The evolution of Polytetrafluoroethylene (PTFE) – more commonly known as Teflon® – from a niche product used only in high-value applications to a mainstream requirement has been very gradual.
However, over the past two decades PTFE usage seems to have crossed a critical mass, allowing it to become commercially viable in over 200 industrial, consumer and medical applications. And while sheets, rods, coatings and components corner the bulk of the market for PTFE products, PTFE tubing and PTFE hose are now emerging as the key growth area.
The use of PTFE tube has spread across various applications including automotive, chemical, electrical and medical. Table 1 shows the key properties which outline the versatility of PTFE tubing, while Fig 1 shows its uses in various fields.
Property
Comments
Applications
Heat resistance
Dielectric strength
Low friction
Corrosion resistance
Table 1: Key properties and applications of PTFE tubing
Depending on the application, PTFE tubing is divided into three broad categories – each defined by the tube’s diameter and the wall thickness (see Table 2).
Diameter (mm)
Wall thickness (mm)
Spaghetti tubing
0.2-8
0.1-0.5
Pressure hose
6-50
1-2
Pipe Liner
12-500
2-8
Table 2: Categories of PTFE tubing
Even within categories, PTFE tubing lends itself to different variations, each allowing for a different application (see Table 3):
Type
Description
Purpose
Multi-lumen
Single outer tube with multiple inner tubes
Each inner tube holds a different fluid/ wire - useful in medical applications
Split
Ridge on tube wall allowing it to be split longitudinally
Surgeon can remove a PTFE introducer from a patient while the primary device remains in place
Corrugated/ convoluted
Folds on outer wall
Gives higher bend-ability, reducing risk of kinks when tube is passed through tight angles
Heat shrinkable
Thin tubing which shrinks in diameter when hot air is applied to it
Used to sheath wires, glass tubes for insulation or protection
Filled
Chemical additive giving radiopaque properties
Used in medical inserts - to show up in X-rays
Table 3: Variants of PTFE tubing
In general, small diameter spaghetti tubing is used in medical applications. The use of PTFE in this area centers on two key properties: lubricity and biocompatibility. Fluoropolymers exhibit very good lubricity compared with other plastics. PTFE is the most lubricious polymer available, with a coefficient of friction of 0.1, followed by fluorinated ethylene propylene (FEP), with 0.2. These two polymers represent the vast majority of all fluoropolymer tubing used in medical devices.
The biocompatibility of any polymer used in a medical device is an obvious concern. PTFE excels in this area and has a long history of in vivo use. Medical-grade fluoropolymers should meet USP Class VI and ISO 10993 testing requirements. Of course, processing cleanliness is also an important factor.
The uniqueness of PTFE tubing rests in the complexity of PTFE as a polymer. While most polymers lend themselves easily to injection moulding – allowing them to be made into complex shapes, PTFE due to its high melting point and melt viscosity can only be compression moulded. The high melting point of PTFE also means that extrusion – as conventionally practiced – cannot be applied to it. PTFE paste extrusion has therefore become a process which is increasingly sought after – given the growing demand for PTFE tubing.
Extruded grades of PTFE were first used in the wire and cable industry in the 1950s, where the good dielectric properties of the material proved critical to the developing electronics market. The first tubing was made by extruding PTFE over a wire and then removing it-a labour-intensive process. In the 1960s, technology emerged that could perform the extrusion of PTFE without a wire core. This process enables PTFE tubing to be economically produced in long continuous lengths.
PTFE paste extrusion follows 6 broad steps as illustrated below:
Fig 1: Typical extrusion die
PTFE Tubing and Poly Fluoro Ltd. - FluoroTube™
Poly Fluoro Ltd. was established in 1985 – at a time when India was not yet fully aware of the properties of PTFE material or its usefulness across so many industries.
The company has built its expertise in mainly industrial applications – making machine components, slideway bearing materials (Turcite/Lubring) and PTFE tapes – and become a reputable player in the industry.
More recently, Poly Fluoro Ltd. has embarked on a plan to strengthen its presence in medical applications. With this in mind, the company has invested heavily in developing laboratory wares, PTFE coated guidewires (used extensively in urology) and PTFE tubing.
FluoroTube™ marks the entry of Poly Fluoro Ltd. into the PTFE tubing segment. With this product, Poly Fluoro is looking to build a tubing brand, which assures the client the highest quality of PTFE tubing.
FluoroTube™ will also be the first PTFE tubing manufactured in India – giving the local market
PTFE tubing at a price point that would greatly improve their cost dynamics and allow the full demand for PTFE tubing to be met in India.
The grades and sizes available make FluoroTube™ ideal for applications such as medical, chemical and automotives.
FluoroTube™ comes in sizes ranging from 1mm to 25mm diameters and is unique in many ways when compared to conventional polymer tubing. Table 3 shows the technical properties for FluoroTube™.
In the near future, Poly Fluoro will also be embarking on the manufacture of FEB Tubes and FEP hose. FEP belongs to the same family of PTFE, but being melt processable, the material can be drawn into longer tubes with far thinner wall thicknesses. The entry into FEP will again see Poly Fluoro as pioneers into a new area of fluoroplastics manufacturing.
Fig 2: FluoroTube™
Table 3 : Technical specifications of FluoroTube
Property ASTM test ValuePhysical properties
Specific gravity D792 2.15 Water absorption ( % ) D570 / 24 hrs 1/3" t < 0.00 Mold shrinkage ( cm / cm ) 0.02 – 0.05 Contact angle ( degree ) Angle to level 110Thermal properties
Thermal conductivity (cal/sec/cm2, o /cm )
C1776 x 10-4
Coefficient of liner thermal expansion(1/oC) D696 / 23 - 60oC 10 x 10-5 Melting point (oC ) 327Melt viscosity ( poise )
10^11–10^13
(340 -380oC)
Maximum temperature for continuous use (oC / oF) 260 / 500Mechanical properties
Tensile strength ( kgf / cm2 )D638 / 23oC
140 - 350 Elongation ( % ) D638 / 23oC 200 - 400 Compression strength ( kgf / cm2) D695 / 1 % deformation, 25oC 50 - 60 Tensile modulus ( kgf / cm2 ) D638 / 23oC 4,000 Flexural modulus ( kgf / cm2 ) D790 / 23oC 5,000 – 6,000 Impact strength ( ft - lb / in ) D256 / 23oC, Izod 3 Hardness (Shore) Durometer D50 - D65 Deformation under load ( % ) D621 / 100oC, 70 kgf / cm2, 24 hrs 5 D621 / 25oC, 140 kgf / cm2, 24 hrs 7 Static friction coefficient Coated - steel surface 0.02Electrical properties
Dielectric constant
D150 / 103Hz2.1
Dielectric dissipation factor D150 / 106 Hz 2.1 D150 / 103 Hz < 1 x 10-5 Dielectric break down strength (V / mil) D149 / Short time,1/ 8 in 480 Volume resistivity( ohm - cm ) D257 > 1018 Chemical resistance Excellent Weather ability Excellent Combustibility ( % ) D2863 / Oxygen concentration index > 95
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