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Designing with Plastics

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Designing with Plastics
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An ePublication of the International Association of Plastics Distribution

December 2008 | Focus: Polyphenylene sulfide (PPS)

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The unsung hero of high-performance thermoplastics

REPRINTED FROM THE IAPD MAGAZINE

PPS products by ENSINGER include extruded stock shapes and rings machined from tube, engineered profiles, injection molded components, compression molded components and stock shapes, thin gauge sheets, coils/rolls, strips and punched parts.

PPS products by ENSINGER include extruded stock shapes and rings machined from tube, engineered profiles, injection molded components, compression molded components and stock shapes, thin gauge sheets, coils/rolls, strips and punched parts.

Polyphenylene sulfide (PPS) is truly the unsung hero of high-performance thermoplastics. PPS has been specified in thousands of highly engineered applications in every market from aerospace and automotive to medical, electronics and construction for over 20 years. Whenever extreme conditions and environments called for higher heat capacities with low smoke generation, exceptional chemical resistance, or exacting dimensional stability and strength, PPS has been quietly called upon to meet the most demanding requirements.

In the new millennium, PPS is offered in more formulations, through more manufacturing processes, and in more end products than ever before. The complete list of available formulations is growing so rapidly that it is difficult to track it all. Neat grades that exhibit high purity levels are complemented by glass-filled variations and impact modifiers for enhanced mechanical properties. Advances in process technology have kept pace and even expanded the market potential of PPS greatly just within the last few months.

Injection molding
PPS has been heavily specified in injection molded products for over two decades. The versatility of PPS allows it to be molded into components for demanding applications that require exacting tolerances. PPS is very often utilized in overmolding and insert molding processes for finished and semi-finished products.

Applications include aerospace and automotive products where strength-to-weight ratios combine favorably with the material’s inherent flame resistance and chemical resistance. Electronics manufacturers select PPS for insulation and connector applications when high continuous operating temperatures are a consideration. Medical products that require low moisture vapor transmission and repeated autoclave cycles are prime candidates for PPS materials.

Extruded stock shapes
Fabricators have enjoyed the availability of PPS for manufacturing high-performance products since the early 1990s. PPS machines well in conventional processes and is known for its ability to hold demanding tolerances with minimal creep. It can be bonded, welded and painted with minimal, if any, preparation.

PPS is available in thick-walled tubing having diameters to 14" that can be machined into shorter sections or rings. Extruded rods come in standard and custom lengths with diameters that range from 0.250" to 2.5". Plates range in thickness from 0.250" to 2.75" and are available in stock and custom lengths and widths.

End markets for extruded stock shapes closely mirror those of other processes as defined by the economics of fabricated production. Applications in the semiconductor industry for wafer and disk production and/or polishing had been prominent before the downturn in that industry.

Compression molding
Compression-molded PPS is available in stock shapes, as well as in detailed finished and semi-finished custom molded products. Compression molding can produce very heavy-section molded products within exacting tolerances. As with most thermoplastics, heavy wall sections are not available through injection molding.

Stock shapes of compression-molded PPS include heavy plate sections up to 3.5" thick in custom widths and lengths. Short section rods are molded up to 4" in diameter and tubing is available up to 58" diameter and up to 6" thick. Disks for fabrication are available with diameters to 26" and thicknesses from 0.5" to 3.5".

View the complete article online.

This article was written by Michael J. Gehrig, ENSINGER.

In This Issue:
The unsung hero of high-performance thermoplastics
PPS continues to serve quietly in extreme applications.

A practical guide to high-temperature plastic shapes
PPS' many advantages include excellent chemical and hydrolysis resistance.

Polyphenylene sulfide (PPS) in review
Compared to higher-temperature polyesters PPS offers greater dimensional stability and thermal, chemical and creep resistance.

About PPS
Properties of this versatile material.

Test your knowledge
What do you know about PPS?

Online plastic resources
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About IAPD
The International Association of Plastics Distribution, founded in 1956, is an international trade association comprised of companies engaged in the distribution and manufacture of plastics materials.

Members include plastics distributors, processors, manufacturers, resin manufacturers, manufacturers’ representatives and associated products and services, all of whom are dedicated to the distribution channel.

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A practical guide to high-temperature plastic shapes

REPRINTED FROM THE IAPD MAGAZINE

Examples of compression molded shapes of high-temperature plastics include a mold for making paper bowls made of 40 percent glass polyphenylene sulfide (PPS), gears made of 40 percent glass filled PPS, and a tray for charring computer chips made of a static dissipative polyetherimide (PEI) materials.

