PLASMA SURFACE MODIFICATION OF POLYMERS USING ATMOSPHERIC PRESSURE by uwn15494

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									      PLASMA SURFACE MODIFICATION OF POLYMERS
       USING ATMOSPHERIC PRESSURE DISCHARGES*


                     Rajesh Dorai 1 and Mark J. Kushner 2

                             University of Illinois
                    1
                     Department of Chemical Engineering
             2
               Department of Electrical and Computer Engineering
                               Urbana, IL 61801


                         e-mail: dorai@uiuc.edu
                                 mjk@uiuc.edu



                           http://uigelz.ece.uiuc.edu




*
    Work supported by 3M and NSF (CTS99-74962)
                                 AGENDA

• Introduction
       • Plasma processes for polymer surface treatment

• Description of the model
     • GLOBAL_KIN
     • Surface site balance model for heterogeneous chemistry
     • Reactions in air and at the polypropylene surface

• Atmospheric pressure plasma processing of polypropylene (PP)
     • Periodic steady states in radical densities
     • Effect of energy deposition
     • Effect of relative humidity
     • Low-Molecular Weight Oxidized Materials (LMWOM)

• Conclusions




                                                    University of Illinois
 ICOPS02-02
                                                Optical and Discharge Physics
              PLASMA SURFACE MODIFICATION OF POLYMERS

• Polymer materials typically require
  surface activation to improve their
  wetting (for dyeing) and adhesion
  properties.

• Atmospheric     pressure  plasma
  treatment is well suited for this
  purpose because of the ease of
  generation of gas-phase radicals
  which can react with and modify
  the polymer surface.

• The typical plasma equipment for
  treatment are corona discharges.

• These devices operate as dielectric
  barrier discharges (DBDs) owing to
  dielectrics on the electrodes and the capacitance of the polymer.


                                                     University of Illinois
ICOPS-02-03
                                                 Optical and Discharge Physics
  POLYMER TREATMENT: LOW vs. ATMOSPHERIC PRESSURE

• Low pressure processes

         • Advantages

                More uniform treatment compared to atmospheric pressure.
                Less contamination problems (a controlled gas mixture is used).
                Flexibility of using gases of various types.

         • Disadvantages:

                Equipment is expensive (vacuum).
                Problems in using in continuous mode.

• Atmospheric pressure processes

         • Equipment is simple, cost effective.
         • Can be used in continuous operation.



                                                         University of Illinois
 ICOPS-02-3AA
                                                     Optical and Discharge Physics
                COMMERCIAL CORONA PLASMA EQUIPMENT
• Commercial atmospheric pressure plasma equipments treat
  conducting/non-conducting materials at line speeds ~ 400 m/min.

• Suppliers include Enercon Inc., Tri-Star Technologies, Pillar Technologies,
  Sherman Treaters.




  ENERCON’s PLASMATREAT3 TM               SHERMAN TREATER’s PBS/12Cx1

                                                      University of Illinois
 ICOPS-02-03A
                                                  Optical and Discharge Physics
              THE PLASMA SURFACE MODIFICATION PROCESS
       TYPICAL PROCESS CONDITIONS:
       Web speed: 10 - 200 m/min
       Residence time: a few s
       Energy deposition: 0.1 - 1.0 J cm-2
       Applied voltage: 10-20 kV at a few 10s kHz
       Gas gap ~ a few mm

                                           GROUNDED                FEED ROLL
                                           ELECTRODE


                                                        PLASMA
                              PROCESSED
                             POLYMER FILM
                                                       POWERED
                                                       SHOE
                                                       ELECTRODE



                         COLLECTOR                        ~   HIGH-VOLTAGE
                                                              POWER SUPPLY
                           ROLL

                                                           University of Illinois
ICOPS-02-04
                                                       Optical and Discharge Physics
                             THE OVERALL PROCESS

