Study On Application Of Supercritical CO₂ To Assist Processing Of Flame Retardant Polymer Composites And Structure-properties Relationship

Polymers have been widely used due to its light weight,easy processing,low cost and outstanding comprehensive performance,etc.However,polymer materials show burning characteristics of easy flammability,which would cause serious casualties and great economic losses when a fire is initiated.Hence,under the pressure of the strict regulation of law and the requirement of sustainable development,flame retardant modification of polymer materials is of great importance to meet the fire safety standards and thus to widen their applications.Recently,supercritical carbon dioxide?scCO₂?has versatile and extensive applications in foodstuff,pharmaceutical and other chemical fields because of its mild supercritical condition?31.1oC and 7.38MPa?,environmental friendliness,extensive sources,low cost,easy remove,etc.Meanwhile,scCO₂ has plasticizing effects on polymers and can increase the free volume and lower the viscosity,thus can increase mobility of macromolecules and the mass transfer rate.However,up to now,scCO₂ has seldom been used in the field of flame retardant polymers.In this thesis,the main purpose was to augment the application of scCO₂ as a green processing medium to flame retardant materials.Possible mechanisms were proposed for the scCO₂-aided intumescent flame retardant dispersion and the consequent improved flame retardancy.The main contents and results as follows:?1?In this thesis,a new approach to enhance the flame retardancy of polypropylene / intumescent flame retardant?PP/IFR?composites through improving IFR dispersion via continuous extrusion with different content of sc CO₂ as the processing medium were studied.The IFR used in this thesis consisted of ammonium polyphosphate?APP?and pentaerythritol?PER?at a weight ratio of 3:1.It was found that scCO₂ as the processing medium could significantly improve IFR dispersion in PP matrix and thus increase the efficiency of the IFR flame retardant and enhance the flame retardancy of the PP composites.This new approach could allow PP/IFR composites to pass the UL-94 V-0 rating at a lower IFR content,which presence a novel method to improve materials' flame retardancy.?2?In order to further optimize the dispersion of polypropylene / intumescent flame retardant?PP/IFR?composites and explore the optimal foaming conditions,we prepared PP/IFR composites by adjusting processing conditions such as temperature,pressure and die.It was found that lower temperature and higher pressure within suitable conditions could help to improve the expansion rate of PP/IFR composites.Besides,compared with the previous work,better dispersion,carbon residue,smoke suppression effects and flame retardancy were gained by scCO₂ foaming technology.?3?In order to expand the application of scCO₂ as a green processing medium in the field of other flame retarded polymers,using a new macromolecular brominated flame retardant?FR-122P?and a brominated epoxy resin?2200HM?as flame retardants and synergistic effect system,and carbon dioxide?CO₂?as a blown agent,studied the effect of composited macromolecular flame retardants on modification of polystyrene?PS?and PS foam.It was found that flame retarded PS could pass UL-94 V-0 rating and had a LOI value of 25.8 with the composited macromolecular flame retardants at a content of 25wt% and a ratio of 4:1.With 40wt% of the composited macromolecular flame retardants,the flame retarded PS foam showed high expansion ratio,high cell density and small cell sizes,and it could pass HF-2 ratio.