METHOD OF COMPOUNDING POLYMERS

The extruder has at least: one melting zone, two de-gasification zones, and a mixing zone for an entrainment gas. Degasification of the melt is achieved using inert entrainment gas. This is introduced into the polymer melt. It is subsequently removed from the extruder, bringing out the volatile compounds with it. The gas and volatiles are removed from the extruder by pressure reduction to below 500 mbar. The gas is nitrogen, a noble gas or carbon dioxide. The polymers are thermoplastics. The polymers compounded together, are selected from two groups; the first reverts by thermal cracking, the second does not. The first group includes polystyrene, its co- or graft copolymers, polyacrylates, polyalkylenes and polyamide. The second group comprises polycarbonate, polyester carbonate and polyalkylene terephthalate. A combination of acrylonitrile butadiene styrene graft copolymer and polycarbonate is used. Mixing ratios of polymers from the two groups, range from 1 : 10 to 2 : 1. There are two successive stages of entrainment gas injection and de-gasification. A two-shaft, co-rotating screw extruder is used. The screw shaft length-to-diameter ratio is 32-44. Further possible zone combinations are elaborated. The quantity of entrainment gas amounts to 0.1% to 0.5% based on the total throughput of starting materials. Entrainment gas is added in the screw mixing zone, or immediately ahead of it.