Design And Preparation Of Core-shell Structure For Intumescent Flame Retardant And Study On Their Flame Retardant Properties

Ammonium polyphosphate(APP),a well known component of the intumescent flame retardant(IFR) systems is easily attacked by moisture,migrates to the surface and leads to a decrease in the properties of the polymer composites,not only flame retardancy,but also some other properties.To deal with the problems of the moisture absorption and poor compatibility with polymers,microencapsulation with water-insoluble polymers is a good choice.The research work of this dissertation is composed of the following parts:1.Microencapsulated ammonium polyphosphate(MFAPP) with a melamine-formaldehyde(MF) resin coating layer is prepared by in situ polymerization.MFAPP is characterized by Fourier transform infrared(FTIR),X-ray photoelectron spectroscopy(XPS),etc.The results show that the microencapsulation with the MF resin leads to a decrease in the particles' size and water absorption.The flame retardant action and mechanism of MFAPP and APP in polypropylene(PP) are studied using limiting oxygen index(LOI) and UL 94 test,and their thermal stability is evaluated by thermogravimetric analysis(TG).The LOI value of the PP/MFAPP composite at 30 wt%loading is 30.5%,whereas the corresponding value of the PP/APP composite is only 20.0%.Moreover,the PP/MFAPP/PER composites with suitable ratios of MFAPP to pentaerythritol(PER) can reach the V-0 rating in UL-94 test.2.Since the water resistance of the urea-formaldehyde(UF) resin is weak compared with the MF resin and melamine can be used as a blowing agent to improve the flame retardant efficiency of the IFR system,the microencapsulated APP (UMFAPP) with a urea-melamine-formaldehyde(UMF) resin was prepared in this work by in situ polymerization.The microencapsulation of APP with the UMF resin leads to a decrease in the particle's water solubility.The flame retardant action of UMFAPP and APP in PP are studied using LOI and UL 94 test,and their thermal stability is evaluated by thermogravimetric analysis.It is found that the LOI value of the PP/UMFAPP composite is higher than the value of the PP/APP composite.In comparison with the PP/UMFAPP composites,the LOI values of the PP/UMFAPP/DPER composites at the same additive loading increase,and UL-94 ratings of most composites are raised to V-0.The water resistant properties of the PP composites containing APP and UMFAPP are studied.Moreover,the combustion behavior of the PP composites is investigated by the cone calorimeter.Above results show that UMFAPP/DPER is a novel IFR system which has better water resistance and flame retardance compared with traditional APP based IFR system.3.We microencapsulated APP with UF resin as primary layer,and then coated the particles with MF resin compactly.The double shell outside APP particles can be used as a protective layer and carbonization or blowing agent synchronously. Microencapsulated ammonium polyphosphate(MUFAPP) with a double shell is characterized by FTIR,XPS and SEM,etc.The microencapsulation of APP can increase its flame retardance and water resistance in PP.The flame retardant action of MUFAPP and APP in PP are studied using LOI and UL-94 test,and their thermal stability is evaluated by TG.The LOI value of the PP/MUFAPP composite at the same loading is higher than that of PP/APP composite,and the UL-94 rating of PP/MUFAPP can pass V-0 at 40 wt%loading.The results of the cone calorimeter also indicate that MUFAPP is an effective flame retardant in PP.The thermal degradation behaviors of APP and MUFAPP are studied using TG and dynamic FTIR,and their flame retardant mechanisms in PP are explained.4.Due to the comparatively weak water resistance of dipentaerythritol(DPER), co-microencapsulated ammonium polyphosphate and dipentaerythritol(M(A&D)) is prepared using a melamine-formaldehyde(MF) resin by in situ polymerization method.The co-microencapsulation of APP and DPER leads to a great improvement in water solubility of the additives.The flame retardant effect of M(A&D) in PP is evaluated using limiting oxygen index(LOI) and UL 94 test,and the water resistance of the PP/M(A&D) composites is also studied.The flame retardant properties and water resistance of the PP/M(A&D) composites are much better than the ones of the PP/APP/DPER composites.Moreover,the thermal stability of the PP/M(A&D) composites is improved compared with the PP/APP/DPER composites. 5.With a shell of PVA-melamine-formaldehyde(VMF) or starch-melamine-formaldehyde (SMF) resin,core/shell-like ammonium polyphosphate(VMFAPP or SMFAPP) is prepared by in situ polymerization,and is characterized by SEM,FTIR and XPS.This core/shell-like intumescent flame retardant contains three components of a typical IFR system:APP(as an acid source),PVA/starch(as a carbonization agent) and melamine(as a blowing agent).The results show that shell leads VMFAPP and SMFAPP a high water resistance and flame retardance compared with APP in PP.UL 94 ratings of PP/VMFAPP and PP/SMFAPP can reach V-0 at 30 wt%loading.The flame retardant mechanism of VMFAPP and SMFAPP is studied by dynamic FTIR, TG and cone calorimeter,etc.6.Biodegradable PVA/glycerol-plasticized thermoplastic starch(TPS) and its intumescent flame retarded composites are prepared.Microencapsulated ammonium polyphosphate(MFAPP) was used not only in order to utilize the charring capacity of the polyhydric compounds in TPS,but also restrain the reaction between APP and starch during processing.The flame retardancy and thermal stability of TPS and TPS/MFAPP were characterized by LOI,UL-94,TG,Microscale Combustion Calorimeter(MCC),etc.TPS/MFAPP composites with only 2 wt%MFAPP can pass V-0 in UL-94 test.However,neat TPS can't pass any rating.The presence of MFAPP can reduce the total heat release of TPS sharply in MCC test.The thermal degradation and gas products of TPS and TPS/MFAPP were monitored by TG-FTIR and dynamic FTIR.XPS and SEM measurements were utilized to investigate the chemical structure, as well as the surface morphology of the residual char.