Preparation And Properties Of Flame Retardant Rigid Polyurethane Foam

Polyurethane rigid foam(PURF)is a kind of thermosetting resin.Because of its low thermal conductivity and excellent thermal insulation performance,it is widely used in building exterior wall,road frost-proof,cold storage heat insulation,transportation and other fields.However,its structure leads to poor flame retardancy,which limits its application.Therefore,it is important to study the flame retardant rigid polyurethane foams.The traditional flame retardant modification of PURF is to add additive flame retardants containing flame retardant elements and structures into the matrix by physical blending.This method not only greatly reduces the mechanical properties,but also has limited flame retardant effect of PURF.In this paper,a reactive flame retardant was synthesized by structural flame retardant method,and the flame retardant of PURF was modified by adding phosphorus-containing flame retardant dimethyl methylphosphonate(DMMP).In this paper,a reactive nitrogen-containing flame retardant,Hydroxymethyl Melamine(HM),was synthesized from melamine and formaldehyde.Its structure was characterized by FTIR,solid-state nuclear magnetic resonance hydrogen spectroscopy and carbon spectroscopy,elemental analysis(EA).The effects of raw material ratio,reaction time,reaction temperature and solution pH value on hydroxymethylation products and the crosslinking curing reaction time,reaction temperature,pH value and dehydration time on HM properties,water content and free formaldehyde content were investigated.The optimum reaction conditions were as follows:the molar ratio of melamine to formaldehyde was 1:2.5,the catalyst was 10wt%NaOH,the pH was adjusted to 8.5-9.2,the hydroxymethylation time was 40-50 min,and the hydroxymethylation temperature was 80-90 ℃.The crosslinking curing reaction pH is 6～7,the curing time is 15～20 min,and the reaction temperature is 80～90℃.The dehydration time was 7 h.Thermogravimetric analyzer(TG)and EA results show that HM has good thermal stability with a nitrogen content of 43.6%.It can be used as structural flame retardant of PURF.The synthesized HM was added into PURF foaming system to obtain HM/PURF series.The HM-DMMP/PURF series was obtained by adding 10wt%DMMP into the HM/PURF series.The compressive strength,impact strength,LOI,vertical combustion test,thermogravimetric analysis,morphology of cell and carbon layer,water absorption and dimensional stability of the two series were tested respectively,and the optimum addition amount of HM and flame retardant PURF were obtained.The experimental results show that when HM content reaches above 30wt%.the LOI of HM/PURF series increases from 18.1%to 22%,and reaches 24.6%at HM40wt%.Compression strength decreases with the addition of HM.When 30wt%HM is added,the compression strength of PURF decreases by5.6%,water absorption and dimensional stability increase slightly,and the comprehensive physical performance is the best.The optimum combination ratio of HM-DMMP/PURF series is 30wt%HMF and 10wt%DMMP.At this time,the LOI rises to 25.9%,the compressive strength is 0.135 MPa,and the water absorption and dimensional stability are the best.The flame retardant PURF was tested by Thermogravimetric Analyzer-Fourier Transform Infrared(TG-FTIR).Combined with the test results,the nitrogen-containing gas products decomposed by HM at high temperature can inhibit the combustion of PURF.With the use of DMMP,the decomposition products of PURF can be protected at all stages of thermal decomposition,and the decomposition rate of the foam decreases significantly.