الفهرس 
Natural PolymersOnly 14 pages are availabe for public view
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Abstract
Due to the fibrous, hydrophilic and highly porous nature, paper is
easily subjected to microbial attack, ultraviolet degradation and higher
water vapor transmission rate. Thus, the present work aims at using
ionizing radiation to prepare formulations to be applied by surface
coating on papers for different applications. In this work gamma
irradiation has been used for the preparation of protective composite for
papers against the attack of microbes.
The results obtained throughout this work may be presented in the
following parts.
In this part, blends based on plasticized starch (PLST) as major
constituent, poly(viny1 alcohol) (PVA) were prepared in the form of thin
films by casting solutions. The gamma irradiated blends were
characterized by IR spectroscopy, thermogravimetric analysis (TGA),
differential scanning calorimetry (DSC), mechanical testing, swelling and
scanning electron microscopy (SEM). As an application in the field of
paper surface modification, solutions of gamma irradiated PLSTIPVA
and PLSTICMC blends in the presence of zinc oxide, as an antimicrobial
agent, were applied to paper by surface coating.
(A) Effect of Gamma Irradiation on the Physical and Chemical
Properties of Plasticized Starch (PLST)/Poly(vinyl alcohol) (PVA)
Blends
In this part, blends based on plasticized starch (PLST) as major
constituent, poly(viny1 alcohol) (PVA) were gamma irradiated and
characterized by IR spectroscopy, thermogravimetric analysis (TGA),
differential scanning calorimetry (DSC), mechanical testing, swelling and
scanning electron microscopy (SEM). The results of may be summarized
in the following points: 1) The results of TGA indicated that PLSTIPVA blends are thermally
more stable than pure PLST.
(2) DSC scans do not show the glass transition temperature (T,) of PVA
or PLST, but instead a new single glass transition, indicating the
occurrence of compatibility. The rate of decomposition reaction curves
displayed similar trends, in which all the blends goes through one
maximum indicating a good distribution between PLST and PVA in their
blends. The temperatures of maximum value of the rate of reactions
(T,,) indicate clearly that gamma irradiated PLSTPVA blends possess
higher thermal stability than unirradiated blends.
(3) The mechanical properties of PLSTIPVA blends showed that the
tensile strength and elongation at break was found to increase by
increasing the ratio of PVA. For unirradiated blends, the tensile strength
and elongation at break were found to increase by increasing the ratio of
PVA. At any ratio of PLSTPVA, the tensile strength and elongation at
break was found to increase with increasing irradiation dose.
(4) The addition of PVA to PLST decreased the water swelling. In this
regard, the swelling (%) for the unirradiated PLST is - two times that for
PLSTPVA (90110%) blend. On the other hand, the swelling (%)
decreases with increasing irradiation doses up to 75 kGy. At higher doses,
the water absorption was affected with PVA crosslinking, starch
degradation and formation of oxygenated groups in PLST. Thus, the
decrease of swelling (%) of these blends is expected to prevent the attack
by microorganisms.
(5) The SEM micrographs showed that the fracture surface of pure PLST
is smooth and characterized with the presence of white particles due the
gelatinization. However, the SEM micrographs of unirradiated
PLSTPVA blends showed a different surface morphology, in which the
surface is not smooth with increasing the PVA ratio in the blend. The effect of gamma irradiation is very clear, in which it is difficult to
distinguish the PLST phase, which seems to become a part of the whole
matrix.
(B) Effect of Gamma Irradiation on the Physical and Chemical
Properties of Plasticized Starch (PLST)/Carboxymethyl Cellulose
(CMC) Blends
In this part, blends based on plasticized starch (PLST) and
carboxymethyl cellulose (CMC) were gamma irradiated and
characterized by IR spectroscopy, thermogravimetric analysis (TGA),
differential scanning calorimetry (DSC), mechanical testing, swelling and
scanning electron microscopy (SEM). The results of may be summarized
in the following points:
(1) The IR analysis showed that no significant shift in the position of the
IR peaks of PLSTICMC blends compared to those of the IR spectrum
of pure PLST, which indicates that there is no intermolecular
interaction between PLST and the CMC.
(2) The TGA studies showed that overall the decomposition temperatures
up to 600•‹C the PLSTICMC blends are thermally more stable than PLST.
However, blends of PLSTICMC which contain higher ratios of CMC
possess higher thermal stability than these blends containing lower ratio.
The curves of the rate of reaction for PLST and those for blends
PLSTICMC go through one maximum over the entire range of
temperatures.
(3) The DSC thermograms of PLSTICMC blends showed two
endothermic peaks due to the glass transition temperature (Tg) and the
melting temperature (Tm) either before or after gamma irradiation. It was
found that the value of Tg increases with adding CMC to starch but, decreases with irradiation dose and also, there is a DROP in the T, due to
the gamma irradiation of the blends.
(4) It was found that the tensile stress was decreased fiom 60.13 kgflcm3
for unirradiated PLST to 20.16 kgflcm3 for unirradiated PLSTICMC at
ratio 50150 and the elongation at break increased fiom 6.25 to 15.04% by
increasing the ratio of CMC.
(5) The degree of swelling of all the PLSTICMC blends increases
progressively with increasing the ratio of CMC in the blends. Also, the
degree of swelling was found to decrease with increasing the irradiation
dose. This is due to the higher hydrophilic character of CMC than PLST.
(6) The SEM micrographs of unirradiated PLSTICMC blends showed a
different surface morphology, in which the surface is smooth and
changes with increasing the CMC ratio in the blend. The effect of gamma
irradiation is very clear, in which it is difficult to distinguish the PLST
phase, which seems to become a part of the whole matrix. Also, there is
an evidence for the formation of crosslinking and degradation of the
PLST phase.
(C) Antimicrobial Properties of Gamma Irradiated Plasticized
StarchlPoly(viny1 alcohol)/ZnO and Plasticized Starch1
Carboxymethyl CelluloseIZnO Composites as Protective Coating for
papers
As an application in the field of paper surface modification,
solutions of gamma irradiated PLSTIPVA and PLSTICMCI blends in the
presence of zinc oxide, as an antimicrobial agent, were applied to paper
by surface coating. The results of may be summarized in the following
points:
(1) For the Effect of plasticized starch (PLST)/poly(vinyl alcohol)
(PVA)/ZnO composites, the photographs of the antimicrobial inhibition zone showed that the unirradiated ones is completely covered with the
microbes. It was found that the gamma-irradiated films of
PLSTIPVAlZnO blends with improved mechanical and thermal
properties will eventually withstand and protect the paper against
microbes. The results showed this technique might provide suitable
materials for the protection of papers against microbial attack.
(2) For the Effect of plasticized starch (PLST)carboxymethyl cellulose
(CMC)/ZnO composites, the photographs of the antimicrobial inhibition
zone showed that the unirradiated ones is completely covered with the
microbes. It is clear the gamma-irradiated films of PLSTICMClZnO
blends with improved mechanical and thermal properties will eventually
withstand and protect the paper against microbes. On the basis of the
inhibition zones, it may conclude that the composition PLSTICMClZnO
(70130%) is more resistant against microbes than the composition
containing 20% of CMC component.