| Front page | | Contents | | Previous | | Next |

Emission of chemical substances from products made of exotic wood

1 Introduction

• 1.1 Wood Species
• 1.2 Composition of Wood
• 1.3 The Use and Import of Wood
• 1.4 Exotic Wood
• 1.5 Sustainable Forest Management
• 1.6 Surface Treatment

1.1 Wood Species

Approximately 12,000 truly large wood species are identified; out of which approx. 1,000 are used industrially. Europe is very poor in species, and in Denmark there are only approx. 20-30 wild species, which are used industrially. For comparison there are in Brazil and Java approx. 3,000 species.

1.2 Composition of Wood

Wood consists mainly of carbon (C), oxygen (O), hydrogen (H) and nitrogen (N) and inorganic sub-compounds. The elements form cellulose, hemicellulose and lignin, which are the main ingredients of the cell walls.

Cellulose, which consists of polymers of glucose anhydrides, constitutes 40-50% of the cell wall. The cellulose molecule forms chains, in which the number of internodes of a chain (the polymerisation degree) in average is 10,000.

Hemicellulose consists primarily of chains of pentosanes and hexosanes. Hemicellulose constitutes 25-30% of the cell wall and contributes to stabilise the cellulose structure.

Lignin, which is amorphous constitutes 20-35% of the wood, and contributes like hemicellulose to strengthen the cellulose structure.

Together with the main components of the wood wood contains numerous other organic and inorganic compounds. Content and composition of these compounds vary from species to species; like the variation within same species and within the individual tree can be extensive. The compounds contribute to the resistance to biological degradation.

Among the compounds there are terpenes and resins, which primarily are composed of abetin, sylvinite, sapin and pimaric acid. Often complex nitrogen containing compounds named alkaloids are present. These can be very toxic. The odour of the wood origins a.o. from the ethereal oils, which are emitted from the wood during drying.

1.3 The Use and Import of Wood

There are approx. 2,000 wood industrial companies in Denmark (Straarup, 2002). The furniture industry constitutes approx. 1,000. The primary wood industry, which is the part of the industry that buys and processes raw wood, is sawmills, parquet factories, packing factories etc. Furniture factories, workmen, manufacturers of construction parts, glulam manufacturers and manufacturers of panels belong to the secondary industry.

The wood applied origins partly from the Danish forestry and partly from import. The annual consumption of wood and wood products in Denmark is 3-4 times larger than the annual felling in Denmark. Thus some wood and wood products should be imported to cover the consumption.

Statistics Denmark makes estimates of the import to Denmark of all kinds of timber and all types of wood. The category "wood and products made of wood" all consist of wood products, which are categorised under chapter 44 in Statistics Denmark's Foreign Trade distributed on products and tasks (Statistics Denmark, 2002). The category covers timber, doors, windows, boxes, and kitchen fittings, but not furniture, which is summed up under "Miscellaneous goods", chapter 94 "furniture".

The category "timber" is a part amount of the imported woods, which is not processed to anything but round timber, sawn timber, veneer or plywood. In 2001 timber constituted approx. 2/3 of Denmark's total import of wood, when evaluated according to value. It should be noted that tropical timber the same year only constituted approx. 3% of the imported volume, and that the import of all types of tropical wood constituted approx. 6% of the total import of all types of wood.

What the designation "tropical wood" covers, will be elaborated in the following paragraph.

As for the timber it is to a great extent transported to Denmark by ships in regular traffic. A lot of these ships sail depending on type and container content, not longer north than Holland or Germany, where the cargo will be re-loaded. At the re-loading the content of the cargo will be recorded by the customs authorities of the country in question. This means that when a ship unloads tropical wood in a European port to go on to Denmark, the cargo will be recorded as originating from the European country in question and not the country of origin. This is the primary reason why large parts of the Danish import of tropical wood seem to origin from countries such as Germany and Holland. This practice makes it at the same time hard to trace the country of origin of the timber.

The use of different wood species indoors is in excess of completely mechanical properties also due to the colour of the wood. E.g. the use of wood for floorings, furniture and kitchen fittings is to a high extent dependent on changing fashions. In some periods dark wood is fashionable, while it in other periods is the light wood that "sells".

1.4 Exotic Wood

Tropical wood, exotic wood and overseas wood are some of the designations that are used for wood species imported from far away. In this project we will use the designation exotic wood, as we not only describe tropical or overseas wood species.

