JW Latex Consultants (and Rubber Consultants) 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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Thursday, April 17, 2014

Thickener for Natural Rubber Latex Adhesives

Manufacturer:  I have a very small business related to rubber latex and I am based in West Bengal district of India. My work involves making rubber latex (centrifuged, 60% DRC) thick for adhesive applications.

In the process, first I prepare a solution using thickeners such as CMC, PVA, Sodium alginate etc. But I have not yet achieved the desired success with the help of these chemicals.

Last week, I came in contact with your website and found a reference of SODIUM POLYACRYLATE. Now, I request you to please suggest me whether I can make a thick solution with the help of Sodium Polyacrylate and water (Cold or Hot?) and whether this solution can be added to latex.

I do hope that you would be kind enough to address my query and send me a solution that might help me improve my work.
John Woon (Senior Latex Consultant): Yes, you can try "Polyacrylate" type of thickener. Sodium polyacrylate is quite widely used.

This should be readily available either already in solution form or powder form or the polyacrylic acid which you have to react with sodium hydroxide. These should be available in India.

You can prepare a 1 to 5% solution by dissolving sodium polyacrylate powder in warm water with stirring. The powder should be added in small quantity slowly and gradually to prevent lumping.

Talk to your suppliers who can further advise you on how to use this for latex.

In addition, you can also add about 5 phr of bentonite clay.

Monday, March 17, 2014

Secrets to Succesful Dipping for Toy Balloons

Manufacturer: We are toy balloons manufacturer who have just started commissioning our new dipping dipping line. We would appreciate very much if you could guide us on the "Do's and Don't's" on how to produce good quality balloons. Our full dipping parameters and video clips of our process have been sent to you.

John Woon (Senior Latex Consultant): Thanks for the dipping parameters and video clips which are very helpful for me to understand your process. Obviously, there are a lot of rooms for improvement in your process.

As requested by you, my full report has been sent to you separately but only a summary of the content is revealed in this "forum".

The following are the areas you need to concentrate on:

1) How to Overcome Latex Quality and Stability Problem 
- You need to know how to assess the suitability of centrifuged latex concentrate 

2) Importance of Prevulcanized latex vs Post-vulcanisable latex
- How to produce and handle both these latices

3) Types of Plasticizer to Be Used for Making the Balloons Softer
- Techniques on how to prepare the plasticizer

4) The Dipping Parameters
- The "Secrets" you need to know from formers cleaning stage to final stripping and drying stages

5) Analysis of Balloon Defects and How To Overcome Them
- Some examples of defects frequently encountered by manufacturers include the following:

Thin patches/uneven latex pick-up
Horizontal lines (Striation)
Fish-eyes and windows
Bubbles at bottom of balloons
Fungus growth
Premature bursting/popping
Balloons becoming stiffer on storage
Balloons sticking together 
Tearing of balloons
Blemished surface
Specky particles
Vertical lines with windows and particles
Star-like particles
Vertical lines along the folds

Crystallization and Gel Content of Polychloroprene

Manufacturer: We are using polychloroprene latex (e.g. Neoprene) for making latex dipped products including gloves. We have been advised to consider the "crystallinity" and "gel content" of the polymer in order to select the right grades for the right jobs. Can you tell us how these two properties can affect the properties of my finished products?

John Woon (Senior Latex Consultant): Generally, as you increase the level of "crystallinity" or "crystallization rate", you get the following effects:

1) Cohesion strength, modulus and hardness would increase
2) Elongation, hot oil swell, resistance to permanent set would drop

As you increase the level of "gel content", you get the following results:

1) Cohesive strength, modulus, resilience, resistance to permanent set would increase
2) Elongation, dry tack and hot oil swell would decrease

You should use this information as a guide in conjunction with the curative recipe design to get the optimized final physical properties required for your products.

Thursday, March 06, 2014

Get Your Copy of "Practical Latex Technology"

The 128-paged book, "Practical Latex Technology" contains answers to more than 100 questions plus other very useful tips and ideas! 

