Table 2.

Experimental levels of the independent factors.

Variables	Levels
	-α	-1	0	+1	+α
Concentration of epichlorohydrin (%, w/w)	0.31	3	9.5	16	18.69
Length of cross-linking time (h)	0.86	1	9.5	10	11.86

α = 1.41412.