Materials
Sintered Thermoplastic Materials
Sintering thermoplastic materials forms a porous mass by heat or pressure without melting those materials to the point of liquification. Average pore size and porosity depend on:
- Particle control of the input materials
- Compacting pressure
- Thermal dwell
- Other proprietary processing variables
Average pore sizes of components from Polystar Technologies typically range from 3 µm to 350+ µm. However, additional products with voids much larger are simply described as open pore components due to having such little restriction, that they cannot be quantified using our standard test methodologies. Typical void volumes range from 40% to 60% but can be produced as high as 70% or as little as 30%. Controlling pore size and void volume helps engineers achieve optimal flows, restriction, and barrier protection required for their application.
Polystar controls the required pore size and void volume in our products based on consultation with our customers’ requirements, selection of polymers, and our proprietary PolySmart™ manufacturing process. With many of our material being sterilizable, our sintered porous components can be manufactured utilizing a wide variety of polymers and polymer-additive blends, including:
HDPE
High-Density Polyethylene (HDPE) is a versatile thermoplastic polymer used in a wide range of applications. Rigid and slightly opaque, it exhibits excellent strength and tear resistance. It has a wide melting point range 120° C to 180° C (248° F to 356° F), with an average melting point of approximately 130° C (266° F). It also shows good chemical resistance to various substances.
Key Strengths
- Superior Strength: HDPE offers exceptional strength, making it suitable for demanding applications.
- Chemical Resistance: Resistant to corrosion and chemical damage.
- Inexpensive: As a raw material, HDPE costs less than many other thermoplastics.
Key Weaknesses
- Less Flexible: HDPE is less flexible compared to other thermoplastics like UHMWPE or PTFE.
- Heat Limitations: Softening at relatively low temperatures limits its use in high-temperature applications.
- Less Durable: HDPE is less durable than UHMWPE due to its shorter molecular chains.
UHMWPE
Ultra-High Molecular Weight Polyethylene (UHMWPE) has exceptionally long molecular chains (longer than HDPE), which results in outstanding mechanical properties, including exceptional wear resistance, impact strength, and chemical resistance. It is well-suited for applications where durability is critical.
Key Strengths
- Highly Rugged – With molecular weights ranging from 1-8 MM g/mol as compared to 300-500K g/mol for most HDPE, UHMWPE excels in harsh, wear-intensive environments.
- Ease of Fabrication – UHMWPE is an exceptional choice for complex and non-uniform cross-sectional geometries.
- Alternative to PTFE – In many cases, UHMWPE serves as a lower-cost, hydrophobic alternative to PTFE, without the PFAS considerations that accompany fluoropolymers. Additionally, UHMWPE is significantly more structural than PTFE.
- Biocompatibility – Medical grades of conventional and highly-cross-linked UHMWPE are available.
Key Weaknesses
- Heat Resistance – Like HDPE, UHMWPE does not resist high heat levels as effectively as PTFE, PVDF, PEI or some other thermoplastics. However, products tend to out-perform expectations in applications where thermal exposure occurs for a short duration.
- Limited Hydrophobicity – Although naturally hydrophobic, UHMWPE is not as hydrophobic as PTFE and exhibits lower Water Entry Pressure (WEP) ratings than PTFE.
PTFE
Polytetrafluoroethylene (PTFE or Teflon™) is known for its exceptional chemical resistance, low friction coefficient, and stability at high temperatures. It is used in many medical, clinical, laboratory, and industrial applications.
Key Strengths
- Chemical Resistance – PTFE is almost entirely chemically inert and highly insoluble in most solvents or chemicals. It withstands a broad range of corrosive substances without degrading.
- Thermal Stability – PTFE remains stable between -200° C and +260° C (-328° F and +500° F). Like PVDF, PTFE is extremely heat resistant and can withstand more than four times the temperature than PE can at continuous use.
