再生碳纤维的商业化之路
By www.carbonfiber.com.cn
随着首套商业规模的碳纤维回收系统上线，越来越多的商家参与到再生碳纤维项目的研发之中。碳纤维回收利用是一个非常吸引人的市场定位，因为它不仅会得到金融业及政府研究奖励措施的支持，同时也符合许多制造商追求“绿色”的意愿。
几乎从飞机制造商波音和空客公司发出信号，表示他们有意在新飞机的设计中添加更多的轻质复合材料的那一刻起，一些大学、研究所及追逐利益的企业便加入了复合材料的再利用研发中。
美国Allstreams公司的总经理Carl Ulrich表示：复合材料的回收利用之所以展示出如此高的姿态，其中的一大原因是，飞机制造商在处理铝和其它金属的方面长久以来都实现了非常高的回收率，这让人羡慕不已。这在一定程度上也表明了，在过去的几年里波音和空客公司为何一直参与大量有关碳纤维回收利用的研究工作。以波音787为例，每架飞机携有近18，144千克可回收的碳纤维。波音公司、飞机再生利用协会的行业合作伙伴及空客公司希望在未来几年里通过PAMELA项目将飞机再生材料的回收率从70%提高到90%。
Ulrich介绍说：“碳纤维回收利用是一个非常吸引人的市场定位，因为它不仅会得到金融业及政府研究奖励措施的支持，而且制造商希望采用绿色生产工艺及制造绿色产品的愿望也会促进碳纤维回收利用项目的发展。”
材料创新技术公司是一家回收利用公司，其首席执行官Jim Stike声称，碳纤维的回收利用实际上为我们带来了三种绿色。它不仅可以阻止原始碳纤维在首次使用后被浪费在垃圾填埋场，而且利用再生碳纤维生产的部件还可被再次利用。因为碳纤维在回收时会保持其原始碳纤维的大部份性能，即使是在二次利用后也依然如此。此外，回收利用工艺还能显著减少能源消耗。据波音公司推算，回收碳纤维的费用大约是生产原始碳纤维的70%（每磅8到12美元VS 每磅15到30美元），而电能消耗量还不足生产原始碳纤维的5%（每磅1.3到4.5千瓦时VS每磅25到75千瓦时）。
考虑到这种潜能，处在不同发展阶段的可行性机械和热解技术都会被载入研发史册。波音公司飞机及复合材料回收部门的项目经理Bill Carberry说：“目前，不管是需要催化剂还是无需催化剂的热解工艺似乎都是领先技术。在研发的过程中还有其它一些回收技术，其中包括超临界流体和微波技术，不过这些技术大多只能在实验室中实现。”
最近，空客及PAMELA联合集团采用热解工艺来提取A380机身上的碳。PAMELA项目此阶段的目标是把在初期试验中学到的东西，尤其是拆除A300机身，应用在较大的A380飞机上，并设法扩大工艺规模，确定回收先进材料的最佳方法。据悉每架飞机含有25吨复合材料。
据Carberry透露，目前全球只有两家具有商业规模，可实现连续生产的回收企业，且都采用热解工艺。这两家企业分别位于英国和日本。
再生碳纤维有限公司（Recycled Carbon Fibre Ltd.）位于英国西米德兰兹郡，是这两家企业之一。该工厂装有一套长37米的高精准热解设备。据悉该设备具有回收约2，000吨废弃材料的能力，每年的再生纤维产量大约为1，200吨。
日本碳纤维制造商协会再生委员会成员包括日本东丽股份有限公司（Toray Industries Inc.），帝人集团分支机构东邦泰纳克公司（Toho Tenax Co.）及日本三菱公司（Mitsubishi Rayon Co.）。这几家公司联合创立了一家合资企业进行碳纤维回收。该回收工厂位于日本福冈县大牟田市，为日本三井矿业冶炼公司所有。2007年其实验厂开始运营，并在2008年通过检定。据报道，随着市场需求的增长，该工厂再生碳纤维的年产量将从最初的几百吨增加到1000吨。这些再生材料经组合后主要应用于家用电子产品及汽车行业。
在欧洲，再生碳纤维有限公司（RCF Ltd.）可以说只是冰山一角。许多潜在竞争者正在向大规模运营转型。例如，德国Hadeg Recycling 股份有限公司和CFK Valley Recycling 股份有限公司均已具备初级发展阶段的系统。另外，波音公司和意大利阿莱尼亚航空工业公司也将携手在意大利开启一家复合材料回收企业。
在美国，Adherent Technologies公司计划在不久的将来开启一个年再生材料生产能力为1000吨的工厂。美国火鸟先进材料有限公司（Firebird Advanced Materials Inc.）研发了一种专利连续微波回收方法，计划于今年实现商业化生产。麻省理工学院希望在本月底在离波音公司北查尔斯顿机身安装工厂不远处的莱克城开启一个占地4，645平方米的回收工厂。工厂成立之初，采用热解工艺每年可生产453.6吨再生碳纤维。Stike表示：“随着我们获得的废弃物的增多，我们会根据需要增加工作班次或工作单元。”
再生碳纤维有限公司（RCF Ltd.）销售及业务发展经理Martin Spooner很快就感到了压力。然而，成功的开启一个碳纤维回收工厂并非想象的那么容易。你需要进行大量的可行性调查研究，实验设备检测，并就未来的商业运行进行讨论。Spooner介绍说：“在较小试验机运行了近两年后，我们还花费了大约六个月的时间才使我们的新机器得以正常运行。”他又补充到：“从理论上讲，这很容易实现，但真正在现实中成规模的做起来的确是一项非常艰难的工作。”
其中的障碍之一是寻找优质碳纤维废弃物来源。Ulrich说：再生碳纤维的市场的规模实际上并非取决于需求，而是供应物的可用性。
Spooner认为这是再生材料制造商面临的最大挑战之一。为了满足这一需求，近日再生碳纤维有限公司（RCF Ltd.）邀请Leslie Cooke加入了其在美国的团队。Leslie Cooke是日本东丽公司（Toray Composites）在美国华盛顿州塔科马港市的分公司的前任销售/市场总监。据再生碳纤维有限公司首席执行官Steve Line透露，Cooke将协助他们获取北美市场上的碳纤维原料。这些原料将在欧洲工厂进行加工处理，直到未来美国工厂开始运营。
据Ulrich 推测：短期内来自航空航天领域的加工废料、报废飞机及部件可产生4536到6804吨碳纤维再生材料。截止到2029年，回收的碳纤维数量可能会达到2.26806万吨。
Ulrich表示：“交通运输业何时会采用连续碳纤维复合材料仍未确定，但如果易于使用的材料得到发展，那么其影响将会非常巨大。”他认为，在短期内汽车市场很有可能会成为再生短切碳纤维的大型的客户基础而并非供应基础。
相比之下，风能市场有巨大潜能成为未来碳纤维废弃物的供应源。Ulrich补充到：“飞机叶片预期会增加4535.92吨废弃碳纤维。对获得长期合同的回收商来讲，回收大型飞机叶片将会是一个有利可图、极具吸引力的目标。不过这要发生在20年后，风机叶片使用期满之时。”
我们面临的另外一个挑战是对回收原料的各种自然属性的处理。Spooner表示：“我们可对干燥废弃物、预浸料的下脚料、过期预浸料、层压材料下脚料、工具及报废零部件进行回收。我们也可能会对高模量或标准模量的航空航天废弃物进行回收，但不管是何种材料我们都要对其进行处理。加工过程中产生的废料是再生材料最持久不断的来源。例如，在制造过程中几乎40%的预浸料会被废弃。
在再生碳纤维有限公司（RCF Ltd.）的热解工艺中，层压制品在热解前先被切碎，其背衬也必须从预浸料中移除。Spooner表示：“在废弃材料的准备阶段，我们需要做大量的处理工作。”同时他还指出：“大部份处理工作都是手工完成的。”对热解工艺进行精确控制，在无氧环境中加热复合材料，并使其温度保持在400°C 到500°C之间，这样生产出的清洁碳纤维就能保持90%-95%的原始性能。
Spooner介绍说：“我们面临的问题还有废物原料是否一致，我们生产的成品的性能是否一致。我们所使用的原料均由航空航天及一级方程式锦标赛赛车产生，其中含有优质的碳材料。然而，就工业应用来说，它们的硬度可能太高了。我们试图采用一种方法对原料进行混合使再生材料具备固定的特性。
再生碳纤维有限公司（RCF Ltd.）不仅可生产再生压制碳纤维（长100微米到300微米）还可生产再生短切纤维（长3毫米到25毫米）。他们会对每批再生材料进行测试，以确保其满足公司的最低标准：抗张强度为3000 MPa，拉伸模量为200GPa。
由废弃到新生
