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Dissolution Behaviour of Bark Extractives in Polyurethane Synthesis Media: A Comprehensive Study
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25 July 2023
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26 July 2023
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Abstract
The production of polyurethane films from bark-derived polyols requires the complete solubility of all components in the polyurethane synthesis media. In this study, a comprehensive investigation was conducted to achieve the copolymerization of black alder bark water extract-derived polyol with isocyanate for polyurethane film synthesis in THF solution. A fractionation approach using tetrahydrofuran (THF) as a solvent was employed to dissolve the extract, followed by filtration and removal of the solvent. The resulting THF-soluble fraction comprised 62±1% of the dry weight of the alder bark extract, mainly consisting of the xyloside form of the diarylheptanoid compound oregonin, along with oligomeric flavonoids and carbohydrates. The THF-insoluble fraction was the most enriched with carbohydrate compounds, followed by the crude extract and THF-soluble fraction. Another approach was aimed at obtaining bark extractives based liquid polyols suitable for producing rigid PU foams. For this purpose, oven-dried crude black alder bark water extract was liquefied with polyethylene glycol (PEG 400). The liquefaction of black alder bark and pine bark extractives was studied under different conditions, including varying temperature ranges (130-170⁰C), catalyst concentrations (0-1,5%), and bark extract content in the mixture (15-30%). The results showed that the use of sulphuric acid as a catalyst (1-1.5%) significantly improved the solubility of both extractives, enabling the attainment of extract concentrations up to 25% at 170⁰C. However, increasing the extract content beyond a certain threshold led to incomplete solubility. It was shown that the PEG-insoluble fractions consist mainly of carbohydrate components. To increase the content of biomass in liquid polyols, the effect of glycerol additions into the liquefaction agent is under study. The findings provide insights into tailoring bark-sourced polyols for polyurethane foam production through appropriate liquefaction conditions.
Keywords:
Subject: Chemistry and Materials Science - Polymers and Plastics
Generation of biopolyols for polyurethane film synthesis. To facilitate the copolymerization of bark-derived polyol with isocyanate and achieve the production of polyurethane films using casting method, complete solubility of all components in THF was imperative. Therefore, the most promising approach involved fractionating the black alder bark water extract, obtained through microwave-assisted dynamic heating at 90℃, by dissolving the extract in anhydrous THF. In this process, 20 grams of extract were weighed and placed in an Erlenmeyer flask, followed by the addition of 200 mL of THF. The solution was stirred for 24 hours and subsequently filtered. The resulting THF solution was separated, and the solvent was removed using a rotor evaporator. The obtained fraction was then redissolved in water and dried through lyophilization. The yield of the THF-soluble fraction was determined to be 62±1% based on the dry weight of the alder bark extract. Briefly, the composition of the fraction can be summarized as follows: it consists of 74% by weight of the xyloside form of the diarylheptanoid compound, oregonin, along with 26% oligomeric flavonoids and carbohydrates. The average molecular weight (Mn) of the fraction is 750 g·mol-1, and it has an OH content of 15 mmol·g-1. The hydroxyl groups are evenly distributed between aliphatic and phenolic groups.
To assess the chemical alterations in the crude alder bark extract subsequent to the isolation of a fraction suitable for polyurethane film synthesis, analytical pyrolysis (Py-GC-MS/FID) was employed in conjunction with other analytical techniques. This method enables the simultaneous analysis of diverse components present in the bark by subjecting the sample to thermal degradation, resulting in the production of a complex mixture of volatile products. By characterizing the pyrolysis products, valuable insights into the chemical structure and functional groups of the components can be obtained. Py-GC/MS/FID analysis was conducted at a pyrolysis temperature of 500°C with a heating rate of 600°C·s⁻¹. The analysis was performed using a Micro Double-shot Pyrolyzer Py-3030D (Frontier Laboratories. Ltd., Fukushima, Japan) directly coupled with the Shimadzu GC/MS/FID-QP ULTRA 2010 apparatus (Japan). The apparatus was equipped with a capillary column RTX-1701 (Restec, Metairie, Louisiana, USA) 60 m × 0.25 mm × 0.25 μm. The injector temperature was set at 250°C, and the ion source had an electron impact (EI) of 70 eV. The mass scan range of the MS was from m/z 15 to 350. The carrier gas used was helium at a flow rate of 1 mL min⁻¹ with a split ratio of 1:30. For the analysis, the mass of the sample probe was in the range of 1.00-2.00 mg, with a residual moisture content of less than 1%. The oven program consisted of an initial isothermal hold at 60°C for 1 minute, followed by a temperature ramp of 6°C min⁻¹ up to 270°C. The final temperature was held at 270°C for 10 minutes. Identification of individual compounds was performed based on GC/MS chromatography using the Library MS NIST 11 and NIST 11s. The relative area of each compound's peak (% from chromatogram) was calculated using Shimadzu software, which utilized GC/FID data.
The Py-GC/MS results indicate that the THF-soluble fraction produces significantly higher levels of aromatic volatiles, primarily derived from phenolic extractives, and lower levels of aliphatic volatiles, mainly derived from carbohydrates, during the pyrolysis process compared to the crude extract (Table 1, Figure 1).
On the contrary, the THF-insoluble fraction exhibits a significantly increased ratio of summary peak areas between aliphatic (carbohydrate-derived) and aromatic (phenolic extractives-derived) pyrolysis products (Figure 1).
It can be hypothesized that carbohydrates transfer to the THF-soluble fraction only when bonded with other compounds, such as phenyl glucosides. To validate this hypothesis, Fourier transform infrared (FTIR) spectra were recorded in KBr pellets by Spectrum One apparatus (Perkin Elmer) by scanning from 500 to 4000 cm-1, scan resolution and number of scans were 0.4 cm−1 and 64, respectively. The significantly increased ratio of the peak at 1035 cm-1, attributed to the C-O-C vibrations of carbohydrates, to the peak at 1510 cm-1, attributed to the aromatic ring vibrations, in the THF-insoluble fraction confirms that it contains a higher amount of carbohydrates compared to the crude extract. Conversely, the ratio of these peaks decreases in the THF-soluble fraction, indicating a reduced content of carbohydrates (Figure 2).
