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Not all cleaning and disinfectant materials are the same

Comparing the relative efficacy of wipes and mop heads

By Tim Sandle

Introduction

Cleaning and disinfection are important components of the contamination control strategy (1). Cleaning removes soil and this is necessary since the presence of soil, especially an organic load, will interfere with disinfectant activity. The role of the disinfectant is then to kill or inactivate microorganisms. With cleaning using a detergent a number of microorganisms, as well as soil, will be disassociated and some will be taken away by the wipe itself, by means of mechanical action (2). The advantage of disassociation is where microorganisms in the planktonic state are easier to kill with a disinfectant than those in the sessile state.

The success of cleaning and disinfection is influenced by a number of factors, including the material used to construct wipes and mop heads (3). Given the different intents of ‘cleaning’ and ‘disinfection’, the optimal materials for the wipe or the mop head differ and there is also a choice to be made when selecting materials for different grades of cleanroom.

This paper looks at different material types and integrates the review into the success factors required for effective cleaning and disinfection.

Success factors for cleaning and disinfection

Material world

When evaluating the efficacy and relative advantages of different wipes and mopheads, there are multiple factors to consider:

  • The material used to manufacture the wipe or mophead.
  • The disinfectant (s) types and its concentration (4).
  • Application methods. Here technique is important and care must be paid to the transfer of microorganism to other parts of the surface, especially with avoiding simply transferring microorganisms to another place of the treated surface instead of being removed or inactivated.
    • While technique is important, this transfer mechanism also depends by the wipe retaining ability and the bactericidal activity of the disinfectant adsorbed into the wipe.
  • The amount of the disinfectant (active ingredient) that can be drawn into the wipe (its capacity), the time taken (sorbency), and then released from the material, is an important consideration. This relates to the material, the quantity and concentration of active ingredient, and the type of surface.
  • Interaction between wipes and active ingredients.
  • Target surface.
  • Presence of any soiling on the surface, especially the organic load.
  • Wiping strategy, including frequency of application and the association between cleaning and disinfection.
  • The types of microorganisms and the population, both in terms of innate resistance and the binding of microbial cells to surfaces.

Of the above factors, with materials the overall efficacy is ultimately dependent upon:

  • The inherent properties of the wiping material such as surface energy, fabric structure and fibre types (5).
  • The cleaning method, in terms of the applied pressure force, the geometry of the mechanical action, the number of passages and type of microorganism adhesion mechanism (6).

Therefore, it follows that wipes and mopheads should be designed with consideration to both the properties of the material and the interaction with the detergent or disinfectant (7) and this needs to be considered synergistically for when two materials interact each has an influence on the function of the other.

Material types

Across the healthcare and pharmaceutical sectors, the wipes and mopheads used for disinfection are generally divided between those composed either of:

  • Textile materials, such as cellulosic fibres (cotton, wood pulp, viscose, lyocell).
  • Thermoplastic fibres, such as polyethylene terephthalate (otherwise known as PET), and polypropylene.
Generally synthetic materials have longer fibres that are cleaner than natural fibres.
 
Materials for wipes and mop heads differ in their cost, the likelihood of releasing fibres, and the absorbency of the cleaning or disinfectant solution (8). Materials should be woven to reduce the potential of shedding particles and reduce the breakdown of the material matrix in use which could lead to further particle generation. Materials should also be lint free or at least low linting (therefore having only a low possibility of releasing fibres). The seal of the material is also important and some wipes have laser sealed edges to reduce any particle generation or fibre release. Wipes and mop heads designed to minimise particle and fibre release should be used in higher grade cleanrooms in order to safeguard products from material adulterants.

The absorption of active ingredients onto the material substrate will differ according to both the type of disinfectant and the type of fabric (9). These factors are additionally influenced by the soaking time and the way the solution binds to specific wiping materials (10), a process that varies according to the liquor ratio, pH, temperature, concentration of electrolytes and type of pre-treatment applied to the wipe material substrate (11). An assessment of these combination needs to be considered by the user since good adsorption of active ingredients onto the wipe substrate in the bulk solution, release of the liquid, and retaining sufficient active ingredients are essential for the application (12).

Differences in materials for cleaning and disinfection

Wipes and mop heads used for cleaning and disinfection are made from different materials, and they can be categorised in different ways. One division is between textiles and thermoplastics. Within this division, there are further differences in relation to finishes and seals. An example of a textile is a material made from cellulosic fibres. These are a relatively inexpensive material, compared with thermoplastics, and they have traditionally been used for wipe materials to ensure high water retention and storage capacities (13). However, such wipes are not suited to higher grade cleanrooms due to fibre release. An example of a thermoplastic is a material composed of polyester and viscose fibres (14). Such materials more suited for higher grade cleanrooms. In making decisions about wipes, there is sometimes the need to trade-off the risk of particle generation and the absorption capabilities of a wipe.

