PSU is the acronym for Polysulfone. PSU is part of Sulfone polymers, which are high performance polymer exhibiting very attractive properties such as high temperature performance, good chemical resistance, outstanding toughness, excellent colorability and very good dimensional stability. As with the other sulfone polymers, PSU is an amorphous polymer and therefore displays very good creep resistance, isotropic thermal and mechanical properties (if non-reinforced) and is naturally transparent. properties. PSU is used in various applications including plumbing, food services, medical, aerospace, wire & cable, etc.
Thermoplastic polymers can be divided into two categories based on their molecular structure: amorphous and semi-crystalline.
Amorphous polymers have a randomly ordered molecular structure that lacks a sharp melting point. Instead, they soften gradually at temperatures above their glass transition temperature (Tg), which is approximately 190°C for Udel® PSU. Because these materials are isotropic in flow, they possess better dimensional stability than semi-crystalline plastics and are less likely to warp. Amorphous thermoplastics offer superior impact strength along with excellent resistance to hot water and steam, good chemical resistance, and good stiffness and strength. PPSU, PESU, PSU and PEI are good examples of amorphous thermoplastics offering these qualities.
Semi-crystalline thermoplastics have a highly ordered molecular structure with both crystalline and amorphous regions. Due to the presence of crystals, they are generally opaque and have sharp melting points. Semi-crystalline polymers are anisotropic in flow, so they shrink more in the direction transverse to flow than they do along the direction of flow. This results in dimensional instability, compared to amorphous polymers. These materials have two different thermal transitions: the glass transition temperature (Tg), which corresponds to the softening of the amorphous phase, and the melting point (Tm), which corresponds to the melting of the different crystals and the flow of the material. The Tm is generally above that of the upper range of amorphous thermoplastics.
Udel® PSU is commercially available in transparent, opaque and glass-fiber reinforced grades in natural and colored formulations. Syensqo has carefully formulated color technology to achieve the most stable colors for the high temperature environments seen by Udel ® PSU. Product approvals can change from one color to another, therefore please contact the Syensqo Specialty Polymers representatives for more details or for specific regulatory needs.
As for most sulfone polymers, Udel® PSU is UL94 V0 and HB rated, respectively for 4.5mm and 1.6mm thickness.
Some Udel® PSU compounds comply 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. Certification of each Udel® grade is generally mentioned on the related Technical Datasheet. As regulatory action is an ongoing activity, please contact your Syensqo Specialty Polymers representative for the latest information regarding a specific application requiring agency approval or recognition.
Udel® P-1700 NT11 (natural), P-1700 BK937 (black), P-1700 WH7407 (white) and several glass reinforcement Udel® GF-110, GF-120 and GF-130 compounds comply with DW approvals required for use as components of parts in continuous contact with drinking water and plumbing applications. Certification of each Udel® grade is generally mentioned on the related Technical Datasheet. As regulatory action is an ongoing activity, please contact your Syensqo Specialty Polymers representative for the latest information regarding a specific application requiring agency approval or recognition.
Udel® PSU displays a very good chemical resistance to many chemicals including: aqueous systems, caustics, inorganic acids, aliphatic hydrocarbons, detergents and soaps and certain alcohols. In general, the chemical resistance of Udel® PSU is known to be lower than Veradel® PESU and Radel® PPSU material. More details about the chemical resistance can be found in the Udel® design guide (available in the "Documents" section) or by contacting directly the Syensqo Specialty Polymers Technical Marketing representative.
The natural color of Udel® PSU is a very light amber tint, with good light transmission and low haze. The light amber tint is due to the high temperatures needed to produce and process Udel PSU. Special grades of Udel® PSU have been formulated to mask the light amber tint and provide a more water clear appearance if desired.
Since Udel® PSU has a good chemical resistance, common solvents are generally ineffective. In order to dissolve the PSU polymer, specific and sometimes hazardous chemicals must be used such as N, N-dimethylacetamide (DMA), N,N-dimethylformamide (DMF), Chlorobenzene, N-methylpyrrolidone (NMP), Tetrahydrofuran (THF), 3-Methylsulfolane or tetrachloroethane. Please carefully read the associated SDS prior to handling any of these solvents. Please contact the Syensqo Specialty Polymers Technical representative for more details.