回收利用过程中必须强制执行的一方面可能是制造商们要对所购买的原始纤维进行优化使用。Carberry声称：“如果你能够从制造过程中选取废料并将其转化成产品其它部件的原料，那么这些产品就具有明显的耐用性和成本优势。”不过Carberry承认，这些优势的整体范围仍不明确。“首先我们必须清除技术障碍，并在对潜在市场进行估测前对飞机上使用的再生碳纤维进行资格认证”
为了实现这一目标，波音公司与再生碳纤维有限公司，麻省理工学院，诺丁汉大学及Adherent科技公司携手合作，利用波音787飞机前期制作产生的再生碳纤维生产一种理念验证型模塑扶手。尽管在航空航天制造中再生短切纤维不能代替连续纤维，但可将其用在三级航空航天部件中！
Spooner声称：“与原始碾磨及短切纤维相比，我们总能保持竞争力。”对此，他解释到：“从理论上说，我们的产品要便宜一些。因为我们不受全球碳纤维价格的影响，我们清楚生产成本。另外，我们可以提供连续性供应。与传统碳纤维制造商相比，我们拥有各种各样的供应渠道。”
鉴于这种情况，Stike表示，麻省理工学院希望利用再生短切碳纤维的潜在高性能创造一种处于原始航空航天产品与工业级产品之间的高效中模量材料。为了实现这一目标，麻省理工学院根据碳纤维废弃物的模数对其进行分离，并在热解前将其切成一英尺长。Stike报道说, 麻省理工学院与多家主要混合物制造商合作，对其再生材料在混合材料中的应用进行资格认证。此外，麻省理工学院计划将其再生纤维更多的应用在房屋中，并通过其专利3D设计预成型工艺为零部件制造商生产复杂的碳纤维预成型产品。
Stike解释说：“对我们而言，真正的增值前景是为那些希望利用短且纤维生产预成型产品的下游加工业提供材料。” Stike指出：最近麻省理工学院对这一能性进行论证，拆除并分解了波音公司提供的F-18安全平尾的碳纤维。麻省理工学院采用其3-DEP工艺制造了一个预成型件，随后由Molded Fiber Glass Co.将其模塑成一个精致的概念验证型雪弗兰Corvette驾驶室。Stike说：“目前我们正与汽车行业及航空航天行业的潜在终端用户进行合作”。
据火鸟公司总裁Thomas Hunter说，不管如何那些将目标设为终端使用的再生碳纤维制造商都会遇到一些挑战。他指出：“尽管制造商们已经做了大量有关碳纤维回收的调查研究，但这些研究并未真正的集中在产品的应用上。”
他声称，通常由热解产生的纤维若不经进一步的处理对大多数模塑操作来说是不太适合的。尽管热解工艺为碳纤维创造了非常吸引人的表面，促进了纤维/树脂的粘合。不过，该工艺也除掉了纤维的成份，导致其变得松软，成为纤维“棉球”。Hunter透露：“火鸟公司将对其微波回收技术进行调整，以生产出更加类似与原始纤维的再生纤维原材料。”
Spooner对Hunter的观点持相同意见，他表示：“我们不能将松软的干燥纤维放入热塑性机器，因为机器是不会工作的。” Spooner认为，为促进新产品的发展而对纤维原材料回收以外的步骤所做的改进是广大用户接受再生碳纤维产品的关键性因素。以再生碳纤维有限公司为例，该公司已将其碾磨和短切纤维组合到了注塑商的热塑性颗粒物中。不过，Spooner认为到这些工作最终很难引起关注。他解释说：“我们希望使我们的纤维恢复成一种板材类产品。复合材料市场上的毡类物，而非碳纤维芯块或碳纤维袋状物。因此研发一种类似于毡类物的产品是我们必须要做的事情。”
然而波音公司的Carberry则将纤维定向作用视为重点。他表示：“与原始纤维材料相比，再生纤维除了较短且比较分散外，其强度及表面结构都非常有利。对纤维进行调整是打开注塑成型类应用产品外再生碳纤维制造未来的关键。”波音公司将与其它商家携手合作对此项技术进行研究。鉴于相同的情况，诺丁汉大学的研究人员采用非连续性再生碳纤维及一种相对简单的纤维调整工艺制造了一种粗糙的单向性纤维毡。
废料制造者与回收商的合作
再生碳纤维在很大程度上具备其固有价值。碳纤维废弃物制造者及碳纤维回收商进行合作的结果是更高质量废弃原料的产生。如此一来，更高质量的再生纤维将保留更多的固有价值。Hunter表示，如果废弃物制造者更大程度的参与到废料的分类及废料成份的规模减少中，那么废料中存在污染物的风险就会降低，同时还能减少回收商的加工压力。
碳纤维回收商与大量废料制造者不断增加的合作在一定程度上可能会决定回收商建造工厂的地址。Stike说：“我们预计在废料产生地建造工厂。”
Stike总结说：“你不能像回收铝那样以每磅1美元的代价处理碳废料。 如果你对该废料是认真的，那么你就需要关心其前端产品。你要将其视为先进的材料，认为可对其进行回收利用，并能使它保持原有的性能。”
碳纤维回收利用：大量研究
再生碳纤维领域有大量不断进行着的调查研究。除此之外，研究人员还在不断的寻找更好的处理受污染碳纤维增强聚合物废料的方法，增强再生纤维总体性能的途径以及提高再生纤维可加工性的渠道。
由来自诺丁汉大学的Nicholas Warrior及Steve Pickering教授带领的工作组一直在从事流化床技术应用的研究。该工作团队认为此方法非常适合那些可能含有其它混合物及污染物的报废部件，而其它回收途径并不适合这些部件。在流化床工艺中，将压碎的复合材料废料放入位于炉床的反应堆中，在550°C的高温度下，大量液体被升高并通过这些原料。在这个过程中有机材料被氧化掉，包括复合材料的树脂基体。气流的速度如此快以至于当有机物被烧掉时，轻质纤维被迫上升，而较重的物质，如金属材料则仍保留在反应堆的“床”上。
这样一来，通过气流将清洁碳纤维分离出来。这些气流推动清洁碳纤维进入旋风分离器-一个圆柱形或圆锥形的腔室，在这里气体以一种向下旋转的方式流动，之后定向上升，穿过腔室中心，流出顶口。分离器的形状及气流速度是以这样的方式确定的。碳纤维在类似于龙卷风式的气流上由离心力作用而被驱向外部，它们不断的冲击外壁，然后沉入分离器底部，并在此被收集起。此工艺使用户可以从完全氧化的聚合物中提取热能，以此来减少系统的能源消耗。不过，据Pickering说，目前采用此方法对碳纤维进行回收利用会使碳纤维的强度减少25%-50%。
尽管如此，Pickering认为在此类工艺中采用超临界流体具有巨大的潜能。在温度和压力均高于其热力学临界点时，这些液体可通过复合材料固体物，像气体一样分散开，然后将这些固体材料像液体一样分解开。在200到300摄氏度的高温高压下，采用热流体工艺中对超临界流体，如丙醇，进行测试，使其将环氧树脂分解成更多基本材料，且这些基本材料可在化学产品中重复使用。经加工处理后，就可获得优质的清洁碳纤维。据报道，再生纤维的拉升强度可达到其原始材料的97%且模数不发生任何改变。
此外，Adherent科技公司对碳纤维回收利用继续进行调查研究。最近，该公司研发了一种多阶段回收方法，用以处理波音787飞机上标准环氧树脂复合物的热塑性塑料加固层。Adherent公司的此工艺并非为回收纤维而专门设计的，它还可以处理聚合物的废弃物，将这些废弃物分解成更多最终可被加工成有价值的化学产品或燃料的基础性化学成份。
与此同时，英国帝国理工学院的研究人员就由再生纤维生产的复合材料的机械性能进行了大量测试。在这些测试中采用失效机理建造模型，并对由再生纤维制造的复合材料的性能加以预测。目前他们发现了一个非常有趣的测试结果，当采用热解工艺将再生纤维束聚集在一起时，烧焦物在新模塑产品中就会起到加固材料的作用，事实上这增强了复合材料的结构韧性。
原文：
Almost from the moment aircraft manufacturers The Boeing Co. (Seattle, Wash.) and Toulouse, France-based rival, Airbus, signaled their intention to reduce fuel consumption and emissions by incorporating more lightweight composites into new airplane designs, an array of universities, laboratories and for-profit enterprises have been involved in researching and developing ways and means to recycle them.
