Transcript Document

Crystallization and
Adsorption Behavior in
Bio Derived Polymers
D. Savin, S. Murthy, University of Vermont
NEGCC – University of Maine
31 May 2006
Crystallization Studies of
PE-PEG Graft Copolymers
P. R. Mark, G. Hovey, and N. S. Murthy
Physics Department, University of Vermont
K. Breitenkamp, M. Kade and T. Emrick
Department of Polymer Science and Engineering,
University of Massachusetts, Amherst
Polymers in Agriculture
• Water management
– Retention and release of water
• Delivery of nutrients and pesticides
– Targeted delivery to prevent runoff
• Soil management
– Prevent soil erosion
• Green platform for plant growth
– Polymer capsule for germination, growth or maturity
Motivation
• To transform commodity conventional polymers in to
green polymers by making them aqueous processible
while maintaining the properties inherent in the
backbone (PE or PET)
– Grafting PEG provides a means by which these polymers
could have aqueous processibility
• To study the crystallization behavior in these unique
copolymers as a way to control the strength and
processbility
Tm vs. Grafted PEG Length
20.0
20.0
(b)
(a)
25 repeats
PEG
PE
10.0
Exothermic Heat Flow (mJ)
10.0
50 repeats
15.0
5.0
0.0
-5.0
-10.0
PE
5.0
0.0
-5.0
-10.0
PE
-15.0
PE
PEG
-15.0
-20.0
-10
20
50
80
110
Temperature (°C)
140
170
-20.0
-10
200
20
50
80
110
140
170
200
Temperature (°C)
20
(c)
The full line is initial heat .
This is followed by cooling
shown in dotted lines.
The last reheated scan is
shown in dashed line
100 repeats
PEG
15
Exothermic Heat Flow (mJ)
Exothermic Heat Flow (mJ)
15.0
10
PE
5
0
-5
PE
-10
-15
PEG
-20
-10
20
50
80
110
Temperature (°C)
140
170
200
Dependence of Tm on PEG chain-length
80
Tm
60
40
20
0
-20
0
0.02 0.04 0.06 0.08 0.1
1/n
0.12 0.14 0.16
Nearly quantitative agreement between Tm for grafted PEG
domains upon initial heating with PEG homopolymers
Tm is the melting point and 1/n along is the reciprocal of the chain-length.
Data compiled from the information sheet from Dow Inc. for Carbowax
In te n sity (L o g S ca le )
Small-angle X-ray Scans of Homo- and
Co-polymers
0 .0 0
0 .5 0
1 .0 0
1 .5 0
2 .0 0
Q (nm -1 )
* Blue – PEG homopolymer
* PEG repeats = 25, 50 and 100 for red, orange and green respectively
* The arrows between Q = 0.25 nm-1and 1.5 nm -1 indicate the various orders
of the 15 nm lamellar spacing in PEG domain
Ambient X-ray Diffraction Scans
PEO
PE
70
PEO
PE
Intensity (Counts)
60
#1 = 25 repeats
50
40
#2 = 50 repeats
30
20
10
x10^3
12
#3 = 100 repeats
PEG
16
20
2 (Degrees)
24
28
Variable Temperature X-ray Diffraction
Scans: 50 Repeats of PEG
Intensity (Counts)
(a)
20.0
25°C
15.0
80°C
10.0
135°C
5.0
40°C
25°C
x10^3
12
16
20
24
2
(Degrees)
* Domain sizes are retained upon heating and cooling
28
Changes in the cell-dimensions
(a- and b- axes) of the PE domains
(b)
(a)
4.98
b dimension (Å)
a dimension (Å)
7.7
7.65
7.6
7.55
4.975
4.97
4.965
4.96
4.955
7.5
40
40
60
80
100
60
120
80
100
120
Temperature °C
Temperature °C
7.65
(c)
(d)
7.6
b dimension (Å)
a dimension (Å)
4.97
7.55
7.5
7.45
4.96
4.95
4.94
4.93
40
60
80
Temperature °C
100
120
40
60
80
100
Temperature °C
Dark circles – heating, Light circles - cooling
120
Effect of hydration
200
(a)
5000
150
Intensity (Counts)
Intensity (Counts)
7500
As-prepared
Wet
2500
(b)
As-prepared
100
50
Wet
Re-dried
0
10
15
20
2 (Degrees)
25
(a) 25 repeats of PEG
30
x10^3
10
15
20
2 (Degrees)
25
(b) 50 repeats of PEG.
* The data show that PEG domains dissolve in water
* The process is reversible
30
Conclusions
• PE and PEG chains crystallize into separate
domains, especially when PEG chains are long
(~ 50 repeat units), and behave like homopolymers
• PEG domains can be dissolved in water without
significantly affecting the mechanical properties of
the graft copolymer films.
