Question 1

In nylon-6 production from caprolactam, the typical conversion level achieved in the polymerisation step is approximately what percentage?

Accepted Answer

Introduction / Context: Conversion in nylon-6 polymerisation impacts molecular weight, residual monomer content, and downstream devolatilisation requirements. High conversion is desired to minimise extractables and improve mechanical properties. Given Data / Assumptions: Nylon-6 melt polymerisation is typically driven to high conversion before finishing/stripping. Residual caprolactam is later reduced via extraction or vacuum devolatilisation. Concept / Approach: Industrial practice aims for high monomer-to-polymer conversion, often around 90% or above in the main reactor stage, followed by finishing steps to remove unreacted lactam and cyclic oligomers and to tune molecular weight by controlled solid-state or melt treatment. Step-by-Step Solution: Select a high, realistic conversion target.90% aligns with common operations prior to finishing. Verification / Alternative check: Process descriptions indicate high conversion with subsequent extraction to meet low residual monomer specs for fibres and films. Why Other Options Are Wrong: 25–70% are too low for efficient industrial practice and would leave excessive lactam. Common Pitfalls: Assuming 100% conversion in practice; polymer processes usually approach but do not reach complete conversion before finishing. Final Answer: 90

Question 2

Name the polymerisation process in which two or more chemically different monomers participate together to form a macromolecule.

Accepted Answer

Introduction / Context: Copolymers allow tuning of mechanical, thermal, and chemical properties by incorporating more than one monomer into the polymer chain. This is central to modern materials design (e.g., SBR, ABS, EVA). Given Data / Assumptions: We require the term for multi-monomer polymerisation. Other terms (addition, chain) describe mechanism, not monomer variety. Concept / Approach: Copolymerisation refers specifically to polymer formation from two or more distinct monomer species, regardless of whether the underlying mechanism is chain-growth or step-growth. Step-by-Step Solution: Match definition to term: copolymerisation.Exclude mechanism-oriented alternatives. Verification / Alternative check: Examples include SBR (styrene + butadiene), EVA (ethylene + vinyl acetate), and ABS (acrylonitrile + butadiene + styrene). Why Other Options Are Wrong: Addition and chain polymerisation address kinetics/mechanism, not monomer diversity. Common Pitfalls: Conflating copolymerisation with polymer blends; blends are physical mixtures, not chemical copolymers. Final Answer: Copolymerisation

Question 3

Ebonite identification in rubber technology: what is ebonite most accurately described as?

Accepted Answer

Introduction / Context: Ebonite (hard rubber) is produced by vulcanising natural rubber with a very high sulphur content, creating a stiff, hard, and chemically resistant material used historically for electrical components, battery cases, and laboratory ware. Given Data / Assumptions: Ebonite contains far more sulphur than typical soft rubbers. High crosslink density produces rigidity and dimensional stability. Concept / Approach: Vulcanisation introduces sulphur crosslinks between polyisoprene chains. Increasing crosslink density transitions behaviour from elastic to rigid. Ebonite represents the extreme—thermoset network with minimal elasticity and high hardness. Step-by-Step Solution: Relate “ebonite” to “hard rubber” → heavy vulcanisation.Eliminate unmodified natural rubber and uncured gum.Recognise it is not an adhesive but a structural material. Verification / Alternative check: Materials references list ebonite as containing roughly 30–40% sulphur with high hardness and dielectric strength. Why Other Options Are Wrong: They describe different materials or uses unrelated to ebonite. Common Pitfalls: Assuming ebonite retains rubber-like elasticity; it behaves more like a hard plastic due to dense crosslinking. Final Answer: Highly vulcanised rubber

Question 4

Polyvinyl chloride (PVC): select the correct statement about its polymer type and common manufacturing method for resin production.

