Man-made plastics

For the most part, plastics are man-made since very few plcistlcs are natural, i.e.- nature-made. Natural plastics include large molecular-wei t proteins and similar molecules. Man-made plastics can be classified as either thermoplastic or thermosetting. Each class derives its physical properties from the effects of application of heat, the former becoming "plastic" (that is- it becomes soft and tends to flow) while the latter becomes less "plastic" and tends to remain in a softened state. This difference in change of state derives from the actual nature of the chemical bonds in the polymer. Thermoplastic polymers generally consist of molecules composed of many monomeric units. A good example is that of polyethylene where the monomeric unit is -(CH2-CH2)-. The molecule is linear... 

Polymers such as proteins and nucleic acids w unicellular organism appeared on earth. Other ni cellulose and starch, have been utilized for food, thousands of years. Cellulose, polyisoprene, and s useful man-made plastics, fibers, and elastomers in t conversions were based primarily on empirical kno... 

Just in the USA during 2001, the man-made plastic fiber industry had over 90 plants with sales of 13 billion and employed about 45,000 people. Fabrication processes are diverse both in technology and equipment design. They have common steps that include preparation of reactants, polymerization, plastic recovery, plastic extrusion, and supporting operations. In some preparation operations, solvents are used to dissolve or dilute monomer and reactants. Solvents are also used to facilitate the transportation of the reaction mixture throughout the plant, to improve heat dissipation during the reaction, and to promote uniform mixing. Solvent selection is optimized to increase monomer... 

The first man-made plastic was nitrocellulose, made in 1862 by nitrating the natural polymer, cellulose. Nitrocellulose, when mixed with a plasticizer such as camphor to make it more workable, was originally used as a replacement for ivory in billiard balls and piano keys and to make Celluloid collars. This material, from which the first movie film was made, is notoriously flammable. 

It should be remembered that most museum objects have been used or displayed before they are collected. They have an unknown past, usually, which contributes greatly to the rate and type of deterioration. Instability of the earliest plastics, cellulose nitrate and acetate is expected due to their poorly stabilised formulations and because they are the oldest man-made plastics in museums. However, PVC was first developed in 1926 and is still in use, so its deterioration is rather unexpected. 

Figure 16.1. World production of man-made plastics, excluding rubbers and fibers, is expected to grow from 30 thousand tons in 1900 to 151 million tons in 2000, i.e., by...

Cellulose nitrate is derived from cellulose, a natural polymer. The first truly man-made plastic came 41 years later (in 1909) when Dr. Leo Hendrick Baekeland developed phenol-formaldehyde plastics (phenolics), the source of such diverse materials as electric iron and cookware handles, grinding wheels, and electrical plugs. Other polymers — cellulose acetate (toothbrushes, combs, cutlery handles, eyeglass frames) urea-formaldehyde (buttons, electrical accessories) poly(viryl ehloride) (flooring, upholstery, wire and cable insulation, shower curtains) and nylon (toothbrush bristles, stockings, surgical sutures) — followed in the 1920s. 

The first man-made plastic, a form of cellulose nitrate, was prepared in 1838 by A. Parker and shown at the Great International Exhibition in London in 1862. It was intended to be a replacement for natural materials such as ivory and was called parkesine. in 1840, Goodyear and Hancock developed the vulcanization procedure that eliminated tackiness and added elasticity to natural rubber. The change in the properties of the natural rubber was obtained by the addition of sulfur powder that produced additional chemical bonds in the bulk of the rubber. 

Landmarks of the Plastics Industry, Imperial Chemical Industries Ltd, Plastics Division, Welwyn, 1962. An anonymously authored volume published to mark the centenary of Alexander Parke s invention of the world s first man-made plastic. A very interesting account of the subject to the year of publication. Well illustrated and containing references to many sources for the history of the subject. 

One salient property of PHAs is their biodegradability. Until the introduction of man-made plastics, manufactured goods using materials derived from plants and animals were biodegradable and completely recyclable in the environment. Although plastics have dramatically improved human life, the durability of discarded plastic wares in the environment has created a serious waste-management problem. Use of the biodegradable PHAs as a substitute for the petroleum-based plastics can help preserve the quality of life as well as the natural environment, if PHAs can be produced economically. 

Phenol-formaldehyde (PF) resins were the first man-made plastics to be used, being first exploited commercially in 1910. Early applications were in the electrical industry where much of the development and manufacture was accomplished. 

Most non-specialists do not believe that man-made plastics ever biodegrade in the environment. Farmers who are by nature sceptical of new technology but... 

---