Читать книгу Packaging Technology and Engineering - Dipak Kumar Sarker - Страница 23

Washed sand is the main ingredient needed for the fabrication of most types of glass. However, glassy materials produced using only pure silica result in a glass that is too fragile for commercial handling. Consequently, soda (sodium oxide) is added to increase the durability and simultaneously decrease the melting point temperature, making the product easier to handle. Limestone minerals, such as dolomite (calcium carbonate), are incorporated into the sample to increase the chemical resistance of the glass and confer an inertness to a corrosive product. Secondary additions, such as broken pieces of preformed glass (cullet), are further added to this ‘combination’ during production; this is then heated to approximately 1500 °C and shaped into the desired glass packaging. Using broken cullet that has been through certain recycling processes provides technical, environmental, and economic advantages over virgin materials.

Glass packaging has a natural gloss and sheen and is smooth and easy to clean or rinse and dry, so it represents a convenient material for many applications. It is also aesthetically pleasing to the eye because it is optically transparent and can be fine‐tuned to possess a range of optical properties. Given the high amount of energy required for original manufacture it is convenient that glasses can be both reused and recycled. Many pharmaceutical and liquor producers prefer the material because of its inertness and non‐reactivity to chemicals but also because of its high gas and water barrier properties, combined with its ability to withstand very high pasteurisation and sterilisation temperatures. The technical properties of glass have also increased as a result of new techniques discovered for cutting, carving, moulding, and surface engraving. Using computer‐programmed cutting to form numerous designs, including same strength but lightweight versions of vessels, is now possible. Glass beer bottles account for nearly 55% of glass packaging usage followed by 18% for food, 12% for wine, alcoholic drinks, and liquor, 7% for soft drinks, and others, including pharmaceuticals, which account for only 5%. In the past stoneware, ceramic vessels, or pottery were used for pharmaceuticals, chemicals of medical use (e.g. opium elixir, Epsom salts, cold cream, quicksilver [mercury]), and foods (honey, beers, spirits, ginger beer). However, stoneware is now used as a value‐adding tool and to aid product marketing but there are no current forms of medicines making use of pottery. Part of the downfall of ceramics and their replacement with glass is a result of its lower cost in earlier times, e.g. Victorian and pre‐Victorian periods. In recent times, the return of stoneware has been used to infer a traditional basis for the manufacture of products (typically beverages and food) and thus extra value. Stoneware‐mimicking glasses have now also been made possible by frosting and compounding or pigmenting of the glass, and these have replaced nearly all food uses of ceramic containers.