Live chat with fabric technologist Ian Strudwick

For our third live chat we had the pleasure to speak to Ian Strudwick, technical manager of Shirley Technologies in Manchester. This is a collection of laboratories involved in independent testing on textiles and polymers using standardised washing tests. Ian is therefore the perfect person to answer all our washing machine related question, and we haven’t missed our chance to pick his brains in what was a very fascinating and in depth chat.

Below you’ll be able to read the questions asked during our chat with Ian and his answers.

Q: Washing machines used for International Standards cost a minimum of £8000, why is the price so high for these?
A: The £8000 machines are designed to be replicative – every wash identical to the last one, which is crucial for testing. Washing machines from the local Currys/Comet at £200 are comparatively far more variable in terms of mechanics. The thing to perhaps remember is that the £8000 machines are not necessarily designed to replicate real-life machines. They are used only for testing and, whilst they are available to the public, almost never will you see them domestically.

Q: A report stated that domestic machines don’t reach 60 degrees. Do you think that is true?
A: Yes, your Hotpoint, Indesit and the like are the cheapest machines and these are very unlikely to reach an exact 60deg C no matter what the dial on the front might say.

Q: How are you measuring temperature to that kind of accuracy and in a consistent manner? Are there fixed thermocouples or something else?
A: Yes, the control is by means of diodes and fixed K-type thermocouples, which are extremely accurate.

Q: So do all the labs have to co-ordinate machine calibrations and things like that?
A: all labs are accredited by their local ILAC accredited body. In the UK this is UKAS

Q: So how much variation do you think there is in domestic washing machines? How wide is the variation in the temperature they would reach on a supposed 60deg cycle?
A: The simple answer is comparatively a wide difference. A cheap domestic machine running at a dial setting of 60 deg C is probably achieving no more than 55 deg C at best.

Q: So, would nappies be effectively cleaned, given that they are heavily soiled items, at 55 degrees C?
A: The temperature requirement for effective cleaning of an uncoloured cotton nappy is 60 degrees C, any lower and the cleaning will be affected. Perhaps not noticeably, but at a microscopical level there will be a difference. If you want to sanitise the nappy by killing bacteria then you need to rise above 74 degrees C, but this gives other issues. Hospitals sanitise linens at 74 degrees C, but they also use different procedures, so you would never get a truly effective sanitisation using a domestic machine. By truly effective sanitisation I mean so clean that the nappy doesn’t support bacterial growth, but this is far more ‘clean’ than a nappy really has to be.

Q: Most domestic machines go 30/40/60/90 though so hitting 74 just isn’t possible!
A: True, you would have to go up to 90 degrees C, or reduce to 60 degrees C and load the machine with chemicals. Complete sanitisation can only ever realistically happen in a laboratory situation. Washing at 60 degrees C with effective detergents is practically achievable and will give a perfect serviceable nappy for future use.

Q: So does that mean laundry sanitisers don’t really add much benefit?
A: Laundry sanitisers have a slight benefit but at low temperatures it is negligible. Use of these (and the whole 30 deg C washing issue) is really just marketing by the manufacturers

Q: Most people, in my experience, have a range of cloth nappies made up of different fabric types which they wash together in their ‘nappy wash’. Do bamboo nappies, cotton nappies and microfibre nappies need to be treated differently or can they all go through the same type of washing cycle? I have read that some manufacturers suggest that biological detergent ‘eats’ the bamboo fibres which results in balding of the nappies.
A: Practically, I’m sure that all nappies go through the same cycle, just to make it easier for the householder. The ‘lab’ answer would be that all nappy types should probably be treated differently because of their different composition. For example a microfibre nappy won’t be affected by enzymes, optical brighteners, acids etc, whereas a cotton nappy will. The cotton nappies will not so much immediately fall apart but over time the degradation will become obvious.

Q: So for all round advice would you suggest that non bio would be a better choice for nappies in terms of getting them clean and keeping them in good condition – assuming most people use them for 2-3 years on one child and would like to use them again on another child?
A: In terms of detergent, bio detergents give better stain removal because of the way they react with the stain by ‘eating it away’. However, these can lead to detergent build-up which can give skin rash issues. Non-bio detergents react a different way, using chemistry in association with the heat, moisture and agitation in washing to release the stain into the liquor and hold it there.

Q: So detergent build-up isn’t completely a myth? It does happen?
A: Detergent build-up certainly can happen, it’s not a myth. However it can easily be avoided with simple steps and it really comes down to common sense. Every time a nappy (or any other garment) is washed, it builds up a small amount of detergent that beds into the structure and reacts with the fibres. Over time this build-up can get so severe that it leads to odour formation and loss of absorption. The solution is to give the nappy a treatment in excess of normal: on occasions, perhaps once a month, wash the nappies using a higher temperature than normal, say 60 deg C. As well as doing this, take steps to make sure that you are not repeating the detergent build up. Firstly run the machine empty but with normal detergent, to clean out the pipes. Products such as Calgon can also help at this step. Then do three rinses of the machine at the same high temperature but with no detergent, to rinse out the residual chemicals. When you have a nicely clean, rinsed-out machine, wash the nappies at the same high temperature but without detergent. This loosens, dissolves and holds the built up detergent which is flushed away. It’s probably best to wash the nappies three successive times without detergent just to make sure the cleaning process is effective.

