Which Thickener to Use for Latex?

Manufacturer:   Nice to meet you!!! We manufacture dipped latex dolls in Siluri, West Bengal.  We use to dip in the latex for 7 to 8 times to get required thickeness. Sometimes the thickeness is not even. We have decided to use latex thickeners. Can I know which thickenere is best. It is CMC or sodium polyacrylate. Many recommend CMC. But I don't know which grade to be used.  Is it better to use CMC with 350 centipodes ( 1 gram cmc in 100 grams water)?

Can I add CMC directly in latex or I should dilute in water. Can you also recommend the maximum dosage.

     

We use Cenex. And I want to reduce dipping from 8 to 5 times. By adding CMC will it cause drying problems???

John Woon (Senior Latex Consultant):  Both CMC and polyacrylate can be used. The sodium salt of CMC is generally recommended when choosing CMC.

You need to also seek the advice of your suppliers because CMC is available in a wide range of chain length and the degree of substitution. You should start with the "medium" viscosity at 2 to 5% solution.

Sodium or ammonium salts of polyacrylate have been widely used for latex. The solution viscosity is comparatively higher at low concentration. Some manufacturers prefer this to CMC because of this reason.

A 2 to 5% solution in water of the thicker should first be prepared before adding to the latex compound. Actual dosage can only be determined by lab experiments.

Any hydrophilic and water soluble materials such as latex thickeners might retard the drying and the finished products might have higher water sensitivity.

What is the Best Alternatives to Ball Mills?

Manufacturer:  Hello Sir, Good Evening. First I'm very grateful to you because you give lot of information to many people very openly.           

Sir, I would like to know which equipment is best in place of ball mill because ball mill is very slow for grinding even fillers, you need big ball mills. So I want an equipment which is very fast in grinding for sulfur, accelerators, zinc oxides, pigments, fillers and other. Can I use colloid mills or any other options?

John Woon (Senior Latex Consultant): Good question! Yes, ball mill is one of the oldest mills used in the latex industry. To upgrade to one with higher throughput, very briefly, you have the following choices:

1) Attritor (Different people define this differently)

This is basically a batch process based on a stirred pot with minimal process variability. It is sometimes referred to as an internally agitated "high energy" ball mill.

2) Vertical or Horizontal Mill

This is a continuous process with controlled pump speed and is able to use smaller grinding media for finer particle size.There is an intensive agitation and mixing as a result of impact and shear.

3) Top Mill

This involves a rotating basket that constantly sucks the chemical into the basket whereby the particles are continuously "filtered" and ground by the media into fine particles. This is claimed to be simpler to operate and have a narrower particle size distribution compared to horizontal mill.

Amazon Fungus Eats Polyurethane

By Barry Copping

Students on a Yale University rainforest expedition have discovered a fungus with an appetite for polyurethane, offering the potential to solve the intractable problem of PU waste.
The Pestalotiopsis microspora fungus is the first to be found which can survive on a steady diet of polyurethane alone. A bonus is that it does this in an anaerobic (oxygen-free) environment similar to ambient conditions at the bottom of landfills.

The students were in the Ecuadorian jungle on Yale’s annual Rainforest Expedition and Laboratory with molecular biochemistry professor Scott Strobel. The mission was to allow "students to experience the scientific inquiry process in a comprehensive and creative way."

The group cultured the microorganisms found within the tissue of jungle plants they had collected, and assayed the bioactivity of the organisms.

The microbe’s remarkable behaviour was recorded by student Pria Anand, and Jonathan Russell isolated the enzymes by which the fungus degrades plastic as its food source. The Yale team conclude that the microbe is "a promising source of biodiversity from which to screen for metabolic properties useful for bioremediation." They speculate that in the future, waste compactors might be replaced by giant fields of voracious fungi.
The work is published in the peer-reviewed journal Applied and Environmental Microbiology.

Doubts About Air Bubbles in Natural Rubber Latex

Student:  I'm actually a student of University Malaya. Currently, I am studying the cause of bubble formation in natural rubber latex and attempting to control and diminish it.

Referring to journals, bubble forms when gas is introduced into solution which containing either surfactant or protein.

Below are some doubts from me:

What are the surfactant that usually applied in latex processing? Is that Tween 80, Trixton 100?2. Hevein and Ovalbumin are the protein in the natural rubber latex ? Besides Biuret test, any other simpler to test the protein level?3. As I know, oil based antifoam is usually used to control bubble. However, is there any other ways?

