Rubber cure characteristics

Cure Characteristics. Methods of natural rubber production and raw material properties vary from factory to factory and area to area. Consequentiy, the cure characteristics of natural mbber can vary, even within a particular grade. Factors such as maturation, method and pH of coagulation, preservatives, dry mbber content and viscosity-stabilizing agents, eg, hydroxylamine-neutral sulfate, influence the cure characteristics of natural mbber. Therefore the consistency of cure for different grades of mbber is determined from compounds mixed to the ACSl formulation (27). The ACSl formulation is as follows natural mbber, 100 stearic acid, 0.5 zinc oxide, 6.0 sulfur, 3.5 and 2-mercaptobenzothiazole (MBT), 0.5. 

Ishiaku, U.S., Chong, C.S., and Ismail, H., Cure characteristics and vulcanizate properties of blends of a rubber compound and its recycled DE-VULC, Polym. Polym. Comp., 6, 399, 1998. 

An apparatus for determining the curing characteristics of rubber compounds. 

When the curve of a particular property (usually tensile strength) of vulcanised rubber plotted against time of vulcanisation shows a levelling off or only a slow fall after the maximum has been reached, the compound or compounding ingredient under test is said to be flat curing, to have flat curing characteristics or to show a plateau effect. 

Care must be taken when choosing an oil for rubber processing to ensure that its content of polar fractions is low. These polar fractions contain some of the most chemically active compounds in the oil. Polar materials are thought to interfere with cure characteristics and play a part in polymer degradation. These effects will also be accompanied by a drastic reduction in weather resistance, although usually heat resistance is not affected. 

Nonblack fillers such as the precipitated silicas can reduce both rate and state of cure. The mechanism appears to be one of a competitive reaction between rubber and filler for the zinc oxide activator. Use of materials such as diethylene glycol or triethanolamine prevents this competition thereby maintaining the desired cure characteristics. Neutral fillers such as calcium carbonate (whiting) and clays have little or no effect on the cure properties. 

This depends on the cross link density. With a tighter cure, permanent sets are low. Some high saturation polymers such as butyl rubbers have characteristically high permanent set. 

Laboratory measurement of curing characteristics was revolutionised by the introduction of so-called curemeters in the middle of the last century, which quite rapidly became almost universally used for the routine control of fully compounded rubbers. These instruments were so successful that the use of the Mooney to measure scorch and the need for routine measurement of physical tests on moulded test pieces has been much reduced. 

Materials. Two types of standard tire cord obtained from Gen Corporation were used in this investigation polyester, 1300/3, and nylon 66, 1260/3. The rubber composition to which the adhesively dipped cords were bonded had the following composition in parts by weight styrene-butadiene rubber (SBR) 1502, 100 N330 carbon black, 50 zinc oxide, 5 stearic acid, 0.5 sulfur, 1.7 2-morpholinothio-benzothiazole, 2. Master batches were mixed 7 min in a 350-ml Brabender Plasticorder, and curatives were added on a cool two-roll mill. Cure characteristics at 155 °C were determined with an oscillating disc rheometer (ASTM D 2084). The time to reach 90% of the final cure state was 23 min, and the Shore A hardness of the final vulcanizate was approximately 60. 

Vulcanization rate was determined by a Monsanto Rheometer. The Monsanto Oscillating Dii Rheometer is designed to measure the ccanplete curing characteristics of a single rubber specimen, heated and maintained utder continuous pressure during vulcanization. Sinusoidal oscillation of a conical dirir, embedded in the vul-canizable mix confined in a heated square carity, exerte a riiear strain on the speci-... 

As can be seen from Table 5, the blends made with the surface devulcanized reclaimed rubber crumb did not have cure characteristics that differed substantially from the blend made without including any of the reclaimed rubber (the series labeled None ). In fact, the blends made with the surface devulcanized reclaimed rubber crumb had cure characteristics that... 

Ismail, H. Suzaimah, S. Hairunezam, H.M. Curing characteristics, mechanical properties and oil resistance of styrene butadiene rubber/epoxidized natural rubber blends. J. Elastomers Plast. 2002, 34 (2), 119-130. 

Laboratory measur ent of curing characteristics have been somewhat revolutionized by the introduction of the cure meters. There were two types of cure meter the reciprocating paddle type as in the Wallace-Shawbury curometer, and the oscillating disc type such as the Monsanto rheometer. In the oscillating disc type (ODR) a biconical disc is embedded in the rubber in a closed cavity. The disc is oscillating through constant angular displacement, and the torque required monitored. 

