Parylene deterioration

Humidity levels were maintained at <5%, 50%, 70% or 90% +2% RH and a constant temperature of 90°C for a fixed time of 17 days. Samples of historic silk fabric were exposed at 90 °C and 80% RH for either 10 or 30 d. ys to induce further deterioration of mechanical properties. These materials were then coated with 1 and 5 Jim of Parylene-C. Silk samples were loosely affixed by sewing to temperature-resistant coarse polyester mesh which allowed both free air flow and also avoided contact between the metal and the fabric surfaces during the thermal aging tests. 

Samples of coated and uncoated silk fabric were removed at various intervals up to an exposure of 605 kJ at 340 nm. Maximum exposure of coated cloth was 242 kJ (340 nm). In addition, for a fixed total energy of 86 kJ (340 nm), the irradiance was maintained at 0.42 W/m2, 0.35 W/m2, and 0.28 W/m2 to evaluate reciprocity effects. Samples of both types of historic silk were exposed to 100 kJ (340 nm) and 360 kJ (340 nm) to induce additional deterioration. These highly exposed samples were coated with both 1 and 5 im of Parylene-C. 

Historic fabric samples that were further deteriorated by heat or light exposures prior to coating with Parylene-C showed the same trends increased breaking-load and initial modulus with no added strain-to-break. The absolute increase in breaking-load was small when compared with the increase that resulted when modern silk fabric was coated, but the percentage increase was higher due to the initially low absolute values of the tensile properties. 

The coating of Parylene-C did not have an effect on the thermal degradation rates of the silk broadcloth tensile properties or yellowing. The coating deteriorated when... 

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