@article { ISI:000269197400020, title = {Some mechanistic insights into the gelation of regenerated silk fibroin sol}, journal = {Industrial \& Engineering Chemistry Research}, volume = {48}, number = {17}, year = {2009}, month = {SEP}, pages = {8014-8023}, publisher = {AMER CHEMICAL SOC}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

We provide some new insights into the kinetics and mechanism of sol-gel transition as it pertains to regenerated silk fibroin, which is the principle structural protein of silkworm silk fiber. Silk fibroin was dissolved in lithium bromide and dialyzed against deionized water to prepare a regenerated fibroin solution. This solution was found to be unstable at lower pH and transformed into a colloidal gel. The kinetics and mechanism of the sol-gel transition were investigated using rheology and light scattering. We show that gelation proceeds in two steps. In the first step, a weak gel is formed almost immediately upon lowering the pH, while in the second step further gelation proceeds rapidly after a long induction time to form a self-similar structure.

}, issn = {0888-5885}, doi = {10.1021/ie801723f}, author = {Nagarkar, Shailesh and Patil, Avinash and Lele, Ashish K. and Bhat, Suresh K. and Bellare, Jayesh R. and Mashelkar, Raghunath Anant} } @article { ISI:000276190900021, title = {Structure and gelation mechanism of silk hydrogels}, journal = {Physical Chemistry Chemical Physics}, volume = {12}, number = {15}, year = {2010}, month = {FEB}, pages = {3834-3844}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

Silk fibroin was regenerated from cocoons produced by the silkworm Bombyx Mori. Light scattering showed that an aqueous solution of the regenerated silk fibroin (RSF) was made of individual proteins with a weight average molar mass of about 4 x 10(5) g mol(-1) and a hydrodynamic radius of about 10 nm. Gel formation of RSF in acidic solutions was investigated as a function of the pH (2-4), concentration (0.5-10 g L(-1)) and temperature (5-70 degrees C). The structure of the gels was studied using light scattering and confocal laser scanning microscopy. The structure was found to be self-similar from length scales of less than 15 nm up to length scales of about 1 mm, and characterized by a correlation length of a few microns. Gel formation was tracked using turbidity, rheology, light scattering and circular dichroism. Gelation involves the formation of self-similar aggregates with a growth rate that increases exponentially. The protein aggregation is correlated to, and perhaps caused by, the formation of beta-sheets, the fraction of which also increases exponentially with time.

}, issn = {1463-9076}, doi = {10.1039/b916319k}, author = {Nagarkar, Shailesh and Nicolai, Taco and Chassenieux, Christophe and Lele, Ashish K.} } @article {46151, title = {Structure-property relations in regenerated cellulose fibers: comparison of fibers manufactured using viscose and lyocell processes}, journal = {Cellulose}, volume = {26}, year = {2019}, month = {APR}, pages = {3655-3669}, type = {Article}, abstract = {

Regenerated cellulose fibers are produced using two industrially dominant technologies: the viscose and lyocell processes. Here, we compare commercially available fibers, prepared using the viscose and lyocell processes. Single fibers are subjected to a variety of mechanical deformations to obtain stress-strain, stress relaxation and stress recovery data. These are fitted to a phenomenological model, whose parameters are interpreted in terms of the fiber semicrystalline microstructure. This simple model does not incorporate the complexities of semicrystalline microstructure. Rather, it represents structure in a semicrystalline polymer fiber in terms of an elastic crystalline phase that coexists with a viscoelastic Voigt-like glassy amorphous phase. Lyocell fibers are characterized by higher values of crystalline modulus relative to viscose. Lyocell fibers also have a higher amorphous phase modulus and a wider relaxation spectrum than viscose, suggesting that amorphous and crystalline phases are dispersed in close connectivity in lyocell. Viscose and lyocell fibers exhibit qualitative similarities in their mechanical response. On stretching, there is a transition in the stress-strain curve from a low strain elastic response at a critical value of strain. This critical strain has been incorrectly attributed to yielding of the fiber. We establish that this critical value corresponds to an apparent yield. When subjected to strains higher than this apparent yield point, the fibers develop a memory of the mechanical deformation. This memory decays slowly, logarithmically with time and is lost over about a day as the fiber structure transitions back to the original as spun fiber. Finally, we demonstrate that on wetting the fibers with water, there is an increase in the apparent yield strain for viscose fibers, but not for lyocell. We interpret these results in terms of the semicrystalline microstructure of the fibers.

}, keywords = {mechanical properties, Model, Regenerated cellulose, Yielding}, issn = {0969-0239}, doi = {10.1007/s10570-019-02352-w}, author = {Sharma, Aakash and Nagarkar, Shailesh and Thakre, Shirish and Kumaraswamy, Guruswamy} }