Cure of thermosetting resins

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. 

Several researchers have described changes in the isothermal viscosity behavior during the cure of thermosetting resin systems with respect to time by the following expression ... 

Vergnaud JM. and J. Bouzon. 1992. Cure of Thermosetting Resins. Springer Verlag, London. 

During the complex chemical reactions which take place during the cure of thermosetting resins, as volatile gases are released and become encapsulated in the cross-linked resin [3],... 

Transitions, Properties, and Molecular Mobility During Cure of Thermosetting Resins... 

Barcol hardness n. The resistance of a material to penetration by a sharp steel point under a known load with an instrument called the Barcol Impressor. Direct readings are obtained on a scale from 0 to 100. The instrument has often been used as a way of judging the degree of cure of thermosetting resins and harder materials. The ASTM test, www.astm.org, is referred to as Indentation Hardness of Rigid Plastics . 

Figure 6.25 Higher mold temperatures shorten the flow time in the mold and accelerate cure of thermosetting resin systems.

The autocatalytic model has been shown to predict the cure of thermoset resins accurately [92] some of the more recent studies in this area are cited in a number of references [90, 91, 93-%]. 

Several models have been proposed to describe the curing of thermoset resins [11-13]. The phenomenological model developed by Kamal [14] is mostly used for isothermal kinetic analysis. The general equation for an n order reaction [15, 16] can be written as ... 

With the aid of modern dielectric spectrometers, real-time observations can he carried out. For example, DS can be used to monitor the curing of thermosetting resins, the absorption of water by polymers, or film formation and coalescence in polymer lattices [92]. 

APPLICATION OF INFRARED SPECTROSCOPY AND THERMAL ANALYSIS IN MONITORING THE CURE OF THERMOSETTING RESINS USED IN THE AIRCRAFT INDUSTRY... 

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