Synthesis of coconut shell nanoparticles via a top down approach: Assessment of milling duration on the particle sizes and morphologies of coconut shell nanoparticles

doi:10.1016/j.matlet.2015.07.063

Materials Letters

Volume 159, 15 November 2015, Pages 514-519

https://doi.org/10.1016/j.matlet.2015.07.063 Get rights and content

Highlights

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A novel synthesis of coconut shell nanoparticles via a top down approach was studied.
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Coconut shell powders were milled for a maximum of 70 h and analysed.
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Absorbance of Co Kα X-ray by particles occurred in the nano-wavelength range.
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There was a decrease in particle sizes with an increment in milling duration.
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New phase was formed due to increased particle surface area during milling.

Abstract

Coconut shell nanoparticles (CSNPs) were synthesised from coconut shell powders using a top down approach. Effects of milling time on the particle morphologies and sizes of CSNPs were studied. CS powders were milled for a maximum of 70 h using ceramic balls and a planetary mill. Milled samples taken at 16, 46 and 70 h were analysed using scanning electron microscope with attached energy dispersive X-ray spectrometer, X-ray diffractometer and UV–vis spectrophotometer. SEM micrographs revealed a difference in morphologies and appearances of the CSNPs. Particle size determination depicted a decrease in CSNPs' sizes with an increment in milling duration. The CSNP size determination from SEM aided with software and XRD aided with Scherrer's equation agrees with each other. This implies that the SEM observed CSNP sizes are in line with XRD crystalline sizes. The decrease in particles' Co Kα X-ray absorbance with increment in milling duration is an indication of reduction in CSNPs' opaqueness. This agrees with fading of brownish colour of CS powders as the milling duration increased. The smaller the wavelength at which maximum absorbance of the Co Kα X-ray occurred the smaller the CSNPs' sizes. Hence, an increase in surface area as the CSNPs' sizes decreased during milling led to particle agglomeration and formation of new compounds.

Introduction

Coconut shell (CS) are naturally occurring structural composites which form a protective chamber for coconut and its juice [1]. A coconut fruit contains three layers namely: endosperm, endocarp and mesocarp. The endosperm is the thick albuminous testa which is the white and fleshy edible part of the coconut fruit harbouring the coconut juice. The endocarp is the inner, hard lignocellulose composite known as coconut shell and the mesocarp is the ductile fibre-spongy husk called coir [2]. The coconut fruit is the product of coconut tree which was originated from South Asia. Now, it is found in South American and Africa [3]. It grows in tropical and rain forest climates. The coconut tree belongs to Plantae kingdom and Arecales order. Its tribe, genus and species are Cocoeae, Cocos and C. nucifera respectively; hence the botanical or binomial name Cocos nucifera. Coconut shells are agro wastes from household and coconut processing industries when the edible parts of the coconut fruit have been removed.

Globally, many researches are now concentrating on agro wastes such coconut shell, palm kernel shell, banana peel, cashew shell, walnut shell, groundnut shell and others in order to have replacement for the high cost conventional glass and carbon reinforcements for metallic and polymer composite development which are structural composites for aircraft and automobiles [4], [5], [6]. The agro waste or natural fillers have advantages over conventional filler which includes low cost, high toughness, excellent specific strength and enhanced energy recovery.

Reports from many researches have proven to the fact that the mechanical milling/alloying otherwise called top down approaches are suitable techniques for the synthesis of nanoparticles or nanoalloy especially when the size of initial materials is within the micro-metre range. Synthesis of nanomaterials through mechanical milling depends on charge ratio, rate of rotation of vial, brittleness of materials, milling duration, size of the milling balls and materials of which the balls are made. These parameters dictate the size of the particles obtained from the milling process. However, milling time between 14 and 120 h have been reported from different authors for nanoparticle synthesis [7], [8], [9]. In contrast to the background, processing of CSs at nanometric level is rare. Processing of CSs to obtain potential nanofillers will not only add values to CSs but also lead to environmental cleanliness and wealth creation. However, in this work CSNPs have been synthesised using top down approach (mechanical milling). The produced coconut shell nanoparticles can be used as natural nanofillers for the reinforcements of polymers and metals for green production of natural particle reinforced nanocomposites and nanoparticle-carburisation to harden the surface of materials for wear resistance application. The research work was aimed at studying the morphology and sizes of coconut shell nanoparticles (CSNPs) with respect to milling durations.

Section snippets

Materials and methods

CS powders (less than 37 µm size) used in this work were produced from the bulk CSs using a hardened steel crusher and a disc grinder. The scanning electron micrograph and proximate analysis of the bulk CSs are presented in Fig. 1A and B. The CS powders were milled for a maximum of 70 h at 5 h per day using a planetary ball mill, model: 87002 LIMOGES; type machine 28A2092 with mixture of ceramic balls of different sizes (5–60 mm). The milling was carried out at 10 charge ratios and the rate of

Results

CSNPs have different sizes and morphologies as the milling duration increased (Fig. 1C–E). Many CSNPs formed networks of agglomeration with few individual particles appeared alone. Decrease in particle size with an increment in milling durations led to an increase in surface area (high surface energy) of the CSNPs. Physical and chemical interactions among extremely fine particles are responsible for particle agglomeration (due to cold welding) and formation of new compounds (Fig. 2A–D). The

Summary and conclusion

Summarily, synthesis of coconut shell nanoparticles through mechanical milling was achieved. The size of the CSNPs decreased with an increment in the milling duration. Formation of new phases such as C₂MgO₆ is attributable to high surface energy of the CSNPs leading to chemical combination of the phases present in the particles. Absorption of X-ray of extremely low wavelengths by CSNPs is an indication of their extremely small sizes. The synthesised CSNPs can be used as low cost natural

Acknowledgement

Authors wish to express their gratitude to Mrs. Bello Haneefah A. for her sponsorship of this research work. Also appreciated is Rasheed Abiodun Jimoh and Abdul Wahab Abass Olayinka of Department of Materials Science and Engineering, Kwara State University, Dr. Fayomi of Department of Chemical and Metallurgical Engineering, Tshwane University of Technology, Pretoria South Africa and the staff of Ceramic Department, Federal Industrial Institute of Research Oshodi (FIIRO), Lagos Nigeria, for

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Featured LetterSynthesis of coconut shell nanoparticles via a top down approach: Assessment of milling duration on the particle sizes and morphologies of coconut shell nanoparticles

Highlights

Abstract

Introduction

Section snippets

Materials and methods

Results

Summary and conclusion

Acknowledgement

Alloy. Compd.

Alloy. Compd.

The effect of vacuum carbonisation of waste maize stalk on the thermal resistance of polyester/maize stalk particulate composites

Plast. Polym. Technol. (PAPT)

JETEAS

Mech. Milling: Nanosci. Nanotechnol.

Featured Letter
Synthesis of coconut shell nanoparticles via a top down approach: Assessment of milling duration on the particle sizes and morphologies of coconut shell nanoparticles