Paper Making

The Egyptians first used papyrus for writing around 3000 BC, but the invention of paper is credited to Ts’ai Lun of China in 105 AD. This was made from the bark of mulberry trees, which was treated with lime, bamboo and cloth. The technology was kept a secret for over 500 years, but in the early 700’s, the Arabs captured a Chinese town containing a paper mill and learnt the method. Paper was first made in England in 1496, the first US paper mill began operating in 1690. Development of the paper machine was largely led by the Fourdrinier brothers, who made the first practical paper making machine in England in 1804. Cotton was the main constituent used in paper originally, but during the mid-19th Century, the technology for converting wood to pulp was developed, originally using water-driven mills (from which the term paper mill is derived). Irrespective of the method of making paper, there are several common steps to the process. The raw material is pulped by chemical or mechanical means (or a combination of the two), which allows for the separation of individual fibres. The fibres may be bleached and are treated by beating or refining to roughen the surface and improve fibre-fibre bonding. Paper is formed by running a dilute suspension of the fibres over a wire/polymer screen, through which the water drains. Additional water is removed by pressing and, finally by heating. Pulps for the manufacture of paper come from a variety of fibre sources, such as wood, cotton, hemp, recovered fibre etc., although wood is the main source. Hardwood pulps (mainly eucalyptus) are used mostly to obtain the required optical properties, such as sheet formation and opacity. Softwood pulps, with their longer fibres are used to provide strength. Increasing amounts of recycled fibre are used to make paper (especially newsprint and card board) and it is very important to have pure sources of recycled (secondary) fibre. This is usually divided into: mixed office waste, magazine grade, old corrugated containers (OCC), and newspaper, with value decreasing along the series. In practice, newspapers and magazines are often mixed. Waste paper is de-inked to produce higher quality paper, with the remainder being used to produce paperboards, chipboard, and lining materials. However, there is a limit to how much recycled fibre can be used to make paper because the fibres deteriorate with each cycle. It is therefore essential to use virgin fibres in the higher quality papers (such as glossy magazines or office paper), which then get downcycled to lower quality paper when recycled. The virgin fibres are obtained from managed plantation forests, which are restocked after felling to ensure a sustainable supply, or taken from forestry thinnings.

 

Contributor:       Dr Callum Hill FIMMM