As for many other polymers, resistance of Udel® PSU to UV depends strongly on the wavelength of the incident UV radiation as well as on the exposure time. UV radiation will have the most obvious effect on the material color upon initial exposure. Longer term exposure will start to show a loss of ductility and impact strength. However, UV radiation does not have an immediate effect on mechanical strength or modulus. Applications that see direct exposure to UV light; such as visors, lenses, transparent covers, etc., should consider protective clear coats for enhanced protection. Samples are available for further testing. Please contact the Syensqo Specialty Polymers Technical representative for more details.
Udel ® PSU material displays a good resistance to the most common sterilization methods including steam, EtO, Gamma, X-ray, Hydrogen Peroxide and other gaseous chemical sterilizations. Except for Radel® PPSU; Udel ® PSU has better retention of mechanical properties than amorphous transparent polymers including PEI, PC or PS. The material can withstand to repeated sterilization cycles and is therefore particularly recommended for use in medical applications. For more data, please contact the Syensqo Specialty Polymers Technical representative.
Design of a new part must take into account two different points.
First, the use of a radius on inside corners helps to reduce localized stresses. This is most critical in corners that will see external loadings, such as the inside corner of an L-bracket. The larger the radius the lower the stress under load; therefore, inside corner radii should be equal to half of the nominal wall thickness. A fillet radius of 0,8mm (0.032 in.) must be considered as minimum in any case. Radiused corners also align with the need to take advantage of the flexibility of polymers and allowing a design to flex under load rather than stiffening a design. This has been a clear lesson as we have worked with customer in metal to plastic designs. If a stiffer design is required then consider glass-filled Udel grades, but when using an unfilled grades a good radius and flexibility allows for the widest load tolerance range.
Second, overall design should attempt to minimize residual stress. Stress cracking is the most common failure mode for Udel PSU. Residual stress is a function of processing and part design. Besides radii for inside corners it is important to look at all features for the use of uniform wall thickness, drafted features and extremely thin walls (<1mm) will help to minimize design stress and reduce residual stress from processing.
More details can be found in the Udel® design guide (available in the "Documents" section) or by contacting Syensqo Specialty Polymers Technical representative. Design of a new part must take into account two different points.
First, the maximum stress level and deflection created in the part during use must remain lower than the corresponding appropriate material property, i.e. tensile, compressive, or shear strength. This will allow deciding whether the initial design incorporates a sufficient safety factor to be viable or whether the design should be modified by changing wall thickness or incorporating ribs or contours to increase the section modulus. Special attention must be paid to parts submitted to tensile stress. In any cases, the design stress should stay below the yield strength of the material.
Secondly, as already mentioned, Udel® PSU is sensitive to stress cracking. Therefore, stress concentrations areas, which may lead to premature failure under impact, creep or fatigue should be avoided. Therefore, inside corner radii should be equal to half of the nominal wall thickness. A fillet radius of 0,8mm (0.032 in.) must be considered as minimum in any case. Outside corners should have a radius equal to the sum of the radius of the inside corner and the wall thickness to maintain a uniform wall thickness.
More details can be found in the Udel® design guide (available in the "Documents" section) or by contacting Syensqo Specialty Polymers Technical Marketing representative.
A quick molding guide is available on the web site for operators at production site. For more detailed information, please refer to the complete Sulfones processing guide (available in the "Documents" section). You can also find general recommendations for starting points for processing on our Technical datasheets. Please remember these are recommendations for where to start and a general range that is typical for Udel PSU. The specific process settings can be very different based on type of melt process, equipment used, design of mold or die or the specific grade being used.
Consult with Syensqo Specialty Polymers Technical representative for concerns if you need to process outside the typical range.
In general, open flow channels and larger gates allow for reduced shear and a wider processing window for Udel PSU. Small restricted gates can lead to very high injection pressure and cosmetic issues on the part surface. A quick molding guide is available on the web site for operators at production site. For more detailed information, please refer to the complete Sulfones processing guide (available in the "Documents" section).
In order to have the lowest level of residual internal stresses in the molded parts and to avoid premature part failure during use, it is highly recommended to mold Udel® PSU at mold temperatures in the range of 138-160°C measured directly at the tool surface.
As Udel® PSU must be molded at in the range of 138-160°C, mold heating systems based on circulating oil are recommended. Pressurized hot water systems can also be considered for use in clean-room settings if needed but my limit the higher end of the recommended range. Use of insulation plates on the mold bases is also highly recommended. Electrical heaters are not recommended due the poor cooling performance and will limit the number of shots possible before the mold becomes too hot.
