Laboratory Gloves

Ned Leverage

Dean Kirk

When you think of your first day working in the research environment you can probably remember wearing protective gloves. It seems as if protective gloves have always been around. However, we know better. Natural rubber has been used since the 16th century but, until 1839 when Charles Goodyear discovered vulcanization, its use was limited. Charles Goodyear’s discovery revolutionized the rubber industry and made possible the ability to make pneumatic tires and tubes, balloons, and of course gloves. In the 19th century most of the raw latex was harvested from South and Central America and Africa. The Para rubber tree of the Amazon basin was the most popular. In 1876, seeds of the Para rubber tree were smuggled from Brazil to England. The seeds were then sent to Ceylon (Sri Lanka) and then on to many tropical regions, particularly the Malay area. This began the enormous East Asian rubber industry. In 1927, the Germans invented buna rubber. When the East Indies cut off the supply of natural rubber during World War II, the United States began large-scale production of Buna S (Nitrile). Today over 1.7 billion rubber gloves are consumed by the United States each year. Now everyone from mechanics to surgeons use gloves for a variety of reasons.
In the 1950’s and 1960’s most gloves used in the laboratory environment were made of a vinyl polymer. They didn’t fit well and had limited tactile sensitivity but they were inexpensive, available, and afforded an acceptable level of protection for the time. Things are very different now. Basically, the changes that have taken place within the glove industry have been driven by changes in research models and research protocols. These changes along with an increased awareness of the research environment have made laboratory personnel more attentive to the need for personal protection in the laboratory environment. But providing protection means identifying the types of potential hazards.

Gloves that protect and serve

Over the years, technicians have required increased protection from blood born pathogens and microbial contamination of both themselves and the research animals. Some laboratory procedures as well as cleaning and decontamination protocols include more aggressive chemicals, which in turn need gloves with increased chemical resistance. Technicians require gloves with better tactile sensitivity to allow safe manipulation of laboratory equipment and computers, which have invaded the real time laboratory environment. While these are relatively new challenges, some things never change and technicians still require protection against staining reagents and other general laboratory contaminants.

These technical needs created a void that could only be met with latex resins. Latex is more elastomeric than vinyl and affords more chemical resistance and a higher degree of personal protection. Additionally, latex resins offer the flexibility in manufacturing required to create needed design changes.

How that latex glove you wear everyday is made

The manufacture of gloves is a fairly simple process today. Latex in its raw form is not a desirable glove material. It must be formulated with compounds that help it maintain its flexibility, assist curing, increase tensile strength, and help the latex adhere to the mold during the molding process among other things. In essence, the process of formulating the raw latex is responsible for the performance specifications of the glove itself. Although all latex gloves fall under the same general heading of latex, the final performance quality is determined by the individual formulations.

The mold form determines the glove size and the surface texture design. The form is basically a hand model used to dip into the liquid formulation.

The speed of the production line (the number of “dips” a mold form makes) determines the mil thickness and strength of the glove. The slower the mold runs through the vat and the more dips are made the thicker the glove and vice versa. Durability, puncture resistance, pinhole free, and chemical resistance are all affected to some degree by the thickness of the glove. Gloves destined for medical and biomedical uses, for example, will have been processed more slowly and dipped more times than standard non-medical ambi-latex gloves. In instances where cut or puncture resistance are a premium concern (as in cage handling areas) some manufacturers are now providing a 14 mil thick latex glove.

When the dip or forming process is completed, the gloves are subjected to a vulcanization process to remove excess chemicals remaining from the mold process, to reduce odor, and add elasticity to the latex. Next, the gloves are stripped from the mold formers. After stripping, the gloves enter the final cleaning and treatment phase, which determines much of the final application for the gloves.

*Powder and Powder-Free

Hydrolyzed cornstarch is added by tumbling the gloves in a slurry of starch and biocide. Powder makes donning easier and the manufacturing process shorter. Studies on the starch slurry, however, show that the starch binds to the latex proteins and acts as a vector transfer of protein to the skin. Powder-free gloves are not exposed to the hydrolyzed starch process but require additional cleaning of production impurities and therefore require a longer manufacturing time.

*Chlorination

Clean room gloves are chlorinated during the washing process. Chlorination smoothes the surface and eliminates shedding by hardening the latex. This reduces the particulate count, a needed feature in clean room applications. While chlorination yields desirable clean room characteristics, it reduces the shelf life of the product. (Be sure to ask your glove representative about the positive and negative aspects of specialized treatments.)

*Polymer Coating

Some manufacturers offer a process known as polymer coating. Polymers can be applied either to the outside of the glove or to both the inside and outside. This process gives the glove additional barrier protection. A double polymer coated glove, inside and out, has the ability to resist viruses such as Hepatitis B and C and HIV. This process also adds strength to latex gloves to reduce tearing or ripping while in use and gives the glove better wet/dry grip properties.

