Soluble Lignin Research Articles

Multi-step purification method of water-soluble oligosaccharides produced from hardwood and softwood

Abstract Pressurized hot water pretreatment was performed on softwood (SW) and hardwood (HW) chips following the same conditions (1 h at 170 °C) in order to partly hydrolyse hemicelluloses. The complete characterization of these sugar enriched autohydrolysates (AH) being rather complex, two different purification methods were conducted. Nanofiltration (NF) 1kDa membrane and ultrafiltration (UF) 3 and 5kDa membranes were used to separate oligosaccharides (OS) from undesired compounds and for their molar mass fractionation. Granulated activated charcoal (GAC) adsorption was also used for hydrolysates detoxification. The chemical nature of OS and side charge groups vary significantly depending of the fractions obtained, e. g. xylans' chain length is positively correlated with the degree of acetylation. UF at 5kDa allows for the total separation of galactoglucomannans (GGMs) from xylans, in SW AH, however, this result was not achieved with HW. From the acid soluble lignin (ASL) removal point of view, membrane filtration from 1kDa is more efficient than activated carbon treatment concerning HW AH, on the contrary to SW AH. Regarding the lignin to OS ratio, for both species, GAC leads to a better sugar purity.

Pretreatment of Hazelnut Shells as a Key Strategy for the Solubilization and Valorization of Hemicelluloses into Bioactive Compounds

Hazelnut industries generate a large amount of byproducts. Among them, waste hazelnut shells (which account for about 50% of the nut weight), are potential raw materials to produce value added products. Hydrothermal pretreatment enables the solubilization of hemicelluloses, while cellulose and lignin remain in the solid phase almost unaltered, allowing their subsequent processing for an integral valorization of the feedstock. When the reaction was performed at the optimal temperature (210 °C), hemicelluloses were mainly converted into soluble substituted oligosaccharides (OS). Further membrane processing of the liquid phase from hydrothermal pretreatment enabled the refining of the OS, which accounted for up to 90.87 wt% of the nonvolatile solutes (NVC) in the refined solution, which also contained 5 g of natural bound phenolics/100 g NVC. The target products showed a dose-dependent antioxidant activity, conferred by the phenolic components. Substituted OS were made up of xylose backbones with a wide degree of polymerization distribution, and showed structures highly substituted by acetyl and uronic groups. The data included in this study provide the basis for assessing the large-scale manufacture of substituted oligosaccharides with bound phenolics as bioactive components of functional use in foods, cosmetics, or pharmaceuticals.

Impact of natural disturbance, forest management and vegetation cover on topsoil biochemical characteristics of Tatra Mts. (Slovakia)

Perturbations caused by windstorms usually lead to the harvesting and clearcutting of fallen trees and wood debris, especially in the areas of managed forest ecosystems. Induced shifts in soils due to management practices play a crucial role in the restoration and maintaining of key ecosystem services. This paper focuses on topsoil chemical properties in relation to vegetation type (trees, shrubs and herbs) evolving at windstorm damaged (in 2004) areas with former Norway spruce (Picea abies) forests in the Tatra Mts. region (Slovakia). We assessed the content of topsoil organic matter fractions (extractives, holocellulose (HC) and lignin (Lig)), carbon in microbial biomass (Cmic), soil organic matter (SOM) and the content of elements N, C, H and S. The study plots represent different types of post-windthrow disturbance history/regime: wooden debris extraction (EXT), wooden debris not extracted (NEX), wooden debris extraction followed by wildfire (FIR), affected by the windstorm in 2014 with the subsequent wooden debris extraction (REX) and unaffected (REF). Our results revealed significant differences among sites in the content of dichloromethane extractives (EXT vs. REX and FIR), acetone extractives (NEX vs. EXT, FIR and REF), ethanol extractives (FIR vs. EXT, NEX and REF), water extractives (FIR vs. REX, NEX) and Cmic (EXT vs. NEX, FIR and REF). The topsoil of Vaccinium myrtillus and Picea abies showed a higher ratio of C/N, N/Lig, and Lig/HC compared to Rubus idaeus, Avenella flexuosa, Calamagrostis villosa, and Larix decidua. The content of N, C, H and S varied between topsoil with shrubs (Vaccinium myrtillus, Rubus idaeus) and grasses (Avenella flexuosa, Calamagrostis villosa). A positive correlation between soil organic matter (SOM) and polar extractives (r=0.81) and a negative correlation between SOM and HC (r=−0.83) was revealed. The carbon content in microbial biomass (Cmic) is positively correlated with acid soluble lignin (ASL) (r=0.85). We also identified a strong correlation between Klason lignin (KL) and the Lig/HC ratio (r=0.97).

