Polymer testing: mechanical, thermal and rheological properties

Polymer / Plastics / Rubber Technology (B.Tech) · Testing and characterisation · free study notes for exams, placements and interviews

In short

Polymer testing measures how a plastic or rubber responds to force (mechanical), to heat (thermal) and to flow (rheological), so that a grade can be specified, a mould or die can be designed, and a failure can be explained. Unlike metals, polymers are viscoelastic - their stiffness and strength depend on temperature, time, strain rate and thermal history - so every test result is quoted with its test conditions. In India these tests are run to IS, ASTM and ISO methods in NABL-accredited (ISO/IEC 17025) laboratories, CIPET centres and BIS-recognised labs, and they back the ISI mark on polymer grades and pipes covered by Quality Control Orders. The topic carries heavy marks in university testing-and-characterisation papers and in GATE-type questions on stress-strain behaviour, MFI, Tg/Tm and shear thinning, and it is the core of QC and R&D interviews at Reliance, Supreme, Astral, Finolex, Apollo Tyres, MRF, SRF, JK Tyre, Nilkamal, Sintex and auto Tier-1 moulders.

Explained

Why polymer testing is different - viscoelasticity

A polymer's response = elastic (spring) + viscous (dashpot); modelled by Maxwell (spring and dashpot in series - stress relaxation) and Kelvin-Voigt (parallel - creep) elements, and realistically by a generalised/standard linear solid with a spectrum of relaxation times.
Consequences: creep (strain grows under constant load), stress relaxation (stress decays at constant strain), hysteresis (energy loss per cycle, heat build-up in tyres), time-temperature equivalence (a slow test at low T ≡ a fast test at high T).
Therefore results must always carry temperature, strain rate (or crosshead speed), specimen type, conditioning and moisture state. Standard conditioning is 23 ± 2 °C and 50 ± 5% RH; for India's humid plants, 27 ± 2 °C / 65 ± 5% RH is the alternative tropical atmosphere.
Transitions that govern all behaviour: Tg (glass transition - amorphous chains gain segmental mobility), Tm (crystalline melting), Tc (crystallisation), and for thermosets/rubbers the degree of cure.

Mechanical testing

Tensile (ASTM D638 / ISO 527 for plastics; IS 3400 Part 1 and ISO 37 for vulcanised rubber using dumb-bells). Dumb-bell/Type-I bar in a universal testing machine with extensometer; gives modulus of elasticity, yield stress, yield strain, tensile strength, elongation at break, toughness (area under the curve). Rubber adds modulus at 100/200/300% elongation (M100, M300).
Four typical curve shapes: brittle (PS, PMMA - breaks before yield), ductile with necking and cold drawing (HDPE, PP, nylon), rubber-toughened (HIPS, ABS - stress whitening), elastomeric (low modulus, huge elongation, upturn from strain-induced crystallisation in NR).
Flexural - three-point bend (ASTM D790 / ISO 178). Span-to-depth 16:1, strain rate 0.01 mm/mm/min; gives flexural strength and flexural modulus; preferred for stiff, brittle and filled grades because no gripping damage. Flexural modulus is usually a little higher than tensile modulus.
Compression (ASTM D695) for foams, bearings and rubber pads; rubber also has compression set (IS 3400 Part 10 / ISO 815) - permanent deformation after a fixed compression at fixed temperature and time, the key test for gaskets and seals.
Impact. Izod (ASTM D256 / ISO 180 - cantilever, notched, pendulum strikes the notched face side), Charpy (ISO 179 - simply supported, struck opposite the notch), falling dart / instrumented puncture (ASTM D1709 for film, D5628 for sheet), tensile impact. Notch radius controls the result: a sharper notch gives a lower value because of stress concentration; notch sensitivity is the practical ranking (nylon, POM, PP and PC are all markedly notch sensitive - PC is tough unnotched but needs generous radii - while rubber-toughened grades like ABS and HIPS are far less so).
Hardness. Shore A (soft rubber), Shore D (hard rubber/rigid plastics) per ASTM D2240; IRHD (ISO 48 / IS 3400 Part 2) for rubber, needed for small or curved parts; Rockwell R, L, M scales (ASTM D785) and Ball indentation hardness for rigid plastics; Barcol for FRP.
Tear (IS 3400 Part 17 / ISO 34 - trouser, angle, crescent), abrasion (DIN abrader, IS 3400 Part 3), flex cracking and De Mattia flexing, adhesion of rubber to fabric or metal, rebound resilience, heat build-up (Goodrich flexometer) - the tyre and conveyor-belt set.
Long-term and environmental. Creep rupture and creep modulus (for pressure pipes), fatigue (S-N, with self-heating a real risk), ESCR - environmental stress cracking resistance (bent strip in detergent, ASTM D1693 - critical for HDPE containers and PE pipes), hydrostatic pressure testing of pipes, accelerated ageing in hot air or oxygen bomb (IS 3400 Part 4 / ISO 188), weathering (xenon-arc, QUV) and ozone cracking of diene rubbers.
Fillers and reinforcement move properties in opposite directions: glass fibre raises modulus and strength but cuts elongation and impact; plasticiser and rubber toughening do the reverse.

