Chapter-3A MATERIALS AND METHODS 1....

Nanocomposite From Depolymerized PET Waste For Food packaging Application

32

Chapter-3A

MATERIALS AND METHODS

1. MATERIALS

Discarded PET bottles from soft drinks was procured from scrapers, cleaned

thoroughly and cut in to small pieces (6 mm x 6 mm). Virgin PET (G 5761, bottle grade),

with intrinsic viscosity of 0.76 and crystallinity >50 % was obtained from Reliance Industries

Ltd., Bombay. Zinc acetate, minimum assay 99 %, ethylene glycol (EG), diethylene glycol

(DEG) and styrene were procured from E. Merck (India) Pvt. Ltd, Bombay and used as

received. Phthalic anhydride (PA), maleic anhydride (MA), acetic anhydride (acetylating

agent), pyridine, benzoyl peroxide (BPO), p-toluenesulphonic acid and hydroquinone were

procured from CDH (India) and used as received. Montmorillonite (K-10) having surface

area 270 m2/g and pH 3-4, dodecyl trimethylammoniumbromide (DTAB) C15H34BrN and

cetyl trimethylammonium bromide (CTAB) were purchased from Aldrich Chemical

Company (Milwaukee, MI) and were used as received.

11. METHODS

Glycolysis

The used PET scrap was a solid material having its melting point at around 260 ± 2

ºC. The high melting temperature of waste PET requires it to digest with glycol at high

temperature. Anaerobic glycolysis was employed, to avoid the side reactions like oxidation

at high temperature. Virgin PET (bottle grade) was taken in different proportions along with

waste PET are shown in (Table 3.1). In the presence of EG, the melting of PET waste started

at around 200 °C and took 8 hours to complete the glycolysis process. The glycolysis was

carried out with excess EG in the presence of zinc acetate as catalyst under anaerobic


33

conditions and normal pressure. The GPET on depolymerization for about 7 to 8 hours was

light brown in color and its viscosity increased with the decrease in ethylene glycol content.

Glycolysis of PET scrap has been done in a 1000 ml three-necked glass reactor equipped

with a reflux condenser, a gas bubbler (argon), a mechanical PTFE blade stirrer and a

thermometer. The whole reaction was carried out in inert atmosphere (argon atmosphere)

under reflux with constant stirring (Figure 3.1).

Table 3.1: Ratios of virgin and waste PET used

S. No. Glycolyzed Product Virgin PET/Waste PET (%)

1 GPET1 90/10

2 GPET2 75/25

3 GPET3 65/35

4 GPET4 50/50

Synthesis of Unsaturated Polyester from Glycolyzed PET

Unsaturated polyester was synthesized from GPET by reacting glycolyzed PET with

MA in the presence of p-toluenesulphonic acid. The relative amount of the monomers by

parts was (GPET:MA) 146 and 200 respectively. Unsaturated polyester resins typically

contain maleic anhydride (fumaric acid is used in some specialized applications). Since, this

is the component that provides the unsaturation that permits crosslinking, so there must be a

balance between diacids and glycols. The only way to control crosslink density is by

introducing different diacids, or to a lesser extent by the use of higher molecular weight

glycols.


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Figure 3.1: Five necked glass reactor

Consequently, dilution of the maleic concentration with another diacid is generally

necessary. In most cases dilution of maleic concentration is accomplished by the use of an

aromatic diacid. Aromatic diacids thus do not directly contribute corrosion resistance, but

rather influence the ability to create the high molecular weight needed for corrosion

resistance and mechanical strength. Subsequently, MA was replaced by PA by 100:0, 90:10,

80:20, 70:30 and 60:40 (wt %) respectively. The desired amount of reactants is charged in a

reaction kettle. The temperature is maintained in the range of 120-150 oC for first five hours

and then to 170 oC for subsequent 3 hours. Distillation is done through reaction to ensure

water removal. 30 ppm hydroquinone is added to prevent premature gelation of resin. Then

prepolymer is dissolved in 40 wt % styrene. It is mechanically mixed for 3 hours. Constant

stirring is done throughout the reaction. To initiate polymerization, 1 wt % of a free-radical

peroxide initiator BPO is added at 60 oC.


