Deconvolution Protocols for Melt Crystallization Peaks in Recyclate Blends
Deconvolution of DSC melt crystallization peaks isolates PE and PP fractions in recyclates to verify composition before compounding.
Melt Crystallization
Meaning
Solidification process for polymers involves the transformation from a disordered liquid state to a structured crystalline solid upon cooling. Melt crystallization defines the time and temperature window required for a part to reach its final density and dimensions within the mould. During this phase, polymer chains disentangle from the melt and fold into ordered domains.
The speed of this process is a function of both the resin chemistry and the presence of any nucleating agents.
Thermodynamic Driving Force
Supercooling, which is the difference between the equilibrium melting point and the actual temperature of the resin, initiates the nucleation and growth of crystals. As melt crystallization proceeds, the material releases latent heat which must be removed by the mould cooling system. If the cooling is uneven, the resulting crystallinity will vary, leading to internal stresses and potential part warpage.
Economic Consequence
Reduction of cycle time relies on accelerating this phase without sacrificing the required mechanical properties. Fast-crystallizing resins like polybutylene terephthalate allow for rapid ejection, whereas slow-crystallizing polymers require longer cooling times or heated moulds.
Part Specification
Final shrinkage is determined by the total volume change during this transition. This value must be factored into the tool design to ensure dimensional accuracy.