Category Archives: General Knowledge

Selecting Plastics For Wet Benches


Wet Benches

Description: “Wet Benches” are stations for wet etching and cleaning of wafers and devices. (“Litho Benches” in contrast, are used for resist processing.) The various wet benches differ in the specific process modules available and the materials allowed at each station. For information about some of the various wet processes available, click <here>. The available Wet Benches are:

Diffusion Wet Bench (wbdiff)
Solvent Wet Bench (wbsolvent)

Gallium Arsenide Wet Bench (wbgaas)
General Use Wet Bench (wbgeneral)
Metal Wet Bench (wbmetal)
Nitride Wet Bench (wbnitride)
Nonmetal Wet Bench (wbnonmetal)
Silicide Wet Bench (wbsilicide)


Wet Bench Fire Safety: Update
By: Lise Laurin and Marcia Tate
February 2000

Where there’s smoke there’s fire…but where there’s fire there doesn’t have to be smoke, corrosive fumes, or catastrophic damage, because cooperation between semiconductor and plastics manufacturers, industrial insurance providers, and wet bench manufacturers has resulted in safer, more efficient wet benches.

Today’s wet benches, made from specially engineered plastics, have come a long way from their beginnings in the 1970s, when they were simply modified work benches made of painted steel. By the 1980s, specialized manufacturers were making wet benches from plastics such as polypropylene. In the late 1980s, attempts to produce safer wet benches led to the development of fire retardant polypropylene (FRPP); subsequent research, however, has shown that although the FRPP formula lengthens ignition time, the corrosive smoke from burning FRPP actually causes more damage than was caused by the earlier generations of polypropylene. All plastics burn, but not all burn in the same way.

Readily available, easily fabricated, and able to resist corrosive chemicals without deteriorating or leaching out into the bath, specialized plastics are the material of choice for wet bench construction. Yet in the semiconductor industry, the very nature of the wet bench process—an electronically controlled process usually containing corrosive chemicals and sometimes incorporating electrically heated baths—means there will always be a potential source of ignition nearby. While fire isn’t the only safety issue associated with wet benches, it’s certainly the one that attracts the most attention because of the astronomical amount of damage one fire and its resulting smoke and corrosive fumes can cause.

With loss control as motivation, industrial insurance pro-viders joined plastics manufacturers and wet bench manufacturers to find plastics that don’t propagate fire, release little smoke, and don’t produce corrosive fumes as they burn.

Factory Mutual Research, a division of FM Global, began the move toward safer wet benches by establishing an index against which to measure cleanroom materials: Test Standard FM4910, Cleanroom Materials Flammability Test Protocol (1997). The first and most important feature of the FM4910 test standard is the Fire Propagation Index (FPI), which indicates tendency of a material to propagate fire. The test also indicates the comparative amounts of smoke generated according to the Smoke Development Index (SDI). Initially, the test also measured corrosive fire byproducts (CDI), but that measurement was later dropped.

In order for a material to be considered “fire-safe,” it must have an FPI equal to or less than the established acceptable level of 6. Regular polypropylene, FRPP, and polyvinyl chloride (PVC)—the conventional wet bench materials and the first materials tested—do not meet this minimum requirement.

With this measure as a guide, plastics manufacturers began formulating plastics to meet the specifications and submitting them for testing. Semiconductor manufacturers became concerned that while these new materials might be fire-safe, they might not be compatible with their processes. To address these fears, International SEMATECH, a research consortium of semiconductor manufacturers, established testing procedures to determine the process compatibility of materials destined for use in wet bench construction. The aim was to establish a set of parameters that would allow anyone to test the compatibility of any plastic material.

The Price of Progress

International SEMATECH’s tests of new plastics show that many concerns about the need to compromise purity to gain fire safety are unwarranted. The new standards have not only given plastics manufacturers an incentive to develop new materials, but also provided guidelines as to what criteria the new products must meet. As a result, many of the materials submitted for testing are proving to be superior to conventional wet bench materials.

While most new plastics are more expensive than conventional ones, the materials usually represent only a small percentage of the cost of a wet bench; in most cases the added cost of new materials is less than the cost of the built-in fire suppression system.

Complicating the conversion to new materials, however, is the lack of “off-the-shelf” parts made of fire-safe materials. To maximize safety, wet bench manufacturers must custom-build parts, and this adds to costs. Todd Thomas, president of Amerimade Technology, a wet bench manufacturer, states that at present his company is choosing its new plastics from the poly-propylene family. Since many of the smaller parts, such as fittings and latches, are not yet available in the new materials, keeping materials’ properties as similar as possible allows for easier construction and welding. Although new materials may meet criteria for construction of the wet bench structure, no test results are yet available to qualify these materials for use in process baths. To achieve a totally fire-safe system, the process baths must be upgraded to Teflon or PVDF, materials that are inherently fire-safe.

