| Polyvinyl fluoride (PVF) is semi-crystalline polymer, which has many characteristics of general fluorine-containing materials, such as chemical stability, thermal stability, weather resistance ability, low surface energy, as well as comparatively high mechanical strength and abrasion resistance. PVF film is used as laminate in aircraft interiors, solar battery backplane, transportation, and cladding material for houses, providing durable, and easy-to-clean surfaces. However, PVF does exhibit a small amount of degradation at processing temperature, so that PVF first undergoes molten condition, and then begins thermal decomposition. The study on thermal decomposition characteristics and the service life of PVF is extremely essential. PVF films are always converted into laminates, however, low surface energy determines it is difficult to bonding with other materials. So it is necessary to research the adhesion of PVF film.The thermal decomposition kinetics and the pyrolytic mechanism of polyvinyl fluoride (PVF) in air and nitrogen were investigated by two techniques:thermal gravimetric analyzer (TGA) and Fourier transform infrared spectroscopy (FTIR). Then, the service lifetime of PVF were predicted by means of kinetic parameters. The reaction activation energy (E) was calculated using the Kissinger method and Flynn-Wall-Ozawa method, and the kinetic decomposition based on the Coats-Redfern method was the first-order reaction. Kissinger method showed the reaction activation energy in air (Ea为297.558kJ·mol-1) was lower than that in N2(Ea为297.558kJ·mol-1), meaning PVF was more easily decomposed in air than N2. Flynn-Wall-Ozawa method showed thant an increase in the reaction activation energy of the thermal decomposition was observed as the weight loss fraction increased. With5%weight loss taken as the failure index of the material, the maximum working temperature of PVF was118.4℃in N2for25years, and the maximum working temperature of PVF was89.4℃in air for25years. By online coupled techniques TG-FTIR, the mechanisms thermal decomposition of PVF in air and nitrogen comprised the removal of HF; then, with temperature rising, the C-C bond broke and corresponding products cyclized to be the volatiles of aromatic compounds such as benzenes. The difference of PVF decomposition in air and nitrogen lied in the fact that a partial carbon chain under air atmosphere would be oxidized into long-chain carboxylic acid.The fluorination of polyurethane (PU-F) was made by PU prepolymer and (DFMA-HEMA-BA) terpolymer. The (DFMA-HEMA-BA) terpolymer was synthesized by free radical polymerization of dodecafluorohepthl methacrylate (DFMA), hydroxyethyl methacrylate (HEMA), butyl acrylate (BA).4,4’-Methylenebis(phenylisocyanate)(MDI), hexamethylenediisocyanate (HDI), polytetramethylene ether glycol (PTMEG) and polypropylene glycol(PPG) were used for synthesized the PU-1. The PU-1and the (DFMA-HEMA-BA) terpolymer reacted by their end groups of-NCO and-OH, and made the PU-F. The structure of PU-F was characterized by Fourier-transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). Different fluorine content of PU-F was designed and its adhesive property was investigated by shearing strength and peeling strength.The result showed that fluorine content being0-8%, bonding strength was first rising then droping and reached the peak value at fluorine content2.7%. At this time, the shearing strength of PVC films was0.29MPa, peeling strength was0.58N·cm-1, and could be used at the temperature of60℃in long time without debonding. For the PVF-PET films, the peeling strength was8.12N·cm-1at fluorine content2.7%, and after boiling at water about24h, the peeling strength was7.71N·cm-1, meeting the requirement of bonding glud of solar battery back. |
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