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Biokemistri
Nigerian Society for Experimental Biology
ISSN: 0795-8080
Vol. 23, Num. 2, 2011, pp. 81-89
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Biokemistri, Vol. 23, No. 2, June, 2011, pp. 81-89
Polymer Applications in Agriculture
L. O. Ekebafe1,
D. E. Ogbeifun2* and F. E. Okieimen2
1Department
of Polymer Technology, Auchi Polytechnic, Auchi, Nigeria
2University
of Benin, Centre for Biomaterials Research, Benin City, Nigeria
*Author to whom correspondence should be addressed. E-
mail address:daveogbe@yahoo.com
(Received April 12, 2011; Accepted May 19, 2011)
Code Number: bk11011
ABSTRACT
The use of polymer in agriculture is gaining popularity in science,
particularly in the field of polymer chemistry. This has provided solutions to
the problems of the present day agriculture which is to maximize land and water
productivity without threatening the environment and the natural resources.
Superabsorbent polymer hydrogels potentially influence soil permeability,
density, structure, texture, evaporation and infiltration rates of water
through the soils.
Functionalized polymers were used to increase the efficiency of pesticides and
herbicides, allowing lower doses to be used and to indirectly protect the
environment by reducing pollution and clean-up existing pollutants. This account;
a detailed review study, has been put together as an expose on the myriad
application of polymer in the field of agriculture, highlighting present
research trend , impact on food security and future outlook.
Keywords: Agriculture, soil, plants, polymeric materials.
1
Introduction
World population is increasing at an alarming rate and is expected to reach seven
billion by the end of year 2050. Population growth and the resultant
development of large high-density urban populations, together with parallel
global industrialization, have placed major pressures on our environment,
potentially threatening environmental sustainability and food security. This
has resulted in global warming and the buildup of chemical and biological
contaminants throughout the biosphere, but most notably in soils and sediments
[1].
During the 20th century, the main emphasis of agricultural development all over
the world was the increasing productivity per unit area of land used for crop
production to feed the ever-increasing population. This was substantially
accomplished through over exploitation of natural resources such as water and
plant resources and excessive use of fertilizers and pesticides [2]. Although
this practice resulted in considerable increase in crop yields in the
short-tem, it was not sustainable in the long-run. The productive capacity of
the arable land was impaired; the natural water resources were depleted and
also polluted with hazardous pesticides and chemical fertilizers which
threatened the survival and well being of all life forms on earth. Therefore,
the emphasis on agricultural development in the present century has shifted to
the sustainable use of land, water and plant resources in agriculture. The
major goal of the present day agriculture is to maximize land and water
productivity without threatening the environment and the natural resources.
As a matter of priority, one major role of agriculture is in the provision of
food supply and security. However, emerging trends indicate an increasing role
with respect to soil and water management and conservation. With reference to
global climatic anomalies, drought due to protracted absence, deficient or poor
distribution of precipitation has occurred over many parts of the globe in
varying scales of severity and duration throughout human history.
Many nations have experienced considerable distress arising out of drought
occurrences -mass starvation (even famines), cessation of economic activity particularly
within the developing world where economies are inextricably and intrinsically
tied to agriculture [3].
Within the sciences, the study of polymers has helped to foster the emergence
of agricultural polymers through focus on natural/synthetic macromolecular
substances such as proteins, polyacrylates, polyacrylamides, and
polysaccharides. Through the concerted efforts of polymer chemists, a series of
commercially natural/synthetic polymers have been successfully used in many
applications in the field of agriculture.
In this regard, this account; a detailed review study, has been put together as
an exposé on the myriad applications of polymer in the field of agriculture,
highlighting present research trends , impact on food security and what the
future holds.
2
Functionalized Polymers in Agriculture.
Synthetic polymers play important role in agricultural uses as structural
materials for creating a climate beneficial to plant growth e.g. mulches,
shelters or green houses; for fumigation and irrigation, in transporting and
controlling water distribution. However, the principal requirement in the
polymers used in these applications is concerned with their physical
properties; such as transmission, stability, permeability or weatherability; as
inert materials rather than as active molecules. During the last few years, the
science and technology of reactive functionalized polymers [4] have received
considerable interest as one of the most exciting areas of polymer chemistry
for the production of improved materials. They have found widespread
applications as reactive materials based on the potential advantages of the
specific active functional groups and the characteristic properties of the
polymeric molecules. Their successful utilizations are quite broad including a
variety of fields, such as solid-phase synthesis, biologically active systems
and other various technological uses [4].
