Volatile acetic acid and formaldehyde emission from plywood treated with boron compound

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Abstract

The effects of plywood on formaldehyde and volatile acetic acid emissions treated with borax and boric acid were investigated. The treated plywood samples were manufactured by using two different methods; each veneer was first impregnated by a dipping method before the first group of plywood was manufactured. The second group of plywood panels was produced by adding preservatives (borax, boric acid) into the glue mixture. Two types of urea formaldehyde resin and phenol formaldehyde resin were used as adhesives. The formaldehyde emissions of the plywood were measured by using desiccator method (JIS-A-5908). The amount of acetic acid in distilled water taken from the desiccator was determined by using high performance liquid chromatography. The results revealed that boron compounds affected the emission values of panels differently. Borax showed decreasing effect on the formaldehyde emission, whereas boric acid showed increasing effect.

Introduction

Over the past several decades, air pollution in homes and office buildings has become a matter of increasing concern. Formaldehyde emission has been the major concern associated with bonded wood products. Recently, interest has turned to other volatile organic chemicals (VOCs) [1]. Composite wood products such as particleboard, plywood and MDF are widely used in indoor products such as subflooring, door cores and furniture [2]. Emissions of VOCs potentially can arise from any of the materials that compose a panel; until recently attention has been on emissions of formaldehyde from UF adhesive [3]. It was concluded that the wood products were responsible for the elevated levels of terpenes, aldehydes, and acetic acid. Along with the air pollutant, volatile acids in woods are of great technical importance because of their corrosion of metals, iron–tannin discoloration of woods, influence on curing time of synthetic lacquers and glues and fixation of wood-preserving salts [4]. Air pollution is different from other contaminations in that air is freely exchanged among regions. Therefore, global solutions are required. Also, these chemicals have adverse health effects such as eye and respiratory irritation, irritability, inability to concentrate and sleepiness [5]. Because of increased emphasis on indoor air quality, accurate information is needed regarding the amounts and types of VOCs emitted from building materials or used in the indoor environment. On the other hand, many methods and chemicals have been devised to reduce some troublesome inherent properties (degradable by insect and fungi attack, flammable) of wood-based panel products. Boron compounds may be the most investigated preservatives for wood based panel products because of their beneficial effects such as preservative effectiveness, a broad spectrum of activity against insects and fungi and less impact on mechanical properties compared to other flame-retardant chemicals [6]. However, previous studies have not shown how formaldehyde and volatile acetic acid emissions of wood products are affected by these chemicals and preservation methods. Especially acetic acid emissions of treated plywood panels were investigated because of technological significance besides the other necessity mentioned above.

Section snippets

Material and method

In this experimental study, 2mm-thick rotary cut veneers were obtained from beech (steamed) and alder (non-steamed) logs at laboratory conditions. The veneers were then dried to 6–8% moisture content and weighed after dipping into 5% aqueous solution of preservative for 20min. After impregnation, the veneers were subjected to a second drying process at industrial conditions, and then conditioned to 7% moisture content again and re-weighed. The net uptake of borax and boric acid was calculated

Results and discussion

The mean retentions of veneers were found for borax as 12.8kg/m3 (min. 11.4; max. 17.1) and 11.8kg/m3 (min. 8.8; max. 13.3), for boric acid as 13.3kg/m3 (min. 10.1; max. 18.3) and 12.8kg/m3 (min. 10.4; max. 14.7), beech and alder, respectively.

Conclusion

The formaldehyde emissions of plywood panels treated with boric acid increase. On the contrary, treatment with borax has a small decreasing effect for formaldehyde emission. The difference between formaldehyde emission values of the beech panels treated with boric acid and untreated beech panels was higher than that of the alder plywood panels. The increases in the amount of formaldehyde release from the panels produced by adding boric acid into the glue mixtures of UF1 and UF2 were 2.52 and

Acknowledgements

This study was financially supported by the research fund of Karadeniz Technical University. The authors express their gratitude for the financial support.

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