Study On The Preparation, Application And Flame Retarding And Smoke-suppressing Mechanism Of Microencapsulated Red Phosphorus

In the present day,the fire from combustible polymers has become a severe social problem as they were extensively used in various fields.For polymers,the flame retarding by way of flame retardant is the main approach to achieve flame retardancy.Red phosphorus(RP) is important one of phosphorus flame retardants,which has good flame retardancy. However, there exist two key problems for it to be solved in application. One is its chemical instability, release of poisonous PH₃ and blast from the powder. The other is its heavy color(dark purple) to limit its applied range. Therefore, red phosphorus can be used in practice only after surface processing. In this dissertation,the new-style microencapsulated red phosphorus(MRP) is prepared by new coating technology. Its application in polymeric materials and mechanism of flame retarding and smoke-suppressing were also studied systematically.The parameters of experiment were provided and the foundation was laid for its wide application in the future.1. The process for producing the flame retardant of microencapsulated red phosphorus with manifold coating materials in different coating ways was studied in detail in this paper. The microencapsulated red phosphorus coated in single layer has better chemical and thermal stability, compared with red phosphorus. On the basis of selection, red phosphorus was coated by zinc borate/ modified melamine resin in double layers. The technics conditions had been optimized through orthogonal test so as to achieve the best product. The MRP in double layers has excellent properties: 628K self-ignite temperature (530K for RP),718K thermal decomposition temperature(645K for RP), 0.3% moisture absorption ratio(11.8% for RP), 1.2 mg NaOH ·g^-1·h^-1 antioxidation(173 mg NaOH ·g^-1·h^-1 for RP), < 1μg·(g·24h)^-1 PH₃ release(in air,21μg·(g·24h)^-1 for RP)and 1.3μg· (g·24h)^-1(in water, 493μg· (g·24h)^-1 for RP).2. At first, superfinening and whitening of microencapsulated red phosphorus were systematically studied. Effects of grinding time, rotating speed, dispersant, pH value, supersonic, coating time and coating content on superfinening were observed in detail. Under those conditions,the superfine one was obtained with smooth surface, narrow distribution of particlediameter and average particle diameter of 0.8um. The main factors that affect the whiteness of microencapsulated red phosphorus were studied. The MRP was obtained with whiteness of 65.07% for coating content of 20 wt %, >90.22% for 40 wt %. Different colour MRP can be achieved with different theca species; The higher the theca content, the higher the whiteness; There was synergic effect on whitening of MRP in double layers; The system of narrow distribution of particle diameter has better whiteness than the wide.3. The studies of flame applications indicated that the microencapsulated red phosphorus had excellent flame retardancy for PU, EP, PVCand PE. The additive mass to retard flame were 3phr(per hundred resin), 5phr, 6phr and 8phr respectively. After microencapsulated, red phosphorus had better flame retardancy and smoke-suppressing property, of which the flame retardancy increased with the decrease of particle size. The microencapsulated red phosphorus had little effect on the mechanics properties of materials. The studies also indicated that the composite systems of microencapsulated red phosphorus and zinc borate had excellent synergism of flame retarding and smoke suppressing in PU, that the complex systems of MRP and zinc borate and melamine had good synergistic effect of flame retarding and smoke suppressing in EP, that the compound systems of MRP and aluminum hydroxide, MRP and magnesium hydroxide, MRP and zinc borate, MRP and zinc borate and decabromodiphenyl oxide, MRP and aluminum hydroxide and magnesium hydroxide had good synergistic effect of flame retarding and the compound systems of MRP and MOO3, MRP and ferrocene,MRP and zinc borate had distinct synergistiv effect of smoke suppressing in PVC, that the composite systems of MRP and zinc borate and decabromodiphenyl oxide, MRP and aluminum hydroxide and magnesium hydroxide, MRP and zinc borate and melamine had good synergistic effect of flame retarding in PE. The best formulations of EP, PU, PVC and PE flame-retarded with MRP were put forward.4. DTA and TG were employed to