Rigid Polyurethane Foam/Cellulose Whiskers. Preparation, Characterization and Properties

Transcription

1 Rigid Polyurethane Foam/Cellulose Whiskers Nanocomposites: Preparation, Characterization and Properties Yang Li, ongfeng Ren, and Arthur J. Ragauskas School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA School of Polymer, Textile & Fiber Engineering, Georgia Institute of Technology, Atlanta, GA

2 Cellulose structure and characteristics Polymeric chains of β-(1,4)-d-glucose units 12 Abundance - Annual biomass production of tons Renewability - Environment biocompatible products 1 4 Cellulose molecule C 2 C 2 n Inter- and intra-molecule hydrogen bonding Plant cell Macrofibril Elementary fibril Microfibril Fiber 2

3 Preparation of cellulose whiskers Under certain acid hydrolysis conditions, transverse cleavage happens along the amorphous regions and releases needle-like monocrystals, which refer to whiskers. 45 C 45 min Sedimentation Centrifugation Dialysis(water) Sonication nm in diameter nm in length Bending strength ~10 GPa Elastic modulus ~143 GPa Dialysis (PEG) C 2 C 2 S 3 n 2 S 4 C 2 n C 2 n n 2 3

4 Polyurethane structure Polyurethane (PU)is any polymer consisting of a chain of organic units joined by urethane links. Rigid PU foam is a highly crosslinking polymer with a closed-cell structure. Strong but with Significantly lower density Dimensional stability Thermal insulation Good adhesive properties Impervious to moisture Low cost But not as stiff as traditional materials 4

5 bjective-improve improve mechanical properties Solar energy Physical, chemical or enzyme treatment Feedstock Rigid PU nanocomposite foam ther polymers e.g. PU Cellulose whiskers 5

6 Reagents Sucrose-based polyol (S polyol), F = 4.4 Glycerol-based polyol (G polyol), F = 3 Polymeric methylene diphenyl diisocyanate (MDI), F = 2.7 Dimethylcyclohexylamine (DMCA) Potassium octotate Silicon surfactant n-pentane (boiling point 36.1 C) 2 C NC 2 C C 2 NC 2 C n NC Sucrose Polymeric MDI 6

7 Preparation of pure PU foam (control) Polyols, surfactant and catalysts Polymeric MDI Polymerization Self-rising Solidification S polyol G polyol MDI DMCA octotate pentane surfactant wt% Preparation of PU nanocomposite foam Polyols Freeze dried whiskers in DMF 7

8 Foam structure characterization Rigid PU Foams reinforced with 0, 0.25, 0.50, 0.75 and 1.0 wt% whiskers were prepared. Closed cells had a homogeneous dispersion, and cell sizes were all around 200 µm. Scale bar: 100 nm. Whisker wt% Density (kg/m 3 ) ± ± ± ± ±

9 Fourier transform infrared spectroscopy 1.0 wt% C wt% -C C- Urethane linkage ce Absorban N 0.50 wt% C= N wt% C-N Polyether polyols Cellulose whiskers control Interrupt -bonding wavenumber (cm -1 ) 9

10 Whiskers and PU interactions Crosslinking liki happens between cellulose lll whiskers hik and disocyanates during polyurethane synthesis. control wt% whiskers sorbance Abs 1.0 wt% nanocomposite wavenumber (cm -1 ) 10

11 Tensile stress-strain curves str ress, σ (M MPa) Tensile modulus 4.37 ± 0.14 MPa Yield strength ± MPa 1.0 wt% Tensile strength ± MPa control foam 025wt% wt% 0.75 wt% 1.0 wt% strain, ε (%) Changes (%):

12 Compressive stress-strain curves 1.0 stre ess, σ (MP Pa) t l f Gain (%): control foam 0.25 wt% 0.50 wt% 0.75 wt% 1.0 wt% strain, ε (%) Modulus 3.29± ± 085MP 0.85 MPa Strength ± MPa 12

13 Thermal stability heat flo ow control foam 0.25 wt% wt% 0.75 wt% 1.0 wt% 80 weight (%) wt% 0.25 wt% 0.5 wt% 075wt% wt% temperature t ( o C) temperature ( o C) Whiskers (wt%) T g (ºC ) T d (ºC

14 Conclusions Novel nanocomposites of rigid PU foam reinforced with cellulose whiskers up to 1 wt% have been prepared. The well-dispersed closed cells of different foams were all around 200 µm in diameter. Additional bonding were developed din the nanocomposite, and crosslinking occurred between the whiskers groups and NC groups. A substantial improvement of mechanical properties was obtained. Thermal stability of the nanocomposites was also enhanced. 14

15 Acknowledgements NSF PSE Fellowship program at Dr. Ragauskas group 15