Study On Synergistic Modification Mechanism And Industrialization Of Dithiopyrophosphate-based Flame Retardant Viscose Fiber

Cellulose is the most widely distributed and abundant natural polymer material in nature.It has the advantages of biodegradability,abundant reserves,renewable,and environmental protection.Viscose fiber(VF)is a regenerated cellulose fiber that does not change the chemical structure of cellulose,but only rearranges the physical structure.It has the advantages of good moisture absorption,easy dyeing,and antistatic,which is very popular among consumers.However,the flammability of cellulose limits its application in many fields.At present,the mainstream flame retardant technology of viscose fiber for domestic and foreign textiles uses pyrophosphate as the flame retardant through blending and wet spinning.This technology has problems such as large addition of pyrophosphate(≥15%),low flame retardant efficiency,poor interface compatibility between dithiopyrophosphate and cellulose macromolecules,and low fiber mechanical strength.In this thesis,a one-step method was used to synthesize dithiopyrophosphate(DDPS)flame retardant,and then a stable aqueous dispersion of DDPS was prepared by an ultrafine processing.Three synergistic flame retardant technologies were used to improve dithiopyrophosphate flame retardant viscose fiber(DDPS/VF)by the Sol-Gel finishing,microcapsule encapsulation modification on DDPS surface and two-dimensional nanomaterial blending.The synergistic flame retardant effect can reduce the release of toxic smoke,improve the mechanical strength of the flame retardant viscose fiber,and reveal the synergistic flame retardant mechanism.Among them,graphene oxide synergistic dithiopyrophosphate flame retardant viscose fiber(GO/DDPS/VF)has the best effect on the flame-retardant.By studying the rheological behavior and spinning process of the blending soluti on of GO,DDPS and viscose,pliot scale production of high quality graphene oxide synergistic dithiopyrophosphate flame retardant viscose fiber(H-GO/DDPS/VF)was achieved..The main research work is as follows:(1)The synthesis method of DDPS has been improved.It is proposed to synthesize DDPS by a one-step method under the catalysis of 4-dimethylaminopyridine with neopentyl glycol and phosphorous trichloride as raw materials and triethylamine as acid binding agent.The method has the advantages of simple process,short reaction time and high yield.The reaction time is within 12 hours,and the yield can reach more than 85.30%.In view of the large size of the DDPS flame retardant particles,uneven distribution and easy agglomeration,and poor interface compatibility with the viscose fiber matrix,we reduce the size of DDPS particles by an ultra-fine dispersion technology,and improve the dispersion stability of DDPS particles in water.The experimentally obtained dispersion process is:the amount of DDPS accounts for 20%of the total mass of the system,the amount of dispersant SDS is 20%of the content of DDPS,and the wetting agent diglycol is 5%of the DDPS content,the thickener sodium carboxymethyl cellulose(CMC)is 1%of the total mass of the system,the grinding speed is 3000 r/min,and the time is 150 min.DDPS aqueous dispersion has an excellent dispersion stability and alkali resistance,and DDPS particle size is about 321 nm.(2)Using Sol-Gel technology,a dense reticulated silica flame-retardant coating is formed on the surface of DDPS/VF fibers through TEOS hydr olysis,which strengthens the heat and mass barrier,smoke suppression and attenuation.The use of the synergistic flame retardant effect between P and Si elements to improve the flame-retardant properties of DDPS/VF fiber.The results showed that after TEOS finishing of DDPS/VF fiber,the combustion residue content increased from 3.22%to 7.93%,an increase of 146%;the limiting oxygen index(LOI)increased from 27.8%to 28.9%;the ignition time was extended from 7 s to 11 s,peak heat release rate(p HRR)decreased by 11.34%,and peak smoke production rate(p SPR)and peak CO production rate(p PCR)decreased by 52.24%and 14.52%,respectively.The heat hazard and smoke toxicity were significantly reduced.However,when TEOS finishes DDPS/VF fiber under weak acid conditions,the glycoside bonds in the cellulose molecules are easily hydrolyzed and broken,thus the cellulose macromolecular chain is broken and the fiber strength is reduced.(3)Aiming at the problem of poor interface between DDPS and cellulose matrix,this study used in-situ polymerization to form a sulfonated melamine-formaldehyde(SMF)resin shell on the surface of DDPS to prepare a core-shell structure of dithiopyrophosphate microcapsules(MDDPS).To explore the flame retardant effect of MDDPS on viscose fiber,the characterization of MDDPS by TEM,SEM,FTIR,EDS and microscope showed that the sulfonated melamine formaldehyde resin was successfully coated on the surface of the flame retardant,and the dispersion uniformity was improved.The P-N synergistic flame retardant effect of MDDPS increases the limiting oxygen index of the fiber to 32.8%.Compared with the DDPS/VF fiber,the char residue increased by 20.4%at 750℃,and the thermal stability was improved.The p HRR,THR,p SPR and p CPR of MDDPS-5/VF fibers were decreased by29.37%,34.63%,66.42%and 30.65%,respectively.The heat hazard and smoke toxicity of the flame-retardant modified fiber are reduced.The char residue after burning MDDPS-5/VF fiber shows that the surface of the char layer present foaming and expansion phenomena,and has a closed-cell structure.The I_D/I_G value of carbon slag decreases and the graphitization degree increases.The stability and density of the layer are improved,which reflects the flame-retardant mechanism in the condensed phase.(4)In order to improve the mechanical properties and flame retardant properties of DDPS/VF fiber,this study used two-dimensional nanomaterial graphene oxide(GO)to be added to the fiber matrix by blending wet spinning to prepare GO/DDPS/VF fiber.The oxygen-containing functional groups on the surface of GO can form a strong interface interaction with viscose fiber to enhance the mechanical properties of the fiber.At the same time,the GO sheet structure can inhibit heat and mass transfer during the combustion process,improve the flame retardancy of DDPS/VF fiber,and reduce the release of toxic smoke.Compared with DDPS/VF fiber,the dry breaking strength of GO/DDPS/VF-2.0 fiber increased from 2.08 c N/dtex to 2.20c N/dtex,the limiting oxygen index increased from 27.8%to 29.1%,p HRR,THR,p SPR and p CPR were decreased by 51.9%,52.1%,74.6%and 66.1%,respectively,and the heat hazard and smoke toxicity of GO/DDPS/VF fiber were significantly reduced.The I_D/I_G of the carbon residue decreased from 2.54 to 1.70.The addition of GO helped to improve the graphitization degree and density of the fiber carbon layer,and enhance the heat and mass barrier effect of the char layer,which reflects a condensed phase flame retardant mechanism.(5)Compared with DDPS/VF/TEOS and MDDPS-5/VF fibers,GO/DDPS/VF fiber has the advantages of excellent flame retardancy,low smoke toxicity and high mechanical strength.To study the rheological behavior of GO,DDPS and viscose blend solution:The blend solution is a shear thinning fluid,the flow curve lg?increase with the increase of lg?,the structural viscosity index first decreased and then increased with the increase of DDPS to cellulose content.We study the spinning technology of blend solution,realize the pilot-scale production of H-GO/DDPS/VF fiber,give the production line industrialization transformation plan,and apply the theoretical research results to practice.The results show that the flame retardancy and mechanical strength of H-GO/DDPS/VF fibers are similar to those of Lenzing-FR~?fiber,and have excellent flame-retardant and washing resistance.