Thus, supervisor and PhD student carried on a thesis:” Effect of surface fillers modification on phase interaction and mechanical properties of thermoplastic materials” 2.. The aim of th
Trang 1PREFACE
1 Urgency of the thesis
Reinforcement of thermoplastic by using particle has studied in few decades ago Until now, it plays an important role in as well [1] The flexibility of thermoplastic composite materials expands the scope of application in the life and research field When the materials are reinforced by fillers, their properties are changed Typically, the filler impacts in hardness, thermal conductivity, thermal expansion However, they improve strength and elasticity as well because of the filler properties and the changing of morphology matrix The inorganic filler are used wide in thermoplastic such as CaCO3, talc, SiO2, mice and Mg(OH)2
Most of the researches carried paying attention on the factors such as (i) component; (ii) shape and size; (iii) composition; (iv) compatibility of matrix and filler Some of them showed a polymer layer locating aninteraction phase between filler surface and matrix which have special property However, the role, influenceand a parameters relationship ofthe phase interaction betweenthe filler and the matrix on the mechanical properties (i.e tensile strength, impact resistance) is not determined clearly
Thus, supervisor and PhD student carried on a thesis:” Effect of surface fillers modification on phase interaction and mechanical properties of thermoplastic materials”
2 The aim of thesis
To study relation of molecular structural changing between polypropylene microcomposite system and the particle fillers with varies phase interactions by using solid-state NMR(ss-NMR) spectra.Therein,emphasizing the molecular flexibility on mechanical properties of materials
3 Main contents of thesis
a Preparing polypropylene composites materials by using the filler was modified/unmodified surface at varies contents
b Research phase interaction morphology, determine the mechanical properties of materials including tensile strength and impact resistance (integral J)
c Application of solid-state nuclear magnetic resonance (ss-NMR) method to determine molecular mobility in polymer composite materials, study the relation of mechanical properties of material Outline of the thesis: The thesis has 24 pages including introduction, 4 chapters of content, contributions and a list of publication
The main results of the thesis are published in:
- 01 article in an international journal in the ISI list (IF = 3.7)
- 04 articles in national journal
- 05 reports in the International Science Conference (1 international conference to publish ISBN)
Trang 2Chapter 1: INTRODUCTION 1.1 Thermoplastic polypropylene
Polypropylene (PP) was invented by research groups in the United States and Europe in the early 1950s The commercial production of PP began in 1957 in the US and in 1958 in Europe On the other hand, PP ranks first in the largest volumes group of thermoplastic products used such as: polyethylene (PE), polyvinylchloride (PVC) and polystyrene (PS) Average consumption of PP increases about 10% per year and the trend will keep increasing in future
The flexibility is important property of PP The structure and characteristics (including processing)
of PP can be adjusted according to usage requirements Polypropylene has many advantagedproperties such as low density, chemical resistance, easy processing and recyclability In addition, its mechanical properties are well suited to engineering plastics Besides, PP also has some disadvantages such as deteriorationin properties at low temperatures and low impact resistance Thus, PP copolymers and their blendsare studied to develop in commercial fields
1.2 Polymer composite materials base on fillers reinforced PP
Fillers reinforced PP composite materials have been used in large quantities in many different fields such as automotive, furniture, electrical equipment, etc Because of the relation between cost and achieved properties, filler reinforced PP composites are used widely and gradually replaced ABS inthe traditional fields Other materials like Many efforts have been made to expand its scope of application in engineering thermoplastic materials
There are many types of reinforced fillers using in PP, however, CaCO3, talcand fiber glass play the most important role and will keep it in the near future including In thermoplastic market, CaCO3 consumptionmakes up a majority of the filler field However,talc mineral ranks first inthe PP market, CaCO3 only ranks second and glass fiber follow Hence, glass fiber reinforced PP is studied to improve its capabilities and expand its scope of application In despite of many efforts,they are still potential and expectant researches In reality, application and the growth rate of fiber glass for PP are lower than that of particle fillers