As more plastics measure up to the FM4910 and SEMA-TECH standards, and as wet bench manufacturers become more comfortable with the characteristics of the new plastics, the costs associated with their use are decreasing. Customers, too, are becoming aware of and educated about the new materials. At first, semiconductor manufacturers showed some reluctance to switch from the materials with which they were familiar; there was uncertainty about whether the change was necessary and concern about potential adverse effects on production. Increased research results, several catastrophic fab fires, and the potential of reduced insurance coverage, however, helped overcome these obstacles. According to Thomas, as recently as one year ago, wet benches constructed of the new fire-safe plastics accounted for only 10-15% of his company’s sales; that figure is now up to 50%. Informed customers are now requesting specific materials.

Latest Developments

As plastics manufacturers rushed to submit materials for testing, it became apparent that the limited availability of the Factory Mutual Research test equipment and subsequent high cost and long lead time of the tests were hindering the process. Acceptable alternative materials were not becoming available soon enough to meet demand. Many materials that passed the fire propagation and smoke tests (20% of those submitted for testing) failed the corrosion tests. Specifically, most of the semitransparent plastics suitable for windows in minienvironments were found to produce corrosive fumes as they burned.

Concerned engineers proposed eliminating the corrosion index, allowing the use of materials that do not comply to FM4910 as long as they are not close to an ignition source, and moving to qualify more labs to run the 4910 tests. In response to industry pressure and after a review board concluded that the CDI results were not adequately repeatable, Factory Mutual Research removed the corrosion damage index from the FM4910 test standard. Factory Research Mutual researchers and others involved felt that if a material passes the stringent fire propagation and smoke development tests, it would likely cause minimal corrosion damage.

Still, there was pressure to speed up the qualification process and to make it more economical. HSB Industrial Risk Insurers chartered Underwriters Laboratory (UL) to formulate a less expensive test that could produce results as reliable as those of FM4910. While Factory Mutual Research’s tests require equipment with limited availability, the UL test uses a standard cone calorimeter. No one involved disputed Factory Mutual Research’s contributions, but input from another source was welcome. This “second opinion” validated Factory Mutual Research’s effort and research.

Working with samples donated by plastics distributors, UL and Factory Mutual Research have completed a round-robin of testing to verify the equivalency and repeatability of their tests. Representatives from UL, FM Global, HSB, and several plastics manufacturers met on November 17, 1999, to discuss the results of UL’s test. UL disclosed the results of the tests using the standard cone calorimeter. Valid test results from this less costly, more readily available equipment (installed in more than 100 laboratories worldwide), would enable quicker, less expensive testing and result in more options and lower prices. It would also allow testing in intermediate steps during R&D.

The goal of the round-robin was to formulate a single set of “fire-safety” testing standards to present to the National Fire Protection Association (NFPA) at its annual spring meeting. This would align all parties involved (insurers, materials manufacturers, semiconductor manufacturers, and process equipment manufacturers) striving for the same result, which would ultimately result in better products and safer cleanrooms.

Factory Mutual Research retested eight of the nine plastics used in the UL tests; the results of this round of testing were consistent with Factory Mutual Research’s previous findings but not identical to UL’s findings.

Two types of tests include a “full-scale” test (Photo 1) and a “small-scale” test (Photo 2). Results of the full-scale (“Parallel Panel”) test are obtained by setting up two 2 x 8 ft. panels of the same plastic and starting a fire between the panels. Researchers monitor the panels to discover how quickly they ignite and what happens to them as they burn.

In the small-scale test, small samples of material are burned in a piece of laboratory equipment, where they are monitored to measure the time it takes the material to ignite, how much heat it releases, and the amount of smoke it generates. Since a much smaller sample of plastics is used in the small-scale test, results must be compared to the Parallel Panel test results. UL correlated the cone calorimeter tests (ASTM E1354) to the Parallel Panel tests.

UL and Factory Mutual Research achieved very similar results from the panel tests, but slightly less clear-cut results from the small-scale testing. Factory Mutual Research’s apparatus and the standard cone calorimeter yielded slightly different data. Factory Mutual Research felt that further testing on a wider selection of plastics was advisable; only nine plastics were thoroughly tested using the UL procedure as opposed to the hundreds that have been tested using FM4910. While there was total agreement on the properties of the plastics at the extremes of the test parameters, there were gray areas in the middle ranges.

After reviewing the data, the NFPA committee responsible for presenting recommendations for updating the NFPA 318, the standard of protection of cleanrooms, to the NFPA annual spring meeting discussed adopting FM4910 and UL2360, the new UL subject test standard, as reference standards. A note was included indicating that the subject test standard UL2360 was under development, since UL had not completed its internal standards review process. The recommendation, which will be submitted for final approval at the international annual conference in May 2000, is that in order for a material to be considered fire-safe or noncombustible, it must pass a reference standard test conducted by a recognized testing laboratory and be “listed” by that laboratory. Robert Pearce from HSB stated that both UL and Factory Mutual Research are acceptable testing laboratories.

