Lignin derivative (the commercial  product -Protobind  2000)  offered by the Granit Recherche Developement S.A. company, Lausanne-Schwitzerlandwas  synthesized  from  annual  plants. The  present study’s aim was tomodify commercial lignins by the reaction of hydroxymethylation (produced in alkaline medium)  and epoxydation  (reaction  with  epichlorohydrin  was  performed  in basic  catalysis,  aiming  at  increase  the  functionality) and  to  characterize  the lignin derivatives chemical, spectral (1H NMR) and thermogravimetric analysis (TG). Studies have revealed some functional changes related to the difference in reactivity and reaction conditions

Jităreanu, Doina

Popa, V. I.

Trofin, Alina

Ungureanu, Elena

Ungureanu, O. C.

Jităreanu, Carmenica-Doina

Trofin, Alina-Elena

Ungureanu, O.C.

Popa, V.I.

ALSE Repository

LUCRĂRI ŞTIINŢIFICE SERIA HORTICULTURĂ, 60 (1) / 2017, USAMV IAŞI 17 LIGNIN DERIVATIVES MODIFIED BY HYDROXYMETHYLATION AND EPOXYDATION REACTIONS  DERIVAŢI LIGNINICI MODIFICAŢI PRIN REACŢIILE DE HIFROXIMETILARE ŞI EPOXIDARE   UNGUREANU Elena1, JITĂREANU Doina 1, TROFIN Alina1, UNGUREANU O.C. 2, POPA V.I. 3 e-mail: eungureanu@uaiasi.ro  Abstract. Lignin derivative (the commercial product - Protobind 2000) offered by the Granit Recherche Developement S.A. company, Lausanne-Schwitzerland was synthesized from annual plants. The present study’s aim was to modify commercial lignins by the reaction of hydroxymethylation (produced in alkaline medium) and epoxydation (reaction with epichlorohydrin was performed in basic catalysis, aiming at increase the functionality) and to characterize the lignin derivatives chemical, spectral (1H NMR) and thermogravimetric analysis (TG). Studies have revealed some functional changes related to the difference in reactivity and reaction conditions.  Key words: Protobind 2000, lignin, hydroxymethylation, epoxydation, spectral and thermogravimetric analysis.   Rezumat. Lignina derivativă (produsul comercial Protobind 2000) oferită de firma Granit Recherche Developement S.A. Lausanne-Elveţia a fost sintetizată din plante anuale. Scopul prezentului studiu este a de a modifica ligninele comerciale prin reacţia de hidroximetilare (produsă în mediul alcalin) şi epoxidare (reacţie cu epiclorhidrina în cataliza bazică ce creşte funcţionalitatea) şi de a caracteriza derivaţii ligninici prin analize chimice, spectrale (1H RMN) şi termogravimetrice (TG). Studiile au relevat unele modificări funcţionale legate de diferenţa de reactivitate şi condiţiile de reacţie. Cuvinte cheie: Protobind 2000, lignină, hidroximetilare, epoxidare, analize termogravimetrice şi spectrale. INTRODUCTION Lignin is a macromolecular compound, much more active than cellulose or other natural polymers, due to functional groups contained in its macromolecule, constituting the main aromatic component of vegetal tissues, representing 20-40 % of the higher plants’ mass located in the cellular wall and in intercellular spaces (Benar et al, 1999; Ungureanu, 2011).                                                   1University of Agricultural Sciences and Veterinary Medicine Iasi, Romania 2“V.Goldiş” West University of Arad, Faculty of Biology, Romania 3Gh. Asachi”Technical University of Iasi, Faculty of Chemical Engineering and Environmental Protection, Romania LUCRĂRI ŞTIINŢIFICE SERIA HORTICULTURĂ, 60 (1) / 2017, USAMV IAŞI 18 It is known that lignin has a very complex structure, which varies depending on the plant species, separation method and modification reactions that may induce particular characteristics. Regarding functional groups lignin presents at least three base functional groups in its structure: methoxylic, hydroxylic (alcoholic and phenolic) and the lateral propanic chain. Alongside these functional groups, in lesser amounts, there can be found carbonylic groups (approximate 1 group of CO at 5 C9 units), most of the times, fixated at the lateral chain. In some cases, the presence of carboxylic groups into the lignin can be noticed under the form of phenol carboxylic acids or of some small quantities of lactonic groups (Ungureanu et al, 2009, 2016). Lignin modification through hydroxymethylation and epoxydation offers possibilities of developing its functionality and this allows the extension of the application area for the synthesized derivatives. Taking into account all these aspects, the objectives of this study are the modification of some lignin’s from annual plants through a reaction of hydroxymethylation produced in an alkaline medium in the presence of formic aldehyde and of