Thermo-mechanical pulps (TMP) and chemo-thermo-mechanical pulps (CTMP) were prepared from chips of oak wood with more than 70% heartwood. The fibres retrieved by both processes were separated by sieve analysis into different fibre fractions [≤ 0.1 mm (fine fraction) and > 1 mm (coarse fraction)]. Both fibre fractions were analysed for their extract content. The pH-value and buffering capacity of cold and hot water extracts, the formaldehyde release as well as the emission of volatile organic acids (formic and acetic acid) were also determined for the different fibre fractions. Further, the monosaccharides in the extractives before and after hydrolysis using trifluoroacetic acid (TFA) were assessed. The results make abundantly clear that the fine fraction (≤ 0.1 mm) contains a higher amount of water-soluble extracts than the coarse fraction (> 1 mm). After hydrolysis with TFA the amount of monosaccharides in the extractives, in particular the xylose content, increased tremendously, indicating that after pulping a part of the liberated carbohydrates is still in the oligomeric state. With increasing fineness of the fibres, the formaldehyde release, as determined by the flask method (EN 717-3), soars to higher values. The formaldehyde release of CTMP fibres was much lower than that of the TMP fibres. In contrast, the emission of acetic and formic acid from the CTMP was much higher than that from TMP. This may be due to the saponification of acetyl groups in the hemicelluloses of oak wood under the alkaline environment of the CTMP-process. The results explain in-depth why removing the water-soluble carbohydrates through washing the fibres negatively impacts their bondability by UF-resins, as established in previous publications.

Chemo-thermomechanical pulps (CTMP) from oak wood release more formic and acetic acid than thermomechanical pulps (TMP) made from the same wood. In contrast, the emission of formaldehyde from CTMP is lower than that from TMP. Medium density fibreboards (MDF) made from TMP and CTMP emit less formic and acetic acid compared to the fibres, from which they are made. The formaldehyde release from MUF-bonded MDF made by using TMP and CTMP is higher than from the fibres (TMP and CTMP) used to make the boards.

Fibres obtained by the TMP- and CTMP-process from old oak (200–250 years) contain higher amounts of cold water extractives than those obtained from young oak (20–30 years). Moreover, water soluble extractives from old oak fibres are, in general, more reactive towards formaldehyde. This result supports the finding that medium density fibreboards (MDF) made from fibres of old oak emit less formaldehyde than MDF from young oak.

Washing of CTMP-pulps ahead of board making decreases the amount of extractable acetate and formate ions from the boards. The decrease in the amount of releasable acetic acid due to washing is enormous, whereas washing seems to have no detectable effect on the releasable amount of formic acid. This is likely due to the fact that formic acid is a much stronger acid than acetic acid.

The gas analysis method (EN 717-2:1994), originally destined for measuring the formaldehyde release from wood-based panels, can also be used to determine the emanation of volatile organic acids such as acetic acid. However, the profile of release of formaldehyde and acetic acid seems to be quite different in the course of the gas analysis test.

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.

Wood contains primary extractives, which are present in all woods, and secondary extractives, which are confined in certain wood species. Extractives in wood play a major role in wood-bonding processes, as they can contribute to or determine the bonding relevant properties of wood such as acidity and wettability. Therefore, extractives play an immanent role in bonding of wood chips and wood fibres with common synthetic adhesives such as urea-formaldehyde-resins (UF-resins) and phenol-formaldehyde-resins (PF-resins). Extractives of high acidity accelerate the curing of acid curing UF-resins and decelerate bonding with alkaline hardening PF-resins. Water-soluble extractives like free sugars are detrimental for bonding of wood with cement. Polyphenolic extractives (tannins) can be used as a binder in the wood-based industry. Additionally, extractives in wood can react with formaldehyde and reduce the formaldehyde emission of wood-based panels. Moreover, some wood extractives are volatile organic compounds (VOC) and insofar also relevant to the emission of VOC from wood and wood-based panels.

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.