Thank you. Hope to hear from you soon.


John Woon (Senior Latex Consultant): The following are the answers to your questions:

1) The surfactant usually used by both the latex producers and latex products manufacturers is ammonium laurate. Occasionally, latex products manufacturers also uses potassium laurate, oleate and other anionic surfactants such as sodium lauryl sulphate.

Non-ionic surfactants such as Tween 80, Trixton 100 are seldom added into the latex unless one encounters a severe loss of chemical stability.

2) Proteins in latex are found on both the rubber particles and the aqueous phase of the latex. These are mainly the alpha-globulin and hevein.

To measure the total protein level, you could determine the Nitrogen content using the Kjedahl method and multiply the result by a factor of 6.25.

For water extractable protein, you can use the so-called Modified Lowry method as that used by the medical glove industry, namely,ASTM D5712 - 10 (Standard Test Method for Analysis of Aqueous Extractable Protein in Natural Rubber and Its Products Using the Modified Lowry Method)

3) Although foaming is due to reduced surface tension as a result of the addition of surfactants, there are other factors that could lead to foaming tendency. Pure liquids do not foam while a solution and a mixture often do.Hence, you have to also study the effect of other ingredients in the latex besides the surfactants.

Not all antifoam agents are oil based. Carefully selected non-ionic surfactants with the right HLB ratio could act as an effective anti-foaming agent.         

                                           

Merry Christmas and A Happy New Year!

To all clients, friends and visitors,

Best wishes for a Merry Christmas and a Happy New Year !

 

May this season bring you Success, Happiness and Prosperity !

From JW Latex Consultants 

World Rubber Week in Singapore - May 22 - 24, 2012

The biggest gathering of business and political leaders for the rubber industry - The World Rubber Summit 2012 is to be held at the Raffles City Convention Centre in Singapore, on May 22-24, 2012.

The Guest-of-Honor, Teo Ser Luck, Minister of State for Trade and Industry, will deliver the opening speech at the summit. Held under the umbrella of “Rubber Week”, the World Rubber Summit will be combined with the International Rubber Study Group’s inter-government and industry meetings plus the Rubber Traders Association of Singapore Annual Gala Dinner and Golf Day event on May 25, 2012.

Themed “How rubber will bounce in a volatile world” the summit will examine how world leaders and global CEOs are adjusting to the rapidly changing world economy and new paradigm occurring globally that may impact the rubber industry. During the conference, panel sessions will feature discussions on how best in a volatile macro-economic environment to strategize and harness opportunities in sectors such as automobiles, tires, smallholder sustainability, natural and synthetic rubber innovations, commodities and pricing volatility, development aid plus China and India growth engines.

More than 25 prominent CEOs and business leaders have been invited to speak at the conference, including for example Renault-Nissan, Goodyear, Michelin, Bridgestone, Lanxess, World Bank and Government representatives.

How to Increase Wet Gel Strength

Manufacturer:  We are using both prevulcanised latex and post-vulcanisable latex compound. We also use some synthetic latex such as SBR and NBR. Our process is very sensitive to wet gel strength of the latex. Poor gel strength always lead to high rejection. What shall we do to improve the wet gel strength?
  
John Woon (Senior Latex Consultant):  First of all, prevulcanisd latex has poorer gel strength compared to post-vulcanisable compound and synthetic latices tend to have weaker gel strength compared to natural rubber latex.

When using post-vulcanisable latex compound, enough pre-vulcanisation should be allowed for maximum build up of the gel strength. However too much pre-vulcanisation would also lead to poor gel strength. You have to decide what degree of prevulcanisation is best for your process.

Avoid using prevulcanised latex if maximum gel strength is a must.

The types and level of surfactants you used for latex stability are also important. Extra heating and drying of the gel before proceeding to the next stage of your process would help.

How to Achieve Maximum Transparency in Latex Products

Manufacturer:  We manufacture a range of products using both natural rubber and synthetic latex. Our problem is our inability to achieve the transparency requested by our customers. Please advise us as soon as possible.
 
John Woon (Senior Latex Consultant):  All ingredients used should have a refractive index close to that of the base rubber. Accelerators selected should have maximum solubility in the the rubber. Chemical blooming should be prevented.