Furthermore, the radical scavenging activity of the extract fractions, which is dependent on the phenolic compound content, was evaluated using the stable 2 2-diphenyl-1-picrylhydrazyl free radicals (DPPH•) test and expressed as the IC50 value (the concentration required to inhibit 50% of the initial free radicals). A lower IC50 value indicates higher radical scavenging activity. The THF-soluble fraction exhibited the highest activity, surpassing both the crude black alder bark extract and the widely used synthetic antioxidant Irganox 1010 in PU materials. Conversely, due to the increased content of free carbohydrates and decreased content of phenolic compounds and their derivatives, the THF-insoluble fraction displayed significantly reduced radical scavenging activity compared to the crude extract (Table 2).
Generation of bark-sourced polyols for polyurethane foam synthesis. Another approach was used to utilize the bark-derived polyols for the synthesis of polyurethane foam. The crude black alder bark water extract was mixed with polyethylene glycol (PEG 400) under different conditions. These conditions included a temperature range of 150-170℃, a catalyst concentration of 0-1% of H2SO4, and a bark extract content range of 20-30% in the PEG 400-extract mixture. Consequently, the crude black alder bark water extract was fractionated into PEG-soluble polyol and PEG-insoluble fraction. The acid used as a catalyst was neutralized through the reaction represented by equation (1), and the resulting water generated during the reaction was eliminated from the obtained biopolyol through continuous heating of the liquefied mixture at the designated temperature while blowing nitrogen through it. The moisture content of the samples was monitored using the Karl Fischer method.
H2SO4 + 2NaOH → Na2SO4 + 2H2O
During a 6-hour-long dissolution process, it proved challenging to fully dissolve the black alder bark extract in PEG400 to achieve a 20% content without the use of a catalyst. Even with the addition of 0.5% catalysts, the complete dissolution of the introduced extract in PEG400 (at a weight ratio of 20%) was not achieved, resulting in an insoluble residue of approximately 16-20%. However, when the catalyst concentration was increased to 1%, a notable improvement in solubility was observed at these PEG-extract ratios. At a temperature of 130 °C, the insoluble portion decreased to only around 9%, while at 150 and 170 °C, all of the introduced bark extract dissolved, enabling the attainment of a 20% concentration in PEG400 (refer to Figure 3).
Further examination of the extract to PEG400 ratio, using a 1% catalyst concentration, revealed that a ratio of 15:85 successfully enabled the dissolution of the extract at all tested temperatures (refer to Figure 4). However, at a higher extract content of a 20:80 ratio, complete dissolution was not achieved at 130 °C, but at 150 and 170 °C, complete dissolution was observed. Furthermore, when the extract content was increased to 30%, complete dissolution was not possible at any of the temperatures utilized (see Figure 4).
The dissolution of pine bark extracts in PEG400 followed the same procedure as for the black alder bark extract. However, unlike the black alder extract without catalyst (refer to Figure 3), the pine bark extract introduced in PEG400 at a weight ratio of 20:80 without catalyst exhibited significantly poorer dissolution results at all temperatures (see Figure 5). With the addition of a 0.5% catalyst, the insoluble portion of the introduced pine bark water extract varied between 21-37%, decreasing as the dissolution temperature increased. In contrast, the use of 1% catalysts led to complete solubility of the introduced pine bark extract, allowing for the achievement of a 20% extract concentration in PEG400 at all liquefaction temperatures.
Increasing the pine bark water extract content in its mixture with PEG400 to 25% at a 1% catalyst concentration resulted in incomplete solubility of the pine bark extract at all tested temperatures. However, by increasing the catalyst concentration to 1.5% while maintaining the extract content in PEG400 at 25%, it can be observed that complete solubility (100%) can only be achieved at a temperature of 170 °C (refer to Figure 6).
Depending on the liquefaction conditions, the bark extracts can be completely liquefied using PEG400 as a solvent, resulting in polyols suitable for the synthesis of polyurethane foams. Alternatively, they can be fractionated into a PEG-soluble polyol fraction and a PEG-insoluble fraction. The PEG-insoluble fractions exhibit notable differences compared to the crude extract, as indicated by the varying composition of volatile degradation products formed from biomass components during thermal decomposition using analytical pyrolysis (refer to Table 3). These composition differences can be attributed to the insolubility of carbohydrate components in the extract in polyethylene glycol, leading to an increased content of their derivatives in the PEG-insoluble fractions. The PEG-insoluble fractions of the black alder bark extract obtained without a catalyst at 150 and 170℃, using a 20:80 ratio of extract to PEG, exhibit similar compositions. However, the fraction that remains insoluble in PEG after treatment at 170℃ with 1% H2SO4 as a dissolution catalyst and a 30:70 extract-PEG ratio shows significant differences from them (Table 3, Figure 7). It can be hypothesized that the use of a catalyst promotes the hydrolysis of glucoside bonds within the structure of the components of bark extracts, including phenyl glucosides, resulting in the formation of new PEG-soluble (aromatic) and insoluble (carbohydrate) products.
The obtained data revealed a significant increase in the content of aliphatic volatiles, primarily derived from carbohydrates, and a drastic decrease in the content of aromatic pyrolysis products, mainly derived from phenolic extractives, in all PEG-insoluble fractions (Figure 7). Based on these findings, we can conclude that unlike the PEG-insoluble carbohydrates, the phenolic extractives of black alder bark can be incorporated into PEG-based mixed polyol compositions.
