A.J. Varma

Lactic acid production from waste sugarcane bagasse derived cellulose

Production of L(+)lactic acid from sugarcane bagasse cellulose, one of the abundant biomass materials available in India, was studied. The bagasse was chemically treated to obtain a purified bagasse cellulose sample, which is much more amenable to cellulase enzyme attack than bagasse itself. This sample, at high concentration (10%), was hydrolyzed by cellulase enzyme preparations (10 FPU g–1 cellulose) derived from mutants generated in our own laboratory. We obtained maximum hydrolysis (72%), yielding glucose and cellobiose as the main end products. Lactic acid was produced from this bagasse cellulose sample by simultaneous saccharification and fermentation (SSF) in a media containing a cellulase enzyme preparation derived from Penicillium janthinellum mutant EU1 and cellobiose utilizing Lactobacillus delbrueckii mutant Uc-3. A maximum lactic acid concentration of 67 g l–1 was produced from a concentration of 80 g l–1 of bagasse cellulose, the highest productivity and yield being 0.93 g l–1 h–1 and 0.83 g g–1, respectively. The mutant Uc-3 was found to utilize high concentrations of cellobiose (50 g l–1) and convert it into lactic acid in a homo-fermentative way. Considering that bagasse is a waste material available in abundance, we propose to valorize this biomass to produce cellulose and then sugars, which can be fermented to products such as ethanol and lactic acid.

A study of crystallinity changes in oxidised celluloses

Abstract Cellulose was oxidised to dialdehyde cellulose (DAC), sodium dicarboxy cellulose (NaDCC) and dicarboxy cellulose (DCC). Products having oxidation levels of 12, 30, 60, 80 and 98% based on glucose monomer units, were obtained by adjusting the quantity of oxidising agents. The wide-angle X-ray diffraction peak at 2θ = 22·7° for the various oxidised cellulose samples, which indicates the crystallinity of the cellulose, was found to decrease almost proportionately to the degree of oxidation of the starting cellulose. The differences in crystallinity between DAC, NaDCC and DCC of the same degree of oxidation are expected to result from differences in their hydrogen bonding ability with adjacent molecules. Their ability to hydrogen bond with water is reflected in their water absorption capacity. NaDCC has an exceptionally high water absorption capacity owing to its polyelectrolyte nature. DCC absorbs more water than the corresponding DAC since the carboxy group forms stronger hydrogen bonds than the aldehyde group. Thermogravimetric analysis of the three oxidised celluloses showed that DCC decomposes at a somewhat higher temperature than DAC in the initial stages up to around 400°C, reflecting greater stability, possibly due to better intermolecular hydrogen bonding. However, as the temperature is increased further, DCC degrades somewhat faster than DAC, NaDCC, as expected, being a polyelectrolyte shows much less weight loss, and the weight loss occurs over a very wide range. The changes in the structure and crystallinity are also seen in the CP-MAS C-13 NMR studies of these molecules.

Thermal stability of cellulose and their nanoparticles: Effect of incremental increases in carboxyl and aldehyde groups

Oxidized cellulose containing carboxyl and aldehyde functional groups represent an important class of cellulose derivatives. In this study effect of incrementally increasing COOH and CHO groups at C2, C3, and C6 positions of cellulose and nanocellulose has been investigated, with a view to understanding their effect on thermal treatment of cellulose. The results show that 2,3-dialdehyde cellulose (DAC) is the most thermally stable oxidized product of cellulose while the most unstable derivatives contain carboxyl group at the C6 position (6CC). Carboxymethylcellulose (CMC), with carboxymethyl group on C6 position, is more stable than 6CC. Multi-functionalized celluloses 2,3,6-tricarboxycellulose and 6-carboxy-2,3-dialdehyde, have the same level of thermal stability as 6CC, showing that the presence of carboxyl at the C6 is a key destabilizing factor in the thermal stability of oxidized cellulose products. More the number of reducing end groups on the polymer chain, lower the thermal stability of the cellulose, as proved by comparing the TGA/DTG of monomeric analogs dextrose, cellobiose and glucuronic acid with the oxidized celluloses. The thermal stability trend observed for oxidized celluloses was DAC>DCC>nanoparticles>dextrose>glucuronic acid, caused by extent of reducing ends and COOH groups.

Towards biodegradable polyolefins: strategy of anchoring minute quantities of monosaccharides and disaccharides onto functionalized polystyrene, and their effect on facilitating polymer biodegradation

A hypothesis was developed, and successfully tested, to greatly increase the rates of biodegradation of polyolefins, by anchoring minute quantities of glucose, sucrose or lactose, onto functionalized polystyrene (polystyrene-co-maleic anhydride copolymer) and measuring their rates of biodegradation, which were found to be significantly improved.

