Toxicity of Rubber Accelerators - What is LD 50?

Manufacturer: When referring to the toxicity information of the Material Safety Data Sheets of the accelerators for our latex compounds, we always come across the terms "Acute Oral LD50 (mg/kg)" or "Acute Dermal LD50 (mg/kg)". What do these mean?

John Woon (Senior Latex Consultant): Simple. LD stands for "Lethal Dosage" or "Lethal Dose". LD 50 means the amount of the chemical concerned (rubber accelerators in your case)when introduced to the test animals (rats, mice, hamsters, guinea-pigs, rabbits etc), that causes 50% of the animals to die. If the chemical is given to the animals through the mouth, it is known as "Acute Oral" whereas if it is given by applying to the skin, it is referred to as "Acute Dermal". The result refers to mg of the chemicals per kg of the animal's body weight.

It goes without saying that the lower the figure, the more toxic is the chemical. To give you an idea, 1 to 50 gm/kg infers a very high toxicity while 5000 to 15,000 gm/kg means that chemical is practically non-toxic or harmless.

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The Language of Rubber – Part 4 (Resilience, Heat Built-Up and Hysteresis) By John Woon (Senior Latex Consultant)

Resilience is usually expressed in percentage and it measures the ratio of energy given up on releasing or recovery from the strain (i.e. deformation) to the energy required to produce the deformation.

When a natural rubber ball is dropped on the floor from a certain height, the impact or stress the ball gets when it hits the hard surface would force the rubber molecules to strain, stretch, reorganize or deform. This results in potential energy being stored in the molecules when the ball is in a state of strain. At the end of the impact i.e. when the stress is released, the rubber molecules would retract like a spring to its original unstrained state. The stored potential energy is hence recovered in the form of "bouncing" of the ball.

Natural rubber, being a very elastic elastomer, has good rebound resilience of more than 80%. On the other hand, in semi-elastic rubbers such as Butyl, the bouncing recovery is poor at normal ambient temperatures as most of the energy is turned into heat on impact. (For this reason Butyl rubber is sometimes used for damping applications)

Hysteresis is the percentage energy lost after the cycle of deformation i.e. 100% minus the resilience percentage. Hysteresis is due to internal friction of the rubber molecules resulting in the formation of heat energy. The higher the elasticity, the higher would be the resilience and hence the lower would be the hysteresis.

It would be interesting to compare an elastic latex glove with a lesser elastic glove like a Nitrile glove by repeatedly stretching and releasing and feeling the difference in the resultant increase in the warmth of the gloves.

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Vietnam targets broader export market for rubber

Ho Chi Minh -- According to an article in Viet Nam News, "The Ministry of Industry and Trade has set higher targets for rubber exports and an expansion of its markets beyond China, the biggest buyer of Viet Nam’s unprocessed rubber products. Viet Nam ranks fourth worldwide after Thailand, Indonesia, and Malaysia in rubber exports, but the ministry believes that it can increase both the quality and number of rubber exports. China imports 64 per cent of the country’s rubber, with Singapore, South Korea, Germany and the US the next highest among the 40 countries that buy Viet Nam’s rubber. The lack of a trademark is one reason Vietnamse rubber sells at low prices. The country exported 760,000 tonnes of rubber last year while the target was 780,000 tonnes. This year, the Ministry of Industry and Trade targets a 4 per cent increase in export output and a rise of 12.4 per cent in export value compared to 2007. Viet Nam Rubber Association’s management board said higher demand on the world market and fewer supplies should contribute to higher prices. Rubber prices rose in some markets, including US$165 per tonne in Russia, $130 per tonne in Turkey, $70 per tonne in China and $64 per tonne in Japan."

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Malaysian rubber prices reach new high

According to an article on Bernama, "Malaysian rubber prices extended their gains today [May 16], hitting another new all-time high, taking cues from the uptrend in regional markets like Singapore, Thailand and Indonesia, a dealer said. According to him, Singapore's SMR prices hit 954 sen per kg, Indonesia 928.5 sen and Thailand 931 sen. "The uptrend in the regional markets has provided support to the local market. Tight supplies still remains as one of one the contributing factors," he said. The unofficial sellers' closing price for tyre-grade SMR 20 hit a new all-time high of 934 sen per kg, up 11 sen from yesterday's 923 sen, while latex in bulk also touched a new high of 613 sen per kg, increasing 5.5 sen from 607.5 sen previously.

At noon, the Malaysian Rubber Board official physical price for tyre-grade SMR 20 went up 11.5 sen to 928 sen from 916.5 sen yesterday while latex in bulk rose six sen to 610 sen from 604 sen previously. He said SMR 20 is set to touch 955 sen per kg level next week as the market is expected to rise further due to supply concerns.

