R Dhamodharan

Investigations have been made to determine the usage of inexpensive agro-waste products as an alternative carbon source for the production of degradable bacterial polyester. Among 33 bacterial isolates, a gram-positive bacterium PPECLRB-16 isolated from rice bran dumping yard was found to accumulate a relatively higher quantity of PHB and identified as Bacillus sp. through 16S rRNA gene sequence analysis. The higher PHB producing bacterial isolate was grown with different inexpensive agro-wastes to determine the suitable carbon source for its growth and PHB production. The one-factor-at-a-time approach comparatively enhanced PHB yield (5.64 g/L) when grown for 48 h with 1.5% (w/v) of defatted oil cake at a pH of 7.0. The bacterially accumulated PHB was isolated from the cells, purified, and characterized using solid-state 13C NMR, FT-IR, Powder XRD, TGA, GPC, Tensile and HR-SEM analyses. The hydrophobicity and printing accessibility of recovered PHB were demonstrated using contact angle measurement by coating on different surfaces. The results obtained in the present investigation have thrown light on the potential usage of agro-waste by-products, mainly oil cake, as an appropriate carbon source for the commercial production of PHB by Bacillus sp. in a cost-effective way.

Poly(butylene adipate-co-terephthalate) (PBAT), a compostable polymer, filled with different weight percentage of unbleached nano chitin (NC; 10%, 30% and 50%), a biodegradable filler from crustacean waste, were prepared from the extruded blends by injection moulding and 3D printing. The nanochitin required was prepared from chitin isolated from prawn shells (Fenneropenaeus indicus). The nanochitin crystals were observed to contain carboxylic acid surface functional groups as assessed by FT-IR, 13C solid state NMR (SS NMR) spectroscopy, zeta potential measurements and the extent of the same was estimated by potentiometric titration. The PBAT-NC nanocomposites were characterized SS NMR spectroscopy, FT-IR spectroscopy, wide angle X-ray diffraction, dynamic mechanical analysis, DSC and TGA. Thermal and mechanical properties of the nanocomposites were determined. The moulded nanocomposites changed more and more rigid with increasing weight percentage of NC without significant change in the tensile strength. The TGA indicated that the thermal stability of PBAT could be improved but not significantly by the addition of NC. Wound healing was enhanced in the presence of the nanocomposite while in vivo toxicity was significant at high concentration. The PBAT-NC nanocomposites could be moulded in to useful articles such as laptop charger cover, rat cover for washing machine, planters and key holders under conditions similar to that used in the processing of LDPE.

The preparation of super water-absorbing hydrogel through the hydrothermal reaction of a mixture of chitosan (CH), itaconic acid (IT) and urea (UR), all of which are sustainable materials, is reported. The structure of the new material, CHITUR, is established by 13C solid-state NMR spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, powder X-ray diffraction analysis (PXRD) and thermogravimetric analysis (TGA). It consists predominantly of unmodified CH and a small fraction of ionotropically cross-linked CH involving ITUR salt as cross-links. The structure of the CHITUR was independent of the composition of IT, UR as well as water content used in the preparation, while the morphology differed significantly. CHITUR exhibited high water and aqueous sodium chloride (0.01 w/v%) absorption. Compared to all the CHITUR preparations, the one with CH:IT:UR of 1:3:3 (all by weight) and 7.5 mL of water per gram of chitosan provided high water absorption, but when the CH:water ratio is increased for this composition of CH:IT:UR, water absorption did not increase significantly. The best water uptake of about 100 g/g (10,000%) was obtained with CHITUR prepared with the following weigh ratio of reactants, namely CH:IT:UR of 1:3:3 with the chitosan:water weight ratio being 1:7.5. In preliminary studies, CHITUR was observed to be suitable for hydroponic growth of seeds.

Tough gels and foams (CHTAUR) based on chitosan were prepared by the hydrothermal reaction of a mixture of chitosan (CH), tartaric acid (TA), and urea (UR). The structure of purified CHTAUR in the solid state was analyzed by Fourier-transform infrared spectroscopy, cross-polarization magic angle spinning 13C-nuclear magnetic resonance spectroscopy, powder X-ray diffraction, and thermogravimetric analysis. CHTAUR is observed to be predominantly chitosan although a minor extent of TAUR salt is present as physical cross-links. The morphology of CHTAUR, as assessed by SEM, suggests the formation of macroporous structures with pore sizes in the range of 90 μm to 1.5 mm. X-ray CT analysis, on the other hand, suggests that the as-prepared CHTAUR foam exhibited open pores of cellular structures with a porosity of around 75% and the average pore size could be in the range of hundreds of μm to few mm. Under conditions of excess water usage, the foams turn into tough gels through water absorption. The suitability of CHTAUR for different applications was examined. Tough gels formed by using a higher extent of water were found to be suitable for compressive loading. The water absorption of the foam was around 25 g/g. A compressive strength study of foams enabled the estimation of the Young’s moduli of CHTAUR foams to be 44.28, 43.80, and 9.96 kPa for foams prepared with CH/H2O weight ratios of 1:5, 1:6, and 1:7.5, respectively. Cytotoxicity studies carried out using the NIH-3T3 cell line showed that CHTAUR, after purification through solvent extraction, supported cell growth and was not toxic to the cell growth, a feature that is also shown by CH. CHTAUR, consisting predominantly of CH, could find use as a biodegradable packaging material and also as a scaffold for tissue engineering applications.

