Preparation of lignin-containing porous microspheres

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ecules: modification with acrylic acid and modification with epichlorohydrin ..... Lignin and its vinyl derivatives (LA, LEA) were copolymer- ized with St and DVB in ...
Holzforschung 2015; aop

Beata Podkościelna, Magdalena Sobiesiak, Yadong Zhao, Barbara Gawdzik and Olena Sevastyanova*

Preparation of lignin-containing porous microspheres through the copolymerization of lignin acrylate derivatives with styrene and divinylbenzene Abstract: A novel method for synthesizing microspheres from lignin or lignin acrylate derivatives through copolymerization with styrene (St) and divinylbenzene (DVB) has been developed. The copolymers were obtained by the emulsion-suspension polymerization with a constant molar ratio of DVB to St of 1:1 (w/w) and different amounts of lignin or its derivatives. The morphologies of the obtained materials were examined by scanning electron microscopy. Two types of lignin modifications were performed to introduce vinyl groups into the lignin molecules: modification with acrylic acid and modification with epichlorohydrin plus acrylic acid. The course of modification was confirmed by attenuated total reflectance Fourier transform infrared spectroscopy. The thermal stability and degradation behavior of the obtained microspheres were investigated by thermogravimetric analysis, and the pore structure was characterized via nitrogen sorption experiments. Owing to the presence of specific functional groups and the well-developed pore structure, the obtained Lignin-St-DVB microspheres may have potential application as specific sorbents for the removal of phenolic pollutants from water, as demonstrated by the solid-phase extraction technique. Keywords: ATR-FTIR, lignin acrylation, polymeric microspheres, porous materials, solid-phase extraction

*Corresponding author: Olena Sevastyanova, Department of Fibre and Polymer Technology, KTH The Royal Institute of Technology, SE10044 Stockholm, Sweden; and Wallenberg Wood Science Center, KTH The Royal Institute of Technology, SE-10044, Stockholm, Sweden, e-mail: [email protected] Beata Podkościelna, Magdalena Sobiesiak and Barbara Gawdzik: Faculty of Chemistry, Department of Polymer Chemistry, Maria CurieSkłodowska University, pl. M. Curie-Skłodowskiej 5, 20-031 Lublin, Poland Yadong Zhao: Department of Fibre and Polymer Technology, KTH The Royal Institute of Technology, SE-10044 Stockholm, Sweden

DOI 10.1515/hf-2014-0265 Received September 26, 2014; accepted January 16, 2015; previously published online xx

Introduction Lignin is one of the primary components of lignocellulosic materials and the second most abundant biopolymer after cellulose. Various technical lignins are currently available in large quantities as low-value by-products from the pulp and paper industry. However, the structural features of lignin have a high potential for chemical modifications, which can lead to value-added polymeric materials with specific properties (Dournel et  al. 1988; Lindberg et  al. 1989; Stewart 2008; Hatakeyama and Hatakeyama 2010). The modifications are typically aimed at the derivatization of phenolic and aliphatic hydroxyl groups (OHphen and OHaliph) situated at the C-α and C-γ positions of the propane side chain (Figure 2a) to obtain more reactive functional groups. The ratio of OHphen to OHaliph varies depending on the origin (hardwood or softwood) of the lignin and on the pulping process (e.g., kraft, alkali, organosolv pulping, etc.). Etherification, esterification, and reaction with isocyanates, silylation, phenolation, and oxidation/ reduction are the common approaches for the OH-group modification (Laurichesse and Avérous 2014). Esterification, as the easiest way for modification, can be performed by means of acidic compounds, acid anhydrides, and chloride acids, with the latter two being the most reactive. Often, the agents for esterification are bi-functional, which results in lignin-based polyester networks. The synthesis of polyesters, epoxy resins and elastomeric materials are performed via lignin esterification (Kondo et al. 1987; Guo and Gandini 1991; Guo et al. 1992; Hirose et al. 2005; Fang et al. 2011; Sivasankarapillai and McDonald 2011; Luong et al. 2012; Saito et al. 2012; Sivasankarapillai et al. 2012).