Towards oilcane: Engineering hyperaccumulation of triacylglycerol into sugarcane stems

AbstractMetabolic engineering to divert carbon flux from sucrose to oil in high biomass crop like sugarcane is an emerging strategy to boost lipid yields per hectare for biodiesel production. Sugarcane stems comprise more than 70% of the crops' biomass and can accumulate sucrose in excess of 20% of their extracted juice. The energy content of oils in the form of triacylglycerol (TAG) is more than twofold that of carbohydrates. Here, we report a step change in TAG accumulation in sugarcane stem tissues achieving an average of 4.3% of their dry weight (DW) in replicated greenhouse experiments by multigene engineering. The metabolic engineering included constitutive co‐expression of wrinkled1; diacylglycerol acyltransferase1‐2; cysteine‐oleosin; and ribonucleic acid interference‐suppression of sugar‐dependent1. The TAG content in leaf tissue was also elevated by more than 400‐fold compared to non‐engineered sugarcane to an average of 8.0% of the DW and the amount of total fatty acids reached about 13% of the DW. With increasing TAG accumulation an increase of 18:1 unsaturated fatty acids was observed at the expense of 16:0 and 18:0 saturated fatty acids. Total biomass accumulation, soluble lignin, Brix and juice content were significantly reduced in the TAG hyperaccumulating sugarcane lines. Overcoming this yield drag by engineering lipid accumulation into late stem development will be critical to exceed lipid yields of current oilseed crops.

Potential for combined production of food and biofuel: Cultivation of Pleurotus pulmonarius on soft- and hardwood sawdusts

This study aimed at developing an integrated process of production of edible summer oyster mushroom (Pleurotus pulmonarius) and preprocessing of the substrate lignocellulose for producing 2nd-generation biofuels based on softwood. Sawdust-based mushroom substrates of softwood spruce (Picea abies) versus hardwood alder (Alnus glutinosa) as a reference were used for production of summer oyster mushrooms. The substrates had been either hot-air pasteurised or steam sterilised before growing the mushroom. The potential of using spent substrate (SMS) after harvest for biofuel production was evaluated by examining the lignocellulosic composition and enzymatic convertibility. The biological efficiency of the substrates ranged 14.0–33.8% and no significant difference was observed between the treatments. The fruiting bodies had similar total protein concentrations ranging between 26.0 and 28.5% regardless of differences in treatments. The average mass degradation of Klason lignin and acid soluble lignin in the substrates after mushroom production were 35.0 and 22.6%, respectively. Glucan, the major carbohydrate component, was initially present in concentrations ranging from 24 to 29% of total dry matter and with similar concentrations observed in both alder-based and spruce-based substrates. After mushroom production, a significant difference was observed between the substrates with the lowest consumption of glucan, 3.9% of the initial mass, in the spruce-based substrate. The selective degradation ability of P. pulmonarius on the lignin fraction, rather than the cellulose component of softwood, is suggested in the present study. Between 84 and 126 g glucose was yielded per kg of dry SMS, spruce based substrates resulted a higher yield than alder substrate from enzymatic saccharification of the spent substrates. The heat treatment of the mushroom’s substrate had in general a minor impact on the mushroom production and fungal pretreatment of the substrates; hot-air pasteurisation is apparently more energy efficient method than steam sterilisation.

