Fate of Antioxidative Compounds within Bark during Storage: A Case of Norway Spruce Logs

Softwood bark is an important by-product of forest industry. Currently, bark is under-utilized and mainly directed for energy production, although it can be extracted with hot water to obtain compounds for value-added use. In Norway spruce (Picea abies [L.] Karst.) bark, condensed tannins and stilbene glycosides are among the compounds that comprise majority of the antioxidative extractives. For developing feasible production chain for softwood bark extractives, knowledge on raw material quality is critical. This study examined the fate of spruce bark tannins and stilbenes during storage treatment with two seasonal replications (i.e., during winter and summer). In the experiment, mature logs were harvested and stored outside. During six-month-storage periods, samples were periodically collected for chemical analysis from both inner and outer bark layers. Additionally, bark extractives were analyzed for antioxidative activities by FRAP, ORAC, and H2O2 scavenging assays. According to the results, stilbenes rapidly degraded during storage, whereas tannins were more stable: only 5–7% of the original stilbene amount and ca. 30–50% of the original amount of condensed tannins were found after 24-week-storage. Summer conditions led to the faster modification of bark chemistry than winter conditions. Changes in antioxidative activity were less pronounced than those of analyzed chemical compounds, indicating that the derivatives of the compounds contribute to the antioxidative activity. The results of the assays showed that, on average, ca. 27% of the original antioxidative capacity remained 24 weeks after the onset of the storage treatment, while a large variation (2–95% of the original capacity remaining) was found between assays, seasons, and bark layers. Inner bark preserved its activities longer than outer bark, and intact bark attached to timber is expected to maintain its activities longer than a debarked one. Thus, to ensure prolonged quality, no debarking before storage is suggested: outer bark protects the inner bark, and debarking enhances the degradation

Fate of Antioxidative Compounds within Bark during Storage: A Case of Norway Spruce Logs

Softwood bark is an important by-product of forest industry. Currently, bark is under-utilized and mainly directed for energy production, although it can be extracted with hot water to obtain compounds for value-added use. In Norway spruce (Picea abies [L.] Karst.) bark, condensed tannins and stilbene glycosides are among the compounds that comprise majority of the antioxidative extractives. For developing feasible production chain for softwood bark extractives, knowledge on raw material quality is critical. This study examined the fate of spruce bark tannins and stilbenes during storage treatment with two seasonal replications (i.e., during winter and summer). In the experiment, mature logs were harvested and stored outside. During six-month-storage periods, samples were periodically collected for chemical analysis from both inner and outer bark layers. Additionally, bark extractives were analyzed for antioxidative activities by FRAP, ORAC, and H2O2 scavenging assays. According to the results, stilbenes rapidly degraded during storage, whereas tannins were more stable: only 5–7% of the original stilbene amount and ca. 30–50% of the original amount of condensed tannins were found after 24-week-storage. Summer conditions led to the faster modification of bark chemistry than winter conditions. Changes in antioxidative activity were less pronounced than those of analyzed chemical compounds, indicating that the derivatives of the compounds contribute to the antioxidative activity. The results of the assays showed that, on average, ca. 27% of the original antioxidative capacity remained 24 weeks after the onset of the storage treatment, while a large variation (2–95% of the original capacity remaining) was found between assays, seasons, and bark layers. Inner bark preserved its activities longer than outer bark, and intact bark attached to timber is expected to maintain its activities longer than a debarked one. Thus, to ensure prolonged quality, no debarking before storage is suggested: outer bark protects the inner bark, and debarking enhances the degradation

