Transcript Poly(vinyl alcohol) / Cellulose Barrier Films Shweta Paralikar John Simonsen

Poly(vinyl alcohol) /
Cellulose Barrier Films
Shweta Paralikar
John Simonsen
Wood Science & Engineering
Oregon State University
John Lombardi
Ventana Research Corp.
OUTLINE
Introduction
Materials
Results and Discussion
Conclusions
Acknowledgements
Introduction
Barrier Films?
Designed to reduce/retard gas migration
Widely used in the food and biomedical
industries
Another application is as a barrier to toxic
chemicals
Chemical Vapor Barrier
To prevent the diffusion of toxic chemical vapors,
while allowing water vapor to pass through
Hydrophilic barriers to protect from hydrophobic
toxins
Should be tough and flexible
Useful in protective clothing
Materials
Poly(vinyl alcohol) = PVOH

Nontoxic, good barrier for oxygen, aroma,
oil and solvents
 Prepared by partial or complete hydrolysis
of poly(vinyl acetate)
Structure:
PVOH Water Stability
PVOH films have poor resistance to water
Crosslinking agent reduces water sorption
and the crosslinks also act as a barrier to
diffusion
Poly(acrylic acid)-PAA
Poly(acrylic acid) PAA:
Crosslinking reaction
Source: Sanli, O., et al. Journal of applied polymer science, 91( 2003)
Heat treatment forms ester linkages
Cellulose Nanocrystals(CNXLs)
CNXLs were prepared by acid hydrolysis of
cellulose obtained from cotton
Amorphous region
Native cellulose
Crystalline regions
Acid hydrolysis
Individual nanocrystals
Individual cellulose polymer
Proposed structure
PAA
PVOH
Objectives
Prepare chemical barrier films with
PVOH/ PAA/ CNXL system
To understand the chemistry and physics of this system
Select optimum time and temperature for heat treatment
Find combination which allows moisture to pass through
but restricts diffusion of toxic chemical vapors
Surface modify CNXLs to improve interaction with matrix
Methods
Film Preparation