Thermal testing

DSC (differential scanning calorimetry). Measures heat flow against temperature; gives Tg (step change in heat capacity, read at midpoint), Tm (endothermic peak), Tc (exothermic peak), ΔHm → % crystallinity, oxidation induction time (OIT), and cure exotherm/residual cure of thermosets. Standard heat-cool-heat run: the second heating removes processing history. ASTM D3418 / ISO 11357; DSC measures heat flow, DTA only a temperature difference.
TGA (thermogravimetry). Mass loss against temperature in N₂ or air: moisture and volatiles, onset of decomposition (Tonset, T5%, Tmax from the DTG peak), filler/carbon black and ash content, char residue, and decomposition kinetics (activation energy by Kissinger/Flynn-Wall-Ozawa from several heating rates). ASTM E1131 / ISO 11358.
DMA (dynamic mechanical analysis). Applies oscillating strain and resolves storage modulus E′, loss modulus E″ and tan δ = E″/E′ against temperature or frequency. The most sensitive Tg measurement (tan δ peak or E″ peak - the E′ onset gives a lower value, so always state which), detects secondary β/γ relaxations, filler-matrix coupling, and the rubbery plateau modulus which rises with crosslink density. ASTM D4065 / ISO 6721.
TMA (thermomechanical analysis): dimensional change - coefficient of linear thermal expansion (CLTE) and softening under a probe.
HDT (heat deflection temperature, ASTM D648 / ISO 75): temperature at which a bar under 0.45 MPa (HDT-B) or 1.80 MPa (HDT-A) deflects 0.25 mm at 2 °C/min. Vicat softening temperature (ASTM D1525 / ISO 306): temperature at which a 1 mm² needle under 10 N (A50) or 50 N (B50) penetrates 1 mm. Both are service-temperature indicators, not transitions; semi-crystalline grades show a large gap between HDT-A and HDT-B.
Flammability: LOI - limiting oxygen index (ASTM D2863), the minimum % O₂ in an O₂/N₂ stream that just sustains burning (PVC ~45, PP ~17); UL 94 rating (V-0/V-1/V-2, HB), glow-wire and smoke-density tests; cone calorimetry for heat release rate.
Thermal conductivity and specific heat (guarded hot plate, modulated DSC) for heat-transfer and cooling-time calculations.

