Optical bifunctionality of europium-complexed luminescent graphene nanosheets

Graphene is an intriguing two-dimensional material, which could be modified for achieving tunable properties with many applications. Photoluminescence of graphene due to plasmonic emission is well-known, however, attempts to develop strong luminescent graphene have been difficult. Synthesis of a graphene-based material with a dual optical functionality, namely quenching the fluorescence of organic dyes while maintaining its own self-luminescence, is an interesting and challenging proposition. Here, we demonstrate this optical bifunctionality in a lattice-modified luminescent graphene, where europium(III) cations are complexed with graphene through oxygen functionalities. After excitation at 314 nm, a hypersensitive red emission is observed at 614 and 618 nm showing the complexation of europium(III) with graphene. We demonstrate dual functionality of this graphene by the quenching of luminescence of Rhodamine-B while displaying its own hypersensitive red emission. The decay lifetime observed through the time-resolved spectroscopy confirms its potential for applications in biosensing as well as optoelectronics.     

Natural leathers from natural materials: progressing toward a new arena in leather processing

Globally, the leather industry is currently undergoing radical transformation due to pollution and discharge legislations. Thus, the leather industry is pressurized to look for cleaner options for processing the raw hides and skins. Conventional methods of pre-tanning, tanning and post-tanning processes are known to contribute more than 98% of the total pollution load from the leather processing. The conventional method of the tanning process involves the "do-undo" principle. Furthermore, the conventional methods employed in leather processing subject the skin/ hide to a wide variation in pH (2.8-13.0). This results in the emission of huge amounts of pollution loads such as BOD, COD, TDS, TS, sulfates, chlorides and chromium. In the approach illustrated here, the hair and flesh removal as well as fiber opening have been achieved using biocatalysts at pH 8.0, pickle-free natural tanning employing vegetable tannins, and post-tanning using environmentally friendly chemicals. Hence, this process involves dehairing, fiber opening, and pickle-free natural tanning followed by ecofriendly post-tanning. It has been found that the extent of hair removal and opening up of fiber bundles is comparable to that of conventionally processed leathers. This has been substantiated through scanning electron microscopic analysis and softness measurements. Performance of the leathers is shown to be on par with conventionally chrome-tanned leathers through physical and hand evaluation. The process also exhibits zero metal (chromium) discharge and significant reduction in BOD, COD, TDS, and TS loads by 83, 69, 96, and 96%, respectively. Furthermore, the developed process seems to be economically viable.     

Gauge length effect on the tensile properties of leather

Tensile properties are important basic characteristics of materials and influence their end‐use and performance. More importantly, in the case of leather due to end‐use applications such as shoe uppers, automotive and furniture upholstery, mechanical properties such as tenacity are of extreme importance. Therefore, fundamental studies on the tensile properties of leather are needed. In this study, an attempt has been made to examine the effect of gauge length (GL) on the tensile properties of shoe upper leather. Two different specimens in the form of rectangular and dumbbell shapes have been cut from parallel and perpendicular directions to the body axis of the leather and have been tested. Results showed that the maximum breaking load and the percentage extension at break decreased with the increase in GL. Rectangular specimens showed a 30% decrease in maximum breaking load and a 13% decrease in percentage extension at break, while dumbbell specimens showed reductions in the order of 28 and 6%, respectively, as the GL increased from 9.53 cm to 23.5 cm. Highly varying supramolecular architecture of the collagen matrix and the frictional slippage caused by the free ends present in the collagen fibrils, which induce a weak‐link effect similar to the one found in cotton fibers and yarns, are considered to be the probable reasons for this behavior. A limited scanning electron microscopic study has been undertaken to pictorially represent the breakage of leather at different GLs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1202–1209, 2006     

Removal of chromium from aqueous solution using cellulose acetate and sulfonated poly(ether ether ketone) blend ultrafiltration membranes

A process for purifying aqueous solutions containing heavy and toxic metals such as chromium has been investigated. Chromium salts are largely used in various industries including leather-manufacturing industry. Ultrafiltration processes are largely being applied for macromolecular and heavy metal ion separation from aqueous streams. Cellulose acetate and sulfonated poly(ether ether ketone) blend ultrafiltration membranes were prepared by precipitation phase inversion technique in 100/0, 90/10, 80/20 and 70/30% polymer blend compositions and subjected to the rejection of chromium at different concentrations such as 200, 400, 600, 800 and 1000 ppm with a water-soluble macroligand (polyvinylalcohol). Factors affecting the percentage rejection and permeate flux such as pH, concentration of solute, concentration of PVA, transmembrane pressure and composition of blend membranes were investigated. It was found that percentage rejection improved at a pH 6 and a macroligand concentration of 2 wt.%. The transmembrane pressure and concentration of solute also have an effect on the separation and product rate efficiencies of the blend membranes.     

