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FUNCTIONALIZATION OF COTTON-CELLULOSE VIA HIGH

ENERGY IRRADIATION INITIATED GRAFTING AND

CYCLODEXTRIN IMMOBILIZATION

Gilles Desmet

Promoters: prof. dr. Judit Borsa and prof. dr. ir. Paul Kiekens

Supervisor: prof. dr. Erzsébet Takács

Master’s thesis submitted in order to obtain the degree of

Master of Science in Textile Engineering

Department of Textiles

Head: prof. dr. ir. Paul Kiekens

Faculty of Engineering

Academic year: 2009-2010

Association

of

Universities for Textiles

FUNCTIONALIZATION OF COTTON-CELLULOSE VIA

HIGH ENERGY IRRADIATION INITIATED GRAFTING

AND CYCLODEXTRIN IMMOBILIZATION

By Gilles DESMET

Master’s thesis submitted as finalization of the ETEAM (European Master’s degree in

Advanced Textile Engineering) program in order to obtain the academic degree of


Supervisor:

Prof. dr. Erzsébet TAKÁCS

Head of the Department of Radiation Chemistry

Institute of Isotopes

Hungarian Academy of Sciences

Promoters:

Prof. dr. Judit BORSA

Department of Physical Chemistry and Materials Science

Faculty of Chemical Technology and Biotechnology

Budapest University of Technology and Economics

Prof. dr. ir. Paul KIEKENS



University of Ghent


Head: prof. dr. ir. Paul KIEKENS


University of Ghent

Academic year 2009 - 2010

Preface i

Functionalization of cotton-cellulose via high energy Gilles Desmet

irradiation initiated grafting and cyclodextrin immobilization

PREFACE

This thesis is the finalization of a 2 year master’s program, known as ETEAM

(European Master’s degree in Advanced Textile Engineering) organized by the

Association of Textile Universities (AUTEX) of which the secretarial department is

situated at the Department of Textile at the University of Ghent. This program allowed

me to study at the technical universities of Tampere, Dresden, Ljubljana and Budapest,

where this master’s thesis was created. Professor Judit Borsa, from the Department of

Physical Chemistry and Materials Science at the Faculty of Chemical Technology and

Biotechnology at the Budapest University of Technology and Economics (BME: Budapesti

Műszaki és Gazdas{gtudom{nyi Egyetem), handed me the subject of my thesis and served

as my initial supervisor. Because of the thoroughgoing collaboration between professor

Judit Borsa and professor Erzsébet Takács, head from the department of Radiation

Chemistry at the Institute of Isotopes (IKI) from the Hungarian Academy of Sciences

(HAS), I would perform my research activities at this institute under the daily

supervision of professor Erzsébet Takács. This would allow me to work with

professional equipment and experienced researchers and technicians. For the practical

experiments, technical assistant Éva Koczogné Horváth, or Evike, would aid me.

My sincere thanks go in the first place to those three people, who proved to be

invaluable to the realization of this work. Both professor Borsa and professor Takács

possess a combination of unremitting kindness and profound knowledge which could

not make me imagine better supervisors, and Evike’s practical skill and help was

indispensable for the experimental part. Köszönöm szépen!

Secondly, I would like to thank professor Paul Kiekens, who made it possible for me to

go abroad, professor László Wojnárovits for his thorough editing of the manuscript,

Katalin Gonter and dr. Péter Hargittai for their help making the SEM-pictures, Zoltán

Papp for irradiating all the samples, dr. Enikő Földes for making the DSC

measurements and all the other people of the Radiation Chemistry department for

their support and making my time spent over there so pleasant!

Preface ii



Special thanks to my parents, for supporting me throughout the entire duration of my

studies and to Ilka, for her love and support.

Copyright :

The author gives permission to make this Master’s thesis available for consultation and

to copy parts of the Master’s thesis for personal use. Any other use falls under the

limitations of the copyright, especially with regard to the obligation of mentioning the

source explicitly on quoting the results of this Master’s thesis.

Budapest, 30th of May

Gilles Desmet

Summary iii



Association

of

Universities for Textiles

SUMMARY

FUNCTIONALIZATION OF COTTON-CELLULOSE VIA HIGH

ENERGY IRRADIATION INITIATED GRAFTING AND

CYCLODEXTRIN IMMOBILIZATION

By Gilles DESMET

Master’s thesis in order to obtain the degree of



Promoters: prof. dr. J. BORSA and prof. dr. ir. P. KIEKENS

Supervisor: prof. dr. E. TAKÁCS


Head: prof. dr. ir. P. KIEKENS


Ghent University


A study was made investigating the surface functionalization of cotton-cellulose using

i) pre-irradiation grafting (PIG) and ii) simultaneous grafting (SG) of glycidyl

methacrylate (GMA). This topic requires significant knowledge in several scientific

disciplines, viz. material sciences, chemistry and physics. The first major part of this

thesis consists therefore of an in-depth literature survey, compiling the relevant

information out of over 80 reference works, and supplies all the necessary knowledge

in order to fully understand the followed experimental procedures.

The second major part consequently grasps the experimental research: Glycidyl

methacrylate (GMA) will be grafted on cotton-cellulose according to the two

distinguished methods: i) pre-irradiation grafting (PIG) in which the substrate is

irradiated first and only afterwards immersed into a grafting solutions and ii)

simultaneous (or mutual) grafting (SG) in which substrate and grafting solutions are

irradiated together. Both reactions will result in a material consisting of a cellulose

backbone and grafted GMA side chains.

Summary iv



Using visual analysis, SEM, gravimetrical measurements and FTIR spectroscopy, it is

found that PIG leads to more homogeneous samples with no obvious signs of

homopolymerized GMA, while SG leads to much higher yields under the same

reaction conditions but showed, however, clear indications of GMA-homopolymer. By

careful control of the reaction parameters, viz. consistence of the reaction mixture,

absorbed dose, moisture content, grafting temperature and grafting time, a degree of

grafting (in mass percentage) of 125% for PIG and 350% for SG can be reached. It is

shown that the moisture content has a significant impact on the grafting yield during

PIG, a result which has not been published earlier.

The thermal properties are measured using DSC and the grafted samples show an

increased thermal stability. UV/VIS spectroscopy and a gravimetrical determination of

the swelling percentage showed that the samples have increased adsorption properties

and an increased hydrophobicity, this hints for a possible future application as a

reactive filter. A special application of the grafted GMA is that they impart epoxide

groups which can, theoretically, serve as anchoring points for β-cyclodextrin (β-CD).

The immobilization of β-CD is further investigated. Dependent on the procedure, two

immobilizing procedures are considered: i) after PIG or SG, using a catalyst to open the

epoxide ring or ii) during SG. Only this second method, however, has showed clear

results. The resultant material is characterized using SEM, gravimetrical measurements

and adsorption measurements. Using SEM, little bolls were observed on the surface at

sufficient magnifications which were not observed in the simultaneous grafting

without β-CD in the grafting solution, and the adsorption properties were clearly

enhanced.

Keywords:

cotton-cellulose, pre-irradiation grafting, simultaneous (mutual) grafting, GMA, cyclodextrin

immobilization.

Extended Abstract v



EXTENDED ABSTRACT

Functionalization of cotton-cellulose via high energy irradiation

initiated grafting and cyclodextrin immobilization

Gilles Desmet

Promoters: prof. dr. Judit Borsa, prof. dr. ir. Paul Kiekens

Supervisor: prof. dr. Erzsébet Takács

Abstract: A study was made investigating the

surface functionalization of cotton-cellulose

using i) pre-irradiation grafting (PIG) and ii)

simultaneous grafting (SG) of glycidyl

methacrylate (GMA). The influence of the

reaction parameters was determined. It was

found that PIG leads to more homogeneous

fiber surfaces while SG leads to attached flakes

of homopolymerized GMA, despite the

addition of styrene as homopolymer

suppressor. Additionally, the immobilization

of β-cyclodextrin on both kinds of surfaces was

looked into.

