Question 1

Nomenclature check: polyhexamethylene adipamide is commonly known as which engineering polymer?

Accepted Answer

Introduction / Context: Engineering polymers are sometimes referred to by systematic chemical names and sometimes by industry trade names. Recognising equivalences avoids confusion in specifications and material selection. Given Data / Assumptions: Polyhexamethylene adipamide forms from hexamethylene diamine (six carbons) and adipic acid (six carbons). Common trade/designation name is nylon-66. Concept / Approach: The “66” in nylon-66 denotes the number of carbons in the diamine and diacid monomers, respectively. This contrasts with nylon-6, which is produced from a single monomer (caprolactam). Step-by-Step Solution: Map the systematic name to monomers: hexamethylene (6) + adipamide (6 derived) → nylon-66.Exclude unrelated thermosets (Bakelite, epoxy) and elastomers (silicone rubber). Verification / Alternative check: Standards and datasheets list nylon-66 with the chemical repeat unit derived from HMDA and adipic acid. Why Other Options Are Wrong: Bakelite and epoxy: thermosets.Silicone rubber: polysiloxane elastomer.Polycarbonate: carbonate-linked thermoplastic; different chemistry. Common Pitfalls: Confusing nylon-6 with nylon-66 due to similar naming. Final Answer: Nylon-66

Question 2

Biopolymers by monomer type: which natural biopolymers result from polymerisation of amino acids?

Accepted Answer

Introduction / Context: Biopolymers are categorised by their building blocks: sugars, amino acids, or nucleotides. Knowing the monomer identities clarifies structure–function relationships in biology and materials science. Given Data / Assumptions: Amino acids polymerise via peptide bonds to form proteins. Starch and cellulose are polysaccharides (sugars). Nucleic acids are polymers of nucleotides. Natural rubber is polyisoprene (terpene), not amino-acid based. Concept / Approach: Proteins are linear chains of amino acids linked through amide (peptide) bonds, folding into complex structures for enzymatic, structural, and signalling roles. Carbohydrate and nucleotide polymers have different monomers and linkages. Step-by-Step Solution: Identify the monomer class: amino acids.Match to the polymer class: proteins.Exclude polysaccharides, nucleic acids, and terpenes. Verification / Alternative check: Biochemistry fundamentals: proteins = polypeptides; polysaccharides = sugar polymers; nucleic acids = nucleotides. Why Other Options Are Wrong: Starch/cellulose: glucose-based.Nucleic acids: nucleotide-based.Natural rubber: isoprene-based. Common Pitfalls: Mixing up “polyamide” (nylon) with “peptide” bonds in proteins; while both are amide linkages, their monomers and contexts differ. Final Answer: Proteins

Question 3

Name the polymer formed from hexamethylene diamine and adipic acid.

Accepted Answer

Introduction / Context: Condensation polymerisation of diamines and diacids yields polyamides whose numeric designations reflect monomer carbon counts. Correctly pairing monomers to nylon designations is a frequent materials question. Given Data / Assumptions: Hexamethylene diamine has 6 carbons. Adipic acid also has 6 carbons. Polymer naming convention: nylon-x,y where x and y are carbon counts. Concept / Approach: Nylon-66 results from 6-carbon diamine and 6-carbon diacid. Nylon-6 would arise from a single 6-carbon monomer (caprolactam). Nylon-6,10 uses a 6-carbon diamine and a 10-carbon diacid (sebacic). Step-by-Step Solution: Identify monomers: 6 + 6 carbons.Apply naming convention → nylon-66.Select nylon-66 from the options. Verification / Alternative check: Standard polymer handbooks confirm nylon-66 composition and properties. Why Other Options Are Wrong: Nylon-6: from caprolactam, not a diamine/diacid pair.Nylon-6,10: requires sebacic acid (10 carbons), not adipic acid.Epoxy/ PET: different polymer families and monomers. Common Pitfalls: Confusing the numeric code (6,6 vs 6; 6,10) and their monomer sources. Final Answer: Nylon-66

Question 4

Melamine–formaldehyde (MF) resin has very high anti-tacking and excellent hardness. In industrial practice, MF resins are used for many applications; identify the application from the list below for which MF resin is generally not used.

