Thesis by Mazlinda SHM


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Lets together concern about our health and live. Are you one of dental cement consumer?Are you know the composition of the cement itself? Here my thesis/report serve you analytical chemistry description and may answer your curiousness. Check it out in my dental research of GPC.

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Thesis by Mazlinda SHM

  1. 1. INFLUENCE OF MONMORILONITE CLAY ON THE SETTING REACTION AND COMPRESSIVE STRENGTH OF GLASSPOLYALKENOATE CEMENTS FOR LG3 (NON-SODIUM GLASS) AND LG66 (WITH-SODIUM GLASS) by MAZLINDA BINTI SARIHASAN A Project Submitted in a Partial Fulfillment of the Requirement For Bachelor of Science (Honours), in Petroleum Chemistry Department of Chemistry Faculty of Science Universiti Putra Malaysia April 2011
  3. 3. DECLARATIONI hereby declare that the thesis is based on my original work except for quotations and citations,which have been duly acknowledged. I also declare that this thesis has not been previously orconcurrently submitted for any other degree at Universiti Putra Malaysia or other institutions. ……...……………………………… (MAZLINDA BINTI SARIHASAN) Date:……………………………
  4. 4. ACKNOWLEDGEMENTAll praises to ALLAH the Almighty for giving me the strength to complete this study. Thespecial thanks dedicated to my helpful supervisor, Dr. Norhazlin Zainuddin. The supervision,guidance, encouragement and support that she gave truly help the progression and smoothnessof my final year project. The co-operation is much indeed appreciated.Special appreciation goes to my project’s senior, Nur’Izzah Md Nasir for her big contributionduring the progression of this project. I really hope that she can complete her study in masterlevel with flying colours.Sincere thanks forwarded for staffs of Faculty of Science: Mrs Rusnani Amiruddin,Mrs.Zaidina Md Daud and Mr. Then for their assistance in running my samples on the FTIR,TGA and XRD analysis. Also, big thank to Faculty of Engineering and Institusi TeknologiMaju (ITMA) for allowing me to do compressive test and grind my sample. A big contributionfrom all staffs throughout my project is very great indeed.I am grateful to my lovely parents, family, course-mate and friends for giving me greatsupport, inspiration, reminder and advice through all difficult time. Thanks all.
  5. 5. ABSTRACTINFLUENCE OF MONMORILONITE CLAY ON THE SETTING REACTION ANDCOMPRESSIVE STRENGTH OF GLASS POLYALKENOATE CEMENTS FOR LG3 (NON-SODIUM GLASS) AND LG66 (WITH-SODIUM GLASS) By MAZLINDA BT SARIHASAN APRIL 2011Supervisor : Dr.Norhazlin Bt ZainuddinFaculty : Science UPMDepartment : ChemistrySeveral features such as mechanical, physical and chemical properties play vital role inselection of dental cement. Glass ionomer cement (GIC) that is a modern version of silicatecement becomes the most significant dental material due to the existence of these features. Inthis study, the (GIC) also known as Glass Polyalkenoate Cement (GPC) was produced via acid-base neutralization reaction of aqueous polyacrylic acid (PAA) with finely ground calciumfluoro-alumino silicate glass powder. Two of glass formulation were used, LG3 (33.3 SiO2-22.2Al2O3-11.1 P2O5-22.2 CaO-11.1 CaF2) and LG66 (33.3 SiO2-22.2 Al2O3-11.1 P2O5-17.8 CaO-11.1 CaF2-4.4 Na2O). This study emphasized the influence of montmorillonite (MMT) on thecompressive strength of GPCs. For this study, it was found that 2.5 wt% is the best percentageof MMT that could be mixed with GPC. The excess amount of MMT leads to difficulty in
  6. 6. mixing the glass powder and PAA and thus unable to mix homogenously. GPCs werecharacterized using XRD, FTIR spectroscopy and TGA. The amorphous phases of GPCs wereproven from XRD pattern. From FTIR spectroscopy, the setting reaction of GPCs at variousaging time can be determined. The original glass powder give major absorption band around920 cm-1 correspond to Si-O(Si) stretch. For PAA, strong band with medium width occurred inthe region 1700 – 1660 cm-1 was due to COOH stretch of carbonyl group. In GPC, new bandappears between 1710 cm-1 – 1390 cm_1. The appearance of this new peak was caused by theformation of COO-M+ (M = Ca, Al) from the cross linking of metal ions with carboxylate groupof PAA. Band around 920 cm-1 which had formed earlier was disappeared as aging timeincrease. This phenomenon was due to formation of Si-O-Si. This study found that the additionof MMT improved the compressive strength of GPCs. The addition of MMT in LG3 and LG66cements increased the compressive strength from 53 to 74 MPa and from 10 MPa to 66 MPa at14 and 28 days aging time respectively. The presence of sodium influences the working timeand compressive strength at early of setting reaction. However, the compressive strength valueand setting reaction of both glasses become almost similar at 28 days aging time.
  7. 7. ABSTRAK PENGARUH ‘MONMORILONITE CLAY’ TERHADAP ATURAN TINDAKBALASDAN DAYA MAMPATAN DALAM GELAS POLYALKENOAT SIMEN PADA GELASLG3 (TIADA KANDUNGAN SODIUM) DAN GELAS LG66 (DENGAN KANDUNGAN SODIUM) Oleh MAZLINDA SARIHASAN APRIL 2011Penyelia : Dr.Norhazlin Bt ZainuddinFakulti : Sains UPM Jabatan : KimiaBeberapa ciri seperti sifat mekanik, fizikal dan kimia memainkan peranan penting dalampemilihan simen gigi. Gelas ionomer simen (GIC) merupakan versi moden simen silikat yangpenting kerana adanya ciri-ciri ini. Dalam kajian ini, GIC juga dikenali sebagai GelasPolialkenoat Simen (GPC) telah dihasilkan melalui tindakbalas penuetralan asid-bes poliakrilatcecair (PAA) dengan serbuk kaca halus fluoro-alumino kalsium silikat. Dua formulasi gelas telahdigunakan, LG3 (33.3 SiO2-22.2 Al2O3-11.1 P2O5-22.2 CaO-11.1 CaF2) dan LG66 (33.3 SiO2-22.2 Al2O3-11.1 P2O5-17.8 CaO-11.1 CaF2-4.4 Na2O). Kajian ini menekankan pengaruhmontmorilonit (MMT) terhadap daya mampatan GPC. Untuk kajian ini, didapati bahawaperatusan pemberat 2.5 % adalah pemberat paling sesuai yang boleh dicampurkan dengandengan GPC. Jumlah yang berlebihan menyebabkan kesulitan dalam pencampuran serbuk gelasdengan PAA dan tidak bercampuran secara homogen. Pencirian GPC dilakukan dengan
  8. 8. menggunakan analisis XRD, spektroskopi FTIR, dan TGA. Fasa amorf GPC dapat dibuktikanmelalui pola XRD. Daripada FTIR, aturan tindakbalas GPC pada pelbagai tempoh penuaandapat ditentukan. Serbuk gelas asli memberikan serapan utama pada panjang gelombang 920cm-1yang menunjukkan renggangan pada ikatan Si-O(Si). Untuk PAA, puncak yang besar dan lebarberlaku di kawasan panjang gelombang antara 1700 – 1660 cm-1 adalah selaras dengan kehadirankumpulan COOH. Dalam GPC pula, satu puncak baru muncul antara panjang gelombang 1770 –1390 cm-1. Kemunculan puncak ini adalah disebabkan berlakunya pembentukan COO-M+ (M =Ca, Al) dari persilangan ion logam dengan kumpulan karbosilik dari PAA. Puncak di sekitarpanjang gelombang 920 cm-1 yang terbentuk pada awalnya telah menghilang apabila masameningkat. Fenomena ini berlaku kerana pembentukan ikatan Si-O-Si. Secara umumnya,penambahan MMT dapat meningkatkan kekuatan GPC. GPC daripada gelas LG3 tanpa dandengan penambahan MMT masing-masing memberikan nilai daya mampatan yang maksimumsebanyak 53 dan 74 Mpa. GPC dari gelas LG66 memberikan daya mampatan 10 Mpa dengantiada penambahan MMT dan 66 Mpa dengan adaya penambahan MMT. Kehadiran sodiummempengaruhi masa kerja dan daya mampatan pada awal aturan tindakbalas.Walaubagaimanapun, nilai daya mampatan dan aturan tindakbalas pada kedua-dua gelas menjadisama pada tempoh penuaan 28 hari.
