Corrosion Resistant Plastics for Demanding Industrial Environments
Corrosion resistant plastics are comprised of two groups: Polyolefins and the polyvinyl chloride group. The common attributes of corrosion resistant plastics are excellent chemical resistance with relatively low cost. The Fluoroplastics group also exhibits excellent chemical resistive properties; however, products within this group are chemically more difficult to formulate resulting in higher product cost.
The polyolefin group is represented by polyethylene and polypropylene. Both of these products are recognized for their light weight and comparatively low cost. Polyethylene and polypropylene are available in various densities and molevular structture which provide a wide selection opportunity for the design engineer.
Plastics of the polyolefin group, because of their excellent resistance to solvents, are not chemically bondable. However, when bonding is required, they can be bonded by thermal wielding with low cost hot air welding equipment. This group is produced in a variety of forms: sheets, shapes, rod, tubing and film.
The polyvinyl chloride group consists of PVC and CPVC. This group possesses similar outstanding chemical resistance properties as the polyolefin group but is 35% to 40% heavie and structurally more rigid. CPVC, chlorinated polyvinyl chloride, is PVC with the addition of a chlorine atom. Properties of PVC and CPVC are identical with the exception of temperature resistance where CPVC is clearly superior. Both PVC and CPVC are chemically and thermally bondable. PVC is the oldest corrosion resistant plastic. Both PVC and CPVC are available in sheet, rod, tubings as well as profiles.
For the product designer, this section offers excellent prodcut choices whenever chemical resistance, ease of fabrication, and relative low cost are required.
| CPVC | L.D. POLY ETHYLENE | H.D. POLY ETHYLENE | POLYPRO PYLENE | PVC | |
|---|---|---|---|---|---|
| PHYSICAL | |||||
| SPECIFIC GRAVITY | 1.55 | 0.917 – .932 | 0.952 – .965 | 0.90 – .91 | 1.30 – 1.58 |
| WATER ABSORPTION, 24 hr. (%) | 0.05 | <0.01 | <0.01 | 0.01 – 0.03 | 0.04 |
| MECHANICAL | |||||
| TENSILE | |||||
| Strength, Yield (10³ psi) @ 73°F | 8.4 | 1.3 – 2.1 | 3.8 – 4.8 | 4.5 – 5.4 | 7.8 |
| Elongation, Ultimate (%) @ 73°F | 4.5 – 65.0 | 100 – 650 | 10 – 1200 | 100 – 600 | 150 |
| Modulus, Yield (10³ psi) @ 73°F | 425 | 25 – 41 | 155 – 158 | 165 – 225 | 506 |
| FLEXURAL | |||||
| Strength (10³ psi) @ 73°F | 15.6 | 35 – 48 | 145 – 225 | 6.0 – 8.0 | 14.7 |
| Modulus, Yield (10³ psi) @ 73°F | 474 | 170 – 250 | 518 | ||
| COMPRESSIVE STRENGTH | |||||
| 2% Offset (10³ psi) | 11.1 | ||||
| IMPACT STRENGTH | |||||
| Izod, Notched (ft-lb/in.) @ 73°F | 1.0 – 5.6 R118 | No Break D44-50 | 0.5 – 20.0 D66-73 | 0.4 – 1.2 R80-102 | 1.3 R113 |
| HARDNESS | |||||
| COEFFICIENT OF STATIC FRICTION | |||||
| Against steel | |||||
| Against itself | |||||
| THERMAL | |||||
|
CONDUCTIVITY (BTU/hr/sq ft/°F/in.) | .95 | 1.2 | |||
|
COEFFICIENT OF THERMAL EXPANSION (10⁻⁶/°F) | |||||
|
SPECIFIC HEAT (BTU/lb/°F) | |||||
| HEAT DEFLECTION TEMP (°F) | |||||
| At 66 psi | 238 | 100 – 121 | 175 – 196 | 225 – 250 | 165 |
| At 264 psi | 221 | 90 – 105 | 120 – 140 | 156 | |
| MAX. CONTINUOUS TEMP (°F) | |||||
| ELECTRICAL | |||||
| VOLUME RESISTIVITY (Ohm-cm) | 10¹⁵ | >10¹⁶ | 10¹⁶ | 2.3 × 10¹⁶ | |
| DIELECTRIC STRENGTH (V/mil) | 1220 – 1500 | 450 – 1000 | 450 – 500 | 600 | 410 |
| DIELECTRIC CONSTANT | |||||
| At 60 Hz | 3.08 | 2.25 – 2.35 | 2.25 – 2.35 | 2.2 – 2.6 | 3.2 – 4.0 |
| At 1 MHz | 3.2 – 3.6 | 2.25 – 2.35 | 2.25 – 2.35 | 2.2 – 2.6 | 2.8 – 3.1 |
| DISSIPATION FACTOR | |||||
| At 60 Hz | 0.018 – 0.02 | <0.0005 | <0.0005 | <0.0005 | 0.007 – 0.020 |
| At 1 MHz | 0.020 | <0.0005 | <0.0005 | <0.0005 | 0.006 – 0.019 |
| ARC RESISTANCE (SECONDS) | 135 – 160 | 136 – 185 | 60 – 80 | ||