Influence Of Gamma Radiation And Solvent On The Structure And Properties Of Poly(Vinylidene Fluoride-Chlorotrifluoroethylene)

In recent years,more and more attention has been paid to elastomer materials which still have good mechanical properties after being stimulated by extreme conditions(such as temperature,radiation,etc.)with the rapid development of aerospace,military defense and other fields.For example,elastomeric materials can be found in polymeric explosive binders,aircraft tires,and sounding balloons,etc.It can provide new ideas for the design of high performance elastomer materials when in-depth understanding of the structural evolution of polymer elastomer materials after treatment under harsh conditions such as high temperature and radiation.At present,although the research on the relationship between the structure and properties of elastomers mainly focuses on the influence of external conditions(such as crystallization temperature,crystallization pressure,deformation rate)on the structural evolution during the deformation process,the changes of the properties of the polymer itself is unclear.In addition,the structure of the elastomer material itself is also relatively complex,which is mainly in the two dimensions of time and space.On the spatial scale,thermoset elastomers usually contain the rubber matrix and different kinds of fillers while thermoplastic materials usually contain the microphase-separated structure,and these properties bring multi-scale structural properties to the material.On the time scale,each structure exhibits multi-scale properties with different relaxation kinetics at different temperatures and stress external fields.The macroscopic mechanical behavior of elastomers is essentially the result of the coupling between their structure,relaxation dynamics and external field excitation.Which makes the study of the relationship between the structure and properties of elastomers a great challenge for both academia and industry.As an important explosive binder,F2313(CTFE:VDF=3:1)has many comprehensive performance requirements of polymer materials in terms of usability,and its physical and chemical properties directly affect the mechanical properties of energy content materials.Therefore,this thesis attempts to reveal the mechanism of the change of the polymer structure of the typical elastic material F2313 on its mechanical properties when stimulated by external conditions,which will guide the wider application of elastomer materials.In this paper,the changes of structure and properties of F2313 film before and after gamma irradiation and ammonia water treatment were studied by experimental techniques such as infrared spectroscopy(FTIR),nuclear magnetic resonance spectroscopy(~1H NMR,¹⁹F NMR),gel permeation chromatography(GPC),X-ray diffraction(XRD),X-ray small(wide)angle scattering(SAXS/WAXS),thermal analysis(DSC-TGA).The main research contents and conclusions of this paper are as follows:(1)The amorphous F2313 film was prepared by solution casting and the thickness of the film was about 500?m.The samples were irradiated with ⁶⁰Co at a dose rate of 5.4k Gy/h and the total doses of the irradiated samples were 0k Gy,43.2k Gy,86.4k Gy,172.8k Gy,345.6k Gy and 561.6k Gy,respectively.It was found by FTIR that the strength of C=C bond and C=O bond gradually increased with the increase of irradiation dose,indicating the dehalogenation reaction and oxidation reaction occurred during the irradiation process;The molecular weight of F2313 decreased gradually with the increase of irradiation dose by GPC and the degree of cross-linking increased with the increase of irradiation dose under high irradiation dose by gel content determination,indicating the F2313 undergone degradation and cross-linking reaction after irradiation;It was found by TG-DSC and RSA that the thermal decomposition temperature of F2313 decreased after irradiation,the glass transition temperature and tensile strength increased with the increase of gel content,but the fracture strain decreased with the increase of irradiation dose;Finally,it was found by SAXS/WAXS characterization that the network-like aggregated structure is generated after irradiation,which become gels due to their too large molecular weight,and the fiber bridges or pore structures cannot be formed in the vertical stretching direction because it is not easy to be oriented during the stretching process.This is also the reason why the tensile strength increases and the fracture strain decreases with the increase of irradiation time.(2)To study the relationship between weak molecular structure and group changes,microphase separation domain/crystal changes,mechanical properties and structural evolution changes.The samples with different degrees of molecular structure change were prepared by soaking the F2313 film prepared by solution casting in ammonia water(soaking modification time:0 days,1 day,3 days and 6 days).The FTIR and NMR results showed that the molecular structure and molecular groups of the polymer changed greatly with the increase of modification time;The RSC characterization showed that the tensile strength of the modified F2313 samples was found to be enhanced;The WAXS results showed that the original crystals were gradually transformed into oriented fibrillar crystals and the modification treatment had a great inhibitory effect on the transformation of the crystals;The SAXS results showed that the F2313 sample not only undergoes changes in crystal shape and arrangement,but also experienced multi-layer structure evolution events at the mesoscale during the deformation process,including crystal interlayer and intralayer separation,orientation,etc.In general,the external stimuli will destroy the molecular structure,molecular chain regularity and molecular weight of F2313,resulting in the destruction of its internal molecular structure,which in turn has a huge impact on macroscopic properties.Studying the relationship between the structure and properties of F2313 under external stimuli has a good reference value for the use of fluoropolymer.