The authors are grateful for the financial support from the Netherlands Organization for Scientific Research (NWO) (grant 023.007.020 awarded to Jack van Schijndel).

1. Green Knoevenagel condensation of syringaldehyde towards sinapinic acid with 5 mol% ammonium bicarbonate
<ol>
	<li>Add malonic acid (20.81 g, 200.0 mmol) together with syringaldehyde (36.4 g, 200.0 mmol) to a 250 mL round-bottom flask. Dissolve both constituents in 20.0 mL of ethyl acetate and add ammonium bicarbonate (790 mg, 10.0 mmol) to the flask. 
	NOTE: To ensure full completion of the condensation reaction, the rotary evaporator can be used to distill the ethyl acetate and concentrate the reaction mixture, resulting in a solvent-less reaction.</li>
	<li>Keep the reaction mixture for 2 hours at 90 &#176;C in the open flask without stirring for complete conversion to sinapinic acid. 
	NOTE: During this reaction, several morphological changes are observed. The reaction mixture changes from a dense grey mixture to a dissolved yellow mix due to the formation of water during the condensation step of the reaction. After evaporation of the condensate, the reaction mixture solidifies again, indicating full conversion.</li>
	<li>In the work-up of the sinapinic acid product, dissolve the residue in 100 mL of a saturated aqueous NaHCO3-solution. Transfer the solution to a beaker and subsequently acidify it to a pH of 2 using 6 M HCl. 
	NOTE: While adding the saturated aqueous NaHCO3-solution, the crude product dissolves slowly and requires some time and manual scraping to dissolve fully. Once wholly dissolved and transferred to the beaker, the acidic solution of 6 M HCl is added drop-wise. Sinapinic acid will precipitate quickly, and the release of CO2 gas will cause the product to foam.</li>
	<li>Separate the resulting residue by vacuum filtration and wash it with demineralized water. 
	NOTE: At this point, the purity of the product can be analyzed by HPLC. If the product appears contaminated, the next purification step (e.g., recrystallization) must be applied.</li>
	<li>After recrystallization in a mixture of water-ethanol (4:1, v/v), separate the crystals by vacuum filtration. Dry the residue at 60 &#176;C in a vacuum oven, resulting in 42.56 g of pure sinapinic acid. 
	NOTE: The purity of sinapinic acid is measured by melting point analysis and HPLC.</li>
</ol>
2. Hydrogenation of sinapinic acid towards dihydrosinapinic acid with RaneyTM nickel.
<ol>
	<li>Charge a 450 mL flask (using a hydrogenation apparatus) with sinapinic acid (33.6 g, 150 mmol). Dissolve the sinapinic acid in 300 mL of 2 M NaOH solution and add 1.5 g of nickel slurry (see Table of Materials) before fitting the flask to the apparatus. 
	NOTE: The color of the reaction mixture changes due to the addition of the alkaline solution. Sinapinic acid will be yellow in its crystalline form, but when deprotonated by the base, the color of the solution will change to red. The addition of nickel will turn the color black.</li>
	<li>Pressurize the reactor with three bar of hydrogen gas and mechanically shake the reaction at 80 &#176;C for three hours.</li>
	<li>Cool the reactor to room temperature and depressurized slowly. Recover most of the nickel catalyst with a magnet and subsequently filter the solution under reduced pressure. 
	NOTE: The reaction mixture should change from red to green color, visible after filtration. The notable color change is because the conjugated system is interrupted by hydrogenation of the double bond.</li>
	<li>Acidify the solution with a 4 M HCl solution towards a pH of 2. Subsequently, perform an extraction with ethyl acetate (4 times 50 mL). Remove the solvent under reduced pressure after drying over MgSO4. Dry the solid product dihydrosinapinic acid at 60 &#176;C in a vacuum oven. 
	NOTE: Theoretically, the polycondensation reaction can be processed on dihydrosinapinic acid, but there are some practical drawbacks. Due to the molecular structure, dihydrosinapinic acid sublimates above the melting point. An acetylation reaction can be performed to prevent sublimation and increase reactivity.</li>
</ol>
3. Acetylation of dihydrosinapinic acid towards acetylated monomers and oligomers (prepolymer).
<ol>
	<li>Add dihydrosinapinic acid (22.6 g, 100 mmol) to a 250 mL round-bottom flask, followed by acetic anhydride (14.2 mL, 150 mmol) and sodium acetate (0.82 g, 10 mmol). 
	NOTE: The dihydrosinapinic acid does not fully dissolve in the acetic anhydride at room temperature.</li>
	<li>Heat the solution to 90 &#176;C while stirring for one hour for complete conversion of dihydrosinapinic acid towards 4-acetoxy-dihydrosinapinic acid and its acetylated oligomers. 
	NOTE: All the products remain dissolved in acetic anhydride. To increase the total precipitation of 4-acetoxy-dihydrosinapinic acid, add a small amount of water-soluble solvent in the next step.</li>
	<li>Dissolve the solid in 25 mL of acetone, precipitate (solvent-non solvent) into 250 mL of 0.1 M HCl while stirring vigorously&#160;and filter under vacuum. 
	NOTE: The best result shows an entirely precipitated white, sticky solid. If the product solution is added to the HCl solution too quickly, the product remains as a brown liquid at the bottom of the acidic solution. In this situation, extract the entire product solution with ethyl acetate (4 times 50 mL). After drying over MgSO4, remove the ethyl acetate under reduced pressure. The product is 4-acetoxy-dihydrosinapinic acid and prepolymer.</li>
</ol>
4. Polymerization of acetylated monomers and oligomers.
<ol>
	<li>Add the monomers, 4-acetoxy-dihydrosinapinic acid (20.8 g, 100 mmol), and prepolymer to a 100 mL round-bottom flask and add finely powdered NaOH (400 mg, 10.0 mmol). Heat the reaction mixture for three hours at a set temperature of 140 &#176;C in the open flask while stirring at 100 rpm. 
	NOTE: During this reaction, water and acetic acid condense from the open flask. The pH of the vapor can be measured to confirm the condensation of acetic acid. The morphology of the reaction product changes from a molten state to a compact, light-brown product. The setup is subjected to a nitrogen flow to promote the evaporation of the condensate and prevent oxidation. Such reactions are usually stirred with a mechanical stirrer due to the high viscosity of the mixture. However, the use of a magnetical stirrer is sufficient, and the difference is negligible on this scale.</li>
	<li>Set up a solvent assisted polymerization by adding zinc(II)acetate (180 mg, 1 mmol) and 25.0 mL of 1,2-xylene to the flask. Raise the set temperature to 160 &#176;C. 
	NOTE: Raise the set temperature to 160 &#176;C to ensure the reflux of 1,2-xylene and full reactivity of the polymerization. The temperature of the reaction itself remains at 144 &#176;C, due to the boiling point of the 1,2-xylene.</li>
	<li>Reflux the mixture at 144 &#176;C for three hours with constant water and acetic acid removal using a Dean-Stark head. 
	NOTE: After adding the 1,2-xylene and heating the reaction flask to the required temperature, the reagents form a brown slurry with a lower viscosity. This lower viscosity is presumed to benefit the mobility of the end-groups of the polymer, promoting reactivity.</li>
	<li>Cool the reaction mixture down and remove the 1,2-xylene by applying a vacuum (&#60;10 mbar). 
	NOTE: The reaction mixture solidifies while evaporating the solvent and turns into an off-white solid.</li>
	<li>Raise the temperature to 240 &#176;C during the final stage of the polymerization and apply a high vacuum &#60;1 mbar for thirty minutes. 
	NOTE: Only a slight amount of condensate evaporates during this step because only a small amount of condensation is needed to boost the chain length substantially at this stage of polymerization.</li>
	<li>Cool the polymer poly-S to room temperature and wash with methanol to eliminate 4-acetoxy-dihydrosinapinic acid and prepolymers. The obtained product is a light-brown solid. 
	NOTE: After the process, the chain length and thermal properties of the polyester are investigated by GPC and DSC.</li>
</ol>
5. Representative procedure for the depolymerization of poly-S in 1 M NaOH:
<ol>
	<li>Finely grind and sieve poly-S into particles smaller than 180 &#956;m to measure hydrolytic degradation. 
	NOTE: To grind the particles to the required size, use a mortar and pestle with liquid nitrogen-cooled poly-S, followed by a mechanical sieving step.</li>
	<li>Load several test tubes with 20 mg of poly-S and add 1.0 mL of 1 M NaOH solution. Incubate the tubes at three different temperatures (RT, 50, and 80 &#176;C), with an agitation of 500 rpm using a controlled environment incubator shaker. 
	NOTE: Use a heating-block/shaker with multiple entries for this reaction to ensure all the reactions take place in precisely the same (thermal) conditions.</li>
	<li>Neutralize a test tube at regular time intervals with 1.0 mL of 0.5 M H2SO4 and add 2.0 mL of methanol after cooling. 
	NOTE: Small amounts of poly-S and only 1.0 mL of 1 M NaOH are used because these concentrations can, after the addition of methanol, be directly injected in HPLC and do not require any further dilution.</li>
	<li>Filter all samples using 0.45 &#956;m PTFE syringe filters and inject (20 &#956;L) on HPLC using an autosampler. Monitor the absorbance at &#955; = 254 nm, and calculate the concentrations from a calibration curve of known dihydrosinapinic acid standard solutions. 
	NOTE: The standard solutions of the calibration curve should be made in the same solvent mixture as the work-up after the depolymerization.</li>
</ol>