Nowadays, not only the technical and aesthetic requirements but also the costs of processing and raw materialsare increasing To meet these requirements, the researchers need understanding the relevant properties of fillers as well as their influence on the structure and properties of composite materials touse all the advantages of fillers or just use them as diluents forreducing costs
1.3 Solid state magnetic resonance spectroscopy and its application for molecular mobility in polypropylene composites
Today, the high-resolution 13 C NMR spectrum is a common tool for studying the structure of polymers 1 H-NMR isa standard technique in structural analysis of liquid-state substances, but in solid-state substances Isotactic polypropylene isa polymorphic material due to a modifying arrangement of polymer chains Hence, ss-NMR spectroscopy technique showed complicatedanalysis for polypropylene.It is more complicated particularlyif the composition of these components that plays a decisive role changing the properties of polymer is significantly lower than composition of the matrix This difference prevents the use calibration curve analysis Therefore, special method must be used to
Trang 3describe the small differences between the amorphous and crystals disordering in the phase interaction region
However, the less attention has been paid to the multi-molecular analysis of the ss-NMR spectrum for amorphous or disordered solids, which can be considered an extreme limit due to the frequency range being too much for signals for which only one signal is available are defined Therefore, the thesis also demonstrates that 13 C MAS ss-NMR spectrocopy is a fast, reliable tool for describing extremely complex crystal forms in PP material for clarifying the relationship between spectral data at the molecular level and the macroscopic properties of materials such as mechanical properties
1.4 These studies were carriedon in Vietnam
The basic researches in Vietnam on thermoplastic composite materials in general and polypropylene in particular were studied by Hoang Thai and et al at the Institute of Tropical Technology and Dieu Tran Vinh and et al at Hanoi University of Technology
Hoang Thai et al treated titan dioxide or nano BaSO4 surface by silane coupling agent for studying mechanical properties and morphological structure of titan dioxide or nano BaSO4 filled polypropylene composites This surface modification process improved significantly the mechanical properties of composite materials Tensile strength and elastic modulus of PP composite materials with 2% of surface-modified nanoparticles are 42 Mpa and 979 Mpa, respectively Based on results of the cumulative module (G ') and phase interaction from X-ray diffraction analysis and FE-SEM, they showed that the properties and phase interaction of the material containing modified nanoparticle are better than these of the material containing unmodified nanoparticle
Besides, the research team of Prof Hoang Thai mixed melting polypropylene and vinysilane modified fly ash particles The effect of fly ash content on viscosity, mechanical properties and material morphology was determined The results indicated that the viscosity of the mixture decreased with increasing fly ash content Tensile strength and elongation at break of the material with different loading
of untreated fly ash are lower than the original PP After modifying by vinyl silane,PP / fly ash composite material showed higher tensile strength and elongation at break while viscosity of the mixture was lower The research team of Prof Dieu Tran Vinh had many studies on composite materials based organic fibers reinforced polypropylene They was considered that the adhesion between the plastic substrate and polar organic fiber affects incredibly the properties of the composite Thus, maleic anhydride–grafted polypropylene (MA-g-PP) compatibilizer or acetic anhydride and acrylonitrile was used Comparing the mechanical properties of polypropylene composite materials containing jute fibers and glass fibers, although tensile strength and elastic modulus of jute were lower than that of fiberglass, the specific module of jute was higher than glass fiber, and the module cost of jute is much higher than that of fiberglass The effect of jute and MAPP on PP tensile and flexural strength were determined When 50% weight of jute is loaded, the flexural strength of PP increases from 31.33 Mpa to 49.97 Mpa and increases sharply to 87.66 Mpa when adding 3% of MAPP weight Tensile strength does not increase much without MAPP However, when MAPP has tensile strength, composites increase about 2 times (from 28.92 MPa
Trang 4fibers and determined the effect of this process on the reinforcement of polypropylene based composite material Acetylation reduces the hygroscopic of bamboo fibers, increases the adhesion between bamboo fibers and PP resin 50% of short bamboo fibers reinforced PP composites has the highest tensile strength (36.45 MPa), increase of 2% compared with its raw PP
