Paper and Wood Pulp

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Paper and Wood Pulp

Introduction

Paper is one of the most versatile products of everyday life, with hundreds of different uses. It is vital for comunication and education, as well as in sanitary and household applications and packaging. Paper is basically a mat of fibers derived from plant material, and it is mostly made of fibers derived from wood. Making paper from wood has long been an important industry in countries such as Canada and Finland.

Paper is biodegradable, recyclable, and a source of energy if it is burned. If it is produced in a sustainablemanner, then paper is an environmentally friendly product. The introduction of personal computers and electronic mail could possibly have led to a paper-free office, but the reverse has happened with demand for paper growing in recent years. This need not be a problem if paper is recycled and reused wherever possible.

Historical Background and Scientific Foundations

To the naked eye, paper looks smooth, but if examined under a microscope it reveals itself as a network of plant fibers laid down as a sheet. It is made by draining most of the water from a suspension of these fibers known as pulp. Today, most paper is made from wood pulp, but it can also be made from other plant sources such as hemp, cotton, and, of course, recycled paper.

The ancient Egyptians made a type of paper that they called papyrus by pressing together the strips of the grasslike sedge Cyperus papyrus. Then, in the second century AD, the Chinese began to make paper that was more like the material in use today. They used a pulp of mulberry fibers and lifted it up in a silk sieve to drain the water, leaving a sheet of paper, which was dried in the sun. This paper was high quality and long lasting. Indeed, samples still survive in the British Museum in London. It was not until the nineteenth century that wood pulp was used as the main source of paper, and papermaking was accomplished by machine instead of by hand. Previously papermakers used cotton and hemp as a raw material.

Wood consists of cellulose fibers held together by a substance called lignin. In wood pulp production, timber is sawed from the tree and its bark removed. Then the fibers are separated by either mechanical or chemical treatment to create pulp, which may then be bleached, depending on application. Trees suitable for paper production include pine, spruce, birch, and eucalyptus. The property of the paper is tailored to its intended end use. Therefore, durability is important for bank notes, which are made of cotton and flax fibers. Tissues, toilet paper, and sanitary towels need good absorbency. Cardboard is a heavy-duty type of paper, sometimes layered, which is widely used in packaging. Different types of pulp are used for these various applications.

Impacts and Issues

Around four billion trees are cut down each year to make paper. This is about one third of all trees harvested for commercial purposes. World consumption of paper has increased four-fold in the last 40 years, with around 300 million tons being used each year. Around one third of this now comes from recycled paper. Because of the varying grades of paper and the different applications, it is difficult to estimate how much paper one tree yields. However, according to the Wisconsin Paper Council, a single tree could give rise to 250 copies of a newspaper or 90,000 sheets of writing paper.

The paper industry is often portrayed as being wasteful and harmful to the environment, but it should be remembered that paper pulp is not harvested from

tropical rain forests. Moreover, paper can have a beneficial effect on the carbon cycle. If wood is burned, carbon dioxide is released immediately into the atmosphere, contributing to global warming. If it is made into paper, the carbon is trapped and will be released over a longer period of time.

Unlike fossil fuels, wood is a renewable resource and planting more forests for wood production creates a carbon sink, as trees absorb carbon dioxide from the atmosphere. However, the paper industry does use various harmful chemicals, such as chlorine dioxide, in production, and has been responsible for various pollution inci-

WORDS TO KNOW

BIODEGRADABLE: capable of being degraded in the environment by the action of microorganisms

CARBON SINK: A location like a forest where there is net storage of carbon as sequestration exceeds release.

RENEWABLE RESOURCE: Any resource that is renewed or replaced fairly rapidly (on human historical time-scales) by natural or managed processes.

SUSTAINABLE: Capable of being sustained or continued for an indefinite period without exhausting necessary resources or otherwise self-destructing: often applied to human activities such as farming, energy generation, or the maintenance of a society as a whole.

WOOD PULP: a suspension of wood tissue in water which is the source of most paper

dents. Sustainable forest management, emission control, and recycling of paper products wherever possible are key to an environmentally friendly paper industry.

See Also Forest Resources; Logging