Polymer processing and recycling - Domande aperte e a risposta multipla per l'esame

MULTIPLE CHOICE QUESTIONS

1)​ Why do polymers lack a gaseous state?

A.​ Their molecular weight is too low to evaporate.

B.​ Increasing temperature leads to chain breakage before evaporation can occur.

C.​ They are only stable in a disordered solid structure.

D.​ Secondary physical interactions are too weak to allow gas formation

B 2)​ Which of the following describes a polymer melt?

A.​ A purely elastic solid.

B.​ A purely viscous Newtonian liquid.

C.​ A viscoelastic liquid with hybrid behavior.

D.​ A disordered glassy structure.

C 3)​ Thermosets differ from thermoplastics primarily because:

A.​ They have higher molecular weights.

B.​ They are interconnected by chemical cross-links and cannot melt.

C.​ They are always flexible, whereas thermoplastics are rigid.

D.​ They are obtained only through chain-growth polymerization.

B 4)​ An ionomer is characterized by:

A.​ Permanent chemical cross-links that cannot be reversed

B.​ Ionic clusters that act as reversible physical cross-links.

C.​ High solubility in non-polar solvents at all temperatures.

D.​ A completely linear structure with no branches or interactions

B 5)​ The Polydispersity Index (PI) is defined as:

A.​

B.​

C.​ M +M

W N

D.​ M -M

W N

B 6)​ In Step-Growth Polymerization, high molecular weight is typically reached:

A.​ At low conversion of monomers.

B.​ Immediately after the initiator is added.

C.​ Only if radical species are present.

D.​ Only at very high conversion of monomers

D 7)​ Which polymer is an example of Chain-Growth Polymerization?

A.​ Polycarbonate

B.​ Polyamide (Kevlar)

C.​ Polyethylene (PE)

D.​ Polyester

C 8)​ If a monomer has three functional groups in a step-growth reaction, the result is

likely:

A.​ A linear polymer.

B.​ A branched or cross-linked polymer.

C.​ A random copolymer.

D.​ A low molecular weight gas.

B 1

9)​ Below the Glass Transition Temperature (T ), a polymer behaves like a:

G

A.​ Rubber

B.​ Viscous liquid

C.​ Glassy solid

D.​ Semicrystalline melt

C 10)​Which factor would typically lead to a lower Glass Transition Temperature (T )?

G

A.​ High crystallinity.

B.​ Presence of stiff aromatic groups in the chain.

C.​ High degree of cross-linking.

D.​ Presence of plasticizers.

D 11)​The "center of gravity" of macromolecules prevents flow phenomena at which

point?

A.​ Above the melting point (T ).

M

B.​ At the Glass Transition Temperature (T ).

G

C.​ During radical initiation.

D.​ Only in the gaseous state.

B 12)​For amorphous polymers, what happens when T > T ?

G

A.​ The material transitions from glass-like to rubber-like behavior

B.​ The material melts isothermally.

C.​ The material becomes a semicrystalline solid.

D.​ The material reaches its boiling point.

A 13)​A "Spherulite" is a complex structure composed of:

A.​ Only amorphous chains.

B.​ Only linear branches.

C.​ Crystalline lamellae and amorphous fractions.

D.​ Ionic heads and non-polar tails. 2

C 14)​High Density Polyethylene (HDPE) has a higher melting point than LDPE

because:

A.​ It has more branches that prevent crystallization.

B.​ It has fewer branches, allowing for a more ordered crystalline structure.

C.​ It is a thermoset material.

D.​ It is produced via step-growth polymerization.

B 15)​Which configuration is most likely to result in a crystalline structure?

A.​ Atactic

B.​ High steric hindrance functional groups.

C.​ Low kinetic chain flexibility.

D.​ Isotactic

D 16)​How does high crystallinity affect the optical properties of a polymer?

A.​ It causes light scattering, making the polymer opaque or translucent

B.​ It makes the polymer perfectly transparent.

C.​ It prevents the polymer from absorbing any UV radiation.

D.​ It has no effect on optical behavior.

A 17)​What is the effect of crystallinity on mechanical properties?

A.​ Increases strength but also increases fragility.

B.​ Decreases strength and increases tenacity.

C.​ Makes the polymer soluble in all solvents.

D.​ Decreases the density of the material.

A 3

18)​Secondary physical interactions (like hydrogen bonds) are important for

determining:

A.​ The Polydispersity Index.

B.​ The melting point (T ) and solubility.