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2      B. Podkościelna et al.: Copolymerization of lignin acrylate derivatives

Alternatively, reactive groups can be introduced into the macromolecular structure of lignin allowing for crosslinking reactions with various polymeric systems. The introduction of acrylate functionality is one example. Naveau (1975) acrylated kraft lignin with methacrylic anhydride and methacryloyl chloride followed by copolymerization with methyl methacrylate. Glasser and Wang (1989) used isocyanatoethyl methacrylate to modify hydroxybutyl lignin, as well as lignin and lignin-like model compounds. The copolymerization characteristics of the acrylated lignins were investigated with styrene and methyl methacrylate. Styrene-divinylbenzene (St-DVB) is among the first developed and most popular polymeric sorbents. Because of its hydrophobic character, St-DVB interacts with analytes through van der Waals forces and π-electron interaction of the aromatic ring. To improve the sorption of polar analytes, the specific area of the adsorbent can be enlarged or polar functional groups can be introduced into the copolymer. The latter can be achieved either by copolymerization with at least of one monomer that contains polar functional groups or by chemical post-modification of the hydrophobic St-DVB polymer to introduce polar moieties into its structure. Monomers containing various functional groups, such as methyl methacrylate, N-vinylpyrrolidone, acrylonitrile, cyanomethylstyrene, or derivatives of amines or amides, are common agents for the copolymerization with St and DVB. Chemical postmodifications of hydrophobic St-DVB polymers can be performed by introducing sulfonic, acetyl, hydroxymethyl, benzoyl, hydroxyl or carboxyl groups (Davankov and Tsyurupa 1990; Gawdzik and Osypiuk 2000). In the present paper, kraft lignin was activated by modification with acrylic acid (AA) and epichlorohydrin (ECH) plus AA before copolymerization with St and DVB. A novel method for synthesizing porous microspheres via the outlined reactions was tested. The aim was to develop novel sorbents with specific chemical structures and properties of lignins of different origin. The shape, pore structure, and thermal properties of the obtained lignincontaining functionalized microspheres were investigated and the potential of the obtained microspheres were tested as sorbents for phenolic environmental pollutants by solid-phase extraction (SPE).

Lignin

Direct modification with AA

Modification with ECH and AA

L

LA

LEA

Synthesis of microspheres: St+DVB+L/LA/LEA

Solid phase extraction (SPE) experiments with phenol and its chlorinated derivatives

Figure 1: Schematic representation of the experimental steps.

bis(2-ethylhexyl)sulfosuccinate sodium salt (DAC, BP) were obtained from Fluka AG (Buchs, Switzerland). α,α′-Azoiso-bis-butyronitrile (AIBN) were obtained from Merck (Darmstadt, Germany). All of these chemicals were of reagent grade. ECH, sulfuric acid, propan-2-ol, benzene, NaOH, acetone, and hydroquinone were obtained from POCh (Gliwice, Poland). Triethylbenzylammonium chloride (TEBAC) was prepared in the laboratory of the Department of Polymer Chemistry, UMCS (Lublin, Poland) by reacting benzoyl chloride with triethylamine in a molar ratio of 1:3. The reaction time was 72 h and the product was filtered, washed with benzene, and dried. Modification of lignin directly with AA (Figure 2b,I): To a 250  ml round-bottom, three-necked flask equipped with a mechanical

a

OH Lignin

L

SH

=

H3C

O

H (or lignin) OH

b

O

I

L-(Aliph-OH)

+

COOH

L-O LA

L-(Ph-OH)

+

NaOH

Cl

L-O

O

II

O

L-O O

c

+

COOH

CH2

CH2

L-O LEA

+

LA or

St

The schematic representation of the major experimental steps is shown in Figure 1. Kraft lignin from softwood was obtained from Sigma-Aldrich (Stockholm, Sweden). DVB, St, AA, decan-1-ol, and

H2C

DVB

O OH

L or

+

Materials and methods

O

LE

LEA

CH3O

SH OH

Figure 2: Schematic representation of the a) kraft lignin molecule, b) reaction of lignin directly with acrylic acid (I) and with epichlorohydrin and acrylic acid (II), and c) copolymerization of lignin and its acryl derivatives (LA and LEA) with St and DVB.

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B. Podkościelna et al.: Copolymerization of lignin acrylate derivatives      3