For easy of reference, it is divided into 5 Parts:

Part 1: Vulcanisation (Vulcanization), Vulcanisation of Latex and Prevulcanised Latex
Part 2: Properties of Rubber and Latex
Part 3: Problems of Latex Processing and Finished Products
Part 4: Compounding Ingredients and Processing Aids
Part 5: Miscellaneous Subjects

Get your copy for a one-time investment of only $85.00!

NOTE: If you do not receive the book online immediately after making your payment, please contact John Woon at woonsungliang@yahoo.com.sg and john@jwlatexconsultants.com and he would ensure that the book is sent to you without undue delay.

Monday, February 24, 2014

Storage Conditions of Natural Rubber Products

Manufacturer: We have just received a complaint from one of our major customers regarding the shelf-life of our natural rubber products in their warehouse. We have investigated our formulation and manufacturing process and found that both are already at their optimum levels. Careful design and curatives and antioxidant system had been adhered to. We would appreciate if you could offer further assistance.

John Woon (Senior Latex Consultant): Maybe you should help your customer by advising them on the conditions of storage for your products.

Rubber products can normally be stored for many years without any loss of their inherent properties provided the following precautions are taken:

1) Do not deform the products to prevent stressing the rubber.
2) Do not expose the products to elevated temperatures for long period. If possible do not exceed 35C.
3) Do not expose the products to light i.e. direct sunlight and artificial light. If possible store the products in the dark.
4)  The products should be properly wrapped and covered also to minimize exposure to air (oxygen) and ozone. Ozone is particularly harmful. The warehouse should not have any electrical equipment that can generate ozone such as high-voltage equipment, electric motors and mercury vapour lamps.
5) Excessive humidity and moist condition especially due to condensation should be avoided.
6) Do not allow the products to come into contact with brass, copper, iron, solvents, oil, greases, etc.
7) Do not unduly store the products for too long by ensuring the stocks are used in rotation.

Sunday, February 16, 2014

Zinc Oxide in Natural Rubber Latex

Students: We are a group of students studying the effect of ZnO in ammoniated natural rubber latex concentrate. We hope you could help us with some information on the solubility of ZnO in natural rubber latex especially the effect of pH.
John Woon (Senior Latex Consultant): I am assuming you are already familiar with the phenomenon of "ZnO thickening due to Zinc-amine complex".

Studies had been done on the factors controlling the solubility of ZnO in Hevea natural rubber latex using model solutions containing ammonia and ammonium salt at a given pH. It had been found that the solubility of ZnO in the latex is proportional to the total concentration of ammonia and ammonium salt.

Also, at a constant concentration of free ammonia and ammonium ions, maximum solubility of ZnO can be achieved at a pH of 9.5.

Tuesday, February 04, 2014

European Commission Backs ECHA on Phthalates in Toys

The European Commission has concluded that the use of high molecular weight phthalates in certain toys and childcare products poses no risk to infants. The findings, which also include adult sex toys, are in line with the conclusions presented last August by the European Chemicals Agency (ECHA).

Based on ECHA’s assessment, the Commission has concluded that “no unacceptable risk has been characterised for the uses of DINP and DIDP in articles other than toys and childcare articles which can be placed in the mouth”. The Commission further concluded that “in the light of the absence of any further risks from the uses of DINP and DIDP, the evaluation of potential substitutes has been less pertinent."......CLICK HERE to read more

Monday, January 27, 2014

Happy Chinese Lunar New Year!

For those who are celebrating the Chinese New Year of the Horse on Friday, January 31, we would like to wish you,


"A Very Happy and Prosperous Chinese Lunar New Year"

Sunday, January 26, 2014

Why Can't We reinforce Latex Products with Reinforcing Fillers?

