Intensity cure time

Studies were performed to demonstrate the effects of process variables such as light intensity, cure time, initiator concentration, and fiber loading on the evolution of the mechanical properties of the polymers and composites. Even with moderate incident light intensities (less than 500 mW/cm2) and high fiber loadings (60 wt.% random fibers) the photopolymerizations proceed to completion in minutes and exhibit mechanical properties equivalent to samples prepared by traditional... 

Figure 6. Flexural modulus as a function of cure time for fiber loadings between 0 and 60 wt.% with an incident light intensity of 480 mW/cm2.

As expected [2-4], when the solid and liquid cement components were mixed, the anthracene-toluidine complex fluorescence increased in intensity over time as the cure proceeded and nonfluorescence pathways for energy disposal were blocked. Although the change in peak shape made it difficult to comment on the relative fluorescence intensity from the exciplex compared to that from independent molecules, it was clear that the exciplex... 

The run-to-run reproducibility of the profile shape of the FOCS fluorescence-intensity signal is good however, the reproducibility of the absolute intensity values is unsatisfactory. The run-to-run variations in the fluorescence intensities are caused by the differences in resin thickness at the small area "viewed" by the optrode. In addition, substantial resin flow takes place during cure, causing the resin thickness to vary as a function of cure time. However, since this variation in resin thickness mi t be reproducible from run-to-run (if other cure parameters remain unchanged), it may be possible to develop a suitable... 

The optrode-laminate Interface. The exact geometrical arrangement in which a tool-mounted optrode is in contact with the layer of resin covering the carbon fibers and the dimensions of the layer "viewed" by the optrode strongly affect the level of the FOCS intensity signal at a given cure time. 

Cholli, Ritchey, and Koenig75 characterized the epoxy system DGEBA with solid state C-13 NMR. This study followed the disappearance of intensity of the epoxy carbons and the increase in intensity of the methylene carbons attached to the oxygen atoms. In Fig. 19, these intensity changes are plotted versus the curing time of the epoxy resins. Figure 20 plots the increase in methylene carbon intensities versus the decrease in epoxide group intensities. 

In the 30-90 min cure time range there is a 30% increase in the ROH intensity, despite 95 % of the P.A. s being consumed after 30 min. This increase could be caused... 

The effect of curing on the diffusion of polymer and the curing agent is studied for the system of hydroxyl-terminated polybutadiene (R-45-M)/isophorone disso-cyanate (IPDI). Both components contribute to the echo intensity and the plot of In P(x)/I(0)] vs (G5)2 (A — 5/3) consists of two exponentials (Eq. (22)) the fast component (the steep intial slope) is attributed to the IPDI, and the long component to the R-45-M. The dependence of both diffusion constants on the curing time is shown in Fig. 19. The accuracy for Dfast data is less pronounced than for the polymer D(Mn), because only the first few data points are relevant for its determination. Furthermore, the low tail of the R-45-M molecular weight distribution nearly coin-... 

Figure 17 Plot of the phosphorescence intensity at 500 nm for the DGEBA/DDS epoxy system as a function of cure time at 433 K. (From Ref. 99.)...

The new resonances, which appear with vulcanisation in the presence of carbon black, are qualitatively the same as observed for the unfilled formulation systems, i.e., new resonances at 50.7, 50.2, and 37 ppm were detected at lower cure times. At longer cure times these three resonances disappeared and new resonances were detected at 58, 64, and 45 ppm along with new peaks at 17 and 12 ppm and the growing of the intensity of the peak at 14 ppm. As the amount of carbon black content increased, the latter features were observed at an earlier stage of cure. 

At low cure times, doublet peaks at 50.7 and 50.2 ppm were detected along with the peak at 37 ppm, and these peaks disappeared at longer cure times. The intensities of these two peaks were comparable for every detected pair. In the previous studies, the peaks at 50.7, 50.2, and 37 ppm were assigned to a quaternary carbon of Ale polysulfide, a methine carbon of Ale polysulfide, and a P methylene carbon of Ale polysulfide, respectively. 

While at longer cure times, resonances at 58, 64, 45, 17, and 12 ppm were detected along with increasing intensity of the 14 ppm peak. The peaks at 58, 64,17 and 12, and 14 ppm are assigned to Bit monsulfide (a methine), Bit polysulfide (a methine), Blc polysulfide ((3 methylene), and Bit polysulfide (P methylene), respectively. 

To conclude, it is worth reiterating that the only orchid used as a spice, the vanilla pod, has been recognized for its culinary and medicinal uses since the time of the Aztecs. Vanilla is the world s third most expensive spice, from which is obtained the popular commercial flavouring agent, vanillin. The characteristic aroma of vanilla is obtained only after a time-consuming and labour-intensive curing process. The main aroma compound in vanilla is vanillin over 100 volatile compounds have been detected, including aromatic carbonyls, aromatic... 

The reaction of the epoxy resin with phthalic anhydride using curezol catalyst, 3(2-ethyl-4-methylimidazolyl) propanenitrile. shows an exotherm with its minimum at 154°C and a curing time of five to six minutes depending on the concentration of phthalic anhydride (Figure 1). At mole ratios of epoxy/phthalic anhydride of 1.7-1, 2-1, and 3.5-1 a small exotherm appears at 117°C before the main exotherm at 154°C. This exotherm decreases in intensity with decreasing phthalic anhydride concentration. The heats of reaction for the curing process are given in Table I. 

The intensity ratio increased steadily with cure time, reaching a plateau value at 70 minutes. This intensity ratio is not sensitive to the inhomogeneity or the deformation of the sample, ffe can therefore use this ratio to monitor the cure of samples which shrink during polymerization or contain reinforcing fibers or particles. 

Figure i. Ratio of monomer fluoresence intensity at 377nm (Fm) to excimer fluorescence intensity at 488nm (Fd) for 1,3-bis-(I pyrene)propane in epoxy as a function of cure time. The excitation wavelength was 345 nm. 

Figure 3. Fluorescence intensities of DMA-DPH at 480 nm (circles) and of DPA at 415 nm (triangles) as a function of cure time.

Figure 4. Ratio of the fluorescence intensity of the probe DMA-DPH (Fp) and the fluorescence intensity of the internal standard DPA (Fr) as a function of cure time.

However, when the DAA label is excited, for example at U56 nm, the fluorescence intensity exhibited strongly cure dependent behavior. Fig. 1 shows such fluorescence spectra for DGEBA-DDS-DAA and DGEB-DDS-DAA respectively in the spectral range of U50 nm to 800 nm. In both epoxy matrices, at zero cure time, hardly any fluorescence is observed. But with increasing cure time, fluorescence Increases with a broad emission peak around 56O nm. At long cure times, the emission peak seems to have red-shifted slightly (by 5 10 nm). This small red shift is in sharp contrast to much... 

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