Preparation Of Reactive Intumescent Flame Retardant And Study On Flame Retardant Polypropylene

Polypropylene (PP) as the second largest common plastic is widely used in manyfields, such as chemical industry, building, household appliances, packaging,automobiles, etc., because of its non-toxicity, easy processing, good chemicalresistance, excellent mechanical properties and low cost advantage. However, it iseasily flammable, generates a lot of heat and produces droplet during burning due toits low limiting oxygen index (LOI) value which is the fatal shortcoming restrictingits wider application. Therefore, it is particularly important to improve the flameretardancy of PP. With the increasing consciousness of safety and environment, theenvironmental protection has been paid more and more attention. Phosphorus-nitrogen intumescent flame retardants (IFRs) have gradually been focused on due toits advantages, such as low smoke, non-toxicity and no corrosive gas release duringburning. However, IFRs have still some shortcomings, such as poor compatibilitywith matrix resins, moisture sensitivity and deterioration of material mechanicalproperties, and so on. How to prepare a kind of IFRs bearing good compatibilitywith PP, showing excellent flame retardancy and maintaining mechanical propertiesof PP, has become an important subject in the research of environmental friendlyflame retardants. The basic design principle is described as following:Due to non-polar crystalline resin of PP, we should synthesize the reactiveintumescent flame retardant not only having a functional group reacting with PP toimprove the compability, but also bearing acid source, blowing agent and charforming agent within one single molecule, together with a suitable ratio ofphosphorus, nitrogen and carbon for good synergistic effect of acid source, blowingsource and char forming agent. Then, the flame retardant PP would be achievedthrough reactive blending and its chemical structure, flame retardant properties,mechanical properties would be improved.Based on the above design principle, this work includes: A reactive intumescentflame retardant with a double bond is synthesized from phosphorus oxychloride, pentaerythritol, hydroxyethyl methacrylate and melamine. Its chemical structure ischaracterized by FTIR,1H-NMR and elementary analysis. The thermal stability andchar morphological structure are investigated by TG, SEM and FTIR. Then, flameretardant PP composites are prepared through reactive blending. The chemicalstructures of flame retardant PP composites are characterized. Flame retardancy,flame retardant mechanism, mechanical properties, thermal behaviors and charformation mechanism are investigated in detail. The non-isothermal crystallization,melting behaviors and crystalline morphology are analyzed.In order to further improve the flame retardancy and to optimize the mechanicalproperties of flame retardant PP composites, several synergists are added into flameretardant PP. The synergistic effects, synergistic mechanism and mechanicalproperties are investigated.The main research results are listed as following:1. A reactive intumescent halogen-free flame retardant bearing acid source,blowing agent and char forming agent within one single molecule,2-((9-((4,6-diamino-1,3,5-triazin-2-yl)amino)-3,9-dioxido-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5] undecan-3-yl)oxy)ethyl methacrylate (EADP), is synthesized through two-stepreaction with a certain ratio of phosphorus, nitrogen and carbon (1.00:1.68:2.84).The temperature at5%weight loss of EADP is270.5oC, indicating enough thermalstability under the molding process of polypropylene. The char yield of EADP ismeasured to be53.66%at700oC. The char takes on a compact surface and a cellularinner structure.2. PP/EADP composites are composed of PP, graft copolymer of EADP and PP,EADP homopolymer and unreacted EADP. For example, EADP is reacted in aconversion ratio of29.08%with PP in PP/EADP-30with the addition of30wt%EADP.PP/EADP composites show excellent flame retardancy. When the addition ofEADP is25wt%, the LOI value of PP/EADP-25is32.5%, passing the UL-94V-0rating. The peak heat release rate (PHRR), total heat release (THR) and averageeffective heat of combustion (av-EHC) are212.61kW/m2,90.38MJ/m2and39.47MJ/kg, which are decreased about65.50%,20.18%,19.51%compared with those of PP, respectively. Moreover, the addition of EADP decreases the smokeemission. The char yield of PP/EADP-25is measured to be11.82%at600oC. Thechar has a compact surface and a porous inner structure.While PP/EADP composites are heated and burned, the acid source, blowingagent and char forming agent react with each other generating a swollen porous charand releasing nonflammable gas such as NH3, H2O, indicating the condensed-phaseand gas-phase flame retardancy synergistic mechanisms for PP/EADP composites.PP/EADP composites have outstanding water resistance. For example,PP/EADP-30could still obtain a LOI value of31.5%and a UL-94V-0rating afterbeing soaked in70oC water for168h.The temperature at5%weight loss and the maximum weight loss rate ofPP/EADP-25are respectively measured as286oC and5.95%/min, which affordsenough thermal stability to meet the molding process.PP/EADP composites show comprehensive excellent mechanical properties.Compared with PP, the flexural strength, flexural modulus and tensile strength ofPP/EADP-25are respectively increased about18%,38%,8%except that the Izodnotched impact strength is decreased about7%.The crystallization onset temperature, the crystallization peak temperature and thedegree of crystallization of PP/EADP composites are higher than those of PP. ForPP/EADP-30composite, the crystallization onset temperature, the crystallizationpeak temperature and the degree of crystallinity are respectively increased about7.73oC,9.00oC and9.70%compared with those of PP and about4.86oC,4.57oC and1.72%compared with those of non-reactive intumescent flame retardant PP(PP/MAPP-30). One of them, the rate of crystallization and the degree ofcrystallinity of PP/EADP-25are the biggest.Compared with neat PP, the crystal size of PP/EADP composites is obviouslysmall. With the increasing content of EADP, PP crystal size turns smaller. PP inPP/EADP composites exhibits ?-form and ?-form crystal structures.Compared with neat PP, the melting onset temperature and melting endtemperature of PP/EADP composite are slightly decreased and the melting peaktemperature is increased a little. 3. Halloysite nanotubes (HNT) are the most effective synergistic agent. Comparedwith PP/EADP-25, the LOI value of PP/EADP-HNT(PP/EADP/HNT=75/24/1)composite with1wt%addition of HNT is increased from32.5%to35.5%with theheat release rate, total heat release, effective heat of combustion, specific extinctionarea and total smoke release decreased. The char yield of PP/EADP-HNT isincreased from11.82%to13.53%at600oC, passing the UL-94V-0rating.Compared with PP/EADP-25, the crystallization onset temperature andcrystallization peak temperature of PP/EADP-HNT composite are the almost sameas those of PP/EADP-25. Besides, the degree of crystallinity, the melting onsettemperature and the melting end temperature of PP/EADP-HNT composite aresmaller than those of PP/EADP-25.Compared with neat PP, the flexural strength, flexural modulus and tensilestrength of PP/EADP-25are increased about26%,64%,11%, respectively. The Izodnotched impact strength is the same as that of PP.The flame retardant mechanism of synergistic flame retardant PP is similar toPP/EADP composites.All the synergistic flame retardant PP composites show the coexistence of ?-formand ?-form crystal structures while the content of ?-form crystal is higher than thatof PP/EADP-25. The crystal size of PP/EADP-HNT composite is close to that ofPP/EADP-25.With the addition of elastomers into flame retardant PP, the flame retardantparameters and static mechanical properties are slightly decreased and the Izodnotched impact strength is improved.