MIL-HDBK-17-3F Volume 3,Chapter 11-Environmental Management CHAPTER 11 ENVIRONMENTAL MANAGEMENT 11.1 INTRODUCTION The objective of this chapter is to provide information for the environmental management of compos- ite materials.Requirements for recycling of all classes of materials are increasing on a global basis and are not likely to be reduced.Many industries have found that taking a proactive approach to environ- mental management of their products can help to head off the enactment of complex regulations,which can be costly and less effective than market based solutions.Reuse and recycling of automobiles and components,for example,is performed by an efficient,nationwide network of used parts shops,automo- bile shredders,and resellers that extracts the maximum value out of recycled vehicles.This network is directed and motivated by interest in the value of the components and materials in end-of-use vehicles, rather than by an innate desire to comply with regulations. The creation of a similar network for composite materials is an ongoing process at this time.It in- volves the development of size reduction and matrix digestion technologies,the organization of a collec- tion system,identification of uses for recycled fibers and matrices,and perhaps most importantly,the education of the composites production and user community about recycling needs and opportunities. Efforts to recycle composite materials are in an early stage of development compared with other as- pects of composite's usage,and so much of the information in this chapter describes immature technolo- gies.They are nevertheless included to provide an overview of the state-of-the-art and a resource for those interested in applying or developing composite reduction,reuse,and recycling technology. 11.1.1 Scope The scope of this chapter is to provide guidance for the environmental management of composite materials as it pertains to the"reduce,reuse,and recycle"paradigm for controlling environmental impact. It does not address issues such as styrene emissions,handling of toxic materials,or disposal require- ments for hazardous waste.Some aspects of composite manufacturing and use,such as lightweighting (defined later),prepreg usage,and the use of hybrid composites,are treated as they pertain to environ- mental management.These aspects will be discussed in this chapter only in the context of recycling,with other parts of the handbook referenced for broader discussions. 11.1.2 Glossary of recycling terms Broad Categories--General classifications of recyclable material,such as glass,plastic,metal,or paper. Broker--refers to an individual or group of individuals who act as an agent or intermediary between the sellers and buyers of recyclable materials. Collector--refers to public or private haulers that collect nonhazardous waste and recyclable materials from residential,commercial,institutional,and industrial sources. Comingled recyclables--refers to a mixture of several recyclable materials in one container. Disposal Facilities--refers to repositories for solid waste,including landfills and combustors,intended for permanent containment or destruction of waste materials. Drop-Off Center--refers to a method of collection whereby recyclable or compostable materials are taken by individuals to a collection site and placed in designated containers. End-of-Service--Components that have been used until failure or obsolescence. 11-1
MIL-HDBK-17-3F Volume 3, Chapter 11 - Environmental Management 11-1 CHAPTER 11 ENVIRONMENTAL MANAGEMENT 11.1 INTRODUCTION The objective of this chapter is to provide information for the environmental management of composite materials. Requirements for recycling of all classes of materials are increasing on a global basis and are not likely to be reduced. Many industries have found that taking a proactive approach to environmental management of their products can help to head off the enactment of complex regulations, which can be costly and less effective than market based solutions. Reuse and recycling of automobiles and components, for example, is performed by an efficient, nationwide network of used parts shops, automobile shredders, and resellers that extracts the maximum value out of recycled vehicles. This network is directed and motivated by interest in the value of the components and materials in end-of-use vehicles, rather than by an innate desire to comply with regulations. The creation of a similar network for composite materials is an ongoing process at this time. It involves the development of size reduction and matrix digestion technologies, the organization of a collection system, identification of uses for recycled fibers and matrices, and perhaps most importantly, the education of the composites production and user community about recycling needs and opportunities. Efforts to recycle composite materials are in an early stage of development compared with other aspects of composite’s usage, and so much of the information in this chapter describes immature technologies. They are nevertheless included to provide an overview of the state-of-the-art and a resource for those interested in applying or developing composite reduction, reuse, and recycling technology. 11.1.1 Scope The scope of this chapter is to provide guidance for the environmental management of composite materials as it pertains to the "reduce, reuse, and recycle" paradigm for controlling environmental impact. It does not address issues such as styrene emissions, handling of toxic materials, or disposal requirements for hazardous waste. Some aspects of composite manufacturing and use, such as lightweighting (defined later), prepreg usage, and the use of hybrid composites, are treated as they pertain to environmental management. These aspects will be discussed in this chapter only in the context of recycling, with other parts of the handbook referenced for broader discussions. 11.1.2 Glossary of recycling terms Broad Categories -- General classifications of recyclable material, such as glass, plastic, metal, or paper. Broker -- refers to an individual or group of individuals who act as an agent or intermediary between the sellers and buyers of recyclable materials. Collector -- refers to public or private haulers that collect nonhazardous waste and recyclable materials from residential, commercial, institutional, and industrial sources. Comingled recyclables -- refers to a mixture of several recyclable materials in one container. Disposal Facilities -- refers to repositories for solid waste, including landfills and combustors, intended for permanent containment or destruction of waste materials. Drop-Off Center -- refers to a method of collection whereby recyclable or compostable materials are taken by individuals to a collection site and placed in designated containers. End-of-Service -- Components that have been used until failure or obsolescence
MIL-HDBK-17-3F Volume 3,Chapter 11-Environmental Management End User--Facilities that purchase or secure recovered materials for the purpose of recycling.Examples include recycling plants and composting facilities.Excludes waste disposal facilities. Exports--Waste and recyclables that are transported outside the state or locality where they originated. Generators--Producers of solid waste. Imports--Solid waste and recyclables that have been transported to a state or locality for processing or final disposition,but that did not originate in that state or locality. Incinerator--A furnace for burning solid waste under controlled conditions Industrial Process Waste--Residues produced during manufacturing operations. Industrial Waste--Nonhazardous wastes discarded at industrial sites from packaging and administrative sources.Examples include corrugated boxes,plastic film,wood pallets,and office paper.Excludes in- dustrial process wastes from manufacturing operations. Lightweighting--Reduction of system weight by using lighter weight materials,careful design,avoidance of overdesign,and other engineering changes. Large Generator--Commercial businesses,institutions,or industries that generate sufficient quantities of solid waste and recyclables to warrant self-management of these materials. Material Recovery Facility(MRF)--A facility