One big reason recycling has assumed such a high profile is that airframers, owing to a long history of working with aluminum and other metals, already had achieved an enviably high metal-recycling rate, says Carl Ulrich, managing director, Allstreams LLC (McLean, Va.). That explains, in part, why Boeing and Airbus have been integrally involved in much of the research into carbon fiber recycling over the past several years. Each Boeing 787, for example, carries approximately 40,000 lb/18,144 kg of salvageable carbon fiber. Boeing, with its industry partners in the Aircraft Fleet Recycling Assn. (AFRA, Washington, D.C.), and Airbus, through its Process for Advanced Management of End-of-Life Aircraft (PAMELA) consortium, are looking to increase the amount of aircraft recycled material from roughly 70 percent today to upwards of 90 percent in the coming years.
Revenue-capable and responsible
“Carbon fiber recycling is an attractive market niche because it's driven not just by the financials, but also by government research incentives, and by the desire for manufacturers to have green manufacturing processes and products,” explains Ulrich.
Jim Stike, the CEO of recycling firm Materials Innovation Technologies (MIT, Fletcher, N.C.) contends that carbon fiber recycling, in fact, offers “three shades of green.” It not only prevents the waste of virgin carbon fiber in landfills after its first use, but components produced using the recycled fiber are themselves recyclable, because carbon can retain a significant portion of its virgin properties even after a second reclamation. Further, the recycling process itself significantly reduces energy costs. Boeing estimates that carbon fiber can be recycled at approximately 70 percent of the cost to produce virgin fiber ($8/lb to $12/lb vs. $15/lb to $30/lb), using less than 5 percent of the electricity required (1.3 to 4.5 kWH/lb vs. 25 to 75 kWH/lb).
Given this potential, a number of viable mechanical and thermal recycling techniques are in various stages of development, an R&D history chronicled along the way in HPC (see first two items under "Editor's Picks," at right, and the sidebar at the end of this article). But one clear leader has emerged. “Pyrolysis, with and without the aid of a catalyst, seems to be the front-running technology at the present,” says Bill Carberry, program manager for Boeing's Airplane and Composite Recycling. “There are some other technologies in development that include supercritical fluids and microwaves, but these are still pretty much in the laboratory scale.”
Most recently, Airbus and its PAMELA consortium used pyrolysis to extract carbon from an A380 airframe. The goal of this phase of the PAMELA project was to take what had been learned during earlier experiments, most notably the dismantling of an A300 airframe, and apply it to the much larger A380 in an effort to scale-up the process and determine best practices for recovering advanced materials, including 55,000 lb (25 metric tonnes) of composites per plane
According to Carberry, there are, at present, only two commercial-scale, continuous production operations in the world, and both use pyrolysis. One is in the United Kingdom and the other in Japan.
In the U.K., Recycled Carbon Fibre Ltd. (RCF Ltd., West Midlands) now operates one of the two. Its plant houses a highly sophisticated 120-ft/37m long pyrolysis machine reportedly capable of recycling approximately 2,000 metric tonnes (4,409,250 lb) of waste material. The system's capacity is approximately 1,200 metric tonnes (2,645,550 lb) of recycled carbon fiber output per year.
In Japan, members of the Recycling Committee of the Japan Carbon Fiber Manufacturers Assn. (JCMA), including Toray Industries Inc. (Tokyo, Japan), Toho Tenax Co. (Tokyo, Japan), a member of the Teijin Group, and Mitsubishi Rayon Co. (Osaka, Japan), have formed a joint venture to recycle carbon fiber at a plant owned by Mitsui Mining Co. in Omuta City, which is in Japan's Fukuoka Prefecture. A test plant began operation in 2007, followed by verification in 2008. Reportedly, annual output of recycled carbon fiber at the plant will ramp up from several hundred metric tonnes initially to 1,000 metric tonnes (2.2 million lb) as demand increases. The recyclate, after compounding, is targeted primarily at the consumer electronics and automotive industries.
In Europe, RCF Ltd. is the tip of the iceberg. Potential competitors are moving toward commercial-scale operations. In Germany, for example, Hadeg Recycling GmbH and CFK Valley Recycling GmbH (both in Stade, Germany) have systems in the early stages of development. And Boeing and Alenia Aeronautica (Rome, Italy) continue joint efforts to open a composite recycling operation in Italy.
In the U.S., Adherent Technologies Inc. (Albuquerque, N.M.) plans to open a facility in the near future capable of processing 1,000 metric tonnes (2.2 million lb) of recyclate annually. Firebird Advanced Materials Inc. (Raleigh, N.C.) has developed a proprietary continuous microwave recycling method and plans to begin its commercialization this year. And in Lake City, S.C., not far from Boeing's North Charleston, S.C., fuselage subassembly plant, MIT expects to open a recycling plant by the end of this month. Initially, the 50,000-ft2 (4,645m2) facility will be capable of generating 1 million lb (453.6 metric tonnes) of carbon fiber per year using a pyrolysis process, says Stike. “As we get more scrap, we can add shifts or work cells as needed.”
Martin Spooner, sales and business development manager at RCF Ltd., is quick to stress, however, that even though there is a lot of viable research, testing of pilot machines and talk of upcoming commercial operations, successfully starting up a carbon fiber recycling plant is not as easy as it looks. “It took about six months for us to get our new machine up and running well,” says Spooner. “That was after running a smaller pilot machine for nearly two years,” he adds. “In theory, this is easy to do, but actually doing it in practice and at scale is a very difficult job.”
Securing & controlling feedstock
One obstacle is securing sources for high-quality carbon fiber scrap. In fact, the size of the market for recycled carbon fiber will be determined not by demand, but rather by the availability of supply, says Ulrich.
Spooner sees it as one of the recyclers' biggest challenges. To meet it, RCF Ltd. recently added Leslie Cooke to its U.S. staff. Formerly director of sales/marketing at Tacoma, Wash.-based Toray Composites (America) Inc., Cooke will, according to RCF's CEO Steve Line, help RCF secure carbon fiber feedstocks from the North American market. Those feedstocks will be processed at the European facility until a forthcoming U.S. plant is operational (circa. 2010-2011).
In the short term, Ulrich estimates a stable potential for 10 million to 15 million lb (4,536 to 6,804 metric tonnes) of carbon fiber recyclate from a combination of process scrap and end-of-life aircraft and parts from the aerospace sector. By 2029, Ulrich estimates the potential to reclaim more than 50 million lb (22,680.6 metric tonnes) of carbon fiber. “The timing of the transportation industry's adoption of continuous CFRP Carbon Fiber Composites is still speculative, but the impact could be significant if user-friendly materials develop,” he says. In the short term, Ulrich believes the automotive market is more likely to become a big customer base for recycled chopped carbon fiber, rather than a big supply base.
By contrast, wind energy has great future potential as a scrap supply source. “Wind turbine blades are expected to add more than 10 million lb [4,535.92 metric tonnes] of carbon fiber in large units of homogenous fiber,” Ulrich adds. “Recycling of large wind turbine blades will be profitable, attractive targets to the recyclers that win long-term contracts,” he foresees,”but that is 20 years into the future, at the end of their useful life.”
Another challenge is dealing with the diverse nature of the feedstock. “We can recycle dry waste, prepreg off-cuts, out-of-date prepreg, laminate off-cuts, tooling and end-of-life components,” says Spooner. “We might have high-modulus aerospace scrap or standard-modulus scrap, but we have to treat it all the same.” Processing scrap is the most consistent and continuous source of recyclable materials. For example, as much as 40 percent of a prepreg material can be scrapped during the manufacturing process.
At RCF Ltd., laminates are cut up prior to pyrolysis and the backing must be removed from prepregs. “There is a lot of processing involved in preparing the scrap,” says Spooner, noting that “much of it is done by hand.” When precisely controlled, the pyrolysis process, which heats the composite, in the absence of oxygen, to temperatures ranging from 752°F/400°C to 932°F/500°C, produces a clean carbon fiber that maintains 90 to 95 percent of its original properties. (Harmful gases emitted by epoxy resins during pyrolysis are siphoned off and incinerated, in accord with environmental guidelines, separately from the carbon to guard against fiber damage.)
“The issue for us is the consistency of the raw material and the consistency of the properties of our final product,” says Spooner. “We're using feedstock from aerospace and Formula One that is very good carbon. However, for industrial applications the stiffness can be too great,” he adds. “We try to blend the feedstock in a way that allows for constant properties.”
