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The Development of Nitrile Gloves

Published: 10th Jan 2011

Aeronautics has progressed rapidly over the past 100 years, beginning with the first 12 second flight by the Wright brothers, to mass intercontinental transit today.

At each stage of the development there have been external pressures making designers and engineers produce faster and more economical aircraft - this may be the need for improved manoeuvrability of a fighter, or the need to move greater numbers around the world.

The development of gloves has probably not been so fast or dramatic, but it has been impressive. In the not too distant past surgeons’ gloves were reusable, utilising ground up sphagnum moss as the donning aid.

Clearly today we would laugh at reusable surgeons’ gloves, just as at the effort of a 12 second flight.

The development of disposable gloves has been no less spectacular - over the past few decades it’s become a multibillion pound business.

I want to look at the pressures which have helped to shape the products currently available and consider probable future developments.

Examination gloves

Examination gloves have traditionally been manufactured from natural rubber latex because the technology is relatively easy and the product is exceptionally soft and comfortable in use. So what are the drivers to seek alternative materials?

1) Latex allergy

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When AIDS burst on the world the use of latex gloves exploded exponentially - product was unavailable and this encouraged new manufacturers to enter the market. The companies had to develop their skills on dipping gloves; however, they often were not aware of the need to leach excess protein from the glove, or even if they were aware, many did not want to spend the money on hot water to leach the gloves. This resulted in gloves entering the market which had very high levels of latex protein. This resulted in the sensitisation of many laboratory and health care workers, and in many cases latex allergy which caused them to have an anaphylactic shock. Individuals once sensitised, who have not reacted to latex protein, will continue to be sensitised on further latex contact.

This is a particular problem with powdered latex gloves (rarely used in the UK). Powder free gloves have been leached to protein levels less than 50µg/g. The general accepted level of sensitisation is 100µg/g - in this case, someone starting to use latex gloves now using low protein gloves is unlikely ever to become sensitised. However, many companies and institutions have banned the use of latex gloves simply to eliminate any potential problems with previously sensitised individuals.

Chemical Resistance

Natural rubber latex gloves have an excellent physical barrier; however, they do not offer great protection against solvents. Laboratory and industrial customers are demanding greater protection.

2) Price

Natural rubber latex is derived from a rubber tree, Hevea brasiliensis.

The material was once collected by low cost labour, which meant the raw material was exceptionally low cost. In the past few years world demand for latex has exploded, at a time when plantations are reaching the end of their productive life, thus pushing prices up exponentially.

Quite apart from the demand for latex to make gloves with, China now has become the world’s largest automobile market - 15 million vehicles were sold in 2010. This alone has created an enormous demand for latex (tyres). India is also developing an automobile industry to meet the growing needs for transportation in the continent.

Latex gloves are purchased in US $, so the effect of a rapidly fluctuating dollar on the latex price results in significant price fluctuations of gloves in the market place. In the past few months the raw material costs of latex has imposed a 30% increase in prices which have already seen large increases over the past 12 months. This ever increasing price of latex has caused users to actively seek an alternative material.

Alternative materials

The ideal glove would be produced from a material which is soft and comfortable to wear for extended periods, and in addition have chemical resistance. One of the key issues is that the material should not be subject to wild price fluctuations, which in effect means it would have to be a manufactured material.

The materials available are:

1) Vinyl - PVC is a petroleum based film, which is not molecularly cross linked. As a result of the lack of cross linking, the individual molecules of vinyl tend to separate when the film is stretched or flexed. Vinyl gloves have a poor resistance to chemicals and cannot be used with cytotoxic drugs.

In order to make the gloves flexible it is necessary to add a plasticiser. This can be a significant amount - up to 45%. The most common plasticisers in use are phthalates - this material does not bind to the PVC and is readily leachable.

There is concern over the environmental impact of PVC gloves into landfill as the leachate can affect the reproduction of fish and other aquatic animals The alternative disposal method is incineration - this requires a sufficiently high temperature to eliminate noxious emissions.

