Coláiste Lorcáin Leaving Certificate Engineering Polymers History 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. The history of plastics is difficult to pin down. Man has been using polymers such as shellac, horn, gutta, percha, bitumen, lacquer and amber for centuries.

Coláiste Lorcáin Leaving Certificate Engineering Ploymers History of polymers It is not surprising that 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:

Coláiste Lorcáin Leaving Certificate Engineering Polymers History of Polymers 1- from earliest time to 1900: the realisation of a new material group, The birth of a plastic technology, Plastics as substitute materials The “Plastics” age now Engineering Plastics.

Coláiste Lorcáin Leaving Certificate Engineering Polymers S tructure 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.

Coláiste Lorcáin Leaving Certificate Engineering Polymers structures Polymers consist of long chains, which are composed of simple structural units (mers) strung together. mer “poly” = many Mers strung together to form polymers

Coláiste Lorcáin Leaving Certificate Engineering 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. However, if two people link together with one hand each and don’t use the other hand they can only form pairs, such molecules can’t form mers. Polymers structures

Coláiste Lorcáin Leaving Certificate Engineering Polymers structures 1 One-handed Closed molecule Two-handedLinear molecule Three or more handles Cross-linked polymers

Coláiste Lorcáin Leaving Certificate Engineering Polymers structuresTypes of chains 1-Linear chains Thesse 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.

Coláiste Lorcáin Leaving Certificate Engineering Polymers structures  Level 1The types of mers  Level 2Combining mers together  Level 3The way mers are joined together  Level 4The degree of order in polymers  Level 5Polymer mixtures

Coláiste Lorcáin Leaving Certificate Engineering Polymers structuresThermoset 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.

Coláiste Lorcáin Leaving Certificate Engineering Polymers structuresThernmoset and Thermplastics 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.

Coláiste Lorcáin Leaving Certificate Engineering Polymers [Polymerisation] Methods of sticking Mers together The process of sticking mers together is called polymerisation. The two ways of doing this are; 1- Additional polymerisation, this is the most important of the two because most important polymers are made this way and, 2- Condensation polymerisation. This method tends to yield rigid plastics.

Coláiste Lorcáin Leaving Certificate Engineering Polymers Addition Polymerisation  The basic idea of sticking mers together like this is similar to a zip. The mers are added onto the end of a growing chain. There are three basic parts to the process:  Initiation - Polyethylene C 2 H 4, has a double bond between the carbon atoms. One of these bonds is stronger, while the other is weak. Each bond contains two electrons. The weak bond is attacked by a radical.

Coláiste Lorcáin Leaving Certificate Engineering Polymers Addition Polymerisation This radical grabs an electron and leaves one electron behind.  Propagation -When other ethylene molecules come near the ethylene radical they too are attacked and a mer is attached. The combined molecule is a growing chain radical. The process continues by adding other ethylene molecules in a similar fashion.

Coláiste Lorcáin Leaving Certificate Engineering Polymers Addition Polymerisation  Termination - Possible stops to the growing chains could simply be running out of mers or radicals. R-C-C + -C-C R-C-C-C-C- H H H Addition Polymerisation Radical Ethylene polyethylene

Coláiste Lorcáin Leaving Certificate Engineering Polymers Condensation Polymerisation This process depends on splicing rather than zipping. The starting molecules are spliced or joined together with small molecules, like water, being condensed out of the reaction at the end of polymerisation. The remaining structure is a comples 3D structure which is rigid and has a significant cross-linking feature.

Coláiste Lorcáin Leaving Certificate Engineering Polymers Condensation Polymerisation OH H C = O H OH HCHHCH +H 2 O OH. Pheno l Formaldehyde

Coláiste Lorcáin Leaving Certificate Engineering Polymers Types of Polymers Thermoplastics: These are thermosoftening polymers and make up about % of the bulk of polymers. They include ; High Density Polyethylene --HDPE Low Density Polyethylene --LDPE Poly Vinyl Chloride --PVC Polystyrene -- PS Polypropylene -- PP

Coláiste Lorcáin Leaving Certificate Engineering Polymers Types of Polymers Thermosetting: The important ones in this group include; Phenolics - This is a group of polymers based on phenol formaldehyde (PF) the original developed by bakeland. It is a cheap, brittle, muddy-brown (0r black or blue) polymer. Urea-formaldehyde - A white polymer that can be easily coloured. Uses include electric plugs, sockets, and other fittings.

Coláiste Lorcáin Leaving Certificate Engineering Polymers Types of Polymers Melamine-formaldehyde. This is harder, more scratch resistant and clearer. It can be found in ‘melaware’ and formica table tops Polyesters - This is the resin used in fibreglass production. Epoxies - Tis polymer is used in adhesives. Polyurethanes - Are hard to classify as they can exist as hard glassy polymer or as a soft flexible sponge.

Coláiste Lorcáin Leaving Certificate Engineering Polymers Additives for Polymers Just as metals are alloyed to improve their properties, substances are added to polymers to improve theirs. A typical example