Unravelling Polymers

The Definitive Blog on Polymers by Poly Fluoro Ltd.

Expanded PTFE (ePTFE) Joint Sealant - A miracle product with varied applications

Starting in 2015, Poly Fluoro Ltd. will be among the few companies globally, with the capability to manufacture expanded PTFE (ePTFE).

While the uses of ePTFE are numerous, it falls upon a select few manufacturers to produce this material. As we have covered in an earlier article, the production of ePTFE is as diverse as its applications. Some of the variants that exist include:

  1. Mono-axially stretched ePTFE tape
  2. Bi-axially stretched ePTFE tape and sheet
  3. ePTFE membranes
  4. ePTFE tubes and rods
  5. ePTFE gland packing

Each of these products comes with unique production methods and specific nuances. However, the most commonly used variant at this point is the mono-axially stretched ePTFE tape.

ePTFE tape – also referred to as PTFE joint sealant or PTFE Gasket Tape, is widely used for creating a sealing joint between pipes and other mating metal parts. Specifically, as a chemically inert material, this tape finds application in chemical plants, biotech plants, and oil and gas pipelines. In fact, any pipe-lining application, where two pipes are connected using flanges, would benefit from using ePTFE tape, as the pliable nature of the material ensures that no gaps are left unfilled.

The tape has a soft texture and is easily compressed. Typically, the compression set of the tape is one of the parameters that define the material. The tape needs to be soft enough to compress under minimal load and ensure that it decompresses just enough to guarantee a complete sealing. At the same time, the tape needs to have adequate tensile and compressive strengths to allow for heavy loads to work upon it, without fatigue. In addition to its excellent chemical resistance, ePTFE tape also has a high temperature resistance, which allows it to be employed in applications involving a high temperature fluid transfer.

ePTFE tape comes in 2 variants: adhesive and non-adhesive. The application of the adhesive is not highly complicated, but for on-site convenience, it is preferred as else the installation of the tape is difficult.

The application of the tape is very simple. As the visual below shows, the tape is laid along the flange and allowed to overlap at the ends. The soft texture of the tape means that at the point of overlap, the tape does not bulge once compressed, by simply compressed further to make a uniform seal.

ePTFE joint sealant tape is among the most sought after materials for all sealing applications.

Visit our website for more details

PTFE Tubing: Process Parameters And Their Impact

PTFE Tube extrusion is among the most difficult processes within the polymer space. All polymers have their peculiarities and these certainly play a part in both their processing and machining. But PTFE tube comes with a set of so many different process parameters, that finding a combination that works consistently is something that not every tube manufacturer is able to discover. We have undertaken so many trials on tubes, each time assuming that we have looked into all the aspect. However, even after years of manufacturing, a new parameter may present itself that had hitherto gone unnoticed.

We would like to take a look at some of these parameters and their effect on the end-product:

  1. Handling: Handling resin is among the most easily overlooked aspects of PTFE processing. While many resin manufacturers specifically layout guidelines for limiting the shear on the resin before processing, these become even more important where tubing is concerned. Due to the structure of PTFE tubing, the fibrils that form during extrusion are paramount to the strength of the final tubing. Excessive shearing of the resin before extrusion can cause a poor formation of fibrils and seriously hinder the achievement of good final properties
  2. Blending: The parameters within blending include the type of extrusion aid used (the surface tension of the aid needs to be less than that of PTFE, while also not having a volatility and/or flash point that can cause fires during sintering), the amount of extrusion aid used, the RPM of the blending process and the post blending storage of the fine power mixture. Since our unit is in India, we need to follow a slightly different process to that in colder countries. For starters, we need to artificially cool the resin to allow of a more easy mixture of the PTFE with the extrusion aid. Such nuances are only learnt through extensive trial and error. But unless the blending is done in the correct manner, the final extrudate will be either too soft or too dry. Furthermore, unless the blend is uniform, the preform billet will have uneven densities, causing issues during extrusion.
  3. Preforming: Preforming is done purely as a means to create a shape that can be fitted into the extruder. Preforming has two functions: first, it gives shape and second, it removes any air pockets from within the material. The process needs to be done keeping in mind that too little pressure will not allow for an adequate venting of the air within the material. Air pockets result in bursts during the extrusion, which damage the tubing and render it unusable. Too much pressure and the extrusion aid may get squeezed out of the preform, causing the extrudate to be too dry and increasing the extrusion pressure required to form the tube.
  4. Extrusion: While extrusion is understandably the most important step, by the time the preform billet is loaded into the extruder, the preceding processes have already defined a lot of the tube’s final characteristics. Nonetheless, extrusion offers the tube it’s the final shape and this process needs to maintain both adequate pressures on the billet while ensuring the concentricity of the final tube. If the pressure is too high or too low, the tube will experience either too much shear, or too little pressure to form a proper end-product respectively. Concentricity is dependent not only on the tooling within the extruder (which needs to be precise and offer the correct extrusion angles depending on the size of the tube being drawn) but also on the uniformity of the billet’s density (discussed above). Finally, the extruder itself needs to be capable of offering a uniform load, so as to ensure the billet is under constant and non-erratic pressure throughout the extrusion run.
  5. SinteringWhen heating the tube, the temperature needs to account for both a drying section as well as a sintering section. The drying section needs to be warm enough to evaporate all traces of vapour from the tube. At the same time, if it is too warm, there is a risk of the vapours igniting. Sintering needs to account for the fact that if the tube is heated too quickly, there is a chance of over-sintering. Also, although PTFE does not melt, it may under its own weight, elongate during sintering, causing dimensional deviations. Therefore the temperature has to be sent to ensure that the PTFE reaches its ‘gel state’ just before it leaves the sintering chamber, so it can cool down at room temperature.

