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Supporting information

Tunable thermosetting epoxies based on fractionated and well-characterized lignins

Claudio Gioia,*‡ Giada Lo Re, Martin Lawoko,*‡ Lars Berglund

Wallenberg Wood Science Center, WWSC, Department of Fiber and Polymer Technology. KTH Royal

Institute of Technology, 100 44 Stockholm, Sweden

E-mail cgioia@kth.se; lawoko@kth.se

Materials

All Chemicals were of analytic grade and used as received unless stated otherwise.

Softwood KL was obtained from the Lignoboost process. Before use, it was washed with acidic water (pH 2) to remove impurities and dried in a vacuum oven (24 h at 40°C), ethyl acetate (EtOAc), ethanol absolute (EtOH), Methanol (MeOH), Acetone, sodium hydroxide (NaOH, ≥98%), epiclorohydrin, HCl, Jeffamine D2000.

Methods

Nuclear magnetic Resonance (NMR). (1H-, 31P-, and 2D hetero nuclear single quantum coherence

(HSQC)) was recorded at room temperature on a Bruker Avance III HD 400 MHz instrument with

a BBFO probe equipped with a Z-gradient coil for structural analysis. Data were processed with

MestreNova (Mestrelab Research) using 90° shifted square sine-bell apodization window; baseline

and phase correction was applied in both directions. 31P-NMR samples were prepared and analysed according the procedure reported by Argyropolous in 1994.

Fourier Transform Infrared Spectroscopy (FT-IR) was performed using a Perkin-Elmer Spectrum 2000 FT-IR equipped with a MKII Golden Gate single reflection ATR system of Specec LTD. All spectra were recorded in the range of 600 to 4000 cm-1 with 32 scans averaged at 4.0 cm-1 resolution at room temperature. All data were analysed using PerkinElmer Spectrum software V10.5.1.

Differential scanning calorimetry (DSC) was conducted using a Mettler-Toledo DSC equipped with a sample robot and a cryo-cooler and evaluated with Mettler Toledo STARe software V15.00a. Unless otherwise stated, the measurements had a heating and cooling rate of 10 K/min and were performed under N2-atmosphere.

Size Exclusion Chromatography (SEC), using a SEC 1260 infinity (Polymer standard service, Germany) equipped with a PSS precolumn, PSS column 100 Å and PSS GRAM 10000 Å analytical columns thermostated at 60°C, was performed to determine the molecular weight and dispersity of the different lignin samples. The detection system included a UV detector in series with a refractive index detector.

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DMSO + 0,5% LiBr was used as eluent with a constant flow rate of 0,5 ml/min. A calibration plot was constructed with pullulan standards.

Tensile tests and Dynamical Mechanical Thermal Analysis (DMTA) were performed on cured samples (35.0×5.0×0.5 mm3) conditioned for 100 h at 23 °C and 50% RH using a Single Column Table Top Instron 5944 tensile micro tester 5944 with a with a load force of 500 N and a Q800 DMA apparatus from TA Instruments in three-point bending mode, respectively. The Tensile tests were performed according to the ASTM D3013-13 and D638-14. The DMTA measurements were carried out according to the Standard Test Method for Plastics: Dynamic Mechanical Properties: In Flexure (Three-Point Bending) ASTM D5023-07 at a constant frequency (1 Hz), amplitude of 20 mm, a temperature ranges from -100 to 150 °C, and with a heating rate of 3 °C/min. Five replicates were performed for each formulation and data scattering was below the 5% for the both the tensile test and the DMTA measurements. The glass transition temperatures (Tg) were determined as the peak of the loss modulus E’’ according to the standard ASTM D4092−07 (reapproved 2013).

High resolution Scanning Electron Microscope analysis (SEM) was carried out by using a Hitachi SEM S-4800 (Japan) with an accelerating voltage of 1 kV. Samples of the different resins for the SEM observation were recovered from the tensile tests. In particular, their fracture surfaces were sputtered for 40 s at a current of 80 µA with Pt/Pd (60/40) using a Cressington 208HR sputter coater prior to imaging.

Fractionation of Kraft Lignin

General procedure

Lignoboost Kraft lignin (20g) and the first solvent of the sequence (200 ml) were introduced into a round bottom flask equipped with magnetic stirring. The resulting suspension was stirred at room temperature for 2 hours. Afterward the insoluble lignin was removed from the mixture by filtration on paper filter while the solution was dried under reduced pressure. The filtrated insoluble fraction was therefore extracted, according to the same procedure, with the subsequent solvent. The solvents chosen for the fractionation were respectively: ethyl acetate, ethanol, methanol and acetone. Finally, the residue insoluble in any of the mentioned solvents was separated by filtration. All the obtained extracted fractions were furthermore solubilized in acetone (20 ml) and precipitated with deionized water to obtain homogeneous dispersions. The resulting mixtures were freeze dried to obtain a thin brown powders.

