Valorization of Willow Lignin Recovered in a Pilot-scale Biorefinery Based on Hot Water Extraction
Aditi Nagardeolekar, Mathew Ovadias, Kuo‐Ting Wang, Christopher Wood and Biljana Bujanovic*
SUNY‐ESF, Department of Paper and Bioprocess Engineering, Syracuse, NY – 13210.
Introduction:
The United States consumed a record 101 quadrillion British thermal units (Btu) worth of energy in the year 2018. Fossil fuels contributed to 80% of this energy. Primary sources of energy under focus in the US have undergone several changes over the course of history. These include wood in the 18th and 19th centuries, later coal and petroleum, followed by renewable sources, such as nuclear energy in the 20th century and more recently, modern renewable sources, such as hydropower, biomass, wind and solar in the 21st century. Modern renewable sources contributed to ~11.4% of the total energy consumption in the year 2018[1]. With energy research becoming increasingly focused on the renewable resources, coal consumption has fallen to the lowest since year 1970[1]. Biomass has been the largest renewable energy source for the last several years, making up around 44% of the total renewable energy and ~5% of the total energy consumed in the US in the year 2018[2]. It is estimated that ~331 million Mg of biomass is used annually in the US for energy production with an additional 750 million to 1 billion Mg of biomass being potentially available, while still meeting food, feed, and fiber demands[3]. The world‐ wide interest in biomass as an energy source has largely been stimulated by the heightened threat of climate change caused by emission of greenhouse gases. Latest agricultural growth has enabled biomass surplus, while the technological growth has enabled higher biomass to energy conversion efficiency[4]. Several types and species of biomass have been suggested as potential energy crops. An ideal energy crop is expected to have following characteristics: high yield of dry biomass per hectare, low cost and energy input to produce, low nutrient requirements, and low amounts of contaminants within the biomass[4]. Short rotation woody plants such as willow (Salix spp.) and herbaceous plants such as perennial grass miscanthus (Miscanthus spp.) fit well into these criteria. Previous experiments in our research group have focused on utilization of miscanthus biomass[5], while current experiments focus on willow. Willow, a short rotation coppice has been increasingly researched as a dedicated energy crop in the US over the past several years, e.g. as a part of the Salix Consortium’s Willow Biomass project, under which willow biomass has been planted in the Northeastern and Midwestern regions of the US[6]. Commercial willow biomass has been planted over 500 hectares in the Northeast region alone[3]. In the NY State, the average yield of Salix clones is 13.6 odt/ha/year, with minimal chemical and energy input (net energy ratio of 55)[6]. In addition to the high yields that can be sustained in 3‐4 years rotation, willow has a favorable chemical composition and energy content (average 8340 Btu/dry pound of three‐ year old willow stems)[7]. It also offers an easy propagation from dormant hardwood cuttings, wide genetic base for selective breeding, and an ability to sprout back after multiple harvests. Therefore, it is suitable to select for specific characteristics and to sustain[8]. In addition to energy provision, willow biomass is expected to provide economical benefits such as creation of new markets and jobs in rural areas. Also, it allows an array of environmental benefits, such as enhanced landscape diversity and wildlife habitat, increased erosion resistance due to its perennial nature and extensive fine root systems, carbon sequestration, significant reduction in greenhouse gas, NOx, SO2 and particulate emissions during energy production and land remediation[3][6][7][8]. Willow, however, is a lignocellulosic biomass (typical composition: extractives 2‐10%; lignin 20‐26%; glucose 35‐42%; xylose 20‐25%; mannose, galactose, arabinose, glucuronic acid 3‐6%; acetic acid 3‐4%)[9] and hence, presents recalcitrance toward the chemical and/or mechanical treatments employed to harness the energy and the chemicals within the biomass.
In this report, we outline the results of applying hot‐water extraction (HWE) as the first step toward utilization of willow biomass for the production of a wide range of products, including chemicals and materials/polymers, in biorefineries. Hot‐water extraction (autohydrolysis) is a suggested pretreatment ideal for xylan‐rich angiosperms, viz. hardwoods and grasses[10]. It is an environmentally preferred process, which only uses water at subcritical conditions, thus eliminating the costs associated with use and recovery of harmful chemicals, and which has moderate energy requirements in contrast to supercritical hydrothermal treatments. Its goal is to selectively remove xylan‐based hemicelluloses, by up to 80% of the original xylan content, while leaving cellulose mostly intact[10,11]. Lignin is also partially removed during this process[12]. Applications of cellulose and hemicelluloses have been well explored in literature. The cellulose‐enriched biomass can be utilized in a wide range of cellulose fiber based applications, while the removed xylan‐based carbohydrates can be recovered from the hydrolyzate and further utilized to produce an array of chemicals such as ethanol, furfural, lactic acid and polyhydroxyalkanoates [10,13,14]. Lignin on the other hand has been traditionally underutilized, mainly treated as a waste and burned for energy[15]. However, lignin is the most abundant naturally occurring aromatic polymer, which offers a range of favorable characteristics: a large number of chemically‐reactive sites, film‐forming ability, high carbon content, compatibility with a large number of industrial chemicals, good UV and mechanical stability, moderate thermal stability, good rheological and viscoelastic properties and availability in high volumes at relatively low cost[15]. Considering a critical need to increase use of lignin in biorefineries, this report also outlines the exploratory results of lignin recovered from willow hot‐water hydrolysate for use in synthesis of hydrogels. These hydrogels were synthesized for potential applications in agriculture (for sustained release of bioactive solutions, such as pesticides, fertilizers, and pharmaceuticals) and in wastewater treatment (by selective adsorption of textile dyes and metal ions). Additionally, this lignin has also been evaluated for the production of thermoplastic materials in blends with polylactic acid (PLA), one of the most commercially available biopolymers. Lignin‐PLA blends may be utilized as a packaging material with lignin being an antioxidant and providing UV absorbing functionality[16–18]. Both of these properties would extend the lifetime of the material by preventing free radicals and UV light from degrading PLA[19]. Willow lignin was explored as recovered from the hydrolysate of hot water extraction of willow, and also after esterification, which was performed to improve lignin compatibility with PLA. Lignin esterification replaces the free hydroxyl groups, which are thought to inhibit compatibility with plastics, with a hydrocarbon chain through an ester linkage. Two methods of esterification were considered to improve lignin compatibility with PLA in the production of a thermoplastic blend. These two methods included a short‐chain esterification, acetylation (C2–saturated hydrocarbon chain), and a long‐chain fatty acid esterification with lauric acid
(C12–saturated hydrocarbon chain), as described in later sections. The reported studies have a goal to suggest applications for lignin as an underutilized component of willow biomass, in order to promote willow, a short rotation energy crop (SRWC), as a resource for not only energy, but also for novel bio‐based products for additional revenues in a modern biorefinery.
Experimental Materials and Methods:
1. Biomass: Willow biomass (Salix spp., Family: Salicaceae; a blend of commercial cultivars with bark) was provided by Dr. T. Volk from SUNY‐ESF Tully Field Station. The biomass was milled into approximately 2 cm long chips and was stored covered in super sacks until it was used for the experiment, at an average moisture content of 20.1%w/w.
