Hello and welcome to our 27th live chat with our favourite water scientists and Nappy Science Gang helpers, Mark Smith and Adrian Clark! We spoke to them many months ago, right at the start of our project, when we were trying to get our heads around the science of water, detergents and washing machines. Now, after nearly 6 months, they have kindly agreed to join us again for another live chat where we delve deeper into the chemistry of surfactants, stabilisers and salts. Be prepared, this chat isn’t the lightest of reads, but it is packed with information that might change forever the way you look at your washing machine…
Mark : First of all I wanted to clear up a misconception that came up in one of your previous live chats concerning drinking or potable water standards. The maximum levels set in standards for Copper, Iron and Manganese are not based upon health effect levels but on levels that can cause staining of washing, baths and toilets.
@Mark, would I be right to assume that any health effects would be felt at much higher concentrations than that?
Mark : Yes many orders of magnitude
Q: I’d like to ask a question about about build up. Is it correct to say that detergent can build up? Are there any scientific studies showing build up (or not) of detergents?
Mark: There is no peer reviewed published data on detergent build-up on fabrics. Ian Studwick reported that in some cases they have found detergent residues on fabrics being tested. For clarity, in this chat when I refer to detergents I am referring to a formulation containing essential constituents, surfactants and subsidiary constituents that are required for the product to perform. This is the same definition used in the Bianchetti paper. [there’s a copy of this publication available from The Nappy Science Gang facebook group]
@Mark, so what would we call something like Bold 2-in-1 or Fairy Non Bio Liquid?
Mark: I would call them detergents as they are a formulation. The formulations contain surfactants and other ingredients.
Adrian: Detergents are complex formulations which all work together. These are, by their nature, proprietary mixtures, although they contain some common components.
Q: Is there any peer reviewed published data on mineral build-up in fabrics?
Mark: Again I am sorry there is no peer reviewed data on mineral build-up on fabrics, but it is quite possible if insoluble calcium and magnesium compound are formed in the washing machine. They will nucleate out of solution and the particle size will grow. These insoluble particles may reach a size where they are trapped in the fabric.
SOAP: WHAT IS IT AND HOW IT DIFFERS FROM OTHER SURFACTANTS
Q: We have been told that in the US things labelled as “detergent” can’t by law contain more than 2% soap. Are there equivalent regulations in the UK? We’ve been looking at labels and some things labelled “detergent” in the UK clearly have a much higher percentage of soap than that.
Mark : There are no EU regulation concerning soap levels and all the active ingredients are given on the product labels. The problems with soap, which is a specific type of surfactant (a sodium or potassium salt of a fatty acid) is that it forms insoluble calcium and magnesium salts with the calcium and magnesium ions contained in the water. These insoluble salts precipitate out This is the basis of the formation of scums, which may deposit on nappy fibres. This is avoided using synthetic surfactants, such as anionic or nonionic surfactants, which don’t form precipitates (scum). However, this said, a small amount of soap is often included in most formulations as it is very effective at removing certain types of stains.
Q: So if a soap-free surfactant binds to minerals it will be washed away, but if soap binds to minerals it could fall out of solution and stick to the surfaces and fabrics. Is that right?
Adrian: Yes. Also some surfactants are better than others at maintaining salts in solution and preventing them from forming deposits. It is also usual to incorporate water softening agents, such as zeolites, which bind water hardness salts such as calcium and magnesium. Nonionic surfactants are also less inclined to cause insoluble deposits.
@All, Which other variables might affect the precipitation of calcium and magnesium salts?
Mark : The precipitation of insoluble calcium and magnesium salts depends upon the stability of the water. The harder the water, the more calcium and magnesium ions it contain.
@Mark can you explain what you mean by ‘the stability of the water’?
Mark: Water stability is complex and depends upon the concentration of various ions, pH, temperature, dissolved gasses and it is a term water scientist use for precipitation of solids out of solution.
