Wally Hansen

Wally Hansen
Business Development Manager
Belmont, CA

Editorial April 2015

whirlpool-waves

Water is everywhere…just not always where we want it. This past winter, the Eastern U.S. was inundated with snow and ice, while California and the Western U.S. are suffering from extreme drought. Availability of water is a growing concern around the world as it is a vital resource for the seven billion (and counting) people on Earth.

While representing only a small fraction of water usage as compared to that used in agriculture and for energy production, industrial use of water is on the rise. A staggering 18.2 billion gallons of fresh water are used every day for industrial use in the U.S. – about 4% of the total water used for all purposes.

Manufacturing one ton of automotive steel requires about 75,000 gallons of water. Actual manufacture of the vehicle itself requires an additional 39,000 gallons. Two and a half gallons of water are needed to produce a gallon of gasoline – and 20 gallons are needed to produce a pint of beer!

Critical part cleaning, for adhesion-related applications, represents a significant portion of industrial water use. Since the replacement of Freon and other solvent cleaning processes starting in the 1980s, U.S. industrial use of aqueous cleaning processes has become the norm.

But aqueous cleaning is a cost-intensive process, whether you’re looking at it from an environmental standpoint, a dollars-and-cents standpoint, or a labor standpoint.

Water needs to be delivered; detergents, surfactants and other chemicals are added and need to be kept in balance to control the washing process; additional processing is required to treat the waste water for recycling or disposal. Rinse water must also be clean and controlled. There is an old saying that “You are only as clean as your last rinse.”

Even after the part has been washed, it is still not ready for bonding, coating, painting, or printing. It needs to be dried, requiring additional energy costs, equipment footprint, time, and labor.

Furthermore, as mentioned above, water tends to not always go where we want it. Even with the best washing and drying processes, water’s influence remains at the molecular surface where adhesion occurs, interfering with a strong bond.

Molecular water resides in the oxides of aluminum and other metals. Water is absorbed and bonded within many polymers such as ABS and nylon. However, water molecules are not usually well-bonded and do not provide a robust bonding surface.

What if there was a better way for critical cleaning of organic contaminants? What if a process did not use water or other liquids but instead actually removed water from the molecular surface while vaporizing organic contaminants? It would be even better if this nano cleaning could be accomplished without touching the part and a chemical activation could occur to chemically bond to the adhesive, coating paint, or printing ink.

Save Water

Stay Dry

Plasma Clean

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Category: Miscellaneous
14. April 2015   3:04 pm
Khoren Sahagian

Khoren Sahagian

file000527241311

May the force be with you: Not just for Star Wars anymore.

Boeing, according to reports in Popular Science and other media outlets, has been granted a patent for a plasma-generated “force field” that protects combat vehicles from the impact of explosions.

The idea is that explosions in the vicinity of the sensor-equipped vehicle trigger the rapid formation of a superheated plasma layer around the vehicle. The plasma creates a buffer zone to reduce the impact of shock waves, protecting both the vehicle itself and the occupants within it.

Even better, it’s not just land vehicles that could benefit from this incredible technology. The patent filing notes that the “protected asset” could be a surface vessel, a submarine vessel, an offshore platform, a land structure, or even “a human.”

Personally, I love the idea of being surrounded by a protective plasma shield, though I am fortunate that I don’t usually need one in the course of my daily activities! I am continually amazed by the new applications for plasma and excited to be working at Plasmatreat, which is always at the forefront of this technology.

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2. April 2015   4:03 pm
Andy Stecher

Andy Stecher
Elgin, IL

magnifying glassIn some ways, what we do here at Plasmatreat is like a less gory “CSI”: We are often called upon to solve mysteries of the manufacturing persuasion. And, while we don’t usually get it nailed in an hour flat (minus time for commercial breaks), we do manage to crack the case more often than not.

In today’s installment, I’ll explain how we helped Ford Motor Company and The Preh Group, an automotive component supplier, solve a seemingly intractable adhesion challenge.

The new Ford Lincoln MKZ features a sophisticated control panel that combines climate control with various infotainment functions (telephone, navigation, and music), all in a streamlined central console known as the “center stack.”

