Question 1

Which statement about synthetic rubber is generally correct in comparison with its behaviour across temperatures and environments?

Accepted Answer

Introduction / Context:Synthetic rubbers (e.g., SBR, NBR, CR) span a wide property range. However, a common generalisation in basic exams is their relatively poorer low-temperature flexibility compared with certain natural or specialty elastomers, leading to brittleness in the cold. Understanding temperature effects helps in selecting elastomers for service environments.Given Data / Assumptions:Many general-purpose synthetics (e.g., SBR) stiffen markedly at low temperature and can become brittle below their glass transition.At higher temperatures, most rubbers soften rather than harden.Chemical resistance and permeability vary widely and cannot be generalised as “highly permeable and readily attacked” for all synthetics.Concept / Approach:Low-temperature brittleness is a recognised limitation for several synthetic rubbers because their glass transition temperatures are higher than that of natural rubber or silicone elastomers. Thus, among simplified textbook statements, “brittle at low temperature” is the most broadly correct. The other options are overgeneralised or incorrect.Step-by-Step Solution:Consider temperature dependence of modulus near Tg.Note that many synthetics show embrittlement at low temperatures.Select the statement that reflects this behaviour.Verification / Alternative check:Data sheets report brittle points and Tg values; many synthetics have brittle points above those of natural rubber or silicone.Why Other Options Are Wrong:Permanent deformation at 2x stretch: depends on formulation; not universally true.Harder at higher temperature: elastomers generally soften with heat.Highly permeable/attacked by most chemicals: too broad; many synthetics offer good chemical resistance.Always stronger than natural rubber: not universally true.Common Pitfalls:Assuming one synthetic rubber represents all; properties vary significantly among SBR, NBR, EPDM, CR, etc.Final Answer:It is brittle at low temperature.

Question 2

Bakelite is correctly identified as which type of polymeric material?

Accepted Answer

Introduction / Context:Bakelite is one of the earliest commercial plastics and a prototypical thermosetting resin formed by the condensation of phenol with formaldehyde. It established the modern concept of crosslinked polymer networks with good heat resistance, electrical insulation, and dimensional stability.Given Data / Assumptions:Bakelite is a crosslinked network (thermoset) produced via step-growth condensation.Once cured, it cannot be remelted or reshaped.It is organic (based on phenolic chemistry), not an inorganic polymer.Concept / Approach:Match the historical and chemical identity: phenol–formaldehyde → thermoset phenolic. The other options deliberately mismatch polymer class or falsely equate Bakelite with unrelated materials.Step-by-Step Solution:Identify Bakelite’s chemistry (phenolic condensation).Recognise crosslinked thermoset behaviour.Select “thermoset phenol–formaldehyde resin.”Verification / Alternative check:Handbooks and historical accounts of plastics clearly define Bakelite as the first fully synthetic thermoset.Why Other Options Are Wrong:PTFE: fluoropolymer; unrelated.Inorganic polymer: incorrect classification here.Not a polymer: inaccurate; it is a polymeric network.Polyolefin: unrelated chemistry and structure.Common Pitfalls:Confusing “phenolic” with “phenyl” (aromatic ring) and misclassifying the resin as a linear thermoplastic.Final Answer:A thermoset phenol–formaldehyde resin

Question 3

“Unbreakable” crockery and dinnerware (hard, durable tableware) are typically made from which polymeric material?

Accepted Answer

Introduction / Context:So-called “unbreakable” crockery refers to hard, scratch-resistant, heat-tolerant tableware widely used in homes and institutions. These products are molded from melamine–formaldehyde resins, a class of thermosetting aminoplasts valued for surface hardness, stain resistance, and dimensional stability.Given Data / Assumptions:Tableware must withstand hot foods/liquids, repeated washing, and moderate impacts.Melamine resins cure to a crosslinked network with excellent surface properties.Commodity thermoplastics like polystyrene can be brittle and scratch easily; PVC and PU are not typical for rigid, high-heat tableware.Concept / Approach:Melamine–formaldehyde offers high hardness and gloss with good heat resistance, making it suitable for durable crockery. While no polymer is literally “unbreakable,” melamine tableware is far more durable than PS or brittle clear plastics in everyday service.Step-by-Step Solution:Identify required properties: hardness, thermal tolerance, cleanliness.Match these to polymer families: aminoplast thermosets fit best.Select melamine–formaldehyde resin.Verification / Alternative check:Product specifications and regulatory standards for melamine tableware confirm the typical resin system and performance requirements.Why Other Options Are Wrong:Polystyrene: prone to brittleness and stress cracking.PVC: plasticised grades are flexible; rigid PVC lacks the desired heat resistance for crockery.Polyurethane: used for foams or elastomers, not rigid dinnerware.Acrylic (PMMA): good clarity but can crack/chip; used for tumblers, not typical for “unbreakable” plates.Common Pitfalls:Assuming toughness equals thermoplastic; many durable dinnerware items are thermoset because of their superior surface hardness and heat resistance.Final Answer:Melamine (melamine–formaldehyde resin)

