--- title: "Biodegradable polymers; epoxy resin and polystyrene" subject: "Engineering Chemistry" chapter: 4 key: "semester_2/engineering_chemistry:biodeg-epoxy-polystyrene" source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/biodeg-epoxy-polystyrene site: BCT Engineering --- # Biodegradable polymers; epoxy resin and polystyrene Engineering Chemistry · Chapter 4: Engineering Polymers - Asked in: 2070 Bhadra, 1+4 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/biodeg-epoxy-polystyrene - Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-4 ## Question What are biodegradable polymers? Give the preparation and uses of epoxy resins and polystyrene. ## Short answer Biodegradable polymers are broken down by microorganisms into CO2, water, and biomass; examples: PHBV, PLA. Epoxy resin is made by condensing bisphenol-A with epichlorohydrin, then cured with amines; uses: adhesives, coatings, electrical insulation, composites. Polystyrene is prepared by free-radical polymerization of styrene; uses: packaging, cups, toys, insulation. ## Answer #### Biodegradable polymers **Biodegradable polymers** are polymers that can be broken down by the action of microorganisms (bacteria, fungi) and enzymes in the environment into CO₂, water and biomass. They contain links such as ester or amide groups that enzymes can attack. Examples: **PHBV** (poly-β-hydroxybutyrate-co-β-hydroxyvalerate; from 3-hydroxybutanoic and 3-hydroxypentanoic acids), polylactic acid (PLA), polycaprolactone, starch- and cellulose-based plastics, and nylon-2-nylon-6 (glycine + aminocaproic acid). Uses: packaging, carry bags, disposable cutlery, surgical sutures, implants, and controlled drug delivery capsules. #### Epoxy resin Epoxy resins are thermosetting polymers containing epoxide (oxirane) groups. They are made by condensing **bisphenol-A** with **epichlorohydrin** in presence of NaOH (about 50–60 °C): ```text HO–R–OH + 2 ClCH₂–CH–CH₂ --NaOH, –2HCl--> (bisphenol-A) \ / O (epichlorohydrin) CH₂–CH–CH₂–O–R–O–CH₂–CH–CH₂ (n = 0) \ / \ / O O where R = C₆H₄–C(CH₃)₂–C₆H₄ Higher polymers: more –CH₂–CH(OH)–CH₂–O–R–O– units inside. ``` The product is a liquid or low-melting prepolymer with epoxide end groups. It is **cured** (hardened) by adding a hardener such as a polyamine (ethylenediamine, triethylenetetramine) or an acid anhydride, which opens the epoxide rings and forms a cross-linked network. **Uses:** - Strong adhesives (Araldite) for metal, glass and ceramics. - Surface coatings, paints and protective linings for tanks and pipes. - Electrical insulation and potting of electronic components; glass-epoxy laminates for printed circuit boards. - Matrix of fibre-reinforced composites (aircraft, boats, sports goods). - Flooring, castings, moulds and tools. #### Polystyrene Prepared by free-radical addition polymerisation of styrene using benzoyl peroxide: n C₆H₅CH=CH₂ → [–CH(C₆H₅)–CH₂–]ₙ. **Uses:** packaging, disposable cups and plates, toys, CD cases, appliance housings, and expanded polystyrene (thermocol) for insulation and cushioning. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why can biodegradable polymers be broken down in the environment? A. They contain groups such as ester or amide that microbes and enzymes can attack B. They are completely cross-linked C. They contain only C–C backbones like polyethylene D. They melt at room temperature Answer: A. Enzymes attack ester/amide links, converting the polymer to CO2, water and biomass. (Key point: Biodegradable) 2. Which pair of compounds condenses with NaOH to give epoxy resin? A. Phenol and formaldehyde B. Bisphenol-A and epichlorohydrin C. Styrene and benzoyl peroxide D. Adipic acid and hexamethylenediamine Answer: B. Epoxy resin is made from bisphenol-A and epichlorohydrin in the presence of NaOH (50–60 °C). (Key point: Epoxy monomers) 3. How is the epoxy prepolymer cured into a hard solid? A. It is cooled below 0 °C B. It is dissolved in water C. A hardener such as a polyamine opens the epoxide rings and cross-links it D. Benzoyl peroxide adds styrene units Answer: C. Polyamine or anhydride hardeners open the epoxide rings to form a cross-linked network. (Key point: Curing) 4. How is polystyrene prepared? A. Condensation of styrene with formaldehyde B. Ring-opening polymerisation of caprolactam C. Condensation of styrene with water loss D. Free-radical addition polymerisation of styrene using benzoyl peroxide Answer: D. Styrene, C6H5CH=CH2, undergoes free-radical addition polymerisation initiated by benzoyl peroxide. 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