  9. 9. LIST OF TABLESTABLES PAGE1.1: Comparison among dental restorative materials 33.1: LG3 and LG66 composition in mole percent, % 223.2: Weight ratio of glass, PAA, MMT clay and water 244.1: Compressive strength of LG3 cement as a function of time 394.2: Compressive strength of LG66 cement as a function of time 39
  10. 10. LIST OF FIGURESFIGURES PAGE2.1: Classification of cement 72.2: Schematic depiction of the setting reaction of glass ionomer cements 92.3: Schematic representation of aluminium coordination states in glasses and GICs 144.1: XRD pattern for LG3 cement without and with addition of MMT 284.2: XRD pattern for LG66 cement without and with addition of MMT 294.3: Thermogram for LG3 glass 304.4: Thermogram for LG66 glass 314.5: Thermogram of PAA 324.6: Thermogram of MMT 324.7: Thermogram of LG3 glass without addition of MMT 354.8: Thermogram of LG66 glass without addition of MMT 354.9: Thermogram of LG3 glass with addition of MMT 364.10: Thermogram of LG66 glass with addition of MMT 364.11: Compressive strength of LG3 cement without and with addition of MMT 404.12: Compressive strength of LG66 cement without and with addition of MMT 404.13: Infrared spectrum for LG3 glass 444.14: Infrared spectrum for LG66 glass 444.15: Infrared spectrum for polyacrylic acid, PAA 454.16: Infrared spectra of LG3 cement without MMT addition with aging time from 5 47minutes to 28 days
  11. 11. 4.17: Infrared spectra of LG66 cement without MMT addition with aging time from 495 minutes to 28 days4.18: Comparison of FTIR spectra of LG3 cement and LG66 cement without MMT 53at 5 minutes aging time4.19: Infrared spectrum of MMT 544.20: Infrared spectra of LG3 glass with and without addition of MMT at 5 minutes 554.21: Infrared spectra of LG66 glass with and without addition of MMT at 555 minutes
  12. 12. LIST OF ABBREVIATIONSADA-MMT 12-amino-dodecanoicacid treated montmorilloniteCa-MMT Calcium montmorilloniteFTIR Fourier transform infraredGICs Glass ionomer cementGPCs Glass polyalkenoate cementIR InfraredMAS-NMR Magic-angle spinning nuclear magnetic resonanceMMT MontmorilloniteMPa Mega PascalISO International Organization for StandardizationPAA Polyacrylic acidTEM Transmission electron microscopyTGA Thermal gravimetric analysisWt% Weight percentXRD X-Ray diffraction
  13. 13. CHAPTER 1 INTRODUCTION 1.1 Dental CementDental cement is a kind of material used as clinical dentistry to restore lost tooth functions due tocavity formation. Therefore, it must have properties that close to natural tooth. In studies ofdental cement, several terms have to be understood such: chemistry of the setting reaction,consistency in proportion of powder to liquid ratio in mixing cements, maximum solubility anddisintegration, dimensional change, working and setting times, bonding strength for theirintended use (MPa), optimum film thickness, thermal and electric conductivity, amount of heatgenerated during setting, and safety (should not be toxic, carcinogenic, mutagenic, irritating, orsensitizing).Nowadays, dental researcher have wide opportunity to develop the newer cements and achievebetter understanding of the clinical and biological performance of cements since it is necessary toproduce the ideal cement to use in dentistry. There are many types of dental cement are availablebut none of them are perfect (Nicholson and Anstice, 1999). Even thought the amount of dentalcement required is so small but clinical investigators and investigations on cement performancestill on demand in order to improve the properties of dental restorative materials. Changes in the
  14. 14. pattern of caries and the emergence of an aging, longer-lived population in many countries alsowill increase the need for the better quality, effective and durable cementing agents.Dental cement has multiplicity applications since it was ideal artificial materials that have rolesas luting agents, cavity linings and bases, and restorations for teeth thus make them perhaps themost important materials in clinical dentistry. Through available dental cement, glass-ionomerachieved the best number of application since it comes with good adhesion and ability to releasefluoride. Other clinical application of glass ionomer include in various non dental applicationsuch as ear, nose, throat surgery and craniofacial reconstruction (Nicholson, 1988).In this current age, improved formulation of glass ionomer cement have gone through deepinvestigation since it shows unique properties such as adhesion to wet tooth structure and basemetals, anticariogenic properties due to release of fluoride, thermal compatibility with toothstructure, biocompatibility and low cytotoxicity ( Moshaverinia et al., 2011). Besides, GPCs alsohave been recognized to have thermal compatibility with tooth enamel (Craig, 1997) and providea better clinical retention of non-carious cervical restorations as compared with conventionaladhesives (Peumans et al., 2005). From the clinical point of view, this cement has ability to self-hardening, chemically bonded to dental tissues, excellent translucency thus suitable for severalapplications in the dental practice.Currently, there are four major dental restorative materials being used in the field of dentistrysuch are: amalgam, resin composite, conventional glass ionomer cement (CGIC), and resin
  15. 15. modified GIC (RMGIC). CGIC and RMGIC are classification of GIC. Several comparisonsamong these materials are shown on table below: Table 1: Comparison among dental restorative materials (Jun Zhao,2009)Properties Dentin Amalgam Resin CGIC RMGIC compositeCompressive 297 310 ~ 445 280 ~ 390 235.6 212.7Strength(MPa)Tensile 98.7 27.3-54.7 32.0 ~ 63.8 8.7 ~ 12.9 12.6 ~ 14.2Strength(MPa)Flexural 212.9 119-146 61.4 ~ 139.4 11.1 ~ 31.4 71.1 ~ 82.1strength(MPa)Wear Resistance - 0.3 0.8 1.8 1.2(nm/cycle)Biocompatibility - Controversial Poor Good MediumSetting Time - 2~6 <1 4 <1(min)Thermal 8.3-11.4³ 22.1 ~ 28.0 25-68 <1 25Expansion(10-6·°C-1) 1.364 0 54.0 2.61 1.3 ~ 1.6 0.49 ~ 0.66ThermalConductivity(ᵒC.m2)Esthetic - Bad Good Good GoodPropertyDurability - Durable Durable Low LowJun Zhao (2009) had summarized and did several comparisons between all above materials. Idealcompressive, tensile and flexural strength of dental cement are very important to give properfunction of the cement itself. From the compressive strength, it clearly showed that amalgam has
  16. 16. the highest compressive strength compare to other. For the tensile strength and flexural strength,amalgam is significantly higher than any of current dental restorative materials. CGIC orRMGIC is much weaker than amalgam or resin composite. Amalgam show less wear resistancecompare with other restorative materials. Wear is the tribological process which could cause lossof material due to the interaction of opposing surfaces (Mair et al., 1996). The degree of weardetermines the usage of dental restoratives. For instance, GIC cannot be used for class IIrestorations because greater occlusive and abrasive wear are present in the area. However,addition of suitable type and amount of clay could decrease the wear resistance of the CGIC andRMGIC (Dowling et al., 2006).William (1987) defined biocompatibility as the ability of a material to perform with appropriatehost respond in a specific application. Regarding to health and environmental concerns, CGIC isthe best material since it have good biocompatibility than RMGIC and the other two materials.Regarding to the unique properties, GPCs can be used as an alternative for the replacement ofamalgam that susceptible to corrosion, toxicity, non-tooth coloured and non adhesive. However,GPCs face with some limitation due to brittleness, poor fracture toughness material andsensitivity to moisture in the early stages of the placement (Moshaverinia et al., 2011). Majordisadvantage of GIC is the mechanical weakness. This cement can achieve Young’s modulusvalues in the range 4-8 GPa and flexural strength between 25-35 MPa (Kenny and Buggy, 2003).GIC have inferior fracture toughness compared to amalgam and therefore limited its applicationas posterior filling material for the class I and II cavities (Lewis, 1989).
  17. 17. 1.2 Significance of the studyGlass polyalkenoate cements (GPCs) are important material for the modern clinical dentistry thatremain success until today as result of their capacity to chemically bond to the apatite mineral ofteeth, avoid second carries, inherently good adhesion and their ability to release fluoride.However as mentioned before, GPCs have limitation in terms of brittleness, poor inferiorfracture toughness and wear resistance compared to amalgams thus limited its application to low-stress bearing sites and use as filling material on front teeth only. Amalgam has been applied forquite a long time in dental clinics. But then, in oral environment amalgam are susceptible tocorrosion, non-tooth coloured and the presence of mercury in its composition bothers healthprofessionals and dental patients. This lead to a set of fundamental should be considered bydental profession to investigate alternative of restorative material to replace the application ofamalgam. Therefore, the aim of this laboratory study was to investigate GPCs associated withsufficient mechanical strength that is essential for the proper function of dental restorativesbeside to follow its setting reaction.