Materials for cleaning

For cleaning, studies have examined the relative efficiencies of different materials. Microfibre materials are occasionally presented combination with viscose, although microfibre alone is superior. Compared with other materials, microfibres tend to demonstrate enhanced cleaning ability. Microfibre refers to a material where the fibres are 1 denier or less (a denier is a measurement of fineness equal to a unit of fibre that weighs one gram for each 9000 meters; approximately, a microfibre is 1/100 the diameter of a human hair). Microfibre wipes are created by different types of materials. Superior microfibre materials are formed of a 100% polyester microfiber yarn, presented as a tightly knit filament structure.

The advantages of microfibres for cleaning are based on:

  • The fibres, in combination with physical action and the activity of a detergent, help loosen, absorb and dispose of dirt and other matter from the surface (15).
  • The cleaning efficiency have been evaluated by numerous studies. These demonstrate that microfiber system has superior particle, soil and microbial removal efficiency compared with most other materials (16, 17).

Care must be taken when using microfibre materials, since improper use of microfiber cloth can spread the bacteria onto other surfaces (18). However, overall, the materials are superior to wipes composed of less fine materials and these differ in their chemistry, denier and shape) (19).

For lower grade cleanrooms, less fine materials can be used where the concern over the release of fibres is less exacting.

Materials for disinfection
Higher grade cleanrooms

Generally, polyester (a synthetic petroleum-based fibre) is a good choice for higher grade cleanrooms. The monofilament structured material has good absorbency and release, able to dose efficient disinfectant to achieve the required contact time. These materials are often formed of multilayers and thermally bonded which aids the greater absorbance properties and greater resistance to abrasion in use. Wipes are typically laser edged sealed in order to reduce linting at the edges and thus any particle or fibre generation. Furthermore, optimal materials for higher-grade cleanrooms must be:

  • Strong, will not tear, non-shedding.
  • Low particle generating.
  • Non-abrasive.
  • Can be gamma irradiated for sterility, without damage.
  • Highly absorbent.

For mop heads, the polyester wipe is typically bound to a much larger inner core of polyurethane foam. The foam aids increased absorbance and it follows that the greater the amount of foam the larger the fluid capacity of the mop system. Heads only composed of polyurethane foam should be avoided as these are prone to damage and snagging when moved over uneven surfaces.

As well as the material, the geometry of the mop head is an important consideration. Large mop heads are suitable to cover bigger areas relatively quickly but they can present a problem when attempting to access spaces within a restricted space. Smaller size heads can cover deadspaces more easily.

Materials for disinfection
LOWER grade cleanrooms

Other materials, such as those formed from viscose, a viscose/polyester combination, or polycellulose can be used in Grade C and D cleanrooms. Cotton wipes (either pure cotton wipes or a mixture with cellulose) are sometimes used by these are not recommended. This is because the material is produced in a tight twill construction leading to individual fibres splitting and breaking free from the weave.

Materials used in lower grade cleanrooms are less likely to be laser sealed and instead they will be cut edge. Overall, such materials are more likely to shed fibres, which restrict their use to lower graded areas. In addition, the materials may contain trace impurities that could interact with cleaning agents leading to some deactivation of the active ingredient.

In summary, these types of materials are:

  • Economical.
  • Relatively high absorbency.
  • Strong.
  • Low linting.
  • More resistant to acids and other chemicals (which might be found in lower grade cleanrooms), especially polypropylene/cellulose materials.

To reiterate, such wipes, whilst relatively effective, are not suitable for higher grade cleanrooms.

Sterility and bioburden

Detergents and disinfectants used in higher grade cleanrooms (Grades A and B) need to be sterile. The importance of this emphasised in the draft EU GMP Annex 1 revision (20). To maintain sterility, this requirement extends not only to the detergent or disinfectant but also to the method of application, in the form of wipes and mop heads. Due to the desirability of minimising contamination, the Annex suggests that disinfectants used in lower graded cleanrooms - Grade C and D - may also be sterile. While this remains something to be determined by the user, knowing that the agents used are themselves not a source of contamination provides a further level of assurance for the cleanroom manager. Where sterility is required, the method of sterilisation should not adversely affect the material.

As well as sterilisation, for higher-grade cleanrooms there is the additional requirement that wipes are low in bacterial endotoxin. This is especially important where there is a direct risk to product or indirectly via product components.

Ageing performance

The ageing performance of materials is not always studied. Important parameters relate to the manufacture and finish of the wipe. Wipes should remain stable across the storage time, in relation to their chemical and thermo-mechanical properties. Generally, wipes subjected to a finishing process have a superior breaking force and elongation, especially once wetted.

Conclusion

The efficacy of cleaning and disinfection is often discussed in terms of concentration, contact time, and method of application. Whilst these remain very important, effective surface disinfection also includes selection of an appropriate fabric. This paper introduces the importance of material compatibility (combination of wipe and disinfectant) and the liquor ratio (wipe mass in relation to disinfection solution volume) as additional factors to consider when making purchasing choices.

This leads to the outcome that different types of wipes have different advantages for different situations, in terms of both cleaning (such as microfibre wipes) and disinfection (such as polyester wipes) and between different cleanroom grades. It is important that wipes used in higher grade areas are the lowest in terms of particle generation and have good sorbency.

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