2. Pilot Scale HWE of Willow Biomass: HWE was performed in a 65ft3 capacity stainless steel lined digester (Struthers‐Well, Santa Fe Springs, CA, USA; one experiment), at 160oC, for 2 hours, with P‐factor of 691 (Table 1)[20]. The digester was heated with a combination of direct steam injection and indirect heating system.
Table 1: Loading and operating conditions for hot‐water extraction of willow biomass
Variable Value
Biomass chip size ~20mm
Biomass loading weight 244.21 kg OD
Deionized water/biomass 4.5
Time to ramp up to 160oC 51 minutes
The extracted chips were washed with tap water of volume equivalent to that of the hydrolyzate. The resultant biomass was then air dried, and ground to #30 mesh particle size for further characterization.
3. Willow Lignin Recovery from the Hot‐water Hydrolyzate: The hydrolyzate in the storage tank was acidified to pH 2 with 20% sulfuric acid to precipitate the dissolved lignin. The precipitation process was aided by storing the acidified hydrolyzate in a cold room at 8oC for several days. The precipitated lignin was separated from the supernatant by decantation. The lignin recovered from the willow hot‐water hydrolyzate (henceforth referred to as ‘willow lignin’) was then air dried and was used for further characterization and for preparation of hydrogels and composite films.
4. Characterization of Willow Biomass and Willow Lignin: The chemical composition of willow biomass, before and after HWE, and recovered lignin (extractives, carbohydrates, lignin, ash, and cellulose content), free phenolic hydroxyl group content of biomass and molecular weight distribution of recovered lignin were determined as reported in our previous publication[5]. Free phenolic hydroxyl group content of recovered lignin was determined by UV differentiation method and P‐NMR method[21]. 5. Synthesis of hydrogels from willow lignin: Lignin acrylamide hydrogels were prepared by graft polymerization of acrylamide on willow lignin in presence of initiator ammonium persulfate (APS), cross linker N,N’‐methylene bisacrylamide (NMBA) and kaolin clay[22]. Briefly, 1.5 g of kaolin was dispersed in deionized water under constant stirring in vacuum. 1g of acrylamide and 300mg of willow lignin were then incorporated into the kaolin‐water dispersion, followed by addition of 150mg of APS and 50mg of NMBA. The reaction mixture was then immediately immersed into a bath sonicator maintained at 50oC and 40kHz to aid hydrogel formation (Branson 3510 Ultrasonic Cleaner, Branson Ultrasonics Corp, Danbury, CT, USA). Lignin‐poly(ethylene glycol) diglycidyl ether (PEGDGE) hydrogels were made by cross linking PEGDGE grafted lignin units in presence of alkali and hydrogen peroxide[23]. Briefly, 1g of willow lignin was dissolved in 1.6ml of 3.3M sodium hydroxide solution, and was activated with 5%v/v hydrogen peroxide. 1 mmol PEGDGE was then grafted onto per gram of activated lignin units. Both hydrogels were frozen immediately after synthesis and lyophilized to remove water without inducing shrinkage and associated pore deformities (Labconco FreeZone 4.5 liter freeze dry system, Labconco Corporation, Kansas City, MO, USA).
6. Applicability tests on the synthesized hydrogels: Moisture‐free lignin‐PEGDGE hydrogel was broken into small roughly polygonal irregular pieces (~0.5cm thick, 0.5‐1cm long, ~0.5cm wide), which were immersed in an ascorbic acid solution (1mg/ml) for 30 minutes, to check the absorption capacity of the hydrogel when in contact with a bioactive solution. The pieces were weighed before and after contact with ascorbic acid solution and the swelling degree was calculated using Equation 1.
Swelling degree, Q = 609%.
Q = (Ws – Wd) / Wd*100%;
(Ws = Weight of swollen hydrogel, Wd = weight of dry hydrogel) …..Eqn (1)
Similarly, moisture free lignin‐acrylamide hydrogel was also broken into pieces, which were immersed in a cationic dye solution (methylene violet, 40μM) for 2 hours, to measure the selective adsorption of pollution‐causing cationic dye molecules on the hydrogel surface. Concentration of the dye solution was measured before and after contact with the hydrogel. Alternately, the hydrogel pieces were immersed in a solution of metallic ions overnight (silver nitrate, 0.01N). Accumulation of silver ions on the uncoated hydrogel surface was then observed under a scanning electron microscope (JEOL JSM IT100LA InTouch Scanning Electron Microscope, JEOL USA Inc, Peabody, MA, USA) in low‐vacuum BEC mode (AV 15kV, WD 11mm, 30Pa, 370x) and further analyzed in EDS mode.
7. Synthesis of Willow Lignin Ester Derivatives:
Willow lignin was functionalized by two methods of esterification; acetylation and long‐chain fatty acid esterification (FAE). For acetylation, willow lignin was dissolved into 20 mL/g‐lignin of pyridine and acetic anhydride (1:1 v/v). The solution was allowed to mix on a stir plate for at least 24 hours and up to 72 hours in order to ensure complete acetylation[24]. The acetylated lignin was precipitated by pouring the solution into 300 mL of ice‐cold water for one gram of starting lignin. Once the acetylated lignin had completely precipitated the mixture was vacuum filtered and washed with ice‐cold water to remove excess pyridine, acetic anhydride and acetic acid (a byproduct of the reaction). The acetylated lignin was dried overnight in a vacuum oven (40 °C) prior to use in lignin‐PLA blends. Willow lignin was subjected to FAE by dissolving into 30 mL of N, N‐dimethylformamide per gram of lignin in the presence of pyridine (5.5 mL) and triethylamine (1.5 mL). Once the solution was homogenized, 1.2 mmol‐lauroyl chloride/mmol‐OH, a chloride derivative of lauric acid, was added to start the reaction. The reaction was allowed to proceed for 2 hours while mixing on a stir plate. The FAE lignin was precipitated by pouring the solution into 600 mL of ice‐cold 2% HCl for one gram of starting lignin. The mixture was vacuum filtered and washed with ethanol and water (1:1 v/v) to remove excess solvent, catalyst and unbound fatty acid. The FAE lignin was dried overnight in a vacuum oven (40 °C) prior to future use[25]. It was determined that washing was not able to sufficiently remove the unbound fatty acid. Therefore, hexane extraction was attempted to remove the unbound fatty acid by soaking one gram of the FAE lignin in 10 mL of hexanes for 30 minutes, decanting the solvent and repeating once more. The FAE lignin after hexane extraction was allowed to air dry in the hood overnight then placed in a vacuum oven (40 °C) for 24 hours prior to use in lignin‐PLA blends.
8. Characterization of Lignin Ester Derivatives:
Fourier‐transform infrared (FTIR) spectroscopy of lignin samples was conducted on a PerkinElmer Frontier FT‐IR/NIR Spectrometer. Calibration was done with no sample loaded, and the spectra averaged over 16 readings. Sample analysis was conducted by loading the sample evenly over the beam and recording the spectra from 4,000 cm‐1 to 650 cm‐1, averaged over 16 readings.
Phosphorous NMR (31P NMR) was done to determine the hydroxyl group content of the lignin‐ester derivatives in comparison the crude HWE recovered willow lignin[26]. Thermal properties of lignin samples were analyzed by Differential Scanning Calorimetry (DSC) for the glass transition temperature
(Tg) and melt temperature (Tm) with a TA Instruments Q200 and Thermogravimetric Analysis (TGA) for the degradation temperature (Td) with a TA Instruments Q5000. DSC samples were heated from room temperature to 160 °C at 2 °C/min under a N2 atmosphere. An empty pan was used as a reference. The
Tg was determined to be the start of the endothermic slope while the Tm was measured at the bottom of the endothermic valley. TGA samples were heated from room temperature to 700 °C at 10 °C/min under a N2 atmosphere. The Td was identified as (the) peak(s) of the rate of the thermogravimetric change (dm/dT).