Highly efficient lignin removal from the waste liquor of chemical pulping with an integrated polyaluminium chloride-assisted acidification/activated carbon adsorption process

To separate and utilize the saccharides from the waste liquor is an essential subject with significant economic and environmental benefits for wood bio-refinery of pre-hydrolysis kraft-based dissolving pulp production processing. However, the presence of lignin-derived substances makes this application still a quite challenging problem. In this paper, a novel process is proposed by integrating the polyaluminium chloride (PAC) -assisted acidification and activated carbon adsorption concepts to enhance the lignin removal from the premixed liquor of prehydrolysate and black liquor. The results show that 95.4% of acid-insoluble lignin (from 23.8 to 1.1 g/L) was removed by PAC-assisted acidification at a mild acidification of pH to 6.0 with the condition assisted by PAC concentration of 300 mg/L. This can dramatically reduce the acid consumption compared to traditional acidification when pH around 3.0 was required during the acidification of waste liquor to obtain higher lignin removal. After the removal of acid-insoluble lignin, 70.2% of acid-soluble lignin (from 10.4 to 3.1 g/L) can be removed by the treatment of optimized adsorption of activated carbon. Meanwhile, it was found that the presence of acid-insoluble lignin would deposit and block the pore structure on the activated carbon, thus affecting the further adsorption of acid-soluble lignin on the activated carbon. When the concentration of acid-insoluble lignin was over 1.5 g/L, this negative effect became very obvious, which was confirmed by the analysis of specific surface area and the observation of scanning electron microscope. This is an important, if not major, finding that will offer valuable reference on the optimization of acid soluble lignin removal by adsorption treatment in the future.

Insight into papermaking characteristics of D0EPD1-bleached soda, soda-AQ and kraft pulps of citronella grass (Cymbopogon winterianus Jowitt)

Grasses have emerged as potential alternative raw materials which can replace wood for pulp and paper products. Various species of grasses have been explored previously for pulp and paper production. This study is aimed to investigate pulp and papermaking characteristics of a grass species namely Cymbopogon winterianus Jowitt which is commonly known as citronella grass. This grass was subjected to proximate chemical characterisation; fibre morphology analysis; soda, soda-AQ (soda-anthraquinone), and kraft pulping; elemental chlorine free bleaching using D0EPD1 (D = ClO2 in acidic medium; EP = alkaline extraction with addition of H2O2; 0 and 1 = initial and final stage) sequence; and evaluation of physical strength properties of paper hand sheets. The pulp and paper hand sheets were also examined through SEM (scanning electron microscope) and FTIR (Fourier-transform infrared) spectroscopy to observe the structural and functional group variations. The proximate chemical analysis of citronella grass was found superior in terms of α-cellulose (38.10%), pentosans (22.30%) and alkali solubility (28.20%) while inferior in terms of ash (8.20%), lignin (25.10%) and alcohol benzene solubility (6.31%) with respect to some other grass species used for pulp and papermaking. Fibre length (0.69–0.74 mm) and fibre width (13.8–15.1 μm) were also comparable to other grass species. Brown pulp characteristics such as screened yield (44.67%), brightness (~24 %ISO) and kappa number (~20) revealed superiority of soda-AQ pulping among all the pulping processes while the kraft pulp exhibited the highest brightness (83.05 %ISO) and intrinsic viscosity (17.6 cP) after D0EPD1 bleaching. Tear index, tensile index and burst index of paper hand sheets obtained from bleaching of soda-AQ and kraft pulps were almost similar but higher to that of bleached soda pulp. The citronella grass was found suitable for producing writing and printing grade paper based on processes and optimised parameters described in this study.

