Preparation Of Novel Carbon Nanomaterials And Their Modification Of Polyurethane Elastomers

Carbon material/polymer composites are novel composite materials in which carbon nanomaterials are embedded in a polymer matrix.Graphene oxide and carbon nanotubes are two widely studied carbon nanomaterials at present,both of which have similar sp~2heterostructures and can exhibit better enhancement and functionalities.Nanocomposite modification of carbon nanomaterials to polyurethane elastomers exhibited prospective future to improve the mechanical properties,thermal and electrical conductivity of polyurethane elastomers.The agglomeration and difficulty in dispersion when carbon materials are compounded with polymers are recognized scientific problems.To solve the problem of poor dispersion for graphene oxide and carbon nanotubes in polyurethane matrix when polyurethane is modified,this thesis adopted novel technical route to covalently modify carbon nano materials with diisocyanate,and then the modified carbon nanomaterials are employed to modify polyurethane to study the structure and properties of polyurethane composites and explore the effect of new carbon nanomaterials on the properties of the composites.The main research work of this thesis consisted of the following three parts:A series of novel carbon nanotubes with isocyanate characteristics were prepared by covalently grafting reaction of hydroxy carbon nanotubes(OH-MWCNTs)with toluene diisocyanate(TDI),p-phenylene diisocyanate(PPDI),isophorone diisocyanate(IPDI),1,5-naphthalene diisocyanate(NDI)and 4,4'-diphenylmethane diisocyanate(MDI),respectively TDI@MWCNTs,PPDI@MWCNTs,IPDI@MWCNTs,NDI@MWCNTs,and MDI@MWCNTs.Compared with OH-MWCNTs substrate,the modified carbon nanotubes showed shorter aspect ratios,uneven folds in the tube walls,and randomly oriented distribution in the organic solvent,which proved that the organic molecular chains were successfully grafted onto the carbon nanotube surfaces and the entangled agglomeration of carbon nanotubes was improved.Thermogravimetric analysis of the series of modified carbon nanotubes showed that the weight loss steps of MDI@MWCNTs were the most obvious,indicating the highest grafting rate on MWCNTs via MDI,MDI@MWCNTs showed improved dispersibility and thermal stability.IPDI@MWCNTs,NDI@MWCNTs,and MDI@MWCNTs were used as nano-reinforcing modifiers,respectively.The structural evolution of carbon nanotubes before and after modification and the modification effect of activated carbon tubes(NCO@MWCNTs)content on polyurethane elastomers were investigated.The results showed that the NCO@MWCNTs exhibited similar high reactivity of isocyanate to diisocyanate monomer and could be uniformly dispersed into the polyurethane matrix,and the reactive hybridization of NCO@MWCNTs did not change the micro phase separation characteristics of polyurethane.When the content of IPDI@MWCNTs,NDI@MWCNTs and MDI@MWCNTs is 0.10wt%,the tensile strengths of the polyurethane elastomers reached extreme values of 67.3 MPa,68.6 MPa and 69.4MPa,respectively,which were about twice as high as those of the blank polyurethane elastomers,showing excellent enhancement effects.With an increase of NCO@MWCNTs in content,the stress at fixed-elongation monotonically increased and the elongation at break showed a gradual decrease.The thermal stability of PU was improved by the barrier effect of the unique sp~2heterostructure of MWCNTs and the delocalization effect on the cleavage radicals,and the initial decomposition temperature of NCO@MWCNTs/PU increased by 6?8?compared with that of blank PU.With an increase of MDI-MWCNTs in content,the electrical conductivity of polyurethane elastomer composites gradually increased,and the electrical conductivity reached 1.71×10^-4when the addition of MDI-MWCNTs was 0.20%.The composite technology of novel carbon tubes made the polyurethane show excellent reinforcement and good electrical conductivity.Highly dispersed multi-dimensional active carbon nanomaterials were prepared by reaction of hydroxyl groups from the carbon nanomaterials mixture of graphene oxide(GO)and hydroxy multi-walled carbon nanotubes(OH-MWCNTs)with MDI,and then the polyurethane was modified by compounding the multi-dimensional active carbon nanomaterials with different mass fractions.The experimental results showed that the modified carbon nanotubes were interspersed between GO lamellae and the degree of GO exfoliation increased,which greatly improved the dispersibility of carbon nanomaterials.The coexistence of multidimensional structures of MWCNTs-g-GO was better compatible with the polyurethane matrix,and the increase in tensile strength of the polyurethane composites was confirmed again,while the three-dimensional super-conjugated electron delocalization effect constructed by MWCNTs-g-GO played the role of trapping free radicals and inhibited the aging reaction,and the tensile strength of the polyurethane composites with 0.10wt%loading compared with the blank PU sample increased from 33 MPa to 69.5 MPa,exhibiting the super enhancement effect,and the aging reinforcement time extended from 10 h to 25 h.With an increase in content of MWCNTs-g-GO,the conductivity of the composites improved substantially,reaching a maximum conductivity of1.75×10^-4with 0.20%addition,which was 2.3%higher than that of PU modified with carbon nano tube alone.