Inadequate venting may result in the gas being compressed in the cavity, which may then heat up to the point of causing burn marks on the part and a deposit on the mold surface. Poor venting may also result in poor weld line strength and the inability to completely fill the cavity. Recommended total volume of vents should be equal to about 25% of the cavity perimeter. Venting below the parting line can be accomplished by incorporating vents at ejector pins. Recommended standard vent dimensions can be found in the Udel® processing guide (available in the "Documents" section).
The following tool steels are recommended for molding PSU material: DWN 1,2767 ; 420 Stainless Steel or High Density Chrome Plated S-7 steel. Equivalent steel reference in terms of composition are also accepted.
Udel® PSU as other sulfones polymers can react at high temperature with the steel of the injection unit through a reaction known as sulfidation. Sulfidation is a chemical reaction leading to the creation of iron sulfide (noted as Fe + S = FeS) that occurs whereby unprotected steel reacts at processing temperatures with sulfur that’s liberated during the processing of sulfur containing polymers like sulfones polymers. Sulfidation can occur on the inside of the injection molding machine screw/barrel assembly and/or within a hot runner system. Sulfidation reaction produces a very thin, brittle film of iron sulfide (deep black in color) on the surface of the steel which is easily removed by injection pressure. The thin black film that’s removed is pushed (or injected) into the molded part, causing small black “chip-like” specks or thin grey “smoky” appearing traces. Experience has shown that use of steel containing at least 20% chromium or an additive package based on Stellite® can dramatically improve corrosion and delay sulfidation. The use of highly nickel-based alloys should be avoided.
Use of hot runners is generally not recommended for molding Udel® PSU. However parts can be successfully molded if precise recommendations are followed including no internal heating, precise temperature control, corrosion resistant alloys and no polymer dead zones. More details can be found in the Sulfone processing guide (available in the "Documents" section) or by contacting Syensqo Specialty Polymers Technical representative.
Udel® PSU is an amorphous polymer and is therefore sensitive to stress cracking. To prevent risk of premature failure, it is important to minimize the level of residual internal stresses or molded-in stresses when working with fabricated sulfone parts. A procedure has been developed to estimate the magnitude of the residual internal stresses. The procedure entails exposing the parts to a series of chemical mixtures. The stress level required for crazing to occur for each mixture was determined using specimens at known stress levels, the basic procedure can be found in the Sulfone Processing Guide in the Documents section. Contact your Syensqo Specialty Polymers technical representative for more details.
The level of residual internal stresses in molded parts depends on different factors such as part design, thickness, tool design and processing conditions. However, a maximum level of residual internal stresses of 5MPa for Udel® PSU molded parts can be considered to be acceptable in most cases. Contact your Syensqo Specialty Polymers technical representative for more details about the procedure and the targeted level.
The desired moisture content for injection molding is below 500 ppm (0.05%) and for extrusion below 100 ppm (0.01%). Hopper drying requires sufficient insulation and minimal system leakage. Inlet air temperature must be high enough to maintain a polymer pellet temperature of at least 135°C (275°F), and the dew point of the inlet air should be -40°C (-40°F). These conditions must be sustained long enough for the polymer moisture content to drop to below the minimum levels suggested for the processing technique to be used. Recommended drying times and temperatures for Udel® resins about 4 hours at 135°C (275°F). It should be noted that molding wet Udel PSU will not degrade the polymer, but just generally create cosmetic defects on the surface. Parts produced with wet resin can be ground, dried and reprocessed with no significant loss of properties.
Samples pellets for molding trials and several shapes of molded articles can be supplied for testing purposes directly from Syensqo. There is a wide range of products and sample types available. Stock shapes or other thick walled semi-fabricates for machining prototype parts for example, are readily available through partner companies. Please consult your Syensqo Specialty Polymers representative for further information or sample requests.
Udel PSU has very good thermal stability and can be held at standard process temperatures for extended times, upto an hour in some cases. However, it is recommended that reducing the heat in the barrel by at least 100C and purging excessive material can greatly extend the residence time. If a full machine purge is required, information about start-up, shutdown and purging procedure can be found in the Sulfone processing guide (available in the "documents" section) or by contacting Syensqo Specialty Polymers Technical representative.
Primary grades of Udel® PSU grades are fully characterized to run FEA analysis or rheological analysis. Data are openly available in most of Commercial Rheological Softwares (Moldflow, Moldex, CADFlow, etc.). Please contact your Syensqo Specialty representative to help with your development work.
You can find technical datasheets of Udel® PSU products on the specific grade pages.
Material Safety Datasheet of Udel® PSU products can be obtained on the specific grade pages.