Polymerization reaction cure exotherm

Exotherm heat It is heat given off during a polymerization reaction by the chemical ingredients as they react and the plastic cures. 

In the second dual photo/thermal initiation strategy, the approach described above is augmented by the inclusion of a thermal initiator. Upon illumination, active centers produced by fragmentation of the photoinitiator start the polymerization reaction. The heat evolved from the exothermic photopolymerization elevates the temperature of the system and results in the production of additional active sites by the thermal initiator. This dual initiating strategy provides both the cure on demand (temporal control) afforded by photopolymerization, and the completeness of cure provided by the thermal initiator. 

One of the main problems in the selection of a cure cycle is to achieve control of the exothermic polymerization reaction, particularly for the case of large parts. The exothermic character of the polymerization reaction arises from the evolution of the Gibbs free energy ... 

The time to tQ is the time for the wood-monomer mass to reach oven or curing temperature at T5. During the period of constant temperature, the induction period, the inhibitor is being removed by reaction with the free radicals. Once the inhibitor is eliminated from the monomer and wood, the temperature rises to a maximum which corresponds to the peak of the exothermic polymerization reaction. Polymerization continues to completion although at a decreased rate and the temperature returns to that of the curing chamber. The time to the peak temperature depends upon the amount of catalyst present, the type of monomer, the type of crosslinker, and the ratio of the mass of monomer to that of the wood. The wood mass acts as a heat sink. Figure 4 illustrates the effect of increased Vazo catalyst on the decrease in time to the peak temperature, and the increase in the peak temperature(10)... 

Exothermie The exothermic polymerization reaction releases considerable amounts of heat, which will in turn fnrther accelerate the cure. Some... 

When mixing the two components, the polymerization of the liquid monomer starts to yield a solid mass. As the redox reaction is exothermic, a high level of heat is generated, leading to a temperature increase [74]. Due to the thermal behavior of the curing reaction of the bone cement, it is not possible to load the cement with every drug. It is mandatory for the drug to be thermally stable. 

Some of the curing adhesives require heat, whereas others react at room temperature with the help of catalysts, and in some instances with activation by light. Again, it is an advantage to make a bond without the aid of an oven. Among the adhesives which can be processed in the cold, with proper formulation, are resorcinol formaldehyde, unsaturated polyesters, methyl methacrylate, cyanoacrylate esters, epoxies, and urethanes. The polymerization reaction is usually exothermic, so that the glue line may become somewhat warmer than the ambient... 

DSC Studies. DSC analyses of blends of 1 and 3a show a homogeneous reaction initially to a thermoset. The DSC scans to 400 C of the blends exhibit only one cure exotherm for each of the compositions studied (see Figures 1 and 2). For example, mole percent mixtures (10/90, 25/75 and 50/50) of 1 and 3a display exotherms (polymerization... 

Many physical and process constraints limit the cycle time, where cycle time was defined as the time to the maximum exotherm temperature. The obvious solution was to wind and heat the mold as fast and as hot as possible and to use the polymer formulation that cures most rapidly. Process constraints resulted in a maximum wind time of 3.8 minutes where wind time was defined as the time to wind the part plus the delay before the press. Process experiments revealed that inferior parts were produced if the part gelled before being pressed. Early gelation plus the 3.8 minute wind time constrained the maximum mold temperature. The last constraint was based upon reaction wave polymerization theory where part stress during the cure is minimized if the reaction waves are symmetric or in this case intersect in the center of the part (8). The epoxide to amine formulation was based upon satisfying physical properties constraints. This formulation was an molar equivalent amine to epoxide (A/E) ratio of 1.05. 

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