Halloysite nanotubes as polyolefin fillers

Abstract

Halloysite nanotubes (HNTs) are a promising type of naturally occurring fillers for polymers. We review the recent progress in HNTs characterization, methods of their modification, as well as the morphology and mechanical properties of polyolefin/HNT nanocomposites. Modified HNTs well dispersed in a polyolefin matrix bring an improvement to the mechanical properties of nanocomposites. It seems that the connection of well-known advantages of polyolefins with unique properties of HNTs may result in the large-scale utilization of this type nanocomposite.

Comparing Multi-Walled Carbon Nanotubes and Halloysite Nanotubes as Reinforcements in EVA Nanocomposites

“…It is related to the hydroxyl groups that are located on the HNTs surfaces. Moreover, the tubular morphologies with a relatively high aspect ratio limit the possibility of creating large-area contact between tubes [ 19 ]. Consequently, a very uniform dispersion of HNTs in the EVA matrix was obtained ( Figure 1 c,d).…”

“…For each polymer-CNT composite, thermal stability may be due to one mechanism or the combined action of several processes, which depend on the different components, microstructures, and exterior conditions [ 59 ]. Similarly, also HNTs are found to be a promising additive for improving the thermal stability and flame retardancy of polyolefins and other polymers [ 19 ]. The improvement of thermal stability and flame retardancy resulted from the barrier properties of HNTs combined with an encapsulation process of the polymer’s degradation products inside the HNT lumens [ 60 ].…”

“…The improvement of thermal stability and flame retardancy resulted from the barrier properties of HNTs combined with an encapsulation process of the polymer’s degradation products inside the HNT lumens [ 60 ]. What is also important, because of their structure and chemical character, HNTs can be more easily dispersed into polyolefin matrices in comparison with other nanofillers, such as montmorillonite (MMT) [ 16 , 19 , 61 ]. This is a crucial factor for obtaining nanocomposites with better mechanical properties, higher thermal stability, and reduced flammability.…”

“…HNTs are 1:1 phyllosilicates that have a hollow tubular morphology which results from the wrapping of silicate sheets, consisting of one tetrahedral and one octahedral sheet, that are connected through hydrogen bonding and weak Van der Waals interactions [ 18 ]. HNTs were found to occur in soils all over the world, but the most important deposits are located in the United States, New Zealand, and Poland [ 19 ]. The pure material is white, however, as a result of impurities from ferric ions, it may be slightly red [ 20 ].…”

“…Typically, the HNTs lengths range between 300 and 1500 nm, while their inner diameters are 15–100 nm, and outer diameter 40–120 nm [ 21 , 22 ]. HNTs are low-cost, and eco-friendly materials that can be more easily dispersed in a polymer matrix than carbon nanotubes [ 19 ]. Compared to other layered silicates, they are characterized by relatively low hydroxyl content on their outer surfaces.…”