stirrer, thermometer and an azeotropic trap (Dean-Stark apparatus), 20 g of lignin, 75 ml of benzene, 75 ml of AA, 2 ml of sulfuric acid, and 2 g of hydroquinone (polymerization inhibitor) were added, and this mixture was refluxed for 5 h. The modified lignin was isolated by filtration, washed with distilled water (1 l) and acetone (100 ml), and dried. Modification of lignin with ECH and AA (Figure 2b,II): In the first step, 15 g of lignin, 60  ml of ECH and 45  ml of propan-2-ol were added to a 250 ml round-bottom, three-necked flask equipped with a mechanical stirrer, a thermometer and a dropping funnel, and this mixture was heated at 75°C for 1 h. An aqueous solution of NaOH was added dropwise for 30  min through the dropping funnel. The reaction continued for 1 h at 75°C. The lignin (modified with epoxy groups) was isolated by filtration and then sequentially washed with MeOH, distilled water, and acetone. The product was dried at room temperature. In the second step, 15 g of lignin with epoxy groups, 50 ml of AA, 0.4 g of TEBAC (a catalyst), and 0.005 g of hydroquinone (polymerization inhibitor) were added to a 150  ml round-bottom, two-necked flask equipped with a mechanical stirrer, thermometer and condenser, and this solution was heated at 90–95°C for 5 h. The product was isolated by filtration, washed with distilled water (2 l), and dried. Synthesis of microspheres (Figure 2c): The copolymerization of St with DVB and lignin was performed in an aqueous medium. Redistilled water (150 ml) and 0.75 g of DAC,BP (as a surfactant) were stirred for 0.5 h at 80°C in a three-necked flask fitted with a stirrer, a water condenser, and a thermometer. Then, the solutions containing DVB and St in a molar ratio of 1:1 and various amounts of lignin, unmodified or modified (Table 1), were added under stirring together with the initiator AIBN (1%) and a mixture of pore-forming diluents (10 ml of toluene and 10 ml of 1-decanol). The reaction mixture was stirred at 350 rpm for 18 h at 80°C. The microspheres were obtained by filtration, washed with hot distilled water (2 l), and then dried and extracted in a Soxhlet apparatus with boiling acetone (Podkościelna et al. 2012). Polymer characterization: Hydroxyl and carboxyl groups in the lignin were quantified by phosphorus NMR (31P NMR) analysis with a 90° pulse angle, inverse gated proton decoupling (delay time of 10 s). Prior to analysis, lignin samples were purified by consecutive extraction with toluene and pentane. A 20–25 mg lignin was functionalized

by 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane in a 1/1.6 mixture (v/v) of CDCl3 and pyridine for 2  h at room temperature (Granata and Argyropolous 1995). Elemental analysis (C, H, N, and S) was performed in a Flash EA 1112 elemental analyzer (Thermo Finnigan, USA; external service provided by the Elemental Analysis Unit at the Santiago de Compostela University, USC, Santiago de Compostela, Spain). Attenuated total reflectance (ATR) spectra were recorded in a Bruker TENSOR 27 Fourier transform infrared (FTIR) spectrophotometer (resolution 4 cm-1; 32 scans were accumulated). Prior to the field-emission SEM analysis (FE-SEM; Hitachi S-4800 FE-SEM), the samples were coated with a 3 nm thick gold layer (Cressington 208HR high-resolution sputter coater). The pore structures of the copolymers were characterized by N2 adsorption at 77 K (ASAP 2405 adsorption analyzer, Micrometrics Inc., USA). Prior to the analysis, the copolymers were degassed at 140°C for 2 h. Specific surface areas were calculated by the BET method, assuming that the area of a single N2 molecule in the adsorbed state is 16.2 Å2. Pore volumes and pore size distributions were determined by the BJH method. Thermogravimetric, derivative thermogravimetric, and differential scanning calorimetric thermograms were obtained usng STA 449 F1 Jupiter thermal analyzer (Netzsch, Selb, Germany) with Al2O3 crucible with a sample weight of ∼10 mg under He atmosphere (40 ml min-1) and a heating rate 10 K min-1 between 30–800°C. SPE experiments with phenol and its chlorinated derivatives: Aqueous solutions of the phenolic compounds were prepared by diluting a standard MeOH solution containing 100 mg l-1 of phenol (P), 2-chlorophenol (ChP), 2,4-dichlorophenol (DChP), and 2,4,6-trichlorophenol (TChP). The final concentration in the water-diluted solution was 2 mg l-1. The phenols were pre-concentrated by laboratory cartridges filled with 100  mg of the substance. Different volumes of the solutions were passed through the cartridge filled with samples (adsorbent) and connected by PTFE tubing (Chrompack, Middelburg, The Netherlands) to a water pump jet (Figure 3). The vacuum was then maintained for 5 min to dry the sorbent bed. Afterwards, the phenolic compounds were eluted with 2 ml of MeOH for each 100 ml of aqueous solution. The quantities of the eluted phenolic compounds were determined by HPLC (three independent determinations). The recovery calculations were based on the assumption that MeOH completely

Syringe

Table 1: Experimental and pore structure parameters of the St-DVB copolymers. Parameter of synthesis a

Pore structure

Copolymer

St (g)

DVB (g)

L (g)

LA (g)

LEA (g)

SBET (m2 g-1)

VTOT (cm3 g-1)

W (nm)

St-DVB St-DVB-1L St-DVB-3L St-DVB-6L St-DVB-LA St-DVB-LEA

8 8 8 8 8 8

10 10 10 10 10 10

0 1 3 6 – –

– – – – 3 –

– – – – – 3

235 166 154 149 196 105

0.84 0.41 0.36 0.25 0.66 0.12

15.6 10.9 11.0 8.0 11.9 13.0

a

Porous teflon

L, the amount of unmodified lignin in grams (g).

