By: Muhammad Haseeb Iqbal National Textile University Lecture # 04 Classification of Polymers Polymer Science and Engineering (TM-2052) By: Muhammad Haseeb Iqbal National Textile University

Concepts to be covered General classification of polymers on the basis of Origin Structure Chemistry Thermal behavior Properties Morphological behavior Usage

On the basis of origin Natural : Polymers that occur in nature in plants and animals and are very essential for life. Starch, cellulose, protein, nucleic acid, natural rubber etc. Semi synthetic: Polymers are derived from naturally occurring polymers by chemical modifications. Viscose rayon, acetate rayon Synthetic: Synthetic polymers are man-made polymers Polyethylene, polypropylene, polystyrene, polyvinyl chloride (PVC), nylon, Bakelite etc.

On the basis of structure Linear: Monomeric units are joined in the form of long straight chains, such polymers have high densities, high tensile strength and high melting point. Polyethylene, nylons and polyesters Branched: Chain are mainly linear in nature but also possess some branches along the main chain. They have less densities, lower tensile strength and low melting point Low density Polyethylene (LDPE) Crossed Linked: Monomeric units are linked together to constitute a three dimensional network. They are hard, rigid, and brittle. Bakelite, Melamine formaldehyde resin

Classification on the basis of structure (a) Linear, (b) Branched, (c) polymer with crossed bonds and (d) network

On the basis of chemistry Organic polymers: They have chains consisting of C-C linkages and have hydrogen, oxygen, nitrogen, sulfur and halogen atoms in the side chains apart from carbon atoms. Elementoorganic polymers: Macromolecules whose chains are composed of (i) carbon as well as hetroatoms (except N, S, O, and halogen atoms) and (ii) inorganic chains Polydimethylsiloxane Inorganic polymers: Polymers containing no carbon atoms but have Si-Si, Si-O, N-PX, P-O, and B-O linkages e.g. polysilanes, polysiloxanes, polyphosphazenes, polyphosporic acid, polyphosphates and polyboron oxides

On the basis of thermal behaviour Thermoplastics: These polymers consists of large number of independent and intertwined molecular chains. When heated, these chains can slip past each other and cause plastic flow. Polyethylene, polypropylene, PVC, nylon etc. Thermosetting polymers: These are prepared from low molecular mass semifluid substances. When heated in a mould, they get highly cross-linked to form hard infusible and insoluble products. The common example is Bakelite. Activity: Comparison between thermoplastics and thermosetting polymers

THERMOPLASTIC VS THERMOSETTING (1) These soften and melt on heating. (2) These can be remolded recast and reshaped. (3) These are less brittle and soluble in some organic solvents. (4) These are formed by addition polymerization. (5) These have usually linear structures. (1) These do not soften on heating but rather become hard in case prolonged heating is done these start burning. (2)These can not be remolded or reshaped. (3) These are more brittle and insoluble in organic solvents. (4)These are formed by condensation polymerization. (5) These have three dimensional cross linked structures.

Polymers (Based on Properties) Thermoplastics Elastomers Thermosets e.g. polystyrene (amorphous), Polyethylene (crystalline), etc. e.g. phenol resin, epoxy resin, etc. Thermoplastic Elastomers (TPE) Vulcanized e.g. polystyrene-b-poly butadiene-b-polystyrene (Kraton®) e.g. styrene-butadiene rubber (SBR)

Elastomers Cross linked (networked) rubbery polymers that can be stretched easily (3-10x original size) Rapidly recover original dimensions when applied stress is released. Low degree of cross linking

Elastomers Uses – examination gloves, rubber bands, bouncing balls, automobile parts Not recyclable Degrades (burns) when heat is added Natural elastomers – natural rubber, latex

On the basis of morphological behaviour Polymer morphology is the arrangement of the polymer molecules. There are two type of possible arrangements

On the basis of Usage Form Type Polymeric materials Fiber Natural Cotton, wool, silk, asbestos Semisynthetic Viscose rayon, acetate rayon Synthetic Polyolefins, polyamides, polyesters Plastics Cellulosic plastics Celluloid(First thermoplastic), cellophane Vinyl plastics Polyolefins, polystyrene, polyvinyl chloride, polyvinyl acetate Polyacryloids Polyacrylic acid, polymethylmethacrylate Rubber Polyisoprene NBR, SBR, butyl rubber, polysulfides, polysiloxanes Resins Water soluable Modified starches, cellulose derivatives, PVA, Water insoluable Phenol plasts, amino plasts, polyurethane resins, epoxy and unsaturated polyester resins

Summary