Cleanroom Gloves – Particles, Extractables and Selection

Cleanroom Gloves - Particles, Extractables and Selection

Cleanroom gloves are worn throughout the electronic, aerospace, solar, medical device and pharmaceutical industries to protect products from contamination during manufacturing.   Nitrile cleanroom gloves are a popular choice.   Compared with latex gloves, nitrile gloves offer better abrasion resistance and therefore less particulate shedding.  They provide excellent biohazard protection, and can be laundered to deliver the lowest particle and extractable levels.

Particle Levels

Cleanroom gloves, along with other cleanroom garments, are worn to protect the product or process from particle contamination caused by the shedding of human skin.  So the gloves themselves should have low airborne and liquid-borne particle contamination.  Particulates can arise during the manufacturing process, and glove manufacturers routinely test in order to trace and reduce sources of contamination.

The lowest contamination levels are obtained through multiple rinses in deionized water, followed by drying cycles in HEPA filtered driers.  To ensure the gloves stay very clean, they are then sorted and packed in double polyethylene bags in an ISO 5 or 4 cleanroom environment.

Ion Extractables

Ionic extractables are traces of elements that can leach out of a glove and harm the product being manufactured.  They include elements such as calcium, chloride, sodium, silicon, sulfites and zinc.  The type, mobility and amount of ion extractables can seriously affect the manufacturing process.  In the semiconductor industry, ions like sodium can induce conduction and low field breakdown in devices.  In disk drive manufacturing, chlorides can cause corrosion.

Testing for inorganic ions present on a glove’s surface include using an ion chromatograph and Couple Plasma, Flame-AA or GF-AA in accordance with ASTM guidelines.  It’s important to note that in this stringent test the extractable levels are much higher than ion transfer under normal, dry glove use.

Cleanroom Gloves – Selection Criteria

Cleanroom requirements vary from one manufacturer to another, even within the same industry.  When selecting cleanroom gloves, the particle levels should match the cleanroom environment.  The extractables should be as low as possible, but taken in consideration with the glove’s overall barrier properties, such as AQL, or pinhole rate.  A glove with impressively low extractables, but with a high pinhole rate will not keep the manufacturing environment as clean as a glove with a lower AQL.

What is most important for your cleanroom application (particles, extractables, grip, ergonomics) and why?  Share your comments below.

Disposable Glove Quality Testing

The FDA sets high standards to ensure the disposable gloves you purchase here in the U.S. perform as expected and provide an adequate barrier for their intended use.  To meet these standards, glove manufacturers have tight quality controls and manufacture gloves according to ASTM specifications and testing requirements.

A key quality measurement that glove manufacturers publish on glove boxes, bags and product literature is AQL, or Acceptable Quality Level.

Stated as a percentage, the AQL is a statistical measurement of the quality of the gloves.  An AQL of 2.5% means that statistically, only 2.5 gloves for every hundred gloves will fail a quality test.

How AQL is Determined

Let’s say a glove manufacturer produces 10,000 gloves from the same material, settings and processes.  Two hundred gloves would be pulled randomly from the line, throughout the batch, to be tested.  To meet an AQL of 2.5%, no more than 10 gloves can fail the quality tests.  If more than 10 gloves fail, the entire batch fails, and each glove must be tested individually for quality, or else the whole batch is discarded.  An AQL of 1.5% would mean that no more than 7 gloves could fail.

ASTM D5151 Test for Detection of Holes in Medical Gloves

Disposable gloves are subjected to numerous ASTM tests throughout the manufacturing process.  One test that medical and cleanroom gloves have in common is a test for pinholes.

ASTM D5151 is the Standard Test Method for Detection of Holes in Medical Gloves, often referred to as the “watertight” test or “water leak” test.   In this test, the gloves are each filled with 1000 ml of water at room temperature, secured at the cuff and hung vertically for two minutes to check for pinholes.  If water does not leak from the glove, it gets a “pass.”

The current FDA mandated maximum AQL for examination and cleanroom gloves on this test is 2.5%, down from the previous 4.0% prior to December 2008.  Some gloves, however, are manufactured and tested to meet the lower AQL of 1.5% required for surgical gloves.  This means higher quality and fewer pinholes.

Are Your Cleanroom Nitrile Gloves Full of Pinholes?