Manufacturer: We are manufacturing rubber products using both natural rubber latex and dry rubber such as SMR 10 and SMR 20. To improve the strength of our products, we usually add reinforcing filler such as carbon black and silica. However we find that this only works with dry rubber compounds and not the latex compounds. Why?

John Woon (Senior Latex Consultant): In dry rubber compounding and mixing, one has to masticate the rubber either in a 2-roll mill or an internal mixer such as Banbury before other additives such as curatives could be added and homogeneously mixed. In the process of mastication, rubber molecules are broken down with the formation of free radicals which would initiate the chemical bonding with the reinforcing fillers especially carbon black. The following diagram shows how a dry rubber compound is being mixed in a two-roll mill:
The difference in the speed of the two rolls results in the required shear force for the mastication of rubber.

No such free radicals are produced in normal latex compounding and hence no significant reinforcing can be achieved with fillers as in the case of dry rubber compounding although in some cases, there could some marginal improvement in tear strength..

Stability of Carboxylated SBR Latex

Manufacturer: How do we stabilize the carboxylated SBR latex compared to normal SBR latex? We do use high loading of filler (e.g. calcium carbonate).

John Woon (Senior Latex Consultant): Compared to standard SBR latex, carboxylated SBR latex generally offers better chemical and mechanical stability due to the carboxylation.

Hence, no extra stabilizer is required to be added at your end unless it is to be blended with other latices with different pH range. Please note that some soaps (stabilizers) are most efficient in the pH range of 8.0 - 9.5 while others are workable only outside this range.
You need to check with your supplier to confirm this.

It is advisable to premix your filler with a chelating agent or similar phosphate type of dispersing agent before use.

How to Cure Carboxlylated SBR Latex?

Manufacturer: We have been advised to use carboxylated SBR latex as an althernative latex for our products. Please advise us the best curing system for this.

John Woon (Senior Latex Consultant): Carboxylated SBR latex can sometimes be used without any cross-linking. However to further enhance its physical properties, you can cure it with sulphur system or ZnO. Sodium aluminate with urea or melamine can also be added for cross-linking. A combination of all these possibilities have been successfully used commercially.

Saturday, December 28, 2013

Low ZOT Latex

Manufacturer: We have been having latex stability problem after compounding for months and was advised by some experts to use "low ZOT" latex. Can you please tell us more about ZOT?

John Woon (Senior Latex Consultant): Sometimes the common test such as MST is not very useful when accessing the suitability of the latex for production use after compounding with curatives, particularly, ZnO.

"ZOT" refers to a test on the degree of increase in viscosity of the latex compound after adding a given amount of ZnO, sometimes also referred to as "Zinc Oxide Thickening Test".

Although there is a British Standard Zinc Stability test (ZST) you can easily design your own ZOT test for your own purpose by adding some amount of ZnO (depending on the level you used in your compound  formulation) followed by stirring and allowing to stand for a given period at room temperature and also at elevated temperatures (e.g. 45 to 60C) before measuring the viscosity using Brookfield viscometer.

Tuesday, December 24, 2013

Merry Christmas and A Happy New Year!

We would like to wish all our customers, clients and students "A Very Merry Christmas and a Happy New year!

     =>            http://youtu.be/jtyshfWDX5Q


Saturday, December 21, 2013

Ozone Cracking of Rubber Products

Manufacturer: We have recently received complaint from one of our customers indicating that our products made from natural rubber had poor resistance to ozone attack. Please tell us more about this.
John Woon (Senior Latex Consultant): Symptoms of ozone attack include signs of a few deep cracks or patches of very small cracks. These usually occur at right angles to the direction of the stress to which the rubber products are being exposed to. Therefore your products must have been stressed during it's service life. Unstressed rubber is attacked at a very much slower rate, if there is any.

Ozone is universally present in atmosphere. Ozone is being created by oxygen in the air by sunlight (UV light) and also high voltage discharge.

I suggest you try adding antiozonant and wax to your compound failing which you should look into switching your base rubber to polychloroprene.

