Heli Kangas

Effects of commercial cellobiohydrolase treatment on fiber strength and morphology of bleached hardwood pulp

Abstract Development of fiber strength properties and morphological changes on the surface of bleached hardwood kraft pulp after treatment with commercial cellobiohydrolase (CBH) was evaluated. Tensile and tear indices showed no significant effect of the treatment. The treatment resulted in reduction of wet zero-span strength, while the dry zero-span values increased. The decrease in wet zero-span values was most likely caused by preferential action of CBH on structurally irregular zones in the fiber wall coupled with greater sensitivity of wet zero-span testing towards the localized fiber defects. The fracture zone of the wet zero-span tested samples was imaged by scanning electron microscopy (SEM). Visual observation revealed differences in fiber fracture between treated and control samples. The straighter and cleaner fractures of the treated sample could be attributed to the localized hydrolytic action of CBH. Visual analysis of the treated fiber surface morphology by SEM showed an increase of more visible fiber wall dislocations, particularly on fibers of smaller diameter. The increased presence of the fiber dislocation correlates with the decrease in the wet zero-span values of treated samples.

Characterization of dissolved lignins from acetic acid Lignofibre (LGF) organosolv pulping and discussion of its delignification mechanisms

Abstract Birch chips were cooked by means of the Lignofibre (LGF) organosolv process in acetic acid (AA) and phosphinic acid (H3PO2) at 150°C. The delignification rate and structure of the dissolved lignin was followed as a function of time. The degree of delignification increased steadily up to 88% during the 120 min treatment time. The dissolved lignins were precipitated from the spent liquor (SL) by water addition, washed, and purified for the analyses. Elemental analysis, 31P nuclear magnetic resonance (NMR), heteronuclear single-quantum coherence (HSQC) NMR, pyrolysis-gas chromatography/mass spectrometry (GC/MS), and gel permeation chromatography (GPC) were applied for the structural elucidation. It was found that the cleavage of the β-aryl ether linkages is the main reaction leading to delignification, accompanied by the formation of free phenolic hydroxyl groups and reduction in the content of aliphatic hydroxyl groups. The structure of the dissolved lignin remained the same after the drastic changes at the early stages of cooking (up to 30 min cooking time), indicating that secondary reactions (e.g., condensation) do not take place to a significant extent. H3PO2 probably enhances the acidolysis reaction via an ester derivative that both boosts the cleavage reaction and prevents the formation of the carbocation intermediate that induces condensation. Homolytic cleavage reactions may take place parallel to the acidolytic reactions.

Effect of cellulose microfibril (CMF) addition on strength properties of middle ply of board

Cellulose microfibrils (CMF) are a promising biobased material with unique nanospecific properties, giving them potential for use in numerous applications. Based on this, cost-effective and novel high-consistency enzymatic fibrillation (HefCel) technology was used to produce CMF, which was further used to reinforce middle ply of board structure and the results compared with those obtained without CMF addition and with addition of CMF produced by traditional Masuko grinding (VTT Native grade). The results showed an average increase in tensile index of middle ply of board of approximately 50% with VTT Native grade and approximately 15% with HefCel grade at 3% CMF dosage. According to special board measurements, ~100% improvement in Scott bond, ~117% improvement in Z-directional strength, as well as ~13% improvement in bending stiffness were achieved with VTT Native grade compared with the reference case, while addition of HefCel resulted in improvements of ~35% in Scott bond, ~40% in Z-directional strength, and ~20% in bending stiffness. Addition of HefCel CMF generated a bulkier handsheet structure compared with VTT Native CMF, which had a direct impact on the bending stiffness. The differences in the strengthening effect between HefCel CMF and VTT Native CMF are most probably due to the fibril morphology; VTT Native CMF with long and flexible fibrils provided tensile strength, while HefCel CMF consisting of short fibrils had a more substantial impact on the bending stiffness. The bending stiffness is one of the most important characteristics in board applications, indicating that HefCel CMF has potential for use as a reinforcement material in packaging applications.