Aside from the above-mentioned parameters, PTFE tube also undergoes pigmentation, the addition of anti-static fillers and extrusion of specific profiles. Each of these needs to re-look at all of the above processes and understand how they need to be modified to allow for a proper end-result.

Kynar - The universal polymer

Among fluoropolymers, there are few with the processing versatility as Kynar (PVDF). Kynar – or polyvinylidene fluoride – is particularly useful because it lends itself to numerous applications while also allowing itself to be processed in a number of different methods.

While PTFE shares – and possibly exceeds – the range of Kynar when it comes to multiple applications, the fact that PTFE cannot be melt processed means there are limitations in part shape and design. It is here that Kynar comes out ahead.

Product Properties

Kynar (PVDF) offers the user the option to combine rigid and flexible materials when processing. As a material of construction for pumps and pipes, it exhibits excellent resistance to abrasion. Kynar (PVDF) can also be manufactured in thin, flexible and transparent sections such as films, filament, and tubing. Unlike many polymers (including PTFE) the material is unaffected by sunlight and can therefore be used in an exposed condition outdoors without the risk of degradation.

Strength and toughness

Kynar (PVDF) is inherently strong and tough as reflected by its tensile properties and impact strength. An ambient temperature tensile strength at yield of 35-55 MPa and an un-notched impact strength of 800-4270 kJ/m offered by select resins emphasize this. These characteristics are retained over a wide range of temperatures.

Creep properties

Compared to many thermoplastics, Kynar (PVDF) has excellent resistance to tensile creep and fatigue. The long-term resistance of Kynar (PVDF) to flexural creep at elevated temperatures is significant. Kynar (PVDF) is suitable for many applications in which load bearing characteristics are important. Likewise, the short-term flexural creep resistance of the material reflects superior load bearing performance.

Kynar (PVDF) is rigid and resistant to creep under mechanical stress and load.

It is able to maintain a low tensile creep when subjected to constant stress. For example, when Kynar (PVDF) is subjected to a stress of 0.69 MPa (100 psi), the resin is able to maintain outstanding resistance even at temperatures as high as 140°C.

Temperature resistance

Kynar (PVDF) exhibits high thermal stability. Prolonged exposure at 250°C in air does not lead to weight loss. No oxidative or thermal degradation has been detected during continuous exposure to 150°C for a period of ten years.

In general, Kynar (PVDF) is one of the easiest fluoropolymers to process. The resins can be recycled up to three times without detriment to their mechanical properties because Kynar (PVDF) is inherently thermally stable and does not contain additives. Similar to most thermoplastics, Kynar (PVDF) resins discolour and degrade during processing if the processing temperature is too high, the residence time is too long, or the shear rate is too high.

Electrical properties

Kynar (PVDF) exhibits a combination of high dielectric strength and excellent mechanical properties over a broad temperature range. This has led Kynar (PVDF) to be used for thin-wall primary insulation and as a jacket for industrial control wiring. Kynar (PVDF) has a high dissipation factor that lends an advantage as a material for parts requiring dielectric high heating strengths such as impedance welding. With proper shielding, Kynar (PVDF) can be used as jacketing for high frequency data cables because of its excellent flame and smoke performance.

Chemical resistance

Kynar (PVDF) is chemically resistant to a wide range of chemicals. Most acids and acid mixtures, weak bases, halogens, halogenated solvents, hydrocarbons, alcohols, salts and oxidants pose little problem for Kynar (PVDF).

Many factors can affect a material’s chemical resistance. These include, but are not limited to, exposure time, chemical concentration, extreme temperature and pressure, frequency of temperature and pressure cycling, attrition due to abrasive particles, and the type of mechanical stress imposed. The fact that certain combinations of chemical exposure and mechanical load can induce stress cracking in many otherwise chemically resistant materials, both metallic and non-metallic, is of particular significance. In general, the broad molecular weight distribution of Kynar (PVDF) results in greater resistance to stress cracking.

