Question 1

Polystyrene is a light, transparent, thermoplastic. Which of the following is a common application consistent with its properties and processing?

Accepted Answer

Introduction / Context: Matching polymer properties to applications is a core skill in materials engineering. Polystyrene (PS) is rigid, transparent, easy to mould, and economical, making it suitable for consumer goods requiring shape stability and surface finish. Given Data / Assumptions: PS is amorphous, with good clarity and stiffness but relatively low toughness. It processes well by injection moulding. We seek the application that best fits these traits. Concept / Approach: PS’s clarity and mouldability lend themselves to products like toys, combs, disposable cutlery, and housings. For thin films such as flexible packaging bags, polyethylene (LDPE/LLDPE) dominates due to superior toughness and flexibility. Non-stick cookware surfaces require PTFE (Teflon), not PS. High-voltage cable insulation is typically crosslinked polyethylene (XLPE) or specialised polymers with better dielectric strength and thermal resistance than PS can provide in that service. Step-by-Step Solution: Compare application demands with PS traits.Injection-moulded consumer items like toys/combs align well.Eliminate film packaging, non-stick coatings, and HV insulation as mismatches. Verification / Alternative check: Product catalogues and polymer handbooks list PS for rigid consumer goods; PE for films; PTFE for non-stick; XLPE for power cables. Why Other Options Are Wrong: Packaging bags: usually LDPE/LLDPE due to flexibility and toughness.Non-stick surfaces: PTFE, not PS.High-voltage insulation: materials with higher dielectric/thermal performance than PS. Common Pitfalls: Assuming any transparent plastic suits films or cookware without considering toughness and thermal stability. Final Answer: Toys and combs

Question 2

Definition check: a copolymer is formed by the chemical combination of two or more different monomer species. Which option best matches this idea in simple exam convention?

Accepted Answer

Introduction / Context: In elementary polymer chemistry exams, “copolymer” commonly refers to addition copolymers such as SBR (styrene–butadiene rubber) or ABS (acrylonitrile–butadiene–styrene). While copolymers can also be made by condensation, many question banks emphasise the simple addition model to test monomer identity recognition. Given Data / Assumptions: The prompt asks for the best match “in simple exam convention”. Options distinguish addition versus condensation and same versus different monomers. Concept / Approach: A copolymer requires at least two different monomer types incorporated into one macromolecular chain. In many standard MCQs, the default mental model is addition polymerisation of vinyl monomers without elimination of small molecules. Therefore, the option that explicitly states “without the elimination of water” and involves chaining monomers fits the expected exam framing. Step-by-Step Solution: Identify options that involve two different monomers.Select the addition-type description as the conventional answer.Note that more advanced courses accept condensation copolymers too, but the question’s framing points to the addition view. Verification / Alternative check: Common examples of addition copolymers in textbooks include SBR, SAN, ABS; they involve no elimination of water or alcohol during chain growth. Why Other Options Are Wrong: (b) Describes condensation (can form copolymers, but the exam convention here leans to addition).(c) Same monomer → homopolymer, not copolymer.(d) Invalid because a suitable description exists. Common Pitfalls: Over-generalising: in reality, copolymers may form via condensation; however, follow the exam’s intended emphasis unless stated otherwise. Final Answer: In a chain without the elimination of water (addition route).

Question 3

Traditional toothbrush bristles are commonly manufactured from which polymer grade due to its stiffness, abrasion resistance, and moisture tolerance?