FM Global and its insureds are already working under a version of the fire-safe standard. Since most wet benches are custom fabricated, Factory Mutual Research must inspect each of its clients’ wet benches, both at the manufacturer’s site and on-site in its final location, to determine whether or not the bench can be considered fire-safe without the addition of a fire suppression system. Once manufacturers have a full complement of fire-safe materials, along with a set of clear-cut standards to follow, this process will flow more smoothly.

Factory Mutual Research has submitted the FM4910 to the NFPA Fire Test Committee, ASTM, and ANSI, which effectively puts it in the public domain. The test would become NFPA Standard 287 upon final review and acceptance in 2000. The test is undergoing final review and comment from ASTM, and adoption is also expected in 2000.

What’s Next

Looking beyond wet benches, other major applications for fire-safe materials in semiconductor applications include wafer carriers, parts cleaners, wall panels, and insulation materials that can represent significant combustible loads. FM Global’s Paul Higgins states that his company is planning to partner with several wafer transport equipment manufacturers to move away from ordinary polypropylene and polycarbonate carriers. New 300 mm wafer carrier storage systems, known as stockers, could present fire protection challenges. Sprinkler systems would not prevent smoke and water damage to their contents, and the larger enclosures required could be very difficult and expensive to protect with fire suppression systems.

So far, the push for fire safety has been a win-win process for all involved. The reduced risk of fire will simplify business for the risk managers and insurers. Semiconductor manufacturers will benefit from more stable insurance coverage—from the knowledge that their facilities and workers are more secure and from knowing that wet benches made from new materials are more process-compatible than their predecessors. Plastics manufacturers have created new markets for superior materials, tailored specifically to their clients’ needs.

From the very beginning of the research to the presentation of the joint findings to the NFPA, there has been a spirit of cooperation among all parties involved. Everyone stands to gain from a clear definition of “fire-safe” and the adoption of standards to ensure uniform requirements throughout the industry.


Thanks to Todd Thomas, Amerimade Technology (Pleasanton, CA); Paul Higgins, FM Global (Johnston, RI): Robert Pearce, HSB Industrial Risk Insurers, (San Francisco, CA).

Leave a comment

Filed under Fabrication, General Knowledge, Industrial Plastics

Medical Plastics: Avoiding Biological Interface Reactions

Surface Modification of Plastics for MEDICAL DEVICE APPLICATIONS -
By: June-Jim Schepple,Jeff Dykhouse
June 1999

Plastics, polymers, and resins have become widely accepted for in vivo and in vitro medical applications. Many of these materials have properties that lend themselves well to the manufacture of medical appliances or devices; they are relatively inexpensive and easily molded or formed into complex shapes, and bulk physical properties may be selected from a wide range of parameters such as rigidity and temperature stability. Unfortunately, fabrication procedures that require bonding are difficult to achieve, and biological interface reactions within the body or in the laboratory can limit their in vivo and in vitro performance.

Gas plasma technology offers a technique for easing these limitations by modifying the surfaces of these polymers. By altering just the first few atomic layers, the surfaces of most medical polymers can be rendered wettable so that adhesive bonding can be achieved to troublesome materials such as polyolefins, silicones, and fluoropolymers. In a similar fashion, more exotic processes such as plasma grafting and polymerization can produce totally new custom surfaces without loss of the desirable characteristics of the bulk material.

Plasma is a low pressure, gaseous “glow discharge” process that has been used in the aerospace, semiconductor, and electronics industries for more than 30 years for cleaning, etching, and surface treatment of various materials. Plasma treatment does not affect the bulk of the materials and plasma treated parts are generally visually and physically indistinguishable from untreated parts.

Plasma is now routinely used for controlling the wettability of test tubes and lab vessels, for pre-bonding preparation of angioplasty balloons and catheters, for treating blood filtration membranes, and to manipulate surface conditions of in vitro structures to enhance or prohibit culture cell growth.


Given enough energy, any gas can be excited into a “plasma,” which is a mixture of ions, electronics, excited species, and free radicals. There are many temperature and pressure conditions where this phenomenon will occur, but for practical considerations, radio frequency or microwave energy is commonly used, enabling these processes to take place at low temperatures (25-100¡C) and low pressure (0.1-1 torr), where surface reactions with polymers are feasible without bulk interactions.(1,2)

Plasma “treatment” usually refers to a plasma reaction that either results in modification of the molecular structure of the surface or atomic substitution. Even with be-nign gases such as oxygen or nitrogen, plasma treatment can create highly reactive species at low temperatures. High energy ultraviolet light is emitted in the process, which along with the high energy ions and electrons provide the energy necessary to fracture polymer bonds and initiate chemical reactions at the surface. Only a few atomic layers on the surface are involved in the process, so the bulk properties of the polymer remain unaltered by the chemistry, while the low process temperature eliminates concerns about thermal modification or distortion of the bulk. Unique reactions can be promoted by appropriate choice of reactant gases, and unusual polymer byproducts and structures can be formed.