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Modification of Montmorillonite

The procedure for the modification of clay is shown in Scheme 3.1.

Scheme 3.1: Modification of montmorillonite

Montmorillonite clay was dispersed in DI water by stirring. The modifiers Cetyl

trimethyl ammonium bromide (CTAB)/dodecyl trimethyl ammonium bromide (DTAB) was

added to the dispersion. The whole dispersion was heated at 80 oC for 4 h. The exchanged

clays were filtered and washed with DI water until they were free from bromide (tested by

titration with silver nitrate). The modified clay was dried at 80 oC under vacuum. The cation

Montmorillonite Clays are dispersed in DI water by stirring

Dodecyl trimethylammoniumbromide (DTAB)/Cetyl

trimethylammoniumbromide (CTAB) is added to dispersion

The whole dispersion is heated at 80 oC for 6 h with vigorous

stirring

A white precipitate formed, which was isolated by filtration and

washed several times with hot water/ethanol

The treated clay was dried at 100 oC in the vaccum oven for 24 h


36

exchange capacity (CEC) of the modified clay was calculated by titrating the supernatant

against a standard iodine solution. Only those sodium ions which are exchanged during

stirring of the clay react with iodine, giving the equivalent weight of the sodium in the

supernatant. CEC calculated from the titre value for CTAB was 29.92 and for DTAB 152.84

meq/100 gm of clay.

Synthesis of Unsaturated Polyester-layered Silicate Nanocomposites (In-Situ Method)

The flowchart of the specimen preparation procedure by the In-situ method is shown

in Scheme 3.2.

Scheme 3.2: The flowchart of the specimen preparation procedure by the in-situ

method

In the In-situ method, the organoclay is added to the reaction medium simultaneously

with the monomers. The penetration of the monomers into the clay layers is followed by

Prepolymer +

MMT

Styrene 40 wt

%, 50 oC

Mechanically mixing 3 h

Cooling to room temperature (RT)

Addition of initiator & mixing at

RT

Cast into molds

Cured at 80 oC for 3 h & post cured

for 4 h at 120 oC

MA + PA + GPET +

MMT

Reaction for

120-150 oC for 5 h + 170

oC for 3

h

1 h vacuum

Prepolymer + MMT


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polymerization. The nanocomposites contained 0 to 6 wt % organoclay with DTAB

modifier. These reactants were fed together to the five necked glass reactor having

mechanical agitator assembly. The whole reaction was carried out about 8 h with constant

stirring at temperature up to 180 oC. The mixture was then cooled down to 90-100

oC and

hydroquinone was added to prevent premature gelation of resin. Then, the prepolymer and

clay was dissolved in 40 wt % styrene. The reaction mixture was mechanically stirred for 3 h

and then, curing was done by initiator at 1 %. Materials were cured for 6 h at 60 oC. The

temperature was gradually increased from room temperature to 60 oC at the beginning and

then cooled from 60 oC to room temperature at the end of the curing stage in order to prevent

craze and cracks due to sudden crosslinking and cooling. The detailed feed compositions are

reported in Table 3.2 (a) and Table 3.2 (b).

Table 3.2 (a): Detailed feed composition of the unsaturated polyester nanocomposite

synthesized from GPET with varied acid and clay content

Sample ID Maleic anhydride

(%)

Phthalic anhydride

(%)

Clay

Montmorillonite

(K-10) (%)*

60UP0 60 40 0

70UP0 70 30 0

80UP0 80 20 0

90UP0 90 10 0

100UP4 100 0 4

60UP4 60 40 4

70UP4 70 30 4

80UP4 80 20 4

90UP4 90 10 4

100UP4 100 0 4

90UP2 90 10 2

90UP3 90 10 3

90UP5 90 10 5


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Table 3.2 (b): Detailed feed composition of the unsaturated polyester nanocomposite

synthesized from GPET with varied acid and clay content

CCRD Experimental Design

Central composite rotatable design (CCRD) is employed to fit a second order model.

