JW Latex Consultants (and Rubber Consultants,乳胶顾问) offer solutions to your problems in Natural Rubber latex and Synthetic Rubber latex processing and the manufacturing of latex products (condoms, catheters, medical gloves, baby teats and soothers, toy balloons etc) Quick answers through e-mails are possible at reasonable cost.



[Advantages of Prevulcanization] [Air Permeability] [Applications of PV Latex] [Bacteria and Latex] [Chemical Toxicity] [Cross-Linking Density] [Biodegradability] [Black Articles] [Blooming] [Bouncing Ball] [Compression Set] [Condoms] [Copper Staining] [Creaming] [Defoamer] [FDA] [Fatty Acid Soaps] [Flame Retardant] [Flocking] [Food Packaging] [Glove Demand] [Glove Discoloration] [Glove Selection] [Guayule Latex] [History of Gloves] [Joul Effect] [Lab Equipment] [“Latex” Definition] [Natural Rubber Latex Stability] [Natural Rubber Latex Thread] [Milling Problem] [Mixing Equipment Directory] [MREPC Articles] [Nano Polymer Particles] [Nano ZnO] [Permanent Set] [Polychloroprene] [REACH] [SMG] [Storage Hardening] [Stress Relaxation] [Surfactants Directory] [Tensile Properties] [Vulcanization] [Vytex] [Yulex]


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Wednesday, March 25, 2015

How to Achieve Maximum Transparency in Latex Coagulant Dipped Products

Manufacturer: We are manufacturing a wide range of latex dipped products using the coagulant dipping process with calcium nitrate. In one or two of our product range, we need to achieve maximum transparency in the final products. We have minimized or eliminated ZnO in our formulations but the degree of transparency still leaves something to be desired. Our prcess does not allow for straight dipping without coagulant.

We hope you could help us after viewing and studying our compound formulations.

John Woon (Senior Latex Consultant): Your formulations need some adjustment. Your choice of accelerators is wrong because different accelerates would have different solubility in the rubber and hence would affect the transparency of the rubber products. Three improved formulations which you can use have been sent to you separately.

You might also have to consider changing your coagulant because calcium nitrate would form rubber-insoluble salts/soaps and hence would reduce the transparency. One possible alternative is CHA (Cyclohexylammonium acetate) the by-products of which are more rubber soluble.

Friday, March 20, 2015

Successful Manufacture of Fabric-Lined Gloves

Manufacturer: We are manufacturing industrial supported gloves. Please explain the importance of coagulant and latex stability to ensure good quality gloves.

John Woon (Senior Latex Consultant): The strength of the coagulant (e.g. calcium nitrate) should be adjusted so that it is sufficiently strong to ensure adequate latex pick-up but not too strong that it prevents the penetration of the coagulant into the fabric otherwise the rubber to fabric adhesion would be poor.

The latex stability must be adjusted so as not to penetrate the fabric liner right through (i.e. strike through).

My detailed report on "Successful Manufacture of Fabric-Lined Gloves" has been sent to you separately.

Sunday, February 22, 2015

Alcohol-Based Coagulant Vs Water-Based Coagulant

Manufacturer: While most of the latex dipped products manufacturers today are now using water-based coagulant, we observe that some are still using alcohol-based coagulant despite the higher cost, health and fire hazards. Do you know why?

John Woon (Senior Latex Consultant): While the alcohol-based coagulant have the disadvantages you mentioned, it has the advantages of better flow control and faster evaporation. As a result, coagulant drainage problem can be minimised and more even deposit on the former attained.

Compared with water-based coagulant, it is also more effective in covering uniformly uneven former surfaces such as finger crotches and textured patterns.  

Former Cleaning with Hard Water

Manufacturer: We are glove manufacturers. We have heard that some of our competitors are using softened water for their former washing. What's the danger of using hard water?

John Woon (Senior Latex Consultant):

In some countries it is extremely important that after the online washing process, the formers are thoroughly rinsed with softened water. This is because the hardness of the water would deposit traces of inorganic salts on the former surface leading to potential formation of pinholes in the rubber film.