A laminator is used to bond the interactive PET touch foil, which has an adhesive backing, to the injection-molded polycarbonate panel of the center stack. Everything initially looked good from a manufacturing standpoint – until the climactic test, when the adhesive detached and large bubbles formed in the boundary layer between the plastic substrate and the foil.

This delamination would ultimately cause the control panel to fail, so Preh went back to the drawing board to troubleshoot the problem. Simple adhesives produced large bubbles; high-tech adhesives produced smaller bubbles. But the bottom line remained the same: The adhesive film continued to detach.

With time and money clicking away, Preh decided to take a closer look at the PC panel itself. Preh concluded that the bubbles were most likely being caused by a release of gases from additives in the plastic due to the extremes of the climactic test.

Changing the material used for the panel was not an option – but pretreating its surface was. As Preh was already using Plasmatreat technology for microfine cleaning and activation of sensor circuit boards, it sent the PC panel out to one of its labs for a preliminary plasma test.

When the test panel was removed from the climactic chamber after four days of extreme temperatures and high humidity, the Preh developers breathed a sigh of relief. “There was not a bubble to be seen,” says Markus Ledermann, Preh’s manufacturing technology engineer. “With the foil adhesion fully intact, the adhesive bond had met the stringent requirements.”

Case closed, thanks to Plasmatreat! What manufacturing mysteries can we help you solve, automotive or otherwise? Let us know – we love a challenge.

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20. March 2015   9:48 am
Dr. K. L. Mittal, Dr. Robert H. Lacombe

Dr. K. L. Mittal, Dr. Robert H. Lacombe

The previous issue of the “SURFACES: THE INVISIBLE UNIVERSE” blog focused on the topic of polymer surface modification. In this issue we continue on this topic and would again like to remind the reader of the upcoming Tenth International Symposium on Polymer Surface Modification: Relevance to Adhesion, to be held at the University of Maine, Orono, June 22-24 (2015). All readers are cordially invited to join the symposium either to present a paper on their current work in this field or to simply attend and greatly expand their awareness of current developments. Further details are available on the conference web site at: www.mstconf.com/surfmod10.htm

 

PLASMA CHEMISTRY OF POLYMER SURFACES

We continue our discussion on the topic of polymer surface modification via a book on this most important subject:

The Plasma Chemistry of Polymer Surfaces: Advanced Techniques for Surface Design, by Jörg Friedrich (WILEY-CVH Verlag GmbH& Co. KgaA, 2012)

The author began his studies in Macromolecular Chemistry at the German Academy of Sciences in Berlin and has been active in this field ever since and is now professor at the Technical University of Berlin. He is best know to us through his past participation in previous gatherings of the above mentioned Polymer Surface Modification symposium series going back to 1993.

In his introduction Prof. Friedrich points out the apparently incredible fact that more than 99% of all visible matter is in the plasma state. A moments reflection, however, easily confirms this statement since the Sun above, which of itself accounts for more than 99% of all matter in the solar system, is in fact an exceedingly dense and hot ball of plasma. Here on earth the plasma state is rarely observed outside of special devices and consists mainly of low and atmospheric pressure plasmas which are a source of moderate quantities of energy mainly transferred through the kinetic energy of free electrons. Such plasmas have sufficient energy to produce reactive species and photons which are able to initiate all types of polymerizations or activate the surface of normally inactive polymers. Thus plasmas offer the opportunity to promote chemical reactions at surfaces which would otherwise be difficult to achieve. However, the very active nature of plasma systems also present a problem in that the broadly distributed energies in the plasma can also initiate a wide range of unwanted reactions including polymer chain scission and cross linking. The problem now becomes how does one tame the plasma into performing only the chemical reactions one desires by eliminating unwanted and destructive processes. This is the topic to which we will give more attention to shortly but first a quick look at the contents of the volume.

