18.1 Paper is made of cellulose fibers Paper was first made in China as early as AD 100, of mulberry bark, and then introduced to Western world by Arabs in eighth century. The first paper mills were built in Spain in 11th century.
The use of wood to produce paper was started in USA. Additives such as rosin ( ) and alum ( ) were added to strengthen paper and make it accept ink well. Chlorine as used to bleaching paper and titanium dioxide was used to make the paper white. Acidic paper, acid-free paper and alkaline paper Plants alternative to trees: willow ( ), kenaf ( ). They usually have high fiber content and grow fast. 70 million tons of paper are used in USA: one person 230 kilograms or six trees.
18.2 The development of plastics involved experimentation and discovery The search for a lightweight, nonbreakable, moldable material began with the invention of vulcanized rubber ( ). isoprene polyisoprene polymerization Fig18.5 isoprene molecules react with one another to form polyisoprene, the fundamental chemical unit of natural rubber, which comes from rubber trees
Charles Goodyear discovered the rubber vulcanization in 1837. (a) Original form Stretched with little tendency to snap back to original form Stretched with great tendency to snap back because of cross-links (b) Original form with disulfide cross-links Fig18.6 (a) when stretched, the individual poly-isoprene strands in natural rubber slip past one another and the rubber stays stretched. (b) when vulcanized rubber is stretched, the sulfur cross-links hold the strands together, allowing the rubber to return to its original shape Polymer strands
Nitrocellulose and celluloid Fig 18.7 nitrocellulose, also known as cellulose nitrate, is highly combustible because of its many nitrate groups, which facilitate oxidation Nitrate group Nitrocellulose (cellulose nitrate)
Bakelite and phenolic resin ( ) Polymers win in World War II Synthetic rubber, radar, tank and tent Polymer and environment Fig 18.9 the molecular network of bakelite shown in two dimensions. The actual structure projects in all three dimensions. The first handset telephones were made of bakelite Formaldehyde phenol polymerization Phenol-formaldehyde resin (Bakelite)
18.3 Metals come from the Earths limited supply of ores Metallic bond is responsible for the high conductivity and high gross. Fig18.14 metal ions are held together by freely flowing electrons. These loose electrons form a kind of electronic fluid that flows through the lattice of positively charged ions
The form in which a metal is most likely to be found in nature is a function of its position in periodic table. Fig 18.19 which compound of a metal is most prevalent in nature is related to the metals position in the periodic table
Metal-containing compounds can be converted to metals Sheets of impure copper Sheets of pure copper Solution containing CuSO 4 Transforming the metal- containing compound to a metal is less energy intensive Transforming the metal- containing compound to a metal is more energy intensive Fig 18.21 high-purity copper is recovered by electrolysis. Pure copper metal deposits on the negative electrode as copper ions in solution gain electrons. The source of these copper ions is a positively charged electrode made of impure copper
Some metals are most commonly obtained from metal oxides Fig 18.22 a mixture of iron oxide ore, coke, and limestone is dropped into a blast furnace, where the iron ions in the oxide are reduced to metal atoms
Steel Manufacturing via the Oxygen Process (oxidation process)
Metal resources are not unlimited Fig 18.24 steel is stronger than iron because of the small amounts of carbon it contains External pressure Pure iron is fairly soft and malleable because of voids between atoms When the voids are filled with carbon atoms, the carbon helps hold the iron atoms in their lattice. This is strengthened metal is called steel Fe void C
18.4 Glass is made primarily of silicates 18.5 Ceramics are hardened with heat brittle, but withstand extremely high temperature Ceramic engine and superconductors ( ) Fig 18.32 Engine parts made of Ceramic Silicon Nitride,which is a High-strength material
18.6 Composites ( ) combine fibers and a thermoset medium Fig 18.34 a few examples of composite materials wood Rocket cone Fiberglass Graphite fiber composite
More Important! The properties of materials are decided by their chemical structure. (Structure – Property Relationships) Features of each type of material. (Advantages and shortcomings) Selection of materials!
TypeMetalsCeramicsPolymers Chemical structureMetal bondCovalent bondCovalent bond Change of atom position easydifficultyeasy Hardnessmediumhighlow Toughnesstoughbrittletough Thermal stabilitymediumhighlow Chemical stabilitylowhighmedium Moldabilityhighlowhigh Processing costmediumhighlow Ability to form filmmediumhardeasy Conductivityhighlowlow Costmediumhighlow Recycleabilityhighlowmedium
Property requirement and Selection of materials Valve: hard, friction resistance, metal Valve in contact with chemicals? Plane: metal or alloy Supersonic planes? Tennis racket: wood is not strong enough and too heavy, so?
Composites To combine the advantages of different materials Expansive! Difficulty to recycle! So any new type of composites?