Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE


This shift led to the increased importance for biocides resulting in willingness of manufactures to spend more on good quality biocides to increase their product performance. Biocides generally constitute 2-3% of the MWF concentrate formulation. Apart from this, some biocides like isothiozolinones are also added to the sumps directly. This dosing mechanism is called tankside additions. The tankside additions are generally performed when there is any untimely microbial issue (pH drop, foul smell, etc) in the running machine. The manufacturer generally provides these tankside biocides for free as part of their technical support to their customers. There are few limitations with tankside additions:


1. It constitutes additional cost. 2. It is not a permanent solution to the problem 3. Sometimes customers are reluctant to add biocides tankside because of safety concerns.


In these circumstances, there is a need for robust biocide in the concentrate MWFs formulation itself to drastically reduce the use of tankside biocides and save money for manufacturers.


Microbial issues in the coolant sump are universal and not only the small and local manufacturers are facing this problem, but even multinational companies are struggling to provide prolonged life to their semi-synthetic MWFs. A big limitation with multinational companies is that their formulations are decided globally but microbial problems are very much locally dependent (geography, climate, culture, plant design, plan operation etc.). In such a scenario, even though their product faces local microbial challenges, it becomes difficult for them to modify their formulation independently. On the contrary, local and small MWF manufacturers are independent and take decisions that satisfy their customer’s need within their cost limits to stay and maintain their brand name in the market.


Based on complexities of chemistries, physics, formulation and microbiology disciplines involved in MWF design, focused microbiological knowledge is rather scarce. Despite the use of biocides (and unfortunately due to inappropriate biocide application), problems are faced very frequently. Although, these problems are considered seriously, unfortunately often temporary solutions are devised to these problems, which later sometimes lead to catastrophic results.


The above mentioned limitations in knowledge and focus results in the continuing use of traditional biocides which are cheap, well established but provide very limited protection against specific bacterial problems. This results in a strong focus on cost comparison with limited emphasis on thorough understanding, quality and innovation.


Based on above described scenario, it is obvious that the microbial control challenges in the use of MWFs is immense and needs to be addressed. The elaboration on biofilm, illustration of biocidal actives and their features, and examples provided


38 LUBE MAGAZINE NO.138 APRIL 2017


No.109 page 2


in case studies shall contribute to advancing understanding of microbial control in MWF applications.


MICROBIAL CONTROL CHALLENGES: Biofilms: A new concept in sump management In metalworking fluids, one of the main issues is biofilm development’. The issue is hardly heard of, and remains largely unaddressed. Biofilms are cluster of different bacterial species which stick to each other on a surface under a complex matrix of extracellular polymeric substances (EPS). The EPS matrix consists of polysaccharides, proteins, DNA and RNA secreted by the microbial cells itself. In MWF operations, the typical surface on which biofilms form are usually the sump walls, the pipe interiors and machine surfaces (Fig 2). The biofilms generally can go undetected when located in places where the human reach is difficult and so are difficult to remove. The biofilm EPS matrix can protect microbes and make it more difficult for tankside biocide treatments to be effective. EPS matrix of a biofilm will limit the penetration of oxygen into them. In low oxygen environments, sulphate reducing bacteria (SRB) and iron-reducing bacteria (IRB) can proliferate. SRBs produce H2


S (hydrogen sulphide) gas which smells similar to


rotten eggs and will reacts with and corrode metal surfaces of the machine. The SRBs and IRBs present inside the biofilms results in the formation of iron sulphide (FeS) which is black in colour and is a by-product of microbial corrosion. This causes discolouration in the emulsion (Fig 3). The H2


S gas produced in the sump can


deactivate isothiazolinones which are commonly used as tankside biocide additions resulting in the need for higher and more frequent dosing.


Efficacy and limitation of commonly used biocides in India: Triazine (1,3,5-tris(2-hydroxyethyl)-s-triazine): Some of the best selling products in the Indian MWF market today is the class of triazine based biocides either as stand-alone or in combination with a fungicide. Triazine can be considered as one of the commonly used biocides for MWF concentrate applications because it has high pH stability, a lower cost option, and it is well known and widely available. However, there are few limitations with triazine chemistry. First, triazine based biocides display an efficacy gap against sulphate reducing bacteria (SRB) and so, the fear of bio-film formation and fouling of fluids is always there. It is true that triazine acts well against many other bacterial species and provides decent protection. However, in order to make the fluid full-proof against microbial contamination, especially Indian conditions where the fluid management practices are below standards, triazine chemistries have not yielded adequate results. Triazine also display an efficacy gap against Mycobacterium species. These bacterial species are slow growing and are difficult to quantify thus are often not appropriately identified. However, they have been implicated in causing an occupational illness called hypersensitivity pneumonitis.


Another crucial problem associated with triazine is that its mechanism of action is by immediate excess release of formaldehyde. Although it results in faster killing of bacteria, formaldehyde, being very volatile, evaporates rapidly, which


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