In many instances, plasma cleaning with benign gases such as oxygen or nitrogen provides adequate surface activation for enhanced wetting and adhesive bonding. With other targeted end results or substrate materials, it may be necessary to utilize reactants which result in “grafting” or surface chemistry modification to achieve the desired results.
It is frequently possible to select reactants that form volatile byproducts upon reaction of the plasma with the substrate material. These, upon desorbtion from the surface of the treated material, are removed by the vacuum pump, resulting in etching of the surface without the necessity for further scrubbing or neutralizing.


Oxidizing species such as air, oxygen, water vapor, or nitrous oxide are often used to remove organics, leaving functional oxygen-containing groups on the surface. These groups greatly enhance wetting, improve adhesive bonding, and, in some instances, create acidic surfaces.(3,4) In at least one instance, sterilization of components has been reported with the use of strong oxidizers such as ozone or hydrogen peroxide vapors.

Reducing gas species such as hydrogen or methane-often diluted with argon, helium, or nitrogen-may be used to remove organics from surfaces sensitive to oxidation. This chemistry may also be used to partially substitute hydrogen atoms for fluorine or oxygen in polymer surfaces. The noble gas species, such as argon or helium, are chemically inert, so they do not combine or become part of the surface chemistry. Instead, they transport energy to break chemical bonds in polymer chains. Broken polymer chains result in “dangling bonds,” which recombine with other reactive sites, resulting in significant molecular restructuring and cross-linking. The creation of dangling bonds allows for chemical “grafting” reactions to occur. This process is involved in several of the biomedical applications.(5)

Active gases, such as ammonia, are used to create amino groups on the surface. This type of functionality has an influence on important surface properties such as pH and Lewis basicity.

Fluorinated species such as Tetrofluoromethane (CF4), Sulfur Hexafluourine (SF6), and perfluorohydrocarbons may be used to induce substitution of fluorine atoms for hydrogen atoms in the surface structure. Teflon-like structures may be created, resulting in a very hydrophobic, chemically inert surface with significant chemical stability.

Polymerization, or deposition, processes may include reactions utilizing a wide variety of gases, including some of the organic or organo-metallic compounds, which deposit nonvolatile polymer films.6 In many instances these reactant gases maybe toxic, corrosive, or otherwise hazardous and require special handling such as heated gas transfer plumbing and measurement instrumentation, reactor exhaust scrubbing, and trapping of reaction byproducts. Polymerization processes will generally necessitate frequent cleaning of the reaction chamber, since all surfaces ex-posed to the plasma will be coated.


Surface Wetting.  Plasma treatment of polyethylene or polypropylene disposable Petri or Assay dishes greatly enhances wetting. Contact angles as low as 22û have been demonstrated on these materials after only a few minutes of oxygen plasma exposure (see Table 1). When these parts are properly packaged after treatment, the contact angle has been seen to be stable for several years.

Conversely, many medical polymers can be made extremely hydrophobic. Teflon-like films and other similar surface treatments can be easily accomplished on most polymers using fluorinated gases. For example, small diameter tubes can be treated so that when immersed in aqueous solutions they do not draw fluid by capillary action.

One of the simplest techniques used to evaluate plasma surface treatment is a wetting angle test using a contact goniometer. Surface roughness and substrate cleanliness need to be tightly controlled to obtain quantitative data. Standard wetting solutions are often used to obtain accurate surface energy values.

Most untreated polymers are only poorly wettable. Initial contact angles may vary from 60-100û. Table 1 shows a sample of some typical contact angle measurements:

Table 1.
Typical wetting angles,
before and after
Oxygen plasma treatment.(7)

Before After
Polyptopylene 87° 22°
Polyethylene 87° 22°
Polyamide (nylon) 73° 15°
Polyimide 79° 10°
Polycarbonate 75° 33°
Tefzel 92° 53°


96° 68°

After 5 min. of oxygen plasma treatment, the contact angle decreases significantly.

Adhesive Bonding. Many intravascular devices, such as balloon catheters, are assembled by adhesive bonding of polyethylene components. Chemical surface activation or mechanical surface roughening techniques provide only modest bonding performance, with bond failures noted after as few as eight repetitive inflations. With plasma treatment, up to 40 repetitions are achievable. Typical bond strength data are shown in Table 2.(7)

Table 2.
Typical lap-shear bond
strengths (psi), without and
with plasma treatment.

Without With
Polypropylene 370 1380
(low density)
370 1450
(high density)
315 3125
Nylon 850 4000
Polystyrene 570 4000
410 928
Tefzel 410 3200

An oxygen plasma not only removes organic residues but also chemically reacts with the surface to form strong covalent carbon-oxygen bonds, which are much more polar and more reactive than the initial carbon-hydrogen bonds. The increased polarity of the surface accounts for the substantial increases in wettability and adds a degree of covalent bonding to the surface-adhesive interface. (Note that other gases may be used to attain similar results in instances where oxidizing species may be harmful to components of the assembly.)

