Size-dependence hydrophobicity in nanocrystalline talc produced by high-intensity planetary ball milling
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Size-dependence hydrophobicity in nanocrystalline talc produced by high-intensity planetary ball milling 1
Rebeca Caban-Nevarez,
1,2
1
Food Science and Technology Program
2
Department of Engineering Science and Materials
Oscar J Perales Perez
University of Puerto Rico at Mayaguez, Mayaguez, PR 00680, United States
ABSTRACT Micron-size talc samples were ground using a high- intensity planetary ball mill at different milling times as an attempt to reduce particle size and study the effect on the corresponding hydrophobicity. XRD and SEM results confirmed the decrease in the particle size. FTIR spectroscopy analyses revealed the talc characteristic bands centered on 669 cm-1 for the O-H bonds and 1018 cm-1 for the Si-O bonds, as well as a degradation in the talc structure for prolonged milling times. BET results indicate an increase of specific surface area, which also confirms particle size reduction, reaching a maximum at 1 h, after which the particles agglomerate. Contact angle measurements show a decrease in the hydrophobicity of talc after milling. Although talc retains its hydrophobicity after short milling periods, prolonged grinding causes the mineral to have a more hydrophilic character.
INTRODUCTION Food packaging represents the application with the largest plastics demand.1 There has been a strong research interest in bioplastics due to environmental concerns associated with the waste management linked to conventional plastics and modern efforts to reduce dependence on fossil fuels. However, bioplastics possess some limitations which limit their commercial application as packaging materials, particularly for food products. Biopolymers have low barrier properties to gases and vapors, lower thermal resistance, poor mechanical properties, poor water resistance, and lower shelf stability, among other issues, that complicate their processability and performance.1,2 One strategy that has been implemented in order to improve and enhance the properties of biopolymers is the addition of nanomaterials as reinforcement compounds3 . These fillers can be of an organic or inorganic nature and can have a variety of morphologies. Many different types of fillers have been evaluated for the envisioned application, such as carbon nanotubes, silica, hydroxyapatite, silver, organic nanofillers, graphene4,5 , among others; however, layered silicates clays (e.g. nanoclays) have considered very promising for food packaging applications.6
Talc, a layered silicate mineral with an ideal formula of Mg3 Si4 O10 (OH)2 , has excellent potential as a material in biocompatible nanocomposites for food packaging applications due to its chemical inertness, high aspect ratio, and platelet-like morphology7 . The hydrophobic nature of talc is peculiar among layered silicates. It possesses Si-O-Si links on its basal surfaces that show minimal interactions with water at high relative humidity, due to the predominance of cohesive water-water interactions8 . This hydrophobicity is of special interest as it could potentially improve water
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