Meaning
Crystallization rate equations model radial growth rates of spherical crystalline aggregates expanding into supercooled polymer melts. Analyzing spherulitic growth kinetics determines the time required for crystal boundaries to collide and complete solidification during mold cooling. Datasheet isothermal crystallization data must be translated to non-isothermal cooling conditions present in industrial molds.
Growth velocity peaks between glass transition and melting temperatures, where chain mobility balances thermodynamic driving forces.
Growth Mechanism
Radial expansion proceeds as crystalline lamellae branch and fan outward from central primary nuclei. Chain-folding kinetics at the growing front dictate radial growth rate, which remains constant under isothermal conditions until impinging on neighboring spherulites. Higher undercooling accelerates nucleation rate relative to growth velocity, producing smaller spherulites.
Thermal dissipation limits dictate local crystal growth speeds in thick part sections.
Morphological Limit
Unchecked growth forms large spherulites with distinct inter-spherulitic boundaries where impurities and low molecular weight chains concentrate. Micro-cracks initiate easily along these weak boundary planes under impact loading. Adding clarifying or nucleating agents increases nucleation density, arresting individual spherulite growth before large crystalline domains develop.
Regrind contamination introduces irregular nucleation sites, disrupting uniform radial growth patterns.
Performance Outcome
Controlling crystal aggregate growth rates optimizes optical clarity and impact resistance in semi-crystalline parts. Fine spherulitic structures enhance flexural modulus while maintaining structural ductility. Kinetic control secures consistent mechanical properties across varying wall thicknesses.