Novel betaine-amino acid based natural deep eutectic solvents for enhancing the enzymatic hydrolysis of corncob

A novel natural deep eutectic solvent (NDES) with water content ranging from 65 to 93 wt%, in which betaine (Bet) acts as the cation and amino acids (AAs) as the anions, was prepared by a simple and green chemical route. [Bet][AA] NDES showed excellent xylan and lignin solubility, however, scare cellulose solubility. A mild and facile pretreatment process with [Bet][AA] NDES was carried out at 60 °C for 5 h. The enzymatic hydrolysis efficiency of cellulose and corncob was significantly improved. Detailed characterization showed that the enhancement of cellulose digestibility derived mainly from xylan and lignin removal. Xylan and lignin removal for [Bet][Lys]-W87 was 47.68 and 49.06%, while it was 42.20% and 57.01% for [Bet][Arg]-W82, respectively. FT-IR, SEM, XRD, and HSQC NMR studies confirmed the effectiveness and mechanism of [Bet][Lys]-W87 and [Bet][Arg]-W82 on biomass pretreatment.

Sodium hydroxide or urea pretreatment of acerola (Malpighia emarginata) fruit residue increases dry matter degradability and reduces methane production in in vitro rumen fermentation.

The aim of this study was to evaluate the effect of adding different concentrations of either urea or NaOH in dehydrated acerola (Malpighia emarginata) fruit residue (DAFR) on chemical composition, in vitro rumen degradability, and gas and methane production. A completely randomized design was used with the following seven treatments: control, without chemical treatment, or pretreatment of DAFR with urea or NaOH at 20, 40, or 60g/kg dry matter (DM). DM degradability and gas and methane production of DAFR were evaluated by semi-automated in vitro gas production technique. DAFR treated with urea or NaOH at concentrations of 40 and 60g/kg DM decreased its neutral detergent fiber (P = 0.0115) and lignin (P < 0.0001) content, and this reduction was greater with the highest concentration (60g/kg DM). In all tested concentrations, urea and NAOH were effective to increase the DM effective degradability of DAFR compared with the control treatment, although treatments with a concentration of 60g/kg DM presented the highest values (P < 0.0001). Treatment of DAFR with NaOH or urea at 60g/kg DM promotes greater lignin solubilization and DM degradability and lower gas and methane production in in vitro rumen fermentation.

Recovery of nano-lignin from anaerobic treated palm oil mill effluent (AT-POME)

Lignin is the main polymers in woody biomass aside cellulose and hemicelluloses Recently, nano-lignin is gaining importance due to the increasing demand for bio-based and bio-active nanomaterial fillers for many applications such as in composite and textile industries. Palm oil mill effluent (POME) is the main wastewater produce by palm oil mills. Anaerobically treated (AT-POME) contains high soluble lignin due to the anaerobic digestion of cellulosic material in POME. Nano-lignin was precipitated by adjusting the initial pH of AT-POME during the sonication process. Sulfuric acid (H2SO4), nitric acid (HNO3), hydrochloric acid (HCl) and phosphoric acid (H3PO4) were used to adjust the initial pH of AT-POME. Result shows that sulfuric acid was the most suitable acid to be used as it could recovered 96% of the soluble lignin in AT-POME. The presence of ultrasonic during the precipitation process had reduced the size to 383.4 nm. The optimum operating parameter for lignin recovery is at pH 4 using sulfuric acid and sonicated at 80 watts for 15 minutes. This study shows that sonication could reduce the size of precipitated lignin from AT-POME. In addition, removal of lignin from AT-POME also reduced the COD content of AT-POME.

