simple apparatus for elongational test of molten polymers is presented. Its realiability is demonstrated by means of stress growth in constant stretching rate experiments and relaxation test on a low density polyethylene sample.

Constant stretching rate experiments on low density polyethylene

A novel experimental setup for the uniaxial extension of uncured elastomers is presented, and room temperature experiments at constant Hencky strain rate are performed by means of a commercial Rheotens tensile tester originally designed for the determination of the melt strength of polymer melts. Successful results are obtained for materials related to many aspects of the elastomers production, namely, gum elastomers and carbon black compounds. Stress growth experiments are reported for filled and unfilled high-cis-polybutadiene, and the extensional behavior is related to the carbon black dispersion. Although originally thought as an experimental tool for polymer melts, the proposed Rheotens setup can also perform constant strain rate tensile testing on thermoplastic rubbers. Stress-strain experiments are performed on a microphase separated polystyrene-b-poly(ethylene butylene)-b-polystyrene (SEBS) copolymer and related blends with polypropylene, showing the effect of a constant deformation rate on the network response. Relaxation experiments after cessation of extensional flow are also reported for the investigated materials. With respect to commonly used tensile testing procedures for elastomers at constant elongation rate and time decreasing strain rate, a complete and accurate investigation of the extensional behavior of many uncured elastomers can be carried out with the additional advantage of using a reduced amount of material.

A Rheotens-based setup for the constant strain rate uniaxial extension of uncured elastomers

Publisher Summary
This chapter elaborates rheological behavior and processing of un-vulcanized rubber. The fabrication of rubber parts generally involves the mixing and processing of bulk un-vulcanized compounds and sometimes solutions and emulsions through complex equipment. Post-World War II studies of the rheological properties of un-vulcanized elastomers have been dominated by the idea that these materials are viscoelastic. The first 40 years of the 20th century saw an enormous increase in the production of rubber products especially in the tire industry. Today three available quality control instruments offer stress relaxation or recoil capability. These are the BF Goodrich DSR, the Defo System Bayer, and the new Monsanto Mooney viscometer. The origins of flow simulation of processing should probably be traced to the establishment of the Navier-Stokes equations and its early solutions.

6 – Rheological Behavior and Processing of Unvulcanized Rubber

A new instrument for measurement of extensional viscosity was designed and employed in the evaluation of SBR compounds containing carbon black and other non-black fillers. It was shown that carbon black filled rubbers generally do not reach steady-state viscosity ; the stress continues to increase with increasing strain up to the point of rupture, due to rapid orientation of molecular chains during extensional flow. The data was evaluated in terms of the Denn-Marrucci equation, and the effect of carbon black on the two adjustable parameters was found. It was found that higher carbon black loading or structure increases only the viscosity coefficient, i.e., it changes the relative level of the flow curve without changing its shape. On the other hand, an increase in surface area increases both the viscosity coefficient and the relaxation time, i.e., it increases the upward curvature of the flow curve. A very good correlation was observed between Mooney viscosity values and calculated viscosity coef...

J. L. Thiele

Papers

Influence of Carbon Black on Processability of Rubber Stocks III. Extensional Viscosity