What is delamination and when does it occur?
Delamination is a process where thin glass flakes detach from the inner glass surface. The process is already known since the 1950s. Unfortunately, it can not reliably be predicted if and when delamination will occur because the factors influencing this are too many and too complex. There is e.g. the converting process which with hotter converting has a bad influence. But also the drug solution has an important part in this. The buffer or even the drug itself can accelerate the process by attacking the glass and complexing selectively certain elements, e.g. aluminum. If this is the case, it can be seen from the composition of the flakes as they also contain elements from the solution. As this topic became quite prominent in the pharmaceutical industry, the USP released a guideline in Chapter <1660> proposing different methods with which the propensity to delaminate can be investigated. But as mentioned already, this can only be hints but not reliable information. If one had a delamination case, the best thing to do is to have investigated by an experienced lab (e.g. SCHOTT Pharma Services) who can tell exactly if it was only the glass or also the drug solution being involved in the reaction. This is a valuable information according to which the whole process has to be evaluated and if needed changed.
How temperature resistant are glass containers, e.g. in the depyrogenation oven?
Borosilicate glasses usually are good heat resistant. In the converting process they undergo temperatures of above 100°C without changing the chemical composition. After converting they go through the annealing oven at around 600°C. In the filling process, the temperature of around 300°C is easily bearable for them even if they are standing there for a few hours. The point is not so much the temperature itself but rather the temperature difference if they are exposed to heat and cold at the same time. Here the strength depends on the the Coefficient of Thermal Expansion (CTE). The lower the CTE is, the higher is the temperature shock resistance. E.g. a FIOLAX(R) container (CTE of 4.9) with a wall thickness of 1.0 mm can bear a temperature difference of around 200°C meaning the container can be thrown from 200°C into cold water without bursting. A soda-lime container (CTE of around 9) with a wall thickness of 1.0 mm e.g. can only bear 110°C. This is important for the lyophilisation process where the glass is frozen inside and at the same time heated from the bottom. It should be kept in mind that this relates to a container without any defects on the glass surface. Any defect lowers the resistance. The temperature shock resistance can be influenced by the wall thickness. As glass is a bad conductor of heat, the temperature shock resistance increases with decreasing wall thickness.