Question 4

In polymer engineering, caprolactam is polymerised to produce nylon-6. At what reactor temperature range (°C) is this condensation/ring-opening polymerisation typically maintained for efficient conversion?

Accepted Answer

Introduction / Context:Nylon-6 is produced industrially by the ring-opening polymerisation of caprolactam. The reaction is commonly referred to as a condensation-type step growth with water participation, and it requires elevated temperature to open the lactam ring, achieve adequate molecular weight, and keep melt viscosity manageable for processing.Given Data / Assumptions:The product is nylon-6 from caprolactam.We seek a realistic melt-phase reactor temperature window used in practice.Higher temperature promotes ring opening and polymer chain growth but must avoid thermal degradation.Concept / Approach:Caprolactam undergoes ring opening and polycondensation with added water (or generated in situ). Industrial reactors maintain a high temperature to drive equilibrium toward polymer formation and to reduce viscosity for efficient mixing and devolatilisation. Typical practice keeps temperature well above 200°C, commonly around 250–280°C, balancing conversion and stability.Step-by-Step Solution:Identify the reaction: caprolactam → nylon-6 via ring opening.Note industrial melt polymerisation is conducted at high temperature.Select the realistic range: 250 to 280°C.Verification / Alternative check:Process descriptions for nylon-6 list polymerisation near 250–280°C followed by finishing/annealing and devolatilisation to achieve target number-average molecular weight for fibers, films, or engineering resins.Why Other Options Are Wrong:-20 to 25°C and 50 to 75°C: far too low to open the lactam ring and achieve polymerisation.100 to 150°C: still insufficient; reaction would be extremely slow with poor molecular weight.Common Pitfalls:Confusing hot vs. cold emulsion polymerisation (used for SBR) with melt polymerisation of lactams; mechanisms and temperature needs are very different.Final Answer:250 to 280

Question 5

Copolymer identification: in a copolymer, the repeating chain contains two different monomer units. Which of the following is a copolymer used widely in tyres?

Accepted Answer

Introduction / Context:Classifying polymers as homopolymers or copolymers is foundational to predicting performance. Copolymers combine two (or more) different monomers to tailor elasticity, glass transition temperature, strength, and chemical resistance. The tyre industry especially relies on specific copolymers for abrasion resistance and grip.Given Data / Assumptions:Buna-S is styrene-butadiene rubber, commonly called SBR.PTFE is polytetrafluoroethylene from tetrafluoroethylene (one monomer).PMMA is polymethyl methacrylate from methyl methacrylate (one monomer).Polycaprolactam is nylon-6 from caprolactam (ring-opening of one monomer).Concept / Approach:Copolymer definition: polymer chains built from at least two distinct monomer species. SBR fits precisely: chains incorporate styrene units and butadiene units, giving a rubber with improved processability and balanced properties for treads and general-purpose elastomer uses.Step-by-Step Solution:Evaluate each choice: identify number of monomers.Recognise SBR (Buna-S) = styrene + butadiene → copolymer.Eliminate PTFE, PMMA, and nylon-6 as homopolymer/ring-opening cases.Verification / Alternative check:Materials references list SBR as the predominant tyre copolymer blended with natural rubber and other additives for performance.Why Other Options Are Wrong:PTFE, PMMA, Nylon-6: each derived from a single monomer → not copolymers.Common Pitfalls:Assuming “nylon” implies two monomers; nylon-6 forms from one lactam via ring opening, not a diacid/diamine pair like nylon-6,6.Final Answer:Buna-S

Question 6

Silicone materials are known for water repellency and heat resistance. Which application is unsuitable specifically for silicone resins (crosslinked), even though other silicone forms may be used?

