The following is an excerpt from a presentation given by Dr. Paul
Cacioli at the LatexAllergy Meeting, Toronto, Canada, September 1994.
In 1993, the total global demand for gloves was estimated at 21.9
billion pieces with the USA and European markets accounting for 96% of
this total. These numbers continue to rise, and it is forecasted demand
will reach 32 billion pieces in the near future.
Research indicates that high levels of extractable proteins arising from
shortcuts being taken in the leaching and washing processes have had
major impact on sensitizing the population. The following describes good
manufacturing processes as undertaken by Ansell.
Protein and Raw Latex
Effect of Centrifugation. The approximate composition of the
liquid natural rubber obtained from the Havea Braziliensis tree is:
| 30-40% |
Rubber |
|
1.5-3.5% |
Resins |
|
(cis-1, 4-polyisoprene) |
|
0.5-1.0% |
Ash |
| 2.3% |
Protein |
|
1.0-2.0% |
Sugars |
| 0.1-0.5% |
Sterol Glycosides |
|
55-65% |
Water |
Field latex is concentrated to approximately 60% rubber by a process
called centrifugation. In this process, an ammonia preserved blended
field latex is fed into a centrifuge bowl rotating at a speed of about
7000 rpm which exerts an average centrifugal force of 8000 G on the
latex particles causing the latex to separate into two fractions: a
rubber rich less dense concentrate and denser skim.
The centrifugation process reduces the nonrubber content down to 1.8 to
1.5% of which the bulk (approximately 1%) is protein.
The protein content is reduced by up to 50% by a single pass through the
centrifuge. It is uneconomical to repeat this process to reduce the
protein levels further.
Effect of Ammoniation. Latex is ammoniated for preservation against
microbiological growth and subsequent destabalization of the latex
leading to its coagulation. Timely ammoniation aids in the hydrolysis of
proteins.
Deproteinized Latex. The proteins in latex stabilize the latex rubber
particles in the aqueous phase. Consequently the deproteination of latex
cannot occur unless an artificial stabilizer, such as a surfactant, is
added to replace the protein.
Pre- and Post-Vulcanization
The pre-vulcanization of latex is achieved by adding small quantities of
the curatives to the latex and then heating latex to a predetermined
temperature until consistent pre-cure values are reached. The latex
remains liquid. The molds are then dipped into the latex and passed
through an oven to finish the cure.
Materials are more easily leached from pre-vulcanized films than
post vulcanized films and this also applies to protein extractability.
On-Line Leaching. Most latex-dipped goods are subjected to an
online leaching process while the rubber is still in a wet-gel stage. At
this point, the film has not been cured and the interstitial spaces
between the latex particles are large and full of water. High levels of
protein can be removed by effective leaching.
Most processes use water or acidic solutions for the leaching. It is
important at this stage to have high flow rates with continuous fresh
makeup as well as temperatures above the 50oC mark for the leaching 4 be effective.
Dry-flm Washing. Once the latex has been cured and removed from
the mold, protein levels can be reduced by agitating the articles in hot
water containing detergent.
Enzymes. While trials using proteolytic enzymes either during,
the online leaching stage or the post-washing stage show that some
reduction in proteins is obtained, the enzymes usually are difficult to
remove from the final product and would lead to further complications.
Chlorination. Chlorination, the washing of gloves in chlorine water,
detackifies the rubber surface by hardening. Chlorination is used to
produce powder-free gloves as it facilitates donning. This process can
result in a 10-fold reduction of the amount of protein in a film.
Proteins and Sterilization
Gamma Irradiation. Gamma irradiation has been shown to have no
effect on the extractable protein levels or allergenicity content of the
finished latex goods.
Autoclaving. Autoclaving using steam rather than hot air, has
been shown to reduce protein levels to below detectable levels when
using the Bradford or modified Lowry method for protein measurement.
Ethylene Oxide Sterilization. Ethylene oxide sterilization has been
shown to have no effect on allergenicity or protein levels in finished
latex articles.
Testing for Proteins
Refer to article Tests Available for Diagnosis of Individuals with NRL Allergy, and Methods Used for the Estimation of Total Allergenicity of NRL Products.
Conclusion
Manufacturers are working closely with the FDA and scientific research
groups to provide better products for their customers.