The volume is divided into 12 separate chapters as follows:

  1. Introduction
  2. Interaction Between Plasma and Polymers
  3. Plasma
  4. Chemistry and Energetics in Classic and Plasma Processes
  5. Kinetics of Polymer Surface Modification
  6. Bulk, Ablative and Side Reactions
  7. Metallization of Plasma-Modified Polymers
  8. Accelerated Plasma-Aging of Polymers
  9. Polymer Surface Modifications with Monosort Functional Groups
  10. Atmospheric-Pressure Plasmas
  11. Plasma Polymerization
  12. Pulsed-Plasma Polymerization

Given the above list I think it can be fairly said that the volume covers the entire range of surface chemistries associated with plasma processes and far more topics than can be adequately addressed in this review. Thus the remainder of this column will focus on the above outlined problem of controlling the surface chemistry by taming normally indiscreet plasma reactions. This problem is discussed in chapters 9 and 12 of Prof. Friedrich’s book.

Chapter 9 attacks the problem of controlling an otherwise unruly surface chemistry initiated by aggressive plasma reactions through the use of “Monosort Functional” groups. For the benefit of the uninitiated we give a short tutorial on the concept of functional group in organic chemistry. The term functional group arises from classic organic chemistry and typically refers to chemical species which engage in well known chemical reactions. The classic example refers to chemical species attached to hydrocarbon chains. As is well known the hydrocarbons form a series of molecules composed solely of carbon and hydrogen. The simplest which is methane or natural gas which is simply one carbon atom with 4 hydrogens attached in a tetrahedral geometry and commonly symbolized as CH4. The chemistry of carbon allows it to form strings of indefinite length and in the hydrocarbon series each carbon is attached to two other carbons and two hydrogens except for the terminal carbons which attach to one other carbon and 3 hydrogens. Thus moving up the series we get to the chain with 8 carbons called octane which is the basic component of the gasoline which powers nearly all motor vehicles. Octane is a string of 8 carbons with 6 in the interior and two on the ends of the chain. The interior carbons carry two hydrogens and the two end carbons carry 3 hydrogens each giving a total of 18 hydrogens. Octane is thus designated as C8H18. Moving on to indefinitely large chain lengths we arrive at polyethylene which is a common thermo-plastic material used in fabricating all varieties of plastic containers such as tupper ware® , plastic sheeting and wire insulation. Outside of being quite flammable the low molecular weight hydrocarbons have a rather boring chemistry in that they react only sluggishly with other molecules. However, if so called functional groups are introduced the chemistry becomes much more interesting. Take the case of ethane C2H6 the second molecule in the series which is a gas similar to methane only roughly twice as heavy. If we replace one of the hydrogens with what is called the hydroxyl functional group designated as -O-H which is essentially a fragment of a water molecule, ie H-O-H with one H lopped off, we get the molecule C2OH6 which now has dramatically different properties. Ethane the non water soluble gas becomes ethanol a highly water soluble liquid also known as grain alcohol and much better known as the active ingredient in all intoxicating beverages. Thus through the use of functional groups chemists can work nearly miraculous changes in the properties of common materials and Prof. Friedrich’s monosort functionalization is a process for using plasmas to perform this bit of magic on polymer surfaces by attaching the appropriate functional groups. The process can be rather tricky, however, and requires understanding of the physical processes involved at the atomic and molecular level.

The following example illustrates the nature of the problem and how successful functionalization can be carried out using plasma technology.

Figure (1a) illustrates the basic problem with most common plasma surface treatments. The exceedingly high energy associated with the ionization of oxygen coupled with the equally high energies associated with the tail of the electron energy distribution give rise to a panoply of functional groups plus free radicals that can give rise to degradation and crosslinking in the underlying polymer substrate. Thus it would be difficult to control the chemical behavior of the nonspecific functionalized surface shown in Fig.(1a) with regard to further chemical treatment such as the grafting on of a desired molecule. In essence the wide range of chemically reactive entities make it very difficult to control any further chemical treatment of the surface due to the presence of a wide range of reactive species with widely different chemical behaviors.

Prof. Friedrich points out that unfortunately most plasma gasses behave as shown in Fig.(1a) but somewhat surprisingly use of Bromine (symbol Br) is different due to a special set of circumstances related to the thermodynamic behavior of this molecule, which are too technical to go into in this discussion. It turns out that bromine plasmas can be controlled to give a uniform functionalization of the polymer surface as shown in Fig.(1b). The now uniformly functionalized surface can be subjected to further chemical treatment such as grafting of specific molecules to give a desired well controlled surface chemistry.