Accepted Answer

Introduction / Context:Silicone chemistry spans fluids (oils), elastomers (RTV and HTV rubbers), and resins (crosslinked networks). Their performance varies with structure: fluids flow and transfer heat; elastomers provide sealing; resins give coatings and laminates. Choosing the right silicone form for the job is critical.Given Data / Assumptions:“Silicone resins” denote crosslinked polysiloxane networks used as varnishes, binders, and laminating resins.Silicone oils (not resins) serve as heat-transfer or hydraulic fluids.Silicone greases and RTV adhesives are common product forms.Concept / Approach:Application suitability depends on physical state and rheology. Crosslinked resins are solids or highly viscous, non-flowing networks once cured; they are excellent for high-temperature coatings/laminates, not for circulation as heat-transfer fluids. Conversely, silicone oils possess low volatility and thermal stability, suitable for heat transfer and hydraulic service—but these are fluids, not resins.Step-by-Step Solution:Identify “resin” as crosslinked → not pumpable.Compare applications requiring flow (hydraulic/heat transfer) versus structural uses (adhesive/lamination).Select the unsuitable use for resins: hydraulic heat-transfer fluid.Verification / Alternative check:Product data sheets separate silicone resins (coatings/laminates) from silicone fluids (heat transfer) and greases (lubrication).Why Other Options Are Wrong:Room-temperature adhesive and lamination: typical for silicone resins/RTV systems.Grease and lubricant: silicone greases are common, though they are based on silicone oils thickened with fillers, not resins.Common Pitfalls:Equating all “silicones” with the same use; specific architecture determines capability.Final Answer:Hydraulic heat-transfer fluid

Question 7

Compare nylon-6,6 with nylon-6: which property statement correctly characterises nylon-6,6 relative to nylon-6?

Accepted Answer

Introduction / Context:Nylon-6,6 (from hexamethylenediamine and adipic acid) and nylon-6 (from caprolactam) are closely related polyamides used in fibres and engineering plastics. Subtle chemistry differences affect melting point, hardness, and abrasion resistance, guiding material selection in high-temperature and mechanically demanding applications.Given Data / Assumptions:Nylon-6,6 typically melts around 260–265°C; nylon-6 around 220–225°C.Abrasion resistance for nylon-6,6 is generally superior in comparable unfilled grades.Hardness and heat-deflection temperature are typically higher for nylon-6,6.Concept / Approach:The higher amide linkage density and crystallinity of nylon-6,6 raise its melting point and improve high-temperature mechanical properties. These structural features also tend to yield higher hardness and better wear resistance, though compounding can tune both families significantly.Step-by-Step Solution:Assess melting point: nylon-6,6 > nylon-6 → (a) true.Assess wear: nylon-6,6 commonly shows better abrasion → (b) true.Assess hardness: nylon-6,6 generally higher → (c) true.Therefore, (d) “All of the above” is correct.Verification / Alternative check:Datasheets and handbooks corroborate the higher Tm and improved heat resistance of nylon-6,6 compared with nylon-6 under similar conditioning.Why Other Options Are Wrong:Choosing any single property ignores the broader, well-documented advantages of nylon-6,6 across these metrics.Common Pitfalls:Over-generalising: additives, moisture content, and processing history can narrow or reverse differences for specific grades.Final Answer:All of the above

Question 8

Trade names for polymethyl methacrylate (PMMA): which of the following is NOT a commercial name for PMMA?

Accepted Answer

Introduction / Context:Recognising polymer trade names prevents mis-specification during procurement and design. PMMA is marketed widely as Perspex, Lucite, or Plexiglass for transparent glazing. Teflon, however, refers to a completely different polymer family with distinct properties and applications.Given Data / Assumptions:PMMA = Perspex/Lucite/Plexiglass.Teflon = PTFE (polytetrafluoroethylene), a fluoropolymer.Concept / Approach:PMMA is an acrylic thermoplastic known for optical clarity and scratch resistance; PTFE is a fluoropolymer known for low friction and extreme chemical resistance. Confusing them can lead to severe performance mismatches in temperature resistance, friction, and processability.Step-by-Step Solution:Identify PMMA trade names: Perspex, Lucite, Plexiglass.Identify outlier: Teflon (PTFE), not PMMA.Verification / Alternative check:Supplier catalogs list PMMA under these trade names for panels and displays; Teflon products are PTFE sheets, rods, and coatings.Why Other Options Are Wrong:They are widely accepted PMMA trade names.Common Pitfalls:Assuming transparency implies PMMA; polycarbonate is also transparent but sold as Lexan/Makrolon.Final Answer:Teflon

Question 9

Among common plastics, which one is a true copolymer (composed of two different monomer species in the chain)?