<ol><li>Rahimi, A., García, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Chemical+recycling+of+waste+plastics+for+new+materials+production%5BTitle%5D)+AND+%22Nature+Reviews+Chemistry%22%5BJournal%5D)">Chemical recycling of waste plastics for new materials production.</a> Nature Reviews Chemistry. 1 (6), 41570(2017).</li>
<li>Sardon, H., Dove, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Plastics+recycling+with+a+difference%5BTitle%5D)+AND+%22Science%22%5BJournal%5D)">Plastics recycling with a difference.</a> Science. 360 (6387), 380-381 (2018).</li>
<li>Jones, G. O., Yuen, A., Wojtecki, R. J., Hedrick, J. L., García, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Computational+and+experimental+investigations+of+one-step+conversion+of+poly%28carbonate%29s+into+value-added+poly%28aryl+ether+sulfone%29s%5BTitle%5D)+AND+%22Proceedings+of+the+National+Academy+of+Sciences+of+the+United+States+of+America%22%5BJournal%5D)">Computational and experimental investigations of one-step conversion of poly(carbonate)s into value-added poly(aryl ether sulfone)s.</a> Proceedings of the National Academy of Sciences of the United States of America. 113 (28), 7722-7726 (2016).</li>
<li>García, J. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Recyclable%2C+Strong+Thermosets+and+Organogels+via+Paraformaldehyde+Condensation+with+Diamines%5BTitle%5D)+AND+%22Science%22%5BJournal%5D)">Recyclable, Strong Thermosets and Organogels via Paraformaldehyde Condensation with Diamines.</a> Science. 344 (6185), 1251484(2014).</li>
<li>Brutman, J. P., De Hoe, G. X., Schneiderman, D. K., Le, T. N., Hillmyer, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Renewable%2C+Degradable%2C+Chemically+Recyclable+Cross-Linked+Elastomers%5BTitle%5D)+AND+%22Industrial+%26+Engineering+Chemistry+Research%22%5BJournal%5D)">Renewable, Degradable, Chemically Recyclable Cross-Linked Elastomers.</a> Industrial & Engineering Chemistry Research. 55 (42), 11097-11106 (2016).</li>
<li>Hong, M., Chen, E. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Completely+recyclable+biopolymers+with+linear+and+cyclic+topologies+via+ring-opening+polymerization+of+%CE%B3-butyrolactone%5BTitle%5D)+AND+%22Nature+Chemistry%22%5BJournal%5D)">Completely recyclable biopolymers with linear and cyclic topologies via ring-opening polymerization of γ-butyrolactone.</a> Nature Chemistry. 8 (1), 42-49 (2016).</li>
<li>Lochab, B., Shukla, S., Varma, I. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Naturally+occurring+phenolic+sources%3A+monomers+and+polymers%5BTitle%5D)+AND+%22RSC+Advances%22%5BJournal%5D)">Naturally occurring phenolic sources: monomers and polymers.</a> RSC Advances. 4 (42), 21712(2014).</li>
<li>Fache, M., Boutevin, B., Caillol, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Vanillin%2C+a+key-intermediate+of+biobased+polymers%5BTitle%5D)+AND+%22European+Polymer+Journal%22%5BJournal%5D)">Vanillin, a key-intermediate of biobased polymers.</a> European Polymer Journal. 68, 488-502 (2015).</li>
<li>Pinto, P. C. R., Costa, C. E., Rodrigues, A. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Oxidation+of+Lignin+from+Eucalyptus+globulus+Pulping+Liquors+to+Produce+Syringaldehyde+and+Vanillin%5BTitle%5D)+AND+%22Industrial+%26+Engineering+Chemistry+Research%22%5BJournal%5D)">Oxidation of Lignin from Eucalyptus globulus Pulping Liquors to Produce Syringaldehyde and Vanillin.</a> Industrial & Engineering Chemistry Research. 52 (12), 4421-4428 (2013).</li>
<li>Llevot, A., Grau, E., Carlotti, S., Grelier, S., Cramail, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((From+Lignin-derived+Aromatic+Compounds+to+Novel+Biobased+Polymers%5BTitle%5D)+AND+%22Macromolecular+Rapid+Communications%22%5BJournal%5D)">From Lignin-derived Aromatic Compounds to Novel Biobased Polymers.</a> Macromolecular Rapid Communications. 37 (1), (2016).</li>
<li>Hernández, N., Williams, R. C., Cochran, E. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+battle+for+the+%22green%22+polymer.+Different+approaches+for+biopolymer+synthesis%3A+bioadvantaged+vs.+bioreplacement%5BTitle%5D)+AND+%22Organic+%26+Biomolecular+Chemistry%22%5BJournal%5D)">The battle for the "green" polymer. Different approaches for biopolymer synthesis: bioadvantaged vs. bioreplacement.</a> Organic & Biomolecular Chemistry. 12 (18), 2834-2849 (2014).</li>
<li>Kricheldorf, H. R., Stukenbrock, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((New+polymer+syntheses+85.+Telechelic%2C+star-shaped+and+hyperbranched+polyesters+of+%CE%B2-%284-hydroxyphenyl%29+propionic+acid%5BTitle%5D)+AND+%22Polymer%22%5BJournal%5D)">New polymer syntheses 85. Telechelic, star-shaped and hyperbranched polyesters of β-(4-hydroxyphenyl) propionic acid.</a> Polymer. 38 (13), 3373-3383 (1997).</li>
<li>Gilding, D. K., Reed, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Biodegradable+polymers+for+use+in+surgery-poly%28ethylene+oxide%29+poly%28ethylene+terephthalate%29+%28PEO%2FPET%29+copolymers%3A+1%5BTitle%5D)+AND+%22Polymer%22%5BJournal%5D)">Biodegradable polymers for use in surgery-poly(ethylene oxide) poly(ethylene terephthalate) (PEO/PET) copolymers: 1.</a> Polymer. 20 (12), 1454-1458 (1979).</li>
<li>Jiang, Y., Loos, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Enzymatic+Synthesis+of+Biobased+Polyesters+and+Polyamides%5BTitle%5D)+AND+%22Polymers%22%5BJournal%5D)">Enzymatic Synthesis of Biobased Polyesters and Polyamides.</a> Polymers. 8 (7), 243(2016).</li>
<li>Kricheldorf, H. R., Stukenbrock, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((New+polymer+syntheses%2C+92.+Biodegradable%2C+thermotropic+copolyesters+derived+from+%CE%B2-%284-hydroxyphenyl%29propionic+acid%5BTitle%5D)+AND+%22Macromolecular+Chemistry+and+Physics%22%5BJournal%5D)">New polymer syntheses, 92. Biodegradable, thermotropic copolyesters derived from β-(4-hydroxyphenyl)propionic acid.</a> Macromolecular Chemistry and Physics. 198 (11), 3753-3767 (1997).</li>
<li>Kreye, O., Oelmann, S., Meier, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Renewable+Aromatic-Aliphatic+Copolyesters+Derived+from+Rapeseed%5BTitle%5D)+AND+%22Macromolecular+Chemistry+and+Physics%22%5BJournal%5D)">Renewable Aromatic-Aliphatic Copolyesters Derived from Rapeseed.</a> Macromolecular Chemistry and Physics. 214 (13), 1452-1464 (2013).</li>
