Polymer Crystallization

At low supercooling, the crystallization behavior of PA11/PA12 random copolymers is typical for eutectic systems, involving segmental segregation and crystallization into separate PA11 and PA12 crystals. At high supercooling, the PA11 and PA12 sequences cocrystallize into mesomorphic solid solutions. Mesomorphic and crystalline matter grow simultaneously over a rather wide intermediate temperature range.

For poly(4-methyl-1-pentene) (P4MP1) with high orientation, an enlargement of the density contrast between crystalline phase and amorphous phase can be observed before voids were induced during solid-state stretching. For P4MP1 with random orientation, the longitude direction of voids was perpendicular to the stretching direction once they were formed, and then transferred to stretching direction at larger deformation. In addition, two types of voids were observed concerning the existence of fibrils within the voids.

A miscible mixture of stereoisomeric isotactic and syndiotactic polypropylene (iPP and sPP) block chains confined within the common lamellar microdomains formed highly defective crystalline domains, in which iPP and sPP crystallites intervened each other. These crystallites exhibited low melting points due to an excess surface free energy.

Molecular simulation is an effective method to investigate molecular mechanisms of polymer crystallization. Based on the molecular simulation, the crystallization behaviors of polymer nanocomposites, such as crystallization rate, nucleation process, conformational change, and crystalline morphology, can be directly observed, and then the corresponding effects of nanofillers on polymer crystallization can be successfully revealed.

Concerning polymer/montmorillonite (MMT) nanocomposites, the presence or absence of organic modifier on the surface of silicate layers determines the type and intensity of the interaction between the matrix and nanofiller. In turn, such interaction is one of the key parameters governing the nanostructure, as well several properties of the obtained material. In this way, a model comprising the presence/absence of organic modifier, nanostructure, and final properties is proposed for a typical polyamide-based nanocomposite.

The dielectric constant and vapor pressure of the spinning solvent influenced the crystallization behavior of PEO, in PS/PEO blend electrospun nanofibers.

A key experiment demonstrates that tailoring the morphology of XLPE offers enormous potential to favorably influence the space charge accumulation under HVDC fields. It is shown that crystallizing XLPE constrained to an optimized oriented morphology already reduces the field exposure by a factor of 4.