PA6 and Halloysite Nanotubes Composites with Improved Hydrothermal Ageing Resistance: Role of Filler Physicochemical Properties, Functionalization and Dispersion Technique

Abstract

Polyamide 6 (PA6) suffers from fast degradation in humid conditions due to hydrolysis of amide bonds, which limits its durability. The addition of nanotubular fillers represents a viable strategy for overcoming this issue, although the additive/polymer interface at high filler content can become privileged site for moisture accumulation. As a cost-effective and versatile material, halloysite nanotubes (HNT) were investigated to prepare PA6 nanocomposites with very low loadings (1–45% w/w). The roles of the physicochemical properties of two differently sourced HNT, of filler functionalization with (3-aminopropyl)triethoxysilane and of dispersion techniques (in situ polymerization vs. melt blending) were investigated. The aspect ratio (5 vs. 15) and surface charge (−31 vs. −59 mV) of the two HNT proved crucial in determining their distribution within the polymer matrix. In situ polymerization of functionalized HNT leads to enclosed and well-penetrated filler within the polymer matrix. PA6 nanocomposites crystal growth and nucleation type were studied according to Avrami theory, as well as the formation of different crystalline structures (α and γ forms). After 1680 h of ageing, functionalized HNT reduced the diffusion of water into polymer, lowering water uptake after 600 h up to 90%, increasing the materials durability also regarding molecular weights and rheological behavior.

Thiahelicene-grafted halloysite nanotubes: Characterization, biological studies and pH triggered release

“…Moreover, their structural and morphological properties exhibit substantial differences across different geological deposits: phase impurity, specific surface area, size polydispersity, aspect ratio, and surface charge are all affected by the specific extraction site of the HNT sample [35]. Some of us have recently shown how the physicochemical properties of differently sourced HNT can affect surface coverage in the case of APTES [41]. Even though HNT from homogeneous source were here employed, the HNT morphology within the adopted batch displays polydispersity in the aspect ratio and surface defects (see Figure S1).…”

Design of halloysite modification for improvement of mechanical properties of the epoxy based nanocomposites

“…Halloysite nanotubes represent nano-structured tubular silico-aluminate clay [3] with large aspect ratio, low density, natural availability, rich functionality, good biocompatibility, high mechanical strength, thermal properties, and flame retardancy [4][5][6][7][8][9][10] . The ideal molecular formula of HNT is Al 2 Si 2 O 5 (OH) 4 ÁnH 2 O.…”

Manufacturing and Characterization of Coatings from Polyamide Powders Functionalized with Nanosilica

“…For this reason, in this work, extrusion has been employed as a mixing method, since it can obtain homogeneous polyamide materials (coatings and composites) with different nanoreinforcements [ 32 ]. In situ polymerization method also leads to an excellent distribution of nanoparticles [ 33 ], but it cannot be considered as the work is focused on the functionalization of a commercial powder coating.…”