The Preparation Of MMT/PVA Composite Flame-retardant Fiber And Its Flame-retardant Properties

With the continuous improvement of people’s living standards,the use of polymer materials such as organic polymers has gradually increased,it has provided many conveniences for people’s lives.However,there is a risk of fire in the use of flammable organic polymer materials.Therefore,in order to minimize the casualties and property losses caused by flammability during the use of polymer materials such as organic polymers,it is imperative to strengthen research on polymer flame retardant materials such as organic polymers.As a flame retardant material,montmorillonite(MMT)has the advantages of low cost,environmental protection,non-toxicity and harmlessness.However,due to the rigid nature of the bulk montmorillonite and the montmorillonite nanosheets obtained by delaminating,it is very limited as a flame retardant material,while it is generally used as a flame retardant additive in combination with a flexible polymer.Although MMT is compounded with organic polymer as a flame retardant additive,the flame retardant effect of the material was improved obviously the flame retardant effect of the prepared composite flame retardant material is insufficient due to factors such as dispersibility of MMT in the polymer.In addition,the existing MMT/polymer composite flame retardant materials are mostly applied in the form of film or block,thus their application fields are limited.Therefore,how to improve the dispersibility of MMT in polymer,how to prepare high MMT content flexible MMT/polymer composite:flame retardant fiber is a problem that needs to be concerned about flame retardant materials.In this thesis,the layered montmorillonite is firstly delaminated in the aqueous medium by liquid phase delamination method,and the montmorillonite nanosheet suspension is obtained.By suspending the montmorillonite nanosheets obtained by delaminating with aqueous polymer polyvinyl alcohol(PVA),MMT/PVA composite flame retardant fibers with different MMT contents are prepared by wet spinning technology,and their morphology,structure,mechanical property and flame retardancy are systematically characterized.The effects of montmorillonite content on the properties of flame retardant fibers are studied.This thesis consists of four chapters.The first chapter is the introduction,in which the classification of flame retardants,the research status and challenges of MMT/PVA composites,and the research contents and innovations are discussed.Chapters 2 and 3 are experimental parts,mainly including the optimal condition for the preparation of single-layer MMT nanosheets by liquid exfoliation and the preparation of MMT/PVA hybrid flame retardant fibers with different MMT amounts by wet spinning technology,as well as their mechanical property and flame retardancy are analyzed.Chapter 4 is a summary of the thesis.The main research contents are as follows:(1)The sodium montmorillonite was used as the raw material,and the precursor Na-MMT was dispersed in the water medium,and stirred under different stirring conditions for different time,Na-MMT was delaminated into MMT nanosheets,and MMT nanosheets suspension was obtained.The morphology and structure of the MMT nanosheets and nanosheet assembled layered materials were systematically characterized by XRD,FTIR,FE-SEM,AFM and TEM.The MMT nanosheets dispersion was centrifuged,and the MMT nanosheet dispersion was obtained and freeze-dried,the MMT layered structural material was obatined by assembling MMT nanosheets.The optimum delaminating condition of Na-MMT in the aqueous medium was that it was treated in water medium for 15 days.The obtained MMT nanosheets had a lateral dimension of about 200 nm and a sheet thickness of 0.98 nm,indicating single layer characteristic of MMT nanosheets.By freeze-dry the delaminated MMT nanosheet suspension,MMT layered material with a regular structure was prepared.The MMT layered material obtained by assembling MMT nanosheets showed good thermal stability and dispersibility in an aqueous medium,and can be applied to flame retardant materials.(2)Under heat condition,the delaminated MMT nanosheets were mixed with PVA,a spinning dope having a concentration of 60 mg mL-1 was obtained.MMT/PVA composite flame retardant fiber with different MMT content and good flexibility and flame retardancy was prepared by using methanol as coagulation bath and wet spinning.The structure,morphology,mechanical property and flame retardancy of composite fibers were systematically investigated by FTIR,FE-SEM and MCC.The prepared composite fiber exhibited a characteristic layered structure of MMT as a whole,and the surface of the fiber gradually became rough and their diameter increased with the increase of the MMT content.The mechanical property of the composite fiber vary significantly with the change of MMT content.When the MMT content of the composite fiber was 50%,the obtained composite fiber had the best mechanical strength and its tensile strength reached 53 MPa.In the composite fiber,MMT can promote the formation of carbon layer.With the increase of MMT content,the decrease of PHRR,TP and THR of the material is continuously improved,and the flame retardant performance of the material was gradually optimized.When the MMT content in the composite fiber increased to 60%,its PHRR and THR were no longer changed.When MMT content was 55%,the mechanical property and flame retardancy of the composite fiber were optimized.MMT 55%composite fiber not only had excellent mechanical property,it can withstand 200 g weight,but also shown excellent flame retardancy,and its PHRR was only 93 W g’1.In addition,the single composite fiber MMT 55%needed 10 s for complete combustion,while the fiber bundle can maintain good morphology without boiling phenomenon after heating for 90 s.These results indicate that the prepared MMT/PVA composite flame retardant fiber has broad application prospect.