9. Production of lignin‐PLA blends:
PLA blends with lignin were produced with a Dynisco Laboratory Mixing Extruder (with a 1/8 inch die). PLA pellets, grade 2003D, were purchased from NatureWorks LLC. Alkali lignin was from Sigma‐Aldrich; as the most abundant technical lignin available today, this lignin served for comparison in this study. Willow lignin, acetylated willow lignin, and FAE willow lignin (before and after hexane extraction) were each blended with PLA via extrusion. The pellets were prepared by drying overnight in the vacuum oven (40 °C) prior to use. For lignin‐PLA blends the lignin of choice was dissolved in acetone and the solution was used to coat the pellets with lignin. Following this step the lignin coated PLA pellets were dried in the hood overnight and then the vacuum oven (40 °C) for 24 hours. The mass of the pellets were recorded at each step to monitor the exact lignin content of the blends.
For 100% PLA and lignin‐PLA blends of 1% lignin content by mass, the screw and die of the extruder were heated to 180 °C and 170 °C, respectively. Blends with higher than 1% lignin content required the screw and the die to be heated to 200 °C and 190 °C, respectively. Once the temperature of the extruder stabilized the extruder was set at 15‐30 rpm (varied between blends for optimal production) and the pellets were loaded into the hopper and extruded. The resulting filament was cut into 3 inch rods and stored in a conditioning room consistent with ASTM D618 for at least 72 hours prior to analysis and characterization.
10. Analysis of Lignin‐PLA Blends:
The resulting 1% lignin blends were examined under a Nikon Eclipse E600 light microscope to observe which of the studied lignins had the greatest compatibility (homogeneity) or least aggregates of lignin.
Elongation tensile tests of all blends were conducted in accordance with ASTM standard D638, utilizing a MTS Sintech 1/S Elongation Tensile Tester and calculations by TestWorks 4 software. The samples were tested in the form of 3‐inch rods. The diameter of each rod was measured in three different spots and averaged for the final diameter used in calculations. Fixed serrated grips were utilized with an initial distance between grips to be 1 inch and an initial speed of elongation to 5 mm/min. A load cell rated for up to 1,250 N and a grip pressure of 60 psi were employed. A stress vs strain curve was produced for each sample. The tensile strength (peak stress), strain at peak, strain at yield, and the elastic modulus were calculated based on the stress vs strain curve consistent with ASTM D638.
UV absorbance of the 1% acetylated lignin‐PLA blend was compared to that of 100% PLA by dissolving the blends in chloroform. Samples were further diluted, if necessary to obtain absorbance values within the specifications (0.1‐2.0 Abs) for the spectrophotometer used. A Thermo Scientific Genesys UV Vis Scanning Spectrophotometers 10S was used to collect the spectra of each blend from 200‐400 nm. A baseline was collected over this range using chloroform. The total area under each curve was used to compare the UV absorbing properties of each blend.
Results and Discussion:
1. HWE Yield and Hydrolyzate pH:
The yield of HWE process (solid willow biomass recovered after extraction, EW) was 77.5%w/w of the initial mass, while the hydrolyzate pH was mildly acidic at 3.87. This yield is higher than the yields observed at pilot scale for Miscanthus spp. (67%w/w), another energy crop of interest, and wheat straw (Triticum spp.; 62%w/w), but is similar to that of another hardwood species, sugar maple (Acer Saccharum; 77%w/w)[5,10]. The relatively higher digester yields of hardwoods as compared to the graminaceous biomass imply that chemical constituents of graminaceous biomass are more accessible for dissolution under the conditions of HWE as compared to the hardwoods. The higher water/biomass ratio used in case of the graminaceous biomass is also a contributing factor (8 instead of typical value of 4.5 used for hardwoods [10]).
2. Chemical Composition of Willow Biomass Before (W) and After Hot‐water Extraction (EW):
In terms of the content of extractives, ethanol/toluene (1/2, v/v) solvent mixture (ET[27]) was the most effective on untreated willow and removed extractives similar in amount as reported in literature for willow[28], while dichloromethane (DCM; ideal for extractives rich in waxes, fats, resins, sterols and non‐volatile hydrocarbons) was the most effective on hot‐water extracted willow (Table 2). As reported in our previous studies on Miscanthus spp. and sugar maple, the content of extractives increased after HWE regardless of the solvent used, possibly due to an increased porosity of the biomass. An increased porosity has been also considered to contribute to an easier delignification of biomass after HWE[5,29]. Contents of the three major components in the untreated biomass – cellulose, lignin and hemicelluloses, were found to be a relatively good agreement with average reported values for willow cultivars (Table 2 and Table 3)[28,30,31]. HWE was successful in retaining most of the cellulose originally present in willow biomass, while selectively removing ~49% hemicelluloses (xylose), and causing partial delignification by ~17% and deashing / removal inorganic compounds by ~45%, relative to original individual amounts of lignin and ash, respectively. These results are also in agreement with previously reported studies on HWE[30]. The extent of xylose removal is lower in case of willow as compared to other hardwoods, which may be attributed to the presence of bark on willow chips, which has a significantly different chemical composition than debarked xylem[5,10,11]. The almost two‐fold decrease in the acetate content and five‐fold increase in the free phenolic hydroxyl group content (PhOH) in the hot‐water extracted willow biomass demonstrate that the reactions of deacetylation and the cleavage of acid‐ labile aryl ether (α‐O‐4 and β‐O‐4) and/or phenylglycosidic bonds take place during HWE [5].
