Realizing the enhancement of interfacial interaction in semicrystalline polymer/filler composites via interfacial crystallization

Critical examination finds that the longest chains play a catalytic role in the formation of shish kebabs recruiting other chains into the formation of this morphology. The longest chains in an ensemble are stretched by shear flow to form the “shish” upon which the bulk of the material crystallizes as “kebabs”. A universal parameter for the formation of shish kebab structures, the specific mechanical work, and a method by which it may be measured for any given ensemble of polymers is provided. In rotating parallel-plate flow a clear boundary is observed between oriented and unoriented material which is dependent on both the shear rate and the total strain. It has been found that the necessary conditions for the formation of oriented nuclei is that the shear rate should be larger than the inverse Rouse time of the longest chain in the ensemble and that mechanical work above a critical threshold is required. The experimental procedure required to make such measurements, and the precautions necessary to avoi...

Control of Structural Morphology in Shear-Induced Crystallization of Polymers

Shish–kebab of polyolefin by “melt manipulation” strategy in injection-molding: A convenience pathway from fundament to application

Quiescent and shear-induced crystallizations were performed on several well-defined linear monodisperse hydrogenated polybutadiene blends with a high-molecular-weight long-chain branched (LCB) comb-shaped additive. The connection between microscopic molecular motion and crystallization kinetics has been quantitatively studied with respect to the formation of either isotropic or oriented shish kebab crystal morphology using time-resolved X-ray scattering techniques. Using a constant preshear rate, the addition of small amounts of LCB combs to the sample blends, at concentrations below and just above the overlap concentration c*, has significantly increased the crystallization rates compared to quiescent conditions. However, only one blend showed the formation of an oriented shish kebab morphology. Also, for these model blends, the transition between isotropic and oriented crystals occurs quite sharply between 5 and 10%, which is around c*. We explain these data by using a shish formation mechanism in which...

Shear-Induced Crystallization in Blends of Model Linear and Long-Chain Branched Hydrogenated Polybutadienes

Kinetics of polymer crystallization under processing conditions: transformation of dormant nuclei by the action of flow

A novel extensional rheometer for creep experiments has been presented in part I. The device can be used also for an investigation of the influence of short term elongational flow on the structure development in crystalline polymers. It enables the application of defined portions of mechanical work to the polymer sample in its state of undercooled melt. For the purpose short-term elongational creep is used. With increasing mechanical work the number density of nuclei in iPP increases by decades. Results, as previously obtained with shear flow, are introduced for comparison. Prospects of a theoretical description are discussed.

E. Ratajski

Papers

New extensional rheometer for creep flow at high tensile stress. Part II. Flow induced nucleation for the crystallization of iPP