This document outlines the use of natural polymers for adsorption applications. It defines natural polymers and classifies them, describing their properties and preparation methods. It then defines adsorption and the differences between physisorption and chemisorption. Factors affecting adsorption are discussed. Examples are given of using chitosan, gelatin, and starch for adsorbing dyes, metals, and proteins based on their hydrophilicity, biocompatibility, and functional groups. The document concludes that natural polymers are advantageous adsorbents due to their renewable sources, low cost, and distinguishable physicochemical properties.

1. Natural Polymers and their Adsorption
Properties
By
Asabuwa N. F.

2. Presentation Outline
Introduction
 Definition of natural polymers
 Classification of natural polymers
 Properties and advantages/disadvantages
 Methods of preparation
 General areas of application for natural polymers
 Adsorption definition
Types of adsorption processes
Difference between physisorption and chemisorption
Factors affecting adsorption
 Properties of natural polymers based on adsorption
 Conclusion

3. Introduction
Definition:
A polymer is a large molecule
(macromolecules) composed of many repeated
subunits, known as monomers
Thus a natural polymer is a polymer produced
from living organisms and result from only raw
materials that are found in nature
Why great attention for natural polymers?
Because they are biocompatible and
biodegradable, so they can be hydrolysed into
removable and non-toxic products.

4. Classification of Natural polymers based on source

5. Classification of Natural polymers based on structure

6. Polysaccharides
Polypeptide
Bacterial polyesters

7. Properties and advantages/disadvantages
Due to the great properties exhibited by natural polymers, this makes them of great research interest
Natural polymers are;
 Readily biodegradable by showing no adverse effects on the environment or human beings.
 Non-toxic/ non-inflammatory due to their source in nature.
 Biocompatible based on positive interaction in other living organisms or tissues.
 Highly porous
 Have high molecular weight making them exhibit high viscosity
 Easy and cheap to prepare/produce in comparison with synthetic polymers
 Capable of attachment with other molecules with their varying functional groups creating easy modification
 Easily available and are from renewable resources:
Disadvantages:
 Possible microbial contamination during production due to their natural sources.
 Batch to batch variation as a result of difference resources and resource regions.
 Slow process as production rate depends upon the environment and many other factors,
 Potential impurities may also result in unwanted immune reactions.
 Heavy metal contamination often associated with herbal polymeric excipients(An excipient is a natural or
synthetic substance formulated alongside the active ingredient of a medication).

8. Method of preparation
Generally most natural polymers are naturally built by condensation
polymerization method. Other polymerisation methods include; free
radical polymerization, grafting and photo-polymerization.
Formation of cellulose glucose units
Preparation of PLA from lactic acid
+

9. General Applications areas of natural polymers
NATURAL
POLYMERS
Industrial
applications
 Bioplastics
 Packaging
materials
Biomedical
applications
 Drug delivery
 Tissue engineering
Wastewater
treatment
Agricultural
applications
 use in biocontrol
 Fertilizer release

10. Adsorption definition
Definitions:
 Adsorbate: It is the the substance which is adsorbed on the surface Examples are: gases,
dyes, metals.
 Adsorbent: It is the substance on which surface the adsorbate is adsorbed . Examples
chitosan, cellulose, Starch, PLA

11. Chemical Adsorption (chemisorption)
 Involves molecules or atoms stick to the surface of
adsorbent by forming a chemical bond ( usually
covalent ), and tend to find sites that maximize their
coordination number with the substrate. The distance
between the surface & the closest adsorbate atom is
also typically shorter for chemisorption
 Example of adsorbent include functionalised polymers
and their composites such as chitosan crosslinked
hydrogel beads.
Physical adsorption (Physisorption)
 Involves a van der Waals interaction
between the adsorbate and the
substrate.
 Examples of adsorbents involve
activated carbon and alumina
Adsorpton phenomenon
Types of adsorption
processes

12. Physisorption
a. Not very Specific
b. No electron transfer , although
polarization of adsorbate
c. Rapid, non-activated & reversible
d. No dissociation of adsorbed
species
e. Monolayer or Multilayer
f. Only significant at relatively low
temperatures
g. Enthalpies are in the region of -20
kJ/mol
h. As the temperature increases,
Physisorption decreases
Chemisorption
a. Highly Specific
b. Electron transfer may occur leading to
bond formation between adsorbate &
adsorbent
c. Activated , may be slow & irreversible
d. May involve dissociation
e. Monolayer or Multilayer
f. Possible over a wide range of
temperatures
g. Enthalpies are in the region of -200
kJ/mol
h. With the increase in temperature,
Chemisorption first increases & then
decreases
Difference between physisorption and chemisorption

13. Factors affecting adsorption
Factors Effect on adsorption
Nature of Adsorbate Gas, liquid or solid (↑↓)
Mass of adsorbent (↑) Amount (↑)
Pore size of adsorbent (↑) Micro or macrospores (↑)
Solubility of adsorbate (↑) Polarity (↓)
Size of adsorbent (↓) Particle size (↑)
Number of carbon atoms (↑) Depending on adsorbate or adsorbent (↑↓)
Temperature Depends on enthalpy and entropy
pH Depends on extent of ionization of species
Affinity between adsorbent and adsorbate (↑) Interaction (↑)
Degree of ionization of adsorbate (↑) (↑)
Contact time (↑) (↑)
Crosslinking density (↑) Swelling, pore size (↓)
↑= increase ↓= decrease

14. Properties of natural polymers based on adsorption
Based on literature so much research work has been performed on natural polymers for adsorption application in
various area. And most of the natural polymers use are of polysaccharide origin.
Case study natural based polymers;
Chitosan:
Introduction:
 Chitin is a macromolecule found in the shells of
crabs, lobsters, shrimps and insects
 Chitosan is obtained by partial deacetylation of
chitin.
 Chitin and chitosan are insoluble in water
Chemistry:
Linear co-polymer of β(1-4) linked glucosamine and
N- acetyl-D-glucosamine.

15. P
Physiochemical properties:
Biodegradable
Biocompatible
Non toxic
Chelates many transitional metal ions
A cationic polysaccharide of which in acidic pH, it gets solubilized due to protonation of free amino groups and
the resultant soluble polysaccharide is positively charged.
hydrophilic in nature thereby it has the ability to form gels at acidic pH.
Exhibit good swelling properties
Chitosan product Area of
application
Substance
adsorbed
Adsorption
capacity (mg/g)
Reference
Chitosan/bentonite
composite
Dye removal Methyl orange 224.8 (Huang, Liu, Zhang, &
Yang, 2015)
Chitosan hydrogel beads Dye removal Congo red 223.35 (Chatterjee, Lee, Lee, &
Woo, 2009)
Chitosan film Dye removal Tartrazine and
amaranth
413.8 and 278.3 (Rêgo, Cadaval Jr, Dotto, &
Pinto, 2013)
Hydroxyapatite chitosan Metal
removal
Pb(II) 264.42 (Lei et al., 2015)

16. Gelatin:
Introduction:
Gelatin is a natural water soluble functional polymer (protein) that is derived by partial hydrolysis of collagen
(chief protein component in skin, bones and white connective tissues of the animal body).
It is commonly used for biomedical and other suitable applications due to its biodegradability and
biocompatibility in physiological environments.

17. Physicochemical properties:
Forms of thermo-reversible gels in water: When gelatin granules are soaked in cold water they hydrate into
discrete, swollen particles. On being warmed, these swollen particles dissolve to form a solution.
Soluble in aqueous solutions of polyhydric alcohols such as glycerol and propylene glycol.
Insoluble in less polar organic solvents such as benzene, acetone, primary alcohols and dimethylformamide.
It gives typical protein reactions and is hydrolyzed by most proteolytic enzymes to yield its peptide or amino acid
components.
Gelatin product Area of application Substance
adsorbed
Adsorption
capacity (mg/g)
References
PVA/gelatin
hydrogel beads
Metal removal Pb(II) 203.4 (Hui, Zhang, & Ye,
2015)
Gelatin
microspheres
Dye removal Direct red 81
Direct blue 78
584.2
566.5
(He, Wang, Xue, &
Hao, 2011)
Gelatin-starch
microsphere
protein Bovine serum album 120 (He, Song, Zhang,
You, & Tu, 2015)

18. Starch:
Introduction:
Carbohydrate polysaccharide, occurring naturally in green plants as energy store.
Consist of large number of glucose units joined by glycosidic bonds
Consist of a mixture of linear amylose (15-20%) and branched amylopectin (80-85%) units
Chemistry:
The glucose units are linked by of α(1→4) glycosidic bonds linked for amylose and α(1→6)-linked branches
for amylopectin.

19. Properties:
Biodegradable
Biocompatible
Non-toxic
Non- immunogenic
Non-inflammatory
Very hydrophilic
Readily soluble in water at temperature of 50-70 °C
Exhibits good swelling properties in aqueous media
Starch product Area of application Substance
adsorbed
Adsorption
capacity (mg/g)
Reference
Porous starch
Xanthate
Metal removal Pb(II) 109.4 (Ma, Liu, Anderson,
& Chang, 2015)
Cationic starch clay
composite
Dye removal Brilliant blue X-Br 122 (Xing, Liu, Xu, &
Liu, 2012)
Chitosan-starch Dye removal Direct red 80 345.23 (Asabuwa thesis;
2011)
Starch/acrylic acid Metal removal Pb(II) and Hg(II) 123.2 and 131.2 (Huang, Xiao, &
Chen, 2011)

20. Conclusions
Based on literature studies natural based polymers still remain one of the suitable available polymeric material
for enhance adsorption process based on their
 Ready availability from renewable sources
 Low cost
 Distinguishable physicochemical properties of;
 Biodegradability
 Biocompatibility
 Non toxicity,
 High swelling due to their hydrophilicity
 Available modifying functional groups and
 Ready solubility in various solvent make these natural polymers very advantageous for the adsorption of
metal, dyes, other organic solvent and gases from aqueous media and the environment.
As a research perspective is concern enormous works are still been performed using natural polymers for
various applications of adsorption, biomedical and other suitable application both at the industrial and
academic research institutes.