Testing methods
Water solubility - Optimize heat treatment
Fourier Transform Infrared Spectroscopy - Bond analysis
Polarized Optical Microscopy - Dispersion
Water Vapor Transmission Rate (WVTR)
Universal Testing Machine - Mechanical properties
Differential Thermogravimetric Analysis - Thermal degradation
Chemical Vapor Transmission Rate (CVTR)
Preparation of the Blends
5 wt % solution of PVOH and PAA
1 wt % solution of dispersed CNXLs in DI water
Composition
0% CNXL
10% CNXL
20% CNXL
0% PAA
0/0
0/10
0/20
10% PAA
10/0
10/10
10/20
20% PAA
20/0
20/10
20/20
•Remaining composition of the film consists of PVOH
Film Preparation
Compositions were mixed, sonicated and then air
dried for 40 hours
The thickness of the film was controlled by the
concentration (%solids) of the dispersion before
drying
Heat treatment optimization
Evaluate via water solubility test
 At 125 °C/1 hr films were completely soluble
in water after a day
 At 185 °C/1hr color of the films changed to
brown
 At 150 °C and 170 °C/45 min films were
clear and had good water resistance
Total % Solubility after 72 hours of soaking time
% Solubility =
(Weight1  Weight 2)
*100%
Weight1
50
Lower = Better
40
30
20
10
20PAA/ 0CNXL
20PAA/ 0CNXL
10PAA/ 20CNXL
20PAA/ 10CNXL
Film
10PAA/ 10CNXL
10PAA/ 0CNXL
0PAA/ 20CNXL
0PAA/ 10CNXL
0
0PAA/ 0CNXL
Total % solubility
60
150
170
Temperature of Heat
Treatment (°C)
Fourier Transform Infrared
Spectroscopy
PVOH
PAA
Blue: Non heat treated film
Absorbance
Absorbance
Red: Heat treated film
3500 cm-1
2500 cm-1
1500 cm-1
3500
2500
Wavenumbers (cm-1)
1500
FTIR of 10% CNXL/10% PAA/80% PVOH
Red: Heat treated film
Blue: Non heat treated film
1715 cm-1
Absorbance
1723 cm-1
2500
2000
1500
1000
Wavenumbers (cm-1)
0.0
3500
3000
2500
2000
Wavenumbers (cm-1)
1500
1000
Polarized Optical Microscopy
Dispersion of CNXLs
a) 5% CNXL/ 10%PAA
b) 10% CNXL/ 10% PAA
c) 15% CNXL/ 10% PAA
Water Permeability
Water Vapor Transmission Rate
D
Test were conducted at 30°C
and 30% relative humidity
M
Mass change( g )
J ( Flux ) 
2
A * t Area(m ) * time(day )
O
H
/1
0P
A
NX
L
PV
A
10
CN
XL
/0
PA
A
10
CN
XL
/1
0P
AA
20
CN
XL
/1
0P
AA
0C
NX
L/
20
PA
A
20
CN
XL
/0
PA
A
10
CN
XL
/2
0P
AA
20
CN
XL
/2
0P
AA
0C
10
0
Flux g/m
2
day
WVTR
40
35
30
25
20
15
10
5
0
Composition
Mechanical tensile testing
27 micron thick films were cut into a dogbone
shape
Strain rate: 1 mm/min
Span: 20 mm
Stress, MPa
Stress vs Strain Curve
Strain, mm/mm
Ultimate Tensile Strength
Ultimate tensile strength, MPa
120
150 %
Increase
100
80
60
40
20
20
10
0
0
% CNXL
0
10
20
% PAA
Tensile Modulus
2.5
Almost
Double
Tensile Modulus, GPa
2
1.5
1
20
0.5
10
0
0
0
10
%CNXL
20
%PAA
% Elongation
Elongation, % mm/mm
140
120
20%
reduction
100
80
60
70%
reduction
40
0
20
10
0
0
20
10
%CNXL
20
%PAA
Toughness
50
2.5 times
increase
Energy to break, Nmm
45
40
35
30
25
20
15
10
20
5
10
0
0
0
10
%CNXL
20
%PAA
Thermal degradation
Thermo gravimetric Analysis
•Change in weight with
increasing temperature
•Test is run from room
temperature to 600°C
•Ramping 20°C/min
PAA boosts initial Tdegradation
CNXL no effect
- dW/ dT, % wt/ 0C
1.2
CNXL
1
PVOH
PAA
0.8
10PAA/0CNXL
10PAA/10CNXL
0.6
0.4
0.2
0
0
100
200
300
400
Temperature, °C
500
600
700
Chemical Vapor Transmission
Rate-CVTR
ASTM standard F 1407-99a (Standard method of
resistance of chemical protective clothing materials to
liquid permeation).
Permeant = 1,1,2 Trichloroethylene (TCE), listed in
CERCLA and EPCRA as hazardous
CVTR Assumptions
The assumptions made for the experimental
setup are as follows.
 1) Mass transfer occurs in the z-direction only, as the
lateral directions are sealed
 2) The temperature and relative humidity of the
system remains constant throughout the experiment
 3) A semi-steady state mass transfer occurs, where
the flux becomes constant after a certain time
interval
 4) The concentration of the simulant outside the film
is zero as it is swept away by the air in hood
2500
100% PVOH
2000
cumulative flow, g/m
2
flux = slope of steady state
1500
1000
breakthrough
500
time lag = intercept
0
0
20
40
60
Time, h
80
100
120
Chemical Vapor Transmission Rate
2500
Cumulative flux, g/m2
2000
100% PVOH
1500
10% CNXL/0% PAA
1000
500
10% CNXL/10% PAA
0
0
20
40
60
Time, h
80
100
120
Surface Modification of CNXLs
OBJECTIVES
To improve the interaction between CNXLs
and PVOH
To understand if the CVTR observations
are more influenced by CNXLs or PAA
Surface modification of CNXLs
TEMPO
NaBr
NaClO
CNXLs
C.CNXLs
Source: Araki et.al, Langmuir, 17: 21-27, 2001.
• Titration of C.CNXLs indicated the presence of 1.4 mmols of acid/ g
CNXLs
• Titration of PAA indicated the presence of 13.2 mmols of acid/ g PAA
1.32 mmols/g
of acid groups.
% acid groups from C.CNXLs
120
% acid groups from PAA
% Carboxylate Content
100
80
60
40
20
0
0
5
10
15
20
% C.CNXL
Acid content (mmols) of C.CNXLs+PAA = Acid content (mmols) of 10 wt% PAA
Methods
Polarized optical microscopy
Water vapor transmission
Thermal degradation
Chemical vapor transmission
Dispersion of C.CNXLs
CNXLs
C.CNXLs
10%
10%
15%
15%
Composition
Flux : g / m2 * day
20
15
10
%
C
%
C
NX
L
NX
L
/1
0
/1
0
%
PA
A
%
PA
A
%
PA
A
/0
%
PA
A
/0
%
PA
A
/0
%
PA
A
0P
VO
H
/1
0
NX
L
NX
L
NX
L
NX
L
%
C
%
C
%
C
%
C
20
15
10
10
Flux
Water Vapor Transmission Rate
40
35
C.CNXL
30
CNXL
25
20
15
10
5
0
CVTR
60
time lag CNXL
time lag C.CNXL
Time lag, h, or flux, g/m2
50
flux CNXL
flux C.CNXL
40
30
20
10
0
5% CNXL/ 10% PAA
10% CNXL/ 10% PAA
15% CNXL/ 10% PAA
Thermal degradation DTGA
CNXL
1.4
PVOH
- dW/ dT, %wt/ 0 C
1.2
PAA
10%CNXL/10%PAA
1
10%C.CNXL/10%PAA
0.8
0.6
0.4
0.2
0
200
300
400
Temperature, °C
500
Conclusions
170 °C temperature and 45 minutes of heat treatment
were found to be optimum temperature and time to
reduce dissolution of films
CNXLs were well dispersed in blend films of PVOH and
PAA up to 10% by weight content
The presence of CNXLs with PAA crosslinking
approximately doubles the strength, stiffness and
toughness, while the elongation is reduced by 20%
compared to the control (PVOH)
The CVTR experiments show a significant increase in
the time lag and reduced flux compared to pure PVOH
Conclusions
Mechanical properties not significantly different between
CNXLs and C.CNXLs
C.CNXLs show better dispersion at 15% filler loading
than CNXLs
C.CNXLs showed slightly reduced flux and increased
time lag
DTGA showed significant increase in thermal stability
Acknowledgements
This project was supported by the National
Research Initiative of the USDA Cooperative
State Research, Education and Extension
Service, grant number 2003-35103-13711.