| abstract |
The invention relates to a method for producing granules from polyethylene terephthalate by generating a melt of polyethylene terephthalate material, generating granules from the melt by means of underwater granulation in a process fluid, conducting the granules away from the site of the underwater granulation in the process fluid, crystallizing the granules in the process fluid, discharging the granules in the process fluid, and separating the granules from the process fluid, wherein only the surface of the granules is crystallized in the crystallization step such that the inside of the granules remains amorphous, wherein the temperature of the process fluid is set to a value at which, depending on the formulation of the polyethylene terephthalate material, the previously experimentally determined maximum crystallization rate of the polyethylene terephthalate material of the granules is achieved, and wherein after the crystallization step, the turbidity of the surface of the granules is determined as a measure of the achieved crystallization degree and of the achieved crystallization depth on the surface of the granules. |