Examples of compression molded shapes of high-temperature plastics include a mold for making paper bowls made of 40 percent glass polyphenylene sulfide (PPS), gears made of 40 percent glass filled PPS, and a tray for charring computer chips made of a static dissipative polyetherimide (PEI) materials.

As the requirements for plastic materials to perform in demanding services continue to increase, so too must the availability of stock shapes produced from these materials. Having these materials available for injection molding is not good enough. Either the volume is too low to justify the capital expenditure for a mold or the size is such that injection molding is not a viable option.

What materials are we discussing? For the purposes of this article, they must meet the three following criteria:

  1. Operate continuously at a temperature of 400°F (204°C).
  2. Maintain a minimum tensile strength of 4,000 psi at that temperature (400°F/204°C).
  3. Be available as a stock shape from one or more manufacturers (stock shapes being rod, plate, tube or rings). In order to more effectively highlight the resin properties, the discussed materials are all available in shapes as “neat” resins (non-reinforcing additives) with one exception. Other formulations may be available, but the focus on properties is based on the basic polymer.

Infornation on polyphenylene is listed below. See the complete article online for other high-performance materials.

Polyphenylene sulfide (PPS)
PPS is available as a branched or linear material. The branched material is not practical to extrude, and unless it has a minimum of 40 percent glass or carbon fiber (in which case it can be injection or compression molded), it is too brittle to be of any use. The linear material (while it can be extruded without fillers) has a low continuous service temperature (by the criteria described in this article) and rather mundane physical properties.

With 40 percent glass fiber, PPS is an excellent cost-effective material.

Advantages:

  • Has no known solvent below 392°F (200°C).
  • Excellent chemical and hydrolysis resistance.
  • Resistant to creep, deformation under load and compression set.

Disadvantages:

  • The material tends to be brittle.
  • Shapes available (reinforced only).
  • Compression molded rod to 4" O.D.
  • Compression molded plate to 3" O.D.
  • Miscellaneous tubular bar, rings (up to 58" O.D.) and discs.

View the complete article online.

This article was written by Bob Alberts, ENSINGER.

Polyphenylene sulfide (PPS) in review

REPRINTED FROM THE IAPD MAGAZINE

Automotive thermostat housing molded from Ticona’s  Fortron® PPS.

Automotive thermostat housing molded from Ticona’s Fortron® PPS.

Manufacturers often rely on polyphenylene sulfide (PPS) to meet demanding conditions. Not only is this high-performance thermoplastic extremely strong, rigid and tough (see Properties Table I below), but also it retains these attributes at temperatures well above 200°C (392°F).

PPS is inherently flame retardant, absorbs little moisture, and has exceptional chemical resistance, dimensional stability and creep resistance. In addition, its low ionic content makes it an excellent electrical insulator.

This polymer is commonly used in extruded and injection molded components. It is available in partially branched and linear forms. The branched version is more rigid, while the linear form has greater tensile, flexural and notched impact strength. Linear PPS also has fewer ionic impurities, better melt stability, a wider viscosity range and shorter cycle times, and provides for easier and more consistent extrusion and molding.

Meeting thermal and chemical stresses
PPS has striking thermal stability. Grades containing 30 to 40 percent glass reinforcement have deflection temperatures under load (DTUL) of more than 250°C (480°F) at a load of 264 PSI. Its continuous use temperature is as high as 220°C (428°F) and it can withstand excursions to 260°C (500°F). It melts at 285ºC (545°F) and has a glass transition temperature of about 90ºC (190°F).
PPS is inert to many chemicals and resists oxidation and hydrolysis. It does not dissolve in most common solvents below 200ºC (392°F) and is virtually unaffected by acids, bases, alcohols, oxidizing bleaches and many other substances at elevated temperatures. It is relatively impermeable to liquids and gases, so emissions through PPS walls and linings are relatively low.

PPS is inherently flame retardant without additives and is rated UL 94 V-0/5V. Neat PPS has an oxygen index of 44 (the lowest oxygen concentration at which it burns on its own), while its compounds have indices up to 53.

Its hardness, abrasion resistance, weld line integrity and other properties are better than most high-temperature thermoplastics. Compared to higher-temperature polyesters, for instance, PPS offers greater dimensional stability and thermal, chemical and creep resistance. Also, since it absorbs little water, it swells less in moist environments than nylons, polyetherimides and polyesters.

View the complete article online.

This article was written by Ed Hallahan, Ticona.