                                                                              e            e
                                                   e        e                     N2
      HUMID-AIR PLASMA       e         e               O2                     N            N
                                 H2O                                                       O2
                                                   O        O O2
                                                                     O3           NO
                             H         OH



                                                                                  NO
       BOUNDARY LAYER                                           OH, H2O
                                                                                                O2
                         O        OH           OH, O                              OH
                             H                                  O                      O2
                                                                ||
                             C     C       C   C   C            C    C    C            C             LAYER 1

                                                        H
        POLYPROPYLENE
                             C     C       C   C   C    C       C    C    C            C             LAYER 2

                                                                              OH

                             C     C       C   C   C    C       C    C    C   C        C             LAYER 3


                                                                             University of Illinois
ICOPS-02-04AA
                                                                         Optical and Discharge Physics
                POLYMERS MODIFIED USING PLASMAS
• Plasma surface modification is used on:

      • Polyethylene                    • Polypropylene
      • Poly (ethylene terephthalate)   • Polystyrene

• The extent of modification depends on factors relating to the polymer
  structure:

      • Unsaturation in the backbone (presence of multiply bonded carbon
        chains)
      • Functional groups attached to the backbone
      • Orientation of the attached groups with respect to the backbone
      • Crystalline/amorphous nature of the polymer

• In this study, we address polypropylene (PP).

  • Apparel (Active wear or sportswear)
  • Home furnishings (indoor and outdoor carpets, upholstery)
  • Packaging


                                                       University of Illinois
 ICOPS-02-04A
                                                   Optical and Discharge Physics
                POLYPROPYLENE (PP) - STRUCTURE

• Polypropylene polymer:

                            1
                   CH3 H    CH3 H       CH3 H
                                                    1 - Primary C
                        2               3
                    C   C   C       C   C       C   2 - Secondary C

                    H   H       H   H       H   H   3 - Tertiary C


• Three types of carbon atoms in a PP chain:

  • Primary C – attached to only one another carbon;
  • Secondary C – attached to two carbon atoms; and
  • Tertiary C – attached to three carbon atoms.

• The reactivity of an H-atom depends on the type of C bonding.

• Reactivity scales as: HT > HS > HP (HT=tertiary H; HS=secondary H;
  HP=primary H).


                                                             University of Illinois
 ICOPS-02-05
                                                         Optical and Discharge Physics
               FUNCTIONALIZATION OF THE PP SURFACE

• Untreated PP is a saturated hydrocarbon chain which is hydrophobic
  (repels water).

• The increase in surface energy of PP after corona treatment is attributed to
  the functionalization of the polymer surface with hydrophilic groups
  (attracts water).

• An air-corona-processed PP film contains hydrophilic functional groups
  such as:
    • Aldehydes (-CHO)         • Ketones (-C=O)
    • Alcohols (-C-OH)         • Hydroperoxides (-COOH)

• The hydroperoxides photolytically degrade to produce alkoxy radicals (-C-
  O) and OH.

• Energy deposition and relative humidity (RH) of air plasmas significantly
  affect this functionalization.



                                                       University of Illinois
 ICOPS-02-06
                                                   Optical and Discharge Physics
     LOW-MOLECULAR WEIGHT OXIDIZED MATERIALS (LMWOM)

• Corona-treatment also produces cross-linking and degradation.

• Smaller chain-length oxidized compounds soluble in polar solvents (e.g.,
  H2O, ethanol) are formed. These are called LMWOM.

• The role of LMWOM in improving ink adhesion is not well understood.

• Strobel et al. suggest that LMWOM may be beneficial to the adhesion of
  polyamide inks on corona-treated PP. 1

• Briggs et al. observed poor ink adhesion (nitrocellulose-based ink) in the
  presence of LMWOM and attributed it to the weak bonding of the LMWOM
  to the polymer. 2

1
    Strobel et al. J. Adhesion Sci. Technol. 3, 321 (1989).
2
    Briggs et al. Polymer 24, 47 (1983).



                                                           University of Illinois
    ICOPS-02-06A
                                                       Optical and Discharge Physics
                  GOALS OF THIS INVESTIGATION

• Oxidized functional groups incorporated onto the surface are responsible
  for increased adhesion.

