Packaging Technology and Engineering. Dipak Kumar Sarker

of course to make paper and cardboard but also for direct use in pallets and crates (tertiary packaging). Wood can also be used as a source of cellulose for cellophane and in modern‐day bioplastics, which are made from hydroxypropyl methyl or ethyl celluloses (see Sections 3.4 and 3.4.1). Plant and animal materials may include starch and gums for use in paper and bioplastics, proteins, waxes, exudates such as natural rubber or amber, leather, and natural biodegradables. Finally oil and gas are most routinely used to make polyolefins (plastics), waxes, dyes, and synthetic polymers [6]. Figure 2.1b highlights the inter‐relationships and end products of the principal sources of raw materials and also of the process aids used in making the packaging. The five starting materials are also sources of key functionalising additives, including pigments, silicates (for paper sizing), natural biodegradable materials, dyes, and the polymers that are used across all packaging media. Smelting of ore is a prime example of taking a crude starting commodity in the form of an inorganic mineral ore and creating an entirely different material. When extracting the metal for direct or indirect further use, this can create many derivative product materials; common examples would be bauxite (aluminium) or haematite–magnetite (iron). High temperatures are needed in this energy‐intense and highly polluting fabrication process [7], such as 1560 °C for iron and 660 °C for aluminium (see Table 3.9). Glass‐making (discussed in Section 2.4) takes various adjuvants and sand, cullet, soda, and lime and occasionally other compounds such as boric oxide to create a supercooled highly viscous amorphously structured fluid or ‘glass’. Pigments such as cobalt are used to give the glass a blue hue or colour.

      Wood chips, another starting material, are mechanically or chemically degraded to fabricate paper that, after further bleaching processing, produces white paperboard. Plant and animal matter can be used to harvest cellulose and exudates or proteins [8] that can be used in bioplastics and leather. Finally, crude oil, by processes such as cracking and fractional distillation, is used to create polyolefin plastics such as PE. The breakdown products of the oil and gas industries such as aniline are also used to create a range of nitrogenous azo dyes, such as mauveine (aniline purple), which was invented by William Perkin in 1856.

2.2 Building Blocks, Extraction, and Raw Materials

The Earth's crust and therefore the most valuable ores consist of about 12 or so of the 115 possible elements found in the natural environment, where base metals are present at concentrations much less than 1%. In descending order of abundance for the most common elements these are (percentages are approximate values): oxygen (47%), silicon (28%), aluminium (8%), iron (5%), calcium (4%), potassium (3%), sodium (3%), and magnesium (2%). The most abundant rock minerals in the crust are plagioclase (40%; e.g. diabase), feldspar (12%), quartz (12%), pyroxene (11%; e.g. augite), amphibole (5%), mica (5%; e.g. biotite or muscovite), and clay minerals (5%). A mere 8% of the Earth's crust is made from non‐silicates, e.g. carbonate rocks such as limestone, the source of lime used in glass and iron manufacture. Obviously, the Earth's surface or subsurface is not just populated by mineral rocks but also by vegetation and a subterranean source of oil, natural gas, and coal all derived from chemically degraded plant and animal materials. Iron and aluminium ores are among the most common components of the crust, with common iron ores being magnetite, haematite, siderite, goethite, and limonite. More than 95% of iron ores recovered from the crust (mostly magnetite and haematite) are converted to iron and steel. The principal and most abundant aluminium ore component of the crust is bauxite, followed by corundum and cryolite. Common copper ores include copper pyrite, copper glance (chalcocite), and malachite. Tin ores frequently encountered include tin pyrite and cassiterite, but these represent a relatively rare ore in the Earth's crust. Indonesia and China are two of the more common sources of mined tin ore.

Figure 2.2 shows commodities and the raw materials, core ingredients, and fabrication aids used in their manufacture. Iron and steel melt at approximately 1540 °C, for example, and are converted from iron ores though smelting to crude high‐carbon cast iron and then through various subprocesses to remove high concentrations of carbon to wrought iron and mild steel. Stainless steel involves mixing mild steel with traces of chromium (see Section 3.3). The basic ingredients for cast iron (pig iron) ingot production are coke (coal), lime, and iron ore; production is usually undertaken in a blast furnace or metallurgical furnace [7] at around 2000–2300 °C. Blast furnaces are also used for metals such as lead or copper. Iron from a blast furnace is typically converted to steel in a process developed by Henry Bessemer in 1855, which involves blasting air via tuyère pipes through molten pig iron or using a more expensive electric arc furnace (EAF) process developed in full working form by James Readman in 1888. Melting is accomplished by supplying energy to the furnace interior. This energy can be electrical or chemical. Electrical energy is supplied via the graphite electrodes and is usually the largest contributor to overall powering cost in melting operations. Initially, an intermediate voltage tap is selected until the electrodes bore into the scrap. As the furnace atmosphere heats up the arc stabilises and, once the molten pool of steel is formed, the arc becomes quite stable and the average power input increases.

Figure 2.2 Commodities and principal types of raw materials used for packaging. *Polyolefins, cellulosics, and rubber.

      The iron ore blast furnace as the basis for all iron‐ and steel‐making via the production of pig iron is used in a form that is little altered from the original 1855 Bessemer configuration or the simpler format that Abraham Darby used in 1709. At the base of the furnace is a hearth (at 1300 °C); above this portion of the furnace is a zone called the bosh (at 1700 °C), which is the hottest part; at the bosh, molten iron exits the furnace and liquid or gaseous fuel and air are injected via tuyère pipes. The bosh lies below the barrel (at 1500 °C), which ascends up the furnace to the upper portion and to the stack, the throat (at 1000 °C), and finally the flue (at 500 °C). The lining of the blast furnace is constructed from refractory fire bricks that insulate the material and retain a suitable melt temperature in the core of the furnace. Chemical energy is also supplied to the liquid pool of metal via oxygen fuel burners and oxygen lances. Oxygen fuel burners use natural gas mixed with oxygen or a blend of oxygen and air. Heat is transferred to the metal by flame radiation and convection by the hot products of combustion, and heat is transferred within the molten metal by simple conduction. Modern cylindrical blast furnaces can be 20–40 m tall with a maximal width at the base hearth of 5–15 m. Output varies but modern production can make between 1000 and 10 000 tonnes of pig iron per daily campaign. The modern blast furnace process starts with a means of placing the iron ore as a starting point in the furnace with a top‐loading filling device, which charges the furnace with coke, iron ore, recycled iron, and limestone. At the base of the furnace is a sage hole to remove waste and a tap hole to extract the liquid pig iron. Waste gases such as carbon dioxide, carbon monoxide, and various sulfurous gases leave via the stack and through the flue gas [7].

      There are, in principle, six main types of materials used for packaging materials (Figure 2.2). The main categories are aluminium, steel‐iron, glass, paper, plastics (of which there are many types), and wood. Of course, as shown in the figure, the individual types and sourcing for all materials have a large influence on the manufactured end product. Taking wood as an example, there are softwood and hardwood varieties with different grain structures that can be used to produce different types of transport crates, palettes, or shipping boxes as well as different grades of paperboard and paper. With metals, plastics, and glass the background concentration of impurities