Preparation,structural And Performance Regulation Of Melamine Resin Rigid Foam

As an intrinsic flame retardant material,the melamine resin rigid foam has excellent flame retardant performance and is expected to replace flammable polymer foam（polystyrene foam,polyurethane foam,polyvinyl chloride foam,etc.）as a new heat preservation and energy saving material applied in the field of construction.However,due to the rigid molecular structure of triazine ring connected by methylene bridge and methylene ether bridge,the melamine resin rigid foam has the disadvantages of high brittleness and easy crushing,which seriously hinders its application.In addition,the current use of most chemical toughening agent is given priority to with high carbon content of organic compounds,although the toughening agent on the melamine resin rigid foam toughening have certain effect,but also due to the introduction of too much carbon source,reduce the nitrogen content of its own,resulting in a decline in the flame retardant performance of the original bubble,lost its excellent flame retardant properties.In this study,vermiculite containing silicon and aminopropyl end of polydimethylsiloxane as toughening agent,using the active hydroxymethyl in melamine resin,vermiculite or silane into the rigid molecular structure,to achieve the purpose of toughening and flame retardant,so as to prepare a series of modified melamine resin rigid foam.1.Using vermiculite as raw material,acidified vermiculite（acid-EV）containing hydroxyl was prepared by expansion,ball milling,acidification and other treatments.Then,melamine resin was prepared by in-situ synthesis,and then microwave-foaming was prepared by vermiculite toughened melamine resin rigid foam（MF-xacid-EV,x represents the addition amount of acid-EV relative to melamine）,and the mechanical,flame retardant and thermal stability properties of MF-xacid-EV were studied.Compared with pure melamine resin rigid foam,the mechanical properties of MF-xacid-EV are significantly improved.The maximum compressive strength of MF-2%acid-EV is 293 k Pa,which is 159%higher than that of pure melamine resin rigid foam.At the same time,the thermal stability and limiting oxygen index（LOI）of MF-xacid-EV were also significantly improved,and the final residual amount of m F-xacid-EV rigid foam was increased from11.69%to 22.58%,and LOI was increased to 34.5%.2.The acid-EV reacted with isophorone diisocyanate,and then in situ petrified with PPG600 to prepare polyurethane/vermiculite hybrid toughening agent（PU-EV）with isocyanate end,and used this toughening agent to prepare melamine resin rigid foam（MF-PU-EV）.The mechanical properties of MF-PU-EV are better than those of pure melamine resin rigid foam and polyurethane toughened melamine resin rigid foam（MF-PU）.The compressive strength and bending strength of MF-PU are 253.03 k Pa and 297.95 k Pa,respectively,which are 41.1%and 58.9%higher than those of pure melamine resin rigid foam.The LOI of MF-PU-EV was 35%compared with that of MF-PU.Meanwhile,TG test showed that the residual amount of MF-PU-EV was 19.61%,which was 27%higher than MF-PU.These results indicate that the acid-EV peel layer can mitigate the effect of polyurethane on the flame retardancy of melamine resin rigid foam.3.In order to reduce the water absorption rate of melamine resin rigid foam,aminopropyl terminated polydimethylsiloxane（NH₂-PDMS）was selected as toughening agent to prepare melamine resin rigid foam with closed cell structure（MF-x NP,x represents the filling amount of NH₂-PDMS relative to melamine resin）.Compared with pure melamine resin rigid foam,MF-x NP has closed bubble structure and higher apparent density.The maximum compressive strength of MF-0.3NP is 641.87 k Pa,5.6 times that pure melamine resin rigid foam.The water absorption rate of MF-0.3NP was the lowest 11.88%,indicating that the introduction of NH₂-PDMS improved the mechanical properties and water absorption rate of the foam.First,the amino group in NH₂-PDMS reacted with the aldehyde group in the melamine resin,and the flexible silicon oxygen chain was introduced into the rigid molecular structure of the foam to achieve the purpose of toughening.Second,the methyl side chain in NH₂-PDMS also endows the foam with certain hydrophobicity and reduces the water absorption rate of the foam.Third,because MF-x NP is closed cell foam,it will also play a role in toughening and reducing water absorption.In addition,the LOI of MF-x NP is 36.7%,indicating that the introduction of NH₂-PDMS and the closed cell structure are conducive to the improvement of flame retardant performance.