RCF Ltd. produces both milled carbon fiber (from 100 to 300 microns long) and chopped fiber (3 mm/0.12 inch to 25 mm/1 inch in length). Each batch is tested to ensure it meets the company's minimum standards: tensile strength of 3000 MPa and modulus of 200 GPa.
End-of-life to new life
One compelling aspect of recycling is the potential for manufacturers to optimize usage of the virgin fiber it buys. “There are clear product sustainability and cost advantages when you can take scrap from one manufacturing process and turn it into a feedstock for another part of your product,” Carberry claims, although he admits that the full extent of that advantage is not yet clear. “First, we have to clear the technological hurdles [of working with new technology], and then we have to qualify recycled carbon fiber for use on aircraft before we can begin to forecast the market potential.”
Toward that goal, Boeing worked with RCF Ltd., MIT, the University of Nottingham (U.K.) and Adherent Technologies to produce a proof-of-concept molded armrest using carbon fiber reclaimed from pre-production Boeing 787 parts. Although the short, chopped fibers yielded by recycling processes cannot replace continuous fibers in aerospace manufacturing, they could be used on tertiary aerospace parts. Further, Spooner sees high-quality recycled carbon fiber, milled and chopped, competing well with industrial-grade virgin fiber.
“We can always be competitive with milled and chopped virgin carbon fiber,” Spooner contends. “In theory, we're a little cheaper because we're not affected by carbon fiber prices in the world, and we know our costs to manufacture,” he explains. “Also, we can offer a consistency of supply because we have different supply routes than traditional carbon producers.”
Also in this vein, Stike says that MIT hopes to capitalize on the potential high quality of the recycled chopped carbon fiber, creating an effectively intermediate-modulus material that falls between virgin aerospace- and industrial-grade products. Toward that end, MIT separates carbon fiber scrap by modulus and then chops it to one-inch lengths prior to pyrolization. Stike reports that the company has worked with a number of major compounders to qualify its reclaimed material for use in compounded materials. MIT also plans to use much of its reclaimed fiber in-house, to manufacture complex fiber preforms for part manufacturers via its proprietary three-dimensional (3-D) engineered preform (3-DEP) process.
“The real value-added prospect for us is to feed our downstream processing in order to make preforms out of chopped fiber,” explains Stike, noting that MIT recently demonstrated this potential, dismantling and recycling carbon fiber from an F-18 stabilator provided by Boeing. Using its 3-DEP process, MIT produced a preform that was subsequently molded into a finished proof-of-concept wheelhouse for a Chevrolet Corvette by Molded Fiber Glass Co. (Ashtabula, Ohio). “We are currently working with potential end-users in both the automotive and aerospace industries,” says Stike (see photos, at right).
According to Firebird's president Thomas Hunter, however, carbon fiber recyclers who target end-uses will face several challenges along the way: “A lot of research has been done in the area of recycling the carbon fiber,” he says, but points out that “this research hasn't really focused on product applications.”
Typically, he contends, fiber produced from pyrolysis is not well suited for most molding operations without further treatment. Although the pyrolysis process creates a very active surface on the carbon fiber, which can promote good fiber/resin bonding, the process also removes the sizing and results in a fluffy, “cotton ball” of fibers. Firebird is working to fine-tune its microwave recycling technologies to produce raw recycled fibers that more closely resemble virgin fiber, says Hunter (see photo comparison, at right).
“You can't put a fluffy, dry fiber into a thermoplastic [compounding] machine, because it won't work,” Spooner agrees, and he believes that stepping beyond the recycling of raw fiber to facilitate new product development will be critical to widespread customer acceptance. RCF Ltd., for example, has compounded its milled and chopped fiber into thermoplastic pellets for injection molders. But Spooner also recognizes that such efforts are ultimately too narrowly focused. “We would like to get our fiber back into a broadgood,” he explains. “The composites market understands mats, not pellets or bags of fiber, so developing a mat-like product is something we feel like we must do,” he adds.
Boeing's Carberry, however, sees fiber orientation as a priority. “The recycled fiber strength and surface structure compares very favorably with virgin materials, with the exception that the fibers are short and random,” says Carberry. “The key to unlocking the manufacturing future for recycled fiber beyond injection molded applications is aligning the fibers.” Boeing is collaborating with others to develop that technology. In the same vein, Researchers at the University of Nottingham (U.K.) formed a roughly unidirectional fiber mat, using reclaimed discontinuous carbon fibers and a relatively simple fiber-alignment process (see the illustration at right, and see “Editor's Picks”).
Coordinating generator/recycler efforts
Although reclaimed scrap carbon fiber has a good deal of inherent value, all agree that cooperation between the scrap generator and the recycler will result in higher quality feedstocks and, therefore, a higher-quality recycled fiber that will retain more of that inherent value. Hunter suggests that greater involvement of the waste generator, in terms of material sorting and scrap component size-reduction, will reduce the risk of contaminants in the scrap and reduce the processing burden on the recycler.
Increased collaboration between carbon fiber recyclers and large scrap producers could dictate to some extent where recyclers build their plants, says Stike. “We envision building facilities in locations where the scrap is generated,” he says.
“You can't treat carbon scrap like it's aluminum being recycled for $1/lb,” Stike sums up. “If you're serious about this material, you need to take care of it on the front end. You have to treat it like it's an advanced material and realize that it can be reclaimed and the properties can be maintained.”
Carbon fiber recycling: Ongoing research
There is much ongoing research in the area of recycling carbon fiber. Among other things, researchers are looking for better ways to deal with contaminated carbon fiber-reinforced polymer (CFRP) scrap, methods to improve the overall properties of reclaimed fibers, and approaches to improve the processability of reclaimed fibers.
A team lead by Dr. Nicholas Warrior and Dr. Steve Pickering at the University of Nottingham (U.K.) has been studying the use of fluidized bed technology. The group believes the approach is well suited for end-of-life components that may contain a mixture of materials and contaminants and, therefore, are unsuitable for other recycling methods. In the fluidized bed process, crushed composites scrap material is placed in a reactor on a grate, and a stream of fluid (in this case, a gaseous airstream) is forced up through the material at a temperature of 550°C/1022°F. Organic material, including the composite’s resin matrix, is oxidized. However, the velocity of the airflow is such that as the organics burn off, the lightweight fiber is forced upward while heavier matter, such as metallic material, remains in the reactor “bed.”
The now clean fibers are removed from the reactor by the gas stream, which propels them into a cyclone separator, a conical /cylindrica chamber in which the air flows in a downward spiral pattern, and then is directed upward through the center of the chamber and flows out the top. The chamber geometry and airflow rate are set in such a way that carbon fibers in the tornado-like airstream are driven outward by centrifugal force, strike the outside wall and fall to the chamber bottom, where they can be collected. The process also provides users the potential to recover the heat energy from the fully oxidized polymer and use it to reduce the system’s energy consumption. However, according to Pickering, carbon fibers recovered using this approach currently exhibit a loss of strength, ranging from 25 to 50 percent.
However, Pickering sees great potential in the use of supercritical fluids in such processes. At a temperature and pressure above their thermodynamic critical point, these fluids can diffuse through the composite solids like a gas and then dissolve the materials like a liquid. Supercritical fluids, such as propanol, are being tested in thermal fluid processes under high pressure and at temperatures of 200°C to 300°C (392°F to 572°F) to break down epoxy resin into more elementary materials that, potentially, could be reused as chemical products. After processing, high-quality clean carbon fibers can be recovered. The reclaimed fibers reportedly retain up to 97 percent of the tensile strength of the virgin material, with no change in modulus.
Adherent Technologies Inc. (Albuquerque, N.M.) also continues research into carbon fiber recycling. Most recently, the company has developed a multistage recycling approach to address the thermoplastic toughened layers between the standard epoxy composite on Boeing’s 787. Adherent’s process is designed not only to reclaim the fiber but also to process the polymeric waste, breaking it down into more basic chemical building blocks that subsequently could be preprocessed into valuable chemicals or fuels.
Meanwhile, at Imperial College (London, U.K.), researchers are conducting extensive mechanical testing of composites manufactured from recycled fibers. Failure mechanisms are being used to build models and predict the performance of composites made from recycled fibers. One intriguing result, so far, is that testing indicates that when reclaimed fiber bundles held together by pyrolytic char are used as a reinforcement in a new molded product, they actually enhance the fracture toughness of the composite.
