Preparation and Characterization of Polymer TiO 2 Hybrid Nanocomposites Via In-situ Polymerization

Transcription

1 Preparation and Characterization of Polymer TiO 2 Hybrid Nanocomposites Via In-situ Polymerization Feng Lin, Leonardo C. Simon Institute for Polymer Research, Department of Chemical Engineering University of Waterloo, 200 University Av. W., Waterloo, ON, Canada, N2L 3G1 lsimon@uwaterloo.ca;

2 Abstract Polymer nanocomposites have important applications in automotive and aerospace, electronics and electrical engineering, household products and appliance components, packaging, and defense systems. Among many nanocomposite precursors, TiO 2 nanopowder is being increasingly investigated due to its specific properties. This poster will discuss the preparation characterization of hybrid polymer-tio 2 nanocomposites. When dispersed at the nanoscale level, TiO 2 nanopowders can act as visually transparent UV filters and high mechanical performance materials. Unfortunately, the dispersion of nanoscale TiO 2 in hydrophobic polymers, like polyolefins, is difficulty to obtain because most of the TiO 2 available from commercial sources has agglomeration of primary nanoscale particles forming secondary particles in the micrometer range. The objective of this research is to prepare hybrid nanocomposites using in-situ polymerization. The synthesis strategy involved two steps. Firstly, TiO 2 was modified with 3- (trimethoxysilyl)propylmethacrylate. The grafting density and efficiency were quantified and the particle size distribution and dispersibility characteristics in suspension were measured. Secondly, styrene was polymerized using free radical mechanism to attempt copolymerization with groups on the surface of the modified TiO 2 resulting in the formation of nanocomposites with polymer chains chemically bonded to the surface of TiO 2 nanopowders. The final polymer nanocomposites structure and properties have been and are being investigated.

3 TiO 2 Surface Characteristics Introduction H O H O O H H O Ti Ti Ti Ti Ti e Basic and acidic Strong photo-oxidizing power Ti Ti OH OH O H H [O]. HO. HO 2 Low visible absorption but high UV adsorption Highest refractive index High dielectric constant Ti + X _ Figure 1 The principal surface features of a TiO 2 particle

4 Size Dependent Phenomena of Nanoparticles High surface to volume (S/V) ratio High activity Discrete electronic structure Size induced conductive-nonconductive transition phenomena Do not scatter light significantly Magnetic moment per atom increases with the decreasing size of a particle No large stress build-up Synthesis methods of Polymer TiO 2 Nanocomposites Direct mixing Sol gel process In-situ polymerization

5 Properties of Polymer TiO 2 Nanocomposites Increase in elastic modulus polyimide nanocomposites was around 30% at 9% nano-tio 2 loading over its microcomposites (Chiang, Thin Solid Film, 2004,147, p359) 3-7% of nano TiO 2 was effective to increase the degradation temperature of polybenzoxazine-based nancomposites by C and the effect of titania on flame resistance was also remarkable (Agag, Polymer, 2004, 45, p7903) Transparency but strong UV adsorption was observed for polyvinyl alcohol nanocomposites up to 35% TiO 2 loading (Nussbaumer, Macromol. Mater. Eng., 2003, 288, p44) Refractive index of PVL nanocomposites rose linearly from for neat PVL to at 35% TiO 2 (Nussbaumer, Macromol. Mater. Eng., 2003, 288, p44) Electrical breakdown strength of nanotio 2 -filled LDPE nanocomposites was 50% higher than that for micro-filled (Ma, J Mater. Res.,2004,19,857) Dielectric constant of nanotio 2 -dispersed polyimide hybrids increased with the increasing titania content (Chiang, Thin Solid Film, 2004,147, p359)

6 Overcome three challenges Use two-step strategy Objective Synthesize polymer-tio 2 nanocomposites acting as visually transparent UV filters and improved mechanical performance materials i) Strong tendency of particle agglomeration ii) Hydrophilic TiO 2 is incompatible with hydrophobic polymers iii) Photoactivity of TiO 2 make polymer degrades Step 1 Preparation and characterization of modified TiO 2 Step 2 Synthesis and characterization of TiO 2 nanocomposites by in-situ polymerization

