Formulation science is an interdisciplinary subject where knowledge of material science and physical chemistry joins with the art of arriving a optimum combination of correct proportion of components. Whereas chemistry deals with chemical reactions between various substances, formulation science deals with co-existence of several components in a formulation and the combined and simultaneous activity of individual components. It is basically science of mixtures coexisting without real chemical reactions (breaking and forming of chemical bonds).
The advantage of blending was understood by mankind thousands of years before industrialization. The concept of blending evolved in various walks of human life. A best example is music. Music can be generated by a single musical instrument like violin guitar. A team of musicians work together adding their own musical ingredients to make a rich performance.
In materialistic sense, formulation is a blend of substances prepared by combining two or more constituents. Examples are herbal formulation, coating formulation, drug formulation, Fertilizer formulation, Pesticide formulation etc. A formulation defines the quantity and constituents in what we normally call a compound, mix, mixture, blend, or a concoction. The mixture result is increased activity and performance to meet a particular action or performance requirement.
FORMULATIONS – WHY?
Formulation (developing a formula for a preparation) is carried out to achieve desired characteristics that make it suitable for a specific action or application. Formulations are hyperactive compared to its individual components for a particular action or application, and this is the basic motivation to design and development of a formulation.
Formulations are normally made from its constituents for one or more of following reasons.
- To achieve characteristics that can not be obtained from simple components
- To achieve higher degree of effectiveness: Achieve a higher degree of effectiveness than its individual components for a particular action or application. Certain drug formulations for example ‘pain killers’ has multiple active ingredients which works better when administered together.
- Synergetic Action of Components: Two or more components in a formulation may act simultaneously in a synergetic fashion.
- Discrete, simultaneous or sequential functions: The components in a formulation may do discrete functions, which when act together or sequentially performs more effectively. A sustained release formulation is an example for this. The active component (drug) is released slowly by other ingredients in the sustained release capsule or tablet.
INGREDIENTS IN A FORMULATION
Number of ingredients can vary from simple two-component system to several components. Formulations with tens of components are not uncommon.
Each ingredient in a formulation is to serve a specific function in the mixture. The content (relative amount of specific ingredients) of each ingredient is decided depending up on the function it serve. There may be functionally inert medium namely “vehicle” or “base”, which acts as carrier for active ingredients. There may be certain “additives” with very small content compared to other items, which has some supportive function towards the application of the formulation. Many ingredients will have specific role in a formulation
Each individual component in a formulation can be
- Pure solids or liquids
- “Pure” solids or liquid with some moisture content
- Solutions which are of a particular activity (%), or
- A solid with certain purity
- A formulation on its own
Pure table salt is an example for pure component. Table salt which is of 93% Sodium Chloride and 7% water is an example of the second. Salt solution with 10% sodium chloride and remaining water as carried/solvent is an example for the third. Impure salt with 80% NaCl content is example for the fourth variety. A flavoring formulation added as an ingredient of ice-cream is example for the fifth one.
Consider a two-component polyurethane paint system consisting component A and component B as separate packing. Suppose Component A is a formulation consisting a1, a2, a3, a4, a5 and a6 and the second component consist of b1, b2 and b3. These individual components a1…a6 or b1…b3 may be pure substances or substances with certain % of active contents. Suppose we mix 70% of A and 30% of B to make a coating formulation prior to application. In this case, a formulation is made by mixing two different formulations.
The biggest difference between what we experience in college chemistry lab versus a formulation lab is in the interaction between ingredients. In an organic lab, we mix chemicals together, and probably heat or stir and hope we expect to get a chemical reaction. In a formulation lab, we mix chemicals together and hope nothing radical molecular or chemical changes happen. We just except mixing to a desired level and its stability.
NON-REACTIVE NATURE OF FORMULATIONS
Chemical interactions during the formulation stage are extremely rare, though some specially designed formulation may interact chemically when premixed or after its application. A chemical equation does not exist for a formulation normally. Exceptions are there for this and examples are certain reactive adhesive, coatings, resin systems, etc. where calculations are not simply by weight or volume, but in terms of chemical equivalents. Certain formulations remain inert in the storage condition and triggers reaction during its application. UV curable coatings are examples.
All focus is on to the particular characteristics to be achieved, to meet a specific action or application. Consider a formulation of a paint system for brush application on a particular substrate. A successful paint should have ingredients which will result in to a high performance protective film, it should have correct viscosity to apply by brush, good adhesion on to the substrate, good wetting on to the substrate, good leveling characteristics, and good foam breaking properties to mention few. The paint should have some resistance towards fungi during its storage.
The ingredients that are used to make may be classified as per its function as below:
- Film forming agent
- Viscosity (Rheology) component
- Wetting agent
- Leveling agent
- Anti-forming agent
- Antifungal agents
Normally, the components with specific roles that suit this individual functions need to be stable and so chemically inert during the course of its application. This is because a chemically reactive component can not be considered to certainly serve a particular function in a mixture.
Though direct chemical reaction is not there in majority of formulations unless specifically so designed, the basic knowledge in chemistry is helpful for a formulator to efficiently design a formulation. Chemical principles about each of the individual function of the ingredient and regarding the intended final application of the formulation are essential knowledge needed for a formulator. In case of reactive formulations, the knowledge of chemistry of the reaction is extremely essential.
PHYSICAL CHEMISTRY OF INTERACTIONS
Importance of chemistry does not diminish if some chemical reactions do not take place. Molecular interactions exist in any mixture of chemical entities. This molecular interaction governs the characteristics of the formulation.
Following a list of important characteristics of a formulation (in the stage of formulation) resulting due to such molecular interactions.
- Stability of mix
- Viscosity and related characteristics (Rheology)
- Surface Tension
- Wetting and Dispersing
- Easy bursting of air entrapments
The qualities of a formulation that effect its performance are,
- Substrate wetting
- Adhesion to the substrate
- Correct color, texture, feels etc.
- Dirt removal property
- Microbial stability
Any formulation technician would have to master skills of calculating formulations. Softwares based on MS Excel are available for this purpose. An excellant example is FORMULATION DOCTOR supplied along with the reference (1) sited below.
Some of the most common calculations include
Calculating % or fractions when any one or more of the components are repeatedly added and tested after each addition.
For testing purposes, a portion of formulation is withdrawn each time and further adition calculation based on the remaining quantity of initial formlation. This is a very essential calculaton for formulation research
Calculation of a withdrawn quantity when individual components are further added
Calculations of mixing of two or more already made formulations
Adjustment of composition (mostly a mistaken formulation of known composition) to a required value
And many related calculations
SOME AVAILABLE REFERENCES
1) "FORMULATIONS - Chemistry, Fundamentals, Units, Calculations, Research, Manipulation, and Data Management" by Dr R N Kumar and Anilkumar M: FORMULATIONS HANDBOOK