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Mechanical Characterization of
Microfibrillated Cellulose (MFC)-poly(lactic acid)
                nanocomposites
              Application of the Concept
       of the Essential Work of Fracture (EWF)


        Jie Ding, Lech Muszyński , John Simonsen
       Department of Wood Science and Engineering
Background
         Poly(lactic acid) (PLA) and its products
  Poly(lactic acid) PLA is a versatile polymer made from
  renewable agricultural raw materials and is compostable.




                                    Applications         Known issues
                                    • disposable cups, • weak & brittle
                                      plates, containers Needs reinforcement
                                    • plastic bags
                                    • food wraps
  http://www.ecothefriendlyfrog.co.uk/pla.shtm
Background

Potential reinforcement: Microfibrillated Cellulose (MFC)

MFC are cellulosic fibrils
disintegrated from plant cell walls
(usually aggregates of microfibrils).

Typical thickness range: 20-40 nm
(aggregates), could be as small as
3-10 nm (individual fibrils)
(Svagan et al. 2007)

                                        Structure and appearance of MFC
                                        by SEM (by Jie Ding)
Background

MFC/Poly(lactic acid)(PLA) Composites

Advantages:
  Both components derived from renewable materials
  Both are environmentally friendly
     carbon neutral
     compostable
  Small addition of MFC improves strength and elastic
   modulus of PLA (Mathew & Oksman 2006)
  No satisfactory formulation commercialized to-date
Background

 Many formulations are generated in the search of “the
  perfect one “
 Prototype formulations are generated in small amounts of
  thin transparent films
 There is a need for a quick and efficient way of evaluating
  mechanical properties of new formulations
   Properties of interest
   • Strength
   • Elastic modulus
   • Toughness
Objective


Develop a quick and efficient method for
evaluating the
   strength,
   elastic modulus and
   toughness
in thin transparent polymer films.
εyy
Approach                                   0.032


We have successfully applied non-
contact optical methods for full-field
measurement of deformations and            0.024

strains in thin transparent films

                                           0.016




                                           0.008




                                           0
εyy
Approach                                  0.032


Optical methods also allow analysis
of failure modes, work to failure and
fracture mechanisms.                      0.024




                                          0.016




                                          0.008




                                          0
Approach

Fracture toughness concept OK for brittle
  materials




                                            Stress
    work to failure  work of fracture


Not true for ductile materials:                      Strain

work to failure 




                                            Stress
       essential work of fracture
       + work of plastic deformation
                                                     Wp
                                                              We
                 Wf = We + Wp                        Strain
Approach
Essential Work of Fracture (EWF)
•   Represents the energy consumed within the
    fracture zone where new surface is generated
    (Kwon and Jar, 2007)

•   Well correlated to fracture toughness for ductile
    polymers (Barany et al, 2003)
•   Therefore it is a material constant, independent of
    sample geometry (Wu and Mai, 1996)
Approach
Measurement of EWF
Wf = We + Wp

Liu & Nairn (1998) used
                              Plastic
double-edge notched           Deformation
                              Zone

tension (DENT) specimens
Wf= welt + wpVp


Wf/lt=wf= we + βwpl

               Shape factor
Approach
                  Theory of the EWF Method
Typical experimental results for measuring the essential
work of fracture.

wf


                     βwp

we
     0                     W
                               l
 Schematic drawing of the relationship between specific
 total fracture work wf and ligament l
         Large amount of samples needed
Opportunities
Drawbacks of the traditional EWF experimental Method
•   Large amount of samples
•   Assumes knowledge of the shape of the plastic
    deformation zone (β factor)
•   Assumes uniform level of plastic deformation within
    the zone
Solution: optical measurement of strains
•   The actual distribution of plastic deformation can be
    readily measured
•   No need to make assumptions regarding the shape of
    plastic deformation zone
•   No need for multiple tests
Materials & Methods

                  P




                        After
        tension         failure

        Strain
        mapping




                      Permanent
                      strain
                  P
Materials & Methods
 Evaluate EWF using Digital Image Correlation (DIC)

                               Case 1
          Case 1




                      Stress
          Case 2                                    Case 3
                                  Strain




                                           Stress
          Case 3
                               Case 2
                                                       Wp    +   We
                      Stress




                                                        Strain
                                  Wp


                                  Strain
Materials & Methods
Polyester film
• Ductile and transparent (to substitute for MFC/PLA composite)
• Identical speckle pattern printed on all specimens
• Use double-edge notched specimens and calculate we in both ways
Tensile tests on thin film
specimens
 (Modified ASTM D 882-09)
 •   1 kN Instron (ElectroPuls
                                                    specimen

     E1000) testing frame
 •   Optical measurement of
     deformations and strains:
     Digital Image Correlation
     (DIC), precision ± 0.4 μm
Materials & Methods

 Evaluate EWF using Digital Image Correlation (DIC)

    Aj




                               Plastic
                               deformation
εyy
Future work                              0.032