The bond strength ultimately realized will certainly be affected by:

1. Initial cleanliness of the surface(s).
2. Wetting of the surface by the adhesive.
3. Cross-linking effects.
4. Chemical interaction of the adhesive with the surface.

Any mold release compounds, unpolymerized monomers, plasticizers, or additives that may have migrated to the surface must be removed either by plasma cleaning or washing before surface modification is attempted. Immediate assembly is usually advised after the surface has been prepared. Once the surface has been optimized and bonded, the bond is permanent and does not degrade over time.

In-vivo and in-vitro applications. To increase biocompatibility in vivo, the issue of thrombogenesis (the propensity of a surface to form or initiate clotting) must be addressed. Many unmodified materials encourage protein binding and thus initiate the process of clot formation. To combat this process, antithrombonin (anticlotting) coatings are often applied to the surface, but when dealing with polymers these antithrombonin coatings often fail to effectively bond to the target surface.

Using an active gas plasma, surfaces may be modified by heparinizing or by grafting of antithrombotic functional groups, which achieve effective chemical bonding to previously inert material surfaces. Process variables are dependent upon a range of factors including selection of the base materials, composition of the antithrombotic, and the expected product lifetime.

Animal test results of the procedure on surface modified and heparin coated polyure-thane catheters revealed no protein attachment after a 30-day indwelling. Simultaneous testing on surface modified but uncoated polyurethane catheters disclosed only slight protein attachment, while unmodified and uncoated catheters show severe thrombus formation.

In tests performed on plasma modified blood filters, results showed substantial reduction in platelet retention compared to untreated materials.

Attachment of in vitro cultures. It is sometimes necessary to manipulate surface conditions of in vitro structures so as to encourage or enhance culture cell growth. In specific cases where cell attachment is necessary to ensure proliferation, plasma modified in vitro culture cell containers yielded dramatic improvement over untreated containers. Testing has confirmed that, by using gas plasma surface modification procedures, materials such as PET, polyethylene and K-Resin can yield substantially higher performance than in the untreated state.


1 J.R. Hollohan and A.T. Bell, Techniques and Applications of Plasma Chemistry, John Wiley & Sons, New York, NY, 1974

2 Chapman, Glow Discharge Processes, John Wiley & Sons, New York, NY, 1980

3 T.J. Hook, J.A. Gardella, and L. Salvati, Journal of Materials Research, 2, 132, 1987

4 D.S. Everhart and C.N. Reilly, Annals of Chemistry, 53, 665, 1981

5 M. Szycher and W.J. Robinson, Editors, Synthetic Biomedical Polymers, Technomic, Westport, CT, 1980

6 R. d’Agostino, Editor, Plasma Deposition, Treatment, and Etching of Polymers, Academic Press Inc., San Diego, CA, 1990

7 E.M. Liston, Journal of Adhesion, 30, 198, 1989

Leave a comment

Filed under General Knowledge, Medical

New Water-Based Acrylic Pressure-Sensitive Adhesive


New Water-Based Acrylic Pressure-Sensitive
Adhesive Grabs Higher Performance Applications

PHILADELPHIA, Oct. 10 /PRNewswire-FirstCall/ — Rohm and Haas announced today that it has developed a new water-based acrylic adhesive, ROBOND(TM) Prohesion, designed for pressure sensitive tapes and other demanding applications traditionally served by solvent-based adhesives. The product exhibits characteristics and stamina never before seen or thought possible in an aqueous acrylic adhesive.

“Water-borne acrylic PSAs may have traveled a long way, but until now, solvent-based choices have continued to dominate most higher-performance adhesive requirements,” says Chris Urheim, Rohm and Haas North American region marketing manager, pressure sensitive adhesives. “With ROBOND(TM) Prohesion, we have taken another significant leap forward in delivering a cost effective acrylic adhesive that doesn’t compromise performance. Feedback from our customers so far has been amazing.”

Shear adhesion and resistance properties of this new technology are said to be groundbreaking. No other emulsion PSA has ever come close to the product’s heat resistance capabilities while retaining its level of adhesion. Tests indicate that ROBOND Prohesion withstands punishing hot shear tests at 150 degrees F (62 degrees C) for more than 50 hours, exceeding values of some solvent-based choices. In addition, the product’s humidity resistance is outstanding, eliminating a traditional shortcoming of aqueous systems. ROBOND Prohesion retains more than 80 percent of its peel adhesion after prolonged exposure to moisture under severe conditions of 90 percent humidity at 95 degrees F (35 degrees C).

ROBOND Prohesion offers an environmentally advanced formulation that holds up to performance demands of the automotive, construction and general industrial markets, all of which are requesting that suppliers lower volatile organic compounds in their products. The adhesive adheres aggressively and exhibits superior anchorage to substrates ranging from high surface energy applications, like stainless steel for example, to equally challenging low surface energy materials like high-density polyolefin foams.

