A Study on exfoliation of Expanded Graphite Stacks in Candelilla Wax.

Lionetto Lionetto,Maffezzoli Maffezzoli,Rodríguez-Fernández Rodríguez-Fernández,Espinoza-González Espinoza-González,Mis-Fernández Mis-Fernández,López-Muñoz López-Muñoz

doi:10.3390/ma12162530

Lionetto Lionetto, Maffezzoli Maffezzoli + Show 4 more

Open Access

https://doi.org/10.3390/ma12162530

Copy DOI

Abstract

A novel, green route for pre-exfoliation of graphite based on a biodegradable polymer and high-power ultrasound is presented. Candelilla wax (CW), derived from the leaves of the candelilla plant, has been used for the first time as a natural non aqueous medium to induce the pre-exfoliation of expanded graphite (EG) under ultrasonic irradiation in an economical way. The proposed method uses also D-limonene as a natural organic solvent for reducing viscosity and increasing the affinity between the polar groups of EG and candelilla wax, thus improving the intercalation/exfoliation of EG. The quality of dispersion of the nanofiller in the natural wax matrix has been evaluated using multiple techniques. The addition of EG to wax and use of ultrasonic treatment leads to a reduced crystallinity, probably due to restrictions of the molecular movements, improved thermal stability of wax, and to an increased shear thinning exponent, which are all indicative of a high degree of EG dispersion. The ultrasonic dynamic mechanical results suggest a reduction in the cluster size and a better filler dispersion in the wax matrix promoted by polar or chemical reactions between the CW fractions and the graphite stacks, which was observed by XPS analysis. The results were compared to those obtained with paraffin, a synthetic wax, and confirmed the dispersion improvement obtained by using natural wax as a pre-exfoliating medium.

Highlights

In recent years, the great concern of environmental pollution, has led to great interest in biodegradable polymers that are synthesized entirely or partially from annually renewable resources [1].Among these, natural waxes are emerging materials that have continuously increased in their application possibilities
Multiple techniques have been applied for studying the dispersion of a high amount (10% by weight) of expanded graphite in natural wax obtained by a novel, green approach involving high-power ultrasound and an organic natural solvent, D-limonene
Differential scanning calorimetry (DSC) analysis suggests that the reduced crystallinity in the expanded graphite (EG)–Candelilla wax (CW) samples can be ascribed to a possible confinement of the chain segments, which hinders the segmental rearrangement during crystallization and restricts the formation of perfect crystals in the polymer matrix

Summary

Introduction

The great concern of environmental pollution, has led to great interest in biodegradable polymers that are synthesized entirely or partially from annually renewable resources [1]. Natural waxes are emerging materials that have continuously increased in their application possibilities. Natural wax is a mixture of long-chain, non-polar compounds, including hydrocarbons, waxy esters, sterol esters, ketones, aldehydes, fatty alcohols, and fatty acids [2]. Natural waxes are present on the outermost layer of plant surfaces, and they have the function to protect the plant from the loss of water and attack from insects [3]. To survive the harsh environmental conditions, this plant secretes a thick wax layer.

Methods

Results

Conclusion