Abstract: A method for forming an article from recyclable plastic materials includes progressively heating thermoplastic solid particles simultaneously with mixing, melting and conveying the particles, prior to delivery of molten material to an extruder. The process is particularly suitable for the continuous extrusion of elongated members having a plurality of internal wall surfaces defining elongated cavities within the member. The apparatus embodying the present invention includes a heated mixer-conveyor that simultaneously heats, melts, mixes and conveys thermoplastic material from an inlet port at which the material is received in solid particulate form, to a discharge port at which the material is in a substantially liquid state. A die particularly adapted for the continuous extrusion of an elongated member having internal walls shaped by surfaces within the die cavity is also disclosed.