Meaning
Microstructural dimensions of the folded-chain crystals in a semi-crystalline polymer determine its physical behavior. Lamellar thickness refers to the height of these crystalline plates, which are separated by amorphous regions. This value is a fundamental characteristic that influences the melting temperature and the mechanical stiffness of the resin.
Variations in this thickness occur based on the cooling conditions and the molecular weight of the polymer.
Crystallinity Degree
Total volume fraction of the crystalline phase is closely linked to the size and arrangement of the lamellae. A higher lamellar thickness generally correlates with a higher overall degree of crystallinity and a more rigid material. This relationship is required for applications demanding high chemical resistance and low permeability.
Measurable shifts in the thickness of these plates can lead to significant changes in the optical clarity of the finished part.
Yield Stress
Resistance to permanent deformation is governed by the energy required to disrupt the crystalline plates. Increased lamellar thickness raises the yield stress of the polymer, making it harder to stretch or bend. This property is useful for load-bearing components like gears or hinges.
During a tensile test, the lamellae must be pulled apart or reoriented, a process that absorbs energy and defines the toughness of the material.
Annealing Effect
Post-moulding heat treatment provides the thermal energy necessary for the crystals to thicken and reorganize. This process increases the lamellar thickness and relieves internal stresses that were frozen in during the initial cooling. Annealing is often used to stabilize the dimensions of a part and to improve its long-term performance at high temperatures.
The specific temperature and duration of the treatment must be carefully controlled to avoid degrading the polymer chains. Thick lamellar structures provide the best resistance to creep under constant load.
