Plastics semi-synthetic

During World War II a large amount of research was carried out in seeking fully synthetic polymeric materials which could substitute a semi-synthetic polymer such as nitrocellulose. This research was connected with the immense development of plastics chemistry, which began shortly before World War II and is still advancing at a great pace. 

Synthetic polymer materials are so ubiquitous in modem life that we now take them for granted. But, the first commercially significant, completely synthetic plastic was only introduced at the beginning of the 20th century. This was Bakelite, invented by Leo Baekeland and a short account of his contributions will form the subject of one of our Polymer Milestones in the next chapter. The introduction of this new material was preceded by roughly 40 years of the development of what can be called semi-synthetics based on chemically modified forms of cellulose. 

Cellulose nitrate is a semi-synthetic plastic based on cellulose from wood or cotton. It is mixed with nitric and sulphuric acids, and uses camphor as a plasticiser. It is another compound that was being developed by various people in different places at the same time, but was launched in England in 1862 as Parkesine . It was later called Xylonite . Cellulose nitrate was finally patented in America in 1870 under the name celluloid , but has been known by over 60 different trade names during the years it has been in production. 

At the International Exhibition of 1862, Alexander Parkes [2] first introduced an organic derivative of cellulose that could be moulded when heated and retain that shape when cooled. He invented the treatment of cellulose fibres with nitric acid forming cellulose nitrate that was the first semi-synthetic plastic material. He used this to make decorative brooches, trinkets and knife handles. He claimed that it could do anything that rubber could do but could be produced at a lower price. He formed a company making a... 

The first polymers were developed in 1862, known as semi-synthetics and formed a technological bridge between natural (those produced by trees, plants and insects) and fully synthetic polymers. Semi-synthetic plastics were made by treating a natural material chemically to modify its properties, usually with the aim of producing a mouldable product. In 1909, the first fully synthetic polymer was produced by reacting two chemicals (monomers) together. 

Preparation of semi-synthetic polymers. Cellulose plastics, particularly cellulose nitrate and acetates, were the most commercially-important semi-synthetics, and have been used to prepare photographic films, textile fibres and lacquers. 

Plastics are semi-synthetic or synthetic materials which can be manipulated to form films, fibres, foams or three-dimensional olgects. Natural polymers from plants, insects and animals are not discussed in this book. Synthetic paints, synthetic textiles and photographic film contain plastics but will not be discussed in this book because their conservation is the focus of specialist publications (Chiantore and Rava, 2005 Learner, 2005 Timar-Balazsy and Eastop, 1998 Lavedrine et al., 2003). Plastics are based on polymers, also known as macromolecules, which are large molecules made by joining together many smaller ones. The chemical and physical properties of liquid polymers are modified with additives and shaped to convert them into solids with dimensionally stable forms. 

Chapter 2 describes the factors which were instrumental in the history of plastics and the development from natural materials to semi-synthetics and then to the synthetics we know today. Collections contain examples of aU groups of plastics. They represent both the materials and technology available at different periods of the nineteenth, twentieth and twenty-first centuries. The future of plastics and, thereby, of future collections is presented. 

Although we consider plastics to be new materials, only semi-synthetic and synthetic plastics are modem (Table 2.1). Naturally occurring polymers, those formed by plants, trees, insects and animals, were first documented as coatings and waterproofing agents in the form of bitumen, referred to as slime in the Old... 

Semi-synthetic plastics are natural polymers which have been treated chemically to modify their properties with the aim of producing physically stable, mouldable products. The Swiss chemist, Schonbein, unwittingly prepared the first semi-synthetic polymer by treating paper (cellulose) with a mixture of nitric and sulphuric acids in 1846. The resulting cellulose nitrate was soluble in organic liquids and was softened by heat. It was highly flammable and only thought to be useful as an explosive, which was named gun cotton . 

