Could 'liquid wood' replace plastic?

    液體木材能替代塑料嗎？

    Almost 40 years ago, American scientists took their first steps in a quest to break the world's dependence on plastics. But in those four decades, plastic products have become so cheap and durable that not even the forces of nature seem able to stop them. A soupy expanse of plastic waste – too tough for bacteria to break down – now covers an estimated 1 million square miles of the Pacific Ocean.

    Sensing a hazard, researchers started hunting for a substitute for plastic's main ingredient, petroleum. They wanted something renewable, biodegradable, and abundant enough to be inexpensive.

    Though they stumbled upon a great candidate early on, many US chemists had given up on it by the end of the 1990s. The failed wonder material: lignin, the natural compound that lends strength to trees. A waste product from paper production, much of the lignin supply is simply burned as fuel.

    But while many scientists turned to other green options, a German company, Tecnaro, says it found the magic formula. Its "liquid wood" can be molded like plastic, yet biodegrades over time.

    Now, Tecnaro's success could revive interest in lignin and propel the search for better and cheaper bioplastics.

    "The lignin itself was misunderstood completely by [leaders in the field] and the majority of people," says Simo Sarkanen, an environmental science professor at the University of Minnesota.

    The formula is everything

    This past holiday season, nativity figurines made from Tecnaro's "liquid wood" raised eyebrows among the bioplastic community. Sold as Arboform, the tough mixture is chock full of lignin – sometimes more than 50 percent, compared with the 30 percent threshold where many researchers would max out. The rest is fiber from wood, flax, or hemp, as well as a few additives.

    Raw Arboform consists of dark brown pebble-sized pellets. It is processed using the same equipment used to make

    conventional plastic. The granules are dropped into a barrel and heated until they melt. Then the contents are highly pressurized and forced into a rigid mold – that of a figurine, perhaps.

    As the liquid cools, Arboform actually conforms better than most plastics to the boundaries of complex molds, says Benjamin Porter, a researcher with Tecnaro. The 10-year-old, 10-person operation based in Ilsfeld, Germany, is very secretive about its ?liquid-wood formula – so proprietary that Dr. Sarkanen is a little skeptical. In 2001, his lab patented a simpler lignin-based plastic, one that lacks the secret combination of additives in Arboform.

    With several years of successful sales, the company takes on one or two new employees annually. And as the company grows, so does the catalog of Arboform products, according to Mr. Porter. The current lineup includes watches, keyboards, hairbrushes, and, recently, caskets. Future possibilities include car interiors and furniture. "We haven't built a house though – yet," Mr. Porter jokes.

    Arboform's nativity figurines showcase a new grade of the material. Its sulfur content is much lower than Tecnaro's original recipe, says Emilia Regina-Inone of the Franhoefer Chemical Institute, which works with Tecnaro to test Arboform. And it can be broken down and reused eight or 10 times without wrecking the material's mechanical properties, such as its relatively high fire-resistance and durability.

    But there are tradeoffs. All versions of Arboform are heavier, more brittle, and more expensive than conventional plastics. Arboform costs about $1.60 per pound when purchased in bulk, compared with less than a dollar for a pound of polypropylene, a traditional plastic. Tecnaro produces about 6.6 million pounds of Arboform each year, a capacity that Porter says consistently increases 10 percent each year.

    America has a taste for starch

    Tecnaro's products sell in Australia, Brazil, and Colombia, but mostly in Europe, where consumers are more willing to pay for environmentally conscious products – and producers must pay to recycle petroleum-based plastics.

    The US mostly backs a different plastic substitute. After giving up on lignin, American scientists focused on starch – a cheap and renewable resource, though one also important to food production.

    Cereplast, based in Hawthorne, Calif., harnesses starch from corn, tapioca, wheat, and potatoes to produce a resin capable of replacing at least 50 percent of the petroleum in conventional plastics. Dwarfing upstarts like Tecnaro, the company's California facility can pump out 50 million pounds of starch-based plastic a year for compostable forks and biodegradable containers.

    But tapping the potential of long-neglected lignin could not only cut the amount of plastic thrown away each year, but could also slow current greenhouse gas emissions. In trees, lignin naturally stores carbon dioxide during photosynthesis.

    When papermakers discard unwanted lignin, the carbon is still trapped inside it – until they burn the lignin. At that point, much of the CO2 is released into the atmosphere.

    "If you can make plastics, or any useful kinds of polymeric materials from lignins … this, of course, would help reduce the rate of global warming quite significantly," Sarkanen says.

    And the question of what to do with lignin instead of burning it is quickly becoming an urgent one. The US Department of Agriculture has mandated that 30 percent of transportation fuels must come from plant materials by 2030.

    大約40年前，為了讓世界擺脫對塑料的依賴，美國科學(xué)家開始了最初的研究。但是在過去40年，塑料制品變得廉價且耐久，甚至沒有任何自然力能阻止他們。由于很難被細(xì)菌分解，估計塑料垃圾如今已密布100萬平方英里的太平洋。

    感到危害嚴(yán)重，研究者們開始尋找塑料主要成分--石油--的替代品。他們想要可再生、可降解并且豐富，價廉的材料。

    雖然研究者早就偶然發(fā)現(xiàn)了一種不錯的替代材料，但是在20世紀(jì)90年代末許多美國化學(xué)家放棄了它。這種不成熟的神奇材料就是木質(zhì)素，一種能使樹木強(qiáng)壯的自然化合物。它是造紙產(chǎn)生的廢物，多數(shù)木質(zhì)素僅被當(dāng)作燃料燒掉了。

