Molecular mobility and the thermomechanical properties of chitosan films

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Molecular mobility and the

thermomechanical properties of

chitosan films

Joana F. Fundo

1

_{, Mafalda A.C. Quintas}

1,2

_{Cristina L. Silva}

1

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CATÓLICA PORTO

BIOTECNOLOGIA



Consumers’ awareness of environmental issues related with packaging

 Limited availability of Petroleum

Why use Edible Films?



Consumers’ demand for healthier and more convenient foods (e.g.

minimally processed foods)

 Changes in retailing practices and/or in way of life force the development

of convenient food products with longer shelf-life

 Driving force to use of biodegradable biopolymers

from renewable sources

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Why Molecular Mobility in Edible Films?

 Edible films are partially crystalline partially amorphous materials

 Interesting physical properties

 Good models for other food systems

 The molecular mechanisms that control functionality in polymeric films are

poorly understood

 Specially in edible materials where water plays an important role as

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Methodology

– preparation of films

Chitosan

(1, 2 and 3% w/v) Glycerol

(10, 50 and 90% w/w)

1% lactic acid solution

Solvent Casting

40º C until equilibrium

RH = 53% and T= 22ºC

FILMS

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Methodology

– characterization of films

Y = A₁ exp (-X/T2gly) _{+ A}

2 exp (-X/T2water) + Y0

Bruker AVANCE III 300 MHz

sample relaxation time was determined (T2) : - glycerol component (T2gly)

- water component (T2water)

Free Induction Decay and Spin Spin Relaxation

NMR Measurements

Film Characterization

• Water Content

• Water Activity

• Chitosan and Glycerol Content

ASTM D 882-91 (1991)

Mechanical Properties

Instron universal testing machine -elongation at break (EB)

- tensile strength (TS)

Thermal Analysis

- glass transition temperature (Tg) - Crystallinity (melting ∆h)

DSC TA-60WS

Scan from -150 to 200ºC 20ºC/min

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Results

– characterization of films

FFS

Films

Chitosan (mg/g film)

Glycerol (mg/g film)

1%10%

388

11 1%50%

196

32 1%90%

158

48 2%10%

357

13 2%50%

172

30 2%90%

164

37 3%10%

388

15 3%50%

182

46 3%90%

196

53 Glycerol Content in the Film Forming

Solution is responsible for the Chitosan

Content on the obtained film!

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Results

– characterization of films

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0 1 2 3 4 T hic k nes s of t he obt ained film (m m )

Film Forming Soultion Chitosan Content (%w/w)

90% 50% 10%

Chitosan Content in the Film Forming Solution

is responsible for films thickness

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Results

– characterization of films

90% 50% 10% 0 50 100 150 200 250 300 350 400 450 0.00 0.05 0.10 0.15 0.20 0.25 0.30 C hit os an (m g/ g film ) Thickness (mm)

Films with same composition have significantly

different thickness!

Structure of the polymeric matrix?

- Crystallinity

- Water Content

- Free Volume

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Results

– NMR water and glycerol mobility

10%

90%

50%

90%

50%

3%

2%

1%

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Results

– Characterization of films

3%

2%

1%

Moisture content

10%

90%

50%

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Results

– Mobility vs Moisture Content

0.E+00 1.E+03 2.E+03 3.E+03 0 10 20 30 40 50 60 Relax ation time w ater component (ms) Moisture Content (%) 90% 50% 10%

Different Moisture Content and same mobility:

Water is linked to polymer chains and cannot move?

Same Composition different

mobility:

differences in the film

structure?

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0.480 0.500 0.520 0.540 0.560 0.580 0 10 20 30 40 50 60 W ate r ac ti v ity Moisture content (%)

Results

– Mobility vs Water Activity

0.E+00 1.E+03 2.E+03 3.E+03 0 10 20 30 40 50 60 R elax at ion tim e w at er c om ponent (m s ) Moisture Content (%) 90% 50% 10%

Constant T2 for different aw

Samples with high Chitosan and very low Glycerol content.