To learn more about ROBOND(TM) Prohesion, visit us at,

About Rohm and Haas Company

Leading the way since 1909, Rohm and Haas is a global pioneer in the creation and development of innovative technologies and solutions for the specialty materials industry. The company’s technologies are found in a wide range of industries including: Building and Construction, Electronics and Electronic Devices, Household Goods and Personal Care, Packaging and Paper, Transportation, Pharmaceutical and Medical, Water, Food and Food Related, and Industrial Process. Innovative Rohm and Haas technologies and solutions help to improve life every day, around the world. Based in Philadelphia, PA, the company generated annual sales of approximately $8.2 billion in 2006. Visit for more information. imagine the possibilities(TM)

Leave a comment

Filed under Acrylic, General Knowledge

Selecting Plastic Animal Cages


Selecting Plastic Animal Cages
By Dave Demorotski
September/October 2005

Buying on price is one way. But if you can answer a few what’s and how’s about your facility caging needs and procedures, you can purchase cages that will last longer plus add value.

For many, selecting the right plastic caging for housing rodents can be a “poly nightmare.” There’s “poly-this type cage” and “poly-that type cage.” And the “poly-that type cage” must be better because it costs 20% more than the “poly-this type cage.” Yet the “poly-that type cage” didn’t last 20% longer because it became cloudy and hazy after only a few times through washing and sterilizing cycles.

So how should you determine what is the right caging to buy for your vivarium? The best answer probably lies in understanding how your cages are used and how they move through your facility… from the animal housing room to washing/sterilizing, to storage and back to holding the animals. Below are some questions to consider that can help you determine which plastic cages may best serve your facility.

Questions to Consider Before You Buy
• First, of course, is how many new plastic cages does your facility need? Do you have an absolute minimum (number of cages) to purchase or is there a budgeted amount to spend?
• What is the budget level or limitation?
• How long does the caging need to last?
• For what type of research are the cages being used?
• Does the study require only a one time or very limited use?
• Does it involve dangerous or toxic materials that need disposal? Or, do the cages just need to last as long as possible?
• How frequently do you changeout cages?
• How is the caging handled throughout your facility? What processes will they go through? For example, how is the soiled bedding removed, by hand or mechanically? How is sticky bedding removed? How are the cages transported and stored? In general, how much does your caging get knocked around in moving it from the animal lab through cleaning and sterilizing and back to the animal room?
• What kind of detergents are used in cleaning? How much alkali does the detergent have, <pH7.0?
• How hot is the water? Is it hard or soft water? Is the rinse cycle sufficient to make sure all residue is removed?
• What chemicals are used to disinfect your plastic cages?
• Will the cages be autoclaved? What are the usual autoclave settings? Are amine corrosion inhibitors added to the central boiler steam supply to protect the pipes? Will the cages be autoclaved with the bedding, feed, and water bottles in them? If so, what type of bedding is used?
• Finally, how will the sterilized cages be stored? How high will they be stacked?

Okay, so it’s more than a few questions. But the more you can find out about how the cages are handled and treated within your facility, the better you will be able to select the type of plastic that will serve your requirements, at the price you can afford.

Suppliers and cage manufacturers conduct a variety of
tests on polymers. Most are to determine durability, chemical resistance, material clarity and steam resistance. This photo highlights an autoclave test of materials at 270° F for50 cycles under induced stress levels of 500 psi.

Selecting the Appropriate Type of Plastic Cage
Once you have completed your cage usage/care review and determined your caging requirements and budget, you can begin to quickly narrow the plastic options to the one or two polymers that will best fulfill your needs.

POLYSTYRENE OR POLYETHYLENE – These materials are low temperature and cannot be used in an autoclave. Polystyrene begins to distort at temperatures over 176°F (80°C) and polyethylene at temperatures over 200°F (93°C). The cages are rigid and are relatively low cost. For these reasons, cages of these materials are usually considered disposable and used in studies involving dangerous mate rials such as radiation. Polystyrene is a clear material so it is easy to view the animals, but its toughness and abuse resistance is fairly low. Polyethylene is opaque or translucent while offering a much higher level of impact resistance than polystyrene.

POLYCARBONATE (PC) – Polycarbonate is a popular material for animal cages and water bottles. It is also relatively inexpensive. PC can’t take the higher autoclave temperatures (>250°F/121°C) or the steam very well. It most likely will distort in the autoclave because of the temperature. Also, PC wants to absorb water (steam) which leads to its molecular breakdown evidenced by stress cracking after only a few sterilizer cycles. Stress cracking also occurs from chemical cleaning solutions such as alkalai and strong acid detergents as well as aromatic and chlorinated hydrocarbons.

HIGH HEAT POLYCARBONATE (PPC) – High heat PC is much the same as polycarbonate, just a little higher temperature tolerant (>270°F/132°C). The heat distortion is higher than PC, but the chemicals that attack it and the water absorption problem remain about the same.

