Acrylic acid-corona treated polypropylene (PP) films: Acrylic acid-corona treated polypropylene (PP) films: A new approach for long lasting surface modification A new approach for long lasting surface modification

using single-step corona discharge treatmentusing single-step corona discharge treatment

Presented by Presented by

Miss Nanticha Kalapat

Ph.D. Candidate in Materials Science and Engineering Program

MAHIDOL UNIVERSITY, THAILAND

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Flexible packaging film

Limitations: Limitations:

• Lack of reactive site

• Poor hydrophilicity

2http://company.unipack.ru/eng/8605/

Advantages:Advantages:

• Low cost

• Good mechanical properties

• Excellent chemical resistance

• Ease of processing and recycling

Polypropylene (PP)

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<90ºHydrophilic surface

High wettability

90ºHydrophobic surface

Low wettability

Wettability on polymer surface

Water contact angle and surface energy measurement

Dro

p su

rface tensio

n

Surface energy of test surface

• To use for ink-printing, need high surface energy.

• The adherence between ink and polymer film

Surface energy of PP

Corona-discharge treatment

4Chi-Ming C. Polymer surface modification and characterization, New York: 1994

Products with and without scission

Cross-links

A schematic diagram of a corona-discharge setup

AdvantagesAdvantages

• Very simple technique

• Cost effective

• Continuous and online operation

Reaction on polymer surface

• Oxygen containing functional groups on film surface

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Reorientation on polymer surface

- Novak, I. and Florian, S. (2004) Journal of Materials Science, 39, 2033-2036.

: Polar group

Overturn Migration

- Ryutoku, Y. and co-workers. Adhesion and Bonding in Composites, New York :1989.

Novak and Florian; 2004

Surface energy (SFE) of BOPP

After corona treatment; 34.0 39.2 mJ/m2

SFE

Polar component

After 1 month of aging; 39.2 37.0 mJ/m2

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Hydrophobic recovery

• Limited shelf life

• Expensive storage system

• Limit the shipping export distance (Countries)

Problems for the film making industriesProblems for the film making industries

Untreated Corona-treated Recovered

7- Novak, I. and Florian, S. (2004) Journal of Materials Science, 39, 2033-2036.

Overturn Migration

- Ryutoku, Y. and co-workers. Adhesion and Bonding in Composites, New York :1989.

Thin layer grafting of polar polymer onto the surface can maintain wettability of the surface

HypothesisHypothesis

The problem solving method

: Polar group

Discharge electrode

Ground electrode

Polymer surface

The proposed method

- To evaluate the potential of corona technique for poly(acrylic acid) deposition

- To study surface behavior of the treated films during aging time

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Objectives

: Acrylic acid (AAc)

AAc-corona treated surface

Film

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BOPP film supporting by

THAI FILM INDUSTRIES PUBLIC CO., LTD.

• BOPP films Commercial product

Thickness 20±4 μm

Acrylic acid corona treatment

Schematic of process for AAc-corona treatment

Materials Experiment

• Acrylic acid, AAc

(98 %wt aqueous solution)

purchased from Fluka

E of L-1 = 15.3 kJ/m2

E of L-4 = 38.2 kJ/m2

E of L-8 = 76.4 kJ/m2

E

Aging conditionAging condition; Ambient temperature for 90 days

T. Amornsakchai, N. Kalapat., “The surface modification process of polymer films for hydrophilic surface and durability”, Thai patent No.1201005284

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Samples

Area ratio1740/1456

1725/1456

1715/1456

1640/1456

Untreated BOPP film - - - -Air-corona treated

BOPP film15.3 kJ/m2 0.21 0.00 0.15 0.1938.2 kJ/m2 0.72 0.01 0.45 0.3976.4 kJ/m2 1.68 0.01 0.60 0.86

AAc-corona treated BOPP film15.3 kJ/m2 0.17 0.19 0.05 0.5838.2 kJ/m2 0.38 0.80 0.15 0.8576.4 kJ/m2 0.59 1.47 0.71 1.05

Chemical composition on the surface

Comparison of ATR-FTIR peak area ratio of air-corona and AAc-corona treated BOPP films by curve-fitting

ATR-FTIR spectra of untreated BOPP , air-corona and AAc-corona treated BOPP using different corona energies

Air-corona treated films

AAc-corona treated films

-CO2H -C=C-RC(=O)R'RCO2R'

Air-corona

AAc-corona

•Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy

-OH

-OH

-C-

O

-C-

O

-C-

O

-C-

O

Untreated

15.8 kJ/m2

38.2 kJ/m2

76.4 kJ/m2

Untreated

15.8 kJ/m2

38.2 kJ/m2

76.4 kJ/m2

Ab

sorb

ance

Ab

sorb

ance

Wavenumbers (cm-1)

