Glass containers are among the primary packaging material that has found use in the pharmaceutical industries. A large number of pharmaceutical formulations have been packaged using glass containers glass containers and they are usually the first choice of packaging materials. Glass is an inorganic material (mostly silicates) or mixture of materials which when heated up and then cooled, solidifies without crystallization.
- 1 Composition of glass
- 2 Classification of Glass
- 2.1 i. Type I glass containers (Borosilicate glass / Neutral glass)
- 2.2 ii. Type II glass containers (soda-lime-silica glass/ treated soda-lime glass/ De alkalized soda lime glass)
- 2.3 iii. Type III glass containers (Regular soda lime glass)
- 2.4 Type IV glass containers (Type NP glass/General-purpose soda lime glass)
- 3 Process of Forming Glass Containers
- 4 How Glass containers are made
- 5 Evaluation studies on glass containers
- 6 Factors that influence the choice of a glass container
- 7 Advantages glass containers
- 8 Disadvantages glass containers
Composition of glass
Glass is principally made up of silica (59-80%) with varying degree of calcium oxide (5-12 %) sodium oxide (12-17 %) aluminium oxide (0.5-3.0 %), barium oxide, boric oxide, potassium oxide, and magnesium oxide. The high melting point of glass is due to the presence of silica. The melting point and melt viscosity of the glass is modified by the addition of oxides.
Classification of Glass
Glass containers are classified into Type I glass, Type II glass, Type III glass and Type IV glass based on their degree of chemical/hydrolytic resistance to water attack. The degree of attack is dependent on the degree of alkaline release under the influence of the attacking media.
i. Type I glass containers (Borosilicate glass / Neutral glass)
This is a type of glass container that contains 80% silica, 10% boric oxide, small amount of sodium oxide and aluminium oxide. It is chemically inert and possess high hydrolytic resistant due to the presence of boric oxide. It has the lowest coefficient of expansion and so has high thermal shock properties.
Uses of Type I glass containers
- Type I glass is suitable as packaging material for most preparations whether parenteral or non-parenteral.
- They can also be used to contain strong acids and alkalis
ii. Type II glass containers (soda-lime-silica glass/ treated soda-lime glass/ De alkalized soda lime glass)
This is a modified type of Type III glass container with a high hydrolytic resistance resulting from suitable treatment of the inner surface of a type III glass with sulfur. This is done to remove leachable oxides and thus prevents blooming/weathering from bottles. Type II glass has lower melting point when compared to Type I glass and so easier to mould.
Uses of Type II glass containers
- They are suitable for most acidic and neutral aqueous preparations whether parenteral or non-parenteral.
iii. Type III glass containers (Regular soda lime glass)
This is an untreated soda lime glass with average chemical resistance. It contains 75% silica, 15% sodium oxide, 10% calcium oxide, small amounts of aluminium oxide, magnesium oxide, and potassium oxide. Aluminium oxide impacts chemical durability while magnesium oxide reduces the temperature required during moulding.
Uses of Type III glass containers
- They are used as packaging material for parenteral products or powders for parenteral use ONLY WHERE there is suitable stability test data indicating that Type III glass is satisfactory.
- They used in packaging non-aqueous preparations and powders for parenteral use with the exception of freeze-dried preparations
- It is also used in packaging non-parenteral preparations.
Type IV glass containers (Type NP glass/General-purpose soda lime glass)
This type of glass container has low hydrolytic resistance. This type of glass containers are not used for products that need to be autoclaved as it will increase erosion reaction rate of the glass container.
Uses of type IV glass containers
- It is used to store topical products and oral dosage forms
Process of Forming Glass Containers
Glass containers are formed through the following methods
- Blowing – this involves the use of compressed air to form the molten glass in the cavity of a mold.
- Drawing – this involves the pulling of molten glass through dies that shape the soft glass into ampoules, vials etc.
- Pressing – The glass is formed by the use of mechanical force which presses or forces the molten glass against the ride of a mold.
- Casting –the force of gravity or centrifugal force is used to initiate the formation of molten glass in the cavity.
How Glass containers are made
a. How glass bottles are made
b. How glass vials are made
c. How ampoules are made
Evaluation studies on glass containers
- Hydrolytic resistance test
i. Glass Grains test – used to distinguish Type I glass from Type II and Type III glass
ii. Surface Glass Test – used to distinguish Type I and Type II glass containers from Type III glass container. It is based on hydrolytic resistance of the inner surfaces of glass containers.
iii. Surface Etching Test/Comparison of Glass Grains Test and Surface Glass Test data – this is to determine whether high hydrolytic resistance of Type I or Type II glass containers are due to inner surface treatment or due to the chemical composition of the glass containers
- Light/spectral transmission for coloured glass containers
- Arsenic release – used to detect the presence of arsenic in aqueous parenteral preparations
Factors that influence the choice of a glass container
There are various factors that influence selection process of glass containers as primary packages. These factors include:
- Limit of alkalinity and hydrolytic resistance of the glass container
- Thermal expansion properties of the glass container (freeze drying)
- Sensitivity of the glass container to barium or calcium ions
Advantages glass containers
- Glass containers are mainly used in packaging liquid preparations due to their rigidity and their superior protective qualities
- Its high transparency allows easy inspection of its contents.
- It offers better protection because of it is relatively impermeable to air and moisture
- It is chemically resistance to most medicinal products
- Colored glass (amber glass and red coloured glass) can protect its content from ultraviolet rays and certain wavelengths
- Glass containers can be easily sterilized using heat
Disadvantages glass containers
- Glass containers are expensive to manufacture
- They are fragile and relatively heavy
- During heat sterilization, some types of glass containers have the tendency of shedding some part of the silica into the formulation.
- Nasa P. (2014). A Review on Pharmaceutical Packaging Material. World Journal of Pharmaceutical Research, 3(5): 344-368.
- Pillai S. A., ChobisA D., Urimi D. and Ravindra N. (2016). Pharmaceutical Glass Interactions: A Review of Possibilities. Journal of Pharmaceutical Sciences and Research, 8(2), 103-111.
- Shivsharan U. S., Raut E.S. and Shaikh Z. M. (2014). Packaging of Cosmetics: A Review. Journal of Pharmaceutical and Scientific Innovation, 3(4), 286-293.