Vulcanization characteristics

By weighing the first and last passes, the mill homogenization procedure is also use to measure volatile matter content. Samples are then allocated to such tests as are required in accordance with ISO methods. In particular, it is specified that volatile matter is measured according to the oven method of ISO 24813. Apparently, we have two measures of volatile matter Mooney viscosity and plasticity retention index are measured as discussed later in the chapter. Although the title and the procedure indicate that the method is intended for raw rubber, it is also specified that vulcanization characteristics are measured. 

For synthetic rubbers, the mill homogenization is generally omitted, although it is specified as an alternative where the appropriate evaluation procedure requires it before measuring Mooney viscosity. Different conditions are given for specific polymers. The mill method of ISO 248 for determining volatile matter is specified but the oven method may be substituted if the material sticks to the mill rolls. Regardless of which volatile matter method is used, the mill procedure is required to dry samples for any chemical tests needed - unless this is not possible. To the uninitiated at least, this is not a model of clarity. Vulcanization characteristics are determined for synthetic rubbers, but not plasticity retention index. 

ISO 289-2, 1994. Determinations using a shearing disc viscometer - Determination of pre-vulcanization characteristics. 

Creed, K,E, J, J, D Amico, M,W, Harman and R,O, Zerbe Vulcanization Characteristics of a Series of 4-Methyl-5-Substituted-2-Thiazolethiols and their derivatives, Ind, Eng, Chem. 46, 8O8 (1954). 

ISO 3417—Rubber—Measurement of vulcanization characteristics with the o.scillating disc curemeter (1991). 

FIGURE 7.11 Vulcanization characteristics given by various accelerators and combinations. 

Different types of accelerators impart vulcanization characteristics that differ with respect to both scorch resistance and crosslinking rate. Figure 7.11 is a map of accelerator system characteristics. Within groups or types, differences can be obtained by choosing the individual accelerators. In the group of benzothiazolesulfenamides, the scorch resistance and vulcanization time increase in the order TBBS or CBS, MBS, DCBS. 

This type of vulcanization-system design was reported by McCall (1969). He found that by judiciously balancing the levels of accelerator, sulfur, and DTDM, he could obtain good vulcanization characteristics, good thermal stability, good flex life, and superior retention of flex life. Others have reported on more recent work on the effects of crosslink type on reversion (Datta et al., 2007 Fan et al., 2001). 

In order to measure the vulcanization characteristics, the rubber is enclosed in a heated cavity (Fig. 5). Imbedded in the rubber is a metal disc that oscillates sinusoidally in its plane about its axis. Vulcanization is measured by increase in the torque required to maintain a given amplitude (e.g., degrees of arc) of oscillation at a given temperature. The torque is proportional to a low strain modulus of elasticity. Since this torque is measured at the elevated temperature of vulcanization, the portion of it due to viscous effects is minimal. Thus it has been assumed that the increase in torque during vulcan-... 

Different types of accelerators impart vulcanization characteristics which differ with respect to both scorch resistance and crosslinking rate. Figure 11 is... 

For many years, it was difficult to independently control the two main vulcanization characteristics, scorch resistance (processing safety) and rate of crosslink formation. In the case of natural rubber (NR), if one had chosen a... 

Different types of accelerators impart vulcanization characteristics, which differ in both scorch resistance and cross-linking rate. Fig. 4.23 is a map of accelerator system characteristics. The effect of the addition of small concentrations of the premature vulcanization inhibitor (PVI), N-(cyclohexylthio)phthahmide, is also given by Fig. 4.23. This retarder is frequently used to independently control scorch resistance with little effect on the rate of cross-linking. 

The type and level of cure-site bearing comonomer, because it is used at low levels, has little influence on the oil swefling, heat resistance, and low-temperature flexihUity. Instead, it determines the cure behavior and cross-link density. Thus, it has effects on mechanical properties, elasticity, and permanent set. Older grades of ACM are being replaced because of their poor vulcanization characteristics. New grades, prepared with undisclosed commoners, are much more rapidly vulcanized and give excellent properties without postcure (e.g., in an oven, as required for earlier grades). 

ACM compounds are difficult to process and processing aids must be used, e.g., stearic acid, zinc soaps, fatty alcohol residues, octadecylamine, or pentaerythritol tetrastearate. This later processing aid does not affect vulcanization characteristics, whereas the others retard or accelerate vulcanization. 

Figure 1 illustrates the curing process as measured by a rheometer. The rheometer follows the development of cure state as a function of time. Vulcanization characteristics such as minimum torque Ml (a measure of compound green viscosity), onset of cure (T1 pt rise), Mh (a measure of maximum cure state reached), and T90% cme (time required to reach 90% cure state) are valuable properties defining cure behavior. Likewise the rheometer cure profile can be broken into three regions of interest, an estimate of scorch safety, an idea of what the cure state development looks like during the cross-linking phase, and how the cross-linked vulcanizate network matures with additional heat. 

Standard Test Method for Rubber Property— Vulcanization Characteristics Using Oscillating Disk Curemeter (ASTM D2084-81). 

ASTM D1646-03, Standard Test Methods for Rubber—Viscosity, Stress Relaxation, and Pre-Vulcanization Characteristics (Mooney Viscometer), 2003. 

The method of a planned experiment [11,12] was used to evaluate the dependence of vulcanization characteristics, gel content, and physical properties of the compounds on their composition. A second-degree polynomial for four factors in form (1) was used as a mathematical model ... 

Although acceptable cure characteristics are obtained with a conventional system based on 2 5 phr sulphur and 0 5 phr sulphenamide, this formulation is not recommended for ENR as the vulcanizates have poor ageing characteristics compared with unmodified NR. The cause of this is discussed in Section 6.9. Semi-EV or EV-type cure systems have been found to be the most satisfactory for ENR. Examples of such systems are recorded in Table 1. The need to compound ENR with a base affects the vulcanization characteristics, and one of the factors to be considered in the choice of base is the processing safety of the mix. " Stronger bases can markedly reduce scorch delay by base catalysis of the vulcanizing system and should only be employed at low levels, whereas the less basic compounds can be employed at higher concentrations (Fig. 9). 

Wulcanized using recipe 2A given in ASTM D 3184-71. The vulcanization characteristics of each stock were determined on a Monsanto Rheometer at 140 C using ASTM D 2084-71T. 

Vulcanization Characteristics of SBR Recipes Silane on Clay Mooney Vise. Data... 

Table 8.3 Vulcanization characteristics of PALF-NR composites with various fiber loadings...

Study of vulcanized characteristics of the rubber mixtures on Monsanto rheometer showed, that experimental mixtures with cauotchouc CDR-2,5 excel serial mixtures almost in two times in the initial vulcanization time... 

For all but the pressure-sensitive adhesives (discussed shortly), the adhesive material is applied as a low-viscosity liquid, so as to cover the adherend surfaces evenly and completely and allow for maximum bonding interactions. The actual bonding joint forms as the adhesive undergoes a liquid-to-solid transition (or cm-es), which may be accomplished through either a physical process (e.g., crystallization, solvent evaporation) or a chemical process [e.g., polymerization (Section 15.20), vulcanization]. Characteristics of a sound joint should include high shear, peel, and fracture strengths. 

Subsequent to the twisting, the tire cord yarns are woven. Because normal fabric structures with nearly constant warp and weft density show less-optimal deformation and vulcanization characteristics, a special construction was developed for tire cord fabrics. Tire cords have only up to 10 weft threads made of cotton yarn per 10 cm and therefore have a very open structure. The weft has no carrying function in the tire. It serves only as a supporting thread to facilitate further processing steps. 

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