原文来源：世界复合材料
复合材料在线翻译
随着首套商业规模的碳纤维回收系统上线，越来越多的商家参与到再生碳纤维项目的研发之中。碳纤维回收利用是一个非常吸引人的市场定位，因为它不仅会得到金融业及政府研究奖励措施的支持，同时也符合许多制造商追求“绿色”的意愿。
几乎从飞机制造商波音和空客公司发出信号，表示他们有意在新飞机的设计中添加更多的轻质复合材料的那一刻起，一些大学、研究所及追逐利益的企业便加入了复合材料的再利用研发中。
美国Allstreams公司的总经理Carl Ulrich表示：复合材料的回收利用之所以展示出如此高的姿态，其中的一大原因是，飞机制造商在处理铝和其它金属的方面长久以来都实现了非常高的回收率，这让人羡慕不已。这在一定程度上也表明了，在过去的几年里波音和空客公司为何一直参与大量有关碳纤维回收利用的研究工作。以波音787为例，每架飞机携有近18，144千克可回收的碳纤维。波音公司、飞机再生利用协会的行业合作伙伴及空客公司希望在未来几年里通过PAMELA项目将飞机再生材料的回收率从70%提高到90%。
Ulrich介绍说：“碳纤维回收利用是一个非常吸引人的市场定位，因为它不仅会得到金融业及政府研究奖励措施的支持，而且制造商希望采用绿色生产工艺及制造绿色产品的愿望也会促进碳纤维回收利用项目的发展。”
材料创新技术公司是一家回收利用公司，其首席执行官Jim Stike声称，碳纤维的回收利用实际上为我们带来了三种绿色。它不仅可以阻止原始碳纤维在首次使用后被浪费在垃圾填埋场，而且利用再生碳纤维生产的部件还可被再次利用。因为碳纤维在回收时会保持其原始碳纤维的大部份性能，即使是在二次利用后也依然如此。此外，回收利用工艺还能显著减少能源消耗。据波音公司推算，回收碳纤维的费用大约是生产原始碳纤维的70%（每磅8到12美元VS 每磅15到30美元），而电能消耗量还不足生产原始碳纤维的5%（每磅1.3到4.5千瓦时VS每磅25到75千瓦时）。
考虑到这种潜能，处在不同发展阶段的可行性机械和热解技术都会被载入研发史册。波音公司飞机及复合材料回收部门的项目经理Bill Carberry说：“目前，不管是需要催化剂还是无需催化剂的热解工艺似乎都是领先技术。在研发的过程中还有其它一些回收技术，其中包括超临界流体和微波技术，不过这些技术大多只能在实验室中实现。”
最近，空客及PAMELA联合集团采用热解工艺来提取A380机身上的碳。PAMELA项目此阶段的目标是把在初期试验中学到的东西，尤其是拆除A300机身，应用在较大的A380飞机上，并设法扩大工艺规模，确定回收先进材料的最佳方法。据悉每架飞机含有25吨复合材料。
据Carberry透露，目前全球只有两家具有商业规模，可实现连续生产的回收企业，且都采用热解工艺。这两家企业分别位于英国和日本。
再生碳纤维有限公司（Recycled Carbon Fibre Ltd.）位于英国西米德兰兹郡，是这两家企业之一。该工厂装有一套长37米的高精准热解设备。据悉该设备具有回收约2，000吨废弃材料的能力，每年的再生纤维产量大约为1，200吨。
日本碳纤维制造商协会再生委员会成员包括日本东丽股份有限公司（Toray Industries Inc.），帝人集团分支机构东邦泰纳克公司（Toho Tenax Co.）及日本三菱公司（Mitsubishi Rayon Co.）。这几家公司联合创立了一家合资企业进行碳纤维回收。该回收工厂位于日本福冈县大牟田市，为日本三井矿业冶炼公司所有。2007年其实验厂开始运营，并在2008年通过检定。据报道，随着市场需求的增长，该工厂再生碳纤维的年产量将从最初的几百吨增加到1000吨。这些再生材料经组合后主要应用于家用电子产品及汽车行业。
在欧洲，再生碳纤维有限公司（RCF Ltd.）可以说只是冰山一角。许多潜在竞争者正在向大规模运营转型。例如，德国Hadeg Recycling 股份有限公司和CFK Valley Recycling 股份有限公司均已具备初级发展阶段的系统。另外，波音公司和意大利阿莱尼亚航空工业公司也将携手在意大利开启一家复合材料回收企业。
在美国，Adherent Technologies公司计划在不久的将来开启一个年再生材料生产能力为1000吨的工厂。美国火鸟先进材料有限公司（Firebird Advanced Materials Inc.）研发了一种专利连续微波回收方法，计划于今年实现商业化生产。麻省理工学院希望在本月底在离波音公司北查尔斯顿机身安装工厂不远处的莱克城开启一个占地4，645平方米的回收工厂。工厂成立之初，采用热解工艺每年可生产453.6吨再生碳纤维。Stike表示：“随着我们获得的废弃物的增多，我们会根据需要增加工作班次或工作单元。”
再生碳纤维有限公司（RCF Ltd.）销售及业务发展经理Martin Spooner很快就感到了压力。然而，成功的开启一个碳纤维回收工厂并非想象的那么容易。你需要进行大量的可行性调查研究，实验设备检测，并就未来的商业运行进行讨论。Spooner介绍说：“在较小试验机运行了近两年后，我们还花费了大约六个月的时间才使我们的新机器得以正常运行。”他又补充到：“从理论上讲，这很容易实现，但真正在现实中成规模的做起来的确是一项非常艰难的工作。”
其中的障碍之一是寻找优质碳纤维废弃物来源。Ulrich说：再生碳纤维的市场的规模实际上并非取决于需求，而是供应物的可用性。
Spooner认为这是再生材料制造商面临的最大挑战之一。为了满足这一需求，近日再生碳纤维有限公司（RCF Ltd.）邀请Leslie Cooke加入了其在美国的团队。Leslie Cooke是日本东丽公司（Toray Composites）在美国华盛顿州塔科马港市的分公司的前任销售/市场总监。据再生碳纤维有限公司首席执行官Steve Line透露，Cooke将协助他们获取北美市场上的碳纤维原料。这些原料将在欧洲工厂进行加工处理，直到未来美国工厂开始运营。
据Ulrich 推测：短期内来自航空航天领域的加工废料、报废飞机及部件可产生4536到6804吨碳纤维再生材料。截止到2029年，回收的碳纤维数量可能会达到2.26806万吨。
Ulrich表示：“交通运输业何时会采用连续碳纤维复合材料仍未确定，但如果易于使用的材料得到发展，那么其影响将会非常巨大。”他认为，在短期内汽车市场很有可能会成为再生短切碳纤维的大型的客户基础而并非供应基础。
相比之下，风能市场有巨大潜能成为未来碳纤维废弃物的供应源。Ulrich补充到：“飞机叶片预期会增加4535.92吨废弃碳纤维。对获得长期合同的回收商来讲，回收大型飞机叶片将会是一个有利可图、极具吸引力的目标。不过这要发生在20年后，风机叶片使用期满之时。”
我们面临的另外一个挑战是对回收原料的各种自然属性的处理。Spooner表示：“我们可对干燥废弃物、预浸料的下脚料、过期预浸料、层压材料下脚料、工具及报废零部件进行回收。我们也可能会对高模量或标准模量的航空航天废弃物进行回收，但不管是何种材料我们都要对其进行处理。加工过程中产生的废料是再生材料最持久不断的来源。例如，在制造过程中几乎40%的预浸料会被废弃。
在再生碳纤维有限公司（RCF Ltd.）的热解工艺中，层压制品在热解前先被切碎，其背衬也必须从预浸料中移除。Spooner表示：“在废弃材料的准备阶段，我们需要做大量的处理工作。”同时他还指出：“大部份处理工作都是手工完成的。”对热解工艺进行精确控制，在无氧环境中加热复合材料，并使其温度保持在400°C 到500°C之间，这样生产出的清洁碳纤维就能保持90%-95%的原始性能。
Spooner介绍说：“我们面临的问题还有废物原料是否一致，我们生产的成品的性能是否一致。我们所使用的原料均由航空航天及一级方程式锦标赛赛车产生，其中含有优质的碳材料。然而，就工业应用来说，它们的硬度可能太高了。我们试图采用一种方法对原料进行混合使再生材料具备固定的特性。
再生碳纤维有限公司（RCF Ltd.）不仅可生产再生压制碳纤维（长100微米到300微米）还可生产再生短切纤维（长3毫米到25毫米）。他们会对每批再生材料进行测试，以确保其满足公司的最低标准：抗张强度为3000 MPa，拉伸模量为200GPa。
由废弃到新生