SEC Analysis

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Figure S1: SEC analysis of the starting lignin compared with the obtained fractions

300 3000 30000

LFEtOAc

LFEtOH

LFMeOH

LFAcetone

KL

M

WLo

gM

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31P-NMR (CDCl3)

Figure S2: 31P-NMR of the starting Kraft lignin (KL)

Figure S3: 31P-NMR of the EtOac fraction (LFEtOAc)

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Figure S4: 31P-NMR of the ethanol fraction (LFEtOH)

Figure S5: 31P-NMR of the methanol fraction (LFMeOH)

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Figure S6: 31P-NMR of the acetone fraction (LFAcetone)

Figure S7: 31P-NMR of the residual lignin

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HSQC analysis of the fractions (DMSO-d6)

O

OMe

ROO

HO

OMe

O

OMe

O

HO

OMe

O

OMe

O

O

OMe

O

A2: ββββΟΟΟΟ44442222

R = CarbohydrateB: ββββ55551111

O

OMe

OMe

O

E: Stilbene

C: ββββββββ1111 D: ββββββββ2222

OH

OMe

O

OH

OMe

O

R

OMe

O

O

R = H; OH

F: Cinnamyl alcoholG: Dehydro

coniferyl alcohol

O

OMe

O

OMe

H: Conjugatedcarbonyls/acids

O

OMe

HOO

HO

OMe

A1: ββββΟΟΟΟ44441111

Figure S8: Inter-unit linkages observed in the fractions

Table S1: Assignment of the main 13C-1H correlation signals of lignin substructures detected in 2D HSQC spectra in DMSO-d6.

δC (ppm) δH (ppm) Description

A1 59.4 3.42/3.71 Cγ/Hγ in βO4 A1 71.4 4.71 Cα/Hα in γ-hydroxylated βO4 A1 83.5 4.27 Cβ/Hβ in γ-hydroxylated βO4 in G-units A2 85.6 4.34 Cβ/Hβ in βO4 in Benzyl Ether structure A2 82.0 4.77 Cα/Hα in βO4 in Benzyl Ether structure B 86.9 5.40 Cα/Hα in Phenylcoumaran C 85.1 4.61 Cα/Hα in resinol structure C 53.5 3.04 Cβ/Hβ in resinol structure C 71.1 3.81/4.15 Cγ/Hγ in resinol structure

Methoxy 55.4 3.71 C/H in -OMe D 33.5 2.42-2.53 Cα/Hα in Secoisolariciresinol D 42.8 1.86 Cβ/Hβ in Secoisolariciresinol E 129.0 7.30-6.96 Stilbene double bond

F 120.9 5.34 Double bond in Cinnamyl alcohol

G 31.1 2.48 Cα/Hα in Dehydrocinnamyl alcohol G 34.4 1.66 Cβ/Hβ in Dehydrocinnamyl alcohol H 124.0 7.78-7.45 Conjugated carbonyls/acids

Ar-2 110.8 6.93 C2/H2 in G-units Ar-5 114.9 6.80 C5/H5 in G-units Ar-6 118.8 6.74 C6/H6 in G-units

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Figure S9: HSQC analysis of the starting Kraft lignin (KL)

Figure S10: HSQC analysis of the EtOAc fraction (LFEtOAc)

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Figure S11: HSQC analysis of the EtOH fraction (LFEtOH)

Figure S12: HSQC analysis of the MeOH fraction (LFMeOH)

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Figure S13: HSQC analysis of the Acetone fraction (LFAcetone)

Thermal analysis of the lignin fractions: DSC and TGA

Figure S14: DSC analysis of the different lignin fractions

0

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0.9

0 50 100 150 200

En

do

Up

°C

LF(EtOAc)

LF(EtOH)

LF(MeOH)

LF(Acetone)

Parent

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Figure S15: TGA analysis of the starting Kraft lignin (KL)

Figure S16: TGA analysis of the starting EtOAc fraction (LFEtOAc)

0

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20

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50

60

70

80

90

100

100 200 300 400 500 600

%

°C

Parent lignin

0

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30

40

50

60

70

80

90

100

100 200 300 400 500 600

%

°C

LF (EtOAc)

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Figure S17: TGA analysis of the starting EtOH fraction (LFEtOH)

Figure S18: TGA analysis of the starting MeOH fraction (LFMeOH)

0

10

20

30

40

50

60

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80

90

100

100 200 300 400 500 600

%

°C

LF (EtOH)

0

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20

30

40

50

60

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80

90

100

100 200 300 400 500 600

%

°C

LF (MeOH)

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Figure S19: TGA analysis of the starting acetone fraction (LFAcetone)

0

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50

60

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90

100

100 200 300 400 500 600

%

°C

LF (Acetone)

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Epoxidation of the lignin fractions

Optimization of the conditions of epoxidation

The reaction of epoxidation was optimized using LFEtOH in order to maximize the conversion of the functional groups. Table S1 reports the different experiments performed. In particular, amount of base used and reaction time were considered.