Adsorbent

Porous teflon

Vacuum

Figure 3: Schematic representation of the experimental set-up for the SPE method.

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4      B. Podkościelna et al.: Copolymerization of lignin acrylate derivatives

Results and discussion

a

Transmittance (%)

eluted the adsorbed compounds. A recovery decrement below 25% of the maximum value was assumed to be a breakthrough volume for the compound. For more details, see Gawdzik et al. (2005), Sobiesiak and Podkościelna (2010), and Sobiesiak (2011).

100

90 1720 cm-1

Lignin (L) LA LEA

80

Acrylation of lignin and analytical data 70 4000

3000

2000

1000

Wavenumber (cm-1) 100

90

80

100

Transmittance (%)

Transmittance (%)

b

96

92

St-DVB St-DVB-3L

70

88 2000

4000

1600 1200 Wavenumber (cm-1)

3000

800

2000

1000

Wavenumber (cm-1)

c

100 90 80 70

Transmittance (%)

The typical functional groups (OH, OMe, and SH) are illustrated on imaginary phenylpropane units in Figure 2a, whereas the other key reactions performed in this study are illustrated in Figures 2b and 2c. The direct anchoring of the double bonds on lignin by acrylation of the aliphatic chain is shown in Figure 2b,I as lignin reacts to LA. Because of its high acidity, the OHphen group does not participate readily in the esterification. In contrast, ECH and AA do react with phenolic groups and the formation of LE and LEA is probable (as presented in Figure 2b,II). The ATR-FTIR (Figure 3a) and 31P NMR spectra confirms that the kraft lignin investigated is a typical guaiacyl lignin (G lignin, softwood lignin). For example, the band at 1270  cm-1 (typical for guaiacyl units) is dominant, the band at 1505 cm-1 is larger than that at 1463 cm-1, and two separate bands at 817 and 858 cm-1 (out-of-plane C-H vibration) are visible (Sarkanen and Ludwig 1971; Faix 1991; Lin and Dence 1992). The kraft lignin in focus contained 2.5% sulfur, as indicated by the elemental analysis (Table 2). In the FTIR spectrum, a very weak band corresponding to the thiol group (-SH) was also perceptible at 2600 cm-1. Based on the 31 P NMR analysis, the lignin sample contained 2.4 mmol g-1 OHaliph and 3.4 mmol g-1 OHphen groups (Table 2). The formation of the aforementioned functional groups can also be seen on the ATR-FTIR spectra (Figure  4a). LA and LEA show strong bands at 1175  cm-1 and 1720 cm-1 (C = O stretch in ester groups), respectively,

1175 cm-1

60

100 90 80 70

100

Table 2: Amount of functional groups in lignin (based on 31P NMR) and chemical composition of unmodified lignin (L) and of lignin modified with acrylic acid (AC) and epichlorohydrin and acrylic acid (LEA) based on elemental analysis. Functional groups OHaliph OHphen cond. OHphen guaiacyl OHphen total COOH

(mmol g-1) 2.43 1.54 1.91 3.45 0.44

Elements C (%) H (%) N (%) S (%) Total (%)

L 62.64 5.92 0.58 2.53 71.67

LA 59.07 6.44 0.36 1.17 67.04

LEA 59.81 6.49 0.22 0.63 67.16

90 80 70 4000

St-DVB St-DVB-LA St-DVB-LEA 3000

2000

1000

Wavenumber (cm-1)

Figure 4: ATR-FTIR spectra of a) lignin (L) and modified lignin (LA and LEA), b) St-DVB and St-DVB copolymer with unmodified lignin (St-DVB-L), and c) St-DVB and St-DVB copolymer with modified lignins (St-DVB-LA and St-DVB-LEA).

