Last month Science had a special issue on "Working with Waste" with a general theme of "More Treasure Than Trash": "Trash is often treasure--a feedstock that can't be overlooked as an expanding world population tries to use resources more efficiently and reduce the strain that our consumption places on natural systems."
Articles in the special issue discuss many technologies for converting specific kinds of wastes into treasure. Let’s consider just one. "Recycling of the #5 Polymer" deals with recycling of a specific kind of plastic: "Polypropylene (PP) is a widely used plastic with consumer applications ranging from food packaging to automotive parts, including car battery casings. To differentiate it from other recyclable plastics, it is designated as #5. Here, the factors contributing to PP recycling rates are briefly reviewed. Considerations include collection and separation efficiency, processing chemistry, and market dynamics for the products derived from recyclates." The article has much about technology, though is not strictly limited to it. Let’s begin with technology.
An unsubdivided Relative Index entry "Polypropylene" leads to 668.4234 Polyolefins, where "polypropylenes" are listed in the including note. An example of a work classed in 668.4234 is Handbook of Polypropylene and Polypropylene Composites. The work has one chapter on recycling, but covers also many other topics in plastics engineering of polypropylene.
What about a work limited to recycling technology of polypropylene? Browsing the Relative Index for "recycling" yields:
Recycling technology 628.4458
Class here recycling technology
For a specific conversion technology, see the technology, e.g., converting garbage into fertilizer 668.6375
In the upward hierarchy of 628.4458 is 628.4 Waste technology, public toilets, street cleaning. Among the notes in that entry are a standard-subdivisions-are-added note and a scatter see-reference note:
Standard subdivisions are added for waste technology, public toilets, street cleaning together; for waste technology alone
For control and utilization of wastes in a specific technology, see the technology, plus notation T1--0286 from Table 1, e.g., waste technology in fuel processing 662.60286
Browsing the Relative Index for "Waste technology" yields many entries, among them:
Waste technology T1--0286
Waste technology 628.4
. . .
Waste technology--plastics 668.4192
If we consider adding T1--0286 Green technology (Environmental technology) to the main number for plastics technology, 668.4 Plastics, we find the bracketed number: 668[.4028] Auxiliary techniques and procedures; apparatus, equipment, materials with a do-not-use note: "Do not use; class in 668.41."
At 668.41 Techniques, procedures, apparatus, equipment, materials is the class-elsewhere note: "Class application to specific kinds of plastics in 668.42-668.45." That class-elsewhere note has hierarchical force; consequently, works on a waste technology such as recycling technology with respect to a specific kind of plastic are classed with the kind of plastic in 668.42-668.45 Specific kinds of plastics, not in 668.4192 Waste technology. Hence a work limited to recycling technology of polypropylene would be classed in 668.4234 Polyolefins. Since polypropylene is in standing room there, no standard subdivision could be added.
General works on recycling technology of plastics are classed in 668.4192 Waste technology. Examples are Introduction to Plastics Recycling and Recycling of Plastic Materials.
What about broader works that include social aspects of recycling? Browsing the Relative Index again for "recycling" yields:
Recycling waste 363.7282
see also Waste control
Waste control 363.728
Unless other instructions are given, class a subject with aspects in two or more subdivisions of 363.728 in the number coming last, e.g., recycling scrap metal 363.7288 (not 363.7282)
Given the preference order, recycling plastics is classed in 363.7288 Specific kinds of wastes (plastics are not mentioned there, but the number has no subdivisions). Examples of works about recycling plastics classed in 363.7288 are Plastics Recycling Kit and Plastics Recycling: Cradle to Grave.
It should come as no surprise that works on recycling specific materials are classed according to the rule of application: recycling applied to plastics classed with plastics, recycling applied to a specific kind of plastic classed with the kind of plastic, recycling of specific kinds of wastes classed with specific kinds of wastes. (See previous discussion of rule of application.) Nevertheless, it is still necessary to check the Relative Index and notes to see exactly what DDC numbers should be used.