Study of fabrication of PMMA microspheres for applications in large scale manufacturing

Reaction conditions for studying effect of BPO on PMMA productsusing 500-ml reaction container...21Table 3.4.. Reaction conditions for studying effect of MMA on PMMA productsusing 500-ml

VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

HOANG MINH KIEN

STUDY OF FABRICATION OF PMMA MICROSPHERES FOR APPLICATIONS

IN LARGE SCALE MANUFACTURING

MASTER'S THESIS

VIETNAM NATIONAL UNIVERSITY, HANOI

VIETNAM JAPAN UNIVERSITY

HOANG MINH KIEN

STUDY OF FABRICATION OF PMMA MICROSPHERES FOR APPLICATIONS

IN LARGE SCALE MANUFACTURING

MAJOR: NANOTECHNOLOGY CODE: 8440140.11QTD

RESEARCH SUPERVISOR:

Dr NGUYEN TRAN THUAT

Dr PHAM TIEN THANH

Hanoi, 2020

I would like to express my gratefulness to my first supervisor Dr Nguyen TranThuat, Nano and Energy Center, Hanoi University of Science, Vietnam NationalUniversity, for giving me guidance and help me finalize the thesis During theresearch, I have learned from him the way of processing results after eachexperiment and important skills when working in scientific field

I would like express my gratitude to my second supervisor Dr Pham Tien Thanh,Vietnam Japan University, for giving me support and encouragement His ideas andsuggestions were useful for not only my current but also future work

I also would like to show my appreciation to MK Group for the fund of the projectfor most of the chemicals and equipment

I would like to sincerely thank Nano and Energy Center for providing me theworking space and allow me to use their equipment for my research

I would like to thank my project group members Nguyen Ngoc Anh, Bui Thi Ngaand Chu Hong Hanh for all the assistance and help me accomplish these results Ilearned a lot from working with them, especially how to work in a team and discusswith others to advance the work

Finally, I am deeply grateful for the knowledge, the encouragement and supportfrom lecturers and my friends from Vietnam Japan University It has been twomeaningful years of studying, training myself and working in this Master program Iwill bring all these experiences with me and utilize them for my career in the future

TABLE OF CONTENTS

Page

1 INTRODUCTION 1

1.1 Poly(methyl methacrylate) microspheres and anisotropic conductive films 1 1.2 Aim of work 3

1.2.1 Particles quality requirement 4

1.2.2 Large scale manufacturing 4

1.3 Poly(methyl methacrylate) fabrication 5

1.3.1 Polymerization 5

1.3.2 Dispersion polymerization 7

1.3.3 Suspension polymerization 8

1.3.4 Microwave-assisted polymerization 10

1.3.5 Seeded polymerization 10

1.3.6 Polymerization using microfluidic system 11

2 EXPERIMENTS 15

2.1 Dispersion polymerization 15

2.2 Suspension polymerization 16

2.2.1 Conventional heating polymerization 16

2.2.2 Microwave-assisted polymerization 16

2.3 Seeded polymerization 17

3 RESULTS AND DISCUSSION 18

3.1 Dispersion polymerization 18

3.1.1 250-ml reaction container 18

3.1.2 500-ml reaction container 21

3.1.3 2000-ml reaction container 24

3.2 Suspension polymerization 29

3.2.1 Conventional heating polymerization 29

3.2.2 Microwave-assisted polymerization 30

3.3 Seeded polymerization 32

3.4 ACF demonstration 34

3.4.1 Silver-plating of PMMA 34

3.4.2 ACF Fabrication 36

4 CONCLUSION 39

REFERENCES 40

Methyl methacrylate Printed Circuit Board Poly (methyl methacrylate) Polyvinyl alcohol

