Science and Technology Plastics There and back again

　　科技 塑料 舊法新用

　　An old idea may help solve the problem of plastic waste

　　PLASTICS were once regarded as wonder-materials. They are still ubiquitous, but find less favour than they used to because of the very stability and persistence that won them plaudits in the first place. Persistence is not a quality to be desired in something that gets thrown away, and so much plastic is used in packaging, and in articles that are disposable, that many people now see conventional petrochemical plastics as a nuisance and a threat.

　　一個老方法也許可以幫助解決塑料垃圾的問題

　　塑料曾一度被認為是材料中的奇跡。如今，塑料仍然無處不在，但是正是由于起初為它們贏得掌聲的穩定和持久性，使得它們不再擁有當初的追捧。對于一些會被丟棄的物品來說，持久性并不是一種值得擁有的性質，而且塑料被大量使用在包裝袋以及一次性物品中。目前，常規石油化工塑料已經被看做是一種公害和威脅。

　　The search is on, then, for biodegradable alternatives. One possibility has recently been explored by David Schiraldi of Case Western Reserve University, in Ohio, and his colleagues. They propose to reach back into history and revive the use of a feedstock that was used to make some of the first plastics invented: milk.

　　此后，尋找生物可降解替代品的研究一直在持續。最近，俄亥俄州凱斯西儲大學的David Schiraldi及其同事已開辟了一條潛在途徑。他們追溯歷史并改良了塑料在發明之初時所使用的原料---牛奶的使用方法。

　　What they actually suggest is using casein, the principal protein found in milk. The curds (of "curds and whey") are mostly made of this protein. In 1889 a French chemist called Jean-Jacques Trillat discovered that if casein is treated with formaldehyde the result is a hard, shinysubstance that does well as a substitute for materials like ivory and tortoiseshell. Sowidespread was the enthusiasm for the new material that Queen Mary herself ordered several pieces of jewellery made from it. However, casein-based plastic of this sort is too brittle for general use. It was eventually superseded by the modern, petrochemical variety, andmanufacture stopped altogether by the 1970s.

　　事實上，他們的建議就是使用牛奶中的主要蛋白質---酪蛋白，凝乳(凝乳及乳清)中的大部分成分都是由酪蛋白組成。1889年，法國化學家Jean-Jacques Trillat發現被甲醛處理過的酪蛋白會生成一種堅硬而有光澤的物質，并可以作為鐵及龜甲類材料的替代品。之后，這種新材料受到了廣泛的熱衷以至于瑪麗女王自己都定制了一些用這種材料制作的珠寶。但是，這類酪蛋白塑料由于過于脆弱而無法成為一種通用材料。其最終被現代石油化工衍生物所超越，并在20世紀70年代全面停產。

　　The thought of reviving it, though, has never quite gone away, and these days the fact that it is made mostly of protein, and could thus be chewed up by bacteria, is regarded as a virtue—if only the structural weakness could be overcome. Dr Schiraldi's approach does this by using a silicate clay called sodium montmorillonite as a skeleton that holds the plastic together.

　　然而對其進行改良的思想一直沒有完全散去，如今看來，只要能夠克服結構脆弱的問題，酪蛋白由蛋白質組成并且會被細菌吞噬的性質反而成為了一大優點。Schiraldi博士的方法是用一種叫做蒙脫土的硅酸鹽粘土作為骨架將酪蛋白塑料固定在一起。

　　Sodium montmorillonite can be freeze-dried into a spongelike material known as an aerogel. Aerogels are famously fragile. But that is because they are mostly empty space. Indeed, they are sometimes nicknamed "solid smoke". This fragility disguises an underlying stiffness. Filling the pores in the aerogel with plastic should remove its fragility and, conversely, the networkof clay molecules in the aerogel will stop the plastic cracking. So the researchers reckoned that if they mixed casein with the clay and added glyceraldehyde (which substitutes for thepoisonous formaldehyde used in the original plastic), they might be able to make something really rather useful.

　　蒙脫土可以被冷凍干燥成一種叫做氣凝膠的海綿狀材料。因為主要是空心，所以氣凝膠是一種有名的易碎材料。事實上，它們有時候也被戲稱為 "固態煙"。 其實，他們的易碎性掩蓋了他們堅強的一面。如果將酪蛋白塑料灌入氣凝膠的細孔，那么氣凝膠將不再易碎，相反，氣凝膠中粘土分子的網狀系統同樣會防止酪蛋白塑料破裂。所以，研究者們認為如果他們將酪蛋白與粘土混合在一起并添加甘油醛(用來取代原先塑料中所使用的含毒性的甲醛)，將形成一種非常有用的材料。

　　To test their ideas the team mixed a solution of casein with glyceraldehyde and sodium montmorillonite and vigorously stirred the result to get rid of the bubbles before freezing it at 80°C below zero. Once frozen, the material was placed in a freeze-dryer that removed all the water from it over the course of four days. It was then cured for 24 hours in an oven at 80°C above zero.

　　為了驗證他們的想法，研究小組將一瓶酪蛋白溶液與甘油醛及蒙脫土進行充分混合以去除氣泡并在零下80度下進行冷凍。在冷凍后，將此材料在冷凍干燥機中放上4天以去除所有水分。隨后，再將其在80度烤箱中存放24小時。

　　The researchers report in Biomacromolecules that their new material matches the stiffness, strength and compressibility of expanded polystyrene, a common packaging material that is thebane of many a rubbish dump. However, unlike polystyrene, it goes away once it has been dumped. An initial experiment suggested that 20% of it vanished within 18 days in a dump-likeenvironment. A comedown, perhaps, from being a queen's brooch. But far more useful.

　　研究者們在《生物大分子》雜志上的報告稱他們的新材料在硬度，強度以及壓縮性上均可以與發泡聚苯乙烯相匹敵，而后者則是一種常見的包裝材料同時也是垃圾場中的一大公害。但是，與聚苯乙烯所不同的是，這種新材料一旦被丟棄并會分解。一個早期實驗顯示，在諸如垃圾場的環境中，此新材料在18天內便可分解20%。也許，它也不再適合做女王的胸針了，但卻有更大的用途。

　　To test their ideas the team mixed a solution of casein with glyceraldehyde and sodium montmorillonite and vigorously stirred the result to get rid of the bubbles before freezing it at 80°C below zero. Once frozen, the material was placed in a freeze-dryer that removed all the water from it over the course of four days. It was then cured for 24 hours in an oven at 80°C above zero.

　　為了驗證他們的想法，研究小組將一瓶酪蛋白溶液與甘油醛及蒙脫土進行充分混合以去除氣泡并在零下80度下進行冷凍。在冷凍后，將此材料在冷凍干燥機中放上4天以去除所有水分。隨后，再將其在80度烤箱中存放24小時。

　　The researchers report in Biomacromolecules that their new material matches the stiffness, strength and compressibility of expanded polystyrene, a common packaging material that is thebane of many a rubbish dump. However, unlike polystyrene, it goes away once it has been dumped. An initial experiment suggested that 20% of it vanished within 18 days in a dump-likeenvironment. A comedown, perhaps, from being a queen's brooch. But far more useful.

　　研究者們在《生物大分子》雜志上的報告稱他們的新材料在硬度，強度以及壓縮性上均可以與發泡聚苯乙烯相匹敵，而后者則是一種常見的包裝材料同時也是垃圾場中的一大公害。但是，與聚苯乙烯所不同的是，這種新材料一旦被丟棄并會分解。一個早期實驗顯示，在諸如垃圾場的環境中，此新材料在18天內便可分解20%。也許，它也不再適合做女王的胸針了，但卻有更大的用途。