Isothermal and nonisothermal crystallization of isotactic polypropylene/graphene oxide nanosheet nanocomposites

Unveiling the Nanoconfinement Effect on Crystallization of Semicrystalline Polymers Using Coarse-Grained Molecular Dynamics Simulations

Semicrystalline polymers under nanoconfinement show distinct structural and thermomechanical properties compared to their bulk counterparts. Despite extensive research on semicrystalline polymers under nanoconfinement, the nanoconfinement effect on the local crystallization process and the unique structural evolution of such polymers have not been fully understood. In this study, we unveil such effects by using coarse-grained molecular dynamics simulations to study the crystallization process of a model semicrystalline polymer-polyvinyl alcohol (PVA)-under different levels of nanoconfinement induced by nanoparticles that are represented implicitly. We quantify in detail the evolution of the degree of crystallinity (XC) of PVA and examine distinct crystalline regions from simulation results. The results show that nanoconfinement can promote the crystallization process, especially at the early stage, and the interfaces between nanoparticles and polymer can function as crystallite nucleation sites. In general, the final XC of PVA increases with the levels of nanoconfinement. Further, nanoconfined cases show region-dependent XC with higher and earlier increase of XC in regions closer to the interfaces. By tracking region-dependent XC evolution, our results indicate that nanoconfinement can lead to a heterogenous crystallization process with a second-stage crystallite nucleation in regions further away from the interfaces. In addition, our results show that even under very high cooling rates, the nanoconfinement still promotes the crystallization of PVA. This study provides important insights into the underlying mechanisms for the intricate interplay between nanoconfinement and the crystallization behaviors of semicrystalline polymer, with the potential to guide the design and characterization of semicrystalline polymer-based nanocomposites.

Microstructure and Mechanical Properties of Nanocomposite Based on Polypropylene/Ethylene Propylene Diene Monomer/Graphene

Polypropylene (PP)/ethylene propylene diene monomer (EPDM)/ graphene nanosheets (GNs) were compounded by a two-step melt mixing process via an internal mixer (brabender plasticorder). The effect of GNs, graphene oxide (GOSs) and graphene oxide functionalized with PP chains (PP-g-GOSs) on various blend properties were investigated. Wide X-ray diffraction (WAXD) patterns and transmission electron microscopy (TEM) images of the prepared nanocomposites revealed that the nanofillers were mostly dispersed into the PP phase and the dispersion state of GNs was improved with functionalization of graphene. SEM photomicrographs indicated that rubber droplets were distributed in the PP phase and a reduction of the dispersed EPDM droplet size was observed most likely due to increase in the viscosity of the PP-phase during melt mixing. The effects of nanofillers on thermal, mechanical and rheological properties were reported, and the obtained results were discussed in terms of morphology, state of dispersion and distribution of the nanofillers within the PP matrix. As for the mechanical properties, an improvement of 56% in tensile modulus and 48% in tensile strength, while 72% reduction in elongation at break was observed. The DMTA results revealed that the nanocomposites based on PP-g-GOSs had lower damping behavior and the intensity of the loss factor decreased by increasing the GNs content. These results indicate the presence of a strong interfacial interaction between the nanoplatelets and the polymer matrix.

Crystallization behavior of functional polypropylene grafted graphene oxide nanocomposite

With an aim to understand a role of grafted graphene oxide (GO) in crystallization process of polymer, isothermal and non-isothermal crystallization behaviors of a functional polypropylene grafted GO nanocomposite were investigated systematically.

Greatly enhanced porosity of stretched polypropylene/graphene oxide composite membrane achieved by adding pore-forming agent

With the combined effects of a pore-forming agent and graphene oxide, greatly enhanced porosity is achieved for a stretched PP composite membrane.