Keywords: cotton-cellulose, pre-irradiation

grafting, simultaneous (mutual) grafting,

GMA, cyclodextrin immobilization

I. INTRODUCTION

ach application demands its own unique

material. The properties of synthetic

materials can be adjusted the way the

end-users defines them. Environmental issues

and the limited supply of petroleum, however,

advise the use of renewable, so-called green

materials. One of the most obvious green

materials is cellulose, being the most abundant

natural polymer on earth [1]. Green materials

however come the way nature supplies them. In

order to make them meet the demand of specific

applications, we can functionalize them. This

means that specific chemical functional groups

will be imparted to the material on a molecular

level. This will have its influence on the

supermolecular and the morphological level, as

well as on the resulting properties. In this work,

an epoxide ring will be imparted to the cellulose

through grafting of glycidyl methacrylate (GMA)

[2-4], initiated through irradiation. This means

that side chains of GMA will be placed on the

cellulose backbone using either pre-irradiation

(PIG) or simultaneous grafting (SG) [5-6]. In the

pre-irradiation grafting method cellulose is

irradiated in the presence of air which yields

peroxide groups [7-8]. The grafting-initiating

radicals are formed by decomposing these

peroxide groups in the grafting solution by

applying heat. A disadvantage of this method is

the degradation of the substrate due to the

radiation directly affecting the cellulose. During

simultaneous (mutual) grafting the irradiation is

carried out in the presence of the monomer

solution [4,9] and mainly solvent radicals are

created (due to their relative amount), which on

their turn may produce radicals in both

monomer and the substrate. Both solvent and

monomer can act as stabilizer, protecting the

cellulose against radiation. The disadvantage is

the formation of homopolymer.

The grafted materials can be used for, among

other things, the adsorption of water

contaminants [10]. The adsorption properties of

this material could be even further enhanced by

reaction between the reactive epoxide group and

β-cyclodextrin. This molecule is known for its

unique ability to form inclusion complexes with

aromatic and phenolic compounds, metals and

dyes [11-14]. Next to filtering purposes, the

inclusion complex forming ability of β-

cyclodextrin can also be used for the

incorporation of antimicrobials [15] or the slow

release of perfumes or drugs [16]. The first goal

of this work is to investigate the two procedures

of grafting GMA on cellulose and their effect on

the resulting material. The second goal is to

elucidate the methods to immobilize β-

cyclodextrin on the procured material,

depending on the precedent grafting technique,

viz. PIG [17-19] or SG [4]. The enhancement of

the adsorption properties will be tested.

II. EXPERIMENTAL

A. Materials

GMA (Aldrich®) and β-cyclodextrin (β-CD)

(CycloLab, Ltd.) were used without purification.

Styrene was purchased from Fluka® Analytical

and 2,4-Dichlorophenoxy acetic acid (2,4-D)

from Aldrich®. Purified water was obtained

E

Extended Abstract vi



from an ion exchanger equipment, type ELGA

Option 4. All solvents were from an analytical

grade. Cotton-cellulose samples (Testfabrics,

Inc.) were washed in boiling methanol for 3

hours.

B. Grafting procedure

B.1. Pre-irradiation grafting (PIG)

Cotton-cellulose fabric samples were irradiated

in air, at room temperature, by 60Co gamma rays

up to 40 kGy (dose rate 6 kGy h-1). Immediately

after irradiation the samples were immersed in a

0,5 – 3 M GMA solution of 20 v% H2O – 80 v%

MeOH at 40 to 70°C for 10 – 120 min. The

material to liquor (M:L) ratio was approx.: 0.1 g

sample per 10 ml solution. N2 bubbling was

applied to deoxygenate the monomer solutions.

Bubbling was started about half hour before

grafting and continued during the whole

grafting procedure. Grafted samples were first

washed carefully in methanol and remaining

monomer was removed by extraction in boiling

methanol for 3 hours. The samples were dried at

room conditions.

B.2. Simultaneous grafting (SG)

Monomer solutions were created containing 0,18

– 1,51 M GMA in 20 v% H2O – 80 v% MeOH as

well as 0,6 M styrene, to suppress

homopolymerization. In 1 experiment, NaOH

(0,5 M) was added. Glass ampoules were filled

with this solution (10 or 17 ml) together with 2

cotton samples and deoxygenated using N2

bubbling for approx. 5 min. The ampoules were

flame sealed in inert atmosphere and irradiated

at room temperature up to 20 kGy.

The same washing and drying procedure as for

PIG was used.

C. β-CD immobilization procedure

C.1. Upon PIG

The procedure as first described by Zhao and He

has been followed [16]. Pre-irradiated samples

were immersed into a 0,017 M β-CD solution of

20% DMF – 80% H2O with 0,25 M NaCl

(catalyst) in a M:L ratio of approx. 1:75 at 70°C

for 24 hours. Next they were extracted with H2O

(1 h), acetone (1 h) and MeOH (1 h).

C.2. Upon SG

Except for the solution, which could contain

NaOH (0,5 M) or HCl (0.5 M) as catalyst instead

of NaCl, the same procedure as for PIG has been

used.

C.3. During SG

0,017 M β-CD was added to the grafting

solution, which was changed to 33 v% H2O – 33

v% MeOH 33 v% DMF due to solubility issues of

β-CD in methanol. The rest of the procedure was

the same as in normal SG.

D. Evaluation of the samples

Sensory perceptions gave a rough idea about the

yield, and the macroscopic influence of grafting.

SEM analysis was performed upon gold coating

of the sample with a JSM 5600LV Scanning

Electron Microscope from JEOL Ltd.

The degree of grafting (DG (w%) = 100 (wg-w0)/w0 )

was determined by weighting the dried samples

before (w0) and after (wg) grafting.

The degree of immobilization (DI (w%) = 100 (wCD-

wg)/wg ) was determined by weighting the dried

samples before (wg) and after (wCD) the

cyclodextrin immobilization treatment.

FTIR spectroscopy was used to determine the

functional groups of the substrate with an ATI

Mattson Research Series 1 FTIR spectrometer in

the diffuse reflectance mode.

The band at 2900 cm-1, assigned to the stretching

vibrations of aliphatic C–H bonds, served as

internal standard.

DSC was performed to assess the thermal

properties with a Mettler DSC30 device. UV-spectroscopy of an aqueous solution of 0,2

mM 2,4-D before and after adsorption on the

grafted samples was performed with a JASCO

U-550 UV/VIS spectrophotometer. Swelling ( = 100(wS-wg)/wg ) was determined by

weighting the dried grafted samples (wg) and

the wet ones, after removing excess water with

blotting paper (wS).

III RESULTS AND DISCUSSION

A. Pre-irradiation grafting

A.1. Characterization of the samples

Grafted samples were considerably stiffer than

untreated samples. A significant change of

surface morphology was observed (Fig. 1).

Fig. 1: Surfaces of an (a) untreated and (b) grafted fiber (PIG,

DG(wt%)=64%). At a magnification of X10.000.

Extended Abstract vii



The changes are homogeneous, as the free radical

graft copolymerization is initiated over the

entire fiber simultaneously.

FTIR-spectroscopy (Fig. 2) also confirmed the

grafting qualitatively. The absorption peak at

1728 cm-1 is attributable to the stretching

vibrations of the carbonyl group and can be

related to the DG as determined via

gravimetrical measurements. Both methods are

in good agreement with each other.

4000 3500 3000 2500 2000 1500 1000 500

0

1

2

3

4

5

b

Ab

so

rba

nce

(A

.U.)

Wavenumber (cm-1)

a GMA

b Cellulose

c GMA-grafted

cellulose

a

c

Fig. 2: FTIR spectra of a: GMA, b: cellulose and c: GMA-

grafted cellulose

A.2. Influence of the reaction parameters

A higher absorbed dose leads to a higher DG,

since more generated radicals lead to more

surviving peroxy compounds which initiate the

grafting.

The plasticizing effect of water in the cellulose

during irradiation increases the decay of the

radicals and ergo significantly decreases the

amount of initiation points: a difference of

humidity of approx. 65% changes the DG (w%)

with a factor 4-5.