Polyvinylpyrollidone Round per Minute Room Temperature

Scanning Electron Microscope

LIST OF TABLES

PageTable 3.1 Reaction conditions for studying effect of MMA on PMMA productsusing 250-ml reaction container 18Table 3.2 Reaction conditions for studying effect of BPO on PMMA productsusing 250-ml reaction container 20Table 3.3 Reaction conditions for studying effect of BPO on PMMA productsusing 500-ml reaction container 21Table 3.4 Reaction conditions for studying effect of MMA on PMMA productsusing 500-ml reaction container 21Table 3.5 Reaction conditions for studying effect of MMA on PMMA productsusing 2000-ml reaction container 24Table 3.6 Polymerization efficiency when varying the monomer amount 25Table 3.7 Reaction conditions for studying effect of BPO on PMMA productsusing 2000-ml reaction container 27Table 3.8 Reaction conditions for suspension polymerization 29Table 3.9 Reaction condition for microwave-assisted suspension polymerization 30Table 3.10 Reaction condition for seeded polymerization 32Table 3.11 Electrical resistance results of conductive sample 36Table 3.12 Electrical resistance result of the fabricated ACF 38

LIST OF FIGURES

Page Figure 1.1 Particles comparison of a) PMMA; b) PS products sharing the same

polymerization process (solvent, initiator and surfactant) 2

Figure 1.2 Bonding mechanism of a conventional ACF 2

Figure 1.3 a) Model for bonding a flip chip and a substrate in a smart card; b) Schematic for connection between bumps of integrated circuit chip and terminals of a glass substrate formed by an ACF 4

Figure 1.4 Three main steps in polymerization A: Initiation, B: Propagation, C: Termination 6

Figure 1.5 Particle size ranges of different polymerization methods 7

Figure 1.6 Schematic for dispersion polymer mechanism 8

Figure 1.7 Schematic for suspension polymer mechanism 9

Figure 1.8 Schematic for seeded polymerization process 11

Figure 1.9 Schematic of the channel layouts 12

Figure 1.10 Patterns of droplet formation observed in the T-junction/pocket 13

Figure 1.11 Microwave heating and conventional heating integrated microfluidic systems 13

Figure 2.1 Apparatus for 250-ml and 500-ml Reaction Containers a) Schematic; b) Real system for 500-ml Reaction Container 15

Figure 2.2 Apparatus for 2000-ml Reaction a) Schematic; b) Real system 15

Figure 2.3 Apparatus for microwave-assisted polymerization a) Schematic; b) Real system 17

Figure 2.4 Schematic of apparatus for seeded polymerization 17

Figure 3.1 Microscopic images of samples a) A% MMA; b) 1.3A% MMA and c) 1.5A% MMA 19

Figure 3.2 Microscopic images of damples a) B% BPO; b) 1.3B% BPO 20

Figure 3.3 Microscopic images of samples a) 1.3B% BPO; b) 2B% BPO and 3B% BPO 22

Figure 3.4 Microscopic images of samples a) 0.5A% MMA; b) 0.8A% MMA and c) A% MMA 23

Figure 3.5 Microscopic image of the sample A% MMA and 2B% BPO 25

Figure 3.6 Microscopic images of samples a) 1.1A% MMA; b) 1.3A% MMA and c) 1.5A% MMA 26

Figure 3.7 Microscopic images of samples a) 2B% BPO; b) 1.7B% BPO; c) 2.3B% BPO and d) 2.7B% BPO 28

Figure 3.8 Microscopic images of samples a) A% MMA; b) 0.3A% MMA 30

Figure 3.9 Microscopic images of microwave-assisted polymerization samples aftera) 2 h of reaction; b) 3 h of reaction 31Figure 3.10 Microscopic images of conventional heating polymerization samplesafter a) 2 h of reaction; b) 3 h of reaction 32Figure 3.11 a) Microscopic image of PMMA seeding particles; b) Microscopicimage of products after 60 min; c) Microscopic image of products after 100 min 33Figure 3.12 Sample fabricated using 2000-ml reaction container, with MMA% =1.1A% and BPO = 2B % a) optical microscopic image and b) SEM image 34Figure 3.13 Silver-plated PMMA particles a) optical microscopic image; b) SEMimage 35Figure 3.14 Schematic for electrical resistance measurement system 36Figure 3.15 Optical microscope of anisotropic conductive films after fabricationusing conductive silver-plated PMMA microspherical particles 37Figure 3.16 Schematic for measuring anisotropic conductivity of fabricated ACFs38

