process for a worm extruder or continuous kneader to produce either a degasses paste or plastic composition is disclosed . a mixture of either solid or liquid organic peroxides in the paste or plastic composition having evaporable constituents are introduced into the device , homogenized and degassed by exposing the mixture to a degassing passage of the extruder . the mixture has a free surface which is more than 40 % of the cross - section of the degassing passage and the minimum gas passage cross - section of the return delivery device amounts to at least about 0 . 1 times the degassing passage cross - section .