| Cotton fabrics are widely applied in clothing,carpets,car cushions,curtains,mattress,etc.due to their good breathability,comfort,softness and degradability.However,the highly flammable feature in the air has limited its further development and application.Hence,it is necessary to take flame retardant treatment to improve the flame resistance of cotton fabrics.At present,the research on flame retardancy of cotton fabrics is mainly focused on the condensed phase flame retardancy of phosphorus flame retardants.Ammonium polyphosphate(APP),as a traditional green flame retardant,is assembled on the surface of cotton fabrics by electrostatically bonding with polycations.It can catalyze the degradation of cotton fibers to form an inorganic carbonaceous protective layer in the condensed phase.But its catalytic efficiency is not high,and usually requires the addition of synergists to meet the application requirements of materials.Metal organic phosphonates are a class of organic-inorganic hybrid materials composed of metal ions and organic ligands.Among them,metal ions have excellent solid acid catalytic effects,which can catalyze the formation of a continuous,dense char barrier layer for thermal and oxygen insulation in the condensed phase.Meanwhile,the inorganic phosphate ceramic body produced by the thermal degradation has high thermal stability and a low coefficient of thermal expansion.It plays an important role in enhancing the stability of the char layer.In addition,due to its certain acidity and adjustable functional group,the organic phosphonic acid part,can not only cooperate with metal ions to participate in the construction of catalytic active sites,but as surface modifier to regulate the surface properties.However,metal organic phosphonates are often difficult to disperse uniformly in the matrix due to their large specific surface area and high surface energy.Now the research on metal organic phosphonates as synergists is limited to simple physical mixing.Uneven dispersion and poor compatibility with the matrix inevitably affect the flame retardancy and mechanical properties of materials.Therefore,how to mix the metal organic phosphonate as a synergist with APP at the molecular level to solve the dispersion in the matrix,and then improve the efficiency of catalytic charring is the focus of current research.Therefore,in this paper,using the designability of surface functional groups on metal organic phosphonate,we designed and synthesized metal organic phosphonates with carboxyl and hydroxyl groups.In addition,metal phosphonates with different morphology and thermal stability were prepared by changing the types of metal ions.The hydrogen bonding between carboxyl group and amino group achieved nano-dispersion of metal phosphonates in APP aqueous solution,and improved its compatibility with aqueous matrix.Next,the above flame retardants were applied to polyethyleneimine(PEI)and cotton fabrics to study the synergistic catalytic performance and flame retardant mechanism between nano-dispersed organic phosphonates and APP.Based on this,the main works carried out are as follows:Firstly,we designed and synthesized an organic iron phosphonate(FeP)with carboxyl group and hydroxyl group in the molecular structure.The hydrogen bonding interaction between the carboxyl group and the amino group made FeP achieve stable nano-dispersion in APP aqueous solution.Next,the FeP/APP nano-dispersion was compounded with water-soluble PEI,and the flame-retardant composite foam was prepared by freeze-drying method.The flame retardancy of FeP/APP on PEI was investigated.The results showed that nano-dispersed FeP and APP have excellent synergistic catalytic performance,and their synergy index was as high as 3.FeP/APP catalyzed the degradation of PEI in the condensed phase to form a continuous,dense and high-quality char,which effectively reduced the heat release during combustion.And when the FeP/APP content reached 45%,the LOI value of PEI foam reached31.8%,and could pass the UL-94 V-0 rating.Secondly,based on the results of above experiment,PEI was used as polycation,and the electrostatic interaction between PEI and FeP/APP was used to construct an intumescent flame-retardant coating(FeP/APP/PEI)on the surface of cotton fabrics,and explored its effect on the burning behavior of cotton fabrics.The results showed that the excellent co-catalyzed char formation between nano-dispersed FeP and APP was also applicable to cotton fabrics.It catalyzed dehydration and carbonization of cotton fabrics and formed a porous expanded char layer under the action of PEI.The protective effect of the char layer could make the LOI value of FeP/APP/PEI-4BL coated cotton reached 28.0%,and its p HRR and THR were significantly reduced by94.8% and 81.0%,compared with uncoated cotton,respectively.Finally,two kinds of metal organic phosphonates with different thermal stability and morphology were synthesized by changing the types of metal ions.Among them,ZnP with rod-like,and ZrP with sheet-like structure.The same method was applied to the flame retardant treatment of cotton fabrics.The effects of morphology and thermal stability on the ability of metal organic phosphonates and APP to synergistic catalytic charring of cotton fabrics were studied.The results showed that both ZnP and ZrP could degraded before the cotton fabric,and catalyzed the dehydration and carbonization of the cotton fabric.The nano-dispersed ZrP exhibited better synergy with APP,its layered structure was more conducive to the formation of compact,thermal and oxygen insulated carbonized layer. |
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