Preparation And Properties Of Conductive Hybrid Isocyanate Polyurethane Materials

With the rapid development of the polyurethane（PU）industry and the requirements for its performance and applications are getting higher and higher,which makes it urgent to modify the PU.Given that PU has a specific structure-performance relationship,it is an effective and easy-to-operate way to optimize performance from raw materials.As one of the raw materials of synthetic polyurethane,the isocyanate is a hard segment of polyurethane,which provides strength,modulus,and high-temperature performance.Therefore,according to the type and proportion of isocyanate monomers in the raw material,the target performance of polyurethane can be optimized.The traditional PU is an insulator,which limits its application in specific fields,so conductive polyurethane was born.Multi-walled carbon nanotubes（MWCNTs）are ideal fillers for preparing high-performance conductive composites due to their excellent physical and mechanical properties,ultra-high thermal conductivity,and unique electrical properties.However,the disadvantage of easy agglomeration also inhibits their application.Therefore,functional modification of MWCNTs is the key to overcome compatibility and adhesion.In the study,a prepolymer method was used to synthesize mixed isocyanate polyurethane（IM-PU）,and the effects of the mixed isocyanate monomer ratio and cross-linking agent TMP on the properties of IM-PU were investigated.The product was confirmed from the urethane bond in the infrared spectrum,and it was found that the intensity of the benzene ring peak increased as the molar ratio of the IPDI:MDI monomer decreased.It is found that when n is 5:5,the maximum tensile strength of IM-PU without TMP is 37.2 MPa and the hardness can reach 88 HD.Currently,IM-PU has the best mechanical properties,thermal stability,and water absorption;When the amount of TMP is2%,the maximum tensile strength is 32.92 MPa and the maximum hardness is 92.5 HD.The hydroxylated and silanized MWCNTs were used as conductive fillers,and IM-PU was used as the matrix when n was fixed at 5:5.The conductive polyurethane（MWCNTs/PU）was prepared by physical blending.According to infrared analysis,thermogravimetric analysis,and scanning electron microscope analysis,it was found that the functional modification of MWCNTs was successful without causing structural damage.It was calculated that a molecular chain of KH-550 was connected to every 75.6 carbon atoms in MWCNTs-KH550.The silanization-modified MWCNTs-KH550 significantly improved the thermal stability,storage modulus,and glass transition temperature of the composites,among which T_g increased from-59.2oC of IM-PU to-36.67oC.SEM photos show that the dispersibility of silanized MWCNTs-KH550 in IM-PU matrix is the best.When the amount of MWCNTs-KH550 is 2.5%,the maximum tensile strength of MWCNTs/PU can reach68.69 MPa,which is about three times that of IM-PU,the maximum hardness is 109.3 HD.And the maximum value of water absorption reduction at this time is 0.835%,so the best water resistance.When the MWCNTs content is 2%,the percolation threshold of the material is reached,and the conductivity changes from 3.3×10^-10 S/cm to 3.7×10^-3 S/cm,an increase of 7 orders of magnitude,and the material changes from an insulator to a semiconductor.