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.
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.
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.
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.
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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.
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.
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.
Glass containers are formed through the following methods
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
There are various factors that influence selection process of glass containers as primary packages. These factors include:
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