Curing reaction, initiation

Effects of Various Additives on Accelerated Grafting and Curing Reactions Initiated by UV and Ionizing Radiation... 

Another curing mechanism is operative in the curing reaction initiated by a polymerization catalyst for epoxy ring opening, where anionic catalysts such as tertiary amines 1S-l9) and imidazols 20 21> and cationic catalysts such as amine complexes of... 

Chaplin, R.R, Dwoijanyn, P.A., Gamage, N.J.W. et al. 1996. The role of partitioning of reagents in grafting and curing reactions initiated by ionizing radiation and UV. Radiat Phys Chem. Al 435-437. 

Promoters. Substances such as acetyl acetone, ethyl acetoacetate, amides of ace-toacetic acid [2.107], acetyl cyclopentanone [2.108] or tertiary aromatic amines have an accelerating effect on the curing reaction initiated by the hydroperoxide/cobalt octoate. Ethyl acetoacetate is most frequently used. The amount added is 1-3%, calculated on the resin supply form. 

All thermoplastic adhesives require heating in order to melt the polymer, hence the name hot-melt. Unlike the majority of structural adhesives, there is no chemical curing reaction. Initially based on natural substances, synthetic hot-melt adhesives first became available in the 1950 s. A great many polymers exist as thermoplastics, providing a wide range of potential hot-melts. Each adhesive formulation contains a cocktail of compounds to modify the properties. These include tackifiers to promote adhesion and waxes to reduce viscosity and cost. 

Aromatic diacyl peroxides such as dibenzoyl peroxide (BPO) [94-36-0] may be used with promoters to lower the usehil decomposition temperatures of the peroxides, although usually with some sacrifice to radical generation efficiency. The most widely used promoter is dimethylaniline (DMA). The BPO—DMA combination is used for hardening (curing) of unsaturated polyester resin compositions, eg, body putty in auto repair kits. Here, the aromatic amine promoter attacks the BPO to initially form W-benzoyloxydimethylanilinium benzoate (ion pair) which subsequentiy decomposes at room temperature to form a benzoate ion, a dimethylaniline radical cation, and a benzoyloxy radical that, in turn, initiates the curing reaction (33) ... 

The cure reaction of structural acrylic adhesives can be started by any of a great number of redox reactions. One commonly used redox couple is the reaction of benzoyl peroxide (BPO) with tertiary aromatic amines. Pure BPO is hazardous when dry [39]. It is susceptible to explosion from shock, friction or heat, and has an autoignition temperature of 79°C. Water is a very effective stabilizer for BPO, and so the initiator is often available as a paste or a moist solid [40], The... 

Biernath et al. concluded that phenolic novolac and epoxidized cresol novolac cure reactions using triphenylphosphine as the catalyst had a short initiation period wherein the concentration of phenolate ion increased, followed by a (steady-state) propagation regime where the number of reactive phenolate species was constant.85 The epoxy ring opening was reportedly first order in the steady-state regime. 

Having made the prepolymer, a reactive diluent, usually styrene, is added, together with an appropriate free-radical initiator system in order to bring about crosslinking. This cure reaction can be made to occur at either ambient or elevated temperatures and, depending on conditions, is complete in anything from a few minutes to several hours. 

Adhesives based on hydrolysis resistant chemistry (i.e., adhesives D and E) show a high retention of initial properties after exposure to an aggressive corrosion environment and the failure occurs cohesively within the adhesive. The cure reactions of these adhesives involve the formation of hydrolysis resistant carbon-nitrogen bonds in reactions involving the free N-H functionality of the Versamid or Genamid hardener with the oxirane functionality of the epoxy resin that is present in the adhesive formulation ... 

Last but not least, DSC is a powerful technique for many other polymer-relevant aspects such as monitoring of curing reactions, detection of degradation, determination of heat capacity of chemical conversions, monitoring of initiator decomposition, etc. 

The cure of thermoset resins involves the transformation of a liquid resin, first with an increase in viscosity to a gel state (rubber consistency), and finally to a hard solid. In chemical terms, the liquid is a mixture of molecules that reacts and successively forms a solid network polymer. In practice the resin is catalyzed and mixed before it is injected into the mold thus, the curing process will be initialized at this point. The resin cure must therefore proceed in such a way that the curing reaction is slow or inhibited in a time period that is dictated by the mold fill time plus a safety factor otherwise, the increase in viscosity will reduce the resin flow rate and prevent a successful mold fill. On completion of the mold filling the rate of cure should ideally accelerate and reach a complete cure in a short time period. There are limitations, however, on how fast the curing can proceed set by the resin itself, and by heat transfer rates to and from the composite part. 

Large-mass parts Conventional coating of large-mass parts requires exceedingly long times in convection ovens. A considerable reduction of times required for cure is to melt the powder with IR and use fast UV-initiated free radical curing reactions. 

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