Monodispersed poly(methyl methacrylate) microspheres with the size from 5 µm to

13 µm were prepared by using a dispersion polymerization method Three reactioncontainers with volume of 250 ml; 500 ml and 2000 ml were used to study thescalability of the fabrication process In the case of 2000-ml reaction container,more than 80 g of microspheres were synthesized with high efficiency, which could

be utilized for the fabrication of more than 100 m2 of anisotropic conductive film.The products were proved to have a good quality and to be ready for carryingforward to the silver-plating process and the fabrication of anisotropic conductivefilms Other two methods including microwave-assisted polymerization and seededpolymerization were also performed to decrease the reaction time and to increaseparticles size However, the two methods still need more optimization to yield better

1 INTRODUCTION

1.1 Poly(methyl methacrylate) microspheres and anisotropic conductive films

Polymers extracted from nature in the early days were already utilized in theproduction of clothing, buildings and daily equipment However, only since therevolution of synthetic polymers in the first half of 20th century - the period whichcan be known as the age of polymers, this material had attracted great deal ofattention and had been developed rapidly due to their surprisingly low density, hightensile strength and good flexibility During this time, especially from 1930 to 1960,almost all the polymers we commonly use today had been discovered, for example,Polyethylene terephthalate (PET) for plastic bottles; Polyvinylchloride (PVC) forpipes or waterproof clothing; and Poly(methyl methacrylate) (PMMA) used fortransparent container such as acrylic glass for aquarium1 Initially, polymers weredeveloped for the use of macroscale manufacturing such as clothing, transportation

or food preservation With the growth of microtechnology, polymer microparticleshave attracted huge attention due to their flexibility, spherical shape and low-costproduction Among the types of polymer particles, PMMA and Polystyrene (PS)microspheres are the most popular The chemicals used for the production of thesetwo polymers are cheap and commercially available as well as the polymerizationyields high efficiency Comparing PMMA with PS, the particles size overall for PS

is smaller, mostly smaller than 5 µm, while size of PMMA can vary fromsubmicron size to hundreds of micro in diameter Figure 1.1 compares the particlesfabricated by polymerization of PMMA and PS using the same reaction condition,size of PMMA microspheres is significantly larger than size of PS microspheres.PMMA can yields larger particles size of 8 µm, and even larger than 10 µm withsome modification In contrary, for PS polymerization, large particles of 7 or 8 µmcan be hardly obtained, even with modified conditions to increase the particlesradius PMMA can be observed to be more flexible in terms of creating polymerparticles having micro size, indeed, PMMA particles can as large as 100 µm

Therefore, for the purpose of providing the polymer microspheres for the use ofmost of current technology, PMMA is chosen to be the main material.

Figure 1.1 Particles comparison of a) PMMA; b) PS products sharing the same

polymerization process (solvent, initiator and surfactant)One of the main reason making PMMA microspheres attracting great attention isthat the surface of PMMA particles can be easily modified using chemical process.Acrolein was used by Songjun Li for the modification of PMMA surface during thepolymerization for the investigation on the polymer immobilization2 With theexistence of ester group having Oxygen carrying negative charge from free electronpair, the surface of PMMA particles can also be modified with metal cation, forinstance, stannous (II) cation can be absorbed on the PMMA surface in thepretreatment of silver-plating process3 Therefore, PMMA can be used as cores forthe preparation of conductive particles, which is one of the essential part inanisotropic conductive film (ACF) fabrication process

Figure 1.2 Bonding mechanism of a conventional ACF4ACF is used to create a mechanical and electrical connection between components

in electrical device Figure 1.2, shows the bonding mechanism of an ACF Heat and

compression is used to create connection between electrodes on two oppositesubstrates Upon heating and compression, adhesion is created and mechanicallyconnect the two substrates Also, conductive particles inside the ACF contactrespective electrodes and create electrical connection between them The mainfeature of the ACF is that the electricity is allowed only along the vertical direction(one direction) from an electrode to the respective one, but not along the horizontaldirection In other word, only the contact between two electrodes is conductive; thenon-contact regions are insulated Because of this feature, ACFs are commonlyused for the connection of the driver electronics on glass substrate in liquid-crystaldevices and for flex-to-flex or flex-to-board of many electronic devices such assmartphones or laptops With the development of technology nowadays, ACFs aremore and more in high demand Especially for the advances in technology inVietnam in this industrial age, the importance for the ACF increases and theprocedure for ACF should be developed to reduce the dependence on foreignproducts.