7 Modification of TiO 2 by MPS Experimental Premixed TiO 2 with ethanol under ultrasonic Added NH 4 OH, H 2 O, MPS, hydrolysis at R.T. ; condense at evaluated temp. Purified and dried after reaction Polymerization of PS-TiO 2 Nanocomposites Dispersed the modified TiO 2 in styrene under ultrasonic Well sealed and purged with N 2 after adding initiator AIBN Free radical polymerization carried out at 60 o C by using a shaker Ethanol precipitated the polymer Centrifuge fractionated the nancomposite gel from the homo-ps

8 Methodology for Modified TiO 2 and Polymer Nanocomposites Characterization and Testing FTIR Chemical composition of modified TiO 2 and nanocomposites 1 H-NMR Quantification of grafting by MPS in modified TiO 2 BI-DCP sizer----- Particle size distribution of modified TiO 2 in ethanol Vis Dispersibility of modified TiO 2 in toluene TGA Quantitative polymer grafting on TiO 2 in nanocomposites DMTA Thermal and Mechanical properties of nanocomposties UV-vis Optical properties of nanocomposites SEM Morphology of modified TiO 2 and nanocomposites

9 Reaction Mechanism Results and Discussions O H + RO X R CH=CH2 Ti Modifier with two functional ends Ti Modification O X R CH=CH2 Polymerization Monomer Polymer TiO 2 nanocomposites Ti Figure 2 Reaction mechanism scheme for the deposition of modifier on TiO 2 surface and the formation of polymer TiO 2 nanocompoistes

10 FTIR Spectra of modified TiO (C=C) 1704 (C=O) 1030 (T i -O-Si ) (C-H) Wavenumber (cm -1 ) Figure 3 FTIR spectra of (red)pure TiO 2 ; (green)pure MPS; and (black) MP S-mo dified TiO 2

11 Quantification of Grafting by MPS SGD (µmol/m 2 ) g/l TiO2 20g/l TiO2 50g/l TiO SGD (molecules/nm2) 1 20g/l TiO Content of MPS (wt%) Figure 4 Surface Grafting Density vs Weight Ratio of MPS to TiO 2

12 How to calculate SGD Figure 5 1H-NMR spectrum of one sample supernatant after centrifuging the modification reaction mixture ( ρ M *V Mo /M WM ) - (V O /V S )*( P D / P M )*((a+b)/c)*( ρ D *V D /M WD ) SGD =10 6 µmol/m 2 * W T * S T ( ρ M *V Mo /M WM ) - (V O /V S )*( P D / P M )*((a+b)/c)*( ρ D *V D /M WD ) =6.023*10 5 molecule/nm 2 W T * S T

13 Quantification of Grafting by MPS 20 Conversion (100%) Content of MPS (wt%) 50g/l TiO2 20g/l TiO2 Figure 6 Surface Grafting Conversion (SGC) vs Weight Ratio of MPS to TiO 2 ( ρ M *V Mo /M WM ) - (V O /V S )*( P D / P M )*((a+b)/c)*( ρ D *V D /M WD ) SGC =100%* ( ρ M *V Mo /M WM )

14 Particle Size of modified TiO 2 in ethanol Particle Size (nm) Unmodified TiO2 TiO2 (50g/l) modified by 0.02 mol/l MPS in ethanol TiO2 (50g/l) modified by 0.04mol/l MPS in ethanol TiO2 (50g/l) modified by 0.08 mol/l MPS in ethanol TiO2 (50g/l) modified by 0.16 mol/l MPS in ethanol TiO2 (20g/l) modified by 0.02mol/l MPS in ethanol TiO2 (20g/l) modified by 0.04mol/l MPS in ethanol TiO2 (20g/l) modified by 0.08mol/l MPS in ethanol TiO2 (20g/l) modified by 0.16 mol/l MPS in ethanol Content of MPS (wt%) Figure 7Average Particle Size vs Weight Ratio of MPS to TiO 2

15 Dispersibility of modified TiO 2 in toluene 3.5 Absorbance (W aveleng th:550nm ) unmodified TiO2 modified TiO2 by 40w t% MPS sedimentation time (min) Figure 8 Dispersibility of unmodified and modified TiO 2 in toluene

