How to Determine PVC Rheology

The rheology (flow behavior) of melted PVC can be determined using a torque rheometer.

Polyvinyl chloride (PVC) is a synthetic thermoplastic resin made of 57 percent chlorine from industrial salt and 43 percent carbon in the form of ethylene from oil and gas sources. Once formed, PVC can be resoftened by heating, with melting occurring at approximately 180 degrees Fahrenheit. To properly manufacture PVC products, manufacturers study its flow properties when melted to learn how to successfully pour it into injection-molding machines. Rheology is the study of how matter flows. So when you determine the rheology of PVC, you determine how it flows when melted.

Things You'll Need

• PVC synthetic resin powder
• Torque rheometer

Instructions

Melting

1. Place your PVC powder in a torque rheometer, which looks like a mixer. The PVC is placed in the torque rheometer's mixing chamber, along with any additives and pigments you choose to add to it. The rheometer is equipped with roller blade rotors that serve the same function as beaters on a mixer. PVC melts at 176 degrees Fahrenheit and the rheometer's rotors will move to exert stress on the melted PVC.

2. Blend the melted PVC for a prescribed amount of time (approximately 10 minutes) so the rheometer can measure the torque (twisting force) required to stir (shear) the fluid PVC with the rotors. The fluid PVC's shear rate is its resistance to being stirred. The torque required indicates the shear stress required and the rotor speed indicates the sheer rate required to stir the mixture

3. Calculate the viscosity and shear rate of the PVC using the numbers for torque and rotor speed produced by the rheometer. These datum will determine the rheology of the PVC resin.

Tips & Warnings

• There are three typoes of rheometers: capillary, parallel plate and torque rheometers. Torque rheometers are the rheometer of choice when determining the flow proerties of polymers.

References

• The Industrial Physicist: What Is Rheology Anyway?
• PVC.org: What Is PVC?;2011
• Society of Plastics Engineers: Using a Torque Rheometer to Characterize Flow in Poly (Vinyl Chloride) Composites
• Google Dictionary: Definition of Shear
• Naturepedic: U.S. Consumer Product Safety Commission (CPSC) Bans Phthalates Found in Crib Mattresses and Baby Bedding

Resources

• Dynalab Corp.:Plastic Properties of Polyvinyl Chloride; 2011