Table 2: Chemical Composition of Willow Biomass Before (W) and After Hot‐water Extraction (EW) (% OD) Original Weight
Component W EW
ET (1:2) extractives1 3.83 9.12
DCM extractives2 1.45 5.00
AW (9:1) extractives3 2.95 ‐
Seifert Cellulose4 36.94 0.03 50.62 0.57
Average Cellulose removal5 ‐ 0
Klason lignin 22.50 0.06 25.58 0.10
Acid soluble lignin 2.42 0.22 1.21 0.07
Total lignin 24.92 0.16 26.79 0.12 Average Lignin removal5 ‐ 16.69
Ash 1.47 0.01 1.05 0.04
Average Ash removal5 ‐ 44.64
PhOH (mmol/g lignin) 6 0.36 0.00 1.69 0.00
1 ET: ethanol/toluene 2 DCM: dichloromethane 3 AW: Acetone/water 4 The seifert cellulose was corrected for residual lignin 5 Component removal =
100*[{content (W) – content (EW) * digester yield}]/content (W) 6 PhOH: free phenolic hydroxyl group content
Table 3: Carbohydrate Composition of Willow Biomass Before (W) and After Hot‐water Extraction (EW) (% OD); Results include hydroxymethyl furfural (HMF) as xylose degradation product and acetate resulting from deacetylation
Component W EW
Glucose (Glucan)1 36.13 (32.52) 48.15 (43.33)
Glucose loss2 ‐ 0
Xylose (Xylan)1 12.59 (11.08) 8.28 (7.29)
Xylose loss2 ‐ 49.03
Arabinose (Arabinan) 0.47 0.00
HMF 0.83 0.36
Acetate 0.13 0.07
1 The conversion factors from glucose and xylose to glucan and xylan are 0.9 and 0.88, respectively. 2 Component removal = 100*[{content (W) – content
(EW) * digester yield}]/content (W)
3. Characterization of Willow Lignin:
The yield of willow lignin was ~0.6% w/w OD initial biomass, which is equivalent to~2.5% w/w total lignin in the starting biomass and ~15%w/w lignin dissolved in the hydrolyzate (Table 4). This yield is much lower than the lignin recovery yields observed for other hardwoods (e.g. sugar maple, 47% dissolved lignin) as well as grasses (e.g. miscanthus, 25% dissolved lignin), but higher than that observed for apricot pit shells (5% dissolved lignin)[5,29,32]. The low yield implies a greater extent of lignin depolymerization through the cleavage of acid‐labile bonds resulting in low‐molecular weight, hydrophilic lignin fragments that do not precipitate readily even at a lower pH and lower temperatures. Presence of polyphenolic constituents contributed by the bark may also be responsible for an increased solubility of these lignin fragments, making recovery difficult. The fragmented nature of willow lignin is also evident by its polydispersity of 2, and a higher PhOH content of the recovered lignin (>2 mmol PhOH/ g lignin) relative to milled wood lignin (1.1 mmol PhOH/g MWL)[33]. The two different methods used for determination of PhOH gave relatively congruous values. The detailed carbohydrate analysis showed glucan and xylan as the main contaminants in the recovered lignin (Table 5).
Table 4: Characteristics of Willow Lignin
Variable (unit) Value
Yield (% OD biomass) 0.61
Yield (% lignin dissolved) 14.80
Mn (Da) 2588.98
Mw (Da) 5201.60
Polydispersity 2.0
PhOH (mmol/g) UV method 2.11 0.009
PhOH (mmol/g) P‐NMR method 2.91
Acetyl bromide coefficient (lg‐1cm‐1) 15.5
Table 5: Chemical Composition of Willow Lignin (%OD Lignin)
Component1 Content
Klason lignin 80.2
Acid soluble lignin 4.48
Total lignin 84.68
Xylan 1.19
Glucan 1.19
Mannan 0.6
Total carbohydrates 2.98
Ash 0.2 1 Analysis was performed at the USDA ‐ Forest Products Laboratory, Madison, WI, USA 4. Synthesis and Characterization of Hydrogels from Willow Lignin:
Both types of hydrogels (Lignin‐PEGDGE, Figure 1a and lignin‐acrylamide, Figure 1b) were mechanically strong, being able to withstand loads of up to 800x dry weight. Lignin‐PEGDGE hydrogel was found to have good absorption capacity for bioactive solutions. The hydrogel absorbed ascorbic acid solution equivalent to ~6 times its dry weight within 30 minutes. The size of the hydrogel increased noticeably after the absorption, and the swelling degree (Q) was calculated as 609 (Figure 2).
1a 1b
Figure 1: Low Density Lignin‐PEGDGE Hydrogel (1a) and Lignin‐Acrylamide Hydrogel (1b) Balanced on Grass.
2a 2b
Figure 2: Lignin‐PEGDGE hydrogel Before (2a) and After (2b) Contact with Ascorbic Acid Solution for 30 minutes.
Lignin‐acrylamide hydrogel was found to have good adsorption capacity for cationic molecules. The hydrogel decreased the concentration of methylene violet dye by 87.5% within 2 hours of contact, leaving a visibly cleaner solution behind (Figure 3). The hydrogel was also able to accumulate silver (Ag+1) ions on its surface removing them from solution of silver nitrate after overnight contact (Figure 4).
3a 3b
Figure 3: Decrease in the Concentration of Methylene Violet Dye from 40μM (3a) to 5μM (3b) Two Hours After Selective Adsorption of the Dye on the Surface of Lignin‐Acrylamide Hydrogel 002 002 4a 4b5.0 5.0
Al 4.0 Ag 4.0 Si +3] +3] 3.0 3.0
O O Al C Si Ag ounts[x1.E ounts[x1.E 2.0 C 2.0 Ti C Cl C N Ti S Ag 1.0 1.0 Ag Cl N S K K Ti Ti
0.0 0.0 0.00 1.00 2.00 3.00 4.00 5.00 6.0 0.00 1.00 2.00 3.00 4.00 5.00 6.00 keV keV
Figure 4: Energy Dispersion Spectra of Lignin‐Acrylamide Hydrogel Before (4a) and After (4b) Overnight Contact with Silver Nitrate Solution, Showing Appearance of a Peak for Ag after Adsorption (4b)
5. Characterization of Willow Lignin Ester Derivatives:
To assess the impact of derivatization, the FT‐IR spectra of the lignin samples were analyzed from 4000‐ 1400 cm‐1 (Figure 5). It can be observed that the absorption from 3500‐3400 cm‐1, which correlates to hydroxyl groups[34], has been greatly diminished following derivatization. In addition, the spectra of
Figure 5: FT‐IR Spectra of Willow Lignin and Willow Lignin Derivatives (‡‐ Indicates either an ester linkage with aromatic ring at 1760 cm‐1 or aliphatic chain at 1740 cm‐1) lignin derivatives display a band that may be assigned to the ester linkages formed in the reaction with phenolic hydroxyl groups of lignin (1760 cm‐1)[25]. The FT‐IR results revealed that only the acetylated ‐1 lignin spectra showed the formation of aliphatic ester linkages at Cα and Cγ (1740 cm )[25]. It may be hypothesized that larger hydrocarbon chains result in steric hindrance that obstructs FAE of primary and secondary aliphatic hydroxyl groups less than of free phenolic hydroxyl groups. Prior to hexane extraction the FT‐IR spectra FAE lignin showed a strong band at about 1700 cm‐1 that represents the unbound fatty acid[35]. Following hexane extraction this band was no longer present indicating that hexane extraction is successful in removing the unbound fatty acid from the FAE lignin.
Hydroxyl group content of the lignin ester derivatives in comparison with that of the willow lignin was analyzed through 31P NMR (Figure 6). Willow lignin following acetylation was observed to have 100% degree of substitution of the phenolic and aliphatic (primary and secondary) hydroxyl groups while following FAE was 89%. However, following FAE the sample contained a large amount of carboxylic acid hydroxyl groups (1.74 mmol /g) compared to willow lignin (0.64 mmol /g). This confirmed that the free fatty acid was still present as indicated by FT‐IR analysis (Figure 5). Hexane extraction was also confirmed to be able to effectively reduce levels of the free fatty acid. This was indicated by the reduction in carboxylic acid hydroxyl groups (0.53 mmol/g) from prior to hexane extraction. Analysis of hydroxyl group content also showed that the degree of substitution following hexane extraction dropped to 80% indicating that hexane may solubilize some of the highly substituted lignin fractions.