Accepted Answer

Introduction / Context: Polyvinyl chloride (PVC) is a widely used commodity plastic for pipes, cables, and profiles. Understanding how PVC is made and classified (thermoplastic vs thermoset; addition vs condensation) is a core materials question in polymers and chemical engineering. Given Data / Assumptions: PVC refers to polyvinyl chloride, derived from vinyl chloride monomer. Options present statements about cure type and polymerisation route. We consider industrial resin production practice. Concept / Approach: PVC is an addition polymer (chain-growth of vinyl chloride) and is a thermoplastic (it softens on heating and can be remelted). Industrial PVC resin is typically produced by suspension or emulsion polymerisation (and sometimes bulk), yielding grains/particles later compounded with stabilisers, plasticisers, lubricants, and fillers. It is not a thermoset, and it is not a condensation polymer. Step-by-Step Solution: Identify class: PVC = thermoplastic, addition polymer.Recall processes: suspension and emulsion are the common routes.Evaluate options: (c) matches industrial practice; (a) and (b) are incorrect; hence choose (c). Verification / Alternative check: Process descriptions for PVC list suspension PVC (S-PVC) and emulsion PVC (E-PVC) as the main commercial resins, confirming option (c). Why Other Options Are Wrong: Thermosetting: PVC does not irreversibly crosslink in normal processing.Condensation polymer: PVC arises by addition; no small-molecule byproduct is formed.None of these: invalid because (c) is correct. Common Pitfalls: Confusing processing additives (stabilisers, plasticisers) with the polymerisation mechanism; assuming “thermoset” because some PVC articles are rigid. Final Answer: Commonly produced via emulsion (and suspension) polymerisation.

Question 5

Identify the polymer produced from terephthalic acid and ethylene glycol in polyester chemistry.

Accepted Answer

Introduction / Context: Matching monomers to their resultant polymers is a frequent exam task. Here, the diacid–diol pair points to a condensation polyester used extensively in fibres and bottles. Given Data / Assumptions: Terephthalic acid (or dimethyl terephthalate) and ethylene glycol are the monomers. We assume standard melt polycondensation. Trade name “terylene” is commonly used for PET fibres. Concept / Approach: Condensation of terephthalic acid with ethylene glycol forms polyethylene terephthalate (PET), known as terylene in fibre applications. Nylon-66 is a polyamide (diamine + diacid), PVC is an addition polymer from vinyl chloride, and polystyrene is from styrene; none match the given monomers. Step-by-Step Solution: Map monomers: terephthalic acid + ethylene glycol → PET.Relate PET to the trade name “terylene”.Eliminate other options due to mismatched monomers. Verification / Alternative check: Polyester process flowsheets show esterification/transesterification followed by polycondensation giving PET chips for fibre and bottle-grade resin. Why Other Options Are Wrong: Nylon-66 uses hexamethylene diamine + adipic acid.PVC and polystyrene are addition polymers of vinyl chloride and styrene, respectively. Common Pitfalls: Confusing “nylon” (polyamide) with “polyester” due to similar applications in fibres. Final Answer: Terylene (polyethylene terephthalate, PET)

Question 6

Flexible plastic pipes for irrigation, conduits, and tubing are most commonly manufactured from which polyolefin?

Accepted Answer

Introduction / Context: Pipe and tubing materials must balance flexibility, toughness, and processability. Within the polyethylene family, density (and branching) strongly affects stiffness and bendability of extruded pipes. Given Data / Assumptions: “Flexible” implies high elongation and easy bending without kinking. Applications include small-diameter irrigation lines and general tubing. Commodity thermoplastics are under consideration. Concept / Approach: LDPE has significant chain branching, reducing crystallinity and modulus, which increases flexibility—ideal for flexible pipes and tubes. HDPE is stiffer and used for pressure pipes and gas mains. PP is stiffer than LDPE and has lower low-temperature toughness. Unsaturated polyesters are thermosets, not typically used for extruded flexible pipes. Step-by-Step Solution: Relate flexibility requirement to polymer structure.Select LDPE for its lower modulus and higher ductility.Eliminate HDPE/PP (stiffer) and thermoset polyester (unsuitable for flexible extrusion). Verification / Alternative check: Datasheets for LDPE tubing show high elongation and low bend radius; HDPE datasheets emphasise stiffness and pressure rating. Why Other Options Are Wrong: HDPE/PP: better for rigid pipes; reduced flexibility versus LDPE.Unsaturated polyester: used in FRP composites, not flexible pipe extrusion. Common Pitfalls: Assuming all “polyethylene” grades have the same flexibility; density and branching matter greatly. Final Answer: Low-density polyethylene (LDPE)

Question 7

Epoxy resin: choose the correct statement about its nature and typical applications (repairing the options to ensure a single correct choice).