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B. Podkościelna et al.: Copolymerization of lignin acrylate derivatives      5

whereas the intensities of the other lignin-related signals in the 1300–1000 cm-1 and 1700–1400 cm-1 regions are significantly reduced. The signal at 1175 cm-1 is weaker for LEA than for LA. Ester C-O-C stretching vibrations in acrylates result in doublets at 1180 and 1260 cm-1, which is more pronounced for the LEA sample. A C = C double bond typically results in a moderate band at 1680–1640 cm-1. However, this area overlaps with the strong aromatic skeletal vibrations of lignin. An indication of the introduced C = C bond is the increased signal at 820 cm-1, which corresponds to the bending vibrations of the  = C–H group. An intensity decrement of the band at 1086 cm-1 (C-O deformation in secondary alcohols) is visible for both the LEA and LE samples. The other typical band for secondary alcohols at 1128  cm-1 is reduced for the former and completely disappeared for the latter. The intensity of C-O deformation band of primary alcohols is also reduced for both modified samples (1035 cm-1). The same is true for the broad O-H stretching band (3600–3050 cm-1) of the LEA sample. Expectedly, the modification with LA proceeds through the OHaliph groups, likely through both Cα (secondary) and Cγ (primary) OH groups, whereas modification with ECH and AA results in the introduction of acrylic groups predominantly into the OHphen groups.

Copolymerization of lignin and its vinyl derivatives with St and DVB When St (as a monovinyl monomer) is copolymerized with DVB (as multivinyl monomer) by suspension polymerization in the presence of a pore-forming diluent (toluene and 1-decanol in the present work), macroporous resin beads are produced that have a permanent porosity in the dry state. The commercially available St-DVB products are generally highly cross-linked polymers that possess a well-developed pore structure. In such products, the diluent controls the pore size, pore-size distribution, and total pore volume (Horák and Benés 1996). The molar ratio of St and DVB monomers was 1:1 in the present study. Lignin and its vinyl derivatives (LA, LEA) were copolymerized with St and DVB in varying quantities, resulting in porous lignin-containing microspheres Figure 2c. Figure 4b presents the FTIR spectra of the St-DVB and St-DVB-L copolymers. The spectral range of 2000–800 cm-1 (inset) shows the significant differences, whereas signals resulting from St and DVB are common to both materials. Bands characteristic of aromatic systems are the 1650– 1430  cm-1 regions (aromatic skeletal vibrations). Bands resulting from C-H out-of-plane vibrations in aromatic rings and vinyl compounds are between 988–830  cm-1.

Some bands with weak-to-medium intensity appear in the 1290–900 cm-1 region, which are a result of in-plane deformational vibrations of C-H bonds. After introducing lignin as a component of the polymer, the bands corresponding to the hydrocarbon moiety (1600–1400, 1067, 1025, and 900 cm-1) and to the vinyl bonds (1629, 988, and 830 cm-1) of the molecule became stronger, indicating that the lignin partially prevented cross-linking of the polymeric network and left some of the vinyl groups unreacted, as illustrated in Figure 4b (inset) for the sample St-DVB-3L (Table 1). The most intense bands of St-DVB-L at 1030 and 1085 cm-1 are attributable to C-O deformations in primary and secondary alcohols, respectively. The broad O-H band at 3050–3600 cm-1 is no longer observed for the lignin copolymerized with St and DVB, whereas the intensity of the signal from the C-H stretch in methyl and methylene groups increased. The spectra of the St-DVB, St-DVB-LA, and St-DVBLEA copolymers are comparable in Figure 4c. Similar to the St-DVB-L copolymer, intensity increments of vinyl bands at 1629, 988, and 830  cm-1 can be observed for LA- and LEA-containing microspheres, indicating that the presence of lignin partially affects the cross-linking reaction between St and DVB. The spectra of St-DVB and St-DVB-LEA are quite similar, with increased signal intensities in the regions around 3000 (methyl and methylene groups), 1500–1700 (aromatic skeletal vibrations), and 800–900  cm-1 (C-H out-of-plane deformations). At the same time, bands of numerous functional groups introduced by modification make the spectrum of St-DVB-LEA quite complex (Figure 4c). The strongest signals are attributable to the presence of methylene groups, and the symmetrical and asymmetrical stretching vibrations at 2854 and 2923 cm-1, respectively. Other bands resulting from these groups can be observed at 1455(deformation vibrations) and 760  cm-1 (rocking vibrations). Another strong band at 1727 cm-1 is due to the C = O stretching vibrations of acrylate. The spectral range of 1300–1000 cm-1 is common for all structures containing oxygen functional groups. Asymmetrical and symmetrical stretching vibrations of C-O bonds in alkyl-aryl ethers (bond joining LEA with lignin) resulted in a band around 1270–1230 and 1050– 1010 cm-1, respectively. For the St-DVB-LEA copolymer, the broad O-H band can be observed at 3600–3100 cm-1. For chromatographic purposes, sorbent particles should possess a uniform spherical shape because this improves the efficiency of the sorption process owing to the regular flow of the mobile phase, which minimizes the diffusion effects. The actual shapes of the obtained lignin-containing microspheres were observed by FE-SEM (Figure 5), which shows particles 10–30 μm in diameter.

