Ryton® PPS - FAQ

Where can I obtain Ryton® PPS stock shapes for machining some prototype parts?

Large stock shapes made from Ryton® PPS injection molding compounds are not available because the injection molding compounds are not suitable for producing thick forms. Some specialty compression molding and/or extrusion processors supply PPS rod, sheet, and tube stock, but it is important to understand that parts machined from compression molded PPS rods, sheets, or hollow forms will not necessarily perform the same as parts injection molded from Ryton® PPS injection molding compounds. For more information, see Stock Shapes.

What does "PPS" mean?

PPS stands for Polyphenylene Sulfide.

Does "Linear PPS" make a superior injection molding compound?

We use uncured linear PPS as well as cured PPS in our various Ryton® PPS products, depending on the desired properties of the product. For the most part, we prefer to use cured PPS polymers for injection molding compounds because they provide more of the benefits generally desired from PPS compounds. PPS curing is a process of heating the PPS polymer in air to increase its molecular weight through thermal-oxidative chain extension and cross-linking reactions. Uncured linear PPS will typically have more ductility than cured PPS of similar molecular weight, however cured PPS exhibits better dimensional stability and creep resistance. Furthermore, since any uncured linear PPS polymer will undergo curing when heated in air, cured PPS tends to exhibit less pronounced changes due to thermal aging. Certain compounds made using cured PPS will provide mechanical properties comparable to any compounds based exclusively on uncured linear PPS.

What is branched PPS?

We refer to branched PPS as PPS polymer produced with a branched backbone structure in the polymerization process. Some other PPS producers refer to branched PPS as PPS that has been post polymerization treated by curing. The two resultant structures are different and impart different performance characteristics. We practice both techniques and utilizes whichever type of PPS polymer is best for meeting the desired performance requirements.

Which is better – linear PPS or branched PPS?

The molecular weight and molecular structure of the PPS polymer affect both processing and finished part characteristics, so you cannot say one is "generally better" than the other. A specific part design and processing technique along with finished part requirements should be defined before statements are made about one polymer type being more appropriate than another for a particular application.

What is the color of your material?

Most of our products are available in either "natural" or black color, but some are available only in black. The natural colors of 40% glass fiber reinforced grades can range from dark brown to off white, whereas the natural colors of glass fiber and mineral filled grades generally range from tan to off-white.

How much color variation can I expect to encounter with natural color Ryton® PPS compounds?

Most of our products are available in either "natural" or black color, but some are available only in black. The natural colors of 40% glass fiber reinforced grades can range from dark brown to off white, whereas the natural colors of glass fiber and mineral filled grades generally range from tan to off-white.

How much color variation can I expect to encounter with natural color Ryton® PPS compounds?

The color of Ryton® PPS compounds depends on several factors, including the PPS base resin that is used, types of fillers and reinforcements, the amounts of those fillers and reinforcements, and the heat history the material sees during processing. Some 40% glass fiber reinforced grades can be a dark brown color, while other grades may be a lighter brown to tan color, and some grades an off-white color. These colors can vary somewhat depending on how the compounds are processed. More heat history typically produces a darker molding, however annealing amorphous (cold molded) parts will result in a lightening of color. Even though there is no color specification for the natural color compounds, they are fairly consistent in color, with only slight variations due to the above factors. Variation in color is no indication of diminished mechanical properties.

Is it possible to pigment Ryton® PPS to make it a different color?

The dark brown color of most 40% glass fiber reinforced grades is not amenable to pigmenting any color other than black. Some of the lighter color grades may be pigmented a variety of colors using commercially available color concentrates blended in at the injection molding machine. However, it is important to understand that the parts will not be color stable if exposed to elevated temperatures, UV light, or outdoor conditions. So, pigmenting Ryton® PPS compounds may be useful in some situations for part identification, but is not recommended for cosmetic or decorative purposes. Although Ryton® R-7-120NA PPS and Ryton® R-7-190NA PPS have UL "All Color" listings when used in conjunction with PPS-based color concentrates, the addition of pigments may void the UL certifications of other Ryton® PPS compounds. In general, if color stability and consistency is required, black color Ryton® PPS compounds should be used.

Can you tell me if Ryton® PPS is compatible with a certain chemical?

