Study On Surface Modification And Functional Modification Of Polylactic Acid Fiber With Deep Eutectic Solvents

As an important new type of biodegradable material,Polylactic acid（PLA）has the prospect of gradually replacing traditional petroleum-based materials.It is recognized as an environmentally friendly material and has significant advantages such as low carbon,green and environmental protection.At present,PLA terminal products have been gradually applied in industry,civil field,agriculture,medicine and other fields.Although prospect is very broad,PLA faces problems such as limited dyeing technology and few types of functional derivatives due to its defects such as hydrophilicity and poor thermostability.Deep-eutectic solvents（DES）with the advantages of low melting point,low cost,biodegradable structure,good solubility performance,non-toxicity,renewability are becoming an important solvent choice in polymer material solution processing,which can modify natural and chemical fibers.Vigorously developing environmentally friendly material fit the current target"double carbon"that proposed.Therefore,this work selects four representative DESs first,from kinds of DESs with different structures,finds the best system and parameters of modified PLA（DES treated PLA）through experimental comparison of the microstructure,chemical structure and hydrophilic properties of various DES treated PLA fibers,and elucidate the fundamental rules of its modification.Then,focus on the lax of PLA dyeing bottlenecks,explore whether DES treated PLA achieves low-temperature dyeing without affecting its basic mechanical properties,and clarify the internal mechanism of its significantly improved dyeing performance.On this basis,the application scope of DES treated PLA continues to be expanded through the prepared two-dimensional transition metal carbide/sericin carbon nanotubes（Mxene/SSCNT）electrolyte is loaded on DES treated PLA fibers,and Mxene/SSCNT@PLA fabrics with strong conductivity,good electric heating and sensing properties are prepared.The specific research content and results are as follows.（1）Surface modification of PLA fiber by choline des:four kinds of DESs with different acid-base properties were proposed from choline DESs which are the most widely used.The treatment temperature and treatment time were set as independent variables successively.The weight loss rate,fiber micro morphology,chemical structure and hydrophilic properties of PLA were compared and analyzed.The results show that:DES of choline chloride/oxalic acid（Ch Cl/OA）system can successfully modify PLA under the reaction conditions of 60℃and 2 h.On the basis of not destroying its original macromolecular structure,the polar groups on the surface of DES treated PLA fiber increase and physical etching phenomenon occurs,resulting in the leap from high hydrophobicity to high hydrophilicity of PLA;Therefore,the modification process of PLA by Ch Cl/OA follows the principle of"short time+low temperature",and the modification process is simple and environmentally friendly.（2）Low temperature dyeing performance of modified PLA fiber:three disperse dyes C.I.disperse red 167（5BL red）,C.I.disperse orange 30（4RL orange）and C.I.disperse blue 79（HGL dark blue）were selected to dye PLA and DES treated PLA under different temperature gradients and the same dyeing process formula.The color gain depth（K/s value）and dye uptake of different PLA samples were compared and analyzed,and the enhancement mechanism of their dyeing properties was explored.The results showed that DES treated PLA with significantly improved hydrophilicity could reach the K/s value of the original PLA at the best dyeing temperature（110℃）at a lower dyeing temperature（90,100℃）.Modified PLA is affected by the surface micro morphology and chemical structure of DES,which directly accelerates the adsorption,penetration and diffusion behavior of disperse dyes on PLA fiber matrix,and promotes its dyeing depth,rate and dye uptake.（3）Preparation and Performance Research of functional conductive PLA:in order to expand the application field of PLA fiber and its fabric and expand the terminal derivatives of PLA materials,DES treated PLA is used as the base material,and Mxene/SSCNT conductive solution can be firmly loaded on DES treated PLA by dip coating method to prepare Mxene with different layers Mxene/SSCNT@PLA,when 16layers are loaded,the surface unit resistance of the fabric is as low as 5.5Ω·squa^-1and has excellent conductivity.At the same time,when Mxene/SSCNT@PLA is used as an electric heating device,its surface temperature increases with the increase of external voltage,and its temperature increases to 49.8℃at 5 V voltage;When Mxene/SSCNT@PLA is used as a wearable human body detection device to detect human movement and breathing,it shows excellent sensitivity and very stable resistance output.In addition,Mxene/SSCNT@PLA shows excellent air and moisture permeability and water washing resistance,which has become the key to its reuse,puts forward a new idea to solve the defects of PLA,and paves the way for deepening the application and development of PLA in the field of functional materials.