Video Extras 2: Lost At Sea Transcript

Ellen and Kathy making rubber

Better latex than ever

How do you make a life-jacket out of kapok, rubber and the chemical process of vulcanisation? Find out more about rubber and vulcanisation.

Follow Ellen as she collects latex and makes rubber, as part of the BBC/OU's programme website for Rough Science 5

Ellen	So this should be able to make us control how quickly the rubber coagulates.
Kathy	So it’s really runny now, it’s just like milk. Enough?
Ellen	Yeah. And a lot - actually, maybe not quite so much.
Kathy	Okay.
Ellen	And a lot of this is actually just water. I really want to separate the rubber part.
Kathy	From the water?
Ellen	Yeah.
Kathy	Okay, shall I get squeezing?
Ellen	Yeah.
Kathy	So, I’m just adding an acid. I’ll add a bit and see what happens, yeah?
[SOUND OF STIRRING]
Ellen	Mmm! It’s getting thicker. Yeah. Can you tell that?
Kathy	It is, it’s like cream.
Ellen	Yeah.
Kathy	So it is coagulating.
Ellen	Mmm.
[SOUND OF STIRRING]
Kathy	Wow! That’s great.
Ellen	Do some more.
Ellen	So we can get it the exact consistency that we want.
Kathy	Okay. But we should keep on adding, to see whether we can add too much.
Ellen	Mmm. Yeah, and then we'd get a lump.
Ellen	Oh my word. [LAUGHTER] …
Kathy	No way!
Ellen	Look at this stuff!
Kathy	That’s fantastic!
Ellen	Wow! And it’s really malleable, look.
Kathy	Fantastic! Hey, that worked so quickly. That’s incredible. So we can, just before we want to coat the life jacket.
Ellen	Mmm.
Kathy	We can tip in some lemon juice. Make it really thick - as thick as we want it.
Ellen	Well actually don’t we want to, tip in some lemon juice, make it begin to get thick, dip it really fast, and then let it coagulate on there.
Kathy	Yep.
Ellen	Wow, this is -
Kathy	That’s fantastic!
Ellen	Yeah, it’s a little bit brittle though. And that’s why we want to finish curing it so it doesn’t -
Kathy	So we can make it tougher.
Ellen	- break so easily.
Kathy	And more elastic.
Ellen	Mmm. Yeah.
[SOUND OF LIQUID BEING POURED]
Ellen	So this is the pure latex and we're going to filter a little bit of it - strain it.
Kate	So what’s the difference between latex and rubber?
Ellen	Latex is -
Kathy	That -
Ellen	Basically the milky stuff that flows in the trees.
Kate	Yeah, because that’s what I was expecting. When you said you were going to get rubber, I was expecting that you come back with something black.
Ellen	No, that happens later.
Kate	Okay.
Ellen	It, it starts off and basically you have molecules, globules -
Kate	Yeah.
Ellen	- of rubber, mixed in with water.
Kate	Okay.
Kathy	And it is just like milk, it’s just held there, in an emulsion.
Kate	Wow.
Ellen	And so our goal is to get it to coagulate just enough for us to put it on the cloth and make it watertight.
Kate	So you’re going to effectively make me like a mackintosh almost!
Kathy	Yes, exactly.
Kate	Alright.
Kathy	Exactly. Now you’re going to help us.
Kate	Yeah.
Kathy	To make it coagulate. So if you just squeeze that into there.
Kate	What lemon juice will start the, the sort of... gumming up process for it?
Ellen	Lemon juice is an acid.
Kate	Right.
Ellen	And so, just a moment ago, we poured about the same amount as we poured in here.
Kate	Yeah.
Ellen	Added lemon juice - and we didn’t move fast enough!
Kathy	Now the thing is Kate, you’ll see this isn’t really strong enough, it’s not elastic enough, it just breaks too easily.
Kate	Yeah, yeah.
Kathy	It’s not like rubber.
Kate	Yeah.
Kathy	What we’re going to do is add a bit of sulphur. Now you can just get this from garden centres and things.
Kate	Yeah.
Kathy	And the vulcanising process involves sulphur.
Kathy	What you want to do, imagine that in here there are lots and lots of molecules. Rubber molecules.
Kathy	And they’re all kinds of strands like this, waving around.
Kate	Yeah. Sort of separate strings?
Kathy	Separate strings, that’s right.
Kate	Okay.
Kathy	Now, when you vulcanise it.
Kate	Yeah.
Kathy	You cross them together and form little bridges between them and you form a net.
Kate	Oh okay.
Ellen	Like a fishing net.
Kate	Yeah.
Ellen	Very uniform.
Kathy	And that net you can kind of stretch. And then it will bounce back. Because of the little sulphur bridges.
Kate	Ahhh. Okay.
Kathy	Without the net. Those strands just come apart.
Kate	Would just, would just snap.
Kate	So this whole process is going to mean that you then have something absolutely workable and hopefully for my sake, waterproof.
Kathy	Strong, elastic, waterproof.
Ellen	Yeah, and that’s also where it will turn from this beautiful white.
Kate	Mmm-huh.
Ellen	To a more smoky, golden or even black. Because when we think of rubber we think of black.
Kate	We think of it being black.
Ellen	Yeah, that’s the vulcanisation process that causes that to happen.
Kate	Brilliant.