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Title Page

Contents

Abstract 10

1. Introduction 12

1.1. Solvothermal liquefaction of sunflower stalk saccharification lignin residue for completely bio-based polyol and its usage for biopolyurethane 12

1.2. Epoxy resin production from methanol-soluble kraft lignin via two-step lignin epoxidation and application to biopolyester synthesis 15

2. Materials and Methods 18

2.1. Solvothermal liquefaction of sunflower stalk saccharification lignin residue for completely bio-based polyol and its usage for biopolyurethane 18

2.1.1. Lignin residue, butanediol, and chemicals 18

2.1.2. Solvothermal liquefaction of lignin residue 18

2.1.3. Biomass conversion measurement 19

2.1.4. Hydroxyl and acid number measurement 19

2.1.5. Lignin-derived biopolyol neutralization 20

2.1.6. Polymerization process for biopolyurethane 20

2.1.7. FT-IR and TGA analysis 20

2.2. Epoxy resin production from methanol-soluble kraft lignin via two-step lignin epoxidation and application to biopolyester synthesis 21

2.2.1. Lignin residue, and chemicals 21

2.2.2. Fractionation of kraft lignin 21

2.2.3. Methanol-soluble kraft lignin epoxidation 21

2.2.4. Purification of lignin-derived epoxy resin 22

2.2.5. Polymerization process for biopolyester 22

2.2.6. Analysis and characterization 23

3. Results and Discussion 24

3.1. Solvothermal liquefaction of sunflower stalk saccharification lignin residue for completely bio-based polyol and its usage for biopolyurethane 24

3.1.1. Determination of solvothermal liquefaction solvent 24

3.1.2. Determination of optimal reaction temperature 26

3.1.3. Determination of optimal acid catalyst loading 28

3.1.4. Determination of optimal reaction time 30

3.1.5. Determination of optimal biomass loading 32

3.1.6. Synthesis of biopolyurethane and FT-IR analysis 34

3.1.7. Thermogravimetric analysis for thermal stability of the biopolyurethane 36

3.2. Epoxy resin production from methanol-soluble kraft lignin via two-step lignin epoxidation and application to biopolyester synthesis 39

3.2.1. Fractionation of kraft lignin and molecular weight analysis 39

3.2.2. Synthesis and characterization of lignin-derived epoxy resin 41

3.2.3. Synthesis and characterization of biopolyester 48

4. Conclusion 53

4.1. Solvothermal liquefaction of sunflower stalk saccharification lignin residue for completely bio-based polyol and its usage for biopolyurethane 53

4.2. Epoxy resin production from methanol-soluble kraft lignin via two-step lignin epoxidation and application to biopolyester synthesis 53

5. References 54

List of Tables

Table 1. Tendency of biomass conversion and hydroxyl and acid numbers according to solvent type in... 25

Table 2. Influence of the solubility of different kraft lignin fractions in epichlorohydrin on the weight of... 40

List of Figures

Figure 1. Tendency of biomass conversion (a) and hydroxyl and acid numbers (b) according to... 27

Figure 2. Tendency of biomass conversion (a) and hydroxyl and acid numbers (b) according to... 29

Figure 3. Tendency of biomass conversion (a) and hydroxyl and acid numbers (b) according to... 31

Figure 4. Tendency of biomass conversion (a) and hydroxyl and acid numbers (b) according to... 33

Figure 5. FT-IR spectra (ATR mode) of sunflower stalk saccharification lignin residue (black,... 35

Figure 6. TGA and DTG curves of sunflower stalk saccharification lignin residue (black, ─),...[이미지참조] 38

Figure 7. Scheme of two-step epoxidation using methanol-soluble kraft lignin. 43

Figure 8. Determination test of the purification solvent using benzene and n-hexane. The results... 44

Figure 9. Final product of lignin-derived epoxy resin synthesized via two-step lignin... 45

Figure 10. FT-IR spectra (ATR mode) of methanol-soluble kraft lignin (Black, ─), lignin-...[이미지참조] 46

Figure 11. ¹H-NMR spectra (300 ㎒) of kraft lignin and lignin-derived epoxy resin. Kraft... 47

Figure 12. Esterification scheme of the epoxide group with phthalic anhydride using pyridine as... 50

Figure 13. FT-IR spectra (ATR mode) of lignin-derived epoxy resin and biopolyester. The... 51

Figure 14. TGA and DTG curves of lignin-derived epoxy resin (─), biopolyester (─), and..[이미지참조] 52

초록보기

Recently, interest about biomass which can replace petroleum feedstock have been accelerate, because petroleum-derived chemicals have problem such as oil depletion and price instability, environmental and health concerns. In this study, renewable bio-based chemicals was synthesized via thermochemical processes using lignin residue that is one of the second generation biomass.

Sunflower stalk saccharification lignin residue was converted to a completely bio-based biopolyol via solvothermal liquefaction using acid catalyst. Different isomer-type biobutanediols were used to replace petroleum-derived reaction solvents. The reaction parameters were optimized according to measurement of the biomass conversion and the hydroxyl and acid numbers. The lignin-derived biopolyol with a biomass conversion of 80.1%, hydroxyl number of 819.0 mg KOH/g, and acid number of 26.5 mg KOH/g was produced in the optimal condition (reaction temperature of 120 ℃, 4 wt% acid catalyst loading, reaction time of 120 min, and 25 wt% biomass loading). The lignin-derived biopolyol was neutralized to decrease the acid number. The neutralized biopolyol was used to synthesize biopolyurethane via polymerization with poly(propylene glycol), tolylene 2,4-diisocyanate terminated. Urethane bond formation was confirmed by FT-IR analysis. The biopolyurethane showed good thermal properties, such as a Td5 of 273.4 ℃, Td10 of 305.8 ℃, and a single degradation peak at 387.2 ℃.

To replace commercial epoxy resins which is most produced using petroleum-derived toxic bisphenol A and synthesize bio-epoxy resin, kraft lignin was utilized as green substitute for bisphenol A. Methanol-soluble kraft lignin was extracted by methanol fractionation for lignin epoxidation, and epoxidized into lignin-derived epoxy resin via two-step epoxidation consisting of epichlorohydrin addition and epoxide ring restructuring. Epoxidized lignin was selectively separated from non- or less-reacted lignin based on their solubility differences in organic solvents. The existence of epoxide groups in the lignin-derived epoxy resin was confirmed using FT-IR, ¹H-NMR and TGA analyses. Epoxidized lignin was used as a reactive lignin macromonomer to prepare biopolyester. The characteristics of the synthesized biopolyester were analyzed using FT-IR and the thermal properties were analyzed by TGA. The thermal decomposition temperature of 5% weight loss (Td5) was determined to be 257.1 ℃, which is comparable to epoxy resins that are used in electronic applications.

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