Accepted Answer

Introduction / Context: Melamine–formaldehyde (MF) resins are thermosetting polymers valued for their high surface hardness, gloss retention, stain resistance, heat resistance, and very good anti-tacking behavior. They cure to a cross-linked network that is dimensionally stable and electrically insulating. This question asks you to separate common, well-documented MF applications from an option that is not a typical or mainstream use in materials engineering practice. Given Data / Assumptions: MF resins are cross-linked thermosets once cured. They exhibit high hardness, abrasion resistance, electrical insulation, and chemical resistance. We consider standard, widely taught industrial uses. Concept / Approach: MF resins are ubiquitous in decorative laminates (as the hard, transparent overlay), electrical insulating components (switchgear, sockets, appliance housings), tableware, and as crosslinkers in coatings and textiles. MF-based resins have also been formulated as retanning agents in leather processing. By contrast, “strengthening of plaster of Paris (POP)” is not a textbook or mainstream application for MF; gypsum systems are more commonly modified with polymer latexes (e.g., polyvinyl acetate, acrylics), fibers, or retarders/accelerators rather than melamine cross-linkers. Step-by-Step Solution: List canonical MF uses: decorative laminates, electrical insulation, tableware glazes/surfaces, crosslinkers.Note specialized leather retanning agents can be based on melamine resins.Contrast with gypsum/POP modification practices, which do not normally rely on MF resins.Identify the out-of-place option as “Strengthening of plaster of Paris.” Verification / Alternative check: Materials handbooks and product literature consistently associate MF with laminates (HPL), molding compounds for electrical parts, dinnerware, and crosslinking agents; POP systems are improved with different polymer modifiers, not MF networks. Why Other Options Are Wrong: Electrical insulation: MF molding compounds are standard insulators. Tanning of leather: melamine resin retanning agents exist in practice. Decorative laminates: MF is the classic overlay/crosslinker. Tableware glazing/surfaces: melamine ware is widely known. Common Pitfalls: Assuming any thermoset “strengthens” all minerals; polymer–gypsum synergy depends on chemistry and water compatibility. Final Answer: Strengthening of plaster of Paris

Question 5

Textile polymers: “Acrilan” fibres used in cloth, carpets, and blankets (a hard, horny, relatively high-melting synthetic fiber) are primarily composed of which polymer?

Accepted Answer

Introduction / Context: Trade names in fibers often mask the underlying polymer chemistry. “Acrilan” is a well-known historical trade name for acrylic fiber types used in apparel and home textiles. Identifying the base polymer helps link properties—such as hand feel, dyeing behavior, and thermal response—to the chemistry of the repeating unit and processing route. Given Data / Assumptions: “Acrilan” is an acrylic fiber trade name. Acrylic fibers are typically derived from acrylonitrile-rich copolymers. We focus on the principal polymer identity associated with Acrilan. Concept / Approach: Acrylic fibers are defined by a high acrylonitrile content in the polymer chain. Polyacrylonitrile (PAN) and its copolymers form hard, “horny,” relatively high-softening fibers with good wrinkle resistance and color fastness. PAN’s nitrile groups confer solvent resistance and a characteristic dyeing profile using appropriate dye classes. Other listed polymers—polyamides (nylons), saturated polyesters (PET), and alkyds—belong to different fiber or coating families with distinct performance and processing (e.g., melt spinning for nylon/PET versus solution spinning for PAN). Step-by-Step Solution: Associate the trade name “Acrilan” with acrylic fiber technology.Recall acrylics are based on acrylonitrile monomer units.Identify the base polymer as polyacrylonitrile.Select “Polyacrylonitrile.” Verification / Alternative check: Textile references list Acrilan as an acrylic fiber made predominantly from polyacrylonitrile or its copolymers; such fibers are commonly solution-spun (wet/dry) rather than melt-spun due to PAN’s decomposition on melting. Why Other Options Are Wrong: Polyamide: corresponds to nylons (e.g., nylon-6,6). Saturated polyester: PET fibers (terylene/dacron) differ in chemistry and processing. Alkyd resin: used in coatings, not apparel fibers. PVC: used in films, cables; not the basis of Acrilan. Common Pitfalls: Confusing “acrylic” with “polyester” due to similar textile applications like sweaters and blankets. Final Answer: Polyacrylonitrile

Question 6

Textile finishing: during fibre and fabric preparation, “scouring” is a finishing operation primarily intended to accomplish which treatment of the fibres?