Accepted Answer

Introduction / Context: Epoxy resins form a large class of thermosetting polymers used in coatings, adhesives, electrical encapsulation, and composites. The original options contained only incorrect statements; applying the Recovery-First Policy, we reconstruct one accurate option so the MCQ is valid and instructive. Given Data / Assumptions: Epoxies cure to crosslinked networks (thermosets). They exhibit excellent adhesion, chemical resistance, and dielectric properties. Question requires exactly one correct statement after repair. Concept / Approach: Cured epoxies are rigid thermosets, not elastomers. They are not used as abrasives (abrasive grains are typically alumina, SiC). They are not linear polyesters; though “epoxy polyester” hybrids exist in powder coatings, epoxies themselves are formed by epoxide ring chemistry (e.g., bisphenol-A diglycidyl ether) crosslinked with hardeners (amines, anhydrides, etc.). One prominent application is high-performance protective coatings. Step-by-Step Solution: Identify epoxy as a thermoset used in coatings and adhesives.Evaluate statements: only (a) correctly represents epoxies.Confirm that (b), (c), and (d) misclassify use or chemistry. Verification / Alternative check: Coatings handbooks list epoxy primers and topcoats for corrosion protection and chemical resistance across marine and industrial sectors. Why Other Options Are Wrong: Abrasives: epoxies may bind abrasives but are not the abrasive itself.Elastomer: cured epoxies are rigid networks, not rubbery without special tougheners.Polyester: incorrect base chemistry for epoxies. Common Pitfalls: Confusing binder vs abrasive; conflating epoxy with polyester due to similar two-part processing. Final Answer: Widely used as a high-performance surface coating due to strong adhesion and chemical resistance.

Question 8

Non-stick cookware coatings: which polymer is commonly used to provide non-stick surfaces on frying pans?

Accepted Answer

Introduction / Context: Non-stick cookware relies on extremely low surface energy to resist adhesion of food. Among polymers, polytetrafluoroethylene (PTFE) stands out for its chemical inertness and lubricity. Given Data / Assumptions: Focus is on the topcoat of frying pans. We consider common trade names. Thermal stability during cooking is required. Concept / Approach: Teflon is the DuPont trade name for PTFE. PTFE has a very low coefficient of friction, excellent chemical resistance, and high continuous-use temperatures suitable for cookware. Bakelite is a thermoset used as handles/insulators, Perspex (PMMA) is an acrylic with poor high-heat performance, and PVC softens/degrades at cooking temperatures and is unsuitable for food-contact non-stick layers. Step-by-Step Solution: Match property requirement (low surface energy, heat resistance) to polymer.Select PTFE as the established non-stick coating material.Eliminate Bakelite, PMMA, and PVC for thermal or functional shortcomings. Verification / Alternative check: Cookware specifications and materials datasheets list PTFE-based multilayer coatings as the standard for non-stick pans. Why Other Options Are Wrong: Bakelite: used for handles, not slick cooking surfaces.PMMA and PVC: inadequate heat resistance and unsuitable for non-stick tasks. Common Pitfalls: Confusing brand names with base material; e.g., ceramic non-stick is different and not PTFE but is outside the given options. Final Answer: Teflon (PTFE)

Question 9

Recyclability of polymer scrap: which among the following scrap types can be remelted, recycled, and re-utilised most readily?

