Defining the Photostabilization Succor Properties of Acetylated Lignin Art J. Ragauskas Yunqiao Pu, Lucian A. Lucia
Succor: something that furnishes relief Seminar utline: Reversion background Reversion mechanism verview of acetylation photostabilization process Research Goal Experimental Design Results Conclusions
Brightness Reversion Background All mechanical pulps exhibit photoreversion properties λ: 300-400 nm Attributed to lignin Influenced by 2, metals, moisture, ph % Reflectance 457nm 90 85 80 75 70 65 60 55 Photoreversion of kraft and HW bleached chemithermomechanical pulp (BCTMP) test sheets -1 9 19 29 39 49 59 Period Irradiation/days 100% BCTMP Kraft 1:1 - BCTMP:Kraft
Brightness Reversion Background ne of the most studied wood chemistry problems 160 140 120 Brightness Reversion Citations 100 80 60 40 20 0 1965-70 1970-75 1975-80 1980-85 1985-90 1990-95 1995-00 C.F. Cross: Described the rapid discoloration of ground wood paper. J. Royal Society of Arts, 45, 684(1897). P. Klemm: Attributed groundwood discoloration, in part, to light. Paper Makers Monthly J., 41:4(1903).
Brightness Reversion: Mechanism Redox Cycle Involved in Photoyellowing. hυ, Ο 2 Lignin Lignin RH -R H Lignin 2 H hυ, Ο 2 H -H 2 Lignin -H 2 Phenols & 2 play a key role
Brightness Reversion Background Free Radical Ketyl Re action H H 3 C H R or R H H 3 C H Yellowed Pulp Ph H CH 3 CH 3 CH 3 Generates reactive phenoxy radicals
Brightness Reversion Background Pathways Involved In Photoyellowing of Mechanical Pulp. Phenacyl Pathway Phenoxy Pathway H 3 C H 3 C H hν Lignin H H + PhH CH 3 CH 3 CH 3 + H CH 3 H. CH 3 Yellowed Pulp Yellowed Pulp Singlet xygen * + 2 (singlet) Yellowed Pulp 2 H 3 C CH 3 Phenols & 2 play a key role H
Photostabilization Technologies Antioxidants Ascorbic Acid/Sulfite, Thiols, Thiosulfinates Note: once consumed photoyellowing continues UV-Absorbers Benzophenones, Benzotriazole, Fluorescent Whitening Agent Note: typically require large applications to be very effective Synergistic Combinations Antioxidants/UV-Absorbers Improved performance with reduced additive dosage
Photostabilization Technologies Fiber Modification (> block reactive phenoxy sites) Hydrogenation (C. Li: remove all aromatic rings) Alkylation (block reactive phenoxy groups) Esterification: Acetylation* (block reactive phenoxy groups) Immerse mechanical pulp sheet in acetic anhydride (80 o -100 o C) for 3 400 min. Paulsson et al., Nordic Pulp Paper Res., 232(1994)
Photostabilization: Acetylation TAPPI Bright. ffice Lighting Aspen CTMP % Acetylation 10.3 & 9.7 6.0 4.1 0 TAPPI Bright. Xe Irradiation time (h) Paulsson and Ragauskas Nordic Pulp Paper Res., J. 1998
Acetylation Photostabilization Mechanism Model Compound Studies
Acetylation Photostabilization Mechanism Model Compounds H H CH 3 Ac 2 /H + Rate of Acetylation PhH > H >> α H H CH 3 Blocking PhH retards photoyellowing chemistry Paulsson et al. Nordic Pulp Paper Res., 11:2 109(1996)
Acetylation Photostabilization Mechanism Model Compounds R Ac 2 /H + R Ac R R Ac Ac Thiele-Winter reaction R CH 3 Ac 2 /H + Paulsson et al. Nordic Pulp Paper Res., 11:4: 220(1996) No Reaction Removes chromophores & hinders proposed redox photoyellowing cycle
Research Goal: Characterize the fundamental changes in lignin structure upon acetylation and their contribution to photostabilizing acetylated BCTMP
Acetylation Induced Reactions of Lignin: Experimental Design SW BCTMP Acetone Extracted 0.01 N HCl Dioxane: Water "White" Residual Lignin Acetylation* Ac2() 105C for 10, 30, 60, 150 min Characterize H/C/P NMR Characterize H/C/P NMR *p-dioxane used as co-solvent to aid solubility of lignin