Grafting time and temperature both influence

the free radical graft copolymerization reaction

positively.

The GMA-monomer concentration giving the

best yield is found at ± 2 M (Fig. 3). Initially, as

the concentration of reactant (GMA) increases,

also more grafted product will be created. At

higher concentrations, viscosity effects start

playing a role and also homopolymerization

may occur, slowing down the reaction.

0,5 1,0 1,5 2,0 2,5 3,0

10

20

30

40

50

60

70

DG

(w

t%)

Concentration (M)

Fig. 3: DG in function of GMA-monomer concentration.

20 kGy, 50 °C, 1 h.

A.3. Properties

The thermal stability of the material increased

together with the DG (Fig. 4).

0 100 200 300 400

-6

-4

-2

0

a DG=0%

b DG=19%

c DG=52%

He

at (m

W/m

g)

Temperature (oC)

exo

the

rmic

a

b c

en

do

the

rmic

Fig. 4: DSC spectrum of a: untreated, b: grafted (DG (w%) =

19%) and c: grafted (DG (w%) = 52%) cellulose fibers.

Swelling experiments showed that grafted

materials become more hydrophobic as the DG

increases.

The adsorption of 2,4-D (which is used as a

model molecule for a phenolic contaminant) is

slightly enhanced (Fig. 8).

B. Simultaneous grafting

B.1. Characterization of the samples

Samples procured upon the same doses and

monomer concentrations as in PIG have

nevertheless a much higher yield (double to

triple). This is because SG goes in 1 step and

takes place in a closed system. The disadvantage

is the visual trace of homopolymer, even after

the thorough washing procedure. SEM-pictures

show homopolymer flakes attached to the fiber’s

surface (Fig. 5). This is in clear contrast with the

samples obtained using PIG, which also looked

more uniform. It is believed that PIG leads to

grafted GMA all over the fiber, while SG leads to

grafted GMA mainly on the surface.

Fig. 5: Surfaces of grafted fibers, using (a): PIG

(DG(wt%)=32%) and (b): SG (DG(wt%)=35%).

At a magnification of X2000.

The FTIR spectra shows that some of the styrene,

which was in fact added to suppress homo-

polymerization; has copolymerized together

with the GMA (Fig. 6). The observed flakes are

most likely copolymers of GMA with styrene.

Extended Abstract viii



4000 3000 2000 1000 0

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

5,0

5,5

a

Ab

so

rba

nce

(A

.U.)

Wavenumber (cm-1)

a Styrene

b Cellulose upon PIG

c Cellulose upon SG

b

c

Fig. 6: FTIR spectra of a: styrene b: GMA-grafted cellulose

using PIG and c: GMA-grafted cellulose using SG.

B.2.Influence of the reaction parameters

The same relevant effects as in PIG are observed,

but yields are a lot higher with SG. As soon as

doses resp. concentrations are increased over 5

kGy resp. 0.5 M large amounts of homo-polymer

are believed to be present, making accurate

estimations of the DG not possible.

Also the influence of NaOH was investigated,

since it is a known swelling agent for cotton.

However, the increase in OH- concentration was

detrimental for the free radical copolymerization

reaction. A similar effect for a decreasing pH is

expected and it is anticipated that the grafting

happens optimal at pH=7.

B.3. Properties

The thermal stability is believed to be further

increased because of the addition of small

amounts of styrene [4].

As SG leads to higher concentrations of GMA on

the fiber’s surface, the hydrophobicity is even

more increased. Also the adsorption properties

(Fig. 8) for an intermediate DG (w%) = ± 50% are

clearly better. Probably because there is more

GMA present on the surface, which is where the

adsorption occurs the easiest.

C. Immobilization of β-cyclodextrin

C.1. After grafting

The use of NaCl was successful as a catalyst for

the immobilization of β-CD on samples grafted

using PIG, but not for the samples grafted using

SG. Probably, the difference in morphology is

the reason. HCl might also successfully catalyze

the immobilization reaction, but does however

hydrolyze the cellulose samples to such a degree

its mechanical properties have become useless.

C.2. During SG

Little bolls appeared on the surface (Fig. 7). They

are believed to be an indication for the

cyclodextrins. Low doses (< 10 kGy) and low

monomer concentrations (< 0,5 M) are advised.

Fig. 7: Surfaces of a fiber simultaneously grafted with β-CD.

At a magnification of (a) X2000 and (b): X10.000.

Simultaneous grafting of SG + β-CD leads to

further enhanced adsorption properties (Fig. 8).

DMF was required in the grafting reaction

mixture to have an effect. Intermediate degrees

of grafting (40-90 wt%) are expected to show the

best adsorption properties.

250 300

0,00

Ab

so

rba

nce

(A

.U.)

Wavelength (nm)

a reference

b grafted using PIG

c grafted using SG

d grafted using SG+-CDa

b

c

d

Fig. 8: UV spectra of a solution in H2O of 2,4–D; a: before,

and after adsorption on grafted cellulose using b: PIG, c: SG

and d: SG + β-CD. All DGs were approx. 50% and each

sample had approx. the same weight, only d was a bit

lighter.

IV. CONCLUSION

A. PIG vs. SG

Cellulose grafted with GMA was produced

according to the 2 known procedures: PIG and

SG. SG leads to higher yields under similar

conditions, it has a higher radiation chemical

yield, which is due to the difference in reaction

mechanism. For the same reason, it is believed

that in PIG the fiber will be more uniformly

grafted with GMA while in SG most of the GMA

will be grafted on the surface [5].

In PIG the initiation points are formed in a first

step under the form of peroxy compounds. Then

in a second step all these initiation points are

activated simultaneously: because of the

temperature of the reaction mixture, the peroxy

compounds are decomposed and alkoxy radicals

are created. Since the initiation points are also in

the interior of the fiber, grafted GMA chains will

be everywhere. In SG, both grafted as

homopolymerized GMA is created as soon as

the reaction is started. The surface will become

coated by a GMA-polymer layer and make

further penetration of monomer impossible.

Extended Abstract ix



The SEM-photographs, the swelling experiment

and the adsorption experiment confirm this

theory.

B. The immobilization of β-CD

The immobilization of β-CD on the procured

GMA-grafted fibers was investigated. If the

treatment happened upon PIG, NaCl could be

successfully used as a catalyst [20]. However,

upon SG no β-CD immobilization seemed to

have occurred with NaCl thus a new route was

investigated using HCl as a catalyst. This

seemed to induce the appearance of little bolls

on the surface. However, the cellulose was

severely damaged by the treatment.

The best adsorption results were found when β-

CD was immobilized during SG. SEM-

photographs showed the appearance of little

bolls.

V. ACKNOWLEDGEMENT

This thesis was performed as a joint project

between the BME (Budapest University of

Technology and Economics) and the IKI

(Institute of Isotopes) of the HAS (Hungarian

Academy of Sciences).

The author would like to thank many people,

but especially Éva Koczogné Horváth for her

help with the experiments and prof. dr. Erzsébet

Takács and prof. dr. Judit Borsa for their

guidance, support and proofreading.

Additionally, I would like to thank prof. dr.

László Wojnárovits for his professional editing.

VI. REFERENCES

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Perrier, Chemical Society Reviews, vol. 38, pp.

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[2] E. Vismara, L. Melonea, G. Gastaldi, C.

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[3] A. Sekine, N. Seko, M. Tamada and Y.

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[4] P. R. S. Reddy, G. Agathian and A. Kumar,

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[5] E. Takács, H. Mirzadeh, L. Wojnárovits, J.

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[6] S. Hassanpour, Radiation Physics and

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vol. 24, pp. 9-16, (1994).