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6      B. Podkościelna et al.: Copolymerization of lignin acrylate derivatives

St-DVB

St-DVB-L

St-DVB-LA

St-DVB-LEA

Figure 5: SEM images of St-DVB microspheres without lignin and with lignin (St-DVB-L) and lignin derivatives (St-DVB-LA and St-DVB-LEA).

Pore structure and thermal properties

0.010 St-DVB Pore volume (cc/g*A)

The St-DVB copolymer formed larger agglomerates. StDVB-L and lignin acrylate formed well-separated spherical granules. The St-DVB-LEA copolymer contained a significant amount of irregularly shaped particles, which likely formed by unreacted lignin derivatives, along with smaller sized microspheres.

St-DVB-1L

0.008

St-DVB-3L 0.006

St-DVB-6L

0.004

St-DVB-LA St-DVB-LEA

0.002 0 10

A well-developed surface area and the presence of microand mesopores are essential for effective sorption processes (Sobiesiak 2011). The pore structure of St-DVB and its lignin copolymers was analyzed by the N2 adsorption-desorption method. The largest specific areas and pore volumes are observed for the copolymers obtained in synthesis No. 1 (StDVB) without the addition of lignin (Table 1, pore structure). Compared with the parent St-DVB, copolymers with modified lignins resulted into a decrement of specific surface areas and total pore volumes, most likely because some pores were blocked by lignin derivatives. This assumption is supported by the fact that the mean pore width for StDVB-L is approximately 11 nm, whereas that for St-DVB copolymers is 15.6 nm. All of the investigated materials are mesoporous with two maximums at 40 Å (4 nm) and at 240 Å (24 nm) (Figure 6). Mesoporous materials are well suited for sorption application in liquid/water systems. Table 3 summarizes the thermal parameters of the materials in focus. The copolymers St-DVB-LA and StDVB-LEA began to decompose at almost the same temperature at 266°C, which is approximately 14°C lower than that of the unmodified St-DVB. The addition of LA or LEA

100 Mean pore diameter (Å)

1000

Figure 6: Pore size distribution curves for St-DVB copolymers with unmodified lignin (St-DVB-1 L/3 L/6 L) and with acrylated lignins (St-DVB-LA and St-DVB-LEA).

Table 3: Results of thermal analysis obtained for St-DVB and St-DVB copolymers with unmodified (St-DVB-L) and acrylated (StDVB-LA and St-DVB-LEA) lignin. Material St-DVB St-DVB-1L St-DVB-3L St-DVB-6L St-DVB-LA St-DVB-LEA

Tinitial (°C)

Tmax. (°C)

Residue at 800°C (%)

280 314 326 340 266 267

418.6 426.0 430.5 431.0 425.3 419.0

4.53 4.97 5.42 5.50 4.63 10.86

to the St-DVB network caused an enrichment of oxygencontaining functional groups in the polymers, which resulted in decreased stability compared with pure crosslinked St-DVB. The temperature of the maximum rate of

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B. Podkościelna et al.: Copolymerization of lignin acrylate derivatives      7

mass loss (Tmax) and the final residue of St-DVB-LA exhibited values similar to those obtained for St-DVB-1L. The thermal behavior of St-DVB-LEA is different in that the Tmax is 419°C, which is very close to the Tmax of St-DVB. However, the final residue exceeded 10%, which is approximately two-fold greater than that for St-DVB.

