International Journal of Biological Macromolecules 72 (2015) 1056–1062
Contents lists available at ScienceDirect
International Journal of Biological Macromolecules journal homepage: www.elsevier.com/locate/ijbiomac
Isolation and characterization of lignin from the oak wood bioethanol production residue for adhesives Soo Jung Lee a , Hyun Joo Kim b , Eun Jin Cho a , Younho Song c , Hyeun-Jong Bae a,b,c,∗ a b c
Bio-energy Research Center, Chonnam National University, Gwangju 500-757, Republic of Korea Department of Forest Products and Technology, Chonnam National University, Gwangju 500-757, Republic of Korea Department of Bioenergy Science and Technology, Chonnam National University, Gwangju 500-757, Republic of Korea
a r t i c l e
i n f o
Article history: Received 18 August 2014 Received in revised form 8 October 2014 Accepted 10 October 2014 Available online 29 October 2014 Keywords: Bioethanol production residue Lignin Reactivity
a b s t r a c t Lignin was isolated from the residue of bioethanol production with oak wood via alkaline and catalyzed organosolv treatments at ambient temperature to improve the purity of lignin for the materials application. The isolated lignins were analyzed for their chemical composition by nitrobenzene oxidation method and their functionality was characterized via wet chemistry method, element analysis, 1 H NMR, GPC and FTIR-ATR. The isolated lignin by acid catalyzed organosolv treatment (Acid-OSL) contained a higher lignin content, aromatic proton, phenolic hydroxyl group and a lower nitrogen content that is more reactive towards chemical modification. The lignin-based adhesives were prepared and the bond strength was measured to evaluate the enhanced reactivity of lignin by the isolation. Two steps of phenolation and methylolation were applied for the modification of the isolated lignins and their tensile strengths were evaluated for the use as an adhesive. The acid catalyzed organosolv lignin-based adhesives had comparable bond strength to phenol-formaldehyde adhesives. The analysis of lignin-based adhesives by FTIR-ATR and TGA showed structural similarity to phenol adhesive. The results demonstrate that the reactivity of lignin was enhanced by isolation from hardwood bioethanol production residues at ambient temperature and it could be used in a value-added application to produce lignin-based adhesives. © 2014 Elsevier B.V. All rights reserved.
1. Introduction With continued depletion of fossil fuel reserves, demand for alternative feedstock to petrochemicals for fuels and energy is growing. Renewable biomass has great potential to serve as an important raw material to replace petroleum-based products. In recent years interest in available wood biomass for bioethanol production has increased worldwide as a result of inflation in food prices caused by increased consumption of starch based crops [1,2]. Wood polysaccharides are converted into monosaccharides during enzymatic saccharification, and the monomer sugar is then converted to bioethanol. Because cellulose modifying enzymes cannot digest lignin, soluble sugars are present with a large volume of insoluble lignin after enzymatic hydrolysis. The residual lignin could be used in value-added production of commercial additives or adhesives instead of being used to generate energy by burning [3,4].
∗ Corresponding author at: Department of Bioenergy Science and Technology, Chonnam National University, Gwangju 500-757, Republic of Korea. Tel.: +82 62 530 2097; fax: +82 62 530 0029. E-mail address: [email protected] (H.-J. Bae). http://dx.doi.org/10.1016/j.ijbiomac.2014.10.020 0141-8130/© 2014 Elsevier B.V. All rights reserved.