Contents x



CONTENTS

Table of Contents

PREFACE ......................................................................................................................................i

SUMMARY ................................................................................................................................ iii

EXTENDED ABSTRACT .......................................................................................................... v

CONTENTS ................................................................................................................................. x

Table of Contents ................................................................................................................... x

List of Figures ...................................................................................................................... xiv

INTRODUCTION ................................................................................................................. xviii

An introduction to the functionalization of green materials ...................................... xviii

The set-up of this thesis ....................................................................................................... xx

NOMENCLATURE ............................................................................................................... xxii

PART I: LITERATURE SURVEY ............................................................................................... 1

1 The characteristics of cotton-cellulose ......................................................................... 1

1.1 Introduction to cellulose ....................................................................................... 1

1.2 Molecular: The chemical structure ...................................................................... 2

1.2.1 The monomer: β-D-glucopyranose .............................................................. 2

1.2.2 The polymer: Cellulose.................................................................................. 3

1.2.3 Single chain conformation ............................................................................ 5

1.2.4 Degree of polymerization and molar mass distribution .......................... 6

1.3 Supermolecular: The crystal structure ................................................................ 7

1.3.1 The fringed fibril model ................................................................................ 8

1.3.2 Crystallinity .................................................................................................... 9

1.4 Morphological: The fiber structure .................................................................... 12

Contents xi



1.4.1 Microfibrils and fibrils ................................................................................. 12

1.4.2 The cotton fiber ............................................................................................. 14

1.4.3 Pore structure................................................................................................ 16

1.5 Chemical reactivity .............................................................................................. 16

1.5.1 Accessibility .................................................................................................. 17

1.5.2 Activation ...................................................................................................... 17

2 Radiation chemistry ..................................................................................................... 19

2.1 Radionuclides ....................................................................................................... 19

2.1.1 Radioactivity ................................................................................................. 19

2.1.2 Radioactive decay ........................................................................................ 20

2.1.3 Cobalt-60 (60Co)............................................................................................. 21

2.2 Ionizing radiation ................................................................................................. 22

2.2.1 Interaction processes between γ-irradiation and matter ........................ 23

2.2.2 Linear energy transfer (LET) ...................................................................... 24

2.3 Radiation dosimetry ............................................................................................ 25

2.3.1 Absorbed dose .............................................................................................. 25

2.3.2 Radiation chemical yield ............................................................................. 25

2.4 Irradiation of cellulose ......................................................................................... 26

2.4.1 The formation of free radicals in cellulose................................................ 26

2.4.2 Caused effects upon irradiation ................................................................. 28

3 Graft copolymerization ............................................................................................... 31

3.1 Grafting principles ............................................................................................... 31

3.1.1 Grafting methodology ................................................................................. 31

3.1.2 Grafting techniques ...................................................................................... 33

3.2 Radiation induced free radical graft copolymerization .................................. 34

3.2.1 The theoretical principles of pre-irradiation grafting ............................. 34

Contents xii



3.2.2 The theoretical principles of simultaneous grafting ............................... 35

3.2.3 The free radical graft copolymerization of glycidyl methacrylate ........ 36

4 Cyclodextrins ................................................................................................................ 38

4.1 Structure ................................................................................................................ 38

4.2 Inclusion complexes ............................................................................................. 40

4.3 Immobilization techniques on textiles .............................................................. 42

PART II: AIM OF THIS WORK ............................................................................................... 45

5 Earlier results ................................................................................................................ 45

5.1 Copolymers of cellulose and PGMA ................................................................. 45

5.2 Immobilization of β-CDs on substrates grafted with PGMA ........................ 46

6 Aim of this work .......................................................................................................... 48

PART III: IMPLEMENTATION AND ANALYSIS OF THE EXPERIMENTS .................. 50

7 Experimental ................................................................................................................. 50

7.1 Materials ................................................................................................................ 50

7.2 Irradiation facility ................................................................................................ 51

7.3 Grafting procedures ............................................................................................. 53

7.3.1 Pre-irradiation grafting (PIG) ..................................................................... 53

7.3.2 Simultaneous grafting (SG)......................................................................... 55

7.4 Material characterization .................................................................................... 58

7.4.1 Morphological analysis using SEM ........................................................... 58

7.4.2 Analysis of the functional groups using FTIR spectroscopy ................. 58

7.4.3 Gravimetrical measurements ..................................................................... 58

7.4.4 Analysis of the hydrophilicity via the swelling percentage ................... 60

7.4.5 Analysis of the adsorption properties using UV/VIS spectroscopy ..... 60

7.4.6 Analysis of the thermal properties using DSC......................................... 60

8 Results and discussion ................................................................................................ 61

Contents xiii



8.1 Pre-irradiation grafting of glycidyl methacrylate (GMA) .............................. 61

8.1.1 Analysis of the pre-irradiated grafted samples ....................................... 61

8.1.2 Influence of the parameters during the pre-irradiation ......................... 66

8.1.3 Properties ...................................................................................................... 71

8.1.4 Cyclodextrin immobilization ...................................................................... 73

8.2 Simultaneous grafting of GMA .......................................................................... 75

8.2.1 Characterization of the samples ................................................................. 75

8.2.2 Influence of the parameters during simultaneous grafting ................... 79

8.2.3 Properties ...................................................................................................... 81

8.2.4 Cyclodextrin immobilization ...................................................................... 82

9 Conclusion .................................................................................................................... 85

9.1 Characterization ................................................................................................... 85

9.2 Influence of the parameters ................................................................................ 86

9.3 Properties .............................................................................................................. 87

9.4 Immobilization of β-CD ...................................................................................... 88

APPENDICES ............................................................................................................................ 89

Appendix A: Experimental data ........................................................................................ 89

A.1 Dependence of the parameters in pre-irradiation grafting ................................. 89

A.1.1 Monomer concentration .................................................................................... 89

A.1.2 Absorbed dose .................................................................................................... 90

A.1.3 Moisture content ................................................................................................ 91

A.1.4 Temperature ....................................................................................................... 91

A.1.5 Grafting time ....................................................................................................... 92

A.2 Dependence of the parameters in simultaneous grafting ................................... 94

A.2.1. Adsorbed dose ................................................................................................... 94

A.2.1 Monomer concentration .................................................................................... 94

Contents xiv



Appendix B: SEM pictures .................................................................................................. 95

B.1 SEM photographs of untreated cotton-cellulose ................................................... 95

B.2 SEM photographs of pre-irradiated grafted cotton-cellulose.............................. 96

B.3 SEM photographs of simultaneously grafted cotton-cellulose ........................... 99

ADDENDUM: NEDERLANDSE SAMENVATTING ........................................................ 103

BIBLIOGRAPHY ..................................................................................................................... 109

List of Figures Figure 1: Structural formula of cellulose. .................................................................................................... 2

Figure 2: Fischer projection (a) and stereo projection (b) of D-glucose........................................................ 2

Figure 3: Representation of α-D-glucopyranose (a) and β-D-glucopyranose (b) in the 4C1 conformation. . 3

Figure 4: Representation of cellulose with cellobiose as repeating base unit. ............................................... 5

Figure 5: Sketch of a random helix to elucidate the meaning of n and h (Rees, 1977 29, p. 42). ................... 5

Figure 6: A schematic representation of the rotation possibilities in the cellulose chain. ............................ 6

Figure 7: Intramolecular hydrogen bonds stabilizing the cellulose chain. ................................................... 6

Figure 8: Intermolecular hydrogen bonding causing the formation of cellulose sheets. .............................. 7

Figure 9: Fringed fibrillar model (Hearle, 1958 38). ..................................................................................... 8

Figure 10: Schematic representation of the unit cell in a cellulose crystalline structure (Wakelyn, et al.,

2007 26, p. 561). ............................................................................................................................................ 9

Figure 11: Illustrative sketch of surface chains (gray) among the crystallite core chains (black)

(Nishiyama, 2009 42). ................................................................................................................................. 12

Figure 12: Schematic representation of a bundle microfibrils. Each microfibril consists of crystallites,

which are represented in the picture as cubes. (Zugenmaier, 2001 34). ...................................................... 13

Figure 13: Photographs of cotton-cellulose microfibrils, created using transmission electron micrography

(Wakelyn, et al., 2007 26, p. 543 and p. 577 ). ............................................................................................ 14

Figure 14: Computer generated montage of the organization of the different layers in a cotton fiber.