• The reaction mechanism and processes leading to the formation of
  LMWOM are still not well understood.

• Based on experimental data (O/C ratios on surfaces, surface densities of
  functional groups), reaction mechanisms are constructed for
  heterogeneous chemistry at the PP surface.

• With the help of a global kinetics model validated against experiments,
  parameterizations are performed over energy depositions and relative
  humidities to study their effect on surface properties.




                                                    University of Illinois
 ICOPS-02-06B
                                                Optical and Discharge Physics
                  DESCRIPTION OF THE MODEL – GLOBAL_KIN

Modules in GLOBAL_KIN:

•    Homogeneous plasma chemistry
•    Transport to surface through a boundary layer
•    Heterogeneous surface chemistry
•    Circuit model


                                            CIRCUIT
                                            MODULE

           OFFLINE                                             N(t+∆t),V,I
                       LOOKUP TABLE        GAS-PHASE
          BOLTZMANN      OF k vs. T e       KINETICS
            SOLVER
                                                                VODE -
                                                              ODE SOLVER
                                           SURFACE
                                           KINETICS




                                                         University of Illinois
    ICOPS-02-07
                                                     Optical and Discharge Physics
                      HUMID-AIR REACTION MECHANISM
• Gas-phase products of humid-air corona treatment include O3, NO, NO2,
  HNO2, HNO3.
                                  OH

                                           HNO2
                                           OH
                      OH         O3, HO2
               HNO3                                  N
                           NO2             NO                N2
                                   O
                                       O2 ,
                                       OH
                                                             O2
                                            N        N2(A)

                                                e
                                                N2
                                                                      O2
                                                          O2 e    O            O3
                                                                                    OH
                                                                                         HO2
                                                                      O2(1∆)
                                                H 2O
                                                 e

                                            H        OH
                                                O2

                                            HO2


                                                                          University of Illinois
 ICOPS-02-7A
                                                                      Optical and Discharge Physics
               SPECIES TRANSPORT TO THE POLYMER SURFACE
• Bulk plasma species diffuse to the PP surface through a boundary layer
  (d~ a few λmfp; λmfp~µm at 1 atm).

• Flux of the radicals reaching the surface is,
                     nv
                 φ = th ,         n = density, vth = thermal speed.
                       4

• Radicals react on the PP based on a user-defined mechanism.



                                   BULK PLASMA

                                  O    OH       CO2

                    BOUNDARY
                             d   DIFFUSION REGIME       ~ λmfp
                       LAYER

                                 POLYPROPYLENE

                                                       University of Illinois
 ICOPS-02-08
                                                   Optical and Discharge Physics
         HETEROGENEOUS PROCESSES AT THE PP SURFACE
• Radicals at the polymer surface react with the surface by addition or
  abstraction.

• After surface reactions, desorbed products diffuse through the boundary
  layer into the bulk plasma.

• Inter-surface-species reactions are also included.
                                            OH, H2O
                                                                   O2
               O       OH       O, OH                    OH
                   H                        O                 O2
                                            ||
                   C   C    C   C   C       C    C   C        C    LAYER 1

                                        H

                   C   C    C   C   C   C   C    C   C        C    LAYER 2

                                                         OH

                   C   C    C   C   C   C   C    C   C   C    C    LAYER 3


                                                             University of Illinois
 ICOPS-02-09
                                                         Optical and Discharge Physics
                       SURFACE SITE BALANCE MODEL
• The total number of sites allowed for reaction is variable.

• When a “hole” is made in the PP chain, radicals are allowed to diffuse
  through it to the layers beneath and react.