Study of the influence of treating pine wood strands with hydrogen peroxide as an oxidising agent and sodium sulphite as a reducing agent on the emission of volatile organic compounds revealed that hydrogen peroxide increases the emission of aliphatic aldehydes (e.g. hexanal) and reduces the emission of monoterpene compounds (like α-pinene). Sodium sulphite as a reducing agent decimated the emission of monoterpene compounds without noticeably affecting the emission of volatile aldehydes.

Emission of volatile organic compounds (VOC) from wood during processing to pellets – significance 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 80°C proved to be more efficient in the reduction of emissions of terpenes and aldehydes than 4 weeks at 40°C. 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 (80°C) is much more effective than at low temperature (40°C). 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 main objective of this study was to evaluate the influence of moisture content on the formaldehyde release of particleboards and medium density fibreboards (MDF) bonded with tannin–formaldehyde (TF-) resins. The results revealed that increasing the moisture content in the TF-bonded boards elicited a decline in the content of extractable formaldehyde (perforator values according to EN 120). This is an opposing behaviour to the general state of knowledge related to the influence of moisture content on the formaldehyde content (EN 120) of particleboards and MDF bonded with urea–formaldehyde based resins. Moreover, the TF-bonded panels showed a decrease in the gas analysis values (EN 717-2), flask values (EN 717-3) as well as formaldehyde emission measured in the 1 m3-chamber (EN 717-1). EN 120 (now also pr EN ISO 12460–5, 2013) does not take into consideration that boards bonded with other binders rather than aminoplastic resins may behave differently at different moisture contents. Insofar, it leaves no leeway to consider different binders systems.

Addition of urea to a melamine modified urea formaldehyde resin in the surface and core layer reduces significantly the formaldehyde release of the particleboards bonded therewith. Under the used boundary conditions (long press time) urea addition seems to have no noticeable negative impact on the physical–mechanical properties of the boards. The reduction of formaldehyde release due to urea addition as a scavenger can be followed by measuring the emission in the chamber according to EN 717-1, the perforator method according to EN 120 and the flask method as described in EN 717-3. The results reveal that under the used conditions a good correlation exists between the emission in the chamber and the corrected perforator values (R2 = 0·865), as well as between the chamber value and the formaldehyde emission measured by the 3h-flask method (R2 = 0·792) according to EN 717-3, a slightly better correlation was found between the measured flask values after 24 h and the emission in the chamber (R2 = 0·869). The correlations seem to hold in the emission range between 0·06 and 0·016 ppm.

Se determinó la disminución de la bioluminiscencia de bacterias como indicador de la actividad biológica de extractos de corteza. Se analizaron cuatro cortezas nativas chilenas. La reducción de la bioluminiscencia fue diferente dependiendo de la especie de corteza. El aumento del tiempo de un tratamiento térmico de la corteza (24, 48, 72 y 144 horas con 103ºC) produjo una reducción de la actividad biológica de los extractos. El estudio indica que los terpenos podrían ser responsables del efecto señalado. Abstract Bioluminescence decrease of bacteria as a biological activity indicator for bark water extracts was determinate. Four Chilean barks were tested. A different reduction on bioluminescence depending on bark species was observed. Increasing time of thermal treatment of bark (24, 48, 72 and 144 hours with 103ºC) produced a reduction of the biological activity of extracts. The study indicates that the terpenes could be responsible for the described effect.

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.

Thermohydrolytic treatment of chips from UF-bonded particleboards using the flask method technique at temperatures of about 103°C resulted in a notable increase in the pH-value of aqueous absorption medium after a reaction period of 24 h, most likely due to degradation of the UF-resin. This leads to neutralisation of the stronger formic acid to a much higher extent than acetic acid. Accordingly, the release of formic acid using the flask technique decreases to a much higher extent compared to that of acetic acid under the same conditions. The release of acetic acid could also be enhanced by possible deacetylation of the wood material induced by the hardener usually present in recovered UF-boards. This indicates that inextricably intertwined reactions unfold on hydrothermic degradation of UF-bonded particleboards.