(Wakelyn, et al., 2007 26, p. 543). ............................................................................................................... 14

Figure 15: Kidney bean shaped cross-sections of cotton fibers (Wilding, 2007 49). .................................... 15

Figure 16: Diagram of the decay of radionuclides via γ-radiation. ............................................................ 21

Figure 17: Diagram of the decay of cobalt 60 towards the stable isotope nickel 60. ................................... 22

Figure 18: Illustration of the excitation mechanism. ................................................................................. 22

Contents xv



Figure 19: Illustration of the ionization mechanism. ................................................................................. 23

Figure 20: Reaction mechanism of the radical at C(4) towards an allyl radical via dehydrogenation. ...... 27

Figure 21: Proposed degradation reaction mechanism leading from the formation of a radical at C(4). The

red fishhook arrows represent electron movement...................................................................................... 29

Figure 22: Schematic representation of the grafting to method (Roy, et al., 2009 1).................................. 32

Figure 23: Schematic representation of the grafting through method (Roy, et al., 2009 1). ....................... 32

Figure 24: Schematic representation of the grafting from method (Roy, et al., 2009 1). ............................ 33

Figure 25: Structural formula of glycidyl methacrylate. ........................................................................... 36

Figure 26: Radical polymerization of GMA. The red fishhook arrows represent the electron movement. R

represents the substrate, in this work, cellulose. XY represents an impurity in the reaction mixture. ..... 37

Figure 27: Structural formulas of α-, β- and γ-cyclodextrin (Skowron, 2006 79). ..................................... 38

Figure 28: Structural formulas of β-cyclodextrin with the glucopyranose units in the 4C1 chair

conformation. ............................................................................................................................................. 39

Figure 29: Schematic illustrative representation of β-cyclodextrin. .......................................................... 39

Figure 30: Inclusion complex of β-cyclodextrin with toluene. ................................................................... 41

Figure 31: 6-deoxy-6-diethylenetriamine-β-cyclodextrin forming an inclusion complex with a metal ion

(M) (Rizzarelli and Vecchio, 1999 82). ........................................................................................................ 41

Figure 32: β-cyclodextrin dimer complex with 4 Cu(II) ions in a frontal view (Chapman and Sherman,

1997 81). ...................................................................................................................................................... 42

Figure 33: BTCA used as a cross-linking agent to bind cyclodextrin to a fiber surface. ........................... 42

Figure 34: Structural formula of (a): NMA-β-CD (a) and (b): MCT-β-CD. ............................................ 43

Figure 35: Reaction scheme of the immobilization of β-CD on a graft copolymer of PGMA with a

substrate R (which in this work represents cellulose). ............................................................................... 44

Figure 36: Structural formula of (a) styrene, (b) 2,4-D and (c) DMF. ...................................................... 50

Figure 37: Gamma-irradiator used for the irradiation of the samples. ....................................................... 52

Figure 38: Immersed 60Co source. .............................................................................................................. 52

Figure 39: Prepared cotton cellulose sample, before numbering (approx. 3,5 cm²). ................................... 53

Figure 40: Immobilization of β-CDPM on a graft copolymer of cellulose (R) with PGMA. The DP of the

β-CDPM is symbolized by ‘p’. ................................................................................................................... 57

Figure 41: Photographs of samples procured upon PIG having a DG (wt%) of (a): 25% and (b): 58%. .. 61

Figure 42: (a): An untreated fiber and (b): a grafted fiber with a DG (wt%) = 32%. PIG at 20 kGy in a

1,5 M GMA solution at 40°C for 1 h. Magnification of X2000. ............................................................... 62

Figure 43: (a): An untreated fiber and (b): a grafted fiber with a DG (wt%) = 64%. PIG at 20 kGy in a

1,5 M GMA solution at 40°C for 1 h. Magnification of X10.000. ............................................................ 62

Contents xvi



Figure 44: FTIR spectra from a: GMA, b: Cellulose and c: GMA-grafted cellulose .................................. 64

Figure 45: FTIR spectra of grafted cellulose, pre-irradiated at several different doses. From high to low:

40 – 30 – 20 – 15 – 10 - 5 - 0 kGy. ............................................................................................................. 65

Figure 46: Relationship between the DG and the intensity of the peak at 1728 cm-1, which corresponds to

the carbonyl group of the grafted GMA. .................................................................................................... 65

Figure 47: Degree of grafting as a function of the absorbed dose. Grafted in a 1,5 M GMA grafting

solution at 50°C for 1 h. ............................................................................................................................. 67

Figure 48: Degree of grafting as function of the water content in the samples. Pre-irradiated at 10 kGy

and grafted in a 1,5 M GMA solution at 50°C for 1 h............................................................................... 68

Figure 49: Degree of grafting as a function of the monomer concentration in M. Pre-irradiated at 20 kGy

and grafted at 50°C for 1 h. ........................................................................................................................ 69

Figure 50: Degree of grafting as a function of the grafting temperature in °C. Pre-irradiated at 20 kGy

and grafted in a 1,5 M GMA solution for 1 h. ........................................................................................... 69

Figure 51: Degree of grafting as a function of the grafting time in minutes. Pre-irradiated at 20 kGy and

grafted in a 1,5 M GMA solution at 50°C. Taken out with a clean metal pair of tweezers. ...................... 70

Figure 52: Degree of grafting as a function of the grafting time in minutes. Pre-irradiated at 20 kGy and

grafted in a 1,5 M GMA solution at 50°C. Taken out with a sterile silicon wire. ..................................... 71

Figure 53: Diagram of the DSC experiment of a: untreated cotton-cellulose, b: cotton-cellulose upon PIG

with a DG (wt%) = 19% and c: cotton-cellulose upon PIG with a DG (wt%) = 52%. ............................. 72

Figure 54: Correlation between the swelling and the DG of pre-irradiated grafted samples. .................... 72

Figure 55 UV-spectra of an aqueous solution of 2,4-D; a: before adsorption, b: after adsorption on

untreated cellulose and c: after adsorption on cellulose, grafted using PIG, with a DG (wt%) = 52,5 %. 73

Figure 56: GMA-grafted cellulose treated with a 0,017 M β-CD solution at 70°C for 24 h using (a) 0,5 M

NaOH and (b) 0,5 M HCl as catalyst. Magnification of X10.000............................................................. 75

Figure 57: SEM photograph at X1000 of a grafted fiber with a DG (wt%) = 35%, simultaneously

irradiated and grafted at 5 kGy in a 0,38 M GMA solution. ..................................................................... 76

Figure 58: FTIR spectra of a: Styrene, b: Grafted cotton-cellulose procured using PIG and c: Grafted

cotton-cellulose procured using SG. .......................................................................................................... 77

Figure 59: Reaction scheme suggesting the copolymerization mechanism between GMA and styrene. The

red fishhook arrows represent electron movement...................................................................................... 78

Figure 60: FTIR spectra of a: GMA monomer and b: Grafted cotton-cellulose having a DG (wt%) of

301% procured upon SG at a dose of 15 kGy in a reaction mixture of 0,38 M GMA. .............................. 78

Figure 61: Degree of grafting as a function of the absorbed dose, grafted in a 0,38 M reaction mixture. . 79

Figure 62: Degree of grafting as a function of the monomer concentration. SG at 20 kGy. ...................... 80

Contents xvii



Figure 63: Correlation between the swelling and the DG of simultaneously grafted samples. .................. 81

Figure 64: UV-spectra of an aqueous solution of 2,4-D; a: before adsorption, b: after adsorption on

cellulose, grafted using PIG, with a DG (wt%) = 52,5% and c: after adsorption on cellulose, grafted using

SG, with a DG (wt%) = 51,5%. ................................................................................................................. 82

Figure 65: Grafted fibers with GMA+ β-CDPM at magnifications of (a): X2000 and (b): X10.000. SG in

a 0,38 M GMA and 0,017 M β-CD 33 v% DMF – 33 v% H2O – 33 v% MeOH solution at 5 kGy. DG

(wt%)+DI (wt%) = 39%. ........................................................................................................................... 83

