Preparation, Structure And Properties Of Lignin/Cellulose-based Grafted Copolymers Via ATRP

Lignin and cellulose are the most important sustainable biomass resource which have many interesting properties such as abundant sources, bio-degradable and environmentally friendly. However, it is the huge waste of biomass resource that lignin and cellulose are not fully utilized, causing the problem of environmental pollution. As a consequence, deep processing of lignin and cellulose to develope lignin-based or cellulose-based polymers is a significant way to the utilization of biomass resources for high value-added products. In this article, from the view of the high-value utilization of lignin and cellulose, we choose lignin, cellulose nanocrystals and ethyl cellulose as the raw materials to prepare multi-armed lignin-based copolymers, in-situ enhanced cellulose nanocrystals composites and ethyl cellulose-based brush copolymer with different side chains by atom transfer radical polymerization(ATRP).A series of lignin-based graft copolymers, lignin-graft-poly(methyl methacrylate-co-butyl acrylate) copolymers(lignin-g-P(MMA-co-BA)) and lignin-graft-poly(tetrahydrofurfuryl methacrylate-co-lauryl methlacrylate) copolymers(lignin-g-P(THFMA-co-LMA)), were successfully synthesized via “grafting from” atom transfer radical polymerization(ATRP) with the aid of lignin-based macroinitiators. By manipulating the monomer feed ratios of MMA/BA or THFMA/LMA, grafted copolymers with varied glass transition temperatures(-10-40°C for lignin-g-P(MMA-co-BA) and 0-40°C for lignin-g-P(THFMA-co-LMA)) were obtained. Thermal stability, UV-absorbent ability and mechanical tensile properties for these lignin-based copolymers were measured by thermogravimetric analysis(TGA), UV-visible spectrophotometer, monotonic and dynamic mechanical analyzer(DMA), respectively. These results suggest that mechanical properties of these thermoplastic elastomers(lignin-g-P(MMA-co-BA) and lignin-g-P(THFMA-co-LMA) copolymers) were improved significantly by comparing with the poor mechanical properties of linear P(MMA-co-BA) or P(THFMA-co-LMA) copolymer counterparts and the percentage of elastic strain recovery value is about 68% determined by the creep-recovery tests. Also, these lignin-based copolymers exhibited high blocking of absorption in the range of UV spectrum, due to the integration of lignin in the grafted copolymers.From the view of the utilization of cellulose nanocrystals(CNCs) as a reinforcing material, we developed a simple method for the preparation of self-reinforced CNCs based thermoplastic elastomers(CTPEs). The CTPEs were designed by using ATRP copolymerization of methyl methacrylate(MMA) and butyl acrylate(BA), which was performed on the ATRP initiators immobilized surface of CNCs with the aid of free initiator(ethyl 2-bromoisobutyrate). In this method, the linear polymer that usually be removed in most cases, was combined with poly(methyl methacrylate-co-butyl acrylate) copolymer grafted CNCs(CNCs-g-P(MMA-co-B A)) to form the CTPEs. Investigations on the influence of CNCs on the thermal, mechanical and morphological properties of CTPEs were investigated by DSC, TGA, DMA, universal tensile testing machine, AFM and TEM. These results showed that the existence of CNCs increased the Tgs and tensile strength of CTPEs. Interestingly, the CTPEs containing 2.15 wt% CNCs yielded a increment of 19.2 oC for the Tg value and a double tensile strength compared with linear P(MMA-co-BA) counterpart. Meanwhile, the compatibility between CNCs and P(MMA-co-BA) counterpart of CTPEs was improved which was confirmed by AFM.A class of sustainable and renewable ethyl cellulose–rosin copolymers was prepared by immobilizing rosin derived polymer chains on the backbone of ethyl cellulose(EC) by “grafting from” atom transfer radical polymerization(ATRP). Four different rosin based polymers derived from dehydroabietic acid(DA), one of the major resin acids in natural rosin, were attached to 2-bromoisobutyryl-functionalized EC. Meanwhile, DA-grafted EC was prepared by the simple esterification reaction between DA and EC for comparison. Kinetic studies showed that the polymerization of all monomers was controlled. These grafted copolymers adopt a worm-like or rod-like structure in tetrahydrofuran, verified by laser light scattering experiments. These copolymers have a tunable glass transition temperature and higher thermal stability in contrast to EC. Surface morphology by AFM analysis indicated good film-forming property when rosin polymers were grafted from EC. Additionally, the introduction of DA and rosin polymers remarkably enhanced the hydrophobicity of EC. The static contact angles of all these modified copolymers are above 90°. XPS analysis revealed that the surface of these rosin-modified EC copolymers was dominated by a hydrocarbon-rich rosin moiety. The UV absorption of modified EC composites is indicative of their potential application in UV-absorbent coating materials.Three kinds of EC brush copolymers with mono random copolymer(poly(tetrahydrofur furyl methacrylate-co-lauryl methlacrylate), P(THFMA-co-LMA)), mono block copolymer(PTHFMA-b-PLMA) and dual polymer side chains(PTHFMA and PLMA) were easily prepared by the combination of ATRP and click chemistry through “grafting from” and “grafting onto” method, respectively. A series of EC brush polymers were prepared by alter the density of initiating site, the molecular weight of EC, the feed ratio of THFMA/LMA or PTHFMA/PLMA. The structure of these brush polymers were confirmed by FT-IR, GPC, HT-GPC and 1H NMR. The thermal behavior and mechanical properties of these EC brush copolymers were investigated by DSC, TGA and universal tensile testing machine. The results showed that EC brush polymers with random copolymer side chains(EC-g-P(THFMA-co-LM A)) only has one Tg, however, EC brush polymers with block copolymer side chains(EC-g-PTHFMA-b-PLMA) and dual polymer side chains(EC-(g-PTHFMA)-g-PLMA) has two. The tensile strength of EC-g-P(THFMA-co-LMA was mainly determined by PTHFMA/PLMA content in the copolymers. In addition, the tensile strength of EC-(g-PTHFMA)-g-PLMA and EC-g-PTHFMA-b-PLMA were higher than that of EC-g-P(THFMA-co-LMA) under the same ratio of PTHFMA/PLMA, but the elongation of EC-g-P(THFMA-co-LMA) was much higher than the EC-(g-PTHFMA)-g-PLMA and EC-g-PTHFMA-b-PLMA.