Post 341 ⇒ by Gautam Shah →
Polymers that we use in our day-to-day life are of Four types
- Plastics, which are relatively stiff at room temperature,
- Rubbers or elastomers, which are flexible and retract quickly after stretching,
- Fibers, which are strong filamentary materials,
- Coatings, have resins with qualities that are somewhere between a plastic and an elastomer.
Commercially available plastic raw materials can be categorized as:
Often some material combinations provide characteristics across these categories, giving very different properties and hence applications.
Properties of a polymer are altered substantially by inclusion of various substances. These are solids, rubbers, liquids and gases. These additive substances serve following functions.
1 Chain addition or curtailment
3 Plasticizing and softening
4 Lubricants and flow promoters
5 Anti aging compounds
6 Flame retarding
8 Blowing agents
9 Cross linking agents
10 Control of Ultra violet effects
Synthesized polymers arrived on the scene just before and after the world war II. Natural polymers, however, have been with us in plants, human and other beings body. The human body contains many natural polymers, such as proteins and nucleic acids. Cellulose is the structural component of plants.
Human body has nearly 100,000 different types of proteins, and all derived from only twenty amino acids. Starch is a carbohydrate found in cereal grains and potatoes, is a polymer made up glucose monomers. Glycogen, is a polymer, stored in the liver and skeletal muscle tissues, as an energy reserve in animals, similar to the starch in plants. Cellulose is most common organic polymer element. Cotton is one of the purest form of cellulose. Chitin, a natural polymer called polysaccharide is similar to cellulose. It is present in the cell walls of fungi. The nucleic acids as nucleotides form DNA and RNA. Natural rubber and Gutta-percha are plant exudate polymers.
Natural polymers, derived from plant or animal sources, are of great interest in the bio-materials fields, such as tissue-engineering, bio-med transplants, medicines, eco-friendly products. Natural polymers have relevance as scaffolds on which to grow cells to replace damaged ones.
Three materials of natural origin, widely used, polymers are chitosan, collagen and alginate. The principal source of chitosan is shellfish waste and cell walls of fungi. Commercial uses include the making of edible plastic food wraps and cleaning up of industrial waste-water. Collagen is used for medical purposes and to produce gums. Alginate is refined from brown seaweeds. In extracted form it absorbs water 200-300 times its own weight. It is used as thickening agent in foods such as ice-cream and as an emulsifying agent.
Naturally available other polymers are: Shellac was used for sealing, lacquer coatings and as foundry casting binder, Casein derived from milk protein is used in distemper colour preparation, Bitumen were used for water proof coating and as a preservative.
Synthetic polymers were initially conceived as replacement of natural polymers or polymer like materials. Gutta-percha was used for insulating electric cables, replaced by polyethylene and vinyls. Cellulose nitrate was conceived to replace ivory and shellac. Bakelite or Phenol formaldehyde, was used to replace wood.
Natural polymers are biodegradable. These materials are favoured for medical use, as they allow cell attachment and growth (as scaffolding) and are non-ionic and non-inflammatory. Many of these materials are highly porous and lightweight.