No need to notch the specimens
because we can trace back the strain
concentrations leading to failure        0.024

anywhere in the specimen

                                         0.016




                                         0.008




                                         0
Preliminary Conclusion

It is possible to measure
• Strength
• Elastic modulus
• Toughness
On a small set of specimens subjected to a simple tensile test
Acknowledgments
 CSREES/USDA NRI CGP #2008-01522 competitive
grant
   Lech Muszyński
   John Nairn
   John Simonsen
 All   graduate students in my project group
jie.ding@oregonstate.edu

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Session 18 ic2011 ding

  • 1. Mechanical Characterization of Microfibrillated Cellulose (MFC)-poly(lactic acid) nanocomposites Application of the Concept of the Essential Work of Fracture (EWF) Jie Ding, Lech Muszyński , John Simonsen Department of Wood Science and Engineering
  • 2. Background Poly(lactic acid) (PLA) and its products Poly(lactic acid) PLA is a versatile polymer made from renewable agricultural raw materials and is compostable. Applications Known issues • disposable cups, • weak & brittle plates, containers Needs reinforcement • plastic bags • food wraps http://www.ecothefriendlyfrog.co.uk/pla.shtm
  • 3. Background Potential reinforcement: Microfibrillated Cellulose (MFC) MFC are cellulosic fibrils disintegrated from plant cell walls (usually aggregates of microfibrils). Typical thickness range: 20-40 nm (aggregates), could be as small as 3-10 nm (individual fibrils) (Svagan et al. 2007) Structure and appearance of MFC by SEM (by Jie Ding)
  • 4. Background MFC/Poly(lactic acid)(PLA) Composites Advantages:  Both components derived from renewable materials  Both are environmentally friendly  carbon neutral  compostable  Small addition of MFC improves strength and elastic modulus of PLA (Mathew & Oksman 2006)  No satisfactory formulation commercialized to-date
  • 5. Background  Many formulations are generated in the search of “the perfect one “  Prototype formulations are generated in small amounts of thin transparent films  There is a need for a quick and efficient way of evaluating mechanical properties of new formulations Properties of interest • Strength • Elastic modulus • Toughness
  • 6. Objective Develop a quick and efficient method for evaluating the  strength,  elastic modulus and  toughness in thin transparent polymer films.
  • 7. εyy Approach 0.032 We have successfully applied non- contact optical methods for full-field measurement of deformations and 0.024 strains in thin transparent films 0.016 0.008 0
  • 8. εyy Approach 0.032 Optical methods also allow analysis of failure modes, work to failure and fracture mechanisms. 0.024 0.016 0.008 0
  • 9. Approach Fracture toughness concept OK for brittle materials Stress work to failure  work of fracture Not true for ductile materials: Strain work to failure  Stress essential work of fracture + work of plastic deformation Wp We Wf = We + Wp Strain
  • 10. Approach Essential Work of Fracture (EWF) • Represents the energy consumed within the fracture zone where new surface is generated (Kwon and Jar, 2007) • Well correlated to fracture toughness for ductile polymers (Barany et al, 2003) • Therefore it is a material constant, independent of sample geometry (Wu and Mai, 1996)
  • 11. Approach Measurement of EWF Wf = We + Wp Liu & Nairn (1998) used Plastic double-edge notched Deformation Zone tension (DENT) specimens Wf= welt + wpVp Wf/lt=wf= we + βwpl Shape factor
  • 12. Approach Theory of the EWF Method Typical experimental results for measuring the essential work of fracture. wf βwp we 0 W l Schematic drawing of the relationship between specific total fracture work wf and ligament l Large amount of samples needed
  • 13. Opportunities Drawbacks of the traditional EWF experimental Method • Large amount of samples • Assumes knowledge of the shape of the plastic deformation zone (β factor) • Assumes uniform level of plastic deformation within the zone Solution: optical measurement of strains • The actual distribution of plastic deformation can be readily measured • No need to make assumptions regarding the shape of plastic deformation zone • No need for multiple tests
  • 14. Materials & Methods P After tension failure Strain mapping Permanent strain P
  • 15. Materials & Methods Evaluate EWF using Digital Image Correlation (DIC) Case 1 Case 1 Stress Case 2 Case 3 Strain Stress Case 3 Case 2 Wp + We Stress Strain Wp Strain
  • 16. Materials & Methods Polyester film • Ductile and transparent (to substitute for MFC/PLA composite) • Identical speckle pattern printed on all specimens • Use double-edge notched specimens and calculate we in both ways Tensile tests on thin film specimens (Modified ASTM D 882-09) • 1 kN Instron (ElectroPuls specimen E1000) testing frame • Optical measurement of deformations and strains: Digital Image Correlation (DIC), precision ± 0.4 μm
  • 17. Materials & Methods Evaluate EWF using Digital Image Correlation (DIC) Aj Plastic deformation
  • 18. εyy Future work 0.032 No need to notch the specimens because we can trace back the strain concentrations leading to failure 0.024 anywhere in the specimen 0.016 0.008 0
  • 19. Preliminary Conclusion It is possible to measure • Strength • Elastic modulus • Toughness On a small set of specimens subjected to a simple tensile test
  • 20. Acknowledgments  CSREES/USDA NRI CGP #2008-01522 competitive grant  Lech Muszyński  John Nairn  John Simonsen  All graduate students in my project group