1.2 Aim of work

Polymer fabrication is the first step of our main project, which is fabrication ACFfor integrated circuit card (ICC) One of the reason why PMMA microspheres is agood candidate for the making of ACF is due to the glass transition temperature ofthe atactic PMMA is 105oC and melting point is 160oC5, which makes the particlesflexible and able to soften during the connection process using heat and pressurefor compression Furthermore, the surface of PMMA microspheres can be modifiedwith the use of chemicals absorption, then use reduction oxidation reaction toperform electroless metal plating on the surface of particles making the particlesconductive In order for the ACF to work in the best condition, quality of particlesinside the film should be taken into consideration Moreover, with the purpose forindustrial application, large scale manufacturing of PMMA will be studied in themain factor of scalability Figure 1.3 shows the model for the integrated circuit chipand printed conductor runs on substrate for an ICC and schematic of using ACF forthe connection of these two components

Figure 1.3 a) Model for bonding a flip chip and a substrate in a smart card6; b)Schematic for connection between bumps of integrated circuit chip and terminals of

a glass substrate formed by an ACF7

1.2.1. Particles quality requirement

The requirement for the PMMA microspheres used for ACF is that the particlesshould have spherical shape and the size distribution should be narrow in order toensure the contact of most conductive particles to both the chip bump of integratedcircuit chip and terminals of printed conductor wires on a glass substrate Anotherrequirement for the particles size is that the particles diameter should be from 5 to

30 µm The particles should not be smaller than this range in order to prevent theagglomeration during the film making and ensure the one layer of particlesconnecting terminals and chip bumps Moreover, the size is kept under 30 µm tomatch the thickness of ACFs which is from 30 to 40 µm – the best thickness forgood adhesion Therefore, particles quality, regarding spherical shape and size, wasinvestigated in the research

Concerning the synthesis of microspherical polymer particles, four commonmethods are often applied, which are emulsion, dispersion, suspension andprecipitation polymerization These methods are presented in details in the nextsection For each desired size of particles, polymerization methods are chosen Inour research, desired range size of particles is from 5 to 30 µm

1.2.2 Large scale manufacturing

In terms of the PMMA microspheres fabrication using for large scalemanufacturing, another main factor studied in the research is the scalability Forexample, in order to produce 1 roll (or 1 tape) of ACF with 100 m in length and 10

mm in width, or 1 m2 of film, 0.6 g of PMMA is needed For the creation of one

ICC, 10mmx10mm of ACF is used, hence, 1 tape of ACF can make the connection

of 10,000 cards Imagine if we can produce 60 g or 600 g of PMMA per day, 100tapes or 1000 tapes can be fabricated, which can be used for 1 million or 10millions of ICCs This number can be considered as large scale manufacturing, andthe goal of our research is to prove the polymer synthesis method not only able toreach this amount but also has the potential to produce more for other industrialpurpose

1.3 Poly(methyl methacrylate) fabrication

1.3.1 Polymerization

In general, the polymerization undergoes three main steps: initiation, propagationand termination Figure 1.4 illustrates the mechanism for all of these three steps Inthe initiation process, energy is provided for the initiator to break their weakestbond and radicals are formed Some of the common initiators are Benzoyl Peroxide(BPO) and Potassium persulphate (KPS), which the weak peroxide O-O bonds arebroken to form oxygen radicals, or azobisisobutyronitrile (AIBN), which the C-Nbonds are broken to form nitrogen and carbon radicals Depend on the type ofpolymerization and solvent used, proper initiator is chosen After the radical isformed by bond-breaking of initiator, the radical will attach to the monomer mostly

by breaking the weak double bond to create a new bond and a new radical Thenthe second step is the propagation, where this new radical attaches to anothermonomer to form a longer free radical molecule This molecule undergoes the sameprocess, and the chain reaction continues until two radicals interact (hydrogentransferring) together (recombination) to eliminate the free radical, in the final step

of termination

Figure 1.4 Three main steps in polymerization A: Initiation, B: Propagation, C:

TerminationThere are four common techniques employed for the manufacturing of polymer,which are emulsion polymerization, dispersion polymerization, precipitationpolymerization and suspension polymerization The main factors that distinguishedthe polymerization method are the initial state of polymerization mixture (regardingthe solubility of initiator and monomer in solvent); kinetics of polymerization;mechanism of particles formation and shape/size of final particles Figure 1.5shows the particle size range for each type of polymerization method For emulsionpolymerization, the synthesized particles are mostly spherical and have a small sizevarying from 50 nm to 500 nm Meanwhile, particles having size ranging from 500

nm to 15 µm can be prepared by dispersion and precipitation polymerization.However, comparing these two techniques, dispersion polymerization yieldsmonodispersed and spherical polymer particles while particles prepared byprecipitation method are mostly polydispersed as well as have irregular shape.Regarding suspension polymerization, spherical particles with size larger than 15

µm and up to 1 mm can be fabricated; however, the monodispersity is difficult toachieve By the resulted particles for each technique, we choose dispersion and

suspension polymerization to be two main techniques for our PMMA microspheresfabrication.

Figure 1.5 Particle size ranges of different polymerization methods8

1.3.2 Dispersion polymerization

Figure 1.6 shows the schematic for dispersion polymerization mechanism Indispersion polymerization, during the initial state, the reaction mixture ishomogenous where the monomer and the initiator both dissolve in thepolymerization solvent During propagation step, macroradicals or oligomers areformed, to a critical point the molecules are insoluble in the solvent and hence,phase separation occurs (Figure 1.6B) These macroradicals then gather for thenucleation to form primary particle, and the polymerization continues withinindividual particles (Figure 1.6C) Then, the particles grow until reachingstabilization (Figure 1.6D)

Dispersion polymerization of PMMA were already reported in past literature.Effect of reaction temperature, initiator concentration and type, monomerconcentration and stabilizer were studied by S.Shen Conditions for synthesizeparticles with narrow size distribution ranging from 0.4 µm to 10 µm wereillustrated9 However, for the large scale production or industrial manufacturing, no

process has been published for fabrication of microspherical particles and with thedevelopment of microtechnology and nanotechnology, the demand for thesepolymers grew and grew In our research, we will prove whether the procedure isapplicable for large scale production purpose.

Figure 1.6 Schematic for dispersion polymer mechanism A: initial step, B:formation of macroradicals – phase transition, C: Nucleation process and particles

growth, D: particles reach stabilization8

1.3.3 Suspension polymerization

In suspension polymerization, the initiator is soluble in the monomer, however,both of them are insoluble in the polymerization medium Figure 1.7 illustrates themechanism for suspension polymerization When the monomer and the initiator aremixed in the solvent, mini droplets of monomer are formed upon high speed ofstirring When energy is provided for the initiation, polymerization occurs withineach individual droplets Instead of continue growing until reaching stabilizationlike dispersion polymerization, the droplet will directly turned into the polymerparticles when finishing polymerization Therefore, to control the size of particles,size of droplets should be considered

Figure 1.7 Schematic for suspension polymer mechanism

In order to control the size of droplets, according to Equation 1, stirring speed, andvolume ratio of monomer to liquid matrix, viscosity of the two phases andconcentration of stabilizer should be taken in consideration.8

̅

where ̅ is average particle size, k includes parameters related to the reaction vessel design, D v is the reaction vessel diameter, D s is the diameter of the stirrer, R is the volume ratio of the droplet phase to medium, N is the stirring speed, ν m and ν d are the viscosity of the monomer phase and liquid matrix respectively, ε is the interfacial tension of the two phases, and C s is the concentration of stabilizer.

