The Development of Plastics

A When rubber was first commercially produced in Europe during the nineteenth century, it rapidly became a very important commodity, particularly in the fields of transportation and electricity. However, during the twentieth century a number of new synthetic materials, called plastics, superseded natural rubber in all but a few applications.

B Rubber is a polymer – a compound containing large molecules that are formed by the bonding of many smaller, simpler units, repeated over and over again. The same bonding principle – polymerisation – underlies the creation of a huge range of plastics by the chemical industry.

C The first plastic was developed as a result of a competition in the USA. In the 1860s, $10,000 was offered to anybody who could replace ivory – supplies of which were declining – with something equally good as a material for making billiard balls. The prize was won by John Wesley Hyatt with a material called celluloid. Celluloid was made by dissolving cellulose, a carbohydrate derived from plants, in a solution of camphor dissolved in ethanol. This new material rapidly found uses in the manufacture of products such as knife handles, detachable collars and cuffs, spectacle frames and photographic film. Without celluloid, the film industry could never have got off the ground at the end of the 19th century.

D Celluloid can be repeatedly softened and reshaped by heat and is known as a thermoplastic. In 1907 Leo Baekeland, a Belgian chemist working in the USA invented a different kind of plastic by causing phenol and formaldehyde to react together. Baekeland called the material Bakelite, and it was the first of the thermosets – plastics that can be cast and moulded while hot but cannot be softened by heat and reshaped once they have set. Bakelite was a good insulator and was resistant to water, acids and moderate heat. With these properties, it was soon being used in the manufacture of switches, household items, such as knife handles, and electrical components for cars.

E Soon chemists began looking for other small molecules that could be strung together to make polymers. In the 1930s, British chemists discovered that the gas ethylene would polymerise under heat and pressure to form a thermoplastic they called polythene. Polypropylene followed in the 1950s. both were used to make bottles, pipes and plastic bags.

A small change in the starting material – replacing a hydrogen atom in ethylene with a chlorine atom – produced PVC (polyvinyl chloride), a hard, fireproof plastic suitable for drains and gutters. And by adding certain chemicals, a soft form of PVC could be produced, suitable as a substitute for rubber in items such as waterproof clothing. A closely related plastic was Teflon, as PTFE (polytetrafluoroethylene). This had a very low coefficient of friction, making it ideal for bearings, rollers, and non-stick frying pans. Polystyrene, developed during the 1930s in Germany, was a clear, glass-like material, used in food containers, domestic appliances and toys. Expanded polystyrene – a white, rigid foam – was widely used in packaging and insulation. Polyurethanes, also developed in Germany, found uses as adhesives, coatings, and – in the form of rigid foams – as insulation materials. They are all produced from chemicals derived from crude oil, which contains exactly the same elements – carbon and hydrogen – as many plastics.

F The first of the man-made fibres, nylon, was also created in the 1930s. Its inventor was a chemist called Wallace Carothers, who worked for the Du Pont company in the USA. He found that under the right conditions, two chemicals – hexamethylenediamine and adipic acid — would form a polymer that could be pumped out through holes and then stretched to form long glossy threads that could be woven like silk. Its first use was to make parachutes for the US armed forces in World War II. In the post-war years, nylon completely replaced silk in the manufacture of stockings. Subsequently, many other synthetic fibres joined nylon, including Orion, Acrilan and Terylene. Today most garments are made of a blend of natural fibres, such as cotton and wool, and man-made fibres that make fabrics easier to look after.

G The great strength of the plastic is its indestructibility. However, this quality is also something of a drawback: beaches all over the world, even on the remotest islands, are littered with plastic bottles that nothing can destroy. Nor is it very easy to recycle plastics, as different types of plastic are often used in the same items and call for different treatments. Plastics can be made biodegradable by incorporating into their structure a material such as starch, which is attacked by bacteria and causes the plastic to fall apart. Other materials can be incorporated that gradually decay in sunlight – although bottles made of such materials have to be stored in the dark, to ensure that they do not disintegrate before they have been used.

How should reading be taught?