Integrated hair removal and fiber opening process using mixed enzymes

The use of enzyme-based products for many areas in leather making has been projected and some have found their way in commercial practices. Proteolytic and α-amylase enzymes are used in hair removal and fiber opening, respectively, producing comparable results to conventional practice of lime and sulfide-based dehairing and fiber opening. However, this process is a two-step sequence in which dehairing is performed by the proteolytic enzyme followed by fiber opening through α-amylase. In this study, an attempt has been made to achieve a single-step dehairing and fiber opening using mixed enzymes. A commercial product containing a mixture of α-amylase and protease is used for simultaneous dehairing and fiber opening of goatskins. Standardized experiments show that the leathers obtained were comparable to that of the conventionally produced leathers in terms of all the physical and bulk properties. The input–output analysis validates the observations made for dehairing and fiber opening in the preliminary trials, which are also confirmed through scanning electron micrographs. Reductions in water consumption, wastewater discharge, COD and TS loads are in the order of 30% when compared to conventional leather processing. There seems to be a significant reduction in the expenditure incurred on the leather processing upon introducing the integrated enzymatic beamhouse process.

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Transforming chromium containing collagen wastes into flexible composite sheets using cellulose derivatives: Structural,thermal, and mechanical investigations

Leather, footwear, and clothing industries produce significant quantity of chromium containing proteinaceous wastes. One of the major uses of these wastes is to convert them into sheets or boards. However, the previous methods could not provide flexible sheets with desired strength. Here, we describe a simple and efficient method for the preparation of flexible composite sheets using chromium containing collagenous wastes (CS) with the use of cellulose derivatives. The leather wastes have been partially hydrolyzed and converted into composite sheets under microwaves with the addition of 2‐hydroxyethyl cellulose (HEC) in varying concentrations from 2.5 to 20 wt%. A comprehensive strength as high as 3.14 ± 0.45 MPa with a softness of 3.8 ± 0.2 mm is achieved with the addition of 20 wt% HEC in the CS/HEC composite sheets. Scanning electron microscopic and mercury intrusion porosimetric analysis demonstrate the reduction in pores, especially micro pores (<50 μm), when the concentration of HEC is higher thereby showing improved interfacial adhesion of HEC onto CS. Infrared spectroscopy result indicates the presence of distinctive bands associated with both CS and HEC. There is also a reasonable increase in the thermal stability of the CS/HEC sheets as the content of HEC increases. Hence, the developed CS/HEC composite sheets were found to be flexible and have improved thermo‐mechanical properties, which are suitable for applications in leather product and allied industries. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

An eco-friendly option for less-chrome and dye-free leather processing: in situ generation of natural colours in leathers tanned with Cr–Fe complex

A chromium–iron tanning agent has been prepared and used for tanning with the objective of high exhaustion of chromium. Chromium–iron tanned leathers exhibit comparable shrinkage temperature and strength properties with those of conventional chromium tanned leathers. There is no change in strength or colour on ageing the leathers for 1 year. Spent tan liquor analysis reveals that the exhaustion of both the metals is more than 90%. Dyes based on synthetic formulations are being widely used in the leather industry. However, it is known that many aryl amine dyes are banned because of their carcinogenic nature. Environmental concern leads one to look for dyes based on natural resources. A novel approach has been taken to achieve an eco-friendly coloration process utilizing the presence of iron in the tanning salt, which gives rise to various colours on reacting with vegetable tannins. Skins have been tanned with Cr–Fe tanning salt and complexed with different vegetable tanning materials such as myrobalan and quebracho at various concentrations. Colours such as brown, black and grey have been developed. The colour shades obtained have been quantified by reflectance measurements. Thus, the study provides not only clean processes for a greener environment but also clean leather without harmful synthetic dyes. Electronic Publication     

Performance characterization of cellulose acetate and poly(vinylpyrrolidone) blend membranes

Hydrophilic ultrafiltration membranes have been prepared by blending cellulose acetate (CA) as a matrix polymer with increasing concentrations of poly(vinylpyrrolidone) (PVP) using N,N′‐dimethylformamide as the solvent. It is observed that the presence of PVP beyond 50 wt % in the casting solution did not form membranes. Prepared membranes have been subjected to ultrafiltration characterizations such as compaction, pure water flux, water content, and membrane hydraulic resistance. The results indicate significant changes in the characteristics upon the addition of PVP, which may lead to improved performance. The porosity, pore size, and molecular weight cut‐off of the membranes also increase as the concentration of PVP increases. It is estimated that the pore radius of the CA/PVP membranes increases from 30 to 63 Å, when the concentration of PVP increased from 0 to 50 wt %. This is in agreement with the results obtained from scanning electron microscopic studies. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Development of formaldehyde-free leathers in the perspective of retanning: part II. Combination of formaldehyde-free retanning syntans

There is a growing demand for the formaldehyde-free leathers in global leather market due to increasing awareness towards eco-labelling. The first part of this work described the optimisation of formaldehyde-free syntans in their applications as single syntans in making leathers with desired properties. In this work the use of formaldehyde-free syntans in combination to produce leathers with desired properties has been attempted. Three combination-retanning systems have been chosen using formaldehyde-free resin, acrylic and protein syntans. The performance of leathers in terms of bulk and strength properties is shown to be comparable or even better for all the combination-retanning systems chosen compared to the control system. In particular, Experiment “C” (resin syntan 3%, acrylic syntan 4% and protein syntan 2%) provides leathers with improved bulk, strength and colour properties as well as reduced COD and TS loads, besides not having free formaldehyde. Scanning electron microscopic study reveals that the extent of filling in all the three combination-retanning systems is similar.