Accepted Answer

Introduction / Context:Copolymers combine properties of two monomers and are engineered for specific applications like tyres, impact modification, and adhesives. Distinguishing them from homopolymers helps predict behaviour under load, temperature, and chemical exposure.Given Data / Assumptions:SBR is polymerised from styrene and butadiene.Polystyrene, PTFE, and polypropylene are homopolymers of styrene, tetrafluoroethylene, and propylene respectively.Concept / Approach:Only SBR fits the definition of a random (or controlled) copolymer in the list, delivering a balance of resilience and processability widely used in tyre treads and general rubber goods.Step-by-Step Solution:Identify number of monomers: SBR uses two; others use one.Therefore SBR is the copolymer.Verification / Alternative check:Polymer handbooks classify SBR as a key copolymer in elastomer technology.Why Other Options Are Wrong:PS, PTFE, PP are homopolymers.Common Pitfalls:Assuming blends (physical mixtures) are copolymers; chemical copolymerisation is different from blending.Final Answer:SBR (styrene-butadiene rubber)

Question 10

Service temperature range comparison for elastomers: which rubber typically offers the widest continuous service window, roughly from −75°C up to about 275°C?

Accepted Answer

Introduction / Context:Elastomer selection often hinges on temperature capability. Applications from cryogenic seals to high-temperature gaskets demand rubbers that retain elasticity across extreme ranges. Silicone rubber stands out for its broad usable window and resistance to heat and ozone.Given Data / Assumptions:Target range: about −75°C to 275°C.Silicone rubbers maintain flexibility at very low temperatures and resist embrittlement at high temperatures.Butyl and nitrile have narrower ranges and poorer high-heat performance compared with silicone.Concept / Approach:The siloxane backbone in silicone rubber provides high bond energy and low glass transition temperature, enabling elasticity at sub-zero conditions and resilience at elevated temperatures. Conventional hydrocarbon rubbers soften/degrade earlier, limiting their upper service temperature.Step-by-Step Solution:Match the exceptional range to silicone performance.Eliminate butyl and nitrile due to narrower service windows.Select silicone rubber as correct.Verification / Alternative check:Datasheets commonly list silicone continuous service up to ~200–250°C with peaks higher; specialized grades can approach 275°C; low-temperature flexibility extends below −60°C.Why Other Options Are Wrong:Butyl and nitrile: limited by higher glass transition and poorer heat resistance.Common Pitfalls:Confusing “silicon” (element) with “silicone” (polymer); spelling matters in specifications.Final Answer:Silicone rubber

Question 11

Elastomers: choose the statement that best characterises elastomeric materials in general industrial practice.

Accepted Answer

Introduction / Context:Elastomers are polymers that undergo large reversible deformations. Understanding their crosslinking state and mechanical profile is important for designing seals, tyres, and vibration isolators. Most industrial rubbers are cured (vulcanised), creating a network that provides elastic recovery without flow.Given Data / Assumptions:Industrial elastomers are lightly crosslinked via vulcanisation or peroxide cure.Crosslinking renders them thermoset in service (no melting on reheating).Neat elastomers are not known for high flexural strength or extreme tensile strength without reinforcement.Concept / Approach:Elasticity requires network junctions that restore the original shape after strain. This is achieved by a sparse crosslinked network, i.e., a thermoset. Fillers (carbon black, silica) and fibers improve tensile and tear properties, but the base elastomer alone does not rival high-temperature engineering thermoplastics in tensile or heat resistance.Step-by-Step Solution:Identify the defining feature: lightly crosslinked networks → thermosetting.Eliminate protein derivatives (not representative of synthetic elastomers).Eliminate claims of inherently high flexural or tensile/heat strength without context.Verification / Alternative check:Rubber technology texts describe vulcanisation and the transition from viscous gum to elastic network as the hallmark of elastomers.Why Other Options Are Wrong:(b) Not a defining class; (c) and (d) exaggerate properties absent reinforcement.Common Pitfalls:Confusing thermoplastic elastomers (TPEs) with conventional vulcanised rubbers; TPEs have physical crosslinks but still behave like thermoplastics in processing.Final Answer:They are typically thermosetting materials (lightly crosslinked for elastic recovery).

