Facts about paper

This FAQ has been compiled using information kindly supplied by Paper Round, PaperlinX and M-Real.

What is paper made from?
The vast majority of paper produced around the world is made from wood pulp.

Can paper be made from non-wood plants?
Excellent quality paper can be made from many sorts of fibrous plants, including cotton, flax, hemp, kenaf and bagasse, if it is processed appropriately. However, each of these resources has its own significant environmental, agricultural, commercial and processing issues — just as wood does.

There seems to be more printed matter than ever before. Are forests suffering because of that?
Wood is a renewable raw material that replenishes itself when forests are managed in a sustainable way. The industrial use of wood assigns a value to the trees in the forest, and provides us with an incentive to look after our natural resources. The industrial use of forests is strongest in Europe and North America. In these areas, the forest area has not decreased — on the contrary, the annual growth in these areas exceeds the wood removed by felling, thanks to planting and natural regeneration. For example, in Europe only about 65% of the annual growth of forests is harvested.

In Finland, where forests cover 86% of the land area, the wood volume is greater than it has ever been. The growing season in Finland is about 80 days in a year and, during one day of the growing season, the increase of timber in Finnish forests is equivalent to a woodpile that is one metre high and wide – and one thousand kilometres long.

How is forest biodiversity taken into account during logging?
There are two main ways of preserving forest biodiversity. One is to maintain a network of conservation areas, and the other is to develop forestry and harvesting methods that take biodiversity into account. Since the 1990s, maintaining forest biodiversity has been an integral part of sustainable forest management.

Improved forestry practices, legislation and forest certification have all been introduced, aimed at preserving forest biodiversity. Sustainable forest management methods include leaving ‘retention trees’ and decaying wood in the forests, conserving habitats of special importance, leaving buffer zones along waterways and favouring mixed forests.

What types of wood are good for papermaking?
There are two broad classes of wood: hardwoods (such as eucalypts) which have short fine fibres suitable for printing grades of paper, and softwoods (such as pine) which have long coarse fibres which are suitable wherever strength is required (e.g. for bag and sack papers, and in small proportions for reinforcing printing papers).

What part of the wood is used to make paper pulp? Wood consists of approximately equal amounts of cellulose fibre and a binder called lignin, which glues the fibres together. It is the cellulose fibres which give paper its structural strength and physical properties. Whether the lignin is used in paper is determined by the pulping process.

How is wood turned into papermaking pulp?
There are two main processes, depending on the end use of the pulp. To make mechanical pulp, the wood is first chipped (a wood chip is typically about 50mm x 30mm x 5mm in size) and then the chips are fed to a refiner which disintegrates the chips into individual fibres, by forcing them between two large ribbed disks which counter-rotate at high speed, very close together. Often the chips are first softened by heating, or soaking in caustic soda or other chemicals. Mechanical pulp is typically used in newsprint, magazine paper and paper towels. In mechanical pulping, the lignin remains with the fibres.

To make chemical pulp, the woodchips are cooked with chemicals (e.g. caustic soda) to dissolve the lignin, leaving the cellulose fibres intact. The dissolved lignin is burnt to (a) provide energy, and (b) recover the chemicals. Chemical pulp makes stronger paper than mechanical pulp (which is why the most common process is called “kraft” — the German word for “strong”). Chemical pulp is thus important for packaging grades like bag and sack kraft and linerboard (for corrugated cardboard boxes). Chemical pulp fibres are much more flexible and conformable than mechanical pulp fibres, so they are ideal for making fine papers (such as copy paper).

How much wood is required to make a tonne of paper?
Green wood consist of roughly 50% moisture, 25% cellulose and 25% lignin. So, 4 tonnes of green wood are required in order to produce 1 tonne of chemical pulp. For a typical fine paper containing, say 3% starch and 15% calcium carbonate filler, this would make 1.4 tonnes of paper.

What do pre-consumer and post-consumer mean?
The formal definitions given in Australian Standard 4082-1992 Recycled Paper — Glossary of Terms are:

Post-consumer waste paper:
Any paper for which the consumer has no further use.

  1. Overruns, returns and waste created in a manufacturing or paper converting operation are not considered post-consumer waste paper, except for that proportion of broke which has previously been identified as post-consumer waste.
  2. This paper is generally less uniform and may contain a higher level of contamination by waste paper contraries than pre-consumer waste paper.

Pre-consumer waste paper:
Any waste paper which is not post-consumer waste paper, overruns and returns or broke, except for that proportion of broke which has previously been identified as pre-consumer waste paper.