The preparation of composite gels through the hydrothermal reaction of a mixture of chitosan (CH), malonic acid (MLA), urea (UR) and cinnamaldehyde (CA), all of which are sustainable materials, is reported. The new material, CHMLAUR-CA, was characterized by 13C solid-state NMR (SS NMR) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analysis. The properties of the material were evaluated by rheometry and thermogravimetric analysis (TGA), while its morphology was assessed by SEM and AFM. The release of cinnamaldehyde by the composite gels displayed sustained release behavior. Also, the antibacterial study proves that composite gels exhibit a commendable and long-standing antibacterial activity against Escherichia coli (Gram-negative) bacteria and Staphylococcus aureus (Gram-positive). The outcome of the studies revealed that the prepared composite gels could be considered to be efficient long-term antibacterial materials.

Applications of poly(vinyl alcohol) (PVOH) are largely limited due to its poor flame resistance. In this work, organosolubility, and flame resistance are imparted to PVOH through green chemical transformation using dichloroacetic acid (DCAA). Unlike the conventional solvent-based strategies, PVOH was modified by simply mixing it with DCAA and heating the mixture without employing any additional reagents/catalysts/solvents. This resulted in the formation of a random copolymer, poly(vinyl alcohol-co-vinyl dichloroacetate), which was not soluble in water but was soluble in organic solvents such as acetone, methanol, and dimethylsulfoxide. Furthermore, the copolymer was inherently self-extinguishing, and did not melt drip or show glowing combustion. Additionally, dummy currency notes coated with this copolymer displayed exceptional self-extinguishing and non-glowing properties when removed from the flame, proving the copolymer's suitability for flame-retardant sizing/coating applications.

Antibacterial nanocomposite films of poly(butylene adipate-co-terephthalate) (PBAT) incorporated with different weight percentage of octakis(3-chloropropyl)octasilsesquioxane (chloropropyl functionalized POSS [Cl-fn-POSS]) nanofiller were prepared. The mechanical, thermal, morphological, barrier, and antimicrobial properties were examined. The mechanical properties of the nanocomposite films were enhanced by the addition of Cl-fn-POSS nanofiller. An optimum filler loading of 3 wt% is identified to be best suited for maximum enhancement in tensile strength (24 MPa for 3 wt% filled PBAT vs 11 MPa for neat PBAT) while a 1 wt% filler loading was adequate to double the tensile strength. The barrier properties (WVTR and oxygen transmission rate) of PBAT was improved by the presence of Cl-fn-POSS. A volume of 3 wt% filler loading results in 50% reduction of water permeation and 10% reduction in oxygen transmission. The thermogravimetric analyses of the nanocomposites indicated that the filler enabled the enhancement of thermal stability of PBAT. The nanocomposite films revealed antimicrobial activity with this activity increasing with increasing filler content. PBAT is compostable under suitable conditions and with a low weight percentage of filler that is largely made of silicon dioxide these nanocomposite films can find application as biodegradable food packaging material given their flexibility.

This study aimed to explore the production of polyhydroxybutyrate (PHB), a polyhydroxyalkanoate (PHA), which has been widely considered as a potential substitute for the synthetic polymers. Among 53 actinomycete isolates, 11 of them were found to be PHB positive and the quantity of PHB from the positive isolates varied from 10.5 to 29.82 wt% on a dry cell weight basis. A strain designated as PPLAT 012, accumulated relatively higher PHB and has been identified as Isoptericola variabilis by 16S rRNA gene sequence analysis. An effort has also been made to optimize the PHB production by the hyper-producing strain using the conventional, one-factor-at-a-time, and statistical response surface methodologies and the maximum PHB production (46.18%) in DSMZ medium, amended with 12% glucose and 9% potassium nitrate with a pH of 7.0. Further, the characteristic properties such as processability, cytocompatibility and biodegradability of the extracted PHB was also demonstrated. The physical properties of the recovered PHB was further improved by blending with PLA and the resultant blends were characterized. The present investigation has demonstrated that the isolate, Isoptericola variabilis, could be utilized as a potential source for the production of PHB with desirable characteristics, suitable for biomedical applications.

The successful N-carboxymethylation and concomitant crosslinking of solid chitosan upon heating its mixture with solid monochloroacetic acid, without the use of solvents or catalysts, is reported. The N-carboxymethylation was confirmed through the analysis of the partially depolymerized product using NMR spectroscopy, as well as a control reaction with lysine. This transformation was facilitated by the nucleophilic nature of the free amine group in the repeating unit of chitosan, which possesses lone pair of electrons capable of attacking the carbon center bearing the leaving group and displacing the leaving group in a concerted manner. The crosslinking, on the other hand, was established by the observed insolubility in aqueous acidic solutions, even when subjected to prolonged heating at 60 °C. This crosslinking occurs due to the electrostatic interactions between the carboxylate groups and the adjacent ammonium groups, as supported by evidence from FTIR spectroscopy and a control reaction involving ethyl chloroacetate. The resulting crosslinked carboxymethyl chitosan demonstrated its usefulness in the adsorption of methyl orange and fluorescein, as well as functioning as an organic catalyst for aza-Michael addition, Hantzsch reaction, and substituted perimidine synthesis.