Cure monitoring

The only way to validate kinetic models is to measure experimentally the degree of cure as a function of time and temperature. It can be done on both macroscopic and microscopic levels by monitoring chemical, physical (refractive index [135], density [136], and viscosity [137]), electrical (electrical resistivity [138,139]), mechanical, and thermal property changes with time [140,141]. The most-used techniques to monitor cure are presented in the next two subsections. 

Monitoring Cure in Multiple Time Temperature Processing Cycles. 145... 

As an aside, we note that the FDEMS sensor input information can also be used to detect the onset of phase separation in toughened thermoset systems and to monitor cure in thin film coatings and adhesive bond lines. It is particularly important that the FDEMS sensor is also very sensitive to changes in the mechanical properties of the resin due to degradation. As such, it can be used for accelerated aging studies and as a dosimeter to monitoring the composite part during use to determine the knockdown in the required performance properties with time. 

Bhargava, R., Wang, S.Q. and Koenig, J. L. (1999) Studying polymer dispersed liquid crystal formation by FTIR spectroscopy 1. monitoring curing reactions. Macromolecules, 32(26), 8982-88. 

Tajima, Y. A. Monitoring cure viscosity of epoxy composite, Polym. Comp., 3, 162 (1982)... 

Chottiner, J., Sanjana, Z, N., Kodani, M. R., Lengel, K. W., Rosenblatt, G. B. Monitoring cure of large autoclave molded parts by dielectric analysis, p. 77, Proc. 26th SAMPE Symp., 1981... 

Sanjana, Z. N., Selby, R. L. Monitoring cure of epoxy resins using a microdielectrometer, p. 1233, Proc. 29th SAMPE Symp., 1984... 

In order to correlate fluorescence intensity at 565 nm with the overall extent of amine reaction, we plotted Ip versus in Fig. 6, for both epoxies cured at three isothermal cure temperatures. In this figure, 5 is estimated from the deconvolution of UV-visible spectra. All -fhe data fall on a single smooth curve whose slope is much sharper at later stages of cure especially after gelation. In other words, fluorescence Intensity constitutes a sensitive gauge for monitoring cure beyond gelation, because it derives mostly from tertiary amine products. 

On a more commercial note, articles have appeared on photocurable pressure-sensitive adhesives, trigger curing of epoxy-resins, and development of a photocolorimeter for monitoring cure rates. ... 

While this paper reports only preliminary findings. It does Illustrate the usefulness of photocalorimetry to define optimum cure conditions for UV curable adhesives. In addition, once the mechanical spectrum of fully cured adhesive has been mapped, mechanical spectroscopy can be used to monitor cure efficiency. In this paper we have not explored the molecular weight Implications of Incomplete polymerization. Preliminary evaluation of loss and storage modulus data would suggest that time-temperature superposition may be necessary to evaluate molecular welght/degree of cure relationships and terminal, plateau, and transition zones (4). 

Compaiison of the various techniques. Table II conq)ares the p ormance analysis for the various analytical methods most commonly used to monitor curing reactions. 

As has been demonstrated here, a valuable technique is available in DSC for monitoring cure reactions independent of operator dependent variables as often enter into empirical tests. This technique can be applied towards monitoring of existing processes and towards optimizing formulations and processes. 

No.26, 28th Dec.1999, p.8982-8 STUDYING POLYMER-DISPERSED LIQUID-CRYSTAL FORMATION BY FTIR SPECTROSCOPY. I. MONITORING CURING REACTIONS... 

The third paper, by Levy and Ames, presents an interesting new way to monitor cure kinetics. They measure the viscosity of an epoxy system as it cures by use of a... 

Dielectric cure monitoring generally relies on measin-ement of the ionic conductivity (a in eq. 19). The conductivity during cure of epoxy-amine systems have been characterized to establish relationships between conductivity and viscosity (103,104), conductivity and Tg (104), and relationships to the conversion of epoxide (103). Recently, models were established to relate changes in the dipole component of the complex permittivity to the advancement of cure through the Tg-con version relationship, expanding the capabilities of dielectric sensing to monitor cure (102). 

The similarity of the Tg-time data in Fig. 2.73 with the conversion-time data of Fig. 2.71 is a consequence of the Tg-conversion relationship and illustrates the ability to monitor cure through measurement of Tg. Figure 2.73 also directly illustrates vitrification, defined as Tg increasing to r ure as a result of cure, and designated at each cure temperature by an arrow. Note that the progress of cure is significantly impeded shortly after vitrification, which marks the shift from chemical control to diffusion control of the reaction, as described at the beginning of this section. 

Dielectric techniques have the particular advantage over other thermal analysis methods of being able to monitor cure-controlled dielectric and electrical properties, continuously and in situ, as the resin changes from low-viscosity... 

The considerable scientific interest for low-frequency dielectric studies and especially the use of ionic conductivity measurements to monitor curing reactions dates back to the pioneering work of Kienle and Race (1934). During cure, the conductivity (a) is best described as a function of frequency, temperature, and degree of conversion (a)... 

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