Noncombustion of a cardboard box [glue]

Starch was added to soufa23% aqueous solution and a flame retarder of the application type was made. It’s applied to following cardboard box and the burning condition is considered.

Application method

A picture after application dryness is indicated.

A combustion test was put into effect 45 ℃.
A testing machine is the following.

Test outcome
It was possible not to pierce a flame and to endure a combustion test for 5 minutes. I can think a foaming bed in soufa and char layer stopped burning.