Figure 6: Hydroxyl Group content of Lignin Samples by 31P NMR (W‐HWE Willow Lignin; WAc‐Acetylated Willow Lignin; W[H]FAE‐FAE Willow Lignin after Hexane Extraction)
In addition to providing the Tg and Tm from DSC (Figure 7) and Td from TGA (Figure 8), thermal analysis revealed that during derivatization lignin also went through the purification process as impurities such as carbohydrates and low molecular weight compounds were reduced. The DSC curve for willow lignin displayed two Tgs, with the more distinct lower Tg representing impurities. Willow lignin derivatives and alkali lignin did not display more than one Tg. TGA of willow lignin exhibited a broad degradative shoulder from 100‐200 °C prior to the lignin degradation above 350 °C. Meanwhile, alkali lignin did not display the degradative shoulder from 100‐200 °C. The willow lignin derivatives have a narrower but stronger degradation peak just above 200 °C but the shoulder is no longer present. This narrower peak may represent the degradation of the acetyl or fatty acid (unbound or bound) groups. This is due to this peak being notably greater for the FAE willow lignin, which was observed to have a large amount of unbound fatty acid in addition to bound fatty acid in the FT‐IR spectra (Figure 5). As expected [34], the Tg of lignin decreased after derivatization [34]. The FAE willow lignin was the only lignin detected to possess Tm; however, this may be a result of the large amount of unbound fatty acid. Figure 7: DSC Curves for Lignin Samples
Figure 8: TGA of Lignin Samples
6. Analysis of Lignin‐PLA Blends: Lignin‐PLA blends produced with 1% lignin by mass were examined via light microscopy to assess the homogeneity of blends (Figure 9). Underivatized alkali lignin and willow lignin blends were analyzed as references to ensure improvement in compatibility following esterification. Acetylated lignin was observed to have the best compatibility with PLA and was selected to be blended with PLA at
A B C D E
Figure 9: Light Microscopy Images of 1% Lignin‐PLA Blends (A‐100% PLA; B‐Alkali Lignin (Sigma‐Aldrich); C‐Willow Lignin; D‐FAE Willow Lignin after Hexane Extraction; E‐Acetylated Willow Lignin) concentrations greater than 1% by mass.
Mechanical properties of lignin‐PLA blends (Figure 10) overall, deteriorated with the addition of alkali or willow lignin. The 1% acetylated willow lignin blends maintained the mechanical properties when compared to 100% PLA. However, at concentrations of more than 1% lignin by mass, mechanical properties began to decrease. The higher concentrated acetylated willow lignin‐PLA blends still had improved strain and elastic modulus when compared to the 1% willow lignin‐PLA blends while peak stress was depleted even below that of the 1% alkali lignin‐PLA blends.
FigureFigure 11: 11: Mechanical Mechanical Properties Properties of of Lignin Lignin‐PLA‐PLA Blends: Blends: Clockwise Clockwise from from upper upper left: left: Peak Peak stress, stress, strain strain at peakatstrain peak, atstrainyield atelastic yield, elasticmodulus modulus(AL‐Alkali (AL‐Lignin;Alkali Lignin;W‐HWE WWillow‐HWE WillowRecovered RecoveredLignin; Lignin;WAc‐Acetylated WAc‐ Acetylated Willow Lignin; W[H]FAE‐FAE Willow Lignin after Hexane Extraction) The UV absorbance of the 1% acetylated willow lignin‐PLA blend was compared to that of the 100% PLA to ensure that UV absorbance capacity was added through the blending with acetylated willow lignin (Figure 11). After taking the total area under each curve it can be seen that the total UV absorbance of
A =0.300 241
A =0.164 280
A =0.073 240 Area=22.02 A =0.015 280 Area=2.72
Figure 10: UV Absorbance of 1% Acetylated Willow Lignin‐PLA Blend and 100% PLA the acetylated lignin‐PLA blend was more than eight times greater than that of the 100% PLA.
Conclusions:
These studies demonstrate suitability of Willow spp. as a fast‐growing energy crop in NY‐based biorefineries at pilot scale, and its applicability as a source for deriving novel lignin‐based products. The willow biomass used in this study contained bark that is characterized by less xylans and a greater content of polyphenolics. This resulted in a lower hemicellulose removal and a lower yield of lignin recovery from hot‐water extraction (HWE) in comparison with other hardwoods and energy crops. Nevertheless, the HWE process was found to be an effective pretreatment for harnessing the energy and chemicals from the willow biomass. In addition to the cellulose‐rich residue and the removed hemicelluloses that can be used for different applications, the partially removed lignin can also be recovered and utilized. The recovered lignin was found to be suitable for use in synthesis of lignin‐based hydrogels which are effective sorbents, and in production of lignin‐PLA blends which can provide valuable UV protection to the packaging material and its contents while maintaining desired mechanical properties of PLA, both of which are applicable in a variety of fields.
Acknowledgments: This work was supported by NYSERDA Agreement 63029 (SUNY‐RF, for enhancing quality of lignocellulosic pellets) and the USDA‐McIntire Stennis: (Lignin‐based thermoplastics grant). We wish to thank USDA‐Forest Product Laboratories (Madison, WI): Fred Matt and Sally Ralph; Oak Ridge National Laboratory (Knoxville, TN): Dr. Xianzhi Meng; Arthur Stipanovic, David Kiemle for their valuable help in chemical analyses and Timothy Volk for providing willow biomass.
References:
