Function and Performance of Hydrocarbon Waxes in Rigid PVC

2008 International Lubricants and Waxes Meeting
NPRA International Lubricants
and Waxes Meeting
Session LW-08-106

Function and Performance of
Hydrocarbon Waxes in Rigid
PVC
• By: Thomas C. Pedersen
Rheogistics LLC
Picayune, MS USA

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.

PVC Compound

PVC Products
Vinyl Siding
Vinyl Siding
PVC Fence

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.

PVC Resin

PVC Processing
• The 1 micron PVC primary particles are
thought to be the primary flow units
during rigid PVC processing

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

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

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

Torque Rheometer Rotors

Torque Rheometry
Energy Balance

Extruder Energy Balance

Effects of Fusion Levels on
Physical Properties
• 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

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

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

• 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 phr
Trial PVC Compound

Torque Rheometry - Classic 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

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

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.

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.

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)

References
• J. W. Summers, “Lubrication
Mechanism in Poly (Vinyl Chloride)
Compounds: Understanding the Three
Distinct Roles of Lubricants” Antec
2006, Society of Plastics Engineers.

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.

Function and Performance of Hydrocarbon Waxes in Rigid PVC

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