*Synthetic Polymers

Gloves made of synthetic polymers such as Nitrile are petroleum based. They are processed and formed in much the same manner as latex gloves. The synthetic Nitrile polymer can be used in lieu of true latex if individuals have true latex allergies. Nitrile has better chemical resistance than latex with petroleum based chemicals and solvents. If manufactured as a medical grade product, they can also serve as a barrier glove for HIV and Hepatitis B and C. If chemical resistance is critical to your operation, check actual samples provided by your glove supplier to assure the proper selection.

*Glove Length

Gloves are manufactured in a variety of lengths. The most desirable length is primarily determined by end use application. Twelve-inch cuffs are generally preferred in applications where protection at the wrist and sleeve junction is important. Mostly these are procedures such as animal handling applications and laminar flow hood procedures. Nine-inch long gloves can have the same performance specifications as twelve-inch gloves; they are just shorter and less expensive. Normally nine-inch gloves are preferred in laboratory applications where wrist protection is not an issue.

Glove supply, demand, and quality

Latex gloves have been made primarily in Malaysia since the mid 1900’s, although other eastern countries do have some manufacturing capabilities. Malaysia is in the center of raw latex production and it makes sense economically to manufacture near the material source. For some time latex gloves were also manufactured in the U.S. but most of that manufacturing capability moved “off shore” in the 1980’s. Now only a small amount of specialty gloves are manufactured in the United States.

Latex glove quality was maintained at an acceptable level until the early 1990’s. At that time the increased public awareness of HIV and its increased occurrence within the general population caused both a sudden and exponential need for latex gloves. It also created a demand for quality gloves that could handle the changing protective needs of the consumer. This new market overpowered the available raw latex supply. Like growing spores for antibiotics, there is a ramp up time. The Para rubber tree for example takes seven years to mature before it can be harvested. Now police forces, fire and rescue workers, dentists, and many other professions that had not traditionally used gloves are using them as part of their Standard Operating Procedures. Even sports referees are now equipped with protective gloves. In an attempt to supply the new emerging market, there was a rapid expansion of production capabilities in Malaysia. There was also a concurrent expansion of manufacturing facilities in other countries not normally accustomed to latex manufacturing.

Unfortunately, with the rapid expansion of manufacturing facilities came the rapid decline in glove quality. Those who were working in the research industry at the time will remember gloves that ripped, had holes and thick hardened spots of latex, pinholes, and many other imperfections. It was also at that time when people started complaining of latex allergies and glove associated rashes. There are a lot of subtle factors that affect glove quality. This appears to be a fact lost on many low cost suppliers. Clean water systems used in the manufacture of gloves for example, are an important issue in glove quality. Not all countries or regions have either the water quality needed to manufacture a quality product or the water treatment facilities to produce high water quality. In addition to chemical purity of the water, there are considerations of microbial contaminants in the production environment that may also affect quality. These and other influences are likely equally influential contributors to what we refer to as latex allergies and irritants as the latex itself.

Regulating gloves - 510K registration

Since the vast majority of gloves were made overseas, the U.S. government could not regulate the manufacturers, making consistent quality a real issue. However, over time, the FDA has been able to establish a registration that foreign manufacturers must meet in order to sell gloves in the U.S. that qualify as a Medical Grade product. This is referred to as a 510K registration. A manufacturer must have a separate certification and lot number for every style glove they produce. It is akin to the AAALAC certification in that it does not “insure” automatic quality but it does insure that the infrastructure and understanding of the U.S. medical grade requirement is in place at the manufacturing facility. Further, if a facility loses its 510K registration, it can no longer sell medical grade gloves into the U.S. market. Gloves without the 510K registration can still be sold in the U.S. but must be limited to the industrial market. Often the end user who is compelled to buy on price alone will unknowingly purchase the less expensive industrial grade gloves. Unfortunately, even though the industrial glove is less expensive, they also do not provide the personal health protection needed in the biomedical industry. Since medical grade commands a higher price from the manufacturer, there is a financial incentive for foreign glove manufacturers to comply with the FDA requirement.

Within the 510K registration there are several tests required for medical grade gloves. One of the most important is to prove gloves are pinhole free. The pinhole free test is ASTM D 5151, a water leak test. No leaks equals no pinholes. The only assurance of quality protection required for biomedical testing is the certification of the 510K registry and proof of ASTM D 5151 testing. Without these assurances, the FDA will not approve the gloves as medical grade. Fortunately, many glove manufacturers comply with these requirements. Be sure you check your supplier for these assurances and certifications.

Even though the last 10 to 15 years have presented some real challenges, there are a number of reputable manufacturers who have accepted the task of maintaining quality in the research glove market. While there are many styles and options to select from, it is best to not overreact to the specialization but rather select the few gloves that best fit your application. Decide the application and the level of personal protection required in your facility. Once those criteria are understood, work with your glove supplier to secure gloves that meet your requirements. Personal protection for your employees is a requirement that is here to stay.

Reprinted with permission.

animalLABNEWS™: March / April • 2003 Vol.2 • NO. 2

www.animallab.com

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