Scientists have found a productive way to dispose of waste caused in the recycling of paper by using it to make building materials. "Ten tonnes of waste paper, when recycled, may create two tonnes of fibrous clay/limestone residue bound up with two tonnes of water.

An Australian online news agency (ferret.com.au) reports that disposal of this residue is now becoming a major problem," professor John McNicholas of Salford University in northern England explained. "On a national scale [in the UK] more than four million tonnes of waste paper is recycled annually and the amount is rapidly increasing driven by legislation. Some mills burn the residue and landfill the ash, while others, at the moment, are allowed to landspread it on farms. Such disposal is expensive and is not the best environmental solution."

The Salford University team has provided an alternative solution: to transform the residue into building products such as boards and blocks, using cheap binders like cement and gypsum. "All wastepaper recycling mills produce a residual waste consisting of short cellulose fibres and fillers," McNicholas said.

Trials conducted at a paper company in England which supports the research used a mixture of newspapers and magazines as an input. More than 200,000 wet tonnes (solids over 100,000 tonnes) of residual waste annually was generated annually. "The glossy magazine pages have a high proportion of clay filler. Other smooth papers may contain limestone filler. This residual waste contains about 45% cellulose fibres and the rest is dominated by clay filler but with a small proportion of limestone filler," McNicholas said. "Wastes from other recycling mills have different compositions depending on the type of wastepaper input and the efficiency of the process."

Binders used are low-cost materials - cement and gypsum already used by the building industry. The Salford team has investigated seven types of cement and two types of gypsum, and assessed four waterproofing additives and five paint systems. Team members also looked at combining the paper recycling waste with other wastes such as granite slurry and old crushed plasterboard. In the laboratory, production was based on wet mixing, press de-watering, curing (for cement boards) and drying.

The dried boards were sawn to provide samples that were tested in bending to establish their strength, stiffness and other properties. Test results were used to generate a database that identifies the optimum formulation and board density for specified values of strength and stiffness.

The results incorporated dimensional stability limits and supplementary structural information. Information about blocks and panels for internal walls was also generated. "The project is ready for commercial exploitation and an advisory service for entrepreneurs and manufacturers is now available," McNicholas said. The project has developed a range of designer materials that can be tailored to satisfy specific requirements.

The materials have good working properties, being easy to saw, nail, drill and tap. In some applications they can replace timber, for instance as sheathing boards for timber-framed construction or in veneered form for furniture manufacture. Boards can have a design impressed into the surface to create a decorative effect at very low cost. "As a homogeneous material free from defects there is also an application in making models and prototypes, replacing much more expensive materials used for this purpose," Professor McNicholas said>http://>