M

C.​ The rate of radical initiation.

D.​ The number of functional groups in a monomer

B 19)​A "Grafted Copolymer" is one where:

A.​ Monomers A and B alternate regularly

B.​ Monomers are distributed randomly

C.​ The main chain is one monomer and side chains are another

D.​ The polymer is made of only one type of monomer.

C 20)​The percentage of crystallinity can be calculated using:

A.​ The ratio of M to M .

W N

B.​ The ratio of the sample's melting enthalpy to the enthalpy of a 100% crystalline

polymer.

C.​ The glass transition temperature divided by the melting temperature.

D.​ The number of branches per 1000 carbon atoms.

B 21)​What is a polymer "compound"?

A.​ A polymer consisting of only one type of monomer.

B.​ A polymer modified after polymerization by adding additives at the molten state.

C.​ A polymer produced through step-growth polymerization only.

D.​ A natural resin with no synthetic additives.

B 22)​Which of the following is NOT a primary reason for using additives?

A.​ To improve mechanical performance

B.​ To provide electrical conductivity.

C.​ To decrease the molecular weight of the base polymer

D.​ To increase stability under working conditions 4

C 23)​What is the main difference between "dosing" and "mixing"?

A.​ Dosing refers to cooling, while mixing refers to heating.

B.​ Dosing is the introduction of a material element; mixing is the homogenization of the

recipe.

C.​ Mixing is done at the solid state; dosing is only done at the molten state.

D.​ There is no difference; the terms are used interchangeably.

B 24)​"Active fillers" or reinforcements are primarily characterized as:

A.​ Minerals used to reduce the cost of the compound.

B.​ Fibers used to improve specific properties like elastic modulus and strength.

C.​ Liquids used to increase the flexibility of the polymer.

D.​ Gases used to create foam structures

B 25)​How do glass fibers typically affect the processing of a polymer?

A.​ They increase the material fluidity.

B.​ They increase the volumetric shrinkage.

C.​ They decrease the material fluidity and increase viscosity.

D.​ They increase the cycle time.

C 26)​What is the purpose of "sizing" glass fibers after spinning?

A.​ To change the color of the fiber.

B.​ To improve the adhesion between the fiber and the polymer.

C.​ To make the fiber more brittle.

D.​ To decrease the specific weight of the fiber.

B 5

27)​In processing, the orientation of fibers during melt flow leads to:

A.​ Uniform mechanical properties in all directions.

B.​ Higher mechanical resistance in the direction parallel to the flow.

C.​ Lower viscosity in the compression zone.

D.​ Increased thermal expansion in the flow direction.

B 28)​A disadvantage of fiber reinforcements compared to mineral fillers is:

A.​ They are much cheaper.

B.​ They cause differential shrinkage, which can lead to part deformation.

C.​ They do not increase the viscosity of the melt.

D.​ They accelerate melt cooling too slowly.

B 29)​When can a polymer undergo degradation?

A.​ Only during its service life

B.​ Only during production.

C.​ During production, transformation (processing), and service life.

D.​ Only when exposed to temperatures above 500°C.

C 30)​The 3-stage radical mechanism of thermo-oxidative degradation consists of:

A.​ Melting, crystallization, and cooling.

B.​ Initiation, propagation, and termination.

C.​ Evaporation, condensation, and solidifying.

D.​ Dosing, mixing, and extruding.

B 31)​What happens during the propagation stage of thermo-oxidation?

A.​ Radicals are generated from the neutral polymer ($RH$).

B.​ Peroxide radicals (ROO●) form and react with the polymer to create hydroperoxides

(ROOH).

C.​ Two radicals combine to form a stable product.

D.​ The polymer chain is completely destroyed by UV light 6

B 32)​Structural cross-linking during degradation results in:

A.​ A softer and more flexible material.

B.​ Hardening of the molecule, increased fragility, and decreased solubility.

C.​ An increase in molecular weight and transparency.

D.​ A decrease in the glass transition temperature.

B 33)​Metal ions (like Copper or Iron) catalyze degradation through:

A.​ Blocking the action of UV absorbers

B.​ A Haber-Weiss mechanism that catalyzes hydroperoxide decomposition.

C.​ Increasing the free volume between polymer chains.

D.​ Acting as secondary plasticizers

B 34)​Primary antioxidants are classified as such because they:

A.​ Decompose hydroperoxides into inactive products.

B.​ Stop the degradation process by reacting with peroxy radicals in the propagation

phase

C.​ Block the path of UV radiation.