Lignin is a highly branched three-dimensional phenylpropanoid polymer with variable functional groups providing reactive sites for chemical modification [5]. However, 50 million tons of lignin extracted during pulp and paper production in 2010 were mostly burned. Only 2% of the recovered lignin was utilized as a powder or as a chemical for industrial production of binders, dispersants, adhesives and surfactants [6–8]. Lignin has been previously considered for use in a based material application as a phenol substitute material due to its similar structure. The precipitated lignin from pulping black liquor produced by common pulping process at high temperatures [9–11] and the by-products from biorefinery [12] are possible sources of lignin that can be used as a phenol substitute. Previously agricultural waste material has been the main source of residual lignin from bioethanol production. For example, residual lignin isolated from enzymatic hydrolysis of corn stalk and Miscanthus (Miscanthus Giganteus) using an alkaline solution and acid-separation treatment [13] could be used in producing ligninphenol formaldehyde adhesives [14]. The residue from bioethanol refineries had a higher reactivity for chemical modification with phenol-formaldehyde (PF) than did the residues from butanol, xylitol and lactic acid from a biorefinery due to their high hydroxyl content [15]. Zhang [16] suggested that lignocellulosic ethanol
S.J. Lee et al. / International Journal of Biological Macromolecules 72 (2015) 1056–1062
residue from agricultural waste biomass could replace phenol, but the replacement of 10% of phenol in their work resulted in a decrease in bonding performance compared to PF adhesives. The major challenge identified in replacing based material as a phenol with lignin is that lignins are less reactive due to the absence of reactive sites for chemical modification [8,17,18]. The lower reactivity of the bioethanol residue is mainly due to its impurity [19]. The residual lignin from the ethanol process of populus wood via acid purification showed high purity but lower carbon content, and contained fewer sites that were reactive to formaldehyde, compared to Kraft lignin [7]. The method of extraction and the source from, which the lignin is purified, have a major influence on the properties of the lignin-based adhesives [4]. Guo [19] compared various isolation methods including benzyl alcohol, dioxane, and ethanol extraction at 50–140 ◦ C, where process conditions at higher temperatures caused volatile solvent loss and there was an increase in operational costs. In the study presented, lignin was isolated by alkaline and organic solvent extraction at ambient temperature from residues generated from enzymatic hydrolysis of oak wood for bioethanol production to improve its purity. The isolated lignin probably has fewer active sites than the lignin from other agricultural waste biomass and softwood due to a higher amount of methoxyl substitution in hardwood lignin. The chemical characteristics of the isolated lignin were determined and quantified to evaluate its reactivity for the chemical modification. The physical bonding properties of prepared adhesives by modification of lignin were compared to those of PF adhesives to assess the potential for high value utilization of the residual lignin from the oak wood the bioethanol process. 2. Materials and methods 2.1. Material Enzymatic hydrolysis residue (ER) was obtained from the process of bioethanol production from oak wood (Quercus acutissima) through popping pretreatment and enzymatic hydrolysis using the modified process of Wi [20]. The obtained ER was washed several times, lyophilized and sieved (
Contents lists available at ScienceDirect
International Journal of Biological Macromolecules journal homepage: www.elsevier.com/locate/ijbiomac
Isolation and characterization of lignin from the oak wood bioethanol production residue for adhesives Soo Jung Lee a , Hyun Joo Kim b , Eun Jin Cho a , Younho Song c , Hyeun-Jong Bae a,b,c,∗ a b c
Bio-energy Research Center, Chonnam National University, Gwangju 500-757, Republic of Korea Department of Forest Products and Technology, Chonnam National University, Gwangju 500-757, Republic of Korea Department of Bioenergy Science and Technology, Chonnam National University, Gwangju 500-757, Republic of Korea
a r t i c l e
i n f o
Article history: Received 18 August 2014 Received in revised form 8 October 2014 Accepted 10 October 2014 Available online 29 October 2014 Keywords: Bioethanol production residue Lignin Reactivity
a b s t r a c t Lignin was isolated from the residue of bioethanol production with oak wood via alkaline and catalyzed organosolv treatments at ambient temperature to improve the purity of lignin for the materials application. The isolated lignins were analyzed for their chemical composition by nitrobenzene oxidation method and their functionality was characterized via wet chemistry method, element analysis, 1 H NMR, GPC and FTIR-ATR. The isolated lignin by acid catalyzed organosolv treatment (Acid-OSL) contained a higher lignin content, aromatic proton, phenolic hydroxyl group and a lower nitrogen content that is more reactive towards chemical modification. The lignin-based adhesives were prepared and the bond strength was measured to evaluate the enhanced reactivity of lignin by the isolation. Two steps of phenolation and methylolation were applied for the modification of the isolated lignins and their tensile strengths were evaluated for the use as an adhesive. The acid catalyzed organosolv lignin-based adhesives had comparable bond strength to phenol-formaldehyde adhesives. The analysis of lignin-based adhesives by FTIR-ATR and TGA showed structural similarity to phenol adhesive. The results demonstrate that the reactivity of lignin was enhanced by isolation from hardwood bioethanol production residues at ambient temperature and it could be used in a value-added application to produce lignin-based adhesives. © 2014 Elsevier B.V. All rights reserved.