The FTIR spectra of the crude black alder bark extract and its PEG400-insoluble fractions obtained under different conditions provide confirmation of the solubility of aromatic constituents in polyethylene glycol and the concentration of carbohydrates in the insoluble fraction. This is evident from the decreased absorption at approximately 1500-1600 cm-1 and 1260-1320 cm-1, which are attributed to vibrations of aromatic rings. Additionally, the absorption bands in the range of 800-1200 cm-1 associated with cellulose and hemicellulose are increased in the spectra of the polyethylene glycol-insoluble fractions compared to the crude extract. The use of a catalyst significantly increases the content of carbohydrates and decreases the content of aromatic compounds in the PEG400-insoluble fractions. This is because the catalyst promotes the hydrolysis of glucoside bonds, leading to the formation of insoluble carbohydrates derived from phenyl glucosides. Additionally, the released aromatic moieties of the latter are dissolved (see Figure 8).
A higher extraction temperature can enhance the solubility of certain carbohydrates, as evidenced by the FTIR data. The PEG-insoluble fraction of the black alder bark water extract obtained using a 20:80 extract-to-PEG400 ratio at 130℃ with 1% catalyst exhibits a significantly higher ratio of absorbance at 1100 cm-1 to 1515 cm-1, indicating a notably higher content of carbohydrate constituents compared to the fraction obtained with 1% catalyst at 170℃ (refer to Table 4).
Summary
The fractions of alder bark water extracts that are insoluble in the medium used for polyurethane foam and film synthesis exhibit an enrichment of carbohydrates compared to the crude extract. This suggests that introducing individual carbohydrate bark components into the polyurethane structure is challenging and requires extensive modification. However, aromatic bark extractives, including those containing sugar units such as phenyl glucosides, can be utilized for polyurethane synthesis as biopolyols obtained under mild conditions.
References
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Figure 1.
The ratio of aliphatic to aromatic constituents as determined by analytical pyrolysis in the crude water extract and its fractions.
Figure 1.
The ratio of aliphatic to aromatic constituents as determined by analytical pyrolysis in the crude water extract and its fractions.
Figure 2.
Normalized (1510 cm-1) FTIR spectra of black alder bark water extract and its fractions.
Figure 3.
Solubility of Black Alder Bark Extracts in PEG400 as a Function of Temperature and Catalyst Concentration after 6 Hours of Dissolution Process.
Figure 3.
Solubility of Black Alder Bark Extracts in PEG400 as a Function of Temperature and Catalyst Concentration after 6 Hours of Dissolution Process.
Figure 4.
Dependence of Black Alder Bark Extract Dissolution on the Extract to PEG400 Ratio at a 1% Catalyst Concentration.
Figure 4.
Dependence of Black Alder Bark Extract Dissolution on the Extract to PEG400 Ratio at a 1% Catalyst Concentration.
Figure 5.
Solubility of Pine Extracts in PEG400 at a 20:80 Extract to PEG Ratio as a Function of Temperature and Catalyst Concentration after 6 Hours of Dissolution Process.
Figure 5.
Solubility of Pine Extracts in PEG400 at a 20:80 Extract to PEG Ratio as a Function of Temperature and Catalyst Concentration after 6 Hours of Dissolution Process.
Figure 6.
Dependence of Pine Bark Extract Dissolution on the Catalyst Content at a 25:75% Extract to PEG400 Ratio.
Figure 6.
Dependence of Pine Bark Extract Dissolution on the Catalyst Content at a 25:75% Extract to PEG400 Ratio.
Figure 7.
Relative contents of aliphatic and aromatic pyrolysis products in the crude black alder bark water extract and its PEG-400 insoluble fractions obtained under different conditions.
Figure 7.