D.​ Are the only additives used in a masterbatch

B 35)​An example of a common primary stabilizer is:

A.​ Thioethers.

B.​ Sterically hindered phenols.

C.​ Tertiary phosphites.

D.​ Carbon black.

B 36)​Sterically hindered phenols neutralize radicals by:

A.​ Absorbing UV energy and releasing it as heat

B.​ Donating a hydrogen from their hydroxyl group (-OH) to the radical.

C.​ Forming a physical barrier on the surface of the polymer.

D.​ Increasing the crystallinity of the polymer. 7

B 37)​To increase the activity of a sterically hindered phenol, it should contain:

A.​ Electron-withdrawing groups like NO 2

B.​ Electron-donating groups like -CH or -OCH

3 3

C.​ Bulky substituents that increase the density of the polymer.

D.​ Halogen atoms like Chlorine.

B 38)​Secondary stabilizers protect the polymer by:

A.​ Replacing the initiator in a reaction.

B.​ Promoting the decomposition of hydroperoxides (ROOH) as they are produced.

C.​ Increasing the temperature of the melt.

D.​ Acting as pigments to reflect light.

B 39)​Which of the following is a secondary stabilizer?

A.​ Sterically hindered phenols.

B.​ Thioethers and tertiary phosphites.

C.​ Chelating agents.

D.​ Nitrogen-based pigments.

B 40)​Chelating agents are used to:

A.​ Increase the molecular weight of the polymer.

B.​ Block the catalytic activity of metallic ions by forming chelate complexes.

C.​ Replace plasticizers in high-temperature applications.

D.​ Neutralize HCl in PVC degradation.

B 8

41)​PVC is highly sensitive to heat because degradation involves:

A.​ The total depolymerization of the main chain.

B.​ The elimination of substituents (chain stripping), specifically Chlorine side atoms.

C.​ The absorption of nitrogen from the atmosphere.

D.​ The immediate formation of gaseous monomers

B 42)​The byproduct of PVC degradation that acts as an autocatalyst is:

A.​ Water.

B.​ Carbon dioxide.

C.​ Hydrochloric acid.

D.​ Methane

C 43)​Discoloration in PVC (yellowing/browning) occurs when:

A.​ The molecular weight increases too much.

B.​ The number of conjugated double bonds exceeds seven, forming chromophore

groups.

C.​ The plasticizer evaporates.

D.​ The polymer reaches its melting point.

B 44)​Stabilizers for PVC work by:

A.​ Increasing the thickness of the part.

B.​ Neutralizing HCl and substituting liable C-Cl bonds with more stable groups.

C.​ Increasing the oxygen content in the melt.

D.​ Turning the polymer into a thermoset

B 45)​Tin (Sn) based organometallic compounds are used in PVC to:

A.​ Act as a lubricant

B.​ Substitute Chlorine in liable bonds with more stable atoms.

C.​ Increase the transparency of the polymer.

D.​ Act as a secondary plasticizer. 9

B 46)​Why are Sterically Hindered Amines (HALS) unsuitable for PVC?

A.​ They are too expensive

B.​ They are deactivated by HCl

C.​ They increase the rate of oxidation.

D.​ They make the PVC too flexible.

B 47)​The UV radiation range most damaging to polymers on the Earth's surface is:

A.​ UVA (315–400 nm).

B.​ UVB (280–315 nm).

C.​ UVC (100–280 nm).

D.​ Infrared (>700 nm).

B 48)​UV radiation causes damage because its energy is:

A.​ Much lower than the energy of covalent bonds

B.​ Of the same order of magnitude as covalent bond energy

C.​ Only able to affect the color of the polymer.

D.​ Absorbed only by the atmosphere

B 49)​How do UV absorbers protect the polymer?

A.​ They reflect 100% of incident light like a mirror.

B.​ They absorb harmful radiation and release the energy in a less harmful way (e.g., as

heat).

C.​ They increase the density of the polymer to block light.

D.​ They chemically bond with UV rays to neutralize them

B 10

50)​Carbon black is an effective light stabilizer because it:

A.​ Is completely transparent.

B.​ Absorbs the entire UV and visible spectrum and transforms it into infrared radiation.

C.​ Acts only as a lubricant.

D.​ Increases the glass transition temperature

B 51)​"Screeners" (pigments) protect polymers by:

A.​ Absorbing and emitting infrared energy.

