Rigid Polyurethane Foam/Cellulose Whiskers …biorefinery.utk.edu/technical_reviews/ACS_CELL_032210...

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Rigid Polyurethane Foam/Cellulose Whiskers Nanocomposites: Preparation, Characterization and Properties

Transcript of Rigid Polyurethane Foam/Cellulose Whiskers …biorefinery.utk.edu/technical_reviews/ACS_CELL_032210...

Page 1: Rigid Polyurethane Foam/Cellulose Whiskers …biorefinery.utk.edu/technical_reviews/ACS_CELL_032210 urethane.pdfcellulose whiskers up to 1 wt% have been prepared. The well-dispersed

Rigid Polyurethane Foam/Cellulose Whiskers

Nanocomposites:

Preparation, Characterization and Properties

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Cellulose structure and characteristics

Polymeric chains of β-(1,4)-D-glucose units

Abundance - Annual biomass production of 1.5 10 tons

Renewability - Environment biocompatible products

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Macrofibril

Plant cell

Microfibril

Elementary

fibril

Fiber

Cellulose molecule

Inter- and intra-molecule hydrogen bonding

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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.

Dialysis (PEG)

Sonication

45 °C

45 min

Sedimentation

Centrifugation

Dialysis(water)

10-20 nm in diameter

100-200 nm in length

Bending strength ~10 GPa

Elastic modulus ~143 GPa

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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

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Objective-improve mechanical properties

Solar

energy

Rigid PU

nanocomposite

foam

Cellulose whiskers

Feedstock

Physical, chemical or

enzyme treatment

Other

polymers

e.g. PU

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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 (DMCHA)

Potassium octotate

Silicon surfactant

n-pentane (boiling point 36.1°C)

Sucrose Polymeric MDI

O

H

H O

H

O H

H

O H H

O H

O

H O

H O H 2 C

C H 2 O H

O H

H

H H

O

H 2 C

N C O N C O

H 2 C

N C O

n

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Preparation of pure PU foam (control)

Polyols, surfactant

and catalysts

Polymeric

MDI Self-rising Polymerization Solidification

S polyol G polyol MDI DMCHA octotate pentane surfactant

wt% 27.9 16.7 40.6 1.30 0.900 11.2 1.40

Freeze dried

whiskers in DMF

Polyols

Preparation of PU nanocomposite foam

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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% 0 0.25 0.50 0.75 1.0

Density

(kg/m3)

537.6

±5.1

414.4

± 5.1

461.6

± 5.6

535.9

± 3.3

820.1

± 5.7

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Fourier transform infrared spectroscopy

4000 3500 3000 2500 2000 1500 1000

Absorb

an

ce

wavenumber (cm-1)

control

0.25 wt%

0.50 wt%

0.75 wt%

1.0 wt%

NH NH

OC=O

CO-NH

CH3

C-O

O-CO

1732

1736 Urethane linkage

Polyether polyols

Cellulose whiskers

Interrupt H-bonding

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Whiskers and PU interactions

4000 3500 3000 2500 2000 1500

Ab

so

rba

nce

wavenumber (cm-1)

1.0 wt% nanocomposite

control + 1.0 wt% whiskers

Crosslinking happens between cellulose whiskers and isocyanates

during polyurethane synthesis.

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Tensile stress-strain curves

0 5 10 15 20 25 300.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

str

ess, M

Pa

strain, (%)

control foam

0.25 wt%

0.50 wt%

0.75 wt%

1.0 wt%

Tensile modulus

4.37 ± 0.14 MPa

Yield strength

0.316 ± 0.031 MPa

Tensile strength

0.485 ± 0.043 MPa

Changes (%):

-30.4 -34.2 -27.0

-20.6 -22.8 -21.4

36.8 15.2 13.8

227 112 99.2

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Compressive stress-strain curves

0 2 4 6 8 10 12 140.0

0.2

0.4

0.6

0.8

1.0

str

ess, M

Pa

strain, (%)

control foam

0.25 wt%

0.50 wt%

0.75 wt%

1.0 wt%

Modulus 3.29 ± 0.85 MPa

Strength 0.145 ± 0.045 MPa

66.6 29.0

118 131

180 143

Gain (%):

210 270

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Thermal stability

-50 0 50 100 150

hea

t flow

temperature (oC)

control foam 0.25 wt%

0.50 wt% 0.75 wt%

1.0 wt%

Whiskers (wt%) 0 0.25 0.50 0.75 1.0

Tg (ºC ) 88 94 100 97 97

Td (ºC ) 333 329 331 336 343

0 100 200 300 400 500 600 7000

20

40

60

80

100

weig

ht (%

)temperature (

oC)

0 wt%

0.25 wt%

0.5 wt%

0.75 wt%

1.0 wt%

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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 H bonding were developed in the nanocomposite,

and crosslinking occurred between the whiskers OH groups

and NCO groups.

A substantial improvement of mechanical properties was

obtained.

Thermal stability of the nanocomposites was also enhanced.

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Acknowledgements