<li>Mialon, L., Pemba, A. G., Miller, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Biorenewable+polyethylene+terephthalate+mimics+derived+from+lignin+and+acetic+acid%5BTitle%5D)+AND+%22Green+Chemistry%22%5BJournal%5D)">Biorenewable polyethylene terephthalate mimics derived from lignin and acetic acid.</a> Green Chemistry. 12 (10), 1704(2010).</li>
<li>Nguyen, H. T. H., Reis, M. H., Qi, P., Miller, S. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Polyethylene+ferulate+%28PEF%29+and+congeners%3A+polystyrene+mimics+derived+from+biorenewable+aromatics%5BTitle%5D)+AND+%22Green+Chemistry%22%5BJournal%5D)">Polyethylene ferulate (PEF) and congeners: polystyrene mimics derived from biorenewable aromatics.</a> Green Chemistry. 17 (9), 4512-4517 (2015).</li>
<li>van Schijndel, J., Canalle, L. A., Molendijk, D., Meuldijk, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+Green+Knoevenagel+Condensation%3A+Solvent-free+Condensation+of+Benzaldehydes%5BTitle%5D)+AND+%22Green+Chemistry+Letters+and+Reviews%22%5BJournal%5D)">The Green Knoevenagel Condensation: Solvent-free Condensation of Benzaldehydes.</a> Green Chemistry Letters and Reviews. 10 (4), 404-411 (2017).</li>
<li>van Schijndel, J., Molendijk, D., Spakman, H., Knaven, E., Canalle, L. A., Meuldijk, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Mechanistic+considerations+and+characterization+of+ammonia-based+catalytic+active+intermediates+of+the+Green+Knoevenagel+reaction+of+various+benzaldehydes%5BTitle%5D)+AND+%22Green+Chemistry+Letters+and+Reviews%22%5BJournal%5D)">Mechanistic considerations and characterization of ammonia-based catalytic active intermediates of the Green Knoevenagel reaction of various benzaldehydes.</a> Green Chemistry Letters and Reviews. 12 (3), 323-331 (2019).</li>
<li>Sheldon, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Fundamentals+of+green+chemistry%3A+efficiency+in+reaction+design%5BTitle%5D)+AND+%22Chemical+Society+Reviews%22%5BJournal%5D)">Fundamentals of green chemistry: efficiency in reaction design.</a> Chemical Society Reviews. 41 (4), 1437-1451 (2012).</li>
<li>van Schijndel, J., Molendijk, D., Canalle, L. A., Rump, E. T., Meuldijk, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Temperature+Dependent+Green+Synthesis+of+3-Carboxycoumarins+and+3%2C4-unsubstituted+Coumarins%5BTitle%5D)+AND+%22Current+Organic+Synthesis%22%5BJournal%5D)">Temperature Dependent Green Synthesis of 3-Carboxycoumarins and 3,4-unsubstituted Coumarins.</a> Current Organic Synthesis. 16 (1), 130-135 (2019).</li>
<li>Bloom, M. E., Vicentin, J., Honeycutt, D. S., Marsico, J. M., Geraci, T. S., Miri, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Highly+renewable%2C+thermoplastic+tetrapolyesters+based+on+hydroquinone%2C+p-hydroxybenzoic+acid+or+its+derivatives%2C+phloretic+acid%2C+and+dodecanedioic+acid%5BTitle%5D)+AND+%22Journal+of+Polymer+Science+Part+A%3A+Polymer+Chemistry%22%5BJournal%5D)">Highly renewable, thermoplastic tetrapolyesters based on hydroquinone, p-hydroxybenzoic acid or its derivatives, phloretic acid, and dodecanedioic acid.</a> Journal of Polymer Science Part A: Polymer Chemistry. 56 (14), 1498-1507 (2018).</li>
<li>Padias, A. B., Hall, H. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Mechanism+Studies+of+LCP+Synthesis%5BTitle%5D)+AND+%22Polymers%22%5BJournal%5D)">Mechanism Studies of LCP Synthesis.</a> Polymers. 3 (2), 833-845 (2011).</li>
<li>Moon, S., Lee, C., Taniguchi, I., Miyamoto, M., Kimura, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Melt%2Fsolid+polycondensation+of+l-lactic+acid%3A+an+alternative+route+to+poly%28l-lactic+acid%29+with+high+molecular+weight%5BTitle%5D)+AND+%22Polymer%22%5BJournal%5D)">Melt/solid polycondensation of l-lactic acid: an alternative route to poly(l-lactic acid) with high molecular weight.</a> Polymer. 42 (11), 5059-5062 (2001).</li>
<li>Wellen, R. M. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Effect+of+polystyrene+on+poly%28ethylene+terephthalate%29+crystallization%5BTitle%5D)+AND+%22Materials+Research%22%5BJournal%5D)">Effect of polystyrene on poly(ethylene terephthalate) crystallization.</a> Materials Research. 17 (6), 1620-1627 (2014).</li>
<li>Kricheldorf, H. R., Conradi, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((New+polymer+syntheses+16.+LC-copolyesters+of+3-%284-hydroxyphenyl%29+propionic+acid+and+4-hydroxy+benzoic+acids%5BTitle%5D)+AND+%22Journal+of+Polymer+Science+Part+A%3A+Polymer+Chemistry%22%5BJournal%5D)">New polymer syntheses 16. LC-copolyesters of 3-(4-hydroxyphenyl) propionic acid and 4-hydroxy benzoic acids.</a> Journal of Polymer Science Part A: Polymer Chemistry. 25 (2), 489-504 (1987).</li>
<li>Chen, Y., Tan, L., Chen, L., Yang, Y., Wang, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Study+on+biodegradable+aromatic%2Faliphatic+copolyesters%5BTitle%5D)+AND+%22Brazilian+Journal+of+Chemical+Engineering%22%5BJournal%5D)">Study on biodegradable aromatic/aliphatic copolyesters.</a> Brazilian Journal of Chemical Engineering. 25 (2), 321-335 (2008).</li>
<li>Han, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+Change+in+Mechanism+from+Acidolysis+to+Phenolysis+in+the+Bulk+Copolymerization+of+4-Acetoxybenzoic+Acid+and+6-Acetoxy-2-naphthoic+Acid%5BTitle%5D)+AND+%22Macromolecules%22%5BJournal%5D)">A Change in Mechanism from Acidolysis to Phenolysis in the Bulk Copolymerization of 4-Acetoxybenzoic Acid and 6-Acetoxy-2-naphthoic Acid.</a> Macromolecules. 29 (26), 8313-8320 (1996).</li>
<li>Lu, X. F., Hay, J. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Isothermal+crystallization+kinetics+and+melting+behaviour+of+poly%28ethylene+terephthalate%29%5BTitle%5D)+AND+%22Polymer%22%5BJournal%5D)">Isothermal crystallization kinetics and melting behaviour of poly(ethylene terephthalate).</a> Polymer. 42 (23), 9423-9431 (2001).</li>
<li>Sánchez, M. E., Morán, A., Escapa, A., Calvo, L. F., Martínez, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Simultaneous+thermogravimetric+and+mass+spectrometric+analysis+of+the+pyrolysis+of+municipal+solid+wastes+and+polyethylene+terephthalate%5BTitle%5D)+AND+%22Journal+of+Thermal+Analysis+and+Calorimetry%22%5BJournal%5D)">Simultaneous thermogravimetric and mass spectrometric analysis of the pyrolysis of municipal solid wastes and polyethylene terephthalate.</a> Journal of Thermal Analysis and Calorimetry. 90 (1), 209-215 (2007).</li>
</ol>