The design was generated by commercial statistical package, Design-Expert version 6.01

(Statease Inc., Minneapolis, USA, Trial version). The levels are calculated and experiments

are performed using CCRD described elsewhere.160

The two independent formulation

variables selected for this particular study are the glycolysis time and temperature. CCRD

was chosen as the experimental design. The actual and corresponding coded values of

different variables are reported in Table 3.3. CCRD is an efficient and proven design,

especially for two factors.161,162

CCRD is also rotatable, which means that all the points in

the design area are at equal distance from center. This leads to distribution of errors among

all points equally.

Sample ID Clay

montmorillonite

(K-10) (%)

Maleic

anhydride

(%)

Phthalic

anhydride

(%)

Styrene

(%)

MONTUP100 4 4 100 0 40

MONTUP90-4 4 90 10 40

MONTUP80-4 4 80 20 40

MONTUP70-4 4 70 30 40

MONTUP60-4 4 60 40 40

MONTUP90-0 0 90 10 40

MONTUP90-2 2 90 10 40

MONTUP90-5 5 90 10 40

MONTUP90-6 6 90 10 40


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Table 3.3: The actual and corresponding coded values of different variables along with

experimental data values

S. No

Coded values Coded values Uncoded

values Uncoded values

Glycolysis

Time

(x1)

Glycolysis

Temp.

(x2)

Glycolysis

Time (h)

(X1)

Glycolysis

Temp.(oC)

(X2)

1 -1.000 -1.000 3.00 150.00

2 1.000 -1.000 10.00 150.00

3 -1.000 1.000 3.00 210.00

4 1.000 1.000 10.00 210.00

5 -1.414 0.000 1.55 180.00

6 1.414 0.000 11.45 180.00

7 0.000 -1.414 6.50 137.57

8 0.000 1.414 6.50 222.43

9 0.000 0.000 6.50 180.00

10 0.000 0.000 6.50 180.00

The numbers of design points in CCRD are based upon a complete 2k factorial. The total

numbers of experiments are:

(3.1)

where N = total number of experiments, k = number of factors, m = number of replicates.

Multiple linear regression analysis was used and the data was fitted as a second-order

equation.


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The general equation that was fitted is:

(3.2)

The number of coefficients in the above equation is 6. The redundancy factor of the

experimental design Rf = number of experiments/number of coefficients. For a CCRD, the

numbers of experiment are 10 and the numbers of coefficients are 6. Therefore, the

redundancy factor is 1.667. The lower limits of the two variables were fixed based on the

previous experimental work carried out by Mahdi.163

Synthesis of Unsaturated Polyester Nanocomposite (Simultaneous Mixing))

The desired amount of monomers (GPET, MA) was fed together to the five necked

glass reactor having mechanical agitator assembly.164

The whole reaction is carried out 8

hours with constant stirring at temperature up to 180 oC. Hydroquinone is added to prevent

premature gelation of resin. Then, the prepolymer and modified clay is dissolved in 40 % wt.

styrene with varying mixing times of 15, 30, 60, 120 and 180 min at 60 oC as shown in

Scheme 3.3. The curing is done by initiator at 1 %. The initiator is thoroughly dispersed in

unsaturated polyester matrix in a glass vial. Materials are cured for 6 h at 60 oC The

temperature is gradually increased from room temperature to 60 oC at the beginning and then

cooled from 60 oC to room temperature. The nomenclature used in this work is based on the

original composition of reactants shown in Table 3.4.


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Scheme 3.3: Simultaneous mixing method

MA + PA + GPET

Reaction for

120-150 oC for 5 h + 170

oC for 3 h

1 h vacuum

Prepolymer + MMT + Styrene 40%, 50 oC

Mechanically mixing with

Varying mixing time


Addition of initiator & mixing at RT

Cast into molds

Cured at 80 oC for 3 h & post cured for 4 h at 120

oC


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Table 3.4: Nomenclature of samples depends upon mixing time of styrene and clay.

