International Wood Products Journal

Physical and mechanical properties of OSB made with mixture of beech and poplar strands were compared to boards made purely of beech, poplar and pine at 650 and 720 kg m⁻³. The mixed beech and poplar strand boards showed better properties in bending strength and IB compared to pure panels. In addition, MOR and MOE were found to reach values two times higher than the levels as specified in EN300 the standard at a density of 720 kg m⁻³. Thickness Swelling (TS) after 24 h for panels of mixed beech and poplar strands were 13%, which is around 35% less than EN300 allows.

This paper reports on first results from a recently finished project dealing with indoor air quality in timber constructed houses. The FLEC method was applied measuring single building products with respect to their emission of VOCs (i.e. volatile organic compounds) on a small scale. Furthermore, total emissions are investigated in full scale model rooms (30 m³) equipped with variable panel product types and coverings. It has been shown that the total VOC (TVOC) value, consisting of a heterogeneous mixture of single substances (from 25 up to 68 within the test setup), decreases significantly with duration time. Within one year, ranking of the TVOC emission level for 26 individual building products including wood based panels, plasterboards, flexible insulations, adhesives, vapour barriers and sealing sheets changed. Approximately 30% of the single substances formed 80% of the TVOC fraction. This actually highlights the complexity of indoor air emissions from building products. Full scale box trials allowed a direct comparison of OSB and OSB that was covered by gypsum plasterboard. Whereas the TVOC level immediately after construction is higher for uncovered OSB, values of both construction setups decline rapidly. After 14 days and onto 19 weeks, TVOC values were comparable for uncovered and covered OSB within the test. Hence, plasterboards have only a small effect on TVOC levels, but are not capable of reducing VOC emissions from building products.

The United Kingdom emitted 628 Mt CO₂ equivalent (CO_2e) as greenhouse gases in 2008. United Kingdom (UK) policy is to decrease these emissions to 154 Mt by 2050. This paper investigates the role that wood construction products and wood-based panels may play in mitigating these greenhouse gas emissions. In this paper, we have concentrated on production and consumption in 2005: all solid wood products and wood based panels consumed in the UK in 2005 contained almost 16 Mt CO_2e. Using established international methodologies and the ‘stock change approach’ to carbon storage, the net increase in CO_2e stored in all UK wood products in 2005 was calculated to be 7·1 Mt CO_2e. Applying the newer UNFCCC ‘production approach’ gave a net increase in CO_2e stored in wood based panels and solid wood of 3·4 Mt CO_2e in 2005, approximately half of this storage was in wood based panels.

The focus of previous UK studies of carbon in construction has been new housing. We estimate that only 10% of CO_2e contained in all UK solid wood and wood based panel products consumed went into new housing in 2005. We have modelled the storage of CO_2e in solid wood and wood based panels for other construction sectors and used this to model changes in construction methods: if current trends in UK housing construction methods continue and are extended to other construction sectors, there is the potential to increase the annual increment of CO_2e stored in wood products in construction from 9 Mt CO_2e to 14 Mt CO_2e (more than 2% of the total annual UK greenhouse gas emissions).

The influence of hexamine formed as byproduct during the UF cure was ignored in the past. However, with the increasing interest on low formaldehyde emission boards, this issue has become more pertinent. Formaldehyde release from hexamine degradation is extensive and could limit the success of the development of low formaldehyde emission adhesives if the conventional latent catalysts remain in use.

In this study, formaldehyde released from recycled wood, hexamine and cured UF resin was assessed. Citric and oxalic acid, in solid form, were used as catalysts for UF resin in the production of particleboard. Mats with solid acids are less susceptible to resin pre-cure than with a latent catalyst. However, they can have higher formaldehyde emissions than latent catalyst. When both catalysts were used, combined with an ultra-low formaldehyde to urea molar ratio resin the internal bond was improved and formaldehyde content was below 4 mg per 100 g of oven dry board.

