Package strength & integrity
If packaging is to provide a barrier to microorganisms, or effectively contain liquids, it must remain intact throughout the food's shelf-life. As well as being suitable for the food it contains and the processing conditions it encounters, food packaging must also be able to withstand the rigours of distribution and storage - in short, everything that might happen to it from when it leaves the process line until the food is used by the consumer.
The burst strength of a flexible pack is a measure of its seal strength and determined by inflating the package with air at a specified rate until it bursts. The position and type (seal or material) of failure is recorded in addition to the burst pressure value. The test is used as a means of evaluating the likelihood of pack failure when exposed to pressure differentials, such as may be experienced in retorting or air transport. By placing the package between restraining plates, the weakest area of the seals are more likely to be detected as the stresses during pressurisation are more uniformly applied along the perimeter of the pack.
The compression strength of individual primary packaging samples such as cartons, bottles and cans is performed at Campden BRI using a Zwick Z3050 materials testing machine with a 50kN load capacity. Larger transit packaging, including fibreboard cases are also routinely tested for their compression strength.
Creep testing is conducted in a similar way to burst testing. However, a burst test is a measure of pack/seal strength, while a creep test is a measure of seal strength and pack integrity. During a creep test the pack is inflated to a percentage of its known burst pressure and held for 30 or 60 seconds for a pass or fail result (in the case of seal leakage). The seals can also be measured for "seal yield" - narrowing of the seals.
Drop tests can be conducted on packaging in various orientations and from a range of heights to determine its impact strength.
Internal pressure resistance testing for containers that are intended for carbonated drinks or are otherwise subjected to changes in pressure during their intended use. This mechanical test determines whether the package meets applicable specifications and is fit for the intended use. Testing is carried out using a ramp internal pressure tester. Bottles are filled with water and the pressure is automatically increased until the bottle breaks or can deforms. The burst or deformation pressure value is recorded along with the location of the failure origin if applicable.
Seals are vital to many types of food packaging; however, the role of the seal will differ from one product to another. Depending on the type of package, it may need to have mechanical strength or hermetic integrity, or be easy to open. So, the amount of force required to peel a lidding material from a pack must balance the importance of seal integrity against the requirement of convienience for consumers wishing to open the packs. When designing new pack formats during product development, it is particularly important to keep food safety/integrity in mind. It is also vital to know how seal strength may alter over time or during/after distribution. At Campden BRI, as part of our package testing services, we have the equipment to measure the peel strength of a range of pack formats. The equipment is capable of running at different angles and speeds during a test cycle so that it can replicate human opening.
Torque testing on (bottle and jar closures) measures the amount of force required to open a jar or bottle closure must balance the importance of closure integrity against the requirement of convienience for consumers wishing to open the packs. A Mecmesin Tornado digital closure torque tester is used for measuring application and removal closure torques.
Pendulum impact testing is used to determine the impact resistance, strength and breakage characteristics of a range of items in order to ensure that they are fit for purpose. Impact testing can be carried out across a range of products including glass and plastic packaging and glassware. Typically, impacts are carried out at the contact point for that particular item, such as shoulder and heel for bottles or the rim of a pint glass and the testing is carried out until failure of the sample occurs. However, testing at other specific impact positions can also be undertaken.
A tensile strength test is a mechanical test performed on packaging materials to determine the maximum load that can be applied to a material before it ruptures or tears. In essence it is a 'pulling' test used to measure the strength of paper, board and plastics. The material will show elastic behaviour up to a certain point and then rupture. The test can be adapted to different needs - it can be used to measure the strength or elongation of a material and its tearing resistance, as well as the force required to separate a seal. T-peel testing is a mechanical strength test conducted in a similar way as tensile testing, but it is performed on a section of a packaging seal to determine the maximum load that can be applied to the seal before it separates.
Tear resistance testing can be conducted on sheet and film materials to measure the force perpendicular to the plane of the sheet required to tear single or multiple plies through a specified distance after tear initiation. A Zwick Z050 materials testing machine is used for this test and the results are stated in mN/ply.
Where we refer to UKAS Accreditation
The Campden BRI group companies listed below are both accredited in accordance with the recognised International Standard ISO/IEC 17025:2005 by the United Kingdom Accreditation Service (UKAS). The accreditation demonstrates technical competence for a defined scope of methods, specific to each site, as detailed in the schedules of accreditation bearing the testing laboratory number. The schedules may be revised from time to time and reissued by UKAS. The most recent issue of the schedules are available from the UKAS website www.ukas.com
Campden BRI (Chipping Campden) Limited is a UKAS accredited testing laboratory No. 1079 Campden BRI (Nutfield) is a UKAS accredited testing laboratory No. 1207