THE DELICATE BALANCE BETWEEN SOAP, SURFACTANTS AND STABILISERS
Q: The Fluff Love admins are pretty adamant that there needs to be a minimum % surfactant and a maximum % soap for a detergent to be effective at washing nappies. Have you found this to be the case? Are there any studies that confirm how much surfactant a detergent should have?
Adrian : It has to be a balance. There also needs to be sufficient surfactant to avoid deactivation and enable removal and emulsification of fats and oils.
@Mark @Adrian, But surely the manufacturers formulate their detergents to suit our water, so that the mixture makes these build-ups unlikely if we use the detergent correctly?
Adrian: Manufacturers will be concerned with the absorbency of things like towels after laundering. Like everything, it partly comes down to what one is prepared to pay for a product when it comes to overall performance, as economics come into it.
Mark: One of the main reasons why the detergent manufacturers say you should increase the detergent dose as the water hardness increases is to ensure you have enough stabilising agents to keep the calcium and magnesium ions in solution. You need a slight increase in soap concentration but not as much as you need to increase the concentration of stabilisers.
@Mark, that is interesting. So it’s not that more surfactant is needed necessarily, it’s that more stabilisers are needed. Can you name a few stabilisers that we are likely to see on the box?
Mark: Zeolites, sodium sesquicarbonates , polycarbonates, hexametaphosphates or it just might state stabilisers.
Adrian: Typical stabilisers or builders include sodium carbonate, complexing agents, soap and zeolites. Chelating agents such as EDTA used to be added but these have generally been replaced by the zeolites.
@Adrian, can you define the difference between a stabiliser and a water softener?
Mark : I use the term stabiliser to include softeners
Q: Things like Percarbonate, vinegar, citric acid, lactic acid are they also stabilisers/softeners? I know that acids soften water as well.
Mark : Percarbonate is mainly used as a bleach. Acids will change the pH of the water and effect solubility of calcium and magnesium salts. However, laundry detergents work under alkaline conditions at a high pH.
@mark, so those acids will soften your water, but also make your detergent work less well?
Mark: Yes, laundry detergents do not work under acid conditions
Q: Do labels on detergents in the EU require to state when stabilisers are used? I am thinking of one ‘natural’ detergent in particular from Germany called Ulrichs. It says ‘It contains especially gentle wash-active substances from coconut oil, pure vegetable soap and right turning lactic acid.’ For me the coconut and vegetable soaps send a red flag since they are soaps. The only other thing in their data sheet besides the coconut surfactant, SLS and lactic acid is Canola Potassium Salt.
Mark : This German detergent does not seem to have any stabilisers. Normally they would be declared on the label if they were there.
@Mark Ulrichs also says “Contents in accordance with EU Directive 648/2004 <15% amfoteric tensides <15% anionic tensides”, are either of those stabilisers?
Mark : No, they are surfactants.
Q: What about Peracetic acid. This is the antimicrobial that Miofresh uses. Would it be effective?
Adrian : Peracetic acid is a very effective biocide and works well in the presence of organic deposits which tend to interact with other oxidising agents.
@Adrian, so why isn’t Peracetic acid in all detergents? Is this acid also bringing down the pH?
Mark: The concentration of Peracetic acid will not affect the overall pH of the wash. In some formulations for stability purposes of the bleaching system, you can use a pH jump system. It is detailed in the Bianchetti paper.
@Mark, this just leaves the question of whether you need an anti-microbial.
Mark : I don’t think you do as detergent and water are quite effective at removing bacteria and viruses.
Adrian : Agreed, washing is mainly about physical removal, along with the dirt.
ENVIRONMENTALLY FRIENDLY AND HOME-MADE DETERGENT
Adrian: At the moment there is also a move to more environmentally friendly products which biodegrade more easily and will cost more.
@Adrian, are more ‘naturally derived’ surfactants likely to biodegrade more easily?
Adrian: Yes, manufacturers have been working on plant derived products which break down more easily, but the use of natural plant surfactants is not new.
