Book Extract #4: What are stains?

We use the word “stain” to refer to anything that does not wash out of our garments or other things (carpets, driveways etc.) easily.  To understand why, we need to zoom right down into the micro structure and see what’s actually happening.

Imagine that you took a packet of potato chips, crushed them between your hands, and then sprinkled them over a thick shag pile carpet.  Vacuuming it up would not be easy, as the tiny little grains would fall into every nook and cranny in the carpet and get stuck as you tried to vacuum them out.

The little bits of chip would not actually be stuck to the carpet in the same way that it would be if it was glue, but simply physically entrapped.  That is, if you got on your hands and knees with a pair of tweezers you would have no difficulty getting all the little bits out – it would just take an awfully long time.

Generally, this is what stains are.  Generally, the substance in question is mostly physically entrapped and it just needs a bit of coaxing to remove.  This can often be achieved by simply using a good detergent and knowing what cycle to set your machine to.

Other forms of stain are more strongly bound because of a chemical interaction of some sort between the stain and the molecular structure of the garment.  In general terms the worst culprits here are natural fibres, particularly cotton and wool.

The reason in the case of cotton is that because it is a carbohydrate it is very oxygen rich, and oxygen is quite a reactive element.  There are many substances which will form a bond with these oxygen groups and at a molecular level this can make the stains quite sticky, and limit the effectiveness of normal washing processes.

With wool, the problem is the sulphur which is is even more reactive than oxygen, and this has always been the downside of pure wool carpets.

Synthetic fibres, on the other hand, are polymer chains, and usually don’t contain as many reactive sites as natural fibres do.

Perhaps the worst type of stain is one that changes form after it gets onto the fabric – in other words, things that “set” like paints or resins.  In cases like these, the degree of chemical bonding with the fabric is not the problem – the problem is the intimacy of the contact.  That is, although the bonds between the paint and the surface are not particularly strong, the fact that there are so many of them, because the liquid ran into every nook and cranny before it set, means that the additive effect is quite substantial.

As it happens this is the principal behind many glues and the reason that they tell you to make sure that the surface is free of oil and water before the glues are applied.

Stains fall into several categories and we will now look at them individually and see what general characteristics they have.

Exploding Roach Bombs

A house in Middle Swan was blown up by roach bombs yesterday.

What happened?  Are these things dangerous?

The short answer is “no” if they are used correctly.  They contain insecticide, water, and a hydrocarbon propellant.  The way they work is you click the valve at the top open, it locks in place, and they dispense the entire contents into the air.  The insecticide then settles on all hard surfaces, and kills any cockroaches in the vicinity for the next few months.

As it comes out of the can, it is not flammable as it contains water.  What happens then, however, is that they separate – the water (and insecticide) fall to the ground, whereas the air fills with the flammable hydrocarbon gas (normally propane or butane).

The only question then is how much is there in the air?  Normally, there is not enough in one can to reach a high enough concentration (the Lower Explosive Limit) to be explosive.  What happens, however, is people think that if one can will work, then five cans will work better.

What’s wrong with that? That makes sense doesn’t it? Well, five cans contain five times as much insecticide as one can, of course. Unfortunately, they also contains five times as much flammable gas. Frequently, this will put enough gas into the air to reach the lower explosive limit and the result is rather spectacular.

Consequently, there are many stories, particularly in restaurants, of places getting blown up because they used too many cans at once, and mythbusters quite elegantly showed what can happen.

So the lesson is, read the instructions on the can.  They will tell you what the area coverage of a single can is, and you don’t need to use any more than this.  In other words, one can at a time!

But if you do want to use more, do it over a few days – don’t let off too many cans at once, or you won’t have a house any more!

Incidentally, 25 years ago when people were less concerned about safety than they are today, fly sprays were a lot more flammable – the legendary Pea-Beu Tri Kill is a case in point!

The Best Spot Cleaner on the Market

This remarkable product is the best spot cleaner on the market:

The reason simply is that the people that make it have taken the consumer (you) seriously, and packed it full of highly effective cleaning chemicals.  Foremost among these is d-limonene, a citrus extract which has remarkable stain removing properties, for the simple reason that as a terpene it is a small organic molecule that is also miscible with water.

This means that it will dissolve stains but at the same time wash out in the water.  And even if it doesn’t wash out, you don’t really mind, as it leaves a nice citrus fragrance behind.  Use it on clothes, hard surfaces,  and even leather (for example ink stains).

Book Extract #3: Shampoos #1

The basic chemistry of hair shampoos and conditioners is remarkably similar to that of laundry detergents and fabric softeners.  The reason for this is that the type of cleaning they have to to do is pretty much the same.

For both hair and clothes the major contaminant is body fat.  Clothes pick it up from contact with your skin, whereas hair gets it from your scalp.

The difference between the two is that whereas clothes may have other stains in them, from food and so on, with hair pretty much body fats are all there is.  For this reason, shampoos are more simple formulations than laundry detergents.

There are three discrete types of shampoos/conditioners.  A cleansing shampoo” is the older type where you shampoo first and then you condition; a conditioning shampoo” is something like Pert, where both shampoo and conditioner are present together, and a mild (or baby)shampoo” is one that is intended for use on sensitive skins (such as babies).

We will look at each separately.

5.9.1 Cleansing Shampoos

These are the simplest of the three.  In essence, since it only needs to remove body fat from your hair, all that is needed in a shampoo is a (primary) alkaline (anionic) surfactant for cleaning (normally around 10 to 20%), a secondary surfactant (normally non-ionic or amphoteric) to produce foam, and a thickening agent to make it into a gel, and this is what you will find it in the cheaper shampoos that you buy from the discount stores.

Other components in the premium brands may be sunscreens, anti-dandruff agents, or various additives such as vitamins and herbs (along with accompanying claims about the wonders they can work for your hair).

Hand in hand with a cleansing shampoo is the need for a conditioner.  This is essentially to neutralise the negative charge that the primary surfactant has placed on your hair.  And it is this negative charge that causes unconditioned hair to feel coarse and get tangled.  The itchy scalp that goes with unconditioned hair is simply due to the highly alkaline pH.

To allow hair strands to neatly lay on top of one another, therefore, this charge must be neutralised and this normally happens with a cationic (positively charged) surfactant.  The positive end of the molecule sticks to the negatively charged sites on the individual hair strands and thus the static charge is neutralised.  The organic part of these molecules are normally long chain fatty acids that then lie along the length of theindividual strandsd,giving themt a smooth feel.

The reason that the shampoo and conditioner must be applied separately, with these formulations, is that because if they were in the same formula the negatively charged (anionic) surfactant would bind with the positively charged (cationic) surfactant and neither would be available to clean your hair.  It’s exactly the same argument as to why fabric softeners are added separately to laundry detergents when washing clothes (section 5.2).