Update on Troubleshooting the PVC Extrusion Process Natami Subramanian Muralisrinivasan Smithers ismithers /Smithers - A Smithers Group Company Shawbury, Shrewsbury, Shropshire, SY4 4NR, United Kingdom Telephone: +44 (0)1939 250383 Fax: +44 (0)1939 251118 http://www.ismithers.net
ontents Introduction 1 Poly (Vinyl Chloride) 5 2.1 Characteristics 5 2.2 Poly (Vinyl Chloride) Structure 6 2.2.1 Crystallinity 8 2.2.2 Thermal Stability of Poly (Vinyl Chloride) 8 2.3 Manufacture of Poly (Vinyl Chloride) Resin..10 2.3.1 Raw Material 11 2.3.2 Energy Requirement 11 2.3.3 Process 11 2.3.4 K-Value 12 2.4 Modification of Poly (Vinyl Chloride) 12 2.4.1 By the Addition of Metal Compounds 12 2.4.2 Structural Modification 14 2.5 Regrind Poly (Vinyl Chloride) Material 14 2.6 Advantages of Poly (Vinyl Chloride) 15 2.7 Disadvantages 16 Additives and Compounding 23 3.1 Poly (Vinyl Chloride) Formulation 23
Update on Troubleshooting the PVC Extrusion Process 3.2 Role of Additives 24 3.3 Classification of Poly(Vinyl Chloride) Additives 26 3.3.1 Heat Stabilisers 27 3.3.1.1 Lead Stabilisers 29 3.3.1.2 Secondary Heat Stabilisers... 29 3.3.1.3 Tin Stabilisers 30 3.3.1.4 Calcium-zinc Stabilisers 31 3.3.1.5 Other Heat Stabilisers 32 3.3.1.6 One-pack Stabilisers 32 3.3.2 Lubricants 33 3.3.3 Impact Modifiers 34 3.3.4 Plasticisers 34 3.3.5 Fillers 36 3.3.6 Flame Retardants 37 3.3.7 Blowing Agents 37 3.3.8 Pigments 38 3.3.9 Coupling Agents 39 3.3.10 Smoke Suppressants 39 3.4 Migration of Additives 39 3.5 Compounding 40 3.5.1 Technology 41 4 Poly(Vinyl Chloride) Extrusion 49 4.1 Basic Requirement of Poly (Vinyl Chloride) Compounds 49 4.1.1 Machine 50 vi
Contents 4.1.2 Processing 50 4.3 Extrusion 50 4.3.1 Extruder: Operating Conditions 51 4.3.2 Screw 52 4.3.3 Processing Technology 53 4.3.4 Processing Temperature 54 4.3.5 Power Consumption 54 4.4 Extrusion 55 4.4.1 Single-screw Extruder 56 4.4.1.1 Advantages/Disadvantages... 57 4.4.2 Twin-screw Extrusion 57 4.4.2.1 Advantages 58 4.4.3 Die Design 59 4.4 Calibration System 60 4.5 Poly (Vinyl Chloride) Pipe Extrusion 60. 4.5.1 Pipe Dies 62 4.5.2 Cooling System 62 4.6 Poly (Vinyl Chloride) Profile Extrusion 63 4.6.1 Calibrator 63 4.6.2 Cooling System 65 4.7 Poly (Vinyl Chloride) Sheet Extrusion 65 4.8 Poly (Vinyl Chloride) Films 67 4.9 Regrind 68 5 Degradation and Stabilisation of Poly (Vinyl Chloride) 71 5.1 Degradation of Poly (Vinyl Chloride) 71 vii
Update on Troubleshooting the PVC Extrusion Process 5.2 Structural Defects 72 5.3 Tacticity 73 5.4 Dehydrochlorination 73 5.5 Stabilisers 74 5.6 Impurities 75 5.7 Photochemical Degradation 75 5.8 Mechanism of Degradation 76 5.9 Polyvinyl Chloride) Stabilisation 78 6 Poly(Vinyl Chloride)-Wood Composites 93 6.1 Additives 94 6.2 Properties of Wood-Poly(vinyl Chloride) Composites 96 6.3 Processing 96 6.4 Advantages of Wood-Poly(Vinyl Chloride) Composites 98 7 Poly(Vinyl Chloride) Extrusion: Problems and Defects 103 8 Troubleshooting Problems in Poly(Vinyl Chloride) Extrusion 107 8.1 Problems and Troubleshooting in Pipe/Profile Extrusion 108 8.1.1 Production Problems in the Extruder 108 8.1.1.1 Problem: Difficult to String-up Melt during Startup 109 viii
Contents 8.1.1.2 Problem: Powder Pulled into a Vacuum 109 8.1.1.3 Problem: High Bearing Throat at Back Pressure 109 8.1.1.4 Problem: Motor Load is too High 110 8.1.1.5 Problem: Low Output 113 8.1.2 Product Problems 114 8.1.2 Production Problems in Downstream Areas...115 8.1.2.1 Problem: A Longitudinal Scratch in Pipe or Profile is Found While Sizing 115 8.1.2.2 Problem: Folding of Material in the Calibrator.. 115 8.1.2.3 Problem: Blowouts in the Cooling Zone 116 8.1.2.4 Problem: Uncontrolled Wall Thickness 118 8.1.2.5 Problem: Poor Inner Surface 119 8.1.2.6 Problem: Regular Wavy Lumps 120 8.1.2.7 Problem: Irregular Lumps (Random With No Regular Pattern) 121 8.1.2.8 Problem: Dimples on the Product 122 8.1.2.9 Problem: Burning or Yellowing of the Extrudate 122 ix
Update on Troubleshooting the PVC Extrusion Process 8.1.2.10 Problem: Poor Overall Appearance 124 8.1.2.11 Problem: Dull Surface Appearance 125 8.1.2.12 Problem: Low Results in the Drop Weight Impact Test.. 125 8.1.2.13 Problem: Gauge Variation 126. 8.1.2.14 Problem: Degassing is Difficult 128 8.1.2.15 Problem: Frictional Heat: Zone-4 Overheating 129 8.1.2.16 Problem: Melt Fracture and Surface Roughness 130 8.1.2.17 Problem: Lumpy, Cold or Oval (egg-shaped) mark Surfaces 131 8.1.2.18 Problem: Over-lubrication 132 8.1.2.19 Problem: Impact Failure... 133 8.1.2.20 Problem: Black Specks 134 8.1.2.21 Problem: Variation in Load 8.1.3 Quality or Amperage from Batch-to-Batch or Between Batches 135 Problems in the End Product 136 8.1.3.1 Problem: Failure in the Methylene Chloride Test... 136 8.1.3.1.1 Problem - Inside Portion Granular 136 8.1.3.1.2 Problem: Middle Portion is Mealy 138 x
Contents 8.1.3.1.3 Problem: Outside Portion is Mealy 139 8.1.3.2 Problem: Bubbles at the Oil Reversion Test at the Inner Surface 139 8.1.4 Quality Problems in Pipes 141 8.2 Troubleshooting for Poly (Vinyl Chloride) Blown Film 143 8.3 Troubleshooting for Poly (Vinyl Chloride) Sheets 145 9 Future Requirements: Developments in Polyvinyl Chloride) 149 9.1 Poly(Vinyl Chloride) Formulation 149 9.2 Wood - Polyvinyl Chloride) Composites... 150 9.3 Medical Applications 150 9.4 Construction 150 9.5 Biodegradation 150 xi