Written by: Dr Jose A. Ramirez, MS, PhD. Chief Science Advisor, i-Team Global
Foaming is a widely used technique in cleaning vertical and horizontal surfaces and equipment in various environments. Foaming provides an efficient, hands-free approach to cleaning, given it combines the key cleaning factors of mechanical energy (pressure), temperature (when relevant), time and chemical energy (in the form of detergents and surfactants). When done properly, it allows the rapid application of the cleaning agent guided by the clear visual foam-cue, followed by a rapid rinse-off with clean water.
Fundamentals of the cleaning process
A simple description of the critical factors governing the kinetics of the cleaning process was first attributed to the Swiss chemist Dr Herbert Sinner. He devised a simple diagram (Fig 1) that expressed the interdependence of mechanical energy, chemical energy, thermal energy and contact time in the cleaning process.
Qualitatively speaking, from Sinner’s circle, it is evident that the quality of a particular cleaning job will be dependent on:
The amount of mechanical action provided (scrubbing, pressure, abrasion, etc.)
The chemical energy provided (the type and concentration of cleaning agents)
Thermal energy (i.e. the temperature during the cleaning process).
And contact time.
The interdependency of factors manifests itself when, for example; less concentration of a cleaning agent is used, it is necessary to make up for it with scrubbing, or pressure (mechanical energy), hot water (thermal energy), prolonged soaking (extended time) or a combination of 2 or all of these.
In light of this, you will obtain an optimal cleaning outcome by providing the correct water pressure in the foaming/rinsing process, delivering the right chemical agent at the proper concentration, and ensuring the cleaning agent stays in contact with the surface for the appropriate amount of time.
Factors to consider for effective foam-cleaning
A series of factors need to be taken into account to fully leverage the benefits of foamed cleaning. These factors can be grouped into the following categories:
Application technique
As we have alluded to before, it is essential to ensure that the foamed cleaning agent is in contact with the soiled surface for a suitable amount of time. Vertical surfaces should be foamed in horizontal strokes, going from bottom to top—this provides a clear view of coverage in real-time, without the interference of foam drainage downwards.
Furthermore, rinsing of the cleaning agents should be done from the top-down, as this takes advantage of the rinse-off from the upper surface, ultimately reducing the total amount of rinse water required. Naturally, the nature of the cleaning agent can help minimise run-off during application and accelerate rinse-off—this is achieved through smart formulation.
Product chemistry
The formulation of the cleaning agent is crucial, as it must contain the right proportions of detergent agents, chelating agents and buffers.
Detergent agents produce a lower surface tension cleaning solution, allowing rapid penetration into micro-environments on the surface and adsorbed soils. Detergent agents also emulsify the soil particles, solubilising them in the cleaning solution to allow their fast rinse off.
Chelants help solubilise mineral deposits and protect detergents from inactivation by water hardness. Buffers ensure the proper pH environment is maintained in the cleaning solution to ensure favourable chemical equilibrium conditions exist according to the cleaning task (e.g. acidity in scale removal and alkalinity in greasy soil removal).
Application equipment
The application equipment should be simple and easy to set up, operate and break down after the job. This ensures training is simple and helps avoid in-use mistakes. You should select equipment that delivers the correct in-use solution, as preparation is prone to errors and wastage and poses a safety hazard.
Foam characteristics
The nature of the foam is important, in the sense that:
It should be of the proper consistency (bubble size, air content, effective viscosity) that gravity drag is not excessive and has good cling to vertical surfaces.
It should be easy to rinse – i.e. rapid break-up on rinsing.
It should not accumulate excessively at the bottom of vertical surfaces (this hampers rapid rinsing from the work area)
It provides the correct contact time to allow for loosening and emulsification of soils (again, adequate cling-time).
The proper selection of equipment and cleaning agents, paired with the right application procedure, will realise the full benefit of foamed cleaning.
The benefits of foamed cleaning can be summarised as:
Productivity
Foam-cleaning has the benefit of being a hands-off process, consisting of essentially two steps in its most basic form. The first step is the application of the foam, and the second step is the rinsing of the foam. With the right application system, cleaning agent and proper technique, you can apply foam at the rate of 1 m2 per sec. This allows the cleaning of large areas relatively quickly, particularly if a one-step cleaning/disinfection approach is viable.
Rinsing off the cleaning agent can add significant time to the overall process. Thick or airy foams that are hard to rinse and tend to deposit and accumulate on the floor due to rapid run-off from vertical surfaces are tough to deal with. The cleaning agent must deliver a stable foam, with adequate cling time to vertical surfaces and bubble size and air content that enables rapid rinse-off.
Equipment set-up and break-down can sometimes be an important contributor to total cleaning time. In this case, equipment that quick-connects to the water hose without tools, along with cleaning agents that do not need further preparation procedures (e.g. dilution, filling of a bottle, etc.), are necessary. For example, a tableted cleaning agent combined with an innovative tablet-based foam sprayer such as the i-Spraywash system allows for rapid set-up and break-down before and after the cleaning job.
Cost savings
Inline tablet-dispensing systems benefit from providing a controlled dose of cleaning agent without the wastage and errors associated with manual preparation of in-use or stock solutions from liquid concentrates. A thin, stable, slightly viscous foam with smaller bubbles applied at the correct rate of 1 m2/sec can result in adequate surface coverages with substantial savings in chemical and water, greatly enhancing the chemical cost per in-use litre or m2.
Environmental
The proper foam consistency and application method ensures the surface is easily rinsed. The end result is a lower concentration of active ingredients in the wash-off, with reduced total rinse-off volume of water to the sewer. Cleaning agent formulations should be based on naturally derived surfactants from responsibly harvested, biodegradable plant stock. According to EN and OECD norms, all ingredients should be rapidly biodegradable and thus broken down entirely in the natural environment.
Performance
The combination of contact time from a high-cling foam and the detersive action of the cleaning agents ensure that soils are loosened and emulsified in the foam phase, facilitating easy removal and wash-off in the water rinse. The clear visual cue of the foam helps reduce missed spots and under-cleaning due to uneven application.
Safety
The end-use solution coming out of the spray nozzle should be non-hazardous per the criteria outlined in the EN CLP regulation. Although it is always recommended to use safety goggles and gloves when handling chemicals, the reassurance of using a safe, non-hazardous product can help mitigate the occasional (inevitable) breach in safety procedures.
When possible, you should avoid hazardous concentrated liquids to reduce the risk of eye or skin injury, especially if they require manual handling and preparation.
Conclusion
Foam-cleaning with the right combination of equipment, cleaning agents, and proper application technique can result in better hygiene at lower cost, higher productivity, improved safety and lower environmental impact.
There are key factors that indirectly affect cleaning outcomes and the total cost and duration of the process. Attention to the type of foam applied and its removal is vital—high cling foams with an adequate air-to-liquid ratio are preferred.
You should also pay special attention to the foaming characteristics delivered by the equipment, the cleaning agent and the application technique.