Sample ID Mixing Time (min) Clay Montmorillonite (K-10) (%)

100UP0 0 0

Simultaneous100UP5-15 15 5





Sequential100UP5-15 15 5





Synthesis of Unsaturated Polyester Nanocomposite (Sequential Mixing)

Sequential mixing is a new approach for preparing unsaturated polyester–layered

silicate nanocomposites.164

In the first step, pre-intercalates of the unsaturated polyester and

MMT nanocomposites are prepared. In other words, the mixture of the UP and

organophillic-treated MMT are prepared in the first step; then the styrene monomer is added

to these pre-intercalates of UP/MMT with varying mixing times of 15, 30, 60 and 180 min at

60 oC as shown in Scheme 3.4. All UP–MMT–styrene mixtures contained 0.01 wt %

hydroquinone as an inhibitor to prevent reaction in the mixing stage. Finally, all mixtures are

cured at 80 oC for 3 h and post-cured for 4 h at 120

oC. All UP/MMT nanocomposites


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contained UP of 60 wt %, styrene monomer of 40 wt % and MMT 5 wt %. The

nomenclature used in this work is based on the original composition of reactants shown in

Table 3.4.

Scheme 3.4: Sequential mixing method.

MA + PA + GPET + MMT

Reaction for

120-150 oC for 5 h + 170

oC for 3 h

1 h vaccum

Prepolymer + MMT + Styrene 40%, 50 oC

Mechanically mixing with

Varying mixing time


Addition of initiator & mixing at RT

Cast into molds

Cured at 80 oC for 3 h & post cured for 4 h at 120

oC


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Synthesis of Saturated Polyester from Glycolyzed PET

Initially, a reference resin (STDPET) was synthesized by direct esterification.165-170

This reaction was a heterogeneous reaction with monomers of phthalic anhydride and

ethylene glycol. The mixture of monomers was charged as a slurry, because TPA was hard

to dissolve in EG. The TPA:EG molar ratio used was 1:1.2 and the reaction temperature was

usually 150–180 oC into a five-necked reaction kettle equipped with a mechanical stirrer,

inlet/outlet to inert gas (argon), thermometer and reflux. The reactor was purged with argon

for 15 min before heating was switched on. Then, the content was heated under argon

atmosphere to 180 oC until approximately 15 mL of water were collected. In the commercial

reaction, some PET prepolymer (BHET) is added in order to shorten the reaction time. Pre-

polymer produced from the direct esterification reaction is gradually heated to 200 oC. In

this step, EG is collected as a byproduct. Generally, catalysts are not for this reaction, since

the acid functional groups of TPA can catalyze the reaction. The overall reaction time,

including the esterification and the polycondensation processes, is long and usually varies

from 8 to 10 h. The above experiment was repeated by replacing the ethylene glycol with

GPET by 100:0, 80:20, 60:40, 50:50 and 40:60 percent respectively. The quantity of TPA

remains the same for all above combinations. The samples were taken out at different time

intervals to study the polymerization kinetics. The polymerization kinetic was studied

through the measurement of acid value and the extent of reaction at different time intervals.


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Table 3.5 (a): Detailed feed composition of the saturated polyester and their

nanocomposites with varied GPET and clay content

Synthesis of Saturated Polyester/Clay Nanocomposites (In-Situ Polymerization)

In-situ polymerization involves the dispersion and distribution of clay layers in the

monomer followed by polymerization. The layered silicate is swollen within the liquid

monomer or a monomer solution so that polymer formation can occur between intercalated

sheets. Polymerization can be initiated either by heat or radiation. The saturated polyester

nanocomposites (GPET waste) were prepared by heating the desired mixture of phthalic

Sample ID Glycolyzed PET (%) Ethylene glycol (%) Montmorillonite

Clay (%)

STD PET 0 100 0

GPET20 20 80 0

GPET40 40 60 0

GPET50 50 50 0

GPET60 60 40 0

GPET50(2)CTAB 50 50 2 (CTAB)

GPET50(3)CTAB 50 50 3(CTAB)





GPET(60)4CTAB 60 40 4(CTAB)

GPET50(4)DTAB 50 50 5 (DTAB)


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anhydride, ethylene glycol, GPET and modified montmorillonite clay in a five necked

reaction kettle.