Question 12

Extrusion processing capability: which product is NOT typically manufactured by plastic extrusion (continuous profile process)?

Accepted Answer

Introduction / Context:Extrusion forces molten polymer through a die to create continuous profiles of constant cross-section. Recognising which products suit extrusion versus injection moulding helps avoid design and manufacturing errors.Given Data / Assumptions:Extrusion excels at continuous shapes: pipes, tubes, filaments, sheets, films, and profiles.Buckets are discrete, hollow articles with complex geometry and non-uniform walls.Concept / Approach:Buckets require closed-mould cavity filling and cooling to a fixed 3D shape—classic injection moulding (or sometimes blow moulding for certain pails). Extrusion cannot form complex, non-constant cross-sections in a single step.Step-by-Step Solution:Match manufacturing method to geometry.Continuous constant cross-section → extrusion (filaments, pipes, tubings).3D discrete article (bucket) → injection moulding, not extrusion.Verification / Alternative check:Processing guides list extrudates as profiles and injection moulded parts as discrete items like housings and containers.Why Other Options Are Wrong:Filaments, pipes, tubings: classic extrusion outputs.Common Pitfalls:Confusing extrusion blow moulding (used for bottles) with pure extrusion; blow moulding still begins from an extruded parison but needs a moulded step for the final shape.Final Answer:Buckets

Question 13

Epoxy resins (epoxide polymers): select the statement that correctly describes a core chemical feature or processing trait of epoxy systems.

Accepted Answer

Introduction / Context:Epoxy resins are versatile thermosetting systems used in coatings, adhesives, laminates, and composites. Understanding their functional groups and curing chemistry ensures correct selection of hardeners and processing windows.Given Data / Assumptions:Common epoxies are diglycidyl ethers (e.g., DGEBA) bearing terminal epoxide (oxirane) groups.Curing (with amines, anhydrides, etc.) converts these reactive ends into a crosslinked network.Manufacture involves step-growth reactions (not solely addition), and prepolymers are not crosslinked until cure.Concept / Approach:The defining feature is the epoxide ring functionality at chain ends or along the backbone, enabling room-temperature or elevated-temperature curing. Prior to cure, epoxies are oligomeric liquids/solids with epoxy equivalents; after cure, they form a thermoset network. Emulsion polymerisation is not the primary production route.Step-by-Step Solution:Identify signature chemistry: terminal epoxy groups.Eliminate claims of “only addition” and “already crosslinked.”Reject emulsion polymerisation as the typical route.Verification / Alternative check:Technical datasheets specify epoxy equivalent weight (EEW), reflecting epoxide groups per mass prior to cure.Why Other Options Are Wrong:(a) and (d) misstate mechanisms and methods; (c) describes the post-cure state, not the resin as supplied.Common Pitfalls:Confusing epoxy “resin” (prepolymer) with the cured epoxy “thermoset.”Final Answer:Contain epoxy groups at the ends of the polymer chain prior to cure.

Question 14

Polyacrylate family check: which polymer below does NOT belong to the polyacrylate (acrylic ester/methacrylate) class?

