Figure 4 — The SEM images of (a) LS and (b) LS-g-SAH
Related Figures (16)
The FTIR spectra in the range of 4000 to 650 cm” were recorded using Perkin Elmer 2000 FT-IR spectrometer. The solid-state '‘C-NMR analysis of samples was done on a _ Bruker Ascend-400 spectrometer operating at 400 MHz. The surface morphology was determined through SEM on EVO 18 Research, Zeiss, instrument. TGA was conducted on Perkin Elmer, Thermogravimetric Analyzer, TGA 4000 in Nitrogen environment with a uniform heating rate of 10 °C/min. XRD measurements were recorded through RIGAKU with source Cu-Ka performed at a voltage of 50 kV. The rheological analysis was carried out using Anton Par Rheometer (Model: Anton Par, Modular Compact Rheometer, Lignosulfonic acid sodium salt (LS) ( Mol wt .~ 52,000) was purchased from Sigma Aldrich. Acrylic acid (AA) and N'N-methylenebisacrylamide (N,N’- MBA) were bought from CDH Pvt Ltd. Potassium persulfate (KPS) were purchased from SD fine chem Ltd. Urea and NaOH were purchased from CDH Pvt Ltd, and Qualikems Fine Chem Pvt. Ltd., respectively. Fig. 1 — Visual representation of the synthesis of LS-g-SAH MANU et al.: LIGNOSULPHONATE-g-POLY (SODIUM ACRYLATE) HYDROGEL MCR 302) with PP-25 parallel plate and 2.5 mm inter-platen gap. The IR spectra of LS, ctrl, and LS-g-SAH are shown in Fig. 2. The -OH stretching vibration of LS is observed as a broad band around 3,303 cm |. LS, ctrl Solid state '*C NMR spectroscopy is a powerful tool for the structural characterization of polymers. The spectra of LS, LS-g-SAH, and ctrl hydrogel prepared by graft co-polymerization are presented in Fig. 3. Peaks around 45 ppm and 185 ppm of LS-g-SAH and ctrl were assigned to saturated aliphatic chains and C from and LS-g-SAH show a band around 2,920 cm ~ due to C-H stretching in —CH, or — CH; groups. The vibration of the aromatic skeleton is observed from the two firm peaks at 1,572 and 1,417 cm !. * The strong peak at 1,046 cm! arises due to C-O-S stretching vibration, and the peak at 1,114 cm! is assigned to O=S=O antisymmetric stretching vibration in the LS.* Both these characteristic peaks confirm the presence of LS in LS-g-SAH. Further, new peaks were found when LS was compared to LS- g-SAH. The strong bands at 1404 and 1554 cm’! are Fig. 3 — SS 3C CP-MAS NMR spectrum of (a) ctrl, (b) LS-g-SAH, and (c) sodium LS carbonyl ester (COONa), COOH, _ respectively. Characteristic peaks of basic aromatic and aromatic rings with branched C-C bonds can be observed in the range of 140-110 ppm and 75-10 ppm. The appearance of signals around 50-10 ppm in LS represents aliphatic C chain”. Most of the peaks of LS merged inside LS- g-SAH due to their low intensity. However, the presence of peaks at 135.1 ppm and 86.2 ppm confirms the presence of LS in LS-g-SAH. The results support the observations of the FT-IR spectra. The presence of free COOH groups and crosslinks probably increased the intensity of the peak at 184.7 ppm. The frequency varied from 0.1 to 500 rad/s during the frequency sweep test while keeping the shear strain % within the LVE region constant. It was observed that the loss modulus was found to be prevalent at higher frequencies while the storage modulus was prevalent at lower frequencies representing the viscoelastic solid behaviour. Tan 0 Fig. 8 — Effect of variation of (a) biopolymer, (b) initiator and (c) crosslinker on the swelling index -ontent reached 0.1 g, the amount of ionic hydrophilic sroups in the hydrogel, such as sulfonic acid and carboxyl groups, could have become higher than the 10n-ionic hydrophilic groups such as amide group and 1ydroxyl group, which further led to the declination of the SI. *° at low frequencies. Frequency sweep data of LS-g- SAH and ctrl hydrogels rae shown in Table 2. The gel content percentage of LS-g-SAH present in Table 1 was calculated using Eq.(2). The gel percentage of hydrogels varied according to the concentration of crosslinker, biopolymer, and initiator. The gel content reduced as the concentration of the crosslinker and biopolymer increased. In contrast, the initiator initially enhanced the gel content but decreased when added in amounts greater than 0.08 g. Gel contents of synthesized hydrogels were found in the 64 - 97 % range. Fig. 9 — Swelling study of hydrogel Fig. 10 — Water retention capacity plot of soil amended with LS-g-SAH Fig. 11 — Water evaporation study of soil amended with different concentrations of LS-g-SAH Fig. 12 — Urea release kinetics using (a) first order, (b) Korsmeyer—Peppas and (c) Higuchi model in distilled water The plant growth performance study using the LS- g-SAH is shown in Fig. 13. The wheatgrass growth can be observed by the changed total dry and fresh weight, the average number of germinated seeds, the average wheatgrass height, and the average shoot height of all samples. All these are mentioned in Table 4. The height of the plants increased with the advancing age of the crops. On the 14” day, significantly tallest grasses (the tallest grass was 27 cm) were recorded in LS-g-SAH, followed by sample B, i.e., ctrl, though the shortest plants were recorded Urea release kinetics studied using different models such as a) first order, b) Korsmeyer—Peppas, c) Higuchi model in distilled water are shown in Fig. 12, The slow-release process of urea through LS-g-SAH occurs in the following manner; firstly, the water tries to enter the hydrogel. Afterward, the hydrogel starts to swell by absorbing water until a dynamic exchange Fig. 13 — Effect of hydrogel treatment on wheatgrass after 14 days using (A) only urea, (B) control hydrogel-loaded urea, and (C) LS-g- SAH loaded with urea Table 4 — Wheatgrass growth parameters on the 14" day: (A) only urea, (B) control hydrogel-loaded urea, and (C) LS-g-SAH loaded with urea References under sample A. The germination and growth of seeds are known to be improved with the prolonged availability of urea. LS-g-SAH showed 100% germination followed by control hydrogel (86.6%), i.e., sample B and untreated soil (80%) urea release, respectively.