Rheological testing

Melt flow index / melt flow rate (ASTM D1238 / ISO 1133). Mass in grams extruded in 10 min through a standard die (2.095 mm × 8 mm) at a set temperature and load - PE at 190 °C/2.16 kg, PP at 230 °C/2.16 kg. It is a single-point, low-shear-rate inverse measure of molecular weight, not a viscosity. The melt flow ratio (MFR = MFI at 21.6 kg / MFI at 2.16 kg) indicates molecular weight distribution and shear sensitivity.
Capillary (extrusion) rheometer. Melt forced through a capillary at known flow rate; wall shear stress from pressure drop and wall shear rate from flow rate; covers the high shear rates of extrusion and injection (10²-10⁵ s⁻¹). Needs the Bagley correction (entrance/exit pressure loss, from several L/D dies) and the Rabinowitsch correction (non-parabolic velocity profile).
Rotational rheometers. Cone-and-plate and parallel-plate (and concentric cylinder for solutions/latex) for low shear rates and oscillatory work: frequency sweep gives G′, G″, tan δ, complex viscosity, the crossover frequency (G′ = G″, which shifts with molecular weight), zero-shear viscosity η₀ ∝ Mw^3.4, and time-temperature superposition with WLF/Arrhenius shift factors to build a master curve.
Flow behaviour. Polymer melts are pseudoplastic (shear thinning): Newtonian plateau at very low shear rate, then a power-law region. Fitted by the power law (Ostwald-de Waele), Carreau or Cross models. Yield-stress behaviour (Bingham, Herschel-Bulkley) appears in highly filled compounds and PVC pastes.
Melt elasticity effects: die swell (extrudate swell), melt fracture/sharkskin, draw resonance, melt strength and extensional viscosity (Rheotens, SER fixture) - decisive for blow moulding, film blowing and thermoforming.
Rubber rheology: Mooney viscometer (ASTM D1646 / ISO 289) reports ML 1+4 at 100 °C - viscosity of the uncured compound, plus Mooney scorch time; oscillating disc (ODR) and moving die (MDR) cure rheometers (ASTM D5289) give the cure curve: ML (minimum torque), MH (maximum torque), ts2 (scorch safety), t90 (optimum cure time), cure rate index; Garvey die extrusion rates extrudability.
Solution viscometry (Ubbelohde capillary) gives intrinsic viscosity [η] and, through the Mark-Houwink relation, viscosity-average molecular weight - the standard route for PET IV and nylon RV.
Cox-Merz rule: steady-shear viscosity at shear rate γ̇ ≈ complex viscosity at angular frequency ω - lets oscillatory data stand in for steady shear.

Standards, laboratories and Indian practice

Indian Standards: IS 3400 (Methods of test for vulcanised rubbers) in many parts - tensile, hardness, abrasion, ageing, tear, compression set; the IS 13360 series (Plastics - Methods of testing), which adopts the ISO methods for tensile, flexural, impact, thermal and flow tests. Product standards call up the test methods, e.g. HDPE pipes for water supply (IS 4984) and PVC-U pipes (IS 4985) specify hydrostatic, reversion, density and MFI checks. Where a particular IS number may have been revised or withdrawn, cite the test by subject and use the current ISO/ASTM method.
BIS certification: a number of polymer resins (PP, PVC, PET, polycarbonate, ABS and others) and plastic products have been brought under compulsory BIS certification through Quality Control Orders issued by the Department of Chemicals and Petrochemicals and other ministries; the covered list and dates have been amended several times, so verify the current QCO schedule before claiming a grade is mandatory. Toys are covered by a QCO requiring ISI marking to the toy safety standards.
Laboratories: CIPET (Central Institute of Petrochemicals Engineering and Technology) centres, BIS laboratories, IRMRA (rubber), and private NABL-accredited labs under ISO/IEC 17025; a plant quality system is normally built to ISO 9001:2026 (current edition), with IATF 16949 for automotive moulders.
Other applicable law and practice: food-contact plastics must meet the Food Safety and Standards (Packaging) Regulations, 2018 with overall and specific migration testing; lab and plant safety now sits under the four Labour Codes in force from 21 November 2025 (the OSH&WC Code replaced the Factories Act), and plastic waste handling under the Plastic Waste Management Rules, 2016 as amended with EPR obligations - the separate Solid Waste Management Rules, 2026 replaced the 2016 SWM Rules from 1 April 2026.
Reporting discipline: report the method and its year, specimen type, conditioning, rate, temperature, number of specimens (usually five, and at least three - five preferred - for rubber tensile), the median for rubber tensile and the mean with standard deviation for plastics.