1. Petroleum, natural gas, and coal continue to dominate U.S. energy consumption ‐ Today in Energy ‐ U.S. Energy Information Administration (EIA) Available online: https://www.eia.gov/todayinenergy/detail.php?id=40013 (accessed on Aug 2, 2019). 2. U.S. Energy Information Administration (EIA) ‐ Data Available online: https://www.eia.gov/totalenergy/data/browser/index.php?tbl=T01.03#/?f=A&start=1949&end=2 018&charted=1‐2‐3‐5‐12‐13 (accessed on Aug 2, 2019). 3. Langholtz, M.; Eaton, L.; Davis, M.; Shedden, M.; Brandt, C. Economic comparative advantage of Willow biomass in the northeast USA. Biofuels Bioprod. Biorefining 2019, 13, 74–85. 4. Energy production from biomass (part 1): overview of biomass. Bioresour. Technol. 2002, 83, 37– 46. 5. Wang, K.‐T.; Jing, C.; Wood, C.; Nagardeolekar, A.; Kohan, N.; Dongre, P.; Amidon, T.E.; Bujanovic, B.M.; Wang, K.‐T.; Jing, C.; et al. Toward Complete Utilization of Miscanthus in a Hot‐Water Extraction‐Based Biorefinery. Energies 2018, 11, 39. 6. Life cycle energy and environmental benefits of generating electricity from willow biomass. Renew. Energy 2004, 29, 1023–1042. 7. Downing, M.; Eaton, L.M.; Graham, R.L.; Langholtz, M.H.; Perlack, R.D.; Turhollow Jr, A.F.; Stokes, B.; Brandt, C.C. U.S. Billion‐Ton Update: Biomass Supply for a Bioenergy and Bioproducts Industry; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States), 2011; 8. Keoleian, G.A.; Volk, T.A. Renewable Energy from Willow Biomass Crops: Life Cycle Energy, Environmental and Economic Performance. Crit. Rev. Plant Sci. 2005, 24, 385–406. 9. Serapiglia, M.J.; Cameron, K.D.; Stipanovic, A.J.; Smart, L.B. Analysis of Biomass Composition Using High‐Resolution Thermogravimetric Analysis and Percent Bark Content for the Selection of Shrub Willow Bioenergy Crop Varieties. BioEnergy Res. 2009, 2, 1–9. 10. Amidon, T.E.; Wood, C.D.; Shupe, A.M.; Wang, Y.; Graves, M.; Liu, S. Biorefinery: Conversion of Woody Biomass to Chemicals, Energy and Materials. J. Biobased Mater. Bioenergy 2008, 2, 100– 120. 11. Duarte, G.V.; Ramarao, B.V.; Amidon, T.E.; Ferreira, P.T. Effect of Hot Water Extraction on Hardwood Kraft Pulp fibers (Acer saccharum, Sugar Maple). Ind. Eng. Chem. Res. 2011, 50, 9949– 9959. 12. Gong, C.; Bujanovic, B.M. Impact of Hot‐Water Extraction on Acetone‐Water Oxygen Delignification of Paulownia Spp. and Lignin Recovery. Energies 2014, 7, 857–873. 13. Xu, J.; Liu, S. Optimization of ethanol production from hot‐water extracts of sugar maple chips. Renew. Energy 2009, 34, 2353–2356. 14. Pan, W.; Perrotta, J.A.; Stipanovic, A.J.; Nomura, C.T.; Nakas, J.P. Production of polyhydroxyalkanoates by Burkholderia cepacia ATCC 17759 using a detoxified sugar maple hemicellulosic hydrolysate. J. Ind. Microbiol. Biotechnol. 2012, 39, 459–469. 15. Thakur, V.K.; Thakur, M.K.; Raghavan, P.; Kessler, M.R. Progress in Green Polymer Composites from Lignin for Multifunctional Applications: A Review. ACS Sustain. Chem. Eng. 2014, 2, 1072–1092. 16. Barclay, L.R.C.; Xi, F.; Norris, J.Q. Antioxidant Properties of Phenolic Lignin Model Compounds. J. Wood Chem. Technol. 1997, 17, 73–90. 17. Gregorova, A.; Košíková, B.; Staško, A. Radical scavenging capacity of lignin and its effect on processing stabilization of virgin and recycled polypropylene. J. Appl. Polym. Sci. 2007, 106, 1626– 1631. 18. Qian, Y.; Qiu, X.; Zhu, S. Lignin: a nature‐inspired sun blocker for broad‐spectrum sunscreens. Green Chem. 2015, 17, 320–324. 19. Spiridon, I.; Leluk, K.; Resmerita, A.M.; Darie, R.N. Evaluation of PLA–lignin bioplastics properties before and after accelerated weathering. Compos. Part B Eng. 2015, 69, 342–349. 20. Handbook of Pulp : Herbert Sixta : 9783527309993 Available online: https://www.bookdepository.com/Handbook‐Pulp‐Herbert‐Sixta/9783527309993 (accessed on Dec 18, 2017). 21. Gartner, A.; Gellerstedt, G.; Tamminen, T. Determination of phenolic hydroxyl groups in residual lignin using a modified UV‐method. Nord. Pulp Pap. Res. J. 1999, 14, 163–170. 22. Ultrasonic‐assisted fabrication of montmorillonite‐lignin hybrid hydrogel: Highly efficient swelling behaviors and super‐sorbent for dye removal from wastewater. Colloids Surf. Physicochem. Eng. Asp. 2017, 520, 903–913. 23. Passauer, L.; Struch, M.; Schuldt, S.; Appelt, J.; Schneider, Y.; Jaros, D.; Rohm, H. Dynamic moisture sorption characteristics of xerogels from water‐swellable oligo(oxyethylene) lignin derivatives. ACS Appl. Mater. Interfaces 2012, 4, 5852–5862. 24. Kubo, S.; Kadla, J.F. Poly(Ethylene Oxide)/Organosolv Lignin Blends: Relationship between Thermal Properties, Chemical Structure, and Blend Behavior. Macromolecules 2004, 37, 6904–6911. 25. Gordobil, O.; Robles, E.; Egüés, I.; Labidi, J. Lignin‐ester derivatives as novel thermoplastic materials. RSC Adv. 2016, 6, 86909–86917. 26. Meng, X.; Crestini, C.; Ben, H.; Hao, N.; Pu, Y.; Ragauskas, A.J.; Argyropoulos, D.S. Determination of hydroxyl groups in biorefinery resources via quantitative 31P NMR spectroscopy. Nat. Protoc. 2019. 27. Sjöström, E.; Alen, R. Analytical Methods in Wood Chemistry, Pulping, and Papermaking; Springer Science & Business Media, 2013; ISBN 978‐3‐662‐03898‐7. 28. Yield, energy parameters and chemical composition of short‐rotation willow biomass. Ind. Crops Prod. 2013, 46, 60–65. 29. Gong, C.; Goundalkar, M.J.; Bujanovic, B.M.; Amidon, T.E. Evaluation of Different Sulfur‐Free Delignification Methods for Hot‐Water Extracted Hardwood. J. Wood Chem. Technol. 2012, 32, 93– 104. 30. Effects of hot water extraction pretreatment on pyrolysis of shrub willow. Biomass Bioenergy 2017, 107, 299–304. 31. Serapiglia, M.J.; Humiston, M.C.; Xu, H.; Hogsett, D.A.; Mira de Orduña, R.; Stipanovic, A.J.; Smart, L.B.S. Enzymatic saccharification of shrub willow genotypes with differing biomass composition for biofuel production. Front. Plant Sci. 2013, 4. 32. Corbett, D.B.; Kohan, N.; Machado, G.; Jing, C.; Nagardeolekar, A.; Bujanovic, B.M. Chemical Composition of Apricot Pit Shells and Effect of Hot‐Water Extraction. Energies 2015, 8, 9640–9654. 33. Landucci, L.L. (US D. of A.; Deka, C.C.; Roy, D.N. A 13C NMR study of milled wood lignins from hybrid Salix clones. Holzforsch. Ger. 1992. 34. Faix, O. Fourier transform infrared spectroscopy. In Methods in lignin chemistry; Springer, 1992; pp. 233–241. 35. Koivu, K.A.Y.; Sadeghifar, H.; Nousiainen, P.A.; Argyropoulos, D.S.; Sipilä, J. Effect of Fatty Acid Esterification on the Thermal Properties of Softwood Kraft Lignin. ACS Sustain. Chem. Eng. 2016, 4, 5238–5247.
