Understanding the Growth Rates of Polymer Cocrystallization in the Binary Mixtures of Different Chain Lengths: Revisited

Comparative experimental and modelling study of the thermal and thermo-mechanical properties of LLDPE/wax blends

The interactions and morphology of molecules in a polymer blend influence the physical properties of the blend. However, little is known about the influence of molecular interaction and morphology on the thermal and mechanical properties of LLDPE/wax blends. Although cooling rate can be used to investigate blends' thermal and mechanical properties, it is inadequate to determine interactions between the molecules in the LLDPE/wax blends. However, since the morphology is related to the thermal and mechanical properties of polymer blends and could be related to the cooling rate, LLDPE/wax samples prepared by melt mixing were cooled at different rates. The thermal and mechanical properties of the LLDPE/wax blends were modelled through molecular dynamic simulations. The modelled transitions were compared to experimentally determined mechanical relaxations of LLDPE/wax blends to investigate the effect of wax addition on the blend crystallinity. The crystallization behaviour of the blends was studied by differential scanning calorimetry, dynamic mechanical behaviour by dynamic mechanical analysis, and differences in crystallinity by X-ray diffraction. There were no significant differences between the results for the slow- and quench-cooled samples, confirming the rapid crystallization of both the LLDPE and the wax. Experiments and molecular dynamics simulations confirmed the cocrystallization of wax with LLDPE.

Intramolecular Crystal Nucleation Favored by Polymer Crystallization: Monte Carlo Simulation Evidence

We performed dynamic Monte Carlo simulations of half-half binary blends of symmetric (double and mutual) crystallizable polymers. We separately enhanced the driving forces for polymer-uniform and polymer-staggered crystals. Under parallel enhancements, polymer-uniform crystals exhibit faster nucleation and growth, with more chain folding and less lamellar thickening, than those in polymer-staggered crystals. We attributed the results to intramolecular crystal nucleation, ruined by enhanced polymer-staggered crystallization. Our observations provide direct molecular-level evidence to support the fact that intramolecular crystal nucleation is favored by polymer crystallization in quiescent solutions and melt, which yields chain folding for the characteristic β-sheet or lamellar morphology of macromolecular crystals.