Even though the suspension polymerization can produce a wide range size ofparticles, the narrow size distribution is quite difficult to achieve due to theversatile of polymer droplets, where the droplets can easily be agglomerated orseparated during polymerization The most common way to control the size is toincrease the speed of stirring, which is the most efficient to ensure stabilized state

of droplets Moreover, the apparatus design and reaction vessel diameter is one ofthe main factor decides the size of particles according to Equation 1 Therefore,changing, for instance, small reaction chamber to lager reaction chamber, newconditions for reaction should be re-optimized, which makes the process notflexible

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1.3.4 Microwave-assisted polymerization

Regarding normal polymerization using heat transfer from a heat source, the timefor the reaction varies from 24 to 48 h, which requires resources to maintain thereaction and quite time consuming Therefore, many studies were carried out withthe goal of reducing the time of polymerization, which includes the use ofmicrowave J Jacob had used microwave with different power of 500 W; 300 Wand 200 W for the polymerization of MMA and obtained the reaction rate enhancecomparing to the thermal method which are 275%; 200% and 138%, respectively10.Not only the reaction rate is faster, but the conversion of polymer using microwave-assisted process was higher than conventional heating, which has been studied byLiu Z in the polymerization of butyl acrylate (BA) to PBA11 The mechanism ofmicrowave on the acceleration of reaction has not yet been demonstrated, but twoeffects of microwave irradiation have been proposed: specific microwave heat andnonthermal microwave effect12 When using normal conventional heating, the heattransfers from outside to inside solution, and the hottest part is the glass containerdirectly contacting the heat source Meanwhile, the microwave can pass throughevery part of reaction mixture including solvent, surfactant, monomer and initiator,allow heat to be generated across the entire reaction volume and most part of thereaction will reach reaction point much faster Regarding nonthermal process,intermediate can absorb the microwave energy and be accelerated or somemolecule under microwave can be enhanced from ground state to transition stateand be more active However, when nonthermal microwave effects are discussed,they are generally invoked as the inaccuracy in comparison with conventionalheating effects12

1.3.5 Seeded polymerization

It is not easy to synthesize particles larger than 15 µm with narrow size distributionvia one-step classic dispersion or suspension polymerization One of the techniquescan be used to increase the size of particles while still keeping the monodispersity

is seeded polymerization Miliang Ma already succeeded in forming 14 µmmonodispersed cross-linked P(GMA-St-EGDMA) from monodispersed 7 µmP(GMA-St) as seed particles13 For seeded polymerization, the most important

process is the swelling process of seed particles in monomers Figure 1.8 shows thephenomena occur during seeded polymerization process When polymer particlescontact with monomer in the solution, the monomer concentration is not high fordissolving the polymer, but the monomer still affect the polymer, surround thepolymer and make the polymer particle become larger We call this phenomenonthe swollen effect When the swollen particles reach the point of stabilization,energy was provided for the initiator in the solution to initiate the polymerization ofmonomer and the monomer will form the new polymer shell outside the seedparticles, hence, results in larger size particles In seeded polymerization,polymerization condition such as the amount of seed particles or swollen timeshould be carefully controlled in order to stop the formation of new particles.

Figure 1.8 Schematic for seeded polymerization process

1.3.6 Polymerization using microfluidic system

When using classical polymerization, mostly, the monodispersity is obtained forsynthesis of particles smaller than 15 µm For larger size of monodispersed particle,

as mention before, seeded polymerization can be used; however, the process isquite complicated as it is a multiple steps method which requires the first step to bethe fabrication of seed particles With the development of microfluidic systems, onestep polymerization for these large particles is attainable as the system alloworganic droplets with same size formed continuously in the flow of aqueous phase.Monodispersed particles of poly(1,6-hexanediol diacrylate) with mean diameteraround 43 µm was made by Takashi Nishisako with the use of T-shape channel forfeeding in microfluidic system14 (Figure 1.9) In Takashi research, feed rate of

aqueous phase were varied why the organic was kept constant, with the resultshowed in Figure 1.10, gives different size of polymer particles This means thatthe factor of feed rate is most essential when concerning microfluidic system LiuZhendong also compared two heating strategies using conventional heating andmicrowave heating to observe the polymerization rate of organic droplets duringthe process Overall, with the assistance of microwave, the polymerization processnot only faster but the conversion is also higher A typical example of microfluidicsystem using two heating strategies is illustrated in Figure 1.11.