About PPS

Polyphenylene sulfide (PPS) is a semi-crystalline engineering thermoplastic suitable for applications requiring thermal stability to 425°F (218°C), structural integrity to 225°F (107°C), high dimensional stability and exceptional resistance to a broad range of chemicals. PPS is synthesized in a polar solvent from 1,4-dichlorobenzene and sodium sulfide. Two distinct forms of PPS exist. One has a partially branched molecular structure, while the other is more nearly linear. Linear PPS usually offers better mechanical strength and higher melt stability. Unfilled linear material is off white in color; branched is gray.

PPS can be highly loaded with fillers. Many grades are available, including:

  • unfilled natural (colors are available)
  • 30% and 40% glass filled
  • glass/mineral filled
  • conductive and anti-static grades
  • internally lubricated bearing grades

Polyphenylene sulfide is melt processable and can be injection molded, blow molded, extruded and compression molded. Machinable shapes are available. Adhesives are available for bonding PPS to itself or other materials. PPS to PPS bonds can also be achieved through thermal and ultrasonic welding. The chemical resistance of PPS makes solvent bonding impractical.

Tensile strength ranges from 10,000 to 13,500 psi (68.90 to 93.0 MPa) in the unfilled material to 29,000 psi (200 MPa) for injection molded 40 percent glass filled PPS. Moduli are typically 500,00 psi (3,450 MPa) unfilled to 1,300,000 psi (8,960 MPa) compression molded 40 percent glass filled, though values as high as 19,300 MPa have been reported for glass/mineral filled resins. Elongation in filled grades can be quite low. Room temperature strength and stiffness are well retained to approximately 200°F (93°C), just above the 194°F (90°C) glass transition temperature of the amorphous phase. Heat deflection temperature at 264 psi (1.80 MPa) for unfilled PPS is 250°F (121°C) and is as high as 510°F (266°C) in glass filled grades, but long-term exposure to temperatures in excess of 425°F (121°C) is not recommended. Melting occurs at 540°F (282°C).

PPS has good creep resistance at elevated temperatures. Apparent modulus after 100,000 hours at 122°F (50°C) under a 5,000 psi (35 MPa) load is 340,000 psi (2,345 MPa). Thermal dimensional stability is also good. Coefficient of linear thermal expansion is 2.8 x 10-5 in/in-°F (0.5 × 10-4/°C) in unfilled PPS, and can be as low as 0.8 x 10-5 in/in-°F (0.14 × 10-4/°C) in highly filled grades. As is typical for semi-crystalline materials, thermal expansion increases dramatically above the glass transition temperature (Tg) and can be as much as five times higher than the values given above at temperatures over 194°F (90°C). Moisture absorption in PPS is negligible (0.03 percent at saturation). Dimensional stability up to Tg is very good. High modulus, low creep and low elongation allow PPS to be machined to very tight tolerances.

Unfilled PPS is not usually considered for bearing or other wear applications, but it has shown superior wear resistance in such applications involving aggressive chemical environments. Bearing grades are available that offer low friction, high limiting PVs (pressure and velocity) and wear resistance.

The property table for PPS is online at www.iapd.org/new/bookstore/free_resources.html. For more information on PPS and other plastic materials, IAPD’s Introduction to Plastics is an invaluable training manual. Details about it and other IAPD educational resources are available online at www.iapd.org.

Test your knowledge

What do you know about PPS? Answers are at www.iapd.org/popquiz.html.

1.Polyphenylene sulfide is resistant to attack by a broad range of chemicals and most strong acids, athough there are some it is susceptible to. Of the following, which acid is PPS resistant to?

  1. hydrofluoric acid
  2. nitric acid
  3. chlorosulfonic
  4. ethylene diamine  

2. What is the tensile strength for unfilled polyphenylene sulfide?

  1. 8,800 psi (60.67 MPa)
  2. 6,000 (41 MPa)
  3. 5,500 to 7,000 psi (15 to 48 MPa)
  4. 10,000 to 13,500 psi (68.90 to 93.0 MPa)

Online plastic resources

Your IAPD Distributor is your choice in finding the right material for your application. Go to www.iapd.org to find a distributor in your area. You can search by company name, location or product category.

The IAPD Magazine web site at www.theiapdmagazine.com allows you to search by material, trade name and fabrication process. You can also search for fabrication capabilities.

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© 2008
IAPD

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Designing with Plastics is published by the International Association of Plastics Distribution. While every effort has been made for accuracy, IAPD encourages you to verify information with a plastics distributor to ensure you select the correct plastic products to meet your needs.