Accepted Answer

Introduction / Context: Polymer recyclability depends strongly on whether the material is a thermoplastic or a thermoset. This question checks the practical distinction from a waste-processing perspective. Given Data / Assumptions: Bakelite and epoxy resins are thermosets. Polythene (polyethylene) is a thermoplastic. We consider mechanical recycling by remelting and re-extrusion. Concept / Approach: Thermoplastics soften and flow when heated, so their scrap can often be reprocessed by melting. Thermosets are crosslinked irreversibly and do not melt; they degrade on heating, making remelting impossible. Therefore, among the choices, polythene is the readily recyclable material via melt reprocessing. Step-by-Step Solution: Classify materials: polythene = thermoplastic; Bakelite/epoxy = thermosets.Apply recyclability rule: only thermoplastics remelt.Select polythene accordingly. Verification / Alternative check: Recycling codes and industry practice list polyethylene (PE) among the most recycled plastics (e.g., HDPE bottles, LDPE films) by melt reprocessing. Why Other Options Are Wrong: Bakelite, epoxy: crosslinked networks do not remelt; only downcycling as fillers/ground powders is possible.None of these: incorrect because polythene qualifies. Common Pitfalls: Assuming all plastics recycle identically; cure chemistry dictates feasibility. Final Answer: Polythene (thermoplastic)

Question 10

Natural rubber chemistry: the main constituent (polymer backbone) of natural rubber is which polymer?

Accepted Answer

Introduction / Context: Natural rubber, harvested as latex from Hevea brasiliensis, is a cornerstone elastomer in tyres and engineering goods. Identifying its chemical backbone is essential in understanding its properties and cure behaviour. Given Data / Assumptions: We focus on the repeat unit of natural rubber. Isomers and microstructure (cis vs trans) matter for properties. Compare with common synthetic elastomers. Concept / Approach: Natural rubber is predominantly cis-1,4-polyisoprene. This cis configuration yields high extensibility, resilience, and strain crystallisation, contributing to strength in tyres. Polybutadiene is a synthetic diene rubber; polychloroprene is neoprene (synthetic); polystyrene is a rigid thermoplastic—none match natural rubber’s composition. Step-by-Step Solution: Identify “natural rubber” → latex polymer.Recall: backbone = cis-1,4-polyisoprene.Eliminate alternative elastomers and thermoplastics. Verification / Alternative check: Rubber handbooks specify natural rubber as cis-1,4-polyisoprene with minor non-rubber constituents (proteins, lipids, inorganic). Why Other Options Are Wrong: Polybutadiene: different monomer, synthetic.Polychloroprene: chlorinated diene (neoprene), synthetic.Polystyrene: unrelated thermoplastic. Common Pitfalls: Confusing “rubber-like” behaviour with identical chemistry; several elastomers share properties but differ in monomer. Final Answer: Polyisoprene (cis-1,4-)

Question 11

Meaning of the numbers in nylon-66: what do the first and second “6” designate?

Accepted Answer

Introduction / Context: Nylon nomenclature encodes the number of carbons in the monomers. Understanding this quickly identifies raw materials and links structure to thermal and mechanical properties. Given Data / Assumptions: Nylon-66 is a condensation polyamide. Two integers refer to diamine and diacid, respectively. Monomers are standard industrial chemicals. Concept / Approach: In nylon-66, the first 6 corresponds to the 6-carbon diamine (hexamethylene diamine), and the second 6 to the 6-carbon diacid (adipic acid). The polymer results from amide formation between these monomers. Options that involve “rings” are distractors; nylon-66 is aliphatic. Step-by-Step Solution: Recall naming rule: first number = carbons in diamine; second number = carbons in diacid.Apply to nylon-66: HMD (6) + adipic acid (6).Select the matching option. Verification / Alternative check: Nylon family naming (e.g., nylon-6,10; nylon-11) follows the same convention, confirming the interpretation. Why Other Options Are Wrong: References to aromatic rings do not apply to nylon-66.“None of these” is invalid because a correct mapping exists. Common Pitfalls: Confusing nylon-6 (from caprolactam) with nylon-66 (from two monomers). Final Answer: Hexamethylene diamine and adipic acid (each has 6 carbons).

Question 12

Solubility of high polymers: pick the single WRONG statement among the following general rules.