On the positive side the material is low cost.

2) Polychlorprene - can produce gloves with a look and feel of latex. The main advantage is that gloves can be produced without chemical accelerators and so can be kinder to the hands.

The material is relatively chemically resistant.

The material is also relatively expensive.

3) Nitrile - this material is becoming the material of choice for many manufacturers because it exhibits outstanding chemical resistance, it can be produced to form exceptionally soft film, can be accelerator free and is very clean, making it ideal for Cleanroom gloves. In addition, the material has static dissipative properties so is ideal for the electronics industry.

With all of the above benefits the material is relatively low cost. Certainly the raw material has significant price advantages over latex.

History

Nitrile examination gloves were pioneered by Best Manufacturing (now Showa Best) who developed the first soft nitrile glove approximately 15 years ago. Once the value of nitrile examination gloves was established, Ansell introduced Touch & Tuff™ and Safeskin (now Kimberly Clark) with Blue Nitrile™ and shortly after Purple Nitrile™. These gloves and later introductions from other manufacturers are premium products aimed at solving specific problems (chemical resistance or latex allergy, for example), not really competing directly with latex examination gloves.

Current developments in thin nitrile examination gloves

In the past year new nitrile gloves have entered the market aimed at widening the utility of nitrile examination gloves to replace natural rubber latex examination gloves. Although there are just a few new entrants to this market we can expect many others in the future.

Advantages

1) Price: Thin nitrile examination gloves can compete directly in price with latex examination gloves, yet offer significant other benefits. 2) Comfort: Nitrile softens rapidly on the skin to provide the most comfortable experience, even when the glove is used for extended periods. 3) Tactility: Close fitting nitrile provides enhanced tactility, especially with micro roughened fingertips. 4) Chemical Resistance: Nitrile is inherently more chemical resistant than latex. 5) Improved Heat Dissipation: The thin film nitrile is able to dissipate heat from the hand faster, reducing sweating and skin irritation

t ∝ where t= temperature dissipation d= thickness of the film.

It can be seen that relatively small decreases in the film thickness make a significant increase in heat dissipation.

6) Environmental Issues: Thin nitrile gloves offer significant environmental benefits, in storage and transportation. Cases of gloves contain up to twice the quantity in the same volume. This results in the halving of transportation costs of gloves from the manufacturing site to the distributor, and additionally from the distributor to end user. Storage costs throughout the supply chain are similarly reduced. Finally the cost of disposal of the used product to landfill or incineration is significantly reduced.

Nitrile glove production is exceptionally competitive and manufacturers will seek to offer a similar product. Clearly not all will have the technical expertise to modify existing formulations to enable them to enter this fast developing market.

Application of Thin Nitrile Gloves

a) Food Preparation

Vinyl disposable gloves for use with food preparation are regulated by 1935/2004/EC, 2007/19/EC and 2008/39/EC. The plasticisers used (phthalates) have been shown to migrate to foodstuffs, particularly fatty foods such as oil, meat and fish. Phthalates are now carefully controlled in gloves used in food preparation; however, confirmation from the manufacturer that the gloves are ‘food safe’ should be secured if you continue to use vinyl. A better alternative is to use thin nitrile gloves which meet the ‘food safe’ requirements.

b) Medical, Industrial, Laboratory and Pharmaceutical

Gloves are widely and increasingly used in hospitals and throughout industry - possibly the same supplier providing gloves to all users.

The protection required in a hospital is not the same as that required in industry - basically in a hospital environment the gloves are to protect the patient from the glove user, whereas in industrial applications it is the user who requires protection from what is being handled.

Not surprisingly, gloves for the different applications require different standards. As these are often confused, or in error used interchangeably, it is worth considering the implications of this. What would be the view taken by an insurance company if a member of staff in a laboratory, for example, had an accident while using gloves designed for medical use? What would be the defence if a skin problem erupted even years after the event? In order to protect the individual and the company it is wise - and mandatory - to use a glove meeting the correct standards.

