The document thanks various people who contributed directly and indirectly to the completion of the thesis. It thanks the author's supervisor for guidance and support. It also thanks professors from the department for imparting knowledge during lectures. The author thanks family for motivational support and friends for their togetherness during the course of study. The author acknowledges labmates for their individual help with literature and assistance. In conclusion, the author thanks all those who contributed in any way to the project.

1. Acknowledgement
Thesis is an outcome of hard work and support of different person involved
directly and indirectly throughout, so I cannot keep myself away from thanking
them. First of all, I would like to express deep gratitude to my supervisor
Professor Youn Cheol Kim for his guidance, expertise comments and suggestion
which made this thesis possible. Also, his constant support, belief and inspiration
played a big role to bring this thesis to the edge. I would like to thank Professor
Jin Heong Im, Professor Hyung Joong Kim, Professor Young Gon Son,
Professor Kuk Young Cho, and Professor Moon-Soo Bang from department of
Advanced Material Engineering for conferring me with knowledge during lectures
and seminar and making me capable to get insight of the subject matters.
Some support that I constantly seeked for during good times and hard times is
important to be thanked. The support of my family always motivated me to focus
in my goal and work hard. I would like to thank my father Mr. Narendra Dahal,
mother Mrs. Tara Dahal, brother Mr. Prabin Dahal and sister Mrs. Pratima
Dahal Poudel for their motivational words and emotional supports. My two years
of stay would not have been so meaningful without my friends Mr. Jeeban
Poudel, Mr. Nawaraj Sanjel, Mr. Malesh Shah and Ms. Rashmi Dhakal, so I
would like to thank them for their togetherness and support in all means.
I owe special thanks to my lab mates Ms. Kyung Hwa Yoon, Ms. Bom Yi Lee
and Mr. Jung Hee Kim for sharing literature and for their individual help, not
forgetting other lab mates and classmates who were always there to help me.
Nevertheless, there are many people who contributed in this project by all
different possible means, so I would like to thank them all for their contribution
and supports.
i

2. Abstract
Polyolefins are mostly used commodity polymers with many applications because
of its price to performance ratio and broad range of modification capabilities
which make it possible to get the tailored end product. Among several tailoring
and modification method, blending and crosslinking is gaining attention of the
researcher because of its relatively easy processability and control. This work was
proposed to fabricate the modified polypropylene by irradiation and analyze the
effect of co-agent and polyethylene (PE) on the physical properties of modified
PP. Blends of PP/PE were prepared by melt mixing in twin screw extruder at
190oC. Polyfunctional monomer TMPTMA (trimethylolpropane-trimetacrylate)
was added to the mixture as a crosslinking co-agent to improve the crosslinking
efficiency of the olefins during irradiation. The effect of polyethylene on the
crosslinking effectiveness and physical properties of polypropylene was
investigated in conjunction with PE loading in the blends. Thermal stability,
rheological properties and electron beam irradiation effectiveness of PP in
presence of PE was analyzed by DSC, TGA and RDS. Solution gel analysis and
the presence of –C=O in FT-IR test supported some crosslinking occurred after
irradiation. Certain decrease in melting temperature (Tm) was noticed after
irradiation, could be the result of chain scissioning which decrease the number of
tie molecule in amorphous region and consequently weakens the laminar
connections. Shear thinning effect and zero shear viscosity was improved by
irradiation in the PE incorporated samples. Hardness was seen to increase with
irradiation.
ii

3. Table of contents
Acknowledgement .................................................................................................. i
Abstract .................................................................................................................. ii
Table of contents ................................................................................................... iii
List of figures ......................................................................................................... v
List of tables ......................................................................................................... vii
Abbreviation .......................................................................................................... 1
I. Introduction ........................................................................................................ 2
II. Theoretical background................................................................................. 3
1.
Crosslinking ........................................................................................................ 3
1.1
High-energy beam irradiation ................................................................................... 3
1.2
Peroxide crosslinking ............................................... Error! Bookmark not defined.
1.3
Saline crosslinking ................................................... Error! Bookmark not defined.
2.
Crosslinking co-agent ....................................... Error! Bookmark not defined.
3.
Gel content ........................................................ Error! Bookmark not defined.
4.
Blending ............................................................ Error! Bookmark not defined.
III. Overview of research ...................................... Error! Bookmark not defined.
IV. Effects of TMPTMA and LDPE on physical properties and irradiation
effectiveness of polypropylene ................................ Error! Bookmark not defined.
1.
Introduction ....................................................... Error! Bookmark not defined.
2.
Experimental ..................................................... Error! Bookmark not defined.
2.1
Materials and fabrication ......................................... Error! Bookmark not defined.
iii

