BACK TO BASICS - PART 3
BACK TO BASICS 3
Why HLB Doesn’t Always Work
by Dom Ruggeri
As you must know by now, in the late 1980’s to early 1990’s I was working for a large formulating house servicing the metalworking fluid market. I had finished developing a high-tech soluble oil and we were going into a field trial. We visited the customer, completed our system survey, and saw no reason not to proceed with the coolant trial.
Back in the late 1980’s to mid 1990’s as I was honing my skills as a formulator, the company I was with began interviewing to fill a chemist’s position. They opted to look outside, and if possible, hire from a competitor. This can be a good strategy as long as one finds the right candidate. The technical manager reviewed many resumes and decided on six candidates. Each one was from a different competitor. Any one of the would fine the purpose of obtaining competitive technology. Five candidates came in; five left. None were a good fit. The sixth candidate was perhaps the most questionable. I spent about 10 minutes with him and said “no way.” A good friend of mine suggested we hire him, but not a senior level position. Over our objections, the lab manager hired him. The reason was that he was a self-proclaimed surfactant expert.
His first project was to reduce the cost of a fluid I had formulated. Easy, use cheaper surfactants. This was exactly the road he chose as he replaced all of my carefully selected low to no foaming surfactants with cheap nonyl-phenols. I was stunned, not so much because he chose those surfactants but because the technical manager went along with him. As we all knew, nonyl-phenols were high-foamers. He insisted no they were not and management bought off on his recommendation and assessment. Further, he pointed out that the HLB of the system was the same as mine was so how could the product foam?
The product foamed out of the customer’s equipment in about twenty minutes. So much for HLB. We were forced to go back to the previous formulation and promise the customer we would not ever change this product again. This particular chemist was eventually given the nickname “Wonder Boy” because we wondered what the boy would mess up next.
Everyone in the metalworking industry knows how to use HLB (Hydrophile Lypophile Balance) yet how many of us know where these HLB numbers come from? The HLB Scale is based on nonyl-phenol surfactants, using a ratio based on the number of moles of EO and the molecular weight of the molecule. This system works well for nonyl-phenol surfactants, but what if you are using EO/PO block copolymers? The common practice is to call the manufacturer, ask for the HLB, and blend accordingly as if you were using nonyl-phenols. Ninety percent of the time everything will be fine, however there is that ten percent where the emulsion will not turn out as expected. What happens is when you move away from nonyl-phenols, manufacturers determine the HLB number of a surfactant by comparing the emulsification properties of a nonyl-phenol surfactant of known HLB. Although this comparison is quite good in your particular fluid, it may not be good enough. At that point you must begin to adjust your surfactant package to get the emulsion stability you desire.
These surfactants contain silicone functionality; to many people in the metalworking industry, silicone is enough to cause them to take ill. However, this surfactant class is very versatile and many of the silicone surfactants are very low foaming. Do the rules of HLB apply to this class of surfactants, no and any HLB number is at best a guess. The reason, these surfactants are multifunctional and conditions determine how the surfactant will perform. I have seen low foaming silicone surfactants foam like the dickens when conditions are right. To use this particular class to achieve emulsion functionality and stability, the formulator must use the time proven method of trial and error. Above all, you must explain the Si peaks in the IR spectra.
There is an HLB system for Silicone surfactants called the Three Dimensional HLB, but since it involves triangle graphs and physical chemistry I will discuss this new HLB system in a future article. To conclude, just because silicone surfactants do not obey the standard rules of HLB is no reason to discount them. You will find this class of surfactants to be very versatile.
As we all know, surfactants are the backbone of the metalworking fluid industry. Any formulator with a good working knowledge of surfactants will develop into an exceptional formulator as their skills develop. As always, should you have any questions please feel free to e-mail me in care of the magazine. Till next month, Happy Thanksgiving!