2.1
Polymeric Biocides and Herbicides.
New technique has recently emerged for the controlled release formulations
designed to avoid or reduced the possible side effects accompanying the use of
biologically active agents. The purpose of this technique include; to protect
the supply of the agent, to allow the automatic release of the agent to the
target at controlled rates, and to maintain its concentration within the
optimum limits over a specified period of time, thereby producing a great
specificity and persistence. There are two different approaches in combining
the biological agents with the polymeric materials. Either by physical
combination (encapsulation or heterogeneous dispersion) to acts as a rate
controlling device, or by chemical combination to act as carrier for the agent
[4].
The polymeric biocide has many advantages and its potential benefits include:
it allows lower amounts than conventional biocides to be used as it releases
the required amount of active agent over a long period, number of applications
is reduced because of long period of activity by a single application, it
eliminates the time and cost of repeated over applications because less active
materials is needed, reduction of toxicity, it eliminates the need for
widespread distribution of large amount of biocide levels in the surrounding
environment, reduction of evaporation and degradation loses by environmental
forces or leaching by rain into the soil or waterways due to the macromolecular
nature, it extends the duration of activity of less or non-persistent biocides which
are unstable under an aquatic environment by protecting them from environmental
degradation and hence , enhances the practical applicability of these
materials, reduction of phytotoxicity by lowering the high mobility of the
biocides in the soil and hence reduces its residue in the food web, extension
of herbicide selectivity to additional crops by providing a continuous amount
of herbicide at a level sufficient to control weeds but without injury to the
crop.
The rate of release of active group from the polymer matrix and the consequent
duration of the effective action is influenced by: chemical characteristics of
the active agents structure, nature of the active - agent - polymer bond (such
as esters, amides, ureas, urethanes, acetals), the distance of the active agent
from the polymer backbone; for achieving an enhanced rate of release; a
permanent spacer group may be necessary to prevent steric hindrance , rate of
breakdown of the bond between the active material and the polymer by chemical,
biological or environmental agents such as UV, moisture and microorganisms,
chemical nature of the polymer backbone, chemical nature of the groups
surrounding the active moieties , dimension and structure of the polymer
molecule as governed by the degree of polymerization, comonomers, solubility,
degree of crosslinking and the stereochemistry.
The main problem with the use of less persistent conventional herbicides that
have greater specificity is the use of excess amounts than that actually
required to control the herb because they are unstable in an aquatic
environment and of the need to compensate the amount wasted by the
environmental forces of photodecomposition, leaching and washing away by rai.
They are also highly toxic to farm workers and expensive on multiple
applications which are required because of their lower persistence. On the
other hand, the applications of large amounts of persistent herbicides are
undesirable because of their frequent incorporation into the food chain.
In an attempt to make connection with the problems encountered in using
conventional herbicides. Some functionalized polymers containing pesticide
moieties as pendandt groups have been prepared by free radical polymerization
of vinyl monomer type and their hydrolysis rates were studied under different
conditions. As active pesticide group, pentachlorophenol (PCP) a major
industrial chemical, represents one of the most widely used biocides in a
variety of agrochemical applications, such as herbicide, molluscide, fungicide,
insecticide, algicide and bactericide. In addition its hydroxyl group provides
also a suitable mean for covalent bonding to a variety of polymerizable units.
A series of vinyl monomers containing PCP via an ester linkage have been
prepared [5]. These monomers have been homo- and co-polymerized with styrene
and 4-vinylpridine to induce hydrophobic and hydrophilic nature to the
polymers. The rates of release of PCP from the polymers have been studied at
four different media (water, pH=4 pH= 10, and dioxane-water) and all at 30°C. A
comparison between the rates of release from these polymers indicate that the
rates increase with increasing the degree of hydrophilicity, that is, copolymer
hydrolyzes faster than the homopolymer which has higher rate than the
hydrophobic copolymer.
Polymer herbicides containing active moieties ionically bound to ammonium salt groups
have been investigated [4] to demonstrate the reactivity displayed by the
polymers through changing the chemical nature of linkage bond and the chemical
characteristics of the active agent structure. In addition to PCP the
herbicides of general use that contain functional group for bonding to the polymer
matrix have also been used, such as 2,4-dichlorophenoxyacetic acid, 2-methyl-4-chlorophenoxyacetic
acid and 2,4-dinitro-6-methyl phenol.
