Power Laws in the Elasticity and Yielding of Plant Particle Suspensions

Abstract

The yielding and flow behaviour of plant suspensions are perhaps the most important rheological properties in process and product design for applications in paper, biofuel and food industries. Studies are reported here on the yield properties and flow behaviour of suspensions of plant particles with different shapes (clusters of cells, individual cells and cell fragments). Carrot and tomato were selected as model plant systems to prepare suspensions at particle dry mass concentrations ranging from 0.010 to 0.065. The flow behaviour was characterised by an apparent yield stress and shear thinning. The HerschelBulkley yield stress obtained from up and return flow curves was compared to the yield stress calculated from oscillatory measurements. The dependence of the yield stress values on particle dry mass concentration is approximately a power-law, with a fitted exponent of 3±0.5 for all the suspensions, independently of the plant origin and particle shape. This same power-law behaviour was found for the elastic modulus G′, and in this case the exponent was 3 for carrot and 4 for the tomato suspensions. The yield strain, calculated from oscillatory measurements, decreased slightly with dry mass fraction, but did not follow a powerlaw. We discuss possible explanations for power law behaviour, and provide a model for G′ based on folded elastic sheets, which predicts an exponent of 3, similar to the values obtained for these suspensions.

Effect of Enzymes on Serum and Particle Properties of Carrot Cell Suspensions

“…Ashwin K Sankaran (1,2), Jaap Nijsse (1) , Ruth Cardinaels (3,4) , Lucy Bialek (1) , Avi Shpigelman (2) , Marc Hendrickx (2) , Paula Moldenaers (3) Effect of enzymes on serum and particle properties of carrot cell suspensions Ashwin K Sankaran (1,2) , Jaap Nijsse (1) , Ruth Cardinaels (3) , Lucy Bialek (1) , Avi Shpigelman (2) , Marc Hendrickx (2) , Paula Moldenaers (3) and Ann M. Van Loey (2,*) the date of receipt and acceptance should be inserted later Abstract Rheological properties of cell wall suspensions strongly depend on particle size and particle-particle interactions. In the present study, an experimental method was developed to study the effect of particle elasticity and electrostatic interactions on the rheological properties of cell suspensions.…”

“…Measuring the weight loss due to evaporation gives the total solid content in the sample. Figure 2 showed the particle morphology of the untreated samples which presents mostly single cells due to the hot break treatment [2]. The mean particle size for the reference sample was found to be 83 μm.…”

“…The storage modulus of the various samples was measured as a function of the total solid content, shown in figure 4. The storage modulus is known to have a power law dependence on the total solid content (equation 1) within the semi-dilute region [2,6,17]. After fitting the curves with a power law model the coefficients obtained for the respective samples are shown in figure 4.…”

“…There is also sufficient evidence to show that there are complex interactions between either the serum-particle or particle-particle phases of the suspensions. The nature of these interactions could be electrostatic, frictional or elastic, depending on the particular system [2]. Electrostatic interactions in the serum phase are common to occur either between protein-pectin [3,4] or pectin-pectin compounds [5].…”

“…As these particles are also deformable, it has been suggested that the elasticity of plant particles can be important to fully understand the rheological properties of plant based suspensions. On shearing, the particles behave like folded elastic sheets that contribute to the storage modulus [2]. It is clear that there are two possible mechanisms of interaction between plant particles, depending on their concentration in the suspensions.…”