Key points

Viscoelasticity - polymer response depends on time, rate and temperature, so no result is valid without its test conditions.
Tensile test - gives modulus, yield stress, tensile strength, elongation at break and toughness; ASTM D638/ISO 527 for plastics, ISO 37/IS 3400 Part 1 for rubber.
Flexural test - three-point bend, 16:1 span-to-depth; flexural modulus slightly exceeds tensile modulus.
Izod vs Charpy - Izod is a notched cantilever struck on the notched side; Charpy is simply supported and struck opposite the notch.
Notch sensitivity - a sharper notch lowers impact strength; it is a material ranking, not an error.
Shore A/D and IRHD - hardness scales for rubber and rigid plastics; Shore A for soft, Shore D for hard.
Compression set - permanent deformation of rubber after compression; the governing test for seals and gaskets.
ESCR - cracking under stress plus a chemical environment; the common failure mode of HDPE containers and pipes.
DSC - Tg (step, read at midpoint), Tm, Tc, ΔHm → crystallinity, OIT and residual cure.
TGA - mass loss gives volatiles, decomposition onset, filler/carbon black and ash content.
DMA - E′, E″ and tan δ; the most sensitive Tg method (tan δ peak), and shows crosslink density through the rubbery plateau.
HDT and Vicat - service-temperature indicators under load, not thermodynamic transitions; quote the load (0.45 or 1.80 MPa; 10 or 50 N).
MFI - g/10 min at a stated temperature and load; inversely related to molecular weight; MFR = MFI(21.6)/MFI(2.16) indicates shear sensitivity.
Shear thinning - melt viscosity falls with shear rate; power-law index n < 1 (typically 0.25-0.6 for commodity melts).
Capillary rheometer corrections - Bagley for entrance pressure loss, Rabinowitsch for the real velocity profile.
Cure rheometer (MDR) - ML, MH, ts2 (scorch safety) and t90 (optimum cure time) set the press cycle.
Mooney ML 1+4 at 100 °C - viscosity of uncured rubber compound, used for batch-to-batch control.
η₀ ∝ Mw^3.4 - zero-shear viscosity is a steep function of molecular weight, which is why MFI controls processability.

Formulas and examples

σ = F / A₀ - engineering stress (MPa = N/mm²); F = load (N), A₀ = original cross-section (mm²)
ε = ΔL / L₀ - strain (mm/mm or %); E = σ/ε in the initial linear region (MPa or GPa)
Toughness (energy to break per unit volume) = area under the σ-ε curve (MJ/m³ = J/cm³)
Flexural stress σf = 3FL / (2bd²); flexural modulus Ef = L³m / (4bd³) - L = span, b = width, d = depth (mm), m = slope of load-deflection line (N/mm)
Izod impact strength = E / t (J/m) or E / (b_net × t) (kJ/m²) - E = energy absorbed (J), t = thickness, b_net = width under the notch
Compression set (%) = (t₀ − t₂) / (t₀ − t_s) × 100 - t₀ original, t_s spacer (compressed), t₂ recovered thickness
MFI = (mass extruded in g / cut-off time in s) × 600 - g/10 min at stated T and load
Apparent wall shear rate γ̇_app = 4Q / (πR³) (s⁻¹); wall shear stress τ_w = ΔP·R / (2L) (Pa); apparent viscosity η = τ_w / γ̇_app (Pa·s)
Rabinowitsch: γ̇_true = γ̇_app × (3n + 1) / (4n); power law: τ = m γ̇ⁿ, so η = m γ̇ⁿ⁻¹; n = d(ln τ)/d(ln γ̇)
G* = G′ + iG″; tan δ = G″/G′; complex viscosity η* = G*/ω (Pa·s), ω in rad/s
% crystallinity Xc = ΔHm / (ΔH°m × w) × 100 - ΔHm measured (J/g of sample), ΔH°m of 100% crystal (PE 293, PP 207, PET 140 J/g), w = weight fraction of polymer
WLF shift: log aT = −C₁(T − T_ref) / (C₂ + T − T_ref); Arrhenius: η = A exp(E_a/RT); η₀ ∝ Mw^3.4
Mark-Houwink: [η] = K·Mᵃ - [η] in dL/g, K and a are polymer-solvent-temperature constants

