Design Of Novel Charring Agents And Investigation On Thermal Stability And Combustion Properties Of Polymer

Nowadays,polymer materials have a wide range of applications in our modern daily lives because of their abrasion resistance,corrosion resistance,and electrical insulation and other excellent properties.However,they are also well known for their high flammability.Once a fire occurs in a place of residence,transportation,and public occasions,the source of fire melts the polymer material and causes it to generate melt drip,which in turn increases the rate of flame spread and is accompanied by the generation of toxic gases and fumes.The high degree of flammability of polymer materials not only restrict its further application and development,but also its vulnerability to fire and the resulting casualties and serious economic losses.Therefore,improving the flame retardancy of polymer materials is still a major challenge.In this dissertation,a large number of the latest literature system have been reviewed on the basis of the commonly used flame retardant technology and methods used in polymer materials(including polypropylene and poly(1,4-butylene terephthalate)).According to the molecular design,a series of charring agents containing phosphorus/nitrogen are prepared with outstanding char forming ability.Then,these polymeric charring agents are used in flame retarded polypropylene matrix to achieve high efficiency flame retardant properties and good water resistant property.In addition,in order to solve the problem of poor water resistance of APP,the microencapsulation technology is recommended.Considering the advantages of nanocomposite technology,a novel nanocomposite flame retardant consisting of triazine-based polymeric char forming agents(HCFAs)and sodium montmorillonite(Na-MMT)is prepared via one-step process.Finally,in order to further broaden the application of HCFA in other polymer materials,the thermal degradation and combustion behaviors of PBT/HCFA/AlPi are studied.The main research progress in the dissertation have the following parts.1.a novel cyclotriphosphazene-based char-forming agent(CPCFA)is synthesized using a one-pot method in high yield(86.5%).Then,it incorporates into PP matrix with microencapsulated ammonium polyphosphate(MAPP)to prepare the flame retardant polypropylene(PP)samples through melt blending method.An increase in the limiting oxygen index(LOI)and the observation of a vertical burning(UL-94)V-0 rating as well as the reduction of the heat release rate(HRR)and residual mass of PP/MAPP/CPCFA blends compared to those for PP/MAPP demonstrate the effectivess of a contribution of MAPP and CPCFA to PP.Thermogravimetric analyses results demonstrate that the presence of CPCFA improved char formation for PP/MAPP/CPCFA blends in either nitrogen or air atmosphere.Finally,an outstanding water resistance is also obtained for compositions in the weight ratio range of 3:1 to 2:1(MAPP/CPCFA).After water soaking for 72 h,a UL-94 V-0 rating is still achievable.2.Taking into account the effectiveness of flame retardants and cost saving,a series of triazine-based polymeric char forming agents(HCFAs)are successfully synthesized and their structures are well characterized.The chemical structure of HCFAs are characterized by using Fourier transform infrared spectroscopy(FTIR),13C solid-state NMR spectroscopy and elemental analysis.The thermal degradation and hydrophobicity of HCFAs are measured by thermogravimetric analysis(TGA)and water solubility tests.The detailed study of HCFAs indicate that HCFAs could act as an effective charring agent in polymer matrix,due to its high thermal stability,good char formation ability,and excellent hydrophobicity.Moreover,PA-HCFA containing triazine and piperazine ring exhibites the highest thermal stability and char formation among all these triazine-based polymeric char forming agents.The novel intumescent flame retardants(IFR)consisting of HCFAs and ammonium polyphosphate(APP)is applied to prepare flame retardant PP compounds.Their thermal degradation,flammability behavior and water resistance for PP/IFR systems are evaluated by TGA,limiting oxygen index(LOI),vertical burning test(UL-94),cone calorimeter and water treatment.The TGA results of PP/APP/HCFAs compounds under nitrogen and air demonstrate that HCFA/APP enhances the char yields and thermal stability for PP/IFR composites at high temperature.The LOI and cone calorimeter tests demonstrate that the incorporation of IFR(APP/HCFAs)greatly increase the limiting oxygen index and decrease the cone calorimeter parameters,such as heat release rate(HRR)and so on.The scanning electron microscopy(SEM)tests indicate the introduction of IFR(APP/HCFAs)benefite to the formation of a sufficient,intumescent and homogeneous char layer on the materials surface during burning,which effectively prevent the underlying materials from further degradation and combustion.Moreover,the hot water treatment has a little influence on the flame retardant PP composites.3.As an extremely important component of intumescent flame retardant(IFR),ammonium polyphosphate(APP),has been' successfully modified with cyanuric chloride and piperazine to enhance the hydrophobic properties.Fourier transform infrared spectroscopy(FTIR),Elementary Analysis(EA),X-ray photoelectron spectroscopy(XPS)and scanning electron microscopy(SEM)has well characterized the structure of the modified ammonium polyphosphate(CFA-APP),whose surfaces are modified by triazine-based charring agent.The water solubility test demonstrate that CFA-APP possesses excellent water resistance.Then,the