Macrocyclic ligands on polymers

Abstract The ion binding properties of linear polymers carrying crown ether ligands as pendent groups are reviewed. The polymers often exhibit selective cation binding different from that of their monomeric crown analogues. One of the polymers, poly(vinylbenzo-18-crown-6), behaves in water as a neutral polysoap and strongly interacts with organic anions. The binding is enhanced and also can be regulated by charging the polymer with crown complexable cations. This polymer also catalyzes solvent sensitive reactions by a micellar type mechanism. In the decarboxylation of 6-nitrobenzisoxazole-3-carboxylate in water the substrate bound to the Cs+ charged poly(crown ether) decomposes 14000 times more rapidly than in water. In benzene the decarboxylation is also accelerated by poly(crown ethers), but in this case as a result of anion activation. Poly-(crown ethers) were also found to form polysalt complexes in water with several polyanions in the presence of crown complexable cations. In the absence of salts, complexes can be formed with polyacids through hydrogen bonding.

Morphology of cellulose and oxidised cellulose in powder form

A series of 2,3-dialdehyde cellulose (DAC), sodium 2,3-dicarboxylate cellulose (NaDCC), and 2,3-dicarboxycellulose (DCC) (30, 60, 80, and 98% based on glucose monomer units) were prepared from commercial cellulose powder. The morphology of these powdered samples were investigated by scanning electron microscopy. The cellulose powder was found to be in the form of fibres having an aspect ratio of 14, and this value decreased for all the 30% oxidised derivatives, in agreement with wide-angle X-ray diffraction results (WAXRD). For DAC and NaDCC, the SEM of higher derivatives (60% oxidation and above) did not show presence of discrete fibres, but for all the DCC derivatives, the SEM showed discrete fibres. The surface effects seen in SEM are not apparent in WAXRD spectra, offering a new insight into the physical form of the oxidised cellulose samples.

Functionalized celluloses and their nanoparticles: morphology, thermal properties, and solubility studies.

Agricultural residues derived cellulose was used to synthesize a new series of carboxy functionalized cellulosic nanoparticles (quasi-spherical shaped, 13.2-21.5% carboxyl content) and macro-sized 6-carboxycelluloses (long-fibril shaped, 1.7-22% carboxyl content). The DP (50-70) and yield (upto 46%) of nanoparticles were manipulated by controlling the reaction temperature and time. TGA/DTG thermographs of the carboxycelluloses gave thermostability data and co-related well with the residual crystalline, amorphous, and anhydroglucuronic acid content. The particle shape and size had no effect on the thermal stability. Some derivatives were fully or partially soluble in aqueous alkali and non-aqueous solvents, which can lead to increased versatility of these polymers.

Wide-angle X-ray diffraction study of the effect of periodate oxidation and thermal treatment on the structure of cellulose powder

Abstract Cellulose and periodate oxidised cellulose powders were investigated for any structural changes occurring when subjected to thermal treatment, since their use as fillers in composites involves prolonged exposure to high temperatures. The wide-angle X-ray diffraction peak at 2 θ = 22·9° for the oxidised cellulose samples was found to decrease almost proportionately to the degree of oxidation of the starting cellulose. Whereas heat treatment of cellulose powder at 120°, 180° and 240°C for three hours also produces a continual decrease in the crystallinity of the cellulose, heat treatment of periodate oxidised cellulose at 120°, 180° and 240°C for three hours produces drastic changes in the crystallinity of the resultant products. For 16% oxidised cellulose heated at 240°C for three hours, almost total crystallinity is lost. This is also seen from the increase in line broadening of the X-ray diffractogram. An interesting feature in the above cases was the appearance of an additional peak at 2 θ ≈ 12°. In DTG studies the temperature at which the major loss in weight (∼ 62%) occurred was ∼ 290°C for most samples. The final weight loss (∼ 85%) generally occurred at 430–450°C. The 16% oxidised cellulose behaved somewhat differently, and reasons for this are explained.

Environment friendly crosslinked chitosan as a matrix for selective adsorption and purification of lipase of Aspergillus niger

Chitosan and its derivatives have been used as affinity matrices for purification of lipase from Aspergillus niger NCIM 1207. Trimellitic anhydride (TMA)-crosslinked deacetylated chitin adsorbed lipase selectively, yielding approximately 5-fold purification of the crude lipase with 70% yield. Further 9-fold purification occurred on eluting through Sephacryl-100. These results suggest that chitosan derivatives can be used as inexpensive biopolymer matrices for the purification of lipases for industrial applications.

Separations based on chemically selective polymer gels

We address the question of separation of mixture of organic solvents using the chemical selectivity of hydrophobic gels. The solvent mixtures selected were such that one of the solvents interacted strongly with the hydrophobic gel (i.e. the gel absorbed significant quantities of the solvent), while the other solvent interacted weakly with the gel (i.e., no significant absorption in the gel compared to the first solvent). We report interesting first results to demonstrate attractive selectivities in the extraction of the stronger solvents from the liquid mixtures (including those of close boiling solvents), which could potentially lead to a new gel-mediated separation process