Surface treatment

Although glass is chemically inert by nature, certain factors can affect its performance in pharmaceutical applications. These factors include:

1. Leaching of alkalis

Under certain conditions, particularly with aqueous or alkaline solutions, ions (e.g. sodium or potassium) can leach from the glass surface into the drug. This process, known as leaching, can jeopardize the chemical stability of the drug.

2. Reaction with sensitive drugs

Certain drugs, especially biologically active or highly sensitive formulations, are sensitive to interactions with glass.

3. Mechanical weaknesses

Glass is susceptible to abrasion and microscopic cracking, which can lead to breakage or impaired sterility.

4. Sterilization and storage

Glass containers often have to withstand high temperatures and chemically aggressive environments during sterilization or long-term storage.

Surface treatment is used to overcome these challenges and improve the chemical and mechanical properties of glass bottles.

The internal surface treatment of glass bottles aims to minimize the interaction between the glass and its contents. The most common methods are:

a) Sulfuric acid treatment (sulfuration)

- Aim: This method is used to make soda-lime glass (type II) more chemically resistant.

- Process: The inner surface of the glass is treated with sulphur dioxide gas (SO₂). This process causes the formation of a thin silicate layer that protects the glass against leaching.

- Application: This method is often used for bottles containing aqueous or slightly acidic pharmaceutical solutions.

b) Silicon oxide coating (SiO₂)

- Aim: Reduction of chemical interactions between glass and pharmaceuticals.

- Process: A silicon oxide coating is applied by chemical vapor deposition (CVD) or sol-gel technology. This layer forms a protective barrier against leaching and improves hydrolytic resistance.

- Advantages: Particularly suitable for highly sensitive drugs such as biopharmaceuticals.

c) Inner polymer coating

- Objective: To protect the drug solution from glass interactions.

- Process: The inner surface of the glass is coated with a thin layer of polymer (e.g. fluoropolymer) to eliminate chemical interactions.

- Application: Suitable for drugs with a long shelf life or sensitive biological formulations.

The external treatment of glass bottles aims to improve their physical and mechanical properties. It includes:

a) Siliconization

- Objective: Reduction of friction and minimization of abrasion.

- Process: The outside of the glass bottles is coated with a layer of silicone to increase slip and reduce mechanical damage during processing.

- Application: Especially in high-volume manufacturing processes where glass containers are moved on conveyor belts.

b) Polymer protective layer

- Objective: To improve break resistance.

- Process: A thin plastic coating (e.g. polyurethane or polyethylene) is applied to the outer glass surface. This layer prevents glass bottles from splintering and breaking in the event of impact.

- Advantages: Improved safety and protection against glass breakage, especially for transport-sensitive medicines.

c) Antistatic coatings

- Objective: Reduction of static charge to prevent the accumulation of dust and particles on the bottle surface.

- Process: Application of an antistatic coating that improves the cleanliness of glass bottles during processing.

The surface treatment of glass bottles offers a number of advantages:

1. Improved chemical resistance

- Reduced leaching of ions into pharmaceutical products.

2. Increased mechanical stability

- Glass bottles become more resistant to abrasion and breakage.

3. Compatibility with sensitive pharmaceuticals

- Special coatings enable the use of glass bottles for biological or highly reactive products.

4. Increased product safety

- Prevents potential contamination or interaction with the glass.

5. Optimization for automated processes

- Treated glass surfaces are better suited for high-speed filling lines as they reduce friction.

Despite the advantages, there are also some challenges in the surface treatment of glass:

1. Cost

- Treated glass bottles are more expensive than untreated ones, which increases production costs.

2. Complexity of the process

- Surface treatment requires high-precision processes and strict quality controls.

3. Coating integrity

- There is a possibility that the coating will wear off over time or be damaged in extreme conditions.

4. Regulatory requirements

- Treated glass bottles must pass extensive testing and approvals to meet the requirements of pharmacopeias (e.g. USP, EP).

The handling of glass bottles is subject to strict regulations defined by organizations such as the United States Pharmacopeia (USP) and the European Pharmacopoeia (EP). The requirements include:

- Chemical resistance testing

The hydrolytic resistance must meet the requirements of Type II or Type III glass.

- Sterilization tests

Verification that the coatings remain stable under sterilization conditions.

- Particle and visual inspection

Ensuring that no coating defects or particles remain on the glass surface.

The surface treatment of glass bottles is an essential process to improve chemical stability and mechanical robustness for pharmaceutical use. With methods such as sulphuric acid treatment, silicon oxide coating and external polymer coatings, glass bottles can meet the stringent requirements of the modern pharmaceutical industry. Despite challenges such as higher costs or regulatory requirements, surface treatment remains key to ensuring drug safety, stability and efficacy. Continuous innovation in this area will continue to help improve the quality and safety of pharmaceutical packaging.