Chapter 2 EXPERIMENTAL 2.1 Materials
2.1.1 Polymer
Isotactic polypropylene homopolymer Mosten 52.412 (Chemopetrol, Czech Republic) was used
as a matrix in this study
2.1.2 Fillers
Glass beads, average size ~ 20 µm supplied by SOVITEC, France
Calcium carbonate, average particle size ~ 1.7 µm (1VA) and ~ 12 µm (15VA), supplied by Omycarb, Switzerland
Talc mineral originated from Thanh Son district, Phu Tho province, Vietnam The main components of this mineral are SiO2 (60,82 %) and MgO (32,16 %) Average particle size ~ 6,58 µm
2.1.3 Surface modification agents
Vinyltriethoxysilane supplied by Momentive (Switzerland) and methacryloxy propyltrimethoxysilane supplied by DowCorning (USA) Oleic and stearic acids (technical grade products supplied by Sigma-Aldrich) were used for calcium carbonate surface modification
2.1.4 Other materials
Dicumyl peroxite (technical grade ) supplied by Sigma-Aldrich
2.2 Methods
2.2.1 Surface modification
The surface modification of filler particles is carried out in 96% ethanol solution containing 2%
of the surface modification agent
2.2.2 Composite preparation
Polypropylene and fillers were been compounded in the twin-screw compounder (extruder) Brabender DSE and subsequently injection-molded into form of specimens (dog-bone) by ENGEL Spex victory 50 machine
Trang 52.3.3 Impact properties
An instrumented Charpy impact tester Ceast Resil Impactor with 7,5J work capacity was used for
the J-integral evaluation
2.3.4 ss-NMR
The ss-NMR experiments were performed using a Bruker Avance 500 WB/US NMR (Karlsruhe, Germany, 2003; B0 ¼ 11.7 T) with 4 mm ZrO2 rotors at a MAS frequency of 6 kHz The 13C crosspolarization (CP) MAS NMR spectra were measured with a B1(13C) field nutation frequency of 62.5
kHz, a contact time of 1.75 ms and a recycle delay of 2 s To record the T1-filtered, domain-selective
spectra of the highly mobile components, the single-pulse 13C MAS NMR spectrawere measured with a repetition delay of 2 s The VT experiments were performed in the temperature range from 295 to 355 K The frictional heating of the sample was compensated, and the sample temperature was calibrated using the 207Pb chemical shift in Pb(NO3)2
2.3.5 Factor analysis (FA)
FA is a method that uses the Singular Value Decomposition (SVD) algorithm to extract specific information from experimental data This technique allows visualization and distinguishing subtle differences between the prepared PP/CaCO3 microcomposites in 2D or 3D maps
Chapter 3: RESULS AND DISCUSION 3.1 Composite based on polypropylene and glass beads
3.1.1 Morphology observation
The introduction of inorganic filler into a polymer matrix results in a heterogeneous system Adhesion among different materials is created by physical or chemical bonds between the adhesive and the substrate, and this depends on the selection of coupling agent Figure 3.1 presents structure morphology taken of the impact fracture cross section of PP/glass beadcomposites with 20% of filler content
a) b) c)
Fig 3.1 Degree of interfacial adhesion between glass bead and PP matrix
As revealed by SEM in the cases of non-treated and NO adhesion, there was a poor interfacial with the strong debonding of particles While in case of GOOD adhesion, a strong bonding achieved between glass bead particles and PP matrix, coated spheres adhere to the matrix
3.1.2 Tensile properties
The effects of glass bead with different surface properties on the mechanical properties of composites are showed in Fig 3.2 It can be sheen that the tensile moduli in all cases of composites
Trang 6increase with increasing filler loading Generally, the addition of rigid particulate fillers increases stiffness, which is measured through Young's modulus This is due to the fact that fillers often exhibit higher stiffness compared matrix polymer Besides, Young's modulus is measured at the very beginning
of a tensile test, where deformation is insufficient to cause particle-matrix debonding However, obtained results indicated slightly change in value among cases of no-treated, NO adhesion and GOOD adhesion This comes from the difference in adhesion between particles and polymer matrix with zero adhesion in case of NO adhesion and a strong adhesion in case of GOOD adhesion The increasing in Young's modulus of glass bead-filled composites indicates an increase in the rigidity of PP related to the restriction of the mobility in PP matrix due to the presence of fillers This mechanical restraint resulted from the enhanced surface interaction between two phases in composites The similar trend also found in other studies that enhancement of the interfacial adhesion between the matrix and glass beads is helpful in improving the stiffness of filled PP composites
Fig 3.2 Tensile properties of PP/Glass beads composites
