Sodium treatment of PTFE sheet
Polytetrafluoroethylene, also known as PTFE or Teflon, is a plastic material with excellent properties and is widely used in many industrial sectors. Due to the unique molecular structure of PTFE, the surface free energy is 0.018J/m2, which is extremely low in solid materials (surface free energy refers to the excess free energy of molecules per unit surface area compared to the same number of internal molecules). This characteristic of PTFE material results in its non adhesiveness to other materials, making it a typical difficult to stick plastic.
However, in the practical application of polytetrafluoroethylene, it is usually bonded with other materials. To ensure the quality of the bonding, surface modification treatment is usually carried out on polytetrafluoroethylene. Sodium naphthalene solution treatment bonding method is currently the most effective and commonly used method among all research methods (simple process, convenient configuration, low cost). Sodium naphthalene tetrahydrofuran is generally used as a corrosive solution and is widely used in the field of polytetrafluoroethylene bonding. PTFE can bond with rubber, metal and other substances after sodiation. In special use, it can compensate for the non stick performance of polytetrafluoroethylene products, especially in the field of polytetrafluoroethylene tight lining, with broad application prospects.
Why can sodium naphthalene treatment solution treat PTFE surface?
Sodium naphthalene treatment solution is composed of equal amounts of sodium and naphthalene dissolved or complexed in active ethers such as tetrahydrofuran and ethylene glycol dimethyl ether. The modification mechanism of PTFE surface by sodium naphthalene treatment solution is shown in Figures (1) to (4): sodium first transfers the outer electrons of PTFE to the empty orbitals of naphthalene, forming anionic radicals, and then forms ion pairs with Na; The naphthyl anion is transferred to PTFE, causing it to lose fluoride ions and generate a neutral functional group. Furthermore, these functional groups regenerate C-C bonds and crosslink; Alternatively, the group can accept another electron to form a negative carbon ion, which then reacts with the proton solvent to form a C-H bond; Or it may lose fluoride ions and form a C=C double bond.
(Single sided sodium treated PTFE plate, please store in the dark)
Therefore, sodium in the treatment solution can break the C-F bonds on the PTFE surface (or a few microns away from the surface), capture F atoms, defluorinate the surface, and form a carbonized layer. Infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) show that the modified PTFE surface contains active functional groups such as hydroxyl, carbonyl, and carboxyl groups, thereby improving the adhesion performance of the PTFE surface.
Simply put, the sodium naphthalene treatment solution comes into contact with PTFE and corrodes it, breaking the C-F bonds and removing some of the fluorine atoms on the surface. This leaves a coffee colored carbide layer with adhesive properties on the surface of PTFE material. At the same time, some polar groups can be introduced on the surface to enhance surface free energy, increase molecular activity on the PTFE surface, reduce contact angle, improve wettability, and transform from difficult to stick to adhesive.
The steps for sodium naphthalene treatment and bonding are as follows:
(1) Preparation of processing solution: Add a certain amount of metallic sodium to a solution of tetrahydrofuran and naphthalene, with the mass fraction of metallic sodium controlled at 3%~5%. Stir at room temperature for about 2 hours until the solution turns dark brown or black;
(2) Clean and air dry the surface of PTFE treated with acetone or alcohol to remove surface oil stains and dirt;
(3) Immerse the PTFE workpiece to be processed in a sodium naphthalene solution for about 5-10 minutes (depending on the degree of treatment);
(4) After treatment, first wash the residue of the treatment agent on the surface of polytetrafluoroethylene with acetone, then clean it with water to remove residues such as NaH and NaOH. When the surface of polytetrafluoroethylene turns dark brown, the treatment is complete;
(5) Air dry or dry in an oven (indoor shade drying, do not expose to outdoor ultraviolet light), directly divide and bond, or pack and roll with black shading film for future use;
(6) Choose epoxy resin, silicone, or polyurethane as the adhesive, evenly apply it to the treated surface to be bonded and immediately bond it. After standing at 24-30 ℃ for 24 hours, it can be firmly bonded;
(Sodium treated PTFE plates can be welded together)
