Synthesis and Characterization of Corn Starch Grafted Guar Gum Composite with Tamarind Kernel Powder

Introduction

Gums are naturally occurring complex carbohydrates, forming gels and mucilages. They are soluble in water. They have specific characteristics, like gelling, moisture retention, stabilization, and emulsification¹. Gums have wide applications in various fields, like in the food industry, the medicinal industry, paint formulations, etc². They are not very efficient under natural conditions, so we must modify some chemical properties to increase the quality by derivatization of functional groups, cross-linking, or grafting with polymers^3,4. In this work, guar gum was grafted with corn starch and derivatized with tamarind kernel powder (TKP). Guar gum (GG) is a novel agrochemical non-ionic polysaccharide that is processed from the endosperm of cluster beans⁵. It is derived from the seeds of the Cyamopsis tetragonoloba plant and is a member of the Leguminosae family, also known as guaran^6,7. GG is a linear chain of β-1,4 linked mannose residue to which the galactose residue is 1,6 linked at every second mannose, resulting in short side branches⁸. Guar gum is an excellent thickener and stabilizer for use in cosmetics, food, and pharmaceutical preparations⁹. It has some properties like water-binding capacity, low-temperature functioning, high viscosity even at very low concentrations, and hydrocolloid compatibility, which makes it useful in various applications.

Figure 1: Structure of Guar gum. Click here to View figure

Tamarind is native to tropical Africa with the botanical name Tamarindus indica and belongs to the Fabaceae family¹⁰. It is a perennial fruit species known for its fruit production and adaptability to different climatic conditions¹¹. Tamarind seed polysaccharide have properties such as high viscosity, excellent water absorption, good binding, adhesivity, etc¹².

Figure 2: Structure of Tamarind Seed Kernel Powder. Click here to View figure

Figure 3: Structure of Corn Starch. Click here to View figure

Corn starch was used for grafting because of its biodegradability¹³. Such composites degrade gradually and enable the bond to transfer gradually from the material to newly grown bone by inducing new bone growth¹⁴. This improved the thermal stability of guar¹⁵. There are many grafting methods, but the most widely used method is the polymerization condensation method because of its higher grafting efficiency, low cost, less degradation of the polymer backbone, etc.¹⁶ In this work, we have tried synthesizing and characterizing a new composite based on guar gum and corn starch.

Materials and Method

Materials

Guar gum (Shri Ram Industries, Basni, Jodhpur), Corn Starch, Potassium persulphate (KPS, Sigma Aldrich), Ascorbic acid (Ases Chemical, Jodhpur), Tamarind Kernel Powder (Ases Chemical, Jodhpur), Methanol, Ethanol (Ases Chemical, Jodhpur), Ammonium hydroxide (5.0 N) and Sodium hydroxide (1%) were used without any further purification.

Method

Synthesis of Corn starch (CS)-g-guar gum

For grafting, guar gum (2 gm) with an equal amount of ascorbic acid and corn starch was added to distilled water (250 ml). This mixture was heated for 30 minutes at 35ºC before adding potassium persulfate as an initiator¹⁷. This mixture was allowed to rest for 1 hour for grafting and poured into a large quantity of DMF (Dimethylformamide) to separate corn starch CS-g-guar gum from the solution and wash it with DMF.

Saponification of CS-g-guar gum

Corn starch was saponified with an alkali NaOH solution (1%) and heated for 1-2 hours at 100ºC. The saponified guar gum was separated using methanol, and washed with ethanol.

Preparation of CG-GT (Corn starch-g-guar gum with TKP) composite

A saponified sample was dissolved in distilled water. In another flask, TKP was dissolved in the required amount of ethanol. Both the solutions were mixed, and then ammonium hydroxide (5.0) was added at room temperature and kept for 18–20 hours. The mixture was then washed with distilled water, and the excess liquid was evaporated by heating at a different range of temperatures, from 20 to 100ºC. The composites were allowed to dry.

Scheme 1 Click here to View scheme

Results and discussion

FT-IR Analysis

Figure 4: FT-IR Spectra of CG-GT composite. Click here to View figure

For the characterization of the CG-GT composite, FT-IR analytical spectra were used. The Figure depicts the assignment of several peaks detected in the FT-IR spectra of the newly synthesized composite. The peaks at 3281 and 2924 cm^-1 are broad due to O-H and C-H aliphatic stretching, respectively. This is the peak of guar gum present in the polymer as its backbone. The 1643 cm-1 peak is caused by C-H bending. This indicated that an aromatic component was present. Stretching of the C=C aromatic group produced a 1558 cm-1 peak. The absorption of CH₂ bending vibration was recorded at a peak of 1325 cm^-1. The peak at 1150 cm^-1 is due to the stretching of the C-O-C bond¹⁸, and the peak at 1077 cm^-1 is due to C-O-C stretching. The 924 cm^-1 peak is due to O-H bending, which shows a carboxylic group¹⁹. C=C bending causes the peak at 850 cm^-1, indicating the existence of alkene. All these distinct peaks indicate grafting and composite formation.

Mass Analysis

Figure 5: Mass Spectra of CG-GT composite. Click here to View figure

At m/z 949.6, the molecular ion peak was discovered. It separates into daughter fragments with m/z 158.99, 163.06, 190.01, 301.16, and 415.23 as peaks. The newly produced composite’s most noticeable and stable state is located at m/z 143.04. This study provides information that will help effectively synthesize the CG-GT composite.

¹H NMR Analysis

Figure 6: NMR Spectra of CG-GT composite. Click here to View figure

The protonic environment of the CG-GT composite was determined using ¹H NMR. CDCl₃ (Chloroform-d) was used as a solvent. The aromatic proton’s peak is at 7.47 ppm. CDCl3 reaches its peak at 7.25 ppm. Alcoholic protons
(-OH) linked to the phenyl ring are seen at 5.52 ppm. At 3.54 ppm, the ether group is detected. The peak at 4.90 ppm indicates the presence of the vinylic group.

SEM Analysis

Figure 7: SEM images of CG-GT composite. Click here to View figure

The surface morphology of the composite was studied using a scanning electron microscope (SEM). The SEM images at various magnifications are shown in Figure 7. The ZEISS instrument is used for SEM analysis. According to SEM analysis, the composite has a smooth surface and an irregular particle size. The particles are evenly scattered across the entire surface area.

Conclusion

The synthesized composite consisting of guar gum, corn starch, and TKP was characterized using FT-IR, Mass spectra, ¹H NMR, and SEM. The grafting was confirmed by FTIR spectroscopy. FT-IR analysis was used to identify functional groups. The surface morphology of the synthesized composite was visible in the SEM images. The protonic environment of the composite was revealed by NMR. The manufactured composite can be used to measure the metal binding capacity using mass spectra.

Acknowledgement

The authors are thankful to the MNIT (Malaviya National Institute of Technology, Jaipur) for NMR and Mass analysis. We also thank the Defence Laboratory, Jodhpur (DRDO) for SEM and FT-IR analysis.

Conflict of Interest

All authors have approved the final manuscript and declare that there are no conflicts of interest.

Funding Sources

There is no funding source.

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