The nimble little silverfish in the bathroom are not a sign of a lack of hygiene. Rather, they are an indicator of a warm and humid microclimate. A single animal is therefore usually harmless, but a mass occurrence serves as an alarm signal for moisture damage, mould or structural defects.
Especially with transparent plastics such as PMMA (known as acrylic glass or Plexiglas®) Stress cracking A particularly insidious defect in the component: you can see every stress crack, no matter how fine, if you hold the affected product up to a light source in such a way that the shiny silver spots around the usually central injection point are reflected in it. This effect is best observed on salad bowls that have been used for a long time and have been regularly washed in the dishwasher.
Cooling down too quickly produces internal damage, frozen tensions. The plastic molecule chains are practically „frozen in a disorganised position“. For this reason, care must be taken during production to ensure that the hot plastic melt is not injected too quickly, that the mould temperature is not too low, that extreme holding pressure is avoided and that the component geometry is designed without large jumps in wall thickness.
Heat helps to counteract the tensions of stressed molecules
After the injection moulding of such, usually optically relevant PMMA moulded parts, for example after the production of car rear lights and indicators, it is advisable to subject the parts to heat treatment (annealing). The components are heated in a controlled manner, the stresses are removed, so to speak, and then allowed to cool down again slowly.
This minimises the risk of encountering silverfish.