Notes from our R&D bench on tuning compostable film for Bangladesh’s heat and humidity — without sacrificing strength.
A compostable bag is only useful if it survives the journey from shop to home before it composts. In Bangladesh’s climate, that journey runs through heat and humidity that punish most bioplastics. This is a working note on how we tune our film to cope.
Two polymers, two jobs
Our base is a blend of PLA and PBAT. PLA (polylactic acid) is made from plant sugars and gives a film stiffness and clarity, but on its own it is brittle and can soften when it gets warm. PBAT is a flexible compostable co-polyester that adds the stretch, toughness and heat-sealing a real bag needs. Used alone, each disappoints; blended, they cover each other’s weaknesses.
The tropical problem
Heat lowers the temperature at which PLA-heavy film starts to lose its shape, and high humidity accelerates the very breakdown that makes the material compostable. A formula that is perfect in a temperate warehouse can arrive limp in a Dhaka summer. So the blend has to be shifted toward toughness and thermal stability without pushing it so far that it no longer composts in a reasonable window.
What we measure
- Tensile and tear strength — can it carry a full load of groceries.
- Seal strength — do the heat-sealed seams hold.
- Humidity ageing — how the film behaves after days in tropical damp.
- Compost timeline — does it still break down on schedule under the right conditions.
The target is a film that feels and performs like ordinary plastic on the day you use it, and behaves like a leaf afterwards. Every blend ratio is a trade-off between those two truths, and finding the right one for this climate is the whole job.