Table 3.5 (b): Detailed composition of the saturated polyester and their nanocomposite

with varied GPET and filler composition

The modified nano filler of a predetermined quantity was dispersed in a reaction

mixture. The dispersion was maintained by constant mechanical stirring at 500 rpm

(overnight for proper intercalation). The mixture was heated at 120 oC for 3 h, followed by

at 150-200 o

C for 3-4 h. The whole mass was transferred to an appropriate mould. The

nomenclature used in this work is based on the original composition of reactants (shown in

Tables 3.5 (a) and 3.6 (b).

Sample ID Glycolyzed PET (%) Ethylene glycol (%) Montmorillonite Clay (%)

STD PET 0 100 0

GPET20 20 80 0

GPET40 40 60 0

GPET50 50 50 0

GPET60 60 40 0

GPET50(2) 50 50 2 (CTAB)

GPET50(4) 50 50 4(CTAB)

GPET50(5) 50 50 5(CTAB)


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Chapter-3B

INSTRUMENTATION & CHARACTERIZATION

Fourier Transform Infra-Red Spectroscopy (FTIR)

The FTIR spectrometry using a Perkin–Elmer RX-I spectrophotometer was used to

characterize the resin before and after curing. Samples were prepared by the KBr pellet

method and spectra were collected as a sum of 32 scans at a resolution of 4 cm-1

.

Specifically, about 1 mg of finely powdered polymer sample was mixed with 100 mg of KBr

powder in a mortar and pestle. The mixture was then pressed in a die at about 100 MPa

pressure for 3 min to get a transparent disk. This disk was then placed in a sample holder and

the peak transmittance recorded.

Wide Angle X-ray Diffraction (WAXRD)

X-Ray Diffraction (XRD) is a versatile method that gives information about the order

of crystallinity of the material. Scanning intensity curves for values of 2θ ranging from 4.00

to 15 degrees were determined by X-ray diffraction analysis (XDS 2000, Scintag Inc., USA)

using powder polymeric samples. The incident X-ray beam (CuKα, 40 kv, 35 mA) was

passed through a graphite filter, and pulse height discriminator to achieve further

monochromatization.

Dynamic Mechanical Analysis (DMA)

There are two types of shear modulus obtained from this test. One is the storage or

elastic modulus, E' the in phase sample response. The other is the loss or viscous modulus,

E" the out of phase portion of the response. The ratio of E"/E' is called tan δ (tan delta).

When tan δ shows a peak, the sample is going through a thermal transition such as glass

transition or melting. The dynamic mechanical analysis of the bulk polymers has been


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conducted by using a Perkin-Elmer dynamic mechanical analyzer DMA Pyris-7e in a three

point bending mode with a 110 mN static force and a 110 mN dynamic force. A rectangular

specimen is prepared by machining the cylindrical product (obtained from heating in a vial)

to specimens of 1.2-2 mm thickness and 5 mm depth. Each specimen is first cooled under

liquid nitrogen to about. -30 oC, and then heated at 5

oC/min and at a frequency of 1 Hz under

nitrogen. The viscoelastic properties, i.e. storage modulus E' and mechanical loss factor

(damping) tan δ are recorded as a function of the temperature. The glass transition

temperature, Tg, of the polymer is obtained from the peak of the loss tangent plot. The

crosslink densities have been determined from the rubbery modulus plateau based on the

theory of rubber elasticity.171-172

(3.3)

where E' is the storage modulus of the crosslinked polymer in the plateau region, R is the

universal gas constant (8.314 Jmole-1

K-1

) and T is the absolute temperature (K).

