Effect of Moisture Content on the Angle of Repose and Coefficient of Kinetic Friction of Sago Trunk (Metroxylon spp.)

Abstract

Starch is one of the food sources that can be extracted from cereals, roots, tubers and stem. Sago palm (metroxylon spp.) is one example of the starch source. The efficiency of the starch extraction process depends on the mechanical properties of process material. This study was conducted to determine the angle of repose between grated sago and kinetic friction of the contact surface between process material and machine. The angle of repose (θ) of grated sago was determined by using a cone shape hopper attached to an adjustable height bar. The cone was filled with a 100g sample of grated sago and slowly adjusted to an upward direction to release the grated sago and will form a conical shape. The cone shape base diameter and height were measured. Next, a square block of debarked sago trunk (8cm × 8cm × 8cm) was placed on a stainless steel plate and attached to a rope at middle connected to force gauges. The pulling speed was at 1.27 mm/min and the result of total pulling load (F) was recorded. The process was repeated for materials with different moisture content (MC) of 60%, 50%, 40%, and 30%. Based on the experimental results, the angle of repose (AoR= 47.000±0.31) and coefficient of kinetic friction (μ k) 0.88±0.005 at MC= 60% showed decrease in value (AoR= 43.610±0.34; μ k = 0.83±0.002) when the MC decrease by 30% (P<0.01).