Preparation Of Novel Intumescent Flame Retardant Coatings And Their Application To Polypropylene

Polypropylene?PP?is widely used in industrial production and daily life due to its good thermal properties,chemical stability,electrical properties,and weatherability.However,PP is a flammable polymeric material,with severe melting drips while burning,which limits its application.Therefore,it is very important to improve its flame retardant performance.Currently,the improvement of PP flame-retardant property is usually achieved by the direct addition of flame retardants into PP matrix via melt-blending.PP will get a good flame retardant performance with high flame retardant loading,but loses its excellent mechanical properties.In this study,therefore,the flame retardant coating was applied to the surface of the PP specimens,which made these specimens obtain a good flame retardant performance and maintain their excellent mechanical properties.Calcium gluconate?CG?is easily prepared in low cost and is also an eco-friendly material.It will self-expand under a heat,and can play a role of carbon source and blowing agent when being blended with ammonium polyphosphate?APP?.It is promising flame retardant for the intumescent system.Basic aluminum magnesium carbonate?BAMC?combines the advantages of magnesium hydroxide and aluminum hydroxide.It has high thermal stability,non-toxicity,smoke suppression,and high efficiency to promote carbonization of the polymeric matrix.CG and BAMC can release CO₂ and water vapor during the decomposition,which contribute to flame retardancy in gaseous phase.Moreover,their decomposed products,metallic hydroxide,can cover the surface of the substrates to be a good barrier for the transfer of heat and oxygen,contributing to flame retardancy in the condensed phase.In this study,polyvinyl acetaldehyde ?PVFA?,9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide?DOPO?and ?-aminopropyltriethoxysilane?KH550?were used as film-forming agent.Two types of intumescent flame retardant coatings were prepared by introducing APP/CG and APP/BAMC respectively and applied to the surface of PP specimens.The flame-retardant tests showed that the flame retardant performance of the coating is the best when the ratio of APP to BAMC is 3 to 1.The PP/KPDA₃C specimen had a LOI value of 34.1 vol.%and achieved V0rating at the UL-94 test with a 220?m thick coating?in average?.In the cone calorimetry test,the peak heat release rate?PHRR?and total heat release?THR?of the PP/KPDA₃C specimen decreased by 88.4%and 19.1%,and its residual weight increased by 25.1%.For the BAMC coating,the best flame retardancy was achieved at the ratio of 3 to 1 for APP to BAMC.The PP/KPDA₃M specimen had a LOI value as high as 35.1 vol.%and passed the UL-94 V0rating with an average coating thickness of 190?m.In the cone calorimetry test,the PHRR and THR of the PP/KPDA₃M specimen decreased by 84.5%and26.0%,respectively,and its residual weight increased by 34.1%.Both flame retardant coatings exhibited excellent flame retardant properties.In addition,the flame retardant mechanisms of the intumescent flame-retardant coatings were discussed,and the adhesion as well as the water resistance of the coatings were studied.