Figure 66: Grafted fibers with GMA+ β-CDPM at magnifications of (a): X2000 and (b): X10.000. SG in

a 0,38 M GMA 20 v% H2O – 80 v% MeOH solution with 1,85 g β-CDPM per 100 ml at 5 kGy. DG

(wt%)+DI (wt%) = 49%. ........................................................................................................................... 84

Figure 67: UV-spectra of an aqueous solution of 2,4-D; a: before adsorption, b: after adsorption on

cellulose, grafted using SG, c: after adsorption on cellulose, grafted using SG with β-CD monomer and d:

after adsorption on cellulose, grafted using SG with β-CDPM ................................................................. 84

Figure 68: Untreated cotton at a magnification of (a): X500; (b): X1000; (c): X2000 and (d): X10.000. . 95

Figure 69: PIG at 20 kGy, 40°C, 1 h, 1,5 M GMA. DG (wt%) = 32%. Magnification of (a), (e): X500;

(b): X1000; (c), (f): X2000 and (d): X10.000. ............................................................................................ 96

Figure 70: PIG at 20 kGy, 70°C, 1 h, 1,5 M GMA. DG (wt%) = 64%. Magnification of (a) and (e):

X500; (b): X1000; (c) and (f): X2000 and (d) X10.000. ............................................................................ 97

Figure 71: (a) and (b): PIG at 40 kGy, 50°C, 1 h, 1,5 M GMA. Magnifications of X2000 resp. X10.000.

(c) and (d): PIG at 20 kGy, 50°C, 15 min, 1,5 M GMA followed by 24 h in 0.5 M NaOH and 0,017 M β-

CD. Magnifications of X2000 resp. X10.000. (e) and (f): PIG at 20 kGy, 50°C, 15 min, 1,5 M GMA

followed by 24 h in 0.5 M HCl and 0,017 M β-CD. Magnifications of X2000 resp. X5000. .................... 98

Figure 72: SG at 5 kGy, 0,38 M GMA. DG (wt%) = 35%. Magnifications of (a) X500; (b) X1000; (c)

and (e) X2000; (e) and (f) X10.000. ........................................................................................................... 99

Figure 73: SG at 5 kGy, 0,76 M GMA. DG (wt%) = 55%. Magnifications of (a): X500; (b): X1000; (c)

and (e): X2000; (e) and (f): X10.000. ....................................................................................................... 100

Figure 74: SG at 5 kGy in 0,38 M GMA and 0,017 M β-CD in DMF –H2O –MeOH (33 v% each).

Magnifications of (a): X500; (b), (c) and (e): X2000; (e) and (f): X10.000. ............................................. 101

Figure 75: SG at 5 kGy, 0,38 M GMA and 1,85 g M β-CDPM per 100 ml in 20 v% H2O – 80 v%

MeOH. Magnifications of (a) and (d): X500; (b) and (e): X2000; (c) and (f): X10.000. ......................... 102

Introduction xviii



INTRODUCTION

An introduction to the functionalization of green materials While technology has brought us (the developed world) an abundance of food,

monster traffic jams and tons and tons of throw-away articles, it came at a price.

During the last decades the awareness for the caused, global, problems has been

growing steadily. Some of the ‘hotter’ topics include, but are not limited to: global

warming, air and water pollution, the hole in the ozone layer, the destruction of the

rain forest and the depletion of the natural reserves. This calls for innovations. One of

the, already followed, paths is the investigation in green materials, or natural materials.

Green materials offer a solution to the problem of the depletion of the natural reserves

since they are renewable, plus they are non-polluting. Many of today’s materials are

specifically designed for their application, but natural materials come in the way

nature supplies them. While bio-engineers already succeed to drastically improve

desired properties, genetic engineering stays a tricky problem and generally, reaching

the same versatility as is applicable for man-made materials is not (yet) possible. A

solution lies in modifying the properties of the natural materials, applying old

technologies used for the conventional synthetic materials as well as new ones. One of

the most obvious green materials is cellulose, being the most abundant natural

polymer on earth (Roy, et al., 2009 1). Cellulose has been the subject of many studies

and its general structure and properties are quite well-known, but nevertheless a lot of

uncertainties remain. Rather than unraveling the remaining mysteries around

cellulose, this work will focus on the already known properties and one of the ways to

alter these or add new ones. In other words, the goal is to functionalize the cellulose.

More specifically, the idea of functionalization is to introduce specific chemical

functional groups on a molecular level to the material. This will have its influence on

the supermolecular and the morphological level, as well as on the resulting properties.

The resulting material possesses the imparted functionality but its bulk still consists

mainly of cellulose and thus the intrinsic properties of cellulose are retained.

Introduction xix



An interesting way to achieve the desired functionalization is via graft copolymerization.

In fact, graft copolymerization of cellulose is one of the key ways to alter its properties

(Roy, et al., 2009 1). This technique allows to combine the best properties of two (or

even more) polymers in one material. By changing the parameters of the graft

copolymerization reaction, viz. polymer type of the grafted chains, degree of

polymerization, the polydispersities of both main and grafted chains, the graft density

and the graft uniformity, it is possible to synthesize tailor-made materials according to

the desired properties. The methods to achieve this graft copolymerization are

numerous, one of them is via a high energy irradiation initiated graft copolymerization, a

topic of radiation chemistry. As the name gives away, this is the study of the chemical

effects of matter induced by radiation, in this work more specifically: γ-irradiation

emitted by cobalt 60 (Takács, et al., 2007 5; Takács, et al., 2010 10; Badawy, et al., 2001 21).

It is obvious that next to the choice of bulk polymer (cotton), also the polymer that will

become grafted on the cotton surface is crucial for the end-product. Poly(glycidyl

methacrylate) (PGMA) is an interesting choice under increasing interest (Vismara, et al.,

2009 2; Sekine, et al., 2010 3), because it has the very reactive epoxide group at one end. A

graft copolymer of cellulose with poly(glycidyl methacrylate) is thus particularly

interesting because i) intrinsically, it already imparts several interesting properties to

cellulose, viz. flame retardancy, the enhanced adsorption of aromatic contaminants and

the adsorption and chelation of metals (Vismara, et al., 2009 2; Le Thuaut, et al., 2000 19),

ii) due to its reactivity it can basically be changed in several other functional groups,

e.g. in a hydroxyl, amine, thiol or phosphoric acid group (Nava-Ortiz, et al., 2009 18) iii)

it is an excellent anchor point for numerous molecules, e.g. cyclodextrins.

This immobilization of cyclodextrins will be examined more closely because of the very

special properties of cyclodextrins, viz. they have a very specific shape which allows

them to form inclusion complexes (host-guest complexes) with several compounds (Del

Valle, 2004 22). This means that within the cavity of the cyclodextrin a guest molecule

can be held, without forming any covalent bonds. There is a dynamic binding between

the guest molecules and the host cyclodextrin. The strength of the binding is merely

depending on how well the host and the guest ‘fit’ together. This property has

Introduction xx



numerous applications, ranging from simple adsorption to the incorporation of

antimicrobials or the controlled release of perfumes or drugs. However, because

cyclodextrins are quite voluminous molecules, steric effects make it impossible to bind

the cyclodextrins directly to the cellulose so this is why it is necessary to work via the

poly(glycidyl methacrylate) chains. This thesis will hence also further investigate how

to permanently bind cyclodextrins onto cotton textiles, a research domain that has been

growing from the early 80’s and is receiving a lot of attention lately (Vončina and Le

Marechal, 2005 11; Heise, et al., 2005 23). Even during the creation of this thesis an article

appeared (Abdel-Halim, et al., 2010 15), which reported the simultaneous grafting with

β-CDs present in the grafting reaction, a procedure also investigated in this work (see

3.2.2 and 8.2).