Accepted Answer

Introduction / Context: Scouring is a standard wet-processing step in textiles that prepares fibres or fabrics for subsequent finishing and dyeing. The operation focuses on removing natural and processing-added impurities so that dye uptake is uniform and final properties are reproducible. Understanding what scouring does helps distinguish it from dyeing, bleaching, and heat-setting steps. Given Data / Assumptions: Scouring is performed before dyeing/printing on many substrates. Typical baths contain alkali and surfactants (detergents/wetting agents). Target impurities include waxes, oils, sizing agents, and dirt. Concept / Approach: In scouring, the fibre or fabric is treated with aqueous solutions—commonly alkaline detergents—under controlled temperature and time to emulsify and saponify fatty substances, remove lubricants, and eliminate processing aids. This increases hydrophilicity, improves wetting, and ensures level dyeing. Scouring is not a mechanical stretching, glycol plasticisation, or the act of dyeing itself; it is a cleaning and preparation operation. Step-by-Step Solution: Identify the purpose: remove natural/added impurities that hinder wet-out and dyeing.Recognise typical chemistry: surfactants, alkali, chelants for hardness control.Conclude that scouring equals detergent solution washing/alkaline boil-off.Select “Detergent solution washing to remove impurities.” Verification / Alternative check: Process flow diagrams in textile finishing show scouring preceding bleaching/mercerisation/dyeing, corroborating its role as a cleaning step. Why Other Options Are Wrong: Improving stretchability: relates to fibre type and thermal/mechanical treatments. Dyeing/colouring: a separate, later operation. Glycol soaking: not a standard scouring practice. Heat-setting: a thermal process to stabilise dimensions, not scouring. Common Pitfalls: Equating scouring with bleaching; bleaching removes color bodies, scouring removes oils/waxes/sizes. Final Answer: Detergent solution washing to remove impurities

Question 7

Rubber processing: the operation used to convert rubber into thin sheets or to apply a uniform rubber coating onto fabric is known as what?

Accepted Answer

Introduction / Context: Rubber goods manufacturing uses several distinct unit operations. When the goal is to form controlled-thickness sheets or apply rubber films to textiles (e.g., tire cord fabrics, conveyor belts), the process of choice is calendering. Discriminating calendering from extrusion, mastication, and vulcanisation is a core skill in polymer processing. Given Data / Assumptions: Objective: create thin, uniform sheets or coat fabric with rubber. Equipment: sets of heavy, polished rolls with adjustable gaps. Material: compounded rubber mixes at elevated but non-curing temperatures. Concept / Approach: Calendering squeezes and stretches rubber stock between counter-rotating rolls, controlling gauge and surface finish while embedding fabric when desired. Extrusion forces rubber through a die to produce profiles or tubing; mastication is mechanical working to soften/shorten polymer chains for processability; vulcanisation is the curing step that creates cross-links, improving elastic recovery, strength, and heat resistance but not used to set sheet thickness or apply coatings by itself. Step-by-Step Solution: Match target (thin sheet or coated fabric) with process capabilities.Recognise roll-gap control and fabric feed of calenders.Rule out extrusion (profiled shapes), mastication (pre-mixing softening), vulcanisation (curing chemistry).Select “Calendering.” Verification / Alternative check: Process layouts for tire manufacturing show calender lines preparing skim-coated cord fabrics and innerliner sheets prior to building and vulcanisation. Why Other Options Are Wrong: Extrusion: produces continuous profiles, not textile coatings. Mastication: conditioning step, not a forming/coating method. Vulcanisation: curing, not sheet/fabric gauge formation. Compression moulding: discrete part shaping, not continuous sheet/fabric coating. Common Pitfalls: Confusing the order of operations: calender to make sheets/coat, then assemble, then vulcanise to final properties. Final Answer: Calendering

Question 8

Vulcanisation effects: which property of rubber is NOT increased by vulcanisation with sulfur or equivalent cross-linking systems?

Accepted Answer

Introduction / Context: Vulcanisation creates cross-links between rubber chains, transforming a soft, tacky gum into an elastic, durable material. Understanding what improves and what diminishes with curing is essential for compounding and selecting service conditions for rubber goods like tires, seals, and belts. Given Data / Assumptions: Vulcanisation introduces chemical cross-links (e.g., sulfur bridges). Network formation restricts flow, reduces tack, and increases modulus. Additives (fillers, antioxidants) may accompany the cure system. Concept / Approach: Cross-linking generally increases modulus, tensile strength (up to an optimum), resilience, heat and oxidation resistance (with suitable systems), and solvent resistance (insolubility/swelling control). However, hardness increases while “softness” decreases. The cured network is less plastic and less tacky than the raw gum. Mass may increase slightly due to added sulfur/fillers, while elasticity and environmental resistance improve relative to the uncured state. Step-by-Step Solution: List properties that rise with cross-link density (modulus, hardness, set resistance, solvent resistance).Note that softness is inversely related to hardness/modulus.Therefore, “softness” is not increased; it decreases upon vulcanisation.Select “Softness.” Verification / Alternative check: Shore hardness curves vs. cure time show increasing hardness with cure. Swelling tests show decreased solvent uptake after cross-linking, confirming increased network integrity. Why Other Options Are Wrong: Oxidation/heat resistance: improved with proper cure/antioxidants. Weight & strength: mass may rise due to additives; tensile often increases to an optimum. Elasticity/insolubility: network enhances elastic recovery and reduces solubility. Common Pitfalls: Over-curing can embrittle and reduce tensile; the question asks the general effect, where softness does not increase. Final Answer: Softness

