Tech Talk Blog

Mid-winter is the thick of flu season, and in this age of H1N1, we are all aware that germs on the hands can spread bacteria that cause infection, disease and even food-borne illness.  In fact, the CDC reports that flu viruses can survive for several hours on hard surfaces we touch all the time, such as doorknobs and shopping carts.

But what if there were a permanent treatment for inanimate surfaces to help us avoid — and even eliminate — the spread of bacteria, pathogens, and viruses?  Our R&D team is at work on such a solution.

Although still in the testing stage, our propylene additive will have a permanent anti-bacterial and anti-fungal effect on hard surfaces.  The key to remaining germ-free?  A nano silver additive that keeps hard surfaces hygienic indefinitely.

Look for more information to follow.

Our team is designing a lens that must withstand military extremes such as salt spray, fog, humidity and temperature.  The coating must be abrasion-resistant and anti-reflective – what is the best treatment?

This is a great question — and a multi-step process. Assuming your lens is a polymer lens like polycarbonate or CR-39, currently there is no single surface treatment for both anti-abrasion and anti-reflective (AR) properties.  Instead, one would apply the anti-abrasion coating first, followed by the AR process, which is done in a vacuum for a uniform and consistent result.

Your abrasion-resistant coating options include:

A)    Polyurethane  – This usually is the most economical coating, which is applied by either sprayed or dip method. This is a popular treatment for end user ophthalmics, but also has the least durability and longevity.

B)    DLC (Diamond-like coating) – An extremely hard, durable coating, that is relatively expensive, but most effective for high-end users.  DLC ensures high-performance and impact-resistance as the resulting surface is very close to the hardness of diamond.

Our team can help you explore your best solution.

What is the best process for removing silicone oil from a catheter made of Pebax® tubing prior to a bonding operation?  Would you use plasma or corona?

Your question is one that we are seeing more frequently. And the short answer is that it all depends on the amount of oil.

If you can see a significant oil collection, then you need to wash the tubing in an ultrasonic bath with an emulsifier. Then, you may simply wipe the tubing with an alcohol wipe to remove any excess. It really depends on the level of contamination. Generally speaking, I’ve found that catheters have a superficial level of oil.

If the amount of oil is superficial, plasma can carry away the excess oil via a specific oxygen treatment. We do not advise corona treatment for this application, since it can make the silicone hydrophilic and give a false impression of being clean. Plasma is a more elegant solution and will “superclean” the surface to promote better adhesion.  Learn how we recently solved this challenge.

With the recent spike in air travel over the holidays, I was reminded of some of the aerospace materials that our team often treats, particularly foam. Foam is a common insulation material aboard aircraft, used to fill open crevices between the passenger compartment and the outer shell.  It serves a number of functions such as regulating temperature, reducing engine noise, and protecting the mechanical systems from moisture and temperature variations that may lead to corrosion.

Currently, micro-light fiberglass is used for aircraft insulation, but it has the tendency to absorb moisture, which can add substantial — and unwanted — weight to the craft.  A typical flight may consist of up to 1,500 lbs of water weight.

Our team is working on an alternative to fiberglass insulation . The following materials are foam products that offer good acoustic, insulative, and weight properties, but have a tendency to absorb moisture like the fiberglass. We treat these foam products to inhibit these properties:

1)      AC 530 — a polyimide material, is lightweight, fire resistant and offers thermal and noise insulation.  It is a flexible material, but holds its shape and conforms to structural inlay. But, this foam is prone to moisture absorption.

2)      Melamine foam — is also lightweight, fire resistant, and offers thermal and noise insulation. This foam is flexible and holds its shape and conforms to structural inlay. But, this foam will naturally absorb moisture particularly well.

Our hydrophobic process offers the distinct advantage of penetrating the entire surface of the material, unlike some processes that may sit only on the surface. Our process enhances the properties to form a better water-resistant property that inhibits the absorption of moisture maintaining the dry weight of the aircraft.

As always – if you are still burning with questions, Ask The Experts!

A recent development at TriStar – Surface Modification Division is a liquid surface treatment to induce a hydrophobic property. Most foam materials are very hydroscopic and absorbent. When our hydrophobic liquid surface treatment is applied to most foam materials, the foam becomes extremely hydrophobic. Below is an image of our treatment on medical grade polyurethane foam.

Though our tests indicate this treatment does not work well on natural materials like wood and cotton, but this treatment performs great on synthetic fibers and fabrics.

If you would like more information on this product, please continue to our website at www.tstar.com.

Recent headlines tell us that everything from our kitchen cutting boards, Tupperware and soda fountain delivery tubing are infected with everything from fecal matter to salmonella. There are solutions available thanks to new polymer technology using antimicrobial additives and surface treatments. Many polymers are now available with silver ions which help to effectively inhibit the potential growth of bacteria, yeast and fungi on the polymer surface. By using unique zeolite carriers with silver ions, a counter force to the sodium ions present in moisture  interrupt respiration, reproduction and metabolism of destructive microbes. TriStar offers several polymer solutions now in molding and extrusion resins to dramatically reduce the potential of microbial growth in your products. Browse through our Video Learning Center for even more information.

The growth of plastics in medical devices is growing exponentially around the world.  Plastics are regulated like any other materials that may come in contact with human tissue or fluids and that usually falls under testing procedures issued under USP or ISO10993. There are three time scales for biocompatible devices. “Limited” would be less than 24 hour exposure, “Prolonged” is 24 hours to 30 days and “Permanent” is 30 days and longer. Device’s are categorized as Surface Devices which would be items such as electrodes for monitoring, contact lenses, catheters, endotracheal tubes, sigmoidoscopes and similar devices. Second would be Externally Communicating Devices such as  laprascopes, blood administration devices, pacemakers, oxygenators and the like. Finally are Implant Devices such as orthopedic pins or plates, heart valves, grafts, stents and similar devices.

