Gelling properties of biodiesel at low temperatures

The gelling properties of biodiesels were studied with rheometer in the modes of small amplitude oscillatory shearing. The results show that in addition to the cooling gelling properties, biodiesels also show obvious isothermal gelling properties at low temperatures. The effects of cooling rate and shear stress on the gelling properties of biodiesels were studied. The gel point of biodiesel decreases and the strengths of gel structure at the same temperature during cooling and isothermal gelling process weaken with the increase of cooling rate under quiescent conditions. At the same cooling rate, the gel strength during cooling and isothermal gelling process is much weaker with increasing shearing stress. However, the gel strength of biodiesel has little difference after isothermal gelling process although the shear stress applied during cooling process is different. During cooling the gel strength decreases with the increase of cooling rate when the applied shear stress is smaller; but the gel strength increases with the increase of cooling rate when the applied shear stress is larger. No matter the shear stress' values applied in cooling process, the gel structure is enhanced with the increase of cooling rate during the isothermal gelling process.