Valorization of Willow Lignin Recovered in a Pilot- scale Biorefinery Based on Hot Water Extraction
Aditi Nagardeolekar ([email protected]), Mathew Ovadias, KuoTing Wang, Christopher Wood, Thomas Amidon and Biljana Bujanovic
SUNY‐ESF, Syracuse, NY, USA
International Bioenergy and Bioproducts Conference October 27‐30, 2019
1 Presentation Outline WILLOW (genus: Salix, • Introduction and motivation family: Salicaceae) • Hydrothermal pretreatment of willow Energy crop and recovery and characterization of willow lignin as a byproduct • Synthesis and characterization of lignin‐based hydrogels • Synthesis and characterization of lignin‐PLA blends
• Conclusions
Lignin‐acrylamide Pilot reactor at SUNY‐ESF Light microscopy image of hydrogel balanced on grass Pilot reactor at SUNY‐ESF Lignin‐PLA blend Image credit: SUNY‐ESF 2 Image credit: SUNY‐ESF The concept of Integrated Biorefinery at ESF
Residue
Sugars Hydrogels PLA blends
Lignin‐ based products
Furfural Image modified from [1]
Collection of processes that efficiently utilizes all components of the biomass to produce bio‐products and bioenergy1
3 HWE as a pre-treatment for recalcitrant lignocellulosic biomass:
Pre‐treatment goals: Make cellulose more accessible by removing hemicelluloses and/or lignin, increasing porosity, reducing cellulose crystallinity
Image credit Mosier et al[2]
HWE: Xylan‐rich Angiosperms are model species for HWE at ESF
Hardwoods, grasses and agricultural residues
Image credit Sorieul et al [3] 4 HWE proceeds via Autohydrolysis: Lignin is also partially dissolved
OH Species Delignification degree (% original lignin) Miscanthus 32% Paulownia 27% Wheat straw 26% Apricot pit shell 24% Sugar maple 12%
5 Why Willow? [4]
. Shrub willow (Salix spp.) can be grown on marginalized land
. High Yield (13.6 odt/ha/year in New York[3])
. Short rotation (harvest at least every 3-4 years)
. Ease of propagation and breeding
6 Objectives:
1. To assess suitability of hot‐water extraction as a pretreatment for willow biomass on pilot scale 2. To recover and evaluate willow lignin as a cheaper and renewable resource in synthesis of lignin‐based hydrogelshydrogels and 3. in synthesis of ligninlignin‐‐PLAPLA blends blends
Traditionally made from petroleum-based Lignin can serve as a UV protecting additive synthetic polymers. Lignin, which is the most to PLA , without significantly impacting abundant natural aromatic polymer can serve thermo-mechanical properties of PLA as a partial replacement.
7 Experimental Scheme
Operating Conditions BiomassHot loading‐water extracted 538 lb O.D. Hydrogels willow biomass (EW) Water / Biomass 4.5 Wastewater treatment, agriculture Temperature 160oC Time 2 hours Willow biomass Hot‐water P‐factor 691 with bark, extraction ~2cm chips 3 (W) digester; 65ft Lignin recovered from hydrolyzate by acidification and precipitation (WRecL) Lignin‐PLA Blends Packaging, coatings, 3D printing
Steps: 1. HWE 2. Recovery 3. Utilization
8 HWE Results: Extracted Willow Biomass (EW) Characterization
HWE digester yield = 77% O.D. initial load Changes in individual components, % Original = 415 lbs weight Xylan removal 49% Hydrolyzate pH = 3.9 GlucanCellulose retention retention HigherChemical heating composition: value W EW ~ 100% Delignification 17% 50 43 45 25 23 Deashing 45% 40 21
value 35 19 33 20 0 20406080100 30 25 27
biomass 25 15
heating 20
(MJ/kg) 10 Selective removal of xylan, leaving O.D. 15 11 % 10 5 7 cellulose‐rich biomass Higher 5 0 1.47 1.05 0 Increased the energy density of willow WEWCoal* xylan glucan total lignin ash biomass
9 Results: Recovery of lignin from the hydrolyzate (WRecL)
70 60
(% 60 50 50 Molecular weight analysis 40 31 6000 PD = 2 5202 recovered
26 dissolved 30 4000 20 15 Da 2589 lignin total
10 2000
Total 0 Willow Sugar Paulownia Miscanthus Wheat 0 maple straw Mn Mw
Willow lignin is polydispersed, more hydrophilic, and doesn’t readily precipitate
10 Results: Composition of WRecL
Chemical composition of WRecL 100 80 80 60 Carb analysis of WRecL WRecL
40 1.4 O.D. 1.19 1.19 % 20 1.2 5 3 0.2 1 0 0.8
Klason ASL Carbohydrates Ash WRecL 0.6 * ASL: acid soluble lignin 0.6 O.D.
% 0.4 Willow lignin is a mixture of lignin and carbohydrates 0.2 0 Glucan Xylan Mannan 11 Results: Analysis of WRecL
Free phenolic hydroxyl group content 3.5 2.94 3 lignin) 2.5 2.11 2 1.5 1.1 OH (mmol/g 1 0.5 Example of PhOH in lignin PhOH structure 0 UV method P‐NMR Willow MWL*
* MWL: milled wood lignin; Literature value5 WRecL possesses reaction sites, useful for combining with other chemicals to form lignin‐based materials
12 Experimental: Lignin-based hydrogels: Lignin + PEGDGE6[2:1]
Reaction scheme between lignin unit and PEGDGE (Mn = 500 Da)
WRecL + + Lyophilize 3M NaOH PEGDGE 48 h 24 h 24 h
* PEGDGE: polyethylene glycol diglycidyl ether 13 Results: Hydrogel application: Absorption of bioactive solution
Lignin‐PEGDGE hydrogel + ascorbic acid solution; 30 minutes.
Swelling degree, Q = 609%. Q = (Ws –Wd) / Wd*100%; (Ws = Weight of swollen hydrogel, Wd = weight of dry hydrogel)
Good absorption properties: Specific applications: ‐ Sustained release of fertilizers and pesticides ‐ Retention of moisture in arid soils ‐ Could also be explored as carriers for fragrances
14 Experimental: Lignin-based hydrogels:Lignin + Acrylamide + Kaolin7 [3:10:15]
Reaction scheme between lignin unit and acrylamide (71.08 g/mol)
Kaolin + DI WRecL + APS + Ultrasound Lyophilize water AAm MBA* 50oC, 90 m 1 h 20 m 48 h
* AAm: acrylamide; APS: ammonium persulfate; MBA: N,N’‐bisacrylamide
Ultrasonicator at SUNY‐ESF 15 Results: Hydrogel application: Adsorption of cationic contaminants
Lignin‐AAm hydrogel
2 hr
Methylene violet solution Methylene violet solution 40 μM 5 μM
Good adsorption properties: Specific applications : ‐ Textile effluent treatment by removal of cationic dyes ‐ Wastewater treatment by removal of metallic cations (e.g. Pb+2)
16 Results: Hydrogel application: Adsorption of cationic contaminants
Reusability studies 400 Adsorption 1 350 y = 1.3674xLignin + 186.59‐AAm
(1/mM) hydrogel
300 y = 1.1491x + 181.14 250 Adsorption 2 200 2 hr y = 0.6224x + 159.21 150 100 Adsorption 3 concentration 50
Dye 0 050100150 Contact time (minutes)
The hydrogels were found to be reusable for at least two uses 17 Results: SEM and EDS analysis: Adsorption of metal cations
Lignin‐AAm hydrogel +
0.01 N Silver nitrate solution overnight
Total silver content = 0% Total silver content ~ 15% w/w 002 002 5.0 5.0 Al 4.0 Ag 4.0 Si 3.0 3.0 ] ] 3 3 + + .E .E 1
