PVC is not hygroscopic so it is therefore it is unlikely that moisture is the problem. It could be any of the following: 1)entrained air due to the back pressure being too low, the rear zone being run too hot, too much decompression, a leaking nozzle 2)degradation due to over heating caused by too high screw speed, too high back pressure, too high barrel temperature - check that the thermocouples are calibrated correctly and that there isn't a heater band out of control. 3)shear degradation on injection due to too high injection speed 4) excessive shear due to the wrong screw configuration - PVC should be run with a screw with a low compression ratio and a low compression rate - ag general purpose screw as fitted to most machines is not ideal. It could be more than one of the above contributing to the problem. Work through them changing one thing at a time allowing enough time for the machine to stabilise between changes in conditions. Best regards, Paul Anderson Consultant Pera Pera Innovation Park Melton Mowbray Leicestershire LE13 0PB UK Tel: + 44 (0) 1664 501 501 Fax: + 44 (0) 1664 501 556 Email: paul.anderson@pera.com Website: www.pera.com

Paul has covered most of what I would say. If you would like to have a conversation with a technical trainer on this subject then call Steve Harratt of Polymer Training on 07867 798253 - he will attempt to talk the problem through with you on a free of charge basis. Shoul you need more in depth help then Steve can discuss training issues iwth you.