7 Oct 2016 11:22:00 am
By Cleancare Australia
It is generally accepted that certain principles apply to cleaning Sun_Temperature
Increased temperature usually improves cleaning. Agitation to loosen the soil helps the cleaning process. A minimum concentration of cleaning chemical is needed for cleaning. Above the minimum level, cleaning improves only slightly with each increment of concentration having a lesser effect until a point is reached beyond which increase in concentration has no effect.
Adequate time must be provided for detergency of the cleaning chemical with soil. Otherwise, agitation or mechanical removal effects become more important. Rinsing away of soil and cleaning chemical is necessary and must take into consideration factors such as:
The amount of soil that can be left without harm, and how much cleaning chemical residue can be tolerated. To remove every trace of cleaning chemical residue may require extensive rinsing. Pressure rinse water or an agitated rinse is far more effective than a "still" rinse. After the rinse water evaporates, residue remains from the rinse itself. This may include salts present in water, soil accumulated or the cleaning chemical itself.
Soil must be kept from re-depositing. This may take the form of a cleaning chemical component to suspend the soil or a system designed so that the soil is separated from the cleaning area, as in the case of pit cleaning.
The cleaning method or solution should not harm the item being cleaned. An economical operation should have "common sense" procedures for removal of as much soil as possible outside the main cleaning solution. This may take the form of pre-vacuuming, or the use of pre-sprays to loosen the soil.
Concentration of chemicals
The ready-to-use concentration of chemicals for good cleaning depends on the amount of soil and the methods employed. For instance, when using a soil-retarding shampoo, such as in an encapsulating product, the ready-to-use concentration of actives can be as high as 1 percent, which translates to about 60g per litre of a high quality shampoo.
The actives of a regular traffic cleaner can be as high as 0.5 percent, which translates to 75g – 85g per litre or 30g per litre of highly concentrated traffic lane cleaner with high actives. For liquid extraction detergents and in-plant operations, the actives can range from 0.08 percent to 0.2 percent actives, and for bonnet cleaning it can vary, depending if the cleaning product is solvent- or water-based.
The basic point is that more detergent does not translate to better cleaning; in fact, it could be detrimental, and cause rapid resoiling of the cleaned carpet.
Time required for cleaning
This is determined by the conditions of temperature, type of soil, concentration of cleaning chemical, agitation, etc. Bear in mind that it takes time for the detergency process to take place, i.e., for the surfactant to cover the surface and displace the soil.
In a static bath as in pit cleaning, it may take five to 15 minutes; in a high-pressure spray of a quality detergent, it may take a few seconds.
It can be expensive in equipment, labor and chemicals to reduce cleaning time, and there are situations in which the expense is not justified. It must be understood that the time available for cleaning is very closely related to the economics of the cleaning operation, not only from output, but also on the basis of time lost in recleaning, such as when a customer complains about inadequate cleaning results caused by an unsuccessful balance of cleaning factors.
The effect of temperature depends on the type of cleaning chemical being used. A first consideration is that enough temperature is used to melt the soil that is being cleaned, such as fat, grease or wax holding the soil, and it makes a tremendous difference in the rate of cleaning.
In many cases, a fat or grease melts to a low viscosity liquid and any further increase in temperature has limited effect. For most oils, increase in temperature reduces the viscosity of the oil, making it more mobile and therefore more easily deterged.
The real temperature at the point of cleaning
There is a misconception that heated water coming out of the truckmount will pretty much maintain the high temperatures emanating from the heat exchanger; however, this is not the case. Before you crank up the heat on your truckmount, let me say that in a typical cleaning operation the temperatures on a carpet does not approach 65C, or even 54C.
In 1986, the fibre producers of carpet started using stain-resist technology and, as part of the warranty, set a temperature limit of 65C to clean stain-resist carpet. The fiber producers soon removed that limitation based on the fact that during a typical cleaning process the temperature at the carpet does not come close to 65C.
Do 'high-heat' products clean better?
Some cleaning chemicals are being hyped as high-heat cleaning products.
Do these products work as good as or better than the traditional nonionic blended products?
Let us examine the two product types.
It is also well known that nonionic-based surfactants separate with increasing temperatures. This is called the cloud point. At the cloud point, the surfactant begins to lose sufficient solubility to perform some or all functions as a surfactant.
It is also known that these nonionic surfactants clean best just above the cloud point, and with any further increase in temperature, the cleaning efficiency rapidly drops off. The so-called "high-heat" cleaning products are free of nonionic surfactants and are basically composed of anionic surfactants and hence do not have a cloud point.
They are higher foaming than nonionic surfactants, thus to keep the foam manageable more defoamer is blended to the finished product, or more has to be added during the cleaning process. The anionics are polar in nature which means that high heat products are not as efficient as nonionics in removing non-polar greases.
These anionics are also adversely affected by presence of hard water. In one of my previous articles, I had written that that the nonionic-based surfactants — being non-polar in nature — are very efficient at removing non-polar oils and greases that tend to bind the soil to the carpet. These nonionic detergents are not affected by hard water.
