Preparation And Properties Of Nano-Carbon/Thermoplastic Polyurethane Elastomer Composites

Thermoplastic polyurethane elastomer(TPU)is a unique polymer material,which not only is able to offer a very good elasticity(typical of rubbers),but also,unlike traditional crosslinked rubbers,it can be processed with the common techniques used for thermoplastics.Because of excellent processability and tunable properties,TPU has been widely used in various applications,such as coatings,adhesives,fibers,foams and various diversified fields of modern technologies.But its shortcomings are the poor heat resistance and mechanical properties,which limit its application in a wider field.In order to further extend TPU applications,an effective way is to incorporate nanosized fillers to control its microstructure and further tune its properties.Therefore,combing the research hotspots in the field of nanomaterials,different dimensions nano-carbon materials(1D carbon nanotubes,2D graphene and 0D carbon dots)were selected as fillers and incorporated into polyurethane.A series of nano-carbon/TPU composites were prepared and studied the effects of nano-carbon materials on the structure and properties of composites.The main research contents and results are as follows:1.1D CNT/TPU composites.The isocyanate functionalized carbon nanotubes(CNT-NCO)were synthesized with toluene-2,4-diisocyanate,which is one common monomer for synthesizing polyurethane,and further polymerized with the other raw materials of TPU via in situ polymerization to prepare a series of CNT/TPU composites with different CNT-NCO contents.The structure of CNT-NCO was characterized by Fourier-transformed infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS),thermogravimetric analysis(TG)and dispersion experiment.TDI successfully grafts onto CNT via the reaction between the groups of–NCO and–COOH,and its content is about 17%.The incorporation of CNT can decrease the extent of microphase separation and improve the crystallinity of hard segment as a heterogeneous nucleation agent;in comparison with the pristine TPU,the thermal properties and mechanical properties of CNT/TPU composites enhance markedly,when the mass fraction of CNT is 0.1 wt%,the Vicat softening temperature raises by 32?,the tensile strength increases almost 15 MPa,and the elongation at break increases about 21%.The dynamic rheological studies show that the storage modulus(G'),loss modulus(G'')and the complex viscosity increase significantly with the incorporation of CNT.The crossover of G'and G'',and the tan?move to low frequency with increasing CNT contents,which indicates the existence of a network structure in CNT/TPU composites.Han plots shift upward and gradually close to the diagonal line,and the van Gurp-Palmen plots shift downward,which implies that the elastic response exhibits an increasing trend.Cole-Cole curves show that the phase separation of composites decrease due to the presence of CNT.2.2D GO/TPU composites.Toluene-2,4-diisocyanate(TDI),one of the monomers used for synthesizing polyurethane,was covalently functionalized on graphene oxide(GO)and then the functionalized GO(TDI-GO)was polymerized with polycaprolactone diol(PCL)via in situ polymerization,leading to chemically linked polyurethane nanocomposites through the covalent bonds between the isocyanate groups on GO and the hydroxyl-terminated PCL.FT-IR,XPS,XRD and dispersion experiments of the nanofillers demonstrated that the TDI was successfully grafted onto the GO.TDI-GO can decrease microphase separation of TPU,and improve the crystallinity of hard segment as a heterogeneous nucleation agent;comparing with the pristine TPU,GO/TPU composites have excellent thermal properties,when the mass fraction of GO is 0.5 wt%,the 5%degradation temperature increases by 9?,and the Vicat softening temperature raises by 18?;the mechanical properties of GO/TPU composites enhance markedly,comparing with the pristine TPU,when the mass fraction of TDI-GO is0.5 wt%,the tensile strength increases almost 10 MPa,and the elongation at breaking increases about 32%.The rheological properties were investigated to establish the structure-property relationships of the nanocomposites.G',G''and complex viscosity of the samples increased monotonically with TDI-GO content,which is attributed to the strong polymer-filler interactions and the effective dispersion of the nanofillers.Additionally,the tan?variation with frequency,the intersection of G'and G'',Han plots,van Gurp-Palmen plots and Cole-Cole plots all showed that the incorporation of TDI-GO decreased the degree of microphase separation and improved the elastic properties of the nanocomposites.3.N and S co-doped carbon dots.N and S co-doped carbon dots with bright blue emission have been synthesized by a facile one-pot hydrothermal treatment.A specific compound,guanidine thiocyanate via a hydrogen bond to form the molecule unit,was chosen as the dopant.In the structure characterization,N and S elements could be sufficiently doped by means of the heteroatom or the functional groups bonded on the surface of carbon dots.The results of the photoluminescence spectra indicated a change of emission process from excitation-independent to excitation-dependent with the optimal excitation wavelength at 396nm,suggesting that some small fluorophore molecules exist in citric acid-derived carbon dots solution and bond on the surface of the carbon dots after carbonization in view of the triexponential feature of fluorescence lifetimes of carbon dots.Now that so many fluorophores attach on the carbon dots surface,the as-prepared carbon dots were used as a sensing probe for the detection of silver ion.As expected,the changes of fluorescence intensities were linearly proportional to the different concentration ranges of silver ion.The–S–C?N group could accelerate the quenching of carbon dots towards silver ion.The facile preparation method and high performace of as-prepared carbon dots provide a possible approach for efficient detection of silver ion for the application in industrial pollutants.4.0D CDs/TPU composites.High performance thermoplastic polyurethane/carbon dots(TPU/CDs)bulk nanocomposites with strong luminescence were fabricated via in situ polymerization.The CDs were synthesized from citric acid and 2-aminothiophenol.Transmission electron microscope(TEM),FT-IR,XPS and systematic characterization indicated the formation of the CDs and the covalent conjugation of the CDs with TPU.All the composites exhibited stronger luminescence behavior than the loading CDs.When the CDs content was 0.5 wt%,the absolute photoluminescence quantum yields(QY)was as high as68%.Furthermore,the rheological,mechanical and thermal properties of the nanocomposites were investigated.The rheological properties established the structure-property relationships of the composites.The incorporation of the CDs enhanced the elastic response in viscoelasticity of the nanocomposites.The tensile strength of 1.0 wt%CDs loaded TPU increased from 18.2 to 28.6 MPa,nearly 57%higher than that of the neat TPU.Given the excellent Ag~+detection performance of the CDs,the high QY and the processability of the nanocomposites,Ag~+detection experiments for the composite film were performed.The study will facilitate the applications of luminescent nanocomposites in potential fields.