Figure 1.9 Schematic of the channel layouts

Figure 1.10 Patterns of droplet formation observed in the T-junction/pocketwhen the flow rate of aqueous phase (Qc) was varied at a fixed monomer flowrate (0.1 ml/h): (a, b) Qc = 0.5 ml/h; (c, d) Qc =1.0 ml/h; (e, f) Qc =2.0 ml/h.

Figure 1.11 Microwave heating and conventional heating integrated microfluidic

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Despite a good control in size of monodisperse polymer microspheres, the limit ofthis method was the amount of particles made The microfluidic system is acontinuous flow system concerning the feed rate of phases rather than the amount

of chemicals used as in batch system And this feed rate is optimized and keptconstant during the process, which results in a fixed amount of particles formed in aperiod of time Meanwhile for batch system, more chemicals can be used, reactioncontainer volume can be changed, and makes the scalability of batch reaction isachievable

In our research, in order to satisfy the particles quality requirement having amonodispersed size in the range from 5 to 30 µm, two main polymerizationmethods were performed, which were dispersion polymerization – which canproduce spherical particles size range from 0.5 to 15 µm – and suspensionpolymerization which produced spherical particles larger than 20 µm In addition,

to study the scalability factor, three types of reaction container with increasing inreaction volume are investigated, which are 250 ml, 500-ml and 2000-ml reactioncontainers

2 EXPERIMENTS

2.1 Dispersion polymerization

Three types of reaction containers, a 250-ml and a 500-ml two-neck, round-bottomflasks and a 2000-ml three-neck, round-bottom flask, were employed for studyingscalability of the process A condenser was equipped to the system along with athermometer for heat control and observation For 250-ml and 500-ml flasks,magnetic stirrer were used while mechanical agitation containing Teflon paddlewere applied for 2000-ml flask system Reaction systems are presented in Figure2.1 and Figure 2.2

Figure 2.1 Apparatus for 250-ml and 500-ml Reaction Containers a) Schematic; b)

Real system for 500-ml Reaction Container

Figure 2.2 Apparatus for 2000-ml Reaction a) Schematic; b) Real system

A solution containing X% PVP surfactant dissolved in Methanol solvent wasprepared in the reaction flask and heated to 65oC while stirring at 600 rpm Thesecond solution containing BPO as initiator dissolved in MMA monomer and thismixture was poured into the reaction flask all at once Then, the reaction wascarried out at 65oC with stirring speed 600 rpm for 24 h After the reaction, PMMAparticles product was then washed by centrifugation, decantation and redispersion

in deionized (DI) water three times to eliminate the residual MMA and PVP Theparticles were obtained and dried in air ambient and observed using an opticalmicroscope

2.2 Suspension polymerization

2.2.1 Conventional heating polymerization

A solution prepared by dissolving X% PVA in 1000-ml DI Water was added to the2000-ml reaction container and heated to 70oC while stirring at 600 rpm After that,

a mixture of BPO dissolving in MMA monomer was poured into reaction flask all

at once The reaction was carried out at 70oC for 24 h with constant agitation.Finally, the PMMA particles was washed by centrifugation, decantation andredispersed in DI Water and dried in air ambient

2.2.2 Microwave-assisted polymerization

A solution containing X% PVA in 1000-ml DI Water was added to the 2000-mlreaction flask and heated to boiling point while agitating at 600rpm Then a mixture ofBPO dissolving in MMA monomer was poured into the flask all at once The reactioncontainer was put into microwave oven, and the cycle of 30 s ON/ 2 min OFF wascarried out continuously for 3 h with microwave power of 600 W Finally, the PMMAparticles then underwent the same purification treatment as other procedure Figure 2.3illustrates the reaction system for microwave- assisted polymerization

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