Relative contents of aliphatic and aromatic pyrolysis products in the crude black alder bark water extract and its PEG-400 insoluble fractions obtained under different conditions.
Figure 8.
FTIR Spectra of crude black alder bark water extract and its PEG400-insoluble fractions obtained at different temperatures, catalyst content, and various extract content in mixture with PEG.
Figure 8.
FTIR Spectra of crude black alder bark water extract and its PEG400-insoluble fractions obtained at different temperatures, catalyst content, and various extract content in mixture with PEG.
Table 1.
Pyrolysis products of black alder bark water extract and its fractions.
| Identified compound | MW | Retention time, min | Normalized peak area, % from chromatogram | ||
|---|---|---|---|---|---|
| Crude extract | THF-soluble fraction | THF-insoluble fraction | |||
| Carbohydrates derivatives | |||||
| Acetic acid | 60 | 7.417 | 3.97 | 2.73 | 6.64 |
| Formic acid, methyl ester | 60 | 8.538 | 0.55 | 0.36 | 0.25 |
| Propanoic acid | 74 | 9.059 | 0.52 | 0.49 | 0.54 |
| 2-Propenoic acid | 72 | 9.469 | 0.15 | ||
| 2-Propenoic acid, methyl ester | 86 | 9.745 | 0.4 | 0.39 | 0.16 |
| Acetic acid, methyl ester | 74 | 10.025 | 0.74 | 0.55 | 0.85 |
| Propanoic acid, 2-oxo-, methyl ester | 102 | 11.004 | 1.42 | 1.02 | 1.43 |
| Butanoic acid, 2-methyl- | 102 | 12.348 | 0.37 | 0.46 | 0.19 |
| Crotonic acid vinyl ester | 112 | 13.56 | 0.07 | ||
| Propanoic acid, 2-methylpropyl ester | 130 | 14.755 | 0.36 | 0.14 | 0.48 |
| Propanoic acid, 2,2-dimethyl-, methyl ester | 116 | 15.363 | 0.07 | 0.09 | |
| 1,3-Propanediol, 2-ethyl-2-(hydroxymethyl)- | 134 | 26.724 | 0.36 | 2.1 | |
| Methylglyoxal | 72 | 5.912 | 3.67 | 3.53 | 1.98 |
| 2,3-Butanedione | 86 | 6.522 | 0.75 | 1.06 | 1.7 |
| 2-Butanone, 1-hydroxy- | 88 | 6.675 | 0.46 | 0.51 | |
| Acetaldehyde, hydroxy- | 60 | 7.141 | 2.5 | 5.92 | 1.15 |
| Glycolaldehyde dimer | 120 | 7.209 | 1.96 | 1.85 | |
| 2,3-Pentanedione | 100 | 7.706 | 0.24 | 0.25 | 0.37 |
| 2-Propanone, 1-hydroxy- | 74 | 8.292 | 6.91 | 6.34 | 6.66 |
| 2-Butanone, 3-hydroxy- | 88 | 8.897 | 0.17 | 0.18 | 0.2 |
| 2-Butanone, 1-hydroxy-, isomer | 88 | 10.135 | 1.18 | 0.8 | 0.88 |
| Propanal and Butanedial | 58/86 | 11.158 | 0.24 | ||
| 3-Hexanone, 4-ethyl- | 128 | 12.083 | 0.1 | 0.09 | |
| 2-Propanone, 1-(acetyloxy)- | 116 | 12.569 | 1.28 | 1.17 | 0.98 |
| 2-Heptanone, 3-methyl- | 128 | 12.958 | 0.13 | 0.11 | 0.2 |
| 2,5-Hexanedione | 114 | 14.507 | 0.07 | 0.03 | 0.09 |
| 2-Butanone, 1-(acetyloxy)- | 130 | 14.826 | 0.25 | 0.1 | 0.31 |
| 2-Propanone, 1,3-dihydroxy- | 90 | 16.796 | 0.75 | 0.81 | 0.44 |
| 2,3-Pentanedione, 4-methyl- | 114 | 18.221 | 0.22 | 0.13 | |
| Pentanal and Pentanadial | 86/100 | 20.855 | 0.27 | 0.18 | 0.45 |
| 2-Cyclopenten-1-one | 82 | 11.606 | 0.51 | ||
| 2-Cyclopenten-1-one, 2-methyl- | 96 | 12.95 | 0.17 | 0.09 | 0.22 |
| 4-Cyclopentene-1,3-dione | 96 | 13.767 | 0.11 | 0.08 | 0.23 |
| 1,3-Cyclopentanedione | 98 | 14.285 | 0.59 | 0.37 | 0.5 |
| 2-Cyclopenten-1-one, 3-methyl- | 96 | 15.461 | 0.16 | 0.11 | 0.32 |
| 1,2-Cyclopentanedione, 3-methyl- | 112 | 16.808 | 0.17 | 0.13 | 0.44 |
| 2-Cyclopenten-1-one, 3-ethyl-2-hydroxy- | 126 | 18.945 | 0.21 | ||
| Furan, 2-methyl- | 82 | 6.256 | 0.41 | 0.21 | 0.33 |
| 2(3H)-Furanone | 84 | 10.499 | 0.08 | ||
| 3(2H)-Furanone | 84 | 10.835 | 0.14 | 0.13 | 0.09 |
| 2(3H)-Furanone, 5-methyl- | 98 | 11.152 | 0.4 | 0.47 | 0.23 |
| Furfural | 96 | 11.55 | 1.19 | 1.57 | 0.91 |
| 2-Furanmethanol | 98 | 12.421 | 0.36 | 0.29 | 0.53 |
| Acetylfuran | 110 | 13.256 | 0.15 | 0.11 | 0.24 |
| 2-Furancarboxaldehyde, 5-methyl- | 110 | 14.937 | 0.12 | 0.08 | 0.16 |
| 2(3H)-Furanone, dihydro- | 86 | 15.604 | 0.26 | 0.2 | 0.42 |
| 2(5H)-Furanone | 84 | 15.948 | 0.21 | 0.1 | 0.37 |
| 2(5H)-Furanone, 5-methyl- | 98 | 16.15 | 0.08 | 0.1 | |
| 2,5-Furandione, 3-methyl- | 112 | 16.437 | 0.43 | 0.34 | |
| 3(2H)-Furanone, 4-hydroxy-2,5-dimethyl- | 128 | 18.039 | 0.34 | ||
| Methyl 2-furoate | 126 | 18.944 | 0.07 | 0.04 | |
