Tribological issues in engineering Teflon

Institute of Chemical Technology, Mumbai, Marathawada Campus, Jalna.

Teflon, scientifically known as polytetrafluoroethylene (PTFE), is one of the most versatile materials known to history of material science; this invention was done by the Dupont research team. It was an accidental invention made by the team working to find the coolant material; they ended up with a white slippery material- Teflon. The C-F bond is termed the strongest organic bond, making Teflon inert in various operating conditions such as thermal, mechanical, surface, and chemical. It shows almost negligible water absorbance due to its hydrophobic surface, making it durable. It is a carbon-based polymer due to the absence of charge carriers. i.e., electrons. Teflon is a bad conductor of electricity and heat. These properties can be regulated by adding conducting inorganic fillers.

Along with all these properties, Teflon blends and composites are famous for their outstanding tribological performance. Tribology is the branch of material science that deals with the study of the performance of a surface by calculating its coefficient of friction and wear loss. A wide range of Teflon-derived products based on their tribological properties, conveyor belts, chain lubes, cleaner kits for increasing the performance of automobiles, etc., are available in the market. The selection of appropriate material at the industrial level significantly affects the cost of operation positively. Industries appreciate polymeric material and their derived products as an alternative to other traditional materials such as metal and inorganic ceramics due to their durability and lighter weight. Though we have a long-range of polymeric materials available at the current date, we must choose wisely as per our requirements to get the most efficient output with the same process. One should select the most appropriate materials, and its periodic maintenance significantly impacts energy consumption and the cost-efficiency of the process. According to information from HMSO, 1966. Lubrication (Tribology) Education and Research, UK Department of Education and Science a quantitative analysis of savings is as shown in the figure below –

                      (Percentage-wise distribution of savings achieved after good tribological practice)

The tribological performance of any material can be examined by comparing and analyzing the contact between the surface of that material and the reference material. All these studies of tribological performance are called tribotesting, and the instrument used for it is called tribotesters. There are four main configurations of tribotesters: Pin on the plate, Pin on disc, Ring on the plate, and Ball on the ball. Tribological performance is determined by varying different parameters such as sliding distance, sliding time, and RPS for the tip of the tribotester. The material undergoes various levels of tribotesting to get permitted for the particular application.
These levels are as mentioned in the figure given below –  

      (Different levels of tribotesting and their respective consequences)

There are some demerits of Teflon, such as low dimensional stability with temperature rise; Insolubility in a long-range solvent, which limits the ease of processing; low thermal and electric conductivity; releases toxic gases at high temperatures (above 320 ⁰C). 

Teflon blends and composites-
Teflon shows a low coefficient of friction and excellent wear performance with high durability due to its chemically inert nature; thus, PTFE is considered as one of the most promising tribological materials known. It also exhibits some results, such as low dimensional stability with increasing load and temperature; the load-bearing capacity value is also low for PTFE. In order to improve these characteristics and overcome the limiting conditions, high-performance engineering polymeric materials such as PEEK and PI are mixed with virgin PTFE. Improvement in creep performance of PTFE is also a topic of research. The operating environment also plays a crucial role in the tribological performance of Teflon; with an experimental study, it was observed that when Teflon is operated in marine water conditions, it shows better results as compared with dry and normal water environments. In a marine water environment, deposition of salts and minerals results in reduced wear loss of the surface. According to researchers, the creep performance of virgin PTFE can be improved by adding glass fiber and carbon fiber. The addition of glass fiber was also found to enhance the performance of PTFE in the oxidizing environment while mixing carbon fibers with virgin PTFE enhances its hardness as well as thermal and electrical conductivity. It is pretty apparent from the above discussion that mixing virgin Teflon improves the individual performance, so to enhance such set of properties; we have to select groups of polymers or fillers to obtain desired results. 

Gujarat Fluorochemicals Ltd (GFL), Chemours, Arkema, and Hindustan Fluorocarbons Limited are the leading industries producing fluoro polymers and derived products. According to the survey conducted, around 200,000 tons of Teflon is manufactured worldwide annually, this number keeps on increasing. From this we can see the increasing demand of Teflon as well as its domain of application. 

Acknowledgment- I would like to express my immense gratitude to Prof. Dr. Girish M. Joshi sir, and thank him for motivating and guiding me to complete this article. Also, I would like to thank the Institute of Chemical Technology, Mumbai, Marathwada Campus, Jalna.  

Sarang Subhashchandra Shindalkar – currently studying Integrated M. Tech in Chemical Engineering with minor material science at ICT, Mumbai, Marathwada Campus Jalna since 2019. Presently working as a student intern at Century paper and pulp, Lal Kuan, Uttarakhand.