Answers for Dr Karl #1: Plastic Bags and Chicken Juice

Dr Karl is a smart guy. He has an extraordinary broad knowledge of science in general, as well as human and animal physiology.

The reason for this, of course, is that as a professional educator he gets to read a lot. I am, of course, intensely jealous – and one day hope to have the kind of job that he has.

I love listening to his regular segments on the ABC on Thursdays where people call in and ask him questions. Mostly he has an answer, but occasionally he gets asked a question relating to chemistry that he is unable to answer.

This should not surprise anyone, of course, – Dr Karl himself would be the first to admit that no one knows everything, and anyone who has a call-in radio show and is never stumped is having a lend of their audience. When I had my radio show on 6PR for example, it was quite common for me to say “I’ll have to look into that and get back to you next week.”

Anyhow, for the chemistry questions that Dr Karl can’t answer, luckily I am here.

Last week a caller asked why “chicken juice” leaks through plastic bags. What he was getting at was that whereas if you put water into a plastic bag it wouldn’t leak, if you had some chicken (or meat) in a plastic bag sitting on your kitchen bench top, when you pick it up later on invariably some of the juice has seeped through.

Why is it so?

The answer is simply that plastics are not completely impervious. That is, if you zoom down into the molecular microstructure of plastic bags you will see that it’s essentially a jumbled mess of strands with holes everywhere. The plastic bags that we get from the supermarket are PVC and because they are so thin there are enough faults in the microstructure to allow some things to seep through.

Imagine if you cooked up a kilogram of spaghetti and then tipped it out onto the floor and let it dry. When it had tried it would be a solid lump spread out on the floor. But although it would be a solid lump, between all the overlapping strands there would be gaps. Plastic is essentially the same. At a microscopic level it is made up of polymer strands all jumbled together with only weak interactions between them.

We know that there is weak interaction between the polymer chains, because the bag is flexible. That is, the polymer chains are able to move and flex in relation to each other.

And the reason that some liquids will leak through the bag, whereas water won’t, is probably related to the surface tension of water. If you put a drop of water on a hard surface and then put a drop of metho next to it you would observe a curious phenomenon: whereas the metho drop would flatten out on the surface, the drop of water would sit proud of the surface and would appear round on the edges.

The reason for this is the surface tension of water, which, because it is a polar compound, is very high. This surface tension would mean that the water would not be able to squeeze through the little faults in the plastic, but if there were other substances dissolved in the water they would tend to have the effect of decreasing the surface tension. This would mean that the liquid might be able to seep more readily through the pores.

Incidentally, anyone who works in the chemical industry knows this. Gloves ain’t gloves. If you are working with a toxic chemical that you need to protect your hands from, you need to know what type of glove to use, as some chemicals will seep right through certain gloves, and the most expensive chemical gloves are made up of multi layers of different plastics, to cover all their bases.

So that clears up one of life’s great mysteries – stay tuned for more “answers for Dr Karl.”

Are White Sugar and White Rice Bleached?

I was asked a very interesting question today – are white sugar and white rice white because they have been chemically bleached?

it’s a good question – if chlorine bleach had been used in anything you ate it would obviously be a cause of concern.

And there have been cases of this kind of thing in the past. It used to be the case that decaffeinated coffee was decaffeinated with dichloromethane, a carcinogenic chemical that you certainly don’t want to be ingesting. At that time there was only one brand that was doing it a different way – HAG.

HAG coffee used supercritical carbon dioxide to decaffeinated their coffee. this was a more expensive process, the much safer as the CO2 quickly evaporated. So be other brands abandoned the dichloromethane and now also use supercritical CO2.

Back to sugar and rice.

As it happens, neither of these products have been bleached. The explanation for the white colour is simply the extra processing.

For sugar, all the brown stuff in brown sugar is impurities that are removed as part of the refining process. In other words, white is the natural colour of sugar crystals (sucrose). So it hasn’t been bleached – it has just been further purified.

And with rice, a similar situation is the case. If you take brown rice and polish it further, you eventually get back to white rice. In other words, brown rice is simply white rice with extra coatings on top. Once these coatings are polished away as part of the refining process, they become white.

Eo there you go – white rice and white sugar are perfectly safe to use. even if they may not be perfectly safe for your waistline.

The Great Preen Con

In 1985 I formulated the first Preen Trigger:







The brief I was given was that I had to mimic the performance of the legendary Preen aerosol – the great unstainer.

This was not easy, as the aerosol contained trichloroethane – dry cleaning solvent – with astonishingly good stain dissolving properties. I couldn’t use this product in the trigger, because it was too volatile, and also the plastic components wouldn’t have survived.

So I eventually came up with a formula that used a paraffinic solvent that worked better than the aerosol on some things (oils and greases) and not so well on others (inks and dyes).

There wasn’t any real competition – there was a product called Charge (an S.C.Johnson product) that was…wait for it….water based.

How we laughed at Charge! What type of bozos would think that they could get away with making a water-based prewash? In my stain tests, Preen killed it in every area except one – clay (not unexpected as the inorganic nature of clay makes it more susceptible to a water based approach).

But then I left the company, and Preen was in someone else’s hands.

And then some years later, a Brent Smyth in marketing had an idea – if they switched to a water based formula they could make more money. So they went to the guys in the lab, and the conversation probably went like this:

Marketing Guy: can we make Preen water-based?

Lab Guy: Are you kidding? It won’t work nearly as well.

Marketing Guy: that’s okay – we’ll change the packaging, and no one will notice.

So now, Preen looks like this







the selection of the bright pink colour no doubt was the result of focus group marketing, which would associate it with cleaning power.

This change, which happened in 2004, was probably marketed as an improvement to the formula, along with an increase in price. But all they are doing is attempting to conceal from you the fact that this is a cheaper product. If they sold the product more cheaply, it may alert you to this fact, so they go the other way and increase the price, thus keeping you into believing it is a superior product.

Well guess what Brent – people have noticed. Whenever people mention Preen to me, the word they most associate it with is “useless.”

But it gets worse than this. There is now not one Preen trigger product but three – Original, Oxy Action, and Ultra-Degreaser. So they now want you to buy three products instead of one. You are being conned.

You see, there is no reason that the ingredients in all these three products cannot be combined into one formula.

The reason they do this is that this way you have to buy three times as many products. So you are being doubly conned – not only are you paying more for a cheaper product, but you are now forced to buy three of them.

The result of Preen going water-based, is that now every man and his dog is making a laundry prewash – Sard, Orange Power, White King, and several others, including Coles and Woolworths.

For my next appearance on Today Tonight, I’m going to carry out a comprehensive tests of all of these, as well as chucking in a few other products that will surprise you.