Factors such as permeability and adhesion affect the chemical resistance of Kynar (PVDF) coatings. Consequently, coatings may not exhibit exactly the same properties as melt-processed resins. Maximum use temperature for dispersion-applied or powder coatings should not exceed 100°C (212°F).

However, assuming chemical resistance is still adequate, laminated systems can be used from 120°- 135°C (248°- 275°F).

Operating parameters are dependent on the particular application of Kynar (PVDF) and differ from those experienced in either laboratory testing or apparently similar field service. Because corrosive fluids or vapours are often mixtures of various individual chemicals, it is strongly recommended that trial installations be evaluated under actual service conditions. For example, immersion testing of Kynar (PVDF) in individual chemicals at a specific operating temperature, will not necessarily predict the performance of fabricated components when they are exposed to an exothermic reaction between the individual chemicals.

The chemical resistance of Kynar (PVDF) is indicated in the chart below. In this chart, the behaviour of Kynar (PVDF) at 93°C (200°F) in contact with nine general chemical species is compared with that of other well-known plastics. The rating system ranges from unacceptable severe attack in the outer segment of the circle to excellent (inert) in the bull’s-eye.

Environmental properties

Kynar (PVDF) films up to 0.125 mm thick are translucent to transparent.

The material shows excellent resistance to UV and film thicknesses above 0.5mm have been shown to completely block UV rays of wavelengths less than 250 Nm.

Many years of outdoor exposure in direct sunlight have little effect on the physical properties of Kynar (PVDF). However, some increases in tensile strength and reduction in elongation do occur over time.

Ozone is a powerful oxidizing agent characterized by a high degree of chemical instability. Kynar (PVDF) offers excellent chemical resistance to ozone exposure.

Kynar (PVDF) is also highly resistant to fungi and does not support the growth of the same.

Resistance to nuclear radiation

The resistance of Kynar (PVDF) to nuclear radiation is excellent. The original tensile strength of the resin is essentially unchanged after exposure to 100 megarads (Mrads) of gamma radiation from a Cobalt-60 source at 50°C (122°F) and in high vacuum (10 -6 torr). The impact strength and elongation are slightly reduced due to cross-linking.

This stability to effects of radiation, combined with chemical resistance, has resulted in the successful use of Kynar (PVDF) components in nuclear reclamation plants.

Processing methods


Smooth Kynar (PVDF) products of all types can be extruded at high rates without extrusion aids, lubricants or heat stabilisers. Resins can be processed on standard equipment with materials of construction similar to those used to process PVC or polypropylene. Drying of Kynar (PVDF) is usually not required; however, it has been shown to reduce some surface blemishes in film, sheet and pipe extrusion.

The extrusion process lends itself to the production of rods, tubes, pipes and profiles.

Injection moulding

Kynar (PVDF) can be injection moulded to produce more intricate parts than can be achieved via machining.

Standard injection moulding equipment and tooling can be used to process Kynar (PVDF) resin. No specialty materials of construction are required, but chrome or nickel plating of polymer contact surfaces is recommended to prevent pitting.



Kynar (PVDF) components are used extensively in:

  • high purity semiconductor market
  • pulp and paper industry
  • nuclear waste processing
  • the general chemical processing industry
  • water treatment membranes

Kynar (PVDF) finds preference as a pipe lining and tank lining material in plants handling corrosive chemicals.

Kynar (PVDF) also meets specifications for food and pharmaceutical processing industries.


Kynar (PVDF) closed cell foams are available in sheets or rolls. Kynar (PVDF) foams are of very high purity, very low flammability and are UV and corrosion resistant.


Kynar (PVDF) film can be used for applications requiring long-term protection. The film is produced by monolayer or multilayer technology as thin, thick, wide or narrow (from 10 to 175 μm), allowing great freedom of design. The commercial range includes both mass-tinted and transparent films, which can be printed with a variety of designs. Film can be laminated onto thermoplastic, thermoset and coated metal supports


Kynar (PVDF) has gained success in the battery industry as binders for cathodes and anodes in lithium-ion technology, and as battery separators in lithium-ion polymer technology.


Kynar (PVDF) resin is a respected membrane material for applications ranging from bioprocess separations to water purification because it is extremely chemically resistant and thus well suited to aggressive chemical environments.

Kynar (PVDF) has a high temperature resistance, which makes it appropriate for applications that require high temperature cleaning. It tolerates ozone (an oxidant increasingly used for water purification) very well, compared to less robust polymer materials.

It is also a high purity resin with FDA and NSF listings, making it compatible with direct food/beverage contact applications.


Select grades of Kynar (PVDF) resin easily achieve the flame spread/smoke developed rating of 25/50 when tested in accordance with ASTM E 84. This enables Kynar (PVDF) pipe to be used in the plenum for applications such as corrosive waste drainage and laboratory chemical systems.