Accepted Answer

Introduction / Context: Polymer solution behaviour differs from small molecules. Viscosity, swelling, and solubility are governed by chain entanglements, solvent–polymer interactions, and crosslinking. This question asks you to isolate an incorrect generalization. Given Data / Assumptions: High polymers refer to long-chain macromolecules. Solubility and viscosity trends are qualitative. Crosslinking is considered in the context of network polymers. Concept / Approach: Statements (a)–(c) are broadly correct: crosslinking suppresses dissolution; “like dissolves like” applies (aliphatic vs aromatic); and higher solvent molecular weight often reduces solvent power and diffusion, lowering swelling/solubility. Statement (d) is wrong: solutions of very high-molecular-weight polymers are highly viscous even at low concentrations due to chain entanglements, so viscosity increases strongly with molecular weight. Step-by-Step Solution: Evaluate each statement against polymer solution theory.Recognize (d) contradicts the known scaling of viscosity with molecular weight.Choose (d) as the single wrong statement. Verification / Alternative check: Empirical Mark–Houwink relations show intrinsic viscosity increases with molecular weight to a positive exponent, confirming (d) is false. Why Other Options Are Not Wrong: (a) Networks resist dissolution.(b) Solubility aligns with solubility parameter proximity.(c) Larger solvent molecules reduce activity and diffusion, decreasing swelling. Common Pitfalls: Assuming polymer solutions behave like low-molecular-weight liquids; ignoring entanglement effects. Final Answer: Very high-molecular-weight polymers give solutions of very low viscosity on dissolving.

Question 13

Intermolecular forces ranking: which polymer class exhibits the strongest intermolecular forces among the following?

Accepted Answer

Introduction / Context: Mechanical behaviour of polymers depends on intermolecular forces and network structure. A common textbook ordering contrasts elastomers, general thermoplastics, and oriented fibres. Given Data / Assumptions: “Fibres” denote highly oriented, often crystalline polymers (e.g., nylon, PET). “Elastomers” are lightly crosslinked with weak intermolecular forces between chains at rest. “Thermoplastics” are moderate, semicrystalline or amorphous materials. Concept / Approach: Fibres are drawn to high orientation with strong secondary bonding (hydrogen bonding in polyamides, dipole interactions in PET) and significant crystallinity, giving the highest tensile strength and effective intermolecular attractions along the axis. Elastomers have the weakest intermolecular attractions (high chain mobility). General thermoplastics lie in between. “Thermosetting polymers” form covalently crosslinked networks; while their covalent network is very strong, the question compares intermolecular forces (secondary forces) between separate chains. On that basis, fibres are the standard answer. Step-by-Step Solution: Identify that fibres possess high orientation and crystallinity.Compare with elastomers (lowest) and general thermoplastics (intermediate).Select fibres as having the strongest intermolecular forces. Verification / Alternative check: Textbook strength order: elastomers < thermoplastics < fibres for tensile strength tied to intermolecular attractions and orientation. Why Other Options Are Wrong: Elastomers: intentionally low secondary forces for elasticity.Thermoplastics: moderate forces.Thermosets: dominated by covalent crosslinks, not merely intermolecular forces. Common Pitfalls: Confusing covalent crosslink strength with intermolecular (secondary) forces terminology. Final Answer: Fibres

Question 14

Condensation of bisphenol-A with phosgene yields which engineering thermoplastic noted for high heat resistance and impact strength?

Accepted Answer

Introduction / Context: Knowing the monomer pairs helps identify the polymer family and its properties. Bisphenol-A and phosgene form carbonate linkages that define a widely used clear engineering plastic. Given Data / Assumptions: Bisphenol-A (diol) and phosgene (carbonyl chloride) are the reactants. Interfacial or melt transesterification routes may be used. We compare to other polymer families. Concept / Approach: Bisphenol-A + phosgene → polycarbonate (PC), featuring carbonate linkages in the backbone. Polyurethanes arise from diisocyanate + polyol; polysulphones involve sulphone linkages; generic “polyesters” are from diols with diacids/diesters (not specifically BPA + phosgene). Step-by-Step Solution: Map BPA + phosgene → carbonate linkages → PC.Eliminate polyurethane, polysulphone, and unspecific polyester. Verification / Alternative check: Manufacturing routes for PC include interfacial phosgenation and phosgene-free transesterification (DPC route), both anchored to BPA. Why Other Options Are Wrong: Chemistries do not match the listed monomer pair. Common Pitfalls: Mixing up carbonate vs ester linkages due to similar names. Final Answer: Polycarbonate

Question 15

Bagasse fibre composition: which of the following is NOT present in bagasse fibres from sugarcane residues?