The effect of malt extract and incubation time on ethanol production from lignocellulose degradation of oil palm empty fruit bunches (OPEFB) using Phlebia sp. MG-60

This study aimed to evalute the effects of the addition of malt extract and incubation time on ethanol production from lignocellulose degradation of OPEFB using Phlebia sp. MG-60. The first experiment was conducted to figure out the best treatment of the addition of malt extract (0; 0.1; 0.2; 0.3 g/L) for the degradation of lignocellulose using Phlebia sp. MG-60 for 28 days, then followed with the ethanol production which incubated into diferent time courses (0, 3, 5, and 7 days). Total reducing sugar (TRS), total soluble phenol (TSP), pH, lignin concentration, weight loss and ethanol concentration were analyzed to identify the changes on the breakdown of lignocellulose. The best treatment was obtained from the addition of malt extract 0.2 g/L with the highest amount on TRS (26.489 mg/g) incubated for 15 days. While weight loss (19.01%) and the lowest lignin residue (12.61%) were obtained from culture incubated for 28 days. Meanwhile the highest ethanol concentration was 0.28% obtained from 5 days culture.

The effect of MnSO4 and unrefined sea salt on bioethanol production by lignocellulose degradation of oil palm empty fruit bunches (OPEFB) using Phlebia sp. MG-60

This study aimed to determine the effects of MnSO4 and sea salt against the degradation lignocellulose and ethanol production generated from Oil Palm Empty Fruit Bunches (OPEFB) using Phlebia sp. MG-60. The factorial experiment in a randomized block design was used, consists of two factors: MnSO4 concentration (0, 300, and 600 mg/L), sea salt concentration (0%, 3%, and 5% (w/v). The results revealed that the addition of MnSO4 and sea salt to substrate, and its interaction were significantly different (ρ value < 0.05) on the change of total soluble phenols (mg/g), total reducing sugar (mg/g), pH, lignin concentration (%), weight loss (%) and ethanol concentration (%). The best treatment from this study was obtained from the addition of MnSO4 300mg/l, sea salt 3% incubated for 20 days. This treatment has the highest value of total reducing sugars (22.471 mg/g), total soluble phenols (0.334 mg/g), weight loss (16.23%), ethanol (0.71%), lignin (19.17%) and pH (6.1).

Near-complete enzymatic hydrolysis efficiency of Miscanthus using hydrotropic fractionation at atmospheric pressure

Enhanced enzymatic saccharification of Miscanthus (MC) biomass, based on a novel benzenesulfonic acid (BA)-induced fractionation at mild condition as the pretreatment, gives a good example for the efficient transformation of energy crops into value-added products with minimal environmental impact. The results indicated that BA could facilitate the rapid and high solubilization of both lignin and hemicellulose, approximately 90.8 % of lignin and 75.5 % of hemicellulose were removed at 80 °C within 20 min. Consequently, the subsequent enzymatic hydrolysis efficiency was greatly enhanced to obtain an improved enzymatic digestibility with a high glucose yield of 97.9 %. Our study opens up an innovative avenue for the efficient valorization of the recalcitrant energy crops as MC.

Optimization of temperature and pretreatments for methane yield of hazelnut shells using the response surface methodology

In this study, NaOH pretreatment, H2SO4 pretreatment, thermal pretreatment and production temperature were optimized to ensure maximum methane yield from hazelnut shells (HS) using the response surface methodology (RSM). A Box-Behnken design was achieved with four different independent variables and one dependent variable (methane yield). A total of 29 tests were performed after pretreatment according to the RSM design and to different production temperatures, suggesting optimum values for NaOH pretreatment, H2SO4 pretreatment, thermal pretreatment and production temperature were 3.5% w/v, 2.56% v/v, 145.66 °C and 34.65 °C, respectively. Under these conditions, the RSM-predicted methane yield was 215.896 mL/g volatile solid (VS). The high R2 value (0.9904) showed that the model could be applied effectively in the digestion of HS for the predicted methane yield according to the production temperature and pretreatments. In addition, lignocellulosic solubilisation was tested after pretreatment of the reactors according to the RSM operating conditions, which showed that the highest cellulose, hemicellulose and lignin solubilisation that could be achieved was 38.7% w/w (R10), 36.9% w/w (R22) and 50.5% w/w (R10), respectively. The modified Gompertz model supported the experimental cumulative methane yields (CMYs).

