Thermal Properties of Rubbers

Most of the available thermal property values are each measured at only one temperature, which is much lower than the usual processing temperature. But the diffusivity and conductivity of black-loaded natural rubber compounds deaease with increasing temperature. The decrease, over the temperature range from ambient to 200°C, can be as much as 45% [5]. This large temperature dependence should obviously be taken into account in heat-flow calculations at processing temperatures. 

In the last few years, the value of an analytical approach to heat transfer problems has been increasingly realized and considerable effort has been devoted to developing techniques and convenient methods of calculation. However, the measurement of thermal properties has remained a very specialized subject, there is little evidence of standard procedures and the tests are carried out in relatively few laboratories [6-9]. 

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The thermal properties of rubber are of very great importance, particularly in the processing stages, but there is a remarkable dearth of reliable data. Traditionally, the approach to heating and cooling problems was empirical rather than by careful analysis. The data needed for such analysis was not available, largely because of the undoubted experimental difficulties to be overcome but, even with data, somewhat complicated calculation is required. 

Abdul M., B. Rochette, A. Sadr, and J.M. Vergnaud. 1984. Effect of variation in the values of the thermal properties of rubber on the vulcanization of thin and thick sheets. Thermochim. Acta. 80 287-96. 

R. Rashmi, A. Devi, T.K. Maji, and A.N. Banerjee, Studies on dimensional stability and thermal properties of rubber wood chemically modified with styrene and glycidyl methacrylate. /. Appl. Polym. Sc. 93,1938-1945 (2004). 

Handbook of Chemistry and Physics, 52d ed.. Chemical Rubber Company, 1971-1972. l Table of Thermal Properties of Gases, NBS Circular 564, 1955. 

W8. Winding, C. C., Dittman, F. W., and Kranich, W. L. Thermal Properties of Synthetic Rubber Latices, Report to Rubber Reserve Company. Cornell University, Ithaca, 1944. 

CdO is used in connection with the stabilization of poly(vinyl chloride). This is discussed below in more detail. It also finds application in modifying the thermal properties of teflon and some rubbers. CdS is used in some smoke detectors, in lasers and in phosphors. The cadmium(II) halides are important as catalysts and are also used in pyrotechnics. Cadmium borates of the general type (Cd0)x(B203), are also used as phosphors. CdS04 is employed in the Weston cell, which is important as a voltage standard.137... 

The effect of synthesized modifiers on fluorosiloxane rubbers is determined on the basis of fluorosiloxane rubber CKTFT-100 As seen fix)m data presented in Table 3, characteristics of fluorosiloxane rubber depend on quantity of introduced modifier and its molecular mass Properties of rubber compounds are highly dependent on modifier concentrations. Optimal modifier content amounts to 6 - 7%. Increase in molecular mass of modifier on transition from modifier II to modifier VI leads to increase in tear strength and relative elongation in comparison to the control specimen (modifier concentration = 0). Also, after thermal treatment at 250 °C for 24 h in the presence of modifier VI, improvement of all fluorosiloxane rubber compound properties is observed. 

The mechanical and thermal properties of a range of poly(ethylene)/po-ly(ethylene propylene) (PE/PEP) copolymers with different architectures have been compared [2]. The tensile stress-strain properties of PE-PEP-PE and PEP-PE-PEP triblocks and a PE-PEP diblock are similar to each other at high PE content. This is because the mechanical properties are determined predominantly by the behaviour of the more continuous PE phase. For lower PE contents there are major differences in the mechanical properties of polymers with different architectures, that form a cubic-packed sphere phase. PE-PEP-PE triblocks were found to be thermoplastic elastomers, whereas PEP-PE-PEP triblocks behaved like particulate filled rubber. The difference was proposed to result from bridging of PE domains across spheres in PE-PEP-PE triblocks, which acted as physical crosslinks due to anchorage of the PE blocks in the semicrystalline domains. No such arrangement is possible for the PEP-PE-PEP or PE-PEP copolymers [2]. 

Another utilized approach for preventing reversion involves crosslinking of the siloxanes. For Instance, a number of methyl silicone rubbers were crosslinked, (about 1 crosslink per 3,000 to 20,000 units (10-21) for crosslinked products mainly composed of dimethylsiloxane Refs. IJ and I8). DSC and TM was utilized to evaluate the thermal properties of the products. TM was utilized to determine crosslink density along with typical modulus properties. Both enhancement and decrease in thermal properties were observed depending on the mode and conditions of crosslinking. 

Due to the incorporation of the rubber, the thermal properties of the cured polymer are somewhat lower than those of the triazine alone. The thermal properties, along with the electrical properties, are given in Table II. 

Chapters 8 and 9 consider the mechanical properties of rubber- and ceramic-particle toughened-epoxy materials. The importance of rubber cavitation is highlighted in Chapter 8. It is well known that this mechanism can relieve the high degree of triaxiality at a crack tip in the material and enable subsequent plastic hole growth of the epoxy resin, which is a major toughening mechanism. We return to rigid particles in Chapter 9, which examines their use to increase the thermal shock resistance of epoxy resins. 

Thermal transport properties of rubber depend not only on the temperature but also on the type of rubber and the type and quantity of filler. It is generally thought that they are not greatly affected by vulcanization [5],... 

As a conclusion, it seems difficult to give some values of the thmnal parameters of rubbers in one or several tables, as the rubber compounds are so different from one to another. And generally, people working on a rubber ctxnpound have to determine themselves the thermal properties of their material. Nevertheless, in our calculations for the profiles of temperature or of state of cure developed through the thickness of the sample during the cure, the values taken for these thermal prqterties will be given beforehand. 

Hands D. 1977. The thermal properties of polymers. Rubber Chem. Technol. 50 480-522. 

In this case, the process of cure is similar as that described with a metal. The fabric-rubber system is heated under the conditions necessary for the rubber to be cured, and the theory of the process is also similar as that described in this subsection all that is changed are the thermal properties of the fabric material. 

IPN TPEs offer physical and thermal properties of thermoset rubber, the processability of a thermoplastic, and a wider hardness range than available to other TPEs. 

PROPERTIES OF SPECIAL INTEREST In general, thermoplastic elastomers (TPE) provide the mechanical properties of rubber in combination with the processing characteristics of plastics recyclable Kraton G s are low cost TPEs with oxidative and thermal stability, good weathering, and ozone resistance. 

The total concentration of inorganic ions in fresh latex is about 0.5%, the major ions being potassium, magnesium, copper, iron, sodium, calcium and phosphate.Even in small quantities they are key co-factors in metabolic pathways, and are also involved in the technological properties of rubber, such as susceptibility to thermal oxidation." ... 

Nakason, C., Panklieng, Y., and Kamesamman, A. 2004. Rheological and thermal properties of thermoplastic natural rubbers based on poly (methyl methacrylate)/epoxidized-natural-rubber blends. Journal of Applied Polymer Science 92(6) 3561-3572. 

Mina, M. R, Alam, A. K. M. M., Chowdhury, M. N. K., Bhattacharia, S. K., and Balta Calleja, R J. 2005. Morphology, micromechanical, and thermal properties of undeformed and mechanically deformed poly (methyl methacrylate) /rubber blend. Polymer Plastics Technology and Engineering 44(4) 523-537. 

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