For our sixth live chat we had the pleasure of having with us Jessica Liley, who did her PhD on detergents and how to make them more environmentally friendly. She investigated the use of alternative “bio” detergents for use in laundry products, in the hope of ultimately replacing synthetic chemicals (surfactants) with biological ones (biosurfactants) derived from bacteria and yeast. She specifically looked at what happens at the air/water interface for a variety of surfactant mixtures, to see how the molecules behave with each other in solution and hence figure out how effective they are at cleaning.
Here is the write up of the chat we had with her, enjoy!
Q: Are the alternative detergents better for the environment than synthetic ones?
A: They are better in the fact that they come from natural sources like plant based fats and oils, rather than synthetic chemicals. This means they are non-toxic and much more biodegradable so they are more easily broken down when released into the environment. The biosurfactants which I investigated actually are by-products of various types of bacteria and yeast!
Q: Why were you looking at the air/water interface in particular in your PhD?
A: Understanding the effect of surfactants at the air/water interface is crucial because that is where surfactants tend towards. They have a water-loving (hydrophilic) head which will turn towards the water and a water-hating (hydrophobic) tail which sticks out of the water. Surfactants lower the surface tension of water and make it easier for greasy substances/dirt/grime and water to mix. Foam is also a consequence of activity at the air/water interface!
Q: If your load is already wet (wet nappies!) would that affect how your detergent works?
A: I don’t think it would, because the amount of detergent we tend to use is at such a concentration that it would override any initial wetness of the nappies. If anything it may help: I actually read recently that this may help with the mechanical action of the washing as they are heavier to start with!
Q: Are the bio-detergents as effective as synthetic ones?
A: I can only really speak from the studies that I performed on the five surfactants I used (3 synthetic, 2 bio), but I found that the bio ones actually had better wetting properties and better foaming than the synthetic ones. However, the most often used synthetic surfactants (like sodium laureth sulfate which is normally written on the back of your shampoo, washing up liquid, etc) are fantastic cleaners.
Q: I’m interested to see your stand on eco “detergents” like Ecoegg, Soapnuts etc and also what is your take on bio vs. non bio detergents?
A: Soapnuts contain saponins which are natural surfactant-type compounds, and so they work in exactly the same way as normal detergents, by breaking up the dirt/oils and lifting them from clothes to clean them. I haven’t used them before but I can imagine from a purely chemistry sense that they would work well. They are also natural so have very little negative effects on the environment. I am a little sceptical about Ecoeggs to be honest. The ingredients weaken the adhesive forces between dirt and fibres, and “activated” oxygen helps lift this dirt, but I think that scientifically, you need the chemical structure that a detergent has in order to solubilise hydrophobic dirt and lift it to wash it away, all the while keeping it in suspension in the wash and not allowing it to redeposit onto the clothes. In case you’re interested, they lift the dirt because the detergents used are mostly negatively charged, the same as the negative charge on our clothes, so these two forces repel!
Q: So detergents basically work by making the dirt better at mixing with water, so it dissolves in the water and comes off your nappies (or whatever else it is stuck to)?
A: Yes that’s exactly right. The water-hating tail of the detergent surrounds the droplets of fat/oil/dirt while the water-loving head sticks out into the water, this creates a spherical structure of detergent molecules with dirt inside! On a grand scale, this means the dirt is all broken up so it’s easier to be removed from the clothes.
Q: There is a negative charge on our clothes? Does that vary according to the fabric?
A: Yes I think so as hair carries a slight negative charge, so detergents work in exactly the same way by repelling the hair and lifting the dirt from it. I’d say that fabrics that get static more easily carry more of an electric charge.
Q: Is occasional chlorine bleach soaking safe for nappies and for the baby?
A: Using a dilute bleach wash every now and then would certainly be a great disinfectant for the nappies. Chlorine would wash out easily as long as it is rinsed well enough. Apparently most of the sodium hypochlorite (household bleach) returns back to its salts and water after reacting, so in dilute-enough quantities I wouldn’t think that it is too awful for the environment either.
Q: Nappy manufacturers usually recommend using a half measure of detergent to avoid build up. Do you have any thoughts on the cleaning effect of this?
A: I think getting the right dosage is probably a bit of a trial and error situation. If you’re on your final rinse and you can still see foam produced (even a little) probably too much has been used, but if the nappies still smell a little after washing it’s possible you need to use more detergent. I personally am a bit more generous with how much I use when I wash, because a higher concentration will ultimately mean better cleaning. But the temperature of the water, water hardness, and the mechanical action of the washing machine are all important too, not just how much detergent you use.
Q: So what effect does temperature have on detergent action? Is there much of a difference between washing at 30 and washing at 60?
A: From a scientific point of view reactions happen faster and more easily at higher temperatures, and also there is a linear decrease in surface tension of water as temperature increases, meaning if the water is hotter then it can wet things more easily. Also, at 60 you’re more likely to kill bacteria (only “more likely” as the temperature rarely reaches as high as 60 and only for a short amount of time, and the detergent itself may kill some types of bacteria anyway)
Q: Can you say something about what difference hard water makes?
A: One of my thesis chapters was about the effect of hard water and it’s quite an interesting topic! Hard water is mostly made up of positive magnesium and calcium ions dissolved in water, and these react with the negatively charged surfactants (you can get positive surfactants too but in laundry detergent you only have negative ones because they work against the charges of the clothes as discussed before). This reaction forms neutral compounds which precipitate out of solution and form scum. This really reduces the effectiveness of the detergent because they no longer have a charge, so that’s why in hard water environments foaming is more difficult, and cleaning is not as effective, whereas when you wash your hair in soft water, for example, an awful lot of foam is produced. Commercial laundry detergents contain builders which are basically water softeners, they complex with the hard water ions instead of the surfactant.
Q: But I guess even though you use more detergent (to counteract some being used up by these ions), you’ve still got the problem of this scum being formed?
A: Yes, exactly. Having said that though, scum mainly forms when hard water reacts with soap (similar structure to laundry detergents), but I think this is less of a problem for soapless surfactants like the ones used in laundry detergents.
Thanks a lot to Jessica for telling us more about the chemistry of surfactants and therefore of cleaning. This was really useful and insightful and also demonstrated further what other scientists and experts have told us in the previous live chats!