where recyclables are sorted into specific categories and processed or transported to processors for remanufacturing. Mixed Plastic--Recovered plastic that is not sorted into specific categories(HDPE,LDPE....) Nonhazardous Industrial Process Waste--Waste that is neither municipal solid waste nor considered a hazardous waste under Subtitle C of the Resource Recovery Act. Other Plastic--Plastic from appliances,furniture,trash bags,cups,eating utensils,sporting and recrea- tional equipment,and other nonpackaging plastic products. Other Solid Waste--Nonhazardous solid wastes,other than municipal solid waste,covered under Subti- tle D of the Resource Conservation and Recovery Act,such as municipal sludge,industrial nonhazardous waste,construction and demolition waste,agricultural waste,and mining waste. Plastics Handler--Companies that prepare recyclable plastics by sorting,baling,shredding,granulating. and/or storing plastics until a sufficient quantity is on hand. Plastics Reclaimer--Companies that further process plastics after the handling stage by performing at least one of the following functions:washing/cleaning,pelletizing,or producing a new product. Postconsumer Materials/Waste--Recovered materials that have been used as a consumer item and are diverted from municipal solid waste for the purpose of collection,recycling,and disposition.Excludes materials from industrial processes that have not reached the consumer,such as glass broken in the manufacturing process. Preconsumer Materials/Waste--Materials generated in manufacturing processes,such as manufacturing scrap and trimmings/cuttings.Also includes obsolete inventories. Primary recycling-Recycling clean materials and products to produce products that are similar to,or the same as,the original product. 11-2
MIL-HDBK-17-3F Volume 3, Chapter 11 - Environmental Management 11-2 End User -- Facilities that purchase or secure recovered materials for the purpose of recycling. Examples include recycling plants and composting facilities. Excludes waste disposal facilities. Exports -- Waste and recyclables that are transported outside the state or locality where they originated. Generators -- Producers of solid waste. Imports -- Solid waste and recyclables that have been transported to a state or locality for processing or final disposition, but that did not originate in that state or locality. Incinerator -- A furnace for burning solid waste under controlled conditions. Industrial Process Waste -- Residues produced during manufacturing operations. Industrial Waste -- Nonhazardous wastes discarded at industrial sites from packaging and administrative sources. Examples include corrugated boxes, plastic film, wood pallets, and office paper. Excludes industrial process wastes from manufacturing operations. Lightweighting -- Reduction of system weight by using lighter weight materials, careful design, avoidance of overdesign, and other engineering changes. Large Generator -- Commercial businesses, institutions, or industries that generate sufficient quantities of solid waste and recyclables to warrant self-management of these materials. Material Recovery Facility (MRF) -- A facility where recyclables are sorted into specific categories and processed or transported to processors for remanufacturing. Mixed Plastic -- Recovered plastic that is not sorted into specific categories (HDPE, LDPE....) Nonhazardous Industrial Process Waste -- Waste that is neither municipal solid waste nor considered a hazardous waste under Subtitle C of the Resource Recovery Act. Other Plastic -- Plastic from appliances, furniture, trash bags, cups, eating utensils, sporting and recreational equipment, and other nonpackaging plastic products. Other Solid Waste -- Nonhazardous solid wastes, other than municipal solid waste, covered under Subtitle D of the Resource Conservation and Recovery Act, such as municipal sludge, industrial nonhazardous waste, construction and demolition waste, agricultural waste, and mining waste. Plastics Handler -- Companies that prepare recyclable plastics by sorting, baling, shredding, granulating, and/or storing plastics until a sufficient quantity is on hand. Plastics Reclaimer -- Companies that further process plastics after the handling stage by performing at least one of the following functions: washing/cleaning, pelletizing, or producing a new product. Postconsumer Materials/Waste -- Recovered materials that have been used as a consumer item and are diverted from municipal solid waste for the purpose of collection, recycling, and disposition. Excludes materials from industrial processes that have not reached the consumer, such as glass broken in the manufacturing process. Preconsumer Materials/Waste -- Materials generated in manufacturing processes, such as manufacturing scrap and trimmings/cuttings. Also includes obsolete inventories. Primary recycling – Recycling clean materials and products to produce products that are similar to, or the same as, the original product
MIL-HDBK-17-3F Volume 3,Chapter 11-Environmental Management Processors--Intermediate operators that handle recyclable materials from collectors and generators for the purpose of preparing materials for recycling (material recovery facilities,scrap metal yards,paper dealers....)Processors act as intermediaries between collectors and end users of recovered materials. Quaternary Recycling-Waste-to-energy conversion by incineration. Recovery--The diversion of materials from the solid waste stream for the purpose of recycling.Excludes reuse and source reduction activities. Recyclables--Materials recovered from the solid waste stream and transported to a processor or end user for recycling. Recycling --The series of activities by which discarded materials are collected,sorted,processed,and converted into raw materials and used in the production of new products.Excludes the use of these ma- terials as a fuel substitute or for energy production. Recycling Plant--A facility where recovered materials are remanufactured into new products. Residues--The materials remaining after processing,incineration,composting,or recycling have been completed.Residues are usually disposed of in landfills. Reuse--The use,more than once,of a product or component of municipal solid waste in its original form. Secondary recycling-Recycling mixed materials or products to produce a product that is lower in quality than the original product. Source Reduction--The design,manufacture,purchase,or use of materials,such as products and pack- aging,to reduce the amount or toxicity of materials before they enter the solid waste management sys- tem.This may involve redesigning products or packaging;reusing products or packaging already manu- factured;and lengthening the life of products to postpone disposal.Also referred to as "waste preven- tion." Sortation--The process of sorting comingled recyclables into separate types of materials for the purpose of recycling. Tertiary Recycling--Recycling that is accomplished by completely breaking down a material to its chemi- cal constituents and restoring it to its original quality. Transfer Station--A facility where solid waste is transferred from collection vehicles to larger trucks or rail cars for longer distance transport. Waste Characterization Studies--The identification and measurement(by weight or volume)of specific categories of solid waste materials for the purpose of projecting landfill capacity,determining best man- agement practices,and developing cost-effective recycling programs. Waste Generation--The amount (weight or volume)of materials and products that enter the waste stream before recycling,composting,landfilling,or combustion takes place. Waste Stream--The total flow of solid waste from homes,businesses,institutions,and manufacturing plants that must be recycled,incinerated,or disposed of in landfills;or any segment thereof,such as the "residential waste stream"or the "recyclable waste stream." Waste-To-Energy Facility/Combustor--A facility where recovered municipal solid waste is converted into a usable form of energy,usually through combustion. 11-3
