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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Monday, June 27, 2016

Sodium Soaps vs Potassium Soaps as Latex Stabilisers

Manufacturer: We use both KOH and NaOH for making our fatty acid soaps as  stabilizers for our latex compounds. We are experiencing more problem with sodium soaps especially when there is a change in ambient temperatures. Why?

John Woon (Senior Latex Consultant): Simple. The reasons are as follows:

1) Sodium soaps are less soluble than potassium soaps.
2) Sodium soaps are harder than potassium soaps.
3) Sodium soaps tend to gel at lower temperatures although this phenomenon is reversible.

Therefore from technical point of view, there is no reason why you should use sodium hydroxide although it might be cheaper than potassium hydroxide.

Monday, June 06, 2016

Blowing Agent (Foaming agent) for PVC Plastisol

Manufacturer: We are manufacturers of products based on PVC plastisols including PVC gloves. We are now venturing into making foamed products but our initial work has not been successful. We believe that this could be due the wrong choice of blowing agent as our processing temperature is quite low at about 120 C.  We would appreciate very much if you could suggest some suitable blowing agents for our use.

John Woon (Senior Latex Consultant): Some of the most common blowing agents used for rubber and plastic do have high decomposition temperatures of more than 150°C which would of course not work satisfactorily if your processing temperature is only 120°C.

I suggest you evaluate the following:

Azo nitriles, bezene sulphonic acid hydrazide and ditroso pentamethylene tetramine.

Let me know the outcome in due course.

Thursday, May 26, 2016

Wetting Agent in Coagulant

Manufacturer: We are in the process of improving the wetting property of our coagulant mix to overcome pinhole and thin spot problems. We would appreciate very much if you could advise us on the temperature, level of wetting agent, cloud point, etc.

John Woon (Senior Latex Consultant): You need to pay attention on the following factors:

1) Temperature of the coagulant should be as high as possible but not exceeding the could point or 65°C to achieve maximum wetting.

2) Level of wetting agent is to be high enough but not to the extent of causing foaming and retarding drying.

3) You should determine the could point on your own instead of just relying on surfactant suppliers' cloud points because salts such as calcium nitrate and other ingredients in the coagulant mix can affect the cloud point.

Details has been sent to you separately at your request.

Thursday, May 19, 2016

Reducing Ammonia Content of Latex Concentrate with Formaldehyde

Manufacturer: We are manufacturing dipped tubes, for medical in small scale.
Can we add formaldehyde to reduce the concentration of ammonia in high ammonia latex, so that even dip could be produced?
John Woon (Senior Latex Consultant): Yes, you can add formaldehyde to reduce the ammonia content in the latex.When you add formalin to the latex, pH would drop and latex would tend to destabilise. Therefore you need to add a non-ionic surfactant first. Stir for two hours before adding formalin.

You can try Emulvin W or equivalents as the surfactant. If you continue to encounter stability problem such as viscosity rise it could be due to the latex quality problem, in which case I suggest you remove the ammonia by stirring with a fan over the surface of the latex.

Thursday, April 21, 2016

Curatives for the Vulcanisation of Nitril Rubber

Manufacturer: We are manufacturing rubber parts using dry natural rubber (SMR) via compression molding and are about to conduct some trials using dry carboxylated nitrile rubber. We would be obliged if you could give us some guide lines in terms of curatives compounding.

John Woon (Senior Latex Consultant): For general applications, you can used practically the cure systems for both NR and SBR such as thiazoles and sulphenamide cure system. For high temperature applications and also where low compression set is required, both thiuram and peroxide cure systems should be used.

You should also get the advice from the rubber suppliers or manufactueres because the following factors involved in polymerization, etc. are also affecting the vulcanisation of nitrile rubber:

1) Coagulant
2) Emulsifiers and surfactants
3) Polymerization additives
4) Polymer rheology
5) Process aids in polymerization

Friday, April 08, 2016

Blending of Different Latices and Addition of Fillers in Latex Adhesive Compounds

Manufacturer: We are manufacturer of latex-based adhesives. Please give us some general guidance in blending of two different latices and the addition of fillers in terms of latex colloidal stability.