  1. Pre-consumer waste paper may be generated in a manufacturing, printing or converting operation other than the papermaking process itself and includes paper after it has left the paper mill, but before it has reached its end use.
  2. This waste paper is relatively less contaminated and more uniform than post-consumer waste paper.

What are the differences between pre-consumer and post-consumer waste?
In many cases there is no difference at all. However some pre-consumer waste, such as trimmings from a printing plant or envelope manufacturer, has little or no printing on it. This is an ideal resource for making high brightness papers such as copy paper. In general, pre-consumer waste paper is likely to be less contaminated and more uniform in its properties than post-consumer waste paper.

The environmental benefits (see below) of recycling are identical, whether the source of the waste paper is pre-consumer or post-consumer.

In Australia both pre-consumer and post-consumer waste are now collected with high efficiency, so there is no need to give extra encouragement to recycling either type of paper.

What is “broke”?
This is a papermaker’s term for paper which usually has some fault (i.e. it does not meet the relevant specifications), and is to be re-pulped and fed back into the papermaking process.

Is broke counted as recycled fibre?
Re-using broke is a fundamental part of the papermaking process, and is not considered recycling. Broke is only counted as recycled fibre to the extent that it was originally made from recycled fibre.

Is recycled fibre the same as new fibre?
At a molecular level, there are subtle differences between fibres which have never been through the papermaking process (new or virgin fibres — AP prefers the term “new”), and those which have recycled fibre. These differences can manifest themselves as reduced bonding power leading to weaker paper, and improved dimensional stability in the face of changing moisture levels.

Depending on the way the fibres are treated, they may also contain specks of ink, and traces of “stickies” (residue from contaminants such as hot-melt glue), but the papermaker has means for dealing with these if necessary.

Is paper containing recycled fibre inferior in its properties?
If the recycled fibre is from an appropriate source, and it is properly treated, it is possible to make products such as copy paper which contain a significant proportion of recycled fibre, yet are virtually indistinguishable from paper made only from new fibres.

In the case of envelope papers and some forms of cardboard, the properties of recycled fibres are actually an advantage. It makes sense to steer recycled fibres towards such applications.

How does recycling paper help the environment?
The main consequence of recycling fibre is that it reduces the amount of paper dumped in landfill. Over 1.5 million tonnes of paper is kept out of landfill every year by recycling in Australia.

Recycling paper also reduces the demand for new fibre, which reduces the land required for pulpwood plantations. Whether or not this “saves trees” depends on the alternate use to which the land is put.

Whether it is pre or post consumer waste, recycling paper helps reduce the amount of fibre needed to manufacture paper products but, as importantly, it significantly reduces the amount of waste going to landfill. For example, Australian Paper uses 100,000 tonnes of waste paper each year that would otherwise fill up our landfill space.

What is recycled white paper used for?
It may seem that the only appropriate thing to do with recycled copy paper, say, is to turn it back into copy paper. But there are many other good uses for recycled copy paper, and any other form of recycled white paper. These are some of the applications in Australia (not all of these are done by Australian Paper):

  • Brown cardboard
  • White or white-topped cardboard
  • Newsprint
  • Tissue
  • Envelope papers
  • Bag and sack papers
  • Offset and specialty papers
  • Photocopy papers

All of these uses achieve the same environmental benefit: reduction of landfill.

Is 100% recycled paper sustainable?
No it is not. Manufacture and use of paper damages the fibres, and there is a practical limit to the number of times a fibre can be recycled, before it has disintegrated. It is not easy to establish what that limit is, but the real limitation is the collection efficiency. Currently Australia recycles about half the paper it uses, which means that only one fibre in 32 gets recycled more than 5 times, for example.

Even if all paper available for collection were collected, there would still be paper which will be kept permanently, and there are inevitable losses in processing.

New fibre is therefore continually needed to replenish the fibre lost from the system.

Why isn’t all paper made from recycled fibre?
Recycled paper is an important raw material for the paper industry. Paper is one of the few materials that is recycled efficiently, and the recycled material has real market value. The majority of recovered paper is used for packaging grades, newsprint and tissue.

However, even though paper is collected efficiently, there is not enough recycled fibre available for all paper needs. Also, higher-quality paper grades require fresh fibre, due to their demanding technical requirements. You can only circulate fibres about 3-5 times, as during each recycling, the fibres deteriorate. Eventually, they become so weak that you can’t use them any more. Without fresh fibre, we would run out of paper in a few months.

Why is pulp bleached?
Mechanical pulps are fairly bright as prepared, but usually require some brightening to reach an adequate level of brightness and whiteness.