epoxydation effected out in an alkaline medium in the presence of epichlorhydrin and the characterization of lignin derivatives from a chemical, spectral (1H NMR) and thermogravimetric methods. MATERIAL AND METHOD The following materials have been used: - Protobind 2000 (Pb2000), commercial lignin offered by Granit Recherché Dévelopement Switzerland, with the following chemical characteristics presented in table 1. Table1 The characteristics Protobind 2000 Characteristics Protobind 2000 Solide, % 95 Ash, % 1.3 pH (10 % dispersion) 4.80 Densitatea, g/mL ~ 0.6 Aromatic OH, mmole/g 1.6-1.8 COOH, mmole/g 2.1-2.3 T softening, °C ~ 130 Solubility in furfuryl alcohol, % 41  Solubility in aqueous alkali, % 95  - Formic aldehyde (37 %);  - Dimetil sulfoxid (DMSO); - NaOH solution 0.1 N;  - Epichlorhydrin. Work procedure: The hydroxymethylation reaction The method used in the hydroxymethylation of the three lignin products was performed in a basic medium, in the presence of formic aldehyde (37 %), according to the technical literature (Ungureanu, 2011). LUCRĂRI ŞTIINŢIFICE SERIA HORTICULTURĂ, 60 (1) / 2017, USAMV IAŞI 19 Determination of total hydroxyl groups The total OH groups content was determined by chemical method with acetic anhidryde in pyridine medium and from FT-IR spectral analysis.The Ar-OH group’s content was determined by a UV-VIS method.  The epoxidation reaction The epoxydation method achieved in a basic medium in the presence of epichlorhydrin through which the three types of lignin studied have been modified has been effected out according to the technical literature (Ungureanu, 2011). Epoxydation index Determination of the epoxy group was effected out by HCl addition on the epoxy group and titration of the acid excess with NaOH solution 0.1 N.  Proton nuclear magnetic resonance spectroscopy (1 H NMR) Nuclear magnetic resonance (NMR) offers the richest and most complete information on the structure of organic compounds. For this purpose it was used a Bruker Avance DRX 400 MHz spectrometer. Process: For investigation was necessary lignin acetylation and derivatives for a better dissolution in DMSO-d6. To obtain a "good" spectrum it is required to have concentrations of about 0.2 mmol/mL. Spectra processing was performed with a specialized program from SpectraManager series. Thermogravimetry The thermal analysis was performed using the METTLER TOLEDO derivatograph in N2 atmosphere with a flow of 20mL/min and a heating rate of 15ºC/min, in the temperature range 25-800 °C and sample mass of 4 ÷ 6 mg. RESULTS AND DISCUSSIONS During the reaction of hydroxymethylation performed for lignin, the reaction conditions have been varied (50°C temperature, 90°C respectively, reaction duration of three hours and pH 10.5, pH 12 respectively) in order to obtain highly functional products.  The content of functional groups was determined according to the methods presented by different research groups. The other methods applied for chemical characterization were: the determination of carboxylic groups and of the metoxyl groups, the determination aromatic hydroxyl groups, the calculation of the fenolic groups/aliphatic groups’ ratio, as well as, the determination siringyl/guaiacyl unit’s ratio (S/G).  The information obtained has allowed the determination from this point of view of the optimal reaction conditions, namely: 90°C temperature, pH 10.5 and the reaction duration of three hours (tab. 2).  Table 2 The content of functional groups of modified and unmodified lignins Sample T, OC pH OH total groups Ar-OH groups OCH3 groups Ak/Ar ratio C=O groups S/G ratio   Pb 2000 - - 1.11 0.89 1.05 1.17 0.89 0.83 90 12.0 1.23 0.98 1.15 1.27 0.95 0.96 90 10.5 1.15 0.98 1.13 1.20 0.91 0.96 50 10.5 1.14 0.98 1.12 1.22 0.95 0.96 50 12 1.16 0.99 1.14 1.21 0.94 0.96 LUCRĂRI ŞTIINŢIFICE SERIA HORTICULTURĂ, 60 (1) / 2017, USAMV IAŞI 20 The lignin obtained in optimal conditions there was characterized from the point of view spectral and thermogravimetric. As a consequence of the thermal analyses, it can be noticed that the modified product has a higher degradation temperature in the third stage, compared to the unmodified sample (tab. 3).  Table 3 Characteristics of the thermal degradation process of the lignin derivatives Samples Degradation  stage Ti (C) Tmax (C) Tf (C) Mass losses (%) Pb2000 I 205 234 326 22.78 II 326 381 496 39.23 III  56  79 115 5.06 Pb2000H I 216 248 328 12.90 II 329 3374 580 36.37 III 205 234 326 22.78 (Ti - initial temperature at which the degradation starts; Tmax – temperature corresponding to the maximum rate of degradation, Tf –final temperature şi W – mass losses %).  