Because of the many interesting imparted properties, there are multiple applications

possible for both the GMA-grafted cellulose as for the subsequent cyclodextrin-

immobilized material. One of the most interesting and useful applications receives a lot

of attention recently, i.e. the uptake of water contaminants (Vismara, et al., 2009 2;

Sekine, et al., 2010 3; Takács, et al., 2010 10; O’Connell, et al., 2008 24; Sokker, et al., 2009

25), because water contamination may lead to heavy environmental damage and pose a

serious hazard for human health. While the GMA-grafted cellulose is already able to

filter many contaminants, a following cyclodextrin immobilization is supposed to even

further enhance the adsorption properties and make them more specific towards

aromatics and phenols, dibenzofuran molecules, metals and dyes (Crini, 2008 13)

The set-up of this thesis It may already become clear that this thesis situates at the interface of several scientific

disciplines, viz. material sciences, chemistry and physics. It requires a significant

background in order to fully appreciate and understand the performed mechanisms.

This is why the first part of this work exists out of an in-depth literature survey

reviewing the theoretical principles behind the used techniques, an endeavor

undertaken in the first place for myself, to achieve a deeper knowledge, and in the

second place for the reader, who might not be an expert in every scientific field. I

attempted to represent the important findings in a relevant yet complete way. Since an

Introduction xxi



image says more than a thousand word, a lot of results are represented using pictures.

The second part is the link between the literature survey and the practical aspect of this

thesis. In the first place, some of the most important articles considered directly linked

to the practical research in this work will be reviewed in a very condensed way,

presenting the experimental methods and results of importance. And in the second

place and directly linked to this follows the aim of this work: i.e. investigating the

grafting of glycidyl methacrylate on cotton, according to the two known procedures, viz.

pre-irradiation (PIG) and simultaneous grafting (SG). A special application is the use of

the imparted epoxy groups in the material to immobilize cyclodextrins.

The third part consists of the experimental implementation in order to fulfill the

stipulated investigation and a discussion linking all the information gained in this

work + the results from previous authors. This discussion is built around the personal

experimental research and includes:

i) The assessment of the grafted material procured by both methods (PIG and SG),

characterized using several complementary analytical techniques, viz. visual and other

sensory perceptions, SEM, gravimetrical measurements and FTIR spectroscopy. Some

of the most interesting SEM-photographs can be found in Appendix B: SEM pictures.

ii) The influence of the reaction parameters during the grafting, viz. absorbed dose,

moisture content, temperature, time, monomer concentration, moisture concentration

and pH, dependent on the method. The gathered data are collected in Appendix A:

Experimental data.

iii) Examination of some of the properties which are believed to be directly enhanced,

viz. thermal properties, hydrophilicity, adsorption properties.

iv) Investigation of one special application, i.e. the immobilization of β-cyclodextrin;

which is depending on the precedent grafting method.

v) On basis of i) - iv), a conclusion can be reached, allowing a detailed comparison

between PIG and SG of GMA on cotton, and its consequences for a subsequent

cyclodextrin immobilization This will logically form the finale of this work.

Nomenclature xxii



NOMENCLATURE

Where possible, terms and units as defined by the International Union for Physics and

Applied Chemistry (IUPAC) and the International System of Units (SI) are used. They

are considered general knowledge and will not necessarily be explicitly mentioned in

the following list.

60Co = cobalt 60

AGU = anhydroglucose unit, or glucose residue

C(X) = the Xth carbon of the molecule, starting the numbering at the carbon with

the highest functional group (according to IUPAC)

CD = cyclodextrin

CX (M) = molar concentration of the substance X, thus in moles per liter

D = absorbed dose (in Gy)

DG = degree of grafting

DI = degree of immobilization

DMF = N,N-dimethylformamide

DP = degree of polymerization

DSC = differential scanning calorimetry

E = energy, expressed in joules (J)

eV = electron volt (1 eV = 1,602 10-19 J)

FTIR = fourier transform infrared

GMA = glycidyl methacrylate (or IUPAC: 2,3-epoxypropyl methacrylate)

Gy = gray (1 Gy = 1 J kg-1), SI unit of absorbed dose

Nomenclature xxiii



LET = linear energy transfer

m = mass

M = molarity (equal to moles per liter)

M:L = material to liquor ratio (in gram per liter)

M X = molar mass of the substance X

PGMA = poly(glycidyl methacrylate)

PIG = pre-irradiation grafting

S = swelling (in mass percent)

SEM = scanning electron microscopy

SG = simultaneous grafting

u = unified atomic mass unit, equal to one twelfth of the mass of an isolated

atom of 12C at rest and in its ground state, equal to 1,660 538 782 10−27 kg

v% = volume percentage

wt% = mass percentage

W0 = mass of the samples upon numbering, before any treatment

WCD = mass of the samples upon β-cyclodextrin immobilization

Wg = mass of the samples upon grafting

Ws = mass of the samples upon the swelling treatment

Wt = mass of the samples after grafting and β-cyclodextrin immobilization

β-CD = β-cyclodextrin

β-CDPM = β-cyclodextrin polymer

Literature survey 1



PART I: LITERATURE SURVEY

1 The characteristics of cotton-cellulose Understanding the structure of cellulose is a prerequisite towards controlling its modification,

so at least the main structural elements will be glanced through. The discussion will take place

on three levels: molecular, supermolecular and morphological; followed by how these structural

parameters affect the reactivity of the cellulose, which is of course paramount regarding further

reactions. An introduction sketching cellulose as a natural polymer originating from cotton will

precede this. Where possible, values are given, with the sole intention to give an idea of

magnitude.

1.1 Introduction to cellulose

Cellulose is the most abundant and renewable polymer on earth, being the structural

component in the cell wall of green plants. Cotton, hemp, flax, jute, ramie are the more

classical examples of cellulose sources, but also rice husks, wheat straws, banana peels,

etc. are possible (Takács, et al., 2010 10). Of all these sources, cotton is the most

important one; being the most produced natural textile fiber worldwide with 20,4 - 23,8

million metric tons, accounting for 38% of the global fiber consumption. The cotton

plant belongs to the Malvales order, family Malvaceae, tribe Gossypieae, and genus

Gossypium. Currently there are thirty-three different species recognized of which four

have commercial value, viz. hirsutum, barbadense, aboreum and herbaceum (Wakelyn,

et al., 2007 26, pp. 523-526). Of more importance is, however, that cotton is reported to

be the purest source of cellulose. After treatments to remove the naturally occurring

non-cellulosic materials, the cellulose content of the fiber is over 99% (Wakelyn, et al.,

2007 26, p. 537). Cotton fibers are long (25 mm or more) elongated single cells, growing

from the surface layers of the cotton seed and are also known as cotton lint. Along with

the lint also shorter fibers grow, which are known as linters. Those linters however are

from an inferior quality. In the scope of textile processing, cotton lint is used and will

also be the structure considered in everything that follows.

Literature survey 2



1.2 Molecular: The chemical structure

Chemically, cellulose is referred to as linear (1 → 4)-β-D-glucan (McNaught, 1996 27). A

glucan molecule is a polysaccharide of D-glucose monomers linked by glycosidic bonds.

The structural formula of cellulose is represented in Figure 1.

O

OH

OH OOH

OH

O

OH

OH O

OH

O

OH

OH OH

OHn-2

Figure 1: Structural formula of cellulose.

1.2.1 The monomer: β-D-glucopyranose

Glucose, with as chemical formula C6H12O6, is part of the aldohexose family. As

aldohexoses possess four chiral centers, this leads to 24 ( = 16) possible configurations.

Two of these stereoisomers are known as glucose, D-glucose and L-glucose, being

enantiomers (mirror images) of each other. Since L-glucose is not biologically active

and does not occur naturally, D-glucose is meant when speaking of simply glucose,

however not strictly correct. A common and clear way of picturing aldohexoses is via

the Fischer projection. The numbering of the carbons becomes also clear via this

projection, starting from the carbon C(1) with the preferred functional group, i.e. the

aldehyde group (McNaught, 1996 27), see also Figure 2.

1

2

3

4

5

6OH

O

H OH

OH H

H OH

H OH

23

45

6

1

OH

OH

OH

OH

O

OH

(a) (b)

Figure 2: Fischer projection (a) and stereo projection (b) of D-glucose.

