Unvulcanized rubber

ASTM D6048, Standard practice for stress relaxation testing of raw rubber, unvulcanized rubber compounds and thermoplastic elastomers. New ASTM standard prepared in Stress Relaxation Task Group to D11.12, Subcommittee on Processability. 

ISO 289—Rubber, unvulcanized -Determinations using a shearing-disc viscometer Part 1, Determination of Mooney viscosity Part 2. Determination of prcvulcanization characteristics (1994). 

ISO 2007 Rubber, unvulcanized—Determination of pla.sticity Rapid plastimetcr method (1991). 

Natural rubber, unvulcanized Natural rubber, cured Polyamide, Nylon 6 Polyamide, Nylon 6,6... 

Fig. 14. Variation of the spin-lattice relaxation time with the reciprocal of the absolute temperature for natural rubber, unvulcanized and vulcanized to a semihard state (ref. 12)...

Solid rubber - - sponge sealants Solid rubber - - unvulcanized rubber sealants Solid rubber - - sponge rubber - - metal sealants Sponge rubber - - unvulcanized rubber sealants... 

In all the compositions, the DCP-cured blends showed better properties than the corresponding unvulcanized samples. Choudhary et al. [30] further demonstrated the use of EPDM, chlorinated PE, chlorosulfo-nated PE, maleic anhydride modified polyethylene, and blends of epoxidized natural rubber-sulfonated EPDM as compatibilizers in NR-LDPE (low-density PE) blends. 

Dynamic mechanical measurements for elastomers that cover wide ranges of frequency and temperature are rather scarce. Payne and Scott [12] carried out extensive measurements of /a and /x" for unvulcanized natural mbber as a function of test frequency (Figure 1.8). He showed that the experimental relations at different temperatures could be superposed to yield master curves, as shown in Figure 1.9, using the WLF frequency-temperature equivalence, Equation 1.11. The same shift factors, log Ox. were used for both experimental quantities, /x and /x". Successful superposition in both cases confirms that the dependence of the viscoelastic properties of rubber on frequency and temperature arises from changes in the rate of Brownian motion of molecular segments with temperature. 

Elastomers are often blended with plastics either to improve the impact resistance or to develop new materials having both plastic and elastic behavior. When the elastomer in the blend is dynamically vulcanized, the product is called a thermoplastics vulcanizate (TPV). Blends with unvulcanized mbber phase are usually known as thermoplastic elastomers. TPVs are discussed in another section of this book. This section will deal with recent developments in rubber-plastic blends. 

The specimen was prepared by the following method. After mixing HAF carbon black (50 phr) with natural rubber (NR) in a laboratory mixer, carbon gel was extracted from unvulcanized mixture as an insoluble material for toluene for 48 h at room temperamre and dried in a vacuum oven for 24 h at 70°C. We made the specimen as a thin sheet of the carbon gel (including carbon black) by pressing the extracted carbon gel at 90°C. The cured specimen was given by adding sulfur (1.5 phr) to the unvulcanized mixture and vulcanized for 30 min at 145°C. The dynamic viscoelastic measurement was performed with Rheometer under the condition of 0.1% strain and 15 Hz over temperatures. 

Matsushita et al. [127] prepared compositions showing good vulcanizability containing EPDM reclaim. Weather-strip wastes comprising of sulfur-cured EPDM mbber (containing 50% carbon black) were kneaded at 300°C and 3 MPa and extruded to give a rubber (Mw 200,000 gel content 65%), 25 parts of which was mixed with unvulcanized SBR 75, carbon black 37.5, and sulfur 1.3... 

Gee ° has applied this method to the determination of the interaction parameters xi for natural rubber in various solvents. Several rubber vulcanizates were used. The effective value of VelV for each was determined by measuring its extension under a fixed load when swollen in petroleum ether. Samples were then swollen to equilibrium in other solvents, and xi was calculated from the swelling ratio in each. The mean values of xi for the several vulcanizates in each solvent are presented in Table XXXVI, where they are compared with the xi s calculated (Eq. XII-30) from vapor pressure measurements on solutions of unvulcanized rubber in some of the same solvents. The agreement is by no means spectacular, though perhaps no worse than the experimental error in the vapor pressure method. 

Figure 15. Behavior under strain of an unvulcanized tire ply (conventional recipe) based on NR (natural rubber 100%), 1R (synthetic cis-7,4-polyisoprene 100%), BP/1R (a 50/50 blend of IR and txans-butadiene-piperylene copolymer).

The characteristic property of elastomers is their rubber-elastic behavior. Their softening temperature lies below room temperature. In the unvulcanized state, i.e. without crosslinking of the molecular chains, elastomers are plastic and thermo-formable, but in the vulcanized state—within a certain temperature range — they deform elastically. Vulcanization converts natural rubber into the elastic state. A large number of synthetic rubber types and elastomers are known and available on the market. They have a number of specially improved properties over crude rubber, some of them having substantially improved elasticity, heat, low-temperature, weathering and oxidation resistance, wear resistance, resistance to different chemicals, oils etc. 

In most cases the pigments used are also required to be migration-resistant. The suitability test is also carried out with 5 different pigment concentrations. To test the fastness to bleeding, the unvulcanized colorations are brought into defined contact with a white milled sheet of specific composition and vulcanized wet for 20 minutes in open steam at 140°C. During this process, half the coloration is often covered with a wet cotton cloth to determine whether the cloth, the rubber or both are stained by bleeding. 

TPOs, comprising TPEs with a polyolefin matrix and an unvulcanized rubber. They can be produced by blending or by block copolymerization of polypropylene and EPDM (reactor TPOs). Sometimes TPVs are included in TPOs. 

The extrusion process takes unvulcanized rubber and forces it trough a die, which results in long lengths of rubber of a dehnite cross-section. There are two general subdivisions of this technique one extrudes simple products and the other builds products by extruding the mbber onto metal or fabric reinforcement. Products from these techniques include tire tread, cable coating, and rubber hose. 

Which would tend to be more crystalline when stretched (a) unvulcanized rubber or (b) ebonite ... 

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