4. Results and discussion ...................................... Error! Bookmark not defined.
3.
3.1
Basic properties of the modified PP ......................... Error! Bookmark not defined.
3.2
Crystallization kinetics of PP/LDPE blends............. Error! Bookmark not defined.
3.3
Rheological property ................................................ Error! Bookmark not defined.
3.4
Hardness of the modified PP .................................... Error! Bookmark not defined.
Conclusion ........................................................ Error! Bookmark not defined.
4.
V.Effectsof LLDPE and its monomer content on physical properties and
irradiation effectiveness of polypropylene ............ Error! Bookmark not defined.
1.
Introduction ....................................................... Error! Bookmark not defined.
2.
Experimental ..................................................... Error! Bookmark not defined.
2.1
Materials and fabrication ......................................... Error! Bookmark not defined.
Results and Discussion ..................................... Error! Bookmark not defined.
3.
3.1
3.2
Rheological Property ............................................... Error! Bookmark not defined.
3.3
4.
Basic Properties of the Modified PP ........................ Error! Bookmark not defined.
Hardness of the modified PP .................................... Error! Bookmark not defined.
Conclusion ........................................................ Error! Bookmark not defined.
VI. Summary of Research..................................... Error! Bookmark not defined.
VII. Referances ...................................................... Error! Bookmark not defined.
VIII. 요약 ............................................................... Error! Bookmark not defined.
iv

5. List of figures
Figure 1: Schematic of possible irradiation crosslinking mechanism ............ Error!
Bookmark not defined.
Figure 2: Schematic of possible peroxide crosslink mechanism . Error! Bookmark
not defined.
Figure 3: Schematic of possible crosslinking reaction with multifunctional
monomer by irradiation ......................................... Error! Bookmark not defined.
Figure 4: Overview of study for PP modification . Error! Bookmark not defined.
Figure 5: Change in crosslinking behavior of POE/LDPE blended with various
sensitizers, depending on the amount of absorbed dose. ...... Error! Bookmark not
defined.
Figure 6: Chemical structure of irradiated PP/LDPE blends Error! Bookmark not
defined.
Figure 7: Heating Curves of PPs ........................... Error! Bookmark not defined.
Figure 8: Heating Curves of PP/LDPE blends ...... Error! Bookmark not defined.
Figure 9: Melting temperatures of PP/LDPE blends ............ Error! Bookmark not
defined.
Figure 10: Cooling curves of PPs .......................... Error! Bookmark not defined.
Figure 11: Cooling curves of PP/LDPE blends ..... Error! Bookmark not defined.
v

6. Figure 12: Crystallizations temperatures of PP/LDPE blends .... Error! Bookmark
not defined.
Figure 13: TGA graph of PP/LDPE blends ........... Error! Bookmark not defined.
Figure 14: TGA graph of PP/LDPE blends ........... Error! Bookmark not defined.
Figure 15: Conversion of PP/LDPE blends and Avrami’s plot... Error! Bookmark
not defined.
Figure 16: Plot of log[-ln(1-c)] versus logα of PP /LDPE ... Error! Bookmark not
defined.
Figure 17: Complex viscosity of PPs .................... Error! Bookmark not defined.
Figure 18: Complex viscosity of PP/LDPE blends Error! Bookmark not defined.
Figure 19: G”- G’ plot of PPs ................................ Error! Bookmark not defined.
Figure 20: G”- G’ plot of PP/LDPE blends ........... Error! Bookmark not defined.
Figure 21: Loss tangent of PPs .............................. Error! Bookmark not defined.
Figure 22: Loss tangent of PP/LDPE blends ......... Error! Bookmark not defined.
Figure 23: Hardness of PP/LDPE blends .............. Error! Bookmark not defined.
Figure 24: FT-IR spectra of irradiated PP/LLDPE blends ... Error! Bookmark not
defined.
Figure 25: Heating curves of PP/LLDPE blends... Error! Bookmark not defined.
Figure 26: Melting temperatures PP/LLDPE blends ............ Error! Bookmark not
defined.
Figure 27: Cooling curves of PP/LLDPE blends .. Error! Bookmark not defined.
vi

7. Figure 28: Crystallization temperatures of PP/LLDPE blends ... Error! Bookmark
not defined.
Figure 29: TGA graph of PP/LLDPE blends ........ Error! Bookmark not defined.
Figure 30: Complex viscosity of PP/LLDPE blends ............ Error! Bookmark not
defined.
Figure 31: G’-G” of PP/LLDPE blends ................ Error! Bookmark not defined.
Figure 32: Loss tangent of PP/PE blends .............. Error! Bookmark not defined.
Figure 33: Hardness of PP/LLDPE blends ............ Error! Bookmark not defined.
vii

