Humidity Exposures

In recent years acetylene terminated resins (AT-resins) have shown promise in the area of high temperature applications and are possible replacements for state-of-the-art epoxy resin systems where humidity exposure is expected. Acetylene terminated resins have two important advantages over previously developed systems ... 

Organic coatings are commonly evaluated using salt water immersion, salt fog or spray, modified salt exposure tests (e.g., salt fog with added SO2), and various cyclic exposure tests. Humidity exposure and water immersion, and, for many applications, physical resistance tests (adhesion, impact resistance, etc.) are widely used preliminary tests. Standard methods for most of these tests are given in compilations of standard tests such as the Annual Book of ASTM Standards (16). Test methods have been extensively reviewed (e.g., 17-23). 

Solubility. A simple parabola fits the water solubility data of the resin in the prepreg equilibrated at different relative humidity exposures as follows [13] ... 

The final diameter of a pure water void for different initial relative humidities of the resin is shown in Figure 6.8. The marked increase in the final void size illustrates the pronounced effect that initial relative humidity exposure has on the final void size. This behavior is described by Equation 6.28 in which CTO (which is fixed during the cure cycle and determines the driving force) increases with the square of the initial relative humidity exposure. Thus, increasing the initial relative humidity by a factor of 2 would result in a four-fold increase in C oo. This would in turn increase the driving force 4-fold when the other conditions of growth are kept identical and when Csat [Pg.197]

Figure 6.8 Effect of initial relative humidity exposure of the prepreg on the final void size in the laminate for the process conditions shown...

Initial Pure Water Void Diameter = 0.1 cm 21 Initial Humidity Exposure - 75%... 

Figure 6.10 Void stability map for pure water void formation in epoxy matrixes. Note the significant effect of initial relative humidity exposure of the resin...

Figure 6.12 Profiles of typical resin pressures monitored by the laminate, tool, and bleeder transducers. The profiles of time-temperature and the corresponding time—Pmjn for 35% and 85% initial relative humidity exposure of the prepreg—are also shown. (Source From [25])...

A pressure-temperature stability map can be constructed as a function of humidity exposure, which identifies the resin pressure values for each temperature below which void growth is possible and above which voids cannot grow but rather tend to collapse via dissolution. 

Adhesion of polyimides to ceramics Effects of aminopropyltriethoxysilane and temperature and humidity exposure on adhesion... 

Water-borne finish 42 50-75 30 min 1 h For use over water-borne primer for light to moderate chemical or high humidity exposure good resistance to mechanical damage... 

Other Transient Interactions. The PVA/borax example dealt with the effects of surface exposure of a two-component polymer system to a wetting liquid. We discovered a practical example of this class of phenomena in a plasticized poly (vinyl chloride) (PVC) system. A peculiar plasticizer (tetraethyl methylene bisphosphonate) for PVC has been found (6) which has the unusual property of exuding out of PVC immediately upon exposure to high humidity. The plasticizer quickly re-enters the resin when the humidity is reduced. A film of 60% resin and 40% plasticizer was solvent cast from tetrahydrofuran onto an impedometer bar and was subjected to sudden high humidity exposure. 

Figure 5. SIMS depth profiles of Ti/thin Cu films on polyimide as deposited, showing O18 from polyimide and ambient humidity exposure exposed to H2018 and annealed in nitrogen at 350 C...

Figure 8. SIMS depth profiles of Cr/thin Cu films on polyimide (a) as deposited, showing O 8 from ambient humidity exposure (normalized for isotopic abundance) (b) exposed to H2018 and (c) exposed to H,018 and annealed in forming gas at 350 C (200 W, 30 min RF) and (d) exposed to H20 8 and annealed in forming gas at 350 (50 W, 10 min RF).

A sample taken through repetitive cycles of relative humidity exposure between 0 and 100% tends to follow the adsorption and secondary desorption curves repetitively. The adsorption isotherm (A) is always lower than the corresponding desorption isotherm (D) and their ratio, designated as the A/D ratio, cannot exceed unity. 

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