The chemical structure of fluoropolymers (also called fluoroplastics) primarily consists of carbon and fluorine. The particular combination of these two chemical elements arranged along the molecular chain imparts a unique set of properties to these types of carbon - fluorine based polymers.
The commercially available fluoropolymers are as follows: PTFE (Poly tetra-fluoro ethylene) - is a fully fluorinated polymer available in various unmodified and modified grades. Methods of forming products include paste extrusion, ram extrusion, moulding and calendaring between rolls. Many formed PTFE products are consolidated by sintering in an oven or used in unsintered form ( eg: thread sealant tape). Paste extrusion and calendaring methods are used with fine powder PTFE resins while granular PTFE resins are processed by ram extrusion and moulding. Unlike PTFE, all of the following polymers are melt processable. FEP (Fluorinated ethylene propylene) - is a fully fluorinated copolymer. PFA, MFA - Perfluoroalkoxy, fully fluorinated copolymers. ETFE - Ethylene tetra-fluoro ethylene, partially fluorinated polymer containing hydrogen. ETFE has the ability to withstand exposure to high temperature withour rapid embrittlement. ECTFE - Ethylene chloro tri-fluoro ethylene, a copolymer of ethylene and chlorotrifluoroethylene. PCTFE - Poly chloro tri-fluoro ethylene, copolymer containing chlorine. PVDF - Poly vinyledene fluoride, partially fluorinated polymer containing carbon to carbon double bond (which is weaker than single bonds of fully fluorinated polymers).
PTFE, FEP, PFA - INOFLON TM, Teflon®, Neoflon®, Hyflon® MFA - Hyflon® ETFE - Tefzel®, Neoflon® ECTFE - Halar® PCTFE (or CTFE) - Neoflon® (originally Kel-F®) PVDF - Solef®, Hylar®, Kynar® INOFLONTM is a trademark of Gujarat Fluorochemicals Limited. ALGOFLON®, is a registered trademark of Ausimont ,USA, Ltd. Fluon®, is a trade mark of AGF Ltd. Dyneon®, is a registered trade mark of Dyneon. Polyflon® is a registered trademark of Daikin Industries Ltd. Teflon®, Tefzel® are the trademarks of E.I. DuPont de Nemours Company Neoflon®, Polyfon® are the trademarks of Daikin America Inc. Hyflon®, Halar®, Hylar® are the trademarks of Solvay Solexis, Inc. Kynar® is the trademark of Elf Atochem North America, Inc. Kel-F® was the trademark of 3M Company ( this trade name is now discontinued)
In general, the chemical resistance of these materials are superior to most other families of plastics. This "chemically inert" characteristic is closely allied to their superior performance in ultra pure environments. The chemical inertness varies between the fluoropolymers. The fully fluorinated resins such as PTFE, FEP, PFA and MFA exhibit chemical inertness to a wider range of chemicals than do the partially fluorinated polymers such as CTFE (or PCTFE) and ECTFE. A better property in one or two areas is accompanied by a diminished property in others (for example PTFE properties is better than PVDF in chemical resistance but it has lower mechanical properties at normal ambient temperatures. Fully fluorinated polymers (Perfluoropolymers) such as PTFE, FEP and PFA offer better thermal (higher use temperature) and chemical resistance properties than their partially fluorinated counterparts like ECTFE or PCTFE. However, partially fluorinated resins posses better mechanical properties, such as tensile strength, toughness, abrasion and cut-through resistance at ambient temperatures. The flex modulus of PVDF tubing is considerably higher than PTFE (relatively most flexible), FEP, PFA or MFA. This makes PVDF tubing considerably more rigid than the other materials; however it has higher tensile strength at ambient temperatures.
The selection of a resin for a specific use is based on criteria for that application; for example permeability at the use temperature may be a critical requirement and may override other features such as chemical resistance and tensile strength. In each case the choice of material is made by comparing the key property requirements and, of course, cost. The chemical resistance properties of PTFE are so broad that its use is not only restricted to a limited list of chemicals. PTFE is generally acceptable for a wide variety of industrial and commercial applications. Due to lack of additives and extreme chemical inertness these materials also qualify for ultrapure applications, such as using deionized (DI) water in the semiconductor, biological and pharmaceutical industries.
In general, it is safer to assume that fabrication procedures affect some properties of PTFE, FEP and PFA products. Certain physical properties such as tensile strength, permeability and dielectric strength vary with fabrication conditions. Examples of causes of these may be macroscopic flaws, microporosity (for PTFE properties) and crystallinity. The extent of the variation depends upon the specific conditions of fabrication. Properties of PTFE, FEP and PFA that are relatively unaffected are as follows: Chemical resistance. Long-term weathering. Non-stick. Non-flammability Low dielectric constant and low dissipation factor. High arc resistance, surface and volume resistivities. Flexibility at low temperatures and thermal stability at high temperatures. Low coefficient of friction.