Cleanroom Gloves and Pinholes

Cleanroom and controlled environments have unique glove requirements.  While healthcare workers primarily wear gloves to protect themselves from bloodborne pathogens, a person working in a clean manufacturing environment primarily wears gloves to protect the product or process from contamination.

Pinholes in gloves provide a path for human-borne contaminants in the clean manufacturing environment.   Just one square inch of the surface of a person’s hand can contain 10,000 microorganisms!

So how common are pinholes in cleanroom gloves?

A study published in May 2011, Integrity of Disposable Nitrile Exam Gloves Exposed to Simulated Movement,  compared cleanroom nitrile gloves to medical-grade, low-modulus and general duty nitrile gloves.  A total of thirty different glove products were tested, including six cleanroom and nine medical-grade nitrile glove products.  A modified water-leak test was used to detect a 0.15 to 0.05 mm hole in different areas of the glove, including the thumb and pinky.  What did they discover?

“The cleanroom gloves, on average, had the highest percentage of leaks, and 50% failed the water-leak test.”

Two of the cleanroom nitrile gloves tested had an out of the box failure rate of 6.25%.  The medical grade and low modulus gloves had the lowest percentage of leaks.  Even the general duty gloves performed better than the cleanroom gloves tested.   However, two of the six cleanroom gloves tested had a failure rate of zero percent.  Why such a significant difference?

The study authors indicate that it could be due to differences in nitrile material formulation.  A low-modulus nitrile glove with a higher percentage of plasticizer, which is more water resistant, was expected to perform better in the water leak test.

What was not discussed in the paper is the AQL, or Acceptable Quality Level, of the gloves tested.  The AQL for the water leak test, a test that indicates what percentage of the gloves can fail a water test for pinholes, is set by ASTM at 2.5% for cleanroom gloves.  Many manufacturers, however, use the medical grade requirement of 1.5%.  This means that less than 1.5% of the gloves from any given lot could fail due to pinholes – substantially less than 2.5%.

Clearly, there are significant differences in the quality of cleanroom gloves on the market.  To protect your cleanroom environment, select cleanroom gloves made from consistently high quality low-modulus NBR materials, and an AQL of 1.5% or less.

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What is Nitrile Anyway?

Disposable nitrile gloves have become a mainstay in the medical, dental, lab, cleanroom and food handling industries.  We enjoy their strong, latex-free comfort.  But what is nitrile anyway?

The Science of Nitrile

Nitrile is a shortened term for Nitrile Butadiene Rubber, or NBR.  Although it is also referred to as NBR latex, there is no natural rubber latex (or latex proteins) in the material.  Nitrile is a synthetic rubber copolymer of acrylonitrile and butadiene.  These two materials (monomers) are placed in a stainless steel vat, and using hot or cold polymerization, a chemical reaction occurs, and voila!  Nitrile is born.

The nitrile latex is filtered and blended with an antioxidant to stabilize the material.  Next, the liquid is solidified by adding coagulating agents, then finally washed and dried.  The resulting material is referred to as “crumb rubber.”  Crumb rubber can be liquefied by product manufacturers to make nitrile rubber materials, such as floor mats, footwear, adhesives and gloves.

Low-Modulus Magic

Nitrile alone, without anything added, is a fairly rigid material.  So glove manufacturers add a small percentage other chemicals to NBR in order to create a soft, or low modulus, nitrile glove.  Over the past decade, these manufacturers have continued to improve their nitrile glove material formulations.  Disposable nitrile gloves have grown softer and more elastic.  The latest innovations in nitrile glove development include accelerator-free formulations that lower the risk of Type IV contact dermatitis in wearers.

These thin and flexible gloves are what we have all come to rely on to keep ourselves, our patients, products and food items safe.  Nitrile gloves are more resistant to oils and acids than natural rubber (latex) gloves.  The material is resistant to abrasion and puncture, making it suitably durable for many tasks.  Low modulus nitrile gloves also conform well to the hand and provide excellent tactile sensitivity.

As disposable nitrile glove formulations evolve, hand protection is becoming ever safer and more comfortable.  We look forward to continuing to bring you the very best nitrile gloves made from the latest materials.

Have you noticed the improvements in disposable nitrile gloves over the years?  We’d love to hear your comments.  Share them with us below!

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