Disposable gloves are classified - Council Directive 89/656/EEC for laboratory and industrial gloves and Council Directive 93/42/EEC for the Medical Device Directive.

1) Medical Gloves

These will conform to EN455 - non sterile gloves registered according to the Medical Device Directive are examination gloves. The product is self certified by the manufacturer.

The basic elements of EN455 are:

EN455-1 Water tightness on a batch will meet AQL 1.5 that is approximately 3% defects. This shows the level of protection to the patient EN455-2 Covers the physical dimensions and the strength of the glove EN455-3 Describes the determination of natural rubber latex proteins by aqueous extraction On the glove box you will find the CE mark: There will also be the statement “Class 1 Medical Device” and a note that the gloves conform to BS EN455:2000.

2) Industrial, Laboratory and Pharmaceutical Gloves

Gloves to be to be considered as Personal Protection Equipment (PPE) are considered either simple design (Category 1) or complex design (Category

3), with a Category 2 glove which does not fall into the categories 1 or 3.

The basic elements are: Category 1 Simple Design: for minimal risk only Category 3 Complex design: designed to protect against the highest level of risk - irreversible or mortal risk. Disposable gloves in this category are designed to protect against chemicals and micro-organisms. These gloves will be evaluated against the following EN420 requirements of a glove: EN374-2 Testing for protection against liquid penetration and micro-organisms EN374-3 Testing against chemical permeation EN388 Testing against cut and abrasion

On the box you will find: Where the numbers alongside the CE mark indicate the independent test house - the notified body that carried out the article 11 (a or b) certification of the manufacturing facility to ensure the production quality and monitoring system meets the requirements of the PPE directive. (0134 SATRA, 0120 SGS, 0493 Centexbel, 0123 TUV).

Of particular interest to us is EN374-2 which is the resistance to penetration. This is a particularly important test for laboratory staff using disposable examination gloves as it indicates the barrier properties of the glove. This is normally designated on the box as 0.65, 1.5 or 4. The test is a water tightness test for the determination of holes. This clearly indicates the protection afforded to the user from holes which may allow the ingress of bio-organisms or chemicals into the glove. For laboratory use the minimum standard for a glove should be AQL (Acceptable Quality Limit) of 1.5; however, if the glove had an AQL of 0.65 this would provide the user a greater level of security.

The AQL figure is a statistical monitor of production; it is based on the batch size which would tell you the size of a sample of the gloves to be tested for defects.

Thin Nitrile gloves meet the needs of both medical, laboratory and industrial users. The Kimberly Clark Kimtech Science™ Sterling Nitrile™ gloves are available in both a medical and industrial options. New to the Range - launched in January 2011 - is the Kimtech Science™ Green Nitrile, an even thinner, more dextrous glove offering Category 111 chemical protection, but at the price of latex.

The Semperit Sempermed Xtra-Lite was launched as a food grade glove. A separate version is Nitrile skin2 which is a medical/industrial glove. Ansell have the Starpak thin nitrile.

So, having told you how good Thin Nitrile Gloves are, what are the drawbacks?

a) Chemical Resistance

A significantly thinner glove will clearly allow chemicals to pass through the nitrile film faster. This can be represented by the following formula: P ∝ where P= penetration d= thickness of the film.

Where it can be seen 25% reduction in film thickness can result in as much as 50% reduction in penetration time.

Clearly if you are concerned over chemical resistance then ensure that the chemical resistance data provided by your supplier is as a result of testing that glove material - NOT generic test data, which may have been produced 20 years ago, and on a different formulation of nitrile.

Note: A thin film nitrile glove should be used for splash resistance only - the glove should be replaced once it is contaminated.