In addition to PTFE, FEP and PFA tubing, there are other fluoropolymers such as THV, ETFE, ECTFE, CTFE, and PVDF tubing. Although these materials are members of the same family, they have slightly different thermal and mechanical properties. PTFE and PFA tubing have a slightly higher upper use temperature than FEP tubing. FEP and PFA are clear (PTFE is translucent), and have better mechanical properties than PTFE. The other key differences are in the areas of chemical inertness, corrosion resistance, permeability, and FDA approval.
PTFE stands for PolyTetraFluoroEthylene, which is the chemical term for the polymer (CF2)n. INOFLONTM is a registered trademark of Gujarat Fluorochemicals Ltd.(GFL) and is used in relation to products manufactured with GFL's fluoropolymer products. Other manufacturers of PTFE resins and their trademarks are: TEFLON ® is a registered trademark of Dupont. FLUON ® is a registered trademark of AGF Ltd. DYNEON ® is a registered trademark of Dyneon. POLYFLON ® is a registered trademark of Daikin Industries, Ltd. ALGOFLON ® is a registered trademark of Ausimont USA, Ltd. What are Fillers? Practically any material that can withstand the sintering temperature of PTFE can be used as filler. Characteristics such as particle shape and size, and the chemical composition of the filler greatly affect the properties of the compound. All fillers used in PTFE compounds have been carefully selected and were in several cases specially developed to give the best balance of properties. The following paragraphs discuss the main features of the most commonly used fillers. GLASS Glass fibre is the most widely used filler. It improves the creep resistance of PTFE, both at low and high temperature. It is chemically stable (except to strong alkalis and hydrofluoric acid - HF).It has little effect on the electrical properties of PTFE, and improves its wear and friction behavior. A not uncommon problem with glass-filled PTFE is discoloration of the finished parts, in particular on the inside of large billets. The glass used in PTFE compounds has been treated by a proprietary process to reduce this discoloration. GLASS Type : E-glass Milled fibres nominal diameter : 13 um Nominal length : 0.8 mm Aspect ratio : min. 10 Density : 2.5 CARBON Amorphous carbon is one of the most inert fillers, except in oxidizing environments where glass performs better. Carbon adds to the creep resistance, increases the hardness and raises the thermal conductivity of PTFE. Carbon filled compounds have excellent wear properties, in particular when combined with graphite. The combination of the above properties makes carbon/graphite compounds the preferred material for non-lubricated piston rings. The use of softer carbon has the additional advantage that it lowers tool wear during machining, thus allowing machining to very close tolerances. Carbon-containing compounds have some electrical conductivity and are therefore antistatic. CARBON Base : Amorphous petroleum-coke Purity : > 99% C Particle size : 99% C Particle size : 99% C Irregular shaped Particle size : < 75 um Density : 2.26 BRONZE Bronze is an alloy of copper and tin. Addition of high percentages of bronze powder to PTFE results in a compound having high thermal conductivity and better creep resistance than most other compounds. Bronze-filled PTFE is often used for components in hydraulic systems, but is not suited for electrical applications and is attacked by certain chemicals. Bronze has a tendency to oxidize: bronze-filled compounds should therefore be used fresh and containers should always be kept closed. Some discoloration of the finished part during the sintering cycle is normal and has no impact on its quality. BRONZE Cu / Sn : 9 / l Low in phosphorus Particle size : 98% Particle size : < 65 um Density : 4.9 ALUMINA (A1203) Alumina or aluminium oxide is an excellent electrical insulator and is used to improve mechanical properties of compounds used in high voltage applications. As it is very hard, machining of the sintered part should be avoided whenever possible. Complicated shapes should be made by isostatic moulding. CALCIUM FLUORIDE (CaF2) Calcium fluoride is a suitable filter for PTFE in uses where it comes in contact with chemicals that attack glass, such as hydrofluoric acid and strong alkalis. High purity grades of CaF2are also used in electrical applications. POLYMERS In recent years, polymeric fillers with sufficient heat stability to be used in PTFE have become available. Some remarkable properties have been obtained with polymer filled compounds, particularly with respect to friction against soft metal. MICA Mica is a mineral with a plate like structure. During processing, the particles orient themselves perpendicular to the pressing direction. This results in very low shrinkage and low thermal expansion in the cross direction. Tensile properties are poor, so that mica- filled compounds are only suitable for parts under compressive stress. PIGMENTS It is possible to pigment PTFE, using inorganic pigments that withstand the sintering temperature of PTFE. Pigments do not significantly change the properties of PTFE. Combinations of pigments and other fillers can be used.