Question 9

Polymer networks: cross-linked polymers, once cured into an infusible three-dimensional network, belong to which broad processing class?

Accepted Answer

Introduction / Context: Classifying polymers by their thermal response is fundamental to processing choices. Thermoplastics soften and flow upon heating, allowing reshaping; thermosets form permanent, cross-linked networks that do not melt. The question probes recognition of where cross-linked materials fit in this dichotomy. Given Data / Assumptions: Cross-linking yields a covalently bonded 3-D network. Heating a cross-linked network does not lead to viscous flow; instead, it may char or degrade. Examples include epoxy, phenolic, melamine, vulcanised rubber (to varying degrees). Concept / Approach: Thermosetting polymers are those that cure irreversibly. Their cross-linked topology prevents chain slippage required for melt flow. In contrast, thermoplastics consist of linear or lightly branched chains that can be melted and remolded repeatedly below decomposition temperatures. Cross-linked architecture equates to thermosetting behavior in standard polymer science terminology. Step-by-Step Solution: Identify the meaning of “cross-linked”: 3-D covalent network.Recall thermal response: no melting; softening is minimal before degradation.Map this behavior to “thermosetting.”Select “Thermosetting.” Verification / Alternative check: Differential scanning calorimetry and rheology confirm absence of melt flow in cured thermosets; gel fraction measurements indicate insolubility consistent with network formation. Why Other Options Are Wrong: Thermoplastic: contradicts the inability to melt/flow. Either class: cross-linked state specifically defines thermosets. “Fibres only”/“Elastomers only”: describe product forms, not thermal class. Common Pitfalls: Confusing partially cross-linked TPV (thermoplastic vulcanizates) with fully cross-linked thermosets; TPVs behave overall as thermoplastics due to continuous thermoplastic phase. Final Answer: Thermosetting

Question 10

HDPE via Ziegler (Ziegler–Natta) solvent polymerisation: typical low-pressure conditions for producing high-density polyethylene are approximately what pressure–temperature pair?

Accepted Answer

Introduction / Context: Ziegler–Natta catalysis revolutionized polyethylene by enabling high-density polyethylene (HDPE) at low pressures and moderate temperatures compared with earlier high-pressure free-radical LDPE processes. Recognizing the order of magnitude of process conditions helps distinguish catalyst families and product structures (branching, density, crystallinity). Given Data / Assumptions: Solvent/slurry polymerisation using organo-aluminium and transition-metal catalysts. Objective: HDPE with high crystallinity and low branching. “Typical” refers to exam-standard representative values. Concept / Approach: HDPE with Ziegler–Natta catalysts is produced at low pressure (roughly 1–10 kgf/cm²) and relatively low temperatures (around 60–80 °C in many solvent processes). These mild conditions contrast starkly with LDPE free-radical methods that require hundreds to over a thousand kgf/cm² and elevated temperatures. Options listing extremely high pressures or unrealistically high temperatures do not match Ziegler low-pressure technology. Step-by-Step Solution: Recall that Ziegler–Natta polymerisations are “low-pressure” processes.Associate HDPE production temperatures ~60–80 °C in common solvent systems.Select the pair closest to 7 kgf/cm² and 70 °C.Reject alternatives implying high-pressure radical conditions or thermal degradation. Verification / Alternative check: Process descriptions for slurry/solution loop reactors cite pressures on the order of a few atmospheres and temperatures near 70 °C for HDPE grades with Ziegler catalysts. Why Other Options Are Wrong: 1000 kgf/cm²: characteristic of LDPE radical processes, not Ziegler HDPE. 7 kgf/cm² & 700 °C: temperature far exceeds polymer stability. 1 kgf/cm² g: pressure too low for typical industrial solvent systems in exam context. 200 kgf/cm² & 300 °C: mismatched to low-pressure catalysis. Common Pitfalls: Conflating LDPE autoclave/tubular conditions with Ziegler–Natta processes. Final Answer: 7 kgf/cm² and 70 °C

Question 11

Linear vs. cross-linked/branched polymers: compared to linear chains, cross-linked or highly branched polymers generally exhibit which change in bulk mechanical behavior?