               C   C   C   C   C        C   C   C       C   LAYER 1



               C   C   C   C   C   C    C   C   C       C   LAYER 2



               C   C   C   C   C   C    C   C   C   C   C   LAYER 3



                                       CARBON SITES
                                       AVAILABLE FOR
                                       REACTION

                                                        University of Illinois
 ICOPS-02-10
                                                    Optical and Discharge Physics
                            REACTIONS AT PP SURFACE
• O and OH abstract H from the PP chain to produce alkyl radicals.

• Further reaction of O atoms with alkyl radicals produce alkoxy radicals
  which undergo scission reactions to form aldehydes and ketones.
               (POLYPROPYLENE)           (ALKYL RADICAL)                      (ALKOXY RADICAL)
                      H                                                              O
                                 O, OH                           O
               ~CH2   C   CH2~           ~CH2       C   CH2~                  ~CH2    C    CH2~
                      CH3                           CH3                               CH3
                                 OH, H2O
                                                     O2

                                                        O                                 NO2
                                                    O
                                                                         NO
                                         ~CH2       C     CH2~
                                                CH3
                                         (PEROXY RADICAL)

                                                a
                                                        ~CH 2    C       CH2~ + CH3
                          O
                                                                 O
                 ~CH 2    C   CH2~
                       CH3                                           CH3
                                                b
                 (ALKOXY RADICAL)                       ~CH 2    C            +   CH2~
                                                                     O

                                                                                   University of Illinois
 ICOPS-02-13
                                                                               Optical and Discharge Physics
                                              BASE CASE: ne, Te
• As the voltage across the gap increases, electrons gain energy and by
  ionizing the background gases, produce an electron avalanche,

  e + N2 → N2+ + e + e,                  e + O2 → O2+ + e + e,               e + H2O → H2O+ + e + e.

• Once the gap-voltage decreases below sustaining, electrons decay by
  attachment (primarily to O2).
                                      51, 102, ... , 921              8
                    1014
                                                                      7                    51, 102, ... , 921
                    1013                                              6
                                                                      5




                                                           T e (eV)
        ne (cm-3)




                    1012                                              4
                    1011                                              3       1st of 921
                                                                      2
                    1010                                              1
                                 1st of 921
                                                                      0
                    109                                                   10-12 10-11 10-10 10-9    10-8
                      10-11 10-10 10-9 10-8       10-7                             Time (s)
                                 Time (s)

                           • N2/O2/H2O=79/20/1, 300 K, 1 atm, 10 kV at 9.6 kHz.
                           • Web speed=250 cm/s, gas gap=2.5 mm.
                                                                               University of Illinois
 ICOPS-02-11
                                                                           Optical and Discharge Physics
                    GAS-PHASE RADICALS: O, OH, N
• Electron impact dissociation                                7                            51
  of O2, H2O and N2 produces O,
  OH and N,                                                   6


      e + N2 → N + N + e,                                     5                        N




                                       OH, O, N (1014 cm-3)
                                                                                                           921
      e + O2 → O + O + e,
      e + H2O → H + OH + e.                                   4
                                                                                           O
• O consumption in the gas-                                   3                                   921

  phase occurs primarily by
                                                                           51
  ozone (O3) formation,                                       2                            OH
                                                                                                  921

      O + O2 + M → O3 + M.                                    1
                                                                      51
                                                                                1st        O    N, OH
• Although large densities of N                               0
                                                               10-9    10-8           10-7          10-6         10-5
  atoms are produced, they are                                                         Time (s)

  relatively unreactive with PP compared to O and OH.

• After 100s of discharge pulses, the radicals attain a periodic steady state.

                                                                               University of Illinois
 ICOPS-02-12
                                                                           Optical and Discharge Physics
                                   GAS HEATING
• Typical energy deposition for PP
  treatment is a few J cm-2
                                               AIR
                                               FLOW
                                               500 cm s-1
  = a few 10s of J cm-3                                                            FEED FILM

     (few mms gas gap).

