New generation of super absorber nano-fibroses hybrid fabric by electro-spinning

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Abstract

PAM (polyacrylamide) has been used in granular like shapes as a water super absorber and soil erosion resistant agent in irrigation systems as well as in conservation systems. The idea of making fibers out of PAM seems to be very interesting since the surface area per unit mass will increase tremendously from granular to fibroses like shape structures.

In this paper electro-spinning technique has been used to investigate the ability to produce ultra-fine PAM fibers. Effect of electro-spinning parameters such as Berry's number, spinning height, and spinning angle on PAM fiber diameter have been studied till successfully 290 nm average fiber diameter has been collected.

To enhance the amount of collected electro-spun PAM nano-fiber and to study its absorption characteristics PAN (polyacrylonitrile) nano-fibroses membrane has been suggested as a good candidate to carry the electro-spun PAM nano-fibroses structure since PAN has been proved its ability to coagulate in water keeping all its morphological behavior. PAM/PAN hybrid nano-fibroses fabric has been produced at the optimum electro-spinning conditions. The new super absorber PAM/PAN nano-fibroses hybrid fabric has been tested and proved its ability to enhance water absorption 4.3–3.6 times more than commercial PAM granular like shape based on experimental calculations on the macroscopically and microscopically levels, respectively.

Introduction

A super-absorbent polymer is a network of flexible cross-linked molecules that exhibits an intriguing combination of the properties of both liquids and solids. Super-absorbent polymer gels can swell up to hundreds of times (about 300 times) their own weight in aqueous media. The term encompasses a number of cross-linked polymers such as poly(vinyl alcohol), polyvinylpyrrolidone, poly(ethyleneoxide), carboxymethylcellulose and polyacrylamide, all having the basic ability to swell in water. There has been increasing interest in the synthesis and applications of super-absorbent polymer or hydro-gels. They have been studied intensively in recent decades for their promising applications in chemical engineering as sensors, in the biomedical field as materials in medicine, in pharmacy as drug delivery systems, in agriculture and industry as adsorbents and separation membranes, in solving some ecological problems and in other modern technologies. Acrylamide hydro-gels have found extensive commercial applications as absorbents in personal care (for example in diapers applications 14,475 baby diapers per second consumed all over the world) and for agriculture purposes. The swelling behavior of the hydro-gel is very sensitive to the network microstructure and its interaction with water (Abd El-Rehim, 2005; www.gpoabs.com.mx/cricher/industry.htm).

In the past decade, electrostatic processing has been routinely employed to obtain ultra-fine fibers (Srinivasan and Reneker, 1995, Warner et al., 1998, Reneker et al., 2000, Norris et al., 2000, Deitzel et al., 2001, Ali, 2006). The process consists of applying a high voltage to inject charge into a polymer solution of adequate concentration. As the voltage is increased, the drop of liquid presented at the tip of the syringe is attracted to the ground electrode thereby forming a Taylor cone. Above a critical voltage, the electrical energy, a consequence of the injected charge overcomes the surface tension and a continuous jet of liquid is ejected from the Taylor cone and accelerates towards the target electrode. Ultra-fine fibers are deposited on the collector due to evaporation of solvent en route. This technique has been employed to numerous polymer/solvent systems to obtain fiber diameters ranging from tens of nanometers to microns. A vast majority of studies reported in the literature concentrate on applications of electro-spun fibers. However, fundamental understanding of the electro-spinning process is limited. Only recently has there been a concerted push to gain deeper insights into the electro-spinning process. For example, a number of efforts have concentrated on modeling the whipping instability and fiber diameter. However, there has been a lack of knowledge with regards to fiber formation and its relationship to the polymer solution properties. Recently, McKee et al. (2004) investigated the solution properties, in particular, the viscosities of linear and branched polyesters, and proposed that fiber formation occurs at the entanglement concentration. Over the past year, Shenoy et al. (2005) have particularly interested in the effect of polymer solution properties on fiber initiation/formation or ‘electro-spin-ability’ (spin-ability in electrostatic processing). In this regard their work have clearly demonstrated a link between chain entanglements in the polymer solution and electro-spin-ability, in particular, a semi-empirical methodology to a priori predict the transition from electro-spraying to electro-spinning (or beads to fiber with beads) in good solvents has been presented. Additionally, their work has been able to predict the transition from fiber with beads to solely fibers (complete fiber formation).

The present study is an attempt to optimize the electro-spinning process for PAM nano-fibers through three main processing parameters Berry's number, spinning height and spinning angle. As well as to study the ability to produce new generation of super absorber electro-spun nano-fibroses PAM/PAN hybrid fabric for diapers, agriculture and similar applications.

Section snippets

Polymer

Commercial polyacrylamide PAM supplied from El-Nasser Co. Egypt—molecular weight over 5,000,000 g/mol and PAN polymer emulsion polymerized in NRC, Egypt of about 100,000 g/mol average weight molecular weight based on theoretical calculation.

Solvent

Distilled water and DMF of 99.8% purity from El-Gomhoria Co., Egypt (Fig. 1).

It is very important to get an idea about the minimum fiber diameter that can be produced within any available technique for PAM polymer which, can be known theoretically by

Morphological results and analysis

An optical microscope, model AXIOSKOP2-ZEISS, has been used to investigate all electro-spun samples and to measure fiber diameters.

The pictures for each electro-spun group have been taken and the fiber diameters for each picture have been measured by using calibrated lenses. An average value from all measurements has been considered. The average fiber diameter and the standard deviation have been calculated for each sample. Also, a constant magnification, with some small variation to keep the

Conclusions

  • 1.

    The optimum value for Berry's number to be used in the electro-spinning of PAM/water solution was found to be 134 giving 370 nm average fiber diameter.

  • 2.

    The optimum spinning height found to be 15 cm and giving 300 nm average fiber diameter.

  • 3.

    The optimum spinning angle of 30° produced 290 nm average fiber diameter.

  • 4.

    The recommended spinning conditions for PAM/water polymer solution found to be 134 Berry's number, 10–15 cm height, 30–45° spinning angle, 2–2.5 kV/cm charge density giving PAM nano-fiber

Acknowledgement

The authors would like to thank Prof. A. Zeni professor of electrical engineering, Zagazig University, Egypt for the help he has provided with high voltage source.

References (9)

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