If possible, ZnO should be eliminated or minimised in the recipe. Improve your leaching would also help.
In response to your request, detailed recommended recipe for the curatives was sent to you separately.

Selection of XSBR Latex for Carpet Backing

Manufacturer: We are manufacturer of Carpets. We are using XSBR for primary backing of Tufted Carpets. Nowadays various XSBR grades with different properties are available in Market.
For example I am attaching one specification sheet. Can you tell me which specification is better for our carpet backing?
Can you explain the effect on latex while these properties goes up and down? Like what if viscosity is 50 or 200 or 500, Tg, Ph, Surface Tension.

Thanking you for your support.



John Woon (Senior Latex Consultant): As mentioned in the product specification, it all depends on what you have in mind in terms of the final properties of your carpet.

1) You want to choose a viscosity that is workable with your own process. Higher viscosity means heavier coating weight and lesser problem of "strike through" (i.e. excessive penetration).

2) Tg means Glass Transitional Temperature which is the temperature at which the polymer becomes as brittle as glass. The lower the Tg, the softer would be the coating. For low ambient temperatures during the winter, lower Tg is a better choice.

3) pH should be of lesser concern to you unless the fibre of your carpet is sensitive to low or high pH.

4) Lower surface tension latex would offer better wetting property and hence better adhesion of the latex to your carpet. But too much wetting might also lead to excessive penetration although this can be overcome by a higher viscosity.

Malaysia's Natural Rubber Production May Climb by 6 Percent

Malaysia's natural rubber production may climb by 6 percent in 2011 from last year, rather than by 5.6 percent estimated at the start of the month, according to the Association of Natural Rubber Producing Countries. Output from countries representing 92 percent of global supply might increase to 10.06 million metric tons from 9.5 million metric tons.

Rubber futures have lost 29 percent this year in Tokyo on concern that a slowing U.S. economy and a deepening European debt crisis will reduce demand for the commodity used in tires and gloves. Prices increased 4.6 percent to 295.10 yen per kg recently on the Tokyo Commodity Exchange as European leaders inched toward a strategy to contain the debt crisis.

The impact of the rains and floods in Thailand, the biggest grower, was of “less significance” as supply for natural rubber was mainly concentrated in the south. The country might produce 3.38 million metric tons this year compared with 3.25 million metric tons in 2010. Production in Indonesia was predicted at 2.96 million metric tons versus 2.74 million metric tons, while in Malaysia, output was estimated at 1.02 million metric tons compared with 939,000 metric tons, the group said. Exports might rise 2.6 percent this year to 7.67 million metric tons, less than the 3.1 percent growth estimated until a month ago and versus 10.4 percent in 2010.
While the lower rate mostly reflected weak demand because of the global economic slowdown, floods in Thailand had reportedly disrupted some movements to ports.

Demand from China, India and Malaysia, representing 45 percent of the global total, was likely to grow only 0.7 percent this year compared with a 4.7 percent gain in 2010.(Excerpt from Rubber World News)

EPDM from Bio-based Ethylene

LANXESS recently announced that it plans to commercially produce EPDM from bio-based ethylene by the end of the year. It will be the first form of bio-based EPDM rubber in the world and will be sold under the brand name Keltan Eco.

EPDM is conventionally produced using the petroleum-based raw materials ethylene and propylene. Alternatively, LANXESS plans to use ethylene derived purely from the renewable resource sugar cane. This bio-based form of ethylene is produced by dehydrating ethanol from Brazilian sugar cane. The company Braskem S.A. will supply the bio-based ethylene via pipeline to LANXESS' existing EPDM plant in Triunfo, Brazil.

Silicone Conference - "Silicone Elastomers US 2011"

Leaders from the silicone elastomers industry will gather in Rosemont, IL December 6-7, for Silicone Elastomers US 2011. Speakers from BlueStar Silicones, Momentive Performance Materials and Wacker Chemical are among the key players in the silicones elastomers industry who are scheduled to present at this inaugural event.

Silicone Elastomers US 2011 is presented by iSmithers, which has held similar conferences in Europe for the past four years. This is the first time iSmithers will hold a silicone elastomers event in North America. Scheduled presentations include Elastomer Quality and Purity, Innovation in Fluorosilicone for Automotive Applications, Peroxide Curing of Silicone Elastomers, New Developments in LSR Molding and Silicone Elastomers for Medical Use: A Practical Guide to Compliance.