| 5-(Hydroxymethyl)dihydro-2(3H)-furanone | 116 | 20.161 | |||
| 2(3H)-Furanone, 5-acetyldihydro- | 128 | 22.117 | 0.22 | ||
| 2,4(3H,5H)-Furandione, 3-methyl- | 114 | 22.725 | 0.12 | 0.09 | 0.12 |
| Benzofuran, 2,3-dihydro- | 120 | 23.481 | 3.83 | 3.13 | 5.53 |
| 2-Furancarboxaldehyde, 5-(hydroxymethyl)- | 126 | 24.698 | 0.61 | 0.2 | 0.33 |
| 5-Hydroxymethyldihydrofuran-2-one | 116 | 25.188 | 0.22 | 0.3 | |
| 4-Hydroxy-,5,6-dihydro-(2H)-pyran-2-one | 114 | 16.244 | 0.11 | 0.4 | 0.04 |
| 4H-Pyran-4-one, 2,3-dihydro-3,5-dihydroxy-6-methyl- | 144 | 20.397 | 0.64 | ||
| 1,6-Anhydro--D-glucopyranose | 162 | 31.935 | 1.09 | 1.04 | 0.32 |
| Non-methoxylated aromatic compounds | |||||
| Phenol | 94 | 17.331 | 3.7 | 4.26 | 3.04 |
| Phenol, 2-methyl- | 108 | 18.503 | 0.41 | 0.46 | 0.38 |
| Phenol, 3-and 4-methyl- | 108 | 19.38 | 2.03 | 2.85 | 0.67 |
| Phenol, 2-ethyl- | 122 | 20.302 | 0.06 | 0.09 | |
| Phenol, 3,4-dimethyl- | 122 | 20.493 | 0.13 | 0.19 | 0.15 |
| Phenol, 4-ethyl- | 122 | 21.45 | 1.32 | 1.77 | 0.86 |
| Phenol, 2,6-dimethyl- | 122 | 22.093 | 0.09 | 0.15 | |
| Phenol, 2-ethyl-5-methyl- | 136 | 22.475 | |||
| Benzene, 4-ethyl-1,2-dimethoxy- | 166 | 22.542 | 0.06 | 0.18 | |
| Benzene, (ethenyloxy)- | 120 | 23.131 | 0.07 | 0.08 | |
| Benzene, 2,4-dimethyl-1-(1-methylethyl)- | 148 | 25.205 | 0.13 | ||
| Phenol, 4-(2-propenyl)- | 134 | 25.547 | |||
| Benzaldehyde, 3,4-dimethyl- | 134 | 25.551 | 0.34 | 0.67 | |
| Phenol, 2,4,6-tris(1-methylethyl)- | 220 | 25.699 | 0.49 | 0.94 | |
| 1,4-Benzenedicarboxaldehyde, 2-methyl- | 148 | 25.805 | |||
| Benzenemethanol, .alpha.-ethynyl- | 132 | 25.903 | 0.23 | 0.23 | |
| Phenol, 2-(2-methyl-2-propenyl)- | 148 | 26.384 | 0.31 | 0.55 | |
| 1,4-Benzenediol | 110 | 27.074 | 1.24 | 0.66 | 2.49 |
| 1,4-Benzenediol, 2-methyl- | 124 | 27.925 | 0.18 | ||
| 2-Propyn-1-ol, 3-(4-methylphenyl)- | 146 | 28.327 | 0.45 | 0.7 | |
| 1,4-Benzenediol, 2-methoxy- | 140 | 28.537 | 0.27 | 0.46 | 0.05 |
| 2-Butanone, 4-(4-hydroxyphenyl)- | 164 | 31.533 | 1.07 | 1.97 | 0.15 |
| Guaiacyl derivates | |||||
| Guaiacol | 124 | 17.949 | 1.5 | 2.16 | 0.93 |
| p-Methylguaiacol | 138 | 20.405 | 0.27 | 0.24 | trace |
| p-Ethylguaiacol | 152 | 22.323 | 0.19 | 0.26 | 0.09 |
| p-Vinylguaiacol | 150 | 23.67 | 0.73 | 0.8 | 0.36 |
| Eugenol | 164 | 23.979 | 0.7 | 0.9 | 0.13 |
| trans-isoeugenol | 164 | 26.5 | 0.14 | 0.16 | 0.08 |
| Guaiacylacetone | 180 | 29.777 | 0.18 | 0.15 | 0.13 |
| Acetoguaiacon | 166 | 30.791 | 0.12 | 0.09 | 0.13 |
| Dihydroconifery alcohol | 182 | 32.172 | 0.23 | 0.29 | |
| Syringyl derivates | |||||
| Syringol | 154 | 24.82 | 0.83 | 1.44 | 0.49 |
| Syringol, 4-vinyl- | 180 | 29.38 | 0.39 | 0.28 | 0.17 |
| N-containing compounds | |||||
| 1H-Pyrrole, 1-ethyl- | 95 | 8.508 | 0.07 | ||
| Formamide, N,N-dimethyl- | 73 | 11.042 | |||
| Butanal, O-methyloxime(C5H11NO) or Acetamide, N-methyl- | 101/73 | 14.948 | 0.16 | ||
| Other compounds | |||||
| 1,4-Dioxin, 2,3-dihydro- | 86 | 8.099 | 0.33 | 0.32 | 0.18 |
| 2-Pentene, 4-methyl- | 84 | 8.819 | 0.13 | ||
| 2-Cycloocten-1-one | 124 | 12.083 | 0.14 | ||
| 2-Cyclohexen-1-one | 96 | 14.061 | 0.08 | ||
| Linalool oxide | 170 | 15.87 | 0.08 | ||
| 1,3-Dioxolane-2-methanol, 2,4-dimethyl- | 132 | 19.55 | 0.19 | 0.09 | |
| 2-Naphthalenol | 144 | 30.626 | 0.17 | 0.25 | |
| 1-Tridecanol | 200 | 32.569 | 0.13 | 0.11 | 0.1 |
| 1-Naphthalenol, 2-methyl- | 158 | 32.832 | 0.18 | ||
| 2-Naphthyl methyl ketone | 170 | 33.783 | 0.17 | 0.14 | |
Table 2.
DPPH• scavenging activity of the black alder bark water extract and its fractions.
| IC50 mg·L-1 | |
| Crude black alder bark water extract | 7.4 |
| THF-soluble fraction | 5.06 |
| THF-insoluble fraction | 31.07 |
| Irganox1010 | 7.72 |
Table 3.
Pyrolysis products of black alder bark water extract and its PEG 400-insoluble fractions obtained under different conditions.
Table 3.
Pyrolysis products of black alder bark water extract and its PEG 400-insoluble fractions obtained under different conditions.
