Natural rubber thermal properties

The reactive extrusion of polypropylene-natural rubber blends in the presence of a peroxide (1,3-bis(/-butyl per-oxy benzene) and a coagent (trimethylol propane triacrylate) was reported by Yoon et al. [64]. The effect of the concentration of the peroxide and the coagent was evaiuated in terms of thermal, morphological, melt, and mechanical properties. The low shear viscosity of the blends increased with the increase in peroxide content initially, and beyond 0.02 phr the viscosity decreased with peroxide content (Fig. 9). The melt viscosity increased with coagent concentration at a fixed peroxide content. The morphology of the samples indicated a decrease in domain size of the dispersed NR phase with a lower content of the peroxide, while at a higher content the domain size increases. The reduction in domain size... 

Chemical pretreatments with amines, silanes, or addition of dispersants improve physical disaggregation of CNTs and help in better dispersion of the same in rubber matrices. Natural rubber (NR), ethylene-propylene-diene-methylene rubber, butyl rubber, EVA, etc. have been used as the rubber matrices so far. The resultant nanocomposites exhibit superiority in mechanical, thermal, flame retardancy, and processibility. George et al. [26] studied the effect of functionalized and unfunctionalized MWNT on various properties of high vinyl acetate (50 wt%) containing EVA-MWNT composites. Figure 4.5 displays the TEM image of functionalized nanombe-reinforced EVA nanocomposite. 

Choudhury N.R., Chaki T.K., Dutta A., and Bhowmick A.K. Thermal, x-ray and d3mamic mechanical properties of thermoplastic elastomeric natural rubber-polyethylene blends. Polymer, 30, 2047, 1989. Marasch M.J., TPU s Growth from versatility, 53rd Annual Tech. Conference, Antech 95 4088, Boston, May 7-11, 1995. 

There are a number of papers in the open literature explicitly reporting on the properties of boron cluster compounds for potential neutron capture applications.1 Such applications make full use of the 10B isotope and its relatively high thermal neutron capture cross section of 3.840 X 10 28 m2 (barns). Composites of natural rubber incorporating 10B-enriched boron carbide filler have been investigated by Gwaily et al. as thermal neutron radiation shields.29 Their studies show that thermal neutron attenuation properties increased with boron carbide content to a critical concentration, after which there was no further change. 

If solid polymer objects are fluorinated or polymer particles much larger than 100 mesh are used, only surface conversion to fluorocarbon results. Penetration of fluorine and conversion of the hydrocarbon to fluorocarbon to depths of at least 0.1 mm is a result routinely obtained and this assures nearly complete conversion of finely powdered polymers. These fluorocarbon coatings appear to have a number of potentially useful applications ranging from increasing the thermal stability of the surface and increasing the resistance of polymer surfaces to solvents and corrosive chemicals, to improving friction and wear properties of polymer surfaces. It is also possible to fluorinate polymers and polymer surfaces partially to produce a number of unusual surface effects. The fluorination process can be used for the fluorination of natural rubber and other elastomeric surfaces to improve frictional characteristics and increase resistance to chemical attack. 

By analogy with the works which dealt with cellulose micro crystal-reinforced nanocomposite materials, microcrystals of starch [95] or chitin [96, 97] were used as a reinforcing phase in a polymer matrix. Poly(styrene-co-butyl acrylate) [95,96], poly(e-caprolactone) [96], and natural rubber [97] were reinforced, and again the formation of aggregates or clustering of the fillers within the matrices was considered to account for the improvement in the mechanical properties and thermal stability of the respective composites processed from suspensions in water or suitable organic solvents. 

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). 

Polybutadiene, CAS 9003-17-2, is a common synthetic polymer with the formula (-CH2CH=CHCH2-)n- The cis form (CAS 40022-03-5) of the polymer can be obtained by coordination or anionic polymerization. It is used mainly in tires blended with natural rubber and synthetic copolymers. The trans form is less common. 1,4-Polyisoprene in cis form, CAS 9003-31-0, is commonly found in large quantities as natural rubber, but also can be obtained synthetically, for example, using the coordination or anionic polymerization of 2-methyl-1,3-butadiene. Stereoregular synthetic cis-polyisoprene has properties practically identical to natural rubber, but this material is not highly competitive in price with natural rubber, and its industrial production is lower than that of other unsaturated polyhydrocarbons. Synthetic frans-polyisoprene, CAS 104389-31-3, also is known. Pyrolysis and the thermal decomposition of these polymers has been studied frequently [1-18]. Some reports on thermal decomposition products of polybutadiene and polyisoprene reported in literature are summarized in Table 7.1.1 [19]. 

CHEMICAL PROPERTIES flammable liquid thermally unstable corrosive to natural rubber hydrolyzes slowly with heat in water to form boric acid reacts with ammonia to form a diammoniate reacts vigorously with strong oxidizers decomposes very slowly at 150°C (302°F) FP (30°C, 86 F) LFL/UFL (0.42%, 98%) AT (35°C, 95 F) HF (42.7 kJ/mol liquid at 25°C). 

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. 

A sample variability exists for the thermal properties, especially for rubber filled with carbon filler, while such a variation is not seen with gum natural rubber [5]. 

The applications of the rubbers stem from their important properties, which include thermal stabflity, good electrical insulation properties, nonstick properties, physiological inertness, and retention of elasticity at low temperatures. The temperature range of general-purpose material is approximately — 50°C to -l-250°C, and the range maybe extended with special rubbers. Silicone rubbers are, however, used only as special-purpose materials because of their high cost and inferior mechanical properties at room temperature as compared to conventional rubbers (e.g., natural rubber and SBR). 

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. 

Nakason, C., Tobprakhon, A., and Kaesaman, A. 2005. Thermoplastic vulcanizates based on poly(methyl methacrylate) /epoxidized natural rubber blends Mechanical, thermal, and morphological properties. Journal of Applied Polymer Science 98 3) 1251-1261. 

Nakason, C., Saiwaree, S., Tatun, S., and Kaesaman, A. 2006. Rheological, thermal and morphological properties of maleated natural rubber and its reactive blending with poly (methyl methacrylate). Polymer Testing 25(5) 656-667. 

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

Natural rubber (NR) is widely used in various applications and products for its excellent properties such as elasticity, low hysteresis, high resilience, toughness, etc NR is the basic constituent of many products in the consumer goods, health and medical sectors, and it is widely used in transportation. The properties of NR can be improved by the addition of fillers. The inclusion of inorganic fillers in polymers usually results in improvement in strength, toughness, processability, dimensional stability, wear and lubrication properties, and in some cases resistance to thermal and UV radiation of the matrix. 

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