Cure yield

Dioxime cures yield vulcanisates with good ozone resistance and moisture impermeability and, as such, are frequently used for curing electrical insulating compounds. 

The cure yield, calculated in terms of the average absorbed dose delivered to the layer of interest multiplied by the conveyor speed per unit effective beam current. It can be estimated by measuring the dose over the range of beam currents at different speeds. 

Although colorimetric methods are tedious and require much time, they remain useful for measurements in materials with low Mo concentrations. A modified stannous chloride-thiocyanate procedure described by Marmoy (1939) and Johnson and Arkley (1954) has been used extensively in our laboratory for many years and has yielded useful results (Sims and Atkinson, 1974 Pal et al., 1976 Hawes, Sims, and Wells, 1976 Sims, Leggett, and Pal, 1979 Sims, 1996). An example of such data is shown in Figure 7.1 (Sims and Atkinson, 1976). In that study, an acid soil (pH 5.4) had been treated with various amounts of agricultural limestone and N, P, and K fertilizers in the form of NaNOa or urea, concentrated superphosphate, and K2SO4, respectively. Maximum cured yields of hurley tobacco were associated with leaf-tissue Mo concentrations of about 0.42 mg kg in this largely acid soil environment. 

Uses Epoxy tor adhesive, casting, potting, encapsulation, and wet layup applies., marine/protective coatings Features After cure, yields highly crosslinked thermoset polymers a high-visc., fast-reacting resin for adhesive applies. 

Cure begins near 75 C and ends just prior to 150 C in the uncatalyzed resin. The temperature range (72°C to 148 u. Figure 2) selected for the evaluation of reaction kinetics was based on FT-IR spectra. These results indicated that the disappearance of styrene, and presumably its copolymerization, begins and ends between these temperatures. Evaluation of the kinetic parameters for gel coat cure yielded a reaction order of 1.56, close to the anticipated value of 1.50, an activation energy of 25.1 kcal/mole and an InA of 28.4. 

Semi-SINs using amine-cured epoxies and butadiene-acrylonitrile rubber " were found to yield adhesives with extremely high bonding strength to metal. The rubber was based on Hycar, and the epoxy was based on a range of compositions, including epoxidized soy bean oil (Example 2). Sometimes the rubber was sulfur cured, yielding an IPN. 

Another factor to be considered with flexing is the effect of sulfur concentration. The rate of oxidation is proportional to the amount of combined sulfur, and with lower sulfur levels, better aging is obtained. It would appear, therefore, that it is better to compound with low sulfur. However, these low sulfur cures yield poor... 

Ra.dia.tlon. Use of radiation to affect fixation of some flame retardants is being investigated (110). Electron-beam fixation requires the selection of compounds that can be insolubilized inside or outside of the fiber with high yield in a short time. Polyunsaturated compounds, eg, Fyrol 76, have shown promise (see Radiation curing). 

Eig. 1. The key steps for the Phillips PPS process are (/) production of aqueous sodium sulfide from aqueous sodium hydrogen sulfide (or hydrogen sulfide) and aqueous sodium hydroxide 2) dehydration of the aqueous sodium sulfide and NMP feedstocks 5) polymerization of the dehydrated sulfur source with -dichlorobenzene to yield a slurry of PPS and by-product sodium chloride in the solvent (4) polymer recovery (5) polymer washing for the removal of by-product salt and residual solvent (6) polymer drying (7) optional curing, depending on the appHcation and (< ) packaging. 

Diallyl Isophthalate. DAIP polymerizes faster than DAP, undergoes less cyclization, and yields cured polymers of better heat resistance, eg, up to ca 200°C. Prepolymer molding materials such as Dapon M of EMC, are not sticky. Maleic anhydride accelerates polymerization, whereas vinyl isobutyl ether retards it and delays gelation in castings. Copolymers with maleic anhydride are exceptionally hard and tough and may scratch homopolymer surfaces. 

Semi-EV cures represent a compromise between conventional and EV cures. Although semi-EV cures do yield polysulftde cross-links, they tend to minimize formation of kiefficient moieties such as sulfur bridging with itself, accelerator-terminated sulfur linkages, etc. This cleaner usage of sulfur is the reason for thek compromise properties between conventional and EV cures. 

Cements and Ceramics. Refractory cements and ceramics (qv) are prepared from slurries of siUca, 2irconia, alumina, or magnesia and a prehydroly2ed siUcate (see Cement). Calcining at 1000°C yields cured refractory shapes (48,49). 

Two factors emerged to turn the focus of durable press the discovery that incorporation of a level of nylon or polyester in the fabric can substantially increase the garments abrasion resistance, and the reali2ation that the marketplace preferred cotton—polyester blends in delayed cure operations, even though 85% cotton—15% nylon fabric yields a suitable product. The 50% cotton—50% polyester fabric seemed particularly appropriate because it contained sufficient ceUulosic to benefit from a chemical finish and sufficient synthetic to provide strength and abrasion resistance. 

Another method iavolves an electric-arc vaporizer which is >2000° C before burning (25,32). One of the features of the process is a rapid quench of the hot gas flow to yield very fine oxide particles (<0.15 nm). This product is quite reactive and imparts accelerated cure rates to mbber. Internally fired rotary kilns are used extensively ia Canada and Europe and, to a limited extent, ia the United States (24). The burning occurs ia the kiln and the heat is sufficient to melt and vaporize the ziac. Because of the lower temperatures, the particles are coarser than those produced ia the other processes. In a fourth process, ziac metal which is purified ia a vertical refining column is burned. In essence, the purification is a distillation and impure ziac can be used to make extremely pure oxide. Also, a wide range of particle sizes is possible (33). 

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