Transcript treatment_of_polymeric_surfaces

Some materials are not very compatible with ink, printing processes. Ex.
Polypropylene
• Surface energy is an important factor in terms of wetting behavior of the
material
• When material is exposed to ink, it might not spread on the material as
required
• We have to change the surface energy of the material so that we can
modify our surface in terms of its appearence
•
 Used
for increasing the surface energy
 Exploits the corona effect
 Result of this treatment is usually better adhesion and
better wettability properties
 Usually employed in film production
 Its effect degrades over time, that is why inking or
printing is done after corona treatment
 Corona
treatment is a surface modification
technique that uses a low temperature corona
discharge plasma to impart changes in the
properties of a surface. The corona plasma is
generated by the application of high voltage to
sharp electrode tips which forms plasma at the
ends of the sharp tips.
 Electromagnetic
field is produced by magnetic field
generator
 Film winded on a roll goes under the corona generators
 Excited species in the air modifies the surface
 Important parameters are voltage, pressure of the air,
sample/electrode geometry
 Again
used for wetting and printing purposes
 Usually used for polyolefin surfaces
 Basic apparatus: Flame generators and mold holding the
material
 Flames located at certain points scans the material for the
time of treatment
 Scan time, material-flame distance, flame temperature
are important in this treatment
 Introduction
of plasma to the surface
 Process resembles corona discharge
 Has to be done in a vacuum chamber for a better
homogeneity in gaseous mixture
 Anode and cathode are used to form plasmas
 Plasmas generated modify surface via increasing surface
activity in micro level
 There are
two types of plasma treatment
 Cold Plasma vs Hot Plasma
 Temperature of plasma is very high at atmospheric
pressure
 This can be utilized in melting of a powder to be used as a
coating.
 This is called hot plasma treatment
 It is usually used for deposition of coatings
FUNCTIONALIZATION OF POLYMER SURFACES
 Functionalization occurs by chemical interaction of plasma
produced species - ions, radicals and photons with the surface.
(a)
(b)
(c)
 Example: H abstraction by O atom
enables affixing O atoms as a peroxy site.
 Increase surface energy  increase
wettability.
 Process treats the top few layers.
Wettability on PE film with 3 zones of treatment.
Courtesy: http://www.polymer-surface.com
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SURFACE MODIFICATION OF POLYMERS
 Pulsed atmospheric filamentary discharges (coronas) routinely treat
commodity polymers like poly-propylene (PP) and polyethylene (PE).
 Filamentary Plasma 10s – 200 mm
COMMERCIAL CORONA PLASMA EQUIPMENT
 Sherman Treaters
 Tantec, Inc.
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PRIMER ON SURFACE CHEMISTRY
 Polypropylene structure
 Functional groups are when treated in O2 containing plasmas:
Alkyl
Alkoxy
Carbonyl
Alcohol
Peroxy
R
R-O
R=O
R-OH
R-OO
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Acid
O=R-OH
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PRIMER ON SURFACE CHEMISTRY
 Ratio of O, OH, O2 and O3
fluxes determine surface
composition.
 Magnitude of fluxes and
residence time determines
importance of surfacesurface reactions.
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FORCED GAS FLOW AND WEB MOVEMENT
Gas Flow
 Polymer surfaces are continuously treated at web speeds of a
few m/s with residence times in plasma of up to a few ms.
 Non-air gas mixtures are often “forced flowed” through gap
to customize radicals to surface.
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There are two types of ICP geometries:
planar and cylindrical.
In planar geometry, the electrode is a coil
of flat metal wound like a spiral.
In cylindrical geometry, it is like a helical
spring.
When a time-varying electric current is
passed through the coil, it creates a timevarying magnetic field around it, which in
turn induces azimuthally electric currents in
the rarefied gas, leading to the formation
of a plasma.
Argon is one example of a commonly-used
rarefied gas.
Plasma technologies in Plasma lab
Used for biocompatible materials (polymers, composites, artificial blood vessel, etc.)
• sterilization
• functionalization
PLASMAS USED IN PLASMA LAB
Plasmas are created in oxygen,
hydrogen, nitrogen and argon
For medical purposes the inductively coupled oxygen plasma is
used. Typical parameters of weakly ionized fully dissociated
oxygen plasma
• Electron temperature 5 eV
• Electron density 1015 m-3
• Positive ion density 1015 m-3
• Degree of dissociation up to 100%
• Neutral gas kinetic temperature about 50C
• Density of O atoms depends on pressure
• Density of O atoms often over 1021 m-3
Plasma sterilization
1μm
1μm
SEM image of Bacillus subtilis before (left) and after plasma treated.
AFM investigations of biological samples
Atomic Force Microscope (AFM) (left) and
image of Staphylococcus aureus (right).
Plasma functionalization of organic
materials
Reactive particles from oxygen plasma are incorporated on the
surface forming O-rich functional groups.
C-OH
C-O COOH C=O
Surface polymer
oxygen plasma
Polar groups on a polymer surface cause a dramatic increase of
surface wettability.
Surface wettability is measured by water
drop
untreated
treated 0.5s
The contact angle of a water drop on a polymer surface
versus plasma treatment time
Appearance of functional groups is best analysed by X-ray
photoelectron spectroscopy (XPS = ESCA)
hn
Photoelectrons
sample
Instrument PHI-TFA
Principle
Appearance of functional groups is monitored by XPS
Survey spectra of PES (poly(ether sulfones)) polymer before
(bottom) and after different plasma treatment (middle and top).
A … C-C or C-H
High resolution C 1s peak
B … C-O
Intensity (arb. units)
A
C … C=O
D … O=S=O
B
A
300
295
290
285
Binding Energy (eV)
Untreated PES
O
I
c
o
II
c
Intensity (arb. units)
D
280
B
C
D
300
295
290
285
Binding Energy (eV)
Plasma activated PES (1s)
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 Ion
assisted vs ion implantation
 Ion implantation is a process in which ion beam is
introduced directly to the surface
 Ion assisted treatment is to target species which will then
form a coating on the surface
 Apparatus includes ion gun and closed system
 Used in
coatings whose material can be found in liquid
form and evaporates easily. Ex. Aluminium
 Electron gun hits the coating material in liquid form
 Evaporated material is coated on the polymeric film
 Beam emitted has to be controlled
 In
surface treatment, UV, laser, X-ray could also be
employed
 Their main impact is to maintain cross-linking on the
surface
 Closed system is required because the process has to be
precise
 Properties like diffusion coefficient, permeability,
adhesion can be modified
 In
the treatment of polymeric surfaces, chemical
composition of polymer surfaces can be modified
either by direct chemical reaction with a given
solution (wet treatment) or by the covalent
bonding of suitable macromolecular chains to the
sample surface (grafting).
Wet treatments were the first surface modification
techniques used in order to improve surface
properties of polymers.
 Hot chromic acid was used to oxidize polyolefins
 Specific solutions were prepared in order to exploit
specific liquid-polymer interaction.
 The effectiveness of the treatment depends on the
interaction of the different modification mechanisms

