Machining Polyphenylene Oxide (PPO): A Plastics Guide

An Informational Brief on Polymer Machining

Polyphenylene Oxide (PPO), also known by its trade name NORYL™, is an amorphous engineering thermoplastic. It is generally used commercially for electrical components, automotive parts and in medical grade sterilizable medical instruments that require high heat resistance, dimensional stability and accuracy. Some of its benefits include being low cost, light-weight with very low moisture absorption.

AIP has over 37 years of experience machining complex components from thermoplastics like polyphenylene oxide. In this insightful technical brief, we will discuss what goes into machining PPO and how it differs from other manufacturing options such as metal machining, injection molding, and 3D printing.

Properties of PPO

Keeping information about the properties of a thermoplastic beforehand is always beneficial. This helps in selecting the right thermoplastic for a project. Furthermore, it assists in evaluating if the end use requirement would be fulfilled or not. Here are some of the key properties of polyphenylene oxide:

PPO (Polyphenylene Oxide) is characterized by an extremely low moisture absorption rate and low thermal expansion. As a dimensionally stable thermoplastic, PPO also has high dielectric strength and a flammability rating of UL94 V-1 at .058” thickness. For machined parts, it is available in black, natural or a 30% glass filled gray version.

Although it has many attractive properties, PPO is susceptible to thermal oxidation in relation to its high glass transition temperature, which poses a problem for melt processing. To offset this, commercial resins are often blended with high-impact polystyrene (HIPS) or polyamide (PA).

Properties	Value	Units	Method
Resistance to Weathering	Good	–	–
Tensile Strength at Break	9200	psi	ASTM D638
Elongation at Break	25.0	%	ASTM D638
Thermal Expansion	3.3 x 10-5	in/in/oF	ASTM D696
Impact Strength, Notched @ -40 oF	2.5	ft-lb/in	ASTM D256
Impact Strength, Notched @ 73 oF	3.5	ft-lb/in	ASTM D256
Dielectric Strength	500	V/mil	D149
Heat Deflection Temperature, @264psi	254	F	D648
Flammability, @ .058”	V-1	–	UL94
Flammability, @ .236”	V-0	–	UL94

Key features of polyphenylene oxide:

Flame Resistance
Flexural Strength
High Dielectric Strength
Insulated
Low Moisture Absorption Rate
Low Thermal Expansion

Applications of PPO

Polyphenylene Oxide blends are used for structural parts, electronics, household and automotive items that depend on high heat resistance, dimensional stability and accuracy. They are also used in medicine for sterilizable instruments made of plastic. Common applications include the following:

Manifolds
Pump, valve and fitting applications
Scientific and analytical instrument components
Housings
Covers
Electrical components

Grades of PPO

At AIP, we machine various grades and brand name polyphenylene oxide. Branded names include the following: NORYL™, NORYL™ EN 265, NORYL™ PPO, NORYL™ RESIN, NORYL™ SE-1 GFN3, NORYLUX™, SUSTAPPO™, TECANYL™.

Our close ties with the industry’s leading plastics manufacturers give us even further insight and access to technical help in material selection, sizing and manufacturing procedures. Whatever your application, our machinists can help you in material selection, sizing and manufacturing techniques from concept to completion.

Machining PPO

Annealing PPO

If machined with coolants, lubricants and untrained procedures, this material is subject to cracking and crazing. Therefore, annealing is necessary for a quality, precision machined part out of the stock shape. The annealing process at AIP greatly reduces the chances of these stresses occurring from the heat generated during machining PPO and other polymers. Our machinists use computer controlled annealing ovens for the highest quality precision machining.

Machining PPO

We recommend non-aromatic, water-soluble coolants because they are most suitable for ideal surface finishes and close tolerances. These include pressurized air and spray mists. Coolants have the additional benefit of extending tool life as well.

This plastic is processed by injection molding or extrusion; depending on the material, the processing temperature is 260-300 °C. The surface can be printed, hot-stamped, painted or metallized.

Some companies machine both metals and plastics, which has detrimental outcomes for machined polymer products. Many past experiences have shown parts going to customer without cracks, only to develop surface cracks and warping over time due to exposure to metal machine shop fluids. Be sure to use a facility like AIP that only machines polymers.

Preventing Contamination

Contamination is a serious concern when machining polymer components for technically demanding industries such as aerospace and medical sciences. To ensure the highest level of sanitation down to the sub-molecular level, AIP Precision Machining designs, heat-treats, and machines only plastics with any sub-manufactured metalwork processed outside our facility. This allows us to de-risk the process from metallic cross contamination