PolymersHistory of Polymers A plastic material is one that is easily shaped and takes on a permanent set. The term polymer refers to a material which has been made by some polymerisation process. Additives and polymers combined yield plastics. Man has been using polymers such as shellac, horn, gutta, percha, bitumen, lacquer and amber for centuries.
PloymersHistory of polymers Research was undertaken to develop and improve on nature, thus synthetic polymers were developed. With an increase in understanding in the structure of these materials there was rapid development in the technology of polymers. Their historical development generally follows five stages:
PolymersHistory of Polymers 1- from earliest time to 1900: the realisation of a new material group, 2- 1900 -1930 The birth of a plastic technology, 3 - 1930 -1950 Plastics as substitute materials 4 - 1950 1970 The “Plastics” age 5 - 1970 - now Engineering Plastics.
PolymersStructure of polymers New polymers are being discovered and developed all the time. Many are developed for particular property combinations which are required for specific tasks. Until 1920 people thought polymers were just thick jellies or liquids like bitumen. Nobody really understood them fully. In 1920 Staudinger showed that polymers were composed of very large molecules,- thus the term polymer was developed.
Polymersstructures Polymers consist of long chains, which are composed of simple structural units (mers) joined together. “poly” = many mer mer mer mer mer mer mer mer mer Mers strung together to form polymers
There are lots of different types of mers that can join together to form polymers. Mers are simple organic molecules. These are special molecules that will link together such as double link molecules. These are like linking arms together to form a human chain. Polymersstructures
Polymersstructures 1 Closed molecule One-handed Two-handed Linear molecule Three or more handles Cross-linked polymers
PolymersTypes of chains 1-Linear chains These are formed when chains are built up without any deviation. They are generally formed when the mers used have only two reactive sites. 2-Branched chains Deviation can occur when the chain is being formed and chain branching can result. 3- Cross-linking The branches can join up to give cross-links between adjacent chains.
Polymersstructures Level 1 The types of mers Level 2 Combining mers together Level 3 The way mers are joined together Level 4 The degree of order in polymers Level 5 Polymer mixtures
PolymersThermoset and Thermplastics The basic structure of polymers is that the mers are strung together in chains. Analogies like paper clip chains and spaghetti are very useful. There is a strong covalent bond along the length of the chain. The way the chains relate to each other determines the type of structure and, hence properties. If the bonds between the chains are primary then a rigid 3D network is constructed and a Thermoplastic polymer will result.
PolymersThermoset and Thermoplastics If the bonds between the chains are weak secondary bonds, then these will easily be disrupted by heat. Such polymers are termed Thermoplastics. The difference is explained by describing how butter can be melted in a frying pan and when allowed to cool, will harden again. Whereas if an egg is broken and fried in the pan until hard, it cannot be resoftened.