Mark: Naturally derived surfactants use a feedstock which is plant or animal based, rather than oil based. These still require a lot of chemical transformation to produce your surfactant. A few surfactants are now being made in bioreactors, but these are mainly confined to surface cleaning products as they tend not to be anionic surfactants.
@All, Sounds a bit like the bamboo issue: bamboo nappies have a reputation for being sustainable and natural but they take a lot of processing to make viscose from bamboo fibre.
Mark: I have seen recipes on various websites or even an online version of a national newspaper yesterday for people to make their own. These seem to consist of borax, sodium carbonate and soap or an oxygen based bleach. For hard waters, I doubt there will be enough stabiliser present, so you probably will have insoluble salts precipitating out.
@Mark so even if you were to add something like Calgon to a homemade detergent it probably wouldn’t be enough to prevent the soap from precipitating? Also, when the soap binds to the minerals it can no longer interact with the dirt on the laundry, correct? So it is effectively useless
Mark: Correct, if soap has bound to minerals it will not act as a surfactant. You have to get your stabiliser concentration right.
[added after the chat]
Mark: Borax was added to the Substance of Very High Concern (SVHC) candidate list on 16 December 2010. The SVHC candidate list is part of the EU Regulations on the Registration, Evaluation, Authorisation and Restriction of Chemicals 2006 (REACH), and the addition was based on the revised classification of borax as toxic for reproduction category 1B under the CLP Regulations. Substances and mixtures imported into the EU which contain borax are now required to be labelled with the warnings “May damage fertility” and “May damage the unborn child”. It was proposed for addition to REACH Annex XIV by the European Chemicals Agency (ECHA) on 1 July 2015. If this recommendation is approved, all imports and uses of borax in the EU will have to be authorized by the ECHA.
DIFFERENT SURFACTANTS FOR DIFFERENT STAINS
Q: What stains are more difficult for a detergent, poo stains or oil stains? I found Lidl’s own brand removed my husband’s really dirty oily coats with half of the powder, is this perhaps due to the type of water, more than the power of the powder?
Mark : Different surfactants are better at removing different contaminants. That is why detergents normally have more than one surfactant in them. Some of the specific laundry additive stain removers have surfactants or surfactant blends for the particular stain classes they are targeting. If you look at Which? or Good Housekeeping ratings they test the various detergents against a typical pallet of stains on cotton cloth using domestic washing machines. But I am afraid that poo and urine are not included in the test stains.
@Mark, “Different surfactants are better at removing different contaminants”! So, we should try to find out what surfactants are best at targeting poo and wee!
@Mark, Yes, that’s the golden shot! I foresee our influence on the industry becoming massive and all major brands offering a “poo and wee” edition. I wonder if Fairy, choosing to target baby users, is tuned for baby-related stains.
Q: In terms of telling people how to wash their nappies, hard water can cause mineral build up, which in turn may cause detergent build up. How would people strip this off?
Mark: On your build up issue, I think your experiments on strip-washing will provide very useful information on this. This is why I originally suggested that a question should be asked about the amount of detergent used in the washing routine compared to the manufacturers dose. My guess was that if not enough detergent was being used, you wouldn’t have enough stabilisers present in the wash.
@Mark So you think too little detergent could be the cause of mineral build-up, if it happens?
Mark: I am not sure , but if you don’t have enough stabiliser you will have insoluble calcium and magnesium salts being precipitated out which could get trapped in the absorbent fabric.
HOW TEMPERATURE AFFECTS DETERGENTS
Q: On temperature, could you tell us which elements of a detergent product perform differently at different temperatures, and how?
Mark: In the Bianchetti paper figure 10 shows the effectiveness of different oxygen bleaches at various temperature and pHs. In general terms for chemical reactions, the higher the temperature the faster the reaction
@Adrian, so almost everything would probably work better hotter?
Adrian: Yes and this is mostly the effect on promoting chemical action and solubilising of greasy soils by weakening binding forces and assisting with emulsification.
