Who can guess what a mild hypnotic, cardiac drug, cough and cold preparation, stool softener, stage blood, Easter egg, colouring kits, and paintball all have in common? One is a gelatin shell and the other is some of the most demanding chemistry in die health and beauty and recreational industries.
You see all of the above products are soft, elastic, gelatin capsules - softgels. Softgels are one piece, hermetically sealed capsules that are comprised of a liquid fill contained in a gelatin shell. The fill material can be a simple solution or a complex suspension containing oils, waxes, polymers, drugs, dyes, pigments, fragrances, and other components whose names would challenge even the most astute organic chemist. Organic chemists are not the only discipline that can be involved in the development of a paintball. There is room for the inorganic chemist, physical chemist, biochemist, and even a physicist or two.
Now for a little history about the sport of paintball: The first use of paintballs was to mark livestock and trees for slaughter or harvest with oil-based paint. Well of course it did not take long for one yahoo to shoot another yahoo and the game of paintball was born. Well the wives of these yahoos did not appreciate the permanent marks these early paintballs left on the clothes (nor did the landowners who found more trees and animals marked for roundup than intended). Well the yahoos figured this burgeoning sport was too good to give up so they got word back to the manufacturer of the paintballs that there was a demand for a water-soluble paint for recreational use. The formulators in this case were the Production Chemist, Quality Control Manger, and Quality Control/Product Development Chemist. These people knew the most about what may or may not work for this project.
The original paintball was filled with oil-based paint because the fill material of a softgel must be anhydrous (gelatin dissolves in water!) Regular latex paint contains a high percentage of water and would not work so the product development team knew that it was up to them to develop something unique to the manufacturing process.
The fill material had to be water-soluble, anhydrous; capable of carrying dyes and/or pigments, non-staining, thick enough not to run off once it hits its target, and compatible with the gelatin shell. The material of choice was a combination polyethylene glycol with a molecular weight of 400 (PEG 400) and a molecular weight of 3350 (PEG 3350). The PEG 400 would be the main carrier and the PEG 3350 the thickener to support the pigments. Lower molecular weight PEG's were not chosen because these smaller molecules are capable of penetrating the triple- helix coil of gelatin and acting like a plasticizer. The main plasticizer in the shell (remember these are soft gelatin capsules) is glycerin. Now glycerin is soluble in the PEG 400 and will migrate into the fill material causing the capsule to become brittle over time. Thus a small amount of glycerin was added to the paint formula to establish equilibrium with the shell. This equilibrium is dynamic and will fluctuate depending on the humidity. Therefore, a secondary plasticizer is added to the gelatin shell that is less soluble in the PEG 400. Because this secondary plasticizer is not as efficient a plasticizer as glycerin it cannot be used alone.
The primary pigment is titanium dioxide because of its superior opacity (rutile structure of course). Six (6) food and pharmaceutical grade dyes are used to produce the myriad of colours found in paintballs. Eventually fluorescent pigments would be introduced to brighten things up a bit.
The gelatin shell of the paintball required special attention as well. The gelatin shell had to withstand the sudden acceleration from zero (0) to 300 feet per second (200 mph) in a span of 14 inches then hit a relatively soft body at 100 feet and break. So the shell had to be strong, yet brittle. Now remember that there is interaction between the shell and the fill material. The plasticizer has a habit of going into the fill material while the entire capsule, fill and shell, is like a sponge and is sensitive to fluctuations in humidity and temperature Well, when all appears hopeless there are a few more tricks in the chemistry bag. to try.
First we adjust the plasticizer to gelatin ratio to minimize the amount of plasticizer in order to make a brittle shell. This also minimized the amount of plasticizer to migrate in the fill. Secondly, we used a gelatin derived from pig skins as opposed to the connective tissue of cows. It appears that the molecular weight distribution and the structure of the triple-helix coil from pigs make better paintballs.
In summary, there are few centre’s in the world that are capable of manufacturing paintballs. Without a doubt, paintballs are the most challenging and difficult product an encapsulator can run. At one point, ALL the paintballs in the world were being produced in Windsor, Ontario. This is because this is where the paintball as we know it today was invented. That was many years and billions of paintballs ago.
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