- Biocompatible – PTFE is biocompatible and used in many MedTech applications.
- Durability and Strength – Sintered PTFE exhibits remarkable strength and sturdiness when compared to expanded PTFE (ePTFE), which is delicate and easily damaged. Sintered PTFE retains its structural integrity even when subjected to physical contact.
Key Weaknesses
- Mechanical Ruggedness – When compared with UHMWPE, PTFE has only moderate mechanical ruggedness and can handle only 20% of the load.
- Regulatory Uncertainty – PTFE is intricately linked with PFAS concerns, but the extent varies based on manufacturing processes and use cases. While debate continues regarding PFAS of Concern and Polymers of Low Concern (PLC), PTFE use could become more tightly regulated.
- Cost – PTFE is more expensive than HDPE, UHMWPE, and other thermoplastics.
PVDF
Polyvinylidene fluoride, also known as polyvinylidene difluoride (PVDF or Kynar®) offers excellent mechanical strength, UV resistance, and flame retardancy. It is commonly used in chemical processing, energy production, semiconductor processing, and the production of microelectronics.
Key Strengths
- High Resistance – PVDF exhibits high resistance to various chemicals and UV radiation. It is also very flame retardant.
- Rugged – PVDF is exceptionally rugged in environments experiencing extreme temperature variations.
- Piezoelectric Properties – PVDF can generate an electric charge when mechanically stressed.
Key Weaknesses
- Mechanical Ruggedness – PVDF has moderate mechanical ruggedness when compared to UHMWPE.
- Chemical Resistance – Although exhibiting significant chemical resistance, PVDF is outperformed by other fluorinated polymers such as PTFE.
- Cost – PVDF is more expensive that HDPE, UHMWPE, and select PTFE products
PEI
Polyetherimide (PEI or Ultem™) offers high-temperature performance, mechanical robustness, chemical resistance, and flame retardancy. When exposed to hot water and steam, it resists hydrolysis and can withstand repeated cycles in a steam autoclave. It is particularly suited for use where high purity is required. It is hydrolytically stable and retains 100% of its tensile strength after 2000 steam autoclave cycles at 270° F (132° C).
Key Strengths
- Exposure Resistance – PEI effectively withstands elevated temperatures and shows outstanding resistance to a broad spectrum of chemicals, making it suitable for use in harsh environments.
- Mechanical Strength – PEI also exhibits high tensile strength and modulus, both of which contribute to mechanical performance in sintered components.
- Electrical Insulation – It maintains stable electrical properties and is often used in electronic applications.
- Flame Retardancy – PEI has inherent flame-retardant properties, enhancing safety in applications where fire resistance is critical.
Key Weaknesses
- Mechanical Ruggedness – although it has high chemical resistance and stability, PEI has only moderate mechanical ruggedness compared to UHMWPE.
- Cost – PEI is more expensive than many thermoplastics and has lower impact strength when compared to PEEK. Its temperature range is also less than that of PEEK.
PP
Polypropylene (PP) offers excellent mechanical strength, chemical resistance, and low water absorption. It is commonly used in medical syringes and other medical consumables, in packaging, industrial applications like equipment housings, consumer goods, and protective gear.
Key Strengths
- Outstanding Durability – PP exhibits superior strength and resilience under stress.
- Chemical Resistance – It is highly resistant to corrosion and cleaning agents.
- Insulating Properties – PP is an excellent insulator and is suitable for use in certain electronic applications.
- Low Water Absorption – PP absorbs less than 0.01% of water and is an excellent candidate for projects involving submerged products or the need for waterproof materials.
Weaknesses
- UV Degradation – PP is affected by UV exposure, which limits its suitability for high-altitude or UV-intensive environments.
- Limited High-Temperature Use – PP chain degradation can contribute to oxidation and cracks at elevated temperatures.
- Cost – Although thought of as a low cost material, specialty grades of virgin PP which are suitable for porous sintering are more expensive when compared to HDPE and UHMWPE.