Information on the compatibility of Ryton® PPS with a wide variety of chemicals is available in our Chemical Resistance Guide. If you cannot find the information you need, please contact us. Our chemists can provide opinions about the suitability of Ryton® PPS for particular chemical environments, based on our knowledge of the chemistry of PPS and our compounds. However, testing under conditions as similar as possible to actual service conditions is always the best way to determine chemical compatibility for a particular application.

Will a crystalline part or an amorphous part have better properties?

Ryton® PPS in the crystalline state provides better performance in the areas for which PPS is usually chosen. Although amorphous PPS moldings may have somewhat better mechanical strength, crystalline PPS moldings will have higher modulus (stiffness), better creep resistance, and better high temperature dimensional stability. Furthermore, amorphous PPS parts may deform when exposed to temperatures above about 88°C (190°F).

Is there some way to determine whether a Ryton® PPS part is crystalline or amorphous?

Yes. The crystalline or amorphous state of the PPS polymer may be determined by Differential Scanning Calorimetry (DSC). Contact our technical specialists for support.

Does Ryton® PPS contain any halogenated flame retardants?

No. Since polyphenylene sulfide is inherently flame retardant, Ryton® PPS compounds can achieve UL94 V-0 and V-0/5VA flammability ratings without any flame retardant additives.

Do you have any "FDA approved" grades of Ryton® PPS?

Ryton® PPS injection molding compound R-4-232NA complies with U.S. FDA and European Union (EU 10/2011 and 1183/2012) regulations for use as components of articles intended for repeat use in contact with all types of foods. Additionally, in accordance with U.S. FDA Food Contact Notification (FCN) 1083, all Ryton® PPS production polymers may be used as components in the manufacture of articles for repeat-use food-contact applications, in contact with all types of food, under Conditions of Use A-H, and J, and also meet EU 10/2011 and 1183/2012 requirements. 

Polyphenylene sulfide resins are also specifically permitted under 21 CFR 177.2490 as coatings or components of coatings of articles intended for repeated food contact use, subject to certain limitations. Several Ryton® PPS injection molding compounds have also been certified to comply with the requirements of various standards for use in contact with potable water. It is the responsibility of the manufacturer of the final article to determine the safety and suitability of Ryton® PPS for such applications.

Do any of your Ryton® PPS products contain a fluoropolymer lubricant such as PTFE?

Ryton® BR42B PPS contains PPS blended with PTFE (polytetrafluoroethylene) for improved surface lubricity.

Is Ryton® PPS suitable for use in applications where it is exposed to ultraviolet (UV) light?

Although exposure of Ryton® PPS to UV light may cause some surface degradation, the properties of the bulk material will be relatively unaffected. Several Ryton® PPS compounds have been rated suitable for outdoor use with respect to UV light exposure, water exposure and water immersion, in accordance with UL746C.

Does Ryton® PPS meet the fungus resistance requirements of military specification (MIL-STD-45-4)?

Yes, two Ryton® PPS products, R-4 and R-4-02XT, have been evaluated by an independent laboratory (Truesdail Laboratories, Inc.) in accordance to MIL-STD-810D test method 508.3 and found not to allow fungus growth. The study was conducted over the prescribed twenty-eight days with the five fungi required by the test method. Observations were taken every seven days. No fungus growth was observed on the Ryton® PPS test specimens.

Do you have a chart cross-referencing the different Ryton® PPS compounds with PPS compounds from other manufacturers?

We have no literature that cross-references our products with those of other suppliers. If you would like to substitute some other supplier's product with a Ryton® PPS compound, but are unsure which Ryton® PPS compound to use, please contact us.

Is it really necessary to use a mold temperature of 275°F (135°C)? We are able to reach temperatures of 200°F to 250°F (93°C to 121°C) using hot water. Is this sufficient?

We generally advise using a mold surface temperature of 275°F to 300°F (135°C to 149°C) to achieve a near maximum degree of crystallinity for optimum long-term thermal stability, dimensional stability, and consistent part performance. Consult the Ryton® PPS Processing Guide for more information on this issue.

In our injection molding facility, we have several methods to heat our molds: circulating water or oil, and electric cartridges. Do you recommend one of these methods in particular for molding Ryton® PPS?

Yes, hot oil should be used to heat and cool molds when molding Ryton® PPS thermoplastic compounds. Remember, we typically advise molding Ryton® PPS in a mold with surface temperatures of 275-300°F (135-149°C). Because this is well above the boiling point of water, using water to heat and cool the mold to 275°F (135°C) results in very high line pressures and a potential safety hazard. On the other hand, the typical line pressure for oil heating/cooling systems is about 30 psig (2.1 bar). Electric cartridges do not offer the temperature control provided by oil systems. Oil systems are capable of both heating and cooling the mold, resulting in more consistent mold temperatures and improved shot-to-shot consistency.