Monday, December 02, 2013

Thursday, November 14, 2013

Is There Such a Thing as PVC-Free Plastisol?

Manufacturer: Some of our products are made from PVC plastisol including household gloves. Our customers are now requesting us to switch to non-PVC plastisol. Is there such a thing and what are the main concerns over PVC?

John Woon (Senior Latex Consultant): We have all heard about many markets moving away from all things made from PVC for the following reasons:

1) Generation of chlorine during processing and aging sometimes in the form of HCl which not only corrodes the equipment but is also a health hazard. (The Japanese car companies like Toyota, Nissan and Honda have eliminated PVC in their car interiors since 2007)

2) Carcinogenicity of residual monomer i.e. vinyl chloride.

3) Emission of Dioxins when PVC is burnt or incinerated. Dioxins which are a group of polyhalogenated compounds are considered as toxic environmental pollutants that are health hazards.

4) There is of course the issue with phthalate plasticizers but this is a different problem which I've dealt with earlier in this "Forum".

But is there a possibility of making plastisols without using PVC? The answer is “Yes”. PVC could in fact be replaced with a “core-shell” structured acrylics resin (also in powder form). The price of this acrylic powder could be more expensive but  it can be gelled in shorter time and at lower temperatures than PVC (i.e. less than 120C vs 140C) meaning it would save energy cost for the users.

                                                        Click on the image for a clearer picture

The list of potential suppliers have been sent to you separately.

Freeze-Thaw Stability of Latex Compounds

Manufacturer: We are manufacturing synthetic latex based coating compounds for EU markets. Recently we have had complaints about the Freeze-Thaw stability of our products. Can you please suggest a good but easy method to measure this? Would appreciate if you could advise us on how to improve freeze-thaw stability.

John Woon (Senior Latex Consultant): You can use the following method:

1) Fill up a glass bottle (of capacity of about 250 gram) with the latex compound to three-quarter full.
2) Subject the bottle to 10 cycles of 18 hours freezing at - 20°C followed by 6 hours thawing at room temperature.
3) Examine the sample for signs of gelling and precipitation (coagulation).

If the test confirms that the compound has poor resistance to freeze/thaw, proceed to do the following:

1) Add ethylene glycol at 1 to 2% into a fresh sample of the latex compound and stir gently for 1 hour.
2) Repeat the freeze-thaw test.

If ethylene glycol cannot work, please let me know and I would suggest other alternatives.

Sunday, October 13, 2013

Selecting Natural Rubber Latex Compounds for Slingshot Bands

Student:  I am a PhD student in organic chemistry. My hobby is sling shooting, there are many slingshot clubs and tournaments in Europe.

Over the last years, it has become more and more difficult to find rubber sheetings that are suitable to craft long lasting slingshot bands from. I believe that the modern vulcanization packages which are used to create most latex sheeting offer advantages in the manufacturing process, but diminish the dynamic properties of the product.

I therefore want to conduct a few experiments in my laboratory, and ideally come up with a possibility to start small-scale production of a rubber sheeting that can supply us sling hooters with good rubber bands - and would be very grateful if you could answer me two questions:

- Am I right to assume that rubber with long sulfur crosslink chains has a better rebound elasticity than rubber types made with strong sulfur donors?
-Does prevulcanisation of the latex affect break elongation and resilience of the final product?

John Woon (Senior Latex Consultant): Generally, polysulphidic crosslinks (i.e. long sulphur crosslinks) give higher tension set and hence lower elasticity. On the other hand, with an EV system (Efficient vulcanization) with the use of sulphur donors, one gets better elasticity. However, EV system gives lower tensile strength. Hence it is advisable to take the middle road, i.e. Semi-EV system.

Generally PV gives higher elongation at break and lower resilience compared to a good postvulcanisable latex compound. However, the actual elasticity properties also depend on the curative recipes used for making the prevulcanised laetx (PV).


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.