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| 教 育 專 題 深 入 報 導《2007-06-01》 |
| 本期內容 | |
| ◎國際專題：Plastic: Past, present and endangered future塑膠──過去、現在與消逝的未來 | |
| ◎英國地方超市停用塑膠袋 | |
| 國際專題：Plastic: Past, present and endangered future塑膠──過去、現在與消逝的未來 | |
| 策劃、編譯■唐澄暐 | |
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當比利時化學家貝克蘭在1907年7月11日的日記中寫下「我知道這會是個重大發明」的時候，他恐怕還沒想到他的成果，未來居然能夠形塑現代生活的全貌。 貝克蘭帶著化學學位移民美國紐約，在自家的車棚裡和一堆樹脂髒東西共事了5年。這些東西是甲醛和酚類的反應副產品，又經過一台叫「電木爐」的爐子加熱後，產生了一種又硬又輕巧，又能做成任何形狀的物質。 這種被稱為「電木」的物質，是全球有史以來第一種完全以合成方式產生的物質。一百年過去，電木所衍生的塑膠已形塑了、甚至覆蓋了我們的世界。環顧四周，從手機、電腦、信用卡，甚至你環顧四周時戴著的隱形眼鏡，這些物質都是塑膠，這種「萬用物質」的變形。 當貝克蘭在1944年過世時，美國每年已經製造了40萬噸的塑膠。今天，全球的塑膠製造量已達到恐怖的每年1億噸，等於是每秒鐘做出6萬個兩公升塑膠桶，而且這數量還在繼續增加中。 尋找替代原料 但就在我們越來越倚賴這種物質的時候，有一個基本概念是不能忘記的：製造塑膠不可缺少的原料就是石油。要把一桶石油做成塑膠，就得再花一桶油的能量來當燃料。統計起來，塑膠每天消耗掉7百萬桶油，佔全球供應量的8％。由於石油的存量預計數十年間就將耗盡，尋找替代物質的方案也跟著加快腳步。 解決辦法之一，是由可循環的作物來製作塑膠。基本上，生物塑膠並不是什麼新概念。由木材和棉花製成的賽璐珞，早在1850年代就被發明出來作為象牙撞球的替代品。但就像其他早期發明的可循環塑膠一樣，賽璐珞缺乏合成塑膠的可變性和發展性，因此現在多半只能拿來做領口襯料和乒乓球。 用玉米或甘蔗做成的生物塑膠現在已較為廣泛使用，用來製成可分解的購物袋或是托盤，但缺點是造價過高，而且容易融化。 環保塑膠 細菌做的 不過，如果美國的生物科學公司的計劃可行，問題就可迎刃而解。上個月，美國麻州研究公司Metabolix發表了新塑膠的大量製造計畫，這種塑膠只需要用細菌、甜玉米和空氣就可以製造。公司總裁吉姆‧巴柏表示，這種可分解的聚合物稱作Mirel，遇滾水也不會融化，是目前市面上最環保的塑膠。「相比起石油塑膠，Mirel可將製造過程產生的溫室氣體減少1／3。而且因為不是由石油製成，因此整個製造所需的石油用量幾乎少了80％。」 但Mirel最聰明的就是其「生長」方式。目前大部分的生物塑膠生產方式，都是從玉米或穀物萃取出澱粉，發酵產生酸類，並經過多種化學配方來完成。然而，Metabolix的科學家培養了一種細菌來完成所有上述的工作。科學家只須加入玉米的糖分和氧氣，然後就只要看細菌慢慢在體內生成塑膠。然後，利用某種尚未公開的方式，細菌體內的塑膠可以「收成」並製造塑膠小球、塑造成各種產品。 「Mirel具備替代傳統塑膠的體質。」巴柏表示。「但我們一開始會專注在用後即丟的物品上，例如剃刀、塑膠袋和包裝這些用量大、使用次數少的塑膠產品。」 以英國為例，每年丟棄的塑膠達到3百萬噸，其中一半以上都是包裝用，其中只有10％有回收，其他多半拿去掩埋，或散落在海灘、路邊，繼續在那裡存在個幾十年或一個世紀。但Mirel不一樣，「它可以在任何環境中分解，包括土壤、或是在家用或公用的堆肥，甚至在河湖海洋中。」巴柏表示。 這種新物質確實有環保的條件，但Mirel等可循環物質真能滿足我們對塑膠貪得無饜的需求嗎？英國國家非食用股務中心的科學家約翰‧威廉斯博士表示，過去兩年的需求快速成長讓生物塑膠有了更大的潛力。「人們常跟我說：『你看，世界上有幾百萬噸的塑膠，你要用什麼東西來把它全部替換掉啊？』但我們回頭看看1940年的塑膠聚丙烯，當時只被認為是一種廢棄物，沒有人想得到後來反而會生產那麼多。我相信可循環塑膠也會依這個過程發展。」 在美國，Metabolix則開始小步進展。公司正在玉米大洲愛荷華建造廠房，大量生產Mirel，預計每年生產5萬噸，然而這只是目前塑膠產量的九牛一毛。但Metabolix的科學家即將有所突破，他們採取的方式幾乎有點科幻：放棄使用無污染的鋼桶來製造Mirel，而改用植物的葉與莖。 科學家也放棄從玉米中取出糖份，加入細菌發酵的過程。公司栽種了一種體內具有酵母菌的草。草中的細菌直接攝取草中的醣分，生產天然的塑膠，並儲存在葉或莖中。這種「塑膠植物」收成後，就可以萃取塑膠。Metabolix已經使用了柳枝稷（switchgrass）來「試種」塑膠。這種草遍佈於北美的草地中，公司希望未來的3、4年可以在野外栽培這種塑膠草。 巴柏表示，製造大量生物塑膠的關鍵，就是在多功能精煉廠中結合塑膠生產與生物燃料製造。當塑膠從從柳枝稷提煉出來時，柳枝稷剩下的90％可以用來製作乙醇燃料，甚至直接拿來發電。而且，生產的過程也不受限於氣候。在歐洲，芒草也被拿來製造生物燃料，也同時可以製作塑膠。在其他較溫暖的地區，甘蔗也可以產生同樣的用途。「利用這種方法，你真的可以將天然塑膠視為石油塑膠的可行替代品，至少一半的量。」 發展生物塑膠也有風險 以全球規模來說，這樣的生產等於是每年5千萬噸，更引起越來越多的環保人士對其土地衝擊感到憂心。在巴西，生產乙醇的玉米和其他穀物替代了40％的汽車汽油，但也替換了上百萬英畝的草原和雨林。上個星期，聯合國的報告警告，如果缺乏完善經營，生產生物燃料可能造成比本來更嚴重的危害。 「這是一個議題」，巴柏表示。「但在今年，美國將栽種9千萬英畝的玉米，足以滿足現在的需求，因此未來也就會有休耕地來種植柳枝稷和其他作物。」 威廉斯承認，這類工業仍在初步階段，但他相信生物塑膠很快就能趕上石油塑膠。「我不認為在20年內可以達到50％的占有率，但也許能達到20％，何況在一兩年前，這還是完全無法想像的事情。」 不知道一百年前創造出劃時代科技的貝克蘭，面對「塑膠農場」和「生物精練」會有什麼反應？「我覺得他會感到興奮而好奇」，蘇珊‧摩斯曼，《早期塑膠：1850～1950透視圖》的作者表示。「他過世前曾說，如果他能再活一次，他會想為人類做善事，所以我想如果他看到塑膠能夠幫助環境，他應該會極度著迷。」 