The authors have nothing to disclose.

When dihydrosinapinic acid was heated in a reaction vessel, sublimation of the starting material occurred, and this effect was enhanced when a vacuum was applied. Acetylation has been performed on dihydrosinapinic acid to avoid sublimation. Kricheldorf et al.12,27 recognized that not only acetylation but similarly di- and oligomerization occurred. However, these esterified monomers and oligomers no longer sublimate and are suitable as monomers for the melt polycondensation28. Also, the formation of the prepolymers from 4-acetoxy-dihydrosinapinic acid confirms the hypothetical reaction mechanism29.
1H NMR measurements were used to determine the number average degree of polymerization, and GPC measurements were used to generate further chain length data. GPC measurements were always performed after forcing amorphicity by mixing polystyrene and quenching with liquid nitrogen.
The obtained results presented in Table 1 show the GPC Mn values of the polymer samples correspond to about 670 repeating units of poly-S, on average, throughout the generations. These values are considerably higher than the corresponding values obtained with 1H NMR measurements presented in Figure 2 since these values are about 43 repeating units of poly-S. This variation is related to the trace impurities of the acetoxy-group containing compounds within the synthesized polymers, decreasing the number average degree of polymerization (DPn) of poly-S, calculated with 1H NMR measurements. Another explanation is related to the differences in hydrodynamic volumes of the polyesters and polystyrene standards used during the GPC measurements. The polydispersity PDI is below 2.0. This relatively low value can be attributed to high molecular polymer filtering out before GPC analysis.
Thermal characterization was carried out by using DSC and TGA techniques, whereby thermal properties were found comparable to PET. DSC analysis showed that the molecularly recyclable polymer poly-S has a melting temperature of 281 &#176;C. This melting temperature is sixteen degrees higher related to PET30. The glass-rubber transition temperatures of poly-S are also higher compared to PET, namely 113 &#176;C versus 67 &#176;C with PET. A higher glass-rubber transition temperature is often beneficial for many applications.
Finally, during the cooling cycle, poly-S has a lower crystallization temperature related to PET, namely 151 &#176;C versus 190 &#176;C. The thermal gravimetrical analysis of poly-S indicated a decomposition temperature of 341 &#176;C of poly-S. Compared to PET with a decomposition temperature of 470 &#176;C, the decomposition temperature of poly-S is lower31 (Supporting Information: Figure S11).
The depolymerization of the formed polymeric material was observed for over two hours, at a temperature of 80 &#176;C. HPLC-samples were taken to analyze the concentration of released dihydrosinapinic acid in a solution of 1 M NaOH. The samples were measured against a calibration curve of pure dihydrosinapinic acid to determine the HPLC yield. (Supporting Information: Figure S12)
A mass balance has been established to determine the loss of mass during a complete cycle of polymerization and depolymerization. An exact amount of 5.00 grams of dihydrosinapinic acid has been introduced into the polymerization process. After one cycle of polymerization, depolymerization to dihydrosinapinic acid, and work-up, 4.70 grams of dihydrosinapinic acid was produced, which corresponds to a yield of 94%. During the first cycle, most of the material was lost by manual handling (Supporting Information: Figure S13-S14). The loss of the monomer dihydrosinapinic acid was reasonably limited so that after three generations, approximately 85% of the initial amount of monomer remained.
This publication describes how a new polymeric material that is specifically suitable for molecular recycling has been designed. The combination of polymerization, depolymerization, in which the monomers are recovered, and repolymerization, has created an utterly sustainable cycle with only minimal losses. When the principles of Green Chemistry are applied further, it is possible to optimize the conditions of different steps. For example, subsequent studies can investigate hydrolysis under acidic conditions to prevent excessive salt-formation.

In contrast to the incineration of polymeric waste, chemical recycling offers the possibility to recover the monomers. Chemical recycling is a logical choice at the end of the technical life of polymeric materials since these polymeric materials are produced chemically1. There are two ways to recycle the polymeric material chemically, pyrolysis and molecular recycling2. With pyrolysis, the polymeric material is transformed into products of higher value by using extreme conditions3,4. Molecular recycling is an efficient method for recovering the starting materials using depolymerization. After depolymerization, the monomeric units can be repolymerized into virgin polymeric materials5. The availability of suitable monomers to apply molecular recycling on a larger scale is wanting. The current plastic problem dictates that society demands sturdy and robust polymeric materials. At the same time, it is also preferred that the same polymeric materials are easily recyclable and do not endure in the environment. Current polymeric materials with good thermal and mechanical properties do not depolymerize easily6.
Lignin, commonly found in vascular plants, is responsible for 30% of the world&#39;s natural carbon content and is the second most abundant biopolymer after cellulose. Lignin has a complex amorphous structure and appears to be a suitable alternative to replace aromatics extracted from fossil materials. The three-dimensional structure of lignin provides strength and stiffness to wood, as well as resistance to degradation. Chemically speaking, lignin is a very complex polyphenolic thermoset. It consists of varying composition of three different methoxylated phenylpropane structures. Syringyl, guaiacyl, and p-hydroxyphenyl (often abbreviated as S, G, and H, respectively) are derived from the monolignols sinapyl alcohol, coniferyl alcohol, and p-coumaryl alcohol7. The distribution of these units differs per biomass type, with softwood, for instance, consisting of mostly guaiacyl units and hardwood of guaiacyl and syringyl units8,9. Renewable natural sources, such as trees and plants, are desirable for the production of redesigned monomers for innovative polymeric materials10. These monomers, isolated and synthesized from natural sources, are polymerized to so-called biobased polymers11.
Aromatic carboxylic acids are several orders of magnitude less electrophilic than the equivalent aliphatic carboxylic acids for electronic reasons12. Various commercial polyesters use aromatic carboxylic acids instead of aliphatic carboxylic acids. As a result, the fibers in polyester textiles made from poly(ethylene terephthalate) (PET) fibers are almost insensitive to hydrolysis during washing or, for example, rain13. When the molecular recycling of polyesters is wanted, it is advisable to use aliphatic esters in the build-up of the polymer.
For the reasons mentioned, we have investigated the possibilities of making polyesters from 4-hydroxy-3,5-dimethoxy-dihydrocinnamic acids14. Previous studies by Kricheldorf15, Meier16, and Miller17,18 show that it is challenging to build polymers using 4-hydroxy-3,5-dimethoxy-dihydrocinnamic acid. Decarboxylation and crosslinking hindered the polymerizations, and so limiting the success of these syntheses. Also, the mechanism of the polycondensation remained unclear. The presented paper describes the conditions in which the polyester poly(dihydrosinapinic acid) can be synthesized regularly and in high yield, thus paving the way for using semi-aromatic polyesters that are molecularly recyclable.
We have developed a green and efficient way to synthesize sinapinic acid using a condensation reaction between syringaldehyde and malonic acid19,20. After this Green Knoevenagel, hydrogenation produces dihydrosinapinic acid, which is suitable for reversible polycondensation. This publication visualizes the synthetic steps to the molecularly recyclable polymer poly(dihydrosinapinic acid), referring to the base units of lignin, called poly-S. After analyzing the polymeric material, poly-S is depolymerized to the monomer dihydrosinapinic acid under relatively favorable conditions and repolymerized over and over again.

