A growing 2D spherulite and calculus of variations Part II: A 2D spherulite of polypropylene in a linear temperature field

J of Applied Polymer Sci

2002

ABSTRACT:The influence of temperature gradient on the lamellar structure of isotactic polypropylene spherulites was studied. Polypropylene films were crystallized in a constant temperature gradient of 35 K/mm with the free surface and studied by means of atomic force microscopy and scaning electron microscopy. Samples crystallized isothermally were also prepared and examined for comparison. The results show that the temperature gradient influenced only the alignment of lamellae within spherulites. The lamellae deviated from a radial direction in a stepwise manner. The lamellae became less and less inclined and finally assumed a direction parallel to the temperature gradient. The change of the lamellae alignment in spherulites was the result of the competition of lamellae to fill the space during growth in the temperature gradient.

Section: Introductionmentioning

confidence: 56%

Morphology of iPP spherulites crystallized in a temperature gradient

Pawlak

Chapel

J of Applied Polymer Sci

2002

“…It is also known that the temperature gradient leads to anisotropic spherulite growth and shapes and affects the directions of spherulite growth. The growth trajectories bend in the temperature gradient, being normal to the growth front 2–4. The changes in interspherulitic boundary shapes have also been reported 2, 4.…”

Section: Introductionmentioning

confidence: 61%

“…Shulze and Naujack3, 21 derived an analytical equation describing the anisotropic shape of the spherulite and the variable growth directions in a uniaxial field of the growth rate by introducing the condition of the minimum time along the growth lines. The growth lines were always normal to the growth front.…”

Section: Introductionmentioning

confidence: 99%

Modeling of polymer crystallization in a temperature gradient

J of Applied Polymer Sci

2002

ABSTRACT:The crystallization of polymer films in a temperature gradient was simulated. The curvature of lamella growth directions observed experimentally was taken into account. The computer simulation permitted the visualization of the evolution of the spherulitic pattern and also the calculation of the conversion of the melt into spherulites. The mathematical model was also elaborated and allowed the prediction of the kinetics of conversion during the crystallization of polymers in the temperature gradient. A good agreement between the computer simulation results, the mathematical model predictions, and the experimental data for isotactic polypropylene crystallized in a temperature gradient was obtained.

“…[6,7] Spherulites are no longer circular or spherical but exhibit shape anisotropy caused by the temperature dependence of the growth rate. [6,7] Spherulites are no longer circular or spherical but exhibit shape anisotropy caused by the temperature dependence of the growth rate.…”

Section: Introductionmentioning

confidence: 99%

New Possibilities in the Description of Overall Crystallization of Polymers

Journal of Macromolecular Science, Part B

Gałęski

2003

Applications of the probabilistic model of spherulitic structure formation are demonstrated. The model permits prediction of the conversion of melt into spherulites in complicated crystallization conditions, including crystallization in a finite volume, in the presence of reinforcing fibers, and in a temperature gradient. The progression of interspherulitic boundary formation can also be described, thus giving insight into development of the spherulitic pattern. The predictions based on the model are verified by a computer simulation of the spherulitic structure formation. They are also in agreement with experimental data.The modeling of polymer crystallization during cooling of thick-walled products is also reported. The obtained information allows for the geometry of a product and its size to be related with a time and temperature range of polymer crystallization.