Study On The Microporous Structure And Properties Of Polyurethane Nanocomposite Foam

Compared with other insulation materials,rigid polyurethane foam has excellent thermal insulation performance,chemical corrosion resistance and aging resistance,and is widely used in cold chain logistics insulation,building insulation,pipeline insulation and other fields.However,the mechanical strength is lower than other insulation materials.Therefore,how to improve the mechanical properties of rigid polyurethane foam has important practical value for expanding its application.Carbon nanotubes and graphene oxide have been widely used as reinforcing materials for rigid polyurethane foams in recent years.Carbon nanotubes,which have the advantages of high strength and high conductivity,are the most commonly used as one-dimensional fibrous carbon materials,and can be used for nano-reinforced materials of polymer matrix and heterogeneous nucleating agents.However,its larger surface inertia,larger aspect ratio and larger specific surface lead to agglomerate in polymer matrix.The uneven dispersion in the polymer matrix affects the nucleation effect,thereby the surface modification of the carbon nanotubes can strengthen the its interaction with polymer matrix,and can make it evenly dispersed and obvious nucleation effect.Graphene oxide has two-dimensional layer structure,which not only retains the unique sheet structure of graphene,but also has a large number of oxygen-containing functional groups on the surface,such as carboxyl groups and hydroxyl groups,so that it can be reacted with many small molecules or polymer.The chemical reaction is carried out to realize the functionalization of the covalent bond,and the interaction force with the polymer matrix is improved to achieve uniform dispersion,which plays a good role in nucleation.The surface modification of the carbon nanotubes and the graphene oxide by grafting reaction was studied in this thesis.The amino and hydroxyl groups was introduced onto the surface of the carbon nanotubes,and the amino and isocyanate groups onto the surface of graphene oxide,then the modified graphene oxide and carbon nanotubes are respectively introduced into the polyurethane foam matrix to improve their interface compatibility with the polyurethane matrix,to promote their uniform dispersion and heterogeneous nucleation.The heterogeneous nucleation,which in turn regulates the microscopic cell structure,optimizes the mechanical properties and thermal conductivity of the polyurethane foam.The main research work is as follows:1.Polyurethane foams were prepared by physical foaming agents HCFC141b,HFC-245fa,HFC-365mfc and LBA.The cell structures of polyurethane foam prepared by several new foaming agents were analyzed and compared.The performance indicators such as the average cell diameter,the number of cells in per unit area,the apparent density,the closed cell ratio,the compressive strength and the thermal conductivity were studied.It was concluded that:HFC245fa and LB A can be used as.the new type of physical foaming agents for polyurethane foam considering the cell structure and nucleation process;but considering the thermal conductivity and diffusion coefficient,LBA may be the best choice,meanwhile LBA has zero ODP value and very low GWP value.2.The amino-modified MWCNTs were prepared by grafting amino compounds onto multi-walled carbon nanotubes(MWCNTs)by esterification and amidation reaction.The effect of amino-modified MWCNTs on the foaming behavior of polyurethane foam were further studied.The.The structure of amino-modified MWCNTs were characterized by Fourier transform infrared spectroscopy,thermogravimetric analysis,transmission electron microscopy and elemental analysis.The effect of amino-modified MWCNTs on the microscopic cell structure,the apparent density,and the compressive strength were studied.The results showed that,increasing the amount of amino-modified MWCNTs,the number of cells in per unit area,the apparent density and the compressive strength of polyurethane foam increased first and then decreased,the pore size was the opposite.When adding 0.9%amino-modified MWCNTs,the polyurethane foam has the best performance,and the average cell diameter is 0.23mm,the apparent density is 49.8kg/m3,and the compressive strength is 620kPa,achieving the purpose of reinforcement.3.The hydroxyl-modified multi-walled carbon nanotubes(MWCNTs)were prepared by grafting glycerol onto MWCNTs by esterification reaction.The effects of glycerol-modified MWCNTs on the foaming behavior and the properties of polyurethane foam were further studied.The structure of glycerolmodified MWCNTs was characterized by Fourier transform infrared spectroscopy,thermogravimetric analysis and transmission electron microscopy.The effect of glycerol-modified MWCNTs on the cell structure,the compressive strength and the apparent density of polyurethane foam were researched.The results showed that increasing the amount of glycerol-modified MWCNTs,the pore size of polyurethane foam decreases first and then increases,and the apparent density and the compressive strength both were the opposite.When adding 0.6%glycerol-modified MWCNTs,the properties of the polyurethane foam were the best,and the average cell diameter was 0.26 mm,the apparent density was 48.9 kg/m3,and the compressive strength was 560 kPa.4.A two-dimensional layered carbon material,graphene oxide,was prepared by Hummers method with the aid of low-middle temperature ultrasound.The graphene oxide was modified by amidation reaction using polyetheramine and triethylenetetramine.The structure of graphene,graphene oxide and amino-modified graphene oxide were characterized by FT-IR analysis,XPS analysis,XRD analysis,thermogravimetric analysis,SEM analysis.The two amino-modified graphene oxides were introduced into the polyurethane foams and their effects on the morphological structure,the apparent density,the compressive strength,the thermal conductivity,the storage modulus and the glass transition temperature of polyurethane foam were compared.The effect of the amount of amino-modified graphene oxide on the nucleation process was used to regulate the microscopic cell structure of the foam.The results show that,the additions of polyetheramine modified graphene oxide and triethylenetetramine modified graphene oxide resulted in a smoother cell wall,a more uniform cell structure and a smaller average pore size which reached 0.22 mm and 0.23 mm,respectively.The analysis of mechanical properties showed that the addition of graphene oxide caused the apparent density,the compressive strength and modulus of the foam to decrease.But the additions of two amino-modified graphene oxide had the opposite effect.The thermal conductivity analysis showed that the thermal conductivity of the polyurethane foam increased slightly regardless of the type of graphene oxide,but the increase range was still within the acceptable range.DMA analysis showed that the platform of the storage modulus curve appeared slightly ahead,indicating that polyetheramine modified graphene oxide is more suitable for polyurethane foam matrix.Finally,adding 1.5%polyetheramine modified graphene oxide,the apparent density was 48.1kg/m3,the compressive strength was 520 kPa and the thermal conductivity was 22.2/mW/(m·K).5.A two-dimensional layered carbon material,graphene oxide,was prepared by Hummers method with the aid of low-middle temperature ultrasound.The graphene oxide was modified by reaction using isophorone diisocyanate(IPDI).The structure of isocyanate-modified graphene oxide was characterized by infrared spectrum,XPS spectrum and XRD spectrum.The effect of the reaction time and the amount of isocyanate-modified graphene oxide on the foam morphology and the performance of the foam.The results showed that when adding a small amount of isocyanate-modified graphene oxide,it can only slightly improve the morphology of the pores of polyurethane foam,and its effect on the average pore diameter is not large.When increasing the amount to 1.0%,the cell morphology can be approximately as a circle,and its structure is relatively uniform.When the amount continued to increase,a small number of larger cells gradually appeared in the system,and the uniformity of the cell structure became worse.Increasing the amount of isocyanate-modified graphene oxide,the apparent density and the compressive strength of the foam first increased and then decreased,reaching a maximum at its amount of 1.0%;the thermal conductivity first increased slightly,then decreased and then increased,also reaching a minimum at its amount of 1.0%.Finally,the optimal reaction time of isocyanate-modified graphene oxide was 20h,and the optimum amount was 1.0%.At this time,the apparent density of the foam was 49.3 kg/m3,the compression strength was 596 kPa,and the thermal conductivity was 22.4/mW/(m·K).