The major drawback to the economic use of these polymeric herbicides is the
large amount of inert control that must be employed as a carrier for the
herbicides and the disposal of the herbicide residual materials which may be harmful
for the soil and the plant. Some attempts have been made to reduce this
problem, which mainly based on the concept of attaching the pesticides to
biodegradable carriers of similar structures to agricultural residues
consisting of polysaccharides such as bark, sawdust, cellulose and other
cellulosic wastes. However, the main disadvantages with the use of such
naturally occurring polymers are the difficulties encountered with their
chemical modification. Hence the use of excessive amounts of such bioactive
polymers usually necessary for herb control is inevitable.The hydrophilic and
cross linking nature of these polymers lead to a faster rate of hydrolytic
cleavage of the pendant pesticide. Another factor is their rapid deterioration
in soil by biodegradation and the subsequent destroying of the polymeric matrix
within a short period of time, which leads to shorter period of effectiveness
of the herbicide.
In order to eliminate or at least to reduce the disadvantage of using excessive
amounts of inert polymers as carriers, in addition to the drawbacks of using
soluble nitrogen fertilizers. The principle of a duel application of controlled
release herbicide-fertilizer have recently been used. This principle is based
on the use of appropriate polymers as carriers in which the residual products
after the degradation of the polymer become beneficial to the plant growth and
the soil by acting as fertilizer. For example, herbicide derivatives of
bifunctional compounds have been prepared and polymerized under condensation
polymerization conditions. The second attempt is based on the concept of
attaching the herbicides to polymeric hydrogels in order to alter the basic
character of sandy soil. In addition to the primary function of these polymers
to control the rate of delivery of herbicides, they can also play an important
role to increase the water retention by sandy soil through avoiding its rapid
leaching. Hence, the use of such dual combination of controlled release herbicide-water
conservation can contribute positively to change the conventional agricultural
irrigation especially for sandy soil[5].
2.2
Polymeric Molluscicides
Bilharzia is one of the most widespread trematode endermic diseases in tropical
countries where the spreading of cultivated areas increases, Since the use of
molluscicides is responsible to combat various mollusks, the applications of
large quantities of these chemicals are required for combating bilharzias
disease through the control and eradication of the schistosoma snails. As
active molluscicide, Niclosamide (5,2-dichloro-4'- nitrosalicylanilide) has
been introduced by Bayer Co., under the trademark Bayer 73 and is applied for
combating the bilharzias disease. However, the use of great amounts of this
compound has offered some economic and environmental toxicity problems.
The
chemical combination of molluscicides with the functionalized polymers has been
use in an attempt for enhancing the eradication of the snails with the
elimination of the side effects associated with the use of a relatively massive
Niclosamide dosage. Accordingly, molluscicide polymers containing Niclosamide
via covalent and ionic bonds have been prepared by chemical modifications of
polymers [6].
3.
Super absorbents polymers and composites for agriculture
Polymeric soil conditioners were known since the 1950s [7]. These polymers were
developed to improve the physical properties of soil in view of:
(i) increasing their water-holding capacity,
(ii) increasing water use efficiency
(iii) enhancing soil permeability and infiltration
rates
(iv) reducing irrigation frequency
(v) reducing compaction tendency
(vi) stopping erosion and water run-off
(vii) increasing plant performance (especially in
structure -less soils in areas subject to drought).
The presence of water in soil is essential to vegetation. Liquid water ensures
the feeding of plants with nutritive elements, which makes it possible for the
plants to obtain a better growth rate. It seems to be interesting to exploit
the existing water potential by reducing the losses of water and also ensuring
better living conditions for vegetation. Taking into account the water imbibing
characteristics of SAP materials, the possibilities of its application in the
agricultural field has increasingly been investigated to alleviate certain
agricultural problems. Super absorbent polymers (SAPs) are compounds that
absorb water and swell to many times their original size and weight. They are
lightly cross-linked networks of hydrophilic polymer chains. The network can
swell in water and hold a large amount of water while maintaining the physical
dimension structure [8,9]. It was known that commercially used water-absorbent
polymeric materials employed are partial neutralization products of
cross-linked polyacrylic acids, partial hydrolysis products of
starchacrylonitrile copolymers and starchacrylic acid graft copolymers. At
present, the material's biodegradability is an important focus of the research
in this field because of the renewed attention towards environmental protection
issues [10]. The half life is in general in the range 5 - 7 years, and they
degrade into ammonium, carbon dioxide and water.