  18. 18. 1.3 Objectives of studyThe main objectives of this study were: 1. To synthesize and characterize GPCs with the addition of MMT. 2. To study the influence of MMT clay on the compressive strength of GPCs. 3. To investigate the influence of Na on the setting reaction of cement
  19. 19. CHAPTER 2 LITERATURE REVIEW2.1 Glass Polyalkenoate Cement (GPCs)Glass polyalkenoate cement (GPC) is also known as water based glass ionomer cement (GIC).Although named as glass ionomer cement, there is evidence that the structure of the GIC doesnot fully exhibit the properties of ionomer (Milne et al.,1997). GICs were developed in the late1960s at the Laboratory of Government Chemist, London, United Kingdom (Wilson and Crisp,1972). Figure 1 shows that GICs are composed of glass powder which is alumino-silicate glassand aqueous solution of polyacrylic acid. Figure 2.1: Classification of cement (3M ESPE in Technical Product Profile)
  20. 20. GPCs became well known in dental community due to its unique properties such are adheredirectly to tooth structure and base metals , anticariogenic due to release of fluoride (Forsten,1977), thermal compatibility with tooth enamel and dentin due to low coefficients of thermalexpansion similar to that of tooth structure minimized microleakage at the tooth–enamelinterface due to low shrinkage (Craig, 1997), biological compatibility (Sasanaluckit et al., 1993)and have low cytotoxicity (Hume et al., 1988).GPC consist of a basic glass powder and a water-soluble acidic polymer, such as poly(acrylicacid). The main structure of glass is still alumina and silica which form the skeletal bone of theglass. When glass powder mixed with water, acid degrades the network structure and releasingmetal ions that further determine the extent of crosslinking and polysalt bridge in the polysaltmatrix (De Barra and Hill, 1998). The general equation for the reaction between the glass andPAA is: as: MO. SiO2 + H2A MA + SiO2 + H2OWhere M is a metal ion such are Ca2+, Sr2+, or Al3+ within the glass and A is the conjugated baseof the acid (Noort, 1994).
  21. 21. Figure 2.2: Schematic depiction of the setting reaction of glass ionomer cements (3M ESPE in Technical Product Profile)Once basic glass fillers and acidic poly(acryliclic acid) solution are mixed together, the outerlayer of filler particle reacts with the acid via neutralization and involves initial formation ofcalcium or strontium polyacrylate and later formation of aluminium polyacrylate (Beata et al.,2007) Multi-charged cations (Al3+ and Ca2+) are then released from the glass particles. Thesereleased cations are chelated by the carboxylate groups and crosslink with PAA chain (Kennyand Buggy, 2003). The COO− groups and the released Al3+ and Ca2+ ions enables cross linkingof these chains, giving a solid network around the glass particles. The binding of the COO−groups with Ca2+ ions from the enamel occur and form a chemical bond between the cement andthe tooth structure (Tjalling et al., 2006). Reaction involved is acid-base reaction where glassbeing a base in sense that it accepts protons from acid even though it is not soluble in water. The
  22. 22. number and type of anions and cations released from the glass particle will determine the extentof cross linking in polysalt matrix (De Barra, 2008).However, GPC also consists of unreacted glass particle in that complex matrix which includecalcium and aluminium polyacrylates (Crisp et al., 1974) in the form of inorganic network. Thisnetwork has been suggested to be responsible for maturation process that will lead to theincreasing of compressive strength and binding water into the structure (Nicholson, 1988).GIC is known to contain fluoride and there are very extensive literatures on fluoride release fromGIC. Fluorides are used to prevent caries and secondary caries. Secondary caries rarelydeveloped adjacent to silicate cement restorative fillings. The leached fluoride is taken up by thatadjacent enamel to reduce secondary caries formation (Guida et al., 2002). Glass ionomercements release fluoride ions and the effect of the released fluorides on bacteria metabolism hasbeen reported (Hoszek et al., 2008). Noriko and Miroslav (2010) has been reported that therelease of fluoride ions from glass ionomer cements that associated with titanium can begenerated or recharged by the use of solutions of high fluoride concentration and can becontinued for longer than a year.The properties of cement formed depend on the glass composition, powder size, polyacidconcentration, polyacid molar mass and the reaction time. Some researchers conclude that theproperties of the set of cement can be explained entirely by the formation of ionically crosslinked
  23. 23. polymer chain. However, the exact relationship between the composition of the glass and theseproperties is not yet fully understood (De Maeyer et al., 2005).For glass with sodium, Na content, the resulted cement likely to have disportionate influence onits properties ( De Barra and Hill, 1998). Na usually added to lower the melt temperature duringmanufacturing process. However, glass with higher amount of sodium content will hadopalescent apprearance and promotes phase separation during quenching from the melt. Hill etal. (1995) have shown that crosslinking in polysalt matrix for cement based on sodiumcontaining glasses was disrupted, thus facilitating diffusion and exchange of fluoride ions forhydroxyl ion.Reduction in the powder particle size of up to 10 mm will result in a smoother surface. Withregard to surface roughness, it is considered that the smoother surface discourages the occurrenceof defects (such as cracks and flaws) that cause stress concentrations and ultimately promotes thefracture resistance (Mitsuhashi et al., 2002).2.2 Setting Reaction of GPCsSetting reaction of cement is significant for the development of glass materials for their correctapplication in dentistry. There are some issues among the researchers on how the setting reactionmechanism takes place. Some researchers believe that there are three steps could lead to
  24. 24. complete setting reaction (Nicholson et al., 1998). Firstly, the acid degrades the glass structureand leading to release of cations such Ca2+ and Al3+. Secondly, step is rapid reaction betweenCa2+ and Al3+ ions and polyacid chain. These reactions enable more gradual release of latter ionfrom anionic complex. The latter can act as a network modifier by forming Si-O-Na or Si-O-Cabonds, thus breaking down the silica network and rendering the glass more basic. Furtherreaction of metal ions will result crosslink between metal ions and polyacid. The bivalent andAl3+ ions that are leached from the glass form a metal polyalkenoate gel, which acts as a bindingmatrix in the cement (De Maeyer et al., 1998). Thirdly, the reconstruction of the silicate networkof that associated with maturation of glass to yield a matrix of increasing strength, greaterresistance and improved translucency (Matsuya et al., 1996).Another theory of setting reaction is discussed by Wilson and McLean (1988) where they foundthat the setting within cement occurs via two steps mechanism. The primary step is hardeningstep after glass and aqueous polyacid mix each other about 3-5 minutes. Through FTIR study,Crisp and Wilson (1974) assigned that a calcium salt was formed leading to gelation at initialstep. From study of Cook (1983) suggested that Al3+ ions are also involved in the initial settingreaction. The presence of aluminium in the glass structure is important to create negative sites tobe attacked by polyacid. Disintegration of glass release Al3+ ions that will enter the tetrahedronsilicate network and leave a net negative charge on the structure (Nicholson et al., 1998). Despitefrom this, Nicholson et al., (1998) also mentioned that even though Al3+ released early in theinitial setting, a delay and formation of aluminium polyacrylate species is depend on thedecomposition of the aluminium in the aqueous solution. The secondary mechanism is post-
  25. 25. hardening steps. This step is involves the formation aluminum salt species and contribute to theimprovement of mechanical properties that measured relative with time.Glass composition is a major factor that influences the setting reaction. Since GPCs were easilymanipulated, the composition such Al2O3/SiO2 ratio can be varied prior to specific application.Other than that setting reaction also depend on the temperature, storage medium, and storagetime. Tjalling et al.(2005) study was investigated the influence of temperature on the settingtime. Increase in temperature will speed up the setting reaction significantly. Their study provedthat working and setting time decreased with increasing temperature showed by rheometer. Itwas concluded that a temperature between 333 and 343K almost sets conventional GIC’s oncommand. Work done by Roemhildt et al.(2006) verify the previous work as the working timedecreased progressively: 28.2, 14.2, 8.6, 6.3, and 4.4 min, with increasing temperature. Similarly,the setting time decreased: 64.4, 27.5, 17.92, 12.8, and 10.2 min, as the temperature increased.The rate of setting can be affected by the particle size of the glass. A glass with finer particlesizes will set faster and have a shorter working time (Nicholson et al., 1998); that is timeindicates the end of moldability without damage to the developing cement structure (Driessens etal., 1995). Water also the main constituent in setting reaction of glass. As setting continues,water hydrates the matrix. The hydration is important in the formation of a stable gel structureand building the strength of the cement.There are several acceptable techniques have been used to characterize setting reaction of cementsuch as MAS-NMR spectroscopy (Prosser et al., 1982), Fourier transform infrared spectroscopy(FTIR) (Nicholson et al., 1988), Raman spectroscopy (Young et al., 2002), pH study
  26. 26. (Stamboulis et al., 2004), X-ray Diffraction (XRD) (Robert and Atul, 1980) analysis andTransmission Electron Microscopy (TEM) (Hatton and Brook, 1992).The advantages of MAS-NMR spectroscopy are it can probe the structure of amorphous glassesand determine the molecular structure, environment of species and their next neighbors. TheNMR data verified phase purity, specify one molecule per asymmetric unit and provide an initialstructural model including relative stereochemistry and molecular conformation of the glasscement formed (Aliev and Law, 2007). The most important MAS-NMR can show that A13+ ionwas tetrahedrally coordinated by oxygen in theoriginal glass, but a part of the A13+ ion wasoctahedrally coordinated after hardening to form Al polyacrylate gel. In the initial glassaluminium is mostly present in a four coordination or tetrahedral state, Al(IV), and switches to asix coordination or octahedral state, Al(VI), when crosslinking the polymeric chains (Matsuya etal., 1996). Figure 3 illustrates the aluminium coordination in each environment that is Al(IV) inglass and Al(VI) in cement.
