The Applications Of Carbon Nnaodots In Rubber Composites

Carbon-based nanomaterials,such as carbon black（CB）,fullerene,nanodiamond,carbon nanotubes and graphene,are under the spotlight of the science and technology community owing to their fascinating properties.Carbon nanodots（CDs）,a newly developing kind of carbon-based nanomaterials,has drawn great attention in a variety of potential applications by virtue of its facile synthesis with high yield,wide and renewable material sources,low toxicity,excellent biocompatibility and tunable surface functionalities.Typically,CDs possess abundant surface functional moieties,thus imparting them with excellent water solubility and the unparalleled suitability for subsequent functionalization with various species and interfacial regulation in polymer/CDs composites.However,most of the reported researches involving the applications of CDs in polymer composites are focused on the design and preparation of high-performance solid-state luminescent polymer/CDs composites.To the best of our knowledge,there is no reported attempt to develop the application of CDs for diene-rubber composites.Accordingly,in the present thesis,we dedicated to the reinforcement and functionalization of diene-rubber composites by incorporating CDs.The main content of the dissertation involves the following sections:（1）A facile,fast and one-step microwave-assisted pyrolysis method was adopted to synthesize CDs by using critic acid and 1,2-ethylenediamine（EDA）as carbon source and surface passivation reagent,respectively.The as-prepared EDA-passivated CDs（EDA-CDs）with quasi-spherical morphology had a narrow and uniform size distribution.EDA-CDs consisted of a nitrogen-doped（N-doped）carbogenic core and abundant surface amino-functionalities after surface passivation.Furthermore,the resultant EDA-CDs exhibited prominent reactive radical scavenging capacity and antioxidant activity.（2）Styrene-butadiene rubber（SBR）/EDA-CDs composites were prepared by admixing SBR with EDA-CDs in an open two-roll mill.By virtue of the prominent radical scavenging capacity and antioxidant activity,EDA-CDs was used to resist the thermo-oxidative aging of rubber composites.The effect of EDA-CDs on the aging-resistance of SBR composites were systematically studied.In comparison with 4010NA,a acknowledgedly high-efficient antioxidant for rubber industry,an equivalent amount of EDA-CDs performed superior talent in preventing the thermo-oxidative aging of SBR composites.This was because the resultant EDA-CDs could efficiently capture and stabilize the reactive radicals generated during the aging of SBR composites and thus suppress the oxidation process of rubber matrix.（3）By using various amine passivation regents,tunable elemental composition and fluorescence quantum yield（QY）for the resultant CDs were achieved.The correlation between the inherent structure of CDs and the thermo-oxidative aging-resistance of SBR composites was disclosed.The improvement of aging-resistance for SBR composites was proportional to the QY of CDs.This was because the photoluminescence performance and antioxidant activity of amine-passivated CDs were both determined by the surface passivated functionalities and intrinsic doping concentration of CDs,both of which depended on the type of amine passivation reagents.（4）Vacuum pouring technique was utilized for loading the EDA-CDs into the lumen of natural halloysite nanotubes（HNTs）in order to develop core-shell nanovehicles with sustained EDA-CDs release（L-HNTs）.The CDs release kinetics of L-HNTs was investigated.Subsequently,L-HNTs was admixed with SBR in an open two-roll mill.The effect of L-HNTs on the thermo-oxidative aging-resistance of the as-prepared SBR composites was evaluated.Furthermore,the surface modification of L-HNTs with silane remarkably lowered the EDA-CDs release rate.With the incorporation of modified L-HNTs,the retention of elongation at break for the corresponding SBR composite was up to 65%even after 20 days of thermo-aging at 100oC,revealing the long-lasting antioxidative protection of rubber matrix.（5）The EDA-CDs with abundant reactive surface functionalities was employed as high-functionality cross-linker,which implemented both covalent bridge and transiently hydrogen-bonding anchoring between the grafted maleic anhydride moieties of polyisoprene rubber skeleton（g-IR）and EDA-CDs.This biomimetic design enabled us to engineer multiple sacrificial units into a chemically cross-linked network of g-IR/EDA-CDs composites.Upon deformation,the multiple sacrificial units could preferentially detach/rupture from CDs surface to substantially dissipate energy upon different mechanisms,which gave rise to the high-efficiency reinforcement of rubber matrix.The incorporation of 3 phr EDA-CDs with g-IR gave rise to a striking improvement of tensile modulus,tensile strength,and toughness for rubber composite,while the corresponding stretchability has a comparable improvement in the meantime.Such reinforcement efficiency was comparable to that of the IR composite incorporated with 40 phr N330 carbon black.In addition,the present system exhibited unique strain-induced crystallization（SIC）behavior,in which forward onset strain of crystallization and promoted crystallinity were simultaneously accomplished.The contributions of different sacrificial units to the SIC performance and mechanical reinforcement of g-IR/EDA-CD composites were also uncovered.（6）Fe³⁺ions were introduced as intermediaries to directionally anchor epoxidized natural rubber（ENR）chains in the vicinity of particulate EDA-CDs upon implementation of interfacial metal-ligand coordinations,leading to the formation of interfacial metal-enriched regions.The correlation between the topological evolution of interfacial region and the mechanical performance of the corresponding ENR composites was disclosed to specialize the microscopic reinforcement mechanism.Upon increase of Fe³⁺concentration,the volume fraction of interfacial region gradually enlarged,leading to a systemic improvement of mechanical performance of the system.The interfacial metal-enriched region exhibited a“glassy”behavior with much slow relaxation dynamics compared to the bulk polymer,which significantly improved the network rigidity significantly and hence accounted for the prominent elastomer reinforcement.When Fe³⁺concentration exceeded percolation threshold,the discrete metal-enriched domains grew to overlap with neighbors,giving rise to the formation of penetrating interphase in the rubber matrix.We have provided convincing evidences to demonstrate that the reinforcement percolation of the present system stemmed from the formation of penetrating metal-enriched interphase.