Natural Polymers and their Adsorption Properties

By

Asabuwa N. F.

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

Introduction

From the Greek word''POLYMEROS''

''Poly'' meaning Many

''Meros''meaning parts

Many Parts = POLYMER

Natural Polymers:Polymers that occur in natureproduced from living organisms

Synthetic Polymers

What are Natural polymers?

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.

Monomer Monomer DimerPolymer

Reapting units of monomer

Classification of Natural polymers based on source

NATURAL POLYMERS

Plants Animals Microbes

Polysaccahridee.g cellulose,starch

Proteins e.ggelatin, albumin

Polysaccahridese.g chitin,chitosan

Polyesterse.g Poly-hydroxyalkanoate

Polysaccahrides e.g Hyaluronate, pullulan

Classification of Natural polymers based on structure

NATURAL POLYMERS

Agri-Polymer Biopolyesters

Polysaccharides PolypeptidesBacterial Polyesters(microorganisms)

R1

O

OR2

Ester group

H2N CH

CH3

C

O

N

H

CH

CH3

C

O

OH

Peptide bond(Amide group)O

HO

OROH

OH

OH

Glycosidic bond

Examples1. Cellulose2. Chitin3. Chitosan4. Starch

Example Proteins made of 1. Gelatin2. Albumin

Examples1. Polyhydroxybutyrate (PHB)2. Polylactides (PLA)3. Poly--caprolactone (PCL)

Polynucleotides

Examples1. RNA2. DNA

Starch

Polysaccharides

Polypeptide

Bacterial polyesters

H O CH

CH3

CH2C

O

OH

n

polyhydroxybutyrate (PHB)

H O CH

CH3

C

npolylactic acid (PLA)

H O (CH2)5 C

Poly--caprolactone (PCL)

n

O

OH

O

OH

N

H

CH

O

H3C CH3

N

H

C

O

N

OH

C

H

O

N

H

CH3

CH

O

Tetrapolypetide (Val-Gly-Ser-Ala)

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).

Method of preparation

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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

+

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

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

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.

Adsorbate

Adsorbent surface

Van Der Waal forcebetween adsorbent and adsorbate

Physisorption model

Adsorbate sticked adsorbent surface

Adsorbent surfacaee.g Cellulose polymer

Chemisorption Model

Red and Green adsorbatePurple Adsorbent surface

Physical adsorption (Physisorption) Involves a van der Waals interaction

between the adsorbate and the substrate.

Examples of adsorbents involve activated carbon and alumina

Adsorpton phenomenonTypes of adsorption

processes

Physisorptiona. 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/molh. As the temperature increases, Physisorption decreases

Chemisorptiona. Highly Specific b. Electron transfer may occur leading to bond formation between adsorbate & adsorbent c. Activated , may be slow & irreversibled. May involve dissociatione. Monolayer or Multilayerf. Possible over a wide range of temperaturesg. Enthalpies are in the region of -200 kJ/molh. With the increase in temperature, Chemisorption first increases & then decreases

Difference between physisorption and chemisorption

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

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 polymers (Animal polysaccharide)

Gelatin (Polypeptide or protein)

Starch( Plant polysaccharide)

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.

P

Physiochemical properties:BiodegradableBiocompatibleNon toxicChelates 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)

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.

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 81Direct blue 78

584.2566.5

(He, Wang, Xue, & Hao, 2011)

Gelatin-starchmicrosphere

protein Bovine serum album 120 (He, Song, Zhang, You, & Tu, 2015)

Starch:Introduction:Carbohydrate polysaccharide, occurring naturally in green plants as energy store.Consist of large number of glucose units joined by glycosidic bondsConsist 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.

(1-6) Linkage

(1-4) Linkage

Properties: BiodegradableBiocompatibleNon-toxicNon- immunogenicNon-inflammatoryVery hydrophilicReadily soluble in water at temperature of 50-70 °CExhibits 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)

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.