Understanding Microcapsule Properties for Developing Consumer Products

Professor Zhibing Zhang School of Chemical Engineering University of Birmingham, UK Tel: 0121 414 5334 Email: Z.Zhang@bham.ac.uk

Biological and Non-biological Materials (1mm - 1mm)

• animal cells • yeasts • Bacteria • fungal hyphae • plant cells • cell and debris flocs • skin cells and

chondrocytes • starch granules • pollen grains • biofilms and food fouling

deposits

• microcapsules (encapsulates)

• microspheres • agglomerates • granules • textile fibres • ice crystals • bubbles • structured liquids

Formulation and Characterisation of functional microcapsules

• Pressure-sensitive materials (e.g melamine

formaldehyde perfume capsules; capsules for self healing materials)

• Carriers of speciality chemicals (e.g. peroxide, antimicrobial agents, herbicide)

• Drugs (water soluble, non-soluble, protein) • Probiotic cells (bacteria and yeast) • Nutraceutical enzyme (Nattokinase)

http://www.scienceinthebox.com/laundry-perfumes-provide-fresh-scents

Properties of Capsules

• Core and wall chemical compositions • Morphology, size and wall thickness • Mechanical strength • Pore size, structure of wall materials and

release rate • Surface charge • Adhesion on surface • Functionality of active ingredient

Formation of a melamine formaldehyde (M-F) wall on the surfaces of oil droplets . Sun and Zhang (2001) J Microencapsulation

M-F wall

Oil droplet

352 nm

1µm 1µm

Transmission electron microscopy (TEM) image of melamine formaldehyde microcapsules. Long, Preece, York and Zhang (2009) J. Mat. Chem.

Schematic diagram of the micromanipulation rig

Zhang, Saunders & Thomas (1999) J Microencapsulation

-200

0

200

400

600

800

1000

1200

0 1 2 3 4 5 6 7 8 9 10

Probe moving distance, mm

Forc

e, m

N

A

B

C

D E

A: probe touching microcapsuleABC: microcapsule compressedB: pseudo yield pointCD: microcapsule burst and core material

l d

A'

Force versus displacement for compression of a microcapsule to rupture. Sun and Zhang (2001) J Microencapsulation

Mercadé-Prieto et al (2011a) Chem. Eng. Sci.

Micromanipulation to measure the rupture force of single encapsulates and finite element modelling (FEM) to determine their intrinsic mechanical property parameters

20 µm

FEM – Elastic shell Determination of the Elastic Modulus (E): • MF encapsulates are known to be elastic at small fractional deformations e < 0.15

• The force profile depends on h/r at small fractional deformations

• We can estimate h/r using the shape of the force profile

Mercade-Prieto et al. (2011a) Chem. Eng. Sci.

0

0.01

0.02

0.03

0.04

0.05

0.06

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16Fractional deformation

F/Er

h

0.33%1.84%3.23%5.5%7.7%11.1%13.67%

h/r h/r

e

• Once h is known we can estimate Eh • Compare experimental force curve with FEM results at

the appropriate h/r

FEM – Elastic shell – Estimate Eh

-0.10

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0% 2% 4% 6% 8% 10% 12% 14%h/r

coef

icie

nt b

and

c

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

coef

icie

nt a

bcacba

ErhF

++= ee 2

FEA results:

0.03 < e < 0.1

The experimental Eh is calculated at different fractional deformations

cbarFEh

++=

eee

e 2

MF Encapsulates – Elastic shell – Estimate Eh

150

200

250

300

350

400

450

500

5 10 15 20 25 30 35Capsule size (µm)

Eh (N

/m)

Eh is independent of the encapsulate size.

Eh ~355 ± 60 N/m h ~0.2 µm

E ~1.8 ± 0.3 GPa

1µm

MF microcapsules – Elastic perfectly-plastic shell

• At high deformations (e.g. e > 0.1), MF microcapsules deform plastically

• Consider the simplest plasticity scenario: Perfect plasticity

strain

Stre

ss Yield Stress

(σY)

Young’s Modulus (E)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.0 0.1 0.2 0.3 0.4 0.5Fractional deformation

F/E

rh

FullyElastic

0.035

0.029

0.024

0.021

σ E / EsY / E

e

Mercadé-Prieto et al. (2011b) Chem. Eng. Sci.

FEM – Determination of rupture parameters

0.0

0.1

0.2

0.3

0.4

0.5

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7Fractional deformation

F/E

rh

sY

0.022 0.49

T ~1 GPa

0.33

E ~7 GPa

~165 MPa

Strain

Stre

sssB~325 MPa

sY

0.022 0.49

T ~1 GPa

0.33

E ~7 GPa

~165 MPa

Strain

Stre

sssB~325 MPa

Mercadé-Prieto et al. (2012) AIChEJ

Manipulator Electron detector

Particle

Glass cantilever

Manipulator

Tip Slide

Schematic diagram of the nano-manipulation device in an ESEM Liu, Donald and Zhang (2005) Materials Sci. Technol.

Ren, Donald and Zhang (2007) Materials Sci. Technol.