  27. 27. Figure 2.3: Schematic representation of aluminium coordination states in glasses and GICs (Munhoz et al., 2010)The A13+ ions leached into the cement matrix form aluminium carboxylate species (Pires et al.,2007). Besides, by using MAS-NMR, Si measurements also can be used as an indirect structuralprobe, since the chemical shift of the silicon nucleus is dependent on the connectivity of itstetrahedral structure and number of aluminium atoms in their second coordination sphere(Engelhardt and Koller, 1994).From FTIR, we could determine setting reaction by assigning particular peaks that develop dueto acid-base reaction. Crisp S et al.(1974) suggested FTIR studies revealed a calcium salt wasformed during the early stage of reaction. However, this kind of technique only suitable for semi-quantitative analysis since the loss of carbonyl group absorption band from the carboxylic acidgroup during the neutralization can be masked by the asymmetric COO salt band (Nicholson et
  28. 28. al., 1988). The FTIR result also could indicate the structural change of pattern in the silicatenetwork of the glass. The absorption band between 1350 and 800 cm-1 moved toward higherfrequency for longer aging time and finally achieve a maximum around 1060 cm-1 with ashoulder at 950 cm-1.pH also can be used to indicate the neutralization reaction between glass and polyacids.However, pH study was not use widely (Crisp and Wilson, 1974). For XRD and TEM analysis,its serve better understanding of the setting reaction within GPCs. With using XRD, change inphase composition that is expected to continue over a much longer period of time can beobserved. From TEM, we could see the existence of the inorganic network that important toexplain the fact that glass forming-elements such as silicon have been found throughout thematrix (Hatton and Brook, 1992).2.3 Hardening and Maturing of GPCsHardening of GPCs is based on the crosslinking of released metal cations such as Ca2+ and Al3+with PAA. This also lead to the reconstruction of the silicate network of the glass (Nicholson, etal. 1998). This network consist of Si-O-Si bonds which is four-fold coordinated aluminum haspartly replace Si to form Si-O-Al network as A13+ ions leached from the glass. The new formednetwork in silica serves negative sites and become available as attack site by an acid (De Meyeret al.,1988). This step also known as gelation where the reaction promotes subsequent leachingof the glass modifier cations into the cement matrix. Depend on the glass composition, some
  29. 29. cations such Na+ and Ca2+ can be released from the glass and this will form other networks suchSi-O-Na or Si-O-Ca. As a result, another Si network will break and causes the glass becomemore basic and able serves another negative charge. A13+ ions that are leached from the glassupon acid will further attack react with the polyacid anion to form a metal polyalkenoate gel orpolymer interconnected by the cations. Barry et al. (1979) showed that the leaching of Al3+ fromthe glass particles is more difficult than Ca2+. Thus, polyalkenoate forms stronger bonds withtrivalent (A13+) than with bivalent (Ca2+) ions, which then form more mobile bond and lesssolvated Ca2+ ion (Nicholson et al., 1998)In initial hardening, GPC undergo maturation rapidly as a result from bond reconstruction. Thegel formation could occur within several minutes. From the FTIR, the Ca 2+ cations formcarboxylates immediately during gelation, Al3+ cations only react with the polymeric chainslater, during maturation (Matsuya et al., 1996). Recent work by Pires et al. (2007) on the settingchemistry of commercial glass–ionomer cement showed the existence of three different Alspecies in the glass particles that had different leaching characteristics. Thus, faster leaching offive and six coordinated Al species takes place and causes Al3+ in four coordinate environmentsis more resistant to acid attack. Despite from this, the study proved that it is not only Al3+ fromfour coordinate environments is leached into the cement matrix. As previously reported byMatsuya et al. (1996) Al3+ also comes from five and six coordinate environments. Part ofaluminium ions leached into the cement matrix and formed aluminium carboxylate species.Gradual reconstruction in the cement matrix is leading to the increase of compressive strengthwhich arises gradually over some period time to a maximum value as explained by Wilson and
  30. 30. McLean, (1988). Glass ionomer typically can reach a compressive strength of 180-220Mpa atone day and may rise over time. Translucency is also change and become more like natural toothmaterial as a result of maturing (Billington and Williams, 1991)2.4 FTIR technique analysisThe setting reaction of glass ionomer can be investigated according to infrared spectroscopy dueto the structural hardening of cement as glass react with polyacid solution. To see the changepattern of absorption band, the original powder of the experimental cement must be comparedwith the glass produced with different aging time. According to Matsuya et al.(1996) theabsorption of original powder of the experimental cement is totally different with glasses thathave been produced. Original glass powder had a maximum absorption is around 920 cm-1.However, the maximum tended to shift toward higher frequency with time, and finally the broadband showed a maximum at 1050 cm–l with a shoulder at 950 cm-1. At early stage of the reaction,a strong absorption band was observed at 1730 cm-1. This absorption due to the C=O stretchpeak. Then, as time elapsed, a new band appeared around 1620 cm-1, and its intensity rapidlyincreased within 1 hour (Matsuya et al., 1996). During the reaction also, the C=O stretch peakdecrease in intensity as the acids are neutralize with glass (Tomlinson et al., 2007). Anotherfeature is the maximum of a broad band between 1350 and 800 cm-1 moved toward higherfrequency with time, and finally the band showed a maximum around 1060 cm-1 with a shoulderat 950 cm-1. The spectral pattern was quite similar to that of hydrated silica gel, which had a
  31. 31. strong band around 1050cm-1 due to the Si-O-Si stretching vibration (Hanna and Su, 1964) and amedium band at 950 cm-1 due to Si-OH deformation vibration (Soda , 1961). This was happendue to the increasing of degree of polymerization during the hardening.Then, in terms of silicate network, characteristic band appeared around 1000 cm-1 was thenshifted toward high frequency relative with time. The same fact also ever revealed by Soda(1961) and Efimov (1996) where the strong band between 1000 and 1200 cm-1 in the spectrapresent due to the characteristic of the asymmetric stretching vibration of Si-O. These result alsosupported by Matsuya et al. (1996) in which band profile can be observed within this range andstated that the absorptions near 1180 cm-1 and between 1018 and 1073 cm-1 both originate fromthe asymmetric Si-O stretching. The appearance of the band near 800 cm-1 and the decrease ofthe band intensity near 730 cm-1 were related to the Al and other extraneous ions from the silicanetwork, resulting in a shift of the symmetric Si-O stretching vibration band (Farmer et al.,1979).As water also the main constituent in the formation of GPCs, the intensity of H-O-H bendingpeak also appear at early of setting reaction (Nicholson et al., 1998). Band near 1640 cm-1 thatappears after leaching is caused by the bending vibration of water (Davis and Tomozawa, 1996).De Maeyer et al. (1998) whose work with variety types of acid degradable glasses, they foundthat intensity of this band vibration is higher for the glasses exhibiting significant modificationsof the Si-O band profiles. Water is probably included in the sample, since it apparently cannot beremoved by drying (De Maeyer et al. 2002).
  32. 32. 2.5 Compressive strength of GPCsThere are four important mechanical properties need to be determined such hardness,dimensional stability, compressive and flexural strength. Compressive strength testing is widelyused for evaluating brittle material such as glass ionomer cement. Loof J et al.(2003) alreadystated the necessary for mechanical properties according to ISO standard 4049 and 9917.International standard 4049 specifically designed for composite and 9917 for dental evaluationfor GIC. These test were done by using an INSTRON Universal instrument which associatedwith flattened stainless steel discs on the top and bottom of sample to compensate determinedheight and diameter cylindrical GIC.Based on Loof et al. (2003), mechanical strength depends on important parameter that is thegrain size of the filler. A smaller filler grain size such microsize gives the higher hardness thancoarser. Besides, it also could improve the dimensional stability due to the lower expansion. Finegrain size yielded expansion in the interval 0-0.1% compared with coarse grain size with 0.1-0.2% interval after 4 month. This study was also had been investigate the compression strengthfor different form of GPC. GPC with fine grain size filler have compressive strength to be 300MPa and with coarse grain size to be 160 Mpa.To investigate mechanical properties such compressive strength of cement, Lucksanasombool etal. (2002) developed a study to set GIC for different time setting before exposure to aqueous
  33. 33. environment. Some GPC have been used and the result is invariant strength obtained with agingtime of GIC. Previously, Couston (1981) also did some condition of aqueous environment andobtained increase in compressive strength as aging time become longer. However, Cattini-Lorente et al.(1993) come with their statement that compressive strength probably due to thewide variation in GIC composition itself as they work in various commercial GIC.Cattani-Lorente et al. (1993), studied the mechanical properties of GICs when stored in water atdifferent time aging. They found four different pattern changes of the mechanical properties forvarious type of GIC found when stored in water as the function of time. They are an increase instrength to an upper limit value, a gain in strength over a period of 2 or 6 months, followed bydecrease, a continuous decrease in strength with time, and an invariable strength of GIC. Thisstudy also concluded the strengthening of GIC with time resulted from the influence ofcrosslinking in polymer matrix and build up of a silica gel phase, whereas weakening resultedfrom the erosion and the plasticizing effect of water.There were many other factors that influence compressive strength of GIC. Nicholson et al.(1998) studies reported cement has various compressive strengths depend on the concentration oflactic acid used to form the cement. They also reported that the inorganic network that develop insilicon glass also responsible in maturation processes which will lead to increment incompressive strength.