@Adrian are there any parts of a detergent that fail at a higher temperature? (I think you already told us that enzymes still work at 60degC but not so well at 90decC)
Mark: Yes, dioxirane and oxazindine bleaching agents don’t work above about 30degC.
Adrian: You have to remember that the four key cardinal parameters are chemical action (water and detergent), mechanical energy, temperature and time, all of which interact.
@Adrian, and generally if you have less of one you would need more of another, right? For example, less temperature, more time. But that is not always true. A lot of people believe they should use tons of water and 1/4 the amount of detergent for their nappies.
Adrian : Rinsing is important in being able to remove the solids. As we have said, there is likely to be an optimum for the amount of detergent, depending on the soiling, size of load and water hardness.
Q: How familiar are you with enzymes? Could you tell us something about how they work?
Adrian : Each type of stain requires a different type of enzyme (for proteins, oily deposits and carbohydrates). Commercial enzymes are also designed to be robust at higher temperatures than many natural ones but they do assist with hard to remove stains. They can comprise up to 2% of the product.
@Adrian, When we talk about enzymes removing stains, are we just talking about appearance (colour) of the washed item, or are the enzymes actually helping physically shift poo and wee?
Adrian : Enzymes will provide chemical degradation, i.e. breaking down of poo and wee. Bleaching agents are mostly oxidising agents which will remove colour (e.g. grass stains), as well as chemically degrade stains.
@Adrian, Thanks. So colour removal is separate from breaking down the soil. When I wash a dirty nappy and it comes out smelling clean but still has a faint stain, I usually remove this by leaving it in the sun. My question is, was the nappy clean when it came out of the machine, or did it get clear after sunning, or is it never completely clean?
Adrian: It can be difficult to achieve a high level of disinfection in a washing machine and there is published data showing this, but exposure to UV light during drying can be an effective way of killing residual bacteria and viruses. It will also help to bleach any residual stains.
@Adrian but can UV light penetrate the many layers? And can drying in the dryer on low or high heat also aid in live bacteria/virus/fungus reduction? We spoke to a medical microbiologist who said sun can’t sanitise nappies sufficiently, because it will only affect the surface. It might work on terry squares, but not more modern multi-layer nappies.
Adrian: You are right in thinking that UV light penetration can be somewhat limited. Using a dryer would help as most bacteria are fairly heat sensitive. In terms of whiteness, detergents usually include optical brighteners which will help nappies to look whiter, especially after drying in the sun. There is now a move towards unbleached fabrics being more environmentally friendly so yes, it is mainly aesthetic appeal. Whiteness is what we have come to expect as an indicator of cleanliness. Please bear in mind that ‘sanitising’ can be a very loose term and is not the same as ‘sterilising’ when it comes to disinfection. There are some sanitising standards for surface cleansers but these are for specific hard, flat surfaces and not fibrous natural materials.
@Adrian, I bloomin’ love optical brighteners! Judith Mathias from Violet’s described them as “particularly nasty” though she didn’t explain why. I was almost offended I love them so much. I reckon I’ve saved a fortune not buying new things because brighteners keep them looking for ages.
Mark: Optical brighteners by their nature remain on the fabric surface, so whether it causes build up issues over time is the big question. I think some people may be sensitive to them or if you are in the military you do not want your camouflage glowing in UV light.
@Mark, They’re great at discos though!
ON VIRUS REMOVAL
Mark: If you look at published paper by Gerber et al., in 2007 and Sidwell et al., 1967 they were achieving the following log removal rates for detergents: Polio1 log 4, Rotavirus log 5, HAV log 3, Adenovirus log 2. Water alone had a log 2 removal for Polio 1 virus.
@Mark, sorry to sound thick, but what is a log 2 removal?
Mark: When we look at disinfection efficiencies for removal of bacteria and viruses we talk about log removals. 1 log is a concentration decrease by a factor of 10, two log is a factor of 100 removal. So if the count was reduced from 100 to 10 we would state log 1 removal.
@Mark, thanks. Were the experiments done at room temperature or higher temp?