 Polymer
surfaces are rarely homogeneous.
 When the surface composition is constant
throughout the surface, amorphous and
crystalline domains are present on it.
 Wet treatment is not homogeneous on the
surface.
 Sodium
etching of fluoropolymers
 Oxidizing treatment based on chromic acid
solutions
 Hydrolysis of polyesters etc.
Etching is a process of preparing the surface of a
fluoropolymer insulated wire or tubing for bonding to
another material.
 The etching process is used on PTFE, FEP and PFA
fluoropolymers.
 PTFE has superb thermal, electrical and chemical
resistance characteristics.
 PTFE the choice in applications such as coating of nonstick frying pans.

The chemical structure of PTFE results in a non-polar,
non-wettable surface.
 The etching process strips a layer of fluorine atoms
from the surface and leaves the carbon atoms with a
deficiency of electrons.
 When the altered surface is exposed to the
atmosphere, oxygen and hydrogen restore some of
the electrons forming a surface that will accept
bonding.



The effectiveness of etching is measured by calculating the change in
surface wettability.
θ = contact angle
Surface treatment of various polymers by oxidizing
solutions was developed as a result of the low metalto-polymer adhesion.
 In the early studies and papers that were written, the
problem was handled only in a physical manner.
 Later studies, mainly following the development of the
surface sensitive analytical techniques, considered
also the chemical side of the problem.

Removing completely, or to prevent formation of, what
are often referred to as weak boundary layers.
 Protecting the adherend surfaces before bonding.
 Producing a specific adherend surface topography,
thereby altering the surface profile, and possibly
increasing the bondable surface area, that is, to
roughen the surface.

 The attack
of a nucleophilic agent, such as a base,
on an electron-deficient carbon atom, has been
exploited in several different classes of polymers
in order to improve their surface properties.

Hydrolysis of PET by hot
sodium hydroxide
attack is the oldest and
most used technique
which increases the
number of hydrophilic
groups, improves the
moisture-related
properties.
The aim of the functionalization of polymer surfaces is
to create a surface layer of well-defined functional
groups.
 In this way one can create polymeric surfaces of
controlled properties or a rigid substrate of controlled
chemical reactivity.

 In
surface grafting, the aim is to achieve
chemical modification of the surface by the
covalent bonding of new macromolecules on
top of the substrate.
 Fundamental step in grafting is the creation of
reactive groups on the substrate surface.
 It
can either be done chemically or by
irradiation (ionizing radiation, UV light and
glow discharge).
 This grafting-coupling technique is sometimes
followed but it is more common to contact the
activated surface with a suitable monomer, so
that a growing chain starts from the activated
site.
http://www.markelcorporation.com/material10.html
 http://www.devicelink.com/mddi/archive/05/10/006.
html
 http://pubs.acs.org/cgibin/abstract.cgi/jpchax/1994/98/i47/fpdf/f_j100098a046.pdf?sessid=6006l3
 http://www.kobelco.co.jp/p108/p14/sfe05.htm
 http://www.adhesivestoolkit.com/DocuData/SurfacePreTreatment.xtp
 http://www.sciencedirect.com