• Back-of-the-envelope calculation
                                                                                        PLASMA
  N CP ∆TGAS = Energy deposition                                      GROUNDED
                                                                      ELECTRODE

  At atmospheric pressure,
    N ≈ 3×1019 cm-3,                                         PROCESSED
                                                            POLYMER FILM
    CP, AIR ≈ 4×10-23 J molecule-1 K-1.                                     POWERED
                                                                              SHOE
                                                                           ELECTRODE
  ∴ for edep=1 J cm-3,
                                            1
                         ∆TGAS =         19        − 23
                                                        ≈ 1000 K !
                                   3 × 10 ⋅ 4 × 10

• In experiments, this heating is avoided by cooling the electrodes using air.

• An overall heat transfer coefficient has been incorporated into the model
  for this purpose.
                                                                University of Illinois
 ICOPS-02-12A
                                                            Optical and Discharge Physics
                     REACTION PROBABILITIES ON PP
• Probabilities for surface reactions on PP were estimated based on rate
  constants for similar gas-phase reactions with long-chain saturated
  hydrocarbons.

• A gas-kinetic rate constant (~ 10-10 cm3 s-1) ≈ unit reaction probability at PP.

• Results from the model are then compared with experiments (for example,
  O/C ratios).

• To “better” the agreement between model and experiments, probabilities
  for key reaction pathways are adjusted.

• For example, most of the O impregnated on the PP surface was by,

                NO + PP-O2 → NO2 + PP-O
                                   (alkoxy radical)

• For a reaction probability of 0.02, “agreement” was observed between
  model and experiments (of O/C ratios on PP).


                                                          University of Illinois
 ICOPS-02-13A
                                                      Optical and Discharge Physics
                       MODEL VALIDATION: O/C RATIOS ON PP, LMWOM
• O/C ratios on PP as a function of energy deposition were compared to
  experiments*.

• Most of the O on the surface came from aldehydes and ketones (LMWOM).
  At larger energy depositions (> 1 J cm-2), the aldehydes are converted to
  CO2.
                       25                                                          2.5

                                                                                                   KETONES
                       20                                                          2.0




                                                             DENSITY (1014 cm-2)
                       15               EXPERIMENT                                 1.5
             O/C (%)




                       10                                                          1.0               ALDEHYDES
                                   MODEL
                        5                                                          0.5


                        0                                                          0.0
                        0.0      0.5   1.0    1.5      2.0                           0.0       0.5   1.0    1.5      2.0
                              ENERGY DEPOSITION (J cm-2)                                   ENERGY DEPOSITION (J cm-2)

                                             Air at 300 K, 1 atm, 55% RH
*
    Zenkiewicz, M., J. Adhesion Sci. Technol., 15 63 (2001).

                                                                                                 University of Illinois
    ICOPS-02-14
                                                                                             Optical and Discharge Physics
                                          GAS-PHASE PRODUCTS: O3, H2O2
• O3 is produced by the reaction                              • H2O2 is produced by,
  of O with O2,
                                                                                      H + O2 + M → HO2 + M,
                          O + O2 + M → O3 + M.                                      HO2 + HO2 + M → H2O2 + O2 + M.

• At higher energy depositions,                               • At high energy depositions (lower
  more O is produced resulting in                               film speeds), H2O2 density decreases
  increased O3 formation.                                       due to decrease in <HO2>.
                    3.0                                                             2.5
                                                                                                                         4
                    2.5
                                                                                    2.0




                                                                 H2O2 (1015 cm-3)




                                                                                                                             <HO2> (1014 cm-3)
                                                                                                         <HO 2>
                    2.0                                                                                                  3
   O3 (1017 cm-3)




                                                                                    1.5
                    1.5                                                                                      H 2 O2
                                                                                                                         2
                                                                                    1.0
                    1.0

