Unravelling Polymers

The Definitive Blog on Polymers by Poly Fluoro Ltd.

A Comparison of High-Performance Polymers

With new developments being constantly introduced in the polymer space, exciting new products are always entering the market. However, as the scale remains low, most new plastics remain prohibitively expensive but for the niche applications for which they may have been created. Through all this, the erstwhile stalwarts - PTFE and PEEK - have retained much of their effectiveness as increased scale and breath of application has allowed them to become more cost-effective and compete with existing medium-performance polymers on high-volume parts.

Apart from PTFE and PEEK, it is also important to look at FEP and PFA. Both these polymer variants were an offshoot of PTFE. Indeed, few realise that the trade name “Teflon”, which is used so interchangeably with PTFE does in fact cover PFA and FEP as well.

The reason for developing PFA and FEP was quite simple: PTFE has a very low melt flow and hence cannot be injection moulded. This limitation makes PTFE a material that can only be machined, which in turn makes complex parts and high-volume parts a difficult prospect when using PTFE. FEP and PFA both have lower melting points and have melt flows which allow for injection moulding. However, it is important to note that in this trade-off, both polymers surrender various properties, making PTFE the superior material in terms of absolute performance and versatility.

The below table offers some key comparisons between these four polymers, in order to offer an understanding of each one’s advantages, disadvantages, and applications.

 

Name of the Polymer   POLYETHER -ETHERKETONE POLYTETRAFLUOROETHYLENE POLYTETRAFLUOROETHYLENE GF 25 % PERFLUOROALKOXY ETHYLENE PERFLUOROALKOXY ETHYLENE GF 20 % FLUORINATED ETHYLENE - PROPYLENE FLUORINATED ETHYLENE - PROPYLENE 20 % GF
Trade name/ Typical name   PEEK PTFE PTFE 25 % GF PFA PFA 20 % GF FEP FEP20 % GF
Type of the Polymer   Thermoplastic Thermoplastic-Thermoset Thermoplastic Thermoplastic Thermoplastic Thermoplastic Thermoplastic
Advantages   PEEK is a high performance thermoplastic with the characteristics common to this group - strong, stiff, hard, high temperature resistance, good chemical resistance , inherently low flammability and smoke emission. It is pale amber in colour and usually semi-crystalline and opaque, except thin films are usually amorphous and transparent. It also has very good resistance to wear, dynamic fatigue and radiation Outstanding chemical resistance. Low coefficient of friction. High continuous use temp. 180 Cº . Very high Oxygen index. Higher modulus and surface hardness than PTFE. Improved creep resistance, dimensional stability and wear compared with PTFE. Melt processable, has similar chemical resistance to PTFE combined with the highest temperature resistance of melt processable fluoro plastics. Self-extinguishing. Retains room temperature stiffness and strength at elevated temperatures better than FEP. Excellent toughness. Significant increase in HDT and moderate increase in tensile strength compared with unmodified grades of PFA. Very high impact strength. Excellent high frequency electrical properties. Melt processable. Good weathering resistance. Significantly increased tensile strength, HDT and flexural modulus compared with unmodified grades of FEP. The mechanical properties of moulded components can be anisotropic.
Disadvantages   It is difficult to process and very expensive. Low strength and stiffness. Cannot be melt processed. Poor radiation resistance. Lower impact strength, lower tensile strength and more expensive than unmodified PTFE. Stiffness and strength similar to those of PTFE at room temperature. More expensive than PTFE. Decreased elongation at break and notched izod impact strength compared with unmodified grades of PFA. Very expensive, with the lowest strength and stiffness of all the fluoro plastics. Low HDT at c 50°C ( 120°F ) accompanied by poor wear resistance. Elongation at break and notched izod impact strength are reduced compared with unmodified FEP. The mechanical properties of moulded components can be anisotropic.
Applications   Applications include flexible printed circuit boards (film), fibres and monofilaments, injection moulded engineering components and items used in aerospace and radiation environments. Filled grades, including ones designed for bearing-type applications, are also used. Bearings, Chemical vessels linings, pipe and valve linings, gaskets, diapharms, piston rings, high temp. electrical insulation. As a coating of non stick applications. Wear pads, piston rings, and microwave oven rotating platforms. Heater cables, chemically resistant linings for pumps and pipes etc. that require a higher temperature resistance. Chemical plants. Coatings, protective linings, chemical apparatus, wire coverings, glazing film for solar panels. Valves, electrical components and equipment for chemical plants.
PROPERTIES UNIT              
Density g/cm³ 1.26 - 1.32 2.15 2.25 1.6 2.2400000000000002 2.1 2.2000000000000002
Surface Hardness RR M 99 [Rockwell] SD 63 SD72 SD60 SD 68 RR45 RR65
Tensile Strength Mpa 70-100 25 17 29 33 14 40
Flexural Modulus Gpa   0.7 1 0.7 0.7 0.6 5.5
Notched Izod Imapact strength kJ/m 0.85 0.16 0.12 A.06+ 0.7 1.06+ 0.2
Linear Expansion /Cº x 10?5   15 12 21 13.5 5 5
Elongation at Break % 50 400 250 300 4 150 2.5
Strain at Yield %   70 N/Y 85 N/Y 6 N/A
Max. Operating Temp. 250 180 180 170 170 150 150
Water Absorption % 0.1 - 0.3 0.01 0.01 0.03 0.04 0.01 0.01
Oxygen Index % 35 95 95 95 95 95 95
Flammability UL94 V 0 @ 1.5 mm V0 V0 V0 V0 V0 V0
Volume Resistivity log ohm.cm 10¹5-10¹7 18 15 18 18 18 14
Dielectric Strength MV/m 19 @ 50 ?m 45 40 45 40 50 13
Dissipation Factor 1kHz 2.9999999999999997E-4 1E-4 3.0000000000000001E-3 2.0000000000000001E-4 1E-3 2.0000000000000001E-4 5.0000000000000001E-4
Dielectric Constant 1kHz 3.2-3.3 @ 50Hz-10Khz 2.1 2.8 2.1 2.9 2.1 2.5
HDT @ 0.45 Mpa › 260 121 125 74 160 70 260
HDT @ 1.80 Mpa 160 54 110 30 150 50 158
Material Drying hours @ Cº 4-6 HOURS @ 200° NA NA NI NA NA NA
Melting Temp. Range 360-420 NA NA 360-420 360-420 340-360 350-380
Mould Shrinkage % 0.8 - 1.5 NA NA 4 0.8 2.5 0.4
Mould Temp. Range 175 - 200 NA NA 50-250 50-250 50-200 50-200

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