Compounds, curing

Another cure system consideration is the compound scorch behavior. Prior to vulcanisation, mbber is plastic-like and can be processed iato desired shapes such as tires, hoses, belts, or other articles. The time available to accomplish this processiag depends largely on the cure system and is referred to as the scorch time. If a compound cures prematurely duriag the processiag step, it usually becomes useless scrap. Therefore, a key requirement of the vulcanisation step is to minimise premature vulcanisation or scorch (Fig. 4). 

Examples of Cure Systems in NR, SBR, and Nitrile Rubber. Table 6 offers examples of recipes for conventional, semi-EV, and EV cure systems ia a simple, carbon black-filled natural mbber compound cured to optimum (t90) cure. The distribution of cross-links obtained is found ia Figure 9 (24). 

Press control is critical it is essential that the elastomeric compound reaches the required cure state to optimize product performance yet remains in the press the shortest time period to maximize productivity. To meet this objective, both compression and injection presses now use microprocessor controls, which enable variations in platen temperatures and compound cure characteristics to be accommodated without sacrificing product performance or productivity. 

A general term applied to the variety of operations required to convert a raw elastomer into finished products. See Calendering, Compounding, Curing, Extrusion, Mastication, Mixing, Spreading. 

Clear unsaturated oils are vulcanised at room temperature with sulphur monochloride to give a white, friable solid which is nonstaining and suitable for use in coloured compounds. Crosslinking using sulphur monochloride produces a white factice, but care had to be taken in its use, for if not used when fresh it develops a high level of acidity which affects compound cures severely. The acidity can be removed by steaming the factice just prior to use. Modem white factices contain a small addition of alkali to counteract any developed acidity. 

When irradiating a 1 1 blend of polychloroprene and poly(butadiene-acry-lonitrile) (NBR) reinforced by 50 phr furnace black and containing 5-15 phr of tetramethacrylate of bisglycerol phtalate, the product exhibited a tensile strength of 20 MPa (2,900 psi) at a dose of 15 Mrad (150 kGy) with values of elongation at break in the range of 420-480%. These values are equal to or better than those obtained from similar compounds cured chemically. ... 

Thermodynamics of the epoxy compound curing with amines is interesting from two points of view. It concerns all the numerous elementary reactions resulting in the formation of H-complexes in the reaction system and the process as a whole, as well. 

The second important feature of the reaction mechanism of the epoxy compound curing under the action of amines (primary, secondary and tertiary) and their mixtures consists in formation of various hetero-, auto-, inter- and intramolecular donor-acceptor complexes between the components of the reaction system — the starting substances and reaction products. Consideration of this complex formation can adequately explain the reaction kinetics. 

Torque rheometers are multipurpose instruments well suited for formulating multicomponent polymer systems, studying flow behavior, thermal sensitivity, shear sensitivity, batch compounding, and so on. The instrument is applicable to thermoplastics, rubber (compounding, cure, scorch tests), thermoset materials, and liquid materials. 

Most potentially Mutagenic compounds cure likely to be tested for carcinogenicity (Level 3). The results of such testing, perhaps with the results from short-term mutagenicity tests, may be sufficient for a decision. In that case, a mouse test for mutagenicity is not needed, and limited mammalian mutation-testing resources can be conserved. 

Figure 6.10 Relative allyl absorptions of EPM compounds cured with 2 phr of DCP and 3 phr of DATP, measured before and after acetone extraction [110]...

This compounded cured elastomer or rubber99 shares with all the other methyl silicone products the common characteristic of exceptional thermal stability. The material does not melt when heated in air at 300° C., which is far above the decomposition temperature of natural rubber or of any of the synthetic organic elastomers. Service over long periods of time at 150° C. does not destroy its elasticity. 

The compounds cured thermally to form crosslinked polymers with 343 °C stability in air. The curing characteristics of oligoimides end-capped with aminobenzocyclo-butene were also described [93]. 

We have investigated the recovered glassfiber-resin powder for its properties as a filler for epoxy resin compounds which are used as paints or adhesives, and compared it to conventional fillers, such as talc and calcium carbonate. The epoxy resin compound, composed of bisphenol A type epoxy resin (50.0wt%), aliphatic polyamine type hardener (18.0wt%) and filler (32.0%), was prepared. Strength and thermal expansion properties were measured for the molded epoxy resin compound cured 23°C for 7 days. Viscosity was measured for the epoxy resin compound before adding the hardener. Adhesive strength was measured by tearing two ferric boards bonded with the epoxy resin compound which was composed of bisphenol A type epoxy resin (49.2wt%), polyaminoamide type hardener (18.0wt %), and filler (32.8wt%), and was cured at 23°C for 7 days. 

Since 1967 when C. Pedersen discovered the class of compounds known as crown ethers, literally thousands of applications have been developed in which their ability to complex metal ions, solvate inorganic and organic salts in polar and non-polar solvents and facilitate anionic reactions have been exploited.10 The compounds cure cyclic polyethylene oxides. Two obstacles have prevented their wider utilization, particularly in commercial processes. Current synthetic methods are extremely costly. The materials have generally high levels of toxicity. Both these factors coupled with the difficulty in removing the crown ethers by processes other than distillation have hindered wider applications. 

As with the olefin - containing epoxies, much is yet to be done with tertiary carbamate epoxies in order to produce practical systems, but the synthesis possibility has been established. A variety of diisocyanates and tertiary alcohols are available. A general synthesis effort is needed to screen the most effective compositions with regard to solvency, compounding, cure, environmental stability, and the effectiveness of various destruct agents and conditions. 

When compared with compounds loaded with MT black, the compounds cured by sulfur were very much harder, very much weaker and had low values of elongation at break. These effects are generally only very slightly influenced by particle size. 

Rubber compounders also learned to live with a certain number of failures. Accelerators and other additives which reduce curing time and prevent sulfur blooming were developed. The possible effects of the various allotropic forms of sulfur in rubber have been reported (18, 19, 20). Although too costly to have gained wide commercial acceptance, organic sulfur compounds make excellent vulcanizing agents for rubber (21). Related compounds cure bituminous mixtures (22). 

It is critical that the plasticizers that are compatible in the liquid compound remain so when the compound cures to a rubber. Many adhesion failures have been the result of plasticizer migration that destroys the adhesive bond. 

Note Each compound cured with 10 pbw of EH-330 curing agent/100 pbw epoxy. 

Rather than look for a mwe accnrate method for obtaining data for the kinetics of cure, attention was given to evaluating the effect of the lack of accuracy in the kinetic parameters. Some studies were conducted by using calorimetry [13-15]. Thus, the effect of the order of the overall cure reaction on the rate of cure was determined, and profiles of temperature and state of cure were evaluated by varying the value of the rubber compound cured with 3% sulfur [13]. By using the same approach and the same method, the effect of a variation of the activation energy on the profiles of tanperature and of state of cure was also studied [14,15]. 

---