Alireza Kharazipour

Enzymatic activation of wood fibres as a means for the production of wood composites

The incubation of wood fibres with a phenoloxidase (laccase) results in the oxidation of the lignin crust on the fibre surface which finally is released from the fibre surface into the incubation medium. During this reaction, the lignin is highly oxidized, as can be seen from its high carboxyl content. When fibres treated with the enzyme are pressed together under conditions usually employed during the process of making fibre boards, boards are obtained which meet the required standards for German medium density fibre board (MDF). The enzymatically activated fibres in the wood composites made by this process are bound together in a way which is closer to the situation in the naturally grown wood than any other process used today in the present production of wood composites.

Properties of fibre boards obtained by activation of the middle lamella lignin of wood fibres with peroxidase and H2O2 before conventional pressing

Abstraet-When commercially produced wood fibres were treated with the enzyme peroxidase and H2O2 for a certain time and then pressed together under conditions usually employed during the process of making fibre boards, boards were obtained which came close to the required standards for German medium density fibre (MDF) boards. Thus, surprisingly, peroxidase in this system gives the same results as laccase, for which this reaction has been described previously. Successful implementation of this process will yield wood composites which can be produced without any addition of resins, solely from naturally grown products.

Polyphenoles for compounded materials

Abstract The cell walls of woody plants are compounded materials made by an in-situ polymerisation of a polyphenolic matrix (lignin) into a web of fibres (cellulose) catalysed by polyphenoloxidases (laccases) or peroxidases. The transfer of this construction strategy to the actual production of compounded materials required the adaptation of a process that takes weeks in nature to technical conditions in which reaction times of only a few minutes are allowed. Several strategies have been developed to find conditions under which lignin becomes so active that the reaction may be feasible for technical purposes. Thus, the following industrial processes for the production of compounded materials are now available: (1) wood composites either by the addition of adhesives composed of lignin and phenoloxidases or activation of the wood fibres by these enzymes; (2) compound materials made from lignin and carbohydrates; (3) duroplasts from lignin and other monomers. The main advantage of all these substances is that they are totally compatible with the terrestrial carbon cycle.

Effects of Wheat Protein as a Biological Binder in the Manufacture of Particleboards Using a Mixture of Canola, Hemp, Bagasse, and Commercial Wood

Abstract This article deals with the feasibility of the use of wheat protein glue to produce general purpose particleboards from bagasse, canola, and hemp chips and of decreasing the formaldehyde emission by using a bioproduct adhesive. Three series of panels were produced using wood chips in the surface layers and a mixture of annual plants with industrial wood in the middle layers. Particleboards were manufactured using various annual plants. Wheat protein was used in combination with urea-formaldehyde (UF) resin in the surface layers. Pure UF was only used in the middle layer. Panels were tested for some physical and mechanical properties. In addition, the formaldehyde emission according to the perforator method and the bottle method was determined. The data were compared with the respective properties specified by the Deutsches Institut fur Normung EN 312-2 standard for commercial wood-based particleboard. The results showed that all mechanical properties greatly exceeded the standard requirements for...

Studies of enzymatic oxidation of TMP-fibers and lignin model compounds by a Laccase–Mediator-System using different 14C and 13C techniques

In this work, the results of the enzymatic oxidation of TMP-fibers (thermomechanical pulp) and a well-structured lignin model compound, the dehydropolymer (DHP), were investigated by different 14C and 13C methods, caused by a Laccase–Mediator-System (LMS). These methods are the nuclear magnetic resonance spectroscopy (13C-NMR) with DHP (unmarked) and the determination of the 14CO2 release of 14C-marked DHP and TMP-fibers. The 13C-NMR measurements were chosen to analyze the structural changes of the LMS-treated DHP model compounds and TMP-fibers qualitatively and quantitatively. The data of 14CO2 release give an explanation of the demethylation of DHP and TMP-fibers. The effect of the LMS is shown by comparing the results in respect of DHP and TMP-fibers, which were only treated with laccase and of an inactivated LMS as the control. Comparing the results of the 13C-NMR method, in particular the use of the Mediator during the enzymatical treatment, showed significant changes in the structure of the DHP. Also, the TMP-fibers were materially influenced by the LMS. The analysis of the 14CO2 release data of the 14C-marked DHP and TMP-fibers revealed that the rate of 14CO2 increases in the 14C-2 atom as well as in the O14CH3 group within the first hour of Laccase–Mediator incubation. Therefore, the 14CO2 release from the DHP was higher than from the TMP-fibers.

Enzymatic modification of wood fibres for activating their ability of self bonding

Objective is the use of phenoloxidases like laccases to activate the surfaces of fibres for making fibreboards without any adhesive. The concept of using lignin-oxidising enzymes for bonding applications is based on the reactivity of phenoxy radicals in the plant cell wall. A problem is that laccase can only oxidise the phenolic constituents of lignin, due to its lower oxidation potential. Therefore the use of appropriate low molecular-mass compounds (so-called mediators), in combination with laccase, makes this enzyme competent for the oxidation of nonphenolic substrates. The oxidised mediator can rely on an oxidation mechanism that is not available to the enzyme.

Production of innovative hemp based three-layered particleboards with reduced raw densities and low formaldehyde emissions

The possibility to substitute wood by hemp for the production of wood based panels and the possibility to produce lightweight panels by using hemp are the main research focuses of this project. The regular density of three-layered particleboards (650 kg/m³) shall be decreased to less than 400 kg/m³ by the utilisation of hemp. Another quite interesting aspect that we want to analyse in line with this project is to reduce the formaldehyde emissions of urea-formaldehyde-, melamine formaldehyde- orphenol-formaldehyde-resin bonded wood based panels by using natural binder systems such as proteins and starches.

Laccase-Mediator Catalyzed Modification of Wood Fibers: Studies on the Reaction Mechanism and Making of Medium-Density Fiberboard

ABSTRACT Owing to the constant increase of prices of the process for petrochemical resin and the possibility of harmful formaldehyde emissions from industrial produced medium-density fiberboards (M...

Storage-induced emissions from different wood species

Abstract In this study, the extractive contents and the storage-induced emissions from chips of Salix alba, Betula pendula, Populus tremula, and Alnus glutinosa are compared with emissions from Pinus sylvestris chips. Soxhlet extraction was performed, and carbon monoxide (CO) and O2 concentration in the gas phase as well as gas chromatography-mass spectrometry analysis of volatile organic compounds were analyzed. Pinus sylvestris showed the highest extractive content in the petrol ether fraction and emitted CO in the highest concentration. Salix alba, B. pendula, P. tremula, and A. glutinosa have lower extractive contents in the petrol ether fraction and the CO concentrations decreased in the headspace accordingly. The emission of aldehydes was lower in the case of woods with lower petrol ether contents (P. sylvestris, S. alba, and B. pendula), but the situation was not as clear for P. tremula and A. glutinosa. The origin of CO and aldehyde emissions is discussed in view of the possible oxidative degradation processes of lipids and terpenes.

Mechanical behaviour of a lightweight, three-layered sandwich panel based on the raw material maize

Abstract Lightweight construction of composites is one of the strategies for developing material-saving panels, whereas light honeycomb boards or sandwich panels (SPs) based on foam or wood materials seem to be very promising in this context. The objective of the present work was the development of an SP with a reduced density based on nearly 100% expanded maize granular in the core layer, which was combined with 3 mm thin and stiff poplar plywood as face materials. In focus were mechanical and physical properties of the SPs, which should be applicable in the furniture industry and competitive with conventional wood composites such as fibreboards or particle boards.