    然而，正當(dāng)許多科學(xué)家轉(zhuǎn)向其它綠色替代物時，一家叫Tecnaro的德國公司聲稱找到了奇妙的配方。這種 "液體木材",可以像塑料一樣被塑造，但隨著時間卻能生物降解。

    現(xiàn)在，Teconaro公司的成功重新喚起了人們對木質(zhì)素的興趣，同時推動了對更優(yōu)質(zhì)、低廉的生物塑料的探索。

    正如明尼蘇達(dá)大學(xué)環(huán)境科學(xué)教授西莫？薩凱南所言，"木質(zhì)素本身完全被該領(lǐng)域的領(lǐng)導(dǎo)者以及大多數(shù)人所誤解。"

    配方?jīng)Q定一切

    在剛剛過去的假期里，用Tecnaro公司的"液體木材"制成的耶穌誕生小塑像在生物塑料界引起了轟動。這種材料是一種堅韌的混合物銷售時名為Arboform,里面基本上全是木質(zhì)素，有時超過50%,遠(yuǎn)遠(yuǎn)超出許多研究人員認(rèn)為的30% 的上限。其余的材料是木纖維、亞麻、大麻纖維以及一些添加劑。

    Arboform原料是深棕色的鵝卵石大小的顆粒物，可用制造傳統(tǒng)塑料的設(shè)備對其加工。把這種材料的顆粒倒進(jìn)桶里加熱直至熔化。然后施以高壓，最終被擠壓成硬模--或許，那就是一個小雕像的模子。

    正如Tecnaro公司的研究人員本杰明？波特所言，隨著液體冷卻下來，和絕大多數(shù)塑料相比，事實上Arboform材料會更好地將復(fù)雜模具的邊緣塑造成型。坐落于德國的Ilsfeld的這家公司已有10年歷史，擁有10名員工，對它的液體木材配方高度保密--正因為是獨有的技術(shù)，以至于薩凱南博士對此有點質(zhì)疑。在2001年，他的實驗室發(fā)明了一種更簡單的木質(zhì)素基塑料，其中

    不含有Arboform材料里面那些保密的添加劑組合。

    根據(jù)波特先生的介紹，經(jīng)過幾年的成功銷售，這家公司每年都能招收1到2名新員工。隨著公司的成長，由Arboform材料制成的產(chǎn)品也日益豐富起來。當(dāng)前的列表里包括手表、鍵盤、發(fā)梳。最近，還增加了首飾盒。未來有可能推出的產(chǎn)品還包括汽車內(nèi)飾件和家具。波特先生開玩笑說，"雖然我們還未制造過這種材料的房子，但不是不可能的。"

    Arboform材料的耶穌小塑像顯示這是一種新級別的材料。與Tecnaro公司一起測試Arboform的弗勞恩霍夫化學(xué)研究所的艾米莉亞？里賈納·伊諾說，它的含硫量要遠(yuǎn)低于Tecnaro公司原有的配方，可以被分解，并重復(fù)使用達(dá)到8-10次而不損害材料的機(jī)械特性。如較高的防火及耐久性。

    但這種新材料也有一些不足之處。和傳統(tǒng)塑料相比，所有種類的Arboform材料都更重一些，更易碎，而且價格更高。比起每磅不足1美元的傳統(tǒng)聚丙烯塑料，大批量購買的Arboform還得花費(fèi)每磅1.6美元。Tecnaro公司每年生產(chǎn)大約660萬磅的Arboform.波特先生說，其生產(chǎn)能力可以每年10%的速度持續(xù)增長。

    美國偏愛淀粉制品

    Tecnaro公司的產(chǎn)品在澳大利亞、巴西和哥倫比亞銷售，但主要市場還是在歐洲，因為那里的消費(fèi)者更愿意付費(fèi)購買有環(huán)境意識的產(chǎn)品--而生產(chǎn)商則必須為循環(huán)利用那些石油基塑料來埋單。

    但美國卻大力支持另一種不同的塑料替代品。放棄了對木質(zhì)素的研究以后，美國的科學(xué)家們把精力集中到淀粉上--這是一種廉價且可再生的資源。盡管其對食品生產(chǎn)也是十分重要的。

    位于加州霍桑市的Cereplast公司利用來自玉米、木薯、小麥以及土豆的淀粉來生產(chǎn)一種樹脂，能夠替代普通塑料生產(chǎn)中至少50%的石油。這家公司的產(chǎn)能遠(yuǎn)遠(yuǎn)超過像Tecnaro這樣的新貴。它在加州的設(shè)施每年可生產(chǎn)5000萬磅的淀粉基塑料，用來制造全分解的叉子和可生物降解的容器。

    然而開發(fā)長期被忽視的木質(zhì)素的潛能不僅能減少每年被丟棄的塑料，而且能減少當(dāng)前溫室氣體的排放。在樹木內(nèi)木質(zhì)素通過光合作用自然存儲二氧化碳。

    如果造紙商們拋棄不需要的木質(zhì)素，碳仍然存于其中--直到他們燒掉木質(zhì)素。而在燒掉木質(zhì)素時，很多二氧化碳就被排放到大氣中。

    薩凱南教授說，"如果能用木質(zhì)素生產(chǎn)塑料或任何有用的高分子材料……當(dāng)然有助于顯著大大減緩全球變暖的速度。"

    除了燃燒以外，如何處理木質(zhì)素很快將成為一個迫切的問題。美國農(nóng)業(yè)部已經(jīng)下令到2030年以前30%的運(yùn)輸用燃料必須來源于植物材料。