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Introduction

Various plastics and polymeric composites are used in industry today due to their highly resilient properties and ease of manufacturing. The downside to these materials is that their physical and mechanical properties can be unpredictable, especially over the longer term, and due to their uniqueness can be onerous and expensive to fully test or predict. In some industry applications, such as the medical, military, or aviation fields, high reliability is required in material quality up until the end of use. This means that the plastics need to retain its full material properties to ensure the functionality and performance where it is installed is maintained. Some plastics in their final product form are stored for long periods of time without any visible sign of degradation, however, what we need to realise is that from the time a plastic is manufactured, its shelf life is ticking…

Plastic degradation initially occurs on a molecular level and is in most cases not yet visually evident, but the truth of the matter is that the material’s mechanical or physical properties may already be compromised up to a certain extent. Plastic materials tend to degrade at various rates during its lifetime – during usage and during storage time prior to use. In many cases, a plastic component’s degradation can only be noted when it is exposed to external factors such as impact, vibration, atmosphere-related chemical attack, UV radiation, and heat fluctuation. This is because from a molecular level not seen by us, changes had already occurred within the polymer chains/ structures, and these polymer structures govern the plastic’s material properties.

Every unique type of plastic grade consists of a different chemical composition and hence different molecular chain structures. These structures’ susceptibility to various external factors working in on them can be tested by way of simulating artificial environments that reflects the real-time elements present. In addition, these tests can be intensified to accelerate or condense the duration of testing and to quantitatively predict what the outcome would be for a specific plastic type. This means that a particular environmental factor would be simulated at a much higher intensity than expected in real-time conditions and the duration of exposure testing significantly shortened. To obtain the real-time effect, the testing time (typically in hours) are extrapolated to an approximate real-time in years. With the accelerated weathering tests one can evaluate a unique plastic material’s response to a certain environment over an approximate specified time period. This is ground-breaking science in the sense that the previously unpredicted polymers can now be utilised within highly specialised applications at lower costs, increased product efficiency, and quicker turn-around times.

The Case Study

One Eighty recently conducted accelerated weathering tests for a company that manufactures denotator assemblies that are utilised in mining environments.

Detonator assembly with connector pins for exposure testing
Numbered and packed sample batches for testing

Detonators are used to initiate controlled mine explosions and therefore their reliability in performance is highly dependent on, as a non-performance can result in massive health and safety risks, not to mention time-delays and considerable expenses.  The detonator assemblies consist of highly sophisticated electronics that are held in position, covered, and protected by various plastic housings and structures. The detonators are typically stored for prolonged periods of time within well-controlled environments, but during installation they can be exposed to harsh environmental factors. If one of the plastics fail during the time of storage or installation, the electronic equipment may be exposed to and possibly compromised. To ensure that none of the plastic housings will not be compromised after long-term storage, One Eighty evaluated the detonator plastic components’ resistance to a simulated high-fluctuating temperature -and humidity environment. The detonator assembly was exposed to a pre-determined number of weathering cycles after which each individual plastic component was evaluated. The assembly as a whole was evaluated for its resistance to the simulated environment, and more profoundly, the plastic components that failed first could be identified. This allowed us to identify the weakest plastic component(s) and assembly joints within the detonator so as to improve only the components/ areas that are necessary. This served as an overall optimisation of the detonator product, together with data to predict its storage life.

Cracking on cap after weathering cycles

With simulated accelerated environmental exposure testing, the following can be achieved:

  • To build a comparative database for a specific plastics or composite materials.
  • To determine the weakest component/ material type from an assembly consisting of various components.
  • Elucidate and understand a material’s behaviour under certain environmental conditions.
  • Predict a material’s approximate service lifetime and/ or storage time under certain environmental conditions.
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