回收利用过程中必须强制执行的一方面可能是制造商们要对所购买的原始纤维进行优化使用。Carberry声称：“如果你能够从制造过程中选取废料并将其转化成产品其它部件的原料，那么这些产品就具有明显的耐用性和成本优势。”不过Carberry承认，这些优势的整体范围仍不明确。“首先我们必须清除技术障碍，并在对潜在市场进行估测前对飞机上使用的再生碳纤维进行资格认证”
为了实现这一目标，波音公司与再生碳纤维有限公司，麻省理工学院，诺丁汉大学及Adherent科技公司携手合作，利用波音787飞机前期制作产生的再生碳纤维生产一种理念验证型模塑扶手。尽管在航空航天制造中再生短切纤维不能代替连续纤维，但可将其用在三级航空航天部件中！
Spooner声称：“与原始碾磨及短切纤维相比，我们总能保持竞争力。”对此，他解释到：“从理论上说，我们的产品要便宜一些。因为我们不受全球碳纤维价格的影响，我们清楚生产成本。另外，我们可以提供连续性供应。与传统碳纤维制造商相比，我们拥有各种各样的供应渠道。”
鉴于这种情况，Stike表示，麻省理工学院希望利用再生短切碳纤维的潜在高性能创造一种处于原始航空航天产品与工业级产品之间的高效中模量材料。为了实现这一目标，麻省理工学院根据碳纤维废弃物的模数对其进行分离，并在热解前将其切成一英尺长。Stike报道说, 麻省理工学院与多家主要混合物制造商合作，对其再生材料在混合材料中的应用进行资格认证。此外，麻省理工学院计划将其再生纤维更多的应用在房屋中，并通过其专利3D设计预成型工艺为零部件制造商生产复杂的碳纤维预成型产品。
Stike解释说：“对我们而言，真正的增值前景是为那些希望利用短且纤维生产预成型产品的下游加工业提供材料。” Stike指出：最近麻省理工学院对这一能性进行论证，拆除并分解了波音公司提供的F-18安全平尾的碳纤维。麻省理工学院采用其3-DEP工艺制造了一个预成型件，随后由Molded Fiber Glass Co.将其模塑成一个精致的概念验证型雪弗兰Corvette驾驶室。Stike说：“目前我们正与汽车行业及航空航天行业的潜在终端用户进行合作”。
据火鸟公司总裁Thomas Hunter说，不管如何那些将目标设为终端使用的再生碳纤维制造商都会遇到一些挑战。他指出：“尽管制造商们已经做了大量有关碳纤维回收的调查研究，但这些研究并未真正的集中在产品的应用上。”
他声称，通常由热解产生的纤维若不经进一步的处理对大多数模塑操作来说是不太适合的。尽管热解工艺为碳纤维创造了非常吸引人的表面，促进了纤维/树脂的粘合。不过，该工艺也除掉了纤维的成份，导致其变得松软，成为纤维“棉球”。Hunter透露：“火鸟公司将对其微波回收技术进行调整，以生产出更加类似与原始纤维的再生纤维原材料。”
Spooner对Hunter的观点持相同意见，他表示：“我们不能将松软的干燥纤维放入热塑性机器，因为机器是不会工作的。” Spooner认为，为促进新产品的发展而对纤维原材料回收以外的步骤所做的改进是广大用户接受再生碳纤维产品的关键性因素。以再生碳纤维有限公司为例，该公司已将其碾磨和短切纤维组合到了注塑商的热塑性颗粒物中。不过，Spooner认为到这些工作最终很难引起关注。他解释说：“我们希望使我们的纤维恢复成一种板材类产品。复合材料市场上的毡类物，而非碳纤维芯块或碳纤维袋状物。因此研发一种类似于毡类物的产品是我们必须要做的事情。”
然而波音公司的Carberry则将纤维定向作用视为重点。他表示：“与原始纤维材料相比，再生纤维除了较短且比较分散外，其强度及表面结构都非常有利。对纤维进行调整是打开注塑成型类应用产品外再生碳纤维制造未来的关键。”波音公司将与其它商家携手合作对此项技术进行研究。鉴于相同的情况，诺丁汉大学的研究人员采用非连续性再生碳纤维及一种相对简单的纤维调整工艺制造了一种粗糙的单向性纤维毡。
废料制造者与回收商的合作
再生碳纤维在很大程度上具备其固有价值。碳纤维废弃物制造者及碳纤维回收商进行合作的结果是更高质量废弃原料的产生。如此一来，更高质量的再生纤维将保留更多的固有价值。Hunter表示，如果废弃物制造者更大程度的参与到废料的分类及废料成份的规模减少中，那么废料中存在污染物的风险就会降低，同时还能减少回收商的加工压力。
碳纤维回收商与大量废料制造者不断增加的合作在一定程度上可能会决定回收商建造工厂的地址。Stike说：“我们预计在废料产生地建造工厂。”
Stike总结说：“你不能像回收铝那样以每磅1美元的代价处理碳废料。 如果你对该废料是认真的，那么你就需要关心其前端产品。你要将其视为先进的材料，认为可对其进行回收利用，并能使它保持原有的性能。”
碳纤维回收利用：大量研究
再生碳纤维领域有大量不断进行着的调查研究。除此之外，研究人员还在不断的寻找更好的处理受污染碳纤维增强聚合物废料的方法，增强再生纤维总体性能的途径以及提高再生纤维可加工性的渠道。
由来自诺丁汉大学的Nicholas Warrior及Steve Pickering教授带领的工作组一直在从事流化床技术应用的研究。该工作团队认为此方法非常适合那些可能含有其它混合物及污染物的报废部件，而其它回收途径并不适合这些部件。在流化床工艺中，将压碎的复合材料废料放入位于炉床的反应堆中，在550°C的高温度下，大量液体被升高并通过这些原料。在这个过程中有机材料被氧化掉，包括复合材料的树脂基体。气流的速度如此快以至于当有机物被烧掉时，轻质纤维被迫上升，而较重的物质，如金属材料则仍保留在反应堆的“床”上。
这样一来，通过气流将清洁碳纤维分离出来。这些气流推动清洁碳纤维进入旋风分离器-一个圆柱形或圆锥形的腔室，在这里气体以一种向下旋转的方式流动，之后定向上升，穿过腔室中心，流出顶口。分离器的形状及气流速度是以这样的方式确定的。碳纤维在类似于龙卷风式的气流上由离心力作用而被驱向外部，它们不断的冲击外壁，然后沉入分离器底部，并在此被收集起。此工艺使用户可以从完全氧化的聚合物中提取热能，以此来减少系统的能源消耗。不过，据Pickering说，目前采用此方法对碳纤维进行回收利用会使碳纤维的强度减少25%-50%。
尽管如此，Pickering认为在此类工艺中采用超临界流体具有巨大的潜能。在温度和压力均高于其热力学临界点时，这些液体可通过复合材料固体物，像气体一样分散开，然后将这些固体材料像液体一样分解开。在200到300摄氏度的高温高压下，采用热流体工艺中对超临界流体，如丙醇，进行测试，使其将环氧树脂分解成更多基本材料，且这些基本材料可在化学产品中重复使用。经加工处理后，就可获得优质的清洁碳纤维。据报道，再生纤维的拉升强度可达到其原始材料的97%且模数不发生任何改变。
此外，Adherent科技公司对碳纤维回收利用继续进行调查研究。最近，该公司研发了一种多阶段回收方法，用以处理波音787飞机上标准环氧树脂复合物的热塑性塑料加固层。Adherent公司的此工艺并非为回收纤维而专门设计的，它还可以处理聚合物的废弃物，将这些废弃物分解成更多最终可被加工成有价值的化学产品或燃料的基础性化学成份。
与此同时，英国帝国理工学院的研究人员就由再生纤维生产的复合材料的机械性能进行了大量测试。在这些测试中采用失效机理建造模型，并对由再生纤维制造的复合材料的性能加以预测。目前他们发现了一个非常有趣的测试结果，当采用热解工艺将再生纤维束聚集在一起时，烧焦物在新模塑产品中就会起到加固材料的作用，事实上这增强了复合材料的结构韧性。
原文：
Almost from the moment aircraft manufacturers The Boeing Co. (Seattle, Wash.) and Toulouse, France-based rival, Airbus, signaled their intention to reduce fuel consumption and emissions by incorporating more lightweight composites into new airplane designs, an array of universities, laboratories and for-profit enterprises have been involved in researching and developing ways and means to recycle them.