Accepted Answer

Introduction / Context: Bagasse, a by-product of sugarcane processing, is an important lignocellulosic feedstock for paper, boards, and bio-based materials. Its fibrous component contains the typical triad of plant polymers. Given Data / Assumptions: We refer to untreated bagasse fibre composition. “Pentosans” denotes hemicellulose fractions rich in pentose sugars. One option must state that all listed components are indeed present. Concept / Approach: Bagasse fibres contain cellulose (structural backbone), hemicelluloses (pentosans), and lignin (aromatic binder). Therefore, none of the listed components are absent; the correct choice is “None of these.” Industrial pulping adjusts these constituents but the raw fibre includes all three. Step-by-Step Solution: Check each component against known lignocellulosic composition.Confirm presence of cellulose, lignin, and pentosans.Select “None of these.” Verification / Alternative check: Pulp and paper references list typical bagasse composition: cellulose ~40–50%, hemicellulose ~20–30%, lignin ~18–24% (approximate ranges). Why Other Options Are Wrong: Each of (a)–(c) is genuinely present; claiming otherwise would be incorrect. Common Pitfalls: Confusing processed/pulped bagasse fractions with the raw fibre composition. Final Answer: None of these

Question 16

Polycondensation of a saturated dicarboxylic acid with a polyhydric alcohol typically produces which class of resin?

Accepted Answer

Introduction / Context: Alkyds are workhorse coating resins. Recognising their synthetic origin helps distinguish them from epoxies, phenolics, and polyamides which arise from different monomer families and cure chemistries. Given Data / Assumptions: Saturated dicarboxylic acid (or anhydride) reacts with a polyhydric alcohol (polyol). We consider classical resin manufacture used in coatings. Concept / Approach: Alkyd resins are polyesters modified with fatty acids or oils, formed by condensation of diacids/anhydrides (e.g., phthalic anhydride) with polyols (e.g., glycerol, pentaerythritol). Epoxies derive from epoxide monomers; polyamides from diamine + diacid; phenolics from phenol + formaldehyde. Thus the described reaction is characteristic of alkyd formation. Step-by-Step Solution: Match monomers (diacid + polyol) to polyester/alkyd chemistry.Identify coatings context → alkyd resin.Eliminate epoxy, polyamide, and phenolic which use different monomers. Verification / Alternative check: Coatings texts define alkyds as oil-modified polyesters made by polycondensation of polyols and polybasic acids. Why Other Options Are Wrong: Monomer sets and mechanisms do not match the given description. Common Pitfalls: Confusing generic “polyester” with the more specific, oil-modified “alkyd” used in paints. Final Answer: Alkyd resin

Question 17

Free-radical addition polymerisation: which initiators commonly decompose to generate free radicals for chain initiation?

Accepted Answer

Introduction / Context: Free-radical polymerisation requires radical initiators to start chain growth in monomers like styrene, acrylates, and vinyl chloride (in appropriate systems). Identifying initiator classes is fundamental in polymer reaction engineering. Given Data / Assumptions: Initiators decompose thermally or under redox to form radicals. We compare typical initiators vs strong acids. Concept / Approach: Organic peroxides (e.g., benzoyl peroxide, dicumyl peroxide) and azo compounds (e.g., AIBN) are classic radical sources. Strong mineral acids such as sulphuric and hydrofluoric acid are not radical initiators for addition polymerisation; they catalyse ionic mechanisms (e.g., cationic) in other contexts, but not as radical sources by decomposition. Step-by-Step Solution: Recall initiator families for radical polymerisation.Identify peroxides as thermal radical generators.Eliminate acids as non-initiators for radical routes. Verification / Alternative check: Polymerisation handbooks list decomposition kinetics of peroxides/azo initiators and their half-life temperatures for process design. Why Other Options Are Wrong: Acids do not decompose to radicals under normal polymerisation conditions. Common Pitfalls: Confusing radical and ionic polymerisation mechanisms. Final Answer: Organic peroxides

Question 18

Preventing crystallisation in celluloid: which additive is used as a plasticiser to inhibit crystallisation and embrittlement?

