Preparation Of Wheat Straw Soda Lignin/Lignocellulose Aerogels And The Oil Absorption Mechanism

Lignocellulose,an abundant green biomass materials in nature,is composed of lignin,cellulose and hemicellulose.Incorporating these three components or native lignocellulose into gel material could endow them with unique properties due to the distinct character.Lignin-free cellulose and hemicellulose have been widely used as the feedstock to prepare cellulose or hemicellulose based gels.Incorporation of lignin and native lignocellulose into the preparation of functional gels is more complicated due to their complex structure.In this study,a series of lignin/lignocellulose composite gels were fabricated by using lignin and native lignocellulose as the feedstock through a mild solvent treatment.They were applied as absorbents for the wastewater treatment and provide the theoretical support for the high-value utilization of lignocellulose material.Meanwhile,the effects of the existential state of lignin on the gel properties were also investigated.The key results were shown as follows:Soda lignin(SL)was firstly dissolved in 8%Li Cl/DMSO at ambient temperature and its highest solubility could reach 2.28(g/10 g solvent).After immersed in large amounts of deionized water,86.0%of the lignin could be regenerated.FT-IR and 2D HSQC NMR spectra indicated that the dissolution of soda lignin in Li Cl/DMSO was a mild treatment which had little effect on the structural properties of lignin.And a more compact polyhedron shell structure of RL appeared in SEM images,and it is beneficial for the preparation of the following gel materials.In the meantime,highly porous lignocellulose or cellulose/lignin composite aerogels with good absorption performance were fabricated by a simple dissolution-regeneration route from lignin/lignocellulose/Li Cl/DMSO mixture solution.External addition of soda lignin into the lignocellulose matrix had little influence on the formation of aerogels.For all aerogels,the existence of endogenous or exogenous lignin in the aerogel network contributed to the formation of large pores.And the presence of exogenous soda lignin was helpful for improving mechanical properties of the gels.Compared with corresponding lignocellulose aerogels with the same lignin content,composite aerogels exhibited smaller pore size and relatively higher BET surface area(S_BET)values.High lignin content lignin/lignocellulose composite gels were prepared by the same dissolution-regeneration route from lignin/lignocellulose/Li Cl/DMSO mixture solution.The presence of lignocellulose matrix is crucial for the formation of physical cross-linked gels.Monolithic block gel with intact shape and no cracks could be obtained when mass ration of lignin to lignocellulose is 3:7 and 6:4.Moreover,the resulted gels had good flexibility and could bear large compressive strain without breakage.Chemical cross-linked polymers,which composed of lignin and lignocellulose,were prepared by using methylenediphenyl diisocyanate(MDI)as the cross-linker.Then they were also regenerated in acetone to fabricate the gel.The resulted gel showed better compressive property than physical cross-linked composite gels which containing the same mass ratio of lignin to lignocellulose.Incorporating of high lignin content into the materials was beneficial for obtaining the hydrophobic properties,and their maximum absorption capacity of chloroform could reach 629%.Blocky lignocellulose aerogels were hydrophobically modified by using stearyl chloride as the esterifying agent and triethylamine as the acid-binding agent in the liquid phase.And long chain alkyl groups were successfully introduced into blocky aerogel.The modifier which was uniformly dispersed in liquid could rapidly diffuse into the pore of aerogels,and avoid the heterogeneity of hydrophobic modification.Furthermore,no mechanical dispersion was needed before modification.The resulted aerogels still had the porous three-dimensional network,and the relatively small amount of modifier agent could be beneficial for obtaining the gels with the denser and more homogeneous porous morphology which resulted in the higher S_BET values and better compressive properties.The highly porous structure of esterified aerogels provided more immerse area for oily solvent,which endowed them with higher oil absorbency.And the highest saturated oil absorbency of kerosene could reach 39.7 g/g.Meanwhile,the resulted gels could still absorb large amounts of kerosene after 10 times of reuse.The gels with good reusability could be used as an effective oily solvent adsorbent to solve the environmental problems caused by oil spill and industrial wastewater leakage.Thermo-sensitive hydrogels which containing different existensial state and content of lignin were fabricated with N-isopropylacrylamide(NIPAAm)and N,N'-methylenebisacrylamide(MBAAm)by a semi-interpenetrating network(SIPN)strategy from lignin/lignocellulose/Li Cl/DMSO mixture solution.The resulted SIPN hydrogels exhibited classical thermo-sensitivity and external addition of soda lignin into the network had little influence on the formation of hydrogels.The SIPN hydrogels exhibited more favorable mechanical properties than single polymer network due to the physical entanglement of poly-NIPAAm and lignocellulose.The presence of externally added lignin in composite hydrogels was beneficial for mechanical improvement.Furthermore,the prepared SIPN gels showed rapid conversion from being hydrophilic at 20? to being hydrophobic at 45?.All the SIPN gels exhibited obvious oil absorbency at 45?.Also,the addition of exogenous lignin resulted in the 1.3? increase of the lower critical solution temperature(LCST).