Cellulose-based plastics, particularly cellulose nitrate and acetates, were the most commercially important semi-synthetics up to the 1940s and were used as the base for photographic film, textile fibres, moulded goods and in lacquers. Naturally occurring polymer cellulose in the form of cotton linters or wood pulp is chemically treated to increase its solubility. Cellulose has a high molecular weight of between 100000 and 500000 and an empirical formula C0H1OO5. Casein-formaldehyde is the only protein-based moulded plastic that achieved commercial success. It is based on cow s milk and is still produced in very small quantities for specialist items such as hand-coloured buttons. 

The great economic and cultural success achieved by plastics can be attributed largely to their optical properties. The ability of semi-synthetics to mimic the rich colours and opacity or transparency of natural materials endeared them... 

For more recent synthetic polymers, interviews with the artist can provide information about materiak and technique used, although they do not always replace analysis. The date of manufacture or, if unavailable, the date of collection, can provide a starting point in the identification of plastics. If a plastic was manufactured before around 1905, it is likely to be a semi-synthetic or natural material, rather than a fully synthetic plastic. The period between 1939 and 1960 saw a dramatic increase in production of polystyrene, poly (vinyl chloride), nylon, acrylics and polyethylene and the phasing out of semi-synthetics. If a plastic was manufactured before the 1940s, it could not have been shaped by injection moulding, recognized by a small imperfection due to the filling hole. 

Traces of metals are present in most polymers as a result of processing in stainless steel reaction vessels, being transported in metal containers and shaping in metal moulds or rolling between metal rollers. Many metal ions catalyze oxidation by accelerating decomposition of hydroperoxides at room temperature. Observation of plastics materials in museums suggests that copper is a highly effective catalyst for semi-synthetic materials such as cellulose nitrate and... 

In intermediate stages (the 19th century) polymers made by the modification of natural resins have appeared, the most prominent ones being the cellulose derivatives. Celluloid (obtained by nitration of cellulose) represents the first semi-synthetic polymer. It became useful after compotmding with a plasticizer (mamly camphor) to reduce its brittleness. Many cellulose derivatives are still currently in use (as plastomers, textiles or coatings) but the major development in the 20th century is definitely attributed to many families of synthetic polymers—the era of polymers. 

Back to Nature is the solution then Looking at a few numbers in Table 4.7 may prevent hasty judgments reading this questioa About 50 million t of plastics are produced in Europe each year from petroleum. The production of natural polymers is about 0.1% percent of this total virtually all of which is poly lactic acid. These numbers are not promising it would be lunacy to expect that polylactic acid (Fig. 4.30) or any other semi-synthetic and biodegradable polymer could replace petroleum-based plastics in any foreseeable future. 

The first plastic material to be made from non-plastic precursors was cellulose nitrate. This was obtained by Alexander Parkes (1813-1890) by treating cellulose fibres with nitric acid, and was first displayed at the Great International Exhibition in Ijondon in 1862 under the name Parkesine. Parkes moulded his new material into small decorative articles, as well as utilitarian objects such as knife handles. Parkesine was the first semi-synthetic plastic, so called because one of the starting materials was polymeric. The applications of cellulose nitrate were much extended by J. W. Hyatt (1837-1920) in the United States, who found that camphor was effective as a plasticiser, and the resulting mixture was known as celluloid. Another semi-synthetic plastic, cellulose acetate, was introduced around the end of the nineteenth century, and had the advantage over cellulose nitrate of being less flammable. 

A synthetic plastic material is a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products and daily living purpose. They are typically polymers of high molecular mass and monomers of plastics are synthetic organic compounds. 

The development of synthetic adhesives paralleled the development of plastics which began in 1845 with the nitration of cellulose to give cellulose nitrate, the first semi-synthetic plastic, whose ethereal solution was used by the shoe industry in 1910 for bonding leather. The products discovered in 1872 by Adolf Baeyer by polycondensation of phenol with formaldehyde were the basis for the first firlly synthetic plastic, Bakelite, which was obtained by Bakeland in 1909 by thermally curing reactive phenolic pre-condensates. But it was not until 1930 that phenol-formaldehydes and urea-formaldehyde condensates developed by C. Goldschmidt in 1896 (Kaurit) were used widely as adhesives. 

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