Accepted Answer

Introduction / Context: Filament applications (e.g., toothbrush bristles, fishing line, textile fibres) require a balance of stiffness, resilience, abrasion resistance, moisture uptake, and processability. The nylon family (polyamides) has long dominated bristle applications owing to these properties. Given Data / Assumptions: We consider conventional manual toothbrush bristles. The industry standard historically references nylon grades tailored for filament extrusion and end-rounding. Concept / Approach: Nylon-6 is widely used for toothbrush bristles due to its good flex-fatigue resistance, suitable moisture absorption (which softens bristles slightly in use), and ability to be precision-drawn into uniform filaments. Nylon-66 is used in some specialty filaments but is less common for standard toothbrushes. Polystyrene is brittle and unsuitable for repeated bending. PVC lacks the resilience and hygienic performance required for high-quality bristles. Step-by-Step Solution: Match application demands (fatigue, abrasion, moisture tolerance) with polymer properties.Select nylon-6 as the typical choice for bristles.Eliminate alternatives that lack required resilience or biocompatibility traits. Verification / Alternative check: Product specifications from bristle manufacturers frequently list PA6 (nylon-6) for mainstream toothbrush lines; PA612/PA610 may appear in premium variants, but PA6 remains a canonical answer in standard MCQs. Why Other Options Are Wrong: Nylon-66: more common in engineering fibres where higher heat resistance is needed; not the typical bristle baseline.Polystyrene: too brittle and poor fatigue performance.PVC: insufficient resilience and tactile performance for bristles. Common Pitfalls: Assuming any nylon works equally well; subtle differences in moisture regain and bending fatigue matter for user comfort. Final Answer: Nylon-6

Question 4

Material behavior of commodity polymers: at room temperature (≈25 °C), polystyrene typically behaves as which type of plastic?

Accepted Answer

Introduction / Context: Polystyrene is a glassy, amorphous thermoplastic widely used in packaging, disposables, and appliance housings. Its mechanical response at room temperature is governed by the position of room temperature relative to its glass transition temperature. This question checks recognition of the brittle versus ductile nature of polystyrene in everyday conditions. Given Data / Assumptions: Room temperature is around 25 °C. Polystyrene's glass transition temperature (Tg) is well above room temperature (approximately 95–105 °C for general-purpose grades). No rubber impact modifiers are assumed (i.e., not high-impact polystyrene, HIPS). Concept / Approach: When a polymer is tested below its Tg, the polymer chains are frozen in a glassy state. Segmental mobility is minimal, so the material exhibits high modulus and low toughness, failing with limited plastic deformation. This is the classic brittle response. In contrast, ductile behavior requires temperatures sufficiently above Tg to enable significant plastic flow before fracture. Step-by-Step Solution: Compare room temperature to Tg: 25 °C is far below ~100 °C.Below Tg, expect glassy, brittle fracture with low elongation at break.Select the descriptor that matches: brittle. Verification / Alternative check: Drop tests of general-purpose polystyrene articles show crack initiation and catastrophic failure rather than yielding. Impact-modified variants (HIPS) incorporate rubber domains to shift failure toward tougher, semi-ductile modes—but that is a different material. Why Other Options Are Wrong: Ductile/malleable imply significant plasticity, which polystyrene lacks at room temperature in the unmodified state.None of these is incorrect because brittle fits well-established behavior. Common Pitfalls: Confusing general-purpose polystyrene with HIPS; extrapolating from thin foams (EPS) whose cellular structure can cushion impacts but does not change the intrinsic brittleness of the polymer matrix. Final Answer: Brittle

Question 5

Alkyd resins (e.g., glyptal) applications: which of the following is NOT a common use of alkyd resins?

