| Polytetrafluoroethylene (PTFE) shows good mechanical property, high thermal stability,weather and corrosion resistance, it is non-toxic and has good bio-compatibility, theseproperties make it an excellent material and widely applied in many fields. However, the poorcreep resistance, abrasion resistance, radiation resistance and low heat transfer property ofPTFE have limited its application in some areas. The low surface energy, on the one hand,makes it useful as the anti-sticking material and on the other hand, restricts its adhesion andcompatibility with other polymers. The application of water-based PTFE materials isseriously restricted due to the super hydrophobic of PTFE powder. In order to improve thehydrophilicity of PTFE surface, in this thesis, PTFE powder was irradiated at roomtemperature in air with electron beam accelerator, and acrylic acid monomer was grafted ontothe irradiated powder. The grafting behavior of acrylic acid on PTFE and the change of PTFEsurface morphology before and after grafting were studied. We observed a significantimprovement in hydrophilicity and dispersion stability of the grafted PTFE. In addition, bythe analysis of the fluorine-containing compounds, we established a method for determiningthe PTFE content in polymers. The results are concluded as follows:PTFE fine powder formed a strong hydrophobic layer on the surface of water, and aftergrafting, the grafted PTFE samples can be dispersed in water homogeneously, though thedispersion stability is limited and would precipitate gradually when being stilled for a longtime or centrifuged at the speed of5000r/min. However, the stability of grafted PTFE wasimproved significantly after neutralization by NaOH solution, no precipitate was found evenat a centrifugation speed of10000r/min for10min. In comparison, we found a lot ofprecipitate when commercial PTFE emulsion was centrifuged at a speed of5000r/min for5min.SEM analysis showed that the grafted PTFE particles are dispersed in alcohol solutionuniformly, while the non-grafted particles agglomerated together after dispersion by alcohol.TEM analysis further showed the non-grafted particles are pure with nothing on their surface and the grafted particles are covered with substances, which revealed their different surfaceproperties.From the hydrophilicity measurement of PTFE Samples, we found PTFE powder has ahigh water contact angle with a value of145.69, the hydrophilicity of grafted PTFE has beenimproved greatly and the contact angle is103.62, while grafted PTFE after neutralization byNaOH solution showed excellent hydrophilicity, the contact angle is reduced to63.38.The degree of grafting (DG) increased with increasing acrylic acid monomerconcentration, DG growed rapidly in the scope of0~10%of monomer concentration and inthe scope of10%~30%of monomer concentration, the addition of DG slowed down, whichpresented two different linear growth processes. The variation law of DG and reaction timeshowed that DG increased rapidly in the beginning of reaction and then increased with timevery slowly. There is no clear performance difference of the samples prepared in this thesis,the samples with DG more than20%presented well hydrophilicity and dispersion stability inwater.TGA thermal analysis of PTFE samples indicated the thermal stability of irradiated PTFEpowder is slightly lower than the non-irradiated, but the general performance remainunchanged, indicating there is no significant impact on the performance of PTFE by a certainamount dose of radiation, the decomposition of grafted PTFE at low temperature is ascribedto the polyacrylic acid.Determination of PTFE content of polymers, by the analysis of PTFE/PE wax, PTFEmodified engineering plastics, PTFE-modified plastic bearings et al, we found this method isaccurate and easy to operate. When PTFE content is higher than10%, the measurement erroris less than2%. This method is very suitable for the quality control and analysis of unknownsamples and may play an important role in the industrial production and scientific research. |
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