Oftentimes, the first person to notice a cracked and broken capsule is the consumer, obviously the worst case scenario for any quality manufacturer. If the consumer tastes leaking product, the negative impression left may be long-lasting. This then begs the questions: Why wasn’t this observed during manufacturing process or quality checks? Where did the capsule lose moisture along the way?
When manufacturers hear of brittleness in two-piece capsules, their general inquiries turn to capsule storage conditions, or the empty capsule manufacturing. While these are both critical players in the stability of capsule shells, there are many other factors which play a role, and may be combining to cause problems. This is why manufacturers need to understand how to prevent brittleness from the cradle of supply chain, to the consumer purchase point.
Maintaining optimal moisture in capsule shells is the key to preventing brittle capsules. Makers of two-piece gelatin capsules know that shell moisture must be maintained above 13% to prevent breakage. For some hypromellose (“veggie”) capsules, especially those that meet USP dissolution requirements, brittleness can occur when moisture falls below 4%. Loss of moisture can combine with other physical factors, such as filling pressures and impact points.
Following are areas along the supply chain where capsules commonly become brittle and crack.
Warehousing and Transportation
Storing capsules in areas which are too hot or cold will affect the moisture level of the capsules. In all storage areas, make sure that capsules are kept within the recommended temperature range listed on the capsule cartons. If you cannot control humidity in your warehouse area, make certain that temperature ranges are adhered to. The capsule bag liner will provide some protection against low humidity until the capsule bag has been opened; optimum humidity is very important in the capsule filling room. In warehousing, remember that rising heat is trapped near the ceiling levels, and as such, it is best to keep capsules away from high rack locations. Hot spots are also found near ceiling lights and HVAC vents. Capsule cartons wrapped in excessive plastic and kept in hot or humid locations can cause a greenhouse effect, trapping heat and moisture around capsules. When transporting either empty or filled capsules, treat them like you would when moving chocolate; being careful to maintain ideal conditions.
Some formulations are hygroscopic, meaning they pull moisture from their environment. A gelatin capsule contains more moisture than hypromellose, and tends to lose moisture more quickly. Where formulas are hygroscopic, a hypromellose capsule is generally a safer bet. Also, for moisture pulling formulas you may want to avoid using colored capsules with high levels of titanium dioxide (the ingredient which make capsules opaque), as by their nature, opaque capsules are more brittle. In formulating empty capsules, the ingredient Sodium Lauryl Sulfate (SLS) is commonly used as an emulsifying agent, and surfactant. SLS is like the soap which allows grease and water to occupy the same space; hence, SLS-free capsules are prone to having thin spots, where cracking occurs most frequently in the shoulder area of the capsule. If your formula is hygroscopic, consider whether hypromellose could suit the application.
Conditions in the filling room are paramount in terms of both humidity and temperature. During cold winter months, heating systems dry out the facility air to the point where it is commonly recorded at 15-20%Rh. With capsules openly exposed to such dry air, they will lose moisture in a matter of minutes, becoming brittle. For times such as these, portable industrial humidifiers can be used in rooms to maintain relative humidity at an optimal range of 45-50%. Using re-sealable bag ties for opened capsule cartons will make it easier for operators to protect capsules while in the encapsulation room. On the filling machine, ensure you are using only the required amount of vacuum necessary to separate empty capsules, especially when using opaque (colored) capsules. Excessive vacuum can cause pin-hole fracturing in the body dome. In capsule closing, use of a Go no-go gauge can prevent cracking caused by over-closing a filled capsule.
During packaging, there are several heat and impact sources which can contribute to capsule breakage, usually after significant moisture-loss has occurred due to storage, formulation or other processing. Common heat sources include blister equipment and heat tunnels. Capsules which are already brittle may crack while dumping them from bulk containers into capsule counters, or when used with aggressive brush boxes. To avoid capsule cracking in the packaging area, use care in handling. Design material transfer processes which minimize impact, and avoid excessive weight load in bulk hoppers. Avoid extended exposure to heat especially where capsules may sit on hot equipment such as a thermo-former.
Also, understand that capsules packaged with desiccants (which are designed to absorb moisture), can cause brittleness in finished goods inventory and on store shelves.
High quality capsules will withstand the rigors of many manufacturing and formulation challenges. For those exceptions, implementing the practices described above will ensure your capsules arrive at the customer ready to leave the best possible impression.
Technical Service Manager