Yes, however, you must first acid-etch the material.
PTFE can stick to another surface by using a chemical process called etching on one side or two sides. The etching is brown in color and when an epoxy is applied to the etched side it will adhere to another surface.
Etched one side is material prepared for gluing. Pressure sensitive tape is etched material with an adhesive backing paper.
Basically PTFE is nonstick material & adhesion of PTFE to other substrate materials is technically not possible. So when bonding is required as special chemical treatment, (generally sodium etching) must be used to change the molecular structure of surface of PTFE. The chemical treatment generally used sodium etching, facilitates change in structural arrangement of carbon & Fluorine atoms on PTFE surface & removal of some fluorine atoms from the surface leaving a carbonaceous backbone responsible for adhesion. The surface of etched PTFE is light brown to dark brown. As this is only surface treatment, the inherent properties of PTFE remain unchanged. The general purpose ARALDITE can be used for & as gluing agent for bonding. The etched PTFE surface is light sensitive & undergo ageing & should be protected from light, or should be used as soon as possible after treatment. The UV/daylight exposure will fade away etching colour gradually by destroying carboneous layer & reduce bonding ability. Hence PTFE etched components should be stored for long time prior to bonding - be covered wrapped in black opaque plastics film & kept in dry plastic container wrapped in away from day light / sunlight / UV light.
Virgin PTFE has better physical properties and is a good electrical insulator. Virgin PTFE is FDA approved. Reprocessed PTFE is recycled PTFE processed into skived sheet and extruded rod. Both Virgin and reprocessed PTFE are 100% PTFE.
PTFE materials are essentially chemically inert. They are affected only by molten alkali metals, fluorine and chlorine trifluoride at elevated temperatures and pressures.
The maximum service temperature is 500°F (260°C) .
Continuous working temperature recommended for PTFE is 150-200°C. though it can be used as intermittently up to 250°C. After 250°C up to 350°C it does not decompose but it starts loosing its shape and does not remain at place. However the continuous working temperature drops down as the pressure increases.
25% Glass fill increases wear resistance. Increase lubricity? Carbon and graphite exhibit good rubbing or sliding characteristics on contact. What fill offers better creep resistance? Bronze fill has better wear and creep resistance than glass fill.
In fact there is no melting point for PTFE. It really does not melt. It gets soften at 327°C and then directly decomposition is commenced at 400°C plus and the C - F bond starts fracturing and material becomes non reusable.
The pressure rating is a calculated value, using basic mechanical engineering formulas and the tensile or hoop strength. The pressure rating is dependent upon temperature of use. As with any tubing, the pressure rating falls with rising temperature. The smaller the tube size, the higher the pressure capability.
PTFE Bellows can used at 3.5 kg / cm2 at room temperature directly and upto 7.5 kg / cm2 at room temperature with sleeves inside the bellows. Pressure sustaining capacity of PTFE bellows can be further increased by inserting spring steel ring the groove of bellows or further increased by S. S. brading to rate the bellows at 25 to 50 kg /cm2 at room temperature. The increase in temperature considerably drops the rating. PTFE bellows can be fabricated for sustaining more pressure, However its flexibility is inversely affected. PTFE Bellows can be used for vacuum applications with or without sleeves.
Polyethylene is low cost similar material having good chemical resistance, better mechanical properties, slightly inferior electrical properties and poor thermal properties.
Mechanically : No Chemically : Yes Electrically : Yes Thermally : Yes, as compared to other plastics.
PTFE can be directly moulded to intricate shapes by a process known as isostatic moulding. However, the machinery required for processing is costly and high capital cost is involved. This process also demands high quantity to economically viable project. However most of processors use compression moulding , sintering, machining process to manufacture the product where intricate shapes are inforced by final machining. In this low scale quantity is possible to manufacture, however wastage in machining is very high.
PTFE bellows can have the flexibility of around maximum 25% in axial direction & lateral movement of 250 is attainable. The bellows can be designed & fabricated for more flexibility, however their pressure sustaining capacity is adversely affected & there is risk of rupture due to sudden increase in pressure, temperature, vibrations & shocks in the service & hence it is not recommended.
Very Very minute circumferential lines at intervals of 5 to 10 mm are stroke lengths and not defects. However if deep these become weaknesses. The minute lines can be removed by centre less grinding for better appearance.
