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. PedersenRheogistics LLCPicayune, 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 Compound


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.


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


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


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 phr


100 grams of PVC Resin

Assume primary particles are spheresVolume of a primary particle = 5.2x10-13 cm3

Weight of a primary particle = 7.3x10-13 gmsNumber 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

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


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.


Engineering

Function and Performance of Hydrocarbon Waxes in Rigid PVC