Texture Analysis in Action: the Capsule Tensile Rig

The CAPSULE/LOOP TENSILE RIG (A/CLT) measures the force required to split one half of a hard gel capsule.

This allows manufacturers to investigate the effects of certain fillings on the capsule shell and identify changes that may impact their stability and long-term performance.

Prior to testing, the filling of the capsule is removed and the empty shell is mounted to a separating rod fixture on the Texture Analyser. Vertical movement of the upper rod is then applied until the capsule is split apart, while the force required to do so is recorded.

This test highlights three important parameters; elastic stiffness, tensile force and elongation at break point. A reduction in elastic stiffness and tensile strength occurs when capsules become softer and therefore show a tendency to fail. If the texture of a capsule is compromised, it may not be able to withstand handling and storage, resulting in fillings leaking from the capsule.

The Capsule Tensile Rig technique is sensitive enough to differentiate between slightly modified formulations with respect to their effect on capsule integrity, and is therefore a useful tool for formulation screening prior to the initiation of long term stability studies.

Comparison of tensile strength of gelatine capsules

 
 Some more information on this fixture: 

The brittleness, hardness and flexibility of hard gel capsules impacts their ability to be filled and to withstand variable storage conditions. Compressive tests on hard gel capsules do not always adequately distinguish between formulations which are known to experience brittle-related failures and those formulations which perform acceptably. In particular, the early modulus and yield strength of compression tests on hard gel capsules often articulate only slight differences between the extremely different expected behaviours.  

In the past, various methods have been employed to assess the mechanical properties of hard gelatin capsules. Brittleness of capsules has been determined based on their resistance to applied impact. In this test, the capsules either break or stay intact when they are hit or compressed by certain mechanical stress. This method is not suitable for evaluating capsules when the capsules become soft rather than brittle. Tensile testing machines have been widely used to study the mechanical properties of polymers. However, these studies have focused on gelatine films or ribbons rather than the intact capsule shells.

In the previous texture analysis method, the probe interacts with the capsule’s outside surface which is not geometrically homogeneous (i.e. body, cap and banding or sealing site). However, the probe in the current method is only in contact with the inner surface of the empty capsule body which always has a standard dimension. Therefore, only changes to the capsule shell itself are detected. Using this method, it is possible to quantitatively profile some mechanical properties of hard gelatine capsules with a wide range of properties. Thus, the effect of various hydrophilic solvent systems on the mechanical properties of hard gelatin capsules can be easily monitored using the current technique. 
 

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We can design and manufacture probes or fixtures for the TA.XTplus texture analyser that are bespoke to your sample and its specific measurement.

Once your measurement is performed, our expertise in its graphical interpretation is unparalleled. Not only can we develop the most suitable and accurate method for the testing of your sample, but we can also prepare analysis procedures that obtain the desired parameters from your curve and drop them into a spreadsheet or report designed around your requirements.

For more information on how to measure texture, please visit the Texture Analysis Properties section on our website.

The TA.XTplus texture analyser is part of a family of texture analysis instruments and equipment from Stable Micro Systems. An extensive portfolio of specialist attachments is available to measure and analyse the textural properties of a huge range of food products. Our technical experts can also custom design instrument fixtures according to individual specifications.

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