Crystallinity in Polymers Sheaf-like arrangement of lamellae in a blend of polyethylenes System: Polyethylene (PE), Composition: LPE:BPE 3:1 An image of an alkane crystal taken by AFM System: Alkane, Composition: C36H74 An image of a single crystal alkane System: Alkane, Composition: C294H590 Single PE spherulite AFM Maltese cross spherulites
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Crystallinity in Polymers Sheaf-like arrangement of lamellae in a blend of polyethylenes System: Polyethylene (PE), Composition: LPE:BPE 3:1 An image of.
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Crystallinity in Polymers
Sheaf-like arrangement of lamellae in a blend of polyethylenesSystem: Polyethylene (PE), Composition: LPE:BPE 3:1
An image of an alkane crystal taken by AFMSystem: Alkane, Composition: C36H74
An image of a single crystal alkaneSystem: Alkane, Composition: C294H590
Single PE spherulite AFM
Maltese cross spherulites
Thermodynamics of melting and crystallization: First order transitions
Amorphous v Crystalline Polymers Thermo-mechanical properties
Density Increase
Pro
pert
y
Shrinkage, Stiffness, Tensile strength, Hardness, Heat deflection, Chemical resistance
Weatherability
Impact strength, Ductility
Low density polyethylene (LDPE) 915-929 45-65Medium density polyethylene (MDPE) 930-939 65-75High density polyethylene (HDPE) 940-965 75-90
Polymers generally have crystalline and amorphous contributions
Lamellar Structure of Polymer crystals
Polymer single crystals: Graduate students nightmare
Still lamellar structures
Validation of Models
Dislocations in Polymer Crystals
From singhle crystals to Aggregate structures
Polyethylene Spherulites
Spherulite Growth from Lamellar crystals
TEM of spherulite structure in natural rubber(x30,000).• Chain-folded lamellar crystallites (white lines) ~10nm thick extend radially.
Crystalline structures in polymers
crystallineregionamorphousregion
• % Crystallinity: % of material that is crystalline. --TS and E often increase with % crystallinity. --Annealing causes crystalline regions to grow. % crystallinity increases.