Efficient cure systems

Ammonia reacts with ethylene oxide to synthesize morpholine, which is essential for making DTDM (sulfur donor for efficient cure systems) and MBS accelerator. Since morpholine is a secondary amine, this has posed environmental problems in the workplace due to the emission of nitrosamines during curing. 

Sulfur monochloride is reacted with morpholine to produce DTDM (a sulfur donor for efficient cure systems). 

CURVE EQUATIONS FOR DESCRIBING FATIGUE LIFE OF NR/BR BLENDS CURED WITH CONVENTIONAL, SEMI-EFFICIENT OR EFFICIENT CURING SYSTEM... 

Optimised NR bushing compounds were developed using semi-efficient cure systems in which N-tert-butyl-2-benzothiazole was used as the primary accelerator, zinc dibutyldithiophosphate as the secondary accelerator, N-cyclohexyl thiophthalimide as retarder, andhexamethylene bisthiosulphate disodium dihydrate as a stabilising hybrid crosslinker. These cure systems gave compounds with improved stability of mechanical and dynamic mechanical properties and shortened mould cycle times. 

Eor apphcation temperatures below 10°C or for acceleration of cure rates at room temperature, nonredox systems such as ben2oyl peroxide initiated by tertiary amines such as dimethylaruline (DMA) have been appHed widely. Even more efficient cures can be achieved using dimethyl- -toluidine (DMPT), whereas moderated cures can be achieved with diethylaruline (DEA). 

New efficient vulcanization systems have been introduced in the market based on quaternary ammonium salts initially developed in Italy (29—33) and later adopted in Japan (34) to vulcanize epoxy/carboxyl cure sites. They have been found effective in chlorine containing ACM dual cure site with carboxyl monomer (43). This accelerator system together with a retarder (or scorch inhibitor) based on stearic acid (43) and/or guanidine (29—33) can eliminate post-curing. More recently (47,48), in the United States a proprietary vulcanization package based on zinc diethyldithiocarbamate [14324-55-1]... 

For making compatible blends, the polymers should have comparable polarities and viscosities. The oil needs to be selected properly so that its solubility parameter is close to those for blend components. The cure system should be efficient for all constituent rubbers and the filler system needs to be appropriate. Finally, cost consideration should be taken into account to provide a commercially viable product. 

Traditionally, UV curable polymers have been utilized as coatings for wood and vinyl floors, but their applications have increased dramatically over the last twenty years to encompass many diverse areas, including optical fiber coatings (7), adhesives (2), disc replications (3-5), and microelectronics (6). This widespread use of UV cross-linked systems is attributed to their rapid, energy efficient curing and their solvent free, one piece formulations. Typically, UV curable systems require only a small fraction of the power normally utilized in thermally cured systems and their solvent free nature offers an environmentally safer alternative. 

Radiation cross-linking of polyethylene requires considerably less overall energy and less space, and is faster, more efficient, and environmentally more acceptable. Chemically cross-linked PE contains chemicals, which are by-products of the curing system. These often have adverse effects on the dielectric properties and, in some cases, are simply not acceptable. The disadvantage of electron beam cross-linking is a more or less nonuniform dose distribution. This can happen particularly in thicker objects due to intrinsic dose-depth profiles of electron beams. Another problem can be a nonuniformity of rotation of cylindrical objects as they traverse a scanned electron beam. However, the mechanical properties often depend on the mean cross-link density. ... 

Radiometers for spot cure monitor the performance (irradiance), measure fhe light guide degradation, determine optimum positioning of fhe lighf guide cable, and compare the efficiency of spot curing systems. An example of a... 

Radiation cross-linking of PE requires considerably less overall energy and space, and is faster, more efficient and more environmentally acceptable.93 Chemically cross-linked PE contains chemicals that are byproducts of the curing system. These often have adverse effects on the dielectric properties and, in some cases, are simply not acceptable.94... 

An Electrocure radiation curing unit could cost up to 400,000 or a capital expenditure cost of 20/hr. Radiation curable systems also require more maintenance and an inert atmosphere (nitrogen blanket) to ensure efficient curing operations. 

As sulfur content increased, the change in sulfur bond ratios exhibit a transition from a semi-efficient , or lower sulfur/accelerator ratio, to a conventional ,or higher sulfur/accelerator ratio, cure system (4). Overall, the... 

Fillers are often useful in epoxy-polyamide adhesives (41). Fillers aid flow control—particularly at elevated temperatures. Other properties contributed by fillers are exhibited in the cured system. For example, they can increase the modulus of elasticity, modify the coefficient of thermal expansion, increase heat resistance, and even affect bond strength. Of course, the excellent wetting properties of polyamides Increase the dispersion efficiency of these fillers. The type of filler selected and the amount used also have a pronounced effect on adhesive quality. A few of these effects are illustrated in Tables VI and VII (37). (See also Table VIII.)... 

It should finally be emphasized that the use of DPB is not restricted to acrylic compounds since it proved to be also a very efficient photoinitiator for the polymerization of vinyl monomers, like N-vinylpyrrolidone (NVP). In addition, DPB appeared to be particularly well-suited to photo-cure systems that need hydrogen abstraction type photoinitiators, like the thiol-polyenes resins (2), since it is then to be compared to the poor-performing benzophenone. 

Thermo-oxidative stability is primarily a function of the vulcanization system. Peroxide vulcanization or cure systems tend to perform best for reversion resistance as a result of the absence of sulfur and use of carbon-carbon crosslinks. Efficient vulcanization (EV) systems that feature a low sulfur level (0.0-0.3 phr), a high acceleration level, and a sulfur donor similarly show good heat stability and oxidation resistance. Such systems do, however, have poor resistance to fatigue because of the presence of predominantly monosulfidic crosslinks. Conventional cure systems that feature a high sulfur level and low accelerator concentration show poor heat and oxidation resistance because the polysulfidic crosslinks are thermally unstable and readily oxidized. Such vulcanization systems do, however, have better fatigue resistance. Semi-EV cure systems, which are intermediate between EV and conventional systems, are a compromise between resistance to oxidation and required product fatigue performance. 

Figure 3.4 Eco-efficiency portfolio for alternative curing systems.

The nature of the photopolymerizable components such as chemical stmcture, molecular weight, and functionality plays a significant role in the efficiency of the polymerization reaction and physical, chemical, photochemical, mechanical, and stmctural properties of the cured system. When monomers or multifunctional monomers are combined with oligomers, such as in the case of carbonate, carbamate, or oxazolidone acrylates, they become highly reactive, exhibit low residual saturation and good flexibility. " " The mechanical properties sharply increase with functionality of the monomer with an increase in the cross-linking density, but they become more brittle. Solubility, biocompatibility, thermal resistance. 

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