Natural polymeric materials are an interesting alternative to petrochemical products with potential application in almost all areas of human activity. Wishing to expand the field of cellulose acetate application to the biocomposite wood materials, the possibilities of cellulose isolation and its acetylation from two domestic, commercially meagrely used, wood species was investigated in this paper. Cellulose isolated from white willow (Salix alba) and black alder (Alnus glutinosa) was acetylated using acetic anhydride and perchloric acid catalyst, by treatment at room temperature for 45 minutes. Analysis of the laboratory acetylation process, beside chemical analysis of the gained product by infrared spectroscopy (FT-IR), indicated the impact of hemicelluloses, present both in cellulose and cellulose acetate structure, on values of mass increase, number of acetyl groups and the degree of substitution. Results of thermogravimetric analysis (TGA) later confirmed the statement that thermal properties of cellulose acetate were also dependant on hemicelluloses.

Thickness swelling and swelling pressure were determined with 24-hour immersion test. For the swelling pressure measurement, special force gauge device was used. The biggest changes in swelling and pressure were observed when the resin content was changed in core layer. The fastest change in swelling and swelling pressure was observed in the fi rst few hours after immersion in water.

In the present study, the influence of adding natural fillers to a cellulose acetate (CA) matrix, in order to develop biocomposites, on the properties of the achieved materials has been investigated. Extracted wood flour, holocellulose, and alpha cellulose were used as appropriate fillers. The results of the thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) of the fillers and biocomposites suggested the importance of the degree of degradation of filler properties, induced by the chemical treatment necessary for the preparation of the fillers, with emphasis on the content of lignin and the degradation of cellulose. Scanning electron microscopy (SEM) and mechanical analysis revealed that the matrix-filler ratio had a major effect on the prepared CA-based biocomposites, since polarity differences between the two major components caused the reduction of attractive forces in the matrix-filler relation, subsequently altering the properties of the developed materials.

Increasing demand for wood resulted in competition between different branches of wood-based production. High intensity production, like the production of wood-based panels, is forced to look for other lignocellulosic resources. Bark is a possible source for wood-based panel industry, especially for particleboards. Bark chips were crushed into bark dust, which were used for the production of single-layer particleboards. The share of bark dust was 0 %, 0.5 %, 1 %, 5 % and 10 %. The boards were tested on thickness swelling (immersion in water, exposure to humid conditions) and internal bond. The highest internal bond was determined in the particleboard with 1 % bark share. Thickness swelling of boards with added bark was higher compared to boards without bark. The highest swelling was observed in boards with 10 % bark dust (immersion in water) or 5 % (humid conditions). Bark based boards absorbed less water.

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SAŽETAK • Nakon osamostaljenja Republike Hrvatske (RH) osnovni gospodarski cilj bio je uključenje na međunarodno tržište i ulazak u Europsku uniju (EU).

This paper shows the results of fi nite element (FE) models of three-layer particle boards. Two particle board FE models were made with differently defi ned structures. In the fi rst model, the structure of commercial three-layer particle board is defi ned as single-layer with isotropic (PB-1L) properties, while in the second model, it is defi ned as three-layer with orthotropic properties (PB-3L). The results of FE models were compared with values obtained by testing the commercial particle board. Dimensions of FE models and applied loads were prepared according to bending strength testing mode defi ned according to EN 310:1993. Model comparison is based on comparison of sample defl ection and von Mises stress in the middle of the sample. The analysis was done only in linear elastic region. The obtained results show that models with homogenous material (PB-1L) achieved greater agreement with measured results (deviation app. 2 %), while models with three-layer material (PB-3L) displayed deviation of app. 7 %. Lower agreement of results obtained for PB-3L model and measured values of commercial particle board is due to a greater number of approximations (elastic characteristics) involved in the simulation model. Despite the greater deviation, the preparation of a three-layer model would be more acceptable for the analysis of strain distribution across the cross-section of the particle board.

SAŽETAK • U radu su provedena istraživanja konkretnog problema drvnotehnološke prakse u tvrtki koja proizvodi dovratnike od srednje gustih ploča vlaknatica (MDF, engl. medium density fi berboards