4. Conclusions
A superabsorbent product was synthesized by direct grafting of
acrylic acid onto cassava starch in the presence of a polymerization
crosslinker. The increase of grafting parameters at increased
crosslinker concentration indicates that part of the homopolymer
formed in the homogenous reaction system becomes incorporated
in the grafted network. By variation ofthe crosslinker content(CL%),
an optimum in the water absorbency of up to 114 g H2O/g could be
obtained. Interestingly, this optimum is at 2% CL which does not
directly correspond with the best grafting results, obtained at 1.5%
CL. A remarkable feature of the product with the best absorption
capacity is its ability to retain more than half of this maximum
amount of water also under the mechanical strain of severe suction.
The good absorption and retention properties obtained in this
grafted starch would allow for a further development of the material,
e.g. in the agricultural application as a moisture retaining agent
in arid soils. The mathematical analysis of the kinetics of water
absorption shows that Fickian diffusion is only prevailing at low
Na+ content in the gelled network. At a DN of 50% or more, polymer
chain relaxations are the dominant mechanism. At ca 50% neutralization
also the best absorption capacity was found so these are the
conditions of the highest practical interest.