Design And Preparation Of Fe Coordination PBO Fiber And Reasearch On Its UV Resistance

PBO fibers are known for the advantages of low density,high tensile strength,modulus,thermostability and so on.However,the surface chemical inertness,weak lateral compression resistance and especially poor UV-resistance properties of PBO fibers result in the loss of value for application,which hinders the wider application of PBO fibers.In recent years,numerous research groups have paid attention to improving the UV-resistance properties of PBO fibers.Though a large number of literatures have been published,the proposed modification methods still have noticeable disadvantages mainly reflected in the harsh experimental conditions,tedious treatment steps and nondurable modification effects.Under the above background,in this paper,two facile and mild strategies with little negative effects on the mechanical performance of fibers including the direct coordination of Fe³⁺ ions and indirect coordination of Fe³⁺ ions via the mediating effects of metal-organic frameworks?ZIF-8 and ZIF-8/67?have been developed to modify the surface and enhance the UV-resistance properties of PBO fibers based on the fluorescent effect of Fe³⁺ ions.Firstly,two kinds of metal-organic frameworks ZIF8 and ZIF8/67 were synthesized and the preparation conditions that can be applied to obtain the optimum crystalline morphology and particle size were also explored in detail.The results indicated that when the metal salt concentration is 0.25 mol/L,2-methylimidazole concentration is 1.00 mol/L,the oscillation frequency is 120 r/min,and the temperature is 25 °C,the ZIF8 and ZIF8/67 with the optimum morphologies and sizes can be synthesized,which are 730 nm and 940 nm,respectively.In view of the principle that Fe³⁺ ions can coordinate with the benzimidazole units on the ZIF surface,the Fe³⁺ ions were then coordinated to the surface of ZIF8 and ZIF8/67 crystals and the conditions with the largest Fe³⁺ ions loading were further explored.Herein,the n-hexane was chosen as the dispersant of ZIF8 and ZIF8/67.The results demonstrated that the largest loading amounts of Fe³⁺ ions on the ZIF8 and ZIF8/67 were 0.09% and 0.20% when the added volumes of Fe Cl3·6H2O methanol solution?20 mg/m L?were 50 ?L and 100 ?L,respectively.On the one hand,the PBO-Fe fibers were prepared through the direct coordination between benzodioxazole structure of PBO fibers and Fe³⁺ ions.Besides,the modification condition that achieves the largest loading of Fe³⁺ ions was also investigated.Then a series of characterizations and UV-resistance studies on PBOFe fibers were carried out.The results showed that the tensile strength retention of PBO-Fe fibers was 64% after 240 h of UV irradiation.On the other hand,the ZIF8 or ZIF8/67 crystals were in situ grown on the surface of PDA-coated PBO fiber at room temperature,and then served as the medium to coordinate with Fe³⁺ ions.After that,the PBO@ZIF-Fe fibers were successfully fabricated and the corresponding optimum modification conditions were also explored.Then the PBO@ZIF-Fe fibers were characterized in detail and the results suggested that the tensile strength retentions of PBO@ZIF8 and PBO@ZIF8/67 fibers after 240 h UV aging time were 66.2% and 70.5%,respectively.Finally,the improvement effects of direct and indirect strategies proposed in this paper on the UV-resistance properties of PBO fibers are compared with those of reported strategies in published works up to date such as copolymerization,blending,physical coating and nanoparticle modification methods.The detailed UV-resistance mechanisms are also discussed and analyzed in this paper.