Lower crystallinity

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Results

– Mobility vs Moisture Content

0.E+00 5.E+02 1.E+03 2.E+03 2.E+03 3.E+03 3.E+03 0 10 20 30 40 50 60 R elax at ion tim e w at er c om ponent (m s ) MC (%) 3% 2% 1%

For films with the same

thickness, water mobility

correlates with MC!

Increasing Chitosan

Increase strength of the

polymer-water bonds?

Water with high mobility:

Looser polymeric network?

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Results

– Characterization of films

10%

90%

50%

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Results

– Mobility vs Crystallization

0.E+00 1.E+03 2.E+03 3.E+03 -350 -300 -250 -200 -150 -100 -50 R elax ation t im e w ater c om pon ent (m s ) ∆h (J/g) 90% 50% 10%

Increasing Thickness

Increasing Chitosan

0.E+00 5.E+02 1.E+03 2.E+03 2.E+03 3.E+03 3.E+03 -350 -300 -250 -200 -150 -100 -50 0 R elax at ion tim e w at er c om ponent (m s ) ∆h (J/g) 3% 2% 1%

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Results

– characterization of films

10%

50 and 90%

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Results

– Mobility vs Glass Transition

0.E+00 1.E+03 2.E+03 3.E+03 -100 -50 0 50 R elax at ion tim e w at er c om ponent (m s ) Tg(ºC) 90% 50%

10%

_{Molecular mobility at room temperature}

decreases with increasing glass transition

temperature

Differences in structure for films with

similar composition

Same behaviour for films

with similar thickness

Behaviour suggests the

increase of mobility with

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Results

– characterization of films

10%

Mechanical properties

50%

90%

50%

90%

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Results

– Mobility vs Elongation at Break

0.E+00 1.E+03 2.E+03 3.E+03 0 20 40 60 80 Rela x a tio n tim e w a te r com p o n e n t (m s) EB (%) 90% 50% 10%

EB much lower than films with similar composition:

Antiplasticization phenomenon

Increasing Thickness

0.E+00 5.E+02 1.E+03 2.E+03 2.E+03 3.E+03 3.E+03 0 10 20 30 40 50 60 70 Rela x a tio n tim e w a te r com p o n e n t (m s) EB (%) 3% 2% 1%

Films with similar thickness ALSO

do not present a clear tendency.

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Results

– EB vs Crystalinity

90% 50% 10% -400 -300 -200 -100 0 0 10 20 30 40 50 60 70 ∆ h (J /g) EB (%)

Superplasticization?

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Results

– Mobility vs Tensile Strenght

0.E+00 1.E+03 2.E+03 3.E+03 0 2 4 6 8 10 12 14 R elax ation t im e w ater c om pon ent (m s ) TS (MPa) 90% 50% 10%

Tensile Strength increases with

decreasing molecular mobility

Stronger molecular interactions make

the film “harder to break”

Antiplasticization BUT:

TS does not increase

(crystallinity was of the same level )

Super plasticization(?):

TS is higher than expected

Same behaviour for films

with similar thickness

Behaviour suggests the

increase of mobility with

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Conclusions

 Films composition is governed by the amount of plasticizer in the FFS

 Film Thickness

 Is governed by the chitosan content in the FFS

 Correlates with Moisture Content ; Crystallinity and Elongation at Break

(affected also by the film composition)

 Water and Glycerol Mobility is the result of the combined effect of composition and

structure of the film

 Water molecular mobility correlates differently with MC, ∆h and EB

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Conclusions

 Films composition

 Governed by the amount of plasticizer in the FFS

 Film Thickness

 Governed by the chitosan content in the FFS

 Water and Glycerol Mobility

 Result of the combined effect of composition and structure of the film

 Water Molecular Mobility

 Increases with MC of films with the same thickness

 Decreases with crystallinity of films with the same thickness

 EB correlates with crystallinity of films with the same composition

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