<table><tbody><tr><td>&lt;strong&gt;Reaction 1: Green Knoevenagel condensation&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Ammonium bicarbonate</td><td>Sigma Aldrich</td><td>&gt;99%</td><td></td></tr><tr><td>Ethanol</td><td>Boom</td><td>Technical grade</td><td></td></tr><tr><td>Ethyl acetate</td><td>Macron</td><td>99.8%</td><td></td></tr><tr><td>Hydrochloric acid</td><td>Boom</td><td>37%</td><td></td></tr><tr><td>Malonic acid</td><td>Sigma Aldrich</td><td>99%</td><td>used as received</td></tr><tr><td>Sodium bicarbonate</td><td>Sigma Aldrich</td><td>&gt;99.7%</td><td></td></tr><tr><td>Syringaldehyde</td><td>Sigma Aldrich</td><td>98%</td><td>used as received</td></tr><tr><td>&lt;strong&gt;Reaction 2: Hydrogenation&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Magnesium sulfate</td><td>Macron</td><td>99%</td><td>dried</td></tr><tr><td>Raney&amp;trade; nickel</td><td>Sigma Aldrich</td><td>&gt;89%</td><td></td></tr><tr><td>Sodium hydroxide</td><td>Boom</td><td>Technical grade</td><td>dissolved</td></tr><tr><td>&lt;strong&gt;Reaction 3: Acetylation&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Acetic anhydride</td><td>Macron</td><td>&gt;98%</td><td></td></tr><tr><td>Acetone</td><td>Macron</td><td>&gt;99.5%</td><td></td></tr><tr><td>Sodium acetate</td><td>Sigma Aldrich</td><td>&gt;99%</td><td></td></tr><tr><td>&lt;strong&gt;Reaction 4A: Polymerisation&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>1,2-xylene</td><td>Macron</td><td>&gt;98%</td><td></td></tr><tr><td>Sodium hydroxide</td><td>Boom</td><td>Technical grade</td><td>finely powdered</td></tr><tr><td>Zinc(II)acetate</td><td>Sigma Aldrich</td><td>99.99%</td><td></td></tr><tr><td>&lt;strong&gt;Reaction 4B: Depolymerisation&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Sodium hydroxide</td><td>Boom</td><td>Technical grade</td><td>dissolved</td></tr><tr><td>Sulfuric acid</td><td>Macron</td><td>100%</td><td></td></tr><tr><td>&lt;strong&gt;Analysis&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>CDCl&lt;sub&gt;3&lt;/sub&gt;</td><td>Cambride Isotope Laboratories, Inc.</td><td>99.5%</td><td></td></tr><tr><td>CF&lt;sub&gt;3&lt;/sub&gt;COOD</td><td>Cambride Isotope Laboratories, Inc.</td><td>98%</td><td></td></tr><tr><td>Dimethylformamide</td><td>Macron</td><td>&gt;99.9%</td><td></td></tr><tr><td>Hexafluoro-2-propanol</td><td>TCI Chemicals</td><td>&gt;99%</td><td></td></tr><tr><td>Methanol</td><td>Macron</td><td>&gt;99.8%</td><td></td></tr><tr><td>Tetrahydrofuran</td><td>Macron</td><td>&gt;99.9%</td><td></td></tr></tbody></table>

designed for molecular recycling: a lignin-derived semi-aromatic biobased polymer

The development of chemically recyclable biopolymers offers opportunities within the pursuit of a circular economy. Chemically recyclable biopolymers make a positive effort to solve the issue of polymer materials in the disposal phase after the use phase. In this paper, the production of biobased semi-aromatic polyesters, which can be extracted entirely from biomass such as lignin, is described and visualized. The polymer poly-S described in this paper has thermal properties similar to certain commonly used plastics, such as PET. We developed a Green Knoevenagel reaction, which can efficiently produce monomers from aromatic aldehydes and malonic acid. This reaction has been proven to be scalable and has a remarkably low calculated E-factor. These polyesters with ligno-phytochemicals as a starting point show an efficient molecular recycling with minimal losses. The polyester poly(dihydrosinapinic acid) (poly-S) is presented as an example of these semi-aromatic polyesters, and the polymerization, depolymerization, and re-polymerization are described.

Sinapinic acid was synthesized in high purity and high yield (&#62; 95%) from syringaldehyde using the Green Knoevenagel condensation. (Supporting Information: Figure S1) The E-factor is an indication of waste production where a higher number indicates more waste. The E-factor is calculated by taking the total material input, subtracting the amount of the desired end product, and dividing the whole by the amount of the end product. This Green Knoevenagel condensation has an E-factor of 1.0, which can be calculated: [((29.81 g malonic acid + 36.4 g syringaldehyde + 0.790 g ammonium bicarbonate + 18.04 g ethyl acetate) &#8211; 42.56 g sinapinic acid) / 42.56 g sinapinic acid]. The sinapinic acid was hydrogenated with a high yield (&#62;95%) to obtain the intended monomer dihydrosinapinic acid. (Supporting Information: Figure S2) This hydrogenation reaction has an E-factor of 0.84. Subsequently, dihydrosinapinic acid was acetylated to obtain 4-acetoxy-dihydrosinapinic acid and its prepolymer. The E-factor of this acetylation reaction was 0.45, assuming full conversion to 4-acetoxy-dihydrosinapinic acid (Supporting Information: Figure S3).
Usually, the E-factor of organic synthetic reactions of pharmaceuticals is between 5 and 100, and these reactions frequently use relatively harmful chemicals21. The E-factor, calculated for both the Green Knoevenagel and subsequent reactions, is remarkably low compared to these numbers. Yet, the E-factor exhibits some shortcomings. For example, the environmental hazard of a given waste component is not reflected by the E-factor. In principle, this can be compensated by the &#34;environmental quotient&#34; (Q) taking the &#34;environmental unfriendliness&#34; of a given waste into account. Because the catalyst ammonium bicarbonate is relatively harmless, the environmental unfriendliness quotient Q of the Green Knoevenagel is also stated as low. Still, additional research is essential to confirm this22. By applying the mentioned organic synthetic reactions, 4-acetoxy-dihydrosinapinic acid and its prepolymers are ready for the polycondensation to poly-S.
Figure 1 depicts the Proposed mechanism of the step-growth polymerization of 4-acetoxy-dihydrosinapinic acid. In step i, the added base starts the reaction and controls the reaction rate by deprotonating the acid group, thereby stimulating its reactivity23. The formed carboxylate attacks the carbonyl of the acetoxy group and creates a tetrahedral. In this state, the phenoxide group connects to the other carbonyl through a phenoxide shift, which was initially the aliphatic carboxylic acid group. When the phenoxide shift has occurred, the acetate-ion leaves the intermediate, subtracts a proton from the original base and then leaves the reaction as acetic acid. In practice, this step is promoted by creating a vacuum in the reaction vessel24. In each cycle, one novel molecule is added to the chain. During the progress of the polycondensation reaction, it turned out to be challenging to find the exact combination between increasing the molecular weight and degradation of the polymer chains. As the temperature was elevated with a gradient during the melt polymerization, growing amounts of degradation occurred as the viscosity of the polymer increased. A small amount of solvent was added during the second step of the polycondensation to decrease the viscosity. In this solvent-assisted poly-condensation, 1,2-xylene turns out to be a suitable agent for promoting the polycondensation25.
Figure 2 represents three different 1H NMR measurements during the polymerization process. The samples dissolved well and were measured in a mixture of CF3COOD / CDCl3. The 1H NMR spectra were taken after the acetylation of sinapinic acid. The 1H NMR spectrum in the middle is a sample taken from the same reaction. No specific compound was isolated, so acetylated sinapic acid and its prepolymers are shown. The 1H NMR spectrum above was taken from a sample after completion of the polycondensation. The areas of the acetyl end groups decrease during the polymerization process, and the number average degree of polymerization (DPn) increases. After completing the reaction, the degree of polymerization was set at 43 repeating units as determined by 1H NMR measurements.
GPC measurements were performed to investigate the chain length of poly-S, and various GPC-systems have been tested for the analysis. The initial step was to dissolve the polymeric material in several common organic solvents such as chloroform (CHCl3), dimethylformamide (DMF), hexafluoro-2-propanol (HFIP), and tetrahydrofuran (THF). However, it appears that the highly crystalline material of poly-S, visible on DSC thermograms, was sparingly soluble in these solvents. Also, when the polymeric material was melted and then cooled very quickly in liquid nitrogen to increase the amorphicity of the polymer, only the short polymer chains dissolved in DMF. The value measured on GPC was only 1,900 up to 2,100 Da, which corresponds to approximately ten repeating units.
Another pretreatment method has been selected to perform a proper GPC measurement. Additional research26 prescribes that a more amorphous polyester material can be formed when polystyrene in its atactic form is melt-mixed into the polyester. The two polymers (polyester and polystyrene) were placed together in a DSC pan, melted, and subsequently cooled in liquid nitrogen. Washing the quenched mixture with acetone removed the residual polystyrene, and after successfully dissolving in DMF, a high molecular weight polymer could be observed.
When poly-S was hydrolyzed in 1 M NaOH, the molecularly recyclable polyester yielded the starting material dihydrosinapinic acid in less than 10 minutes. HPLC, melting point analysis, and 1H NMR confirmed this observation (Supporting information: Figure S4). Extended reaction times did not increase the yield, as shown in Figure 3.
The thermograms and GPC analysis of poly-S 1.0 and their successive generations poly-S 2.0 and poly-S 3.0 after forced amorphicity with atactic polystyrene are shown in Figure 4 and Table 1, respectively. DSC analysis of poly-S shows a glass transition signal (Tg) at 113 &#176;C and an endothermic melting signal (Tm) at 281 &#176;C. The polymers from re-polymerized sinapinic acid 3a poly-S 2.0 up and poly-H 3.0 exhibit similar thermal properties (Supporting Information: Figures S5-S7). Poly-S is a semi-crystalline polymeric material because glass transition temperatures (Tg) and melting signals are present in the thermograms of poly-S and their successive generations. It can be stated GPC analysis after forced amorphicity with atactic polystyrene displays a constant length of polymeric material throughout the different generations (Supporting Information: Figures S8-S10).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61975/61975fig01.jpg" /> 
Figure 1: Proposed mechanism of the step-growth polycondensation of 4-acetoxy-dihydrosinapinic acid. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61975/61975fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61975/61975fig02.jpg" /> 
Figure 2: Overlay of 1H NMR spectra (25 &#176;C, CF3COOD/CDCl3, with residual solvent peaks at 11.49 and 7.27 ppm for CF3COOH and CHCl3, respectively) of the isolated acetylation product of sinapinic acid (bottom); the prepolymer of poly-S (middle); poly-S after solid-state post condensation (240 &#176;C, 30 min, vacuum) (top). <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61975/61975fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61975/61975fig03.jpg" /> 
Figure 3: Alkaline hydrolysis (1 M NaOH solution, 80 &#176;C) of poly-S over time, determined by dihydrosinapinic acid (DHSA) yield based on HPLC peak areas. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61975/61975fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/61975/61975fig04.jpg" /> 
Figure 4: DSC thermogram of three generations poly-S. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61975/61975fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Generation</td>
			<td>Poly-S (mg)</td>
			<td>PS (mg)</td>
			<td>Mn</td>
			<td>Mw</td>
			<td>PDI</td>
			<td>DP</td>
		</tr>
		<tr>
			<td>1.0</td>
			<td>5.0</td>
			<td>4.8</td>
			<td>120030</td>
			<td>193580</td>
			<td>1.6</td>
			<td>594</td>
		</tr>
		<tr>
			<td>2.0</td>
			<td>5.0</td>
			<td>5.0</td>
			<td>134740</td>
			<td>194410</td>
			<td>1.4</td>
			<td>667</td>
		</tr>
		<tr>
			<td>3.0</td>
			<td>4.7</td>
			<td>4.9</td>
			<td>153620</td>
			<td>237210</td>
			<td>1.5</td>
			<td>760</td>
		</tr>
	</tbody>
</table>
Table 1: GPC measurements of poly-S generations.