Speakers scheduled to present include Martin Neff, manager Midwest Sales & Engineering, Arburg Inc., Mark Neuber, commercial director and business director, Core Fluids & Elastomers, BlueStar Silicones; Paul Tuckner, president, Grace Technology and Development; Charles Olsen, Jr., general manager, KCC America; Chris Claussen, marketing manager, Momentive Performance Materials; Rick Ziebell, technical manager, R.D. Abbott; and Scott Richardson, technical marketing manager, Wacker Chemical.

Blending NR latex with SBR

Manufacturer:  We are manufacturing dipped transparent Natural Latex products. We would like to reduce the product cost by blending with synthetic lattices. We tried using XSBR but  did not get transparency and the product was very weak in strength. Can you suggest any idea to reduce the cost of product by maintaining the transparency and if the strength is reduced marginally then there is no problem. (John Woon's note: Other details not revealed here)


John Woon (Senior Latex Consultant): The physical properties of SBR (Styrene butadiene copolymer) changes progressively from polybutadiene which is flexible and rubbery to polystyrene which is rigid and glassy. I suggest you try those grades with styrene content of 45% and lower. A suitable grade could a high solid (~62%) SBR used for latex foam manufacturing, not XSBR which is carboxylated.

Generally, once you blend NR with SBR you'd get lower tensile strength. Your total rubber content in your latex compound formulation should not change, otherwise you've to adjust the sulphur and accelerator content accordingly.

For maximum transparency, you should select a grade of SBR with a refractive index close to that of NR, i.e. 1.519.

The accelerator you use is not ideal for transparency. You should choose one that's more soluble in rubber and has minimal tendency to bloom.

Effect of Surface Tension on Wetting and Foaming of Latex

Manufacturer:  We are using synthetic latex for our products. Can you please explain the relationship of surface tension on wetting and foaming in a latex system and a substrate.

John Woon (Senior Latex Consultant): A latex system is said to have high surface free energy when it does not wet on certain surfaces such as waxes and oily coatings. As a result,  the surface free energy tends to force the latex into spherical shape. The end results is that the initial thin film of latex breaks up to form smaller semi-spherical pools of liquid separated by dry areas of the substrate.

The term "wetting" is often encountered in latex technology. Some surfaces of substrates have affinity for water which creates a force (surface attractive force) greater than the surface tension of the water resulting in good "wetting" and the surface is readily coated by the water.

On the other hand, other surfaces might have a lower affinity for water but greater affinity for air. In this case, air has to be removed to overcome the initial resistance before the surface could be "wetted" by the water.

Emulsion polymerized synthetic latex depends on a soap or stabilizer system for polymerization and stability. The soap is partly absorbed onto the surface of the latex particles and partly dissolved in the water (or serum). These soaps reduce the surface tension by moving to the surface layers and hence lowering the surface free energy. Therefore latex surface tension is always lower than that of pure water.

The extent of the reduction of the surface tension depends on the amount and type of soaps in the serum.
Generally, as the surface tension reduces, wetting (i.e. wettability) improves while foaming tendency increases.

Invariably, all efficient soap systems used in polymerization would foam to a certain extent. However, by judicious choice of the soap type and level, the latex manufacturers should be able to prevent the undesirable excessive foaming.  

Lanxess to Produce First Bio-Based EPDM Rubber in The World

Lanxess aims to commercially produce ethylene-propylene-diene monomer (EPDM) from bio-based ethylene by the end of the year. It will be the first form of bio-based EPDM rubber in the world. EPDM is conventionally produced using the petroleum-based raw materials ethylene and propylene. Alternatively, Lanxess plans to use ethylene derived purely from the renewable resource sugar cane.

This bio-based form of ethylene is produced by dehydrating ethanol from Brazilian sugar cane. The company Braskem S.A. will supply the bio-based ethylene via pipeline to Lanxess’ existing EPDM plant in Triunfo, Brazil. Triunfo currently produces 40,000 metric tons per year of regular EPDM rubber and it is expected that the first batches of the product Keltan Eco will amount to several hundred metric tons. In addition,

Lanxess is already seeking alternative sources to produce the premium synthetic rubber product butyl rubber, which is used predominantly in the tire industry. Together with Colorado-based Gevo, Inc, Lanxess is developing isobutene from renewable resources starting with corn. Isobutene is a key raw material needed in the manufacture of butyl rubber.

