Study On Of Phosphine-containing Polyamide And Its Composites With Montmorillonite

In the light of the defects of traditional military packing materials,polyamide 66 (PA66)was selected and processed with flame retardant in this paper aimed at improving safety ofPA66,expanding its application fields and scope and further adapting the demand of modernmilitary rear service.Much research has been made to impart flame retardancy of PA66,andhas obtained a great success.However,there are some defects regarding to present flameretarding PA66 still.For example,the"dioxin"problem of halogen-containing flameretarding PA66;higher loading,inferior mechanical properties and un-enduring flameretardant properties of flame retarding PA66 with loading inorganic flame retarder.In orderto solve above problem,high-performance aryl phosphine oxide co-monomer and OMMT assynergistic effect reagen were incorporated into PA66 parent chain by adopting"in-situ anddouble in-situ copolymer technique".And phosphine-containing polyamide and itscomposites with organic montmorillonite (OMMT) were obtained.The fabricated train ofthought and method of halogen-free flame retardant polyamide were provided in thisresearch.First,bis (4-carboxyphenyl) phenyl phosphine oxide (BCPPO) was synthesizedsuccessfully by two step Friedel-Crafts reaction and two step oxidation reaction.And,convenient and quick analytical approach of both bis (4-methylphenyl) phenyl phosphinesulfide (BMPPS) and BCPPO were established firstly.Then,BCPPO was incorporated intoparent chain of PA66 by employing aqueous solution polymerization and meltpolymerization,and inherently flameproof PA66 (FR-PA66) was obtained.The syntheticmethodology and condition of both BCPPO and FR-PA66 were optimized.By employing multiple methods such as limiting oxygen index test,vertical burningtest,differential scanning calorimeter-thermal gravimetric analysis (DSC-TG),gaschromatographic-mass spectrum methods (GC-MS) and so on,the thermal stability,thermolysis behaviors and flame retardant properties of FR-PA66 were characterized and analyzed.The results show that incorporation of BCPPO improved the limiting-oxygen-index(LOI),char residual ratio (CR),heat insulating and oxygen insulating properties of PA66,enhanced the thermal stability of PA66,and FR-PA66 exhibit excellent flame retardantproperties.When the loading of BCPPO higher than 7wt%,the flame retardancy property ofFR-PA66 reachs UL94V-0.But there are dripping phenomenon for burning FR-PA66 still.Experiments results also shows that thermolysis mechanism of FR-PA66 in nitrogen shoulddivided into three stages.At the first stages,phosphorus-carbon bonds in FR-PA66 cleavedfirstly,and primary thermolysis intermediate formed consisted with chain compound mainly.At the second stages,with thermolysising of primary thermolysis intermediate,secondarythermolysis production were formed consisted mainly with cyclical and reductive compound.At the last stages,with further thermoysis of secondary thermolysis production,stabile charprotective layer were formed.The mechanism functions of FR-PA66 in three stages aredescribed as following:In primary stages with decomposition rate less than 0.1,f(α)=(3/2)(1+α)^2/3[(1+α)^1/3-1]^-1;In secondary stages with decomposition rate less than 0.7 andhigher than 0.1,f(α)=2(1-α)^1/2;In finally stages with decomposition rate higher than 0.7,f(α)=(1-α)^1/2[1-(1-α)^1/2]^-1.The flame retardant properties of FR-PA66 are realized byfollowing three main manners.(1) By changing thermolysis mechanism of PA66 bymodifying cleave position and cleave sequence of PA66 molecule chain;(2) By catalyzingcleave of polarity covalent bond,prompting crosslink of molecule chains and formation ofreticular structure,prompting dehydro-cyclo-dehydrogenation of PA66 molecular chain andformation of char residue.(3) By capturing free radical producing by molecule chain cleave.The motion about three stages thermolysis mechanism of FR-PA66 in nitrogen and theanalysis of TPO flame retardant fashion make thermolysis mechanism and flame retardanttheory of polymer abundant,and which show potential application in explaining thermolysisbehavior ofphosphine-containing co-polyamides.Structure,mechanical properties and rheological properties of FR-PA66 werecharacterized with Fourier transform infrared (FTIR),differential scanning calorimeter (DSC)and so on.Experiments results showed that two changes have taken place for FR-PA66molecules chain with incorporating of BCPPO.On the one hand,the rigidity of molecule chain is enhanced.On the other hand,regularity hydrogen bond among PA66 molecule chainhas been destructed by"poor placement"of acylamide function.Therefore,both mechanicalproperties and apparent viscosity of FR-PA66 exhibit increasing firstly,and then decliningwith the increase of BCPPO fraction.When BCPPO fraction is 3wt%,FR-PA66 has themaximum tensile strength,tensile modulus and apparent viscosity.Experiments results alsoindicated that the non-Newton exponent of FR-PA66 is less than 1.FR-PA66 melts is apseudoplastic temperature-sensitive material and exhibited shear-thinning behavior.Crystallization behaviors of FR-PA66 were researched by employing DSC,polarizedlight microscope (POM) and X-ray diffraction (XRD) and so on.The influence of BCPPOsegment on isothermal and non-isothermal crystallization processes of FR-PA66 wereinspected,and discussed.(1) It was found that the Avrami equation is well suitable in treatingisothermal crystallization kinetics process of FR-PA66.And the Ozawa model failed todescribe the non-isothermal crystallization process,while the Avrami equation modified byJeziorny and the Mo's equation combining the Avrami and Ozawa theories exhibited greatadvantages in treating the non-isothermal crystallization kinetics and gave good results.(2)The results also show that there are no differences in nucleation mechanism and nucleationpattern between PA66 and FR-PA66 melts with incorporation of BCPPO.The formation andgrowth of nuclear of FR-PA66 melts is free mainly at the primary crystallization stage,and isin one dimension mainly at the secondary stage.But incorporation of BCPPO is unbeneficialto the formation and growth of nuclear.So crystallization rate of FR-PA66 is lower thanPA66,and crystalline region is decrease.(3) At the same time,incorporation of BCPPOrenders both the crystallization activation energy and the spherulites defects of FR-PA66increase,degree of crystallization decrease.That is to say,incorporation of BCPPO isunbeneficial to the growth of spherulites.However,incorporation of BCPPO exhibitsunobvious influence on the growth ofαandγcrystalline form of PA66.Finally,OMMT/PA66 composites were fabricated by using in-situ intercalationpolymerization and melt intercalation.The influences of fabrication technology on crystallinestate structure,mechanical properties and flame retardant properties were investigated.Basedon above research,both BCPPO and OMMT were induced into PA66 simultaneously byemploying double in-situ intercalation polymerization technology,and OMMT/FR-PA66composites were obtained.Then,mechanical properties and flame retardant properties ofOMMT/FR-PA66 composites were investigated,and concertedness between BCPPO and OMMT were analyzed.The results indicated that OMMT shows excellent synergistic effectwith BCPPO.When the fraction of OMMT and BCPPO is 3wt% respectively,the mechanicalproperties and flamer retardant properties of OMMT/FR-PA66 composites is optimum withthe maximum tensile strength is 103.5MPa,and LOI is 31.1.Incorporation of OMMTenhanced the anti-dripping effect of both PA66 and FR-PA66.And OMMT/FR-PA66composites exhibit excellent flame retardant properties.