Monday, January 26, 2015

Why Is It Important to Remove Coagulant from Rubber Film by Leaching ?

Manufacturer: We are manufacturing toy balloons but without leaching. Why is it important to remove the coagulant from the rubber film by leaching ?

John Woon (Senior Latex Consultant): If the coagulant salt such as calciuum nitrate is allowed to remain in the rubber film, the film would tend to discolour when exposed to warm air, gas fumes and UV light. The physical properties would also be negatively affected due to poor particle-to-particle integration during drying.

I strongly advise you to install a leaching process in your Production as this would also improve the brilliance of the colour and gloss of your inflated balloons.

Factors Affecting Thickness of Latex Dipped Products

Manufacturer:  I am wondering if you can explain the factors that affect thickness and surface finish of dipped latex articles such as gloves. How can thickness be predicted from material properties?

I imagine factors might include:
- Temperature of latex solution
- Temperature of former
- Airflow for drying
- Concentration of water in latex solution
- Type/concentration of of thickening agent
- Type/use of coagulating agent on former

What affects the outside surface finish, to make it really mirror-smooth or relatively rough?

John Woon (Senior Latex Consultant):  Thickness of latex dipped products depends generally on the following factors:

1) Latex stability against cationic chemicals such as calcium nitrate. The higher the stability, the thinner is the latex gel picked up. The reverse is true. Types of surfactants used is important. Nonionic surfactants as opposed to anionic surfactants would tend to increase the latex stability against calcium nitrate.

2) The age of latex. I'm referring to natural rubber latex. The older the latex the thicker would be the latex dipped product.

3) The higher the former temperature, the thicker would be the product especially when the latex compound is sensitive to heat.
(Latex compounds are normally more heat sensitive when the ZnO and ammonia level are high)

4) The higher the latex solid content (i.e. TSC) the higher would be thickness.

5) The higher the concentration of the coagulant (e.g. calcium nitrate), the higher would be the thickness.

6) If the viscosity of the latex compound is increased by adding a thickener, the product would be thicker.

7) The longer the latex dwell time i.e. the time the former with a coating of coagulant remains immersed in the latex, the thicker would be the product.

To make the surface smooth and shiny, include an extra final dip into a much more diluted latex compound.

To make the surface matt i.e. no more shine and gloss, soak the product in chlorine solution (with about 800 to 1000 ppm of chlorine). The surface after this treatment would appear rough under microscope but not the naked eyes.

Sunday, December 28, 2014

Wet Tack and Dry Tack of Latex Based Adhesives

Manufacturer: I am new to latex based adhesive technology. Please exlain the difference between wet and dry tack and how to improve them.

John Woon (Senior Latex Consultant): "Wet tack" is the ability of the latex to hold to layers of materials together before drying. This depends a lot on the nature of the substrates concerned.  A solid impermeable substrate is more difficult to adhere to compared with, for examples, a porous textile or paper board.

Other factors involved in ensuring good wet tack are:

1) Surface tension and wetting - A good wetting with low surface tension is required for the initial spreading and wetting of the substrates.
2) Total solid content - Higher TSC is required for higher initial tack.
3) Mechanical stability - Lower mechanical stability is needed for the quick development of the wet tack.
4) Types of stabilizers used - rosin acid soaps are preferred to fatty acid and non-ionic soaps.
5) Nature of polymer - Lower Tg is preferred to ensure the polymer is soft enough for better particle-to-particle integration and  film formation.

As for "dry tack", I have already covered this in my earlier posting om "Nitrile Latex Adhesives" below.

Friday, December 19, 2014

Nitrile Latex Adhesives

Manufacturer: We are in the process of developing a water-based adhesive based on Nitrile latex. Please let us know the potential areas of application and what one needs to consider in order to make this project a success. Thank you in advance.

John Woon (Senior Latex Consultant): While Nitrile latex has good resistance to non-polar oils its polar nature gives good affinity to polar substrate such as PVC. You should therefore look into the market of PVC floor tiles where Nitrile based adhesive should be the preferred material. It could also be used for paper, boards, fabrics, wood and metal foils.

