Preparation Of Bio-based Molybdenum Disulfide Nanohybrids And Its Application In Flame Retardant Polylactic Acid

With a series of worldwide problems appearing,such as resource depletion,energy crisis and ecological environment deterioration,the development of renewable bio-materials and their derivatives play an important role in our daily life.Poly?lactic acid??PLA?has attracted much attention in virtue of its good biocompatibility and biodegradability.However,the flammability and slow crystallinity of PLA restrict its application in emerging field.Currently,two?dimensional?2D?nanolayers have drawn enormous attention in the thermal,mechanical and fire safety field.Molybdenum disulfide?MoS₂?,as a novel two-dimensional nanomaterial,due to its typical layered nanostructure and brilliant stability,has drawn enormous attention in the flame retardants field of polymer composites.A few works have demonstrated that the thermal and mechanical performances of polymer can be improved obviously by incorporating the exfoliated MoS₂ nanosheets at low loading.Moreover,compared to traditional halogen-based flame retardants,MoS₂ also meets the reqirement of green chemistry and attains environment friendly.However,due to the poor compatibility and low interfacial interaction between the polymer matrix and MoS2,the exfoliated MoS2 nanosheets have obvious agglomeration during the preparation of MoS2/polymer nanocomposites,which limits the dispersion of MoS2 nanosheets in polymer matrices.It is highly desirable to seek for efficient methods to solve the poor interfacial interaction between MoS₂ and polymer matrix,which is important to develop MoS₂?filled PLA composites with high reinforcement effect.In this paper,bio-based materials are loaded on the surface of MoS2 nanosheets to fabricate various functionalized MoS2.And then combined with the nanocomposites science to prepare diverse MoS2-based PLA nanocomposites,the influence of functionalized modification on the dispersion of MoS2 nanosheets,thermal and fire safety performances of PLA/MoS2 nanocomposites are investigated.The primary research works are discussed as follows:?1?As well known,MoS2 nanosheets have low compatibility and poor interfacial interaction with the polymer matrix.Firstly,the exfoliated MoS2 nanosheets are produced by n-Butyl Lithium intercalated-exfoliated method.A novel fMA-MoS₂ hybrid is syhthesized via using melamine phytate?MA-PA?to modify the exfoliated MoS₂nanosheets.The fMA-MoS₂/PLA nanocomposites are prepared by solution blending method.The chemical structures of fMA-MoS₂ are confirmed by XRD,FT-IR,TGA and SEM.The SEM images illustrate that the functionalized MoS₂ is dispersed well in PLA,and the addition of fMA-MoS₂ leads to more obvious improvements in fire resistance.Compared to neat PLA,the PHRR of PLA composites is decreased by 16%.?2?PEI-MoS₂ nanohybrids are firstly synthesized by self-assembly method via electrostatic interaction between the exfoliated MoS2 nanosheets with negative charge and PEI nanosheets with positive charge and then phytic acid is grafted on PEI-MoS₂ to form fPEI-MoS₂ hybrid.The transition metal ion Fe³⁺is loaded on the surface of fPEI-MoS₂ to prepare the fPEI-MoS₂@Fe³⁺hybrids by using abundant phosphoric acid group of phytic acid.The results of SEM demonstrate that the MoS₂ hybrids have good dispersity in PLA matrix with no aggregations.The fPEI-MoS₂@Fe³⁺hybrids show good performance in improving the thermal behavior and fire retardance of PLA composites.When the content of hybrid is 3 wt%,the char residues at 700?for the PLA composites is increased from 0.2%to 5.2%,compared wtih those of pure PLA.Besides,the PHRR and THR are decreased from 718 KW/m² to 523 KW/m² and 74MJ/m² to 67 MJ/m²,respectively.?3?It is well known that the surface of MoS2 nanosheets exhibit inert and there are no any active functional groups.In this chapter,MoS₂ nanosheets are firstly coated with polydopamine?PDA?through the self?polymerization of dopamine?MoS₂?PDA?in a buffer solution.Then the Ni?OH?₂ is decorated on the surface of MoS₂?PDA because of the strong affinity of Ni²⁺with hydroxyl groups in PDA.Finally,the as?synthesized MoS₂?PDA@Ni?OH?₂ hybrids are introduced into poly?lactic acid??PLA?matrix.As confirmed by XRD,FT-IR,TEM,SEM,and TGA,the MoS₂ nanosheets are dually modified with PDA and Ni?OH?₂ without destroying the original structures.The SEM results show that the MoS₂?PDA@Ni?OH?₂ hybrids have good dispersity in PLA matrix.The thermal degradation of PLA with MoS₂?PDA@Ni?OH?₂ generate a notably higher yield of char.Moreover,the crystallinity of composites is higher than that of pure PLA.The cone calorimeter test reveals that the introduction of 3%MoS₂?PDA@Ni?OH?₂ result in lower PHRR?decreased by 21.7%?.