Classifying plastic

The Hildebrand Solubility Parameter. This parameter, 4 can be estimated (10) based on data for a set of additive constants, E, for the more common groups ia organic molecules to account for the observed magnitude of the solubiHty parameter d = EE/V where Erepresents molar volume. SolubiHty parameters can be used to classify plasticizers of a given family ia terms of their compatibihty with PVC, but they are of limited use for comparing plasticizers of differeat families, eg, phthalates with adipates. 

The distinction is by no means as clear-cut as once it was but still it is convenient to classify plastics either as thermoplastic or thermosetting — terms defined in ISO 472 as follows ... 

APME (Association of Plastics Manufacturers Europe, today Plastics Europe), with member companies given in [29] has classified plastic waste in a series of categories and monitors their origin and recycling, according to their field of application. Several early publications are still of interest, to compare past and present. A recent book on plastics recycling is Scheirs [38]. A few sites of interest are also ... 

The process industry has yet to adopt a rigid methodology for classifying plastics and rubbers. Consequently, it is imperative for the user to specify critical parts by manufacturer s designation number and purchase them only from approved suppliers. See Figure 7-4. 

Basically, scratch hardness is a measure of the resistance the test sample has to being scratched by other materials. The most common way of qualifying this property is by means of the Mohs scale. On this scale various materials are classified from 1 to 10. The materials used, as shown in Figure 3.46, range from talc (1) to diamond (10). Each material on the scale can scratch the materials that have a lower Mohs number however, the Mohs scale is not of much value for classifying plastic materials, because most common plastics fall in the 2-3 Mohs range. However, the basic technique of scratch hardness may be used to establish the relative merits of different plastic materials fi om their ability to scratch one another. 

One method of classifying plastics is by their response to heat. Thermoplasts, also known as thermoplastic polymers, soften and liquefy on heating and harden again when cooled. The process is reversible and can be repeated. On heating, the weak secondary bonds between polymer chains are broken, which facilitates relative movement between the chains. If the molten polymer is further heated until the primary covalent bonds also break, degradation of the thermoplast follows. Thermoplastic polymers are linear or exhibit branching with flexible chains and include polyethylene, polystyrene and polypropylene (Figure 4.10). 

Underwriter s Laboratories (UL) during 2001 developed a standard for pallets. The new UL 2335 was created to classify plastic pallets to meet requirements of the recently revised National Fire Protection Assoc, standard NFPA 13. That change allows plastic pallets to be treated like wood pallets if test data indicate that the burning characteristics of the plastic pallets are equal or better than wood (UL telephone 847-664— 1508). 

Polymers are the backbone of what we call plastics. They are chemical compounds that have very large, molecular, chainlike structures. Plastics are often classified into two categories thermoplastics and thermosets. When heated to certain temperatures, the thermoplastics can be molded and remolded. For example, when you recycle Styrofoam dishes, they can be heated and reshaped into cups or bowls or other shapes. By contrast, thermosets can not be remolded into other shapes by heating. The application of heat to thermosets does not soften the material for remolding instead, the material will simply break down. There are many odier ways of classifying plastics for instamce, they may be classified on the basis of their chemical composition, or molecular structure, or the way molecules aue airranged, or their densities. For example, based... 

Plastic pellets inadvertently lost from plastic production and warehouse facilities pose a threat to fish and wildlife. Therefore, the U.S. EPA (Environmental Protection Agency) has classified plastic pellets as significant materials. . The finding of even one pellet in a storm water run-off without a permit is now subject to federal regulatory action with the potential for substantial fines and penalties. As a result, the plastics industry has launched Operation Clean Sweep, an initiative to prevent the accidental release of pellets into the environment. Specific recommendations for handling polyolefins to prevent resin loss into the environment have been developed by the Society for the Plastics Industry (38). 

Figure 6-62, Classifying plastics by range of continuous or rather long-time heat exposure.

In discussions about plasticizers, there are many different classification schemes and proposals. A high-level approach is to classify plasticizers based on their molecular weight. 

The principal plastic piping material specifications are issued by the American Society for Testing and Materials (ASTM). Earlier ASTM standards classified plastic materials by type, grade, and class in accordance with three important properties. ASTM used a code that consisted of four digits and a product letter prefix indicating the resin. The four digits stood for ... 

The selection of a plasticizer type is primarily determined by the performance requirements of the finished product or by special needs that may be required during processing, with the overall basic requirement to meet the needed cost targets. Of the approximate 100 commercially available plasticizers, some form of classification system is needed to help in this selection. Unfortunately, a single classification system is not sufficient in to predict the performance/cost benefits that a plasticizer can bring to the final product. Thus it is necessary to classify plasticizers by both their performance and chemical classifications. 

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