Accepted Answer

Introduction / Context: Molecular architecture strongly influences polymer properties. Linear chains can slide past one another when heated or stressed, whereas cross-links and extensive branching impede mobility. This question asks for the dominant qualitative trend in mechanical behavior when moving from linear to cross-linked/branched structures. Given Data / Assumptions: Cross-linking restricts chain mobility. Branching reduces crystallinity in many systems but increases entanglements. We consider room-temperature bulk properties in typical engineering polymers. Concept / Approach: Increasing cross-link density raises modulus and hardness, often reducing elongation at break and increasing brittleness. Many branched networks cannot truly melt; they soften slightly before degrading. While density and melting behavior depend on chemistry/crystallinity, the robust, exam-relevant trend is that cross-linked and heavily branched polymers are stiffer and more brittle than their linear analogs due to constrained molecular motion and reduced capacity for plastic deformation. Step-by-Step Solution: Recall that mobility enables ductility; cross-links remove mobility.Stiffness (modulus) and hardness generally increase with network formation.Ductility decreases, so brittleness rises.Choose “Higher hardness, rigidity, and brittleness.” Verification / Alternative check: Tensile stress–strain curves of thermosets vs. thermoplastics show higher modulus and lower elongation at break for cross-linked systems, consistent with increased brittleness. Why Other Options Are Wrong: Higher density: not a universal outcome; varies by system. Higher melting point: cross-linked networks do not melt in the thermoplastic sense. Higher tensile with enhanced ductility: contradicts typical behavior. Lower Tg in all cases: Tg usually increases with cross-link density. Common Pitfalls: Assuming “stronger” means “tougher”; cross-linking often raises strength but reduces toughness/ductility. Final Answer: Higher hardness, rigidity, and brittleness

Question 12

Polyamide chemistry: nylon-66 is manufactured from which pair of monomers?

Accepted Answer

Introduction / Context: Nylons are polyamides formed by condensation reactions between diamines and diacids (or by ring-opening of lactams). Naming such as “66” reflects the number of carbons in each monomer. Properly identifying monomers clarifies polymer structure and properties (melting point, crystallinity, moisture uptake). Given Data / Assumptions: Nylon-66: the first “6” denotes a C6 diamine; the second “6” denotes a C6 diacid. Industrial route involves salt formation followed by polycondensation. Concept / Approach: Hexamethylene diamine (HMD, 6 carbons) and adipic acid (AA, 6 carbons) form the nylon-salt that, upon condensation with removal of water, yields nylon-66. Caprolactam is used for nylon-6 (not 66), DMT and ethylene glycol form PET polyester, and maleic anhydride combinations lead to other polyesters or copolymers. Step-by-Step Solution: Map “66” to 6-carbon diamine + 6-carbon diacid.Identify hexamethylene diamine (C6) and adipic acid (C6).Select the correct pair.Reject alternatives linked to nylon-6 or PET pathways. Verification / Alternative check: Polymer chemistry texts consistently specify HMD + adipic acid for nylon-66, with melting point near 255–265 °C depending on grade. Why Other Options Are Wrong: Caprolactam: monomer for nylon-6 via ring opening. Maleic anhydride + HMD: not nylon-66. DMT + EG: polyester (PET), not a polyamide. Common Pitfalls: Confusing nylon-6 with nylon-66 due to similar names; remember “6-6” denotes two C6 monomers. Final Answer: Adipic acid and hexamethylene diamine

Question 13

Ion-exchange materials: strong acid cation exchangers used in water treatment are commonly made from which resin family?

