Flow induced crystallization of LDPE nanocomposites: A rheological and morphological characterization

Abstract

Abstract:The flow induced crystallization behaviour of a LDPE:PE-g-MA:D72T 90:9:1 nanocomposite has been investigated by in-situ Rheo-SALS technique and data have been compared with those obtained from a reference LDPE:PE-g-MA 90:9 sample. Rheo SALS results, confirming thermal analysis findings, indicate that under mild shear flow fields the organoclay exhibits a negligible nucleating effect. Both nucleation density and, as a consequence, crystallization rate, are not appreciably affected by the application of external flow field for both the examined systems, revealing that no evident synergic effects between the organoclay and the shear flow are present. On the other hand, Rheo SALS analysis indicates that the nanocomposite submitted to flow exhibits a higher level of crystal orientation. TEM morphological analyses support this observation suggesting that the orientation of the nanofiller along the flow direction templates the growth of oriented crystals.

Distributive mixing of carbon nanotubes in poly(caprolactone) via solution and melt processing: Viscoelasticity and crystallization behavior versus mixing indices

“…CNTs can act as heterogeneous nucleating agents and accelerate the rate of crystallization under flow, leading to modification of the morphology of the crystallites which form upon flow‐induced crystallization . This is consistent with the overall finding that the heterogeneous nucleation facilitated by the presence of the CNTs, even in the absence of flow, reduces the energy barrier required for polymer crystallization . Clearly the distribution of the CNTs should play a significant role in the flow induced crystallization of PCL, a subject that has not to date been investigated.…”

On the Effect of Particle Size, Shape, Concentration, and Aggregation on the Flow-Induced Crystallization of Polymers

“…This enhancement can be accomplished in several ways. In the case of strongly nucleating fibers or platelets, nuclei formed on the surface are less restricted in the direction perpendicular to it, and will hence form a typical columnar layer which is known as transcrystallinity. , When flow is applied onto a polymer containing such fillers, these become oriented in the flow direction, and hence template oriented crystallization through lamellar growth perpendicularly onto the fibril surface, even if flow-induced orientation or stretch of the matrix is absent or weak. − The enhancement of orientated crystallization in particle-containing polymers has also often been ascribed to a reinforcing of the flow effect by the particles, resulting from a specific interaction or synergy between the particles and the surrounding polymer matrix. The suggested mechanisms for this synergy include stress amplification of the flow by the particles ,, or anchoring of polymer chains on the particle surface. ,,− The former term indicates the reinforcing of the flow effect on the polymer kinetics and morphology by local stresses generated around the particles during the application of flow.…”