The optimization of the cleaning process is critical for minimizing operational costs and down time and for achieving target sustainability goals such as reduction of water and energy consumption.

The aim of this article is to illustrate some cleaning challenges commonly faced by cosmetic manufacturers, and to provide insights into how cleaning and disinfection procedures can be optimized through chemistry choice, cleaning application, and equipment options.

1. Understanding cleaning challenges and requirements of the industry

As of today, a primary challenge for manufacturers of cosmetics is to maintain efficient manufacturing operations with a constantly evolving product portfolio. “On average, large industry companies have a product portfolio of around 10,000 different cosmetic products and reformulate around 25%-30% of their products every year. Out of these reformulations, about 10% contain ingredients that are new to the market or cosmetic industry. Large companies introduce around 80 new ingredients to their product portfolio each year.” ^[1]

In addition, growing demand for multi-functional premium cosmetics results in an increase in complexity of formulations, creating even greater challenges for manufacturers in defining optimized cleaning procedures

For many multinational companies, setting a global cleaning strategy is important to better ensure product safety and cleaning effectiveness. While many personal care products are produced globally with similar formulations, color cosmetics are often locally specific to meet regional preferences and trends.   This mix of global and local portfolio within one manufacturing facility complicates the goal of a global cleaning program.  The regulatory requirements associated with cleaning can also vary regionally, with some markets requiring validation, while others having no such requirement, adding additional complexity to a company’s global standard.

2. Hard to clean ingredients and products

In this section, product types with difficult-to-clean ingredients common in industry will be discussed, as well as possible cleaning strategies to tackle the challenges. For purposes of this discussion, “clean” will be defined as visually clean, meaning that no visible residue is present, and the surface exhibits good “sheeting”. Sheeting is a characteristic wherein surface tension is reduced, allowing water to sheet across the surface rather than bead-up. 

Poor sheeting is illustrated in this photo. 

Waxy soils – large amounts of waxy soils inhibit the ability of an aqueous cleaning solution to penetrate the soil due the hydrophobic nature. As these soils repel water, a tenacious oil or waxy / fatty layer can form on the surface resulting in product residues remaining on the equipment. Cleaning can be performed by leveraging the synergistic action of wetting agents to penetrate the soil coupled with surfactants that allow solubilization. The combined effect is dispersion of the fatty, viscous layer.  

An example of this cleaning challenge is waterproof lipstick. In this test, shown in Figure 1, numerous combinations of surfactants, alkalinities, and other functional additives were not successful in removing the waxy soil.   The detergent that contained wetting agents in the formulation resulted in removal of the waterproof product.

Silicone – Although some silicones are easily cleaned, numerous products on the market are formulated to be hydrophobic to provide a specific consumer experience. This characteristic provides excellent water-proof performance for the consumer but creates cleaning challenges at the manufacturing plant. Frequently, this leaves the plant performing extensive manual intervention or recleans to sufficiently remove the silicone layer. Alternatively, cleaning might be achieved through a selective combination of surfactants and other functional ingredients to break the silicone layer. 

In this example (Figure 2), the combination of specific surfactants boosted with high alkalinity was successful in removing the deodorant stick with silicones.

High Pigment / Mineral Loads – Many pigments are formulated using minerals and other inorganic components.   Although the minerals provide beautiful colors for the consumer, they can leave behind a thin film of powder residue on equipment surfaces that is challenging to remove.   Failure to remove the residue can result in contamination of the next batch with an off-color tint.  Effective cleaning can be achieved through the synergistic action between select surfactants and chelating agents.

High Inert Inorganic loads – Inert components such as clay, mica, or kaolin may provide texture, functionality, or appearance features to a product, while leaving a challenging residue on equipment surfaces. Although a residue layer can frequently be wiped away by hand, it can be difficult to remove chemically or through mechanical action, leaving the manufacturer to manual cleaning as the only effective option.  Efficient cleaning can be achieved by a synergistic selection of surfactants and chelating agents (Figure 3).  

In Figure 4, a clay mask is effectively cleaned using an alkaline detergent built with surfactants and chelating agents.  The chelating agents help keep the clay suspended in the cleaning solution so that redeposition does not occur. This detergent in conjunction with innovative cleaning methods discussed further on in this article can reduce manual cleaning requirements significantly.

3. Designing and optimizing the cleaning process

Selecting the right detergent for the soil to be cleaned is only the first step in designing an efficient cleaning process.   This section will provide an overview of the impact of cleaning parameters on cleaning effectiveness, and discussion on tactics to optimize those parameters.

Foundation for cleaning parameters:   Parameters influencing cleaning are simply described in a model called the “Sinner Circle”, a hypothesis constructed by Dr. Herbert Sinner of Henkel Corp in the mid-1950’s. Dr. Sinner’s hypothesis stated that cleaning is achieved through a balance of four parameters – temperature, mechanical action, chemistry, and time. Optimal cleaning is achieved when these four parameters are in perfect balance. A reduction in any one parameter must be offset by an increase in another parameter to maintain effective cleaning.

(Source: Dr Herbert Sinner 1959)

How one defines optimized cleaning can vary depending on the industry and company-specific goals.   Optimizing can mean reduction in cleaning time, reduced water utilization, improved cleaning quality, and so on.   Let’s go a bit deeper into the impact of each of the cleaning parameters on such optimization metrics. 

