Rubber thermal properties

An extensive new Section 10 is devoted to polymers, rubbers, fats, oils, and waxes. A discussion of polymers and rubbers is followed by the formulas and key properties of plastic materials. Eor each member and type of the plastic families there is a tabulation of their physical, electrical, mechanical, and thermal properties and characteristics. A similar treatment is accorded the various types of rubber materials. Chemical resistance and gas permeability constants are also given for rubbers and plastics. The section concludes with various constants of fats, oils, and waxes. 

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

Jha A. and Bhowmick A.K., Thermoplastic elastomeric blends of nylon 6/acrylate rubber Influence of interaction of mechanical and dynamic mechanical thermal properties. Rubber Chem. TechnoL, 70, 798, 1997. 

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. 

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. 

For materials generally, change in expansion (or density) by dilatometry was traditionally the most often used method for measuring Tg. Thermal properties, for example specific heat, are also widely used, particularly the methods of differential thermal analysis". A method for rubbers using DSC is being developed in ISO TC 45 as ISO 22768, but is not yet published. The inflection point on the heat input - temperature curve is usually obtained automatically by the analyser s software but, if obtained manually, is best found from the derivative of the curve. 

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... 

Mixing process Technical rubbers are blends of up to about 30 different compounds like natural rubber, styrene-butadiene rubber, silicate and carbon-black fillers, and mobile components like oils and waxes. These components show a large variety of physical, chemical, and NMR properties. Improper mixing leads to inhomogeneties in the final product with corresponding variations in mechanical and thermal properties (cf. Figure 7.4). 

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. 

Polypropylene is also used in a number of blends, some of them with applications in rubber industry, automotive industry, home constructions, etc. Some of the copolymers and blends used in rubber industry are vulcanized. Studies on thermal properties and pyrolysis of these copolymers and blends are common in literature [97, 105,110-118]. 

Ethylene has been co-polymerized with virtually any conceivable a-olefin, from propylene to vinyl-terminated PE and PP macromonomers. Ethylene/propylene (E/P) copolymerization to produce saturated rubbers and ethylene/propylene/diene (EPD) terpolymerization to produce unsaturated, vulcanizable rubbers will be discussed in Section 4.09.4.1.3. 1-Butene, 1-hexene, and 1-octene are the most commonly used co-monomers for the production of LLDPE. Ethylene/octene co-polymers, developed by Dow and marketed under the Engage tradename, have been shown to have improved thermal properties compared to ethylene/butene and ethylene/hexene co-polymers.503 In ethylene/a-olefin (E/O) co-polymeriza-tions, the critical parameters are co-monomer reactivity and co-monomer distribution . The former is most conveniently described by the relative reactivity parameter, R, defined as the ratio between polymer composition and reactor medium composition. 

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. 

---