investigate the thermal decomposition process, mechanism and kinetics of red phosphorus and microencapsulated red phosphorus (coated with zinc borate ) in air. Kinssinger method and Ozawa method were employed to treat the DTA curves and the kinetic parameters of red phosphorus and MRP thermal decomposition were obtainedat the first time. Red phosphorus thermal decomposition in air proceeded in four steps, the corresponding average activation energies are 127.02kJ.mor , 167.38kJ.mor1, 181.42kJ.mol"], 195.65kJ.mol"1 respectively. MRP (coated with zinc borate ) thermal decomposition in air proceeded in two steps,the corresponding average activation energies are 63.47kJ.mor1,92.81kJ.mol" respectively. After red phosphorus was coated with zinc borate, the four DTA peaks of heat release of red phosphorus becomed two peaks of heat absorption, and the activation energy of key peak decreased greatly. All this will be in better favor of flame retarding of condensed phase. The thermal decomposition mechanisms of red phosphorus and MRP in air was proposed.5. The thermal decomposition of EP and EP containing MRP (coated with zinc borate ) were also studied. The kinetic parameters and kinetic equations were obtained by Anderson-Freeman method in the first time. The kinetic equations of two kinds of materials are — = 5.36 x 10 V15600 A9IT (1 - af11 and — = 8.28 x 1017 e"30454 MIT (1 - a)1 °3 respectively. The addition of MRP changed the thermal decomposition mechanism and kinetics of EP so as to enhance the activation energy of thermal decomposition and flame-retard the polymer. The remnant char rate of the flame-retarded EP increased by about 14% over the blank , which also indicated that MRP has remarkable flame retardancy. The condition for PU or PE is the same as for EP.6. The means of IR showing trace was employed firstly to study the thermal oxidation degradations of EP/MRP, PU/MRP, PVC/MRP and PE/MRP. The results showed that there existed the bonds of P=O, P—O and P—O—C( 0 ) of ester phosphate in the polymers flame-retarded with encapsulated red phosphorus, which testified the flame-retarding mechanism of condensed phase containing phosphoric acid species. The element contents on inside and outside surfaces of PVC flame-retarded with MRP were analyzed with the use of EDS. The results showed that the phosphorus element bring flame-retardation into play in the condensed phase. XPS was employed first to study the changes of species on the surface of EP containing MRP. It indicated there were distinct signals of P after combustion . When the narrow scan was done for the XPS of P before and after combustion, it can been seen that the peak of P2p after combustion was much bigger than that beforeconbustion, that the binding energy moved upon, and that there existed the structures of -P-O-C, -P-O-P- and -P-OH after the peak was divided, which testified further that the phosphoric acid species formed in the condensed phase have strong dehydration and charring to take the effects of flame-retarding and smoke-suppressing.7. PY-GC-MS was employed to study the constitutes and changes of gas of EP/MRP systems in air for the first time. It indicated that the of phosphoric acid species changed the pyrogenation process and pyrogenatibn mode of EP. This brought about the decrease of flammable ingredients, such as small alkyl, alkene, aldehyde, hydroxybenzene and benzene matters, and the increase of bad combustion ingredients, such as biphenyl, polybenzene oligomers and large ester phosphates. The experimental results showed that the phosphoric acid species of ropy and half-solid state can cover the surface of polymers at combustion, increase the content of char residue, found a film of carbonaceous char which serves as a barrier isolate the material from outside air and heat so as to generate the function of flame-retarding and smoke-suppressing. The flame-retarding and smoke-suppressing mechanism of condensed phase of MRP were then confirmed.The studies indicated that MRP is a kind of flame retardant with high efficient retardancy. It is safe and nontoxic,and it has high whiteness, small particle diameter and little effect on physical and mechanical performances of materials. It can also be combined with other retardant elements or retardants so as to bring synergistic effect. This keeps up with the development trend of halogen-free and high efficiency and low toxicity and low smoke. MRP will have a wide applied foreground.