Watch this Scientific Journal Video about Designed for Molecular Recycling: A Lignin-Derived Semi-aromatic Biobased Polymer at JoVE.com

Designed for Molecular Recycling: A Lignin-Derived Semi-aromatic Biobased Polymer

An example of a closed-loop approach towards a circular materials economy is described here. A whole sustainable cycle is presented where biobased semi-aromatic polyesters are designed by polymerization, depolymerization, and then re-polymerized with only slight changes in their yields or final properties.

The development of chemically recyclable biopolymers offers opportunities within the pursuit of a circular economy. Chemically recyclable biopolymers make ...

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Unit 1

&alpha;-Carbon Chemistry: Enols, Enolates, and Enamines

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3.4K Views.  Avans University of Applied Science. Een voorbeeld van een closed-loop benadering van een circulaire materialeneconomie wordt hier beschreven. Een hele duurzame cyclus wordt gepresenteerd waarbij biobased semi-aromatische polyesters worden ontworpen door polymerisatie, depolymerisatie en vervolgens opnieuw worden gepolymeriseerd met slechts kleine veranderingen in hun opbrengst of uiteindelijke eigenschappen.

Video: Designed for Molecular Recycling: A Lignin-Derived Semi-aromatic Biobased Polymer

Methods for Facilitating Microbial Growth on Pulp Mill Waste Streams and Characterization of the Biodegradation Potential of Cultured Microbes

The kraft process is applied to wood chips for separation of lignin from the polysaccharides within lignocellulose for pulp that will produce a high quality paper. Black liquor is a pulping waste generated by the kraft process that has potential for downstream bioconversion. However, the recalcitrant nature of the lignocellulose resources, its chemical derivatives that constitute the majority of available organic carbon within black liquor, and its basic pH present challenges to microbial biodegradation of this waste material. Methods for the collection and modification of black liquor for microbial growth are aimed at utilization of this pulp waste to convert the lignin, organic acids, and polysaccharide degradation byproducts into valuable chemicals. The lignocellulose extraction techniques presented provide a reproducible method for preparation of lignocellulose growth substrates for understanding metabolic capacities of cultured microorganisms. Use of gas chromatography-mass spectrometry enables the identification and quantification of the fermentation products resulting from the growth of microorganisms on pulping waste. These methods when used together can facilitate the determination of the metabolic activity of microorganisms with potential to produce fermentation products that would provide greater value to the pulping system and reduce effluent waste, thereby increasing potential paper milling profits and offering additional uses for black liquor.

Industrial wastes can be collected and modified to analyze microbial growth. Lignocellulose extraction techniques provide components to analyze specific biodegradation ability. Gas chromatography-mass spectrometry identifies fermentation products of microorganisms grown on pulping waste. These methods determine the metabolic capacity of microorganisms to degrade pulping waste.

The kraft process is applied to wood chips for separation of lignin from the polysaccharides within lignocellulose for pulp that will produce a high ...

Environment

Towards Biomimicking Wood: Fabricated Free-standing Films of Nanocellulose, Lignin, and a Synthetic Polycation

Woody materials are comprised of plant cell walls that contain a layered secondary cell wall composed of structural polymers of polysaccharides and lignin. Layer-by-layer (LbL) assembly process which relies on the assembly of oppositely charged molecules from aqueous solutions was used to build a freestanding composite film of isolated wood polymers of lignin and oxidized nanofibril cellulose (NFC). To facilitate the assembly of these negatively charged polymers, a positively charged polyelectrolyte, poly(diallyldimethylammomium chloride) (PDDA), was used as a linking layer to create this simplified model cell wall. The layered adsorption process was studied quantitatively using quartz crystal microbalance with dissipation monitoring (QCM-D) and ellipsometry. The results showed that layer mass/thickness per adsorbed layer increased as a function of total number of layers. The surface coverage of the adsorbed layers was studied with atomic force microscopy (AFM). Complete coverage of the surface with lignin in all the deposition cycles was found for the system, however, surface coverage by NFC increased with the number of layers. The adsorption process was carried out for 250 cycles (500 bilayers) on a cellulose acetate (CA) substrate. Transparent free-standing LBL assembled nanocomposite films were obtained when the CA substrate was later dissolved in acetone. Scanning electron microscopy (SEM) of the fractured cross-sections showed a lamellar structure, and the thickness per adsorption cycle (PDDA-Lignin-PDDA-NC) was estimated to be 17 nm for two different lignin types used in the study. The data indicates a film with highly controlled architecture where nanocellulose and lignin are spatially deposited on the nanoscale (a polymer-polymer nanocomposites), similar to what is observed in the native cell wall.

