Formulation optimization of psyllium-based binding product by response surface methodology.

Psyllium traditionally is used as a laxative agent and a source of dietary fiber. Recently, in the landscape industry, a psyllium-based binding product was innovatively used to replace chemical binders for pavement in environmentally sensitive areas. The ingredients of the psyllium-based binding product were determined through preliminary experiments by investigating the gelling properties of psyllium husk. Two features of gelation, the elastic modulus Gand critical strain S were investigated simultaneously by Response Surface Methodology (RSM) with respect to three factors: psyllium gum concentration, calcium ion concentration, and pH. Psyllium concentration was found as the major factor affecting the elastic modulus Gwhereas both psyllium and calcium ion concentration affected the critical strain S. Contour plots and a constrained optimization approach were applied to obtain the optimum level of psyllium in the binding product. The optimum formulation was found as psyllium 1.22% (w/w) and Ca 2+ 1.235 mol/L at pH 7.27. In industrial application, lime was used as calcium ion source and soda ash to adjust pH. The breaking force of a three-point bend test for the sand samples was investigated as an indicator for the binding property by RSM, which represents the application of this product in the field. The optimum formula for a psyllium-based binding product was obtained with 1.82% (w/w) psyllium, 1.05% (w/w) lime, and 0.55% (w/w) soda ash. The improved formula demonstrated great feasibility and could bring significant economic benefit for the industry. This study also demonstrated that response surface methodology is a useful tool for the optimization of the psyllium-based binding product.