For particulate filled thermoplastic composites, it is generally believed that the interfacial adhesion between the filler particles and matrix is an important factor affecting strength and toughness of composites On the other hand, yield stress gives information on filler-matrix interactions and consequently it is one of the preferred methods of composite testing In thecase of a poor interaction (non-treated and NO adhesion) between the matrixand the filler, the interfacial layer cannot transferstresswas reflected by the lower yield stress value in comparison with a strong interaction in case of GOOD adhesion (Fig 3.2) Therefore, one can assume that the strengthof a particulate-filled composite is determined by theeffective available area of load borne by the matrix asa result of the absence of the filler
The higher yield stress values in case of GOOD adhesion in comparison with cases of non-treated and NO adhesion at the corresponding concentration reflect the interaction between glass bead particles and polypropylene matrix On the other hand, it can be seen that in all cases, yield stress decreases with increasing filler loading.This is due to the fact that theconcentration of the inclusions is the main factoraffecting the yield strength of a filled polymer besidesthe interfacial adhesion between the fillers and matrix The presence of glass beads has a weakening effect on the composite due to debonding Poor adhesion and debonding reduce the volume fraction which can carry the applied load.Tensile strain at break is a parameter characterizing the extensibility of materialsand it is usually inversely proportional to tensile strength which means that increasing the tensile strength of filled material usually contributes to a decrease in the strain at break The strain at break value for composite of GOOD adhesion had a lowest strain at break value which corresponds with highest tensile strength value
Trang 73.1.3 Impact properties
The J-integral was used to characterize the energy absorption of polymer materials at the initial stage of crack and the resistance for crack initiation Figure 3.3 showed Jld values of polypropylene and
glass bead composites
Fig 3.3 Impact strength of PP/glass beads composites
The fracture behavior of polymers is strongly affected by the addition of rigid particles The incorporation of them into the polypropylene matrix leads to differences in the overall process of crack propagation and fracture The process starts with the plastic deformation of the matrix ahead of the initial crack The adsorption of polymer molecules on the filler surface through chemical bonds leads to the rigidity in structure of polymer chains This leads to earlier crack initiation and propagation with dramatically decreasing of J-integral value in case of GOOD adhesion (Figure 3.3) Plastic deformation of the matrix polymer is the main energy absorbing process in impact and this increases when the interaction between particles and polymer matrix is lowered in case of non-treated and NO adhesion
3.1.4 ss-NMR
In general, narrowing of 1H lineshapes indicates the increase in global segmental dynamics as 1
H-1H dipolar couplings are motionally averaged out As demonstrated in Figure 3.4 in our particular case, the most mobile polymers segments were found in parent PP Slightly hindered segmental dynamics in the composites Non-treated and NO-adhesion is reflected by the broadening of the corresponding signals The most rigid polymer segments were found in the composite GOOD-adhesion that is reflected by the broadest 1H MAS NMR line
Trang 8Fig 3.4 1H MAS NMR spectra of the parent PP and composites recorded at 350 K and MAS 6 kHz Similar trends were found in the 1H MAS NMR spectra measured with Hahn-echo (Figure 3.5) that allowed separation of relatively flexible fractions of polymer chains of amorphous phase
Hình 3.5 1H MAS Hahn-echo NMR spectra of the parent PP and composites recorded at 350 K and
MAS 6 kHz
In contrast to solid-state 1H NMR spectra it is generally accepted that narrowing of 13C CP/MAS NMR signals indicates the increase in conformational ordering, and in extreme cases of perfectly evolved crystal phases very narrow signals are expected In polypropylene systems presence of polymorphic form alpha is reflected by the doublet of CH signal at ca 44 ppm The doublet is schematically indicated by dashed lines in Figure 3.6, and evolution of the narrow symmetric doublet requires long term annealing If considerable amount of amorphous phase is presented than the expected symmetrical doublet disappears
PP
Non-treated and
NO adhesion GOOD-adhesion
PP and
NO adhesion Non-treated GOOD-adhesion
Trang 9Rather an asymmetric broad line is expected Such a signal was detected for the parent PP (Figure 3.6)
In contrast, the prepared composites exhibit symmetrization of the doublet and increase in spectral resolution This finding can be explained by the conformational ordering occurred particularly in the composite NO-adhesion (additional crystallization, reorganization of the amorphous phase, formation of protocrystalline phases etc….)