However, unlike other latices such as natural rubber and polychloroprene, Nitrile latex has low inherent tack (i.e. dry tack). Therefore the addition of a suitable tackifier is recommended. Examples of such tackifier are coumarone indene resins, hydrogenated esters and terpene resins.

However, too much tackiness obtained by the addition of the tackifiers would lead to a drop in the cohesion strength and toughness of the dry adhesive. Hence a balance should be reached between the two  extremes.

You could also look into the addition of reinforcing agents such as phenolics, terpene-phenolics resins.

Saturday, December 13, 2014

JW Latex Consultants would like to wish our Customers, Clients, Students, Associates and Friends "A Very Merry Christmas!"

Sunday, November 23, 2014

HLB (Hydrophile-Lipophile Balance) of Surfactants

Manufacturer: We are latex glove  manufacturer. Further to your various postings on surfactants, can you please briefly explain the meaning of "HLB' and give examples of its uses.

John Woon (Senior Latex Consultant): HLB stands for Hydrophile-Lipophile Balance. It is related to the proportion of hydrophilic (i.e. water loving) and lipophilic (i.e. oil loving) groups in the molecule of the surfactant.

It allows one to predict the surfactant properties and is based on a scale from zero to 20 with HLB of below 10 indicating low water solubility while HLB of above 10 indicating high water solubility.

The following are examples of HLB and areas of applications:


W/O (Water in Oil) emulsifiers
Wetting agents
O/W (Oil in Water) emulsifiers

Hence the surfactants that concern you are those with HLB of around 3 which is the anti-foaming and anti-webbing agents and HLB of about 7-9 which are the wetting agents which you can use in the coagulant.

Thursday, November 06, 2014

Skin Irritaion caused by Nitrile Gloves

Manufacturer: We are manufacturing industrial gloves using carboxylated NBR (Nitrile) latex. Lately we've been receiving complaints from the market about our gloves having skin irritation problems among users. Our extensive investigation revealed that our proprietary curatives used especially the accelerators are not the causes.

What else in the NBR latex do you think could have caused the skin irritation problem?

John Woon (Senior Latex Consultant): It is well known that some surfactants could cause skin problems to some individuals on prolonged use. Therefore if your gloves are not sufficiently leached, the surfactants inherently present in the base latex could cause skin irritation to some users of the gloves especially when their hands sweat. Usually these users find gloves made from synthetic latices to be more troublesome than those made from NR latex since a comparatively higher level of surfactants is required for emulsion polymerization.

Sodium alkyl sulphate is particularly bad for skin.

Some chain-stopper used in polymerization which is of the dithiocarbamate type could also be another possible causative agent.

It has been reported that the carboxylic acids used for carboxylation such as Methacrylic acid/MAA could affect skin, eyes and mucous membranes. Again, proper leaching is required to remove the residual MAA.

Friday, October 24, 2014

KOH Number and Ammonia Content of Natural Rubber Latex

Manufacturer: What does KOH number measure? Does it have any relationship with ammonia content? How can I determine whether the alkalinity is due to the presence of KOH or ammonia?
John Woon (Senior Latex Consultant): KOH Number does not measure the amount of ammonia. It measures total the combination of VFA (Volatile Fatty Acids), higher fatty acid anions and amino acids.

The older the latex the higher would  be the KOH Number. 

As for ammonia content, you need to determine the "Alkalinity" of the latex by titration or indirectly measure the pH although the latter might not be accurate at times due to the buffering effect of the naturally occurring non-rubbers.

If you suspect there is KOH in the latex, you have to drive off the ammonia first by warming the latex with stirring before measuring the alkalinity.

Thursday, October 02, 2014

Blue Gloves Turning Green

Manufacturer: When gloves are dipped in slip-coating (silicone/PUD blend), the glove has a green stain. Gloves should normally be blue. When gloves are not dipped in slipcoating, they are perfectly fine.  No green stain. Sometimes, the slip coating does not make the gloves have a green stain, and sometimes it does.

Any thoughts?

John Woon (Senior Latex Consultant): Under normal circumstances, both silicone and PU dispersions on their own should not affect the colour of the gloves. I therefore suspect other ingredients or additives (or contamination) in either silicone or PU that are the causatives agents for the change of color from blue to green.