Acknowledgment: We thank Dylan Butler (Physics) who assisted
in some of the data collection and analysis, and Herman Minor
(Honeywell) for the DSC data. This work was supported by an
EPA grant to NEGCC
Adsorption of PLA and PCLBased Block Copolymers
K. Murphy, J. Mendes, D. Savin
Department of Chemistry, University of Vermont
Goal: Delivery of Biopesticides
Entomopathogenic fungi:
• Used against bugs
• Safe for humans and the environment
• Leave no toxic residues
• Typically 3-10 mm
• Extremely hydrophobic
Constraints for Delivery
• Water spray application: conventional (mm)
vs. Ultra-low spray (10s of mm) drop size
• Delivery to leaf (hydrophobic) vs. soil
• Use amphiphilic compatibilizer
• Solution:
PEO-PLA and PEO-PCL block
copolymers
Uses of PEO-PLA and PEO-PCL
• PLA/PCL ‘stick’ to fungal spores
• PEO provides water solubility
• Block copolymers form micelles in solution
• PLA from BIOMASS source
• Biodegradable coating – Since PLA and PCL
have different degradation rates, release rate can be
controlled by varying relative amounts of block
copolymers in formulation
Will ultimately result in a reduction
in the amount of pesticide used
Synthesis of Copolymers
O
O
S n(oct) 2
n
+
C H 3O
C H 2C H 2O
H
o
m
O
100 C
O
CH3
C H 3O
C
C H 2C H 2O
m
CH
O
H
2n
O
P E O -P L A
O
O
S n(o ct) 2
n
+
C H 3O
C H 2C H 2O
H
o
m
C H 3O
11 0 C
C C H 2C H 2C H 2C H 2C H 2
C H 2C H 2O
m
H
n
O
P E O -P C L
Procedure from Ahmed, F., Discher, D. J. Controlled Release. 96(1), 2004, 37-53
Block Copolymer Characterization
Theoretical
Weight Fractions
Methoxy Polyethylene Oxide
wPLA = 0.42
wPLA = 0.56
wPLA = 0.59
wPLA = 0.62
wPLA = 0.74
L-Lactide
90
Weight Fraction (%)
80
70
Observed
Weight Fractions
wPLA =
wPLA =
wPLA =
wPLA =
wPLA =
60
50
40
0.44
0.56
0.58
0.62
0.77
PEO114-PLA209
RI (arbitrary units)
100
PEO114-PLA70
30
PEO114-PLA29
20
10
17
18
19
20
21
22
23
24
Elution Volume (mL)
0
0
100
200
300
400
500
600
700
Temperature (°C)
TGA shows nearly quantitative
agreement between theoretical and
observed weight fractions
800
• MeO-PEO macroinitiator
from Aldrich
• As MW increases,
systematic decrease in Ve
• Block copolymer pdi ~ 1.1
25
Dynamic Light Scattering
The scattered intensity at time (t) is
correlated with the scattered intensity at
time (t + τ).
g
 I (t )  I (t   ) 
 I 
2
 1  f ( A )  g
Concentration ~ 0.01 % (w/w)
(1)
( ) 
2
(1)
( )  e
  Dm q
 
2
Dm  Do 
* Plot of  vs. q2 is
linear with slope Dm
kT
6  o R h
Micelle Formation
fPEO
90
16000
14000
80
PEO114-PLA29
Rh = 13 nm
12000
10000
-1
 (s )
70
60
8000
6000
PEO114-PCL22
Rh = 51 nm
4000
Rh /nm
PEO114-PLA70
Rh = 53 nm
50
2000
PEO114-PLA209
Rh = 81 nm
0
40
14
1x10
14
2x10
14
3x10
14
4x10
14
5x10
2
14
6x10
14
7x10
14
8x10
-2
q (m )
30
Systematic decrease in
aggregate size with
increasing hydrophilic
fraction
20
10
0.20
PEO-PLA
PEO-PCL
0.30
0.40
0.50
wPEO
0.60
0.70
0.80
14
9x10
Block Copolymer Adsorption
• Since fungal spores are so large, DLS is illsuited for their characterization
• PS colloids as a model hydrophobic interface
• Adsorption is a 2-step process:
– Micelle adsorption
– Restructuring
Colloid Characterization
scale = 100 nm
8000
scale = 100 nm
7000
6000
Rh = 29 nm
-1
 (s )
5000
4000
scale = 200 nm
Rh = 53 nm
3000
2000
Rh = 131 nm
1000
0
14
1x10
14
2x10
14
3x10
14
4x10
14
5x10
2
-2
q (m )
* Colloidal PS from Bangs Laboratories
14
6x10
14
7x10
14
8x10
14
9x10
Adlayer Thickness vs wPEO
14
14 nm
nm
29
29 nm
nm
39
39 nm
nm
52
52 nm
nm
137
137 nm
nm
45
45
Adlayer Thickness /nm
40
40
35
35
30
30
25
25
PEO114-PCL22
wPEO = 0.65
20
20
15
15
*
*
*
10
10
55
20
20
30
30
40
40
50
50
wt
wt %
% PEO
PEO
60
60
70
70
80
80
Conclusions
* PEO-PLA and PEO-PCL block copolymers self-assemble into
micelles with a radius that increases with polymer MW
* The adlayer thickness was determined for the adsorption of block
copolymer micelles onto model hydrophobic surfaces
* For larger colloids, the adlayer thickness increases with
increasing fraction of the hydrophilic block as expected
* Smaller colloids may become encapsulated into micelles
* The adlayer thickness appears to be stable over time
Funding:
EPA X-83239001
NSF EPS-0236976