                                                                                    0.5                                  1
                    0.5

                    0.0                                                             0.0                                  0
                       0.0       0.5   1.0    1.5       2.0                           0.0       0.5    1.0       1.5   2.0
                             ENERGY DEPOSITION (J cm-2)                                     ENERGY DEPOSITION (J cm-2)


                                                                                                  University of Illinois
 ICOPS-02-15
                                                                                              Optical and Discharge Physics
                   GAS-PHASE PRODUCTS: NO, NO2
• NO and NO2 (combinedly called NOx) are produced by,

      N2 + O → NO + N,                                             14
      NO + O + M → NO2 + M.                                        12                NO2




                                             Density (1013 cm-3)
                                                                   10
• NO is also converted to NO2 by
  reaction with peroxy radicals at the                             8
  PP surface,                                                                           NO
                                                                   6

      NO + R-OO → NO2 + R-O.                                       4

                                                                   2
• At higher energy depositions, most of
  the NOX is converted to N2O, N2O5,                                0
                                                                    0.0    0.5   1.0    1.5       2.0
  HNOX,
                                                                       ENERGY DEPOSITION (J cm-2)


                 NO2 + N → N2O + O,
                 NO2 + NO3 + M → N2O5 + M,
                 NO + OH + M → HNO2 + M,
                 NO2 + OH + M →HNO3 + M.

                                                                            University of Illinois
 ICOPS-02-15A
                                                                        Optical and Discharge Physics
                  GAS-PHASE PRODUCTS: N2O, N2O5
• Nitrous oxide (N2O) and di-nitrogen pentoxide (N2O5) are gases of interest
  from an environmental perspective.

• Increasing amounts of these are generated at higher energy depositions.

• N2O is generated by the reaction                               20
  of NO2 with N,




                                           DENSITY (1015 cm-3)
                                                                 15
      NO2 + N → N2O + O.
                                                                                      N2O
• N2O5 is formed by the reaction of                              10
  NO2 with NO3,
                                                                  5
      O + NO2 + M → NO3 + M,
                                                                                     N2O5
      NO2 + NO3 + M → N2O5 + M.
                                                                  0
                                                                   0.0       0.5   1.0    1.5      2.0
                                                                         ENERGY DEPOSITION (J cm-2)




                                                                             University of Illinois
 ICOPS-02-16
                                                                         Optical and Discharge Physics
                                             ETCH PRODUCTS AND RATES
• The primary etch product is CO2,
                                     H   H                       H                                             H
                                                                                                   +O
                              ~CH2   C   C=O + O     OH + ~CH2   C                           C=O        ~CH2   C   + CO2
                                     CH3                         CH3                                           CH3

• Higher energy depositions result in increased flux of O and OH to the PP
  surface which increases the etch rate.
                    3.0                                                                      60




                                                                 ETCHRATE (monolayers/min)
                    2.5                                                                      50
  CO2 (1014 cm-3)




                    2.0                                                                      40

                    1.5                                                                      30

                    1.0                                                                      20

                    0.5                                                                      10

                    0.0                                                                       0
                      0.0      0.5    1.0    1.5      2.0                                     0.0       0.5    1.0         1.5   2.0
                            ENERGY DEPOSITION (J cm-2)                                              ENERGY DEPOSITION (J cm-2)

                                                                                                         University of Illinois
 ICOPS-02-17
                                                                                                     Optical and Discharge Physics
                                          EFFECT OF RH: O/C RATIO ON PP
• At higher RH, more fraction of input energy is channeled into OH
  production and hence <OH> increases and <O> decreases.

• With higher <OH>, more alkyl radicals (through OH abstraction) are
  produced which leads to increased O impregnation on the PP surface.