Knowing that blue color if mixed with yellow color would give green color, I suspect the "contamination" to be either the free ions from copper or iron.

Both copper and iron ions would react with the commonly used accelerators such as the dithiocarbamates to form a metallic complex which is colored yellowish to brownish, which would in turn converts the blue color of the gloves to greenish.

To confirm this, I suggest you treat an uncompounded nitrile film (i.e. with no curatives added) with the silicone/PU coating and check the color change, if any.


Thursday, September 11, 2014

"Clastogenicity", "Mutagenicity" and "Teratogenicity" of Rubber Chemicals

Manufacturer: When reading about the toxicity of rubber chemicals, I always come across the terms, "Clastogenicity", "Mutagenicity" and "Teratogenicity". What are they?

John Woon (Senior Latex Consultant): This question had been raised a number of times before in this "forum". Please see below:

1) Clastogenicity - "Clastogen" refers to a general class of chemicals which produce changes or alterations in the cell chromosomes.

2) Mutagenicity - "Mutagens" refer to those chemicals which tend to induce changes in the genetic materials carried by both the male and female reproductive cells. Please take note that mutagenic chemicals are also carcinogens. Hence some cancer tests are actually tests of the mutagenicity potential. 

3) Teratogenicity - "Teratogens" are chemicals which interfere with the normal development of the foetus during pregnancy and hence leading to malformation of the baby.

Change in DRC of Natural Rubber Latex Concentrate on Storage

Manufacturer: Why do we see a drop in DRC (Dry Rubber Content) when we test the latex concentrate after storage for some time?

John Woon (Senior Latex Consultant): Good question. DRC is actually not 100% rubber. It also contains naturally occurring non-rubbers which undergo continuous chemical breakdown through, for instance, hydrolysis. Overtime, these non-rubbers on the rubber particles would be lost and hence a lower DRC would be encountered. It has been reported that as much as 0.45% would be lost after about 12 months' storage.

Wednesday, August 13, 2014

Resilience and Hysteresis of Nitrile Rubber Prodducts

Manufacturer: We are manufacturing rubber parts using Nitrile rubber. Please explain the resilience and hysteresis of nitrile rubber products compared to natural rubber. We would also appreciate your comment on ozone resistance of our nitrile rubber products.

John Woon (Senior Latex Consultant): I hate to disappoint you but NBR (Nitrile Rubber) has quite a poor resilience compared to either natural rubber, SBR (Styrene Butadiene Rubber) or
 polychloroprene rubber although they are superior to butyl rubber.

Also, hysteresis is equally poor and hence NBR is not normally used where heat build-up on flexing is to be encountered.


However, you can improved theses properties to some extent by using soft carbon black, ester plasticizer along with a tighter cure. The resilience would increase if the content of acrylonitrile in NBR is reduced.

As regards ozone resistance of NBR, this also leaves a lot to be desired due to the presence of the "butadiene" component in the NBR structure. You could of course improve the ozone resistance by adding good antiozonants and waxes. However, when your products are exposed to oil and chemicals during services (I presume this being the reason for your choice of NBR), the antiozonants and waxes may be extracted leading to the products being prone to ozone again!

Sunday, July 27, 2014

What Solvents Are Best for What Polymers?

Manufacturer: We are manufacturer of water-based adhesives. In response to some customers' request, you are now also looking at manufacturing some solvent based adhesives. We have some polymers in mind such as PVC, EPDM, ABS, NBR, etc. Can you advise us what solvents are best for which polymers?

John Woon (Senior Latex Consultant): Please check out my earlier post titled
"Use of Solubility Parameters in Solvent Based Adhesives" posted on 22 June 2014.
For the list of polymers against their possible solvents, please check out this link => http://goo.gl/p5WhQF

Friday, July 25, 2014

At What Temperatures Should Natural Rubber Latex be Stored?

Manufacturer: Under what temperature condition should natural rubber latex concentrate and prevulcanised latex be stored. We are from a temperate country.

