Could 'liquid wood' replace plastic?

液体木材能替代塑料吗？

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.

大约40年前，为了让世界摆脱对塑料的依赖，美国科学家开始了最初的研究。但是在过去40年，塑料制品变得廉价且耐久，甚至没有任何自然力能阻止他们。由于很难被细菌分解，估计塑料垃圾如今已密布100万平方英里的太平洋。

感到危害严重，研究者们开始寻找塑料主要成分--石油--的替代品。他们想要可再生、可降解并且丰富，价廉的材料。

虽然研究者早就偶然发现了一种不错的替代材料，但是在20世纪90年代末许多美国化学家放弃了它。这种不成熟的神奇材料就是木质素，一种能使树木强壮的自然化合物。它是造纸产生的废物，多数木质素仅被当作燃料烧掉了。

然而，正当许多科学家转向其它绿色替代物时，一家叫Tecnaro的德国公司声称找到了奇妙的配方。这种 "液体木材",可以像塑料一样被塑造，但随着时间却能生物降解。

现在，Teconaro公司的成功重新唤起了人们对木质素的兴趣，同时推动了对更优质、低廉的生物塑料的探索。

正如明尼苏达大学环境科学教授西莫？萨凯南所言，"木质素本身完全被该领域的领导者以及大多数人所误解。"

配方决定一切

在刚刚过去的假期里，用Tecnaro公司的"液体木材"制成的耶稣诞生小塑像在生物塑料界引起了轰动。这种材料是一种坚韧的混合物销售时名为Arboform,里面基本上全是木质素，有时超过50%,远远超出许多研究人员认为的30% 的上限。其余的材料是木纤维、亚麻、大麻纤维以及一些添加剂。

Arboform原料是深棕色的鹅卵石大小的颗粒物，可用制造传统塑料的设备对其加工。把这种材料的颗粒倒进桶里加热直至熔化。然后施以高压，最终被挤压成硬模--或许，那就是一个小雕像的模子。

正如Tecnaro公司的研究人员本杰明？波特所言，随着液体冷却下来，和绝大多数塑料相比，事实上Arboform材料会更好地将复杂模具的边缘塑造成型。坐落于德国的Ilsfeld的这家公司已有10年历史，拥有10名员工，对它的液体木材配方高度保密--正因为是独有的技术，以至于萨凯南博士对此有点质疑。在2001年，他的实验室发明了一种更简单的木质素基塑料，其中

不含有Arboform材料里面那些保密的添加剂组合。

根据波特先生的介绍，经过几年的成功销售，这家公司每年都能招收1到2名新员工。随着公司的成长，由Arboform材料制成的产品也日益丰富起来。当前的列表里包括手表、键盘、发梳。最近，还增加了首饰盒。未来有可能推出的产品还包括汽车内饰件和家具。波特先生开玩笑说，"虽然我们还未制造过这种材料的房子，但不是不可能的。"

Arboform材料的耶稣小塑像显示这是一种新级别的材料。与Tecnaro公司一起测试Arboform的弗劳恩霍夫化学研究所的艾米莉亚？里贾纳·伊诺说，它的含硫量要远低于Tecnaro公司原有的配方，可以被分解，并重复使用达到8-10次而不损害材料的机械特性。如较高的防火及耐久性。

但这种新材料也有一些不足之处。和传统塑料相比，所有种类的Arboform材料都更重一些，更易碎，而且价格更高。比起每磅不足1美元的传统聚丙烯塑料，大批量购买的Arboform还得花费每磅1.6美元。Tecnaro公司每年生产大约660万磅的Arboform.波特先生说，其生产能力可以每年10%的速度持续增长。

美国偏爱淀粉制品

Tecnaro公司的产品在澳大利亚、巴西和哥伦比亚销售，但主要市场还是在欧洲，因为那里的消费者更愿意付费购买有环境意识的产品--而生产商则必须为循环利用那些石油基塑料来埋单。

但美国却大力支持另一种不同的塑料替代品。放弃了对木质素的研究以后，美国的科学家们把精力集中到淀粉上--这是一种廉价且可再生的资源。尽管其对食品生产也是十分重要的。

位于加州霍桑市的Cereplast公司利用来自玉米、木薯、小麦以及土豆的淀粉来生产一种树脂，能够替代普通塑料生产中至少50%的石油。这家公司的产能远远超过像Tecnaro这样的新贵。它在加州的设施每年可生产5000万磅的淀粉基塑料，用来制造全分解的叉子和可生物降解的容器。

然而开发长期被忽视的木质素的潜能不仅能减少每年被丢弃的塑料，而且能减少当前温室气体的排放。在树木内木质素通过光合作用自然存储二氧化碳。

如果造纸商们抛弃不需要的木质素，碳仍然存于其中--直到他们烧掉木质素。而在烧掉木质素时，很多二氧化碳就被排放到大气中。

萨凯南教授说，"如果能用木质素生产塑料或任何有用的高分子材料……当然有助于显着大大减缓全球变暖的速度。"

除了燃烧以外，如何处理木质素很快将成为一个迫切的问题。美国农业部已经下令到2030年以前30%的运输用燃料必须来源于植物材料。