| As a new type of foam plastic in recent years,melamine-formaldehyde(MF)foam plastic has some excellent performances of the traditional foams such as heat preservation,sound insulation,shock absorption,cleaning,etc.besides,it overcomes the flammability which is the biggest defect of traditional foam plastics.However,the unmodified MF foam plastic is very brittle and lost-powder is easy because of the rigid triazine ring in the MF molecular structure.This paper is committed to improve the brittleness,decrease the powder losing-rate and ensure the flame retardant of the MF foam plastic at the same time.Besides,the foaming process was discussed to provide theoretical basis for MF foam plastic products with excellent comprehensive performance,which could be developed in the future.Firstly,the MF resin was prepared by using melamine,formaldehyde and paraformaldehyde as raw materials under alkaline solution by multi-objective orthogonal experiment.The experimental results were analyzed by using comprehensive scoring method and integrated balance method.And the optimum formula of the preparation was hence obtained as F/M=2.5,pH=8.0,T=90?,t=60min.This condition was scientific,reasonable and controllable,under which the density of the foam was 69.4kg·m-3 and the size uniformity was 0.0116.Combined with the infrared spectroscopy and thermogravimetric curves,it illustrated that the hydroxyl methylation reaction has happened between melamine and formaldehyde in experimental conditions.Secondly,the foaming process was selected and optimized:n-pentane and ammonium were selected as foaming and curing agent finally by comparing the foaming effects of different foaming agent and curing agent.The effects of mass ratios of foaming agent to the curing agent(F/C)on the structure and density and the percent of power-lost of the foam were studied.Combined with the micrographs of the MF foam,it showed that F/C affect the hole structure and the properties of MF foam in turn by adjusting the foaming and cure rate,for example,the greater the F/C value is,the faster the foaming rate comparing with the cure rate is,the foam has greater hole size,finer hole stents and less brittle fracture structure,which leads to decreasing of the foam density and the powder lost-rate.By studying the effect of the curing agent dosage,curing temperature on the curing time,combined with the actual operation convenience,the final optimized condition was obtained as the curing agent and surfactant were 2 g respectively to 100g MF resin and the foaming temperature was 80?and the foaming time was 30min.Finally,polyvinyl alcohol(PVA)and polyurethane prepolymer were selected as modifiers to improve the performances of MF foam:?Three methods were adopted to add PVA as modifier which loading sequence were that in the order,method 1:formaldehyde?PVA?melamine;method 2:formaldehyde?melamine?PVA;method 3:formaldehyde?PVA?melamine?PVA,method 3 was selected for the compression strength and powder lost-rate of the modified MF foam decreased by 50%and 68.7%respectively.Besides,the effects of PVA content were studied and the powder lost-rate was the lowest as 2.4%when the PVA content was 7.5%.?The foaming process modified by PU prepolymer was researched firstly,the effects of the PU prepolymer content on the compress strength and bending strength,as well as the power lost-rate of the modified MF foam were studied.The limited oxygen index(LOI)and smoke density of the MF foam modified by different content of PU prepolymer were compared,it concluded that PU prepolymer reduced the LOI value of MF foam(LOI value reduced from 38%to 21%when PU prepolymer dosage was 30%),but delayed the combustion and reduced smoke emission.Combined with the characterization of infrared spectroscopy and thermogravimetric curves,the essence of the modification could be interpreted as the long,flexible C-C-O-O-C and N-C-O-C-N chains were introduced to the rigid structure of the MF molecular. |
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