Study On Active Flame Retardant For Cotton Containing Phosphonates Based On Amino Compounds

Cotton is a kind of natural fiber with the largest production in the world.Cotton is widely used in clothing,home and automobile interior decoration and industries because of its good comfort,degradability and low cost.But cotton is a flammable material（LOI is 16%～18%）,which limits the application of cotton fabrics.It is estimated that a high proportion of fires are caused and spread by textiles.Pyrovatex CP^?and Proban^?are mainly commercial flame retardants for cotton.Cotton fabrics finished with these two kinds of cotton flame retardants show good flame retardancy and durability,but with formaldehyde released while used,which is seriously harmful to human health.Therefore,it is greatly economic and theoretical significance and urgently needed in the market to study the formaldehyde-free and durable flame retardant for cotton.In this study,a new formaldehyde-free durable flame retardant for cotton was designed and synthesized to explore the methods to improve the durability of flame retardants from small molecule diethylenetriamine to bigger molecule tetraethylenepentylamine and then to polymer polyethyleneimine,respectively,which all contain active ammonium phosphonate and self-sealing phosphonate groups.The flame retardant containing ammonium phosphonate groups can react with the hydroxyl groups of cellulose to form P-O-C covalent bond,but only the hydroxyl groups on C₆ position can react,so a large number of ammonium phosphonate groups have no esterification reaction.In the process of washing,ammonium ion is replaced by metal ions in water,which leads to the decrease of flame retardancy.The introduction of phosphonate groups can improve the esterification degree of flame retardant cotton fabrics.Reduce the phenomenon of being replaced by Ca²⁺,Mg²⁺and Na⁺in water during washing.The structure,the thermal degradation,flame retardancy,durability,physical and mechanical properties of three cotton fabrics treated with flame retardants were studied.The main results are as follows:（1）Diethylenetriamine pentamethylene triphosphonate dimethyl ammonium diphosphonate（DETA-P）was synthesized and characterized by NMR and FTIR.The results showed that DETA-P flame retardant was successfully synthesized and grafted with cotton fiber through P-O-C covalent bonds.The cotton fabric treated with DETA-P flame retardant were with excellent flame retardancy and durability.According to the AATCC 61-2013 2A test standard,LOI of cotton fabric reached 40.7%after 30 wt%DETA-P treatment,and the LOI was 29.0%after 50 washing cycles.The results of EDX showed P and N elements in the cotton treated with 30 wt%DETA-P.After 50 LCs treatment,the total metal ion content of DETA-P treated cotton was significantly lower than that of diethylene triamine pentamethylammonium phosphonate（ADTPMPA）treated cotton.The results of scanning electron microscope（SEM）and EDX showed that DETA-P molecules entered the interior of cotton fiber,of infrared spectroscopy（FTIR）and durability analysis showed that the DETA-P flame retardant molecule was grafted with-OH in the cellulose molecule by P-O-C.Thermogravimetric analysis showed that DETA-P changed the thermal decomposition pathway of cotton fiber,promoted the dehydration and carbonization of cotton fiber,and inhibited the further combustion of cotton fabric.The results showed that DETA-P was a condensed phase flame retardant mechanism for cotton.The results of cone calorimetry showed that the heat release rate and total heat release of cotton treated with DETA-P were significantly lower than those of cotton without DETA-P treatment.Therefore,the introduction of phosphonate groups into the flame retardant containing ammonium phosphonate groups is an effective method to improve the durability of flame retardant cotton fabrics.（2）Tetraethylenepentaamine heptamethylene tetraphosphonate dimethyl triphosphate（TEPA-P）was synthesized and characterized by NMR.LOI of cotton fabrics treated with 40 wt%TEPA-P was 43.3%,according to AATCC 61-2013 2A standard;after50 times washing,LOI of cotton fabric treated by TEPA-P was 30.6%.Compared with tetraethylene pentaamine heptamethylphosphonate ammonium salt ATEPAHP（without phosphonate group）,TEPA-P flame retardant cotton showed better durability.Phosphorus exists mainly in phosphonates and does not combine with metal ions in the washing process so avoided reduce its flame retardancy.The contents of P and N atoms in treated cotton fiber were determined by X-ray photoelectron spectroscopy（XPS）.TG analysis showed that TEPA-P promoted the formation of carbon during cotton thermal decomposition,indicating that TEPA-P played a flame retardant role in the condensed phase.The results of cone calorimetry showed that the heat release rate and total heat release of cotton fabrics treated with TEPA-P were significantly lower than those of pretreated cotton fabrics.The analysis of physical and mechanical properties of cotton treated with TEPA-P showed that TEPA-P had little effect on the breaking strength and bending stiffness of cotton fabric,while TEPA-P treated cotton maintained good softness.These results showed that the method of introducing ammonium phosphonate groups and phosphonate groups into flame retardant molecules to improve the durability of flame retardant finishing cotton was universal.（3）Polyethylene imine polymethylene polyphosphonate ammonium polyphosphonate（FR-PEI）flame retardant was synthesized and characterized by infrared spectroscopy（FTIR）.The results of infrared spectroscopy showed that FR-PEI flame retardant was successfully synthesized and grafted onto cellulose.When cotton fabric was treated with 30 wt%FR-PEI,the limiting oxygen index could reach 44.5%.According to AATCC 61-2013 3A standard（more steel balls and higher washing temperature,less soaping liquid volume than 2A standard）,LOI was 34.7%after 50 LCs washing.The vertical combustion test showed good flame retardancy of the cotton treated with FR-PEI.The TG results showed that the cotton fabrics finished with flame retardant had more residual carbon after high temperature,indicating that the flame retardant mechanism of FR-PEI was condensed flame retardant mechanism.The cone calorimetric test results show that the heat release amount and heat release rate of flame retardant are much lower than those of pretreated cotton.The results of EDX showed P and N elements in the cotton treated with 30 wt%FR-PEI.In addition,the treated cotton still maintains a good breaking strength.Polymer FR-PEI had better flame retardancy and durability than DETA-P and TEPA-P flame retardants.The results showed that introducing phosphonate groups into ammonium phosphonate flame retardant and increasing the molecular weight of flame retardant were two effective methods to improve the durability of flame retardant cotton fabric.