Accepted Answer

Introduction / Context: Cation exchange resins are functionalised polymers bearing fixed acidic groups that exchange cations with the surrounding solution. Although modern plants overwhelmingly use sulfonated styrene–divinylbenzene resins, classic materials and many exam syllabi also include sulfonated phenolic (phenol–formaldehyde) resins as cation exchangers. The question targets recognition of that resin family among generic options. Given Data / Assumptions: Focus is on the resin family historically used for cation exchange. Functional groups are sulfonic acids for strong acid cation exchangers. Options list broad resin chemistries rather than specific copolymers. Concept / Approach: Phenol–formaldehyde resins can be sulfonated to introduce –SO3H groups, creating strong acid cation exchangers. Urea/melamine amino resins and epoxies are thermosets used for adhesives and coatings, not typical ion-exchange backbones. While sulfonated styrene–DVB is more common industrially today, within the offered families the correct classical answer is the sulfonated phenolic resin. Step-by-Step Solution: Identify which base network can be functionalised to strong acid sites.Recognise sulfonated phenolic as a known cation exchanger in syllabi.Select “Phenolic resin (sulfonated phenol–formaldehyde).”Exclude resins not used for ion exchange in this context. Verification / Alternative check: Water-treatment texts list phenolic cation exchangers alongside styrene–DVB resins, confirming historical and educational relevance. Why Other Options Are Wrong: Urea/melamine: amino resins used in laminates/wood adhesives. Epoxy: structural adhesives/coatings. Acrylic latex: film-forming binders, not ion exchangers. Common Pitfalls: Assuming only styrene–DVB exists; older phenolic exchangers remain part of exam content. Final Answer: Phenolic resin (sulfonated phenol–formaldehyde)

Question 14

Fibre formation methods: melt spinning forces a polymer melt through spinnerettes into a cooler atmosphere to form filaments. Melt spinning is NOT suitable for which fibre class among the following?

Accepted Answer

Introduction / Context: Spinning method selection depends on a polymer’s thermal stability and melt behavior. Melt spinning requires that the polymer be melted without significant degradation. Acrylic fibres (polyacrylonitrile-based) typically cannot be melt-spun because PAN decomposes before it melts; hence solution (wet or dry) spinning is used. In contrast, polyesters, nylons, polypropylene, and polyethylene are melt-spinnable. Given Data / Assumptions: Melt spinning demands a stable molten state below decomposition temperature. We compare common fibre families and their standard spinning routes. Concept / Approach: Polyacrylonitrile exhibits cyclisation and degradation upon heating rather than forming a stable melt; therefore, it is solution-spun. Polyesters (PET), nylons (polyamides), polypropylene (PP), and polyethylene (PE) melt cleanly (within processing windows) and are conventionally melt-spun into filaments, then drawn and heat-set to develop properties. Step-by-Step Solution: Identify which polymers decompose on heating without a usable melt (PAN).Recall acrylic fibres are produced via wet or dry spinning of dope solutions.Confirm melt-spinnability of PET, nylon-6,6, PP, and PE.Select “Acrylic fibres.” Verification / Alternative check: Fibre manufacturing texts consistently state that acrylics are solution-spun (e.g., from DMF/NaSCN systems) due to PAN’s thermal behavior. Why Other Options Are Wrong: Polyester/nylon/PP/PE: standard melt-spun fibres in commercial practice. Common Pitfalls: Assuming all commodity fibres are melt-spun; acrylics are a key exception. Final Answer: Acrylic fibres

Question 15

Natural vs. synthetic: which of the following is NOT a natural polymer?

Accepted Answer

Introduction / Context: Polymers are broadly categorized as natural (biosynthesized) or synthetic (man-made). Correctly classifying examples is basic to polymer science and helps in predicting degradation, processing, and applications. The task is to pick the synthetic outlier from a list dominated by biopolymers. Given Data / Assumptions: Nucleic acids, polysaccharides, and proteins are macromolecules produced by living organisms. Polyisoprene is the main constituent of natural rubber latex. Polyurethane is produced by reaction of diisocyanates with polyols. Concept / Approach: Natural polymers include DNA/RNA (nucleic acids), cellulose/starch (polysaccharides), proteins (polypeptides), and natural rubber (cis-1,4-polyisoprene). Polyurethanes are synthetic, engineered in countless formulations (foams, elastomers, coatings) by step-growth reactions between isocyanates and polyols; they do not occur as high-molecular-weight materials in nature. Step-by-Step Solution: Classify each option by origin: biosynthesized vs. industrially synthesized.Recognize polyurethane as synthetic.Select “Polyurethane” as not a natural polymer.Confirm others are natural macromolecules. Verification / Alternative check: Standard textbooks list DNA/RNA, polysaccharides, proteins, and natural rubber among natural polymers; polyurethanes are unequivocally synthetic. Why Other Options Are Wrong: Nucleic acids/polysaccharides/proteins: classic natural polymers. Polyisoprene: the principal chain in natural rubber latex. Common Pitfalls: Confusing “found in nature” derivatives (e.g., cellulose acetate) with truly natural polymers; derivatives are modified and count as semi-synthetic. Final Answer: Polyurethane

Question 16

Polymerisation mechanisms: identify the WRONG statement among the following about addition (chain-growth) and condensation (step-growth) polymerisations.

