Tensile properties (Young's moduli, E's, tensile strengths, σ_max's, elongations at break, ε_max's, and toughnesses, T_s's) and tearing energies, T_y's, measured at room temperature (RT) (∼25 °C) at a crosshead speed of 50 mm min⁻¹, of poly(vinyl alcohol) (PVA)/alginate sequential, hydrogen-bonded-ionic dual-physical double-network (DN) hydrogels having mole ratios of the PVA- to sodium alginate (SA) repeat units of 20/1, 30/1, 40/1, 50/1, 60/1, 70/1 and 80/1, against those of their corresponding PVA hydrogen-bonded and alginate ionic single-network (SN) hydrogels^a.

PVA/alginate hydrogel	E (kPa)	σ max (MPa)	ε max (mm mm−1)	T s (kJ m−3)	T y (J m−2)
PVA	49	0.36	2.8	408	63
Alginate	100	0.42	2.2	465	30
20/1	400	0.50	1.4	454	201
30/1	308	1.3	4.8	2494	402
40/1	270	1.5	4.2	3137	433
50/1	267	1.8	5.1	4875	446
60/1	257	1.9	5.1	4461	453
70/1	238	1.7	4.7	4071	441
80/1	220	1.5	4.2	3048	437

^aSince they are both formed by hydrogen bonding of an ∼13–20 wt% of PVA aqueous solution upon its freeze–thaw (RT–−25 °C–RT) cycle of being frozen at −25 °C for 20 h and then thawed back at RT for at least 4 h, followed by its immersion into a large amount of Ca²⁺ aqueous solution of 1.0 mol L⁻¹ at RT for at least 8 h, the DN-gels PVA networks and the PVA SN gel have similar compositions (i.e. water contents) and morphologies (i.e. crosslink structures and -densities) to each other. Likewise, as they are both constructed through ionic cross-linking of an ∼1–3 wt% of SA aqueous solution with the large amount of Ca²⁺ immersion solution of 1.0 mol L⁻¹ at RT for at least 8 h, the DN-gels alginate networks and the alginate SN gel possess analogous compositions and morphologies to each other.