When a Belgian chemist named Leo Hendrick Baekeland ended his diary entry for 11 July, 1907, with the words "I know this will be an important invention", he could not have dreamt of the extent to which his brainchild would shape modern life. Having emigrated to the US with a chemistry degree, Baekeland had spent five years in a converted barn at his New York home experimenting with a resinous gunk - the by-product of a reaction between formaldehyde and phenol - and an oven he named "The Bakelizer". The result: a hard, light substance that could take on any shape. A hundred years on, Bakelite, the world's first fully synthetic material, has spawned a plethora of plastics that have moulded our world. Look around you: your mobile phone; your computer; your credit card; even your contact lenses - they all rely on some variant of plastic, or "the material of a thousand uses", as Baekeland marketed his creation. At his death in 1944, the US was producing 400,000 tons of plastic a year. Today, annual production worldwide has rocketed to 100 million tons - the equivalent of 60,000 two-litre drink bottles every second - and in the UK consumption is still rising by 4 per cent a year. But as we increasingly rely on the polymer, plastic could not exist without one ingredient: oil. For every barrel of oil that goes into making plastic, another is required to fuel the process. In total, plastics account for seven million barrels of petroleum per day - that's 8 per cent of global supply. With reserves expected to last mere decades, the race is on to find an alternative. The solution could lie in plastics made from raw ingredients found growing in fields. So-called bioplastics are not new. Celluloid, which is made from wood and cotton, was developed as an alternative to ivory in billiard balls in the 1850s. But, like other early renewable plastics, it lacked the versatility and viability of synthetic polymers; today, it is more often used to make shirt collar stiffeners and ping-pong balls. Bioplastics made from crops such as maize or sugar cane have become more widespread, turning up in products such as biodegradable shopping bags and tomato trays, but many are expensive to produce, or melt at low temperatures. That could change if an American bioscience company has its way. Last month, the Massachusetts research firm Metabolix announced plans to mass-produce a plastic made using only bacteria, sweetcorn and air. Jim Barber, the company's chief executive, says the biodegradable polymer, called Mirel, can handle boiling water and is the greenest plastic on the market. "Mirel cuts by two-thirds the greenhouse gases released by the manufacture of petroleum-based plastics," he says. "And because it's not made using oil, we cut petroleum use by about 80 per cent." But what's really clever about Mirel is the way it is "grown". Most modern bioplastics are manufactured by extracting starch from maize or other crops and fermenting it to produce an acid, which then undergoes a series of chemical treatments to create a plastic polymer. The scientists at Metabolix have engineered microscopic bacteria to do all that work for them. They add sugar from the maize, as well as oxygen, and watch the microbes swell as tiny plastic particles form inside them. Using