One big reason recycling has assumed such a high profile is that airframers, owing to a long history of working with aluminum and other metals, already had achieved an enviably high metal-recycling rate, says Carl Ulrich, managing director, Allstreams LLC (McLean, Va.). That explains, in part, why Boeing and Airbus have been integrally involved in much of the research into carbon fiber recycling over the past several years. Each Boeing 787, for example, carries approximately 40,000 lb/18,144 kg of salvageable carbon fiber. Boeing, with its industry partners in the Aircraft Fleet Recycling Assn. (AFRA, Washington, D.C.), and Airbus, through its Process for Advanced Management of End-of-Life Aircraft (PAMELA) consortium, are looking to increase the amount of aircraft recycled material from roughly 70 percent today to upwards of 90 percent in the coming years.
Revenue-capable and responsible
“Carbon fiber recycling is an attractive market niche because it's driven not just by the financials, but also by government research incentives, and by the desire for manufacturers to have green manufacturing processes and products,” explains Ulrich.
Jim Stike, the CEO of recycling firm Materials Innovation Technologies (MIT, Fletcher, N.C.) contends that carbon fiber recycling, in fact, offers “three shades of green.” It not only prevents the waste of virgin carbon fiber in landfills after its first use, but components produced using the recycled fiber are themselves recyclable, because carbon can retain a significant portion of its virgin properties even after a second reclamation. Further, the recycling process itself significantly reduces energy costs. Boeing estimates that carbon fiber can be recycled at approximately 70 percent of the cost to produce virgin fiber ($8/lb to $12/lb vs. $15/lb to $30/lb), using less than 5 percent of the electricity required (1.3 to 4.5 kWH/lb vs. 25 to 75 kWH/lb).
Given this potential, a number of viable mechanical and thermal recycling techniques are in various stages of development, an R&D history chronicled along the way in HPC (see first two items under "Editor's Picks," at right, and the sidebar at the end of this article). But one clear leader has emerged. “Pyrolysis, with and without the aid of a catalyst, seems to be the front-running technology at the present,” says Bill Carberry, program manager for Boeing's Airplane and Composite Recycling. “There are some other technologies in development that include supercritical fluids and microwaves, but these are still pretty much in the laboratory scale.”
Most recently, Airbus and its PAMELA consortium used pyrolysis to extract carbon from an A380 airframe. The goal of this phase of the PAMELA project was to take what had been learned during earlier experiments, most notably the dismantling of an A300 airframe, and apply it to the much larger A380 in an effort to scale-up the process and determine best practices for recovering advanced materials, including 55,000 lb (25 metric tonnes) of composites per plane
According to Carberry, there are, at present, only two commercial-scale, continuous production operations in the world, and both use pyrolysis. One is in the United Kingdom and the other in Japan.
In the U.K., Recycled Carbon Fibre Ltd. (RCF Ltd., West Midlands) now operates one of the two. Its plant houses a highly sophisticated 120-ft/37m long pyrolysis machine reportedly capable of recycling approximately 2,000 metric tonnes (4,409,250 lb) of waste material. The system's capacity is approximately 1,200 metric tonnes (2,645,550 lb) of recycled carbon fiber output per year.
In Japan, members of the Recycling Committee of the Japan Carbon Fiber Manufacturers Assn. (JCMA), including Toray Industries Inc. (Tokyo, Japan), Toho Tenax Co. (Tokyo, Japan), a member of the Teijin Group, and Mitsubishi Rayon Co. (Osaka, Japan), have formed a joint venture to recycle carbon fiber at a plant owned by Mitsui Mining Co. in Omuta City, which is in Japan's Fukuoka Prefecture. A test plant began operation in 2007, followed by verification in 2008. Reportedly, annual output of recycled carbon fiber at the plant will ramp up from several hundred metric tonnes initially to 1,000 metric tonnes (2.2 million lb) as demand increases. The recyclate, after compounding, is targeted primarily at the consumer electronics and automotive industries.
In Europe, RCF Ltd. is the tip of the iceberg. Potential competitors are moving toward commercial-scale operations. In Germany, for example, Hadeg Recycling GmbH and CFK Valley Recycling GmbH (both in Stade, Germany) have systems in the early stages of development. And Boeing and Alenia Aeronautica (Rome, Italy) continue joint efforts to open a composite recycling operation in Italy.
In the U.S., Adherent Technologies Inc. (Albuquerque, N.M.) plans to open a facility in the near future capable of processing 1,000 metric tonnes (2.2 million lb) of recyclate annually. Firebird Advanced Materials Inc. (Raleigh, N.C.) has developed a proprietary continuous microwave recycling method and plans to begin its commercialization this year. And in Lake City, S.C., not far from Boeing's North Charleston, S.C., fuselage subassembly plant, MIT expects to open a recycling plant by the end of this month. Initially, the 50,000-ft2 (4,645m2) facility will be capable of generating 1 million lb (453.6 metric tonnes) of carbon fiber per year using a pyrolysis process, says Stike. “As we get more scrap, we can add shifts or work cells as needed.”
Martin Spooner, sales and business development manager at RCF Ltd., is quick to stress, however, that even though there is a lot of viable research, testing of pilot machines and talk of upcoming commercial operations, successfully starting up a carbon fiber recycling plant is not as easy as it looks. “It took about six months for us to get our new machine up and running well,” says Spooner. “That was after running a smaller pilot machine for nearly two years,” he adds. “In theory, this is easy to do, but actually doing it in practice and at scale is a very difficult job.”
Securing & controlling feedstock
One obstacle is securing sources for high-quality carbon fiber scrap. In fact, the size of the market for recycled carbon fiber will be determined not by demand, but rather by the availability of supply, says Ulrich.
Spooner sees it as one of the recyclers' biggest challenges. To meet it, RCF Ltd. recently added Leslie Cooke to its U.S. staff. Formerly director of sales/marketing at Tacoma, Wash.-based Toray Composites (America) Inc., Cooke will, according to RCF's CEO Steve Line, help RCF secure carbon fiber feedstocks from the North American market. Those feedstocks will be processed at the European facility until a forthcoming U.S. plant is operational (circa. 2010-2011).
In the short term, Ulrich estimates a stable potential for 10 million to 15 million lb (4,536 to 6,804 metric tonnes) of carbon fiber recyclate from a combination of process scrap and end-of-life aircraft and parts from the aerospace sector. By 2029, Ulrich estimates the potential to reclaim more than 50 million lb (22,680.6 metric tonnes) of carbon fiber. “The timing of the transportation industry's adoption of continuous CFRP Carbon Fiber Composites is still speculative, but the impact could be significant if user-friendly materials develop,” he says. In the short term, Ulrich believes the automotive market is more likely to become a big customer base for recycled chopped carbon fiber, rather than a big supply base.
By contrast, wind energy has great future potential as a scrap supply source. “Wind turbine blades are expected to add more than 10 million lb [4,535.92 metric tonnes] of carbon fiber in large units of homogenous fiber,” Ulrich adds. “Recycling of large wind turbine blades will be profitable, attractive targets to the recyclers that win long-term contracts,” he foresees,”but that is 20 years into the future, at the end of their useful life.”
Another challenge is dealing with the diverse nature of the feedstock. “We can recycle dry waste, prepreg off-cuts, out-of-date prepreg, laminate off-cuts, tooling and end-of-life components,” says Spooner. “We might have high-modulus aerospace scrap or standard-modulus scrap, but we have to treat it all the same.” Processing scrap is the most consistent and continuous source of recyclable materials. For example, as much as 40 percent of a prepreg material can be scrapped during the manufacturing process.
At RCF Ltd., laminates are cut up prior to pyrolysis and the backing must be removed from prepregs. “There is a lot of processing involved in preparing the scrap,” says Spooner, noting that “much of it is done by hand.” When precisely controlled, the pyrolysis process, which heats the composite, in the absence of oxygen, to temperatures ranging from 752°F/400°C to 932°F/500°C, produces a clean carbon fiber that maintains 90 to 95 percent of its original properties. (Harmful gases emitted by epoxy resins during pyrolysis are siphoned off and incinerated, in accord with environmental guidelines, separately from the carbon to guard against fiber damage.)
“The issue for us is the consistency of the raw material and the consistency of the properties of our final product,” says Spooner. “We're using feedstock from aerospace and Formula One that is very good carbon. However, for industrial applications the stiffness can be too great,” he adds. “We try to blend the feedstock in a way that allows for constant properties.”