a

30

PH

25

ChP

DChP

TChP

St-DVB

20 15 10 5 0

Solid-phase extraction (SPE) If the phenol molecule possesses any electron-withdrawing substituents, its affinity to the polymer in adsorption experiments is stronger. Accordingly, the order of the recovery curves in Figure 6 is consistent with the amount of chlorine substituents in the test compounds, with trichlorinated phenol (TChP) possessing the highest recovery value. By introducing functional groups to the polymer, its surface becomes more hydrophilic and the role of van der Waals forces and the π-electrons of the aromatic ring becomes larger in the sorption processes, and thus the sorption efficiency is improved. Based on the preliminary SPE study with lignincontaining microspheres, the best results were obtained for the St-DVB-LA material, which presented the highest values of recovery (47%) and breakthrough volume (800 ml) (Figure 7c). For St-DVB-6L, the highest recovery also reached 45%, but the breakthrough had already occurred at 600  ml (Figure 7b). Considering the porous structure parameters of these materials (Table 1), the obtained SPE results are promising. For comparison, the recovery values of unmodified St-DVB are also presented (Figure 7a). The values of SBET and VTOT suggest that this material should possess superior sorption ability than its lignin-modified derivatives, but this is not the case. In the investigated range of sample volumes, the recovery values of chlorinated phenols (TChP and DChP) for lignin-containing St-DVB copolymers were higher than those for the pure St-DVB, even after exceeding the breakthrough volume. The difference was observed for non-chlorinated lignin, which had better affinity toward pure St-DVB. The recovery values obtained for the phenol with one chlorine substituent (ChP) were quite similar for all of the investigated porous materials. To explain these observations, the mean pore size (W) should be taken into account. In this trial, the St-DVB microspheres possess the widest pores of all of the presented materials. The wider mesopores promote faster mass transport in the porous structure. However, the sorption capacity of this material is not high enough, particularly for small molecules. For a more detailed investigation and comparison of the sorptive properties, additional

Recovery (%)

b

c

50 45 40 35 30 25 20 15 10 5 0

St-DVB-6L

50 45 40 35 30 25 20 15 10 5 0

St-DVB-LA

0

200

400

600

800

1000

Volume of sample solution (ml)

Figure 7: Recovery curves of phenol (PH) and chlorinated phenol compounds (ChP, DChP and TChP) obtained for a) St-DVB, b) St-DVB-6 L, and c) St-DVB-LA.

optimization of the synthesis should be performed to produce materials with similar pore characteristics.

Conclusions Acrylic derivatives of lignin were successfully prepared through two methods: reaction with AA (LA) and a two-step reaction with ECH and AA (LEA). The chemical structures of all of the new derivatives were confirmed by ATR-FTIR analysis. Polymeric mesoporous materials in the form of microspheres were prepared from St-DVB and lignin or its acrylate derivatives. The mean pore diameter was in the range of 4–24 nm, whereas the surface area and total pore volume for copolymers containing lignin were in the range of 100–200 m2 g-1 and 0.1–0.6 cm3 g-1, respectively. The addition of unmodified lignin to St-DVB improved its thermal stability and as a consequence, the initial decomposition temperatures of the polymers increased from 280 to 340°C. Owing to the presence of different functional groups in the lignin macromolecule, lignin-containing porous St-DVB microspheres had better sorption properties toward

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8      B. Podkościelna et al.: Copolymerization of lignin acrylate derivatives

chlorinated phenolic compounds compared with the pure St-DVB. Thus, it can be concluded that lignin-containing microspheres could be effective sorbents for environmental pollutants after a further optimization of the process. Acknowledgments: We would like to thank the following institutions for supporting the conduct of this study: the Knut and Alice Wallenberg foundation in association with the Wallenberg Wood Science Center (WWSC), The Swedish Institute (Baltic Sea cooperation program, project 0013053), and the Cost Action FP1105 WoodCellNet.

References Davankov, V.A., Tsyurupa, M.P. (1990) Structure and properties of hypercrosslinked polystyrene: the first representative of a new class of polymer networks. React. Polym. 13:27–42. Dournel, P., Randrianalimanana, E., Deffieux, A., Fontanille, M. (1988) Synthesis and polymerization of lignin macromonomers—I. Anchoring of polymerizable groups on lignin model compounds. Eur. Polym. J. 24:843–847. Faix, O. (1991) Classification of lignins from different botanical origins by FT-IR spectroscopy. Holzforschung 45 (Supplementary Volume, September):21–27. Fang, R., Cheng, X.S., Lin, W.S. (2011) Preparation and application of dimer acid/lignin graft copolymer. BioResources 6:2874–2884. Gawdzik, B., Osypiuk, J. (2000) Reversed-phase high-performance liquid chromatography on porous copolymers of different chemical structure. J. Chromatogr. A. 898:13–21. Gawdzik, B., Sobiesiak, M., Puziy, A.M., Poddubnaya, O.I. (2005) Carbon sorbents derived from porous polymers for off-line preconcentration of chlorophenols from water. J. Liq. Chromatogr. R. T. 27:1027–1041. Glasser, W.G., Wang, H.-X. (1989) Derivatives of lignin and ligninlike models with acrylate functionality. In: Lignin: Properties and Materials. ACS Sym. Ser. No. 397. pp. 515–522. Granata, A., Argyropolous, D.S.J. (1995) 2-Chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane, a reagent for the accurate determination of the uncondensed and condensed phenolic moieties in lignins. J. Agric. Food Chem. 43:1538–1544. Guo, Z.X., Gandini, A. (1991) Polyesters from lignin: 2. The copolyesterification of kraft lignin and polyethylene glycols with dicarboxylic acid chlorides. Eur. Polym. J. 27:1177–1180. Guo, Z.X., Gandini, A., Pla, F. (1992) Polyesters from lignin: 1. The reaction of kraft lignin with dicarboxylic acid chlorides. Polym. Int. 27:17–22. Hatakeyama, H., Hatakeyama, T. (2010) Lignin structure, properties and applications. Adv. Polym. Sci. 232:1–63. Hirose, S., Hatakeyama, T., Hatakeyama, H. (2005) Glass transition and thermal decomposition of epoxy resins from the carboxylic acid system consisting of ester-carboxylic acid derivatives of