This study aims to provide information on the mobility of formaldehyde within a mattress of particles during hot-pressing. To this end, adhesive-free mattresses of virgin wood particles, which contain either a small dose of formaldehyde solution or slices of ‘old’ particleboard placed in one corner of the mattresses, were hot-pressed, cut into standard samples and then tested via EN 717-2. The results indicate that formaldehyde is mobile such that the emission levels across the samples were fairly consistent. Strips that contained high quantities of old furniture, however, still exhibited higher emissions than samples that did not contain old furniture particleboard.

The gas analysis method according to EN 717 part 2 is a well-known technique to measure the formaldehyde emission of plywood and coated wood-based materials for quality control purposes. There is an increasing interest to apply this method also for uncoated wood-based panels compared to the perforator method (EN 120: 1992) owing to many reasons. As there is still limited experience in testing particleboard with this method, it is the aim of this study to evaluate the effect of some parameters to ensure correct and precise testing using the gas analysis method. Furthermore, the study aimed to show how the m.c. of panels before testing affects the G_m, and to calculate an m.c. correction factor from these results for particleboard with modern bonding systems at a low emission level. Gas analysis value and m.c. show a very good correlation. Based on this correlation an m.c. correction factor can be determined, which facilitates an m.c. correction of G_m data. This may help to improve the quality of G_m data for quality control and data comparison (i.e. for round robin tests). Combining the sampling for hour 3 and 4 as well as 2, 3 and 4 has no significant effect on the level of formaldehyde emission tested. Also the accuracy of testing was not reduced. Consequently, the change in sampling procedure may lead to a reduction on the required number of water analyses needing to be performed in the laboratory, and therefore to a reduction in consumption of chemical consumables and expenditure of human labour. The reduction of overpressure during gas analysis did not have a major effect on the values as such, but increased the coefficient of variation. Also, an increase in air flowrate did not affect the G_m at lower emission levels.

In the last years, production of particleboards with good overall performance and very low formaldehyde emission has been a challenge to wood based panels (WBP) industry, mainly since the re-classification of formaldehyde by the IARC (International Agency for Research on Cancer) as ‘carcinogenic to humans (Group 1)’. Moreover, a new important limitation to the use of formaldehyde-based resins has been recently imposed by the LEED (Leadership in Energy and Environmental Design) certification for ‘Green Building’ construction: ‘wood composites must contain no added urea-formaldehyde resins’. In this context, the main purpose of this study is to develop a PF resin for particleboard production that fulfils formaldehyde emission restrictions and LEED criteria, while presenting appropriate reactivity and bond strength. The mechanical performance and formaldehyde emissions of particleboards were optimized, changing both the resin synthesis and board production procedures. The synthesis process of these resins was carried out under an alkaline environment, and with an excess of formaldehyde towards phenol, in order to produce resol-type PF resins. The effect of changing the amount of added sodium hydroxide was studied. The particleboard production parameters were also changed, both in terms of blending conditions (amount of hardener and resin) and hot-pressing conditions (pressing time). A PF resin with very good internal bond strength, low formaldehyde strength and reasonable board pressing times was obtained using the following conditions: sodium hydroxide amount of 9% during the synthesis process, and 10% hardener (based on oven-dry weight of resin) together with gluing factor between 4·5 and 5% on the core layer during particleboard production. The best performing resin obtained demonstrated to be appropriate for use in the so called ‘Green Building’ construction.

A new and fast system for determining formaldehyde (HCHO) release of wood based panels (WBPs) for use in manufacturer's labs was developed. For sample preparation, solid phase microextraction (SPME) with a derivatisation step was used. The analytical system consists of a gas chromatographic column (GC) coupled to a high field asymmetric waveform ion mobility spectrometer (FAIMS). The emitted HCHO is determined in gaseous form, i.e. without trapping it in water. The system runs quasi-continuously with a cycle time of 20 min. This paper explains the basic functioning, and presents first results from a field trial.