Name: designed for molecular recycling: a lignin-derived semi-aromatic biobased polymer
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De auteurs zijn dankbaar voor de financiële steun van de Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) (subsidie 023.007.020 toegekend aan Jack van Schijndel).

1. Groene Knoevenagel condensatie van syringaldehyde tot sinapinic zuur met 5 mol% ammoniumbicarbonaat
<ol><li>Voeg malonzuur (20,81 g, 200,0 mmol) samen met syringaldehyde (36,4 g, 200,0 mmol) toe aan een kolf met ronde bodem van 250 ml. Los beide bestanddelen op in 20,0 ml ethylacetaat en voeg ammoniumbicarbonaat (790 mg, 10,0 mmol) toe aan de kolf. OPMERKING: Om de volledige voltooiing van de condensatiereactie te garanderen, kan de roterende verdamper worden gebruikt om het ethylacetaat te destilleren en het rea...

<ol>
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Wanneer dihydrosinapininezuur in een reactievat werd verwarmd, trad sublimatie van het uitgangsmateriaal op en dit effect werd versterkt wanneer een vacuüm werd toegepast. Acetylering is uitgevoerd op dihydrosinapininezuur om sublimatie te voorkomen. Kricheldorf et al.12,27 erkenden dat niet alleen acetylering, maar ook di- en oligomerisatie optrad. Deze veresterde monomeren en oligomeren echter niet meer sublimeren en zijn geschikt als monomeren voor de smeltpo...

In tegenstelling tot de verbranding van polymeerafval biedt chemische recycling de mogelijkheid om de monomeren terug te winnen. Chemische recycling is een logische keuze aan het einde van de technische levensduur van polymere materialen, omdat deze polymere materialen chemisch worden geproduceerd1. Er zijn twee manieren om het polymere materiaal chemisch te recyclen, pyrolyse en moleculaire recycling2. Met pyrolyse wordt het polymere materiaal omgezet in producten van hogere waarde door gebruik te maken van extreme omstandigheden3,4. Moleculaire recycling is een efficiënte methode voor het terugwinnen van de grondstoffen met behulp van depolymerisatie. Na depolymerisatie kunnen de monomere eenheden worden gerepolymeriseerd tot nieuwe polymere materialen5. De beschikbaarheid van geschikte monomeren om moleculaire recycling op grotere schaal toe te passen, is te wensen over. Het huidige plastic probleem dicteert dat de samenleving stevige en robuuste polymere materialen eist. Tegelijkertijd heeft het ook de voorkeur dat dezelfde polymere materialen gemakkelijk recyclebaar zijn en niet in het milieu blijven. Huidige polymere materialen met goede thermische en mechanische eigenschappen depolymeriseren niet gemakkelijk6.
Lignine, vaak gevonden in vaatplanten, is verantwoordelijk voor 30% van 's werelds natuurlijke koolstofgehalte en is het op één na meest voorkomende biopolymeer na cellulose. Lignine heeft een complexe amorfe structuur en lijkt een geschikt alternatief om aromaten uit fossiele materialen te vervangen. De driedimensionale structuur van lignine biedt sterkte en stijfheid aan hout, evenals weerstand tegen degradatie. Chemisch gezien is lignine een zeer complexe polyfenolische thermohardende. Het bestaat uit verschillende samenstelling van drie verschillende methoxylated fenylpropaan structuren. Syringyl, guaiacyl en p-hydroxyfenyl (vaak afgekort als respectievelijk S, G en H) zijn afgeleid van de monolignols sinapylalcohol, coniferylalcohol en p-coumarylalcohol7. De verdeling van deze eenheden verschilt per biomassatype, waarbij bijvoorbeeld naaldhout voornamelijk uit guaiacyleenheden bestaat en hardhout van guaiacyl en syringyleenheden8,9. Hernieuwbare natuurlijke bronnen, zoals bomen en planten, zijn wenselijk voor de productie van opnieuw ontworpen monomeren voor innovatieve polymere materialen10. Deze monomeren, geïsoleerd en gesynthetiseerd uit natuurlijke bronnen, worden gepolymeriseerd tot zogenaamde biobased polymeren11.
Aromatische carbonzuren zijn om elektronische redenen enkele ordes van grootte minder elektrofiel dan de equivalente alifatische carbonzuren12. Verschillende commerciële polyesters gebruiken aromatische carbonzuren in plaats van alifatische carbonzuren. Hierdoor zijn de vezels in polyester textiel gemaakt van poly(ethyleentereftalaat) (PET) vezels bijna ongevoelig voor hydrolyse tijdens het wassen of bijvoorbeeld regen13. Wanneer de moleculaire recycling van polyesters gewenst is, is het raadzaam om alifatische esters te gebruiken bij de opbouw van het polymeer.
Om de genoemde redenen hebben we de mogelijkheden onderzocht om polyesters te maken van 4-hydroxy-3,5-dimethoxy-dihydrocinnamic acids14. Eerdere studies van Kricheldorf15, Meier16en Miller17,18 tonen aan dat het een uitdaging is om polymeren te bouwen met behulp van 4-hydroxy-3,5-dimethoxy-dihydrocinnamic acid. Decarboxylatie en crosslinking belemmerden de polymerisaties en beperkten zo het succes van deze syntheses. Ook het mechanisme van de polycondensatie bleef onduidelijk. Het gepresenteerde artikel beschrijft de omstandigheden waarin het polyester poly (dihydrosinapininezuur) regelmatig en in hoge opbrengst kan worden gesynthetiseerd, waardoor de weg wordt vrijgemaakt voor het gebruik van semi-aromatische polyesters die moleculair recyclebaar zijn.
We hebben een groene en efficiënte manier ontwikkeld om sinapinic acid te synthetiseren met behulp van een condensatiereactie tussen syringaldehyde en malonzuur19,20. Na deze Groene Knoevenagel produceert hydrogenering dihydrosinapininezuur, dat geschikt is voor omkeerbare polycondensatie. Deze publicatie visualiseert de synthetische stappen naar het moleculair recyclebare polymeer poly (dihydrosinapinic acid), verwijzend naar de basiseenheden van lignine, poly-S genaamd. Na analyse van het polymere materiaal wordt poly-S onder relatief gunstige omstandigheden gedepolymeriseerd tot het monomeer dihydrosinapininezuur en steeds opnieuw gerepolymeriseerd.