O [x1 [x O Al ts ts n n C Si Ag u u o o C C 2.0 Ti 2.0 C Cl Ti S N Ag 1.0 N S K K Ti Ti 1.0 Ag Cl 0.0 0.00 0.0 0.00 1.00 2.00 3.00 4.00 5.00 6. 0 1.00 2.00 3.00 4.00 5.00 6.0 0 keV keV 18 Experimental: Lignin-PLA Blends
. Polylactic acid (PLA) is one of the main commercially available biopolymers with a wide range of applications . Packaging, coatings, biomedical applications and even 3D printing . Mainly produced from starch based crops like corn (NatureWorks) . Can also be produced from sugars in lignocellulosic biomass [8]
. Why add lignin? . This work will show that lignin obtained from HWE of Willow can produce blends with higher UV absorbance capabilities and limited impact on properties . PLA is highly susceptible to UV degradation impacting product performance in certain applications, specifically packaging [9]
19 Challenges . Crude willow lignin is relatively hydrophilic when compared to PLA making it difficult to efficiently blend the two PLA . In this research two methods of acylation (with fatty acid chloride and acetic anhydride) have been explored
Hansen Solubility Parameters of PLA and Lignin Solubility Parameters PLA [6] Lignin [7]
ߜD 18.6 21.9
ߜP 9.9 14.1
ߜH 6 16.9 Hardwood Lignin
20 Experimental: Acylation of HWE Recovered Willow Lignin
[10] Acetylation (C2)
Acetic Lignin Acetic Acetylated Anhydride (β-O-4) Acid Lignin [9] Fatty Acid Esterification - FAE (C12)
Lauroyl Lignin FAE Chloride (β-O-4) Lignin 21 Experimental: FAE Challenges – Need for Hexane Extraction
Side Reaction Producing the Free Fatty acid
Lauroyl Chloride Lauric Acid
. During the wash step the unbound fatty acid is not separated from the lignin sample by standard washing procedure . Hexane extraction was explored to purify the lignin-fatty acid derivative
22 Results: FT-IR of Lignin Derivative Samples ‡- Indicates either ester linkage with aromatic ring (1760 cm-1) or aliphatic chain (1740 cm-1). Willow Recovered Lignin ‐ W Long‐chain alkyl FAE Willow Lignin ‐ WFAE
Acetylated Willow Lignin ‐ WAc
FAE Willow Lignin after Hexane Extraction ‡ ‐ W[H]FAE Absorbance
3400 2900 2400 1900 1400 cm‐1
23 Experimental: Production of Lignin-PLA Blends
Willow Lignin Lignin Ester Derivatives Lignin-PLA Blends
Acylation
PLA (NatureWorks 2003D Lignin Coated PLA Dynisco Lab Mixing Extruder (D=1/8 inch) Melt Extrusion
24 Results: Light microscopy 1% lignin-PLA blends (4x magnification)
100% PLA Alkali Lignin (AL) HWE Willow Lignin (W)
FAE Willow Lignin after Hexane Extraction (W[H]FAE) Acetylated Willow Lignin (WAc)
25 Results: Mechanical Properties Stress vs Strain Curve of PLA
Elongation Tensile Testing based on ASTM D638 Standard Test Method for Tensile Properties of Plastics
26 Results: Peak Stress (Tensile Strength) 61.9 60.1 58.4 55.7 56.7 60 54.1 49.3 50
40 Stress 30 (MPa)
Peak 20
10
0 PLA 1% AL 1% W1% WAc 6% WAc 12% WAc 1% W[H]FAE
27 Results: Strain at Peak
9 7.60 7.76 8 6.91 7 6.42 6.24 6.00
6 5.25 at
(%) 5
4 Strain Peak 3 2 1 0 PLA 1% AL 1% W1% WAc 6% WAc 12% WAc 1% W[H]FAE
28 Results: (Young’s) Modulus of Elasticity
2 1.824 1.649 1.746 1.8 1.570 1.583 1.6 1.533 1.365 1.4 1.2 1 Modulus
(GPa) 0.8 0.6 Elastic 0.4 0.2 0 PLA 1% AL 1% W1% WAc 6% WAc 12% WAc 1% W[H]FAE
29 Results: UV Absorbance
25
20
15 (Absorbance^2)
Curve
10 the
5 under
Area 1.600.210.192.00 12.18 4.41 4.30 20.90 12.83 4.35 3.67 20.85 0 PLA 1%[H]FAE 1%Ac UVC (200‐279 nm) UVB (280‐319 nm) UVA (320‐400 nm) UV (200‐400)
Blending of PLA with lignin derivatives increased the UV absorbance more than 10x based on area under the curve
30 Conclusions . Hot‐water extraction is an effective pretreatment for targeted removal of xylans from willow biomass, and for enriching the biomass with cellulose, at pilot scale.
. Lignin recovered from this process is a 85% w/w lignin as measured with carbohydrate impurities.
. It is a suitable partial replacement for synthetic chemicals for synthesis of bio‐based materials, such as hydrogels applicable in wastewater treatment, agricultural and pharmaceutical fields.
. It is a suitable UV protecting additive in lignin‐PLA blends useful for UV‐resistant applications.
31 References 1. Amidon, T. E. and Liu, S. (2009), “Water-based woody biorefinery”. Biotechnology Advances (27): 542-550. 2. Mosier, N. et al (2005), “Features of promising technologies for pretreatment of lignocellulosic biomass”. Bioresource Technology (96): 673-686. 3. Sorieul, M. et al (2016), “Plant fiber: Molecular structure and biomechanical properties, of a complex living material, influencing its deconstruction towards a biobased composite”. Materials (9): 618-623. 4. Volk, T. A., Heavey, J. P., & Eisenbies, M. H. (2016). Advances in shrub-willow crops for bioenergy , renewable products ,and environmental benefits. Food and Energy Security, 5(2), 97–106. 5. Landiucci, L. L. et al (1992), “A 13C NMR study of milled wood lignins from hybrid Salix clones”. Holzfoschung (46): 505-511. 6. Passauer, L. et al (2012), “Dynamic moisture sorption characteristics of xerogels from water- swelleable oligo(oxyethylene) lignin derivatives”. ACS Appl Mater Interfaces (11): 5852-5862. 7. Wang, Y. X. et al (2017), “Ultrasonic-assisted fabrication of montmorillonite-lignin hybrid hydrogel: Highly efficient swelling behaviors and super-sorbent for dye removal from wastewater”. Colloids and surfaces A: Physicochemical and engineering aspects (20): 903-913. 8. Hama, S., Mizuno, S., Kihara, M., Tanaka, T., Ogino, C., Noda, H., & Kondo, A. (2015). Production of d –lactic acid fromhardwood pulp by mechanical milling followed by simultaneous saccharification and fermentation usingmetabolically engineered Lactobacillus plantarum. Bioresource Technology, 187, 167- 172.https://doi.org/10.1016/j.biortech.2015.03.106 9. Gordobil, O., Robles, E., Egüés, I., & Labidi, J. (2016). Lignin-ester derivatives as novel thermoplastic materials. RSCAdvances, 6(90), 86909–86917. https://doi.org/10.1039/c6ra20238a 10. Kubo, S., & Kadla, J. F. (2004). Poly(ethylene oxide)/organosolv lignin blends: Relationship between thermal properties,chemical structure, and blend behavior. Macromolecules, 37(18), 6904–6911. https://doi.org/10.1021/ma0490552.
32 . McIntire‐Stennis / NYSERDA grants (financial support) . Forest Products Laboratory –Fred Matt (analytical support) Thank you! . Dr. T. Volk (provided willow) . Dr. A. Stipanovic (analytical support) . Dr. S. Anagnost (analytical support) . Dr. D. Kiemle (analytical support)
33 Results: Recovery of lignin from the hydrolyzate (WRecL)
WRecL = 15% total dissolved lignin = 2% total lignin in biomass = 0.6% O.D. biomass
34