In a similar vein, in chapter 12 Prof. Friedrich approaches the problem of plasma polymerization through the use of pulsed as opposed to continuous plasma methods. The problem is much the same as with the surface functionalization problem discussed above. Continuous plasmas involve a steady flux of energy which gives rise to unwanted reactions whereas by turning the energy field on and off in a carefully controlled manner limits the amount of excess energy dumped into the system and thus also the unwanted side reactions.

As this blog is already getting too long we leave it to the interested reader to explore the details by consulting Prof. Friedrich’s volume. As usual the author welcomes any further comments or inquiries concerning this topic and may be readily contacted at the coordinates below.

 

Dr. Robert H. Lacombe, Chairman

Materials Science and Technology CONFERENCES

3 Hammer Drive, Hopewell Junction, NY 12533-6124

Tel. 845-897-1654, FAX  212-656-1016; E-mail: rhlacombe@compuserve.com

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Category: LIFE SCIENCES
17. March 2015   12:01 am
Khoren Sahagian

Khoren Sahagian

We were pleased to learn that a team of researchers from the University of California, Berkeley will be presenting their findings related to a method of surface modification introduced by Plasmatreat North America. The work will be shared at the upcoming annual meeting for the American Association for Thoracic Surgery.

Researchers at UC Berkeley worked with the team at Plasmatreat N.A. to identify an effective method for heparin immobilization on electrospun polycarbonate-urethane vascular grafts.  Heparin incorporation provides implantable medical devices with antithrombotic characteristics.

The team explored three surface modification techniques:

  • aminolysis with 1-Ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC) chemistry as a chemical immobilization
  • polydopamine coating as a passive adsorption
  • plasma treatment paired with end-point immobilization to ultimately conjugate heparin on the graft surface.

 

The most effective modification was determined with respect to the heparin density as well as the antithrombogenic activity of the immobilized heparin. Then, the team proceeded with these optimized PCU grafts immobilized with heparin for short-term in vivo studies.

After 4 weeks, plasma-control grafts exhibited approximately 29% (2 of 7) patency, compared to 86% (6 of 7) patency of plasma-heparin grafts. More importantly, the team observed a more complete endothelialization of the luminal surface with a more aligned, well-organized monolayer of endothelial cells.

The team concluded, in vitro, that the combination of plasma treatment and end-point immobilization of heparin drastically improved the performance of the vascular grafts with respect to patency as well as early stages of endothelialization.

These findings are tremendously exciting because they signal a new era for implantable medical devices. In the past, a goal was to evade biological responses by selecting inert materials that delay host rejection.

Now, however, material modification are allowing researchers to immobilize biomolecules or cytokine, which in turn allows the surface of the device to regulate cellular behavior and to engineer surface response.

The team at Plasmatreat N.A. wants to thank our collaborators at University of California, Berkeley for their innovative utilization of plasma surface modification. Surface chemistry and topography play integral roles in biological development and remodeling. Gas plasma technologies are an effective tool for customized surface engineering.

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Mikki Larner

Mikki Larner
Vice President Sales & Marketing
Belmont, CA

Editorial March 2015

I just celebrated my 15th year in the plasma surface modification business. And I have gathered 15 years of misconceptions and have, successfully I think, been able to educate and raise the awareness of the technology’s flexibility for designing working surfaces and dispel many of these.

The most common are:

  • It doesn’t last
  • All equipment is the same
  • All plasmas are the same
  • I tried argon and oxygen and it didn’t work, thus plasma doesn’t work
  • It produces ozone
  • It just oxidizes the surface
  • It is expensive

 

With my colleagues, I have published papers (with a book chapter pending!) and presented at numerous conferences, exhibitions and companies. Plus provided workshops on the technology to a variety of audiences. I love doing this because I’m always dispelling these misconceptions and educating about the diverse field of plasma. One of our advisors has coined the term “plasmersion.” It is a fun way to think about the process (and the work as a noun): the part is typically immersed in the plasma (in the case of the 3-d vacuum plasma treatment) and with Openair the surface to be treated is immersed in the plasma. It also could be used as a verb, and I’m plasmersing folks in our technology.