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Latex Allergy Problem - Can Immunotherapy Work?

Manufacturer: Is there a way a latex sensitized person could be made immune to the same allergen so that he or she could continue to use latex gloves without any negative reaction?

John Woon (Senior Latex Consultant): I am no expert in immunotherapy. At the present moment many authorities are advising the avoidance of latex products for those who are allergic to natural rubber latex. However, this is sometimes easier said than done and the total avoidance could be impractical in some cases. While some sectors believe that there's no easy way out through "desensitization", I'm encouraged by the work done by some researchers in an attempt to desensitize latex sensitive individuals.

Among these researchers is a group from the Department of Internal Medicine, University of Cattolica del Sacro Cuore Policlinico in Italy. Through their "Sublinqual Desensitization Protocol", the preliminary results showed that sublingual desensitization to latex could be an important therapeutic tool in the management of allergic patients. All their desensitized patients could now wear gloves and undergo medical procedures without any allergenic symptoms. I hope they would continue such important work to cover a larger population.

Of course I'd also like to add that the number of patients and health care workers who have had allergic reactions to latex has reduced tremendously since the mid-1990s during which time latex allergy cases peaked at about 8% to 12% of people who are exposed to latex products such as gloves.

The drastic drop in reported allergy incidence is mainly due to a change in the way latex gloves are manufactured to ensure the reduction of the allergen especially those made in Malaysia. Credit must be given to the Malaysia government whose effort had seen the introduction of The Standard Malaysian Glove (SMG) which refers to gloves produced by glove manufacturers under certification by the Malaysian Rubber Board (MRB), with a quality assurance system in line with the technical specifications of the American Society for Testing and Materials (ASTM) and the U.S. Food and Drug Administration (FDA).

In addition, SMG-certified manufacturers must have a Quality Management System conforming to ISO 9001:2000 or equivalent. SMG certification is now well known globally through the effort of The Malaysia Rubber Export Promotion Council (MREPC).

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Biocides, Fungicides and Algaecides Directory

Here is a look at offerings from select suppliers of biocides, fungicides, algaecides and related products. For more information on the products listed, please contact the company directly.


Arch Biocides
Smyrna, GA
800-523-7391
Fax: 866-705-0465
E-mail:sales@archbiocides.com
Web site:www.archbiocides.com

Product name: Proxel Bactericides
Attributes/Comments: A zero-VOC antimicrobial product; broad spectrum activity; long-term storage protection; excellent compatibility; ease of use due to low viscosity.

Product name:Zinc Omadine Antimicrobials
Attributes/Comments: Broad spectrum antimicrobial that inhibits the growth of fungi, algae and bacteria; color-stable, fine particle dispersion (in water) of zinc pyrithione; low VOCs; alkaline pH stable; suitable for masonry coatings.

Dow Biocides
Buffalo Grove, IL
800-447-4369
Fax: 847-808-3710
E-mail: dowbiocides@dow.com

Product  name:Filmguard IPBC Fungicidal Agent
Attributes/Comments: Filmguard IPBC fungicidal agent, a broad-spectrum fungicide developed for the enhanced protection of latex and solvent-based paint dried paint films against mold and fungi, is based on the active IPBC technology (3-iodo-2-propynyl butylcarbamate), a widely-used biocide active ingredient for dry film preservation and wood preservation.

Product  name:Canguard Ultra BIT 20 LE Preservative
Attributes/Comments: Canguard Ultra BIT 20 LE preservative, a high purity broad-spectrum bactericide for the protection of industrial water-based products against harmful bacteria, yeasts and fungi, has exceptional chemical stability and good compatibility with most formulations. The product has a low VOC and non-formaldehyde base.

International Specialty Products Inc. (ISP)
Wayne, NJ
800-622-4423
Fax:973-628-3594
E-mail: rfahmy@ispcorp.com
Web site: www.ispcorp.com/green

Product name:CleanGuard Fungitrol Series
Attributes/Comments:The Fungitrol series of “greener” biocides, fungicides and algaecides includes a choice of 20% (920), 30% (930) and 40% (940) water-based dispersions of IPBC that offer no-VOC, low-odor, broad-spectrum protection against degradation, discoloration and defacement caused by mold, mildew and algae.

Product name: CleanGuard Nuosept Series
Attributes/Comments: The Nuosept series of “greener” in-can preservatives includes a choice of BIT-based, formaldehyde-free Nuosept 498, bronopol-based Nuosept W and BIT/MIT-based Nuosept BMc-422, specially formulated for broad-spectrum protection of water-based and emulsion paints and coatings, adhesives, joint compounds and much more.

