Synthetic Fibres and Plastics - III

Polyester fibers are used for high-quality guitar and piano finishes due to their durability, gloss retention, and resistance to wear and environmental factors. Nylon has different applications (ropes, clothing), Rayon is semi-synthetic (cellulose-based), and Acrylic is used for wool-like textiles.

Acrylic fibers are copolymers made primarily from acrylonitrile (85%+) combined with other monomers like methyl methacrylate, methyl acrylate, or vinyl acetate to improve dyeability and processing. 'Acryloacetate' is not a recognized chemical compound used in acrylic fiber production.

Thermoplastics are characterized by weak Van der Waals forces between polymer chains (allowing melting and reshaping), the ability to melt upon heating, and formation via addition polymerization. They have HIGH molecular weights (typically 10,000-1,000,000 g/mol), not low molecular weights - low molecular weight compounds are usually small molecules or oligomers.

Thermoset plastics (vulcanized rubber, melamine, bakelite) undergo irreversible curing and cannot be remelted. Polystyrene is a THERMOPLASTIC - it softens upon heating and can be reshaped multiple times, making it the correct answer as 'not an example of thermoset'.

Guitar strings (especially for classical and acoustic guitars) are commonly made from nylon due to its strength, flexibility, and tonal properties. While some strings use metal, nylon is the standard synthetic fiber for guitar strings among the options given. Polyester has different applications.

Vulcanized rubber is a thermoset polymer that does NOT melt upon heating, is highly resistant to chemical attack, and is insoluble. However, vulcanization creates STRONG covalent cross-links (sulfur bridges) between polymer chains, not weak covalent bonds. This cross-linking is what gives it its thermoset properties.

This statement is incorrect because plastics are generally LESS expensive than metals. Plastics are light in weight, highly durable, and resistant to corrosion - these are all correct properties. The cost advantage is one of the main reasons plastics have replaced metals in many applications.

Monomers are the smallest repeating units that join together through polymerization to form large polymer chains. For example, ethene monomers join to form polythene. 'Repeating unit' refers to the unit within the polymer chain, not the starting molecule, and 'dimer' means only two units bonded together.

Rayon is called a regenerated fibre because it is produced by regenerating natural cellulose (usually from wood pulp) through chemical processing. Cotton is a natural fibre, nylon and decaron are synthetic polymers, but rayon specifically involves the regeneration of cellulose.

Melamine is a thermosetting plastic that exhibits excellent fire resistance due to its strong cross-linked molecular structure. Teflon (PTFE) has high heat resistance but is not specifically classified as fireproof, while polythene and polystyrene are thermoplastics that can melt and burn.

PET stands for Polyethylene Terephthalate, a common polyester plastic used in bottles and textiles. 'Triacetate' and 'tetracetate' are incorrect prefixes - 'terephthalate' refers to the terephthalic acid component in the polymer.

Electric wires have plastic covering because plastics are excellent electrical insulators (bad conductors of electricity). This prevents short circuits and protects against electric shock. While plastics are also bad heat conductors, the primary purpose of wire insulation is electrical safety.

Melamine plastic is used in firefighter uniforms specifically because of its fire resistance property. It does not burn easily and can withstand high temperatures. While melamine is lightweight and has good tensile strength, the critical property for fire safety applications is its resistance to catching fire.

Disposal of plastics is a major problem because they are non-biodegradable - they cannot be broken down by natural processes. Unlike biodegradable materials that decompose over time, plastics persist in the environment for hundreds of years. While some plastics can be reused, the core issue is their non-biodegradable nature.

Rayon is smooth, cool, and highly absorbent, making it comfortable to wear. However, unlike natural fibres such as wool or cotton, rayon does not insulate body heat well - it can feel cold to the touch. This lack of thermal insulation is the property that rayon does not possess compared to many other fibres.

Rayon is known by multiple names: artificial silk (due to its silk-like appearance), viscose rayon (referring to the viscose process used to make it), and cellulosic fiber (as it is made from regenerated cellulose). All these terms refer to the same material.

Polythene (polyethylene) is formed by the polymerization of ethene (ethylene) monomers. When ethene molecules undergo addition polymerization, they link together to form the long chains that make up polythene. Propene would give polypropylene, ethyne is a different alkyne, and ethane is a saturated hydrocarbon.

Nylon-6,6 is synthesized through condensation polymerization of adipic acid (a dicarboxylic acid) and hexamethylene diamine (a diamine). Formaldehyde and phenol produce bakelite, while acrylonitrile is used for acrylic fibres. The correct monomers for nylon specifically are adipic acid and hexamethylene diamine.

Rayon is chemically identical to cotton because both are composed of cellulose. Rayon is produced by regenerating natural cellulose from wood pulp, so its chemical structure is the same as cotton's cellulose. Nylon (polyamide), silk (protein), and polyester have completely different chemical compositions.

Biodegradable substances can be broken down by natural processes into simpler compounds. Woollen clothes are made from natural animal fibers (protein-based keratin) that decompose naturally. Plastic bags, tin, and aluminum are non-biodegradable - they persist in the environment for hundreds to thousands of years without breaking down naturally.