Granular flows occur widely in nature and industry, yet a continuum description that captures their important features is yet not at hand. Recent experiments on granular materials sheared in a cylindrical Couette device revealed a puzzling anomaly, wherein all components of the stress rise nearly exponentially with depth. Here we show, using particle dynamics simulations and imaging experiments, that the stress anomaly arises from a remarkable vortex flow. For the entire range of fill heights explored, we observe a single toroidal vortex that spans the entire Couette cell and whose sense is opposite to the uppermost Taylor vortex in a fluid. We show that the vortex is driven by a combination of shear-induced dilation, a phenomenon that has no analogue in fluids, and gravity flow. Dilatancy is an important feature of granular mechanics, but not adequately incorporated in existing models.

Natural leather is processed from hides and skins of animals. Synthetic leathers are becoming popular as an alternative material owing to limited availability and varying size of natural leathers. There is a need to understand the properties of natural and synthetic leathers to select proper material for an application. In this study, materials used for apparel application such as natural sheep nappa leather and synthetic polyurethane (PU)-based leather have been chosen and analyzed for comfort, chemical, physical, and structural properties. It was found that natural sheep nappa leather has enhanced water vapor permeability whereas other comfort properties such as softness and drape ability are comparable to synthetic PU leather. Whereas synthetic PU leather dominated most of the physical properties, especially percentage elongation and stitch tear strength, in specific directions on account of polyester knitted base fabric. Chemical properties of natural sheep nappa leather and synthetic PU leather depended on the individual material composition and characteristics. Scanning electron microscopic (SEM) analysis provided convincing evidence for some of the quantified comfort and physical properties. The results of this study would be useful in selection of proper material for apparel application as well as in providing directions for future research in synthetic leather manufacture.

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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