Post 480  by Gautam Shah



Polycarbonate is a tough plastic valued for its transparency. It has very high impact resistance combined with light weight. It is, 1/3 the weight of acrylic, and 1/6 of glass. Acrylic is 17% stronger than glass, where as polycarbonate is nearly unbreakable, being 400 times stronger than glass. It is very ductile, self extinguishing and flame retardant plastic. It remains dimensionally stable in prolonged sunlight exposure. Polycarbonate is more expensive than Glass or Acrylic. It is recyclable and environmentally preferable to PVC. Polycarbonate is attacked by many organic solvents. It is also fairly expensive compared to other plastics.


Polycarbonates were first discovered in 1898, but remained without commercial exploitation for 30 years. In the post war period research resumed in 1953, with Bayer patenting the first linear polycarbonate. One week after this GE USA independently synthesized a branched polycarbonate and filed a conflicting patent. After the patent priority resolution, Bayer began commercial production under the trade name Makrolon in 1958. and GE began production under the name Lexan in 1960. After 1970, the original brownish polycarbonate tint was improved to glass-clear.

Polycarbonate is a versatile plastic, which can be injection moulded, extruded, blow moulded and thermo formed. Unlike most thermoplastics, polycarbonate can undergo large plastic deformations without cracking or breaking. It can, as a result be reshaped at room temperature by using techniques for sheet metal working. This makes it valuable for model or prototype making applications. It can be joined mechanically, solvent bonded, and welded with skill. Virgin polycarbonate is the original polymer, whereas re-ground polycarbonate is waste that has been prilled or formed into pellets. The properties do not change much after such prilling.

Polycarbonate Police shields

Polycarbonate is an amorphous thermoplastic of long-chain linear polyesters of carbonic acid and dihydric phenols. They are called polycarbonate because functional groups of polymers are linked by carbonate groups. An amorphous (non crystalline) polymer has a glass like, transparent appearance due to the random orientation and intertwined nature of its molecules like spaghetti. Polycarbonate has a glass transition temperature of about 147 °C and so begins to soften gradually above this point. It begins to flow at about 155 °C. Working tools or forming nozzles are held at above 80 °C temperature to get a product with a clean surface. The toughest grades have the higher molecular mass, but are more difficult to process.

Twin wall Polycarbonate Sheet

Polycarbonate water bottle

The prime uses of Polycarbonate relate to its transparency, toughness, lightness of weight, and exterior durability. Some of the uses are unbreakable openings’ ‘glasses’, roof domes, greenhouse enclosures, police riot shields, vandal-proof light shields, partitions in taxis, non rattling ‘glass’ for bus and tram sliding windows, bullet and temper-proof covers for the valuables and exhibits. Its easy form-ability allows its use for transparent gift and jewellery boxes, utensil covers, bodies of gadgets like hair dryers, housing for electric meters, switch covers, funerary caskets, safety helmets, and computer parts.

Polycarbonate Greenhouse

Polycarbonate has excellent transparency, durability, and high a refractive index, and so is used to make eyeglasses. A thin polycarbonate formed to required curvature makes it very light in weight eyeglasses for spectacles. The clarity, scratch resistance and ability to take on transparent colours makes it suitable for inspection glasses in industries, air craft interior fittings, mines lights, high voltage switches, sockets, back-lit advertising display boards, see-through floors and bottom lit dance floors.

CDs and DVDs

During the last decade polycarbonate is being used for making CDs and DVDs. Polycarbonate like ABS plastic can receive sputter deposition or evaporation deposition of aluminium without the need for a base-coat. Polycarbonate composites are used for marine utilities like boats, frigates. The addition of glass fibres to polycarbonate increases the tensile strength, flexural strength, flexural modulus, and heat deflection temperature.



POLYMERS -basics

POLYMERS -basics

Post 341 ⇒   by Gautam Shah 


Polymers that we use in our day-to-day life are of Four types

  1. Plastics, which are relatively stiff at room temperature,
  2. Rubbers or elastomers, which are flexible and retract quickly after stretching,
  3. Fibers, which are strong filamentary materials,
  4. Coatings, have resins with qualities that are somewhere between a plastic and an elastomer.

Panton Chair

Polyester Threads

Elastomer Shoes


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.

Packaging nuts from Thermoplastic starch

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

2 Fillers

3 Plasticizing and softening

4 Lubricants and flow promoters

5 Anti aging compounds

6 Flame retarding

7 Colourant

8 Blowing agents

9 Cross linking agents

10 Control of Ultra violet effects

Animal Protein Glue

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.

Jelly -Alginate Polymer

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 Latex Tapping

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.

Objects made of natural polymer Chitosan

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.

Teeth impression in Alginate mould

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.

Lac sealing wax

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.

Sutures made from polyglycolic acid are absorbable and will be degraded by the body over time.

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.