  34. 34. In contrast with this statement, De Barra and Hill (1998) reported the existence of inorganicnetwork do not have significant influence and might be it need to be balanced against the otherstrong evidence for the important of the polymer component on the mechanical properties. Theexposure to aqueous environment has been shown to have deleterious effects on the mechanicalproperties of GIC relative to the disturbance of Al3+ ions activity, which play a major role incrosslinking polymerization of the PAA (Kobayashi et al., 2000). Crosslinking reaction is acontinuous process evident by the increase in mechanical properties of the cement with time.Polymer has been shown to influence the toughness of the set cement (Wilson, 1972). CHAPTER 3 MATERIALS AND METHODS3.1 MaterialsTwo types of glass formulation were used in this study labeled as LG3 and LG66. Both of theseglasses were prepared at the Imperial College, London. The glass consists of silica (SiO2),alumina (Al2O3), phosphorus pentoxide (P2O5), calcium oxide (CaO), calcium fluoride (CaF2),and sodium oxide (Na2O). The mole percent of the glasses composition were shown below. Table 3.1: LG3 and LG66 composition in mole percent, %.Glass Code SiO2 Al2O3 P2O5 CaO CaF2 Na2O
  35. 35. LG3 33.3 22.2 11.1 22.2 11.1 -LG66 33.3 22.2 11.1 17.8 11.1 4.4The medical grade freeze-died PAA (Mw~80,000) was used for cement preparation and wassupplied by Advance Healthcare, Kent, England. Ethanol, liquid nitrogen and distilled waterwere used throughout the experiment in propose to dehydrate the cement, terminate settingreaction, and as reaction medium respectively.3.2 Methodology3.2.1 Preparation of glassBoth glass powders were prepared in the required amounts. The glasses were produced bymelting the reagents: silica (SiO2), alumina (Al2O3), phosphorus pentoxide (P2O5), calcium oxide(CaO), calcium fluoride (CaF2), and sodium oxide (Na2O) in a platinum/rhodium or mullitecrucible at high temperature between 1300-1550⁰C for 2 hours. The resulting melts were rapidlypoured into water. The glass frit was collected and dried overnight in an oven at 100ºC. The glassfrit produced was ground by using Gyro Mill (Glen Creston Gyro Mill, Middlesex, England) andsieved to a fine particle size of less than 45 μm for preparation of GPCs (Zainuddin N et al.,2009).
  36. 36. 3.2.2 Synthesis of GPCs The preparations of the cements were divided into two parts: 1) GPCs without MMT clay 2) GPCs with MMT clayGPCs without MMT clayBoth types of cement were formed by mixing the glass with poly(acrylic acid) and distilled waterwith fixed ratio 2:1:1. For example, 0.5g of glass mixed with 0.25g of PAA and 0.25g of distilledwater. The mixtures were mixed homogenously and allowed to set at 37 C in the oven for 1 hour.The cement was then soaked in water at 37C in the oven for the required ageing time. Timeintervals were used to study the setting reaction of the GPCs: 5 minutes, 10 minutes, 15 minutes,30 minutes, 1hour, 6 hours, 1 day, 7 days, 14 days and 28 days. For cements were with agingtime less than 1 hour, termination of the reaction was done by using liquid nitrogen followed bydehydration with ethanol. Then, the cements were ground to fine powder for FTIR analysis.
  37. 37. GPCs with MMT clayThe determination of the optimum amount of MMT can be loaded to the glasses was studied.The weight percent of MMT clay was correlated with the total amount of glass and PAA. Theweight ratio used in this study is shown in Table 3.2 such below: Table 3.2: Weight ratio of glass, PAA, MMT clay and water Glass LG3/LG66 PAA MMT clay water 2 1 0.5, 1.0, 1.5, 2.5wt% 1It was found that the best ratio of MMT can mix with GPCs is 2.5 wt%. Above this value, thecement will face the difficulties in mixing. Similar procedure was done as preparation of GPCswithout MMT.3.3 Characterization of GPCs3.3.1 X-Ray Diffraction (XRD)XRD is a non-destructive analytical technique for identification and quantitative measurementfor various phases. Recognition of amorphous or crystalline phase of GPCs with and withoutaddition of MMT was determined. XRD pattern was obtained by automated ShimadzuDiffractometer XRD-6000 model by continuous scanning at rate 2º/min.
  38. 38. 3.3.2 Thermal Gravimetric Analysis (TGA)Thermogravimetric analysis is an experimental technique to investigate the behavior and stabilityof material as function of temperature. Thermal stability of glass LG3, LG66, MMT clay, PAAand GPCs were analyzed. TGA analysis was obtained using a computerized Perkin-ElmerThermal Analysis system. Thermograms were recorded from room temperature to 800ºC atheating rate 1°C/min and nitrogen gas as sample purge gas.3.3.3 Compressive Strength TestThe compressive test of the cements was done on the cylindrical specimens. The cement wasmixed and packed in a mold with 6 mm height and 4 mm diameter. Two blocks of stainless steelwere used to compress cement compactly. The resulting cement was allowed to set for 1hour at37⁰C inside the test mould in the oven. Then, the cement was kept in water for 1 to 28 days priorto compressive test. The diameter and length of each specimen were first measured with amicrometer. The specimen was placed between steel plates of INSTRON compressive machine.The specimen was tested with 5kN load cell at a loading rate of 1 mm/min.
  39. 39. 3.3.4 Fourier-Transform Infrared (FTIR)Study on the setting reaction of the cements was done using FTIR spectroscopy. FTIR spectra ofthe GPCs, MMT and PAA were recorded in the range 200-4000 cm-1 by using Perkin ElmerFTIR spectrophotometer associated with UATR accessory. CHAPTER 4 RESULT AND DISCUSSIONIn this study, GPC phase was determined by X-Ray Diffraction (XRD) analysis. The settingreaction of GPC was done by using Fourier Transform Infrared Spectroscopy (FTIR). Thecompressive strength of GPC was evaluated by INSTRON compressive machine. The last,thermal stability of GPC, MMT and PAA were characterized by computerized Perkin-ElmerThermal Analysis.4.1 Analysis of X-Ray Diffraction (XRD)
  40. 40. XRD is an analytical technique for identification of various crystalline forms or known as‘phases’. The X-ray diffraction studies were conducted on GPC without and with addition ofMMT.Figure 4.1 and 4.2 show the XRD pattern for LG3 glass cement and LG66 glass cementrespectively. All pattern show the broad peak that represent the non- crystalline amorphousphases. Amorphous is the condition where the atoms arranged in a random order. This findingwas similar with Wood and Hill (1991) which mentioned that alumina glasses will exhibit thebroad peak in XRD profile. Previous study by Zainuddin N (2009) was also revealing the sameXRD pattern for both glasses.From the entire XRD pattern, there were no significant difference between LG3 cement andLG66 cement. Similar pattern was observed with the addition of MMT into both glasses. Thesesimilarities were probably due to small amount of MMT (2.5 wt %) in the cement formulationwhich did not influence the XRD profile of the original glass cement.