alcoholysis lignin and ethylene glycol with various dicarboxylic acids. Thermochim. Acta 431:76–80. Horák, D., Benés, M.J. (1996) Macroporous polymers. In: Polymeric Materials Encyclopedia, Volume 6. Ed. Salamone, J.C. CRC Press Inc. pp. 3949–3958. Kondo, T., Meshitsuka G., Ishizu, A., Nakando, J. (1987) Preparation and ozonation of completely allylated and methallylated lignins. Mokuzai Gakkaishi 33:724–727. Laurichesse, S., Avérous, L. (2014) Chemical modifications of lignins: towards biobased polymers. Prog. Polym. Sci. 39:1266–1290. Lin, S.Y., Dence, C.W. (1992) Fourier Transform Infrared Spectroscopy. In: Methods in Lignin Chemistry. Springer, Berlin. pp. 86–109. Lindberg, J.J., Kuusela, T.A., Levon, K. (1989) Specialty polymers from lignin. In: Lignin: properties and materials. Eds. Glasser W.G., Sarkanen S. ACS Symp. Ser. No. 397. American Chemical Society, Washington, D.C. pp. 190–204. Luong, N.D., Binh, N.T.T., Duong, L.D., Kim, D.O., Kim, D.S., Lee, S.H., Kim, B.J., Lee, Y.S., Nam, J.D. (2012) An eco-friendly and efficient route of lignin extraction from black liquor and a lignin-based co-polyester synthesis. Polym. Bull. 68:879–890. Naveau, H.P. (1975) Methacrylic derivatives of lignin. Cell. Chem. Technol. 9:71–77. Podkościelna, B., Bartnicki, A., Gawdzik, B. (2012) New crosslinked hydrogels derivatives of 2-hydroxyethyl methacrylate: synthesis, modifications and properties. Express Polym. Lett. 6:759–771. Saito, T., Brown, R.H., Hunt, M.A., Pickel, D.L., Pickel, J.M., Messman, J.M., Baker, F.S., Keller, M., Naska, A.K. (2012) Turning renewable resources into value-added polymer: development of lignin-based thermoplastic. Green Chem. 14:3295–3303. Sarkanen, K.V., Ludwig, C.H., eds (1971) Lignins–Occurence, Formation, Structure and Reactions. Wiley-Interscience, New-York, 1971, pp. 916. Sivasankarapillai, G., McDonald, A.G. (2011) Synthesis and properties of lignin-highly branched poly(ester-amine) polymeric systems. Biomass Bioenerg. 35:919–931. Sivasankarapillai, G., McDonald, A.G., Li, H. (2012) Lignin valorisation by forming toughened lignin co-polymers: development of hyper-branched prepolymers for cross-linking. Biomass Bioenerg. 47:99–108. Sobiesiak, M. (2011) Bead-shaped porous polymers containing bismaleimide – their physico-chemical characteristics and sorption properties towards chlorophenols. Polish J. Appl. Chem. 55:25–32. Sobiesiak, M., Podkościelna, B. (2010) Preparation and characterization of porous DVB copolymers and their applicability for adsorption (solid-phase extraction) of phenol compounds. Appl. Surf. Sci. 257:1222–1227. Stewart, D. (2008) Lignin as a base material for materials applications: chemistry, application and economics. Ind. Crop. Prod. 27:202–207.

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