Glossary - C

Co-Collection:
The act of picking up post-consumer plastic (or secondary) materials or compostable materials simultaneously with garbage. (The Recycler's Lexicon: A Glossary of Contemporary Terms and Acronyms, Resource Recycling Inc., 1995).

Co-Combustion:
The simultaneous combustion of two or more fuel types to provide useful energy. Generally, a primary fuel is combusted with one or more supplemental fuels. Examples would include the co-combustion of wood with coal, or processed combustible materials derived from residential, commercial and industrial sources, which could include plastics-enhanced pelletized fuel products, with coal as the primary fuel in industrial or utility boilers. (Kenneth Smith, Vice President, wTe Corporation, Bedford, Mass., 1996).

Coextrusion:
Involves a process where parts are blow-molded with walls containing two or more layers of different material. Coextrusion offers wide latitude for material selection and also allows the use of recycled materials. A material with good barrier properties, for example, can be used for the inside and outside surfaces of a blow molded bottle, while recycled material can be used for the internal layer. (Modern Plastics Encyclopedia 1995).

Cogeneration:
The simultaneous production of power and another form of useful thermal energy from a single fuel-consuming process. The most common cogeneration systems being constructed today utilize combustion or co-combustion processes to produce electricity via a turbine as the principal product and steam and/or hot water as by-products. The electricity generally is sold to a utility or used for adjacent industrial processes and the steam and hot water generally are exported to adjacent companies for industrial process uses and for space heating. When combusting fuels in typical boilers, cogeneration is significantly more energy efficient than the generation of electricity alone. Approximately 75 percent of the energy value in the fuel can be extracted in a cogeneration facility compared to approximately 35 percent when electricity is produced solely. (Singer, Joseph G., "Combustion Fossil Power," Fourth Edition, Combustion Engineering, Inc., Windsor, Conn., 1991; Lund, Herbert F., "The McGraw-Hill Recycling Handbook," McGraw-Hill, Inc., New York, 1993).

Combustion:
A chemical process in which oxygen rapidly combines with the fuel and converts the fuel into gases, primarily water (H20) and carbon dioxide (C02), and residues. The combustion process produces significant thermal energy (heat) and light, and generally is self sustaining-that is no external source of heat is required to maintain combustion of fuel. In modern, state-of-the-art waste-to-energy facilities, and in other modern energy production facilities, the combustion process is carefully controlled to extract maximum energy value from the fuel source and to reduce the generation of potentially harmful substances significantly well below stringent regulatory levels. Industrial and post-consumer plastic plastics that cannot be economically recycled are excellent fuel sources that combust very well in such facilities. The energy value of these plastics is comparable to oil and can be more than 50 percent greater than coal. (Tchobanoglous, George, Hilary Theisen and Rolf Eliassen, "Solid Wastes, Engineering Principles and Management Issues," McGraw-Hill, Inc., New York, 1977; Lund, Herbert F., "The McGraw-Hill Recycling Handbook," McGraw-Hill, Inc., New York, 1993).

Compatibilizers:
Additives that enable two or more materials to exist in close and permanent association indefinitely. They may be used to blend virgin and post-consumer plastic resins or different types of resins to maintain the quality of the products. (Dr. Ronald Liesemer, Vice President of Technology, APC, Washington, D.C., 1996).

Compounding:
The incorporation of additional ingredients needed for processing in order to have optimal properties. These ingredients may include Additives to improve a polymer's physical properties, stability or processability. Compounding is usually required for recycled materials for the following reasons:

Cradle-To-Grave Analysis:
A methodology that quantifies energy consumption and environmental emissions at each stage of a product's life cycle, beginning at the point of raw material extraction and proceeding through processing, manufacturing, consumer use, and final recycling, reuse or disposal. (Resource and Environmental Profile Analysis of High Density Polyethylene and Bleached Paperboard Gable Milk Containers, Franklin Associates, Ltd., February 1991)

Curbside Collection:
A collection process where consumers place designated recyclables at the roadside or curb, usually in a special container or bag, for collection separate from non-recyclable material such as garbage. (The Blueprint for Plastics Recycling, The Council for Solid Waste Solutions, 1991).

Capillary rheometry
Actual capillary rheometry gives information about flow properties of polymer melts. Results are given as a viscosity function, that is viscosity as a function of shear rate or shear stress. Compared to MFR measurement the shear rate range is much wider and the rates in processing applications are reached. With many products, however, flow instabilities (melt fracture) at high rates limit the useful range. A capillary rheometer consists of a barrel, piston and die. The sample is put into the barrel, heated and pushed by the piston through the die. The piston is driven by hydraulic pressure which allows more flexible choice of rates compared to MFR measurements. In addition, longer dies can be used to avoid the errors coming from the entrance and exit pressure losses.

Carbon Black
Black pigment used in concentrations of about 2.5% in order to ensure excellent UV-resistance. In higher concentrations, 30-40%, Carbon Black is used to obtain semiconductive properties used in Cable applications. The type of CB and the particle size is very important for the end-product properties.

Catalyst
A substance which aids or promotes a chemical reaction without forming part of the final product. It enables the reaction to take place faster or at a lower temperature, and remains unchanged at the end of the reaction.

Cellular Rubber
Low-density rubber products containing a cellular structure. The cells may either be open and interconnecting or closed and not interconnecting; a generic term for materials containing many cells (either open, closed or both) dispersed throughout the mass.

Chain polymerization
A chain reaction in which the growth of a polymer chain proceeds exclusively by reaction(s) between monomer(s) and reactive site(s) on the polymer chain such that the reactive site(s) are regenerated on the same polymer chain by the end of each growth step. A chain polymerization consists of initiation and propagation reactions, and may also include termination and chain transfer reactions. The adjective "chain" in "chain polymerization" denotes "chain reaction". In a chain polymerization, the average degree of polymerization remains constant with monomer conversion (e.g., in steady-state, radical polymerizations) or may increase with monomer conversion (e.g., in the formation of living polymers).

Chain transfer
A chemical reaction, usually occurring during chain polymerizations, in which the activity of the kinetic-chain carrier is transferred from the growing macromolecule or oligomer molecule to another molecule or another part of the same molecule. Chain transfer to another part of the same molecule is often termed backbiting

Closed Cell
An expanded structure consisting of a multitude of individual, nonconnecting, gas-tight cells.

Coking
A thermal cracking process to break up large molecules into smaller ones with the generation of quantities of petroleum coke.

Comonomer
Comonomer is a monomer which is used to modify the polymer properties, e.g. to reduce the density of the polymer. Different types of copolymerisation processes are possible, leading to different structures and properties of the produced copolymer. In polyethylene, higher a-olefins like butene, hexene or octene are used as comonomers, in polypropylene, mostly ethylene and sometimes butene.

Compression Set
The residual decrease in thickness of a test specimen measured 30 minutes or 24 hours after removal from a suitable loading device in which the specimen had been subjected for a definite time to compressive deformation under specified conditions of load application and temperature.

Conductive Rubber
A rubber with a much lower electrical resistivity than normal. This is achieved by high loadings(e.g. 50phr) of one of the more highly conducting grades of carbon black, e.g. super conduction furnace or acetylene black. A typical resistivity is about 1015¥Øcm compared with about 1015¥Øcm in a normal rubber.

Copolymer
Two monomers polymerized together to form a polymer.

Cracking
The process of breaking down large molecules of oil into smaller ones. When this process is achieved by the application of heat only, it is known as thermal cracking. If a catalyst is used as well it is known as catalytic cracking. It is known as hydrocracking if the catalytic process is conducted in a hydrogen atmosphere. Cracking causes molecular decomposition and recombination to produce a range of more useful base chemicals.

Creep tests

1. Solid-state creep tests are used to measure long term behaviour of mechanically loaded material. Creep is time-dependent strain resulting from constant loading. Tensile loading is most common here but flexural loading can be used as well, testing time is typically 1000 hrs. Several loading levels are used to get an overview of creep behaviour of the material.

2. Melt creep tests are a type of rheological measurement for the determination of the creep compliance of a polymer melt; they are carried out in the region of linear viscoelasticity.

Crosslink
A constitutional unit connecting two parts of a macromolecule that were earlier separate molecules. Note: a network may be thought to consist of many "primary chains" that are interconnected by a number of crosslinks. In the vast majority of cases, the crosslink is a covalent bond but the term is also used to describe sites of weaker chemical interactions, portions of crystallites, and even physical entanglements.

Crystallinity
Also designated ¡°degree of crystallinity¡±, it gives the relative fraction of a solid polymer having crystalline regularity. The crystallinity can be determined with various measuring techniques like DSC, density measurement or WAXS, which has the additional advantage that the relative amounts of the different crystal modifications can be determined as well. All crystallinity values are relative and the applied reference values should be quoted.