Best practice for both wipes and mops in a cleanroom environment is to employ single-use disposable products.  This reduces the risk of cross-contamination and ensures that contaminants are physically removed from the cleanroom environment at the end of a session.  However, many facilities are laundering and re-using mops as a potential cost savings alternative to single-use disposable products.    

Even the smallest cleanroom facility will spend tens of thousands of dollars on cleanroom consumables each year. In a large facility, this spend can be hundreds of thousands of dollars.  According to Transparency Market Research, leaders in analytics, research, and advisory services for Fortune 500 companies, the cleanroom consumables market is expanding at a steady compound annual growth rate (CAGR) of +4.2% between 2017 and 2023, to a valuation of $11.3M by 2023.

Careful consideration needs to be given as to whether the reuse of mops, especially microfiber mops, can lead to a reduction in consumable quality that could result in an increased risk of environment and product contamination.  

What is microfiber?

Microfiber textile products were first introduced in the late 1980s. The definition of microfiber is a fiber with less than 1 denier, which is a measurement of the thickness of individual fiber threads or filaments. Typically, a microfiber’s diameter is less than 10 micrometers (µm) ¹ .  To put this into perspective, it is less than the diameter of a silk strand or about 1/5^th the diameter of a human hair.  The tiny fibers are combined to create yarn which can be knitted or woven into a variety of constructions.  Microfiber fabrics can be broken down into two main types: split microfiber and straight filament microfiber.

Straight filament microfibers tend to be made from 100% polyester.  Split microfiber consists of very fine threads of polyester and polyamide (nylon) that are combined to form a single thread.  The nylon is used to glue the tiny fibers together until they are split later in the process.  Split microfiber (Fig 1) possesses numerous wedges rather than the rounded threads found in non-split yarns.  It is these wedges that provide the ability to collect microscopic particles from a surface.  This expanded surface area, combined with the capillary action of the fine threads, dramatically increases the sorbent capacity and sorbent rate of wipes. 

A change in the percentage of the microfiber blend will yield slightly different properties. This split structure impacts the way substrates pick up particles even when dry and can easily remove residues often without solvent.  The split fibers create microscopic spaces that collect and hold dust, dirt, and particles more effectively than standard round fibers, as seen in (Fig 2).

The increased use of microfiber mops

This high level of microfiber sorbency and its ability to pick and up and trap small particles has led to increased use of these types of mops in cleanroom environments.  However, microfibers are less durable than standard filaments and create much higher levels of fine particle contamination.  To be suitable for cleanroom use, microfiber is typically laundered during the manufacturing process and prior to distribution and use so as to reduce these levels of contamination.  This level of processing coupled with the cost of the microfiber yarn itself means the majority of cleanroom microfiber mops are too costly for single-use, and so are laundered, re-sterilized and re-used to be cost-effective.  This process typically involves a contract with external industrial laundry, and if a sterile product is required, either an autoclave process or an irradiation provider.

 

“ The process of relaundering and, where relevant, re-sterilization of cleanroom mops is not without risk.  Microfiber is very delicate and can be easily damaged by high heat or harsh chemicals, which can degrade a mop or wipe over time, affecting both its cleaning ability and sorbent capacity.”

 

Risks of relaundering microfiber

The process of relaundering and, where relevant, re-sterilization of cleanroom mops is not without risk.  Microfiber is very delicate and can be easily damaged by high heat or harsh chemicals, which can degrade a mop or wipe over time, affecting both its cleaning ability and sorbent capacity.  Laundries use mechanical, thermal, and chemical processes in washing and drying which can cause irreversible damage to the delicate microfiber structure. 

The key properties that make a microfiber product such a good cleaning tool, also makes them nearly impossible to be cleaned.  The fine filaments and delicate fiber structure are designed to gather and hold dirt, organic matter and microbes. As a result, it is extremely challenging to consistently remove those contaminants in each successive laundry cycle. So, the laundry facility is left with a paradox – either subject the products to effective laundry conditions that damage the cleaning efficiency of the fibers, or protect the products from degradation by minimizing the harshness of laundry treatment conditions and subsequently risk inadequate cleaning and disinfecting performance of the mop.