MIL-HDBK-17-3F Volume 3, Chapter 11 - Environmental Management 11-3 Processors -- Intermediate operators that handle recyclable materials from collectors and generators for the purpose of preparing materials for recycling (material recovery facilities, scrap metal yards, paper dealers....) Processors act as intermediaries between collectors and end users of recovered materials. Quaternary Recycling – Waste-to-energy conversion by incineration. Recovery -- The diversion of materials from the solid waste stream for the purpose of recycling. Excludes reuse and source reduction activities. Recyclables -- Materials recovered from the solid waste stream and transported to a processor or end user for recycling. Recycling -- The series of activities by which discarded materials are collected, sorted, processed, and converted into raw materials and used in the production of new products. Excludes the use of these materials as a fuel substitute or for energy production. Recycling Plant -- A facility where recovered materials are remanufactured into new products. Residues -- The materials remaining after processing, incineration, composting, or recycling have been completed. Residues are usually disposed of in landfills. Reuse -- The use, more than once, of a product or component of municipal solid waste in its original form. Secondary recycling – Recycling mixed materials or products to produce a product that is lower in quality than the original product. Source Reduction -- The design, manufacture, purchase, or use of materials, such as products and packaging, to reduce the amount or toxicity of materials before they enter the solid waste management system. This may involve redesigning products or packaging; reusing products or packaging already manufactured; and lengthening the life of products to postpone disposal. Also referred to as "waste prevention." Sortation -- The process of sorting comingled recyclables into separate types of materials for the purpose of recycling. Tertiary Recycling -- Recycling that is accomplished by completely breaking down a material to its chemical constituents and restoring it to its original quality. Transfer Station -- A facility where solid waste is transferred from collection vehicles to larger trucks or rail cars for longer distance transport. Waste Characterization Studies -- The identification and measurement (by weight or volume) of specific categories of solid waste materials for the purpose of projecting landfill capacity, determining best management practices, and developing cost-effective recycling programs. Waste Generation -- The amount (weight or volume) of materials and products that enter the waste stream before recycling, composting, landfilling, or combustion takes place. Waste Stream -- The total flow of solid waste from homes, businesses, institutions, and manufacturing plants that must be recycled, incinerated, or disposed of in landfills; or any segment thereof, such as the "residential waste stream" or the "recyclable waste stream." Waste-To-Energy Facility/Combustor -- A facility where recovered municipal solid waste is converted into a usable form of energy, usually through combustion
MIL-HDBK-17-3F Volume 3,Chapter 11-Environmental Management 11.2 RECYCLING INFRASTRUCTURE The development of a viable infrastructure for recycling composite materials should ideally be pur- sued as a coordinated effort by composite suppliers,fabricators,and end users.Such an infrastructure will benefit the entire composites industry by improving the efficiency of composite manufacturing,chang- ing the perception that composites are not recyclable and that metals are therefore preferable,and reduc- ing the environmental impact of composites use.This section outlines some of the requirements for recy- cling infrastructure development. 11.2.1 Recycling infrastructure development models The infrastructures for recycling many other materials have already been developed and can provide guidance for the establishment methods for composite materials recycling.Studying these examples can facilitate composites recycling development work and avoid costly mistakes that have been encountered in other industries. One important lesson learned is that while the technology for actually recycling a material is impor- tant,the logistical,educational,and economic issues are equally important.Advanced recycling tech- nologies cannot succeed unless they are integrated with consistent sources of consistent recyclate sources,stable markets for the recycled materials,an efficient collection and transportation system,and a work force that has been educated in the requirements for proper handling of recyclable materials. One of the most mature and efficient reuse/recycling infrastructures is in place for automobiles.A large,computer-integrated network of automobile recyclers procures end-of-service automobiles,re- moves fluids and toxic components such as batteries,catalogues reusable components,and either dis- mantles the vehicle or warehouses its parts in the vehicle.After all reusable components are removed. vehicles are shredded,ferrous metals are magnetically sorted,and lightweight"fluff"and other materials are separated.The result is that approximately 90%of the steel in automobiles is recycled,more than 12 million tons per year.Automotive manufacturers are increasingly paying attention to design for disassem- bly and recycling,and are giving consideration to the recyclability of the materials in their products. A user-subsidized recycling model that may be instructive is that developed for nickel cadmium (NiCd)batteries in response to concerns about groundwater contamination from the cadmium content. Because of the widely dispersed nature of old NiCd batteries,a network of used battery collection centers was created by placing pre-paid,pre-addressed mailers at electronics retail outlets.When the mailers are filled with batteries,they are given to the parcel delivery service and transported to a single recycling facil- ity for the entire North American continent.The recycler distills out the cadmium and processes the nickel content in an open hearth furnace along with other stainless steel waste.The high nickel content in- creases the value of the stainless steel recyclate and helps to pay for the process. In contrast,the vast majority of end-of-service composite materials and composite waste generated in manufacturing,are commonly thrown into landfills (References 11.2.1(a)-(b)).Although this adds only a small volume to the solid waste disposal problem,it returns no value.As regulations that mandate recy- cling of various products take effect,particularly in Europe,non-recyclable materials will be increasingly excluded from consideration.The desirable environmental influence that advanced composites can have, such as greater fuel efficiency from lightweighting,will be lost if recycling techniques are not implemented. 11.2.2 Infrastructure needs Although technologies exist for digestion of composite matrices and recovery of fibers with high strength retention(References 11.2.1(b)and 11.2.2(a)-(d)),these technologies have only been demon- strated on laboratory prototype or pilot scale.Additional efforts to optimize and scale up these processes to complete implementation are underway. A resource recovery network must be established,or "piggybacked"onto existing networks,to collect and channel post-consumer composites back to these material recovery facilities(MRFs).Because of the 11-4