ESEM (LHS) and TEM (RHS) images of the MF, ripened NP CaCO3 and double shell composite microcapsules Long, Vincent, York, Zhang and Preece (2010) Chem. Commun.

Percentage leakage of the core oil from the MF, ripened NP CaCO3 and double shell composite microcapsules over 24 hours

Schematic diagram of the release of the inner perfume oil through the microcapsule shell.

Mercadé-Prieto et al. (2012) J. Microencapsulation

Saturation concentration (cs) of hexyl salicylate in different water-solvent solutions at 220C

The corresponding mean P/h values obtained using different cosolvents.

Is there any relationship between the fracture strength and oil release rate ?

The fracture strength is mainly determined by the macro-structure. The oil release rate is dominated by the fine structure, particularly for small molecules. ( ) ( )outin)s(out)s(in cch

PcchDJ -=-=

cbaErhF

++= ee 2 0.03 < e < 0.1

Shell thickness h affects both the fracture strength and oil leakage rate!

Cantilever and tip Sample surface

Laser diode

Photo detector

Computer and feedback

electronics

3-D Piezo electric stage

Schematic of an AFM set up.

SEM image showing an encapsulate (11.9 mm) was attached to a tipless cantilever Liu et al. (2013) J. Adhesion Sci. Technol.

Adhesion Investigation by AFM

29

50 μm

Schematic representations of steps during a typical force interaction between an encapsulate and a cellulose film.

Encapsulate colloidal probe

Side view

Top view

He et al. (2014) J Microencapsulation

30

0

20

40

60

80

100

120

0 0.001% 0.01% 0.10%

Adhe

sion/

nN

Concentration (wt.%)

0.01S10S

Adhesion Force between encapsulates and Cellulose Films

Mean adhesion between 5 encapsulates and a cellulose film before and after being modified with chitosan solution.

Schematic Diagram of the Flow Chamber

Syringe Pump Flow Chamber

Computer Camera

Fabric Enhancers

Fabric care R&D in Procter & Gamble

Laundry UnitDose

Laundry Liquid Detergents (HDL)

Conclusions • Perfume microcapsules are required to have non/low

permeability, strong adhesion on fabric surface and optimum mechanical strength.

• Functional perfume capsules with different size, structure, surface property, mechanical strength and permeability have be prepared using various formulation and processing conditions to meet industrial needs.

• Micromanipulation has been demonstrated to be a very powerful tool to characterise the mechanical properties of capsules and to infer their structure, and their mechanical strength can be used as a trigger to control the release of core materials, e.g. perfume.

Acknowledgements • Prof. C. R. Thomas, J. Preece, D.

York, B. Vincent, W.E. Hennink and M. Adams

• Dr G. Sun, R. Stenekes, W.A. Chan, E.S. Chan, J. T. Chung, Y. Ren, B. Huckle , Y. Long, J. Xue, Y. Yan, A. Fernandez, M. Liu, R. Mercade Prieto, R. Allen, Y. He, F. L. Tchuenbou-Magaia and Y. Zhang

• Dr J. Smets, P. Justen, N. Young, M. Gifford and Mr T. Goodwin

Sponsors: ¸ EPSRC and BBSRC, UK; EU; TSB

The Royal Society K C Wong Foundation; The Royal Academy of Engineering

¸ Arjo Wiggins Research and Development Ltd., UK;

¸ Bayer, Germany; ¸ Bavarian Nordic, Germany; ¸ Merck Sharp & Dohme, UK; ¸ Procter & Gamble, UK, Belgium &

USA, China, Japan and Germany; ¸ Unilever, UK and The Netherlands; ¸ Probiotics International Ltd., UK; ¸ Tithebarn Ltd., UK; ¸ IAMS, USA; ¸ Roche, Switzerland; ¸ Phoqus Ltd., UK;

¸ Rhodia, France; ¸ National Starch, USA; ¸ Firmenich, Switzerland; ¸ Givaudan Schweiz AG, Switzerland

and UK; ¸ Appleton Paper Inc. (Encapsys), USA ¸ Philips UK ¸ Lesaffre France ¸ International Favours and

Fragrances, USA ¸ DSM, Switzerland ¸ Cytec, UK ¸ Symrise AG, Germany ¸ Lexon, UK ¸ Guangzhou Municipal Government ¸ Syngenta, UK ¸ Mondelez, USA

Understanding Microcapsule Properties for Developing Consumer ProductsBiological and Non-biological Materials (1m - 1mm)Slide Number 3Slide Number 4Properties of CapsulesSlide Number 6Slide Number 7Slide Number 8Slide Number 9Slide Number 10Slide Number 11Slide Number 12Slide Number 13Slide Number 14Slide Number 15Slide Number 16Slide Number 17Slide Number 18Slide Number 19Slide Number 20Slide Number 21Slide Number 22Slide Number 23Slide Number 24Slide Number 25Is there any relationship between the fracture strength and oil release rate ?Slide Number 27Slide Number 28Adhesion Investigation by AFMAdhesion Force between encapsulates and Cellulose FilmsSchematic Diagram of the Flow ChamberSlide Number 32ConclusionsAcknowledgements Sponsors: