Study On The Green Technology Of Making Intumescent Red Phosphorus Microcapsule Flame Retardant

SC-CO₂ has been applied to make microcapsule extensively. Intumescent microcapsule flame retardants were synthesized by encapsulating red phosphorus within the m-phenyleneisophthalamide (PMIA) resin shell through reaction dipping under the condition of SC-CO₂. Their physical properties and fire retardant properties have been investigated by using Scanning Electronic Microscopy (SEM), Themogravimetry-differential Thermal Analysis (TG-DTA), Elemental Analysis, CONE, etc.Synthesizing PMIA using SC-CO₂ has never been reported as yet. For the purpose of guaranteeing the coating quality, at first, the melt condensation polymerization of making PMIA in SC-CO₂ with di-soda isophthalate and m-phenylene diamine hydrochloride as raw materials has been investigated. Infrared Ray Absorption Spectrum shows that the solvent SC-CO₂ has no effect on PMIA. It is believed that the small molecule condensate can be removed by supercritical CO₂ extraction and reaction temperature can be reduced with CO₂ being the plasticizer.Furthermore, high molecular weight PMIA can be obtained with CO₂ extracting the low molecular weight byproducts. By varying the concentration and purity of monomers, the total reaction time, the pressure of CO₂, reaction temperature and stirring rate, the effects on the inherent viscosity of PMIA have also been investigated. The results show: as the concentration of monomers, the total reaction time, the pressure of CO₂, reaction temperature vary, the inherent viscosity of PMIA varies substantially. The purity of monomerhas no effect on the inherent viscosity of PMIA, and the stirring rate has slighter effect on it compared to ordinary melt condensation reaction.Secondly, the process of making red phosphorus intumescent microcapsule flame retardant by the reaction dipping under the condition of SC-CO2 has been investigated. The analysis of the coating mechanics shows that through the chemical bond between the polar amido on the capsule shell and the polar group on the surface of the red phosphorus, the PMIA prepolymer can be heterogeneous nucleation after polymerization degree reaches a critical index with the red phosphorus as the core, and the growth model was multi-growth and coating. The effect of the reaction time,the CO2 pressure, as well as the agitation rate on the morphological structures, thermal stability, as well as the size and distribution of the microcapsule is investigated. Thermal stability and water absorbing capacity of red phosphorus-based microcapsule are tested. The main conclusions are:(l)The total reaction time has strong effect on the morphological structures and the thermal stability of the microcapsule. The initial decomposing temperature of the microcapsule fire retardant is 350°C, about 70¹20°C higher than that of the current intumescent flame retardants. Such a thermal property can meet the processing requirement of nearly all the engineering polymers.(2)As the pressure of supercritical CO2 increases, the average diameter of capsules decreases and its distribution turns narrow. Because of the properties of SC-CO2, the morphological structures of microcapsule made by the process with supercritical fluid are good.(3)As the stirring rate increases, the average diameter of capsules decreases, and its distribution turns narrow. But the effect of the stirring rate is slighter than the solvent-borne processing.(4) Resin shell PMIA leads microcapsules to reduce their absorption, decelerate the process of oxidation reaction and raise their thermal stability.Polypropylene is used widely, but it is combustible and difficult to flame-retraded, so much attention has been paid to the technique and theory of endowing it with flameretardance. In this paper the flame retardance, combustion behavior and physical properties of intumescent red phosphorus microcapsule flame retardant/PP system are investigated. The results show that the inflatable red phosphorus microcapsule flame retardant/PP intumescent system has better flame retardance than the ordinary red phosphorus microcapsule flame retardant, ring phosphorus inflatable flame retardant, and pure red phosphorus. Furthermore, it can strengthen and soften the PP. The HRR, and MLR, toxic gases and smoke generated during the combustion process are obviously reduced. Thermogravimetric results indicate that the intumescent flame retardance (IFR) takes part in the decomposition reactions of PP and promotes carbonization as the IFR-PP undergoes heating and burning. Elemental Analysis and Infrared Spectrum of the burnt residues and swollen char reveal that the phosphorus is mainly accumulated on the burning surface of IFR-PP and exists in the forms of phosphoric acid and its corresponding ammonium salt. Their formations are related to a series of changes of the IFR while the IFR-PP is heating and burning and are helpful to further carbonize and char the schorched residue and to improve the flame retardance of the material.