Can Ryton® PPS still be used after it has been in a dryer longer than the recommended period of time?

We have conducted tests on drying Ryton® R-4 PPS at 300°F (149°C) and found that the initial melt flow of 28.7 g/10 min varied from a low of 26.0 g/10 min to a high of 30.0 g/10 min, up to 96 hrs. If, however, your drying temperature was too high (400°F, 204°C), the melt flow would decrease from 28.7 g/10 min to 13.9 g/10 min. Therefore, if your dryer is set at 300°F (149°C) or lower, you should have no problem using that material.

What is the recommended moisture content level for Ryton® PPS compounds?

Although we have no recommended moisture level, Ryton® PPS compounds will be more readily processed if dried thoroughly. Less than 0.02% moisture should be sufficient, and following our standard drying recommendations (300-350°F, 149-177°C for 2 to 3 hours) should accomplish this. Longer drying times are not harmful, but temperatures above 400° F (204°C) may reduce melt flow. The resin itself is not hygroscopic, but some mineral fillers may be, so drying is particularly important for mineral filled compounds.

If I need to briefly interrupt production, should I purge the Ryton® PPS from the barrel of my machine?

At normal processing temperatures (600-650°F, 315-343°C melt temperature), Ryton® PPS compounds may be allowed to remain in the barrel for up to two hours without suffering any detrimental effects.

I need to recover some molded-in inserts from some reject parts. Is there a solvent I can use to dissolve away the PPS?

Unfortunately, recovery of molded-in inserts from Ryton® PPS parts is not practical. There is no known solvent for PPS at temperatures below 200°C (392°F), and acids that will degrade the PPS polymer will also likely damage inserts. It is possible to burn away the PPS (with a torch or using a muffle furnace, for example) if the inserts can withstand the temperatures required (over 815°C, 1500°F). If possible, a metal insert may be heated to melt the surrounding PPS (about 316°C, 600°F) to facilitate its removal, but there will still be residual PPS to be removed. Molten PPS can usually be removed using a wire brush or scouring pad. Like chipping or breaking the PPS away from the inserts, these operations generally can not be accomplished without damaging the inserts.

Do you have the properties required for a finite element stress analysis?

Yes. Stress-strain curves and elevated temperature data are available for the most commonly used products. Please contact one of our Technical Service Centers to request the data you need.

Do you have the material parameters required for conducting a flow simulation?

Yes, the material parameters have been developed for the most commonly used products. This includes PVT data which is needed for warpage analysis. Please contact one of our Technical Service Centers to request the data you need.

What types of adhesives are best for bonding Ryton® PPS?

Despite the chemically non-reactive nature of PPS, there are adhesives that will bond PPS providing the surface is properly prepared. Acrylic, cyanoacrylate, and two-part epoxy type adhesives have generally been found to work best with PPS, however surface treatments are often required to attain adequate bond strengths. For more information on this topic see our technical bulletin on Adhesives and Paints for Ryton® Polyphenylene Sulfide. We also suggest contacting adhesive manufacturers regarding their latest recommendations for adhesives that are effective at bonding PPS.

What is the recommended gap for venting around an ejector pin?

Molds for Ryton® PPS compounds may be vented by a 0.0005 inch (0.0125 mm) gap around the radius of the pin (0.001 in, 0.025 mm reduction in diameter). Venting also may be accomplished by flattening pins 0.0007 inches (0.0175 mm) on one to four sides.

I'm analyzing a plastic housing that is attached to an aluminum part. I was told that the coefficient of linear thermal expansion (CLTE) for Ryton® PPS was close to that of aluminum. Is that correct?

The CLTEs of different Ryton® PPS compounds vary, but in general they are close to that of aluminum in the flow direction. Transverse to flow the CLTEs are higher than aluminum. If large temperature variations are expected, the assembly should be analyzed to determine if problems exist.

I was considering PPS for an injection molded part, but I've heard the material doesn't flow very well. Is this true?

Absolutely not! In fact, Ryton® PPS compounds have some of the best flow characteristics of all high temperature engineering thermoplastics. They are used extensively in the connector industry, where part thicknesses of 0.50 mm to 0.75 mm (0.020 to 0.030 inch) are commonplace.