Patent ID: 8557155

Claim:
A process for production of polyethylene terephthalate pellets comprising the steps of: a. production of a melt of polyethylene terephthalate material; b. production of polyethylene terephthalate pellets from the melt by means of underwater pelletization into a process fluid; c. removal of the polyethylene terephthalate pellets from a site of underwater pelletization in the process fluid; d. crystallization of the polyethylene terephthalate pellets in the process fluid, wherein during crystallization a surface of the polyethylene terephthalate pellets is crystallized and an interior of the polyethylene terephthalate pellets remains amorphous, wherein a temperature of the process fluid is adjusted, depending on a formulation of the polyethylene terephthalate material, to a value at which, a previously experimentally determined maximum crystallization rate of the polyethylene terephthalate material of the polyethylene terephthalate pellets is reached, and wherein, after the crystallization step, opacity of the surface of the polyethylene terephthalate pellets is determined as a measure of an achieved degree of crystallization and as a measure of an achieved crystallization depth at the surface of the polyethylene terephthalate pellets, and wherein the opacity of the surface is determined online directly as part of the process; e. extraction of the polyethylene terephthalate pellets in the process fluid; and f. separation of the polyethylene terephthalate pellets from the process fluid.