Emission of volatile organic compounds (VOC) from wood during processing to pelletssignificance of wood extractives. Cellulose, hemicelluloses and lignin are the main components of the cell wall in wood. Moreover, wood contains different amounts of extractives, depending on the wood species. Extractives in softwoods play an important role during processing of wood to different wood products. This work studies the influence of storage on the change of extractives as well as on the emission of monoterpenes (primary emission) and aliphatic aldehydes, as degradation products of fats and fatty acids (secondary emission). In case of pine wood storage for 2 days at 80uC proved to be more efficient in the reduction of emissions of terpenes and aldehydes than 4 weeks at 40uC. Quantitative differences between pine (Pinus sylvestris) and spruce (Picea abies) wood chips in the emission were evaluated and discussed. Pinewood emits about 10 times higher amounts of terpenes and aldehydes than spruce wood. The results indicate that the intense of change in primary and secondary emissions due to storage depends on the wood species as well as on the boundary conditions under which storage is carried out. In general, storage at high temperature (80uC) is much more effective than at low temperature (40uC). The results also reveal that removal of wood extractives from pine wood by extraction with ethanol-cyclohexane or treatment with sodium hydroxide decreases the emission of primary and secondary volatile organic compounds drastically. Nevertheless, after such treatments minute amounts of volatile organic compounds are still detectable.

The work aimed to study the influence of replacing virgin wood fibres by recycled fibres, made from recovered medium-density fibreboards (MDF) by thermo-mechanical pulping, on the physical-mechanical properties and formaldehyde release of urea-formaldehyde (UF)-bonded MDF. It was found that replacement of 33% virgin fibres by recycled fibres decreased significantly the thickness swelling and water absorption of the UF-bonded MDF and mitigated the formaldehyde release. However, supplanting 33% of virgin fibres by recycled fibres had a negative impact on the internal bond strength. UF-bonded MDF with higher amounts of recycled fibres (67 and 100%) could not be produced without applying the hybrid bonding technology, i.e. adding small quantities of polymeric diphenylmethane diisocyanate to the UF resin. MDF made from 100% recycled fibres showed significantly lower thickness swelling values as well as a drastic drop in the formaldehyde release compared with boards made from virgin wood fibres.

The emission of formaldehyde from softwood particles, as measured by the flask method (EN 717-3), depends highly on the particle size. Therefore, no definite value for the formaldehyde release from wood can be given. Die Formaldehydabgabe von HolzspänenZusammenfassung Die Formaldehydemission von Nadelholzspänen verschiedener Größe wurde nach der Flaschenmethode (EN 717-3) bestimmt. Es zeigte sich, dass die Formaldehydabgabe sehr stark von der Partikelgröße abhängt. Demzufolge kann für die Holzspäne kein definierter Formaldehydabgabewert angegeben werden.

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Emission of volatile organic compounds (VOCs) from medium density fibreboards (MDF) containing different proportions of softwoods (SW) and hardwoods (HW) was evaluated. The results reveal that decreasing the proportion of HW in MDF elevates the emission of terpenes and aliphatic aldehydes. The pulping method (TMP, CTMP) seems to have no significant influence on the emission of terpenes or aldehydes from MDF. On using the TMP process, the emission of acetic acid elevates remarkably with increasing the amount of HW in the boards. Compared with the TMP process, the CTMP process leads to a decrease of acetic acid emission at 408C with more than 15% at 35% HW content of the boards and 40% at 65% HW content.