Accepted Answer

Introduction / Context: Understanding the distinction between chain-growth and step-growth mechanisms is central to predicting molecular weight development, kinetics, and typical product families. This question asks you to spot the statement that contradicts well-established polymerisation pathways for common materials. Given Data / Assumptions: Addition polymers arise when monomer double bonds open and add to growing radicals/ions/coordination sites. Condensation polymers form via stepwise reactions often with small-molecule elimination. PTFE, polyethylene, and phenol–formaldehyde (Bakelite) are representative materials. Concept / Approach: Polyethylene and PTFE (Teflon) are produced by chain-growth addition of unsaturated monomers (ethylene and tetrafluoroethylene). Phenol–formaldehyde (Bakelite) forms via step-growth condensation reactions creating methylene bridges with water elimination. Therefore, any claim that PTFE forms by step growth is incorrect. Step-by-Step Solution: Check each statement against known mechanisms.Confirm addition polymers → chain growth; condensation polymers → step growth.Identify PTFE as a chain-growth addition polymer.Mark the PTFE step-growth statement as wrong. Verification / Alternative check: Catalyst and radical processes for vinyl monomers (including tetrafluoroethylene) are well documented as chain-growth; Bakelite synthesis involves stepwise phenol-formaldehyde condensation. Why Other Options Are Wrong: (a), (b), (d), (e) are correct statements; the only incorrect one is (c). Common Pitfalls: Confusing “addition” vs. “addition-condensation” terminologies in older literature; here PTFE is clearly an addition polymer. Final Answer: Teflon (PTFE) is formed by step-growth polymerisation.

Question 17

Polyvinyl acetate (PVAc): identify the application that PVAc is never used for in standard industrial practice.

Accepted Answer

Introduction / Context: Polyvinyl acetate (PVAc) is a widely used polymer noted for its excellent adhesion to porous substrates and film-forming capability. However, its thermal and mechanical profile constrains certain applications. The question seeks the use case that PVAc does not serve in typical materials engineering practice. Given Data / Assumptions: PVAc softens at relatively low temperatures and hydrolyses to PVOH under alkaline conditions. Common PVAc forms include emulsions/latices for adhesives and coatings. We consider mainstream industrial practice, not niche laboratory curiosities. Concept / Approach: PVAc is a mainstay for adhesives (wood glues, packaging), paper and textile binders, and as a precursor to polyvinyl alcohol (via hydrolysis). It is not a fibre-forming polymer for apparel or technical fibres due to its low melting/softening point, thermal instability during drawing, and moisture sensitivity. PVAc moulding is limited, but blends and copolymers can be formed into certain shaped goods; the “never used” option classically highlighted in exams is “fibres.” Step-by-Step Solution: List PVAc’s typical uses: adhesives, paper sizing, coatings, redispersible powders.Assess fibre forming requirements (thermal stability, drawability) vs. PVAc limitations.Select “Fibres” as the application PVAc is never used for.Reject “all of the above” because PVAc is widely used as an adhesive and for surface sizing. Verification / Alternative check: Industry data sheets emphasise PVAc in adhesives/coatings; fibre technology texts do not list PVAc as a commercial fibre polymer. Why Other Options Are Wrong: Adhesives/paper sizing: core applications of PVAc. Moulded articles: niche but possible in blends; not “never.” Common Pitfalls: Confusing PVAc with vinyl acetate copolymers such as EVA, which have broader thermoplastic uses. Final Answer: Fibres

Question 18

Material property: the density of low-density polyethylene (LDPE) is approximately how many grams per cubic centimetre at room temperature?

Accepted Answer

Introduction / Context: Polyethylene density correlates with branching and crystallinity: LDPE is more highly branched and therefore less crystalline—and less dense—than HDPE. Memorising representative densities helps in quick identification of polymer type and predicting stiffness and barrier properties. Given Data / Assumptions: LDPE typically ranges from about 0.91 to 0.93 g/cm³. Density values are at 23–25 °C for solid material. Concept / Approach: Among provided options, 0.91 g/cm³ aligns with standard LDPE values. Numbers such as 0.38 or 0.56 g/cm³ are far below organic solids (closer to foams); 0.81 g/cm³ is too low for non-foamed PE; 1.01 g/cm³ exceeds typical PE densities and approaches aqueous media or filled systems. Therefore, 0.91 g/cm³ is the appropriate selection for compact LDPE. Step-by-Step Solution: Recall LDPE density window: ~0.91–0.93 g/cm³.Compare options to this window.Choose the representative value 0.91.Reject unrealistic or out-of-range numbers. Verification / Alternative check: Materials datasheets for LDPE grades consistently list densities around 0.920 ± 0.010 g/cm³ depending on comonomer and branching. Why Other Options Are Wrong: 0.38, 0.56: not realistic for solid, unfoamed polyethylene. 0.81: too low for solid LDPE; would imply high voids/foam. 1.01: above typical polyethylene density; more like PET blends or filled systems. Common Pitfalls: Mixing up LDPE and HDPE densities; HDPE is typically 0.94–0.97 g/cm³. Final Answer: 0.91