Seasonal changes in eastern hemlock (Tsuga canadensis) foliar chemistry

Eastern hemlock (Tsuga canadensis (L.) Carrière) is an eastern North American conifer threatened by the invasive hemlock woolly adelgid (Adelges tsugae Annand). Changes in foliar terpenes and phenolics were evaluated in new (current-year growth) and mature (1-year-old growth) hemlock needles during the growing season and into plant dormancy. From April through September, foliar concentrations of nonvolatile soluble phenolics, condensed tannins, lignin, mono- and sesquiterpenes, α-pinene, camphene, isobornyl acetate, and diterpene resin were quantified. After September, additional analyses of metabolites that continued to differ significantly between new and mature foliage were carried out. Total soluble phenolic and condensed tannin concentrations in new foliage remained low relative to those of mature foliage throughout the growing season and converged in December. Lignin concentration in new foliage converged with that of mature foliage by July. Concentrations of α-pinene, camphene, isobornyl acetate, and diterpene resin in new foliage converged with those of mature foliage within 1 month of budbreak. The convergence of terpene concentrations in new and mature foliage suggests that these metabolites may play a role in herbivore defense during the peak growing season. Conversely, soluble phenolics, including condensed tannins, may defend foliage from herbivory outside of the spring growth period.

Boosting landfill gas production from lignin-containing wastes via termite hindgut microorganism

Lignocellulose comprises a significant portion of municipal solid waste (MSW) − 40–70% in developed countries, including paper, wood, and yard waste. Cellulose and hemicellulose are often shielded by lignin, posing a barrier to waste decomposition and landfill gas generation. Unfortunately, lignin is resistant to microbial degradation under low-oxygen conditions that normally occur in MSW landfills.The bacterium strain TAV5, microaerophilic and member of phylum Verrucomicrobia, isolated from the hindgut of the Reticulitermes flavipes termite, the most widely distributed subterranean termite in North America. Its genome contains genes associated with methylotrophic competency which code for enzymes that structurally modify lignin. The overall goal of this research was to use TAV5 to modify lignin and boost methane production from MSW.Batch-scale reactors (125 mL) were filled with paper, yard, or wood waste, and four ratios of mixed of waste. Reactors were seeded with different ratios of TAV5 to anaerobic digester (AD) microorganisms (representing landfill anaerobic microorganisms). Based on batch tests, optimal ratios of TAV5 to AD microorganisms were used to seed wastes (mixed, yard, and wood) in 6-gallon reactors.Addition of TAV5 increased methane production from mixed waste, yard waste, and wood, by 49%, 34%, and 297%, respectively. TAV5 decreased acid soluble lignin by 7–39%, depending on waste type. TAV5 grown under aerobic conditions and room temperature (not requiring a heated anaerobic chamber) was found to remain viable and increase methane production under low-level oxygen conditions (1–2%). This finding will potentially lessen costs for growing large volumes of it for seeding landfills.

Silicon mediated improvement in agronomic traits, physiological parameters and fiber content in Oryza sativa

Silicon, a quasi-essential element that is often associated with rigidity and hardiness is an alleviator of biotic and abiotic stresses. Lodging affects the ability of plants especially cereal plants such as rice, Oryza sativa to grow upright, thus reducing yield and increasing harvesting costs. Bending or lodging resistance could be increased by strengthening the rice culm. Here, we tested stage and method of silicon application, each with three levels of treatments to find the right combination to enhance yield and lodging resistance in MR219, a popular rice variety in Malaysia. Application of silicon at the onset of reproductive stage via topdressing improved agronomic and physiological parameters. Plants applied with Si at the reproductive stage by means of topdressing showed a significantly higher leaf area. Number of tillers, weight per panicle and weight of 100 grains were significantly higher when silicon was applied as topdressing at the reproductive stage. Number of spikelets per panicle was significantly higher when silicon was supplied as topdressing or soil incorporation. Percentage of filled spikelets was significantly higher when silicon supplementation was done as topdressing at either reproductive or maturity stages. Mode of application which favoured the increase in soluble lignin and neutral detergent fiber was topdressing and soil incorporation. Meanwhile, cellulose and acid detergent lignin was highest when silicon was applied at the reproductive and maturity stages. Application of silicon at the reproductive stage by means of topdressing was effective in improving growth, yield and stem strength of the rice plant since the method has higher retention time and has residual effect. Foliar application was deemed unsuitable as it can only be applied in minimal amount while showing a temporary effect.