| Identified compound | MW | Retention time, min | Normalized peak area, % from chromatogram | |||
|---|---|---|---|---|---|---|
| Crude water extract of black alder bark | Fraction insoluble in PEG400, no cat., 6 h., 150℃, 20% |
Fraction insoluble in PEG400, no cat., 6 h., 170℃, 20% |
Fraction insoluble in PEG400, 1% cat., 6 h., 170℃, 30% |
|||
| Carbon dioxide | 44 | 5.035 | 11.72 | 21.13 | 21.89 | 10.82 |
| Water | 18 | 5.198 | 19.61 | 19.37 | 19.72 | 15.75 |
| Carbohydrates derivatives | ||||||
| Formic acid | 46 | 6.637 | 1.2 | 0.35 | 0.36 | 0.42 |
| Acetic acid | 60 | 7.091 | 3.18 | 5.09 | 4.62 | 1.98 |
| (S)-2-Hydroxypropanoic acid | 90 | 7.316 | 0.18 | 0.28 | 0.23 | 0.05 |
| Acetic acid, hydroxy-, methyl ester | 90 | 8.21 | 0.02 | 0.06 | ||
| Formic acid, methyl ester | 60 | 8.322 | 0.45 | 0.22 | 0.17 | 0.2 |
| Propanoic acid | 74 | 8.627 | 0.46 | 0.64 | 0.58 | 0.41 |
| 2-Propenoic acid | 72 | 8.985 | 0.16 | 0.19 | 0.33 | 0.21 |
| Acetic acid, methyl ester | 74 | 9.811 | 0.41 | 0.63 | 0.58 | 0.31 |
| 2-Propenoic acid, methyl ester | 86 | 9.492 | 0.29 | 0.28 | 0.17 | 0.1 |
| 2-Propenoic acid, 2-methyl- | 86 | 10.667 | 0.05 | 0.09 | ||
| Propanoic acid, 2-oxo-, methyl ester | 102 | 10.802 | 0.93 | 0.96 | 0.8 | 0.64 |
| 2-Butenoic acid | 86 | 11.822 | 0.07 | 0.06 | 0.05 | |
| Crotonic acid vinyl ester | 112 | 13.284 | 0.09 | 0.1 | 0.1 | 0.08 |
| Propanoic acid, 2-methylpropyl ester | 130 | 14.583 | 0.1 | 0.11 | 0.07 | 0.07 |
| Propanoic acid, 2-hydroxy-, ethyl ester, (S)- | 118 | 15.542 | 0.06 | |||
| 2-Butene, 1,4-diethoxy- | 144 | 23.224 | 0.42 | 1.71 | 1.22 | 0.78 |
| 1,2-Ethanediol | 62 | 9.492 | 0.15 | 0.25 | 0.49 | 0.23 |
| 1-Butanol, 3-methyl- | 88 | 14.506 | 0.09 | 0.18 | 0.2 | 0.14 |
| 2-Propanol, 1-ethoxy- | 104 | 15.091 | 0.12 | 0.13 | 0.23 | |
| 6-Heptene-2,4-diol | 130 | 15.85 | 0.04 | 0.07 | 0.25 | |
| 2-Heptanol, 5-methyl- | 130 | 16.445 | 1.2 | |||
| Glycerin (1,2,3-Propanetriol) | 92 | 18.403 | 0.6 | 0.41 | 0.4 | 0.23 |
| 4-Heptanol, 2-methyl- | 130 | 22.33 | 0.27 | 0.4 | 0.37 | |
| Methylglyoxal | 72 | 5.698 | 2.84 | 3.57 | 3.3 | 2.41 |
| 2,3-Butanedione | 86 | 6.321 | 0.51 | 0.89 | 0.92 | 0.45 |
| 2-Butanone, 1-hydroxy- | 88 | 6.47 | 0.25 | 0.37 | 0.33 | 0.15 |
| Acetaldehyde, hydroxy- | 60 | 6.952 | 5.82 | 4.08 | 4.12 | 2.95 |
| 2,3-Pentanedione | 100 | 7.526 | 0.19 | 0.38 | 0.33 | 0.31 |
| 2-Propanone, 1-hydroxy- | 74 | 8.047 | 3.89 | 4.8 | 4.18 | 1.3 |
| 2-Butanone, 3-hydroxy- | 88 | 8.687 | 0.09 | 0.17 | 0.06 | |
| 2-Butanone, 1-hydroxy-, isomer | 88 | 9.904 | 0.61 | 0.62 | 0.61 | 0.25 |
| Propanal and Butanedial | 58/86 | 10.983 | 0.11 | 0.68 | 1.02 | 0.35 |
| 3-Hexanone, 4-ethyl- | 128 | 11.867 | 0.06 | 0.1 | 0.09 | 0.07 |
| 2-Propanone, 1-(acetyloxy)- | 116 | 12.38 | 0.65 | 1.06 | 0.71 | 0.33 |
| 2-Heptanone, 3-methyl- | 128 | 12.753 | 0.13 | 0.15 | 0.16 | 0.09 |
| 3-Hexen-2-one, 5-methyl- | 112 | 14.042 | 0.06 | 0.05 | 0.06 | |
| 2-Butanone, 1-(acetyloxy)- | 130 | 14.662 | 0.17 | 0.19 | 0.12 | 0.22 |
| 2-Propanone, 1,3-dihydroxy- | 90 | 15.099 | 0.27 | |||
| Glycolaldehyde dimer | 120 | 16.293 | 0.91 | |||
| 2-Butanone, 4-hydroxy-3-methyl- | 102 | 18.517 | 0.55 | 0.23 | ||
| 2,3-Pentanedione, 4-methyl- | 114 | 17.693 | 0.3 | 0.16 | 0.17 | |
| Propanal, 2,3-dihydroxy- | 90 | 19.243 | 0.36 | 0.22 | 0.15 | 0.06 |
| Pentanal and Pentanadial | 86/100 | 20.559 | 0.22 | 0.76 | 0.96 | 0.09 |
| 3-Pentanone, 2-hydroxy- | 102 | 28.236 | 0.57 | 0.59 | 0.61 | |
| 2-Cyclopenten-1-one | 82 | 11.386 | 0.13 | 0.48 | 0.58 | 0.14 |
| 2-Cyclopenten-1-one, 2-methyl- | 96 | 12.742 | 0.09 | 0.24 | 0.21 | 0.04 |
| 4-Cyclopentene-1,3-dione | 96 | 13.508 | 0.14 | 0.17 | 0.12 | 0.12 |