With that said, I’d like to remind you of the services that I offer.

In addition to Plasma Technology Systems’ long history of providing professional commercial solutions (30 years and counting) and our exceptional customer service, we offer what we believe to be the most diverse private-sector atmospheric and low pressure plasma equipment suite and surface chemistry offerings in the world.

We have a global network of partners and subsidiaries in all key industrial markets that enables us to provide our customers with all-in-one solutions (both bespoke and off-the-rack).

Depending on your specific relationship with us, you may not know that we offer all of the following:

  1. Research and Process Development:  We offer a highly creative yet low-risk environment for the evaluation and development of novel gas plasma processes, for small start-ups to Fortune 500 companies. Customers can bring us their own ideas or pull from our extensive (and ever-expanding) process and chemistry library.  We can advise you on specific plasma issues, develop plasma processes to address your specific needs, and assist in the development of a full-scale plasma system tailored to your specific requirements.
  2. Contract Manufacturing Services.  We have a fully equipped ISO: 9001 contract manufacturing division (4th State, Inc.) in Belmont, California (just north of Silicon Valley), where we modify materials on a contract basis. This is an ideal solution for companies that are not ready for the technology transfer. These contract manufacturing services enable a seamless translation of process to production with no capital expense, for your smallest and largest products—from powder to 1.5 meter-wide rolled goods. This is another area where we offer risk reduction. You can test your product in the market first, gain acceptance and confirmation of volumes, and then lease or purchase the equipment.
  3. Equipment Solutions.  From small batch to large batch to fully integrated work cells, our team delivers standard systems and custom platforms for low-pressure and atmospheric plasma technology. Depending on the technology, you have the option to buy the equipment outright or lease it from us with warranty support for the term of the lease. Our equipment solutions also include installation, training support and calibration services. And we maintain a full supply of spare parts in two facilities to support our North American customer base.

If you take nothing else away from this message, remember this: We offer a whole lot more than you probably think we do. So if there’s ever anything we might be able to help you out with, give us a call—you may be pleasantly surprised to find out that it’s the only call you need to make.

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5. March 2015   2:00 pm
Andy Stecher

Andy Stecher
Elgin, IL

NPE2015

If you, like me, are old enough to recall the classic 1967 film The Graduate, you know it features many memorable scenes.

One of my favorites takes place when newly minted college graduate Benjamin Braddock (Dustin Hoffman) is drifting around his parents’ pool, trying to figure out what to do with his life. One of his father’s friends, identified only as Mr. McGuire, stops by and offers a one-word piece of unsolicited advice: “Plastics.”

While the scene is played for laughs, looking back now from a distance of nearly 50 years—unbelievable, isn’t it?—Mr. McGuire was clearly onto something. New technologies are revolutionizing the industry at an incredible pace, which is why I’m very much looking forward to Plasmatreat North America’s participation in the upcoming NPE2015 International Plastics Showcase in Orlando later this month.

As you may know, NPE takes place only once every three years, and it’s a massive, exciting event. If you’re planning to attend, please do stop by our booth (W8078) and say hello.

We will be treating parts on-site in our enclosure and verifying the effects with the handheld Brighton Surface Analyst tool. Additionally, we’ll have a KUKA Agilus robot on display demonstrating some of our advanced automated surface treatment solutions.

Finally, I will be presenting a paper at ANTEC, the annual technical conference that will run concurrently with NPE this year. The topic is “Managing Global Challenges with Micro Solutions: The Role of Plasma Surface Treatment in the Future of Plastics.”

I’ll cover seven global trends in plastic part manufacturing, each of which represents new business opportunities—and technical challenges. Plasma surface treatment poses an elegant, environmentally friendly, cost-effective means for meeting these new challenges, so I hope you will consider stopping by to hear all the details!