Shrinkage of PTFE Components during coarse of period is very common problem. It is result of release of thermal stresses and can be minimised by ultra slow sintering-annealing cycle in down mode. However total removal is not possible.
Taking the factor of safety - 2, it should be @ half of max compressive strength of that grade. E.g. 25 % Glass filled PTFE Compressive Strength @ 60 Kg/cm2 Maximum Design Pressure @ 30 Kg/cm2
25 % Carbon filled PTFE Piston Rings for lubricated / dry running Air Compressors can be used up to 350 - 400 Kg/cm2 pressure and piston velocity 300 m/min.
Filled PTFE Valve seats can be used for valves working up to 50 Kg/cm2 at ambient temperature. V-Ring Packages in filled variety can be used even up to 1000 Kg/cm2 at ambient temperature. PTFE Hoses with helical S.S. Brading can be used for pressure as high as 200 Kg/cm2 at ambient temperature. However this pressure sustaining capacity drops very fast as the working temperature increases.
The welding of conventional PTFE is possible, however the bond strength is weak & joint can not be guaranteed for leakage or service. However chemically modified PTFE can be welded into bond strength as good as base material.
For higher temperature (more than 200) for seats/seals of values, Pure graphite or metal seats can be used.
Nexgen Fluoropolymer does not manufacturer the parts of expanded PTFE. The expanded PTFE is low density PTFE having pores, sponge like flexibility. It is used as Gasketing / Sealing material. Due to it's sponginess, it fills in rough surface of substrate and you get the leak proof joints even at low torque tightening of bolts.
As most of the fillers like Glass / Carbon / Bronze etc have decomposition temperature more than PTFE, Filler content can be measured by decomposition of pre weighed sample at temperature more than 450 & then weighing the residue i.e. filler.
The density of PTFE component can be calculated by simple lit/volume method & if the density is in between the mid of range, the quality of material can be stated as standard. If PTFE component can be machined on conventional lathe & the swarf or cutting chip is continuous, having good tensile properties if stretched, the material can be stated as standard. If the chip is continuous & gets cut without any elongation when stretched, the PTFE material can be categorized as substandard. The surface finish of machined PTFE components, if glossy & shining, the material can be categorized as standard while the material having dull surface finish can be categorized as Non standard.
PTFE once polymerised during sintering, cannot be reused / regenerated / repolymerised. In some countries, PTFE scrap / waste / cutting chips are ground to the regular @ 300 microns size & used in 10 to 15 % as filler in PTFE to reduce the cost. The properties of such compound are inferior to virgin PTFE and fails.
Due to the release of Thermal & Mechanical stresses after peeling , the strips / sheets have warped / curved surfaces, If premium grade - fine powder 50 µ PTFE is used to manufacture this products - these defects can be prevented from occurring. However the cost can be around 25% extra. Also strips / sheets are hot calandered - there can be some improvement. PTFE strips / sheets when opened made flat - you will always find them bent. To avoid this - slitting of edges on slitting machine - is the only solution . However there is heavy cost increment due to labour cost as well as wastage
PTFE Products from Nexgen Fluoropolymers means: Consistent Standard Quality. Quality System. Complete range of Products under one roof. Huge Manufacturing Set-Up to Execute Bulk/Big Orders. Well Equipped Testing Laboratory. Facility of Non-Standard Product Development Work for Critical Applications. Guaranteed Technical Support. Trained Staff and Workmen Value for Money.
The quality of chemically treated PTFE shapes can be verified by following methods : a. Visual b. Peel off test (Type Test) c. Breakage Load test (Type Test) A. VISUAL: i) The surface color of etched PTFE should be light brown to dark brown. ii) The color should be uniform & there should not be any white patches. iii) There should not be any scratches/cuts on etched surface. B. Peel Off Test (Type Test) : etched PTFE strip of around 100 mm w x 300 mm L x 1.5 mm thick is to be glued to stainless steel plate . The glue generally ARALDITE to be applied to both etched PTFE surface & polished S.S. plate in longitudinal & transverse direction & fixed. The max pressure & @ 10 kg/cm2 is applied & curing temperature of 125°C is set. After curing & cooling upto Room temp, the edge of PTFE strip is removed by knife by armed 50 mm The pulling load / weight is applied from 2 kg. onwards - upto commencement of PEEL off from S.S. plate The value of load at peel off commencement should be minimum 2.5 kg/cm width. C. Breaking load test (Type Test) : The single lap joint of sodium etched PTFE strips of 25 x 25 mm2 is prepared after using ARALDITE as gluing agent. After curing, the load is applied from 2 kg. onwards on this joint & the breakage load is measured when the joint is apart. The values should be min 20 kg/cm- width.