Q: So how often would you recommend cleaning out the machine like that? Monthly?
A: It depends on usage, and of all washing not just nappies. Three-monthly is probably sensible and cost-effective for practical reasons.

Q: That’s quite tough if domestic machines don’t get up to 60. Few of us would be willing to wash at 90.
A: True, washing at 90 deg C gives all sorts of other problems. Following the pre-cleaning regime at 60 deg C will generally be effective.

Q: Is build-up more likely to happen depending on the water type or the detergent used?
A: Soft water increases the propensity of chemicals to be dissolved into it . In this case, you may never have to strip-wash because the quality of your water means that the detergent is always effectively dissolved and removed in the rinse/spin stage.

Q: A common advice with washing nappies is to use half a dose of washing powder. I’ve seen some people say on nappy forums that they only use a teaspoonful of powder. Would you say that’s a good way of avoiding detergent build-up?
A: The less detergent the better to reduce build-up which subsequently requires strip washing.

Q: Can you still get effective washing with less detergent though?
A: It’s a balancing act. Because of the absorbency effect of towelling materials such as nappies, detergent build up can become a problem – far more so than for say a woven cotton dress.

Q: So it’s going to be a case of trial and error based on your machine, nappies, detergent and water?
A: To some extent yes. The BSENISO6330(*) standard states that an effective clean is given if the sud height in the washing machine door window is 2-3cm above the water level. Any less and the cleaning may not be effective, any more and it is just detergent for detergents sake: the cleaning won’t improve and you are just creating problems such as detergent build-up. If you’re using powders it is quite simple to adjust the amount and see how it affects the sud height. As you say this will be affected by water quality, detergent type, load, temperature, duration etc.

Q: When you say sud height, is this early in the wash cycle?
A: It is measured as soon as the wash load achieves its target temperature, which is anywhere from 10 to 30 minutes into the cycle depending on the temperature (as all machines are now cold-fill). Certainly it is before any draining takes place.

Q: Penny Broderick (from our previous live chat) recommends that to work out how much detergent you need to use, you should watch the last rinse cycle. If you can see detergent suds, use less next time. I guess your method is more direct.
A: My method is perhaps more quantitative. However, Penny’s subjective method has merit because what she is saying is that if there are suds in the final rinse then there is still detergent present. Thus there was too much at the start and the likelihood of build-up is greater.

Q: Is there a difference between liquid or powder detergent, in effectiveness and in build-up?
A: It all depends on the chemistry of the respective products. Powders are generally more basic, dissolve better and rinse out better compared to liquids. Liquids tend to have more chemicals in because you need emulsifiers etc. This doesn’t mean they are definitely less effective, but they can give different problems. That is partly why BSENISO6330 still specifies a non-biological detergent powder (called ECE) and hasn’t been updated to allow use of liquids. The problems of reproducibility are simply too great from a lab point of view

Q: So does that mean liquid detergents aren’t tested in washing machine lab tests?
A: Liquids are not allowed in BSENISO6330 or any of the various colour fastness to washing tests because their chemical composition is so much more complicated (and occasionally suspect!) than a simple non-bio powder

Q: I often read online that liquid detergent ‘coats the fibres of the nappy’. I’m not sure where this idea originated but it is widely circulated on cloth nappy forums. Is there any evidence to suggest that liquid detergent does ‘coat’ fibres?
A: This is probably more of a psychological question. Certainly liquid detergents still work effectively, I’m not dismissing their usefulness at all. I have also seen these comments on nappy forums during my research for this but there is no evidence that I have ever come across that ‘proves’ that they are more likely to coat fibres and reduce material absorbency.

Q: What would your advice be for the optimum washing routine for a cloth nappy user in terms of detergent choice so bio/non bio, powder/liquid and also washing temperature?
A: It is difficult to summarise the full range of choices but I’d suggest the following. Wash at 60 deg C, any lower is simply not effective enough no matter what additional chemicals go in. Bio gives a better clean on nappy-type stains than non-bio. Powder is probably best for longer term use but I wouldn’t argue with people who used liquids for simple convenience – the difference between powder and liquid is probably not hugely significant. However do the clean and prewash routine every three months or so – this removes detergent build-up and so reduces odours and harsh feel from the fabric. Also it removes biological deposits from the detergent which can be a skin irritation issue.

A huge thank you to Ian Strudwick for being so patient and answering all our questions about washing machine cycles, temperature, suds and build-up, and for being so thorough with his answers!

(*) BSENISO6330 is an accreditation for the £8000 machines: this is 45 pages long and details the machine to the finest detail, such as height of the vanes inside, speed of rotation to 0.01rpm, temperature to 0.01 deg C. All accredited labs to BSENISO6330 have an £8000 machine and all must be identical at any point in time so that tests done in Lab A in the UK will be exactly comparable to tests done in Lab B abroad.


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