TREATMENT OF POLYMERİC SURFACES

SURFACE TREATMENT• 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

CORONA TREATMENT 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.

CORONA TREATMENT 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

FLAME TREATMENT 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

PLASMA 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

PLASMA, PRINCIPLES AND APPLICATIONS

PLASMA TREATMENT 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

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FUNCTIONALIZATION OF POLYMER SURFACES

Functionalization occurs by chemical interaction of plasma produced species - ions, radicals and photons with the surface.

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

(a)(b)

(c)

Pulsed atmospheric filamentary discharges (coronas) routinely treat commodity polymers like poly-propylene (PP) and polyethylene (PE).

SURFACE MODIFICATION OF POLYMERS

Filamentary Plasma 10s – 200 mm

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COMMERCIAL CORONA PLASMA EQUIPMENT

Tantec, Inc.

Sherman Treaters

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PRIMER ON SURFACE CHEMISTRY

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Polypropylene structure

Functional groups are when treated in O2 containing plasmas:

Alkyl Alkoxy Carbonyl Alcohol Peroxy Acid

R R-O R=O R-OH R-OO 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 surface-surface reactions.

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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.

FORCED GAS FLOW AND WEB MOVEMENT

Gas Flow

LAB MADE INDUCTIVE COUPLED PLASMA

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 time-varying 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

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

Plasmas are created in oxygen, hydrogen, nitrogen and argon

Plasma sterilization

SEM image of Bacillus subtilis before (left) and after plasma treated.

1μm

1μm

AFM investigations of biological samples

Atomic Force Microscope (AFM) (left) and image of Staphylococcus aureus (right).

Plasma functionalization of organic materials

oxygen plasma

Surface polymer

C-OH

C-O COOH C=O

Polar groups on a polymer surface cause a dramatic increase of surface wettability.

Reactive particles from oxygen plasma are incorporated on the surface forming O-rich functional groups.

Surface wettability is measured by water drop

The contact angle of a water drop on a polymer surface versus plasma treatment time

untreated

treated 0.5s

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6Treatment time (s)

Con

tact

ang

le (°

)

Appearance of functional groups is best analysed by X-ray photoelectron spectroscopy (XPS = ESCA)

sample

X-ray source Ele

ctro

n detec

tor

Photo-electrons

hn

Instrument PHI-TFA Principle

Appearance of functional groups is monitored by XPS

010020030040050060070080090010001100Binding enegy (eV)

Inte

nsity

(arb

. uni

ts)

untreated

plasma treated

afterglow treated

C

1s

O 1

s

O K

LL

S 2s

S 2p

O K

LLO

KLL

O 1

sO

1s

C

1sC

1s

S 2s

S 2p

S 2s S 2p

Survey spectra of PES (poly(ether sulfones)) polymer before (bottom) and after different plasma treatment (middle and top).

280 285 290 295 300 Binding Energy (eV)

Inte

nsity

(arb

. uni

ts)

A

B

D

280 285 290 295 300 Binding Energy (eV)

Inte

nsity

(arb

. uni

ts)

A

B

C D Untreated PES

Plasma activated PES (1s)

A … C-C or C-HB … C-OC … C=OD … O=S=O

High resolution C 1s peak

c cO oI II

ION BEAM TREATMENT 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

METALLİZATİON 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

OTHER TYPES 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

CHEMİCAL MODİFİCATİONS 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 TREATMENT 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

WET TREATMENT 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.

TECHNİQUES Sodium etching of fluoropolymers Oxidizing treatment based on chromic acid

solutions Hydrolysis of polyesters etc.

ETCHİNG OF FLUOROPOLYMERS 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 non-stick frying pans.

ETCHİNG OF FLUOROPOLYMERS 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.

ETCHİNG OF FLUOROPOLYMERS The effectiveness of etching is measured by calculating the change in

surface wettability. θ = contact angle

SURFACE OXİDATİON AND ETCHİNG Surface treatment of various polymers by oxidizing

solutions was developed as a result of the low metal-to-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.

REASONS 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.

HYDROLYSİS 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.

HYDROLYSİS 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.

FUNCTİONALİZATİON 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.

SURFACE GRAFTING 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.

SURFACE GRAFTİNG 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.

REFERENCES http://www.markelcorporation.com/material10.html http://www.devicelink.com/mddi/archive/05/10/006.

html http://pubs.acs.org/cgi-bin/abstract.cgi/jpchax/1994/9

8/i47/f-pdf/f_j100098a046.pdf?sessid=6006l3 http://www.kobelco.co.jp/p108/p14/sfe05.htm http://www.adhesivestoolkit.com/Docu-Data/SurfaceP

reTreatment.xtp http://www.sciencedirect.com