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