Accepted Answer

Introduction / Context:“Acrylics” often refer to acrylate and methacrylate esters (e.g., PMMA, polyethyl acrylate). Polyacrylonitrile (PAN) is an acrylic fibre precursor but chemically distinct, containing nitrile groups rather than ester functions typical of polyacrylates.Given Data / Assumptions:PMMA and polyethyl acrylate are classic acrylics (methacrylate and acrylate esters).PAN is formed from acrylonitrile and exhibits different reactivity and properties.Concept / Approach:Polyacrylates are ester-containing polymers derived from acrylic/methacrylic acid esters. PAN, while sometimes grouped under “acrylics” in textile terminology, is not a polyacrylate chemically; it belongs to the nitrile family with distinct solubility, thermal behaviour, and carbon-fibre precursor utility.Step-by-Step Solution:Classify each option by functional group.Identify PAN as nitrile-based, not an acrylate ester.Conclude PAN does not belong to the polyacrylate class.Verification / Alternative check:Polymer classifications separate acrylate esters (adhesives, coatings) from PAN (fibre precursor, barrier properties).Why Other Options Are Wrong:PMMA and polyethyl acrylate are canonical acrylics.Common Pitfalls:Equating textile term “acrylic fibre” with chemical class “polyacrylate.”Final Answer:Polyacrylonitrile

Question 15

Catalyst system for low-pressure Ziegler process producing high-density polyethylene (HDPE): identify the correct catalyst combination.

Accepted Answer

Introduction / Context:Ziegler–Natta catalysts revolutionised polyethylene production by enabling polymerisation at low pressure with controlled stereochemistry and higher density. Recognising the classical catalyst pairs is essential in polymer process engineering.Given Data / Assumptions:HDPE via low-pressure routes uses transition metal halides with organoaluminium co-catalysts.Typical systems: TiCl3/TiCl4 with AlEt3 (aluminium triethyl).Concept / Approach:The organoaluminium compound alkylates and activates the titanium species, producing active sites for ethylene insertion. Precious metals like platinum are not used for HDPE Ziegler processes; nickel and molybdenum are not the classical choices here.Step-by-Step Solution:Select the titanium + organoaluminium pair: AlEt3 + TiCl4.Eliminate single-metal options lacking Ziegler pairing.Verification / Alternative check:Polymerisation texts list TiClx/AlEt3 variants as industry standards for HDPE and PP.Why Other Options Are Wrong:Pt, Ni, Mo are not the conventional catalysts for low-pressure HDPE Ziegler systems.Common Pitfalls:Confusing Ziegler–Natta with Phillips (Cr/SiO2) catalysts; both produce HDPE but are different families.Final Answer:Aluminium triethyl activated with TiCl4

Question 16

Radiopaque plastics: which additive is commonly incorporated to make a plastic impervious/opaque to X-rays?

Accepted Answer

Introduction / Context:Medical devices, cable jackets, and non-destructive testing markers often require radiopacity. Adding high-atomic-number fillers to polymer matrices increases X-ray attenuation, enabling visibility under imaging.Given Data / Assumptions:Barium salts (e.g., barium sulfate) are widely used radiopaque fillers.Asbestos is not used for safety reasons; phthalic acid is a plasticiser intermediate; SiC is abrasive, not radiopaque.Concept / Approach:X-ray attenuation increases with atomic number and density. Barium (Z=56) salts dispersed in plastics create radiopaque composites suitable for medical tubing and markers without severely compromising processability.Step-by-Step Solution:Identify heavy element additive: barium salt.Eliminate asbestos (hazard), SiC (not radiopaque), phthalic acid (not a filler).Verification / Alternative check:Material datasheets list BaSO4-filled PVC/PU as standard for radiopaque products.Why Other Options Are Wrong:They do not confer X-ray opacity or are unsuitable.Common Pitfalls:Confusing UV opacity with X-ray opacity; mechanisms differ.Final Answer:Barium salt

Question 17

Epoxy systems and uses: epoxies contain two or more epoxide (oxirane) groups per molecule. Which of the following is a standard application outcome of epoxy resins?

Accepted Answer

Introduction / Context:Epoxy resins are ubiquitous in structural adhesives and protective coatings. Their reactive epoxide groups enable strong bonding to varied substrates and crosslinking into tough, chemically resistant films.Given Data / Assumptions:Typical curing agents: amines, anhydrides, thiols.Applications: structural adhesives, paints, powder coatings, laminates (FR-4), composites.Concept / Approach:Upon curing, epoxies form crosslinked networks with excellent adhesion, chemical resistance, and dielectric properties. They are not polyamide elastomers by themselves; polyamides are a separate polymer family. Thus the combined choice of adhesive and coating best matches real-world uses.Step-by-Step Solution:Identify canonical uses from industry practice.Select both adhesive and coating functions as correct.Verification / Alternative check:Product literature lists epoxy adhesives and epoxy coatings as primary market segments.Why Other Options Are Wrong:(a) describes a different polymer class; individual epoxy formulations may be tough but are thermoset networks, not elastomeric polyamides.Common Pitfalls:Assuming all epoxies are flexible; flexibility depends on formulation (e.g., use of flexibilisers).Final Answer:Both (b) and (c)

Question 18

Common applications of polyvinyl alcohol (PVA): select the most typical use from the options provided.

