Fibers, Moisture Retention and LMC
April 12, 2007
With the increasing use of carpet in the commercial/institutional market, installed in buildings with very low airflow and exchange – and often with no air conditioning during hours of non-use – proper drying may become a challenge.
One of the side effects of this situation is a growing use of low-moisture cleaning (LMC), also referred to as very-low-moisture (VLM) systems. A recent white paper published by the Low Moisture Carpet Cleaners Association defines low moisture cleaning (LMC) systems as “…methods and/or procedures that allow any fiber to dry to its natural state in two hours or less [The paper cites standardizing criteria of 65% Rh and 70 degrees F]. This drying can be accomplished by using less moisture to clean, by using absorbent mediums, higher efficiency vacuums that efficiently extract water from the carpet, by increasing the evaporation rate of the moisture in the carpet by lowering the relative humidity of the environment you are cleaning in and/or by the use of airmovers.”
A carpet’s moisture retention will vary with the fiber being cleaned and the carpet texture. Tighter constructions will retain more moisture due to density of face yarns restricting the flow of air to the vacuum recovery system. One thing common to most VLM/LMC methods is agitation as part of the soil releasing-and-recovery process. This agitation – which may be provided by brushes or absorbent/nonabsorbent pads – when used in conjunction with water-based cleaning solutions may create more problems than it solves.
Typically, the cleaning/rinsing solution will be introduced to the face fibers and then pounded or ground deeper into the yarn structure by the agitation system. From there, removal is much more difficult, resulting in a damper carpet after extraction than if no agitation were used. Some low-moisture processes, including absorbent pad (bonnet) or rotary shampoo with a brush, have been given a reputation of being damaging to the carpet face and adversely affecting manufacturer warranties on the carpet. I am not aware of any lab testing being performed that adds any credence to these beliefs; however, there may be anecdotal evidence supporting the fears of damage due to low-moisture cleaning.
That, however, leaves unaddressed the issue of whether the damage is due to the process or the cleaning technician. My experience over three-plus decades of cleaning is that all systems are safe when used by a trained, motivated technician allowed to perform the cleaning task properly. Actually, it would seem that environmental conditions during and after cleaning are more important than method. Some low-moisture systems provide the advantage of higher production rates, which generally translates to lower cost, allowing more frequent cleaning or maintenance and extended carpet life. It would follow that low-moisture systems, which may be viewed with scorn by some, may actually be a boon to carpet owners and manufacturers due to lower cost and improved standards of care.
Carpet fibers are classified in two groups, natural and synthetic, with varying absorbency properties. Natural fibers, cotton (cellulosic) or wool (protein) are highly absorbent and will generally retain a fair amount of moisture, which makes them prime candidates for low-moisture cleaning. Synthetic fibers including nylon, olefin, polyester and acrylic are less absorbent, but this lower absorbency means that more rinsing water will be shed by the yarns and will make its way down to the base of the yarns, which may cause wicking of residuals, including detergents and soils/stains, during the drying of a less-than-desirable cleaning project. Even the most avid detractor must admit that low-moisture cleaning offers many advantages.