Accepted Answer

Introduction / Context: Celluloid, an early plastic based on nitrocellulose, requires plasticisation to maintain flexibility and reduce brittleness. Classic historical formulations used a specific small molecule to soften the matrix and suppress crystallisation. Given Data / Assumptions: Celluloid = nitrocellulose + plasticiser. We seek the traditional plasticiser. Additive should reduce crystallisation and improve toughness. Concept / Approach: Camphor is the historical and archetypal plasticiser for celluloid. It intercalates between nitrocellulose chains, reducing intermolecular forces, lowering glass transition temperature, and suppressing crystallisation that would otherwise embrittle the material. Glycerol is a plasticiser for other systems (e.g., PVC derivatives), and “nitrocellulose” is the polymer itself, not an additive. Step-by-Step Solution: Identify celluloid composition.Recall camphor as the key plasticiser.Eliminate alternatives that do not match historic practice. Verification / Alternative check: Materials histories and safety data sheets for legacy celluloid goods specify camphor as the principal plasticiser. Why Other Options Are Wrong: Glycerol: not the classic plasticiser for celluloid.Nitrocellulose: base polymer, not an additive.None: invalid because camphor is used. Common Pitfalls: Confusing polymer with its modifier; overlooking the historical role of camphor. Final Answer: Camphor

Question 19

Dacron (PET) classification: among the following, which description best fits Dacron?

Accepted Answer

Introduction / Context: Dacron is a trade name for polyethylene terephthalate (PET) fibres. Classification questions often probe whether you can simultaneously recognize its chemistry and its broader family. Given Data / Assumptions: PET forms by condensation of a diacid (or diester) with a diol. “Polyester” denotes the presence of ester linkages. We allow multi-select logic via “Both (b) and (c)”. Concept / Approach: PET is a condensation polymer (b) and specifically a polyester (c). It is not an addition polymer. Therefore, the most accurate single choice is “Both (b) and (c).” Step-by-Step Solution: Link PET synthesis to condensation chemistry.Identify ester linkages → polyester family.Select combined option (d). Verification / Alternative check: Process descriptions of PET (DMT or PTA routes) confirm esterification and polycondensation steps. Why Other Options Are Wrong: Addition polymer: incorrect for PET.Single options (b) or (c) miss that both descriptors apply. Common Pitfalls: Forgetting that “polyester” is a structural family, while “condensation” describes the mechanism. Final Answer: Both (b) and (c)

Question 20

Bakelite classification (repair applied): which statement correctly identifies Bakelite?

Accepted Answer

Introduction / Context: The original options did not include a correct identification for Bakelite. Applying the Recovery-First Policy, we repair the MCQ by adding one accurate option that reflects standard materials knowledge. Given Data / Assumptions: Bakelite is produced from phenol and formaldehyde. It cures to a crosslinked network (thermoset). We ensure only one option is correct after repair. Concept / Approach: Bakelite is the archetypal phenol–formaldehyde thermoset. It is not an addition polymer (that would involve chain growth like styrene), not an elastomer (it is rigid), and not a thermoplastic (it does not remelt). Hence, the repaired correct description is a thermosetting phenolic resin. Step-by-Step Solution: Identify chemistry: phenol + formaldehyde → phenolic network.Classify as thermoset due to irreversible crosslinking.Select the repaired option (d) as correct. Verification / Alternative check: Historic and modern materials texts list Bakelite as the first widely commercialized thermoset plastic. Why Other Options Are Wrong: Addition polymer: wrong mechanism.Elastomer: mechanical behaviour does not match.Thermoplastic: does not soften/remelt upon heating. Common Pitfalls: Equating “moulded at heat” with thermoplasticity; thermosets also cure under heat and pressure. Final Answer: A thermosetting phenol–formaldehyde resin.

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