resulting CFA-APP containing carbon source,acid source and gas source in one component is used alone to prepare flame retardant polypropylene(PP)via melt blending method.The fire retardancy property of PP,PP/APP and PP/CFA-APP samples are investigated by limiting oxygen index(LOI),vertical burning test(UL-94)and cone calorimetry(CC)test.The corresponding results demonstrate that PP/CFA-APP systems have more efficiency on the flame retardancy compared to PP/APP composites.At 25%content of CFA-APP,PP/CFA-APP system reaches 34.5%of LOI value,and could pass the UL-94 V-0 rating.For combustion performance,The CC results show CFA-APP has much better flame retardant contribution in PP matrix than APP with equal amount of flame retardant,including lower PHRR,lower FGI and lower CO.The thermal degradation behavior of PP composites are conducted by thermogravimetric analysis.The TG results confirm that the triazine-based charring agent shell can enhance thermal stability of CFA-APP and PP composites more effectively compared to unmodified APP.And it promotes the decomposition of PP and CFA-APP ahead of time and leads to a higher thermal stability at high temperature.It benefits the formation of the char layer with high strength and thermal stability on the materials surface during burning,which prevents heat transmission and diffusion.In addition,The surface and fracture morphologies are evaluated by SEM.SEM micrographs and digital photos directly illustrates that the more compact and stable carbon layer is formed during the combustion process for PP/CFA-APP system in comparison with PP/APP.All these results illustrates that chemically modification of CFA-APP is an efficient method to improve the flame retardancy and water resistance of PP systems.4.The organically modified montmorillonite(OMMT)against the flammable polypropylene as a synergist is used with ammonium polyphosphate(APP)and hyperbranched charring foaming agent(HCFA).The experimental results showes that the 20%addition of IFR with OMMT showes a positive effect and improves the flame retardant of the PP systems.The addition of 2wt%OMMT obviously increases LOI values of PP systems with 20%total loading flame retardants from 29%to 31.5%and the samples meet V-0 rating as well as the reduction of the heat release rate(HRR),total heat release(THR),CO2,and CO production.The SEM images reveale that OMMT benefites a dense and strong char on the surface of the material,which results in possessing efficient flame retardancy of PP matrix during combustion.The thermal degradation behavior discussed through thermogravimetric analysis(TGA)indicates that OMMT can improve the thermal stability of PP systems under high temperature,and promotes char residues of PP/IFR systems.Besides,a novel polymeric flame retardant(HCFA)and its corresponding HCFA/Na-MMT nanocomposites with different content of Na-MMT are successfully synthesized.HCFA and its nanocomposites is blended with ammonium polyphosphate(APP)into polypropylene(PP)to prepare flame-retardant PP nanocomposites.The thermal stabilities of the samples are evaluated by thermogravimetric analysis(TG)show that Na-MMT can enhance the thermal stability of PP/IFR composites at higher temperature and plays a key role in promoting the formation of protective char layer.Furthermore,The flammability behaviors of PP/APP/HCFA-NaMMT nanocomposites are evaluated using by limiting oxygen index(LOI),vertical burning test(UL-94)and cone calorimeter tests.With 20 wt%of IFR(APP:HCFA/Na-MMT 2%=3:1),PP/APP/HCFA/Na-MMT nanocomposites can achieve the highest LOI value of 31.5%and UL-94 V-0 rating,and peak heat release rate(PHRR)and total heat release(THR)are reduced compared to that of PP/APP/HCFA without Na-MMT.The results reveal that a small substitution of IFR by Na-MMT impart substantial improvement in flammability performance.The morphologies of the char residues(PP/APP/HCFA/Na-MMT 2%nanocomposites)exhibit intumescent and honeycombed structure with a small number of holes on the surfaces.The honeycombed char structure serves as an outstanding protective layer.5.In the chapter 3,HCFAs have exhibited high charring ability and good thermal stability,in particular,the thermal decomposition temperatures of 1%weight loss(T1%)of PA-HCFA are 468?,which expects to meet the requirements of high temperature processing for polymer materials.Hence,the triazine based char-forming agent(PA-HCFA)combination with AlPi is utilized to flame retard combustible glass-fiber reinforced poly(1,4-butylene terephthalate)(GFPBT)composites.The thermal properties of the GFPBT/AlPi/PA-HCFA composites are studied.Relieved thermal degradation and high temperature oxidation resistance of the char residues in air atmosphere before 600? are obtained.The flame retardancy of the GFPBT/AlPi/PA-HCFA composites is obviously improved.Investigation of combustion behavior reveals that GFPBT/AlPi/PA-HCFA blends(AlPi/PA-HCFA=3/1)can acquire appreciable LOI values,and pass the UL-94 V-0 rating.The improved flame retardancy is mainly thanked to the char which protected underlying PBT matrix from heat and oxygen,in accordant with the results obtained from TG results.In addition,GFPBT/AlPi/PA-HCFA blends(AlPi/PA-HCFA=3/1)exhibit dramatically decreased HRR and THR compared with pure GFPBT.SEM results provide further evidence of the compact char residues,which reduce the transfer of gas and heat during combustion,and ultimately induce improved flame retardancy of GFPBT/AlPi/PA-HCFA composites.These above mentioned are indicated that PA-HCFA is advantageous for the practical application of the polymer matrix.