THE EFFECT OF RECYCLING AND DEGRADATION ON PARISON EXTRUSION

Finished goods manufactured by the extrusion blow moulding process are strongly dependent on the parison formation stage, since it is the pr imary step in the process. The magnitude of the die swell and the degr ee of sag exhibited by the parison, after being extruded from an annul ar die, are dependent on the material's molecular structure and strong ly affect the performance of the final product. Repassing or recycling of polymeric materials results in degradation reactions that modify t he molecular structure, and therefore of parison swell and sag. Polyet hylene simultaneously undergoes crosslinking and chain scission. Polyp ropylene undergoes predominately chain scission. The extent of these d egradation reactions can be minimized with the use of appropriate stab ilizers. This work involves the study of the effects of repassing on t he parison formation stage of extrusion blow moulding. The repassing o f the same material gives a representation of what occurs when recycli ng is undertaken. The effect of stabilizer addition is also studied. P articular emphasis is placed on parison swell and sag.