Accepted Answer

Introduction / Context: Alkyd resins are polyester-based coating binders derived from polyols (e.g., glycerol), dibasic acids/anhydrides (e.g., phthalic anhydride), and fatty acids or oils. They dominate many architectural and industrial coatings due to good film formation, durability, and compatibility with pigments and additives. Given Data / Assumptions: Alkyds are used as primary binders in paints/varnishes. They can act as film-forming materials in coatings. Modified alkyds may contribute plasticising effects in certain formulations. Continuous synthetic fibre production typically requires polymers with melt or solution-spinning suitability and precise molecular architecture (e.g., PET, nylon). Concept / Approach: Coatings require a binder that forms a coherent film after application and drying/curing. Alkyds excel here. Fibre manufacture, in contrast, needs polymers that can be spun into filaments and drawn to achieve strength and orientation; alkyd resins are not used as fibre-forming polymers. Step-by-Step Solution: Identify core alkyd applications: coatings, varnishes, enamels—film formation and adhesion.Recognise that 'fibres' implies melt- or solution-spun filament production (PET, nylon, acrylics), not alkyds.Therefore, 'Fibres' is the excluded application. Verification / Alternative check: Market usage data consistently list architectural coatings, industrial enamels, and air-drying alkyds; no commercial fibre segment exists for alkyds. Why Other Options Are Wrong: Paints/varnishes and film-formers are primary alkyd domains.Plasticiser: alkyd components and modifiers can impart plasticising/flexibility in coating films, though dedicated plasticisers are separate chemicals. Common Pitfalls: Assuming any polymer can be spun into fibres; conflating plasticiser function with true plasticiser molecules (e.g., phthalates) even though alkyds contribute film flexibility. Final Answer: Fibres

Question 6

Vulcanisation effects: which property of rubber DECREASES when raw rubber is vulcanised?

Accepted Answer

Introduction / Context: Vulcanisation chemically crosslinks rubber chains, typically with sulfur or other systems, transforming soft tacky gum into an elastic engineering material. Understanding which properties increase or decrease guides compounding and quality control in rubber goods. Given Data / Assumptions: Raw rubber is soft, exhibits cold flow and surface tackiness. Crosslinking reduces chain mobility and improves elastic recovery. Properly compounded materials include antidegradants and fillers. Concept / Approach: Crosslinks limit viscous flow and interchain slippage. As a result, tensile strength, modulus, abrasion resistance, and service temperature range generally increase up to an optimum cure. Solvent and oil resistance also improve due to the network resisting swelling. The obvious property that decreases is surface tackiness: the vulcanised surface is drier, less sticky, and more dimensionally stable. Step-by-Step Solution: List property trends: tensile strength ↑, solvent resistance ↑, working temperature range ↑.Identify the one that goes down: tackiness ↓ after crosslinking.Select 'Tackiness (surface stickiness)' as the correct choice. Verification / Alternative check: Standard stress–strain and swelling tests (e.g., ASTM D412, D471) show post-cure improvements; adhesion to itself without adhesives (tack) drops markedly versus raw gum. Why Other Options Are Wrong: Tensile strength: typically increases with adequate cure.Resistance to organic solvents: network reduces swelling; it does not decrease.Working temperature range: the usable range broadens, not narrows. Common Pitfalls: Overcure can embrittle rubber, but even then, tackiness does not increase; do not confuse tack with adhesion in formulated pressure-sensitive systems. Final Answer: Tackiness (surface stickiness)

Question 7

Manufacture of plastic articles: which moulding process is most commonly used for thermoplastic parts?

Accepted Answer

Introduction / Context: Mass production of plastic components relies on a moulding process that rapidly cycles, produces tight tolerances, and accommodates a wide range of thermoplastics. Recognising the dominant process is essential for manufacturing and design-for-production decisions. Given Data / Assumptions: The article is a plastic (thermoplastic) part. High throughput and dimensional control are desired. Metal casting methods (green/dry sand, shell) are not plastic processing methods. Concept / Approach: Injection moulding melts thermoplastic pellets and injects the melt into a cooled mould at high pressure. After solidification, the part is ejected and the cycle repeats in seconds to minutes. This process suits complex geometries, integrated features, and large production runs. Other plastic forming processes (compression, blow, thermoforming) have specific niches, but injection moulding is the general workhorse. Step-by-Step Solution: Eliminate metal casting processes (green sand, dry sand, shell) which are meant for metals.Identify the standard thermoplastic process: injection moulding.Select 'Injection moulding' as the correct option. Verification / Alternative check: Industry output statistics consistently show injection moulding as the most widely used process for plastic parts by volume and part count. Why Other Options Are Wrong: Green sand/dry sand/shell: casting of metals, not polymer moulding. Common Pitfalls: Confusing compression moulding (used for thermosets and some thermoplastics) with the broad dominance of injection moulding for thermoplastics. Final Answer: Injection moulding

Question 8

Amino resins in paper treatment: which performance attributes are improved by amino (urea/melamine) resin additives?