<table>
	<tbody>
		<tr>
			<td>Reaction 1: Green Knoevenagel condensation</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Ammonium bicarbonate</td>
			<td>Sigma Aldrich</td>
			<td>&#62;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>&#62;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>Reaction 2: Hydrogenation</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&#8482; nickel</td>
			<td>Sigma Aldrich</td>
			<td>&#62;89%</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium hydroxide</td>
			<td>Boom</td>
			<td>Technical grade</td>
			<td>dissolved</td>
		</tr>
		<tr>
			<td>Reaction 3: Acetylation</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Acetic anhydride</td>
			<td>Macron</td>
			<td>&#62;98%</td>
			<td></td>
		</tr>
		<tr>
			<td>Acetone</td>
			<td>Macron</td>
			<td>&#62;99.5%</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium acetate</td>
			<td>Sigma Aldrich</td>
			<td>&#62;99%</td>
			<td></td>
		</tr>
		<tr>
			<td>Reaction 4A: Polymerisation</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>1,2-xylene</td>
			<td>Macron</td>
			<td>&#62;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>Reaction 4B: Depolymerisation</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>Analysis</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>CDCl3</td>
			<td>Cambride Isotope Laboratories, Inc.</td>
			<td>99.5%</td>
			<td></td>
		</tr>
		<tr>
			<td>CF3COOD</td>
			<td>Cambride Isotope Laboratories, Inc.</td>
			<td>98%</td>
			<td></td>
		</tr>
		<tr>
			<td>Dimethylformamide</td>
			<td>Macron</td>
			<td>&#62;99.9%</td>
			<td></td>
		</tr>
		<tr>
			<td>Hexafluoro-2-propanol</td>
			<td>TCI Chemicals</td>
			<td>&#62;99%</td>
			<td></td>
		</tr>
		<tr>
			<td>Methanol</td>
			<td>Macron</td>
			<td>&#62;99.8%</td>
			<td></td>
		</tr>
		<tr>
			<td>Tetrahydrofuran</td>
			<td>Macron</td>
			<td>&#62;99.9%</td>
			<td></td>
		</tr>
	</tbody>
</table>

