Meaning
Microstructural phase partitioning in semi-crystalline polymers rejects non-crystallisable species from growing lamellar crystal fronts into the intervening amorphous regions. During resin cooling from the molten state, inter lamellar segregation concentrates short-chain branches, atactic segments, low-molecular-weight fractions, and soluble additives into disordered gaps between adjacent crystalline plates. This spatial exclusion governs the local density, mechanical tie-molecule concentration, and long-term environmental stress crack resistance of the solidified matrix.
The segregation mechanism terminates when rapid thermal quenching vitrifies the amorphous phase into a rigid glass, freezing molecular migration before spatial equilibrium occurs.
Morphology Growth
Polymer crystallisation begins with folded chain lamellae growing radially outwards from nucleation sites to form higher-order spherulites. High-molecular-weight chains containing high short-chain branching frequencies cannot enter the regular orthorhombic or monoclinic crystalline lattices due to steric hindrance. The growing crystal faces push these irregular segments forward, crowding them into the narrow interlamellar boundary zones.
Entanglement density inside these confined regions dictates the number of tie molecules spanning adjacent lamellae. Slower cooling rates grant polymer chains extended time to diffuse, intensifying the degree of chemical segregation between lamellar planes.
Moulding Influence
Melt temperature settings and mould cooling profiles directly set the spatial scale of this segregation within injection-moulded components. Moulders using elevated cavity surface temperatures slow local solidification, driving extensive segregation into thick part cores while rapid skin cooling retains a disordered, non-segregated morphology. Excessive segregation within the core leaves interlamellar regions starved of tie molecules, creating microscopic mechanical planes vulnerable to crack propagation under environmental stress.
Selecting nucleation agents alters segregation kinetics by multiplying crystal nucleation points, which reduces final spherulite dimensions and disperses non-crystallisable chains evenly throughout the bulk.
Mechanical Impact
Tensile performance and slow crack growth resistance depend directly on the structural composition of the interlamellar space. Post-consumer regrind resins containing diverse comonomer distributions and thermal degradation products suffer acute segregation during processing. Degraded low-molecular-weight fractions partition aggressively into the interlamellar regions, plasticising or embrittling these zones while weakening inter-crystalline mechanical coupling.
Part failures under constant mechanical load or detergent exposure trace directly to weak, segregated interlamellar zones that yield before the adjacent crystalline lamellae undergo plastic deformation. Material qualification procedures evaluate stress crack longevity to confirm that processing conditions prevent excessive interlamellar segregation in critical structural mouldings.
