Changes of the Structural and Mechanical Properties on Nanocomposites based on Halloysite Nanotubes with the Optimization of Dispersion by Ultrasonic Waves

Abstract

Nanoparticle refers to a particle within the scope of a hundred nanometers and nanoparticles have a wide specific surface area. By controlling their size or using nanoparticles of various types, the properties of material can be improved with only a small amount of particulate filler.

Halloysite is a naturally occurring aluminosilicate in the form of nanotubes, also known as halloysite nanotubes (HNTs). The HNTs are odorless, white particles with the chemical formula H4Al2O9Si2·2H2O. Halloysite nanotubes are readily obtainable and are much cheaper than other tubular nanoparticles such as carbon nanotubes. There HNTs have been considered as a functionally effective material capable of mechanically strengthening resins by restrictive matrix dislocation movement. Especially, there are studies showing that adding HNTs to plastics improves tensile strength, impact resistance, fire retardancy and gives the added advantage of improved cycling time in production by injection molding.

In this study, samples consisted of nanocomposites manufactured by adding HNTs to unsaturated polyester resin (UP). Herein, the contents of HNTs were 0.5, 1 and 3 wt.%. The purpose was to analyze the mechanical properties of nanocomposites on a function of HNTs content and through this, to find the optimal conditions for developing UP matrix HNT reinforced nanocomposites. The HNTs used in this study were treated by heat. Heat-treated HNTs were divided into 4 groups: untreated HNT (UTHNT), 300 (300HTHNT), 500 (500HTHNT), 700 (700HTHNT) and 1000 (1000HTHNT) heat-treated HNT, according to treating temperatures. To achieve a uniform distribution of nanoparticles in the matrix, the factors optimized for dispersion were considered and a suitable process environment for materials to be used was adopted by dividing these factors into constants and variables. The ultrasonic homogenization is used in the production of nano-size materials, dispersions and emulsions, because of the potential in deagglomeration. Ultrasonic homogenization is an easy way to separate particle aggregate, and obtain homogeneous phase. Ultrasonication was carried out by varying some parameters. The operating time and the volume of the sample were maintained at fixed values, namely 300 s and 18 ml, respectively. The output power was divided into two cases, at 45W and 60W.

Finally we established the optimal dispersion condition of HNTs using ultrasonication, and the reinforcement effect of HNTs was studied by X-ray diffraction and evaluation of mechanical properties of nanocomposites such as impact strength and tensile strength. Also, the structural changes of HNT by heat treatment at various temperatures were evaluated.