The difference between PTFE and PCTFE is mainly in the chemical structure. The addition of one Chlorine atom in place of one Fluorine atom leads to a massive change in its properties and application.
PTFE is a versatile and cost effective material of average tensile strength. It has very good thermal properties and excellent chemical inertness, especially to strong acids. The coefficient of friction is unusually low and believed to be lower than any other solids. PTFE is an outstanding electrical insulator over a wide range of temperatures and frequency.
At the molecular level, PTFE is a linear polymer with high molecular weight (Length of Polymer Chains) and Crystallinity level of 50-70% depending on the processing conditions.
Due to its high viscosity, PTFE cannot be processed using conventional polymer processing techniques. Hence, PTFE is processed by cold forming operation followed by heat treatment (sintering) during which polymer particles fuse to form a solid moulding.
PCTFE has a higher tensile strength than PTFE and good thermal characteristics. It is non-flammable and heat resistant up to 180°C. PCTFE is resistant to the attack of most chemicals and oxidizing agents, due to the presence of high fluorine content. However, it swells slightly in halogenated compounds, ethers, esters and aromatic solvents.
PCTFE has one of the highest limiting oxygen index. It has good chemical resistance and also exhibits properties like zero moisture absorption and non-wetting.
PCTFE has a low coefficient of thermal expansion and its dimensional stability makes it attractive for use as a component of a structural part where the high temperature and chemical resistance of fluoropolymers is required.
PCTFE is melt processable by conventional process techniques such as Injection moulding, Extrusion and Compression moulding.
PCTFE is a homopolymer of chlorotrifluoroethylene (CTFE), whereas PTFE is a homopolymer of tetrafluoroethylene. PCTFE is a harder and stronger polymer, with better mechanical properties than PTFE. Though PCTFE has excellent chemical resistance, it is still less than that of PTFE. PCTFE has lower viscosity, higher tensile strength and creep resistance than PTFE.
Even though PTFE remains a niche polymer among more generic materials such as PP (Polypropylene), PVC, PE (Polyethylenes, such as HDPE and LDPE), and even Nylons, within the engineering space it is now quite common. Most applications involving high temperature, corrosive chemicals, high voltages, or high wear/friction now look to PTFE automatically as a solution.
Despite this, there do exist applications where PTFE does not fit the bill and a compromise must be made. For example, applications where high dimensional stability is needed across a wide temperature range, PTFE tends to fall short. The high linear thermal expansion coefficient of PTFE means that it cannot hold its dimensions as temperatures vary. In such a situation, we have seen PEEK being adopted. While PEEK does do the trick, it is also 10X the cost of PTFE.
Similarly, certain applications where cost is a constraint need to make do with POM (Delrin), or even PVC, where PTFE cannot be used. In such a scenario, we possibly forego some of PTFE’s key properties.
Over the years a variety of new polymers that have been developed to fill the performance and commercial gaps between PEEK and PTFE. These include PFA, FEP, PEK, PPS (Ryton), and PCTFE.
Although not well known, PCTFE forms an ideal substitute for PTFE in certain applications where PTFE is unable to perform adequately. The table below is meant to offer a snapshot comparison of the two, such that any application engineer can evaluate the key differences.
As you can see from the above chart, PCTFE and PTFE each have unique advantages and disadvantages when compared with one another. Like all polymers, the application needs to be properly understood and the commercials need to be weighed in before any decision can be made.
However, it is fair to say that when dimensional stability across a temperature range is a must, PCTFE is growing to become the most effective substitute for PTFE.