Sengupta A. and B.B. Konar. 1997. Cure characteristics of ethylene propylene diene rubber-polypropylene blends. J. Appl. Polym. Sci. 66 1231-36. 

Other laboratory instruments able to measure the curing characteristics, the so-called curemeters, are widely used for the routine control of fully compounded rubbers. 

One of the curing characteristics that we would like to control is reversion, which can occur in compounds containing natural rubber. There is more than one approach to reducing the amount of reversion. We can use sulfur donors or increase the ratio of accelerator concentration to sulfur concentration, or we could carry out the vulcanization at a reduced temperature for a longer period. However, these approaches give rise to effects that will have to be compensated. Another approach is use of additives such as certain bisimides, e.g., N,N -m-phenylene-biscitraconimide and N,N -/m-phenylene-bismaleimides (Datta et al., 1997, 1998 Datta and Ivan, 1995) or trialkoxysilylalkylpoly-sulfides such as bis-(3-triethoxisilylpropyl)-tetrasulflde (Tan and Wolff, 1985). 

The antiozonant should have no adverse effects on the rubber processing characteristics (mixing, fabrication, vulcanization, physical properties). In general purpose rubbers, this implies that the antiozonant must be compatible with sulfur curing systems. 

The hydrophilic nature of silica also affects the cure characteristics of rubber compounds, the properties of vulcanized rubber and also the compatibility with non-polar rubber such as natural rubber (NR). Silica retards the vulcanization as it reacts with zinc-accelerator-sulfur complex. These drawbacks can be overcome through the use of silane coupling agents. The most common silane coupling agent used is bis(3-triethoxysilylpropyl) tetrasulfide (TESPT). A silane... 

A similar sol-gel process method, via NR rubber solution, was also conducted to study the effect of in situ silica content, which was varied from 15 to 65 phr, on the cure characteristics and mechanical, dynamic mechanical and thermal properties of the silica-NR nanocomposite.Both the Mooney viscosity and cure time of the sol-gel silica-NR compound increased with increasing silica contents and were lower than those of the commercial silica-filled NR compound at the same amount of silica. This is attributed to the fewer amounts of silanol groups in the sol-gel silica as compared to the commercial silica. Better reinforcement of the in situ silica, compared to the normal silica, was confirmed when higher moduli and improved compression set were observed for the sol-gel silica NR vulcanizate. This observation is consistent with the Guth and Gold equation as well as the TEM micrographs results. The sol-gel silica vulcanizate has lower storage modulus but better thermal stability then the commercial silica vulcanizate. 

Effect of CaCOs addition to NBR on the cure characteristics and results seemed to be dependent mainly on the rubber matrix where cure time, tgo decreased with increasing CaCOs content and also observed that NBR matrix exhibits longer Tcgo than those of NR compounds this result can be related to the fact that CaCOs particles are isotropic in nature, have small nucleation effect " and interact strongly with rubber especially with a polar rubber such as NBR. ... 

ZnO loaded composites of NR have been studied for their curing characteristics. It is inferred that the maximum torque value shows an improvement by 12% for both 5 and 3 phr loading of ZnO nanoparticles in comparison with the conventional rubber grade ZnO, which indicates a better state of cure because of better interaction of ZnO nanoparticles with the matrix. 

Salaeh et al investigated the curing characteristics of the gum rubber compound and the ceramic/NR composites in terms of minimum, maximum and delta torques, scorch time, cure time, and cure rate index (CRI) are summarized in Table 18.11. This suggests that longer cure time but lower CRI in the BaTiOs composites compared with the PbTiOs composites. This indicated lower rate of vulcanization in the BaTi03 compounds. Furthermore,... 

Makled et a/. reported the influence of co-precipitated hexagonal barium ferrite BaFei20ig phase on the cure characteristics and dynamic properties of NR-ferrite composites as a function of ferrite loading up to 2-20 phr (parts per hundred parts of rubber). The results showed that the scorch time decreased dramatically with increasing ferrite content until 160 phr BaF loading, this is because of the heat of mixing increases as the filler loading. 

M. Jacob, K.T. Varughese, and S. Thomas, Natural rubber composites reinforced with sisal/ oil palm hybrid fibers Tensile and cure characteristics. J. Appl. Polym. Sci. 93, 2305-2312 (2004). 

Sahoo, S., Bhowmick, A.K. Influence of ZnO nanoparticles on the cure characteristics and mechanical properties of carboxylate nitrile rubber. J. AppL Polym. ScL 106, 3077-3083 (2007)... 

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