The Fluorinated Hydrophobic Modification Of Poly(vinyl Alcohol) And Its Properties

Poly(vinyl alcohol)(PVA) is one important chemical raw material, it is widely used in all kinds of functional membrane materials due to its excellent film-forming properties, non-toxicity, thermal stability and chemical stability,are. However, PVA has strong hydrophilic properties because of the large amount of hydroxyl groups in side chains, which results in the very large hygroscopicity, poor water resistance and limits the use to some extent. So the hydrophobic modification of PVA becomes the recent interesting research.The present work uses PVA as the basic polymer to do the hydrophobic modification of PVA through two different fluorination method. One is using microwave assisted synthesis to initiate the fluorinated acrylic monomers to do the side graft polymerization. The other is modifying PVA/clad silica(Si O2)composite film with silane coupling agent containing fluoroalkyl to improve its hydrophobic property. Using organic compounds containing fluorine to modify PVA is because organic compounds contain lots of F atom. Moreover fluorine has small radius atom but larger electronegativity, the formed C-F bond is short and the surface energy is low, which results in the hydrophilic property.It is studied that using microwave to heat the reaction has many advantages,such as short reaction time, heating rate, conversion rate, high energy efficiency,clean, and low power consumption. In this paper we use microwave as the driving force and potassium persulfate as the initiator to initiate methacrylate dodecafluoroheptyl acrylate(DFMA) to do the side chain graft polymerization.The graft polymer, PVAF, has hydrophobic properties due to the presence of abundant of low surface energy of fluorine atoms. Fourier transform infrared(FT-IR), solid-state nuclear magnetic resonance(NMR), X-ray diffraction(XRD)were used to study the chemical composition and molecular structure of grafted polymer. The results indicated that DFMA was successfully introduced in to the side chains of PVA. The thermal gravimetric analysis was used to study the thermal decomposition property of grafted polymers, the results showed that the introduction of DFMA is helpful for the thermal stability of PVA. Moreover,the thermal stability of graft polymers increases with the increasing content of DFMA. And the water absorption experiments was used to study the hydrophobic properties of the grafted polymer, it shows that the more fluorine was grafted in PVA side chains the better the hydrophobic effect is.However, because the PVAF prepared by grafting is solid, it is hard to dissolve and to film and measure the contact angle. In order to further improve the hydrophobic property of PVA film surface and prepare super-hydrophobic film of PVA, in this part work, we use PVA as polymer matrix, Si O2 nano particles as inorganic filler, spinning coated PVA/Si O2 onto a glass surface. After that heptadecafluorodecyl trimethoxysilane modified(C13H13F17O3Si, FAS) wasused to graft on PVA and Si O2 to successfully prepare super hydrophobic film based on PVA, PVA/Si O2-FAS. Fourier transform infrared spectroscopy(FT-IR)and X ray diffraction(XRD) were carried out to analyse the structure and morphology of the super hydrophobic surface, the results indicated that the super hydrophobic films were prepared successfully by self-assembled fluorine silane. The content of F on the surface of the films is up to 41.57%. Scanning electron microscope result shows there are many surface spherical protrusions of similar size, particle size of about 30-50 nm, suggesting the formation of micro-nano structure. Contact angle measurement was used to observe the water droplets movement on the surface of prepared film, the results showed that when the PVA/Si O2 is 1:5, the fluorinated PVA/Si O2 membrane surface has better super hydrophobic properties. The static contact angle is over to 151.24°, the rolling angle is about 4°. The good super-hydrophobicity of PVA/Si O2-FAS is mainly attributed to the combined action of low surface energy element F and the nanostructure.The hydrophobic and super hydrophobic film materials based on PVA have great application in the daily life. Such as it can be used on the surface of glass,wood or ships to have special functional properties such as waterproof,antifouling or even self-cleaning effect. The study about fluorided PVA in the present work can improve the water resistance of PVA, and expand its application field.