Accepted Answer

Introduction / Context:Polyvinyl alcohol (PVA) is a water-soluble polymer valued for film-forming, adhesion, and emulsifying properties. It is widely used in paper, packaging, and woodworking where water clean-up and low toxicity are desirable.Given Data / Assumptions:PVA dissolves in water; hydrogen bonding enables strong adhesion to polar substrates.PVA fibres exist (vinylon), but the most ubiquitous commercial use is as adhesive and binder.Non-stick cookware coatings are typically PTFE, not PVA.Concept / Approach:PVA’s hydroxyl functionality promotes cohesive films and adhesion to paper and wood. Ion-exchange resins usually employ sulfonated polystyrene or similar; PVA is not the standard ion exchanger. Textile fibres from PVA are niche compared with its adhesive dominance.Step-by-Step Solution:Match property (water solubility, film formation) to use (adhesive).Eliminate ion exchange and PTFE-type cookware coatings.Verification / Alternative check:Adhesive products (white glues) frequently use PVA or its copolymers (e.g., PVAc emulsions).Why Other Options Are Wrong:Ion exchange and cookware non-stick require different chemistries; PVA fibre is less common than adhesives.Common Pitfalls:Confusing PVA with PVAc (polyvinyl acetate); many adhesives are PVAc that may be partially hydrolysed to PVA.Final Answer:Water-soluble adhesive

Question 19

Effect of plasticisers: adding plasticisers to a polymer primarily increases which property by partially neutralising intermolecular attractions?

Accepted Answer

Introduction / Context:Plasticisers are low-molecular-weight compounds blended into polymers (notably PVC) to improve flexibility and reduce brittleness. They interpose between chains, lowering secondary bonding and glass transition temperature (Tg).Given Data / Assumptions:Plasticiser presence reduces chain–chain interactions.Lower Tg increases softness and flexibility.Tensile strength and chemical resistance usually decrease with heavy plasticisation.Concept / Approach:By spacing macromolecules and enhancing chain mobility, plasticisers shift the polymer into a rubbery regime at use temperature, dramatically boosting elongation and flexibility while typically compromising modulus and strength.Step-by-Step Solution:Identify the direct outcome of reduced intermolecular forces: increased flexibility.Reject strength and chemical resistance increases; these often drop.Verification / Alternative check:Mechanical data for plasticised PVC versus rigid PVC show lower modulus and tensile strength, higher elongation at break.Why Other Options Are Wrong:(a) and (b) contradict typical plasticiser effects; (d) overgeneralises.Common Pitfalls:Assuming any additive toughens a polymer; plasticisers soften and flexibilise rather than strengthen.Final Answer:Flexibility

Question 20

The polymerisation product of C2F4 (tetrafluoroethylene) is PTFE. What is the well-known commercial name for this fluoropolymer?

Accepted Answer

Introduction / Context:PTFE (polytetrafluoroethylene) is a high-performance fluoropolymer prized for chemical inertness, low surface energy (non-stick), and excellent dielectric properties. The most recognised trademark for PTFE is Teflon.Given Data / Assumptions:Monomer: tetrafluoroethylene (TFE), formula C2F4.Resulting polymer: PTFE.Concept / Approach:Brand recognition helps avoid material confusion in specifications. PTFE is not polyurethane, silicone rubber, or an epoxy; it is a distinct thermoplastic processed by sintering and paste extrusion due to its high melt viscosity.Step-by-Step Solution:Match PTFE to trademark: Teflon.Eliminate unrelated polymer families (PU, silicone, epoxy).Verification / Alternative check:Supplier catalogs present PTFE under the Teflon trademark for non-stick coatings and components.Why Other Options Are Wrong:They name different polymers with different chemistries and uses.Common Pitfalls:Confusing PTFE with PFA or FEP; these are related fluoropolymers with melt-processability.Final Answer:Teflon

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