Testing of these devices includes mechanical, thermal, chemical tests as well as systemic injection, intracutaneous and implantation. All of these must be done before a plastic component can be approved. Typical materials for biocompatible applications include medical grades of PVC and Polyethylene, PEEK, Polycarbonate, Ultem PEI, Polysulfone, Polypropylene and Polyurethane. For more specific information on Biocompatible materials as well as special plasma preparation treatments of all of these materials, contact TriStar Plastics at www.tstar.com and visit our Video Learning Center and our Materials Database.

The dynamics of wetting are described below:

Spreading = A – ( B+ C )

Where:

• A = surface energy of solid (given below)
• B = surface tension of liquid
• C = surface energy of solid-liquid interface

If Spreading is:

• Negative. Then, liquid will bead up.
• Zero. Then, liquid will spread.
• Positive. Then, liquid will spread.

If the material surface energy is relatively low, then the coating will not flow well and fisheyes, pinholes, gaps, or air bubbles will form. If the material surface energy is too high, then the paint, ink, or coating may bleed or be difficult to control. Therefore, the surface tension of the liquid and the surface energy of the material must be matched for the application.

Don’t just listen though – take a look! Visit our Video Learning Center for an in-depth look.

There are many ways in which polymer properties or behaviors are classified to make general descriptions and understanding easier. Some common classifications are:

• Thermoplastic / thermoset
• Amorphous / crystalline
• Addition / condensation

Thermoplastic vs. Thermoset

Thermoplastics are materials which can be heated and formed, then re-heated and re-formed repeatedly. The shape of the polymer molecules is generally linear, or slightly branched, allowing them to flow under pressure when heated above the effective melting point.

Thermoset materials undergo a chemical as well as a phase change when they are heated. Their molecules form a three-dimensional cross-linked network. Once they are heated and formed they can not be reprocessed – the three-dimensional molecules can not be made to flow under pressure when heated.

Amorphous vs Crystalline Polymers

Crystalline polymers are polymers with nearly linear structure, which tends to be flexible and fold up to form tightly, packed and ordered “crystalline” areas. Time and temperature during processing influence the degree of crystallinity. Crystalline polymers include: polyethylene, polypropylene, acetals, nylons, and most thermoplastic polyesters. Crystalline polymers have higher shrinkage, are generally opaque or translucent, with good to excellent chemical resistance, low surface friction, and good to excellent wear resistance.

Amorphous polymers are polymers with bulkier molecular chains or large branches or functional groups, which tend to be stiffer and will not fold up tight enough to form crystals. Common amorphous polymers include polystyrene, polycarbonate, acrylic, ABS, SAN, and polysulfone. Amorphous polymers have low shrinkage, good transparency, gradual softening when heated (no distinct melting point), average to poor chemical resistance, high surface friction, and average to low wear resistance.

Condensation vs. Addition Polymers

Condensation polymers such as nylons, acetals, and polyesters are made by condensation or step-reaction polymerization, where small molecules (monomers) of two different chemicals combine to form chains of alternating chemical groups. The length of molecules is determined by the number of active chain ends available to react with more monomer or the active ends of other molecules.

Addition polymers such as polyethylene, polystyrene, acrylic, and polyvinyl chloride are made by addition or chain-reaction polymerization where only one monomer species is used. The reaction is begun by an initiator which activates monomer molecules by the breaking a double bond between atoms and creating two bonding sites. These sites quickly react with sites on other monomer or polymer molecules. The process continues until the initiator is used up and the reaction stops. The length of molecules is determined by the number of monomer molecules which can attach to a chain before the initiator is consumed and all molecules with initiated bonding sites have reacted.

In summary, a polymer is a very large molecule made up of repeating small molecular groups. The elements and bonds of a polymer give the polymer its bulk properties. All too often a polymer will be designed for the easy of molding or processing and not for subsequent processes like bonding, painting, printing, or coating.

It is at this point where surface modification of the polymer is essential. The polymer can be treated after the polymer has been molded, extruded, formed, coated, or cast without changing the bulk properties of the polymer. So, an engineer can specify a material that would best suit high volume manufacturing and device integrity without compromising the device due to a printing of painting process.

Look at our Materials Resource Guide to see all we offer – or simply Ask The Experts if you have a question. Don’t be shy!

The molecular forces and chemical bonding are important to understand the physical properties the bulk polymer exhibits. The covalent bonding in a polymer system is one of the strongest and significant forces and is often referred as primary bonding. A list of common covalent bonds and the energy associated with the bonds are listed below:

This list shows the dissociation (bond breaking) energy to predict which bonds will break first when a polymer is overheated or modified by plasma or UV. For example, the carbon (C) chlorine (Cl) bond will dissociate before a C-H bond in a PVC polymer.

Secondary bonding forces are also important as they can affect the material’s physical properties, such as surface tension, viscosity, friction, volatility, and solubility. The secondary forces are as follows:

Blends are the physical blend of polymers. Unlike a copolymer that is chemically mixed, polymer blends are mixed before or during molding operations. Yet, polymer blends can be just as useful and cost effective as copolymers or terpolymers. The physical property of a blend is determined by the physical properties of each ingredient and miscibility. If the compounds are miscible, the mixture will remain uniformly blended (homogenous). If the compounds are not miscible, the each mixture will separate into its respective phase. It would be here that the physical properties of the material would be compromised if the adhesion between the compounds is poor. Fortunately, if two immiscible polymer need to be blended, an additive can be used or a polymer can be grafted to one of the originals.

If you want to know a little bit more, watch our Plastics Technology 101 Seminar and other videos in our Video Learning Center.