Chemical Functionalization Of Carbon Nanotubes And The Properties Of Their Waterborne Polyurethane Composites

Carbon nanotubes(CNTs)with one-dimensional nanostructures,which have excellent properties: mechanics,heat,electricity,and so on,are ideal reinforcing fillers for the preparation of nanocomposites.As an environmentally friendly polymer,waterborne polyurethane(WPU)with non-toxic,non-polluting,storing easily,and good film-forming properties,is one of the important substrates for the preparation of nanocomposites.CNTs/WPU composites combine the advantages of both CNTs and WPU,which makes them have potential application value in some fields: electromagnetic interference shielding,functional coatings,electronic communication,aerospace,biomedicine,and so on.However,due to the structural characteristics of CNTs,it is difficult to uniformly disperse in the WPU matrix.In addition,the surface of CNTs is chemically inert,so that the interface interaction with the matrix is weak,which leads to the poor reinforcement,so the composites with excellent performance cannot be obtained.In order to overcome these problems,this paper based on the interface structure of CNTs and WPU matrix,chemically functionalized the surface of CNTs,and the composites were prepared bysolution blending with WPU.On the basis of this,the effect of chemical functionalization on the dispersion of CNTs in the WPU matrix and the interface interaction between CNTs and matrix were studied.Moreover,the "structural-property relationship" of composites was studied deeply.The main contents are as follows:1.The pristine multi-walled carbon nanotubes(MWCNTs)were carboxylated and acylchlorinated,and then esterified with ethylene glycol(EG),glycerol(GL),and dimethylolpropionic acid(DMPA)to prepare three hydrophilic MWCNTs,and MWCNTs/WPU composites were prepared by solution blending method.The results showed that the grafting fraction of organic chain was the higher than 19.8% and the functionalized MWCNTs had good dispersibility in water and/or WPU emulsion.Meanwhile,the dispersion of MWCNTs in WPU and their interfacial adhesion with WPU matrix were greatly improved.The higher grafting fraction led to a better dispersion of MWCNTs in water,the smaller average particle size of MWCNTs/WPU emulsion,the more improvement in the mechanical properties and electronic conductivity of the composites,respectively.The tensile strength of MWCNTs-EG,MWCNTs-GL,and MWCNTs-DMPA composites with 1.5 wt%increased by 20.9%,26.4%,and 30.1% compared with the pristine MWCNTs composites,respectively.In addition,the electrical conductivity increased by more than 3 orders of magnitude.2.Three hydrophilic MWCNTs was prepared by amidation of carboxylatedMWCNTs and then undergoing the Michael addition reactions with hydroxyethyl acrylate(HEA),acryloyl morpholine(ACMO),and acrylamide(AM),respectively.The products were mixed with WPU to fabricate MWCNTs/WPU composites.The results showed that the functionalized MWCNTs were dispersible well in water.Moreover,the amide,amine,or hydroxyl groups in the attached moieties can form hydrogen bonds with the amide and carbonyl groups from WPU macrmolecular chain,which improved the compatibility and interfacial adhesion between MWCNTs and the WPU matrix.The mechanical properties and electrical conductivity of the composites were significantly improved.Compared with the pristine MWCNTs,after adding 1.5 wt% of MWCNTs-HEA,MWCNTs-ACMO,and MWCNTs-AM,the tensile strength of the composites was greatly enhanced by about 20.3%,22.5%,and 30.1%,respectively.Furthermore,the electrical conductivity increased by more than 3 orders of magnitude.3.The pristine MWCNTs were carboxylated,and then epoxy ring-opening reaction was carried out with epoxy resin.The epoxy chains were grafted onto the surface of MWCNTs and introduced it into WPU to prepare MWCNTs/WPU composites.The results showed that the epoxy chains on the surface of functionalized MWCNTs could form a three-dimensional network cross-linking structure with carboxylic acid and amine groups in WPU macromolecules,which enhanced the dispersibility of MWCNTs in WPU matrix.Meanwhile,the mechanical property,thermal stability,water resistance,and electrical conductivity of the composites were significantly improved.Compared with the pristine MWCNTs composites,the tensile strength,initial thermal decomposition temperature,and electrical conductivity of the functionalized MWCNTs composites with 1.5 wt% were increased by about108.1%,11.0°C,and 6 orders of magnitude,respectively.4.The pristine MWCNTs were oxidized and then reacted with EG,isophorone diisocyanate(IPDI),and dimethylolpropionic acid(DMPA)to form functionalized MWCNTs containing urethane groups.MWCNTs/WPU composites were prepared by solution mixing method,and the effects of chemical functionalization of MWCNTs on the comprehensive properties of WPU composite films were studied.The result showed that after grafting the hydrophilic chains containing urethane group,MWCNTs was uniformly dispersed in WPU,and the compatibility with WPU matrix was improved.In addition,the mechanical properties,heat resistance,water resistance,and electrical conductivity of WPU composite film were greatly improved.After adding 1.5 wt% functionalized MWCNTs,the tensile strength of the composites was increased by about 52.2%,the initial thermal decomposition temperature was increased by 2.8°C and the electrical conductivity was increased by 4orders of magnitude compared with the pristine MWCNTs composite.