Wavenumbers (cm-1)

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Surface topography

AFM 3D images and surface roughness (Ra) of untreated BOPP film, air-corona treated and

AAc-corona treated BOPP using 76.4 kJ/m2 of corona energy

Untreated BOPP

Ra= 5.44 nm

Air-corona treated BOPP

Ra = 24.49 nm

AAc-corona treated BOPP

Ra = 34.68 nm

After air- and AAc-corona treatment; Surface roughness (Ra)

• Atomic Force Microscopy (AFM)•Surface topography•Surface roughness (Ra)

Surface topology after corona treatment

Vertical distance = 44 nm

Vertical distance = 130 nm

Air-corona treated films

AAc-corona treated films

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• Atomic Force Microscope (AFM)

SEM images of untreated BOPP film, AAc-corona treated BOPP film using corona energy of 15.8, 38.2 and 76.4 kJ/m2

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Surface morphology

Untreated BOPP AAc-treated film(15.8 kJ/m2 )

AAc-treated film(38.2 kJ/m2 )

AAc-treated film(76.4 kJ/m2 )

5 µm5 µm5 µm5 µm

Corona energy Poly (AAc) droplet size

• Scanning Electron Microscopy (SEM)

Untreated 15.3 kJ /m2 38.2 kJ /m2 76.4 kJ /m20

20

40

60

80

100

120

Wat

er C

onta

ct A

ngle

(deg

ree)

Corona Energy

Air-corona AAc-corona

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Surface wettability after corona treatment

Water contact angle and surface energy of air-corona and AAc-corona treated BOPP films after corona

treatment with different corona energies compared with untreated BOPP films

• Water contact angle • Surface energy

Surface wettability AAc-corona film > Air-corona film

Owens-Wendt method;

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Untreated 15.3 kJ /m2 38.2 kJ /m2 76.4 kJ /m20

1

2

3

4

5

Avera

ge P

eel F

orc

e (N

)

Corona Energy

Air-corona AAc-corona

Surface adhesion

An average peel force of air-corona and AAc-corona treated BOPP films

Surface adhesion AAc-corona film > Air-corona film

• T-peeling test Higher surface adhesion Better ink adhesion

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

110

Wat

er C

onta

ct A

ngle

(deg

ree)

Aging Period (days)

Untreated

15.3 kJ /m2

38.2 kJ /m2

76.4 kJ /m2

0 10 20 30 40 50 60 70 80 90 1000

10

20

30

40

50

60

70

80

90

100

110

Wat

er C

onta

ct A

ngle

(deg

ree)

Aging Period (days)

Untreated

15.3 kJ /m2

38.2 kJ /m2

76.4 kJ /m2

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Surface wettability during 90 days of aging

Water contact angle of air-corona and AAc-corona treated BOPP films during 90 days of aging with

different corona energies

AAc-corona films show a long lasting wettability ( >90 days)

Air-corona treated films AAc-corona treated films

• Water contact angle

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Surface topology during 90 days of aging

AFM 3D imaging of corona treated BOPP films during 90 days of aging

• Atomic force microscopy (AFM)

Topology has changed but still shows good wettability during aging

7 days 90 days1 day

Air-corona treated films

AAc-corona treated films

7 days 90 days1 dayUntreated BOPP

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• Vapor of AAc monomer was successfully introduced into the corona region to form polymeric thin film onto BOPP surface.

• AAc-corona treated films exhibited much improved surface wettability and peel adhesion when compared with the normal air-corona treatment.

• The AAc-corona treated films provided long-lasting hydrophilicity.

Conclusions

N. Kalapat, T. Amornsakchai. Surface modification of biaxially oriented polypropylene (BOPP) film using acrylic acid-corona treatment: Part I. Properties and characterization of treated films, Surface and Coating Technology, 207 (2012), 594-601.

N. Kalapat, T. Amornsakchai and T. Srikhirin. Surface modification of biaxially oriented polypropylene (BOPP) film using acrylic acid-corona treatment: Part II. Long term aging surface properties, submitted to Surface and Coating Technology.

Publications

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Acknowledgements

• Assoc. Prof. Dr.Taweechai Amornsakchai, Advisor

• Asst. Prof. Dr. Toemsak Srikhirin, Co-advisor

• Assoc. Prof. Dr. Sombat Thanawan, Co-advisor

• Materials Science and Engineering Program, Faculty of Science, Mahidol University

• Research and Development Centre for the Thai Rubber Industry (RDCTRI)

• This research work is partially supported by RA scholarship from the Faculty of

Graduate Studies, Mahidol University Academic Year 2012.

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Thank you for your kind

attention