Joining of Medical Plastics Using Atmospheric Discharge Pretreatments

of Adherents Prior to Bonding

Rory WolfEnercon Industries Corporation

Presented at a meeting of the Thermoset Resin Formulators Association at the Hyatt Regency Savannah in Savannah,

Georgia, September 10 – 11, 2007

This paper is presented by invitation of TRFA. It is publicly distributed upon request by the TRFA to assist in the communication of information and

viewpoints relevant to the thermoset industry. The paper and its contents have not been reviewed or evaluated by the TRFA and should not be construed as

having been adopted or endorsed by the TRFA.

Enercon Industries CorporationEnercon Industries Enercon Industries CorporationCorporation

Joining of Medical Products Using Atmospheric Discharge Pretreatments

of Adherents Prior to Bonding

Presented byRORY A. WOLF

V.P. BUSINESS DEVELOPMENT

Joining of Medical Products Using Atmospheric Discharge Pretreatments

of Adherents Prior to Bonding

Presented byPresented byRORY A. WOLFRORY A. WOLF

V.P. BUSINESS DEVELOPMENTV.P. BUSINESS DEVELOPMENT

Major Presentation TopicsMajor Presentation Topics

Issue Proposition

Polymers and Adhesives for Medical Devices

Principles of Atmospheric Discharge Surface Treatment Devices

Experimental Design

Experimental Results

Solution Proposition

Issue Proposition

Issue Proposition

Plastics usage in medical devices have sustained an average annual growth rates far in excess of the Gross Domestic Product (GDP).

US demand for medical plastics will increase nearly 3% per year to 3.6 billion pounds in 2008, valued at $5.0 billion.

Issue Proposition

Key Drivers of Medical Plastics Usage:

Aging of the U.S. population, Continuing cost reduction pressures in the healthcare field, Advances in polymer performance, Introduction of new and often life-saving devices, Environmental / Disposable / Non-disposable medical device triad.

Issue Proposition

The strongest advances in plastics usage are expected for engineered resins such as polycarbonate and thermoplastic elastomers, which have favorable cost-performance benefits.

Polypropylene, polyethylene, polyurethane and polyvinyl chloride and will retain leading positions in non-invasive medical products and standard medical packaging due to their low cost and amenability to radiation sterilization.

Polyolefins are difficult materials to effect surface bonding.

Medical Polymers and Adhesives

Polypropylene are crystalline, have excellent thermal and chemical resistance properties, high moisture resistance, good mechanical properties.

Polypropylenes are a difficult-to-bond substrate since they feature no surface functional sites or inherent surface roughness to which an adhesive can secure itself.

Polypropylenes are linear or branched carbon chain polymers, have low surface energies, low porosity, and non-polar surfaces.

Medical Polymers and Adhesives

Polyethylene, and particularly low density polyethylene (LDPE), is a semi-crystalline thermoplastic produced by way of a free-radical-polymerization reaction.

Although polyethylene typically has lower strength and hardness properties, it offers numerous benefits including flexibility, clarity, and enhanced impact and stress cracking resistance.

High-density polyethylene (HDPE) is similar to low-density polyethylene in the polymerization process used to obtain the resin. However, the density of the polyethylene increases, resulting inhigher strengths, increased hardness, and enhanced chemical and abrasion resistance.

Hard-to-bond plastics such as polyolefins are most often assembled using adhesives.

While adhesives are the most versatile assembly method for plastics, only a few industrial adhesives offer suitable bond strengths on hard-to-bond plastics.

Cyanoacrylate, light-curing cyanoacrylate, hot-melt and light-curing acrylic adhesives have typically been used with typical difficult-to-bond plastics.

Acrylic adhesives are also being introduced for use with hard-to-bond plastics.

Medical Polymers and Adhesives

Cyanoacrylate adhesives - polar, linear molecules that undergo an anionic polymerization reaction. A weak base, such as moisture, triggers the reaction causing the linear chains to form. Form thermoplastic resins when cured.

Ethyl monomer-based cyanoacrylates - low impact and peel strengths, low to moderate solvent resistance, and maximum operating temperatures of 160-180 degrees F. Fixture time: 3 seconds.

Rubber-modified cyanoacrylate - improved peel and impact strengths over standard cyanoacrylates. Fixture time: 30 seconds to 2 minutes.

Thermally resistant ethyl cyanoacrylates - can withstand continuous exposure to temperatures up to 250 degrees F.

Medical Polymers and AdhesivesThe Specifics…

Light-curing acrylics - cured by way of free radical reaction to form thermoset resins when exposed to light of the appropriate wavelength and intensity. Fixture time: Immediate

Light-curing cyanoacrylates - ethyl-based with photoinitiators to allow rapid fixturing under exposure to low-intensity light, and to cure in shadowed areas. Fixture Time: Immediate

Polyolefin hot melts - provide good resistance to moisture as well as excellent resistance to polar solvents, acids, bases and alcohols, offering superior adhesion to polypropylene. Fixture time: 80-100 sec.