By Keith Rayncr a Barbara R Foorman

A Learning to speak is automatic for almost all children, but learning to read requires elaborate instruction and conscious effort. Well aware of the difficulties, educators have given a great deal of thought to how they can best help children learn to read. No single method has triumphed. Indeed, heated arguments about the most appropriate form of reading instruction continue to polarize the teaching community.

B Three general approaches have been tried. In one, called whole-word instruction, children learn by rote how to recognise at a glance a vocabulary of 50 to 100 words. Then they gradually acquire other words, often through seeing them used over and over again in the context of a story.

Speakers of most languages learn the relationship between letters and the sounds associated with them (phonemes). That is, children are taught how to use their knowledge of the alphabet to sound out words. This procedure constitutes a second approach to teaching reading – phonics.

Many schools have adopted a different approach: the whole-language method. The strategy here relies on the child’s experience with the language. For example, students are offered engaging books and are encouraged to guess the words that they do not know by considering the context of the sentence or by looking for clues in the storyline and illustrations, rather than trying to sound them out.

Many teachers adopted the whole-language approach because of its intuitive appeal. Making reading fun promises to keep children motivated, and learning to read depends more on what the student does than on what the teacher does. The presumed benefits of whole-language instruction – and the contrast to the perceived dullness of phonics – led to its growing acceptance across American during the 1990s and a movement away from phonics.

C However, many linguists and psychologists objected strongly to the abandonment of phonics in American schools. Why was this so? In short, because research had clearly demonstrated that understanding how letters related to the component sounds in words is critically important in reading. This conclusion rests, in part, on knowledge of how experienced readers make sense of words on a page. Advocates of whole-language instruction have argued forcefully that people often derive meanings directly from print without ever determining the sound of the word. Some psychologists today accept this view, but most believe that reading is typically a process of rapidly sounding out words mentally. Compelling evidence for this comes from experiments which show that subjects often confuse homophones (words that sound the same, such as Jrose and ‘rows5). This supports the idea that readers convert strings of letters to sounds.

D In order to evaluate different approaches to teaching reading, a number of experiments have been carried out, firstly with college students, then with school pupils. Investigators trained English-speaking college students to read using unfamiliar symbols such as Arabic letters (the phonics approach), while another group learned entire words associated with certain strings of Arabic letters (whole-word). Then both groups were required to read a new set of words constructed from the original characters. In general, readers who were taught the rules of phonics could read many more new words than those trained with a whole-word procedure.

Classroom studies comparing phonics with either whole-word or whole-language instruction are also quite illuminating. One particularly persuasive study compared two programmes used in 20 first-grade classrooms. Half the students were offered traditional reading instruction, which included the use of phonics drills and applications. The other half were taught using an individualised method that drew from their experiences with languages; these children produce their own booklets of stories and developed sets of words to be recognised (common components of the whole-language approach). This study found that the first group scored higher at year’s end on tests of reading and comprehension.

E If researchers are so convinced about the need for phonics instruction, why does the debate continue? Because the controversy is enmeshed in the philosophical differences between traditional and progressive (or new) approaches, differences that have divided educators for years. The progressive challenge the results of laboratory tests and classroom studies on the basis of a broad philosophical skepticism about the values of such research. They champion student-centred learned and teacher empowerment. Sadly, they fail to realise that these very admirable educational values are equally consistent with the teaching of phonics.

F If schools of education insisted that would-be reading teachers learned something about the vast research in linguistics and psychology that bears on reading, their graduates would be more eager to use phonics and would be prepared to do so effectively. They could allow their pupils to apply the principles of phonics while reading for pleasure. Using whole-language activities to supplement phonics instruction certainly helps to make reading fun and meaningful for children, so no one would want to see such tools discarded. Indeed, recent work has indicated that the combination of literature-based instruction and phonics is more powerful than either method used alone.

Teachers need to strike a balance. But in doing so, we urge them to remember that reading must be grounded in a firm understanding of the connections between letters and sounds. Educators who deny this reality are neglecting decades of research. They are also neglecting the needs of their students.