Statistics Denmark uses the designation "tropical wood" and in Appendix A, a list is given of the wood species, which Statistics Denmark includes under this designation.

Of the more than 500 of the most known exotic wood species there is in Table 3 stated the most common exotic wood species imported to Denmark (Straarup, 2002; Kopp, 2003). The mentioned wood species are all used indoors and some also outdoors e.g. in connection with water construction and external cladding. Of these wood species the following can be mentioned: Azobé, Purpleheart and Western Red Cedar (Thuja).

The original designations of the trees are often of popular origin and on the language of the individual country. Simultaneously, many of the names are just trade names covering more wood species, which in some cases have very different appearance and properties. It is, therefore, necessary to use the botanical name in order unambiguously to identify a given wood species. In Table 3 and in the following the trade name has been applied in connection with the botanical name.

Unambiguous identification of the wood species is also essential by statistical survey of their health effect on human beings. Unfortunately, such a safe identification is not always available. Information in the literature should therefore be taken with reservations (Mitchell and Rook, 1976).

For more of the wood species mentioned in Tables 3, 4, and 7 there is from literature knowledge of health symptoms due to contact with the wood and/or wood dust. These wood species are listed in Table 9.

Table 3 Trade name, botanical name, origin and typical indoor use of the most common exotic wood species imported to Denmark (Straarup, 2002; Kopp, 2003; Morsing, 2003)

In excess of these exotic wood species cherry is also used indoors. Products made of cherry are, therefore, included in this project. Cherry is imported from different countries. In Table 4 cherry is mentioned with different origin.

Table 4 Trade name, botanical name, origin and typical application for cherry

1.5 Sustainable Forest Management

Formerly, exotic wood species were primary used within very specific areas. There were less wood species on the market, which then seemed clearer. An increased concern for environmental problems and sustainability by the consumers, scarcity of wood species and more focus on the tropical rain forests have, however, changed the demand and the trade with exotic wood (Morsing, 2003).

Certification of exotic wood have had the effect that there now are numerous wood species, which have not formerly been on the Danish market. As importer and manufacturer it is today very important to run an environmental policy, which signals that the company in question contributes to sustainable exploitation of the exotic wood.

Now an environmental guideline for tropical wood is available (the Danish Environmental Protection Agency, 2003).

Close to a fourth of the exotic wood imported to Denmark is sold to the public sector. This sector has, therefore, a great influence on the demand. All public institutions were as per 1st June 2001 by the Folketing (the Danish Parliament) encouraged to ensure that all wood applied is legally and sustainably grown (Parliamentary Resolution B197). FSC (Forest Stewardship Council) is at the same time acknowledged as an example of a guarantee that wood with this certificate meets the requirements made by the Folketing.

The purpose of the certification of forestry is to ensure that the forests are operated sustainably and thereby maintained for the future generations. The idea was created in the end of the 1980's and was seriously developed, when FSC was founded in 1994. At present there are some national and international certification schemes, which can be hard to distinguish from each other.

Examples of international certification schemes:

• FSC (Forest Stewardship Council)
• PEFC (Pan European Certification System)

Examples of national certification schemes:

• SFI (USA)
• CSA (Canada)
• LEI (Indonesia)
• MTCC (Malaysia)

It falls outside the scope of this report to describe these certification schemes closer, like a potential certification does not form part of the subsequent selection of products in this project.

1.6 Surface Treatment

I many cases the products made of wood are surface treated. This surface treatment can have an aesthetic function giving the product more constancy towards use and wear, dirt and/or discoloration/bleaching of sunlight. This surface treatment can in excess also ease the cleaning and the resistance of the products to it.

A potential surface treatment can contribute to reduce the emission of chemical compounds from the wood itself, but the surface itself can at the same time imply emission of (other) compounds.

As described formerly the selection of wood species is partly conditioned by the aesthetic guidelines, which the changing fashion dictates. Same conditions are valid for a potential surface treatment, the type and colour of which are partly dependent on the architectonic and design trends.

Typical surface treatments for different product categories are listed in Table 5 below.

Table 5 Typical surface treatments for different product categories

In Asian countries acid-hardening lacquers are greatly used, which emit formaldehyde. Lacquered products imported from Asia will, therefore, often be treated with acid-hardening lacquer.

| Front page | | Contents | | Previous | | Next | | Top |

Version 1.0 September 2005, © Danish Environmental Protection Agency