Infrared curing

Application of adhesive primer presents another challenge. Most adhesive primers require a high-temperature cure, which presents the potential for damaging existing bondlines. Infrared curing can be used to reduce the likelihood of problems. 

By spot-tests on coatings and immersion-tests on castings the excellent chemical-resistance of phenalkamine-cured epoxy systems has been demonstrated. In addition, near-infrared cure studies have documented the rapid complete cure of epoxies at room temperature and also satisfactory cure at reduced temperatures when phenalkamines are used as the curing agents. 

Infrared cure is gaining increased attention from coaters as a result of shorter cure cycles and the possibihty of smaller flcK)r space requirements when compared to convection oven curing. Figure 14.13 shows an example of an IR oven set up for composite curing. IR curing is limited in its use for composite curing as detailed in Table 14.10 however, it has potential for fast and efficient heating for various applications such as preform binder activation. 

The principal techniques for determining the microstmcture of phenoHc resins include mass spectroscopy, proton, and C-nmr spectroscopy, as well as gc, Ic, and gpc. The softening and curing processes of phenoHc resins are effectively studied by using thermal and mechanical techniques, such as tga, dsc, and dynamic mechanical analysis (dma). Infrared (ir) and electron spectroscopy are also employed. 

Spectroscopy. Infrared spectroscopy (48) permits stmctural definition, eg, it resolves the 2,2 - from the 2,4 -methylene units in novolak resins. However, the broad bands and severely overlapping peaks present problems. For uncured resins, nmr rather than ir spectroscopy has become the technique of choice for microstmctural information. However, Fourier transform infrared (ftir) gives useful information on curing phenoHcs (49). Nevertheless, ir spectroscopy continues to be used as one of the detectors in the analysis of phenoHcs by gpc. 

Nondestmctive testing (qv) can iaclude any test that does not damage the plastic piece beyond its iatended use, such as visual and, ia some cases, mechanical tests. However, the term is normally used to describe x-ray, auclear source, ultrasonics, atomic emission, as well as some optical and infrared techniques for polymers. Nondestmctive testing is used to determine cracks, voids, inclusions, delamination, contamination, lack of cure, anisotropy, residual stresses, and defective bonds or welds in materials. 

Curing with Ultraviolet, Visible, and Infrared Processing Equipment... 

Infrared radiation or closed cycle convection curing furnace... 

No epoxy groups were detectable in the cured polymer by infrared spectroscopy. 

The isocyanate concentration during curing of polyurethane paints has been quantified by tracing the infrared absorption of the isocyanate group (2272 cm- ) with a Perkin Elmer 983 spectrophotometer. 

This work discusses the thermal crosslinking and isomerization reactions occurring in the acetylene terminated isoimide prepolymer Thermid IP600. The techniques of Fourier Transform Infrared Spectrometry and Differential Scanning Calorimetry are used to determine the contribution of these two reactions during the thermal cure including their kinetics at 183° C. 

Many practical applications of cure characterization involve samples for which the data required to convert isocyanate absorbance to concentration is unavailable. The emphasis is often placed on rapid analysis of many samples rather than an exhaustive characterization of a single sample. It is particularly desirable to develop a procedure which can determine the rate constants describing the cure reaction without converting the infrared absorbance curve to concentration. This has been accomplished by normalizing the data in such a way that the rate constants are determined from the shape of the cure curve. 

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. 

Polymerization Behavior. Both Fourier-transform infrared spectroscopy (FTIR) and differential scanning photocalorimetry (DPC) were used to characterize the polymerization behavior, curing time, and maximum double bond conversion in these systems. 

Bisphthalonitrile monomers were cured neat, with nucleophilic and redox co-reactants, or in combination with a reactive diluent. Dynamic mechanical measurements on the resulting polymers from -150 to +300°C turn up several differences attributable to differences in network structure. Rheovibron results were supplemented with solvent extraction, differential scanning calorimetry (DSC), vapor pressure osmometry, and infrared spectroscopy to characterize the state of cure. 

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