POLYETHERIMIDE (PEI) – This polymer doesn’t have great impact strength to start and degrades further after autoclaving. It can withstand higher temperatures, up to 400°F (204°C), than the polycarbonates. It has good chemical resistance, especially against acidic detergents and organic solvents, but is susceptible to breakage because of its initial brittleness. PEI has very poor resistance to low pH solutions of alkaline chemicals. PEI should not survive more than 50 autoclave cycles unless it is given tender loving care. PEI is dark in color which doesn’t allow for much light transmission and makes it more difficult to view animals inside the cages.

POLYSULFONE (PSU) – Polysulfone can withstand higher temperature than PC or high heat PC, about 300°F (149°C) and should withstand about 100 autoclaves with minimal affect. PSU has good chemical resistance to all commercial cage cleaners, only being attacked by high levels of ionic surfactants. While polysulfone is completely unaffected by pure steam, amine corrosion inhibitors used in some central steam supply systems can cause crazing and cracking in areas of cages under high stress. It can also be attacked by ketones, aromatic and chlorinated hydrocarbons.

POLYPHENYLSULFONE (PPSU) – This is the highest level of the transparent polymer materials. Polyphenylsulfone offers great chemical resistance, great steam sterilizing (up to 380°F/193°C) capability, and high impact strength. Heat deflection begins to appear at the high range above 400°F (204°C). Tests have shown PPSU to withstand 2000 autoclave cycles with very little affect. PPSU also shows good to excellent resistance to both inorganic and organic cleaning chemicals. The hindrance to PPSU is a somewhat higher cost than other polymers used for animal cages.

A Little TLC Can Go a Long Way
As described above, the main areas that can determine the longevity of your plastic cages are its chemical resistance, steam resistance and toughness. If you follow some of the practices listed here, you may increase the useful life of your plastics.

Be as careful as possible in handling and transporting cages. In particular, avoid hitting or banging the plastics against hard surfaces. One common practice to avoid is hitting the cage against a surface to remove soiled and stuck bedding. This can significantly shorten the life of your cages. Even the higher end polymers with greater impact strength lose some of their resistance after repeated chemical cleanings and sterilization. To remove stubborn bedding, it is best to use a soft polymer spatula or scraper. Do not use a metal scraper because it can scratch the plastic surface.

Also, do not overstack the caging, especially cages with bedding. The stress on the lower cages can cause cracking. Again, this is especially true for older cages that have been through several cleaning cycles. As a general rule, mouse cages should not be stacked more than 15 high. Rat cages should not be stacked more than ten high.

Plastic cages and bottles should be washed in hot, soft water with a manufacturer recommended detergent solution. Washing plastics in hard water could cause a milky-gray discoloration on the surface after frequent washing. Optimum water temperature is in the 140°-150°F (60°-66°C) range. A short rinse at approximately 180°F (82°C) is helpful for disinfection.
If an alkaline detergent is used, a short acidic rinse cycle followed by a final fresh water rinse is recommended. In general, selecting a detergent with a pH between five and seven will work well for most polymers.

Be sure all residue is removed from cages and bottles by the final rinse. This is especially important if autoclaving is to follow. The extreme heat of autoclaving will most likely cause the residue to be baked onto the plastic, resulting in loss of clarity and gradual deterioration.

To help prolong the life of your plastic materials, you should consult your cage wash supplier to ensure that the cycle times and temperatures are correct for the plastics you are using.

There are many disinfectants that can harm plastics. Check with your disinfectant supplier regarding the use of their products for your particular plastic materials. You should NEVER heat cages that contain a disinfectant residue.

It is important that plastic cages and bottles are washed, thoroughly dried, and free from any residue before autoclaving. Effective autoclaving depends upon proper temperature controls and appropriate steam supply. Autoclaves should be regularly checked to ensure effectiveness.

While polycarbonate (PC) is considered autoclavable, it will deteriorate after repeated autoclaving. It is recommended that PC cages should be autoclaved only on an as needed basis and at a temperature no greater that 250°F (121°C) for a short cycle, about 20 minutes.

While cages with bedding, feed, and water bottles can be autoclaved together, it is important to note that heating these combined materials may possibly release damaging substances which can attack the plastic. This could cause clouding and/or cracking of the polymer material.

For steam sterilization systems supplied by a boiler feed, check for the use of corrosion inhibitors with amine. These could also dull or damage the plastic material.

Answering a few questions regarding the chemical, disinfecting/sterilizing procedures and how your plastic cages are handled within your facility should be the first part of your selection process. Finding answers to the chemical and steam resistance as well as impact strength of the various plastic resins you are considering for your cages is the second step. Finally, determine your budget and longevity goals. With these answered, you will be able to select the plastic animals cages that will best serve the needs of your facility.

Dave Demorotski is Marketing Manager of Alternative Design Manufacturing & Supply, Inc., 3055 Cheri Whitlock Dr., Siloam Springs, AR 72761;479-524-4343;;

Leave a comment

Filed under General Knowledge

Plastic? You Might Be Chewing It


Nonstick Chewing Gum

A U.K.-based company is set to launch a new kind of chewing gum that’s easy to wash off any surface.