| 1,2-Cyclopentanedione | 98 | 13.916 | 0.63 | 0.82 | 0.96 | 0.56 |
| 2-Cyclopenten-1-one, 3-methyl- | 96 | 15.203 | 0.2 | 0.27 | 0.27 | 0.1 |
| 1,2-Cyclopentanedione, 3-methyl- | 112 | 16.47 | 0.3 | 0.85 | 0.79 | |
| 2-Cyclopenten-1-one, 2,3-dimethyl- | 110 | 16.566 | 0.07 | 0.1 | 0.11 | 0.15 |
| 2-Cyclopenten-1-one, 3-ethyl- | 110 | 18.042 | 0.05 | 0.06 | ||
| 2-Cyclopenten-1-one, 3-ethyl-2-hydroxy- | 126 | 18.615 | 0.17 | 0.15 | ||
| Furan, 2-methyl- | 82 | 6.059 | 0.39 | 0.4 | 0.49 | 0.36 |
| Furan, 2,5-dihydro-3-methyl- | 84 | 10.101 | 0.05 | 0.07 | ||
| 2(3H)-Furanone | 84 | 10.284 | 0.05 | 0.05 | 0.07 | 0.04 |
| 3(2H)-Furanone | 84 | 10.549 | 0.27 | 0.29 | 0.35 | 0.84 |
| Furfural | 96 | 11.321 | 1.53 | 1.06 | 0.54 | 2.36 |
| Furan, 2-propyl- | 110 | 11.565 | 0.04 | |||
| 2-Furanmethanol | 98 | 12.107 | 0.51 | 0.55 | 0.44 | 0.21 |
| Acetylfuran | 110 | 13.027 | 0.11 | 0.16 | 0.12 | 0.14 |
| 2(3H)-Furanone, dihydro-4-hydroxy- | 102 | 13.651 | 0.26 | 0.29 | 0.33 | 0.38 |
| 2-Furancarboxaldehyde, 5-methyl- | 110 | 14.672 | 0.14 | 0.11 | 0.08 | 0.27 |
| 2(3H)-Furanone, dihydro- | 86 | 15.387 | 0.21 | 0.26 | 0.22 | 0.07 |
| 2(5H)-Furanone | 84 | 15.643 | 0.25 | 0.39 | 0.49 | 0.32 |
| 2,5-Furandione, 3-methyl- | 112 | 16.174 | 0.29 | 2.09 | 2.8 | 1.92 |
| 2(5H)-Furanone, 3-methyl- | 98 | 16.767 | 0.18 | 0.16 | ||
| 3(2H)-Furanone, 4-hydroxy-2,5-dimethyl- | 128 | 17.699 | 0.56 | |||
| Methyl 2-furoate | 126 | 18.6 | 0.13 | 0.11 | ||
| 3-Hydroxydihydro-2(3H)-furanone | 102 | 18.943 | 0.28 | 0.45 | 0.3 | 0.14 |
| 4-Methyl-5H-furan-2-one | 98 | 19.598 | 0.1 | 0.11 | 0.11 | |
| 5-(Hydroxymethyl)dihydro-2(3H)-furanone | 116 | 19.801 | 0.22 | 0.25 | ||
| 2,5-Furandione, dihydro-3-methyl- | 114 | 19.909 | 0.05 | 0.1 | 0.16 | |
| 2(3H)-Furanone, 5-acetyldihydro- | 128 | 21.943 | 0.04 | |||
| Furan, 4-methyl-2-propyl- | 124 | 21.962 | 0.32 | 0.22 | 0.44 | |
| 2,4(3H,5H)-Furandione, 3-methyl- | 114 | 22.375 | 0.16 | 0.43 | ||
| 2(5H)-Furanone, 4-hydroxy-3,5-dimethyl- | 128 | 22.44 | 0.25 | 0.14 | 0.11 | |
| Benzofuran, 2,3-dihydro- | 120 | 23.162 | 1.19 | 0.65 | 0.55 | 0.43 |
| 2-Furancarboxaldehyde, 5-(hydroxymethyl)- | 126 | 24.383 | 0.91 | 0.77 | 0.05 | 1.94 |
| 5-Hydroxymethyldihydrofuran-2-one | 116 | 24.79 | 0.19 | 0.34 | 0.34 | 0.08 |
| 2(3H)-Furanone, dihydro-4-hydroxy- | 102 | 25.095 | 0.11 | 0.09 | 0.09 | |
| Benzofuran, 3-methyl- | 132 | 25.618 | 0.12 | |||
| 4-Hydroxy-,5,6-dihydro-(2H)-pyran-2-one | 114 | 15.928 | 0.38 | 0.18 | 0.17 | 1.27 |
| 4H-Pyran-4-one, 3-hydroxy-2-methyl- | 126 | 18.827 | 0.07 | 0.09 | 0.09 | |
| 4H-Pyran-4-one, 2,3-dihydro-3,5-dihydroxy-6-methyl- | 144 | 20.022 | 0.23 | 0.11 | 0.08 | 0.15 |
| 4H-Pyran-4-one, 3,5-dihydroxy-2-methyl- | 142 | 20.491 | 0.18 | 0.22 | ||
| 2H-Pyran-3(4H)-one, dihydro- | 100 | 22.533 | 0.05 | 0.16 | 0.19 | |
| 2-Hydroxymethyl-5-hydroxy-2,3-dihydro-(4H)-pyran-4-one | 144 | 25.815 | 0.08 | 0.38 | ||
| Isosorbide (D-Glucitol, 1,4;3,6-dianhydro-) | 146 | 22.171 | 0.05 | 0.07 | ||
| 1,4;3,6-Dianhydro-.alpha.-d-glucopyranose | 144 | 22.976 | 0.28 | 0.34 | ||
| 2-Deoxy-D-galactose | 164 | 26.224 | 1.18 | 0.41 | 0.45 | 1.9 |
| DL-Arabinose | 150 | 27.836 | 0.11 | 0.16 | ||
| 1,6-Anhydro--D-glucopyranose; isomer | 162 | 28.689 | 0.19 | 0.28 | 0.32 | 1.52 |
| -D-Glucopyranoside, methyl- | 194 | 30.048 | 0.13 | 0.11 | 0.68 | |
| -D-Glucopyranoside, methyl 3,6-anhydro- | 176 | 31.054 | 0.49 | |||
| 1,6-Anhydro--D-glucopyranose | 162 | 31.457 | 3.73 | 1.55 | 2.69 | 9.32 |
| 1,6-Anhydro--D-glucofuranose | 162 | 34.05 | 0.18 | 0.93 | ||
| Phenyl and benzyl derivates | ||||||
| Phenol | 94 | 17.019 | 1.42 | 0.44 | 0.47 | 0.34 |
| Phenol, 2-methyl- | 108 | 18.221 | 0.2 | 0.17 | 0.15 | 0.05 |
