Process for the admixture of additives into plastics with simultaneous removal of volatile constituents

In a process for the admixture of additives to thermoplastically processable polymers containing volatile constituents, with simultaneous removal of the volatile constituents, through separately feeding additives and a polymer melt, solution or dispersion into a horizontal devolatilizing screw extruder, and then heating, mixing and conveying the charge whilst vaporizing the volatile constituents, and finally extruding the mixture, the improved steps taken in sequence in the direction of flow along the extruder which comprise:

• first introducing the additives downwardly into the extruder from above;
• then introducing the polymer in a liquid form as said melt, solution or dispersion, preheated to a temperature of from 150.degree. to 250.degree. C, upwardly into the extruder from below under a pressure which corresponds at least to the vapor pressure of the volatile constituents at the temperature concerned, thereby immediately vaporizing said volatile constituents;
• simultaneously withdrawing at least 50 percent of the volatile constituents upwardly from the extruder at an orifice located approximately vertically above the point at which the polymer is being introduced from below;
• and
• advancing the polymer forwardly from its point of introduction under shear by the screw so that the cooling of the polymer due to said vaporization is compensated by the simultaneous heating of the polymer in the screw extruder which is increased by transfer of shear energy from the screw.