Extraction Of Reed-based Cellulose/Lignin And Their Application In Polylactic Acid

With the use of traditional petroleum-based plastics,problems such as"white pollution"and"microplastics"had caused,and the impact on the natural environment and human health is enormous.The shortage of petrochemical resources prompt people to look for alternatives to traditional petroleum-based plastics.Bio-based polymer materials have the advantages of excellent biodegradability and renewability,which can effectively alleviate the problems of environmental pollution and energy crisis.Polylactic acid(PLA),as a representative of bio-based polymer materials,have received extensive attention due to its excellent biocompatibility and biodegradability.However,the disadvantages of PLA such as poor toughness,low thermal stability and flammability hinder its application and development.As a natural biopolymer,reed fiber have the characteristics of high abundance,complete regeneration and excellent mechanical properties.At the same time,the abundant modifiable groups on the surface make it have the potential to become a modified reinforced PLA material.In this study,the reed from Xiongan New Area is used as raw material to extract cellulose and lignin and used to modify PLA.The main research work is as follows:(1)Deep eutectic solvent(DES)that prepared by lactic acid and choline chloride are used to extract lignin and cellulose from reed.The chemical structures of cellulose and lignin extracted from reeds were confirmed by FT-IR and ~1H-NMR.The effects of temperature,time and DES ratio on extraction efficiency and cellulose crystallinity are investigated.The experimental results show that DES can effectively extract cellulose and lignin from reed,and the comprehensive extraction efficiency of reed cellulose and lignin can reach 45.2%and 17.8%.After Reed was treated with DES,most of the lignin was removed,and the extracted reed cellulose had a cellulose I type structure with a relative crystallinity of 62.84%.The infrared characteristic peak of reed cellulose is the same as that of microcrystalline cellulose.And the stability is higher than reed.The structure of reed lignin is G-S-H type lignin,which exists in granular form with particle size ranging from 0.4～1μm.(2)PLA/Reed Cellulose composites are compared with the properties of PLA/Reed Fiber and PLA/Microcrystalline Cellulose composites.After adding Reed to PLA,the thermal deformation temperature of the composite increased from 63.3°C to 76.5°C.The mechanical properties of the three composites decreased to varying degrees.Reed Cellulose had better compatibility with PLA,and the mechanical properties and rheological properties are better than PLA/Microcrystalline Cellulose.The initial thermal decomposition temperature of the three PLA-based composites decreased to varying degrees,and their crystallization properties also decreased.The crystallinity of PLA/Reed Cellulose changed the least,only decreased from44.35%to 38.58%,and its crystal morphology changed from spherulite to microcrystalline.(3)Phosphorus-nitrogen modified reed-based lignin flame retardant(PN-lig)is prepared from reed lignin by grafting reaction with piperazine and Ammonium dihydrogen phosphate,And its chemical structure is characterized by FT-IR.To study the effect of PN-lig on the combustion properties of PLA,a series of PLA/PN-lig composites are prepared.The results of cone calorimetry showes that the peak heat release rate(p HRR)and total heat release(THR)are greatly reduced after the addition of 10 wt%PN lig compared with pure PLA,and p HRR and THR are reduced by 33.13%and 13.64%,respectively,the limiting oxygen index(LOI)of PLA composites increase from 20.6%to 26.8%,and the vertical combustion level reached V-0 level.The addition of PN-lig alleviate the droplet phenomenon of PLA during the combustion process.Pure PLA produces no residual carbon after combustion,and the dense carbon layer formed by PLA/PN-lig after combustion blocks oxygen and heat,improving the flame retardancy of PLA.