heat resistant plastic

by Katie Gerard

CHOOSING THE RIGHT HEAT RESISTANT PLASTIC FOR THE JOB

Heat resistant plastic is taking center stage. These materials are light, versatile alternatives to metal, ceramics and older-generation polymers. When choosing a plastic that will perform well in high heat applications, it is important to pick the correct material for the job. Thus costly damages can be avoided. 

OPERATING TEMPERATURES OF HEAT RESISTANT PLASTICS

A heat resistant plastic has a permanent operating temperature of more than 150° C and often uses special reinforcing materials, such as glass fiber, glass beads or carbon fiber, to increase heat distortion resistance.

Additives also contribute to other desirable characteristics. Glass fiber or beads and carbon fiber contribute to the rigidity of the polymer while adding PTFE, graphite and aramid fibers will also improve sliding friction characteristics as well. Also, the addition of metal fibers and carbon provides better electrical conductivity in heat resistant plastic.

PERFORMANCE OF HIGH TEMP PLASTICS COMPARED TO OTHER TYPES OF MATERIALS

Ceramics are heat resistant and are extremely strong, showing considerable stiffness under compression and bending. Ceramic material is not a plastic. The strongest ceramic has a bend strength similar to steel and can retain it up to 900° C. However, these materials are brittle and may break when dropped or undergo sudden temperature changes.

CORROSION RESISTANT BUT LOWER ELECTRICAL AND THERMAL CONDUCTIVITY

Ceramics are also resistant to corrosion in harsh environments but have lower electrical and thermal conductivity. Metals also have high mechanical strength and better electrical and thermal conductivity than ceramics. Metals can also be formed or cut into new shapes without breaking, but they are vulnerable to corrosion. They also are conductive which may not be useful in an applicaton. Heat resistant plastic is usually not.

1. Vespel ®

Without a doubt Vespel ® (unfilled & graphite filled) can take the heat. This heat resistant plastic is a non-melting polyimide. It can tolerate repeated heating up to 300° C without changing its thermal or mechanical properties.  Therefore, it is a popular choice for jet engines, industrial machinery, cars, trucks, and other vehicles.

Filler Materials Improve Heat Tolerance

Depending on the filler material (unfilled, 15% Graphite, 40% Graphite, 10% PTFE and 15% Graphite, or 15% Moly), Vespel ® can perform well for 350 hours of 398° C heat, losing only 50% of its initial tensile strength: 12,500 psi (unfilled base resin) reduces to 6,000 psi. This loss is due almost entirely to oxidative degradation.  The parts will perform in inert environments, such as nitrogen or a vacuum, with almost no loss of properties over time.

2. Torlon® (Polyamidep-imide)

Torlon®, a polyamide-imide, offers Nylon 6/6’s room temperature properties at 204° C, with exceptional long-term strength and stiffness up to a continuous 260° C.  This heat resistant plastic is an effective alternative to metal in high temperature friction and wear applications. And has excellent resistance to wear, creep, and chemicals, including strong acids and most organic chemicals.  Thus it is ideally suited for severe service environments.

Because it is a heat resistant plastic Torlon® is often used to make aircraft hardware and fasteners, as well as mechanical and structural components, and transmission and power train parts. Additionally it is made into coatings, composites, and additives.

3. Ryton ® (PPS)

This is also a heat resistant plastic. It is also known as polyphenylene sulfide (PPS) and is an organic heat resistant polymer that can be molded, extruded or machined to high tolerances.  And it has a maximum service temperature of 218° C. It has not been found to be damaged by any solvent at temperatures below 200° C. Along with Vespel®, Ryton® PPS compounds have a UL 94 V-0 flammability rating without any flame retardant additives, meaning burning stops within 10 seconds on a vertical specimen.

4. Noryl® (PPO)

Noryl® is another heat resistant plastic. A blend of polyphenylene oxide (PPO) and polystyrene (PS), Noryl® is a rare example of a homogeneous mixture of two plastics.  The addition of PS increases the glass transition temperature above 100° C, making Noryl® stable in boiling water.

Maximum Service Temperature

Noryl® has a maximum service temperature of 105° C and a melting point of 154° C. These properties make it useful in the production of solar panels, because solar panels in the summer only reach 45° C. It also absorbs little water, with values as low as .07%, making it an excellent electrical insulating material.

Heat Resistant Plastics Material Properties
PlasticTensile strength at 26° CFlexural strength at 26° CTensile strength at 26° CMelting Point
Vespel®8,750 psi16,000 psi300° Cnone
Torlon®27,847 psi35,390 psi260° Cnone
Ryton®21,755 psi25,800 psi218° Cnone
Noryl®9,200 psi7,400 psi105° C154° C

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