(单词翻译:单击)
Odds are, you probably have a roll of cling wrap tucked away in a kitchen drawer, ready for wrapping up your leftovers.
你家厨房的抽屉里一定藏着一卷保鲜膜用来包裹你吃剩的食物 。
For a lot of people, it's a kitchen staple.
对于大多数人而言,这是厨房订书机 。
But if you've been buying the stuff for years, you might've thought that it just doesn't work as well as it used to.
但是如果这些年你一直在使用保鲜膜的话,你或许会发现这些保鲜膜的效果没以前那么好了 。
And for once, you're not imagining it.
就那么一次,你就没往下想了 。
The gold standard for cling wrap used to be the Saran Wrap brand, made by the company SC Johnson.
保鲜膜的黄金标准曾是莎伦食物包装膜,这种保鲜膜的生产公司是庄臣公司 。
But around the early 2000s, the company actually changed their formula to a version that was less sticky and generally less effective.
但是早在2000年,该公司就将保鲜膜的配方换成另一个版本:粘性更小、效果也没那么好了 。
Thankfully, they at least had a good reason for it.
不过至少,他们有更改配方的充分理由 。
Saran Wrap was originally made out of a chemical called polyvinylidene chloride, or PVDC.
莎伦食物包装膜起初是有一种被称为聚偏二氯乙烯或PVDC的化学物质制成 。
It was actually discovered by accident by a chemist at another company, Dow Chemical, in 1933.
这种物质事实上是1933年另一家公司陶氏化学的一位化学家意外发现的 。
It formed as a sticky residue in beakers that had been used to develop a chlorine-based dry-cleaning chemical.
它是由烧杯中的粘性残余物形成,烧杯中的物质被用来开发氯基干洗化学制品 。
And not that dry-cleaning isn't fascinating or anything, but PVDC turned out to have some interesting properties of its own.
并不是那种干洗不够惊艳,只是PVDC本身就有些有趣的特质 。
It's a special kind of chemical compound called a polymer, a molecule in which a bunch of identical, smaller molecules are linked to form a long chain.
这是一种特别的化合物—聚合物,在分子内一些相似且更小的分子相连形成一个长链 。
There are all kinds of these, but PVDC was especially useful because it forms a nearly impenetrable barrier to odors,
还有很多其他物质,但是PVDC尤其有效,因为它能形成近乎不可逾越的屏障抵御气味,
making it ideal for wrapping and preserving food.
使之成为包裹和储存食物的理想材料 。
That's because it has a super-low permeability: the rate at which it lets liquid or gases pass through it.
这是因为,它有着极低的渗透性:液体和气体都无法穿过 。
Scientists think this is probably thanks to the densely packed, unbranched, stable structure of its molecular chains.
科学家认为这可能是由于分子链密集包裹、无分支且稳定的结构 。
Dow first sold this super-effective Saran Wrap in 1953, and SC Johnson bought the formula and the brand name in 1998.
陶氏于1953年首次出售这种高效莎伦食物包装膜,1998年,庄臣公司购买了其配方和品牌名称 。
But around that time, concerns started to surface about chlorine-containing compounds like PVDC.
但是大约在那个时期,人们开始担心含氯的化合物,比如PVDC 。
It turns out that when they're thrown away and burned in municipal trash incinerators, they can release toxic chemicals.
原来当这种材料被丢弃并扔进市政垃圾焚烧炉时,它们会释放出有害的化学物质 。
When this came to light, SC Johnson made the responsible decision to eliminate PVDC from all of its products by 2004.
当危害曝光后,庄臣公司决定截止2004年底将消除产品中的PVDC 。
After some research, they made a new cling wrap formula that used chlorine-free polyethylene.
经过一些研究后,他们制成了一种新的保鲜膜配方—使用不含氯气聚乙烯 。
It's another polymer that's okay, but definitely not as good at trapping odors and keeping food fresh.
这是另一种聚合物,不会产生危害,但是却无法有效阻挡气味和保持食物新鲜 。
See, depending on the temperature, one square meter of a thin film of PVDC will let about 1 to 5 grams of water vapor pass through it in a day.
这取决于温度,一平方米的PVDC薄膜一天渗透1-5克水汽 。
But for low-density polyethylene, that ranges from 16 to 31 grams, a big difference.
但是低密度聚乙烯会渗透16-31克水汽,差别还是很大的 。
And the difference in their oxygen transmission rates is even more impressive,
而它们之间的氧气透过率差异甚至更大,
jumping from about 2 to 16 cubic centimeters per day for PVDC to almost 8,000 for polyethylene.
PVDC为每天约2-16立方公分,而聚乙烯将近8,000立方公分 。
That's a lot of numbers, but the bottom line is that this new cling wrap just doesn't have the same odor-trapping, freshness-preserving magic that it once did.
数据很多,但是结果就是新品保鲜膜没有之前的有效 。
And maybe even worse, this polyethylene mix doesn't even seem to be quite as clingy.
甚至更糟糕,这种聚乙烯混合物甚至都没什么粘性 。
But if the switch means putting less toxic pollutants into the atmosphere, I think we can all probably make do.
但是如果这种转变意味着给大气制造的有毒污染物更少的话,我觉得我们还是能接受的 。
Thanks for asking, and thanks to all of our patrons on Patreon for keeping the questions coming.
感谢提问,感谢Patreon上一直提问的赞助人们 。
If you'd like to submit a question or vote on which one we'll answer next, you can go to patreon.com/scishow.
如果你想提问或给问题投票,请登录patreon.com/scishow