Example 1 - tensile test on an HDPE bar. Specimen 10.0 mm wide × 4.0 mm thick, gauge length 50 mm. Load at yield 1,000 N with 5.0 mm extension; in the initial region 320 N gives 0.40 mm extension; break load 760 N at 300 mm extension.

A₀ = 10.0 × 4.0 = 40 mm².
Yield stress = 1,000/40 = 25 MPa; yield strain = 5.0/50 = 0.10 = 10%.
Initial point: σ = 320/40 = 8 MPa, ε = 0.40/50 = 0.008 → E = 8/0.008 = 1,000 MPa = 1.0 GPa.
Stress at break = 760/40 = 19 MPa; elongation at break = 300/50 = 600%.
Note the shape: stress falls after yield (necking), then the neck propagates - classic ductile semi-crystalline behaviour. The 19 MPa is lower than the 25 MPa yield only in engineering stress; true stress keeps rising.

Example 2 - notched Izod impact. ISO specimen 10.0 mm deep × 3.2 mm thick, notch depth 2.0 mm, energy absorbed 1.20 J.

Per unit thickness: 1.20 / 0.0032 m = 375 J/m (ASTM convention).
Net width under notch = 10.0 − 2.0 = 8.0 mm → net area = 8.0 × 3.2 = 25.6 mm² = 25.6 × 10⁻⁶ m².
Impact strength = 1.20 / 25.6 × 10⁻⁶ = 46,875 J/m² = 46.9 kJ/m² (ISO convention). Always state which convention - the numbers are not interchangeable.

Example 3 - capillary rheometer and power-law index. Die R = 0.50 mm, L = 20 mm. Run 1: Q = 60 mm³/s, ΔP = 10 MPa. Run 2: Q = 600 mm³/s, ΔP = 25 MPa.

Run 1: γ̇_app = 4 × 6.0 × 10⁻⁸ / (π × (5 × 10⁻⁴)³) = 2.4 × 10⁻⁷ / 3.927 × 10⁻¹⁰ = 611 s⁻¹; τ_w = (10 × 10⁶ × 5 × 10⁻⁴)/(2 × 0.020) = 1.25 × 10⁵ Pa; η = 125,000/611 = 205 Pa·s.
Run 2: γ̇_app = 6,110 s⁻¹; τ_w = (25 × 10⁶ × 5 × 10⁻⁴)/0.040 = 3.125 × 10⁵ Pa; η = 312,500/6,110 = 51 Pa·s.
n = ln(3.125/1.25) / ln(6,110/611) = ln 2.5 / ln 10 = 0.916/2.303 = 0.40 → strongly shear thinning; m = τ/γ̇ⁿ = 125,000 / 611^0.40 = 125,000/12.9 = ≈9.7 kPa·sⁿ.
Rabinowitsch at run 1: γ̇_true = 611 × (3 × 0.40 + 1)/(4 × 0.40) = 611 × 2.2/1.6 = 840 s⁻¹, so the corrected viscosity is 125,000/840 = 149 Pa·s. The uncorrected value overstates viscosity by about 37%.