Accepted Answer

Introduction / Context: Amino resins such as urea–formaldehyde (UF) and melamine–formaldehyde (MF) are used in paper and board to enhance wet strength and surface durability. The resins form crosslinks with cellulose or act as wet-strength agents within the fibre network, boosting performance in packaging and tissue grades. Given Data / Assumptions: Additives are amino resins added during wet end or applied at the size press. Desired properties include wet tear/burst strength, folding endurance, and wet rub resistance. Application conditions allow adequate cure/retention. Concept / Approach: Under acidic conditions and appropriate cure, UF/MF resins form a network that resists fibre–fibre debonding when re-wetted. This increases wet tensile/burst metrics and helps maintain integrity under folding and rubbing. Melamine-modified systems can further improve moisture and chemical resistance. Step-by-Step Solution: Identify property targets relevant to wet-strength chemistry.Recognise amino resins as standard wet-strength agents.Conclude that all listed properties improve. Verification / Alternative check: Paper testing (e.g., wet tensile, Mullen burst, MIT folding) shows clear gains after amino resin treatment compared to untreated controls. Why Other Options Are Wrong: Each single-property option is incomplete; amino resins improve the full set when properly formulated. Common Pitfalls: Confusing internal wet-strength agents with surface sizes; both can be used, but internal addition is key for through-thickness wet strength. Final Answer: All (a), (b) & (c)

Question 9

Effect of vulcanisation on raw rubber: which statement best describes the change after vulcanisation?

Accepted Answer

Introduction / Context: Raw rubber is soft, tacky, and exhibits plastic flow. Vulcanisation creates crosslinks between polymer chains, converting the material into an elastic network suitable for tyres, seals, belts, and countless elastomeric products. This question focuses on the qualitative transformation produced by crosslinking. Given Data / Assumptions: Sulfur or other systems provide crosslinks. Compounding includes fillers, accelerators, and antidegradants. We compare pre- and post-vulcanisation properties qualitatively. Concept / Approach: Crosslinks restrict chain mobility, thereby reducing viscous flow and enabling elastic recovery when stress is removed. The rubber becomes less plastic and less tacky, shows higher modulus and tensile strength (to an optimum), and withstands higher service temperatures. Therefore, the accurate qualitative description is that vulcanised rubber is more elastic and less plastic. Step-by-Step Solution: Recall raw rubber properties: plastic, tacky, low modulus.Apply crosslinking effect: mobility ↓, elastic recovery ↑, tackiness ↓.Choose the statement that captures this shift: more elastic and less plastic. Verification / Alternative check: Dynamic mechanical analysis shows increased storage modulus and lower tan delta at service temperatures after vulcanisation, consistent with improved elasticity and reduced flow. Why Other Options Are Wrong: Softer overall: often hardness increases; softness is not the defining change.Less elastic: opposite of actual behavior.Tackier: crosslinking reduces tack without special tackifiers. Common Pitfalls: Over-generalising softness; actual hardness depends on formulation and crosslink density, but the fundamental change is the transition from plasticity to elasticity. Final Answer: More elastic and less plastic (reduced tackiness)

Question 10

Glyptal-type alkyd resins (phthalic anhydride + glycerol): which of the following is NOT a typical application?