As always, if you have any questions about our participation in NPE2015 or anything else, please do let us know and we’ll be delighted to chat further. Hope to see you in Orlando in a few weeks, and best wishes for safe and smooth travels to our fellow exhibitors and attendees.

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Khoren Sahagian

Khoren Sahagian
Materials Scientist

Editorial February 2015

My colleague, Wally Hansen, and I have just released a new review paper that may be of interest to those of you in the aerospace industry.

As you know, aerospace has had decades of experience with metal bonding, sealing, and corrosion protection. However, many of these methods have not lent themselves well to automation, and they also generate environmental waste.

But new applications are emerging for atmospherically deposited nano coatings that can address these shortcomings. These nano coatings are formed by direct injection of select vapor chemistries into the plasma jet. Such molecular surface modifications yield long-term, environmentally stable interfaces for bonding.

Cleaning

Plasma surface treatment begins with a fine cleaning of the substrate to remove loosely bound organic contaminants (on metal oxide surfaces, the oxide layer is either removed or pre-conditioned for adhesion).

Atmospheric plasma jets provide a multi-faceted cleaning action. First, the charged species within the plasma neutralizes electrostatically bound particles. Next, a vortex of pressurized gas blows away unbound solids and oils. Finally, the substrate is bombarded by reactive gas plasma species.

Low molecule weight contaminants on the substrate surface are efficiently reduced into nascent compounds and removed from the material system. This final phase of cleaning takes place on the molecular scale.

Coating

After cleaning, a different plasma jet technology deposits a functional coating. The coating thickness is controlled by parameters such as distance to substrate and speed. Coatings have been developed that simultaneously provide adhesion promotion and corrosion protection of the bond line. Furthermore, some of these coatings act as reliable tie layers, effectively bridging contact between inorganic and organic systems. There is opportunity to replace liquid primers or otherwise laborious surface pre-treatments used in composite bonding.

So far, atmospherically deposited plasma coatings have demonstrated utility as a release layer, an adhesion promoter, or a corrosion barrier. In practice, the plasma-deposited nano coating combines with conventional protective top coats to amplify corrosion resistance and suppress ingress at damage sites.

The atmospherically deposited plasma coatings show substantial improvement in corrosion performance even at a thickness of less than 500 nm.

Conclusion

Atmospheric plasma cleaning and coating can offer significant advantages in surface preparation of metals and composite systems for bonding and sealing in the aerospace industry. The technology is scalable and amenable to automation as it enables high-throughput material processing.

Furthermore, some plasma implementations are able to combine multiple process steps into a single step while reducing waste and reducing operating costs – without compromising performance.

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12. February 2015   7:48 pm
Andy Stecher

Andy Stecher
Elgin, IL

I’m pleased and proud to let you know that Plasmatreat was awarded the “Würth Future Champion Award 2015,” which includes a €10,000 prize, at this year’s Summit Meeting for German World Market Leaders.

The award is presented each year by Adolf Würth GmbH & Co. KG, a specialist in the sale and distribution of assembly and fasting materials for professional use. It recognizes mid-sized German companies that demonstrate rapid and sustainable growth at an international level.

In presenting the award to Christian Buske – Plasmatreat GmbH founder, CEO, and managing partner – Joachim Kaltmaier of the Würth Group’s Central Management Board highlighted Plasmatreat’s accomplishments:

The company has discovered a niche market for atmospheric plasma surface treatment using plasma nozzles and has set global standards. Above-average, annual growth rates in double figures are testimony to their outstanding entrepreneurial spirit.

Christian is truly a pioneer in the world of atmospheric plasma treatment, developing technology that can be conveniently incorporated into existing production lines. Since 1995 he has built Plasmatreat to become the global leader in this technology. Many of you are already existing Openair customers, so you know how it works.

Targeted nozzles issue blasts of supercharged air that has been calibrated to a precise degree of ionization in order to effectively clean and modify the treated surfaces. The Openair process eliminates the need for wet chemistry processes and prepares the surfaces for optimal adhesion of subsequent coatings or adhesives.

Hearty congratulations from North America, Christian! I am proud and excited to be part of Plasmatreat’s international team, which is growing every day.

