Kenneth Sundberg

Knots in trees - A new rich source of lignans

Recent research in our group has revealed that knots, i.e. the branch bases inside tree stems, commonly contain 5–10% (w/w) of lignans. Norway spruce (Picea abies) knots contain as much as 6–24% of lignans, with 7-hydroxymatairesinol (HMR) as the predominant (70–85%) lignan. Some other spruce species also contain HMR as the main lignan, but some spruce species have also other dominating lignans. Most fir (Abies) species contain secoisolariciresinol and lariciresinol as the main lignans. Lignans occur also in knots of pines (Pinus spp.), although in lower amounts than in spruces and firs. Scots pine (Pinus silvestris) knots were found to contain 0.4–3% of lignans with nortrachelogenin as the main lignan. Lignans have been identified also in knots of some hardwoods, although flavonoids are more abundant in hardwoods. Knots are detrimental in the manufacture of pulp and paper and should preferably be removed before pulping. This is possible using a recently developed industrially applicable process called ChipSep. Recent research has also established novel synthetic routes to several lignans, such as matairesinol, secoisolariciresinol, lariciresinol and cyclolariciresinol, starting from hydroxymatairesinol by applying fairly straight-forward chemical transformations. We conclude that wood knots in certain spruce and fir species constitute the richest known source of lignans in nature. The lignans occur in knots in free form and are easily extracted by aqueous ethanol, or even by water. Not only HMR, but also other potentially valuable lignans, could be produced in a scale of hundreds of tons per year by extraction of knots separated from wood chips at pulp and paper mills.

Acetylation and characterization of spruce (Picea abies) galactoglucomannans

Acetylated galactoglucomannans (GGMs) are the main hemicellulose type in most softwood species and can be utilized as, for example, bioactive polymers, hydrocolloids, papermaking chemicals, or coating polymers. Acetylation of spruce GGM using acetic anhydride with pyridine as catalyst under different conditions was conducted to obtain different degrees of acetylation on a laboratory scale, whereas, as a classic method, it can be potentially transferred to the industrial scale. The effects of the amount of catalyst and acetic anhydride, reaction time, temperature and pretreatment by acetic acid were investigated. A fully acetylated product was obtained by refluxing GGM for two hours. The structures of the acetylated GGMs were determined by SEC-MALLS/RI, (1)H and (13)C NMR and FTIR spectroscopy. NMR studies also indicated migration of acetyl groups from O-2 or O-3 to O-6 after a heating treatment in a water bath. The thermal stability of the products was investigated by DSC-TGA.

Chemical Changes in Thermomechanical Pulp at Alkaline Conditions

Abstract Chemical changes in thermomechanical pulp (TMP) from Norway spruce at alkaline conditions were examined at pH levels 9, 10, and 11, and temperatures of 40, 50, and 60°C. Alkali treatments were also made in the presence of hydrogen peroxide. The anionic charge of the fibres increased rapidly, following the kinetics of ester bond cleavage. Already at pH 9 and 60°C, acetic acid, methanol, pectic acids, and some lignin material were dissolved. Dissolution of xylans required higher pH. Lignin and xylans slowly leached into the water without affecting fibre charge. Leaching caused substantial material loss during extended alkali treatment. At pH 11, hydrogen peroxide almost doubled the overall loss of wood material compared with alkali only. This was partly due to acceleration of the dissolution of xylans and lignin material, but also due to considerable formation of low-molar-mass oxidation products. The effect of hydrogen peroxide on fibre charge was considerable also during extended treatment.

Determination of surface energy and wettability of wood resins

Abstract The surface energy components of the lipophilic extractives isolated from thermo-mechanical pulp fibers have been determined. The influence of the chemical composition of the resin droplets on the surface properties was investigated. Furthermore, the critical surface tensions, as defined by Zisman [1,2], were determined for layers of the different resins applied on a stainless-steel surface. The resins were found to be rather lipophilic, although extensive acid-base interactions with the surrounding media were detected. We further observed that surface active substances dissolved in the continuous aqueous phase show self-associating tendencies.