A conveyor 4 driven by a motor 5 feeds thermoplastic waste material 2, such as the trimmed-off edges of extruded plastics sheets, to a compression chamber 8 at the inlet of a heating box 10 of an extruder 11. The conveyor operates intermittently in synchronism with the movement of a plunger 40 operated by a hydraulic cylinder 42 which compresses the waste material to the level of a restraining member 50 controlled by a pneumatic cylinder 54. The member 50 comes into operation as the plunger 40 reaches the bottom of its stroke and holds the plastics material in a compressed condition while the plunger 40 rises again, further material 2 is fed to the chamber 8 and the cycle is repeated, the member 50 being withdrawn shortly before the plunger 40 reaches the bottom of its stroke. Plastics material is progressively melted as it passes down the box 10 and under the pressure exerted by the compressed material is extruded through a die plate 16 in the form of strands 18 which, after passing through a water bath 20, are chopped into granules 35 by a rotary cutter 34 and fall into a bin 36 ready for re-use.