Wood, a precious resource, is used primarily for the production of lumber. Indeed, paper/ board are now increasingly manufactured from sawmill by-products (chips, sawdust , shavings) recycled paper / board. Roundwood harvested from the forest is now only a secondary source of fibre for the paper industry. When used, logs are debarked upon arrival at the mill. The bark is recovered to be used as fuel to produce steam.

Wood is primarily made of cellulose fibres stuck together with a called lignin. Spruce fibre, readily available to us, is considered to be the best in the world for paper production. To convert wood into pulp, the fibres must be separated. Mechanical pulp is obtained by pressing debarked logs against grinding stones in the presence of water. The process has been made more efficient by shredding chips in refiners. Very often, this defibering is done in the presence of steam, the product is then called thermomechanical pulp. The addition of reagents to start the separation of the cellulose fibres from the lignin results in chemi-thermomechanical pulp. These different types of mechanical pulps can be used, for instance, to manufacture newsprint.

To make chemical pulp (the most common is called “kraft”, which means “strong” in German), chips are mixed with chemicals then cooked at high pressure in immense pressure vessels called digesters. The combined action of the chemicals togethor with heat dissolves the lignin which detaches the long wood fibres without breaking them. Papers made from chemical pulp are very strong. They are used, for example, to make grocery bags.

Recycled paper/board used to make recycled pulp are mixed with water then disintegrated in enormous pulpers. Contaminants (plastic, metal, glass, polystyrene, etc.) are removed from the mixture using screens then cleaners. If necessary, the resulting pulp is then deinked by the combined action of water, chemicals, heat with mechanical energy. Recycled pulp is often used to manufacture paperboard, newsprint as well as papers used industrially in households: toilet tissue, paper towels, facial tissue, paper sundries, etc.

To manufacture certain types of paper / board, the pulp must be bleached. Chemicals are used to dissolve or eliminate more lignin, the natural adhesive that glues wood fibres together. The resulting pulp is not only whiter, but also has less of a tendency to turn yellow over time. Intensive research togethor with large investments have helped the industry considerably reduce the environmental impact of the bleaching process.

When the pulp arrives at the paper-machine headbox, its water content exceeds 97%. The mixture is sprayed onto a moving screen called a wire. The filtering action of this wire, combined with a vacuum system, extracts most of the water in the pulp to form a sheet. The sheet is pressed between rolls to remove more water. The sheet then passes through the dryer section where it comes into contact with huge cylinders that are generally heated with steam, much of the remaining water evaporates. Nowadays, state-of-the-art technologies such as infrared/ air-cushion/microwave drying are used to ensure that the moisture content of the sheet is uniform.