Accelerated curing

High purity 4-dodecylphenol is used to produce specialty surfactants by its reaction with ethylene oxide. The low color of high purity 4-dodecylphenol is important in this appHcation from a standpoint of aesthetics. 4-Dodecylphenol is also used to produce phenoHc resins which are used in adhesive appHcations and printing inks. 4-Dodecylphenol is also used as an epoxy curing catalyst where the addition of 4-dodecylphenol accelerates curing of the epoxy resin to a hard, nontacky soHd. 

Accelerators are chemical compounds that iacrease the rate of cure and improve the physical properties of the compound. As a class, they are as important as the vulcanising agent itself. Without the accelerator, curing requires hours or even days to achieve acceptable levels. Aldehyde amines, thiocarbamates, thiuram sulfides, guanidines, and thiasoles are aU. classified as accelerators. By far, the most widely used are the thiasoles, represented by mercaptobensothiasole (MBT) and bensothiasyl disulfide (MBTS). 

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). 

Carbonates, especially sodium and potassium carbonates, are often added to plywood and LVL mixes to accelerate cure and reduce delaminations and blows. Calcium carbonates do not show a significant accelerating effect. Occasionally esters are used to accelerate plywood mixes [119]. Carbon dioxide also accelerates PF cure [120]. 

For most electron-curable adhesives, a dose of 100 kGy is required to cure. Fig. 4 shows the speed of curing various widths of material as a function of accelerator power. A reasonably controllable speed for moving parts through an accelerator would be approximately 10 m per minute. Based on this criterion, the lower wattage limit for an accelerator curing an adhesive strip 5 cm wide would be 5 kW. For curing very large parts a 50 kW accelerator would be more suitable. 

Lowering of curing costs in plants where accelerated curing is used. 

Accelerated cure compressive strengths 28-day compressive strength (MPa) (MPa) at age 16-17 h... 

Accelerated curing 3 h procure 4.5°C rise and 58°C for 16-17 h, and subsequently moist cured. 

Studies with model compounds indicate that thiazole-accelerated cures tend to favor reactions at allylic positions. This has been explained (68MI11503) in terms of the structure of the polysulfidic intermediates which allows facile rearrangement and fragmentation reactions to occur (35). 

Once all of the inhibitor has been consumed, the normal accelerated cure can resume, thus the rate of cure and the crosslink density may be little affected. 

Fly ash increases the density, decreases the permeability, and increases the leaching resistance of Ordinary Portland Cement (OPC). It is a truism that The leach resistance of solidified cement-waste systems can be improved by any process which accelerates curing, limits porosity, or chemically bonds fission product or actinide elements. (Jantzen et al., 1984). Supercritical C02 treatment of a modified Portland cement is expected to further increase the density over the untreated material, so that a reduced porosity and improved leachability should result. In addition, the high silica content of fly ash, with its well-known sorbent properties toward actinides and certain other radionuclides, enhances the immobilization characteristics. 

Wilding, C. R. The Performance of Cement Based Systems. Cem. Res. 1992, 22, 299. Wilk, C. M. Stabilization of Heavy Metals with Portland Cement Research Synopsis Portland Cement Association Report IS007 PC A Skokie, IL, 1997. Young, J. F. Berger, R. L. Breese, J. Accelerated Curing of Compacted Calcium Silicate Mortars on Exposure to C02. J. Am. Chem. Soc. 1974, 57, 394—397. 

Accelerated curing 3 h precure 4.5°C rise and 58°C for 16-17 h, and subsequently moist cured. Mix 1 Cement content 351.9 kg m3 Type III cement, conventional carbohydrate type admixture at recommended dosage. 

The effect of solvent type on the curing rate of epoxy reactions has been well defined. Hydroxyl compounds, such as alcohols, act as catalysts and accelerate curing. However, these solvents are not serious competitors with amines for reacting with the epoxy ring. Water, functioning as a hydroxyl compound, also accelerates the reaction, even more than alcohols. Aprotic solvents, such as aromatic hydrocarbons or mineral spirits, have no effect on the amine-epoxy resin and behave as inert diluents. Carbonyl solvents, such as acetone and methyl ethyl ketone, retard the reaction. 

Phosphite functionality reduces epoxy viscosity without accelerating cure... 

D. A. Lewis eta/., The accelerated curing of epoxy-resins using microwave-radiation, Abstracts of Papers of the American Chemical Society, 194, 130-POLY (1987). 

The most important inference is that Chemisorption is a direct response to carboxyl group concentration indicated by the XPS photopeak component at 288.7 eV. It seems likely that weak add functionality is of minor import to applications for surface treatments, while interfacial phenomena such as practical adhesion may be sensitive to small concentrations of very high site energies. Interphase modification in epoxy resins, for example, can occur by direct reaction of epoxide groups with surface carboxyls (17), or by accelerated cure chemistry near the surface (39). Carboxyl groups on carbon surfaces may interact with basic moieties in polymers such as polycarbonate or poly(ethylene)oxide (40=42), or promote interfacial crystallinity that improves impact strength and other aspects of composite performance (43, M)-... 

---