Accepted Answer

Introduction / Context: Glyptal is a classic alkyd resin widely used in coatings. While alkyds can modify flexibility and adhesion in films (and can be blended with plasticisers), they are not used as primary fibre-forming polymers like PET, nylon, or acrylics. Given Data / Assumptions: Composition: phthalic anhydride + glycerol (plus fatty acids/oils). Applications: enamels, varnishes, primers, and as modifiers/plasticisers in coatings. Industrial fibre spinning demands polymers tailored for melt/solution spinning and drawing. Concept / Approach: Coatings require film formation and adhesion; alkyds excel as binders and film-formers. Fibre making requires high-molecular-weight polymers with melt stability and crystallisation behavior compatible with spinning—criteria alkyds do not satisfy. Step-by-Step Solution: Map each option to known alkyd uses.Identify the outlier: fibre making.Select 'Fibre making (as a fibre-forming polymer)' as not typical. Verification / Alternative check: Standards and product literature list alkyds as binders; there is no commercial fibre segment based on alkyd resins. Why Other Options Are Wrong: Automotive/aircraft finishes, plasticiser roles in coatings, and film-forming binders are all legitimate alkyd applications. Common Pitfalls: Interpreting 'plasticiser' as a standalone commodity; here, alkyds act in concert with or as part of film systems to impart flexibility and adhesion. Final Answer: Fibre making (as a fibre-forming polymer)

Question 11

Ion-exchange materials: laboratory and water-treatment cation exchangers (0.3–1 mm beads) are commonly prepared from which resin family?

Accepted Answer

Introduction / Context: Ion-exchange resins are crosslinked, insoluble polymers bearing ionic functional groups. Cation exchangers carry acidic groups (often sulfonic acids) fixed to the polymer matrix. While modern large-scale plants primarily use sulfonated polystyrene–divinylbenzene matrices, sulfonated phenolic resins have also been widely used, especially in laboratory and specialty applications. Given Data / Assumptions: Bead size: 0.3–1 mm typical for packed beds. Functional requirement: strong or weak acid groups for cation exchange. Options list traditional thermoset resins. Concept / Approach: Phenol–formaldehyde networks can be sulfonated to introduce –SO3H groups, producing cation-exchange capability. Urea– and melamine–formaldehyde resins are not commonly used as ion-exchange matrices. Epoxies lack the appropriate backbone/chemistry for efficient sulfonation and exchange capacity in standard practice. Step-by-Step Solution: Identify which resin can be post-functionalised to strong acid groups and shaped into beads.Select sulfonated phenolic (phenol–formaldehyde) as the correct answer. Verification / Alternative check: Historical and specialty resin catalogs list phenolic-based ion exchangers alongside polystyrene–DVB-based products, especially for high-temperature or oxidative environments. Why Other Options Are Wrong: Epoxy, urea–formaldehyde, and melamine resins are not standard cation-exchange bead matrices. Common Pitfalls: Assuming 'ion-exchange resin' always means polystyrene–DVB; phenolic-based cation exchangers are well-established alternatives. Final Answer: Phenol–formaldehyde resins (sulfonated phenolic)

Question 12

Material comparison: compared to polyethylene (polythene), polypropylene is generally…

Accepted Answer

Introduction / Context: Polypropylene (PP) and polyethylene (PE) are closely related polyolefins, but their properties differ due to methyl side groups in PP, which increase stiffness and reduce density. This question checks qualitative property trends designers rely on when choosing between PP and PE. Given Data / Assumptions: Commodity grades compared at ambient conditions. PE reference is LDPE/HDPE range; PP is isotactic, unfilled. Density, stiffness, and strength are considered. Concept / Approach: The methyl group on every other carbon in PP restricts chain mobility and increases crystallinity effects, yielding higher modulus and tensile strength than LDPE and many HDPE grades, while maintaining a lower density (~0.90–0.91 g/cm^3) than PE (~0.92–0.96 g/cm^3). Thus, PP is typically lighter, harder (stiffer), and stronger in many applications. Step-by-Step Solution: Evaluate density: PP < PE → lighter.Assess stiffness/strength: PP > LDPE and competitive with HDPE → harder/stronger.Select 'All (a), (b) and (c)' as the best summary. Verification / Alternative check: Datasheets: PP density ~0.90 g/cm^3; HDPE ~0.95 g/cm^3; modulus and tensile values for PP exceed LDPE and often rival HDPE, confirming the trend. Why Other Options Are Wrong: Single-trait options are incomplete; all three traits are usually observed. Common Pitfalls: Assuming 'hardness' as scratch resistance; here, 'harder' refers to stiffness/modulus—a conventional shorthand in basic MCQs. Final Answer: All (a), (b) and (c)