Thermogravimetric Analysis (TGA)

Thermal analysis may be defined as the measurement of physical and chemical

properties of materials as a function of temperature. Thermogravimetric studies have been

carried out by using a Perkin-Elmer Pyris 7 thermogravimeter under nitrogen (20 ml/min).

The samples have been heated from 50 to 700 oC at a heating rate of 20

oC/min.

Differential Scanning Calorimetry (DSC)

Differential scanning calorimetric studies were carried out using a differential

scanning calorimeter (Perkin Elmer Pyris 7) in the temperature range of 50 to 300 oC at a

heating rate of 10 oC/min. The sample weight used was approximately 4-5 mg. The peaks

were used to determine the thermal properties of the samples.


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Scanning Electron Microscopy (SEM)

The polymeric samples to be scanned were mounted onto the specimen stub. The

samples were sputter coated with a thin layer (approximately 25 nm) of gold under a vacuum by

using a sputter coater (JEOL JFM 1100). The coated samples were examined using a

scanning electron microscope (JEOL JSM 6100) at a 25 kV accelerating voltage and the

images were recorded on 120 B & W Roll Film (100 ASA).

Transmission Electron Microscopy (TEM)

To prepare specimens for TEM, a small sample was microtomed using a Leica

Ultracut Cryo-ultramicrotome with a Diatome diamond knife at a sample temperature of -60

oC to obtain ultrathin (about 100-200 nm) sections. The sections were transferred onto

carbon-coated Cu grids of 200 mesh. Clay layers consisting of silicon atoms appear dark due

to less electron scattering. TEM imaging was performed on a JEOL JEM 2100 operated at

100 KV accelerating voltage.

Swelling Experiments

The samples were cut into circular form using a die of 10 mm diameter. The

thickness of a sample was measured by means of a screw gauge. The dry samples were

weighed on an electronic balance (Citizen, CX 220) and then kept in the solvent in screwed

bottles. The samples were taken out of the solvent at specific intervals and the excess solvent

was rubbed off. The samples are then weighed and again immersed in the solvent till

equilibrium was attained (i.e. 72 h). The time for measuring weight of the sample is kept

minimal (about 30 sec), so that the escape of the solvent from the sample remains negligible.

Equilibrium swelling experiments at different temperatures were carried out at 20, 30, 40 and


50

50 oC (±1

oC) to study the effect of temperature on the swelling. For temperatures higher

than room temperature, the samples were kept in a microprocessor controlled hot air oven.

The mole percent uptake (Qt) at each time interval was calculated by using equation

(3.4)173

:

(3.4)

Where Mt is he mass of the solvent taken up at time t, Mr is the relative molecular

mass of the solvent and Mi is the mass of the dry sample. The mole percent uptake at 72

hours was taken as swelling at infinite time (Q∞).

Determination of Free Glycol

The weighed quantity of the glycolyzed product was extracted with water and

filtered. The filtrate containing water, free glycol and some oligomers was concentrated by

evaporation of water and then distilled in order to precipitate out the water-soluble oligomers.

This was filtered again. The precipitates of the first filtrate were formed under chilling

conditions, which were then filtered. Both the residues of the sample obtained during

filtration as well as the second were weighed together after drying. The difference between

the original and the final weight represents the amount of free glycol removed by water

extraction.

Glycolysis Conversion Percentage

After finishing each glycolysis experiment, the reactor was removed from the heating

filament and 200 ml of boiling water was slowly added into the reactor. The whole product

mixture was quickly filtered using a copper mesh of 0.5 × 0.5 mm pore size. The remaining

polymerized PET flakes were collected, dried, weighed and labeled as the PET fraction. The

conversion for the glycolysis of recycled PET flakes is defined as below:


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(3.5)

where A is the weight of PET flakes before glycolysis and B is the weight of PET flakes after

glycolysis.