16 Morphology of modified TiO2 in toluene a b Figure 9, SEM micrographs of (a) unmodified TiO2 ( severe agglomeration ) (b) modified TiO2 by MPS ( light agglomeration )

17 FTIR Spectra of PS TiO 2 Nancomposites Transmittance Figure 10 FTIR spectra PS-TiO2 Nanocomposites (PSTN) sediment of PSTN supernatant of PSTN Homo-PS Modified TiO2 by MPS Wavelength (nm -1 )

18 TGA of PS TiO 2 Nanocomposites Weight (100%) Figure 11 TGA Unmodified TiO2 Modif ied TiO2 HomoPS PSTN containing 1%TiO2 before fractionation PSTN containing 1%TiO2 after fractionation PSTN containing 4.5%TiO2 before fractiionaton PSTN containing 4.5% TiO2 after fractionation PSTN containing 19.5%TiO2 before fractionation PSTN containing 19.5%TiO2 after fractionation Temperature ( o C)

19 Quantification of PS grafting on TiO Grafted PS on TiO2(wt%) TiO 2 Content in PSTN (wt%) Figure 12 PS grafting efficiency vs TiO 2 concentration

20 T d of PS TiO 2 Nanocomposites Figure 13 Degradation Temp. HomoPS Deriv. Weight (%/min) PSTN containing 1% TiO2 before fractionation PSTN containing 1%TiO2 after fractionation PSTN containing 4.5% TiO2 before fractionation PSTN containing 4.5% TiO2 after fractionation PSTN containing 19.5% TiO2 before fractionation 9 PSTN containing 19.5% TiO2 after fractionation Temperature ( o C)

21 Morphology of PS TiO 2 Nancomposites Figure 14 SEM graphs of PSTN containing 1% TiO 2 (left) Mag. 200,000x; (right) Edx

22 Optical Properties of PS-TiO 2 Nanocomposites Figure 15 UV Spectra Homo-PS PSTN containing 1%TiO2 PSTN containing 4.5%TiO Figure 16 UV Spectra PSTN containing 1% TiO2,taking Homo-PS as reference ABS 0.4 ABS 0.8 PSTN containing 4.5% TiO2, taking Homo-PS as reference Wavelength (nm) Wavelength (nm)

23 Conclusions Modified TiO 2 and PS-TiO 2 Nanocomposites were successfully prepared MPS and PS were chemically bonded on TiO 2 surface Surface grafting efficiency by MPS and PS were quantified MPS improved dispersibility of TiO 2 in nonpolar media TiO 2 of average particle size in the order of 20-50nm was embedded in PS matrix of the nanocomposites TiO 2 did not affect much the degradation temp. of the nanocomposites Relatively visible transparency but stronger UV absorption of the nanocomposites were observed up to TiO 2 contents of 1wt% Future Work Thermal and mechanical properties of nanocomposites Comparison experiments: PS TiO 2 composites made by physical mixing

24 References Agag, T.; Tsuchiya, H.; Takeichi, T.; Polymer, 2004, 45, pp7903 Baurgeat-Lami, E.B.; Lang, J.; J Colloid Interf. Sci., 1998, 197, pp293 Chiang, P.; Whang, W.; Polymer, 2003, 44,pp2249 Jesionowski, T. ; Pigment Resin Tech., 2001, 30, pp287 Ma, D.; Biegel, R.W.; Schadler, L.S.; J Mater Res., 2004, 19, pp857 Nussbaumer, R.L.; Caseri, W.R.; Tervoort, T.; Macromol. Mater. Eng., 2003, 288, pp44 Philipse, A.P.; Vrij, A.; J Colloid Interf. Sci., 1989, 128, pp121 Rong, Y.; Chen, H-Z; Wu, G.; Wang, M.; Mater. Chem. Phys., 2005, 91, pp370 Solomon,D.H.; Hawthorne, D. G.; Chemistry of Pigments and Fillers, 1983 Zhang, X.; Simon, L.C; Macromol. Mater. Eng., 2005, 290, pp573 Zhu, M.; Potschke, P.; Aldler, H-J.; Macromol. Symp., 2004, 210, pp251 Acknowledgements The authors thank the financial support provided by EMK- MMO and OGS-ST