Question 13

Hot SBR vs. cold SBR (styrene–butadiene rubber): identify the incorrect statement about process and properties.

Accepted Answer

Introduction / Context: SBR can be produced by emulsion polymerisation at ~50 °C (hot SBR) or ~5 °C (cold SBR). Changes in temperature, surfactant, and initiator systems alter microstructure, branching, and molecular weight distribution, which affects performance (e.g., abrasion, tensile, resilience). Given Data / Assumptions: Cold SBR: low-temperature emulsion, better wear and tensile properties. Hot SBR: higher temperature, more branching, different distribution. Emulsion pressure differences are not the defining distinction between hot and cold SBR. Concept / Approach: The key distinction is polymerisation temperature and recipe, not pressure. Properties indeed vary with temperature; cold SBR often exhibits improved mechanicals and lower gel. Statements tying superiority to lower pressure are misleading or incorrect because pressure conditions are comparable and not the root cause of property differences. Step-by-Step Solution: Validate (a): widely taught—cold SBR generally superior → correct.Validate (b): temperature strongly influences kinetics and microstructure → correct.Check (c): assertion about lower pressure is not a defining or generally correct statement → incorrect. Verification / Alternative check: Textbook summaries attribute improved properties to lower temperature and recipe, not to lower operating pressure. Why Other Options Are Wrong: (a) and (b) are valid; 'None of these' cannot be correct because (c) is wrong. Common Pitfalls: Overemphasising reactor pressure in emulsion SBR; mixing up cold SBR with solution SBR processes. Final Answer: Cold SBR production employs lower pressure than hot SBR.

Question 14

Fibre science basics: choose the incorrect statement among the following.

Accepted Answer

Introduction / Context: Fibre terminology covers fineness units, crimp, spinning methods, and moisture regain. This question tests familiarity with definitions and common manufacturing routes for important synthetic and regenerated fibres. Given Data / Assumptions: Dacron (PET) is typically melt-spun. Acrylics can be dry- or wet-spun depending on solvent systems. Viscose rayon is wet-spun via coagulation in a bath. Cellulose acetate is often dry-spun. Concept / Approach: The incorrect statement is the one claiming all listed fibres are wet-spun. In fact, PET is a melt-spun polyester; cellulose acetate commonly uses dry spinning; acrylics may use dry or wet depending on the process. Only viscose rayon is consistently wet-spun among those listed. Denier and tex definitions are standard, and nylon's moisture absorption exceeds that of low-moisture-regain polyester. Step-by-Step Solution: Confirm denier/tex definitions → correct.Confirm crimp description → correct.Evaluate spinning methods: statement grouping all as wet-spun → incorrect.Check moisture: nylon > polyester → statement correct. Verification / Alternative check: Process charts show PET melt spinning, cellulose acetate dry spinning, viscose wet spinning; acrylics vary. Why Other Options Are Wrong: They are correct statements; only the spinning-route claim is broadly incorrect. Common Pitfalls: Assuming all solution-spun fibres are wet-spun; overlooking dry spinning of acetates and some acrylics, and melt spinning of PET. Final Answer: Dacron, acrylic, viscose rayon, and cellulose acetate fibres are all prepared by wet spinning.

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