**Acknowledgements**

*Microencapsulation - Processes, Technologies and Industrial Applications*

correlation coefficients established with the expanded varying coating thicknesses. Therefore knowledge of plant metabolic requirement is a prerequisite in the design of CRFs. The sigmoidal model has also proved its usefulness in the description of the controlled release. The constants and correlation coefficients of the sigmoidal model equations were determined and recorded in **Table 1**. *k*p and *n* are the power equation constants, *k*e is the exponential equation constant, and *a, b, c, d* are the

**Power Exponential Sigmoidal**

Raw Urea 0.2994 0.3847 0.888 0.1562 0.986 −0.3146 0.9900 2.7864 4.0190 1 0.1 mm 0.1838 0.5187 0.957 0.1066 0.987 −1.1582 1.0154 6.7805 −0.6027 0.988 2.2 mm 0.0769 0.7416 0.987 0.0638 0.991 −0.1634 0.9581 6.9069 9.7049 0.996 4.3 mm 0.0354 0.9381 0.976 0.0460 0.989 −0.1962 0.8166 5.8552 10.5014 0.993 6.4 mm 0.0143 1.1990 0.969 0.0385 0.972 0.0317 0.7519 3.1002 15.3357 0.999 8.5 mm 0.0075 1.3685 0.963 0.0325 0.965 0.0147 0.6912 2.6945 15.9864 0.999

*kp n* **r** *ke* **r a b c D r**

The effect of coating thickness on lag, constant and decay release characteristic of CRCU has been investigated. It observed that the release time increases with increase in coating thickness. Starch-polyvinyl alcohol (St-PVOH) biocomposite as materials of biodegradable and regenerative resource was found to provide a semi

**120**

sigmoidal equation constants.

*Correlation coefficients of the empirical equations.*

*Coated urea of various coating thickness.*

**4. Conclusion**

**Table 1.**

**Figure 8.**

Tertiary Education Trust Fund (TETFUND), Nigeria, is hereby acknowledged for the research grant given to us to accomplish this study.