Reactive urethane hot melts - perform well on hard-to-bond plastics, processing at temperatures of approximately 250° F, 200° F cooler than EVA, polyamide, and polyolefin hot melts. Fixture time: 30-60 sec.

Medical Polymers and AdhesivesThe Specifics…

To make an adhesive formulation , the fluid adhesive should have a surface tension no higher (and preferably 10 mN/m lower) than the critical surface tension of the solid adherend.

Polymers gc (20°C): mN/mPoly(tetrafluoroethylene) 18Silicone, polydimethyl 24Poly(ethylene) 31cis-Poly(isoprene) 31Poly(styrene) 33Poly(vinyl alcohol) 37Poly(methyl methacrylate) 39Poly(vinyl chloride) 40Poly(acrylonitrile) 44Amine-cured epoxide 44Poly(ethylene terephthalate) 45Cellulose 45Poly(hexamethylene adipamide) (nylon 6,6) 46

Critical Surface Tension

Low Surface Tension

Migration of Formulation ComponentsMold Release AgentsLow temperatureUV light Mechanical Stresses Design and Fabrication Issues

Adhesion Impediments – Medical Plastics

Low Surface Tension

Migration of Formulation ComponentsMold Release Agents

… and other surface anomalies on molded and formed medical parts can impede the performance of adhesives dramatically if they are not addressed with surface pretreatments such as air plasma, flame plasma or atmospheric chemical plasma.

Adhesion Impediments – Medical Plastics

Methods of Surface Preparation

Air Plasma Discharge

Air Plasma SystemsAir Plasma SystemsApplies discharge to surface of medical plastics through an air gap, via an electrode design. When air is exposed to different voltages, an electrical dischargedevelops, causing neutral and electrically charged molecules to collide. Collisions cause neutral molecules to become electrically charged, resulting in filamentary discharges which create a cloud of ionized air - or an “air plasma”. Electrons bombard the treatment surface with energies 2-3x that necessary to break the molecular bonds on the surface of most substrates. The resulting free radicals react rapidly with other free radicals on the same or different molecular chain, resulting in cross-linking. Oxidative affects increases surface energy as a result of polar groups being created on the surface, primarily in the form of hydroxyl groups, carbonyl groups, amide groups and carboxylic acid. Electron and ion bombardment will also create a cleaning effect on surfaces of medical plastics.

Principles of Air Plasma Treatment

Methods of Surface Preparation

Flame Plasma Discharge

Flame Plasma SystemsFlame Plasma SystemsFlame plasma systems are comprised of a combustion/electrical station and a burner assembly, manufactured with two primary burner configurations – ribbon and enhanced velocity. A flame plasma is formed when a flammable gas and atmospheric air are combined and combusted to form an intense blue flame. Medical plastics are made polar as species in the flame plasma affect the electron distribution and density on the surface. Polar functional groups such as ether, ester, carbonyl, carboxyl, and hydroxyl are contained in a flame plasma; these are incorporated into the surface and affect the electron density of the polymer material. This polarization and functionalization is made through reactive oxidation of a surface. ESCA analysis shows that oxidation depth through flame treatment is 5-10nm. Flame plasma treatment’s extensive oxidation, due to reactions with OH radicals in the flame, results in a cleaned and highly wettable surface which is relatively stable upon aging.

Principles of Flame Plasma Treatment

Methods of Surface Preparation

Atmospheric Variable Chemistry Plasma Discharge

Atmospheric Variable Chemistry Plasma SystemsAtmospheric Variable Chemistry Plasma Systems

Much like an air plasma field, a chemical plasma field is Much like an air plasma field, a chemical plasma field is generated in an generated in an electrically charged atmosphere. electrically charged atmosphere.

This method This method blends air (Oblends air (O22, N, N22) with other gases) with other gases that that deposit various chemical groups on the substrate surface deposit various chemical groups on the substrate surface to improve its surface energy. to improve its surface energy.

Chemical plasma treatment is essentially a Chemical plasma treatment is essentially a NanoNano--CleaningCleaning, , MicroMicro--Etching Etching andand FunctionalizingFunctionalizing process process that provides different surface characteristics depending that provides different surface characteristics depending on the gas chemistry employed. on the gas chemistry employed.