Don't get me wrong: Anionic detergents are excellent detergents with some unmatched attributes like easier rinsing, good stability, etc., and work better than nonionic systems in a number of cases, like in shampooing. (See Nonanionics vs. anionics above)
The selling hype of the high-heat cleaning products is that you get better cleaning at higher temperatures. It is based on the perception that the high temperature of the cleaning solution coming from the heat source will be maintained at the carpet, without any appreciable drop. If these very high temperatures cannot be attained — much less maintained — in a typical hot water cleaning system (hence no cloud point), and the nonionic surfactants relatively are more efficient even at higher temperatures than anionics, it becomes an illogical point.
Does the Arrhenius law apply to cleaning?
Most chemical reactions occur faster at higher temperatures. There is a well-established principle that states that the rate of chemical reaction is doubled for each 10C increase in temperature. This is known as the Arrhenius law and applies to all kinds of chemical reactions. Even luminescent butterflies have been found to flash more rapidly on warmer nights, in accord with it. However, the cleaning process is mainly a physical process and very rarely a chemical reaction, and hence the Arrhenius law is not applicable.
An epidemic of ignorance still persists that, somehow, somewhere, someone has tried to correlate the Arrhenius law to the cleaning process, and this artificial correlation refuses to die, even with the evidence that the correlation is not there.
As mentioned earlier in this article, as the temperature moves more and more past the cloud point, the cleaning efficiency drops. A study presented at the 1984 World Surfactant Congress in Munich, Germany, found that temperatures higher than the cloud point caused detergency to decline rapidly; so much for the applicability of the Arrhenius law in cleaning.
Higher heat and real-world cleaning
This does not mean higher temperatures do not help with increased cleaning. I wrote an article for CM/Cleanfax® magazine 1996 titled "Cleaning basics: The temperature paradox"; I stated then and I am stating now that higher temperatures do help in cleaning, but the Arrhenius law does not apply.
You can use heat liberally as long as the material you are cleaning can tolerate it. The higher the heat, the better it is going to clean. Heat not only helps in cleaning and melting the soil holding grease, it makes the cleaning chemical more effective.
The nonionic-based detergents work better than the so-called high-heat cleaning detergents, even at the higher temperatures. The temperature at the wand rarely exceeds 54C during a normal cleaning operation, unless you are tempted to hold the wand in one spot.
The temperature at the heat exchanger or burner system is higher than cloud points of most nonionic detergent systems, but even it if it is higher, it is immaterial because as long as the cleaning solution is in motion, (as long as the pump is running) it goes back into solution.
What is important is the temperature of the solution at the wand, where it hits the carpet. The Arrhenius law applies to chemical reactions (where the rate of chemical reaction doubles for every -7C rise in temperature) and does not apply to physical processes like the cleaning of carpet.
It is up to you, as a professional cleaner, to make an informed choice to use a cleaning system that you are comfortable with. It is our responsibility to inform you about the facts as they relate to science.
Question: At what temperatures can cloud point (where the liquid appears cloudy on heating) occur in different nonionic systems?
The temperature test
To test how much the temperature will drop during hot water extraction cleaning, I did a simple nonscientific test on a hot summer (32C) day.
The carpet was placed near the truckmount and I used a short hose to minimize heat losses. I used a non-contact calibrated thermometer to measure the temperature (any other type of thermometer would have given a lower and erroneous reading as it would take away heat from carpet to get a reading).
The hot water coming from the truckmount under pressure was at 110C.
Guess what the temperature was at the cleaning wand?
You may be surprised to know that at the inside area of the cleaning wand the temperature measured 51C and outside the wand it was only 45C; such was the drop in temperature.
One can surmise that on a colder day with a longer hose, the temperature at the cleaning point would be even lower. Before everyone gets excited and thinks the machine is at fault, consider this question:
Why does the temperature drop so dramatically at the wand?
When a gas or liquid flows from high pressure to low pressure, it expands and, on expansion, loses a tremendous amount of heat. It loses so much that you can solidify carbon dioxide gas to a solid dry ice when you open up a pressurized cylinder at room temperature (the dry ice has a temperature of -78C). This is based on what is known in science as the Joule-Thomson effect.
When hot water under pressure flows from the heat exchanger or burner and goes through the wand, it loses heat as a result. The further the wand is from the heat source, the more it will lose heat, especially in colder weather.
In addition, the hot water coming out as an atomized fan spray from the nozzle loses heat and cools down further.
The carpet also acts like a heat sink, dropping the temperature down further.
Nonionics vs. anionics
In hot water cleaning operations, several studies have shown that nonionics outclass anionic-based detergents. One such study, published in 1972 in the Journal of the American Oil Chemists Society, showed that the nonionics detergency exceeded the anionics considerably, even if the concentration of anionic-based detergent was much higher.
Another study compared the performance of nonionics and anionics containing a variety of builders, and found nonionics were generally superior to anionics in removing both oily and clay soils and less sensitive to water hardness.
Another study, presented at the American Oil Chemists Society Detergents Short Course in Hershey, PA, in 1975, showed that increased cleaning temperature improved the detergency of the nonionic-based system considerably, while the anionic-based system had only a modest increase in cleaning.
Answer: The temperature can range from the melting point to the boiling point of water, from 0C all the way up to 100C. With most detergent systems used for steam cleaning, the cloud point ranges from 60C to 76C, and, in one case I have seen, as low as 35C.
Author: Dr. Aziz Ullah is a leading and respected chemist and scientist to the carpet cleaning industry in the United States. He is a frequent speaker, article writer and contributor to Cleanfax Magazine and other leading industry publications.