1. Introduction With continued depletion of fossil fuel reserves, demand for alternative feedstock to petrochemicals for fuels and energy is growing. Renewable biomass has great potential to serve as an important raw material to replace petroleum-based products. In recent years interest in available wood biomass for bioethanol production has increased worldwide as a result of inflation in food prices caused by increased consumption of starch based crops [1,2]. Wood polysaccharides are converted into monosaccharides during enzymatic saccharification, and the monomer sugar is then converted to bioethanol. Because cellulose modifying enzymes cannot digest lignin, soluble sugars are present with a large volume of insoluble lignin after enzymatic hydrolysis. The residual lignin could be used in value-added production of commercial additives or adhesives instead of being used to generate energy by burning [3,4].
∗ Corresponding author at: Department of Bioenergy Science and Technology, Chonnam National University, Gwangju 500-757, Republic of Korea. Tel.: +82 62 530 2097; fax: +82 62 530 0029. E-mail address: [email protected] (H.-J. Bae). http://dx.doi.org/10.1016/j.ijbiomac.2014.10.020 0141-8130/© 2014 Elsevier B.V. All rights reserved.
Lignin is a highly branched three-dimensional phenylpropanoid polymer with variable functional groups providing reactive sites for chemical modification [5]. However, 50 million tons of lignin extracted during pulp and paper production in 2010 were mostly burned. Only 2% of the recovered lignin was utilized as a powder or as a chemical for industrial production of binders, dispersants, adhesives and surfactants [6–8]. Lignin has been previously considered for use in a based material application as a phenol substitute material due to its similar structure. The precipitated lignin from pulping black liquor produced by common pulping process at high temperatures [9–11] and the by-products from biorefinery [12] are possible sources of lignin that can be used as a phenol substitute. Previously agricultural waste material has been the main source of residual lignin from bioethanol production. For example, residual lignin isolated from enzymatic hydrolysis of corn stalk and Miscanthus (Miscanthus Giganteus) using an alkaline solution and acid-separation treatment [13] could be used in producing ligninphenol formaldehyde adhesives [14]. The residue from bioethanol refineries had a higher reactivity for chemical modification with phenol-formaldehyde (PF) than did the residues from butanol, xylitol and lactic acid from a biorefinery due to their high hydroxyl content [15]. Zhang [16] suggested that lignocellulosic ethanol
S.J. Lee et al. / International Journal of Biological Macromolecules 72 (2015) 1056–1062
residue from agricultural waste biomass could replace phenol, but the replacement of 10% of phenol in their work resulted in a decrease in bonding performance compared to PF adhesives. The major challenge identified in replacing based material as a phenol with lignin is that lignins are less reactive due to the absence of reactive sites for chemical modification [8,17,18]. The lower reactivity of the bioethanol residue is mainly due to its impurity [19]. The residual lignin from the ethanol process of populus wood via acid purification showed high purity but lower carbon content, and contained fewer sites that were reactive to formaldehyde, compared to Kraft lignin [7]. The method of extraction and the source from, which the lignin is purified, have a major influence on the properties of the lignin-based adhesives [4]. Guo [19] compared various isolation methods including benzyl alcohol, dioxane, and ethanol extraction at 50–140 ◦ C, where process conditions at higher temperatures caused volatile solvent loss and there was an increase in operational costs. In the study presented, lignin was isolated by alkaline and organic solvent extraction at ambient temperature from residues generated from enzymatic hydrolysis of oak wood for bioethanol production to improve its purity. The isolated lignin probably has fewer active sites than the lignin from other agricultural waste biomass and softwood due to a higher amount of methoxyl substitution in hardwood lignin. The chemical characteristics of the isolated lignin were determined and quantified to evaluate its reactivity for the chemical modification. The physical bonding properties of prepared adhesives by modification of lignin were compared to those of PF adhesives to assess the potential for high value utilization of the residual lignin from the oak wood the bioethanol process. 2. Materials and methods 2.1. Material Enzymatic hydrolysis residue (ER) was obtained from the process of bioethanol production from oak wood (Quercus acutissima) through popping pretreatment and enzymatic hydrolysis using the modified process of Wi [20]. The obtained ER was washed several times, lyophilized and sieved (