By Prachi Patel-Predd

Most everyone has had the displeasure of stepping on chewing gum in a parking lot. Cleaning up the sticky mess might become easier, thanks to a new gum created by U.K.-based Revolymer. The gum easily comes off roads, shoes, and hair, and it barely sticks at all to some surfaces.The company has conducted extensive trials on the ease of cleaning up the gum and has done independent taste tests. Revolymer’s CEO, Roger Pettman, says that the company is now looking to get a U.S. Food and Drug Administration safety affirmation. If all goes as planned, Revolymer will launch the gum in three different flavors–mint, fruit, and lemon–next year.

About 600,000 metric tons of chewing gum are manufactured in the world every year, Pettman says. A large percent of that ends up on streets and pavements, becoming a pollution issue. “There is no great way to remove it,” says Pettman. Every year, London spends an estimated two million pounds, or more than four million dollars, to clean gum from subway trains and stations, according to a 2005 report by the London city council. The United Kingdom’s Department of Environment, Food and Rural Affairs has launched a national campaign to tackle gum litter, while Singapore has enacted the famous chewing-gum ban.

Revolymer’s product has a formulation unlike most commercially available brands. The main ingredient in most chewing gums is a gum base: a mix of synthetic petroleum-derived polymers, natural latex, resins, and waxes. All of these components are hydrophobic–they stay away from water–which means that they are oil loving, says Pettman. This is the reason that gum traditionally sticks to the grease and grime on sidewalks. The Revolymer gum base has polymers with a hydrophobic part that’s wrapped inside a hydrophilic, or water-attracting, part. So even though the gum sticks to a surface, a film of water can form around it so that it easily washes away with water.

The new gum performed well in tests. When Revolymer researchers stuck it on sidewalks in U.K. towns, rainwater or street cleaning would wash it off within 24 hours. Most commercial gums, on the other hand, remained stuck and were difficult to remove. Tests also showed that when the new gum was stirred into water, it disintegrated completely in eight weeks, which means it could degrade once it goes into a drain.

The gum also did well in blind taste tests, Pettman says, with testers saying that it tasted just as good as leading brands. The texture, though, is slightly softer, he says, because the hydrophilic polymer interacts with saliva.

So far, no other company has developed a nonsticky, degradable chewing gum. Soo-Yeun Lee, a food-science professor at the University of Illinois at Urbana-Champaign, has developed a natural, biodegradable chewing gum that uses corn proteins instead of synthetic polymers. Her work was published in 2004 but is not ongoing.

Lee says that leading gum manufacturer Wrigley has a patent on a similar corn-based gum. According to the London city-council report, Wrigley has spent more than $10 million on research to find a biodegradable product but has yet to report success.

Leave a comment

Filed under General Knowledge

Diploma In Plastics From St. Clair College – Ontario


Plastics Engineering Technology (Co-Op) (T913)

Location: Windsor

Plastics Engineering Technology includes the theory and practical applications of various aspects of plastic parts production from design through to mass production and testing. Topics include properties of plastics and composites, product design, mould design, plastics processing, cost estimating, prototyping and project management. It is a three year diploma program with an optional fourth year leading to a technology degree currently under development.


  • Optional Co-op Work Terms
  • Transfer Agreements with Universities
  • First Year is Common with T826, T841 and T842 providing flexibility to transfer between these programs at the start of semester 3 without loss of credit


  • Interested in concepts and theories
  • Mechanical Aptitude
  • Good communication and interpersonal skills
  • Ability to receive, understand and give instruction
  • Good work habits

Excellent employment opportunities exist for graduates of Mechanical Engineering Technology – Plastics. This program was designed to reflect the current requirements of the plastics industry and will prepare students for diverse and financially rewarding positions in plastic product design, mould design, production supervision and project management.

Leave a comment

Filed under General Knowledge

Thermoplastics For Aircraft Interiors


Thermoplastics for aircraft interiors

By Staff | September 2007

GE Plastics (Pittsfield, Mass.) has launched three new resins designed for use in aircraft interiors. Noryl LS6010 is a polyphenylene ether (PPE) that has a specific gravity of 1.1, which is one of the lowest available for thermoplastics used in aerospace. It also features low smoke, good durability and nonhalogenated flame retardance (FR). Applications include rub strips and seat track covers, for which low smoke propagation is mandated. Lexan FST9705 is a polycarbonate (PC) copolymer said to be suitable for personal service units, window reveals and bezels, and offers full flame/smoke/toxicity compliance, including OSU 55/55 heat-release performance. Flame-retardant Ultem 9085 is a polyetherimide (PEI) resin that is said to offer better flow and ductility than GE’s Ultem 9075 resin and can reduce part weight by 5 to 15 percent via thinner walls. The material also provides the highest modulus of any Ultem resin grade. Potential applications include decompression grilles, window reveals and personal service units. 1197

Leave a comment

Filed under General Knowledge, Industrial Plastics, Mechanical Plastics