Acid Value

The acid value (Ia) is the number of milligrams of potassium hydroxide necessary to

neutralize the acid functions present in one gram of polyester. The sample was dissolved in a

mixture of 20 ml of THF and 4 ml of water, then this solution was titrated by a solution of

potassium hydroxide (0.83 N KOH-ethanol solution). The indicator used during this titration

was Bromothymol Blue. The acid value was calculated according to equation (3.6):

(3.6)

where, V0 = volume in milliliters of the solution of potassium hydroxide used during the

blank test (without sample); V1 = volume in milliliters of the solution of potassium

hydroxide used during the test; m = mass in grams of the sample used; T = titre of the

solution of potassium hydroxide used (in mol/l).

Hydroxyl value

The hydroxyl value was determined following the standard method NF T 52-113.

The hydroxyl value was calculated according to equation (3.7):

(3.7)

where, V0 = volume in millilitres of the KOH standard solution used for the blank test

(without sample); V1 = volume in millilitres of the KOH standard solution used for the test


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with sample); m = mass in grams of the sample; T = titre of the solution of potassium

hydroxide used (in mol/l).

Average Molecular Weight

For linear polymers, the Mn value can be calculated by using equation (3.8).from the

known formula of end group analysis method.174

(3.8)

where Z is the number of groups that can be determined per polymer molecule, 2, m the

mass of polymer sample, and y mmol KOH reacted with polymer.

Water Vapor Transmission Rate Study (WVTR)

WVT was determined according to ASTM E96-80175

, modified by Gontard et al.176

A container with silica gel was closed with a sample of nanocomposite sheet (1 mm

thickness) firmly fixed on top. Then the container was placed in a dessiccator with distilled

water at a temperature of 25 oC. The sheets were weighed daily on a Mettler analytical

balance for 10 days. Water vapor transmission (WVT) was calculated according to equation

3.9:

(3.9)

where WVT is Water Vapor Transmission (g.H2O.mm.m-2

), x is the average thickness of the

sheet and A is the permeation area. WVTR is the mass of water vapour transmitted through a

unit area in a unit time under specified conditions of temperature and humidity. WVTR was

calculated according to equation (3.10):

(3.10)


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Where WVTR is water vapor transmission rate (g.H2O mm h-1

m-2

), and the term x/t was

calculated by linear regression from the points of weight and time, during constant rate

period. The tests were carried out induplicate.

Measurement of Extent of Reaction

The kinetics of the reaction was studied by monitoring the acid group concentration.

The extent of the reaction was determined from the acid number. Polyesterification is a

reversible reaction and can be represented as

Flory suggested that the rate of disappearance of the reactants could be interpreted as

the overall rate of reaction. Generally the rate of polyesterification is monitored by the rate

of depletion of the carboxyl groups of the acid or anhydride. It is well known that

polyesterification reaction reactions are catalyzed by acids and in the absence of any added

catalyst, the diacid itself acts as a catalyst. Therefore in the absence of an external catalyst,

the rate of polyesterification could be represented as:

(3.11)

If the concentration of carboxyl and hydroxyl groups is equal, then above equation (11)

becomes

(3.12)

where C is the concentration of the carboxyl or hydroxyl groups. Therefore

(3.13)

On rearrangement and integration,


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(3.14)

The extent of the reaction p, is defined as a fraction of the functional groups (carboxyl)

initially present that have undergone reaction in a given time t, that is,

(3.15)

where C0 is the initial concentration of carboxyl groups.

On rearrangement of equation 3.15,

(3.16)

From the correlation of equations 3.14 and 3.16,

(3.17)

Measurement of Degree of Polymerization

It is known that any imbalance in the stoichiomerty of the reactants reduces the

degree of polymerization (DPn). The average degree of polymerization is represented as:

(3.18)

where ‘r’ is the ratio of concentrations of the hydroxyl to carboxyl group and is never less

than unity.

Chapter-3A MATERIALS AND METHODS 1....

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