a secret process, the particles are then harvested to create the pellets that can be moulded into a range of products. "Mirel has the physical properties to be a useful alternative to most traditional plastics," says Barber. "But initially we're focusing on disposable items, such as razors, plastic bags and packaging, which use so much plastic and just get thrown away." In the UK, we bin nearly three million tons of plastic a year, more than half of which comes from packaging. And less than 10 per cent of that is recycled - the rest ends up in landfill, or strewn along beaches and roadsides, where it can remain for decades or even centuries. Mirel is different. "It will break down in almost any environment, including soil, in industrial or domestic compost, or even in rivers and seas," says Barber. Its green credentials are clear, but can Mirel and other renewable materials ever hope to satisfy our enormous appetite for plastic? Dr John Williams, a scientist at the UK's National Non-Food Crops Centre, says rapid growth in the past two years has given bioplastics great potential. He says: "People often say to me, 'Look, there are millions of tons of polypropylene in the world - how the heck are you going to replace all that?' But let's go back to the 1940s when polypropylene was just a waste material - nobody could have imagined we would be producing it on such a huge scale today. I believe renewable plastics can go the same way." Back in the US, Metabolix is starting small. The company is building a plant in the "Tall Corn State" of Iowa that will churn out Mirel at an annual rate of 50,000 tons - a fraction of the demand for plastics. But Metabolix scientists are on the verge of a breakthrough: using a process that sounds more like science fiction than fact, they plan to transfer the machinery used to produce Mirel from the stainless-steel vats of the processing plant into the leaves and stems of the plants themselves. Rather than take the sugar from corn and add it to microbes in a fermenter, Metabolix will cultivate a grass already loaded with the bacteria. The modified microbes take some of the sugar produced by the plant every day via photosynthesis and transform it into natural plastic that grows inside the leaves and stems. This "plastic plant" can then be harvested and the polymer extracted for conversion into pellets. Metabolix has already "farmed" plastic in trials using a plant called switchgrass, a prairie grass that grows naturally across swathes of North America. The company hopes to get the grass into the field in the next three or four years. Barber says the key to producing large quantities of bioplastics is to combine plastic making with the manufacture of biofuels in multi-purpose refineries. Once the plastic is harvested from switchgrass, the rest of the plant - about 90 per cent of its biomass - can be used to produce ethanol fuel, or even burned to generate electricity. And the process will not be restricted to climates where switchgrass thrives. A grass called