Lignocellulosic Biomass Mild Alkaline Fractionation and Resulting Extract Purification Processes: Conditions, Yields, and Purities

Fractionation of lignocellulose is a fundamental step in the valorization of cellulose, hemicelluloses, and lignin to produce various sustainable fuels, materials and chemicals. Strong alkaline fractionation is one of the most applied processes since the paper industry has been using it for more than a century, and the mineral acid fractionation process is currently the most applied for the production of cellulosic ethanol. However, in the last decade, mild alkaline fractionation has been becoming increasingly widespread in the frame of cellulosic ethanol biorefineries. It leads to the solubilization of hemicelluloses and lignin at various extent depending on the conditions of the extraction, whereas the cellulose remains insoluble. Some studies showed that the cellulose saccharification and fermentation into ethanol gave higher yields than the mineral acid fractionation process. Besides, contrary to the acid fractionation process, the mild alkaline fractionation process does not hydrolyze the sugar polymers, which can be of interest for different applications. Lignocellulosic mild alkaline extracts contain hemicelluloses, lignin oligomers, phenolic monomers, acetic acid, and inorganic salts. In order to optimize the economic efficiency of the biorefineries using a mild alkaline fractionation process, the purification of the alkaline extract to valorize its different components is of major importance. This review details the conditions used for the mild alkaline fractionation process and the purification techniques that have been carried out on the obtained hydrolysates, with a focus on the yields and purities of the different compounds.

Root cause analysis of cationic polymer additive efficiency decline in virgin and recycle containerboard mills

It is well known that retention, drainage and strength polymers struggle to perform (if at all) in virgin containerboard mills. In-depth studies have been undertaken in this area for more than seven years, investigating the issue from all directions. A key finding of this work is that soluble lignin is detrimental to chemical efficiency. A strong correlation exists between decreased chemical efficiency and high soluble lignin. Both recycled systems and virgin systems have been studied, and this correlation holds true regardless of furnish. The primary area of concern is virgin container-board, because these mills tend to have the highest lignin levels. Some highly closed recycled mills can also build elevated lignin levels that can negatively affect chemical efficiency.

Hemp harvest time impacts on the dynamics of microbial colonization and hemp stems degradation during dew retting

Dew retting, a selective microbial degradation of industrial hemp (Cannabis sativa L.) stems occurring after harvest under local climatic conditions, is an important field process for plant fibre uses. We investigated how the crop harvest time, which depends on the hemp valorization strategy envisaged by the farmer, affected the initial stem quality and the subsequent microbial degradation dynamics of retting. We used simulated rains and dews to carry out retting under laboratory conditions for 42 days at 15 °C with hemp stems harvested at different times (flowering and seed maturity stage). The microbial colonization and changes in the bast tissue architecture were tracked from day 0 to day 42 using colorimetry, surface infrared spectroscopy, chemical analysis, and scanning electron microscopy. The early changes in the microbial colonization and color of the stem surface and the degradation of the bast tissue parenchyma followed the same pattern during retting for the two stem qualities. However, the kinetic of these processes was 7–14 days faster for the flowering stems, which had higher initial soluble and lower lignin contents than the mature stems. The results suggest a promising potential use of colorimetry and surface infrared spectroscopy data as candidate indicators for the dew retting progress in the field. Besides the results of this study indicate that differences in hemp stem chemical composition due to different crop harvest time significantly impacted microbial colonization, biofilm formation and eventually dew retting duration.