It is found from Tables 1 to 3 that the double stage treated coir fiber had better properties compared to the single stage treated and raw coir fibers.
After a total of 5 hours treatment, the corrected Young’s modulus of coir fiber was higher compared to the same of single stege treated coir fiber and was almost twice as much as the Young’s modulus of the raw fiber.
A thin coating layer was forrmed on the fiber surface after single stage chemical reaction between basic CrSO4 and fiber.
Again after double stage chemical treatment, an even thicker coating was formed on the fiber surface due to chemical reaction between basic CrSO4 and NaHCO3 and fiber.
The chemical reactions between cellulose of coir fiber and basic CrSO4 and NaHCO3 are shown in Fig. 10.
The stages of CrSO4 cross linking reactions are as follows:
a) The chrome complexes have reacted with the fiber cellulose carboxyl groups.
b) As pH of the solution is increased, sulfate associated with the chromium becomes displaced by the hydroxyl groups.
c) The hydroxyl groups become shared by chromium atoms.
The activity of chromium still remained incomplete after the single stage chemical treatment; as a result the tensile properties increased less over the raw coir fiber. However after the double stage treatment chromium became fully occupied in reducing hydroxyl groups,
which in turn increased the tensile properties of coir fiber compared to both raw and single stage treated coir fibers (Fig. 12).
The Shaking time is very important. The reaction rate accelerates during shaking. Shaking in solution also cleans the fiber surface.