RCF Ltd. produces both milled carbon fiber (from 100 to 300 microns long) and chopped fiber (3 mm/0.12 inch to 25 mm/1 inch in length). Each batch is tested to ensure it meets the company's minimum standards: tensile strength of 3000 MPa and modulus of 200 GPa.
End-of-life to new life
One compelling aspect of recycling is the potential for manufacturers to optimize usage of the virgin fiber it buys. “There are clear product sustainability and cost advantages when you can take scrap from one manufacturing process and turn it into a feedstock for another part of your product,” Carberry claims, although he admits that the full extent of that advantage is not yet clear. “First, we have to clear the technological hurdles [of working with new technology], and then we have to qualify recycled carbon fiber for use on aircraft before we can begin to forecast the market potential.”
Toward that goal, Boeing worked with RCF Ltd., MIT, the University of Nottingham (U.K.) and Adherent Technologies to produce a proof-of-concept molded armrest using carbon fiber reclaimed from pre-production Boeing 787 parts. Although the short, chopped fibers yielded by recycling processes cannot replace continuous fibers in aerospace manufacturing, they could be used on tertiary aerospace parts. Further, Spooner sees high-quality recycled carbon fiber, milled and chopped, competing well with industrial-grade virgin fiber.
“We can always be competitive with milled and chopped virgin carbon fiber,” Spooner contends. “In theory, we're a little cheaper because we're not affected by carbon fiber prices in the world, and we know our costs to manufacture,” he explains. “Also, we can offer a consistency of supply because we have different supply routes than traditional carbon producers.”
Also in this vein, Stike says that MIT hopes to capitalize on the potential high quality of the recycled chopped carbon fiber, creating an effectively intermediate-modulus material that falls between virgin aerospace- and industrial-grade products. Toward that end, MIT separates carbon fiber scrap by modulus and then chops it to one-inch lengths prior to pyrolization. Stike reports that the company has worked with a number of major compounders to qualify its reclaimed material for use in compounded materials. MIT also plans to use much of its reclaimed fiber in-house, to manufacture complex fiber preforms for part manufacturers via its proprietary three-dimensional (3-D) engineered preform (3-DEP) process.
“The real value-added prospect for us is to feed our downstream processing in order to make preforms out of chopped fiber,” explains Stike, noting that MIT recently demonstrated this potential, dismantling and recycling carbon fiber from an F-18 stabilator provided by Boeing. Using its 3-DEP process, MIT produced a preform that was subsequently molded into a finished proof-of-concept wheelhouse for a Chevrolet Corvette by Molded Fiber Glass Co. (Ashtabula, Ohio). “We are currently working with potential end-users in both the automotive and aerospace industries,” says Stike (see photos, at right).
According to Firebird's president Thomas Hunter, however, carbon fiber recyclers who target end-uses will face several challenges along the way: “A lot of research has been done in the area of recycling the carbon fiber,” he says, but points out that “this research hasn't really focused on product applications.”
Typically, he contends, fiber produced from pyrolysis is not well suited for most molding operations without further treatment. Although the pyrolysis process creates a very active surface on the carbon fiber, which can promote good fiber/resin bonding, the process also removes the sizing and results in a fluffy, “cotton ball” of fibers. Firebird is working to fine-tune its microwave recycling technologies to produce raw recycled fibers that more closely resemble virgin fiber, says Hunter (see photo comparison, at right).
“You can't put a fluffy, dry fiber into a thermoplastic [compounding] machine, because it won't work,” Spooner agrees, and he believes that stepping beyond the recycling of raw fiber to facilitate new product development will be critical to widespread customer acceptance. RCF Ltd., for example, has compounded its milled and chopped fiber into thermoplastic pellets for injection molders. But Spooner also recognizes that such efforts are ultimately too narrowly focused. “We would like to get our fiber back into a broadgood,” he explains. “The composites market understands mats, not pellets or bags of fiber, so developing a mat-like product is something we feel like we must do,” he adds.
Boeing's Carberry, however, sees fiber orientation as a priority. “The recycled fiber strength and surface structure compares very favorably with virgin materials, with the exception that the fibers are short and random,” says Carberry. “The key to unlocking the manufacturing future for recycled fiber beyond injection molded applications is aligning the fibers.” Boeing is collaborating with others to develop that technology. In the same vein, Researchers at the University of Nottingham (U.K.) formed a roughly unidirectional fiber mat, using reclaimed discontinuous carbon fibers and a relatively simple fiber-alignment process (see the illustration at right, and see “Editor's Picks”).
Coordinating generator/recycler efforts
Although reclaimed scrap carbon fiber has a good deal of inherent value, all agree that cooperation between the scrap generator and the recycler will result in higher quality feedstocks and, therefore, a higher-quality recycled fiber that will retain more of that inherent value. Hunter suggests that greater involvement of the waste generator, in terms of material sorting and scrap component size-reduction, will reduce the risk of contaminants in the scrap and reduce the processing burden on the recycler.
Increased collaboration between carbon fiber recyclers and large scrap producers could dictate to some extent where recyclers build their plants, says Stike. “We envision building facilities in locations where the scrap is generated,” he says.
“You can't treat carbon scrap like it's aluminum being recycled for $1/lb,” Stike sums up. “If you're serious about this material, you need to take care of it on the front end. You have to treat it like it's an advanced material and realize that it can be reclaimed and the properties can be maintained.”
Carbon fiber recycling: Ongoing research
There is much ongoing research in the area of recycling carbon fiber. Among other things, researchers are looking for better ways to deal with contaminated carbon fiber-reinforced polymer (CFRP) scrap, methods to improve the overall properties of reclaimed fibers, and approaches to improve the processability of reclaimed fibers.
A team lead by Dr. Nicholas Warrior and Dr. Steve Pickering at the University of Nottingham (U.K.) has been studying the use of fluidized bed technology. The group believes the approach is well suited for end-of-life components that may contain a mixture of materials and contaminants and, therefore, are unsuitable for other recycling methods. In the fluidized bed process, crushed composites scrap material is placed in a reactor on a grate, and a stream of fluid (in this case, a gaseous airstream) is forced up through the material at a temperature of 550°C/1022°F. Organic material, including the composite’s resin matrix, is oxidized. However, the velocity of the airflow is such that as the organics burn off, the lightweight fiber is forced upward while heavier matter, such as metallic material, remains in the reactor “bed.”
The now clean fibers are removed from the reactor by the gas stream, which propels them into a cyclone separator, a conical /cylindrica chamber in which the air flows in a downward spiral pattern, and then is directed upward through the center of the chamber and flows out the top. The chamber geometry and airflow rate are set in such a way that carbon fibers in the tornado-like airstream are driven outward by centrifugal force, strike the outside wall and fall to the chamber bottom, where they can be collected. The process also provides users the potential to recover the heat energy from the fully oxidized polymer and use it to reduce the system’s energy consumption. However, according to Pickering, carbon fibers recovered using this approach currently exhibit a loss of strength, ranging from 25 to 50 percent.
However, Pickering sees great potential in the use of supercritical fluids in such processes. At a temperature and pressure above their thermodynamic critical point, these fluids can diffuse through the composite solids like a gas and then dissolve the materials like a liquid. Supercritical fluids, such as propanol, are being tested in thermal fluid processes under high pressure and at temperatures of 200°C to 300°C (392°F to 572°F) to break down epoxy resin into more elementary materials that, potentially, could be reused as chemical products. After processing, high-quality clean carbon fibers can be recovered. The reclaimed fibers reportedly retain up to 97 percent of the tensile strength of the virgin material, with no change in modulus.
Adherent Technologies Inc. (Albuquerque, N.M.) also continues research into carbon fiber recycling. Most recently, the company has developed a multistage recycling approach to address the thermoplastic toughened layers between the standard epoxy composite on Boeing’s 787. Adherent’s process is designed not only to reclaim the fiber but also to process the polymeric waste, breaking it down into more basic chemical building blocks that subsequently could be preprocessed into valuable chemicals or fuels.
Meanwhile, at Imperial College (London, U.K.), researchers are conducting extensive mechanical testing of composites manufactured from recycled fibers. Failure mechanisms are being used to build models and predict the performance of composites made from recycled fibers. One intriguing result, so far, is that testing indicates that when reclaimed fiber bundles held together by pyrolytic char are used as a reinforcement in a new molded product, they actually enhance the fracture toughness of the composite.
原文来源：世界复合材料
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