TECHNOLOGY FOCUS

METALWORKING FLUID FORMULATION

PART 6 -  HYDROPHIL LYPOPHIL BALANCE  (HLB)

by Dom Ruggeri

May 2001:

Some week’s back an old college friend contacted me she was planning a reunion of our old gang.  This got me to thinking about my times in the Community College of Philadelphia and how I came to the science of Chemistry.  Back in the seventies I was a student at the above college there I, as most students of that time were unsure of the profession we wished to pursue.  Having an interest in science I took my first chemistry course. 

I would like to say that the lecture instructor inspired me to pursue a career in chemistry that was not the case.  However, the laboratory was a different altogether, the Laboratory instructor Professor Rufus H. Cox (deceased) was a dynamic teacher whose pre-lab lectures could stimulate anyone into action.  Anyone but me.  So I stumbled through Chem. 121 doing at best average work, and I received the appropriate grade for my efforts; an incomplete (I).  Since it was the laboratory that gave me the incomplete grade, I had to meet with Professor Cox and work out a plan to complete the Lab (something about 7 missing reports).  To my surprise Prof. Cox was now my lecture instructor.  I turned in the laboratory reports and assumed that was that, on to Chem.  122. 

The first day of class as Prof. Cox entered the room he looked at me and said “See me after class in my office.”  I entered the professor’s office expecting the worst.  We chatted.  “Doc” as I came to call him, stated that he saw a raw talent in me, one that needed to be honed and directed, (i.e., “bound and beaten”).  Further he mentioned that I exerted a lot of effort avoiding the work and if I placed that effort into doing the work I would be brilliant.  From that moment on he challenged me every chance he had forcing me to higher and higher standards.  Funny thing was I actually enjoyed it.  Once I said to Doc, “when I retire I will be ready to take over your job” Doc’s reply was typical of him.  “by that time I may be ready to let you”.  This is my tribute to one teacher whose guidance enabled me to become who I am today.

Through out this series I have used the phrase nonyl phenol surfactant HLB=8.  Many people, including the editor, have asked me what HLB=8 is.  To understand HLB, one must first understand the function of a surfactant.  Rosen defines surfactants in his book “Surfactants and Interfacial Phenomena.”  A surfactant (contraction of the term surface-active agent) is a substance that, when present at low concentration in a system has the property of adsorbing at the surface or interfaces of the system.  Thus altering to a marked degree the surface or interfacial free energies of those surfaces (or interfaces).   So that’s the story and we can end right here.  Yeah, right… 

Surfactants are used in most metalworking fluids to stabilize the emulsion and at times the neat products.  However, a surfactant or blend of surfactants can be the only emulsifier in a metalworking fluid.  

Surfactants are molecules where molar amounts ethylene and/or propylene oxides are added to a carbon backbone thus imparting water sensitivity to that molecule.  Hence, the more ethylene or propylene oxide placed on the carbon backbone, the more water-soluble the molecule becomes.   Therefore, it stands to reason that the amount of the above oxides will determine the function of the molecule in a metalworking fluid.  

The HLB is a numerical system ranging from 1 to currently 30 (perhaps higher).  This numerical system is a guide to the oil and water solubility of a given surfactant or surfactant series.  For instance, if a Surfactant has an HLB=1 it is considered very oil soluble however a surfactant with an HLB=15 is considered to be water-soluble.

How does this relate to formulating? Depending on what emulsion particle size the formulator is looking for he will balance his surfactant system this way:

Blending Surfactants for HLB
 
Surfactants are very versatile molecules.  So much so that in any metal working fluid you could fine more than one each one giving the formulator some part of the desirable properties they seek.  Let’s explore how this works:

Given: A metalworking fluid formulation where an HLB of 8 is necessary to yield a satisfactory emulsion.  However, a surfactant with an HLB value of 8 interferes with the function of another additive. 

This is a typical problem the formulator faces everyday.  The solution is to blend 2 surfactants of known HLB, one high, and one low, to an HLB of 8.  Using the following equation:

HLB desired =(% surfactant A)*(HLB Surfactant A) +(% surfactant B)*(HLB Surfactant B)

Lets look at a real world problem, as I said in the given a single surfactant with an HLB of 8 is not acceptable.  However, if a blend of surfactants having an HLB value of 3 and 10 respectively yields the results you want then this is the way to proceed.  Here’s how:

Assume:

That the level of Surfactant in the fluid must be no greater then 10 %
We will use Surfactants with HLB’s equal to 3 & 10 to equal 8.

Calculation:

8= (X * 10) + ((1-X)*3)
8= 10X + 3-3X
8-3= 7X + 3-3
5= 7X
.71=X
.29=1-X   

Therefore,  29 % Surfactant HLB= 3 and 71 % Surfactant
                 HLB= 10

Which gives a formulation amount of:

2.9 % Surfactant HLB=3
7.1 % Surfactant HLB= 10

Again, a broad-brush approach.  The formulator can adjust the amounts to fine-tune the formulation. 
I hope to see all of our readers at the STLE Annual Meeting in Orlando Florida May 20 – 24.  I’ll be at the crystal booth so please stop by and say hi (I may try to sell you some antifoam, but hey).  As always if I can be of any help please feel free to e-mail me at the magazine.  Good Luck!

All Best
Dom