Lanxess Corp.
Material Protection Products
Pittsburgh, PA
412-809-1000
Fax: 412-809-1068
E-mail: mpp-info@lanxess.com
Web site: www.mpp.us.lanxess.com

Product name: Preventol MP 100
Attributes/Comments: Preventol MP 100 (approximately 99% IPBC) is the latest addition to the Lanxess biocide portfolio. It is a broad-spectrum fungicide for interior and exterior applications. It offers dry-film protection for solvent-based and waterborne paints, stains, latex emulsions, adhesives, construction materials and related applications.

Product name: Metasol TK-25 A.D. Plus
Attributes/Comments: In response to manufacturer and consumer demand for more environmentally friendly products, Lanxess has expanded its portfolio of low-VOC and VOC-free biocides, Metasol TK-25 A.D. Plus, a thiabendazole (TBZ) based dispersion, provides better protection for exterior applications while also offering a favorable toxicological and ecotoxicological profile.

Rohm and Haas Company
Philadelphia, PA
215-592-3000
Web site: www.rohmhaas.com

Product name:Rocima KO Microbiocide
Attributes/Comments: Rocima KO is a fast acting, broad spectrum biocide for treating raw materials, process water and contaminated products and systems. Rocima KO breaks down rapidly to non-hazardous materials.

Product name: Rocima 80 Algicide
Attributes/Comments: Rocima 80 is a specific algicide which should be added to a fungicide for broad spectrum protection. It is an easy to incorporate, low VOC containing flowable dispersion.

Product name: Rocima 30 Microbiocide
Attributes/Comments: Rocima 30 microbiocide provides excellent antimicrobial activity including BIT-resistant organisms. It is effective within minutes and can be used as a co-biocide to provide enhanced protection.

Troy Corp.
Florham Park, NJ
973-443-4200
Fax: 973-443-0843
Web site: www.troycorp.com

Product name: Troysan 1050
Comments/Attributes:Troy introduces an innovative, water-based bactericide, Troysan 1050—the latest addition to Troy’s green family of biocides—designed to inhibit the growth of microorganisms on coated surfaces. This new product is useful for imparting bacterial resistance to surfaces as measured by a significant reduction in the average bacteria counts found on the surface. Troy 1050 is a unique BIT-based dispersion product intended to be a cost effective alternative to silver-based compounds. This new product has no solvents, no VOC and no formaldehyde and does not pose a risk of coating film discoloration.

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Guayule Latex - A Concern?

Manufacturer: We are manufacturer of medical gloves based on both natural rubber latex and synthetic latex. We might also look into the possibility of using Guayule latex in the future but we have a concern. Although Quayule has been cleared by FDA and ASTM, why is that certain market sectors are still quite wary about its perceived "safety" level.

JohnWoon: Guayule latex has lower protein levels compared to Hevea latex. Also, the chemistry of Quayule protein is different from that of Hevea latex. Tests done so far have confirmed that people who are allergic to products made from Hevea latex do not react negatively when exposed to products made from Guayule latex.

Despite these findings, there are still some concern expressed by the market that certain sector of the exposed population might eventually be allergic to the Guayule protein although it might take a longer time compared to Hevea latex. They believe that Guayule while being proven safe for the present moment, as a natural material with naturally occurring protein, will over a period of time cause the same allergic reactions as Hevea latex.

Rodriguez,E., et al had reported that Guayule contained certain ester that had been shown to be a potent elicitor of allergic contact dermatitis comparable to poison ivy.

Whether or not your concern would be confirmed, only time could tell.

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Factors Affecting Latex Stability in Latex Dip Tanks

Glove Manufacturer: What are the factors you would look into to control the coagulum formation in the latex dip tanks?

John Woon (Senior Latex Consultant): I suggest you look into the following:

1) Concentration of calcium nitrate
2) Age and preservation of the base latex concentrate
3) Level of alkali in latex compound
4) Former temperature
5) Turbulence in the latex tank
6) Maturation of latex compound
7) Gelling oven temperature control
8) Water quality
9) pH and temperature of latex compound
10) Rate of latex replenishment in latex dip tank

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Air Permeability of Latex Air Bladders

Manufacturer: Among the products we make from natural rubber latex, are various kinds of air bladders. These bladders require excellent resistance to air permeability during their service life. But we find that natural rubber has too high an air permeability in some range of our products. What could we do to reduce the air permeability of our bladders?

John Woon (Senior Latex Consultant): I'm sorry to say that among all the common elastomers in the market including polychloroprene, nitrile, butyl, etc., natural rubber has the lowest resistance to air permeability. Both polychloroprene and nitrile rubbers have quite good resistance to air permeability with butyl being the best.
My advise to you is to either try blending natural rubber latex with polychlororene (or nitrile latex) or do a "laminate dipping" with natural rubber and polychloroprene or nitrile. Please take note that laminate dipping usually would give you better results compared to blending.