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D-glucose can exist in an open chain form, or in a cyclic form. Since in the open form an

aldehyde group exists on C(1), this form of glucose is also denoted as aldehydo-D-

glucose. Closing of the chain happens via a nucleophilic addition between the oxygen

atom on C(5) and C(1), creating a hemiacetal group (Du Prez, 2007 28). The resulting

cyclic aldohexose is referred to as a pyranose. Since stable molecules have bond angles

according to the tetrahedral configuration (109, 5°), the glucopyranose ring will not be

flat. Instead, glucopyranose exists in several puckered conformations (conformational

isomerism) in order to reduce angle strain to a minimum. The 4C1 is the most stable

conformation; this notation denounces that the molecule takes the shape of a chair with

C(4) above the plane of the ring (formed by C(2), C(3), C(5) and the ring oxygen) and

C(1) below (Rees, 1977 29, p. 14), see Figure 3 for an example. When the nucleophilic

addition takes place, two possibilities arise for the carbonyl group: the resulting

hydroxyl group (at C(1) thus) can orient itself cis or trans with the hydroxyl group on

C(4) which corresponds in the case of D-glucopyranose with α-D-glucopyranose

respectively β-D-glucopyranose (McNaught, 1996 27), see Figure 3. In the 4C1

conformation, this equals an axial, respectively equatorial orientation of the hydroxyl

group on C(1). Note that equatorial substituents cause less steric hindrance within the

molecule, which is why β-D-glucopyranose is thermodynamically more stable.

O

OH

OH OHOH

OH

O

OH

OH

OH

OH

OH

(a) (b)

123

4 5

6

123

4

6

5

Figure 3: Representation of α-D-glucopyranose (a) and β-D-glucopyranose (b) in the 4C1 conformation.

1.2.2 The polymer: Cellulose

The building units of cellulose are β-glucopyranose in the 4C1 conformation linked by

glycosidic bonds (O'Sullivan, 1997 30; Klemm, et al., 1998 31, p. 9). A glycosidic bond is a

bond between the hemiacetal group of a carbohydrate and the hydroxyl group of

another organic compound, which may or may not be another carbohydrate,

Literature survey 4



eliminating water and creating an acetal. In the case where the carbohydrate is glucose,

the term glucosidic bond is also in use by several authors (Wakelyn, et al., 2007 26; Princi,

et al., 2006 32). The linkage between the β-glucopyranose units in cellulose happens

between C(1) and C(4), this is denoted as a (1 → 4) linkage (McNaught, 1996 27). Note

that there will be an unreacted hydroxyl group at each chain end, viz. the C(1) end and

the C(4) end. These ends show clearly different behavior: the C(1) end is reducing

while the C(4) end is non-reducing (Wakelyn, et al., 2007 26, p. 547; Klemm, et al., 1998

31, p. 10). This is because the C(1) end contains a free hemiacetal group which can be

further oxidized. The chemical which would cause this oxidation becomes reduced

during this reacting. This end acts thus as a reducing agent. The other end of the chain

does not have this free hemiacetal group and is thus non-reducing. The reducing ends

are very reactive, but given the number of D-glucopyranosyl monomeric units in one

cellulose molecule, their relative share is rather small. During linkage, each monomer

loses one molecule of water; this is why they are referred to as anhydroglucose units

(AGUs) or glucose residues (C6H10O5), having a molar mass M = 162,15 g mol-1 These

units are oriented with alternating methylol (-CH2OH) groups above and below the

plane of the ring.

If the dimer cellobiose is taken as the basic unit instead of the glucose residue, which

some authors prefer (Wencka, et al., 2007 33; Zugenmaier, 2001 34), cellulose can be

considered as an isotactic polymer of cellobiose (Klemm, et al., 1998 31, p. 9), see also

Figure 4. This is however not really descriptive in any chemical sense, since hydrolysis

doesn’t yield dimers and tetramers rather than trimers and pentamers. Also when

talking about DP AGUs are used, so it seems more appropriate to work with the AGU

as a basic unit. When describing crystal structures however, this cellobiose

characterization can be useful, since the length of one cellobiose unit corresponds with

the crystallographic repeat along the fiber axis.

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O

OH

OH OOH

OH

O

OH

OH OH

OHn

Figure 4: Representation of cellulose with cellobiose as repeating base unit.

1.2.3 Single chain conformation

The cellulose molecules form long and unbranched chains, viz. cellulose is a

syndiotactic (i.e. with alternating oriented substituents) homopolymer of β-D-

glucopyranose units (Klemm, et al., 1998 31, p. 9). This kind of shape can be described as

a helix, having two parameters describing its general contour: h and n (see Figure 5 for

a graphic explanation) respectively denoting the number of monomer units per turn of

helix and the projected length of each monomer on the helix axis (French and Johnson,

2004 35). The value of n is positive or negative in the case of, respectively, a right-

handed or a left-handed screw. For common crystalline cellulose, these parameters are

n = 2 and h = 5,18 Å (Wakelyn, et al., 2007 26, p. 552).

Figure 5: Sketch of a random helix to elucidate the meaning of n and h (Rees, 1977 29, p. 42).

These parameters arise because around the C(1)-O-C(4) bridge between succeeding

AGUs, there exists a rotation possibility around the C(1)-O bond (say φ) and around

the O-C(4) bond (say ψ), see Figure 6, making a single molecule very flexible.

n = 3

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O

OHOH

O

OH

O

OH

OH

OH

Figure 6: A schematic representation of the rotation possibilities in the cellulose chain.

Four chain families arise depending on the values of n and h, the ribbon family, the

hollow helix family, the crumpled family and the loosely jointed family. Thermodynamically,

cellulose is most favored in the ribbon shape (Rees, 1977 29, pp. 42-54), which is reflected

in its crystal structures, cf. paragraph 1.3. Intramolecular hydrogen bonds i) between

the hydroxyl group on C(3) and the pyranose ring oxygen of a following

glucopyranose unit in the chain and ii) between the hydroxyl groups on C(6) and C(2)

of neighboring glucopyranose units in the same chain, stabilize this shape and are

responsible for the considerable stiffness, see Figure 7.

O

OH

OH O

OH

O

OH

OH O

OH

O

OH

OH O

OH

O

OH

OH

OH

Figure 7: Intramolecular hydrogen bonds stabilizing the cellulose chain.

1.2.4 Degree of polymerization and molar mass distribution

The size of one molecular entity is defined by its chain length, which is expressed as

degree of polymerization (DP). The molar mass can then be calculated as the product

of the DP with the mass of the repeating AGU (1 AGU = 162,14 u). Cellulose

originating from native sources is polydisperse (Klemm, et al., 1998 31, pp. 11-13) and

there is thus a broad molar mass distribution (Lin, et al., 2009 36), the length of one

chain can go up to 15.000 (O'Sullivan, 1997 30) or even 20.000 (Wakelyn, et al., 2007 26,

pp. 544, 546) glucopyranose units, according to the source. Both the DP (taken as an

average) and, possibly even more, the molar mass distribution have a big impact on the

Literature survey 7



properties of the polymer. In general: the higher the DP and the narrower the molar

mass distribution, the stronger the polymer.

1.3 Supermolecular: The crystal structure

Besides the intramolecular hydrogen bonds, which play a big role in the single chain

conformation, also intermolecular hydrogen bonds, between the hydroxyl groups on

C(3) and C(6) of an adjacent molecule in the same plane (Roy, et al., 2009 1), exist, see

Figure 8. This hydrogen bonding mainly takes place between hydroxyl groups which

are located on the edges of the cellulose ribbon and are responsible for the tendency of

the cellulose chains to order themselves into long sheets, along the axis of the fibrillar

super unit (the microfibril, cf. 1.4.1). Next to those hydrogen bonds, also extensive Van

der Waals interaction is reported. These Van der Waals interactions happen between the

flat sides of the ribbons and cause the stacking of the sheets in the direction

perpendicular on the fibrillar axis. This high level of intermolecular interaction causes a

very efficient and high density arrangement (up to 1,62 g cm-³); which explains the

remarkable insolubility of cellulose in most solvents; since they must be able to disrupt

the extremely strong network of both hydrogen bonding and Van der Waals

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