Chemical Resistance Data

A useful source of information for chemical resistance of gloves based on test data of manufacturers gloves can be found at:

• www.Chemrest.com - An excellent site which provides information on suitable gloves and also data on the toxicology of the material • www.anselleurope.com - Provides a comprehensive resource on chemicals and also provides information on standards • www.ansellpro.com - An American website. Look at specware which is a superb chemical resistance resource also providing data on chemical risk • www.kcprofessional.com/uk/?PageRequest=techelp/techclotheshelp.asp - This link is from the Kimberly Clark

www.Contaminomics.com website, which provides an easy to use chemical resistance guide for both gloves and apparel

• Sempermed offer a simple paper based guide

b) Touch and Feel of the Material

New nitrile formulations have been developed to provide outstanding softness and tactility, while retaining exceptional chemical resistance. The developments of the formulations are the result of a significant investment in the technology.

While the established glove companies produce excellent gloves, I have become aware that a similar level of softness can be achieved by under curing the nitrile film. This can result in a glove which has insufficient mechanical strength - if the tri-dimensional bonding is not complete then weakness in the film will occur. This may appear to give the gloves an exceptionally soft feel but can result in glove failure (ripping when donning the glove), or colour leaching from the glove to the hand.

Future developments

Nitrile technology is rapidly advancing and a range of developments is predicted:

1) Cleanroom Gloves

Nitrile is a ‘clean’ material and post manufacturing washing will produce a glove which meets the highest Cleanroom requirements, one which is clean and not subject to shedding, and, in addition is exceptionally low in residual chemicals. The gloves may be readily sterilised by irradiation without any reduction in physical characteristics. Nitrile Cleanroom gloves are rapidly taking over as the material of choice in Cleanrooms. With the introduction of the newer thin film nitriles they eliminate the need for latex products.

2) Accelerator Free Gloves

Accelerators are used in gloves to ensure a rapid vulcanisation of the film and are responsible for many of the positive characteristics of a glove - its strength, elasticity and barrier performance (similar or the same accelerators are used in both natural rubber latex and nitrile latex manufacture).

If staff have a problem with the accelerator in a latex glove they may have problems when they use nitrile gloves. Accelerators are linked to Allergic Contact Dermatitis (Type IV, delayed hypersensitivity). These chemicals are in three basic groups of chemicals - thiurams, thiazoles and dithiocaramates - often moving to a glove with a different accelerator can reduce or eliminate a problem.

‘Accelerator free’ gloves are available which utilise optimised manufacturing conditions with exceptionally low levels of accelerator (so low they cannot be leached with water). However, when leached with a solvent then accelerators become apparent.

If it were intended that solvents be present in the proposed application then this could pose a potential problem.

I am aware that one manufacturer has developed a pre-treatment of the dip mix which eliminates the requirement of an accelerator; this is the development stage and has yet to be applied to a production line. Certainly this is an interesting development and I am sure that other manufacturers will enter the market for truly accelerator free gloves. Clearly at present caution should be exercised when individuals who are known to have sensitivity to accelerators use an ‘accelerator free’ glove.

3) AQL 0.65

The AQL - Acceptable Quality Limit - is a measure of the quality of a glove in terms of water leakage and other defects of a glove. This is assessed by random sampling of a batch which is defined according to the batch size and the quantity of gloves to be analysed. The results provide a statistical probability that the result of the random sample will also be valid for the entire batch - the designated AQL. Where a customer places higher demands on the product they require a glove with a lower AQL.

Glove manufacturers are aware of the increasing interest in gloves which will provide greater security when handling sensitive materials. Examination gloves will normally achieve an AQL of 1.5; however, where greater protection is required, then an AQL of 0.65 may be preferred. Already a number of manufacturers including Kimberly Clark’s Kimtech Science™ Purple Nitrile™are achieving this standard and it can only a matter of time before competitive pressure forces other manufactures to follow the trend.

I have discussed the pressures to move from latex examination gloves, price of the raw material, consumers increasing requirement of chemical protection and potential allergy to latex protein, all of which have stimulated manufacturers to seek alternative materials. At present nitrile is the material of choice, utilising the existing dipping manufacturing plant and manufacturing techniques.

As the benefits of the new soft nitrile products become established, it will become clear they offer a real alternative to latex gloves.

Published: 10th Jan 2011 in Health and Safety International

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