miscanthus is already used in parts of Europe to produce biofuels, and could be engineered to make plastic at the same time. In warmer parts of the world, other crops such as sugar cane could do the job just as well. "Using this method you really can look at natural plastic as an alternative to a substantial portion of petroleum-based polymers - I would say around half," says Barber. On a global scale, that would equate to 50 million tons a year, and an increasingly vocal band of environmentalists is expressing concerns about the impact that will have on land. In Brazil, where ethanol derived from corn and other crops has replaced 40 per cent of the gas guzzled by cars, millions of acres of savannah and rainforest have been turned over to bio crops. Last week, a UN report warned that if not managed carefully, growing crops for biofuels can do more harm than good. "It is an issue," says Barber. "But this year about 90 million acres of corn will be grown in the US, which is enough to meet current needs, and in the future there are substantial amounts of set-aside land that could take switchgrass and other crops." John Williams admits the industry is still "dipping its toe in the water" but he is confident that bioplastics will soon catch up with their oil-based counterparts. "I can't see them being 50 per cent of the market 20 years from now, but it might be 20 per cent, and that was unthinkable only two years ago." What would Baekeland, whose iron Bakelizer was at the cutting edge of technology 100 years ago, make of plastic farms and biorefineries? "I think he would have been really excited and intrigued," says Dr Susan Mossman, author of Early Plastics: Perspectives, 1850-1950, and curator of Plasticity, an exhibition which opens at the Science Museum this month. "Before he died he said that if he could lead his life again, he would do something for the good of mankind, so I think he'd be fascinated by the idea of plastics actually helping the environment." http://news.independent.co.uk/sci_tech/article2549917.ece |
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| 英國地方超市停用塑膠袋 | |
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根據英國剛上任的南諾弗克區自治會主席喬‧姆尼表示，為了讓該區更乾淨、明亮而綠化，他要求所有超級市場禁止使用任何塑膠袋。 喬‧姆尼說，他希望在該區域達到超市完全禁止使用的目摽，以保護環境。「以我個人所能言範圍，我認為超市有很大的機會來為環境盡一份心力，我並打算鼓勵他們完全放棄使用塑膠袋。他們必須提供可分解購物袋。我相信消費者的回應，能夠補償超市的多餘支出。」 目前，店家每年送出的購物袋超過130億個，而本週由英國環境大臣大衛‧密爾班提出的垃圾策略評論，也包括了針對超市塑膠袋徵收一便士收費的提案。 英國第4大零售業者Marks and Spencer已經在北愛爾蘭實施每個塑膠袋收費5便士，而在莫德柏力的南德文鎮，則是整個鎮的43家商店一起停用塑膠袋。這些店家提供5便士的可分解玉米澱粉袋，或鼓勵消費者自己帶老式的購物袋。 而Sainsbury超市則販售由英國名牌Anya Hindmarch所設計，價格5英鎊的可重複利用購物袋，上面有造型拉風的一行「我不是塑膠袋」，更引起英國各大媒體的報導。當英國女星綺拉‧奈特莉等名流被媒體拍到攜帶這款購物袋之後，還引發了英國國內排隊搶購購物袋，更使購物袋成為時尚配件。 Sainsbury在諾弗克大雅茅斯的店面，也已全面在櫃檯停止發送塑膠袋，並開始發送可重複利用的「一生之袋」。在上一次的公益活動日當天，大雅茅斯的店面送出了9千個價值10便士的「一生之袋」，這些紙袋可以重複使用20次，這代表這樣一天的活動，整個大雅茅斯的消費者省下了18萬個塑膠袋。 http://www.eveningnews24.co.uk/content/News/story.aspx?brand=ENOnline&category=News&tBrand=enonline&tCategory=news&itemid=NOED28%20May%202007%2009%3A00%3A21%3A657 |
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