As we know, ceramic tiles, both for walls and floors, are marked by important technical and aesthetic performances that make them a unique product, hardly comparable to other categories of materials: resistance to abrasion, foot traffic, test of time, chemical products and natural elements. Just to mention the most important features.
In addition to that, hygiene and sanitation are certainly another two significant topics that distinguish ceramic from all competingmaterials.
If from one hand it is well established that the ceramic’s hygienic and non-toxic nature concern to its inherent characteristics, it is also true that technology innovation and materials engineering have been able to enhance over time its chemical, physical and mechanical performances.
Due also to the recent events that have brought to public attention the increasingly tightening requirements in terms of cleaning and health protection, the ceramic district - that for some time has been offering to the market surfaces with “anti-bacterial properties” - is working hardly with an agenda that put the anti-bacterial topic at the top of list.
Ceramic surfaces, whether they are for floor, kitchen top or tables, are potentially the most vulnerable to contaminations and attack, being daily in contact with external agents that might compromise their behaviour.
With that said, what are anti-bacterial surfaces? How do they work? What kind of features must they have in order to be called as such?
SUBSTANCES AND TERMINOLOGIES
In general, a tile can be defined as “anti-bacterial” when it is able to neutralize the growth of microbes and bacteria thanks to the use of specific substances that may be added within the ceramic body or applied on its top.
Which are these elements?
Anti-bacterial materials, to be such, involve the use of active principles based on silver ion or specific metals among which titanium dioxide is certainly the most popular. There are currently several case histories but we want now to focus on the two main lines.
SILVER: A BIT OF HISTORY AND CURIOSITIES
Silver’s antimicrobial properties are well known from ancient times, being exploited in many healthcare sectors in order to prevent diseases and contaminations. In this field, after the discovery and the use of antibiotics, its use as a microbial agent has drastically decreased. Nevertheless, the presence of persistent and particularly reoffend bacterial strains, has led to a renewed interest towards this substance and its distinctive properties.
Thanks to the achievements of modern science, together with technological advances (such as the use of radioactive isotopes and electron microscopy), it has been possible to deepen the subject by analysing more accurately the action of silver as an antibacterial substance.
The theories are many but they all have a common denominator: silver gets into the cells, damaging them by the use of membrane proteins that, among their several functions, are able to carry the molecules across the membrane by means of pores, ion channels or specific carriers.
In any case, to carry out its antibacterial function, silver must be in ionic form, such as silver nitrate or nanoparticles.
TITANIUM DIOXIDE (TiO2)
Titanium dioxide is a chemical compound in the form of colourless and tending to white crystalline powder. It is naturally occurring in five different forms and it is used in many production fields: pigment in paints, compound for plastics, dye for cosmetics, building cement, etc.
By restricting its use to our field of interest, it is important to underline that we are talking about a catalyst able to degrade, by oxidation, a lot of organic compounds. This means that, by using titanium dioxide, it is possible to produce materials that are able - by means of sunlight - to destroy organic compounds present on their surface. This feature can potentially pave the way for the development of materials with self-cleaning properties.
In terms of terminology, the vocabulary is huge and the words in use, though apparently similar, define with different shades of meaning various levels of action.
Here’s the most relevant.
- ANTIBACTERIAL: Substance that kills or prevent bacteria proliferation. It is different from an ANTIMICROBIAL, acting on different kind of microorganisms.
- BACTERICIDE: A bactericide is an agent able to kill bacteria. It can be of a physical nature (such as heat, electromagnetic radiations or ultrasounds) or of a chemical nature. The latter can be in turn inorganic (acids, alkali, halogen and oxidizers) or organic (alcohol, aldehydes, phenols and surfactants). They act by denaturing bacteria’s proteins or breaking the cellular wall by mechanical stress, therefore resulting in the death of microorganisms.
- BACTERIOSTATIC: You can define bacteriostatic any kind of physical or chemical agent able to partially or completely inhibit bacteria’s reproduction. Unlike bactericides (often used as a synonym of bacteriostatics), it does not cause the death of bacteria but it just prevents their reproduction.
REGULATIONS AND BPR (BIOCIDAL PRODUCT REGULATION)
A ceramic surface can be certified as antibacterial only after being processed under strict lab tests attesting its capability to reduce of the 99,9% the most important bacterial strains found in the environments, responsible of the most aggressive kind of infections:
- 1. Staphylococcus Aureus
- 2. Enterococcus Faecalis
- 3. Escherichia Coli
- 4. Pseudomonas Aeruginosa
The required rate is clearly extremely high and it is not possible to assure a 100% of anti-bacterial effect. This is the reason why, in fact, the efficiency threshold set by researchers is about 90%. If the scientific community detects a lower percentage, the product cannot be definitely defined as anti-bacterial.
Beside this, there are, on a broader basis, very strict rules handled at EU level by the Biocidal Products Regulations that supervises the marketing of all that biocides used to protect from parasites and bacteria – by the action of their active principles – humans, animals or materials.
The regulation has been established in order to increase the governance system, therefore to ensure that the potential risks of harmful effects promoted by biocides are balanced by the expected benefits.
We might argue that all biocides need an authorization before being brought to the market and that the consent depends on the approval of all active principles (such as silver) contained in the biocide.
The approval of the active principles must be on a EU level and the following biocide’s authorization on the Member States level.
BPR regulation finally set the rules concerning the use of all products treated with (or intentionally containing) one or more biocides.
Against this backdrop – that might create a slippery use of naming and terminologies – it is now clear that a surface can be defined as antibacterial only after being submitted to a long series of regulated tests.
CERAMIC PRODUCTION PROCESS AND APPLICATIONS
We are currently in front of a changing panorama and many different application options are still under consideration.
With a view of simplification we could identify two possible choices: the antibacterial protection can be included inside the ceramic body or applied on final protection’s layer.
Depending on the process step and without excluding other methods, in general, it is possible to proceed as follows:
APPLICATIONS BEFORE THE FIRING PROCESS (INSIDE THE CERAMIC BODY)
- Medium inside the glaze (by spray application)
- Medium inside the inks (by digital application)
- Medium inside binders for grit
APPLICATIONS AFTER THE FIRING PROCESS (IN THE LAYER OF FINAL PROTECTION PRODUCTS)
- Additivation of the active principle within the products for final superficial treatment
APPLICATION FIELDS AND DURATION OF THE TREATMENTS
It might seem obvious but is important to underline that all these treatments can be potentially applied on any kind of surfaces, regardless of whether they are for domestic or commercial use.
The benefits are in both cases self-evident.
It must nevertheless be noted that an antibacterial ceramic product (or “with anti-bacterial properties”) cannot ensure a total resistance to infections (100%). This means that even these surfaces need periodic maintenance by using sanitizers and detergents usually available on the market.
The lifespan of the anti-bacterial properties of the surface can also change according to several factors.
If it is true that, after the application/treatment, the constant release of bactericides provides the material with a continuous protection (regardless of whether the action takes place thanks to a photo-catalytic process or without the use of light sources), it is also true that some options seems today to be more eternal than others. In some cases, in fact, a new treatment might be necessary and this difference can be attributed mostly to the chosen application.
Anyway, as already mentioned, we are still in a development phase and it is not possible to put a full stop yet. The ceramic district is, in fact, still trying to give new answers, investing in research and development, consolidating what has been achieved and opening new paths that are currently being explored.
For further information and developments we invite you to contact Z&S Ceramco Lab.
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