Crystallization and Adsorption Behavior in Bio Derived

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Crystallization and Adsorption Behavior in Bio
Derived Polymers

• D. Savin, S. Murthy, University of Vermont
• NEGCC University of Maine 31 May 2006

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Crystallization Studies of PE-PEG Graft
Copolymers
P. R. Mark, G. Hovey, and N. S. MurthyPhysics
Department, University of VermontK.
Breitenkamp, M. Kade and T. EmrickDepartment of
Polymer Science and Engineering,University of
Massachusetts, Amherst
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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

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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

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Tm vs. Grafted PEG Length
25 repeats
50 repeats
100 repeats
The full line is initial heat . This is followed
by cooling shown in dotted lines. The last
reheated scan is shown in dashed line
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Dependence of Tm on PEG chain-length
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
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Small-angle X-ray Scans of Homo- and Co-polymers
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
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Ambient X-ray Diffraction Scans
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Variable Temperature X-ray Diffraction Scans 50
Repeats of PEG
Domain sizes are retained upon heating and
cooling
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Changes in the cell-dimensions (a- and b- axes)
of the PE domains
Dark circles heating, Light circles - cooling
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Effect of hydration
(a)
(b)
(a) 25 repeats of PEG
(b) 50 repeats of PEG.
The data show that PEG domains dissolve in
water The process is reversible
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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
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Adsorption of PLA and PCL-Based Block Copolymers
K. Murphy, J. Mendes, D. SavinDepartment of
Chemistry, University of Vermont
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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

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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

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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

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Synthesis of Copolymers
Procedure from Ahmed, F., Discher, D. J.
Controlled Release. 96(1), 2004, 37-53
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Block Copolymer Characterization
PEO114-PLA209
PEO114-PLA70
PEO114-PLA29

• MeO-PEO macroinitiator
• from Aldrich
• As MW increases,
• systematic decrease in Ve
• Block copolymer pdi 1.1

TGA shows nearly quantitative agreement between
theoretical and observed weight fractions
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Dynamic Light Scattering
The scattered intensity at time (t) is correlated
with the scattered intensity at time (t t).
Plot of G vs. q2 is linear with slope Dm
Concentration 0.01 (w/w)
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Micelle Formation
Systematic decrease in aggregate size with
increasing hydrophilic fraction
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Block Copolymer Adsorption

• Since fungal spores are so large, DLS is
  ill-suited for their characterization
• PS colloids as a model hydrophobic interface
• Adsorption is a 2-step process
• Micelle adsorption
• Restructuring

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Colloid Characterization
scale 100 nm
scale 100 nm
scale 200 nm
Colloidal PS from Bangs Laboratories
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Adlayer Thickness vs wPEO
PEO114-PCL22 wPEO 0.65



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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