                         1.5                                                           20


                         1.2




                                                                 O/C RATIO ON PP (%)
                                              <O>
                                                                                       15
   Density (1014 cm-3)




                         0.9
                                                                                       10
                         0.6
                                              <OH>
                                                                                       5
                         0.3


                         0.0                                                           0
                               1            10             100                              1            10             100
                                   RELATIVE HUMIDITY (%)                                        RELATIVE HUMIDITY (%)

                                              (Energy deposition = 0.34 J cm-2)
                                                                                                     University of Illinois
 ICOPS-02-18
                                                                                                 Optical and Discharge Physics
                                           EFFECT OF RH: O3, H2O2
• Higher RHs result in decreasing <O> and as a result O3 production
  decreases.

• Larger amount of HO2 is produced at higher RH and this leads to increased
  H2O2 production,

                                         HO2 + HO2 + M → H2O2 + O2 + M.
                 3.0                                                        2.0                               5

                 2.5                                                                         H2O2
                                                                                                              4




                                                                                                                  <HO2> (1014 cm-3)
                                                                            1.5




                                                         H2O2 (1015 cm-3)
                 2.0
O3 (1017 cm-3)




                                                                                             <HO2>            3
                 1.5                                                        1.0
                                                                                                              2
                 1.0
                                                                            0.5
                 0.5                                                                                          1


                 0.0                                                        0.0                               0
                       1            10             100                            1           10            100
                           RELATIVE HUMIDITY (%)                                      RELATIVE HUMIDITY (%)

                                                                                          University of Illinois
  ICOPS-02-19
                                                                                      Optical and Discharge Physics
                                                  EFFECT OF RH: NXOY
• NO and NO2 densities increase with RH because of the increased rate of
  the reactions,
                                    N + OH → NO + H,           NO + HO2 → NO2 + OH.
• Larger NO2 leads to increased formation of N2O and N2O5,

                                  NO2 + N → N2O + O,          NO2 + NO3 + M → N2O5 + M.
                      1.2                                                          16
                                                                                  10
                                                                                                   N2O
                                         NO2
Density (1014 cm-3)




                                                                                   15
                      0.8                                                         10




                                                                 Density (cm-3)
                                          NO
                                                                                                   N2O5
                                                                                   14
                      0.4                                                         10



                                                                                   13
                      0.0                                                         10
                            1            10             100                             1            10             100
                                RELATIVE HUMIDITY (%)                                       RELATIVE HUMIDITY (%)

                                                                                                University of Illinois
 ICOPS-02-20
                                                                                            Optical and Discharge Physics
                                     EFFECT OF RH: HNO2, HNO3, CO2
• Increasing RH leads to increased HNOX byproduct formation,
                           NO + OH + M → HNO2 + M,         NO2 + OH + M → HNO3 + M.
• Due to the increased rate of abstraction by OH at higher RH, the etch rate
  increases.

OH + PP-H → PP• + H2O,                             PP• + …. → aldehydes,                       ….+ O → CO2 + ….
                  16
                 10                                                            4


                                   HNO3
                                                                               3




                                                             CO2 (1013 cm-3)
                  15
                 10
Density (cm-3)




                                                                               2
                                   HNO2
                  14
                 10
                                                                               1


                  13
                 10                                                            0
                       1            10             100                             1            10             100
                           RELATIVE HUMIDITY (%)                                       RELATIVE HUMIDITY (%)
                                                                                           University of Illinois
  ICOPS-02-21
                                                                                       Optical and Discharge Physics
                                SUMMARY

• A global kinetics model has been used to study the gas-phase and surface
  chemistries during the air-corona discharge treatment of PP.

• O/C ratio on PP increased with increasing energy deposition and relative
  humidity.

• Continued increase in energy deposition however lead to PP
  decomposition (to CO2).

• Gas-phase products produced in significant amounts (>1015 cm-3) include
  O3, H2O2, HNO3, N2O, N2O5.

• Although increased energy deposition results in more hydrophilic
  surfaces, the production of environmentally sensitive gases could be an
  issue.




                                                      University of Illinois
 ICOPS-02-22
                                                  Optical and Discharge Physics

								
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