Effect of irradiation on physical properties of pp pe blends

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Thesis: Effect of irradiation on Physical properties of PP-PE blends

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Effect of irradiation on physical properties of pp pe blends

  1. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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

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