2008 international lubricants and waxes meeting npra international lubricants and waxes meeting...
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2008 International Lubricants and Waxes Meeting
NPRA International Lubricants and Waxes Meeting
Session LW-08-106
2008 International Lubricants and Waxes Meeting
Function and Performance of Hydrocarbon Waxes in Rigid PVC
• By: Thomas C. PedersenRheogistics LLC
Picayune, MS USA
PVC
2008 International Lubricants and Waxes Meeting
• PVC resin is a free flowing, granular solid with a bulk density of 0.50 to 0.60 gm/ml.
• PVC resin contains 57% chlorine, 38% carbon, and 5% hydrogen.
PVC Compound
2008 International Lubricants and Waxes Meeting
PVC Compound
2008 International Lubricants and Waxes Meeting
PVC Products
Vinyl Siding
Vinyl Siding
PVC Fence
PVC Pipe
PVC• Rigid PVC has great properties
– Typical 7000+ psi tensile strength– Excellent stiffness– Excellent impact strength– Good weatherability– Excellent cost performance
Rigid PVC
• Most rigid PVC properties are affected in one way or another by the lubricant system.
• Getting things right is a constant balancing act.
• Customer quote: “Its always the wax,” VP of manufacturing of a leading building products manufacturer, 1980
PVC Resin• PVC resin grains are approximately 100
microns in diameter. The large grains are composed of 2 to 10 micron sub-grains which in turn are composed of primary particles with a diameter of approximately 1 micron.
2008 International Lubricants and Waxes Meeting
PVC Resin
2008 International Lubricants and Waxes Meeting
PVC Processing
• The 1 micron PVC primary particles are thought to be the primary flow units during rigid PVC processing
2008 International Lubricants and Waxes Meeting
Processing Rigid PVC
• Rigid PVC products are formed by heating and compressing PVC compounds into desired shapes.
• The compound is compressed from a bulk density of approximately
0.50 gm/ml to a product density of approximately 1.40 gm/ml
• PVC is heated to ca. 400°F by mechanical shear and heat transfer.
• During processing, PVC is exposed to pressures of 2000 to 4000 psi.
Processing Rigid PVC
• The function of lubricants in rigid PVC is to manage the fusion process while preventing the polymer from sticking to the processing equipment.
PVC Lubrication
• Paraffin and hydrocarbon waxes are used in conjunction with calcium stearate as primary lubricants
• Ca(C18H35O2)2
2008 International Lubricants and Waxes Meeting
Behavior of Lubricants
• The calcium atom or polar end of calcium stearate is attracted to the machine and PVC resin surfaces
• Paraffin wax is thought to act as a slip agent between the exposed tails of calcium stearate
2008 International Lubricants and Waxes Meeting
Fusion Mechanism for Rigid PVC
• C – Compaction• D – Densification• F – Fusion• E – Elongation• Chemical/Plasticizing Effects
Rigid PVC Fusion in Extrusion
Fusion Characterization in the Lab
• Torque Rheometer– Fixed volume heated chamber– Work imparted into PVC compound by
mixing blades– Measure torque required to turn the blades
and melt temperature
Torque Rheometer
2008 International Lubricants and Waxes Meeting
Torque Rheometer Rotors
2008 International Lubricants and Waxes Meeting
Torque Rheometry Energy Balance
2008 International Lubricants and Waxes Meeting
Extruder Energy Balance
2008 International Lubricants and Waxes Meeting
Effects of Fusion Levels on Physical Properties
2008 International Lubricants and Waxes Meeting
• Tensile Properties– Increase with increasing fusion
• Impact Properties– Peak at an intermediate level of fusion
Trial PVC Compound• PVC Resin 100 parts
• Stabilizer 0.50 phr
• Wax 1.30 phr
• Calcium Stearate 0.65 phr
• Oxidized PE Wax 0.15 phr
• Calcium Carbonate 5.00 phr
• Titanium Dioxide 0.50 phr2008 International Lubricants and Waxes Meeting
100 grams of PVC Resin
Assume primary particles are spheres
Volume of a primary particle = 5.2x10-13 cm3
Weight of a primary particle = 7.3x10-13 gms
Number of primary particles per 100 grams of PVC resin = 1.4x1014
2008 International Lubricants and Waxes Meeting
1.3 grams of Paraffin Wax
Assume molecular weight of 450 gm/mole
# moles = 0.0029 moles
# wax molecules = 0.0029 * 6.023x1023
= 1.75x1021
2008 International Lubricants and Waxes Meeting
Wax Molecules Per PVC Primary Particle• 1.4x1014 PVC Primary Particles
• 1.75x1021 Paraffin Wax Molecules
• Estimated 10,000,000 to 15,000,000 Wax Molecules per PVC PP
2008 International Lubricants and Waxes Meeting
• PVC Resin 100 parts
• Stabilizer 0.50 phr
• Wax 1.30 phr
• Calcium Stearate 0.65 phr
• Oxidized PE Wax 0.15 phr
• Calcium Carbonate 5.00 phr
• Titanium Dioxide 0.50 phr2008 International Lubricants and Waxes Meeting
Trial PVC Compound
Torque Rheometry - Classic Wax
Torque Rheometry - C32
Torque Rheometry – C26
Torque Rheometry – C40
Torque Rheometry – PE Wax
Test Results
Wax Fusion Time Fusion Torque Fusion Temp Equil Torque Equil Temp
C26 166 sec 21.3 Nm 179°C None >195°C
C32 352 sec 15.2 Nm 183°C 13.0 Nm 188°C
C40 2,120 sec 10.1 Nm 184°C 12.4 Nm 188°C
Classic 318 sec 15.5 Nm 183°C 12.6 Nm 188°C
PE 182 sec 18.9 Nm 182°C None >195°C
2008 International Lubricants and Waxes Meeting
Conclusions
• The PVC Industry is a large application for paraffin and hydrocarbon waxes
• Waxes with carbon numbers of C30 to C36 work best as primary PVC lubricants in North America’s tin stabilized formulations
2008 International Lubricants and Waxes Meeting
Conclusions• The lubricant system is adjusted to tune
the formulation to the heating and shearing characteristics of the customer’s processing equipment.
• Changes in any material or any piece of equipment in a customer’s plant results in the need for a lubricant adjustment.
2008 International Lubricants and Waxes Meeting
Conclusions
• Understanding and managing lubricant performance in rigid PVC is complex
• “Its always the wax.” The PVC industry requires in-depth technical support and service.
2008 International Lubricants and Waxes Meeting
References
• T. C. Pedersen, “Process and Material Considerations in the Industrial Application of Lubricants in Rigid PVC Extrusion”, Journal of Vinyl Technology, 6, 104 (1984)
2008 International Lubricants and Waxes Meeting
References
• J. W. Summers, “Lubrication Mechanism in Poly (Vinyl Chloride) Compounds: Understanding the Three Distinct Roles of Lubricants” Antec 2006, Society of Plastics Engineers.
2008 International Lubricants and Waxes Meeting
References
• P. Benjamin, “The Influence of Processing on the Properties of PVC Pipe”, International Conference on PVC Processing, 6 & 7 April 1978, The Plastics and Rubber Institute.
2008 International Lubricants and Waxes Meeting
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