In Britain the National Association of Paper Merchants (NAPM) uses a classification system to identify the proportion and source of waste fibre used to make recycled paper, which uses the letters A to D, each letter accompanied with a figure indicating the percentage of that source. It is important to understand the differences between these four sources of waste.
A: Mill broke
This is pulp which has been on the papermaking machine but not turned into saleable paper. It has virtually the same properties as virgin wood pulp and has always been re-used by paper mills - indeed it could be argued that it is not a waste product at all. Consequently the NAPM scheme does not recognise a paper as recycled if it contains more than 25% mill broke and/or virgin wood pulp. The longer fibres in mill broke are used to increase the strength of a paper.
B: 'Woodfree' unprinted waste
The term 'woodfree' causes the most public confusion, as the paper is anything but 'wood-free'. The name indicates that when originally pulped the 'woody' lignins in the timber were destroyed in a chemical reaction (part of the environmental problem of conventional papermaking), to produce a higher quality paper. If not removed, the lignins - the inflammable part of the wood - cause paper to yellow and become brittle with age (as, for example, old newspapers do). You can see exactly the same process in the way pine furniture changes colour with age.
Category B waste comes mainly from paper mills and converters, for example reel and guillotine trimmings, and has not been printed or 'used' in the generally accepted sense.
C: 'Woodfree' printed waste
This comes nearer to most peoples idea of what recycled paper should be made from, but because it must only include woodfree paper, it tends to come from limited specific sources, for example, scrapped work direct from printers or discarded computer printouts and envelopes from very large companies.
Some would argue that the chief sources of category C waste should themselves be using recycled paper, and that recycling this it is only a cosmetic solution. On the other hand some newer, longer fibre is essential in producing high quality recycled paper, and this is the most appropriate source for making the very best recycled qualities.
Ink in category C waste is either removed by a cleaning process which chemically 'floats' it off or by dispersing it throughout the pulp. The latter is environmentally preferable, but makes the paper less white and so (to the uneducated!) less attractive.
D: Mechanical and unsorted waste
Mechanical paper pulp is more frankly named - the wood is pulped by a combination of heat and maceration, but because it retains the lignins it is only really suitable for short-term uses - for example newspapers and directories. The lignins present in category D waste can survive into recycled paper made from it, unless the pulp is retreated to remove them. Consequently some fading of colours or yellowing when the paper is exposed to daylight make recycled paper containing category D waste more suitable for uses such as photocopies which are filed, or for other items with a more limited life.
Category D covers almost all domestic waste paper, including that collected at local recycling centres and paper banks, and is largely used in making packaging materials (brown paper and cardboard boxes for example). Some of this type of waste is used in making the cheaper recycled office copier and similar types of paper.