TXQ 302
Presentation on
Starch-based superabsorbent polymers

What are Super-absorbent polymers (SAPs) ?
❖ Functional macromolecules with the ability to absorb water.
❖ Release the absorbed water slowly to the surrounding medium.
➢ Can be used to retain moisture in the surrounding soil during plant
growth and transportation.
➢ Hydrogels act as ‘miniature water reservoirs’ in soil, releasing
water into the soil and maintaining moisture balance in the soil.
They have the capacity to release the absorbed water depending
on the moisture equilibrium change of the soil or on the
requirement of plant roots.

Need of starch-based super absorbent polymers?
Hydrophilic polymers exist in three forms, viz.,
1. Natural (polysaccharide derivatives),
2. Semi-artificial (cellulosic primitive derivatives) and
3. Artificial polymers
a. More stable towards environmental breakdown.
b. But are non-biodegradability causing serious and long-term
environmental issues.
c. The importance of using natural polymer based SAPs are due to
their biodegradability, non-toxicity of the base component and their
sustainability.
Thus, starch which is natural and renewable, is used for synthesis of SAPs.

Starch-based Super absorbent polymers.
Natural polymer based SAPs show desirable properties like
biodegradability, non-toxicity of the base component and sustainability.
Starch is the most abundant, natural, renewable, biocompatible, and non-
toxic polysaccharide stored in plants. The main sources are cassava,
wheat, rice, maize or corn, and potatoes.
Cassava starch was extracted from the freshly harvested tubers

The hydroxyl groups in the starch backbone are abundant having a high affinity
towards other hydroxyl groups and hence form hydrogen bonds with water
molecules. Gelatinization of starch allows the interaction of starch chains and a
water molecule.
As a result, the chains move apart and starch granules swell. Finally, the granule
ruptures and starch get dispersed in the water building a viscous colloidal state .
In order to prepare materials with a high liquid uptake capacity, raw starch is
incorporated with more hydrophilic polymers as starch is not so hydrophilic owing
to its granular structure.
Chemical, physical, or biochemical modification of starches enhances its versatility
in various fields. One such application involves the utilization of starch-based SAP
in the field of agriculture.

Applications of starch-based SAPs
● Soil moisture conditioner:
○ Concentration of starch-based SAP is found to have significant effect on
the WHC of the soil.
○ Soil which contained 0.5% SAP retained almost 19% of moisture after 30
days without any further watering
○ Correspondingly water retention got decreased with the decrease in
concentration of SAP.

● Increase in the nutrients of the soil:
○ Significant increase in most of the nutrients was noticed in the SAP
amended soil.
○ An increase in certain microorganisms in soil such as bacteria can lead
to an increase in the nitrogen level of the soil
○ Phosphorus and potassium levels have been declined due to intake of
these nutrients by plan and non-availability of any replenishment source
like Nitrogen.
○ Similar to N, OC content has also increased.

● Effects of amylose/amylopectin ratio on water absorption
○ SAPs based on the starches with higher amylose content generally
recorded higher water absorption.
○ The high molecular weight and branched structure of amylopectin
reduced the mobility of the polymer chains.
○ Amylopectin interferes with any tendency for them to become oriented
closely enough to permit significant levels of hydrogen bonding.

Determination of Water-Holding Capacity of Soil
● Water-holding capacity of the soil significantly increased even upon small
addition of SAH.
● WHC capacity was observed for different soils having:
○ No SAH (Starch-acrylic hydrogel) or untreated soil.
○ SAH 1: Starch: AA = 1:0.78
○ SAH 2: Starch: AA = 1:1.05
○ SAH 3: Starch: AA = 1:2.01
● The values were further improved with increasing the amount of hydrogel
(0.25%)
● It may be due to the increase in the porosity of the soil, as supported by the
determination of soil density.

Three hydrogels were prepared with varying Starch:Acrylic acid compositions which are encoded
as :
SAH 1: Starch: AA = 1:0.78
SAH 2: Starch: AA = 1:1.05
SAH 3: Starch: AA = 1:2.01

● Effect of SAP Hydrogel on plant on growth:
❖ In the chickpea plant experiment, when we took 3 cups, with 20g of soil with 0.05g of
urea-coated hydrogel, only SAH 2 and bare soil.
❖ Chickpea has half buried and left for germination, after a particular time interval, the
growth rate of the plant was observed.
❖ And we can clearly observe the difference that how good the plant growth was in 20g of
soil with 0.05g of urea-coated hydrogel then only SAH 2 and then bare soil.
❖ Plant growth was in 20g of soil with 0.05g of urea-coated hydrogel was maximum then
comes plant growth in only SAH 2 and then bare soil.

Soil with urea-encapsulated SAH Soil with SAH 2 Bare soil

Disadvantages of starch-based SAPs.
It has been observed that with the use of SAPs, there is reduction in Phosphorous
and Potassium levels. The reduced P and K levels in the control and treated soils
could be attributed to the uptake of these elements by plants during growth as
there was no external supply of these nutrients as chemical fertilizers.

Conclusion
1. It was observed that with the addition of Cassava starch-based SAP hydrogel to the
soil, in combination with watering at an interval of once in three days could increase the
porosity and water holding capacity of the soil.
2. It also helps in maintaining higher nutrient levels including the biological property of the
soil and better plant growth in comparison to the control treatment with daily watering in
the absence of the polymer.
3. Due to significant improvement in water retention capacity of soil, it has emerged new
scopes of usage of SAPs especially under the prevailing situation of reduced moisture
availability due to global climate change.
4. Due to its biodegradable nature, it has further scopes for utilisation as bio-based SAP
for slow-release fertiliser, water retention capacity of soil and many more.

Thank You