Temperature. In general, the quality of cleaning increases at a higher temperature. Trends for reducing temperatures for improved worker safety or energy reduction are generally counter to more efficient cleaning.  The loss in cleaning power associated with lower cleaning temperatures can occasionally be circumvented by using an automated cleaning system with increased mechanical action.   Also, new state-of-the-art detergent formulations are designed to tackle personal care soils at lower temperatures, even some of the difficult to clean soils discussed earlier in this article. There are ingredients best cleaned at lower temperatures, such as starches – these are an exception to be aware of when the cleaning process is designed.  

Time: Time spent cleaning is obviously time when production is not running, which negatively impacts productivity metrics.  Historically, companies rarely focused on optimizing cleaning cycles to increase productivity, as cleaning time was seen as a necessary evil.   Cleaning time reduction can be studied within the construct of the Sinner Circle, adjusting other parameters to maintain cleaning quality.  One should be aware that there are product soils that require multiple short burst washes rather than a single, extended cleaning cycle.  In some cases, a single continuous cleaning cycle can redeposit soils rather than suspending them in solution.   Thus, soil characteristics can play into cleaning time as well. 

Chemistry. Chemistry refers to detergents and additives, as was discussed earlier in this article.  Specifically-developed chemistry for the target soil is recommended to remove tenacious residues present in personal care products.   Typical soiling requires high levels of detergency coupled with other functional ingredients (solubilizers, complexing agents, and so on). Commodity cleaning products not specifically designed for the personal care soils often do not remove difficult residues, resulting in repeat or extended cleanings.

Mechanical Action. Mechanical action is often defined by equipment and controls.   A wide variety of operations can be found in the industry, from dedicated CIP systems designed for defined products, to simple vessels without cleaning capability which are cleaned by soaking or manual scrubbing.  Even with automated processes, it is seen in practice that some manual cleaning applications may be required.   This manual cleaning can include high pressure lances used for prewashing or a manual water hose for rinsing.  Tools like sponges, brushes and mops are also often used inside the manufacturing equipment to provide different mechanical actions and must be considered.

4. Optimizing conditions for various cleaning methods

Clean-in-Place (CIP) Cleaning – CIP in a recirculating cleaning system is an industry standard today. The cleaning fluid is recirculated across product contact surfaces at controlled temperature, flow and chemical concentration. CIP cleaning of equipment and pipe circuits is defined as cleaning without disassembly or opening of the equipment, and with little or no interaction of the operator. One CIP system may be designed to deliver cleaning to several different equipment pieces or segments. 

Efficient CIP cleaning is built on effective energy transfer to ensure removal of soil residues. Within a given CIP system, the optimal conditions to remove the soil from all equipment surfaces must be identified and maintained.  Detergents designed for CIP are often low foaming and have the ability to be continuously measured for concentration.  

Cleaning that uses optimal time, temperature, flow rates and detergent concentration is a cleaning cycle designed with proper engineering. A starting point for the effective cleaning regime can be established with laboratory bench scale studies which can identify which detergent delivers the best cleaning for target products, and the most effective temperature for that detergent / soil combination.   The parameters identified in the laboratory trials become the basis for the plant scale CIP system design.

Validation of an effective CIP cleaning is easily achievable because the cleaning parameters are controlled to identical setpoints during each cycle.   To ensure this consistency, a robust change control process and reliable maintenance program related to the CIP system should be in place at the facility.  

Adding CIP capabilities to existing equipment can be challenging and require significant investment.    However, the operational efficiencies, cleaning effectiveness, and cycle reproducibility often outweigh these challenges. Additionally, unique recipe configurations such as reusing rinse water as a pre-wash in the next cleaning cycle allow for ecological and economic efficiencies not available in a manual system.

Cleaning by Soaking – When CIP cleaning is not possible, an alternative for more difficult residues is to soak the equipment, say a tank, in a detergent solution, often using an agitator integrated within the vessel to introduce mechanical action into the cleaning cycle. The drawback of this method is the increased consumption of chemistry, water, energy, and time.  Often, recirculating the water and cleaning solutions within the object being cleaned can simulate some benefits of a CIP system without the full CIP investment.   The benefit of this approach compared to a true soaking procedure is that chemicals, water, energy and time can all be reduced, while introducing some mechanical action.

COP Cleaning – Clean-out-of-place (COP) cleaning consists of disassembling equipment and washing the parts “out-of-place”, often in a separate “COP” room. This mode of cleaning can be effective for both easy-to-clean and hard-to-clean soil. Operators often use medium-pressure sprayer, high-pressure water or manually scrubbing in a sink to provide mechanical action.  In any case, the cleaning performance relies heavily on the operator performance, limiting confidence that the COP process has been repeated reliably. In addition, cleaning parameters are often restricted to ensure employee safety, such as temperature, detergent chemistry, scrubbing or mechanical action.  

The use of a “parts washer” cabinet washer, or a COP Immersion Washer will allow some automation of the COP process and remove the operator from direct contact with the cleaning solution.   This removes operator variability from the process, as well as allowing the TACT parameters (Time, mechanical action, chemistry, and temperature) to be leveraged fully for more efficient cleaning.  

Manual cleaning – Manual cleaning is very easy to set up but introduces several challenges relative to the Sinner Circle model. Employee safety limits wash temperature to about 45’C and detergent pH in a relatively neutral range. These limits constrain detergent performance, resulting in time and mechanical action to be increased to maintain effective cleaning.

Thus, cleaning becomes labor intensive and time consuming. Verification and consistency of cleaning conditions is also a challenge due to operator variation and difficulty monitoring actual conditions.