John Woon (Senior Latex Consultant): Heat would increase the kinetic energy of the rubber particles resulting in the increase of both the frequency and violence of collisions among the rubber particles which could result in the formation of coagulum.  Heat would also evaporate water and drive away the ammonia in the latex with the accompanying drop of pH and skin formation on the surface of latex.  Drop in pH would also lead to latex destabilisation.On the other hand the stabilising system within the latex could be rendered ineffective when the latex is subjected to freezing temperature.  Hence latex must be protected from frost. The latex is therefore best kept in-door at a storage temperature of between 10 to 30°C.

If latex is stored for more than 6 months, some minor adjustment by adding some soap stabiliser might be required.  Excessive loss of ammnoia in storage tanks and partially emptied drums should be prevented as this could lead to destabilisation of latex ( e.g. if pH has dropped to below 10.0, ammonia solution should be added to bring it to about 10.5).

The latex should be agitated at slow rate periodically to prevent excessive creaming.

Monday, June 23, 2014

New Hydrogel Condoms ‘More Like Human Skin'

WOLLONGONG, AUSTRALIA - Latex could be replaced as the primary material in condoms.
Researchers at the University of Wollongong in Australia who were awarded a grant from the Bill & Melissa Gates Foundation are furthering research into substances called tough hydrogels, which are currently used in medicine and robotics.

“We hope to deliver a condom that is safe and feels and looks better,” a UW release states. “It’s designed to feel more like human skin than latex rubber.”

The research team touts other benefits of hydrogel condoms, including invisibility and self-lubrication.
“That would eliminate problems with latex allergies and improper use of oil-based lubricants,” according to the release.

Dr. Sina Naficy, a polymer scientist working on the project, said the so-called “next generation condoms” could also be more environmentally friendly because the hydrogels are mostly made of water.
“Hydrogels can also be made to be biodegradable, which solves the problem of condom disposal,” according to the release........CLICK HERE to read the whole article

Sunday, June 22, 2014

Use of Solubility Parameters in Solvent Based Adhesives

Manufacturer: We are manufacturing water based adhesives based on PVac and natural rubber latex. Recently we have decided into venture into solvent based adhesives due to the response to market requirement of our customers. We were advised to look into "solubility parameters" of both polymers we used and the available solvents to determine what solvents are best for what polymers.

What is "solubility parameters" anyway?

John Woon (Senior Latex Consultant): To cut the long story short, solubility parameter is a numerical estimate of the degree of interaction between materials (e.g. solvent with solvent or solvent with polymers), which indicates how good is the miscibility or solubility of the different materials when mixed together. Materials with similar values of "solubility parameter" are likely to be miscible e.g. a polymer with similar solubility parameter of its solvent would be easily dissolved in that solvent.This makes your life so much simpler when you want to choose a suitable solvent for your polymer such as polychloroprene and natural rubber.

To understand fully the chemistry/physics involved, one has to consider Van der Waals forces, cohesive energy density and heat of vaporization of the materials.

The theory behind solubility parameter was proposed by a renowned chemist and scientist, Dr. Joel Henry Hildebrand (November 16, 1881 – April 30, 1983) hence the term "Hildebrand solubility parameter" is often used.

Friday, June 20, 2014

Controlling of Baby Soothers Thickness with Heat Sensitized Latex

Manufacturer: We are manufacturing baby teats and soothers (pacifiers) with heat sensitized latex compound. We find controlling the product thickness of the soothers to be very difficult. We hope you can give us some practical tips to overcome this problem.

John Woon (Senior Latex Consultant): There are so many factors involved in this dipping process that could lead to inconsistent thickness of your products. Briefly, some of these factors are as follows:

1) Latex pH must  be closely controlled and monitored before and after the addition of the heat sensitizer.
2) Former temperature should be high enough to ensure good pick of latex but must be well controlled so that a latex dwell time of only a few seconds should suffice.
3) Latex temperature should be at around 20°C and must not vary for more than 1°C.
4) Prevulcanised latex offers better control of product thickness compared to post-vulcanisable latex compounds.

If you want I can prepare a detailed report for you.

Friday, May 30, 2014

Differences between SBR Latex and Carboxylated SBR Latex?

