Researchers discovered that the chemical coupling of polyamideimide (PAI) with polytetrafluoroethylene (PTFE) leads to an improvement in crystallisation behaviour and thus influences the application properties of PAI-PTFE coatings.

Investigation of the crystallisation behaviour and application properties of chemically coupled PAI-PTFE coatings. Source: Adobe.Stock

Poly(tetrafluoroethylene) (PTFE) is well known for its very low friction coefficient and thus widely used for antifriction applications, e.g., sliding lacquers, for many years. Because of the high wear rate and cold flow of the original polymer, PTFE is usually added in higher amounts to other polymer matrices as a lubricant. However, the incompatibility of PTFE requires lots of efforts to perform a homogeneous breaking down of agglomerates and particle distribution as well as dispersion stabilization of the physical mixtures during application and curing. PTFE can be functionalized by high energy irradiation and subsequently compatibilized with a polymer matrix by reactive extrusion resulting in chemical bonding of both polymers via suitable reactive groups. In this manner, poly(amide imide) (PAI) was coupled to γ-radiation modified PTFE micro-powder prior to the dispersion procedure.

The study deals with the thermal and crystallization behavior of the PTFE lubricant in chemical bonded (cb) PAI-PTFEcb compound thin layers in comparison with those of the plain radiation modified PTFE depending on the cooling rate by DSC, Flash-DSC and WAXS. A morphological characterization of the extrudate as well as the coating gives information about the fragmentation and distribution of the PTFE phase in the PAI matrix. Furthermore, mechanical and surface properties of sliding lacquer films were analyzed after application on steel substrates by varying dry film thickness and curing.