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. Pedersen
Rheogistics LLC
Picayune, MS USA
2008 International Lubricants and Waxes Meeting
PVC
• 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.
2008 International Lubricants and Waxes Meeting
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 subgrains 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
• Tensile Properties
– Increase with increasing fusion
• Impact Properties
– Peak at an intermediate level of fusion
2008 International Lubricants and Waxes Meeting
Trial PVC Compound
•
•
•
•
•
•
•
PVC Resin
Stabilizer
Wax
Calcium Stearate
Oxidized PE Wax
Calcium Carbonate
Titanium Dioxide
100 parts
0.50 phr
1.30 phr
0.65 phr
0.15 phr
5.00 phr
0.50 phr
2008 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
Trial PVC Compound
•
•
•
•
•
•
•
PVC Resin
Stabilizer
Wax
Calcium Stearate
Oxidized PE Wax
Calcium Carbonate
Titanium Dioxide
100 parts
0.50 phr
1.30 phr
0.65 phr
0.15 phr
5.00 phr
0.50 phr
2008 International Lubricants and Waxes Meeting
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