Natural rubber thermal conductivity

Zinc oxide has many uses. By far the most important is in the rubber industry. Almost half the world s ZnO is used as an activator for vulcanization accelerators in natural and synthetic rubber. The reactivity of the ZnO is a function of its specific surface area, but is also influenced by the presence of impurities such as lead and sulfates. The ZnO also ensures good durability of the vulcanized rubber, and increases its thermal conductivity. The ZnO content is usually 2-5%. 

FIG. 17.2 Generalized curve for the thermal conductivity of amorphous polymers. ( ) silicon rubberr (A) polyisobutylene (O) natural rubber (0) polypropylene (A) poly(trifluoro chloro ethylene) ( ) poly (ethylene terephthalate) (V) poly(vinyl chloride) ( ) poly(methyl methacrylate) ( ) poly(bisphenol carbonate) ( ) poly(vinyl carbazole) lines are drawn according to Eq. (17.9). 

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. 

Hands D. and F. Horsfall. 1977. The thermal diffusivity and conductivity of natural rubber compounds. Rubber Chem. Technol. 50 253-65. 

Figure 10-30. Thermal conductivity k of natural rubber (NR), poly(oxyethylene) (PEOX), and poly (ethylene) (PE) of various densities as a function of temperature. Tg is the glass transition temperature, Tm is the melting temperature. (From data of various authors in the compilation of W. Knappe.)...

THERMAL CONDUCTIVITY OF SOFT VULCANIZED NATURAL RUBBER, SELECTED VALUES. FROM ADVANCES IN THERMOPHYSICAL PROPERTIES AT EXTREME TEMPERATURES AND PRESSURES. 

THERMAL CONDUCTIVITY OF SOFT VULCANIZED NATURAL RUBBER. SELECTED VALUES. 

In this chapter, the study carried out on nanofillers reinforced natural/synthetic rubber has been discussed. After a description on the NR rubber and CaCOs as filler, the development of synthetic composites with the incorporation of micro and nano-CaC03 as a filler material has also been discussed for comparative study. In particular, the role of fillers on the property modification of rubber properties, such as surface properties, mechanical strength, thermal conductivity, and permittivity has been mentioned. The effectiveness of this coating was demonstrated. The importance of well-dispersed nanoparticles on the improvement of the mechanical and electrical properties of polymers is also emphasized. However, one of the problems encountered is that the nanoparticles agglomerate easily because of their high surface energy. 

Figure 18.28 Thermal conductivity vs filler volume fraction for Ti02- and nanosilica-filled natural rubber (NR) composites.

These materials may be divided into two classes those which occur naturally, such as wood, stone, and raw rubber, and those which are produced synthetically, such as glass, graphite, stoneware, plastics, and synthetic rubber. Though metals are of prime importance in the construction of chemical plant, non-metals possess certain qualities, which, in spite of their low thermal conductivity and physical strength, make them a preferable material. For example the transparency of glass or the resilience of rubber are often important. 

J. Ok Jo, P. Saha, N.G. Kim, C.H. Choi, J.K. Kim, Development of nanocomposite with epoxidized natural rubber and functionalized multiwalled carbon nanotubes for enhanced thermal conductivity and gas barrier property. Materials Design, ISSN 0264-1275 83 (October 15, 2015) 777-785. http //dx.doi.Org/10.1016/j.matdes.2015.06.045. 

Thermal conductivity studies have been conducted on a wide range of filled polymers and composites, including carbon fibers [62-68], aluminum powder [65], nitride [66], magnetite, barite, talc, copper, strontium ferrite [67], glass fiber-filled polypropylene and manganese or iron-filled polyaniline, carbon nanotubes [68], and nickel-cobalt-zinc ferrite in natural rubber [70]. 

Song and co-workers [14] point out that in MTA three images based on topography, thermal conductivity and thermal diffusivity can be obtained simultaneously. They used MTA to study the phase separation process in a 50 50 (by weight) PS-polyvinyl methyl ether (PVME) blend and natural rubber-nitrile rubber blends. 

A pioneering study conducted by Varughese and coworkers [16] revealed that the thermal properties of PVC are improved when it is blended with an appropriate amount of epoxidized natural rubber (ENR). The blending of ENR potentially inhibits the formation of chlorine free radicals as the PVC decomposes, thus eliminating the evolution of HCl that may promote chain dehydrochlormation. 

Carbon blacks are principally made by the chemical decomposition of natural gas or oil. Two classes predominate the furnace blacks (95% of black usage) which are active, and thermal blacks (5% of usage) which are inactive. There are a substantial number of blacks for special applications such as electrically conducting and printing ink blacks. The latter are of too fine a particle size for rubber use. The nomenclature used for carbon blacks includes the ASTM designation and the industry type as illustrated in the next table. 

Carbon blacks (c.b.s) have been known since ancient times, for preparing Indian ink. From the 1920s, c.b. has been fabricated industrially on a large scale by the thermal decomposition of hydrocarbons (natural gas) or aromatic hydrocarbons. Of the total production, 90% goes into the rubber industry, and most of this is employed for the reinforcement of tires. Production capacity is at present 7.2 million tonnes/y and the armual production is 6.1 million tormes/y [244] 95% of this global fabrication is by the furnace c.b. process [245]. The specific surface area As (nr/g) in this case covers a range from a few tens up to more than 1500. It should be mentioned that c.b. is used as a filler for conducting polymers [246]. 

The word asbestos is generally applied to two forms of fibrous natural silicates the amphiboles and serpentine. The asbestos minerals do not burn, do not rot, and have low thermal and electrical conductivity. They can be woven into fabrics, compressed into mats, and mingled with such binders as rubber and asphalt to produce strong and dimensionally stable composites. These properties have led to widespread use of asbestos in fireproofing materials, brake linings, floor tiles, pipes, and roofing materials. 

Perhaps the largest volume commercial production of particle-filled polymers is carbon- or graphite-filled rubbers. Carbon blacks are widely used in natural and synthetic rubbers and convey significant improvements in modulus, abrasion resistance, and tear strength as well as additional thermal and electrical conductivity. Carbon blacks are uniquely efficient in these respects the reasons for this are still the subject of debate. A very recent review by Rigbi is an excellent compilation of current theory and experiment. An earlier review by Medalia ... 

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