8. List of tables
Table 1: Structure of the materials used ................ Error! Bookmark not defined.
Table 2: Compositions and quantity of PP/LDPE blends .... Error! Bookmark not
defined.
Table 3: Thermal properties of PP/LDPE blends .. Error! Bookmark not defined.
Table 4: Thermal properties of PP/PE blends at 10 oC cooling .. Error! Bookmark
not defined.
Table 5: Slopes for storage versus loss plot, power law index (n) of PP/LDPE
blends..................................................................... Error! Bookmark not defined.
Table 6: Compositions and quantity of PP/LLDPE blends .. Error! Bookmark not
defined.
Table 7: Thermal properties of PP/LLDPE blend . Error! Bookmark not defined.
Table 8: Slopes for storage versus loss plot, power law index (n) of PP/LLDPE
blends..................................................................... Error! Bookmark not defined.
viii

9. Abbreviation
PP
Polypropylene
PE
Polyethylene
LDPE
Low Density Polyethylene
LLDPE
Linear Low Density Polyethylene
MeV
Mega Volt
Mrad
Mega radian
phr
Parts per hundred resin
ASTM
American Society for Testing and Materials
MI
Melt Index
TMPTMA
Trimethylolpropane-trimetacrylate
DSC
Differential Scanning Calorimeter
RDS
Rheomertic Dynamic Spectrometry
TGA
ThermogravimeticAnalysis
FT-IR
Fourier Transform Infrared
1

10. I. Introduction
Polypropylene (PP) belongs to the family of polyolefins and it is a vinyl polymer
having hydrogen atom substituent (-H2C-CH2-)n or (H2C-CRH-)n and undergoes
dominant hemolytic rupture of C-H bonds to form hydrogen free radicals which
crosslinks with each other. PP is extensively used in many fields because of its
outstanding chemical and moisture resistance, low density, easy processability
and relatively low cost. However it has very low impact toughness, especially at
low temperature and low melt strength at molten state [1, 2]. The melt strength
and impact toughness of PP can be improved by various methods such as
controlling molecular weight and distribution [3, 4] and introducing long chain
branch (LCB) [5-13]. Much effort to produce branched PP has been made in the
polymer industry and academic fields. Several commercial branched PPs have
been created by electron beam irradiation [14]. However, irradiation causes βscission of the PP chains followed by crosslinking and complex branch structures.
Many reports have also described the modification of PP with co-agent in
combination with multi-functional monomers. Radiation process for polymer
processing these days is gaining attention from the researcher as the alternate
method for modifying the structure to chemical methods [15]. Radiation process
of polyolefins is an economically viable and versatile way to produce material
with enhanced chemical, mechanical, and physical properties [16-19]. Polymer
processing by ionizing radiation is environmentally and energetically safe and it
does not need solvents or initiators at high temperature and allows one to avoid
degradation phenomena and other side reaction typical of polymer processing in
melt [20]. The toughness and radiation resistance of PP is expected to increase by
addition of PE, as it undergoes predominantly crosslinking on high energy
radiation [21, 22]. Crosslinking of the polymer can enhance several properties like
hardness, Young’s modulus, heat resistance and solvent resistant. Compared to
2

11. polyethylene (PE), PP exhibit better thermo-mechanical resistance and rigidity
due to its higher melting point and crystallinity, but it is more susceptible to
degradation resulting in considerably poorer resistance to aging, weathering and
irradiation, since its main carbon chain includes tertiary carbon atom at every
other place on the main chain [23]. Ionizing radiation cause chain scissioning and
crosslinking of the polymer chain of PP roughly equal to probability, while crosslinking is predominant in the case of PE [24].
II. Theoretical background
1.
Crosslinking
Crosslinking refers to the linking of one polymer chain with the other polymer
chain by forming bond which may be covalent or ionic. The major focus of crosslinking is to change the physical properties of the polymer. The crosslinking of
the polymer can obstruct the free moment of the polymer chain and can form gel
or solids. Crosslinking can be achieved following three different crosslinking
procedures namely, high energy irradiation, a peroxide and organo-functional
saline.
1.1
High-energy beam irradiation
The process of crosslinking by application of high energy beams like X rays,
gamma rays and electron beams is high energy irradiation. Electron beam
irradiation is more often used for small parts, low density product and linear
product processed. Irradiation creates free radicals in the polymer by separating
hydrogen atom from weak C=C bonds preferentially tertiary hydrogen, which
recombines to crosslink the polymer chains. The crosslinking amount is
dependent upon the polymer used and the applied irradiation dose. Also, together
with crosslinking irradiation can induce scissioning in the polymer chain which
3