Thermal cure profile

The typical application situation is where a new material or structure is being implemented. The question to be resolved is what thermal cure profile (time, temperature, pressure) should be specified. The current approach has been to expend much time and material producing simulated panels for validation. This process is neither rigorous... 

Differential scanning calorimetry directly measures the heat flow to a sample as a function of temperature. A sample of the material weighing 5 to 10 g is placed on a sample pan and heated in a time- and temperature-controlled manner. The temperature usually is increased linearly at a predetermined rate. DSC is used to determine specific heats (Fig. 10-11), glass transition temperatures (Fig. 10-12), melting points (Fig. 10-13) and melting profiles, percent crystallinity, degree of cure, purity, thermal properties of heat-seal packaging and hot-melt adhesives, effectiveness of plasticizers, effects of additives and fillers (Fig. 10-14), and thermal history. 

Photocuring is done for dental resin, contact adhesives, and contact lenses. UV-exposure studies are also run on cured and thermoplastic samples by the same techniques as photocuring to study UV degradation. The cure profile of a photocure is very similar to that of a cake or epoxy cement. The same analysis is used and the same types of kinetics developed as is done for thermal curing studies. 

In order to achieve the most complete curing of both types of functionality, it is recommended to start with the thermal treatment and perform the UV-exposure immediately afterwards on the hot sample. Fig. 9 shows some typical curing profiles obtained by monitoring, by means of infrared spectroscopy, the disappearance of the isocyanate group (2270 cm ) upon heating, and of the acrylate double bond (1410 cm ) upon UV-exposure. 

The simplest way to analyze a resin system is to run a plain temperature ramp from ambient to some elevated temperature [81]. This cure profile allows collection of several vital pieces of information as shown in Fig. 19. Samples may be run neat or impregnated into fabrics in techniques that are referred to as torsional braid. There are some problems with this technique, as temperature increases will cause an apparent curing of nondrying oils as thermal expansion increases friction. However, the soaking of resin into a shoelace, as this technique has been called, allows one to handle difficult specimens under conditions where the pure resin is impos-... 

The industrial value of furfuryl alcohol is a consequence of its low viscosity, high reactivity, and the outstanding chemical, mechanical, and thermal properties of its polymers, corrosion resistance, nonburning, low smoke emission, and exceUent char formation. The reactivity profile of furfuryl alcohol and resins is such that final curing can take place at ambient temperature with strong acids or at elevated temperature with latent acids. Major markets for furfuryl alcohol resins include the production of cores and molds for casting metals, corrosion-resistant fiber-reinforced plastics (FRPs), binders for refractories and corrosion-resistant cements and mortars. 

The objective of the present work was to determine the influence of the light intensity on the polymerization kinetics and on the temperature profile of acrylate and vinyl ether monomers exposed to UV radiation as thin films, as well as the effect of the sample initial temperature on the polymerization rate and final degree of cure. For this purpose, a new method has been developed, based on real-time infrared (RTIR) spectroscopy 14, which permits to monitor in-situ the temperature of thin films undergoing high-speed photopolymerization, without introducing any additive in the UV-curable formulation 15. This technique proved particularly well suited to addressing the issue of thermal runaway which was recently considered to occur in laser-induced polymerization of divinyl ethers 13>16. 

The rate of bleeding is dependent on several factors, including the permeability of the fiber bed, both vertically and horizontally, and the viscosity of the liquid resin. The permeability of the fiber bed will depend on the weave of the fabric, the fiber diameter, and the fiber volume fraction. The resin viscosity is determined by the chemistry of the resin and the thermal profile of the cure cycle. The cure cycle greatly affects resin viscosity and the flow process, both directly through the pressure application and indirectly through the effect of the thermal profile on resin viscosity. 

Figure 9.13 shows the evolution of conversion and temperature profiles in the part. An almost uniform cure takes place up to the time at which Tw reaches the plateau at 177°C. At 132 min, both conversion and temperature attain the maximum values at the adiabatic boundary (z =L). At this time, Tmax exceeds Tw by about 90°C, which may produce an incipient thermal degradation. At 168 min, the final conversion profile is attained (T is almost uniform in the part and equal to Tw). The maximum conversion of the material located close to the metallic plaque is xm = 0.872 due to the effect of vitrification (and the assumption of Rc = 0 when T < Tg). Therefore, vitrification produces a conversion profile in the cured part. A postcure step would be necessary to completely cure the composite material. 

Through the analysis of the particular selected examples it was shown that it is possible to get a good description of temperature and conversion profiles generated during the cure of a thermosetting polymer. Thermal and mass balances, with adequate initial and boundary conditions, may always be stated for a particular process. These balances, together with constitutive equations for the cure kinetics and reliable values of the necessary parameters, can be solved numerically to simulate the cure process. 

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