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1. February 2015   2:11 pm
Dr. K. L. Mittal, Dr. Robert H. Lacombe

Dr. K. L. Mittal, Dr. Robert H. Lacombe

The last issue of the  “SURFACES: THE INVISIBLE UNIVERSE” focused on viewing the chemistry of surfaces through the lens of X-ray Photoelectron Spectroscopy (XPS, aka ESCA).  In this issue we shift focus to the problem of surface modification and in particular polymer surface modification.  This topic is highly apropos in view of the upcoming Tenth International Symposium on Polymer Surface Modification: Relevance to Adhesion, to be held at the University of Maine, Orono, June 22-24 (2015).  This symposium will cover all aspects of polymer surface modification from mechanical roughening to laser modification.  The meeting will be concerned with the those areas where surface modification is a key technology which allows for the processing and manufacture of products which would otherwise be unobtainable.  This meeting will also delve into the realm of biopolymer materials with applications to forest products, medical implants and food processing.  All readers are cordially invited to join the symposium either to present a paper on their current work in this field or to simply attend and greatly expand their awareness of current developments.  Further details are available on the conference web site at:  www.mstconf.com/surfmod10.htm

 SURFACES: LOW VOLUME BUT HIGH IMPACT ENTITIES

 An elementary calculation for just about any cube of a simple atomic or molecular material 1 centimeter on a side indicates that roughly one atom/molecule in ten million resides within ten angstroms of the outer surface.  Though relatively minuscule compared to the roughly 1023 atoms present in the sample, this surface layer determines many of the most important physical and technological properties of the material.  Common examples include optical properties such as reflection of light, all contact properties including friction, surface wetting and adhesion and many chemical phenomena including resistance to corrosion, biofouling and staining.  As important as these properties are, however, surface related phenomena received relatively scant attention during the early decades of the 20th century mainly due to the difficulty in performing careful experiments on such small amounts of material.  Well into mid century the solid state physics community was more focused on bulk properties of solids such as crystallographic structure, electronic band structure and bulk thermodynamic behavior.  What made all this work possible was the relative ease in preparing well characterized samples of uniform quality.  The influence of small amounts of contamination and crystallographic defects is small for bulk samples and more or less in proportion to the amount present. 

 In dealing with surfaces, however, we are faced with an entirely different situation.  The effect of small amounts of contamination and surface defects, rather than being more or less suppressed, can actually dominate the surface properties of the material under investigation.  Thus the basic problem of preparing well characterized surfaces for investigation is far more difficult than in the case of examining bulk properties.  Nonetheless, even though the sensitive properties of surfaces present daunting difficulties for those who want to perform careful investigations, these same properties present opportunities for the technologist who wants to alter surface behavior in order to create useful products and devices.  Nowhere is this opportunity more prevalent than for polymer materials which offer surfaces that can be modified by a number of physico-chemical methods to give specifically tailored results.  What makes this technology even more attractive is the fact that surface modification leaves all the bulk properties of the material intact so that one can, so to speak, have one’s cake and eat it too.  A typical example might be the case of a high modulus fiber being considered as a reinforcing agent in a particular matrix material.  One often finds that the fiber and matrix material are incompatible as obtained off the shelf.  However, appropriate surface treatment of the fiber can make it compatible with the matrix without sacrificing its reinforcing properties making possible the creation of a new composite material.

 MICRO-ORGANISMS AND THE FIBER-MATRIX INTERFACE

 One of the biologically oriented applications of surface modification technology is the removal of pathogens from food products such as berries, fruits and vegetables using atmospheric  plasma technology. Work in this area is currently underway and is planned to be presented at the symposium mentioned above.  However, on the flip side of this development, microorganisms, instead of being removed from a surface can also be added to improve adhesion as was discussed in a most interesting paper given at the first in the Polymer Surface Modification series.

