Epoxy Impregnation without Hardener: To Decrease Yellowing, to Delay Casting, and to Aid Bubble Removal

Epoxy slices often yellow shortly after casting and the few hours following impregnation can be overwhelming as all slices need to be cast in a short period of time. A modified technique for producing epoxy slices was developed as a measure to address these problems. Tissue slices were impregnated using only epoxy polymer; no hardener was used during impregnation. The impregnated tissue slices were cast using modified casting-mixtures of epoxy polymer, hardener and glass separator. This modification of the classic E12 method (Biodur™) was done to determine: 1. If it is possible to indefinitely extend the casting time after impregnation of epoxy slices and produce quality slices; 2. If the impregnation bath could be reused for casting; 3. If transparency, bubble removal and aesthetics of the final sheet could be enhanced; and 4. If yellowing of the cast could be reduced. The unreacted epoxy impregnated slices were stored in the impregnation mixture for up to one year prior to casting. Hardener was painted on random slices prior to casting. All slices were cast with a polymer reaction-mixture containing 20 to 27% El (hardener) and 1 or 4% AE30 (glass separator). All cast manufactured slices cured. Tissue slices, which rested on the glass, had small areas that did not cure properly. These blemishes were corrected by recasting using a thicker gasket, placing polymer reaction-mixture on the blemished surface and covering with a glass, or placing polymer reaction-mixture on the blemished surface with no glass cover. All recast slices cured and were useful. After a few days, over 50% of the slices turned yellow. However, the intensity of the yellow was much less than that of slices produced by the classic E12 method.