MIL-HDBK-17-3F Volume 3, Chapter 11 - Environmental Management 11-4 11.2 RECYCLING INFRASTRUCTURE The development of a viable infrastructure for recycling composite materials should ideally be pursued as a coordinated effort by composite suppliers, fabricators, and end users. Such an infrastructure will benefit the entire composites industry by improving the efficiency of composite manufacturing, changing the perception that composites are not recyclable and that metals are therefore preferable, and reducing the environmental impact of composites use. This section outlines some of the requirements for recycling infrastructure development. 11.2.1 Recycling infrastructure development models The infrastructures for recycling many other materials have already been developed and can provide guidance for the establishment methods for composite materials recycling. Studying these examples can facilitate composites recycling development work and avoid costly mistakes that have been encountered in other industries. One important lesson learned is that while the technology for actually recycling a material is important, the logistical, educational, and economic issues are equally important. Advanced recycling technologies cannot succeed unless they are integrated with consistent sources of consistent recyclate sources, stable markets for the recycled materials, an efficient collection and transportation system, and a work force that has been educated in the requirements for proper handling of recyclable materials. One of the most mature and efficient reuse/recycling infrastructures is in place for automobiles. A large, computer-integrated network of automobile recyclers procures end-of-service automobiles, removes fluids and toxic components such as batteries, catalogues reusable components, and either dismantles the vehicle or warehouses its parts in the vehicle. After all reusable components are removed, vehicles are shredded, ferrous metals are magnetically sorted, and lightweight "fluff" and other materials are separated. The result is that approximately 90% of the steel in automobiles is recycled, more than 12 million tons per year. Automotive manufacturers are increasingly paying attention to design for disassembly and recycling, and are giving consideration to the recyclability of the materials in their products. A user-subsidized recycling model that may be instructive is that developed for nickel cadmium (NiCd) batteries in response to concerns about groundwater contamination from the cadmium content. Because of the widely dispersed nature of old NiCd batteries, a network of used battery collection centers was created by placing pre-paid, pre-addressed mailers at electronics retail outlets. When the mailers are filled with batteries, they are given to the parcel delivery service and transported to a single recycling facility for the entire North American continent. The recycler distills out the cadmium and processes the nickel content in an open hearth furnace along with other stainless steel waste. The high nickel content increases the value of the stainless steel recyclate and helps to pay for the process. In contrast, the vast majority of end-of-service composite materials and composite waste generated in manufacturing, are commonly thrown into landfills (References 11.2.1(a) - (b)). Although this adds only a small volume to the solid waste disposal problem, it returns no value. As regulations that mandate recycling of various products take effect, particularly in Europe, non-recyclable materials will be increasingly excluded from consideration. The desirable environmental influence that advanced composites can have, such as greater fuel efficiency from lightweighting, will be lost if recycling techniques are not implemented. 11.2.2 Infrastructure needs Although technologies exist for digestion of composite matrices and recovery of fibers with high strength retention (References 11.2.1(b) and 11.2.2(a) - (d)), these technologies have only been demonstrated on laboratory prototype or pilot scale. Additional efforts to optimize and scale up these processes to complete implementation are underway. A resource recovery network must be established, or “piggybacked” onto existing networks, to collect and channel post-consumer composites back to these material recovery facilities (MRFs). Because of the
MIL-HDBK-17-3F Volume 3,Chapter 11-Environmental Management relatively low volume of advanced composites in service,the most efficient transportation system may include a network of material transfer stations,which collect recyclables for consolidation into large ship- ments.A single transfer station may receive shipments of process waste and post-consumer composites from a state,or metropolitan area,and reship many small loads in a single truck or rail car load. Throughout this consolidation process,different types of composites must remain separate for the value of the recyclables to be maintained.It is almost always easier for materials to be kept separate in the first place than to go through sortation after the fact. 11.2.3 Recycling education Although methods for reducing,reusing,and recycling thermoset matrix composites exist today,and services are available for exchanging unused fibers,prepreg,and other precursors,lack of awareness limits their application.Producers and users should familiarize themselves with opportunities for recycling as a first step in making it a routine part of their ways of doing business.An interest in recycling that is generated in both a top-down and bottom-up fashion can be the most effective in establishing programs, since programs that are mandated by management are likely to fail if not implemented on the shop floor, while individual efforts will not succeed without management support.Information from this chapter and its references can be used as a starting point for this education process 11.3 ECONOMICS OF COMPOSITE RECYCLING A complete discussion of the economics of recycling composite materials would need to address,in detail,numerous issues that are specific to the particular type of composite.Such a discussion is beyond the scope of this section.Some general considerations of composite recycling economics are helpful in designing and evaluating recycling programs and are discussed in this section. The costs of recycling principally arise from collection,transportation,and processing.These costs should ideally be offset by the value of the products derived from the recycled material.There are also costs associated with disposing of waste,called "tipping fees,"particularly if the material is a hazardous waste,as is the case for uncured resins.The reduction or elimination of disposal costs should be consid- ered when evaluating the cost of a recycling operation. In addition,there are significant costs associated with complying with existing environmental regula- tions and those that may be enacted if an industry fails to take action on its own initiative.Some recycling efforts have been initiated by industries to head off legislation that would place a greater burden on them, and result in a less efficient recycling structure.There are significant public relations benefits from mak- ing good faith efforts to recycle and strong negative effects when these efforts are not made.Large-scale implementation of composite materials in the infrastructure,transportation,offshore oil,and other indus- tries will eventually require the further development of composite recycling programs. Several considerations are involved in identifying the most favorable economics for recycling a mate- rial.Minimization of collection and transportation costs is a vital requirement for efficient recycling.For fiberglass materials,for instance,which are heavy,and which do not yield high value recyclate,these costs could be prohibitive.For this reason it is most effective to situate recycling facilities close to the source of material. Derivation of high value materials is another important requirement.Although carbon fiber compos- ites can be completely incinerated for energy,in an open-hearth furnace,for example,their value would be reduced to that of the energy content.Some of the current technologies for fiberglass recycling grind the composite into a fine powder that is used as filler in new composite.This fill must compete with ex- tremely inexpensive calcium carbonate fillers,and is therefore of low value.The primary benefits of these technologies are that the waste does not become a landfill,or disposal problem,and that the recyclate fill is less dense than mineral fill,resulting in a lighter weight composite. 11-5
