Assuming that you have used the general equation of fibre volume fraction for predicting mechanical properties, there could be some discrepancies between theoretical prediction and experimental findings. The equation fails to consider factors such as:

* Moisture uptake by the natural fibres

* Agglomeration of fibres

* Degree of wetting

* Maximum volume of fibres a polymer can take  which depends on the polymer chosen

I hope this helps!

Thanks for your valuable answer its very helpful.

Differences are observed for Elastic and Ultimate properties.

Other than those given in the previous answer:

Elastic properties in the direction of the fibers: natural fibers misalignments and curling

Elastic properties transverse to the fibers direction: clustering and fiber diameter variability.

Ultimate properties in the direction of the fibers: fiber diameter variance (over the mean value)

Ultimate properties transverse to the fibers: poor adhesion

Thanks for your valuable answers and its very reasonable.

properties of natural fiber varies throught its volume, but in theoretical analysis we have to assume the values to be same. so the difference in reflects in our results.