Mark: The virus removal data was at 20degC.
@Mark, so is it possible that virus removal would be more effective at higher temp? I know bacteria will die at higher temperatures but would viruses do the same?
Mark: Generally yes. The Gerber paper also states that drying in a tumble for 28 minutes was not very effective at reducing virus numbers. The detergent used did not contain any bleaching agent.
PHOSPHATES IN DETERGENTS
Q: What is the role of phosphates in the detergent?
Mark: Phosphates are not allowed in domestic laundry detergents in the EU. They were used as builders in formulations and to assist in water stability, but they are only used in commercial and industrial detergents in the EU. Their use in domestic detergents were prohibited due to them polluting surface waters.
@Mark, so when things say “phosphate free” to prove they are environmentally friendly options, that’s academic because phosphates are banned anyway!
ANTIREDEPOSITION AGENTS, KEEPING DIRT SUSPENDED IN WATER
Q: Could you tell us something about antiredeposition agents, what are they and how they work?
Adrian: Antiredeposition agents such as carboxymethyl cellulose are used to prevent fine soil particles from reattaching to fabrics.
Mark: Though if the insoluble particles are small enough to be trapped within the fabric you might not get them out, as I have found with fine brick dust on a pair of my trousers!
@Mark, a question we had for Ecoegg that hasn’t been answered is how they stop soil being redeposited. Ecoegg told us that their eggs do that, but not how. Have you got any ideas?
Mark: I note that Ecoegg has not yet shared their SATRA test data with you. As I understand they contain tourmaline, which produces a low surfactant concentration. There is mechanical action which may be enhanced by the egg, so that mechanical action may prevent soil being redeposited.
@Mark, yes they said that the eggs contain tourmaline pellets and ‘mineral’ pellets (not sure what’s in the mineral pellets)
@Mark, so are you saying that the main cleaning effect of the Ecoegg may be the mechanical action of it bumping round in your wash? I remember that some laundry eggs (not sure of the brand) used to be bumpy, like a pine cone, presumably to help with agitation.
Mark : Yes, a plastic pine cone would assist in agitation of the wash, just mechanical action in that case.
ON VIOLET’S NATURAL AND TRADITIONAL FORMULATION
Q: Speaking of Violet’s, here are the ingredients of their detergent, which claims to be stripped down to the essentials and all natural. Does it look like an effective recipe? “Handmade pure vegetable soap – Sodium Sesquicarbonate, Sodium Carbonate, Sodium Percarbonate – Natural Zeolite”
Mark: You have stabilisers and soap in the formulation. As the only surfactant is a soap you have to ensure you have a large enough dose of stabilisers to make sure you don’t have insoluble calcium and magnesium salts being precipitated out and forming scum.
Adrian: Violet’s contains some rather old fashioned ingredients which will no doubt work as a detergent and make users feel good they are not relying on petrochemicals, but it will probably be less efficient for intractable stains, especially at lower temperatures.
@Adrian, when you say ‘less efficient’ do you also mean less efficient at removing bacteria, uric acid, or just stains?
Adrian : I mean less efficient than, say, enzymatic detergents at removing deposits which harbour bacteria.
@All, whether or not Violet’s works also depends on how much you use. They recommend just 1 tablespoon and the lady claimed that the tiny volume was because they excluded so many of the “unnecessary” ingredients that mainstream powders use.
Mark : In a detergent, when you formulate you try not to add anything you do not need because everything you add costs money, and you aim to reduce your costs.
Q: One last question, when a detergent gives a dosage for 4-5kg, is that for a drum of that capacity no matter how full, or for that weight of load no matter the size of drum?
Mark: It is about the volume of water used. Dosing volumes are machine dependent, so it is about optimising for you machine, water type and load.
We don’t know how to thank Mark and Adrian as we have really drilled them for information tonight! Thank you so much for giving us so much of your time, it’s been great! And also, thanks to everyone who came along and asked so many interesting questions, I hope this chat helped to clarify a few things!