MIL-HDBK-17-3F Volume 3, Chapter 11 - Environmental Management 11-5 relatively low volume of advanced composites in service, the most efficient transportation system may include a network of material transfer stations, which collect recyclables for consolidation into large shipments. A single transfer station may receive shipments of process waste and post-consumer composites from a state, or metropolitan area, and reship many small loads in a single truck or rail car load. Throughout this consolidation process, different types of composites must remain separate for the value of the recyclables to be maintained. It is almost always easier for materials to be kept separate in the first place than to go through sortation after the fact. 11.2.3 Recycling education Although methods for reducing, reusing, and recycling thermoset matrix composites exist today, and services are available for exchanging unused fibers, prepreg, and other precursors, lack of awareness limits their application. Producers and users should familiarize themselves with opportunities for recycling as a first step in making it a routine part of their ways of doing business. An interest in recycling that is generated in both a top-down and bottom-up fashion can be the most effective in establishing programs, since programs that are mandated by management are likely to fail if not implemented on the shop floor, while individual efforts will not succeed without management support. Information from this chapter and its references can be used as a starting point for this education process. 11.3 ECONOMICS OF COMPOSITE RECYCLING A complete discussion of the economics of recycling composite materials would need to address, in detail, numerous issues that are specific to the particular type of composite. Such a discussion is beyond the scope of this section. Some general considerations of composite recycling economics are helpful in designing and evaluating recycling programs and are discussed in this section. The costs of recycling principally arise from collection, transportation, and processing. These costs should ideally be offset by the value of the products derived from the recycled material. There are also costs associated with disposing of waste, called “tipping fees,” particularly if the material is a hazardous waste, as is the case for uncured resins. The reduction or elimination of disposal costs should be considered when evaluating the cost of a recycling operation. In addition, there are significant costs associated with complying with existing environmental regulations and those that may be enacted if an industry fails to take action on its own initiative. Some recycling efforts have been initiated by industries to head off legislation that would place a greater burden on them, and result in a less efficient recycling structure. There are significant public relations benefits from making good faith efforts to recycle and strong negative effects when these efforts are not made. Large-scale implementation of composite materials in the infrastructure, transportation, offshore oil, and other industries will eventually require the further development of composite recycling programs. Several considerations are involved in identifying the most favorable economics for recycling a material. Minimization of collection and transportation costs is a vital requirement for efficient recycling. For fiberglass materials, for instance, which are heavy, and which do not yield high value recyclate, these costs could be prohibitive. For this reason it is most effective to situate recycling facilities close to the source of material. Derivation of high value materials is another important requirement. Although carbon fiber composites can be completely incinerated for energy, in an open-hearth furnace, for example, their value would be reduced to that of the energy content. Some of the current technologies for fiberglass recycling grind the composite into a fine powder that is used as filler in new composite. This fill must compete with extremely inexpensive calcium carbonate fillers, and is therefore of low value. The primary benefits of these technologies are that the waste does not become a landfill, or disposal problem, and that the recyclate fill is less dense than mineral fill, resulting in a lighter weight composite
MIL-HDBK-17-3F Volume 3,Chapter 11-Environmental Management Technologies that recover fibers in usable condition can achieve higher value for the recyclate,and can pay for the entire recycling process.Technologies that recover glass fibers have this advantage compared to grinding,but the fiber extraction process must still be very inexpensive to justify on an eco- nomic basis,due to the low cost of glass fiber.The greater cost of carbon fibers can,therefore,be an advantage for recycling of this class of material.If carbon fibers can be extracted from the matrix in suffi- ciently good condition to compete with low-end fibers in the $5/pound range,a substantial value can be obtained and the recycling process can be feasible on an economic basis. Composite materials will always have to compete with monolithic metals,which can,in most cases, be recycled back to virtually their original quality,a process known as tertiary recycling.Finding high value secondary uses for composite recyclate is a necessary factor for successful competition. Cyclical markets for recycled materials have been a problem for most types of materials(References 11.3(a)-(b)).Expensive plants have been built and commitments made when the value of recycled ma- terials is high,and then market changes have left companies with unused capability or mandates to pur- chase materials at costs far greater than their value.The primary source of these market fluctuations has been a kind of teething pain,in which,at first,a great deal of material is recycled,but no buyers are avail- able for a product that did not previously exist,and then when a market is created,demand exceeds sup- ply.Paper and plastic materials have been particularly prone to these fluctuations. These cyclical changes can leave manufacturers dependent on a flow of recycled material that can- not be reliably,or economically,procured.Robust manufacturing processes that can exploit recycled materials when possible,but can substitute virgin material when necessary,can alleviate these problems. 11.4 COMPOSITE WASTE STREAMS The advanced composites industry was surveyed in 1991(Reference 11.2.1(a))and 1995(Reference 11.2.1(b))to determine the type,quantity,and current disposal methods of composite waste.As shown in Figure 11.4(a),for waste generated at the manufacturing source,66%was in the form of unused prepreg material.Approximately 18%was in the form of cured parts,14%was trimmings,and one or two percent was comprised of finished parts and bonded honeycomb.Pre-consumer advanced composite waste, therefore,consists of approximately two-thirds prepreg scrap and one-third trimmings and cured parts. Because of the long service life of many military and civilian platforms containing advanced composite materials,it is difficult to predict when the composite components contained within those platforms will enter the composite waste stream at the end-of-service-life.A study (Reference 11.2.1(b))of the compos- ites contained within many military vehicles shows the kind,and in some cases,the quantity of various types of composite materials that will require recycling or disposal at some point in time.The composites in military vehicles are largely comprised of carbon fiber/epoxy,aramid fiber/epoxy,and carbon/carbon composites as shown in Figure 11.4(b). 11-6
