Understanding the effect of silica nanoparticles and exfoliated graphite nanoplatelets on the crystallization behavior of isotactic polypropylene

Abstract

This study explores how the presence of nanofillers with different structural and chemical characteristics, specifically silica nanoparticles and exfoliated graphite nanoplatelets (GNP), alters the crystallization behavior and polymorphism of a semicrystalline polymer, such as polypropylene (PP). The main focus of this research is to investigate how silica and GNP affect the nucleation and growth of PP crystals during isothermal crystallization. The nonisothermal crystallization behavior, including crystal structures, crystallization temperature, and rate, is also determined. PP composites with nanomaterial content up to 7 wt% were produced by melt mixing and injection molding. Both silica and graphite were found to be effective nucleating agents, significantly increasing the crystallization rate during isothermal crystallization, with greater changes observed in case of GNP composites. The effect of filler type and amount on the PP polymorphism and lamella thickness was studied by X‐ray diffraction and modulated differential scanning calorimetry. Both silica and graphite were found to be effective nucleating agents for the less common β‐phase of PP crystals even at low nanomaterial concentration. α‐−crystal perfection and the recrystallization of the β‐form in the α‐form and/or at the transcrystalline regime were found to be responsible for the recrystallization occurring upon melting in nanocomposites at high silica or medium GNP content. POLYM. ENG. SCI., 55:672–680, 2015. © 2014 Society of Plastics Engineers

Flow-induced crystallization of polypropylene in the presence of graphene nanoplatelets and relevant mechanical properties in nanocompsoite fibres

“…Previous works showed no obvious change in the crystallinity of PP/GnPs composites using very low quantity of GnPs [9,10,13,14,22] or for its similar platelet form filler, clay, in PP/clay nanocomposite fibres, even if the some compatibilizers was used [19,[41][42][43][44]. To our best knowledge, our DSC results have, for the first time, shown the flow-induced crystallization for PP/GnPs nanocomposite systems.…”

“…During the last decade, PP/graphene nanocomposites were studied extensively [2,[9][10][11][12][13][14][15][16]. These researches showed that the properties of nanocomposites, such as mechanical properties, are dependent on the state of dispersion of graphene in the matrix and loading amount of graphene.…”

Melt-Mixed 3D Hierarchical Graphene/Polypropylene Nanocomposites with Low Electrical Percolation Threshold

“…At low loadings especially, the increase is quite intense as with just 0.2 wt.% of filler the crystallization temperature increases by 7 °C in comparison with the value observed for the pure polymer (113.6 °C to 120.8 °C). This behavior can be associated with nucleation effects and has been reported in the past for a number of fillers including clay, nanotubes and graphitic platelets [35,61,62]. Polypropylene has a very rich polymorphism form and it has been reported that filler inclusion has an effect of the overall morphology of the system [56].…”

Synergistic effect of graphite nanoplatelets and glass fibers in polypropylene composites

“…The increase in resistance under impact conditions exhibited by the hybrid composites at low filler loadings can be ascribed to (i) changes in the energy absorbing mechanisms (i.e., higher plastic deformation of the matrix along the filler/matrix interface, crack branching due to hindrance by reinforcements, bridging of the crack, creation of voids etc.) and (ii) different crystalline morphology (i.e., spherulite size and polymorphism) occurring upon nanomodification . However, the toughening effect provided by high modulus filler particles ( E ∼70 GPa for GNP) is limited by nanofiller agglomeration.…”