Preparation Of Lignin Dispersed Rosin Sizing Agents Containing Lignin And Mechanistic Research For Application In The Hydrophobicity Of Paper-based Materials

In the midst of the rapid development of society,resource scarcity and environmental pollution have become common problems.Researchers have begun to focus on the high value application of renewable and abundant biomass resources for the preparation of sizing agents.Lignin is the most abundant natural aromatic compound on earth and is mainly sourced from the pulp and paper industry,where it is widely and cheaply available.The lignin molecular structure has both hydrophobic groups in the benzene propane backbone and hydrophilic groups such as phenolic oxygen anions,so its molecules have a certain surface activity.Therefore,when lignin surfactant is introduced into the rosin sizing agent system,it can not only replace the traditional petroleum-based surfactants,but also increase the strength of the paper-based material as a surfactant rich in rigid aromatic rings,which can achieve synergistic enhancement of the hydrophobic and strength properties of the paper-based material,while protecting the environment,which is of great significance to the green and sustainable development of the economy.This dissertation is mainly focus on the preparation of lignin rosin sizing agent.Lignin extracted from black liquor was used as raw material,and the polydispersity of lignin was reduced by fractionation,resulting in the preparation of lignin cationic/anionic rosin sizing agent with high stability and excellent sizing performance.Finally,the prepared lignin rosin sizing agents were used in liquid packaging paperboard（LPB）and paper-based flexible hydrophobic sensors to realize the feasibility of high value application of sizing agents.The main research contents and results of this dissertation are as follows.（1）Lignin cationic surfactant（LCS）was synthesized from acid precipitated lignin and then lignin cationic dispersed rosin sizing agent（LCDRS）was further prepared.LCS can effectively emulsify rosin to prepare sizing agent emulsions with uniform microsphere structure and colloidal stability.Due to the good dispersion of LCDRS microspheres and the strong interaction between LCS and pulp fibers,the obtained LCDRS exhibited good sizing properties.When LCS was added at 2%,the Cobb 120 value of middle layer of LPB was decreased from 31.77 g/m² to 21.30 g/m²,the H₂O₂ edge permeation value decreased from6.32 kg/m² to 4.18 kg/m²,while the hot water edge permeation value decreased from 5.13kg/m² to 3.65 kg/m² and the lactic acid edge permeation value decreased from 3.81 kg/m² to1.01 kg/m² which indicating that the hydrophobicity of the middle layer of LPB was improved.The tensile index of middle layer of LPB was increased from 19.74 N·m/g to 25.96N·m/g.（2）The lignin（L_O）was fractionated using the conventional ethanol grading technique to obtain a high molecular weight L_R fraction.It was also modified by epichlorohydrin and triethylamine to synthesize lignin cationic surfactant（LCS_R）,which was further utilized to prepare lignin cationic dispersed rosin sizing agents（LCDRS_R）with uniform microsphere structure and high stability.The absolute value of zeta potential of LCDRS_R sizing agent was greater than 40 m V,and in view of the good dispersion and high stability of LCDRS_Rmicrospheres.The produced LCDRS_R was superior to ungraded LCDRS_O sizing agent in improving hydrophobicity and increasing strength of middle layer of LPB.When LCS was added at 2%,the Cobb 120 value of middle layer of LPB with LCDRS_R sizing agent was decreased from 21.30 g/m² to 19.53 g/m²,H₂O₂ edge permeation value decreased from 4.18kg/m² to 2.33 kg/m²,hot water edge permeation value decreased from 3.65 kg/m²to 2.03kg/m²,lactic acid edge permeation value decreased from 1.01 kg/m² to 0.76 kg/m² at the same sizing amount,which indicating the improvement of sizing performance.The tensile index of middle layer of LPB was increased by 20.38%and the brightness was increased by17.22%.At the same sizing rate,the tensile index of middle layer of LPB was increased from19.74 N·m/g to 25.96 N·m/g.（3）A lignin anionic rosin sizing agent（LARS）with high stability and high sizing performance was prepared by a simple blending method.The low molecular weight L₉₅fraction was used as the surfactant in the sizing agent system,which gave the sizing agent high stability and excellent sizing performance.The rosin in the sizing agent ensures the good hydrophobicity of the sizing agent.At rosin:L95=1:2,LARS exhibited the lowest particle size（270.00 nm）,highest colloidal stability（zeta potential=-48.84 m V）,low surface tension（35.40 m N/m）and interfacial tension（2.55 m N/m）.Meanwhile,LARS sizing agent exhibited high storage stability（365 days CI=8.00%;coagulation=4.72%）and good sizing properties（Cobb 120 value=6.2 g/m²,edge penetration values of 0.54 kg/m² for H₂O₂,0.67 kg/m² for hot water and 0.75 kg/m² for lactic acid）.（4）A durable,breathable,hydrophobic and biodegradable paper/MXene/sizing agent（PMS）flexible strain sensor was prepared by a simple continuous dip coating method.The MXene layer imparted high sensing performance to the sensor,while the lignin anionic rosin sizing agent（LARS）layer ensured hydrophobicity of the sensor.The PMS flexible strain sensor exhibited high sensitivity in bending angles from 0 to 120°（GF=161）and good durability in bending deformation at 30°for 100,000 cycles.The PMS sensor also exhibited good hydrophobicity（CA=133.4°）,excellent permeability（154.08 mm/s）,and rapid degradability.To prove the concept,the PMS sensor was further demonstrated for human motion detection and wearable Morse code wireless transmission system under water conditions was investigated and the results show that PMS sensors can operate well in water.This work provides practical guidance for the development of practical and comfortable paper-based wearable electronics in human motion monitoring.This dissertation derived from National Key R&D Program of China,identified the potential application of lignin as a surfactant in the preparation of cationic dispersion rosin sizing agent.The sizing effect of lignin cationic dispersion rosin sizing agent and anionic dispersion rosin sizing agent in liquid packaging board was compared and the best sizing effect was found for lignin anionic dispersion rosin sizing agent.In addition,the application of lignin anionic dispersion rosin sizing agent in the field of paper-based sensors expands the application range of sizing agent.