MIL-HDBK-17-3F Volume 3, Chapter 11 - Environmental Management 11-6 Technologies that recover fibers in usable condition can achieve higher value for the recyclate, and can pay for the entire recycling process. Technologies that recover glass fibers have this advantage compared to grinding, but the fiber extraction process must still be very inexpensive to justify on an economic basis, due to the low cost of glass fiber. The greater cost of carbon fibers can, therefore, be an advantage for recycling of this class of material. If carbon fibers can be extracted from the matrix in sufficiently good condition to compete with low-end fibers in the $5/pound range, a substantial value can be obtained and the recycling process can be feasible on an economic basis. Composite materials will always have to compete with monolithic metals, which can, in most cases, be recycled back to virtually their original quality, a process known as tertiary recycling. Finding high value secondary uses for composite recyclate is a necessary factor for successful competition. Cyclical markets for recycled materials have been a problem for most types of materials (References 11.3(a) - (b)). Expensive plants have been built and commitments made when the value of recycled materials is high, and then market changes have left companies with unused capability or mandates to purchase materials at costs far greater than their value. The primary source of these market fluctuations has been a kind of teething pain, in which, at first, a great deal of material is recycled, but no buyers are available for a product that did not previously exist, and then when a market is created, demand exceeds supply. Paper and plastic materials have been particularly prone to these fluctuations. These cyclical changes can leave manufacturers dependent on a flow of recycled material that cannot be reliably, or economically, procured. Robust manufacturing processes that can exploit recycled materials when possible, but can substitute virgin material when necessary, can alleviate these problems. 11.4 COMPOSITE WASTE STREAMS The advanced composites industry was surveyed in 1991 (Reference 11.2.1(a)) and 1995 (Reference 11.2.1(b)) to determine the type, quantity, and current disposal methods of composite waste. As shown in Figure 11.4(a), for waste generated at the manufacturing source, 66% was in the form of unused prepreg material. Approximately 18% was in the form of cured parts, 14% was trimmings, and one or two percent was comprised of finished parts and bonded honeycomb. Pre-consumer advanced composite waste, therefore, consists of approximately two-thirds prepreg scrap and one-third trimmings and cured parts. Because of the long service life of many military and civilian platforms containing advanced composite materials, it is difficult to predict when the composite components contained within those platforms will enter the composite waste stream at the end-of-service-life. A study (Reference 11.2.1(b)) of the composites contained within many military vehicles shows the kind, and in some cases, the quantity of various types of composite materials that will require recycling or disposal at some point in time. The composites in military vehicles are largely comprised of carbon fiber/epoxy, aramid fiber/epoxy, and carbon/carbon composites as shown in Figure 11.4(b)
MIL-HDBK-17-3F Volume 3,Chapter 11-Environmental Management Finished Parts Bonded 2% Honeycomb Other 1% 0% Trimmings 13% Cured Parts 18% Prepreg 66% FIGURE 11.4(a) The reported distribution of advanced composite manufacturing waste by type of material. AR/EP GR/PI C/C 2% 2% Other 5% 0% GUEP GR/EP 37% 54% GL/EP --Glass/Epoxy AR/EP --Aramid/Epoxy GR/EP --Graphite/Epoxy GR/PI --Graphite/Polyimide C/C --Carbon/C FIGURE 11.4(b)The distribution of advanced composite materials in 1995 by matrix and fiber. 11.4.1 Process waste Because of the nature of most current advanced composite manufacturing processes,process wastes comprise a significant fraction of the overall composite waste stream.They are also the portion of the waste stream that must be disposed during production,rather than at the end of service,and so pre- sent immediate handling issues. 11-7
MIL-HDBK-17-3F Volume 3, Chapter 11 - Environmental Management 11-7 Prepreg 66% Other 0% Trimmings 13% Finished Parts 2% Cured Parts 18% Bonded Honeycomb 1% FIGURE 11.4(a) The reported distribution of advanced composite manufacturing waste by type of material. GR/EP 54% GL/EP 37% AR/EP 2% GR/PI 2% Other 0% C/C 5% GL/EP -- Glass/Epoxy AR/EP -- Aramid/Epoxy GR/EP -- Graphite/Epoxy GR/PI -- Graphite/Polyimide C/C -- Carbon/C FIGURE 11.4(b) The distribution of advanced composite materials in 1995 by matrix and fiber. 11.4.1 Process waste Because of the nature of most current advanced composite manufacturing processes, process wastes comprise a significant fraction of the overall composite waste stream. They are also the portion of the waste stream that must be disposed during production, rather than at the end of service, and so present immediate handling issues
MIL-HDBK-17-3F Volume 3,Chapter 11-Environmental Management Prepreg comprises the largest fraction of process waste,as shown in Figure 11.4(a),and is,there- fore,the most important target of source reduction and recycling efforts.Unused fibers,curing agents, and resins also contribute to process waste.After minimization by careful inventory control strategies (Section 11.5),these materials can often be reallocated or exchanged(Section 11.7.2). 11.4.2 Post consumer composite waste Perhaps the greatest challenge for recycling of composite materials is finding a viable approach to collecting,sorting,processing and reusing post consumer composite wastes.Materials that have gone into service are likely to be dispersed geographically,may have picked up contaminants,require disas- sembly,and may contain fiber and matrix types that are not documented.The date of retirement from service for composite components may be decades after their production,making the logistics of planning for recyclability difficult,and of low priority.Nevertheless,addressing the issue of post-consumer com- posite recycling is essential if composite materials are to compete in systems that mandate recycling. The quantities of composite materials that are produced can be derived from fiber manufacturer's data.Another tracking method is to document the quantities and types of composites used in various ve- hicles and other applications,and then to monitor the procurement levels for those vehicles.A pie chart of the percentage distributions of actual usage of various types of advanced composite materials for 1995 is shown in Figure 11.4(b)(Reference 11.2.1(b)). The greatest uncertainty in assessing the post consumer composite waste stream is in the dates of retirement of the systems containing the composite components,or,otherwise,the dates of failure or de- struction of the composite components.Because many military and civilian craft remain in service for decades,while others are rapidly rendered obsolete,the extent and timing of the advanced composite waste stream is difficult to predict. More reliable predictions can be made about the sheet molding compound and other composites used in automotive applications,since the life cycle of automobiles is less variable.Polymers and poly- mer composites currently comprise about 20%of the total weight of new automobiles and are steadily increasing.In contrast to the recyclability of the bulk of automobile constituents,these materials currently contribute to the generation of automotive shredder residue(ASR),a mixture of plastic,rubber,glass,and inorganic materials which is commonly landfilled.Efforts to develop recycling techniques for ASR are un- derway but are beyond the scope of this discussion.Recycling technologies for sheet molding compound are discussed in Sections 11.8.3.2 and 11.8.3.5. 11.5 COMPOSITE WASTE STREAM SOURCE REDUCTION Reduction of the volume of waste materials is the best approach to environmental impact mitigation. Waste that is not created in the first place does not need to be paid for,recycled,or disposed.Efforts to reduce the production of waste materials should,therefore,be given the highest priority.Waste source reduction yields direct benefits in both decreased procurement costs and decreased recycling or disposal costs.Efforts should,therefore,be made to identify the sources of waste material and reduce or elimi- nate them.Approaches to the reduction of composite precursor waste are described below. 11.5.1 Just-in-time and just enough material delivery Just-in-time inventory control systems have made a major impact on the production plans of manu- facturers in recent years.The benefits of having materials arrive shortly before use,include reduced in- ventory and storage requirements,and more efficient production flow.For composites that are produced from prepreg with a limited shelf life and that require refrigeration,even greater benefits can be derived. Great care should,therefore,be taken to ensure that tight control is maintained over inventories of pre- preg,resins,and any other material with limited shelf life. 11-8