Example 4 - crystallinity of a filled PE from DSC. Sample 10.0 mg, melting endotherm 1.60 J, 20% CaCO₃ by weight.

ΔHm = 1.60 J / 0.0100 g = 160 J/g of sample.
Ignoring filler: Xc = 160/293 × 100 = 54.6% (wrong - filler does not melt).
Correct: Xc = 160 / (293 × 0.80) × 100 = 160/234.4 × 100 = 68.3% of the polymer fraction.

Example 5 - MFI and compression set.

MFI: 0.42 g collected in a 30 s cut-off at 190 °C/2.16 kg → MFI = 0.42 × 600/30 = 8.4 g/10 min - an injection-moulding grade (film grades run below ~1).
Compression set: t₀ = 12.50 mm, spacer 9.375 mm (25% compression), recovered t₂ = 11.80 mm after 22 h at 70 °C → set = (12.50 − 11.80)/(12.50 − 9.375) × 100 = 0.70/3.125 × 100 = 22.4%. A nitrile O-ring specification of "≤25%" is met.

Property	Test	Standard	Reported as
Tensile strength, elongation	Dumb-bell in UTM	ASTM D638 / ISO 527; ISO 37, IS 3400 Pt 1 (rubber)	MPa, %
Flexural strength/modulus	3-point bend	ASTM D790 / ISO 178	MPa, GPa
Impact strength	Notched pendulum	ASTM D256 / ISO 180, 179	J/m or kJ/m²
Hardness	Durometer / IRHD / Rockwell	ASTM D2240, ISO 48, ASTM D785	Shore A/D, IRHD, R-scale
Compression set	Compressed plug, hot air	ISO 815 / IS 3400 Pt 10	%
Tg, Tm, crystallinity	DSC	ASTM D3418 / ISO 11357	°C, J/g, %
Decomposition, filler	TGA	ASTM E1131 / ISO 11358	°C, wt %
E′, E″, tan δ, Tg	DMA	ASTM D4065 / ISO 6721	MPa, - , °C
Deflection temperature	HDT	ASTM D648 / ISO 75	°C at 0.45 / 1.80 MPa
Softening point	Vicat	ASTM D1525 / ISO 306	°C at 10 / 50 N
Melt flow	Extrusion plastometer	ASTM D1238 / ISO 1133	g/10 min
Melt viscosity curve	Capillary / rotational	ASTM D3835, D4440	Pa·s vs s⁻¹
Uncured rubber viscosity	Mooney	ASTM D1646 / ISO 289	ML 1+4 @100 °C
Cure characteristics	MDR rheometer	ASTM D5289	ML, MH, ts2, t90

Technique	Measures	Typical use
DSC	Heat flow	Tg, Tm, crystallinity, cure, OIT
TGA	Mass	Filler and ash content, thermal stability
DMA	Modulus under oscillation	Tg, damping, crosslink density
TMA	Dimension	CLTE, softening

Where it is used

Polyolefin and PVC producers (Reliance, GAIL, Haldia, Finolex, Chemplast) - MFI, density, tensile, ESCR and DSC on every production lot before grade release.
Pipes, fittings and water tanks (Supreme, Astral, Prince, Sintex) - hydrostatic pressure, reversion, OIT (for PE pipe oxidative life), MFI and impact to IS 4984 / IS 4985 with BIS surveillance.
Tyre and rubber goods plants (MRF, Apollo, JK Tyre, CEAT, TVS Srichakra) - Mooney and MDR rheometry on every compound batch, plus tensile, hardness, tear, abrasion, heat build-up and ageing; compound labs are the standard entry role for Rubber Technology graduates.
Automotive Tier-1 moulders and OEM labs - HDT, Vicat, flexural modulus, CLTE, DMA and fogging/odour testing against OEM material specifications under IATF 16949.
Packaging and medical devices - dart impact, seal strength, migration testing under the FSS (Packaging) Regulations, 2018, and sterilisation-ageing checks.
Roles and institutions - QC/QA chemist, compounding and formulation engineer, failure-analysis engineer, applications engineer and R&D rheologist; CIPET centres, IRMRA, BIS labs, NABL-accredited third-party labs and institute testing facilities.

