T9 · Testing / StandardsPolymer Testing & Quality ControlGATE 2027 Syllabus (XE5)Shop-Floor Standard

DSC Degree of Crystallinity Percentage Formula

Determines the weight percentage degree of crystallinity (Xc) in semi-crystalline polymers from Differential Scanning Calorimetry (DSC) endothermic melting enthalpy and cold crystallization enthalpy.

Mathematical Canonical Relation

X_c = \frac{\Delta H_m - \Delta H_{cc}}{\Delta H_m^0 \cdot (1 - w_f)} \times 100

Plain Formula: Xc = [ (Delta Hm - Delta Hcc) / (Delta Hm0 * (1 - wf)) ] * 100

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Melting Enthalpy Delta Hm (J/g) (J/g)

dH_m

Range: 10 – 250 J/g

Cold Cryst. Delta Hcc (J/g) (J/g)

dH_cc

Range: 0 – 80 J/g

100% Cryst. Delta Hm0 (J/g) (J/g)

dH_zero

Range: 50 – 300 J/g

Filler Weight Fraction (0-0.5) (fraction)

w_filler

Range: 0 – 0.5 fraction

Calculated Engineering Result:

Xc = 47.5%

Engineering Verification:Net heat of fusion: 98.4 J/g.

When & Where to Apply

Use when analyzing polymer morphology, injection molding cooling rates, annealing effects, and barrier/mechanical stiffness properties.

Common Engineering Pitfalls

Ignoring cold crystallization enthalpy Delta Hcc in PET or PLA
Forgetting to subtract inorganic filler weight fraction (1 - wf) in glass-filled compounds

Physical Assumptions & Validity Limits

Known theoretical 100% crystalline enthalpy Delta Hm0 from literature
Linear or sigmoidal baseline subtraction across melting transition peak
Accurately determined inorganic filler weight fraction wf

Variable Symbols, SI Units & Dimensional Specifications

Symbol	Variable Meaning	SI Unit	Typical Industrial Range
X_c	Degree of crystallinity	%	—
\Delta H_m	Measured melting enthalpy peak area	J/g	95.5
\Delta H_{cc}	Cold crystallization enthalpy (if present)	J/g	0.0
\Delta H_m^0	Melting enthalpy of 100% crystalline polymer	J/g	207.1
w_f	Weight fraction of non-crystallizable filler/reinforcement	fraction	0.0

Worked Industrial Numerical Example: Isotactic Polypropylene (iPP) DSC Crystallinity Measurement

Problem Statement:

A moulded Polypropylene sample displays a DSC melting peak enthalpy Delta Hm = 98.4 J/g. Given that 100% crystalline iPP has Delta Hm0 = 207.1 J/g and the sample has no filler (wf = 0), calculate Xc.

Step-by-Step Numerical Solution:

Apply formula: Xc = (Delta Hm - Delta Hcc) / (Delta Hm0 * (1 - wf)) * 100
Substitute values: Xc = (98.4 - 0) / (207.1 * 1.0) * 100
Calculate: 98.4 / 207.1 * 100 = 47.51%

Final Answer: Xc = 47.5%

💡 Engineering Interpretation: The moulded PP part has 47.5% crystalline lamellae, providing the expected balance of flexural modulus (>1300 MPa) and impact toughness.

Authoritative Technical Reference & Source Provenance

Thermal Analysis of Polymers: Fundamentals and Applications by Joseph D. Menczel (Wiley, 2009), 1st Edition, Page 112-118.

Connected Curriculum Lesson

DSC & TGA Crystallinity & Thermal Degradation

Study Full Lesson