The objective of this research was to form synthetic plant cell wall tissue using layer-by-layer assembly of nanocellulose fibrils and isolated lignin assembled from dilute aqueous suspensions.&#160; Surface measurement techniques of quartz crystal microbalance and atomic force microscopy were used to monitor the formation of the polymer-polymer nanocomposite material.

Woody materials are comprised of plant cell walls that contain a layered secondary cell wall composed of structural polymers of polysaccharides and ...

High-throughput Screening of Recalcitrance Variations in Lignocellulosic Biomass: Total Lignin, Lignin Monomers, and Enzymatic Sugar Release

The conversion of lignocellulosic biomass to fuels, chemicals, and other commodities has been explored as one possible pathway toward reductions in the use of non-renewable energy sources. In order to identify which plants, out of a diverse pool, have the desired chemical traits for downstream applications, attributes, such as cellulose and lignin content, or monomeric sugar release following an enzymatic saccharification, must be compared. The experimental and data analysis protocols of the standard methods of analysis can be time-consuming, thereby limiting the number of samples that can be measured. High-throughput (HTP) methods alleviate the shortcomings of the standard methods, and permit the rapid screening of available samples to isolate those possessing the desired traits. This study illustrates the HTP sugar release and pyrolysis-molecular beam mass spectrometry pipelines employed at the National Renewable Energy Lab. These pipelines have enabled the efficient assessment of thousands of plants while decreasing experimental time and costs through reductions in labor and consumables.

Plant cell wall structure and chemistry traits are evaluated to identify ideal feedstocks for biofuels and bio-materials. Standard methods have limitations when applied to large data sets. These high-throughput pretreatment, enzyme saccharification, and pyrolysis-molecular beam mass spectrometry methods compare large numbers of biomass samples with decreased experimental time and cost.

The conversion of lignocellulosic biomass to fuels, chemicals, and other commodities has been explored as one possible pathway toward reductions in the ...

Extraction of Lignin with High &#946;-O-4 Content by Mild Ethanol Extraction and Its Effect on the Depolymerization Yield

Lignin valorization strategies are a key factor for achieving more economically competitive biorefineries based on lignocellulosic biomass. Most of the emerging elegant procedures to obtain specific aromatic products rely on the lignin substrate having a high content of the readily cleavable &#946;-O-4 linkage as present in the native lignin structure. This provides a miss-match with typical technical lignins that are highly degraded and therefore are low in &#946;-O-4 linkages. Therefore, the extraction yields, and the quality of the obtained lignin are of utmost importance to access new lignin valorization pathways. In this manuscript, a simple protocol is presented to obtain lignins with high &#946;-O-4 content by relatively mild ethanol extraction that can be applied to different lignocellulose sources. Furthermore, analysis procedures to determine the quality of the lignins are presented together with a depolymerization protocol that yields specific phenolic 2-arylmethyl-1,3-dioxolanes, which can be used to evaluate the obtained lignins. The presented results demonstrate the link between lignin quality and potential for the lignins to be depolymerized into specific monomeric aromatic chemicals. Overall, the extraction and depolymerization demonstrates a trade-off between the lignin extraction yield and the retention of the native aryl-ether structure and thus the potential of the lignin to be used as the substrate for the production of chemicals for higher-value applications.

Here, we present a protocol to perform ethanol extraction of lignin from several biomass sources. The effect of the extraction conditions on the lignin yield and &#946;-O-4 content are presented. Selective depolymerization is performed on the obtained lignins to obtain high aromatic monomer products.

Lignin valorization strategies are a key factor for achieving more economically competitive biorefineries based on lignocellulosic biomass. Most of the ...

Comprehensive Compositional Analysis of Plant Cell Walls (Lignocellulosic biomass) Part I: Lignin

The need for renewable, carbon neutral, and sustainable raw materials for industry and society has become one of the most pressing issues for the 21st century. This has rekindled interest in the use of plant products as industrial raw materials for the production of liquid fuels for transportation1 and other products such as biocomposite materials7. Plant biomass remains one of the greatest untapped reserves on the planet4. It is mostly comprised of cell walls that are composed of energy rich polymers including cellulose, various hemicelluloses (matrix polysaccharides, and the polyphenol lignin6 and thus sometimes termed lignocellulosics. However, plant cell walls have evolved to be recalcitrant to degradation as walls provide tensile strength to cells and the entire plants, ward off pathogens, and allow water to be transported throughout the plant; in the case of trees up to more the 100 m above ground level. Due to the various functions of walls, there is an immense structural diversity within the walls of different plant species and cell types within a single plant4. Hence, depending of what crop species, crop variety, or plant tissue is used for a biorefinery, the processing steps for depolymerization by chemical/enzymatic processes and subsequent fermentation of the various sugars to liquid biofuels need to be adjusted and optimized. This fact underpins the need for a thorough characterization of plant biomass feedstocks. Here we describe a comprehensive analytical methodology that enables the determination of the composition of lignocellulosics and is amenable to a medium to high-throughput analysis. In this first part we focus on the analysis of the polyphenol lignin (Figure 1). The method starts of with preparing destarched cell wall material. The resulting lignocellulosics are then split up to determine its lignin content by acetylbromide solubilization3, and its lignin composition in terms of its syringyl, guaiacyl- and p-hydroxyphenyl units5. The protocol for analyzing the carbohydrates in lignocellulosic biomass including cellulose content and matrix polysaccharide composition is discussed in Part II2.

Comprehensive Compositional Analysis of Plant Cell Walls Lignocellulosic biomass Part I: Lignin

Plant biomass is a major carbon-neutral renewable resource that could be used for the production of biofuels. Plant biomass consists mainly of cell walls, a structurally complex composite material termed lignocellulosics. Here we describe a protocol for a comprehensive analysis of the content and composition of the polyphenolic lignin.

The need for renewable, carbon neutral, and sustainable raw materials for industry and society has become one of the most pressing issues for the 21st ...

Biology

Comprehensive Compositional Analysis of Plant Cell Walls (Lignocellulosic biomass) Part II: Carbohydrates

The need for renewable, carbon neutral, and sustainable raw materials for industry and society has become one of the most pressing issues for the 21st century. This has rekindled interest in the use of plant products as industrial raw materials for the production of liquid fuels for transportation2 and other products such as biocomposite materials6. Plant biomass remains one of the greatest untapped reserves on the planet4. It is mostly comprised of cell walls that are composed of energy rich polymers including cellulose, various hemicelluloses, and the polyphenol lignin5 and thus sometimes termed lignocellulosics. However, plant cell walls have evolved to be recalcitrant to degradation as walls contribute extensively to the strength and structural integrity of the entire plant. Despite its necessary rigidity, the cell wall is a highly dynamic entity that is metabolically active and plays crucial roles in numerous cell activities such as plant growth and differentiation5. Due to the various functions of walls, there is an immense structural diversity within the walls of different plant species and cell types within a single plant4. Hence, depending of what crop species, crop variety, or plant tissue is used for a biorefinery, the processing steps for depolymerisation by chemical/enzymatic processes and subsequent fermentation of the various sugars to liquid biofuels need to be adjusted and optimized. This fact underpins the need for a thorough characterization of plant biomass feedstocks. Here we describe a comprehensive analytical methodology that enables the determination of the composition of lignocellulosics and is amenable to a medium to high-throughput analysis (Figure 1). The method starts of with preparing destarched cell wall material. The resulting lignocellulosics are then split up to determine its monosaccharide composition of the hemicelluloses and other matrix polysaccharides1, and its content of crystalline cellulose7. The protocol for analyzing the lignin components in lignocellulosic biomass is discussed in Part I3.