Question 19

Fibre spinning routes: in wet spinning, a polymer solution is extruded through spinnerettes into a coagulation bath to form filaments. Wet spinning is NOT used for which of the following fibre types?

Accepted Answer

Introduction / Context: Spinning processes depend on whether the polymer is handled as a melt or a solution. Wet spinning precipitates the polymer from solution in a coagulation bath; it is appropriate for polymers that cannot be melt-spun due to decomposition before melting or because of very high melt viscosities. Saturated polyesters such as PET are melt-spun, not wet-spun. Given Data / Assumptions: Viscose rayon and cupro rayon are regenerated celluloses made by wet spinning. Many acrylics (PAN-based) are wet- or dry-spun from solutions. Saturated polyester (PET) cleanly melts and is melt-spun. Concept / Approach: Check each polymer’s standard spinning route: regenerated celluloses (viscose, cupro) and many PAN acrylics use wet spinning; PVAc derivatives can be wet-spun in some specialty contexts. PET is produced in massive volumes by melt spinning with subsequent drawing and heat setting. Thus, among the options, the fibre not associated with wet spinning is saturated polyester. Step-by-Step Solution: List known wet-spun polymers: viscose, cupro, PAN acrylics.Identify PET as melt-spun.Select “Saturated polyester.”Confirm the others align with wet-spinning processes. Verification / Alternative check: Manufacturing references describe PET melt-spinning lines; wet spinning lines are associated with viscose and acrylic fibre plants. Why Other Options Are Wrong: Viscose/cupro: canonical wet-spun fibres. Acrylic: widely wet-/dry-spun due to PAN thermal behavior. PVAc: specialty wet-spun derivatised systems exist; exam context accepts as wet-spinnable vs. PET. Common Pitfalls: Conflating dry spinning (evaporation) with wet spinning (coagulation); both are solution processes but distinct mechanisms. Final Answer: Saturated polyester

Question 20

Plasticisers: high-boiling additives impart toughness and flexibility to plastics at ordinary temperature. Which of the following is NOT typically used as a plasticiser?

Accepted Answer

Introduction / Context: Plasticisers are relatively large, high-boiling, often polar molecules that reduce intermolecular attractions in a polymer, lowering glass-transition temperature and increasing flexibility. Identifying the typical chemical families used as plasticisers helps avoid confusion with solvents or monomers that have different volatility and compatibility profiles. Given Data / Assumptions: Common plasticisers include phthalates, phosphates, adipates, sebacates, and certain stearate esters. Ethylene glycol (EG) is a small, low-boiling diol used as antifreeze/monomer, not as a primary plasticiser for engineering plastics. Concept / Approach: Effective plasticisers must be sufficiently non-volatile and compatible to remain in the polymer matrix during service. EG’s low molecular weight and high volatility make it unsuitable as a standard plasticiser; it tends to migrate/evaporate and can act as a solvent or reactant rather than a durable plasticiser. In contrast, phthalate esters, tricresyl phosphate, adipates/sebacates, and stearate esters are classic plasticiser families used in PVC and other polymers. Step-by-Step Solution: List typical plasticiser chemistries (phthalates, phosphates, adipates, sebacates, stearates).Compare volatility and molecular size with EG.Conclude EG is not a standard plasticiser.Select “Ethylene glycol.” Verification / Alternative check: Formulation tables for PVC list dioctyl phthalate (DOP), diisononyl phthalate (DINP), dioctyl adipate (DOA), tricresyl phosphate (TCP), and stearates; EG is absent as a durable plasticiser. Why Other Options Are Wrong: Phthalate esters/TCP/adipates/sebacates/stearate esters: all widely used plasticiser classes. Common Pitfalls: Equating “any liquid” with “plasticiser”; permanence and compatibility are crucial. Final Answer: Ethylene glycol

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