Coating ageing

It was found that the resulting oxygen transmission rate was highly dependent on the age of the coating sols and the storage conditions. An increase in the viscosity of aged coating sols stored at room temperature was observed. This can be explained by chemical reactions in the liquid sol ... 

Figure 21 -25 shows the effect of different epoxy contents of the aged coating sols from Figure 21-24 on the oxygen transmission rates of the cured coating materials. Each of the sols was applied to PP films and cured at 100°C for 2 h. 

With coated fabrics, the damping properties of the bag are controlled by the dimensions of the openings for the air release. This principle is also used, albeit infrequently, with uncoated materials of low air permeability. The essential parameter is the air permeability of the bag, which also needs to sustain aging. Coating materials are polychloroprene and silicone. 

Specimens used in tests were sections of cables with PVC outer coating. PVC was plasticized with DOF softener. The materials considered were exposed to the radiation and thermal aging. The samples have been irradiated at room temperature by hard gamma rays with 10 rad/sec dose power. A number of samples had been heated for long different times at 90°C. Besides a special specimens were cut out from outer coating for test on tensile machine like "Instron". The total doses of irradiation, times of heating and elongations at break obtained with "Instron" are listed in Table 1. 

Poly(vinyl cinnamate) Resists. Dichromated resists exhibit numerous shortcomings which include lot-to-lot variabiUty of the components, aging of the formulated resists in solution and in coated form, poor process stabiUty (due to a sensitivity to variations in temperature and humidity), and intrinsically low photosensitivity requiring long exposure times for adequate insolubilization. 

Examination of oven-aged samples has demonstrated that substantial degradation is limited to the outer surface (34), ie, the oxidation process is diffusion limited. Consistent with this conclusion is the observation that oxidation rates are dependent on sample thickness (32). Impact property measurements by high speed puncture tests have shown that the critical thickness of the degraded layer at which surface fracture changes from ductile to brittle is about 0.2 mm. Removal of the degraded layer restores ductiHty (34). Effects of embrittled surface thickness on impact have been studied using ABS coated with styrene—acrylonitrile copolymer (35). 

Many cellular plastic products are available with different types of protective faces, including composite metal and plastic foils, fiber-reinforced plastic skins, and other coatings. These reduce but do not eliminate the rate of aging. For optimum performance, such membranes must be totally adhered to the foam, and other imperfections such as wrinkles, cuts, holes, and unprotected edges should be avoided because they all contribute to accelerated aging. 

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