Changes During Curing

FIGURE 2 Specific volume and temperature history of the lOOlF/DDS epoxy resin during curing under a pressure of 5 MPa. 

FIGURE 3 Specific volume data from Fig. 2 plotted as a function of the temperature. 

The specific volume history data of the curing 1001/DDS are cross-plotted in Fig. 3, where the specific volume is shown as a function of temperature. The 

FIGURE 4 The specific volume-temperature cooling curves obtained on the fully cured 1007, 1004,1001, and 828/DDS resins. 

The SpeciAc volume-temperature cooling curves obtained on the fully cured 1007,1004,1001, and 828/DDS resins are shown together in Rg. 4. The systematic decrease in speciAc volume with increasing crosslink density is clearly depicted as is the increase of Tg with crosslink density. The glass temperatures for the fully cured 1007,1004,1001, and 828/DDS resins are 101,112, 127, and 204°C respectively. 

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Figure 20. Effect of ram pressure on maximum bed volume change during cure at 80° F.

The work of Huraux, Soualmia, and Sheppard has demonstrated that it is possible to make a quantitative interpretation of the r values (within the limits of an admittedly difficult theory), and that the er value is directly linked to the chemical changes during cure. However, because of the complications introduced by dipole correlations, the relaxed permittivity is not a useful tool for routine quantitative determination of polar reactive group concentrations during cure. 

The relation between the changing relaxation time distribution and the molecular structure of the curing system has not been determined. There is, however, one important experimental implication to these observations. Because both sr and p change during cure, one must actually measure the complete frequency dependence of the e and e" at a given state of cure in order to characterize the relaxation time distribution. Measurements made at one frequency throughout the cure process, when plotted on a Cole-Cole diagram, do not necessarily provide information about the relaxation time distribution. 

In Section 4, we have examined, from a fundamental point of view, how temperature and cure affect the dielectric properties of thermosetting resins. The principal conclusions of that study were (1) that conductivity (or its reciprocal, resistivity) is perhaps the most useful overall probe of cure state, (2) that dipolar relaxations are associated with the glass transition (i.e., with vitrification), (3) that correlations between viscosity and both resistivity and dipole relaxation time are expected early in cure, but will disappear as gelation is approached, and (4) that the relaxed permittivity follows chemical changes during cure but is cumbersome to use quantitatively. 

Bilyeu, B. Brostow, W. Menard, K. Determination of volume changes during cure via void elimination and shrinkage of an epoxy prepeg using a quartz dilatometer cell. Polimery 2001, 46, 794. 

Figure 3.5. Comparison of heat flow as measured by the DSC and calculated heat from the extent of epoxide reaction (measured by NIR Spectroscopy) for TGDDM with 27% DDS at 177 °C for the times indicated. The difference arises from the change in heat capacity change during cure which requires a baseline correction to the DSC trace. Adapted from de Bakker et al. (1993b).

Figure 3.20. Successive FT-IR emission spectra from a thin film of resin from a carbon-epoxy-resin prepreg during cure. Bands that change during cure are marked (George et al., 2006).

Figure 3.26. Near-IR spectra of MY721 plus 27% DDS before and after cure at 160 °C for 3 hours together with the difference spectrum to highlight bands that change during cure. Reproduced with...

Figure 6.12 Resistance change during curing of conductive adhesive.

A thermosetting synthetic resin is one that undergoes an irreversible chemical and physical change during curing to become substantially infusible and insoluble. The term thermosetting is applied to the resin both... 

Torsion-braid analyzer n. An instrument which permits the measurement of thermomechanical properties of polymers that are undergoing structural changes during cure. Shah V (1998) Handbook of plastics testing technology. John Wiley and Sons, New York. 

Conductivity versus reaction time data for the isothermal cure of the DGEBA/DDS epoxy at six ditferent cure temperatures are shown in Figure 54 (123). If the ion concentration does not change during cure, then o is directly proportional to ion mobility. Early in the reaction, the ionic impurities move freely in the system and the ionic conductivity is high. The ionic conductivity decreases as... 

Figure 4.15 Matrix changes during cure. (From Ref. 27)...

Figure 14.33 Variation of volume change during cure at 35 °C of unsaturated polyester resin systems having MEKP as an initiator and cobalt octoate as an accelerator in the presence of PVAc at different concentrations (wt %) (O) 3.5, (A) 6.0, and ( ) 10. (Reprinted from Li and Lee, Polymer 39 5677. Copyright 1998, with permission from Elsevier.)...

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