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

De ontwikkeling van chemisch recyclebare biopolymeren biedt kansen binnen het streven naar een circulaire economie. Chemisch recyclebare biopolymeren doen een positieve inspanning om het probleem van polymeermaterialen in de verwijderingsfase na de gebruiksfase op te lossen. In dit artikel wordt de productie van biobased semi-aromatische polyesters, die volledig uit biomassa zoals lignine kunnen worden gewonnen, beschreven en gevisualiseerd. Het polymeer poly-S dat in dit artikel wordt beschreven, heeft thermische eigenschappen die vergelijkbaar zijn met bepaalde veelgebruikte kunststoffen, zoals PET. We ontwikkelden een Groene Knoevenagel-reactie, die efficiënt monomeren kan produceren uit aromatische aldehyden en malonzuur. Deze reactie is bewezen schaalbaar en heeft een opmerkelijk lage berekende E-factor. Deze polyesters met ligno-fytochemicaliën als uitgangspunt laten een efficiënte moleculaire recycling zien met minimale verliezen. Het polyester poly (dihydrosinapinezuur) (poly-S) wordt gepresenteerd als een voorbeeld van deze semi-aromatische polyesters en de polymerisatie, depolymerisatie en re-polymerisatie worden beschreven.

Sinapinic acid werd gesynthetiseerd in hoge zuiverheid en hoge opbrengst (> 95%) uit syringaldehyde met behulp van de Groene Knoevenagel condensatie. (Ondersteunende informatie: figuur S1) De E-factor is een indicatie van afvalproductie waarbij een hoger getal duidt op meer afval. De E-factor wordt berekend door de totale materiaalinput te nemen, de hoeveelheid van het gewenste eindproduct af te trekken en het geheel te delen door de hoeveelheid eindproduct. Deze Groene Knoevenagel condensatie heeft een ...

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

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.

Ontworpen voor moleculaire recycling: een lignine-afgeleid semi-aromatisch biobased polymeer