SAP
hydrogels potentially influence soil permeability, density, structure, texture,
evaporation, and infiltration rates of water through the soils. Particularly,
the hydrogels reduce irrigation frequency and compaction tendency, stop erosion
and water run off, and increase the soil aeration and microbial activity [11].
In arid areas, the use of SAP in the sandy soil (macroporous medium), to
increase its water-holding capacity seems to be one of the most significant
means to improve the quality of plants [12]. The SAP particles may be taken as
"miniature water reservoirs" in soil. Water will be removed from
these reservoirs upon the root demand through osmotic pressure difference. The
hydrogels also act as a controlled release system by favouring the uptake of
some nutrient elements, holding them tightly, and delaying their dissolution. Consequently,
the plant can still access some of the fertilizers, resulting in improved growth
and performance rates [13-15].
SAPs can also be used as retaining materials in the form of seed additives
(to aid in germination and seedling establishment), seed coatings, root dips,
and for immobilizing plant growth regulator or protecting agents for controlled
release [11]. A distinctive instance for the agricultural application of SAP
has been recently practiced. The SAP effect on the growth indices of an
ornamental plant (Cupressus arizonica) under reduced irrigation regimes
in the field and on the soil water retention curve in a laboratory was
investigated [16].
Additional interesting instance is a research recently conducted on the effect
of SAP materials on the characteristics of sport turf. Turf is of significant
importance as an inseparable part of all kinds of green spaces. Irrigation
water consumption of turf is very huge, especially in the hot and dry climates
due to surface evaporation and infiltration. In the research conducted by
Mousavinia et al. [17] encouraging results were obtained. The turf density,
colour intensity and coverage percentage was increased, while it's wilting
level was substantially decreased when SAP was used [18].
SAP materials have shown excellent influence on decreasing damages (up to 30%)
in the productive process of the olive sapling [19]. Meanwhile,
non-cross-linked anionic polyacrylamides (PAM, containing <0.05% AM) having
very high molecular weight (12-15x106 g.mol-1), have also been used to reduce
irrigation-induced erosion and enhance infiltration. Its soil stabilizing and
flocculating properties improve runoff water quality by reducing sediments,
N-dissolved reactive phosphorus (DRP) , chemical oxygen demand (COD),
pesticides, weed seeds, and microorganisms in runoff. In a series of field
studies, PAM eliminated 80-99% (94% avg.) of sediment in runoff from furrow
irrigation, with a 15-50% infiltration increase compared to controls on medium
to fine-textured soils [20]
The preparation of polymer/clay superabsorbent composites [21] has also
received great attention because of their relative low production costs and
high water absorbency. superabsorbent composites by graft copolymerization
reaction of acylic acid (AA) and acrylamide (Am) on attapulgite micropowder
using N,N-methylene bisacrylamide (MBA) as a crosslinker and ammonium
persulphate (APS) as an initiator in an aqueous solution has been prepared [22].
Acrylamide is a kind of nonionic monomer and has great advantage on its good
salt resistant performance as a raw material for superabsorbent. Attapulgite,
as a good substrate for superabsorbent composite materials, is a layered
aluminium silicate with reactive groups OH on the surface.
Water
- insoluble polymers
This second class of polymers often referred to as gel-forming polymers or
insoluble water-absorbing polymers were first introduced for agricultural use
in the early 1980's. These polymers do not possess linear chain structures as
described previously but the chains are rather cross-linked to form a
three-dimensional network. Cross-linking occurs when polymerization is carried
out in the presence of a small amount of a divinyl compound. Depending on synthetic
conditions, type and density of covalent bonds that form cross-links, these
polymers can absorb up to 1000 times their weight in pure water and form gels.
Three main types of hydrogels (water absorbing) have so far been developed as
agricultural polymers: (1) starch-graft copolymers obtained by graft
polymerization of polyacrylonitrile onto starch followed by saponification of
the acrylonitrile units (2) cross-linked polyacrylates (3) cross-linked
polyacrylamides and cross-linked acrylamide-acrylate copolymers containing a
major percentage of acrylamide units. Most of the hydrogels marketed for
agriculture come from the latter group as they are claimed to remain active for
a much longer time.
Gel-forming polymers are small dry crystals that absorb water similar to
sponges. Contact between the polymer granule and water results in absorption
until equilibrium is reached. When polymers are incorporated into a soil or
soilless medium, it is presumed that they retain large quantities of water and
nutrients. These stored water and nutrients are released as required by the
plant. Thus, plant growth could be improved, and/or water supplies conserved.
