Functional coatings deposited by an Atmospheric Pressure Plasma Jet (APPJ) system over Thermoplastic Elastomer (TPE) substrates stars

Resumen

The study of the friction coefficient and the hydrophobic character has long been of great importance in the automotive industry where some areas of the vehicle are subject to slippage. One example is the space between the window channels and the glass. The polymeric materials that are used in these areas, like thermoplastic elastomers (TPEs), involve a high degree of friction. So, in order to decrease the friction coefficient of the TPE, companies are using techniques as flocking. However, its high energy consumption, irregular distribution of fibers, poor adhesion and superhydrophilic character are the main drawbacks. Since TPE is a heat-sensitive material, an Atmospheric Pressure Plasma Jet (APPJ) system with a Dielectric Barrier Discharge (DBD) was used in this thesis. During the first group of scientific publications, with the objective of reducing the friction coefficient of TPE, the siloxane, aminopropyltriethoxysilane (APTES) was used as precursor. The influence of the plasma power and number of passes was characterized by Profilometry, Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) Spectroscopy, X-Ray Photoelectron Spectroscopy (XPS), Water Contact Angle (WCA) measurements and friction coefficient. The average surface temperature of the samples and the coating thickness seemed to be the key variables in determining the friction behavior. Successful samples (those that have a lower friction coefficient than those of the current industrial solutions) were coated at an average surface temperature of less than 92 ºC and thickness of the coatings was greater than 1000 nm. Sample coated in six passes and the lowest power proved to have the best friction performance. This sample had a friction coefficient that was 46% lower than that of the flocked seals. Whereas in the second group of scientific publications, the aim was promoting the adhesion of an antifriction (based on APTES) and hydrophobic (based on a fluorinated precursor) coating by the adhesion promoter, APTES. Different mixtures of APTES with FLUSI (heptadecafluoro-1,1,2,2- tetrahydrodecyl)trimethoxysilane) and PFH (1-perfluorohexene) were applied. The abovementioned characterization techniques together with the lap-shear test were used to study the influence of each precursor percentage. The main difficulty in this work lied in the hydrophilic character of APTES (for example, -NH2) and the low adhesion of the fluorinated coatings. On one hand, the sample that was coated with 25% of FLUSI and 75% of APTES combined the improvements of both functional properties. It had an average friction coefficient that was 51.5% lower and a WCA that was 4.4% higher than the uncoated TPE sample. A satisfactory stability in humid ambient for twelve months showed a slight decrease of WCA (4.4%) for this sample. On the other hand, the sample coated with a mixture of 50% APTES and 50% PFH was found to be the best one to satisfy both properties at the same time, despite not having the highest dynamic WCA or the lowest friction coefficient. Finally, it can be concluded that an APPJ system has been used to deposit a coating over TPE substrates with a friction coefficient lower than the current industrial solutions (flocked seals and polyamide tape) and a hydrophobicity higher than the uncoated TPE. Thus, it is considered that the two proposed objectives have been successfully fulfilled. This allows one to conclude that this technology could be a promising alternative to the current industrial solutions.