PEEK
Polyetherketone (PEEK) is a semi-crystalline thermoplastic with exceptional heat, chemical, and mechanical load resistance. It exhibits excellent tensile strength, stiffness, and fatigue resistance. It also resists attack from acids, bases, and organic solvents, making it ideal for MedTech and chemical processing applications such as pumps or chromatography columns.
Key Strengths
- High Heat and Chemical Resistance – PEEK exhibits high heat resistance (up to 300° C) and resistance to various chemicals. It is well suited for exposure to disinfectants and various sterilization methods, including, EtO, hydrogen peroxide, steam sterilization, or gamma irradiation.
- Exceptional Mechanical Strength – PEEK has very good tensile and flexural strength. In addition, it can often replace metal components in harsh environments.
- Biocompatibility – PEEK is biocompatible and can be used in direct contact applications involving bodily fluids.
Key Weaknesses
- Cost – PEEK is expensive when compared to other polymers, and processing challenges further amplify costs.
- Hydrolysis Sensitivity – Even though PEEK exhibits excellent mechanical properties, prolonged exposures to hot water can lead to hydrolytic degradation.
PES
Polyethersulfone (PES) can withstand exposure to high, prolonged temperatures in both air and water. Low protein binding, and stability in alkaline pH, suits it for use in microbiological fluid applications, biological samples, and other life sciences applications. PES is also used in seals and lab filters. Additionally, it can be used as packing for absorption and distillation columns, and as filtration media for filters and exhaust scrubbers.
Key Strengths
- High Resistance – PES offers chemical compatibility and hydrolysis resistance; is flame retardant, resistant to thermal aging, and has electrical insulating properties.
- Suited for Tight Tolerance Applications – PES shows little to no dimensional change within a wide range of temperatures.
Key Weaknesses
- Cost – PES is more expensive than many thermoplastics, and also requires specialty processing considerations, which add to unit part costs.
- Chemical Compatibility – PES is not particularly resistant to certain acids, halogenated hydrocarbons, ketones, and alcohols.
PA – NYLON
Polyamide (PA or Nylon) is used in applications where hardiness, reduction in friction, and lubricant use are important. A widely used engineering thermoplastic, it is tough, abrasion-resistant, and highly versatile. Sintered nylon can be found in fluid applicators, filters, venting applications, and in acoustic dampening components.
Key Strengths
- Chemical Resistance – Nylon is resistant to many chemicals.
- Lightweight – Nylon-based porous materials are lightweight.
Key Weaknesses
- Mechanical Strength – Nylon’s tensile strength is typically better than PE, but impact strength is normally less. Other polymers tend to perform better on both measures.
- Limited Temperature Range – When compared with many engineered thermoplastics, nylon performance degrades more readily at high temperatures.
- Hydroscopic Nature – Nylon absorbs water even in ambient conditions, which can affect performance environments.
CUSTOM MATERIALS
Polystar Technologies partners regularly with R&D teams to develop novel, multifunctional, porous plastic components, inclusive of material blends. With our continuously expanding materials expertise, we can help you create custom, precision parts that:
- Adsorb harmful chemicals and provide particulate filtration.
- Dissipate pressure or heat generated by certain components while shutting off flows should liquids threaten to damage those components.
- Remove moisture and particulates from gases while allowing oils to pass for lubrication purposes.
- Absorb liquids, filter particulates, and deliver those liquids in a controlled fashion
- Filter fluids and add antimicrobial protection.
- Serve as a barrier vent while permitting ion exchange.
- Filter contaminants while allowing high liquid or gas flows.
- Vent gases capture particulates and protect from ingress of liquids.
Partner with Polystar to develop functionally targeted, precision, custom components that meet your specific performance requirements.
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Chemical Compatibility Chart
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Contact us today and we’ll collaborate to determine which materials are best suited to meet your specific needs.