Structure and properties of soda-type lignin from a modern biorefinery process

Due to the increasing concerns regarding the use of crude oil for fuel and chemical production, considerable efforts have been made to find renewable and sustainable alternatives. Lignocellulosic biomass is the most abundant carbon containing natural resource on earth and mainly consists of its structural components cellulose, hemicellulose, and lignin. Compared to the carbohydrate constituents, lignin is structurally completely different. It is derived from aromatic monomers which makes it an attractive feedstock for the production of renewable chemicals. For over a century the pulp and paper industry has been fractionating lignocellulosic biomass to isolate cellulose and to use the remaining hemicellulose and lignin for heat and energy production. To develop new products from lignocellulosic biomass, additional fractionation technologies need to be explored. The polymer structure of lignin is inherently complex and will structurally not only vary between plant species, but technical isolation methods will further alter its structure. As such each fractionation technology will yield a different type of lignin with different properties compared to other lignin. Due to these reasons, it is crucial to understand the structural features of different lignin to determine the best application area. In this thesis three different lignin, one hardwood and two softwood lignin, from a pressurized hot water extraction followed by mild soda cooking biomass fractionation technology were thoroughly investigated. A precipitation and purification protocol were developed to yield lignin samples free of contamination. The different lignin fractions were analyzed and compared to native-like lignin samples. A wide variety of analytical methods were used and the combined information from the analysis could be used to determine key structural features and properties of the lignin. Also model compounds with specific structural features were synthesized and the spectroscopic data was used to assist in the structural elucidation of the analyzed lignin. As a proof of concept, the purified lignin was fractionated into even more homogeneous fractions by simple solvent fractionation. Chemical modifications were used to investigate how simple modifications affected the thermal properties of lignin and were also used for to assist the structural determination. During this thesis a 31P PULCON methodology was implemented to one of the most used lignin analysis methods, the quantitative determination of hydroxyl groups in lignin by 31P NMR spectroscopy, which showed to have benefits compared to the standard protocol.På grund av oron kring användningen av råolja för produktion av bränsle och kemikalier har stora ansträngningar gjorts för att hitta förnybara och hållbara alternativ. Lignocellulosisk biomassa är den mest förekommande kolhaltiga naturresursen på jorden och består huvudsakligen av de strukturella komponenterna cellulosa, hemicellulosa och lignin. Jämfört med kolhydratkomponenterna är lignin strukturellt helt annorlunda. Lignin härrör från aromatiska monomerer och är därför en attraktiv råvara för förnybara kemiska produkter. I över ett sekel har massa- och pappersindustrin fraktionerat lignocellulosabiomassa för att isolera cellulosa och använda den resterande hemicellulosan och ligninet för värme- och energiproduktion. För att utveckla nya produkter från lignocellulosisk biomassa behöver ytterligare fraktioneringstekniker utvecklas. Ligninpolymeren är i sig komplex och kommer strukturellt inte bara att variera mellan växtarter, utan tekniska isoleringsmetoder förändrar ytterligare dess struktur. Detta leder till att varje fraktioneringsteknik kommer att ge en säregen typ av lignin med olika egenskaper jämfört med andra lignin. På grund av dessa orsaker är det väsentligt att förstå ligninets struktur för att avgöra det bästa tillämpningsområdet. I denna avhandling undersöktes tre olika lignin, ett från lövträd och två från barrträd. Ligninet hade sitt ursprung från en biomassafraktioneringsteknik som använder sig av vattenextraktion under förhöjt tryck följt av en mild alkalisk sodaprocess. Ett tillvägagångssätt för att utfälla och rena ligninet utvecklades för att ge analytiskt rena ligninprover. De olika ligninfraktionerna analyserades och jämfördes med ligninprov med oförändrad nativ struktur för att förstå hur processen påverkade ligninets struktur. En mängd olika analysmetoder användes och den kombinerade informationen från analyserna kunde användas för att bestämma viktiga strukturella särdrag och egenskaper hos ligninet. Modellföreningar med specifika strukturer framställdes och deras spektroskopiska data användes för att underlätta strukturbestämningen av ligninet. För att vidare validera konceptet fraktionerades det renade ligninet till ännu mer homogena fraktioner genom enkel lösningsmedelsfraktionering. Kemiska modifieringar användes för att undersöka hur enkla modifieringar påverkade ligninets termiska egenskaper och för att underlätta strukturbestämningen. I denna avhandling implementerades även 31P PULCON-metodik för att kvantitativt bestämma mängden av hydroxylgrupper i lignin. Metoden visade sig ha vissa fördelar jämfört med standardprotokollet

Non-thermal gas-phase pulsed corona discharge for lignin modification

Lignin has the potential to become a significant resource of renewable aromatics for the chemical industry. The current work studies pulsed corona discharge (PCD) as an alternative method for lignin modification. The effect of initial lignin concentration and gas phase composition on aldehydes formation was studied experimentally. Kraft lignin was used as a test compound. It was concluded in the work, that treatment in low oxygen content atmosphere and high initial lignin concentration leads to higher lignin conversion to aldehydes. Despite the proven aldehydes formation, the precise nature of the changes in the lignin structure during oxidation with PCD remained unclear. To address this question, a number of advanced analytical techniques were implemented: NMR, GPC, HSQC, HPSEC, and GCMS. The effect of PCD treatment on lignin structure was studied for two types of lignin: kraft lignin, purchased from Sigma Aldrich, and birch lignin acquired from a pressurized hot water extraction and soda pulped biorefinery process (BLN lignin). Changes in solubility, molecular weight and proportion of phenolic and aliphatic OH groups, as well as lignin repolymerization were detected. The findings are of value to efforts to make lignin modification tunable to the production of desired products.Peer reviewe

Structural and Thermal Analysis of Softwood Lignins from a Pressurized Hot Water Extraction Biorefinery Process and Modified Derivatives

In this work we have analyzed the pine and spruce softwood lignin fraction recovered from a novel pressurized hot water extraction pilot process. The lignin structure was characterized using multiple NMR techniques and the thermal properties were analyzed using thermal gravimetric analysis. Acetylated and selectively methylated derivatives were prepared, and their structure and properties were analyzed and compared to the unmodified lignin. The lignin had relatively high molar weight and low PDI values and even less polydisperse fractions could be obtained by fractionation based on solubility in i-PrOH. Condensation, especially at the 5-position, was detected in this sulphur-free technical lignin, which had been enriched with carbon compared to the milled wood lignin (MWL) sample of the same wood chips. An increase in phenolic and carboxylic groups was also detected, which makes the lignin accessible to chemical modification. The lignin was determined to be thermally stable up to (273–302 °C) based on its Tdst 95% value. Due to the thermal stability, low polydispersity, and possibility to tailor its chemical properties by modification of its hydroxyl groups, possible application areas for the lignin could be in polymeric blends, composites or in resins

Reductive Catalytic Depolymerization of Semi-industrial Wood-Based Lignin

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