Acetylation Induced Reactions of Lignin: 13 C NMR Primary Aliphatic Acetates Secondary Aliphatic Acetates Ac/Aromatic Ring 0.8 0.6 0.4 0.2 0.0 Ac/Aromatic ring 0.3 0.2 0.1 0.0 0 10 30 60 150 0 10 30 60 150 Acetylation Time/min Acetylation Time/min Ac/Aromatic Ring 0.3 0.2 0.2 0.1 0.1 0.0 Aromatic Acetates Acetylation is accompanied by a fast & slow phase 0 10 30 60 150 Acetylation Time/min
Acetylation Induced Reactions of Lignin: 13 C NMR 1.6 1.4 Ratio of substituted:unsubstituted Ar H CH 3 Ar-R:Ar-H 1.2 1 0.8 0.6 Slight increase in condensed lignin 0.4 0.2 0 0 10 30 60 150 Acetylation Time/min NMR data also suggests a slight decrease in methoxyl group content
Acetylation Induced Reactions of Lignin: 13 C NMR H 1.2 Content of B--aryl ether/aromatic ring lignin H Me B--aryl ether/ar ring 1 0.8 0.6 0.4 0.2 0 0 10 30 60 150 H Me Slight decrease in - -aryl ether units Acetylation Time/min
Acetylation Induced Reactions of Lignin: 1 H NMR Aromatic H 18 16 14 12 10 8 6 4 2 0 Aromatic Hydrogen Content mmol/gr lignin 0 10 30 60 150 Acetylation Time/min Slight increase in condensed lignin & decrease in methoxyl group Me- 25 20 15 10 5 0 Me Content mmol/gr lignin 0 10 30 60 150 Acetylation Time/min
Acetylation Induced Reactions of Lignin: 31 P NMR H Cl P P CH 3 Aliphatic RH (mmol/g) H P CH 3 4.0 3.0 2.0 1.0 0.0 0 10 30 60 150 Rxn t/(min) Acid (mmol/g) 0.3 0.3 0.2 0.2 0.1 0.1 0.0 0 10 30 60 150 Acetylation follows 13 C NMR analysis Rxn t/(min)
Acetylation Induced Reactions of Lignin: 31 P NMR- RH C5 noncondensed PhH (mmol/g) 0.80 0.60 0.40 0.20 0.00 0 10 30 60 150 Rxn T/(min) C5 condensed PhH (mmol/g) 0.30 0.20 0.10 0.00 0 10 30 60 150 Rxn T/(min) C5-condensed PhH exhibited reduced reactivity to acetylation
Acetylation Induced Reactions of Lignin: 31 P NMR -Quinone P(CH 3)3 P(CH 3)3 P CH3 CH3 CH3 I II III H 2 R R p-quinones yield comparable hydrolyzed adduct R=P(CH3)(H) or H
Acetylation Induced Reactions of Lignin: 31 P NMR Quinone P Quinone Adduct Internal Standard 5 0-5 -10-15 -20 ppm
Acetylation Induced Reactions of Lignin: 31 P NMR Quinone Quinone Content (mmol/gr) 0.05 0.05 0.04 0.04 0.03 0.03 0.02 0.02 0.01 0.01 0.00 0 10 30 60 150 ne of the first documented results demonstrating the loss of quinones in lignin by acidic acetylation Rxn T/(min) Residual quinone content (> 30 min) may be due, in part, to p-quinones that Paulsson found no reaction with Ac 2 /H +
Acetylation Induced Reactions Conclusions No major structural changes in lignin Slight increase in condensed structures Most C5-noncondensed PhH are acetylated Partial acetylation of C5-condensed PhHs Limited reactivity of condensed PhHs could explain why Paulsson reported that not all PhH are acetylated even after extended reaction conditions Acetylated PhH would certainly retard phenoxy based photoyellowing pathways
Acetylation Induced Reactions Conclusions Acetylation removes >60% of quinoidal structures in lignin Retard redox photo-cycle photoyellowing pathway hυ, Ο 2 Lignin Lignin RH -R H Lignin 2 H hυ, Ο 2 H -H 2 Lignin -H 2
Acetylation Induced Reactions Conclusions Acetylation procedure slightly decreases --aryl ether structures Retard free radical ketyl photoyellowing pathway H H 3 C H R or R H H 3 C H Yellowed Pulp Ph H CH 3 CH 3 CH 3
Acknowledgments Member Companies of Institute of Paper Science and Technology US Department of Agriculture, Improved Utilization of Wood Grant #: 99-35103-8603 Special Thanks to T.Edler