1. Acrylic acid-corona treated polypropylene (PP) films: A new approach for long lasting surface modification using single-step corona discharge treatment
Presented by
Miss Nanticha Kalapat
Ph.D. Candidate in Materials Science and Engineering Program
MAHIDOL UNIVERSITY, THAILAND

2. Flexible packaging film
Polypropylene (PP)
Advantages:
Low cost
Good mechanical properties
Excellent chemical resistance
Ease of processing and recycling
Limitations:
Lack of reactive site
Poor hydrophilicity

3. Wettability on polymer surface
The adherence between ink and polymer film
Water contact angle and surface energy measurement
 90º
Hydrophobic surface
Low wettability
<90º
Hydrophilic surface
High wettability
Drop surface tension
Surface energy of test surface
Surface energy of PP
To use for ink-printing, need high surface energy.

4. Corona-discharge treatment Reaction on polymer surface
Oxygen containing functional groups on film surface
Reaction on polymer surface
A schematic diagram of a corona-discharge setup
Advantages
Very simple technique
Cost effective
Continuous and online operation
Reaction on polymer surface
Chi-Ming C. Polymer surface modification and characterization, New York: 1994
Products with and without scission
Cross-links

5. Reorientation on polymer surface
: Polar group
Novak and Florian; 2004
SFE
Polar component
Overturn
Migration
Surface energy (SFE) of BOPP
After corona treatment; mJ/m2
After 1 month of aging; mJ/m2
“Hydrophobic Recovery”
- Ryutoku, Y. and co-workers. Adhesion and Bonding in Composites, New York :1989.
- Novak, I. and Florian, S. (2004) Journal of Materials Science, 39,

6. Problems for the film making industries
Hydrophobic recovery
Problems for the film making industries
Limited shelf life
Expensive storage system
Limit the shipping export distance (Countries)
Untreated
Corona-treated
Recovered

7. The problem solving method
Thin layer grafting of polar polymer onto the surface can maintain wettability of the surface
Hypothesis
Overturn
Migration
: Polar group
- Ryutoku, Y. and co-workers. Adhesion and Bonding in Composites, New York :1989.
- Novak, I. and Florian, S. (2004) Journal of Materials Science, 39,

8. The proposed method Objectives
Discharge electrode
: Acrylic acid (AAc)
Polymer surface
AAc-corona treated surface
Ground electrode
Objectives
- To evaluate the potential of corona technique for poly(acrylic acid) deposition
- To study surface behavior of the treated films during aging time

9. Acrylic acid corona treatment
Materials
Experiment
Film
BOPP films Commercial product
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
BOPP film supporting by
THAI FILM INDUSTRIES PUBLIC CO., LTD.
Thickness 20±4 μm
Schematic of process for AAc-corona treatment
Acrylic acid, AAc
(98 %wt aqueous solution) purchased from Fluka
Aging 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

10. Chemical composition on the surface
Air-corona
Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy
Air-corona treated films
-C- O
-C- O
-OH
AAc-corona
76.4 kJ/m2
Absorbance
38.2 kJ/m2
-C- O
15.8 kJ/m2
Untreated
Comparison of ATR-FTIR peak area ratio of air-corona and AAc-corona treated BOPP films by curve-fitting
Wavenumbers (cm-1)
AAc-corona treated films
-C- O
Samples
Area ratio
1740/1456
1725/1456
1715/1456
1640/1456
Untreated BOPP film -
Air-corona treated BOPP film
15.3 kJ/m2
0.21
0.00
0.15
0.19
38.2 kJ/m2
0.72
0.01
0.45
0.39
76.4 kJ/m2
1.68
0.60
0.86
AAc-corona treated BOPP film
0.17
0.05
0.58
0.38
0.80
0.85
0.59
1.47
0.71
1.05
-OH
RCO2R'
-CO2H
RC(=O)R'
-C=C-
76.4 kJ/m2
Absorbance
38.2 kJ/m2
15.8 kJ/m2
Untreated
Wavenumbers (cm-1)
ATR-FTIR spectra of untreated BOPP , air-corona and AAc-corona treated BOPP using different corona energies

11. Surface topography Atomic Force Microscopy (AFM) Surface topography
Surface roughness (Ra)
Atomic Force Microscopy (AFM)
Untreated BOPP
Ra= 5.44 nm
Air-corona treated BOPP
Ra = nm
AAc-corona treated BOPP
Ra = nm
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
Surface roughness (Ra)
After air- and AAc-corona treatment;

12. Surface topology after corona treatment
Atomic Force Microscope (AFM)
Air-corona treated films
Vertical distance = 44 nm
AAc-corona treated films
Vertical distance = 130 nm

13. Scanning Electron Microscopy (SEM) Poly (AAc) droplet size
Surface morphology
Scanning Electron Microscopy (SEM)
Untreated BOPP
AAc-treated film
(15.8 kJ/m2 )
AAc-treated film
(38.2 kJ/m2 )
AAc-treated film
(76.4 kJ/m2 )
5 µm
5 µm
5 µm
5 µm
SEM images of untreated BOPP film, AAc-corona treated BOPP film using corona energy of 15.8, 38.2 and 76.4 kJ/m2
Corona energy
Poly (AAc) droplet size

14. Surface wettability after corona treatment
Water contact angle
Surface energy
Owens-Wendt method;
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
AAc-corona film > Air-corona film
Surface wettability

15. An average peel force of air-corona and AAc-corona treated BOPP films
Surface adhesion
T-peeling test
Higher surface adhesion Better ink adhesion
An average peel force of air-corona and AAc-corona treated BOPP films
AAc-corona film > Air-corona film
Surface adhesion

16. Surface wettability during 90 days of aging
Water contact angle
Air-corona treated films
AAc-corona treated films
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)

17. Surface topology during 90 days of aging
Atomic force microscopy (AFM)
Air-corona treated films
1 day
7 days
90 days
AAc-corona treated films
7 days
90 days
1 day
Untreated BOPP
AFM 3D imaging of corona treated BOPP films during 90 days of aging
Topology has changed but still shows good wettability during aging

18. Conclusions
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.
Publications
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),
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.

19. 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.

20. for your kind attention
Thank you
for your kind attention