الرحيم الرحمن الله بسمويسر صدرى لى اشرح ربمن عقدة واحلل أمرى لى

قولى يفقهوا لسانىالعظيم الله صدق

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Photo-Induced Modification of Starch

Prepared by

Dr. Manal A. El-Sheikh

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Starch“green”

natural

available

biodegradable

renewable

low cost

why starch?

3“It is predicted that there will be a considerable demand in the near future for modified starches”

UV“eco-

friendly”

environment friendly

economically viable

fast

safenot induce a significant increase in

temperature

no dependence on catalysts

minimal sample

preparation

why UV?

4Bhat, R. and Karim, A.A. (2009). Impact of Radiation Processing on Starch, Comprehensive Reviews in Food Science and Food Safety, 8, 44-58.

Starch

UV

“green” product + environment

friendly process

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Starch

Textile

Hydrogel

Hydrogen production

Biodegradable plasticMedical and pharmaceutical

Petroleum

Food

Starch Utilization

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Starch

Modification

Chemical

BiologicalPhysical

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chemical

hydrolysis

oxidation

esterification

etherificationcationization

grafting

crosslinking

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physical

Pre-gelatinization

annealing

heat-moistureshear

radiation

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radiation

g-radiation

microwave

plasmaultrasonic

UV

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UV Radiation is defined as "that portion of the electromagnetic spectrum between x rays and visible light.“ UV Radiation, like all other electromagnetic radiation, is composed of energy particles called photons. The below image of the electromagnetic spectrum demonstrates the size and frequency of each energy.

What is Ultraviolet Radiation?

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consequence of organic molecules absorbing a quantum of visible or UV light is to promote an electron to a vacant orbital of higher energy

The energy of visible or UV light is of the same order as that of electronic transitions within atoms or molecules

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Once the molecule has absorbed this energy, it is said to be in an excited state from which various reaction possibilities arise.

For an electron to be promoted from an energy level E1 to a higher energy level E2, the incident radiation must have a frequency which gives a value E greater than or equal to

(E2-E1). Thus, E(E2-E1) = h

The energy of the incident radiation is proportional to the frequency of the radiation E= h

Energy is re-emitted from the singlet state at a longer wavelength (S1 to S0 “flourescence”).

Energy is re-emitted from the triplet state at an even longer wavelength (T1 to S0 “phosphorescence”).

The singlet or triplet state undergoes a radiationless conversion to electronic ground state and gives off the energy in the form of heat (excited vibrational states). However, the molecule in its excited vibrational state can undergo a degradation reaction.

Energy is transferred to another molecule which then dissipates the energy by the above three photophysical processes.

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certain functional groups, such as a carbonyl group, can absorb the UV radiation and be excited to higher energy state. The excited electron usually returns ‘unchanged’ to the electronic ground state because the energy is dissipated by one of the following radiative and macroradiative photophysical routes:

?Photosensitizer

compound that absorbs light and transfers energy to a second compound and, in so doing, undergoes no net change. The second compound proceeds to produce radicals by photo cleavage or H- abstraction reactions.

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UV light provides lower energy levels than other sources of ionizing radiation, it is impossible for direct cleavage of C–C or C–H bonds of starch molecules to occur for the formation of free radicals. Hence there is a need for a photosensitizer (photoinitiator) that can absorb a low-energy photon and become activated, leading to the formation of free radicals.

Common photosensitizers

Benzoin and its derivatives

benzophenone and its

derivatives

acetophenone and its

derivatives

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(I.S.C. = Intersystem crossing)

Photoinitiation processThrough photochemical sensitization, an excited triplet state, which would not normally be generated, can be formed. This involves a molecule which can efficiently produce excited triplet states and, through energy transfer to another molecule, revert to its ground state. The result of this is to produce the excited triplet state of the second molecule.

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Under UV light excitation, the photoinitiator (I) is first promoted to its excited singlet state (1Ix). Then, via fast intersystem crossing, it converts into triplet state (3Ix). This transient state can undergo either direct cleavage of the molecule or hydrogen abstraction with amine compounds or hydrogen donors (DH). The triplet transient state can be quenched by the monomer by an energy transfer process that does not undergo any chain initiation. Accordingly, this process must be regarded as a dead loss pathway. The longer the life time of the triplet state, the more efficient the quenching process becomes. Thus,

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Photoinitiation mechanism

BP2

H2O

2

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Effect of UV on starch properties

Decrease in viscosity

Increase in solubility

increases water binding capacity

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Photo-induced modification of starch

Degradation(in absence of oxygen or air)

Oxidation(in presence of oxygen or air)

Grafting (in presence of monomer)

Crosslinking(in solid or in

solution)

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All the energy coming from the Sun, from which the earth receives 1.5x1018 kWh per year, approximately 28000 times the consumption of all the world in that period.

Solar radiation as source of light

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Solar collectors

No concentration or low temperature, up to

150o C

Medium concentration or medium

temperature, from 150o C to 400o C

High concentration and high temperature, over

400o C.24

what is important in photocatalysis is not only the amount of radiation collected, but its wavelength

Non-concentrating solar collectors for domestic heat water application

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Medium-concentrating solar collectors26

High concentrating solar collector27

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Future work can be done on the basis of using photo initiators/UV system by establishing a “solar energy collector” to collect UV from sun light and use it instead of UV from the mercury lamp

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I am greatly thankful to

Prof. James T. Guthrie

Colour Chemistry Department, University of

Leeds, England

For gifting me the UV lamp and

related accessories

Thank you30

Questions?

؟

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