Viscoelasticity of the Bulk Quantities of Eight Saudi Date Cultivars

Viscoelasticity of the bulk quantities of eight Saudi date cultivars namely, Barhi, Khudari, Khlass, Serri, Sukkari, Suffri, Sakkie, and Nubot Saif at Khalal, Rutab and Tamer stages of maturity, were experimentally determined in terms of stress relaxation parameters. Experimental results revealed the significant effect of stage of maturity. The values of initial stress (σ0) and equilibrium stress (σe) were higher at the Khalal stage compared to the Rutab stage for all eight date cultivars. The highest values were for Sakkie cultivar at both Khalal and Rutab stages and equal 9.85, 2.76 kPa and 9.72, 2.76 kPa, respectively. For Tamer stage the values of initial stress (σ0) and equilibrium stress (σe) were higher compared to Khalal for all tested cultivars except for Serri cultivar with values of 4.98 and 0.86 kPa, respectively. The maximum value of initial stress (σ0) at the Tamer stage was for Sukkri cultivar (17.57 kPa). Three mathematical models, namely, Generalized Maxwell, Nussinnovitch, and Peleg were tested for suitability of predicting experimental results. All three models fitted experimental data well; however the Generalized Maxwell model was the best, followed by Nussinnovitch model.

Keywords:

Viscoelasticity , Stress relaxation , Date cultivars , Maxwell model , Maturity stage