Principles of Atmospheric Variable Chemistry Plasma Treatment

Oxygen molecules of the air passing near the Oxygen molecules of the air passing near the electrodes break down into electrodes break down into reactive oxygen speciesreactive oxygen species(ROS)(ROS)Inert gases are ionized as well, increasing the Inert gases are ionized as well, increasing the homogeneityhomogeneity of the discharge and the activation of of the discharge and the activation of surfaces.surfaces.Organic substrates such as Organic substrates such as hydrocarbons, bacteria, hydrocarbons, bacteria, and virusesand viruses that become exposed to these ROS, that become exposed to these ROS, volatilized, and are volatilized, and are destroyeddestroyed or rendered harmless or rendered harmless on contact on contact Surface activation via reactive surface radicals which Surface activation via reactive surface radicals which create chemical bonds and create a create chemical bonds and create a crosscross--linked linked surface.surface.

Atmospheric Variable Chemistry Plasma Systems Atmospheric Variable Chemistry Plasma Systems --How they workHow they work

Principles of Atmospheric Variable Chemistry Plasma Treatment

Principles of Atmospheric Variable Chemistry Plasma Treatment

XPS of Untreated PTFE film w/ CF2 groups on surface

XPS of Treated PTFE Film w/new CH2 groups derived from acetylene injection into plasma stream

Principles of Atmospheric Variable Chemistry Plasma Treatment

Experimental DesignExperimental DesignTheorized

Application of air plasma, flame plasma and variable chemistry plasma surface pretreatment would sufficiently clean the surface of polypropylene, polyethylene and polyurethane - based medical plastic parts of LMWOM following molding and forming processes.

Technologies Applied1) Air Plasma device w/internal air blower to discharge a blown arc at 480W at 25-

250fpm process speeds. 2) Flame Plasma device w/compressed air and methane inputs. The stoichiometric

ratio air/gas ratio was maintained at 10:1 to create a thermal discharge of 11,282 BTUs/hr. at 100-250fpm (min. non-destruct) process speeds.

3) Variable Chemistry Plasma device using a treatment mixture of He/O2 at 25-250 fpm process speeds.

Materials TestedMedical device manufacturers provided common plastic part assemblies for conveyance beneath each of the treatment devices at industry-standard discharge gaps between treatment device head and substrate to achieve optimum treatment.

Experimental ResultsExperimental Results

Air PlasmaAir Plasma Flame PlasmaFlame Plasma Variable Chemistry PlasmaVariable Chemistry Plasma

MaterialMaterial Initial DyneInitial Dyne Final DyneFinal Dyne Initial DyneInitial Dyne Final DyneFinal Dyne Initial DyneInitial Dyne Final DyneFinal Dyne

PPPP 3030 4444 3030 4646 3030 5454

PEPE 3131 4444 3131 4646 3131 5252--5454

PUPU 3131 4040 3131 4242 3131 6060

Treat WidthTreat Width 50.8mm50.8mm 150mm150mm 38mm38mm

Air/Gas FlowAir/Gas Flow 311lpm311lpm 150lpm150lpm (proprietary)(proprietary)

Treat GapTreat Gap 6.4mm6.4mm 41.3mm41.3mm 6.4mm6.4mm

SpeedSpeed 100fpm100fpm 100fpm100fpm 100fpm100fpm

Experimental ResultsExperimental ResultsAtmospheric Surface Activation Treatment Analysis

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ABS Acrylic HDPE LDPE Nylon 12 PP PTFE PVC

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m Air plasmaFlame PlasmaACP

Solution Proposition

Flame plasma effected a higher level of cleaning and surface tension compared to air plasma through higher electron bombardment, increased surface electron density, and high surface oxidation.

The primary effect of a flame plasma discharge device is interpreted to be related to:

1) increased treatment (bombardment) efficiency, 2) greater power density transfer, and 3) a more homogeneous discharge profile

Air and flame plasma surface treatments raise surface tension levels of medical plastics for sufficient interfacial adhesion.

Atmospheric variable chemistry plasma treatment effects higher surface tension levels across all trial materials and potentially offers higher adhesions for medical and difficult-to-treat plastics.

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Solution Proposition

The use of low polarity polyolefins in the manufacturing of medical device assemblies such as catheters, syringes, tubings and other components may be more suitably cleaned of molding and forming organic

contaminations and functionalized using flame plasmas as opposed to air plasmas for improved adhesive adhesion.

Assembly profiles used in this study had sufficient wall thickness so as to

show no thermal pretreatment effects under the flame plasma trial conditions cited.

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Solution Proposition

Air plasma technologies may be just as applicable in achieving cleaning, functionalizing, and adhesion objectives if required processing

speeds are lower and if part wall thicknesses are thinner, relative to flame plasmas.

Nano-Cleaning, Micro-Etching and Functionalizing to full wettability (above 72 dynes/cm) is achievable by all technologies.

Individual medical device adhesion results are primarily dependent upon 1) medical device component material, 2) material contamination, 3) type of adhesive, 4) type of surface treatment, and 5) process dwell time.

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Thank You For Your Kind Attention!