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

Throughout the synthesis described in this paper provides a way to produce a new polymeric material specifically designed for molecular recycling, which is a way of chemical recycling. The depolarization and repolarization of the foreign material poly-S creates a fully sustainable cycle, which is a proof of concept for the future of polymers. The polymer waste of the world accumulates.For instance in the ocean, as the plastic soup, which could be prevented by introducing molecularly recyclable polymers. The polymer presented is an example of a polymeric material designed for molecular recycling. This in our opinion, should be implemented in other materials to prevent accumulation in nature.Green Knoevenagel reaction and subsequent steps have been designed for and by our undergraduated students. So certain robustness is already implemented in these reaction steps. The COVID-19 pandemic creates a situation where online learning becomes more important than ever.Visualization of these experiments helps us and others to deepen practical chemical education. Begin by adding 20.81 grams of malonic acid and 36.4 grams of syringaldehyde to a 215 milliliter round bottom flask. Dissolve both constituents in 20 milliliters of ethyl acetate and add 719 milligrams of ammonia bicarbonate to the flask.Mix and distill the solvent with a water bath. Keep the reaction mixture at 90 degrees Celsius for two hours in the open flask without stirring for complete conversion to sinapinic acid. In the work-up of the sinapinic acid product, dissolve the residue in 100 milliliters of a saturated aqueous sodium bicarbonate solution, then transfer the solution to a beaker, and acidify it to a pH two.Using six molar hydrogen chloride, separate the resulting residue by vacuum filtration and wash it with demineralized water. Charge a 450 milliliters flask with 33.6 grams sinapinic acid. Dissolve the sinapinic acid in 300 milliliters of two molar sodium hydroxide solution, and add 1.5 grams of nickel slurry before fitting the flask to the operators.Pressurize the reactor with three bar of hydrogen gas and mechanically shake the reaction at 80 degrees Celsius for three hours. Cool the reactor to room temperature and depressurize slowly. Recover most of the nickel catalyst with a magnet, then filter the solution.Acidify the solution with four molar hydrogen chloride solution to a pH of two, then perform an extraction with ethyl acetate. Remove the solvent under reduced pressure after drying over magnesium sulfate and dry the dihydrosinapinic acid at 60 degrees Celsius in a vacuum oven. Add 22.6 grams dihydrosinapinic acid to a 250 milliliter round bottom flask.Followed by 14.2 milliliters of acetic anhydride and 0.82 grams of sodium acetate. Heat the solution to 90 degrees Celsius while stirring for one hour for complete conversion of dihydrosinapinic acid to 4-Acetoxy-dihydrosinapinic acid, and it's acetylated oligomers. Dissolve the solid in 25 milliliters of acetone precipitated into 250 milliliters of 0.1 molar hydrogen chloride, then filtered on the vacuum.Add the monomers 20.8 grams of 4-Acetoxy-dihydrosinapinic acid and prepolymer to a 100 milliliter round bottom flask. Then add 400 milligrams of finely powdered sodium hydroxide, heat the reaction mixture for three hours at a set temperature of 140 degrees Celsius in the open flask while staring at 100 RPM. Set up a solvent assisted polymerization by adding 180 milligrams of zinc two acetate and 25.0 milliliters of 1, 2-xylene to the flask, then raise the set temperature to 160 degrees Celsius.Reflux the mixture at 144 degrees Celsius for three hours with constant water and acetic acid removal using Dean-Stark head. Cool the reaction mixture down and remove the 1, 2-xylene by applying a vacuum. Raise the temperature to 240 degrees Celsius during the final stage of the polymerization and apply a high vacuum for 30 minutes.Cool the polymer poly-S to room temperature and wash it with methanol to eliminate dihydrogen sinapinic acid and prepolymers. The obtained product should be a light brown solid. Finally grind and serve the poly-S into particles smaller than 180 micrometres to measure hydrolytic degradation.Load several test tubes with 20 milligrams of poly-S and add one milliliter of one molar sodium hydroxide solution. Incubate the tubes at three different temperatures with an agitation of 500 RPM. Neutralize the test tubes at regular time intervals with one milliliter of 0.5 molar sulfuric acid, and add two milliliters of methanol after cooling.Filter all samples using 0.45 micro meter PTFE syringe filters and inject 20 microliters into HPLC using an auto sampler. Monitor the absorbance at 254 nanometers and calculate the concentrations from a calibration curve of known dihydrosinapinic acid standard solutions. Sinapinic acid was synthesized in high purity and a greater than 95%yield from syringaldehyde using the Green Knoevenagel Condensation, the proposed mechanism of the step growth polymerization of 4-Acetoxy-dihydrosinapinic acid is shown here.Hydrogen one and MR measurements were taken during the polymerization process. When poly-S was hydrolyzed in sodium hydroxide, the molecularly recyclable polyester yielded the starting material dihydrosinapinic acid in less than 10 minutes. As confirmed by HBLC melting point analysis and hydrogen one and MR.Extended reaction times did not increase the yield.The thermal grams and GPC analysis of poly-S 1.0 and their successive generations poly-S 2.0 and polyester 3.0 after forced amorphicity with a tactic polystyrene are shown here. DSC analysis of poly-S shows a glass transition signal at 113 degrees Celsius and endothermic melting signal at 281 degrees Celsius. The polymers from re-polymerized sinapinic acid three eight poly-S 2.0 up and poly-H 3.0 exhibit similar thermal properties.Poly-S is a semi crystalline polymeric material because glass transition temperatures and melting signals are present in the thermograms of poly-S and their successive generations. GPC analysis after forced amorphicity with a tactic polystyrene displays a constant length of polymeric material throughout the different generations. While attempting the Green Knoevenagel reaction, please keep in mind that a correct temperature is used.A slightly higher temperature can lead to different site reactions. We have explored an example of a molecularly recyclable polymer. Closely related building blocks can follow the same procedure, or while maintaining thermal and mechanical properties.This method can be used in organic catalysis by demonstrating of the catalytic intermediates, as well in the still unexplored area of molecular recycling.

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