 Since ancient times mankind has taken advantage of the bio-chemical synthesis skills of micro-organisms to create a number of desirable products.  Wine, beer and cheese derived from fermentation are the most recognized achievements of microbial industry.  However, to the best of my knowledge the work of Pisanova and Zhandarov is the first to put the microbes to work in modifying the surface properties of fibers for use in reinforced composites.[1]  These authors worked with the following fiber materials:

  1.    poly(caproamide) (Abbr. PCA)
  2.    poly(p- amidobenzimideazole) (Abbr. PABI)
  3.    poly(p-phenyleneterephthalamide) (Abbr.
  4.    PPTA)
  5.    poly(m-phenyleneisophthalamide) (Abbr. PPIA)
  6.    polyimde (Abbr. PI)

 The above fiber materials were considered as reinforcements for the following matrix materials:

  1.    polycarbonate   Abbr. PC
  2.    polysulfone   Abbr. PSF
  3.    polyethylene   Abbr. PE

 The fibers were exposed to the following micro-organisms:

  1.    Bacillus vulgaris (bacterium)
  2.    Bacillus cereus (bacterium)
  3.    Pseudomonas (bacterium)
  4.    Aspergillus (fungus)

 The authors knew that the above listed micro-organisms could attack and degrade polymer materials.  However, they reasoned that in the case of densely packed fibers the bacteria would be limited to performing their biochemical antics at the fiber surface leaving the bulk properties intact.  Thus each of the fibers was immersed in a nutrient medium containing one of the micro-organisms for up to two weeks to see what changes in the surface properties could be obtained.  The timing of exposure was important so as to limit the action of the organisms to just the fiber surface.  The mechanical properties of the fibers were measured beforehand by standard methods and the adhesion of the fiber to the matrix material was ascertained using the fiber pullout method. The results of their experiments were quite surprising in that in many cases they saw both improved mechanical properties of the fiber and improved adhesion of the fiber to the binding matrix material.  A sample of their results for the PCA/high density polyethylene (HDPE) system is given in Table I.  A cursory look at the data in Table I shows that the fiber mechanical properties are moderately improved by the micro-organism action with an increase in fiber modulus by as much as 18% and the strain at break by nearly 25%.  However, the bond strength of the fiber to the matrix in some cases could increase by nearly a factor of 2 as seen for the Bacillus vulgaris data.

 Also notable from the data in the table is the deleterious effect of overexposure to the microbial treatment as evidenced by the drop off in properties when the exposure time for Bacillus cereus was increased a factor of 4.

  

TABLE I:  Effect of micro-organism treatment on fiber mechanical properties for PCA and fiber/matrix bond strength for the PCA/HDPE system
TREATMENT (micro-organism) TENSILE STRENGTH (GPa) ELONGATION AT BREAK % BOND STRENGTH PCA/HDPE COMPOSITE (MPa)
No treatment 1.52 16 13.1
Bacillus vulgaris 1.74 17.8 21
Bacillus megaterium 1.74 18.2 17.6
Bacillus cereus 1.79 20.2 20
Bacillus cereus(8 week treatment) 1.23 15.5 19.9

 Though the precise details of the microbial action were not uncovered in these experiments a few things were made clear by microscopic examination.  In particular the first stage of the treatment  involved the filling of cavities, pores and microcracks on the fiber surface with the byproducts of the micro-organism’s metabolism which resulted in the healing of the defects and the subsequent improvement in mechanical properties.

In addition the surface chemistry of the fiber is significantly altered making it more compatible with the binding matrix and thus also improving the performance of the composite material.

 As a final word it is clear that this type of work is in its very early stages and that there is tremendous scope for expansion of the types of systems which can be looked at and the extent of improvement that can be achieved.  In addition, since the types of micro-organisms being used are commonly present in the environment this type of surface treatment could be considered more environmentally friendly than other methods which rely on harsh chemicals.

 Dr. Robert H. Lacombe, Chairman Materials Science and Technology CONFERENCES

3 Hammer Drive, Hopewell Junction, NY 12533-6124

Tel. 845-897-1654, FAX  212-656-1016 E-mail: rhlacombe@compuserve.com

[1] “Modification of Polyamide Fiber Surfaces by Micro-organisms”, Elena V. Pisanova and Serge F. Zhandarov, in Polymer Surface Modification: Relevance to Adhesion, Ed. K. L. Mittal (VSP, The Netherlands, 1995) p. 417

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