MIL-HDBK-17-3F Volume 3, Chapter 11 - Environmental Management 11-8 Prepreg comprises the largest fraction of process waste, as shown in Figure 11.4(a), and is, therefore, the most important target of source reduction and recycling efforts. Unused fibers, curing agents, and resins also contribute to process waste. After minimization by careful inventory control strategies (Section 11.5), these materials can often be reallocated or exchanged (Section 11.7.2). 11.4.2 Post consumer composite waste Perhaps the greatest challenge for recycling of composite materials is finding a viable approach to collecting, sorting, processing and reusing post consumer composite wastes. Materials that have gone into service are likely to be dispersed geographically, may have picked up contaminants, require disassembly, and may contain fiber and matrix types that are not documented. The date of retirement from service for composite components may be decades after their production, making the logistics of planning for recyclability difficult, and of low priority. Nevertheless, addressing the issue of post–consumer composite recycling is essential if composite materials are to compete in systems that mandate recycling. The quantities of composite materials that are produced can be derived from fiber manufacturer’s data. Another tracking method is to document the quantities and types of composites used in various vehicles and other applications, and then to monitor the procurement levels for those vehicles. A pie chart of the percentage distributions of actual usage of various types of advanced composite materials for 1995 is shown in Figure 11.4(b) (Reference 11.2.1(b)). The greatest uncertainty in assessing the post consumer composite waste stream is in the dates of retirement of the systems containing the composite components, or, otherwise, the dates of failure or destruction of the composite components. Because many military and civilian craft remain in service for decades, while others are rapidly rendered obsolete, the extent and timing of the advanced composite waste stream is difficult to predict. More reliable predictions can be made about the sheet molding compound and other composites used in automotive applications, since the life cycle of automobiles is less variable. Polymers and polymer composites currently comprise about 20% of the total weight of new automobiles and are steadily increasing. In contrast to the recyclability of the bulk of automobile constituents, these materials currently contribute to the generation of automotive shredder residue (ASR), a mixture of plastic, rubber, glass, and inorganic materials which is commonly landfilled. Efforts to develop recycling techniques for ASR are underway but are beyond the scope of this discussion. Recycling technologies for sheet molding compound are discussed in Sections 11.8.3.2 and 11.8.3.5. 11.5 COMPOSITE WASTE STREAM SOURCE REDUCTION Reduction of the volume of waste materials is the best approach to environmental impact mitigation. Waste that is not created in the first place does not need to be paid for, recycled, or disposed. Efforts to reduce the production of waste materials should, therefore, be given the highest priority. Waste source reduction yields direct benefits in both decreased procurement costs and decreased recycling or disposal costs. Efforts should, therefore, be made to identify the sources of waste material and reduce or eliminate them. Approaches to the reduction of composite precursor waste are described below. 11.5.1 Just-in-time and just enough material delivery Just-in-time inventory control systems have made a major impact on the production plans of manufacturers in recent years. The benefits of having materials arrive shortly before use, include reduced inventory and storage requirements, and more efficient production flow. For composites that are produced from prepreg with a limited shelf life and that require refrigeration, even greater benefits can be derived. Great care should, therefore, be taken to ensure that tight control is maintained over inventories of prepreg, resins, and any other material with limited shelf life
MIL-HDBK-17-3F Volume 3,Chapter 11-Environmental Management Prepreg inventory can be effectively tracked by logging shipments of prepreg as they are received into a computer database and affixing a bar coded label before storage.The information in the database can be compared with production requirements to plan and time future procurements.The database sys- tem can also be set to flag materials that are in danger of reaching their expiration dates so that process- ing can be scheduled to avoid waste.In some cases,prepreg that has reached its expiration date can still be used if testing is performed to ensure that the quality of the components is not impaired.Prepreg that no longer meets the stringent requirements for primary structures can sometimes be reassigned to less demanding applications,or resold for use in non-critical structures.See Section 11.7 for information on materials exchange. Procurement of excess quantities of material is also a significant source of waste.If arrangements can be made with the material supplier,obtaining the correct amount,with minimal excess,is an efficient means of reducing the generation of wastes. 11.5.2 Electronic commerce acquisition management Electronic commerce is the process of specifying and procuring materials and components by digitally transmitting the required information,usually over the Internet.Composite precursor acquisition by elec- tronic commerce can reduce inventory requirements and shipping lead-time.It can also interface directly with management of inventories to minimize waste. 11.5.3 Waste minimization guidelines Guidelines for implementing procedures that minimize the production of composite and precursor waste are provided in this section. 11.5.3.1 Prepreg Efficient use of prepreg is one of the most effective methods of waste minimization.Prepreg cutting waste typically amounts to 25-50%of the material.This waste adds to both procurement and disposal costs.Efforts to develop recycling methods for prepreg have been made (References 11.2.1(a)-(b). 11.5.3.1(a)-(c)),but most are not fully ready for implementation.Particular emphasis should,therefore, be given to efforts to optimize the nesting of patterns for cutting shapes out of prepreg materials.Com- puter programs are available to facilitate this task. 11.5.3.2 Resin Uncured resin waste is classified as a hazardous waste material in the U.S.,and must be handled and disposed of accordingly.Curing of resin for the purposes of disposal is considered to be processing of hazardous waste,which requires special permitting,even though the same shop cures resin on a rou- tine basis for the purpose of composite production.Unless,and until,these requirements are eased or modified,it is doubly important to minimize the creation of waste resin.Careful planning of procurement and just-enough procurement of resins are tools for this minimization. 11.5.3.3Fber This section is reserved for future use. 11.5.3.4 Curing agents This section is reserved for future use. 11.5.3.5 Autoclaving materials This section is reserved for future use. 11-9
