Study On Toughening Modification Of MF Rigid Foam Material

Rigid melamine-formaldehyde(MF)foam is a kind of foam material synthesized by melamine and formaldehyde prepolymer through chemical reaction and then prepared by foaming process.Because melamine contains a large number of triazines structure,the prepared rigid MF foam material has good flame resistance and thermal stability.However,the MF resin is brittle,and most rigid foam materials have open-cell structure and poor toughness,resulting in larger water absorption ratio,lower compressive strength and more serious dregs.Its application in the field of Insulation Materials for building external wall and cold storage insulation board is limited.Through the chemical and physical modification of MF resin prepolymer and foaming liquid,the rigid MF foam material with high close-cell ratio,remarkable toughness and improved mechanical properties has been prepared.The main contents are described as follows:1)Ethylene glycol was used as hydroxyl modifier to chemically modify MF resin prepolymer,and the toughening effect of ethylene glycol on melamine resin and foam was studied.The condensation reaction between hydroxyl groups at both ends of ethylene glycol and methylated melamine increases the distance between the rigid triazine rings in melamine resin,and increases the flexible carbon chain,which result in the improvement of the toughness.2)Urea was used as amine containing modifier to chemically modify the prepolymer of MF resin,and the toughening effect of urea on melamine resin and foam was studied.Urea is used as modifier instead of some rigid melamine to achieve the purpose of toughening.3)Carbon fiber was used as physical toughening modifier in the foaming liquid prepared from ethylene glycol modified MF resin prepolymer,and the toughening effect of carbon fiber on foam was studied.Carbon fiber has the characteristics of high strength and high modulus,which plays a role of connection in the cell wall,enhances the strength of the cell wall,and prevents the damage of the cell wall.Besides,due to the interaction between CF and the resin matrix,the strength of foam cells was improved,and the combination of cells was effectively suppressed,which was advantageous for obtained a small cell size and a uniform bubble diameter distribution.The results showed that the effect of composite modified rigid MF foam with ethylene glycol and carbon fiber is the best.The most appropriate conditions to chemical modify melamine resin prepolymer are as follow:the proportion of tripolycyanamide and formaldehyde is 1:3,the reaction temperature and time is 85~oC and 2.5h,respectively.Based on the quality of melamine,the dosage of p H regulator of hexamethylenetetramine is 1wt%,and the dosage of glycol is 15wt%.The best preparation process and formula of rigid MF foam are as follow:Based on quality of prepolymer of modified melamine resin,when the viscosity of the prepolymer was 70Pa·s,2wt%silicone oil,5wt%hexane,0.65wt%hydrochloric acid and 0.9wt%carbon fiber were added into the prepolymer to obtain the foaming liquid.Then the foaming liquid was foamed for 40 min at 100?in an oven,and cured subsequently at120?for 6h.The as-prepared toughing MF rigid foams showed the best comprehensive performance with apparent density of 54.26kg/m~3,pulverization rate of 5.21%,compressive strength of 355.3KPa,bending strength of 0.44MPa,closed-cell ratio of79.1%,water absorption of 9.0%,thermal conductivity of 0.030w/(m·K)and LOI of39.6%.