Contec Study

Recently relaundered microfiber mop
versus a routinely relaundered mop.

Contec’s Healthcare team looked into this paradox in more detail and published their findings in a white paper, Clinical Advantages of Disposable Microfiber Mops.²  The study compared hospital relaundered microfiber mops with a single-use disposable microfiber product.  The microfiber mops were analyzed before and after laundering to evaluate the impact of the laundry process on product performance. The study quantified the levels of organic and inorganic residues trapped in the microfiber structure, as well as the bioburden present on the mops after laundering. Other factors included the impact of the residual organics on subsequent quat binding and the actual cleaning efficacy of the relaundered mop versus a disposable mop using ATP analysis.

Although the study parameters may not be directly applicable to a cleanroom environment, particularly as relates to bioburden collected, the overall findings should be considered.

Visual and microscopic analysis

Figure 4	Figure 5	Figure 6
Scanning electron micrograph – new unlaundered microfiber flat mop (mag.=1000x)	canning electron micrograph re-laun-dered microfiber flat mop. (mag.=1000x)	Levels of residue extracted from re-laundered vs. disposable microfiber mops

The effects of repeated laundering can sometimes be obvious to the naked eye, especially with colored mops.  Fig 3.  This visual degradation can be monitored and controlled only if the user has specified a rigorous inspection routine for the mops during their relaundering process.  However, repeated laundering also causes damage that is invisible to the naked eye, as seen in the scanning electron microscope analyses in Figures 4 and 5, which show the dramatic difference between “new” microfiber and microfiber that had been “in the system” for just a few laundry cycles.  As previously mentioned, the fine nature of synthetic microfibers make them susceptible to damage, and the laundering process is harsh, with chemicals, heat, abrasion all playing a part in the cleaning and drying process.  The laundered fibers appear distorted and melted together, which can result in decreased performance in terms of sorbency and ability to hold particles and microbes.  Particulate contamination not removed by laundering (or introduced during the laundering process) are evident as white specks in Figure 5.

Residues in the mops

In addition to particles, it is possible that the laundry process is ineffective at removing trapped residues of the disinfectant or detergent solution.  This can be easily measured by soaking the mop in clean water and then squeezing the extract into a clear, clean beaker.  If the resulting water is dirty, cloudy, or contains suds then the laundry process has failed to sufficiently remove all the trapped chemical residue. 

To compare residuals from laundered re-usable mops versus disposable mop pads, an extraction test was conducted on 18 samples (9 laundered re-usable microfiber mops and 9 new microfiber pads) using the recommended practice published by the Institute of Environmental Sciences and Technology ³.  Samples of each mop were taken only from the microfiber fabric portion. Results of the analysis for residues are shown in Figure 6. The laundered microfiber mops had an average residual level of 0.099 ± 0.102 gm² whereas the average residues from disposable microfiber mops were nearly five times lower (0.020 ± 0.012 gm²) and exhibited much lower variability among the nine samples.  Fig 6

Impact of trapped residues on binding and inactivation of disinfectants

The retention of organic particulates and residues in laundered mops can cause issues when the mops are returned into use.  Disinfectants and sporicides are very reactive and can either readily bind to organic materials or be deactivated by them, whether they are living or not.  If the mop head is contaminated with residual detergents or organic debris left over after laundering, the mop head itself can bind or inactivate the disinfectant chemistry before it ever touches the surface to be disinfected.  Examples of a similar reaction have been demonstrated in previous studies where quaternary ammonium disinfectants (“quats”) readily bind to cotton (cellulose) based cleaning wipes and mops ^4-6 . This type of reaction also can occur with the residual organics in laundered synthetic mop heads. ​

To quantify this binding effect, the study compared using laundered mops vs. disposable microfiber mops with a common quat-based disinfectant.  Both mops were immersed in a 1000ppm commercially available quat solution for up to 60 minutes.  After removing the mops, the residual amount of active disinfectant on the mop was measured in addition to the amount of active disinfectant applied to a prepared surface.  Not unsurprisingly, the level of active disinfectant available decreased by 20% within the first minute of exposure to a laundered microfiber mop.  More interesting though was the concentrations in solution continued to decrease with the longer exposure times. Within 15 minutes, the levels in solution contacting the mop had dropped below the level required for disinfection.