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

1) Blending of two different latices (latexes)

1.1) Make sure the pH of both latices are as close as possible. By changing the latex pH, the latex could sometimes be destabilized in which case, it is advisable to add a non-ionic surfactant to that latex before the pH adjustment.

1.2) Latex with smaller particle size would tend to rob the surfactant already present on the particles of latex with higher particle size. Generally, the level of surfactants required for the blend is more than the total amount required for the two individual latex.

2) Filler addition

2.1) You could either add the filler dry or as a pre-prepared slurry to the latex. The former would require higher level of surfactant than the latter.

2.2) The higher the level of filler, the higher is the level of surfactant required.

2.3) Filler with smaller particle size would tend to rob more of the surfactant from the latex particles compared to filler with coarser particles.

2.4) Filler type is important e.g. clay and talc would have less destabilizing effect on the latex compared to calcium carbonate.

2.5) Generally a combination of surfactants performs better than a single surfactant.

Hope this helps.

Tuesday, March 15, 2016

Mechanism of the Leaching Process

Manufacturer: I am the head of the R&D department in a latex dipped products manufacturing company in Sri Lanka. In order for me to understand the importance of leaching, I need to know the mechanism involved during leaching. Can you help?

John Woon (Senior Latex Consultant): Over the years I've studied and analyzed the factors involved in the leaching process so as to achieve the most optimized leaching effectiveness for a variety of dipped products.

I've identified 7 steps which take place in sequence during leaching. I've sent this along with some details of each step to you separately. Please let me know if this is of any help.

Working Off of Old Latex Compounds

Manufacturer: We are using different latex compound formulations for different products. This always results in the built-up of old latex compounds of more than a few weeks old. How can we make use of old latex compounds to minimise wastage?

John Woon (Senior Latex Consultant): Beware of possible problems when using old latex compounds especially when it has already “over-cured” as it would lead to low elongation at break, high modulus and poor tensile strength and hence premature tearing.

You could try to blend this off into new and fresh compound but lab experiments must be carried out to see if the physical properties (i.e. tensile strength, modulus and elongation at break) are acceptable for the ratios of the blending you've selected

Another alternative is to use prevulcanised latex which does not normally over cure on storage.

Sunday, February 14, 2016

Inorganic Polyphosphates for Latex Stability

Manufacturer: We have been advised to use inorganic polyphosphate to enhance the stability of our latex. How does this work?

John Woon (Senior Latex Consultant): Polyphosphates have been used successfully as deflocculating agents for the dispersion of pigments. They have a mild surface active property and are usually added as the alkali salts.

The alkali polyphosphates have the ability to sequest heavy metal ions and are therefore very useful in countering the destabilizing effect of calcium and magnesium ions that might be present in hard water used in diluting the latex.

Monday, January 25, 2016

Inconsistent Physical Property Test Results

Manufacturer: We are latex catheters manufacturer. For the last 6 months, our Q/C department has been having problem of inconsistent test results from our tensile testing. Our latex compound formulation, production processes have not been changed. The test pieces are cut from films prepared using both casting and coagulant dipping methods.

We would appreciate your input on how to ensure that we achieve consistency in our testing.

John Woon (Senior Latex Consultant): Briefly, please ensure the following:

1) The tensile machine is well calibrated especially the separation speed of the clamps.

2) The thickness gauge is working properly and frequently calibrated.

3) Die cutter must be sharp enough to ensure that there is no jagged edges of the test pieces after cutting.

4) The rubber films are free of micro-flaws caused by air trapped, collusion of dirt, dirty formers or casting plates, etc. (Thicker films could be a better choice)

5) The test pieces must be well conditioned in the testing room at consistent relative humidity and temperature.

6) There is no slippage of the test pieces from the clamps/grips during testing.

Generally, a higher range of results such as tensile strength is more accurate and acceptable than a lower range of results which could be due to any or a combination of the above mentioned factors not being under control.

Saturday, January 23, 2016

Poor Solvent Resistance of Products Made from Prevulcanised Latex

Manufacturer: We are manufacturers of a wide variety of latex products using prevulcanised NR latex. We have been doing quite well until recently when one of our customers complained that one of our products had poorer resistance to solvent compared to a competitive product which is also made from NR latex. Your comment and advice please.

