Recently when talking with one of our customer in the United States, he asked about what kind of the material we made for our glass bottles. So today, we want to talk about the 3 major materials made for glass as below.
For the raw material, sand is the primary raw material used to produce all types of glass. Glass shards are also used to produce new glass. Various substances – e.g. salts, metals and metal oxides – are added to the sand. The main component of glass is silicon dioxide (SiO2), better known as sand. The metal oxides sodium oxide (Na2O) and potassium oxide (K2O) are added to lower the melting temperature, which also increases the material’s water solubility. Calcium oxide (CaO) and barium oxide (BaO) are then added to lower the material’s water solubility again. Furthermore, aluminium oxide (Al2O3) can be added to limit the glass’ expansion when exposed to heat. In the past, lead was added to achieve a higher level of shininess and slightly lower the melting point. Today, lead is no longer used as a component of packaging glass.
Glass containers are classified by a common standard set by the United States Pharmacopeia (USP). This standard regulates the chemical composition and chemical durability of the glass, or the glass’ ability to resist attack by the contents of the container.
Here are the 3 types of glass:
Type I – Borosilicate Glass (also known as Pyrex)
Type II – Treated Soda-Lime Glass
Type III – Soda-Lime Glass or Soda-Lime-Silica Glass
While actually the most common type of glass bottles is Soda-Lime glass or Soda-Lime-Silica Glass (Type III).
- Sodium-calcium glass: the most common and widely used glass material. It has good chemical stability and relatively low cost. For example, some basic skin care products such as lotions, creams packaging bottles will use sodium-calcium glass.
Type I – Borosilicate Glass (also known as Pyrex)
Type I Borosilicate glass offers the best resistance to thermal shock and also superior chemical resistance. This class of glass represents the least reactive glass containers available. Type I glass offers superior durability, chemical and heat resistance. It is commonly used for chemical laboratory equipment.
Borosilicate glass contains a significant amount of boric oxide, aluminum oxide, and alkali and/or alkaline earth oxides. Borosilicate glass has a high hydrolytic resistance due to the chemical composition of the glass itself.
Typically, this glass can be used for most applications, including packaging for parenteral (injectable) and non-parenteral products. Type I glass may be used to package acidic, neutral and alkaline products. Water for injection, un-buffered products, chemicals, sensitive products and those requiring sterilization are commonly packaged in Type I borosilicate glass. Type I glass can be subject to chemical attack under certain conditions, thus container selection must be made carefully for very low and very high pH applications
Type II – Treated Soda-Lime Glass
Type II glass is type III glass which has been surface treated to improve the hydrolytic stability from a moderate to a high level. Type II glass containers are suitable for acid and neutral preparations both for parental and other use.
The outer surface of glass containers may also be treated to reduce friction or for protection against abrasion or breakage.
Test methods and specification limits for determining the chemical resistance of glass can be found in the current revision of the U. S. Pharmacopeia, section: Containers – Glass
660ContainersGlass.pdf
Type III – Soda-Lime Glass
Type III soda-lime glass is a silica glass containing alkali metal oxides. Soda-lime glass exhibits moderate chemical resistance and moderate hydrolytic (water) resistance. Soda-lime glass is inexpensive, chemically stable, and ideal for recycling as the glass can be re-melted and re-formed multiple times.
Type III glass is commonly used for beverages, foods and pharmaceutical preparations.
Type III glass is not suitable for autoclaved products because the autoclaving process will accelerate the glass corrosion reaction. Dry heat sterilization processes are typically not a problem for Type III containers.
While if we add metal or metal oxides to sodium-calcium glass becomes colored glass. E.g. Cobalt oxide is used to make blue glass, and manganese dioxide makes glass purple. In addition to enhancing visual beauty, it can also absorb light to a maximum extent and fully reflect light. The performance of blocking ultraviolet, light and heat is better than that of colorless glass to reduce light and heat entering the bottle, so as to better protect the product. For example, wine bottles are usually dark green or brown, designed to avoid the exposure of light during long-term storage, improve the stability of non-biological wine, and maintain the aroma of wine.