MIL-HDBK-17-3F Volume 3, Chapter 11 - Environmental Management 11-9 Prepreg inventory can be effectively tracked by logging shipments of prepreg as they are received into a computer database and affixing a bar coded label before storage. The information in the database can be compared with production requirements to plan and time future procurements. The database system can also be set to flag materials that are in danger of reaching their expiration dates so that processing can be scheduled to avoid waste. In some cases, prepreg that has reached its expiration date can still be used if testing is performed to ensure that the quality of the components is not impaired. Prepreg that no longer meets the stringent requirements for primary structures can sometimes be reassigned to less demanding applications, or resold for use in non-critical structures. See Section 11.7 for information on materials exchange. Procurement of excess quantities of material is also a significant source of waste. If arrangements can be made with the material supplier, obtaining the correct amount, with minimal excess, is an efficient means of reducing the generation of wastes. 11.5.2 Electronic commerce acquisition management Electronic commerce is the process of specifying and procuring materials and components by digitally transmitting the required information, usually over the Internet. Composite precursor acquisition by electronic commerce can reduce inventory requirements and shipping lead-time. It can also interface directly with management of inventories to minimize waste. 11.5.3 Waste minimization guidelines Guidelines for implementing procedures that minimize the production of composite and precursor waste are provided in this section. 11.5.3.1 Prepreg Efficient use of prepreg is one of the most effective methods of waste minimization. Prepreg cutting waste typically amounts to 25-50% of the material. This waste adds to both procurement and disposal costs. Efforts to develop recycling methods for prepreg have been made (References 11.2.1(a) - (b), 11.5.3.1(a) - (c)), but most are not fully ready for implementation. Particular emphasis should, therefore, be given to efforts to optimize the nesting of patterns for cutting shapes out of prepreg materials. Computer programs are available to facilitate this task. 11.5.3.2 Resin Uncured resin waste is classified as a hazardous waste material in the U.S., and must be handled and disposed of accordingly. Curing of resin for the purposes of disposal is considered to be processing of hazardous waste, which requires special permitting, even though the same shop cures resin on a routine basis for the purpose of composite production. Unless, and until, these requirements are eased or modified, it is doubly important to minimize the creation of waste resin. Careful planning of procurement and just-enough procurement of resins are tools for this minimization. 11.5.3.3 Fiber This section is reserved for future use. 11.5.3.4 Curing agents This section is reserved for future use. 11.5.3.5 Autoclaving materials This section is reserved for future use
MIL-HDBK-17-3F Volume 3,Chapter 11-Environmental Management 11.5.3.6 Packaging materials This section is reserved for future use. 11.5.4 Lightweighting Reduction of the weight of composite components by careful design improves environmental man- agement by reducing the amount of material consumed,and that must ultimately be recycled or landfilled. Although the primary motives for lightweighting are to improve structural efficiency,these additional bene- fits occur at no additional cost.Lightweighting of composite components should,therefore,be considered to be a part of any environmental management plan. Overdesign of composite components commonly occurs because of uncertainties about the failure criteria,material properties,and behavior under complex in-service loading conditions.This overdesign reduces the performance benefits of composites in comparison with monolithic materials.As improved composite design capabilities are developed by ongoing efforts in this area,implementation of those ca- pabilities will help to reduce waste generation. 11.6 REUSE OF COMPOSITE COMPONENTS AND MATERIALS After reduction of waste generation,the next best approach to environmental management involves the reuse of systems,components,and constituents.The greatest value for a complete component can best be realized by reusing it in the same,or,possibly,in some similar application.This section provides information and ideas for reuse of composite components. 11.6.1 Reuse of composite components By far the greatest part of the value derived from recycled automobiles comes from the reuse of ser- viceable or remanufacturable components that are removed and resold by a large network of automobile parts distributors.Used automobile parts are inventoried and shipped to buyers through a sophisticated, satellite-linked database network that exchanges information between buyers and sellers.Similar sys- tems for reallocating composite components that are removed from damaged or decommissioned vehi- cles could avoid disposal costs and return the maximum value for the material. 11.6.2 Machining to smaller components End-of-service or otherwise surplus composite components can sometimes be reconfigured for an- other application by machining.In this manner,sailboat spars have been produced from aircraft compo- nents,for instance.Because such reuse usually returns a greater value than recycling,consideration should be given to reconfiguration,or sale to a company that performs that function,before sending mate- rial to be recycled.The greatest difficulty in machining components to smaller sizes arises from finding matches in material and geometric requirements.Applications that allow some flexibility for the geometry are advantageous for this reason. 11.7 MATERIALS EXCHANGE Materials exchange is a method of reducing waste and lowering acquisition costs by reallocating or reselling unused materials.This can be done either within an organization,or between organizations, often with the assistance of a broker.This section describes quidelines and techniques for exchange of composite precursors. 11-10
MIL-HDBK-17-3F Volume 3, Chapter 11 - Environmental Management 11-10 11.5.3.6 Packaging materials This section is reserved for future use. 11.5.4 Lightweighting Reduction of the weight of composite components by careful design improves environmental management by reducing the amount of material consumed, and that must ultimately be recycled or landfilled. Although the primary motives for lightweighting are to improve structural efficiency, these additional benefits occur at no additional cost. Lightweighting of composite components should, therefore, be considered to be a part of any environmental management plan. Overdesign of composite components commonly occurs because of uncertainties about the failure criteria, material properties, and behavior under complex in-service loading conditions. This overdesign reduces the performance benefits of composites in comparison with monolithic materials. As improved composite design capabilities are developed by ongoing efforts in this area, implementation of those capabilities will help to reduce waste generation. 11.6 REUSE OF COMPOSITE COMPONENTS AND MATERIALS After reduction of waste generation, the next best approach to environmental management involves the reuse of systems, components, and constituents. The greatest value for a complete component can best be realized by reusing it in the same, or, possibly, in some similar application. This section provides information and ideas for reuse of composite components. 11.6.1 Reuse of composite components By far the greatest part of the value derived from recycled automobiles comes from the reuse of serviceable or remanufacturable components that are removed and resold by a large network of automobile parts distributors. Used automobile parts are inventoried and shipped to buyers through a sophisticated, satellite-linked database network that exchanges information between buyers and sellers. Similar systems for reallocating composite components that are removed from damaged or decommissioned vehicles could avoid disposal costs and return the maximum value for the material. 11.6.2 Machining to smaller components End-of-service or otherwise surplus composite components can sometimes be reconfigured for another application by machining. In this manner, sailboat spars have been produced from aircraft components, for instance. Because such reuse usually returns a greater value than recycling, consideration should be given to reconfiguration, or sale to a company that performs that function, before sending material to be recycled. The greatest difficulty in machining components to smaller sizes arises from finding matches in material and geometric requirements. Applications that allow some flexibility for the geometry are advantageous for this reason. 11.7 MATERIALS EXCHANGE Materials exchange is a method of reducing waste and lowering acquisition costs by reallocating or reselling unused materials. This can be done either within an organization, or between organizations, often with the assistance of a broker. This section describes guidelines and techniques for exchange of composite precursors
