Effect of Process Variables in Fluidized Bed Coating on the Coating Structure - 2. X-Ray and Densitometry Measurements.

The X-ray studies and density measurements have revealed that the crystalline form and degree of crystallinity of the polyamides studied are independent of the temperature of preheating and temperature of the fluidized-bed, but they depend exclusively on the procedure of the coating cooling. In the case of polycaprolactam, cooling in air of a temperature of 20 degree C or 185 degree C causes the crystalization of coatings in the alpha -form, whereas their cooling in water of a temperature of 10 degree C or in a mixture of dry ice and toluene at a temperature of minus 65 degree C results in their crystallization in gamma -form. Polyamides 12 always crystallizes in gamma -form.