Manufacturer: Can you explain the main differences between a standard SBR latex and a carboxylated SBR latex for carpet backing and treatment of textile and non-woven fabrics? Why is carboxylated SBR latex a preferred latex?
John Woon (Senior Latex Consultant): The first important property I would like to touch on is the latex colloidal stability. In the case of non-carboxylated SBR latex, the stability is achieved through the addition of surfactants which could be easily "desorbed" from the rubber particles and hence leading to destabilization.

On the other hand, in a carboxylated SBR latex, the carboxylic acid is an integral part of the polymer through copolymerization and by virtue of its ability to ionize, it offers a more permanent stability to the latex.

Briefly, carboxylated SBR latex also offeres the following advantages:

1) Improved wetting for fillers and fibres
2) With improved polarity, adhesion to many substrates is enhanced
3) Improved physical properties (e.g. tensile strength, abrasion resistance, modulus)
4) Improved chemical resistance to non-polar solvents

This question had been raised before in this "forum". Please go to the link below:

Solvent Roughening of Household/Industrial Gloves

Manufacturer: We have been trying to make roughened (kinkled) latex household/industrial gloves with methylene chloride in response to the request of one of our customers but without success.Would appreciate very much if you could guide us in solving this problem.
John Woon (Senior Latex Consultant): I presume you want to make gloves with irregular patterned surface on the outside of the gloves.

This entails careful selection of solvent and coagulant, time of immersion, filler content and the degree of prevulcanization of the latex compound.

It is a complex optimization of all the factors mentioned above. If you want , I could write a separate report for you with more technical details.

In the mean time, I suggest you replace methylene chloride with toluene.

Wednesday, April 30, 2014

Fire Retardant Polychloroprene

Manufacturer: Why is polychloroprene preferred to natural rubber for fire retardant products in the transport industry?
John Woon (Senior Latex Consultant): Since polychloroprene is halogenated i.e. containing chlorine atoms (or Organohalogen compounds), it has good fire retardancy. 

Therefore, unlike natural rubber, when polychloroprene rubber is burnt with a Bunsen burner or a lighter, it will burn but extinguishes itself (i.e. self-extinguishing) immediately once the lighter is removed whereas natural rubber would continue to burn. This is one reason why polychloroprene is used in place of natural rubber in many products, particularly in the building and transport industries (e.g. seating cushions) due to safety reasons. You can therefore “label” your products as “Fire-retarding “or “Fire retardant”. 


What has the bouncing ball to do with tyres?

Latex Gloves Educational Articles from the Malaysian Rubber Export Promotion Council

How do you select your medical gloves?

Rubber Chemicals: Carcinogenicity, Mutagenicity, Clastogenicity.

Why is Compression Set measurement important?

Assessment of Latex Stability

Joule Effect

Poor Flocking Quality Of Household Gloves

Creaming of Latex

What is Vulcanization?

History of Latex Dipped Products

Applications of Prevulcanized Latex

Defoamer Creating Havoc in Glove Factory

Problems With Milling Rubber Chemicals

Medical Gloves From Guayule Latex

Introduction to SMG Gloves



Click on The Following Links to Read More Articles:

[Advantages of Vulcanization] [Applications of PV Latex] [Bacteria and Latex] [Chemical Toxicity] [Cross-Linking Density] [Biodegradability] [Black Articles] [Blooming] [Bouncing Ball] [Compression Set] [Condoms] [Creaming] [Defoamer] [FDA] [Fatty Acid Soaps] [Flame Retardant] [Flocking] [Food Packaging] [Glove Demand] [Glove Selection] [Guayule Latex] [History of Gloves] [Joul Effect] [Latex Stability] [Latex Thread] [Milling Problem] [MREPC Articles] [Nano Polymer Particles] [Nano ZnO] [Polychloroprene] [REACH] [SMG] [Storage Hardening] [Vulcanization] [Vytex] [Yulex]

The information and data contained in this site are believed to be accurate and reliable. However it is the responsibility of the visitors and readers to satisfy themselves that the information is workable under their own processing conditions. Hence the owners of this site make no warranties concerning the suitability of the information given in this site.