Determination of the color stability of an environmentally friendly wood stain derived from laurel (Laurus nobilis L.) leaf extracts under UV exposure

Forest Products Journal, Jan/Feb 2008 by Goktas, Osman, Duru, M Emin, Yeniocak, Mehmet, Ozen, Ertan

Abstract

This study was designed to develop an environmentally friendly wood stain derived from laurel (Laurus nobilis L.) and determine the color stability of this stain when exposed to UV light irradiation. Wood stains derived from L. nobilis were prepared from aqueous solution with alum and iron mordant mixtures. Scots pine (Pinus sylvestris L.) and Turkish oriental beech (Fagus orientalis Lipsky) wood specimens were used as staining substrates. After treatment with the stain, the wood panels were exposed to UV light irradiation for periods of 100, 200, and 300 hours. Results showed that wood stain derived from laurel (bay) extract provided some color stability after UV irradiation.

People are exposed to numerous types of pollutants in modern environments. Wood furniture and decorative elements are potential sources for a number of volatile organic compounds (VOCs) indoors. Salthammer et al. (1998) has identified about 150 different VOCs used in the wood finishes and coatings industry. These chemical compounds can be used to impart desirable properties such as dimensional stability, water repeilency, fire resistance, color, odor, surface hardness, and mechanical strength. A large number of preservative and stain compounds have been introduced to the market; however, many of them have not gained commercial acceptance due to chemical toxicity, low efficacy, high cost, or corrosiveness (Murphy 1990). Most compounds in preservatives and stains belong to the typical group of solvents that are chemically inert under normal conditions. However, a number of substances used for wood stains and preservatives are known as secondary emission products or reactants (Salthammer et al. 2002). These persistent pollutants and their potential inclusion in waste wood have raised concerns about their health effects on humans and wildlife (Asari et al. 2004).

Many stains from synthetic sources can be allergenic and harmful to humans, thus interest in natural stains has increased considerably during the last few years (Bhattacharya etal. 1998, Deo and Desai 1999). Natural stains are generally environmentally friendly and have many advantages over synthetic stains with respect to production and application (Angelini et al. 1997). "Nowadays, there is a growing interest in the revival of natural stains in textile staining; arguments based around keywords such as sustainability, green chemistry, unproved eco-balances and thereby leading to niche products for special markets" (Bechtold et al. 2007). The introduction of natural stains into wood products for staining and finishing processes is one solution for eliminating environmental pollutants.

A number of stain crops continue to be grown in the Mediterranean region. These plant species are mostly native to the Mediterranean region. One example is common laurel (Laurus nobilis L.), which is used in dyeing wool, silk, linen fibers, and cotton (Ölmez 2004).

Laurel (bay) (Laurus nobilis L.) is cultivated in many temperate and warm parts of the world, and its leaves and berries are generally widely utilized (Kilic and Altuntas 2006). Laurel leaf traditionally has been used as an herbal medicine, and recent research has revealed that it can be used in treating diabetes and preventing migraines (Fang et al. 2005). Laurel is one of the most widely used culinary spices in all western countries. The essential oil from the leaves (0.8 to 3%) contains mostly 1.8-cineoI (50%). The food industry uses the essential oil as seasoning for meat, soup and fish, while other industries use it as a fungus inhibitor and an insect repellent (Baratta et al. 1998). Also found in laurel are eugenol, acetyl eugenol, methyl eugenol, a- and ß-pinene, phellandrene, linalool, geraniol and terpineol (Ölmez 2004). Because of these ingredients, the laurel extracts used in this study serve both as a stain and as a preservative.

The objectives of this study were to develop an environmentally friendly natural wood stain derived from laurel plant foliage and to determine its color stability under UV light irradiation. Color measurements were determined according to ISO 7724-2 ( 1984) after periods of 1OO hours, 200 hours, and 300 hours of UV light exposure.

Materials and Methods

Wood specimens

Samples of beech (Fagus orientalis Lipsky) and Scots pine (Pinus sylvestris L.) sapwood were used in this study. Vertical grain specimens measuring 10 mm (radial) by 100 mm (tangential) by 150 mm (longitudinal) were cut and stored in the laboratory at 20±2 0C and 65±5 percent relative humidity to reach equilibrium moisture content (EMC).

Plant material

Laurus nobilis L. (Lauraceae) leaves were collected from the Hatay region in Turkey during April and May. The specimens were identified using the Flora of Turkey (Davis 1982). The voucher specimens (No. L-1OO1 ) were identified by Prof. R. Mammadov, a taxonomist in the Department of Biology, Faculty of Arts and Sciences, at Pamukkale University in Turkey.

Extraction of stain

Air-dried powdered leaves of L. nobilis (800 g) were extracted repeatedly with ethyl alcohol (96%) in a Soxhlet apparatus until the last portion of the extract was colorless. Volume loss due to evaporation was compensated for by the addition of alcohol at the end of the extraction to retain the initial volume. After 3 hours, the suspension was passed through a Büchner funnel filter and a 500 mL sample of the filtrate was taken. The extracts were evaporated under vacuum conditions, which resulted in a residue that was maintained at 4 0C until use.