B.​ Reflecting or absorbing UV radiation at the surface, making the polymer opaque.

C.​ Neutralizing free radicals through a regenerative process.

D.​ Decomposing hydroperoxides.

B 52)​HALS (Sterically Hindered Amines) are effective because they:

A.​ Act as UV absorbers.

B.​ Block radicals from reacting with oxygen through a regenerative process.

C.​ Are used only in high-temperature applications.

D.​ Act as a thermal barrier between the flame and the polymer.

B 53)​Halogenated flame retardants work in the gas phase by:

A.​ Releasing water to cool the flame.

B.​ Replacing highly reactive radicals (H· and OH·) with more stable halogen radicals

(X·).

C.​ Creating a thick char layer on the surface.

D.​ Increasing the oxygen concentration near the flame.

B 54)​What is a disadvantage of halogenated flame retardants?

A.​ They have low efficiency.

B.​ They are non-toxic.

C.​ They are toxic and increase the polymer density.

D.​ They cannot be used in hot runners. 11

C 55)​Phosphorus-based flame retardants act primarily in the solid phase by:

A.​ Evaporating to dilute the gas phase.

B.​ Dehydrating the polymer to form a protective char shield.

C.​ Cooling the mixture by releasing nitrogen gas.

D.​ Acting as a lubricant for the screw

B 56)​Intumescent systems are composed of:

A.​ Halogens, metal oxides, and water.

B.​ An acid source, a carbon source, and a blowing agent.

C.​ Aluminum hydroxide and magnesium hydroxide.

D.​ Phenolic resins and epoxy resins

B 57)​How do Inorganic Hydroxides (like ATH) provide flame retardancy?

A.​ Releasing water vapor that dilutes the gas phase and cools the solid phase.

B.​ Catalyzing the combustion reaction.

C.​ Increasing the mechanical resistance of the polymer.

D.​ Absorbing HCl from the atmosphere.

A 58)​TGA (Thermogravimetric Analysis) measures:

A.​ The change in the color of the polymer.

B.​ The weight loss of a sample as a function of temperature or time.

C.​ The melting point of a semi-crystalline polymer.

D.​ The shear rate of a polymer melt.

B 59)​In TGA, the second step of degradation (under air) usually corresponds to

A.​ High volatile compounds.

B.​ Low volatile compounds.

C.​ Combustion.

D.​ Ash residue. 12

D 60)​What does OIT (Oxidative Induction Time) measure?

A.​ How fast a polymer melts.

B.​ The resistance to thermo-oxidation of a stabilized material.

C.​ The time it takes for a polymer to reach the die.

D.​ The amount of filler in a compound.

B 61)​The end of the induction period in an OIT test is signaled by:

A.​ The heat flux starts to rise under an oxidizing atmosphere.

B.​ The polymer completely evaporates.

C.​ The inert atmosphere is first introduced.

D.​ The sample returns to room temperature.

A 62)​What is the effect of adding a plasticizer to a polymer?

A.​ Higher rigidity and density.

B.​ Better flexibility, ductility, and a lower Tg.

C.​ Resistance to flame and UV radiation.

D.​ Higher thermal conductivity.

B 63)​Primary plasticizers are:

A.​ Non-solvents for the polymer.

B.​ Highly compatible with the polymer and acting essentially as solvents.

C.​ Used only to reduce the cost of secondary stabilizers.

D.​ Made exclusively from agricultural waste.

B 64)​Polymeric plasticizers are preferred when there is a need for:

A.​ High volatility and low molecular weight.

B.​ Low mobility and are therefore difficult to extract.

C.​ The highest cost-to-performance ratio.

D.​ A neutral effect on the glass transition temperature 13

B 65)​Where are Citrates and Epoxidized oils often used?

A.​ Aerospace components.

B.​ Food or medical applications due to their non-toxicity.

C.​ High-density automotive fuel tanks.

D.​ Industrial-grade PVC pipes only.

B 66)​The solubility parameter difference between a good plasticizer and the polymer

should be:

A.​ Greater than 10.

B.​ Less than 1.

C.​ Exactly zero.

D.​ Dependent on the pressure flow (Qp).

B 14

QUESTIONS

1)​ How does the glass transition temperature change as a function of the MW

of the polymer? How do polymers behave below and above T ?

G

Usually the glass transition temperature increases as we increase the MW of the chains

because there will be stronger interactions between them, so it is needed as higher energy to

break these forces.

A polymer:

●​ below T will act mainly as a