Study About Tung Oil-Based Polymer And Its Application In Environmentally Friendly Coatings And Lithium-sulfur Battery Binder

In order to cope with the depletion of petroleum resources and the environmental pollution,it becomes particularly important to find bio-based polymer materials that can replace petroleum resources.Renewable resources in energy and material applications have drawn increasing attention from the industrial and academic fields.Vegetable oil is considered to be one of the most important renewable resource due to its low price,easy availability and biodegradability.Vegetable monomers derived from vegetable oils show satisfactory results in forming polymers with excellent properties.There is a growing demand for new polymers synthesized from components derived from renewable resources with the increased requirements for environmental protection.Therefore,most researchers and enterprises are committed to developing high-performance materials for vegetable oil resources to ease and partially replace traditional petroleum-based products.Tung oil,as a dry oil,mainly consists of triglyceride ofα-eleostearic acid with three unsaturated conjugate double bonds,which endows tung oil with good reactivity to proceed oxidation and polymerization,and it provide a faster drying rate than other vegetable oils.In the present study,tung oil was used as a research object and in view of the shortcomings of tung oil with low comprehensive value in the field of polymer materials.Tung oil was modified to prepare polymer monomers with excellent mechanical properties,strong chemical resistance and high self-crosslinking density through classical chemical reactions such as transesterification reaction,Diels-Alder reaction,and oxidative crosslinking reaction.The relationship between the structure and properties of the synthesized products and its application in environmentally friendly coatings and lithium sulfur battery binders had been studied and discussed in detail.The main research contents are the following four aspects:（1）Tung oil-based methacrylate monomer（MEAM）was synthesized through a two-step synthetic procedure involving amidation and esterification reactions.The chemical structure of MEAM was confirmed by proton nuclear magnetic resonance,Fourier transform infrared and gel permeation chromatography.Then,a series of tung oil-derived thermosets were produced by the polymerization of this methacrylate monomer with different contents of maleic anhydride（MA）.The dynamic mechanical analysis,tensile properties and pencil hardness were conducted on the obtained thermosetting films.It was revealed that with the increase of the content of MA,T_g values,the tensile strength and the pencil hardness of the films varied in the range from 63.3-109.2°C,12.8±0.8-22.7±1.2MPa,and 4 H to 6 H,respectively.And the thermal stabilities and mechanical properties of these films could be adjusted simply by controlling molar ratios of MEAM to MA.Furthermore,the thermosetting films demonstrated comparable corrosion resistance to commercial epoxy methacrylic coating,and had good chemical resistance,adhesion and water boiling resistance.（2）Tung oil was used as a raw material to carry out methylation reaction,low-viscosity and high-purity methyl eleostearate was obtained after purification by column separation,and then tung oil-based polyol（TOP）was prepared by transesterified with diethanolamine.Subsequently,a series of cationic aqueous polyurethanes（WPUs）were prepared by the prepolymer method using TOP,isophorone diisocyanate and polyethylene glycol as raw materials,methyldiethanolamine as the chain extender,and hydrochloric acid as the neutralizer.The effect of TOP content on the particle size,zeta potential and storage stability of WPUDs was detailly investigated by zeta-sizer and centrifugation measurement.The post-curing behavior of these cured films was tested by tracing the gel content.Thereafter,the WPUDs coating properties including mechanical properties,thermal resistance,hydrophobicity,morphology,pencil hardness,adhesion and solvent resistance were also carefully investigated which demonstrated that more introduction of TOP into the dispersions could help improve tensile strength,thermal stability,hydrophobic capability,phase compatibility,pencil hardness for the cured films.More importantly,antibacterial experiments demonstrate that these WPUDs dispersions exhibited well inhibition effect toward Escherichia coli and Staphylococcus aureus.（3）A new aqueous dispersion rich in polar groups such as sulfonic acid group,urethane group and quaternary ammonium salt was prepared by neutralizing sulfamic acid with tung oil-based polyurethane prepolymer.This new polymer was used as an aqueous binder for the sulfur cathode of lithium-sulfur batteries.The relationship between the structure and the electrochemical performance of the battery was investigated,and the influence of each group in the polymer structure on the battery performance was discussed.The study found that compared with PVDF,the electrode based on this binder not only has strong mechanical properties,but also has a significant polysulfide fixing ability due to the large number of polar groups in its structure,which inhibits the dissolution of polysulfides.The sulfur positive electrode based on WPUN binder has a specific capacity of 617 m Ah g^-1after 200 cycles at 0.5 C.At the same time,good rate performance from 0.2 C(899 m Ah g^-1)to 4 C(528 m Ah g^-1)was obtained.（4）A vegetable-oil-based cationic waterborne polyurethane polymer（WPUP）was developed in-situ cross-linking strategy using phytic acid as a neutralizer,and it was as an eco-binder for sulfur cathodes.At the same time,tung oil-based polyurethane polymer（WPUH）with hydrochloric acid as a neutralizer was synthesized as a control.They were used in the electrode fabrication process to achieve homogeneous,dense coating of the active materials on the current collector surface.The WPUP participates in an in situ covalent crosslinking reaction to produce a three-dimensional network with excellent mechanical properties.This ensures robust adhesion,and much shorter ion-and electron-transfer paths.The resultant sulfur cathodes show an initial discharge capacity of1051 m Ah g^-1 at 0.5 C,promising long-term cycling stability(632 m Ah g^-1 after 600cycles at 0.5 C),and a high rate(634 m Ah g^-1 at 4 C).As proof-of-concept,a lithium-sulfur full cell was fabricated with a 350%oversized lithium anode.It provided a good capacity of1.3?m A?h cm^-2 and Coulomb efficiency remains above 99.5% over 300 cycles.