Comprehensive Compositional Analysis of Plant Cell Walls Lignocellulosic biomass Part II: Carbohydrates

Plant biomass is a major carbon-neutral renewable resource that could be used for the production of biofuels. Plant biomass consists mainly of cell walls, a structurally complex composite material termed lignocellulosics. Here we describe a protocol for a comprehensive analysis of the content and composition of wall derived carbohydrates.

Twin-Screw Extrusion Process to Produce Renewable Fiberboards

A versatile twin-screw extrusion process to provide an efficient thermo-mechano-chemical pre-treatment on lignocellulosic biomass before using it as source of mechanical reinforcement in fully bio-based fiberboards was developed. Various lignocellulosic crop by-products have already been successfully pre-treated through this process, e.g., cereal straws (especially rice), coriander straw, shives from oleaginous flax straw, and bark of both amaranth and sunflower stems.
The extrusion process results in a marked increase in the average fiber aspect ratio, leading to improved mechanical properties of fiberboards. The twin-screw extruder can also be fitted with a filtration module at the end of the barrel. The continuous extraction of various chemicals (e.g., free sugars, hemicelluloses, volatiles from essential oil fractions, etc.) from the lignocellulosic substrate, and the fiber refining can, therefore, be performed simultaneously.
The extruder can also be used for its mixing ability: a natural binder (e.g., Organosolv lignins, protein-based oilcakes, starch, etc.) can be added to the refined fibers at the end of the screw profile. The obtained premix is ready to be molded through hot pressing, with the natural binder contributing to fiberboard cohesion. Such a combined process in a single extruder pass improves the production time, production cost, and may lead to reduction in plant production size. Because all the operations are performed in a single step, fiber morphology is better preserved, thanks to a reduced residence time of the material inside the extruder, resulting in enhanced material performances. Such one-step extrusion operation may be at the origin of a valuable industrial process intensification.
Compared to commercial wood-based materials, these fully bio-based fiberboards do not emit any formaldehyde, and they could find various applications, e.g., intermediate containers, furniture, domestic flooring, shelving, general construction, etc.

A versatile twin-screw extrusion process to provide an efficient thermo-mechano-chemical pretreatment on lignocellulosic biomass was developed, which leads to an increased average fiber aspect ratio. A natural binder can also be added continuously after fiber refining, leading to bio-based fiberboards with improved mechanical properties after hot pressing of the obtained extruded material.

A versatile twin-screw extrusion process to provide an efficient thermo-mechano-chemical pre-treatment on lignocellulosic biomass before using it as ...

Engineering

Fractionation of Lignocellulosic Biomass using the OrganoCat Process

The shift from a petroleum-based to a more sustainable and bio-based economy requires the development of new refinery concepts to maintain the supply of raw materials and energy. For these novel and sustainable biorefinery concepts, it is important to use catalysts and solvents that are aligned with the principles of Green Chemistry. Therefore, the implementation of biogenic alternatives can be a promising solution. The lignocellulose pretreatment and fractionation process presented herein-OrganoCat-is an integrated fractionation of lignocellulose into its main components using biogenic acids such as 2,5-furandicarboxylic acid as catalyst. Hemicelluloses and other non-cellulosic polysaccharides are selectively depolymerized by the diluted acid and dissolved, while the crystalline cellulose remains in the solid pulp. In the presence of a second organic phase consisting of biogenic 2-methyltetrahydrofuran, disentangled lignin is extracted in situ. The process allows for the efficient fractionation of the three main components-lignin, cellulose, and non-cellulosic sugars. This helps to focus on the quality of the lignin, the improvement of enzymatic hydrolysis of the cellulose-enriched pulp, and the mild non-cellulosic sugar extraction with low degradation.

OrganoCat is a method for the pretreatment and fractionation of lignocellulose under mild conditions into lignin, fermentable sugars, and cellulose pulp. In a biogenic, biphasic solvent system of water and 2-methyltetrahydrofuran with 2,5-furancarboxylic acid as catalyst, the OrganoCat products are separated in situ for straightforward product recovery.

The shift from a petroleum-based to a more sustainable and bio-based economy requires the development of new refinery concepts to maintain the supply of ...

Ultrafast Lignin Extraction from Unusual Mediterranean Lignocellulosic Residues

Pretreatment is still the most expensive step in lignocellulosic biorefinery processes. It must be made cost-effective by minimizing chemical requirements as well as power and heat consumption and by using environment-friendly solvents. Deep eutectic solvents (DESs) are key, green, and low-cost solvents in sustainable biorefineries. They are transparent mixtures characterized by low freezing points resulting from at least one hydrogen bond donor and one hydrogen bond acceptor. Although DESs are promising solvents, it is necessary to combine them with an economic heating technology, such as microwave irradiation, for competitive profitability. Microwave irradiation is a promising strategy to shorten the heating time and boost fractionation because it can rapidly attain the appropriate temperature. The aim of this study was to develop a one-step, rapid method for biomass fractionation and lignin extraction using a low-cost and biodegradable solvent. 
In this study, a microwave-assisted DES pretreatment was conducted for 60 s at 800 W, using three kinds of DESs. The DES mixtures were facilely prepared from choline chloride (ChCl) and three hydrogen-bond donors (HBDs): a monocarboxylic acid (lactic acid), a dicarboxylic acid (oxalic acid), and urea. This pretreatment was used for biomass fractionation and lignin recovery from marine residues (Posidonia leaves and aegagropile), agri-food byproducts (almond shells and olive pomace), forest residues (pinecones), and perennial lignocellulosic grasses (Stipa tenacissima). Further analyses were conducted to determine the yield, purity, and molecular weight distribution of the recovered lignin. In addition, the effect of DESs on the chemical functional groups in the extracted lignin was determined by Fourier-transform infrared (FTIR) spectroscopy. The results indicate that the ChCl-oxalic acid mixture affords the highest lignin purity and the lowest yield. The present study demonstrates that the DES-microwave process is an ultrafast, efficient, and cost-competitive technology for lignocellulosic biomass fractionation.

Deep eutectic solvent-based, microwave-assisted pretreatment is a green, fast, and efficient process for lignocellulosic fractionation and high-purity lignin recovery.

Pretreatment is still the most expensive step in lignocellulosic biorefinery processes. It must be made cost-effective by minimizing chemical requirements ...

Quantitative 31P NMR Analysis of Lignins and Tannins

The development of sustainable biorefinery products is confronted, among others, with the challenge of lignin and tannin valorization. These abundant, renewable aromatic biopolymers have not been widely exploited due to their inherent structural complexity and high degrees of variability and species diversity. The lack of a defined primary structure for these polyphenols is further compounded with complex chemical alterations induced during processing, eventually imparting a large variety of structural features of extreme significance for any further utilization efforts.
Consequently, a protocol for the rapid, simple, and unequivocal identification and quantification of the various functional groups present in natural polyphenols, is a fundamental prerequisite for understanding and accordingly tailor their reactivity and eventual utility.
Quantitative 31P NMR offers the opportunity to rapidly and reliably identify unsubstituted, o-mono substituted, and o-disubstituted phenols, aliphatic OHs, and carboxylic acid moieties in lignins and tannins with broad application potential.
The methodology consists of an in situ quantitative lignin or tannin labeling procedure using a suitable 31P containing probe, followed by the acquisition of a quantitative 31P NMR spectrum in the presence of an internal standard. The high natural abundance of the 31P nucleus allows for small amounts of the sample (~30 mg) and short NMR acquisition times (~30-120 min) with well-resolved 31P signals that are highly dependent on the surrounding chemical environment of the labeled OH groups.

Quantitative 31P NMR Analysis of Lignins and Tannins

31P NMR is a powerful tool for the structural elucidation of polyphenols. This fast, easy, precise, quantitative, and highly reproducible analytical procedure, that allows for the quantification and differentiation of the different types of hydroxy, phenolic, and carboxylic groups in lignins and tannins has now become a routine analytical tool.

The development of sustainable biorefinery products is confronted, among others, with the challenge of lignin and tannin valorization. These abundant, ...

Designed for Molecular Recycling: A Lignin-Derived Semi-aromatic Biobased Polymer

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