  41. 41. Intensity (a.u) With MMT Without MMT 2-Theta (Deg/°)Figure 4.1: XRD patterns for LG3 cement without and with addition of MMT
  42. 42. Intensity (a.u) With MMT Without MMT 2-Theta (Deg/°)Figure 4.2: XRD patterns for LG66 cement without and with addition of MMT
  43. 43. 4.2 Analysis of Thermal Gravimetric Analysis (TGA)The thermo gravimetric analysis (TGA) is the analytical measurement to measure the amount,rate of change in the weight and degradation of material as a function of temperature. This resultis important in providing insight into the original material structure (Wilkie, 1999). TGA thermograms were obtained by using a Perkin- Elmer Thermal Analysis system. The curves wererecorded from room temperature to 800ºC at a rate 1°C/min and nitrogen gas as sample purge gas.Figure 4.3 and 4.4 show the TGA thermogram of glasses LG3 and LG66 respectively. 100 80 Weight % 60 40 20 0 0 1 00 2 00 3 00 4 00 5 00 6 00 7 00 8 00 Temperature (°C) Figure 4.3: Thermogram for LG3 glass
  44. 44. 100 Weight % 80 60 40 20 0 0 100 200 300 400 500 600 700 800 Temperature (°C) Figure 4.4: Thermogram for LG66 glassFrom both thermogram show the original starting glass composition of LG3 and LG66. Bothglasses haven’t exhibited any decomposition until 800°C. This was happen because the firststages of decomposition of any glass usually take place at temperature 1000°C and above.
  45. 45. Figure 4.5 and 4.6 show the TGA thermogram of glasses PAA and MMT respectively. 94.1% 100 140.4°C 80 66.3% 316.5°C Weight % 60 40 15.3% 491.9°C 20 0 100 200 300 400 500 600 700 800 Temperature (°C) Figure 4.5: Thermogram of PAA 99.98% 100 36.70°C 95 90 Weight % 85 80.28% 80 291.63°C 75 70 65 100 200 300 400 500 600 700 800 900 Temperature (°C)
  46. 46. Figure 4.6: Thermogram of MMTFigure 4.17 shows the thermogram of PAA. It showed three steps of decomposition occuredduring heating PAA from room temperature to 800°C. The first decomposition was at 35-140ºCwith the weight loss of 5.9 wt%. This decomposition supports the decarboxylation reaction inPAA. Second decomposition was at 195-316ºC with the weight loss of 27.8 wt%. This wasthought to be due to anhydride formation. The third decomposition was at 315-491°C whichcorresponded to the polyacrylic anhydride formation. This yielded finding was similar withMoharram and Khafagi (2006).Figure 4.18 shows the thermogram of MMT. It clearly showed one step of decomposition duringheating MMT from room temperature to 800°C.there was no significant decomposition occurred.This could be due to the major decomposition of MMT took place at temperature higher than800ºC. This single decomposition took place at 36-291°C. The weight loss was about 19.7%corresponded to the loss of free water.
  47. 47. Figure 4.7 and 4.8 show the thermograms of both cements without MMT addition. The patternsof decomposition for both cements were similar to each other. However, the temperatures andweight loss percentage were slightly different. For LG3 cement, it initially decomposed attemperature of 49°C whereas LG66 cement at temperature of 63.52°C. Same situation happenedat high temperature. Both thermograms show two major decompositions. First, it was due to thewater contains that produced during setting which at range 49-151°C. Second, it was due to PAAthat involve in the reaction which at range 401-508°C. It may be due to the similarity of theglasses. The only difference in these two glasses was the presence of Na2O in LG66 glass.Therefore, both of glasses showed similar decomposition.Figures 4.9 and 4.10 show the thermograms of cements with addition of MMT. Both cementsundergo almost similar decomposition. The temperature and percentage of decomposition atcertain stage did not change significantly. Similarly, thermograms still showed two majordecompositions as cement without addition of MMT. This situation might be due to the littleamount of MMT in the cement formulation (2.5 wt% of glass powder and PAA) which actuallydid not influence the thermal properties of the cement formed.
  48. 48. 110 99.80% 49.00°C 100 90 Weight, % 80.45% 401.73°C 87.31% 80 139.16°C 70 65.63% 60 504.54°C 50 100 200 300 400 500 600 700 800 Temperature, °C Figure 4.7: Thermogram of LG3 glass without addition of MMT 110 98.01% 100 63.52°C 90Weight, % 78.39% 85.11% 80 402.35°C 151.15° C 70 60 63.30% 507.59°C 50 100 200 300 400 500 600 700 800 Temperature, °C
  49. 49. Figure 4.8: Thermogram of LG66 glass without addition of MMT 110 99.79% 46.00°C 100 90Weight, % 77.85% 84.43% 406.16°C 80 144.58°C 70 60 63.03% 509.60°C 50 100 200 300 400 500 600 700 Temperature, °C Figure 4.9: Thermogram of LG3 glass with addition of MMT 110 99.52% 45.77°C 100 90Weight, % 78.39% 85.25% 402.98°C 80 149.60°C 70 60 63.71% 506.27°C 50 100 200 300 400 500 600 700 Temperature, °C
  50. 50. Figure 4.10: Thermogram of LG66 glass with addition of MMT4.3 Compressive strength of GPCsCompressive strength of GPCs is due to the maturing and hardening reaction. The invariantstrengths are very dependent on the aging time. Many literatures state that the compressivestrength was increase with longer aging time. The compressive fracture strength calculated usingthe formula such below; P = 4F 2The unit is MPa. F is the load at fracture force in Newton (N) and D is the average diameter ofthe specimen in millimeters (mm).It is well known that GPCs increase in strengths in water with time due to constant salt-bridgeformations (Wilson and McLean, 1988). This investigation examined the effect of aging on thecompressive strength of glass cement without and with the addition of MMT. On the whole, bothcements gave a sharp increase of compressive strength as time elapse. It was due to thehardening reaction that took place allow the water uptake for hydrates to fill up the porosity ofthe cement to yield high strength of cement (Lea, 1970).
  51. 51. In this study, compressive strengths for both GPCs were determined within 4 time interval ataging time: 1 day, 7 days, 14 days and 28 days. The compressive strengths of the GPCs fromLG3 cements and LG66 cements without and with addition of MMT as a function of time areshown in the Table 1 and Table 2. The increases of compressive strengths are clearly shown onFigure 4.13 and 4.14.Figure 4.13, the compressive strength of LG3 cements increased rapidly in 14 days period.Without addition of MMT, LG3 cements can achieve maximum strength up to 53.55 MPa whilewith addition of MMT the maximum strength achieved 74.21 MPa. Figure 4.14, the compressivestrength increased slowly between 1 to 7 days aging time. However, rapid increase ofcompressive strength happens after 7 days and continued even after 28 days aging time. Withoutaddition of MMT, LG66 cements can achieve maximum strength up to 53.24 MPa while withaddition of MMT the maximum strength achieved 66.16 MPa. The maximum compressivestrength of LG66 cements was slightly lower than LG3 cements that were 66.16 and 74.21 MParespectively.
  52. 52. Table 4.1: Compressive strength of LG3 cement as a function of timeSetting aging time LG3 cement without LG3 cement with Strength increment MMT MMT % 1 day 38.86 42.6 8.78 7 days 51.61 66.32 22.18 14 days 52.55 74.21 29.19 28 days 53.55 64.16 16.54 Table 4.2: Compressive strength of LG66 cement as a function of timeSetting aging time LG66 cement without LG66 cement with Strength increment MMT MMT % 1 day 10.38 25.15 58.73 7 days 19.81 51.61 61.62 14 days 37.00 52.55 29.59 28 days 53.24 66.16 19.53
  53. 53. 80 With MMTCompressive Strength, MPa 70 Without MMT 60 50 40 30 0 5 10 15 20 25 30 Aging Time, Day Figure 4.13: Compressive strength of LG3 cement without and with addition of MMT 80 70Compressive Strength, MPa 60 50 40 30 20 10 0 0 5 10 15 20 25 30 Aging Time, Day Figure 4.14: Compressive strength of LG66 cement without and with addition of MMT
  54. 54. This study found that the addition of MMT to the GPCs increased the compressive value andenhanced the mechanical properties as well. It was due to the property of MMT itself that able toact as filler by intercalation reaction and fill in the layer within GPCs. The hydrogen bond thatformed between acid and MMT layer also may influence the increase of strength of the GPCs.According to Drowling et al. (2006), the formation of hydrogen bond occurred betweencarboxylic acid group and amine group of ADA-MMT have a greater reinforcing effect on themechanical properties of the material system to which they have been added. The amount ofMMT used that is 2.5 wt% also suitable for both glasses in cements formation. Drowling et al.(2006) highlighted that MMT addition with excess of 2.5 wt% cause in difficulty to mix with theglass.The composition of glass strongly influences the interaction in the cement. The 4.4 mole% ofNa2O might cause the differences interaction in the LG66 cements formation. Small quantities ofsodium in the glass composition have a disproportionate influence on cement properties and mayaffect compressive strength (De Barra and Hill, 1998). When comparing the trends ofcompressive strength for both cements, it was found that LG3 cements showed rapid increasewithin 14 days. After 14 days, the compressive strength became slightly lower. For LG66cements, the compressive strength continually increases even after 28 days. It shows that thesetting reaction of LG3 cements were faster than LG66 cements. This situation most likelyrelated to the alkali metal anions leaching process. The presence of sodium in LG66 cementsinfluence the setting reaction and the dissolution chemistry. Sodium ions have tendency toslower the setting reaction by competes with major interchange crosslinks such calcium andaluminium cations to bind with carboxylate group of PAA. At initial period of aging time,
  55. 55. sodium may disrupt the crosslinking in the polysalt matrix by delaying the crosslinking of metalcations (Al3+ and Ca2+) with carboxylate group. This causes the calcium and aluminium cationsunable to crosslink with the carboxylate group. However, this situation only temporary and takeplace at early stage of reaction. Sodium has mobile properties to move freely and have tendencyto leave the carboxylate group (Akinmade and Hill, 1991). Therefore, after sodium released fromcarboxylate group, calcium and aluminium cations will be available and replace the crosslink andinfluence the compressive strength. Similar finding was obtained by De Barra and Hill (1998). Intheir study, they found that the influence of sodium content glasses give significant reduction incompressive strength at early stage of reaction and became considerably reduced as aging timeincrease.Both cements exhibit different value in compressive strength at certain aging time. Thehydrolytic instability may rise in silicate structure for LG66 cement rather than LG3 cement.According to De Barra and Hill (1998), sodium content glasses would be expected to promotehydraulic instability in the cement. In GPC formation, it showed that aluminium is the primarycomponent that contributing the strength of GPC. The sufficient aluminium ion that able tocrosslink gives effect to the full crosslinking (Leon et al., 2007).In other case, the compressive strength of LG66 cement is too weak without MMT as filler.From the observation, the surface of this glass cement was virtually wet and too soft at early timeafter mixing. However, it becomes slightly hard as time elapse. Again, this situation was due tothe composition of the glass. Sodium obviously affected the working and setting time of the
  56. 56. cements. Despite from this, LG66 glass cement could reach almost the same value ofcompressive strength at 28 days aging time. This might be due to the degree of crosslinking forboth cement almost same at this aging time.The result of mechanical strength demonstrates both of these experimental cements havepotential to be used in application of dental restorative. However other properties such wearresistance, hardness, dimensional stability and flexural strength should be considered as well.