Interview questions

Q: Why must the temperature and strain rate be reported with a tensile result? A: Polymers are viscoelastic, so modulus and strength rise with strain rate and fall with temperature; without conditions the number cannot be compared or reproduced.
Q: What is the difference between HDT and Tg? A: Tg is a true relaxation transition in the amorphous phase; HDT is an empirical deflection temperature under a stated load and only indicates a practical service limit.
Q: MFI is 2 for grade A and 20 for grade B - what does that tell you? A: Grade B has far lower molecular weight and viscosity, so it flows easily (thin-wall injection moulding), while grade A is tougher, has better ESCR and suits film or pipe.
Q: Why is MFI not a viscosity? A: It is a single-point mass flow at one low shear rate and one load; since melts are shear thinning, two grades with the same MFI can behave very differently at injection shear rates.
Q: Which test gives the most sensitive Tg and why? A: DMA - the drop in storage modulus near Tg is two to three orders of magnitude, far larger than the small heat-capacity step DSC detects, so DMA resolves Tg in highly filled or crosslinked samples.
Q: What are ts2 and t90 on a cure curve and why do they matter? A: ts2 is scorch safety - the time before cure starts, which must exceed the mould-filling time; t90 is the time to 90% of maximum torque, used to set the press cure cycle.
Q: Why is the Rabinowitsch correction needed? A: The apparent shear rate assumes a parabolic (Newtonian) velocity profile; a shear-thinning melt has a flatter profile with a higher real wall shear rate, so the uncorrected viscosity is too high.
Q: A nylon part passed impact testing on receipt and cracked in the field. What would you check? A: Moisture conditioning - dry-as-moulded nylon is brittle, and conditioned nylon is tough; also check notch/weld-line position, filler orientation and ageing.
Q: How do you get crystallinity from DSC, and what is the usual error? A: Divide the measured melting enthalpy by the 100% crystal enthalpy; the usual error is forgetting to divide by the polymer weight fraction when filler is present.
Q: Why are rubber tensile results reported as a median rather than a mean? A: Rubber tensile data scatter widely because failure is flaw-controlled, so the median of the (at least three, preferably five) test pieces is a more robust statistic than the mean, which a single low flaw-driven break would drag down.
Q: What does a rising tan δ at service temperature mean for a tyre? A: Higher hysteresis - more heat build-up and rolling resistance; low tan δ at ~60 °C is wanted for fuel economy, while high tan δ at ~0 °C is wanted for wet grip.
Q: How does TGA distinguish carbon black from mineral filler? A: Run in nitrogen to decompose the polymer, then switch to air at high temperature - carbon black burns off as a further mass loss, leaving only inorganic ash.

Common mistakes

Quoting a modulus, strength or MFI without the temperature, load, rate or specimen type - the figure is then meaningless.
Treating HDT or Vicat as Tg or Tm, or comparing HDT values measured at different loads.
Mixing Izod conventions - J/m and kJ/m² differ by the net width under the notch, and the two numbers are not interchangeable.
Computing crystallinity from the sample enthalpy without correcting for filler or additive content, or taking Tg from the first DSC heating scan where processing history and moisture distort it.
Forgetting the Bagley and Rabinowitsch corrections in capillary rheometry, and quoting apparent viscosity as true viscosity.
Unit slips - MPa versus N/m², mm³/s versus m³/s, g/10 min read as g/min, rad/s versus Hz in oscillatory data.
Testing nylon, PET or PC without proper conditioning or drying, and ignoring the standard 23 °C/50% RH (or tropical 27 °C/65% RH) atmosphere.
Assuming Shore A and Shore D readings can be converted by a simple factor, or taking hardness on a part too thin or too curved for the method.