Polymers and Plastics

Bakelite, melamine resin and vulcanised rubber are thermosetting polymers.

Polycarbonates, particularly materials like Lexan, are widely used in bulletproof glass and transparent armor applications due to their exceptional impact resistance and optical clarity. While polyamides like Kevlar are used in bulletproof fabrics, polycarbonates excel in rigid transparent armor. Polycarbonates can absorb tremendous impact energy without shattering and maintain structural integrity.

Vulcanisation is the chemical process of heating rubber with sulphur to improve its properties - making it harder, more durable, and more elastic. Sulphur forms cross-links between rubber polymer chains. This process was discovered by Charles Goodyear and revolutionized rubber industry.

According to ECO GO, cornstarch packaging helps reduce the millions of tonnes of plastic waste that accumulate every year. Cornstarch products are made mainly from cornstarch with blending and polymerising with aliphatic materials (such as PLA, PHBV and PCL). This cornstarch packaging is biodegradable within 72 days and all degradable components can decompose in 180 days.

Polycarbonates are tough, transparent thermoplastics with excellent impact resistance, making them ideal for bullet-proof glass, security windows, and protective gear. Their molecular structure contains carbonate groups that provide exceptional strength. Polyvinyl chloride is used for pipes, polyamides (nylon) for textiles, and polyethylene for packaging.

Polycarbonate is a transparent thermoplastic with exceptionally high impact strength and toughness, making it ideal for bullet-resistant applications. It is widely used in bulletproof glass, riot shields, and ballistic visors where transparency and protection are both required.

Polymers are defined as high molecular mass macromolecules, which consist of repeating structural units derived from the corresponding monomers. These polymers may be of natural or synthetic origin. Polysaccharides are polymeric carbohydrate molecules composed of long chains of monosaccharide units bound together by glycosidic. Examples of natural polymers are- starch, glycogen, cellulose, pectin, wool, silk, rubber, chitin, rayon etc.

Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. Epoxy resins may react (cross-linked) either with themselves through catalytic homopolymerisation, or with a wide range of co-reactants including polyfunctional amines, acids (and acid anhydrides), phenols, alcohols, and thiols. Examples are- Bisphenol A (BPA), Bisphenol F (BPF), Epoxy phenol novolac (EPN), etc. Examples of polyvinyl resins are- PVA (poly vinyl alcohol), PVAc (poly vinyl acetate) etc.

1) PA 6/66 (nylon 6/66) is a copolymer and is made from caprolactam, hexamethylenediamine and adipic acid. 2) PA 6I (nylon 6I) is an amorphous polymer which is made from the polymerisation of hexamethylenediamine and isophthalic acid. PA 66/610 (nylon 66/610) is made from hexamethylenediamine, adipic acid and sebacic acid. 3) A model from Solvay Industries and Trogamid from Evonik Industries are semi-aromatic polyamides and are made from the polymerisation of hexamethylenediamine and terephthalic acid. Hence, 2 and 3 statements are false.

1. Vectran is an aromatic polyester used for reinforcing fibres for ropes and sailcloth. It is also used in manufacturing badminton strings, bike tires and in electronics applications.
   1. HDPE is known for its large strength to density ratio. The density of high-density polyethylene can range from 0.93 to 0.97 g/cm3. Although the density of HDPE is only marginally higher than that of low-density polyethylene, HDPE has little branching, giving it stronger intermolecular forces and tensile strength than LDPE.
   2. Polyethylene terephthalate (PET) or polyethylene terephthalic ester (PETE) is a condensation polymer produced from the monomers ethylene glycol, (a dialcohol) and dimethyl terephthalate (a diester). PET fibers are manufactured under the trade names of Dacron. Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. The best known brand name of PTFE is Teflon by DuPont Co. Hence, statement 2 is false.

1) Vulcanization is a chemical process for converting natural rubber or related polymers into more durable materials via the addition of sulphur or a solution of S₂Cl₂ in CS₂. 2) Buna-N is the copolymer of butadiene and acrylonitrile. 3) Cellulose is treated with sulfuric acid and potassium nitrate to give cellulose mononitrate. This was used commercially as celluloid, a highly flammable plastic used in the first half of the 20th Century for lacquers and photographic film. Hence, the statement 1 is incorrect.

1. Nylon 2–nylon 6 (nylon 2,6) is an alternating polyamide copolymer of glycine and amino caproic acid and is biodegradable.
   1. Glyptal is the condensation polymer of ethylene glycol and phthalic acid. It is used in the manufacture of paints and lacquers. Bakelite is the condensation polymer of phenol and formaldehyde. It is used in the making of combs, electrical switches, hardness of utensils and computer discs.
   2. Urea formaldehyde resin (UFR) is the condensation polymer of urea and formaldehyde and is used in the making of unbreakable cups and laminated sheets. Hence, statement 2 is not true.

Synthetic polymers are human-made polymers. From the utility point of view, they can be classified into four main categories: thermoplastics, thermosets, elastomers and synthetic fibers. An elastomer is a polymer with viscoelasticity (having both viscosity and elasticity) and very weak inter-molecular forces. Examples are- polychloroprene, neoprene, baypren, elastolefin urea formaldehyde resin (UFR) etc.

On the basis of molecular forces, polymers are classified in the following four types-

1. Elastomers: These are rubber – like solids with elastic properties. In these elastomeric polymers, the polymer chains are held together by the weakest intermolecular forces. These weak binding forces permit the polymer to be stretched. A few ‘crosslinks’ are introduced in between the chains, which help the polymer to retract to its original position after the force is released as in vulcanised rubber. The examples are buna-S, buna-N, neoprene etc.
2. Fibres: Fibres are the thread forming solids which possess high tensile strength and high modulus. These characteristics can be attributed to the strong intermolecular forces like hydrogen bonding. These strong forces also lead to close packing of chains and thus impart crystalline nature. The examples are polyamides (nylon 6, 6), polyesters (terylene), etc.
3. Thermoplastic polymers: These are the linear or slightly branched long chain molecules capable of repeatedly softening on heating and hardening on cooling. These polymers possess intermolecular forces of attraction intermediate between elastomers and fibres. Some common thermoplastics are polythene, polystyrene, polyvinyls, etc. 4 Thermosetting polymers: These polymers are cross linked or heavily branched molecules, which on heating undergo extensive cross linking in moulds and again become infusible. These cannot be reused. Some common examples are bakelite, urea-formaldelyde resins (UFR), etc.

The classification based on source is sub categorized in-

1. Natural polymers: These polymers are found in plants and animals. Examples are proteins, cellulose, starch, resins and rubber.
2. Semi-synthetic polymers: Cellulose derivatives as cellulose acetate (rayon) and cellulose nitrate, etc. are the usual examples of this sub category.
3. Synthetic polymers: A variety of synthetic polymers as plastic (polythene), synthetic fibres (nylon 6,6) and synthetic rubbers (Buna - S) are examples of manmade polymers extensively used in daily life as well as in industry.