While boron, a volatile element, is the root cause for delamination – the converting process also impacts a container’s chemical durability. During the converting process, specifically the step where the glass cane is parted (or separated) into two containers, the flame releases the boron from the glass network. Boron-containing compounds move around and evaporate as gas out of the glass network largely in the heel region of the vial.
Like a charged helium balloon sticks to a wall or object, the boron particles adhere to cool regions in the side-walls and heel (bottom) of the vial. A composition already rich in boron is now converted into its final format, with deposits that are richer in boron and sodium than the intended composition. This alters the glass chemistry of the container’s drug-contact surface. These areas rich in sodium borate, are vulnerable to delamination and ultimately pose risk to pharmaceutical product quality.