纤维素水凝胶纤维的制备及其阻燃传感性能

Preparation of cellulose hydrogel fiber and its flame retardancy and sensing property

针对纤维素纤维易燃、功能单一的问题,利用羧甲基化反应引入羧基和金属离子,赋予其阻燃性和吸水性;改性纤维吸水后得到离子导电的水凝胶纤维。借助扫描电子显微镜、氧指数仪、微型量热仪、热重分析仪、单纤维强力仪等分析其阻燃性、热稳定性和力学强度等性能,研究了不同形变条件下纤维素水凝胶纤维的电流信号响应规律。结果表明:纤维素纤维经羧甲基化改性后,极限氧指数从(17.8±0.9)%提高到(35.3±0.9)%;热释放速率峰值和总热释放量分别下降了70.1%和49.4%,基于金属离子优异的阻燃性能和催化成炭能力,燃烧后炭层的致密性高;改性纤维经过吸水后,在不同形变情况下可产生相应的电流响应,具有应变传感能力。纤维素基水凝胶纤维耐燃烧且对物理形变具有灵敏的信号变化,在阻燃及柔性传感领域具有发展潜力。

Objective Lyocell fiber is a novel eco-friendly fiber produced through solvent spinning techniques with excellent flexibility and mechanical strength.Due to the outstanding performance,Lyocell fiber is extensively utilized in the textile,household,and medical sectors,rendering it an ideal substrate for fabricating functional fibers.However,Lyocell fiber is composed entirely of cellulose,poses a significant flammability risk.Simultaneously,its inherent insulating properties also impede the advancement of Lyocell fiber in the realm of flexible electronics.Therefore,enhancing the flame retardancy and electrical conductivity of Lyocell fiber is imperative to expand their functional applications.Method In order to address the issues of flammability and limited functionality in cellulose fiber,this study utilized Lyocell fiber as the primary research material and employed a typically etherification reaction strategy to modify.By introducing carboxyl groups and metal ions(Na+),flame retardancy and water absorption properties were imparted,resulted in the formation of an ionic conductive hydrogel fiber upon water absorption.The surface morphology of the modified fiber was characterized,and flame retardancy of the carboxymethylated fiber as well as the sensing performance of the hydrogel fiber were investigated.Results The carboxymethylation modification of Lyocell fiber had excellent flame retardancy and water absorption properties.The morphology of modified fiber remains similar to original fiber,exhibited a smooth outer surface.In thermogravimetric analysis,due to the introduction of carboxyl and Na+,the residual carbon content of the modified fiber was significantly increased from 17.0% to 24.4%.The limiting oxygen index(LOI)of original Lyocell fiber was merely 17.8%.However,the LOI of fiber can be significantly enhanced to reach an impressive 35.3% through carboxymethylation modification,thereby ensuring its non-ignitability even over prolonged periods in fire.The presence of metal ions exerted a flame retardant effect,resulting in a significant reduction in the peak heat release rate(PHRR)of Lyocell-Na from 184.4 W/g to 55.2 W/g.Moreover,the total heat release(THR)and heat release capacity(HRC)also decreased by 49.4% and 40.7%,respectively.It is noteworthy that Lyocell-Na exhibited a characteristic double heat release peak.This phenomenon arose from the promotion of carbonization in the fiber matrix by Na+,resulting in the formation of a dense barrier carbon layer on the fiber surface during the initial stage of combustion.Once sufficient heat accumulated within this carbon layer,it eventually breaches,leading to the second heat release peak.Compared to pure Lyocell fiber,the tensile strength of the fiber slightly decreased after carboxymethylation,from 3.9 cN/dtex to 3.2 cN/dtex.This could be attributed to that the reaction was carried out in an alkaline environment,and NaOH would decrease the crystallinity of Lyocell fiber,consequently impacted its mechanical strength.The hydrogel fiber showed a sensitive cyclic response to changes in finger bending angle.When the hydrogel fiber was attached to the finger joint for bending cycle action,it underwent deformation to yield and exhibited varying rates of current change corresponding to different bending angles.Conclusion Cellulose-based hydrogel fiber was successfully prepared from Lyocell fiber by etherification reaction.By introducing carboxyl groups and metal ions into the molecular chain,the flame retardancy and water absorption of Lyocell fibers were significantly improved.Moreover,the gelled fiber exhibits a certain level of ionic conductivity upon water absorption.By considering the flame retardant performance,different degrees of deformation can generate corresponding changes in current signals,enabling identification of the operational state.Therefore,this work holds promising prospects for advancement in the field of flexible sensing.