  57. 57. 4.4 Study on setting reaction of GPCs by using FTIR SpectroscopyFigure 4.13, 4.14 and 4.15 shows the infrared spectra of LG3, LG66 and PAA respectively. 100 80 % Intensity 60 Si-O (Si) 40 Stretch 20 0 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber, cm-1 Figure 4.13: Infrared spectrum for LG3 glass 100 80 % Intensity 60 40 Si-O (Si) Stretch 20 0 4000 3500 3000 2500 2000 1500 1000 500 1 Wavenumber, cm- Figure 4.14: Infrared spectrum for LG66 glass
  58. 58. 100 80 % Intensity 60 40 O-H COOH 20 0 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber, cm-1 Figure 4.15: Infrared spectrum for polyacrylic acid, PAAFigure 4.13 and 4.14 show major absorption band between 1050 – 980 cm-1 that provideinformation about the presence of asymmetric Si-O(Si) stretch vibration in the glass. This bondis the major bond in the glass network. The minor absorption bands develop at lower frequenciesis not really important but it can become some evidences to support the other compound thatpresent on glass composition. Such, band intensity near 730 cm-1 are may related to the Al, Caand/or ions from the silica network. Band between 850 – 500 cm-1 due to extraneous ion suchCa2+ and Na+ that incorporated in glass phase (Farmer et al., 1979). Even though LG66 glasshave slightly different composition with LG3 glass, but these spectrum were still unable toconfirm the differences. As observed, glass spectra have almost no important band at frequencyabove 1250 cm-1.
  59. 59. In Figure 4.15, strong band with medium width occurred in the region 1700 – 1660 cm-1 displayspeaks attributed to the C=O stretching vibration. The broad absorption near 3200 cm-1 to 2400cm-1 gives information of acidity character. This stretch peak was very broad due to hydrogenbond in PAA.4.4.1 Setting reaction of GPCs without MMT additionGPC formation involves acid base neutralization reaction. Acid come from aqueous PAA whilebase come from aluminosilicate glass. It also known as water base reaction since water took partas the medium of the reaction. The reaction initiated by the reduction of metallic ions from theglass and causes siliceous hydrogel layers form on the surface of the glass. Associated with thecontinuous reaction, the metal ions crosslink with the conjugated base of the acid and resulthardening and maturing process. Cross linking of these ions result the formation of a primarypolysalt matrix within the set cement (Matsuya et al., 1996).
  60. 60. The setting reaction of the GPC can be followed by FTIR spectroscopy. Figure 4.16 shows theIR spectra of LG3 cement without MMT with aging time 5 minutes to 28days.Figure 4.16: Infrared spectra of LG3 cement without MMT addition with aging time from 5 minutes to 28 days
  61. 61. Figure 4.16 showed the noticeable change pattern of infrared spectra for LG3 glass and itscements. For original glass, there was only one absorption peak between 1050 – 980 cm-1. After5 minutes aging time, two new peaks already developed. The peak appeared between 1710 –1390 cm-1. The appearance of this peak was due to the formation of COO-M+ from the crosslinking of metal ions with carboxylate group. Another peak present as a shoulder at previousasymmetric Si-O(Si) stretch of original glass. This peak at region 900 cm-1 corresponds to theformation of hydrated silica gel (Si-OH). The change of absorption pattern between 1200 – 900cm-1 were related to the evaluation of band as cement formed (Matsuya et al., 1984, 1996). Thestretching vibration observed at 1650 cm-1 due to the binding vibration water that appeared afterthe leaching (Davis and Tomozawa, 1996). Peak at region 3700 to 2400 cm-1 came from O-Hstretch.As time elapsed, the shoulder peak at 1570 cm-1 became increase in intensity. This was due toformation COO-M+ became increase as metal ions (Al3+ and Ca2+) crosslink with the carboxylgroup in the acid (Crisp and Wilson, 1974). In contrast, the intensity of shoulder peak at 1710cm-1 became decrease in intensity. This was because H+ from acid was taken by silica network toform silica gel layer during the cross linking of metal ions and COO - in cements formation.
  62. 62. Figure 4.17: Infrared spectra of LG66 glass without MMT addition with aging time from 5 minutes to 28 days
  63. 63. Figure 4.17 showed the noticeable change pattern of infrared spectra for LG66 glass and itscements. For original glass, there was only one absorption peak between 1050 – 980 cm-1.Generally, the absorption peaks of LG66 cements were similar with LG3 cements. Two newpeaks developed after 5 minutes set of cements. The peak appeared between 1710 – 1400 cm-1.The appearance of this peak was also due to the formation of COO -M+ from the cross linking ofmetal ions with carboxylate group. Another peak present as a shoulder at previous asymmetricSi-O(Si) stretch of original glass. This peak at region 900 cm-1 corresponded to the formation ofhydrated silica gel (Si-OH). The change of absorption pattern observed between 1200 – 900 cm-1and the stretching vibration at 1650 cm-1 were also same with LG3 cements. Peak at region 3700to 2400 cm-1 came from O-H stretch.As time elapsed, the shoulder peak at 1550 cm-1 became increase in intensity. This was due toformation COO-M+ became increase due to the cross-linking in the cement matrix (Crisp andWilson, 1974). In contrast, the intensity of shoulder peak at 1710 cm-1 became decrease inintensity. This was because H+ from acid was taken by silica network to form silica gel layerduring the cross linking of metal ions and COO- in cements.
