Preparation Of Two-dimensional Molybdenum Disulfide/polymer Nanocomposites And Investigation On Their Mechanical,Thermal And Combustion Properties

With the development of polymer science and nanotechnology,polymer nanocomposites have aroused enormous research interests in various areas.For general usage,the mechanical property,thermal stability and flame retardancy of polymer nanocomposites are of special concern.Because of the geometric feature,two-dimensional nanomaterials are becoming increasingly popular in reinforcing polymer materials.There a considerable improvement of mechanical and thermal properties always can be observed at a low inclusion content of two-dimensional nanofillers,as well as a higher fire-retarding effect than commercial flame retardants.Derived from molybdenite,two-dimensional molybdenum disulfide?MoS₂?has been investigated for decades in various fields,many of which are very dependent on itsatomic-layer thickness and lamellar morphology.Due to the geometric character,robust feature and excellent thermal properties,two-dimensional MoS₂ is expected to be a promising nanofiller to enhance the mechanical properties,thermal stability and flame retardancy of polymeric materials.Basically,fabricating two-dimensional MoS₂ in large scale and improving the compatibility of MoS₂ within polymer matrix are pivotal issues to achieve the high-performance two-dimensional MoS₂/polymer nanocomposites.Therefore,developing appropriate methods to obtain two-dimensional MoS₂/polymer nanocomposites and systematic study on their properties are of greatimportance.In this dissertation,firstly,four different techniques were utilized to prepare two-dimensional MoS₂.For the purpose of fabricating polymer nanocomposites,Liintercalation exfoliation and direct sonication exfoliation stood out from these four methods,which are appropriate for achieving the high-performance MoS₂/polymer nanocomposites.Benefited from latex premixing approach,the bare chemically exfoliated MoS₂ nanosheets were homogeneously distributed in polypropylene matrix and serve as a barrier effect enhancing filler.Both covalent and non-covalent methods were adopted to achieve the surface modification of MoS₂ in orderto improve the interface interaction between MoS₂ nanosheets and polymer matrix.Incorporating a low content of the modified MoS₂ nanosheets can obviously improve the mechanical properties,thermal stability and crystallization behavior of polymer nanocomposites.Furthermore,two-dimensional MoS₂ was served as a templateand synergist for conventional flame retardants to fabricate sandwich-like inorganic-organic hybridflame retardants.With this design,the integrated flame retardant effect of these MoS₂ based nanohybrids endowed the polymer nanocomposites with low flammability.In addition,the inorganic hybrid nanotechnology was adopted to further enhance the catalysis performance of MoS₂ based inorganic hybrids during the combustionofpolymers.The research work of this this dissertation is composed of the following parts.1.Four methods such as Li-intercalation exfoliation,mechanical exfoliationbyball milling,direct sonication and electrochemical exfoliation,were performedtoexfoliate MoS₂ nanosheets from initial bulk.The exfoliation results were comparedin line with the complex requirements for fabricating polymer nanocomposites.With the benefits of high quality and easy to tune the surface characters,direct sonication and Li-intercalation exfoliation are regarded as the suitable methods for fabricating MoS₂/polymer nanocomposites.Moreover,a kind of surfactant,cetylpyridinium chloride?CPC?was chosen to modify the chemically exfoliated MoS₂ for improving its compatibility within polyurethane acrylate?PUA?matrix.The inclusion of CPC modified MoS₂ leaded to an obviously increase in the mechanical properties ofPUA nanocomposite films.This considerable reinforcing effect of CPC modified MoS₂ is mainly attributed to the inherent robust mechanical performance and homogeneous dispersion of modified MoS₂ in PUA/MoS₂ systems.These dramaticallyimproved mechanical properties of PUA nanocomposites demonstrated the promisingeffect of two-dimensional MoS₂ as a robust nanofiller in reinforcing polymericmaterials.2.By a facile