Synthesis And Performance Study Of The Polymethylacrylimide Aerogels And Its Hybrid Aerogels

Polymethacrylimide(PMI)is a high performance,rigid thermosetting resin material.The application form of the PMI products was only the close-cell foam in the market.PMI foams is a closed cell rigid foam with higher specific modulus,creep resistance,strength and structural stability than rigid foams such as PVC and PUR.With its high mechanical properties and high strength to weight ratio,PMI foam is the material of choice as a core material for sandwich composites and is widely used in extreme environments such as high temperatures and high loads.Up to now,the application form of the PMI products was only the close-cell foam in the market.The relevant research on open-cell structure PMI has not been reported previously in the literature.Polymer aerogel is a kind of porous material with high porosity formed by polymer chains aggregating with each other to form a three-dimensional open-hole network structure under the action of the interaction force between chain segments.Polymer aerogel has been widely used in the fields of catalyst carrier,aerospace,filter cartridge,construction,thermal insulation and sound insulation due to its excellent properties such as ultra-low density,low dielectric constant,high porosity,high thermal insulation performance and high specific surface area.Among polymer aerogels,the polyimide(PI)aerogel is the aerogel with the best overall performance.Polyimide,produced from poly(amic acid)after thermal or chemical imidization,represent a class of high-performance polymers with imide rings on the backbond.For PMIs,imide rings were introduced into the polymer backbone as side chains.The production process of PI aerogels laid a foundation for the preparation of PMI aerogels.In this paper,the application form of PMI material was expanded to open-cell structure aerogel,and we studied the application of high-performance PMI aerogel in the application field of open-hole structure porous materials.The main raw materials of PMI aerogel are monomer methacrylonitrile(MAN)and monomer methacrylic acid(MAA),and other additives are cross-linker acrylamide(AM)and initiator azo diisobutyronitrile(AIBN).The MAN/MAA copolymer was prepared by free radical solution polymerization by dissolving the raw materials and auxiliaries in organic solvent N-methylene pyrrolidone(NMP)in a certain ratio.The MAN/MAA copolymer ammonium salt was then prepared by waterborne treatment using triethylamine(TEA).The MAN/MAA copolymer ammonium salt aerogels were prepared using the freeze-drying method,followed by heat treatment to prepare PMI aerogels.On this basis,PMI composite hybrid aerogels were successfully prepared by introducing sodium-based montmorillonite(Na-MMT)and carbon fibres into the MAN/MAA copolymer ammonium salts.The qualitative analysis of aerogels were characterised using Fourier infrared spectroscopy(FTIR)and X-ray diffraction(XRD),the microstructure and pore size structure of the aerogels were characterised using scanning electron microscopy(SEM)and Mercury Pressing Instrument,and the mechanical properties,thermal insulation properties and flame retardant properties of the aerogels were characterised by uniaxial compression tests,transient planar heat source thermal conductivity and vertical flame retardant experiments.The results of this article are as follows:(1)PMI aerogels have low shrinkage(<18%)and high porosity(>89%)with good stability of porous structure.PMI aerogels presented better mechanical porperties after heat treatment.With increasing solid content,SEM micrographs showed the more inhomogeneous porous structure and increasing network thickness,and the compression properties and thermal conductivity of PMI aerogels also increase with increasing density.The PMI aerogels show insulation properties with a low thermal conductivity of 43-48m W/(m·K)at room temperature.The compressive properties of PMI aerogel with a density of 0.05 g/cm~3are similar to those of rigid PI aerogel is similar to that of rigid PI aerogel.(2)The sodium-based montmorillonite had good phase solubility in PMI polymer.The PMI/Na-MMT aerogel showed the lamellar-like pore structure and maintains a high porosity(>95%).The shrinkage of PMI/Na-MMT aerogel decreased with the increase of Na-MMT content,and the minimum shrinkage of the prepared sample is 11.8%.the flame retardant properties and mechanical properties increase with the increase of Na-MMT content.Compared with the pure PMI aerogel with the same solid content,the PMI/Na-MMT aerogel with the addition of 20%Na-MMT by quaternary ammonium salt mass showed a 5.9-fold increase in compressive strength at 70%compressive deformation.The flame retardant enhancement of PMI aerogels by Na-MMT was mainly derived from the catalytic carbon formation,heat absorption and the increase of gas flow paths.(3)The acid-modified short-cut carbon fibers were used as the fibrous reinforcing particles of PMI aerogel,and the prepared PMI/carbon fiber hybrid aerogel possessed high mechanical properties and high porosity(>94%),and the lowest shrinkage of the prepared hybrid aerogel was 4.5%.The addition of carbon fibers increases the average pore size of the aerogel.The carbon fiber surface showed the groove structure.The short-cut carbon fibers have a strong enhancing effect on the mechanical properties of PMI/carbon fiber hybrid aerogel.With the increase of carbon fiber content,the mechanical properties of PMI/carbon fiber aerogel also improved.The greater the compression deformation,the more obvious the enhancement of the mechanical properties of carbon fibers on the aerogel.Compared with the pure PMI aerogel with the same solid content,the PMI/carbon fiber aerogel with 20%carbon fiber content in ammonium salt mass had 13.2 times higher compressive strength at 70%compressive deformation.