  64. 64. Both infrared spectra showed the most significant changes especially at early stage of reaction.Setting reaction of LG3 cements is considerably faster than LG66 cements. Both change patternscan be seen clearly between 5 minutes to 10 minutes. As aging time increases, the patternsbecome almost similar. COOH absorption band almost become weak in intensity after 7 daysaging time. This could be due to the fast rate of crosslink of polycarboxylic acid by Ca2+ ion and/or Al3+ within 7 days and thus reducing the COOH intensity of the acid. New band that indicatethe formation of COO-M+ already appeared at 5 minutes aging time. This situation alsocontributed to the gelation of the carboxylate to form hard surface. For both glasses, the intensityof COOH and COO-M+ peaks remains constant after 7 days. This shows that there arepossibilities that cross-linking between metal ions and conjugated base from acid have beencompleted after 7 days setting aging time. During the setting reaction, silica gel and cross-linkingreaction take place simultaneously.From both figures, it clearly showed that during the setting reaction, the absorption band between1100 to 900 cm-1 became unnoticeable as aging time increased. This broad peak moved towardhigher frequency with increase of aging time, and finally the band showed a maximumaround1100 cm-1. The formation of hydrated silica gel caused the condensation of Si-OH bond toform Si-O-Si with around surface of glass being siliceous. The spectral pattern was quite similarto that of hydrated silica gel that proposed by Hanna and Su (1964). Their finding also obtainedthat spectra of GPC had a strong band around 1050 cm-1 due to the Si-O-Si stretching vibration.This fact also supported by Soda (1961) where a medium band around 950 cm-1 was due to Si-
  65. 65. OH deformation vibration. The intensity of Si-O-Si showed no significant changes after 10minutes of setting reaction for LG3 cement and 30 minutes of setting reaction for LG66 cement.It may due to water molecules in glass network were completely eliminated after this desiredaging time. Similar result was reported by Berzins D et al.,(2010). In their study, they found thatthe broad peak centered around 1600 cm-1 show that water was the most abundant decompositionproduct during the reaction between glass and PAA.During hardening and maturing stage, metallic ions typically bind to polyanions via carboxylategroups. The initial cross linking achieved because the more readily available metal ions. Rapidreaction results the formation of hard surface within few minutes from the start of mixing.However, the different composition of metallic ion is leading to the difference of the time taken.LG66 glass contains sodium. According to De Barra and Hill (1998), small quantities of sodiumare likely influence the cement properties. This was because sodium ions have tendency tocompete with other ion like calcium and aluminium cations and inhibit the crosslinking process.Therefore, the presence of sodium will increase the working time. LG3 cements set more rapidlycompare than LG66 cement due to absence of sodium in LG3 glass. The rate of setting for LG3cement and LG66 cement were relatively different when compared at early stage of reaction.From the infrared spectra also, it was clearly showed that the intensity of COO -M+ and COOHpeak significantly different at 5 minutes aging time.From Figure 4.18, at 5 minutes aging time for LG66 cement, the absorption band thatcorresponds to formation of COO-M+ is relatively weak at region 1600 – 1400 cm-1. That mightbe due to the delay reaction of cross linking due to the presence of sodium. This is also the main
  66. 66. reason why the working time in this stage is too slow and GPCs formed have low compressivestrength. The development of shoulder peak on asymmetric Si-O(Si) stretch is also observed butthe absorption still very weak. The setting reaction of LG66 cement seemed slower than LG3cement. It is because even at 10 minutes aging time, the intensity of COO-M+ stretching vibrationstill relatively weaker than LG3 glass at the same aging time. As mentioned earlier, this happenmight be due to the sodium ion that acts to delay setting reaction. Sodium ions have tendency tocompete with other ion like calcium and aluminium cations and may inhibit the crosslinkingprocess. LG3 Intensity, % LG66 Wavenumber, cm-1Figure 4.18: Comparison of FTIR spectra of LG3 cement and LG66 cement without MMT at 5 minutes aging time
  67. 67. 4.4.2 Setting reaction of GPCs with MMT additionFigure 4.19 shows the spectrum for MMT. MMT showed major broad absorption bands around1260 cm-1 to 730cm-1 that corresponded to the structural bending mode (Farmer, 1974). Figure4.20 and 4.21 show FTIR spectra for LG3 and LG66 glass without and with addition of MMT at5 minutes aging time. A slight difference between spectrum of both cements without MMT andwith MMT was the shoulder peak at 920 cm-1 that corresponded to hydrated silica gel. Withaddition of MMT, this peak is seemed hardly to observe. The intensity of this peak was verysmall compared with glass without MMT. This may have been because of hardening reactionthat took place. Cements with MMT easily to form hard surface and less working time comparethan cements without MMT. 100 80 % Intensity 60 40 20 0 2000 1800 1600 1400 1200 1000 800 Wavenumber, cm-1 Figure 4.19: Infrared spectrum of MMT
  68. 68. % Intensity With MMT Si-O(Si) Without Si-O(H) MMT 2 0 0 0 1 8 0 0 1 6 0 0 1 4 0 0 1 2 0 0 1 0 0 0 8 0 0 Wavelength, cm-1Figure 4.20: Infrared spectra of LG3 glass with and without addition of MMT at 5 minutes With MMT % Intensity Si-O(Si) Without Si-O(H) MMT 2 0 0 0 1 8 0 0 1 6 0 0 1 4 0 0 1 2 0 0 1 0 0 0 8 0 0 Wavelength, cm-1 Figure4.21: Infrared spectra of LG66 glass with and without addition of MMT at
  69. 69. 5 minutes CHAPTER 5 CONCLUSION AND RECOMMENDATION5.1 ConclusionThe compressive strength for both GPCs were improved with the addition of MMT. For GPCsfrom LG3 glass, the maximum compressive strength can be achieved was 74 MPa. Without theaddition of MMT it only can achieve 53 MPa. GPCs from LG66 glass gave maximumcompressive strength 66 MPa with addition of MMT and 53.24 Mpa without addition of MMT.It proves that MMT able to act as filler by intercalation reaction within GPCs. The formation ofhydrogen bonding also provides the great effect on the compressive strength.The setting reactions of GPCs were followed by FTIR spectroscopy. For both GPCs, theabsorption band around 1700 cm-1 that represents COOH decreased in intensity. While theintensity of absorption band around 1540cm-1 that represent COO-M+ peak increased with time.It was due to the H+ from acid was taken by silica network during the cross linking of metal ionsand COO- crosslink with metal cations in cements formation. The peak located at region 900cm-1corresponded to the formation hydrated silica gel (Si-OH). In conclusion, the setting reaction ofGPCs from LG3 glass was faster than GPCs from LG66 glass. It was due to the presence ofsodium ion in LG66 glass that disturb the crosslinking process in the cement formation.
  70. 70. 5.2 RecommendationThis study has highlighted the use of FTIR technique to study the setting reaction of the GPCs.However, another technique that equivalent to study this setting reaction also can be used inorder to optimize the finding.For the future work, the setting reaction can be followed by using MAS-NMR spectroscopy. Thistechnique enables us to probe the structure of amorphous glasses and determine the molecularstructure. Other than that, the changes in silicate network structure can be observed as thetetrahedral state, Al(IV) switches to octahedral state, Al(VI).Another recommendation is to study different type of modified MMT in order to increase themechanical strength of the GPCs.
  72. 72. 300200 Intensity (a.u)100 0 20 30 40 50 60 2-Theta (Deg/°) XRD pattern for LG3 glass cement without addition of MMT
  73. 73. 300200 Intensity (a.u)100 0 20 30 40 50 60 2-Theta (Deg/°) XRD pattern for LG3 glass cement with addition of MMT
  74. 74. 3 00 Intensity (a.u)2 001 00 0 20 30 40 50 60 2-Theta (Deg/°) XRD pattern for LG66 glass cement without addition of MMT
  75. 75. 300 Intensity (a.u)200100 0 20 30 40 50 60 2-Theta (Deg/°) XRD pattern for LG66 glass cement with addition of MMT
  78. 78. 1 day 7 days 14 days 28 days40.48 50.21 52.25 58.3237.98 55.44 51.37 51.1331.23 50.61 53.68 53.3745.76 50.17 52.48 50.1738.85 51.62 52.97 54.7638.86 51.61 52.55 53.55 Compressive strength of LG3 glass without addition of MMT Compressive strength of LG3 glass with addition of MMT1 day 7 days 14 days 28 days39.78 70.62 77.51035 69.5044.97 71.82 65.33787 63.2745.42 64.15 71.17567 64.8647.48 66.91 75.60180 61.7235.35 58.10 72.42 61.4842.60 66.32 72.41 64.16
  79. 79. Compressive strength of LG66 glass without addition of MMT1 day 7 days 14 days 28 days10.39 30.03 39.43 55.289.72 18.23 37.44 52.1611.74 21.68 38.54 50.609.34 15.33 32.60 54.9010.71 13.80 36.99 53.2610.38 19.81 37.00 53.24 Compressive strength of LG66 glass with addition of MMT 1 day 7 days 14 days 28 days 24.78 50.21 52.25 68.39314 23.68 55.44 51.37 61.18370 23.56 50.61 53.68 64.40073 26.98 50.17 52.48 47.58641 26.75 51.62 52.97 70.67623 25.15 51.61 52.55 66.16
  81. 81. 100 80 60 Intensity,% 40 20 0 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber, cm-1LG3 glass without addition of MMT at 5 minutes setting reaction
  82. 82. 100 80 60 Intensity,% 40 20 0 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber, cm-1LG3 glass without addition of MMT at 28 days setting reaction
  83. 83. 100 80 60 Intensity,% 40 20 0 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber, cm-1LG66 glass without addition of MMT at 5 minutes setting reaction
  84. 84. 100 80 Intensity,% 60 40 20 0 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber, cm-1LG66 glass with addition of MMT at 28 days setting reaction
  85. 85. 100 80 60 Intensity,% 40 20 0 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber, cm-1 LG3 glass
  86. 86. 100 80 Intensity,% 60 40 20 0 40 0 0 35 0 0 30 0 0 25 0 0 20 0 0 15 0 0 10 0 0 5 00 Wavenumber, cm-1 LG66 glass
  87. 87. 100 80 60 Intensity,% 40 20 0 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber, cm-1 PAA
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