The characterization of the lignin has been achieved by monitoring the influence of temperature (50°C and 70°C respectively), the mass ratio between the lignin (L) and NaOH (L:NaOH = 1:3 and 1:6) and the reaction duration (3, 5 and 7 hours respectively).  It can be noticed from table 4 that the best results can be obtained when the reaction is achieved at 70°C, for a L:NaOH=1:3 ratio and a three-hour reaction duration, appreciated as being optimal reaction conditions. The reaction yield was included in the 50-90 % interval, related to the mass of the reactants and it differs according to the type of sublayer and the purification degree after washing the derivatives. It can also be noticed that along with the temperature increase and the reaction duration, from 3 to 7 hours, appear a decrease of the epoxydation number (tab. 4) (Ungureanu et al, 2015).  Table 4 Characteristics of the modified lignin’s by epoxydation  For characterization by 1H-NMR spectroscopy the lignin was subjected to acetylation to aid dissolution in DMSO-d6. In figures 1 and 2 are shown the 1H-NMR spectra for Pb1000 lignin unmodified (Pb2000N) and hydroxymethylation Sample T, 0C L:NaOH (w/w) t, h CE, % η, % U, % Ash % Const. f.liq, % f.sol. f.liq. Pb2000E 70 1:6 3 1.20 0.21 50 5.5 8.12 16.40 70 1:3 3 1.70 0.64 64 5.1 2.1 18.20 50 1:3 3 1.85 0.36 60 7.2 7.85 16.25 70 1:3 5 1.50 0.32 69 6.78 6.22 12.32 70 1:3 7 1.63 0.40 52 6.27 5.63 15.30 LUCRĂRI ŞTIINŢIFICE SERIA HORTICULTURĂ, 60 (1) / 2017, USAMV IAŞI 21 (Pb2000H), and the results were interpreted using literature data. The spectrum recorded for the two lignins  weak signals in the aromatic domain at 8.64 ppm and the methoxyl groups.  9 8 7 6 5 4 3 2 1Chemical Shift (ppm)6.775.384.974.564.033.793.433.022.732.562.392.262.05 1.971.821.531.291.210.91Pb2000 N Fig. 1 1H-NMR spectra for unmodified lignin Pb2000  9 8 7 6 5 4 3 2 1Chemical Shift (ppm)8.578.147.396.715.324.904.234.143.973.733.372.962.672.512.332.182.021.911.761.541.451.231.150.990.850.65Pb2000 H Fig. 2 1H-NMR spectra for modified lignin Pb2000H  Signals from 9.08-7 ppm confirms the presence of epoxy groups in lignin structure. Also stands out the signals of methoxyl and acetyl groups, more intense in the spectra of epoxidised lignin (fig. 3).  LUCRĂRI ŞTIINŢIFICE SERIA HORTICULTURĂ, 60 (1) / 2017, USAMV IAŞI 22 9 8 7 6 5 4 3 2 1Chemical Shift (ppm)9.099.038.628.46 8.187.516.925.855.445.155.074.774.234.214.103.973.482.962.682.512.342.021.851.691.521.231.151.090.85Pb2000 E Fig. 3 1H-NMR spectra for modified lignin Pb2000E CONCLUSIONS 1. The 1H-NMR spectroscopy shows the change of functionality for lignin as a result of hydroxymethylation and epoxydation reaction. 2. The thermogravimetric analyses have proved that thermal degradation occurs in two and three stages respectively, according to the type and the degree of modification of the products tested but the hydroxymethylated/epoxydated derivatives have a higher thermostability, compared to the unmodified lignin.  REFERENCES  1. Ariton Adina-Mirela, Creangă T., Trincă Lucia Carmen, Borş S.I., Ungureanu Elena, Măluţan Th., Popa V.I., 2015 - Valorization of lignin modified by hydroxymethylation to ensure birch veneer bioprotection, Cell. Chem. and  Technol., 49 (9-10), p. 765-774. 2. Benar P., Gonplves A. R., 1999 - Principal component analysis of the hydroxymetylation of sugarcane lignin: A time-depending study by FTIR, J. Wood  Chem. Technol., 19 (1-2), p.15 1-165. 3. Ungureanu Elena, Jităreanu Carmen Doina, Trofin Alina, Popa V.I., Sandu Tatiana, 2015 - Chemical and spectral characterizations for some lignin products, Lucrări Ştiinţifice, Seria Horticultură, nr.58, vol.1, p.23-28. 4. Ungureanu Elena, 2011 - Lignina, polimer natural aromatic cu ridicat potenţial de valorificare, Ed. PIM, Iaşi, p. 112. 5. Ungureanu Elena, Ungureanu O., Căpraru Adina-Mirela, Popa V.I., 2009 - The chemical modification and the characterization the straw lignin, Cell. Chem. and Technol., 43 (7-8), p. 263-269. 6. Ungureanu Elena, Trofin Alina, Ariton Adina-Mirela, Jităreanu Carmen Doina, Ungureanu Ovidiu, Gîlcă Valerica, Bors S.I., Popa V.I., 2016 - Applications of epoxidated lignins for bioprotection of lignocellulosic materials, Cell. Chem. and Technol., 50 (1), p. 77-85. 

Derivaţi ligninici modificaţi prin reacţiile de hifroximetilare şi epoxidare

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Derivaţi ligninici modificaţi prin reacţiile de hifroximetilare şi epoxidare

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