Pharmaceutical glass: uses, benefits and future directions

The pharmaceutical packaging industry has always used glass as the material of choice for the production of safe packaging. Its characteristics of chemical stability and inertness make glass ideal for the packaging of medicines, from solids to liquids, injectables and reconstitutables.

Glass is a material that does not risk affecting the purity of the contents it comes into contact with, even when its outer surface is exposed to other products and chemicals. Therefore, its prerogative of being highly 'non-reactive' is very advantageous in ensuring that drugs are not damaged and that their properties remain unaltered.

In addition, it is highly resistant to temperature changes, a valuable quality for the pharmaceutical industry, where products often have to be kept at certain temperatures, and also essential in cases where the packaging is subjected to particularly 'stressful' processes, such as sterilisation, freezing or freeze-drying.

Lastly, when produced in an amber colour, pharmaceutical glass reduces light transmission and is particularly suitable for more photosensitive drugs.

Glass types and treatments for pharmaceutical containers

In terms of composition, glass for pharmaceutical use can be classified into three main categories:

• Type I or borosilicate glass: thanks to its special composition, with boron molecules added in place of alkaline oxides, this type of glass is chemically inert and highly resistant. It is the ideal solution for containing all types of injectables and the most delicate treatments.
• Type II glass: with a sodium-calcium base, it undergoes an appropriate surface treatment to make it more resistant. This category is particularly suitable for solutions administered intravenously, such as infusion bottles.
• Type III glass: a sodium-calcium glass, similar in composition to Type II, with a highly versatile use and suitable for both solid and liquid drugs, for oral, topical or injectable use.

Glass containers can also undergo internal treatments using silicone, which, thanks to its hydrophobic properties, makes it possible on the one hand to reduce the interaction between the medicine and the surface of the bottle, and on the other hand to increase the gliding performance of any external components (e.g. rubber closures).

It can also undergo secondary processing on the outer surface with special lubricants to reduce friction and improve impact resistance and smoothness on packaging lines.

The production of hollow glass containers for pharmaceutical use

Hollow or moulded glass containers are obtained through a process of blowing molten material into moulds. The production stages of glass pharmaceutical packaging can be divided into:

• Melting: the raw material, consisting of a mix of silica sand, soda ash and other components, is collected in silos, then dosed, mixed and fed into the furnace to be melted. The furnace, constructed of refractory material capable of withstanding the high melting temperatures (1,600°C), is connected to monitors and process calculators that allow the operating parameters to be constantly checked with the correct vitrification of raw materials.
• Shaping: the molten glass enters thermal conditioning channels and, having reached the appropriate viscosity, is 'cut' into drops. The glowing glass droplet drops into the mould on the moulding machine, which then moulds the finished product using two different moulding technologies. The "blow-blow" technique relies on an initial blowing stage to create a vacuum in the preform, which is then shaped by another jet of air and assumes its final shape. By contrast, the "die-blowing" technique uses a piston to create a vacuum in the preform, which is then blown to its final shape.
• Annealing: the phase that eliminates residual stresses in the material, stabilising the structure of the glass and increasing its strength. Other secondary treatments are also applied. such as siliconizing and sulfurization, which improve the performance of the products, and make them more resistant to mechanical and chemical stresses, and more suitable for in-line processing.

Mould glass is mostly used for the production of containers for oral and solid drugs, but is also extensively used for parenteral treatments. For the latter, there are special ranges of high-performance borosilicate glass bottles manufactured using advanced production technology, which provides them with greater chemical and thermal stability, enhanced resistance and thus improved in-line efficiency and product safety.

The production of tubular glass containers for pharmaceutical use

Glass in this case is usually purchased by packaging companies in the form of long, semi-finished tubes that are then heat-processed into the final product.

Several tubes at a time are loaded vertically onto rotary machines and, as they descend, are heated and cut with high-temperature flames. First the shoulders and mouth of the vial are formed, after which the base is detached and machined. Tubular glass vials, like moulded ones, also pass through an annealing furnace to reduce the stress caused by the hot moulding process.

Tubular glass is extremely thin, transparent and has a uniform surface; it is particularly suitable for undergoing freeze-drying treatments. Because of these characteristics, it is used for the production of vials for injectable or laboratory drugs.

Quality and controls for pharmaceutical glass packaging

Being containers for pharmaceutical use, several, stringent quality controls are carried out by the manufacturing companies on all stages, from the raw materials to the finished product.

The following are performed:

• Preliminary checks on the composition and dosages of raw materials, both the siliceous compound and any cullet reused in the production process.
• Control of the product during processing: each individual piece is subjected to manual and automatic checks on all characteristics: size, shape, thickness, calibration of the mouths, integrity, and strength. Containers not considered suitable are automatically ejected from the packaging line and immediately recycled in the same production process for re-melting.
• Final inspection: checks are carried out on the packaged finished product and the pallets on which it is collected, which must also comply with labelling and storage requirements.

The use of the latest technologies allows the entire production cycle to be managed and monitored by means of computerised equipment, while highly sophisticated and specialised instruments ensure statistic-based checks, in order to obtain the quality level of the finished product that meets the requirements, both functional and aesthetic, of the bottlers, the distributors and the consumer.

Future directions for pharmaceutical glass packaging

While from a technical performance point of view there is no doubt about the robustness of this solution, the pharmaceutical industry will increasingly have to adapt to the demands of environmental sustainability.

Today there are already ranges of recycled glass products especially for type II and type III glass, which use materials from an external supply chain that is certified for pharmaceutical use. Chemical and mechanical processing of recycled materials allows regeneration of the raw material - glass powder - that forms the basis of the new processing cycle.

At the same time, projects are already in place for the creation of low-emission furnaces that use innovative technologies and industrial processes with a lower environmental impact.

This would fuel a Circular Economy model that would result in a lower use of natural resources, lower emissions and less energy usage, without sacrificing the very high quality and safety standards required.