With the disposable microfiber mop, the level of active quat in solution also decreased during initial exposure to the mop.  However, contrary to the laundered product, the concentration of active disinfectant stabilized after one (1) minute and remained at effective levels throughout the duration of the study. The levels of active quat recovered from the stainless steel coupons were lower than the levels from both the relaundered and single-use mops, but the same trends were observed, (i.e., higher levels of active quat were recovered from coupons on which disinfectant had been applied using single-use mops). These results indicate that residual organic matter can impact the efficacy of disinfectants when applied with re-laundered microfiber mops.

Summary

The use of single-use mops is very straightforward: a new mop is used to clean a specified area (floors, walls, etc.), then downgraded (for use in less critical areas), or discarded outright after the primary use. The surface area cleaned per mop is determined by sampling of critical metrics, and validated if the area is sterile.  The amount of particles and fibers shed by the mop is assessed using laboratory work provided by the manufacturer.  The ability of the mop to apply a validated disinfectant for a required contact time is assessed and documented.  This same initial testing and validation is carried out for a reusable mop.

Since single-use mops are made from new materials in a validated process, they provide a consistent and predictable performance and result.  This result remains constant even over a long period of time as a new mop with the same parameters is used every time.  As shown by the study above, the effect that relaundering has on a microfiber mop can lead to diminished performance and quality of the mop over time due to the inevitable degradation of the reused mop.  The laundry process can cause irreversible damage to the delicate microfiber structures that are essential for cleaning, and the retention of particles and/or residue can detrimentally affect the efficacy of disinfectants used.

For the evaluation of a reusable mop project, it is necessary to monitor the performance and quality over time in order to estimate the life cycle and therefore related costs of the mops.  As the actual quality, contamination profile, and performance of reusable mops will deviate over time, such deviation could result in unintended and potentially unacceptable risk to the user’s environment and ultimately finished product. Understanding the real risk of using reusable mops can be accomplished only through repeated validation over the period of relaundering, with the costs for that repeated validation considered as well.  The decision to use single-use versus laundered reusable mops may boil down to a simple question: “Do you really know the mop you’re using?”

Karen Rossington would like to acknowledge the input of Pier de Jong and David Nobile from Contec’s Technical Service Department in the creation of this article.

 

References

1 Textile Terms and Definitions, 11^th Edition, The Textile Institute

2 David J. Flynn, Peter K. Kang, Ph.D. K. Mark Wiencek, Ph.D. Contec White Paper 2017 Clinical Advantages of Disposable Microfiber Mops

3 Institute of Environmental Sciences and Technology (IEST). Evaluating Wiping Materials Used in Cleanrooms and Other Controlled Environments. Recommended Practice (RP), IEST-RP-CC 004.3 Section 7.1.2.

4 MacDougall, K. D., & Morris, C. (2006). Optimizing disinfectant application in healthcare facilities. Infection Control Today, 10, 62-67.

5. Engelbrecht, K., Ambrose, D., Sifuentes, L., Gerba, C., Weart, I., & Koenig, D. (2013). Decreased activity of commercially available disinfectants containing quaternary ammonium compounds when exposed to cotton towels. American Journal of Infection Control, 41(10), 908-911.

6. Boyce, J., Sullivan, L., Booker, A., & Baker, J. (2016). Quaternary Ammonium Disinfectant Issues Encountered in an Environmental Services Department. Infection Control & Hospital Epidemiology, 37(3), 340-342.