PET containers require special consideration during warm weather in order to prevent shrinkage or distortion occurring after the moulding process is completed.
The process of bi-axially orientating the PET polymer leaves residual stress in the walls of the container, which is then prone to relief if the ambient temperature is raised for any length of time.
The amount of shrinkage will depend upon the actual temperature, the length of time and the specific characteristics (stretch ratio) of any given container.
Some general indications are shown below:
- Over 50°C – shrinkage occurs in less than 1 hour
- 42-50°C – shrinkage in less than 12 hours
- 35-42°C – shrinkage in less than 5 days
- 30-35°C – shrinkage in less than 20 days
The following recommendations will assist in minimising this effect:
- Carriers should deliver loads directly and avoid unnecessary delays
- Light coloured vehicles preferred
- Ventilated trailers (without windows or panels)
- Avoid leaving pallets in direct sunlight during load/unloading
- Place pallets into storage away from skylights and heat sources
- Storage under metal roofs with limited airspace not recommended
- Beware of fork-truck exhaust pipes
- Follow GMP for stock rotation
- If shipping via container, seek advice from the shipper