Study On Preparation, Structure And Properties Of Enzymatic Hydrolysis Lignin Graft Copolymers

It is urgent to explore a new renewable resources as an urgent task due to the rapid energyexhaustion and environmental awareness. Seven ministries including the State ForestryAdministration jointly formulated the policies about forestry industry and explicitly pointed outthat a major strategic orientation has become the substitution of renewable resources fornon-renewable resources. Deep processing of lignin is an important way to the utilization ofbiomass resources in the development of high-tech products. Currently, the primary use oflignins to be made for fuel limitied by its natural and irregular molecular structures. Meanwhile,there are abundant hydroxyl and phenyl groups in its molecular structure resulting of the formof hydrogen bonds and π-π bonds, which make lignin in the state of aggregation. These are notconducive to the utilization of lignin. Therefore, the modification and functionalizationof lignin is a favorable method for improving its dispersion and structure regularity. Graftcopolymerization method is a simple and effective way. In this thesis, enzymatic hydrolysislignin graft copolymer were prepared by three polymerization approach and applied tocomposite material which could absorb ultraviolet rays.Three kinds of acrylic monomers (2,2,3,4,4,4-Hexafluorobutyl methacrylate (HFBMA),methyl methacrylate (MMA) and butyl acrylate (BA)) were utilized to modify the lignin (BBL)by "grafting from" Free Radical Polymerization (FRP) respectively. Calciumchloride/Hydrogen peroxide (CaCl2/H2O2) was used as initiator. Effects of monomer type andconcentration, initiator concentration and polymerization time on grafting from BBL werestudied. Grafting of poly (acrylic monomers) onto BBL was verified by the followingcharacterizations and this synthesis method was found to be high efficient and selective forgrafting polymerization of BBL. The presence of the BBL moiety in the backbone also resultedin higher glass transition temperature compared with the homopolymer of each monomer, andsome modified copolymers also improved its thermal stability. All modifications made BBL more hydrophobic and the static contact angles of these modified copolymers were above80°.XPS analysis revealed that the surface of these modified BBL copolymers were dominated byacrylate monomer moiety. Additionally, the BBL-g-PBA copolymers can be used as dispersionmodifers in PLA-based materials to enhance UV absorption.Copolymerization of butyl methacrylate (BMA) with biobutanol lignin (BBL) wasachieved by free-radical polymerization (FRP) using a lignin-based macromonomer. Thelignin-based macromonomer containing acrylic groups was prepared by reacting acryloylchloride with biobutanol lignin using triethylamine (TEA) as absorb acid agentin. From theresults of elemental analysis and GPC, the average degree of polymerization (DP) of BBL wasestimated to be five. A detailed molecular characterization has been performed, includingtechniques such as1H-NMR,13C-NMR and UV-vis spectroscopies, which providedquantitative information about the composition of the copolymers. The changes in thesolubility of lignin-g-poly(BMA) copolymers in ethyl ether were dependent on the length ofpoly(BMA) side chain. TGA analysis indicated that the lignin-containing poly(BMA) graftcopolymers exhibited high thermal stability. The bulky aromatic group of lignin increased theglass-transition temperature of poly(BMA). In order to confirm the main structure ofcopolymer,(AC-g-BBL)-co-BMA copolymer was also synthesized by atom transfer radicalpolymerization (ATRP), and the results revealed that the copolymer prepared by ATRP had thesame solution behavior as that prepared by FRP, and the lignin-based macromonomer showedno homopolymerizability due to the steric hindrance. In addition, the lignin-co-BMAcopolymer had a surprisingly higher molecular weight than poly(BMA) under the samereaction condition, suggesting that a branched lignin based polymer could be formed.The aim of this study was to develop economically UV-absorbent and visible-transparentfilms. For this purpose, lignin was selected because of its strong ultraviolet (UV) absorbingproperty. Lignocellulosic butanol residue, as the by-product of lignocellulosic butanolproduction, is rich in biobutanol lignin (BBL). Herein, BBL was modified with acryloylchloride and then copolymerized with n-butyl acrylate (BA) and methyl methacrylate (MMA) by free-radical polymerization. The chemical structure of poly(BA-co-MMA) chains wereidentifiable by1H-NMR and13C-NMR spectroscopies, combined with UV-visible spectra toconfirm the existence of the aromatic groups that are attributed to BBL in the copolymer. Thisprovided evidence that a BBL graft copolymer was successfully synthesized. The optical,photo-stability, chemical resistance, thermal and mechanical properties of the copolymer wereevaluated. The copolymer film can absorb96.2%of UV light, while allowing70%or highertransmittance in the visible spectrum when the surface concentration of BBL-AC was240μgcm2. In addition, the copolymer film retained excellent absorption capacity in the UV regionand high transparency in the visible light region after75min continuous UV-irradiation orwhen heated at100°C, rendering it potential to use as a UV-absorbent film. The copolymerexhibited good chemical resistance, thermal and mechanical properties compared with purepoly(BA-co-MMA). This strategy not only provides a novel approach for UV-absorbent films,but also greatly extends the comprehensive utilization of BBL.A ‘grafting from’ approach was used to graft poly(ε-caprolactone)(PCL) polymers andgraft poly(L-lactide)(PLA) polymers to BBL by triazabicyclodecene (TBD)-catalyzedring-opening polymerization (ROP). Various graft lengths of BBL-g-PCL and BBL-g-PLAcopolymers were obtained by adjusting the mass ratios of CL monomer to BBL and LAmonomer to BBL. The grafting effciency was evidenced by the long-term stability ofsuspension of PCL-grafted BBL in toluene and PLA-grafted BBL in dichloromethane,combined with FT-IR and NMR spectra to confirm BBL-graft-poly(ε-caprolactone)(BBL-g-PCL) and BBL-graft-poly(L-lactide)(BBL-g-PLA) were successfully synthesized.BBL-g-PCL and BBL-g-PLA were characterized by Differential Scanning Calorimetry (DSC)and thermogravimetric analysis (TGA), and contact angle measurements, respectively. Thevalues of Tmand Xcof BBL-g-PCL were enhanced with the increase of the length of PCL. Thethermal stability of BBL-g-PCL was higher than that of BBL. The values of Tgof BBL-g-PLAwere higher than that of PLA, but the thermal stability of BBL-g-PLA was poorer than that ofBBL due to the existence of the PLA segments. XPS analysis revealed that the surface of these modified BBL copolymers were dominated by grafted PLA and grafted PCL moiety. TheBBL-g-PLA and BBL-g-PCL copolymers are used as dispersion modifers in PLA-basedmaterials to enhance UV absorption. The in vitro degradation rate of BBL-g-PLA andBBL-g-PCL was faster than those of linear PCL, this was because that the linear PCL segmentspossessed a higher crystalline degree than that of the branched BBL-g-PLA and BBL-g-PCLsegments.In conclusion, this strategy not only provides a novel approach for modifying the BBL byGraft polymerization, but also greatly open a simple avenue to improve the compatibility ofBBL with synthetic polymers to preparation biocomposites.