Fig 3.6 13C CP/ MAS NMR spectra of the parent PP and composites recorded at 300 K and MAS 6
The morphology of the compounds up to concentration of 40 wt% treated and untreated CaCO3 are shown in Figure 3.7 and Figure 3.8 The CaCO3 particles are generally supplied as agglomerates, however, it can be seen that aggregates are broken up to the primary particles during the extrusion process In the case of CaCO3 with average particle size ~ 1.7 µm, the interaction between untreated filler particles with the polymer matrix is stronger compared with treated filler particles (Figure 1a) The strong debonding of particles can be observed in cases of treated particles (Figure 3.7-b and 3.7-c)
Figure 3.7 SEM images of morphology of PP filled with a) untreated CaCO3, b) oleic acid
treated CaCO3 and c) stearic acid treated CaCO3, average particle size ~ 1.7 µm, filler content 40 wt%
PP
Non-treated NO-adhesion GOOD-adhesion
Trang 10Similar trend was found in case of CaCO3 with higher size (12 µm, Figure 2) of filler particles, filler-matrix interaction in case of treated filler is lower compared with untreated filler
Figure 3.8 SEM images of morphology of PP filled with a) untreated CaCO3, b) oleic acid
treated CaCO3 and c) stearic acid treated CaCO3, average particle size ~12 µm, filler content 40% wt
3.3.2 Tensile properties
Tensile mechanical properties of composites of PP matrix with calcium carbonate particles were investigated (Figure 3.9) Generally, the addition of rigid particulate fillers increases stiffness, which is measured through Young modulus As can be seen in the figure, all the samples investigated in the present study show monotonic increasing of Young modulus values This is due to the fact that fillers often exhibit higher stiffness compared with polymer matrix Furthermore, Young modulus is measured at the very beginning of a tensile test, where deformation is insufficient to cause particle-matrix debonding Experimental results also indicated that, Young modulus of composites have none effect by particle size and surface modification
Strength and toughness are very important for polymer composites used as structural materials For particulate filled thermoplastic composites, it is generally believed that the interfacial adhesion between the filler particles and matrix is an important factor affecting strength and toughness of composites As revealed by SEM, the lower adhesion in case of treated filler led to a decrease in yield stress of composites compared with untreated filler for both particle size, especially at filler content of 40 wt% In addition to the decreasing yield stress value as the filler content increases, the smaller of the particle size leading to the higher of value of tensile yield stress On the other hand, surface treatment reduced particle-particle interaction, therefore, reduced the aggregation of filler particles, resulting a better dispersion of particle filler in polymer matrix, increasing interface leading to increasing yield stress
The extent of plastic deformation characterized by strain at break is then very sensitive to composition and morphology of the composites As shown in Figure 3.9, various types of calcium carbonate fillers have distinctly different effects in strain at break values
)
Trang 11Figure 3.9 Effects of particle size, surface modification and filler loading on the tensile mechanical
behaviour of injection-moulded specimens
3.3.3 Độ bền va đập
J-integral was originally defined by Rice as a contour integral independent on the path, which express the energy per unit area necessary to create new fracture surfaces in a loaded body containing a
crack Figure 4 show J-integral values of PP/CaCO3 composites with different types of particle size, filler
loading and surface properties
