a closed loop thermoplastic recycling process includes the step of testing particulated processed plastic material to determine the properties thereof . the tested properties are compared with targeted near virgin properties of the processed plastic material to determine any difference therebetween . additives based on the property differences determined during testing are admixed with the particulates in a twin screw extruder . during extruding , volatile constituents are simultaneously withdrawn from the fused particulates . the twin screws of the extruder are provided with a number of screw sections , each having a thread with predetermined degrees of chamfer and pitch length . kneading blocks are mounted on certain screw sections prior to a vacuum vent port disposed along the feed path of the melt stream in the extruder . the extruded material is tested to determine if any property differences exist . if no unacceptable tested differences are found , the extruded material is prepared for reuse in place of or in conjunction with virgin plastic material having the same properties and characteristics .