latex premixing combined with subsequent melt-blending method,bare chemically exfoliated MoS₂ nanosheets were successfully incorporated into polypropylene?PP?matrix.With benefits of this approach,the MoS₂ nanosheets were fully exfoliated and homogeneously dispersed in the PP matrix.The inclusion of bare MoS₂ nanosheets obviously improved the thermal oxidative stability and influenced the thermal decomposition behavior of PP nanocomposites just by its considerablephysical barrier action.Because the MoS₂ is inert under nitrogen atmosphere and it is very stable while treated at high temperature.In detail,the MoS₂ nanosheets with high aspect ratio can disrupt the oxygen and heat supply from the gas phaseto the bulk of composites and prevent the emission of thermally degraded small gaseous molecules during degradation,as well as suppress the evolution of gaseous pyrolysis products under nitrogen,thus reducing the peak heat release rate?PHRR?value of MoS₂/PPnanocomposites.3.The dodecanethiol and Pluronic were introduced to simultaneously exfoliate and modify MoS₂ by direct liquid sonication technique.When exfoliation occurred,the modifier molecules would attached on the surface of exfoliated MoS₂ sheets by covalent and non-covalent bonding,respectively.These two modified MoS₂ nanosheets endowed the different polarity polymers,polyethylene?PE?and poly?ethylene oxide??PEO?,with significantly reinforced mechanical properties,thermal stability and crystallization performance,on the basis of the compatibility principle.In general,the improvement of properties of polymer/MoS₂ nanocomposites are ascribed to the two-dimensional character,homogenous dispersion,robust feature and compatibility of modified MoS₂ nanosheets.Importantly,because the modifiers are well compatible with the polymer matrix,there a gradient region can be formed within the phase interface of polymer/MoS₂ nanocomposites.It can restrict the motion of polymer chains heavily by the molecular level entanglement and provide an effective load transfer region,therefore,leading to a significantly improved mechanical and thermal properties of polymer nanocomposites.4.Two-dimensional MoS₂ is expected to act as a synergistic agent to conventional flame retardants for further reduces the flammability of polymer nanocomposites.Two kinds of sandwich-like organic-inorganic nanohybrids were fabricated by in situ synthesis of melamine cyanurate?MCA?or polyaniline?PANI?on MoS₂ template as high-performance flame retardants for nylon 6?PA6?andepoxy?EP?resin,respectively.By this design,these MoS₂ based hybrids not onlypossess the high specific surface area of two-dimensional character but also exhibit an integrated flame-retarding effect in polymer nanocomposites.The phase interfacial interactions?hydrogen-bonding or covenant-bonding?and the integratedeffect?inherent flame retarding effect,physical barrier performance and catalytic activity of MoS₂ hybrids?are the essential to achieve the enhanced thermal oxidative stability,flame retardancy and smoke suppression performance of PA6/MCA/MoS₂ and EP/PANI/MoS₂ composites,which cannot be reached by solely incorporatingthe bare MCA or PANI.The high residue derived from the synergistic effect of conventional flame retardants and catalytic charring ability of Mo element can be held together by MoS₂ nanosheets to form a compact and adiathermic protective char shield on the innermaterials.5.In order to improve the catalytic performance of MoS₂ during the thermaldecomposition of EP resin,the CoOOH nanoplatelets were in situ synthesized on MoS₂ nanosheets to achieve a MoS₂ based inorganic hybrid.Decoration of metal compound can prevent MoS₂ nanosheets from re-stacking,thus improving their dispersion state within EP matrix.Once treated at high temperature,MoS₂/CoOOH hybrid can degrade into bimetallic oxides with labyrinth-like porous structure.It can lead to a reduction in the release of reducing pyrolysis gas?CO and hydrocarbon?and precursor of smoke particle?aromatic compound?because of the physical absorption and chemical oxidation effects.In the condensed phase,the synergistic effect of MoS₂/CoOOH hybrid also was confirmed by the dense and insulating residue charformation of EP/MoS₂/CoOOH nanocomposites.