| Phenol, 3-and 4-methyl- | 108 | 19.078 | 0.84 | 0.27 | 0.25 | 0.51 |
| Phenol, 2,3-dimethyl- | 122 | 20.217 | 0.11 | 0.05 | 0.07 | 0.02 |
| Phenol, 2,6-dimethyl | 122 | 21.098 | 0.07 | 0.07 | ||
| Phenol, 4-ethyl- | 122 | 21.161 | 0.29 | 0.06 | 0.1 | 0.3 |
| Phenol, 2,4-dimethyl- | 122 | 21.807 | 0.06 | |||
| 1,2-Benzenediol(Pyrocatechol) | 110 | 24.314 | 7.16 | 0.55 | 0.56 | 1.4 |
| 1,2-Benzenediol, 3-methyl-(Pyrocatechol, 3-methyl-) | 124 | 25.116 | 0.29 | |||
| Phenol, 4-(2-propenyl)- | 134 | 25.256 | 0.1 | 0.07 | ||
| 1,2-Benzenediol, 4-methyl-(Homopyrocatechol) | 124 | 25.974 | 2.51 | 0.08 | 0.12 | 0.44 |
| 1,4-Benzenediol (Hydroquinone ) | 110 | 26.606 | 0.45 | 0.64 | 0.54 | 0.2 |
| 1,4-Benzenediol, 2,3-dimethyl- | 138 | 26.729 | 0.05 | |||
| Phenol, 2-ethoxy-4-methyl- | 152 | 27.483 | 0.07 | 0.1 | 0.08 | |
| 1,2-Benzenediol, 4-ethyl- | 138 | 27.771 | 1.2 | 0.08 | ||
| 1,2-Benzenediol, 3-methoxy- | 140 | 28.164 | 0.51 | 0.11 | ||
| Benzoic acid, 2,5-dimethyl- | 150 | 30.749 | 0.27 | |||
| 2-Butanone, 4-(4-hydroxyphenyl)- | 164 | 31.257 | 0.49 | 0.32 | ||
| Benzoic acid, 4-(1-methylethyl)- | 164 | 32.131 | 0.65 | |||
| Guaiacyl derivates | ||||||
| Guaiacol | 124 | 17.708 | 1.41 | 0.51 | 0.49 | 0.1 |
| p-Methylguaiacol | 138 | 20.178 | 0.21 | 0.05 | 0.05 | 0.08 |
| p-Ethylguaiacol | 152 | 22.111 | 0.22 | |||
| p-Vinylguaiacol | 150 | 23.436 | 0.54 | 0.22 | 0.24 | 0.17 |
| Eugenol | 164 | 23.77 | 0.11 | |||
| Vanillin | 152 | 26.899 | 0.16 | |||
| -Hydroxypropiovanillone | 196 | 30.538 | 0.06 | |||
| Dihydroconiferyl alcohol | 182 | 31.837 | 0.44 | 0.17 | 0.15 | 0.12 |
| Syringyl derivates | ||||||
| Syringol | 154 | 24.646 | 0.84 | 0.22 | 0.18 | 0.15 |
| Syringol, 4-methyl- | 168 | 26.502 | 0.08 | 0.05 | 0.07 | 0.07 |
| Syringol, 4-ethyl- | 182 | 28.01 | 0.08 | |||
| Syringol, 4-vinyl- | 180 | 29.151 | 0.13 | |||
| Other compounds | ||||||
| 1,4-Dioxin, 2,3-dihydro- | 86 | 7.855 | 0.19 | 0.18 | 0.14 | 0.11 |
| 2-Naphthalenol | 144 | 30.263 | 0.06 | |||
| 2-Naphthyl methyl ketone | 170 | 33.393 | 0.42 | 0.15 | ||
| Ethanol, 2-[2-(2-propenyloxy)ethoxy]- | 146 | 22.919 | 0.55 | 0.72 | ||
| Triethylene glycol | 150 | 23.002 | 1.65 | |||
| Ethanol, 2-[2-(2-methoxyethoxy)ethoxy]- | 164 | 27.619 | 0.1 | |||
| Ethanol, 2-[2-(2-ethoxyethoxy)ethoxy]- | 178 | 28.603 | 0.23 | |||
| 1,3-Dioxan-5-ol (Glycerol formal) | 104 | 28.851 | 0.56 | 0.34 | 0.29 | |
| Ethanol, 2,2'-[oxybis(2,1-ethanediyloxy)]bis- | 194 | 28.945 | 0.91 | 0.99 | 2.72 | |
| Ethanol, 2-(2-butoxyethoxy)- | 162 | 31.358 | 1.34 | |||
| Ethanol, 2-[2-(2-ethoxyethoxy)ethoxy]- | 178 | 33.844 | 0.32 | |||
| Hexagol (3,6,9,12,15-Pentaoxaheptadecane-1,17-diol) | 282 | 34.292 | 2.3 | 2.27 | 4.62 | |
| Heptaethylene glycol | 326 | 39.649 | 4.64 | 4.46 | 9.17 | |
Table 4.
Proportion of aromatic moieties to carbohydrates moieties according to FTIR data in the crude black alder bark water extract and its PEG400-insoluble fractions depending on liquefaction conditions.
Table 4.
Proportion of aromatic moieties to carbohydrates moieties according to FTIR data in the crude black alder bark water extract and its PEG400-insoluble fractions depending on liquefaction conditions.
| Liquefaction temperature (°C) | Extract-to-PEG400 ratio | Catalyst, % | Concentration of dissolved extract in PEG solution, % | Percentage of dissolved portion of the introduced extract | Ratio of absorbance at 1100 cm-1 to 1515 cm-1 |
|---|---|---|---|---|---|
| Crude black alder bar water extract | 1.7 | ||||
| 150 | 20:80 | 0 | 17.1 | 85.3 | 3.8 |
| 170 | 20:80 | 0 | 17.0 | 85.0 | 2.9 |
| 130 | 20:80 | 1 | 18.2 | 91.0 | 18.0 |
| 170 | 30:70 | 1 | 23.5 | 78.3 | 5.1 |
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