Extrusion rheometry of collagen dough

Abstract

Although collagen is widely used (for example, in the food industry, in the pharmaceutical industry and in biomedicine), the rheological properties of the material are not well known for high concentrations (8% collagen, 90% water). Rheological properties were measured using a capillary-slit rheometer (an extrusion process), where the tested sample of collagen matter was pushed by a hydraulically driven piston through a narrow rectangular slit at very high shear rates of 50–6 000 s<sup>–1</sup>. The Herschel-Bulkley (HB) constitutive equation and a new correlation taking into account the finite gap width was used to evaluate the rheological properties (n = 0.2, K = 879 Pa s<sup>n</sup>, τ<sub>0</sub> = 2 380 Pa). Use was made of a new yield stress measurement method evaluating τ<sub>0</sub> 'post mortem' after extrusion stops. The effects of wall slip and of air bubbles, which caused apparent compressibility of the 'silly putty' collagen material, were also studied. Corrections of the wall slip effect were implemented using sliding layer thickness δ.

Effects of Extrusion and Irradiation on the Mechanical Properties of a Water–Collagen Solution

“…Viscoelastic behavior of the material was detected by a cone and plate oscillating rheometer, modules of G′ 15-18 kPa and G″ of 18-21 kPa were measured, see [30]. Measurements of the thermal properties of the collagen matter by DSC showed thermal capacity values in the range 3700-4400 J/(kg•K) and the transition temperature into gelatin in the range between 33-43 °C, see [31]. The parameters of the power-law model of the shear flow properties were identified as n = 0.28 and K = 700 Pa.s n for the investigated collagen matter, see [3].…”

“…The dimensions of the isotropic samples are presented in Table 1. The same raw collagen mass (isotropic collagen from the same batch) was used to analyze planar samples formed by extrusion of isotropic collagen through a narrow slit (cross-section 2 × 20 mm, capillary length 200 mm) at a very high strain rate of 2000 s −1 , see [31]. The dissipated mechanical energy in the material pushed through the capillary was 2.07 ± 0.31 kJ/kg for the geometry, the process conditions (wall shear stress 11.3 kPa) and the rheology parameters (flow index 0.25 and coefficient of consistency 1700 Pa•s n ) that were used, see [31].…”

“…The same raw collagen mass (isotropic collagen from the same batch) was used to analyze planar samples formed by extrusion of isotropic collagen through a narrow slit (cross-section 2 × 20 mm, capillary length 200 mm) at a very high strain rate of 2000 s −1 , see [31]. The dissipated mechanical energy in the material pushed through the capillary was 2.07 ± 0.31 kJ/kg for the geometry, the process conditions (wall shear stress 11.3 kPa) and the rheology parameters (flow index 0.25 and coefficient of consistency 1700 Pa•s n ) that were used, see [31]. The extruded strips were slightly anisotropic (when clamping the strips, it was necessary to distinguish between the longitudinal orientation and the transverse orientation of the filaments), and the orientation according to the flow direction had to be respected, see Figure 2.…”