Synthesis of superabsorbent from carbohydrate waste

doi:10.1016/j.carbpol.2009.05.006

Carbohydrate Polymers

Volume 78, Issue 3, 15 October 2009, Pages 492-496

https://doi.org/10.1016/j.carbpol.2009.05.006 Get rights and content

Abstract

A mixture of acrylamide (AM) and acrylic acid (AA) monomers were grafted on germinated gelatinized wheat starch using potassium persulfate (KPS) as an initiator to yield superabsorbent. The effects of different parameters such as time, temperature, monomer feed (AM:AA), starch: monomers ratio and initiator concentration on graft add-on were studied, and the optimized values were found to be 2 h, 60 °C, 1:1 (w/w), 1:1(w/w) & 1% (with respect to starch powder), respectively. The product so formed was saponified with 0.1N NaOH, dried and finely powdered sample was characterized using FT-IR, TGA. Product showed maximum absorbency of 150 g/g.

Introduction

Superabsorbent polymers (SAPs) are materials that have the ability to absorb and retain large volumes of water and aqueous solutions. Although there is no specific definition of Super absorbent mentioned in the literature, a number of authors have cited their products of enhanced water absorbency, as “superabsorbent” when , in general the absorbency level was found to be more than 100 times (or >1000%) (Wang et al., 2005, Zhang et al., 2007). This makes them ideal for use in water absorbing applications such as baby nappies, sanitary napkins, agriculture and medicine for drug-delivery system (www.functionalpolymers.basf.com/porta-l/streamer?fid=291074).

Over the past five decades, superabsorbent hydrogel (SHs) have received particular attention as promising material for a series of applications in which the efficient use of water is required such as soil conditioning and disposables. From physical and chemical characteristics points of view, SHs are three-dimensional polymer network capable of expanding upon contact with water which results in the absorption and retention of large amount of liquid (Ratner and Hoffman, 1976).

Recently, there has been increasing interest in the processes which do not cause damage to environment or living organisms. In this context, native starches are very often tailored by modifications. To develop functional properties, such as solubility and absorbency polysaccharide based SHs have emerged as promising substitutes for they are nontoxic and biodegradable materials and are widely available in the environment (Park, Shalaby, & Park, 1993).

In India, untimely rains and hail storms at harvest time and inadequate storage facility for the food grains, a lot of wheat, maize, jowar, rice etc. often get dampened and damaged and these grains slowly start germinating making them unacceptable for edible consumption (Pandey & Raja, 1992). Preharvest sprouting occurs in wet or humid conditions in many regions of the world, including Northwest Europe, North and South America, Australia and New Zealand (Rohera, 2007). This carbohydrate waste instead of dumping can be effectively utilized for extraction of starch which can be used in textiles for sizing and printing. The present paper discusses work on application of germinated wheat starch as base material for synthesis of superabsorbent polymer.

Section snippets

Materials

“Lokawan” variety of wheat (Gluten content 14%, Moisture content 11%, Ash content 4%) commonly grown in India was used for extraction of starch. Chemicals used were of laboratory grade. Acrylic acid, acrylamide, potassium per sulfate, methanol, ethanol and other chemicals were supplied by S.D. Fine Chemical Pvt. Ltd.

Germination

Germination of wheat was done by imitating the actual poor conditions during storage. Wheat grains were packed and allowed to suffocate in a jute sack. Sprinkling of water was done

Swelling power

Swelling power was determined by the method reported by Subramanian and coworkers. (Subramanian et al., 1994). Starch (0.6 g) was heated with 30 ml of distilled water at 95 °C for 30 min. Lump formation was prevented by stirring this mixture at every 5 min interval. The mixture was then cooled and centrifuged (using CRU-5000 centrifuge) at 5000 rpm for 15 min. The supernatant liquid was carefully removed and the swollen starch sediment was weighed. Swelling power (g/g) was calculated as the ratio of

Grafting of starch

The grafting reaction was carried out in a round bottom flask equipped with reflux condenser and a nitrogen inlet. To control the reaction temperature, the flask was placed in a thermostated water bath. The starch slurry was prepared by adding 10 g of starch in 300 ml water. Gelatinized wheat starch was obtained by heating the slurry at 85 °C in the flask for 30 min. Gelatinized starch was cooled to 60 °C 1% (on wt. of starch) potassium persulphate was added to it, to produce free radicals onto

IR spectra

The IR spectra of original and various grafted starch samples were recorded using FTIR spectrophotometer (Shimadzu 8400s, Japan) using ATR sampling technique by recording 45 scan in %T mode in the range of 4000 to 600 cm⁻¹.

TGA

The thermograms of germinated starch and grafted starch sample were recorded using Shimadzu 60H DTG using aluminum pan between temperature range 30–510 °C and under inert atmosphere of N₂ at a flow rate of 50 ml/min.

Water absorbency measurement

The dry sample was weighed (0.2 g) and immersed in water for 24 h to reach absorption equilibrium. The fully swollen hydrogel was separated from the unabsorbed water with a 65-mesh screen and thereafter, the hydrogel was weighed. The relative water absorbency was calculated by formula (Chen, Zhang, Luo, & Fang, 2004) $Water absorbency (g / g) = \frac{(M_{1} - M_{2})}{M_{2}}$ where in, M₁ and M₂ are weight of fully swollen hydrogel and of dry sample, respectively.

Results and discussion

The starches from germinated and non-germinated wheat were extracted, characterized and the results are given in Table 1. These results indicate that the swelling power of the non-germinated wheat starch is 1.36 times of that of germinated one. The transmittance is also higher for non-germinated starch than that of germinated one because of the better paste clarity which was consequent to higher swelling power. The enhanced iodine binding capacity of germinated starch shows relative increase in

Conclusion

The level of grafting in germinated and non-germinated starches was found to be comparable and hence starch obtained from germinated wheat which is otherwise treated as carbohydrate waste could be used effectively for the preparation of superabsorbent materials without significant loss in performance. The graft add-on values and consequently water absorbency values were higher in case of grafting using mixture of AM and AA in 1:1 ratio (w/w). The water absorbency, however, increased after

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Synthesis of superabsorbent from carbohydrate waste

Abstract

Introduction

Section snippets

Materials

Germination

Swelling power

Grafting of starch

IR spectra

TGA

Water absorbency measurement

Results and discussion

Conclusion

Synthesis of superabsorbent polymers by irradiation and their applications in agriculture

Journal of Applied Polymer Science

Starch paste clarity

Cereal Chemistry

Graft copolymerization of methyl methacrylate onto sago starch using ceric ammonium nitrate and potassium persulfate as redox initiator systems

Journal of Applied Polymer Science

A simplified assay for milled rice amylose

Cereal Science Today

Grafting onto polyester fibers. IV. Synergism during graft copolymerization of binary mixtures of vinyl monomers onto polyester fibers

Journal of Applied Polymer Science