Chemical properties of plastics

While orientation gives a broad improvement in physical and chemical properties of plastics, i.e. improvements in clarity, tensile strength, inertness and reduced permeation to gases (oxygen, carbon dioxide), moisture, etc., these properties are lost once deorientation occurs. 

The conservation profession use the same techniques for identification as the plastics industry, although the purpose of examination may differ. In addition to confirming that the polymer type is that expected from the description, function and age of a plastic, industry is ako concerned that the physical and chemical properties of plastics match the required performance or quahty. Industrial analysis is usually concerned with quantifying components of plastics such as additives, while conservation professionak are more concerned with quahtative examination. 

PHYSICAL AND CHEMICAL PROPERTIES OF PLASTICS WITH RESPECT TO THEIR APPLICATIONS. 

Unlike metals and other inorganics, plastics are extremely sensitive to changes in temperature. The mechanical, electrical, or chemical properties of plastics cannot be considered without knowing the temperature at which the values are obtained. The thermal properties of a polymer typically determine its low- and high-temperature applications, impact properties, and processing characteristics. Generally, temperature limitations of PE range between -180 and +90 C. HDPE has superior heat resistant characteristics (up to 900 °C). 

An extensive new Section 10 is devoted to polymers, rubbers, fats, oils, and waxes. A discussion of polymers and rubbers is followed by the formulas and key properties of plastic materials. Eor each member and type of the plastic families there is a tabulation of their physical, electrical, mechanical, and thermal properties and characteristics. A similar treatment is accorded the various types of rubber materials. Chemical resistance and gas permeability constants are also given for rubbers and plastics. The section concludes with various constants of fats, oils, and waxes. 

Steps 3 and 4, however, can be described as chemical plasticization since the rate at which these processes occur depends on the chemical properties of molecular polarity, molecular volume, and molecular weight. An overall mechanism of plasticizer action must give adequate explanations for this as weU as the physical plasticization steps. 

The use of vitamins in humans consumes ca 40% of vitamins made worldwide. The majority of the vitamins, particularly in countries outside the United States, are used in animal husbandry. It is well estabUshed (21) that vitamins are critical to animal productivity, especially under confined, rapid growth conditions. Newer information (22) has shown that vitamin E added to catde feed has the additional effect of significantly prolonging beef shelf life in stores. Additional appHcations of vitamins exist. A small but growing market segment involves cosmetics (qv) (23). The use of the chemical properties of the vitamins, particularly as antioxidants (qv) in foods and, more recently, in plastics (vitamin E (24)), has emerged as a growing trend. 

Functional polyethylene waxes provide both the physical properties obtained by the high molecular weight polyethylene wax and the chemical properties of an oxidised product, or one derived from a fatty alcohol or acid. The functional groups improve adhesion to polar substrates, compatibHity with polar materials, and dispersibHity into water. Uses include additives for inks and coatings, pigment dispersions, plastics, cosmetics, toners, and adhesives. 

Zinc dust is used in the sherardizing process where work pieces are tumbled with zinc dust in rotating steel dmms which are heated electrically or by gas to 370—420°C (149). The steel parts are uniformly coated with zinc. In the chemical and metallurgical industries, zinc dust is used as a reducing agent, in the manufacture of hydrosulfite compounds for the textile and paper industries, and to enhance the physical properties of plastics and lubricants (2). 

Coloiants can and do have a measuiable effect on myriad physical and chemical properties of final plastic products. Often, this is ovedooked both by... 

Random copolymers of vinyl chloride and other monomers are important commercially. Most of these materials are produced by suspension or emulsion polymerization using free-radical initiators. Important producers for vinyl chloride—vinyUdene chloride copolymers include Borden, Inc. and Dow. These copolymers are used in specialized coatings appHcations because of their enhanced solubiUty and as extender resins in plastisols where rapid fusion is required (72). Another important class of materials are the vinyl chloride—vinyl acetate copolymers. Principal producers include Borden Chemicals Plastics, B. F. Goodrich Chemical, and Union Carbide. The copolymerization of vinyl chloride with vinyl acetate yields a material with improved processabihty compared with vinyl chloride homopolymer. However, the physical and chemical properties of the copolymers are different from those of the homopolymer PVC. Generally, as the vinyl acetate content increases, the resin solubiUty in ketone and ester solvents and its susceptibiUty to chemical attack increase, the resin viscosity and heat distortion temperature decrease, and the tensile strength and flexibiUty increase slightly. 

It is essential to appreciate that such plasticisers will considerably modify the chemical properties of the plastics material since the plasticiser may be readily extracted by certain chemicals and chemically attacked by others whilst the base polymer may be unaffected. 

If it is assumed that the physical and chemical properties of the material are the same before and after rupture (so that the concentration of material undergoing deformation is related to the rate constant, K, by x = Kt, where t is time) then it can be shown, as in the following equation, that for plastics ... 

Plastics have found numerous uses in specialty areas such as hypersonic atmospheric flight and chemical propulsion exhaust systems. The particular plastic employed in these applications is based on the inherent properties of the plastics or the ability to combine it with another component material to obtain a balance of properties uncommon to either component. Some of the compositions and important properties of plastics are given in Tables 2-9 and 2-10 that have been developed over the years for use in flight vehicles and propulsion systems that are dependent upon chemical, mechanical, electrical, nuclear, and solar means for accelerating the working fluid by high temperatures. 

Most plastic materials are used because they have desirable mechanical properties at an economical cost. For this reason, the mechanical properties may be considered the most important of all the physical and chemical properties of high polymers for most applications. Thus everyone working with such materials needs at least an elementary knowledge of their mechanical behavior and how this behavior can be modified by the numerous structural factors that can be varied in polymers. High polymers, a few of which have their chemical structure shown in Appendix I, have the widest variety and range of mechanical properties of all known materials. Polymers vary from liquids and soft rubbers to very hard and rigid solids. 

Over the years efforts have been made to understand the various parameters to consider in the choice of plastics for packaging of drug products. Drug-plastic considerations have been divided into live separate categories permeation, leaching, sorption, chemical reaction, and alteration in the physical properties of plastics or products [89]. 

---