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

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

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.

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

Reorientation on polymer surface : Polar group Novak and Florian; 2004 SFE Polar component Overturn Migration Surface energy (SFE) of BOPP After corona treatment; 34.0 39.2 mJ/m2 After 1 month of aging; 39.2 37.0 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, 2033-2036.

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

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, 2033-2036.

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

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.1201005284

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

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 = 24.49 nm AAc-corona treated BOPP Ra = 34.68 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;

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

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

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

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

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)

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

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), 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.

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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