It has been reported that a 171% to 402% increase in the water retention
capacity is recorded when polymers were incorporated in coarse sand [23]. It
has been reported that increased water retention capacity attributed to
polymer addition significantly reduced irrigation frequency [24] and the total
amount of irrigation water required.
Researchers [25] have reported that the use of hydrogels increases the amount
of available moisture in the root zone, thus implying longer intervals between
irrigations. It must be pointed out that the polymers do not reduce the amount
of water used by plants. The water-holding capacity depends on the texture of
the soil, the type of hydrogel and particle size (powder or granules), the
salinity of the soil solution and the presence of ions. Cross-linked
polyacrylamides hold up to 400 times their weight in water and release 95% of
the water retained within the granule to growing plants. In general, a high
degree of cross-linkage results in the material having a relatively low
water-retention capacity. However, the water-holding capacity drops
significantly at sites where the source of irrigation water contains high
levels of dissolved salts (e.g effluent water) or in the presence of fertilizer
salts [26]. The amount of water retained is also adversely affected by
chemicals or ions (Mg2+, Ca2+, Fe2+) present
in the water [49]. It has been suggested that these divalent cations develop
strong interactions with the polymer gels and are able to displace water
molecules trapped within the polymer [27]. Even though monovalent cations (Na+)
can also replace water molecules, the effect is not as pronounced as with the
divalent counterparts as the process is fully reversible by repeated soaking
with deionised water.
Moreover, the use of hydrogels leads to increased water use efficiency since
water that would have otherwise leached beyond the root zone is captured.
During hot days, the hair root system of a plant pulls out and depletes most of
the water from the area close to the root system, thus causing the plant to go
into stress. While increasing the amount of available moisture, hydrogels help
reduce water stress of plants resulting in increased growth and plant
performance [28]. The performance of the gel on plant growth depends on the
method of application as well. It was shown that spraying the hydrogels as dry
granules or mixing them with the entire root zone is not effective [24]. Better
results seem to be obtained when the hydrogels are layered, preferably a few
inches below soil surface. However, generalizations should be avoided when
interpreting results as a number of factors such as type of hydrogel, particle
size, rate of application and type of plant has to be taken into consideration.
Hydrogels are also claimed to reduce fertilizer (NPK) leaching. This seems to
occur through interaction of the fertilizer with the polymer. Cross-linked
polyacrylamide is also being considered as a potential carrier for insecticides,
fungicides and herbicides[29].
Polymers
for soil remediation.
Contamination of soils with toxic metal elements is of great concern to
scientists and the general public. Long-term intake of contaminant metals by
humans may lead to chronic effects, although maximum acceptable limits in food
were already established for several toxic elements by the National agency for
food, drugs and administration and control, European Food Service Authority and
the U.S. Food and Drug Administration. [30,31]
Effects of metals on ecosystems and biological resources are also increasingly
recognized [32]. Metals do not degrade as organic compounds do, and have long
residence times in soils. They can however exist in different forms, which
include water-soluble (ionic and chelated with soluble compounds), adsorbed on
soil surfaces, chelated by insoluble organic matter, precipitated, occluded by
soil oxides and hydroxides, present in living organisms or residues, and as
part of primary and secondary minerals [33]. Ideally, a contaminated soil
should be restored to regain its original potential, but this can be a very
expensive process, and thus depends not only on the expected benefit of the
cleanup and future value of the soil, but also on political and public
awareness of the problem. Conventional remedial approaches to severely
metal-contaminated soils involve removal and replacement of soil with clean
materials or capping the soil with an impermeable layer to reduce exposure to
contaminants [34], chelating agent ethylenediaminetetraacetic acid (EDTA) has
been used extensively for heavy metals extraction from soil [35-37]. Much work
has been done on the recovery of metal-loaded EDTA by electrochemical [38,39]]
or chemical processes [40,41]. Another chelating agent, pyridine-2,
6-dicarboxylic acid has also been shown to be effective in heavy metals
although these are not considered the most economically or environmentally sound
solutions available. Only through the establishment of a vegetation cover to
stabilize metal-contaminated soils will a successful long-term rehabilitation
be achieved [42].
Water-soluble polymers (WSP) have been used extensively for the removal or recovery
of metal ions from aqueous solutions. There are now reviews on the use of this
technology for metal ion separations [43]. However, this technology has only
recently been used to remove metals such as lead from solid surfaces. Three
distinct advantages of using WSP are: 1) The metal bound to the polymer in
solution can be easily concentrated by ultrafiltration (UF) 2) the metal
subsequently released from the WSP can be easily segregated by UF to allow for
recycle of the extraction agent and disposal of the metal; and 3) commercially
available polymers can be modified to selectively bind the target metal ions.
Polyethylenimine (PEI), a highly branched aliphatic polyamine, was chosen as
the backbone polymer for the studies on lead extraction from soil. PEI is readily functionalized with chloroacetic acid to give aminocarboxylate groups which
are known to chelate lead effectively.
2.3
Biodegradable polymer in agriculture
Biodegradable polymers have increasingly been used as plastics substitutes for
several applications in agriculture. One of the problems afflicting
agricultural production is the presence of parasites in the soil that, along
with spontaneous weeds, take away nourishment from the soil. In the past the
elimination of parasites and seeds of undesirable plants, before a new sowing,
was performed through fumigation with methyl bromide, which has been indefinitely
banned for its toxicity. In the 70s', a new approach called solarization,
which involves covering the soil to be reconditioned with polymeric films, was
introduced. The polymeric films for this application have to be mechanically
resistant, transparent to visible light, and opaque to infrared radiation.
The optical properties are important because during the day, visible radiation,
which passes through the film, warms the soil. During the night, when the soil
cools by emitting infrared radiation, the film which is impermeable to infrared
radiation, traps it and thus prevents heat loss. Actually, a film with these
optical properties has a micro green house effect on the soil. This technique
is largely used today, particularly at those latitudes with temperate climate.
It makes use of low-density polyethylene with fillers, such as phosphates, that
increase the opacity to infrared radiation.
Solarization guarantees the decontamination of soils assigned to insemination
within 4-6 weeks. At the end of the treatment, the problem of the removal and
disposal of films has to be resolved. Films made of synthetic polymers should be
treated as waste with additional costs. Moreover, there are several problems
related to environmental pollution for all films that, in violation of the law,
are burned after their use. A biodegradable film made of natural polymers, for
solarization offers advantage that it does not have to be removed from the soil
after they are used. Polymer films for solarization containing alginates,
polyvinyl alcohol and glycerol has been reported [44,45]. Alginates are water
soluble linear copolymer, containing a-gluronic and P- mannuronic acid units,
present in seaweed [46].
2.4
Drag-reducing polymers in agriculture.
Extremely minute concentrations of large polymer molecules, fibres or particles
when present in a fluid cause reduction in the friction resistance in a
turbulent flow compared to that of the fluid alone.
Drag-reducing
polymers reduce the drag in a turbulent flow (by a mechanism not yet fully
understood) while increasing the drag in a laminar flow, due to an increase in
the shear viscosity [93]. This feature of drag- reducing polymers has been
utilized in reducing the energy requirements of sprinkler irrigation system.
The water containing drag-reducing polymers percolates losses of water.
Utilizing this aspect, a slow-release urea has been developed by blending urea
with guargum.[47]
The
list of possible areas of applications has increased enormously to include oil
well fracturing, crude oil and refined petroleum product transport, fire
fighting, irrigation, sewage and flood water disposal, hydrotransport of
solids, water heating circuits, jet cutting, hydraulic machinery, marine
applications and biomedical applications.
3.
Conclusion
Throughout human history, agriculture has been a source of food, fuel and
fiber. Opportunities have arisen through external events and trends that
impacted patterns of production and utilization. Numerous publications describe
the increase in yield of various plants as a result of better soil conditions.
SAPs
have created a very attractive area in the viewpoint of super-swelling
behaviour, chemistry, and designing the variety of final applications. When
working in this field, we always deal with water, aqueous media and bio-related
systems. Thus, we increasingly walk in a green area becoming greener via replacing
the synthetics with the bio-based materials, e.g., polysaccharides and
polypeptides. Considering the high-cost and increasing prices of crude oil, the
necessity of preparing natural based SAPs seems more obvious. This paves the
way for further developments in this area in the mid and far future ahead.
Key opportunities exist to build biodegradable polymers from annually renewable
crops and agro industrial waste-streams. The production of monomers and
polymers with enzymes, microbes, or plants represents a cleaner and safer way
of doing chemistry. However, polymers have provided solution for the need to
develop cost-effective techniques that would contribute to phytostabilization
of severely metal contaminated soils.
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