Preparation And Characterization Of Flame Retardant Expandable Polystyrene Foams By Coating With Modified Thermosetting Resin

Expandable polystyrene (EPS) is a kind of foamed materials with excellent moisture resistance, shock absorption, thermal insulation properties, and has been widely used as packaging, cushioning and insulation materials. However, the oxygen index of neat EPS foam is only 18%, which is highly flammable. The cellular and spongy structure of EPS provide large specific surface areas, and abundant toxic smoke may be released during combustion due to the existence of benzene in the molecule, which would bring great damage and harm to the environment and human beings. Adding flame retardants can improve the flame retardancy of EPS foams. Among them, halogen flame retardants have high flame retardant efficiency, but toxic gases such as hydrogen halide will be released in combustion. Halogen-free flame retardant is non-toxic,but its poor compatibility with matrix has a great effect on the foaming process and mechanical properties of EPS foams. Ammonium polyphosphate is a kind of highly effective and environmentally friendly phosphorus and nitrogen flame retardant. The compatibility and dispersibility will be improved by microencapsulation, and the water absorption rate of flame retardants will be reduced.Flame retardant coating during foaming process has become a promising solution. By this method, each EPS bead can be coated as an independent flame retardant structure unit, which can provide excellent fire protection. Moreover, it can limprove the stability and flame retardant efficiency of flame retardant, and compatibility with the matrix, thus reduce the effect on the mechanical properties of foam. Each EPS bead can be coated as an independent flame retardant structure unit, which can provide good flame retardant properties.In this study, the process of preparing halogen-free flame retardant polystyrene foam by resin coating method were explored, by coating Pre-expansion EPS beads with modified thermosetting resin and microencapsulated ammonium phosphate (MCAPP), and then prepare flame retarded EPS foams by secondary foaming. The flammability of coated EPS was characterized by LOI, UL-94, cone calorimeter test, and smoke density test. The thermal property and morphology of residual char were also characterized by thermogravimetric analysis and scanning electron microscopy, in order to understand the thermal degradation pathway and the flame retardant mechanism. The main work is as follows:For the first part, the pre-foaming, curing process, and flame retardant coating method were explored. The ethylene glycol modified melamine resin (EMF) was prepared. The storage time of EMF resin was improved and the free formaldehyde content was decreased. The flame retardant EPS foam was prepared by coating EMF resin and melamine resin microencapsulated ammonium phosphate (MFMCAPP). The water resistance and the impact resistance of the foam was improved. When the mass ratio of EPS/EMF/MFMCAPP is 100:100:75, the oxygen index was increased from 18.0% to 31.4%, UL-94 was also reached V-0 grade.There was no droplet in combustion and it could self extinguish within a short period of time. The peak heat release rate of treated foams decreased from 933 kW/m2 to 192 kW/m2, and the smoke density also decreased by 60.8%. Both the impact strength and thermal stability were improved, and denser and higher char layer could be formed.For the second part, the process of preparing halogen-free flame retardant polystyrene foam process by resin coating method was explored,by coating pre-expansion EPS beads with EMF resin and flame retardant MFMCAPP/PER/MEL. The research results showed that EPS foam board coated with MF resin and APP/PER/MEL has good comprehensive flame retardant and mechanical performance. The impact strength of the foam increased to a maximum of 0.570 KJ/m2. The LOI value was increased to 30.6%, UL-94 was reached V-0 grade and it could be extinguished in a short period of time. The smoke density of foams was decreased by 35%. The thermal stability and the char residue content of EPS foams were also improved.For the third part, cardanol modified phenol formaldehyde resin(CPF) was prepared. CPF resin had the comprehensive performance when the additive amount of cardanol was 10%. The content of free formaldehyde was decreased obviously, and the impact resistance could reach up to 2.030 KJ/m2. Microencapsulated ammonium polyphosphate(PFMCAPP) was prepared by coating with phenol formaldehyde resin,and flame retardant EPS was prepared by coating with PFMCAPP and CPF. The results indicated that the impact resistance of EPS foams was significantly improved, and reached up to 0.774 KJ/m2 by the presence of 90 phr PFMCAPP. The LOI value increased from 18.0% to 28.9% and passed V-0 rating in UL-94 test.'The total heat release was also decreased to 30.02 MJ/m2 and the smoke suppression was improved. The thermal stability was enhanced and the amount of residue char was increased to 37.4%. There was a synergistic effect between PFMCAPP and CPF,which took effects in both gas and condense phases.