Chemical pulps, as made, are brown. This is fine for many packaging paper grades, but is totally unsuitable for printing and writing grades. Bleaching is therefore necessary to remove the coloured compounds from the fibres, and allow a white sheet of paper to be made.

What does gsm mean?
GSM, or g/m2, is an abbreviation for grammage, or grams per square metre. It indicates the weight of a square metre of paper. Standard copy paper in Australia is approximately 80 gsm, which means that a standard A4 sheet weighs 5 grams, and a 500 sheet ream weighs 2.5 kg.

Is gsm the same as thickness?
Not exactly. Thickness is measured in microns (millionths of a metre, or thousandths of a millimetre). Standard copy paper typically has a thickness of about 100 microns, so a 500 sheet ream is about 5cm thick. If two sheets have the same density, then their thicknesses will be directly proportional to their grammage.

How is the colour of paper measured?
Colour is measured using a reflectance spectrometer, a device which measures the percentage of light of different wavelengths reflected from the paper. The reflectance measurements are converted to three numbers, which give a unique quantitative definition of the colour.

What are CIE L*,a*,b*?
These are three quantities used to define the colour of paper, calculated from reflectance values.
L* measures lightness, on a scale from 0 (black) to 100 (snow white),
a* measures greenness if negative, redness if positive,
b* measures blueness if negative, yellowness if positive.

For a complete definition, it should be stated what combination of standard illuminant (light source) and standard observer is used in the calculation. Typically these are D65/10o or C/2o.

What is ISO Brightness?
This is a traditional measure of blue reflectance. It is not part of the CIE L*,a*,b* or CIE L*,W, T systems, although it can be approximated by a mathematical combination of lightness and whiteness.

Does whiteness or brightness on its own describe white paper colour?
No. It is quite possible to have two papers which have the same brightness, or the same whiteness, but nevertheless look very different. For example, one may look much duller and bluer than the other.

A good description of the appearance of white papers requires at least two variables (e.g. lightness and whiteness) and preferably three (i.e. include tint as well).

What is opacity?
Opacity is a measure of how easy it is to see through the paper. For duplex (both sides) printing, it is important to have a high opacity.

Why are ream wrappers plastic coated?
When copy paper goes though a copier or laser printer, it is heated on one side, to fuse the powdered toner into the surface of the paper. Heating one side of the paper dries it and causes it to shrink, and this in turn introduces a tendency to curl. Too much curl may cause paper jams, so to minimise this effect the paper is made with low moisture content. In order to maintain the low moisture content, the paper must be wrapped in a moisture-proof wrapper.

Typically, the moisture-proof wrapper consists of paper with a thin layer of plastic on the inside or on the outside.

How should I store part-used reams of paper?
It is important not to let the paper pick up too much moisture, or curl problems will occur when it is printed. In a fairly dry air-conditioned office environment, this probably won’t be a problem and the paper can be left unwrapped. But if the environment is exposed to the outside and subject to fluctuations in humidity, then keep part-used reams wrapped, and secured with adhesive tape.

If paper is stored in a cold environment (e.g. a warehouse in winter), bring it into the printing environment and let it warm up for a day before using it. This will prevent humidity condensing out of the air onto the paper.

Which side of copy paper should I print first?
Lay the ream seam up on the table. The side of paper facing upwards is the best side to print first. The reason is that the paper is made with built-in stresses designed to offset the influence of heating of the paper in the copier/printer, thus minimising the possibility of curl and paper jams.

If you are having trouble with curl or paper jams, try inverting the paper in the feed tray.

What is the significance of lignin?
Decomposition of lignin is thought to be one of the mechanisms which leads to the slow degradation of paper in long term storage. This is why newsprint, which contains all the lignin from the wood, has a very short lifetime.

How are the standard paper sizes A4, A5 etc determined?
A4 is the familiar standard paper size for office papers in Europe, Australia and New Zealand and many other countries.

A4 is part of a sequence which starts with A0. An A0 sheet is 1 square metre in area, and its sides are in the ratio of 1.414 to 1. So its dimensions are 1189 mm x 841 mm.

Cutting this sheet in half, parallel to the short side, produces two A1 sheets, each half a square metre in area, with dimensions 841mm x 595. This sheet has the same shape as the A0 sheet, i.e. its sides are in the ratio 1.414 to 1.

Continuing to halve the sheet in this way produces A2 and the more familiar A3, A4 and A5 sizes. A4 is 297 mm x 210 mm. These dimensions are each one quarter of the A0 dimensions, and the A4 sheet is 1/16 square metres in area.


13th July 2016

30 years on!

Thank you to Peter Dearing for 30 years at Printgraphics Printgreen.

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