Viscoelastic evaluations rubbers

Each of the viscoelastic parameters G°, rj0, and Je° has associated with it a characteristic molecular weight which either measures an equivalent spacing of entanglement couples along the chain (Me, deduced from G with the kinetic theory of rubber elasticity), or marks the onset of behavior attributed to the presence of entanglements (Mc and AT, deduced from r/0 and Je° as functions of molecular weight). Table 5.2 lists Me, Mc, and M c for several polymers. Aside from certain difficulties in their evaluation, each is a rather direct and independent reflection of experimental fact. 

TG-DTA Characterisation of carbon black [149], flammability evaluation [64], polymer degradation studies [65], ageing studies [70-72], product control [77, 81], combustion performance [83], safety evaluation [83], antioxidation activity [68], pyrolysis of rubbers [82], thermal stability [67, 69, 76, 77], interfacial junctions in viscoelastic composites [78], weathering [72], vulcanisation [73], oxidative behaviour [79], materials evaluation [80], failure analyses [81],... 

Vulcanised rubbers show viscoelasticity and the departure from perfect elasticity are evaluated by measurement of resilience, creep and stress relaxation. Compounding which contributes to a more tightly knit crosslinking system occupying the maximum possible volume proportion of the vulcanisate will enhance the elastic properties as displayed by resilience. Appropriate antioxidant protection of the polymer will give further improvement. At normal levels of addition softeners and plasticisers have little effect [7]. 

The WET p and Tan 8 were measured in the evaluation of a rubber compound as the tread rubber of tire for the various rubber compounds containing the different tackifiers at the same level of 2.5 phr. The WET p, evaluated by a flat-belt type friction tester, refers to the coeflbcient of friction between the wet surfaces, and would reflect the tire performance in road gripping under wet conditions. On the other hand, the Tan 6 would be related to the rolling resistance of the tire compound and was measured by viscoelasticity tester. In general, as shown in Table... 

Viscoelastic methods for the characterisation of gum rubbers are extended to rubber compounds, and the ways in which the viscoelastic properties of gum rubbers are manifested in the properties of the corresponding compounds are examined. The development of a method for evaluating strain amplification and strain rate amplification is described. Examples are presented of the characterisation of compounds with respect to variations in gum rubbers and carbon black grades, and consideration is given to the unique characteristics of compounds which are not observed in gum rubbers. Quality control tests for gum rubbers and compounds based on viscoelasticity are reviewed. 32 refs. 

However, at higher velocities, and cases for which actual dummy head and the panel were us in the tests, the correlation was poor. This is due to the complications arised from modelling of the dummy head exterior (Butyl rubber) and also the plywood panel onto which a one-inch thick Nomax open all honeycomb with fiberglass laminate on both sides were fixed. From the experimental data, data fitting techniques were used to come-up with an alternative non-linear viscoelastic contact force model such that the contact force f is evaluated from the deformation (indentation) 6 and deformation rate 5 according to... 

Usually, sealants and adhesive materials for construction applications are evaluated by looking at the engineering side, butnotthe chemistry of the material. As a result, only tests that measure the mechanical properties are used. Most of the studies on the viscoelastic properties use traditional tests such as tensile testing to obtain data, which can be used in complicated mathematical equations to obtain information on the viscoelastic properties of a material. For example, Tock and co-workers studied the viscoelastic properties of stmctural silicone rubber sealants. According to the author, the behavior of silicone mbber materials subjected to uniaxial stress fields carmotbe predicted by classical mechanical theory which is based on linear stress-strain relationship. Nor do theories based on ideal elastomers concepts work well when extensions exceed... 

Temperature Retraction - This test (ASTM D-1329) can be used to measure viscoelastic properties of elastomers and rubber-like materials at low temperatures, and also to evaluate crystallization effects. The test specimen is stretched to a specified elongation and frozen at -70°C (-94°F). Then, it is gradually warmed until it begins to retract toward its unstretched dimensions. The temperature at which the specimen retracts 10% has been found to correlate with brittleness temperature. 

Dynamically vulcanized thermoplastic elastomer (TPV)/organoclay nanocomposites based on EPDM/PP containing 2, 4, 6% of organically treated montmorillonite were prepared by using EPDM-g-MA and PP-g-MA as compatibilizer. Dicumylperoxide (DCP) and triallyl cyanurate (TAC) were employed as crosslinking system. X-ray diffraction (XRD) analysis has been performed to evaluate the extent of the intercalation.. In this study, attempts have been made to exclusively reinforce rubber dispersed phase. Rheological behavior and melt viscoelastic properties of the samples such as elastic modulus, and elastic response expressed in terms of relaxation time distribution, H (A), were studied. The results were also supported by differential scanning calorimetry (DSC) and mechanical tests. 

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