John Woon (Senior Latex Consultant): Unfortunately your customer's complaint could be justified. Owing to the structure of the rubber of a prevulcanised latex film with weaker particle to particle integration, the film has inferior resistance to oils, greases and non-polar solvents when compared with a film of the same thickness but made from a post-vulcanisable NR latex compound.

Therefore, unlike post-vulcanised film, a prevulcanised film would easily rupture when solvent is dropped onto it while being stretched.

I believe your competitor's product is made from a post-vuclanisable NR latex compound. Your problem could be overcome or minimised if you could introduce some post-vulcanisable latex compound into your prevulcanised latex.

Having said this, you must take note of the fact that natural rubber has comparatively poorer resistance to oils, greases and non-polar solvents compared to Nitrile and polychloroprene rubbers and should not be used in applications where the finished products are to be exposed to such liquids.

Friday, December 18, 2015

PVC Plastisol Sticking to Substrates

Manufacturer: We are using PVC plastisol for casting and dipping for various products including gloves. Our problem is the occasional tendency of the products to adhere to some substrates such as the moulds. What shall we do?

John Woon (Senior Latex Consultant): Plasticized PVC does have some inherent tackiness problem. I suggest you add some lubricants to the compound such as metallic stearates, stearic acid, waxes and silicone. These should improve your demoulding process.

Thursday, December 17, 2015

JW Latex Consultants would like to wish our clients, customers, students, friends: "Merry Christmas and Happy New Year!!

Heat Sensitivity of Latex Compound

Manufacturer: We have been having difficulty in controlling the heat sensitivity of our NR latex compounds resulting in variation in product thickness, etc. We are now in the process of developing new compounds with improved heat stability.

We would appreciate it very much if you could suggest a simple lab method for us to measure the latex heat sensitivity.

John Woon (Senior Latex Consultant): You can evaluate the heat sensitivity of
your latex compounds by measuring the increase in viscosity when the latex compound is subjected to an extended period in an oven at, say, 35 to 40°C at a given latex TSC and pH. The temperature used would depend on the latex compound formulation.

Other tests we could carry out include MST and coagulum content (including micro-coagulum).

Thursday, November 19, 2015

Non-ionic Surfactant for Natural Rubber Latex Comppounds

Manufacturer: We are looking for a suitable non-ionic latex stabilizer for one of our heat sensitized natural rubber latex compounds. There are so many variations of such stabilizer in the market making selection a nightmare to us. We would appreciate if you can suggest one suitable grade for our work.

John Woon (Senior Latex Consultant): You should try evaluating an alkylphenol ethylene oxide condensate containing about 30 moles of ethylene oxide/mole.

wherein R comprises 8 to 14 C atoms and x varies from 1 to 40 moles

Thursday, October 29, 2015

Polychloroprene Latex as a Substitute to Natural Rubber Latex?

Manufacturer: We understand that some manufacturers have switched from natural rubber latex to polychloroprene latex despite the higher price of the latter due to protein allergy problem associated with natural rubber latex.

What are the typical properties of vulcanisates from polychloroprene compared to natural rubber?

John Woon (Senior Latex Consultant): Generally, polychloroprene rubber has the following superior properties, especially when compared to natural rubber:

1) Excellent resistance to ozone attack.
2) Good ageing resistance.
3) Low gas permeability
4) Good chemical resistance especially against non-polar solvents.
5) Good flame retardant.

While the modulus and elongation at break are similar to that of natural rubber, the tensile strength and tear strength are slightly inferior. 

Sunday, October 25, 2015

Cyclohexylamine Acetate as Coagulant?

Manufacturer: We heard that you had recommended the use of cyclohexylamine acetate as a coagulant for some latex dipped products. Can you please tell us why?

John Woon (Senior Latex Consultant): Usual coagulant such as calcium nitrate would result in poor transparency since it is insoluble in rubber.

One unique coagulant that has been successfully used for many years for the manufacturing of high-clarity (i.e. transparent) baby teats and soothers is cyclohexylamine acetate (CHA).
The main reason for the transparency is that CHA and its by-products are soluble in rubber.


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]

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