You could of course also try dipping with butyl latex but the proccesability could be difficult.

I would also suggest that you include the incorporation of laminar types of fillers (e.g. mica and some clays) in your study.

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The Language of Rubber - Part 3 (Creep, Stress Relaxation)

When subjected to a constant stress, rubber (and most elastomers) gradually increases in deformation over time. This is referred to as "Creep". When the deformation or strain is held constant over a period of time at a given temperature, the force or stress required to maintain this deformation gradually reduce.

This gradual decay or loss of stress is referred to as the "Stress Relaxaton". The higher the Permanent Set (discussed in Part 2), the higher would be the Creep and hence the Stress Relaxation. It is usually expressed as the percentage of the remaining stress after a given time and at a given temperature.

Stress Relaxation would usually lead to product failure, for instance in the case of a rubber sealing ring, the rubber works by virtue of its force against the flanges of the pipe between which the seal is being sandwiched and compressed. This force would fall when the Stress Relaxation is excessive resulting in the leaking of the fluid from the pipe.

As in the case of permanent set, the degree of cross-linking plays an important part in stress relaxation and under-vulcanisation would make it worst. On the other hand the so-called "efficient vulcanisation" system would give lower creep.

Such usually unwanted inherent creep or stress relaxation is taken advantage of by certain Nitrile examination glove manufacturers to claim that the gloves could "relax" and conform to the hands of the wearers after a short period of donning. However if the fingers are in constant movement during use, an excessive stress relaxation would result in poor tactility which is a prerequisite of a good quality glove.

Careful selection and maintaining of the level of Budadiene in Nitrile rubber and its (butadiene's) cross-linking could minimise the degree of stress relaxation.

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Nitrile and PVC blend

Glove Manufacturer: We had been advised to look into the possibility of blending Nitrile and PVC. What advantages could this blend bring us?

John Woon (Senior Latex Consultant): In dry rubber technology, nitrile rubber has been successfully used as a blend with PVC at a ratio of 70/30 to 60/40 for many years since both polymers have quite a good compatibility with each other. Conventionally plasticized PVC compound tends to stiffen too much at low temperatures and nitrile is considered a good alternative plasticizer for PVC. Also, products made from such blend have better thermal stability.

From the point of view of Nitrile, the presence of PVC render the product low in inflammability, resistant to ozone cracking besides being resistant to oil and aromatic fuels. In fact some blends could have superior quality to both Neoprene(Polychloroprene) and Nitrile.

However, too high a level of PVC might lead to an increase of "Permanent Set". PVC latex is preferably pre-plasticized before use.

It goes without saying that you have to ensure good latex stability after the blending.

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The Language of Rubber – Part 2 (Permanent Set)

When rubber is distorted for a given duration, the degree of deformation after the release of the distortion force is often referred to as the Permanent Set.

If the deformation is caused by tension, it is known as Tension Set.
On the other hand if it is caused by compression, it is described as Compression Set.

Permanent Set is therefore defined as the amount of residual displacement after the distortion load is removed. Permanent Set is worse at elevated temperatures.

Generally, the lower the permanent set, the higher would be the resilience and elasticity but the lower would be the tensile strength although there are exceptions.

A poorly or insufficiently vulcanized rubber would usually exhibit high permanent set. Choice of the vulcanizing system also plays an important part in determining the degree of permanent set. If the lowest possible permanent set is required for certain applications especially at elevated service temperatures, the sulphur to accelerator ratio should be low and sometimes the elemental sulphur is totally omitted in the compounding recipe.

Permanent set is closely related to another important property of rubber products, namely the Stress Relaxation which would be discussed in Part 3.

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Mechanisms of Wax Action in Gloves

Student: Please explain how wax emulsion works in a coating.

JohnWoon: I hope the following explanation would be of help to you.

The Blooming Mechanism

Molten wax particles float (or bloom) to the surface. The coating cools and re-crystallization of wax particles takes place, forming a thin but continuous wax-enriched surface layer. Generally, the softer the wax or lower the melting point, the more predominant the blooming mechanism becomes. The compatibility between the wax emulsion and other formulation components determines the wax migration rate.


The Ball Bearing Mechanism



In this case, solid wax particles migrate individually or protrude through to the surface.

By protruding slightly above the coating surface like ping-pong balls floating on a pool of water, they act as a physical spacer and prevent another surface from coming into close contact. Hard and high melting point waxes (HDPE, PTFE) operate using this mechanism under certain conditions. Both the particle density and the extent of protrusion influence the magnitude of the effect.

Once at the surface, the layer of wax particles has the ability to modify the Coefficient of Friction (CoF) of the substrate, imparting the desired characteristics. This explains why waxes are often classified as "Surface Conditioner Additives".

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