Table S2: conditions of reaction used to optimize lignin epoxidation

Entry Equivalents

of NaOH

Time

(h)

Epoxy loading

(mmol/g)

Conversion OH

groups (%)

1 1 5 3.07 56.1 2 3 5 3.30 61.4 3 5 5 3.18 58.6 4 10 5 2.96 53.9 5 3 1 3.18 58.7 6 3 15 2.83 51.0 7 3 24 2.85 51.4

General procedure

In a round bottom flask equipped with magnetic stirring were introduced the respective lignin fraction (300 mg), a mixture of water and acetone (50%v/v, 45 ml), NaOH (3 eq. the number of active OH of the lignin fraction) and epichlorohidrin (20 eq. the number of active OH of the lignin fraction). The mixture was stirred at 55 °C for 5 h. At the end of the reaction time 40 ml of water was poured in the mixture and the pH was lowered to 3.5 with some drops pf HCl 0.1 M. The resulting precipitated product was recovered by filtration on glass filter (pore size 4). The filtrate was washed with 2 portion of deionized water to remove traces of acid. Finally, the product was dissolved in acetone and precipitated with deionized water to obtain a homogeneous water dispersion. The mixture was finally freeze dried to obtain a thin brown powder.

O

OH

OH

OR

HO OCl+

O

O

OH

OR

HOO

O

O

OH

OR

HO

OH

Cl

O

O

OH

OR

HOO

O

P OCl

O

P OCl

phosphotization

phosphotization

O

O

OH

OR

HO

O

Cl

PO

O

Base

O

O

OH

OR

HO

O

Cl

PO

O

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Figure S20: proposed mechanisms involved in the phosphotization reaction

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2D-NMR of the epoxidated fractions (DMSO-d6)

O

OMe

ROO

HO

OMe

O

OMe

O

HO

OMe

O

OMe

O

O

OMe

O

A2: ββββΟΟΟΟ44442222

R = CarbohydrateB: ββββ55551111

O

OMe

OMe

O

E: Stilbene

C: ββββββββ1111 D: ββββββββ2222

OH

OMe

O

OH

OMe

O

R

OMe

O

O

R = H; OH

F: Coniferyl alcoholG: Dehydro

coniferyl alcohol

O

OMe

O

OMe

H: Conjugatedcarbonyls/acids

O

OMe

HOO

HO

OMe

A1: ββββΟΟΟΟ44441111

OO

1

2

3

Oxirane ring

Figure S21: structures observed in the epoxidated fractions

Figure S22: HSQC analysis of the epoxidated EtOAc fraction (Epoxy-LFEtOAc)

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Figure S23: HSQC analysis of the epoxidated ethanol fraction (Epoxy-LFEtOH)

Figure S24: HSQC analysis of the epoxidated methanol fraction (Epoxy-LFMeOH)

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Figure S25: HSQC analysis of the epoxidated acetone fraction (Epoxy-LFAcetone)

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Quantification of the oxirane by 1H-NMR (DMSO-d6)

In a vial were introduced 30 mg of epoxidated lignin and approximatively 5 mg of p-nitro benzaldehyde. The mixture was dissolved in 0.5 ml of d6-DMSO and a 1H-NMR analysis was performed. In particular, the signal comprised from 2.95 to 2.55 ppm related to two protons of the oxirane ring were compared with the signal at 10.16 ppm related to the aldehyde group.

Figure S26: 1H-NMR quantification of epoxy-groups of Epoxy-LFEtOAc with 4-nitrobenzaldehyde as internal standard

Figure S27: 1H-NMR quantification of epoxy-groups of Epoxy-LFEtOH with 4-nitrobenzaldehyde as internal standard

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Figure S28: 1H-NMR quantification of epoxy-groups of Epoxy-LFMeOH with 4-nitrobenzaldehyde as internal standard

Figure S29: 1H-NMR quantification of epoxy-groups of Epoxy-LFAcetone with 4-nitrobenzaldehyde as internal standard

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Synthesis and characterization of the thermosets

Study of the curing condition

DSC experiment: a mixture of each epoxidated lignin fraction with the corresponding amount of JD2000 (10 mg of mixture; 2/1 ratio epoxy groups: NH2 group) were introduced in a DSC crucible and heated at 1 °C/min from room temperature to 200°C. All the mixture presented an exothermic maximum at 100°C (Figure S30).

Figure S30: DSC experiment of curing the mixture of epoxidated fractions with JD2000

Thermal properties of Jeffamine D2000

Figure S31: DSC analysis of JD2000

20 40 60 80 100 120 140 160 180 200

°C

Resin 1 Resin 2 Resin 3 Resin 4

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do

Up

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

-80 -60 -40 -20 0 20

°C

En

do

Up

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Thermal properties of the resins

Figure S32: DSC analysis of the thermosets

Figure S33: TGA analysis of the thermosets

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

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-70 -20 30 80 130

En

do

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°C

Resin 1 Resin 2 Resin 3 Resin 4

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100

60 160 260 360 460 560

%

°C

R(EtOAc)

R(EtOH)

R(MeOH)

R(Acetone)

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Scanning Electron Microscope analysis (SEM) of the thermosets

Figure S34: SEM analysis of the thermosets