Optimization of Environmentally Benign Polymers Based on Thymine and Polyvinyl Sulfonate Using Plackett-Burman Design and Surface Response

Table 3

Levels of the variables tested in the CCD.

Variable	Type	Symbol	Factorial levels		Axial levels		Central level
pH	Numerical	𝑋1	7.50	10.50	6.00	12.00	9.00
Concentration	Numerical	𝑋2	4.00	8.00	2.00	10.00	6.00