Latex Cement Composition

Manufacturer:  We use SBR or XSBR latex as bonding agent and gas block additives in the cementing section. The problem is the XSBR we recently purchased is difficult to mix into a fresh water cement slurry, despite large additions of naphthalene sulfonate dispersant.


John Woon (Senior Latex Consultant): You should try pre-stabilizing the latex with a non-ionic surfactant and Potassium hydroxide first before adding the cement slurry. If you are using Portland cement, switching to albuminous cement would help. Also, instead of using anionic latex, you could use cationic latex.

If you continued to have problems, please contact me at woonsungliang@yahoo.com.sg

Chinese, Malaysian Companies in Joint Venture

The Straits Times/Asia News Network reports that two Chinese companies, Mazhongdu International and Hainan Baisha Industrial, have teamed up with a Malaysian firm, Hateg, for a rubber production joint venture in Indonesia, in what is said to be a 3.5-billion-ringgit ($1.14 billion) investment over the next five years.

The first phase of the project in Kalimantan will cover 1,000 hectares over a year at a cost of 40 million ringgits, while another 40,000 hectares will be planted over five years after that. The joint venture partners are also in discussion to expand the plantation to 200,000 hectares, which will bring the total investment to about 8 billion ringgits.

Probelms with Latex Dipping of Vascular Catheters

Manufacturer:   I am an Engineer from a vascular catheters manufacturer. I found your blog (http://latexconsultants.blogspot.com) during my search for answers to the problems I am facing with my rubber manufacturing process and have found the information on the blog site very useful. However, I still have questions and I hope you will be able to give me some advice based on your technical expertise on rubber manufacturing and many years of experience. This is my first time working on rubber manufacturing and I have little knowledge in this aspect.

I am recently working on my own coagulant mixture of Calcium Nitrate plus Methanol and have used it to dip with natural dipping latex. However, I have been finding extremely bulky tip immediately after the formers have been removed from the latex tank. I have tried adjusting the dipping speed, only to find the same results. I have also adjusted the dipping duration for the coagulant, with similar end results. Is the Calcium Nitrate that I have added too little?

I am also facing balloon recovery issues on my balloon after inflation. What are the possible reasons for recovery problems?

John Woon (Senior Latex Consultant): 

Here's my comment and recommendation:
1) At first I thought what you meant by "bulky tips" was the effect of excessive pick up of either the coagulant or the latex at the tip on withdrawal for the formers from the two respective tanks. However, your photos show that it was the narrowing of the areas just below the tips making the tips appearing bulky and thicker.

2) Anyway, let's assume that it was in fact due to excessive pick up of either coagulant or the latex. To overcome this problem, you have to withdraw the former at a lowest possible speed.

3) Formers should be heated to higher temperature to ensure faster drying of the coagulant. You are now using 37C. Please try 45C. Faster drying of the coagulant would help to "set" it before it has a chance to flow back when the formers are inverted after withdrawal. Excessive flow back might result in thinning of the coagulant and hence latex pick-up as seen in the photos.

4) Ensure the formers are well cleaned (with detergent periodically) after each cycle of dipping. This is to ensure even coating of the coagulant.

5) Add about 0.1% of a non-ionic surfactant as a wetting agent in the coagulant. Triton X100 and Teric 320 are possible examples.

6) For health reason, do not use methanol which is highly toxic. It has been reported that workers who are repeatedly exposed to methanol could suffer from eventual blindness. Replace it  with ethanol or IPA (Isopropyl alcohol)

7) Poor recovery of the balloons after inflation and deflation could be due to insufficient drying of the balloons and also low modulus of the film. Prevulcanized latex is available commercially in three modulus ranges, namely low, medium and high modulus. I suggest you use either the medium modulus grade or a 50/50 blend of medium modulus and high modulus.

Malaysian NR Production Up 17%

Malaysia’s Department of Statistics reported that production of natural rubber for July was 100,281 metric tons, an increase of 14,895 mt (+17.4%) compared to the previous month. For year-on-year, production of NR rose by 23.7% compared to July 2010.

The highest consumption of NR was from the rubber glove industry (65.3%), followed by rubber thread (13.5%) and tires and tubes (7.8%). These three industries consume more than three quarters of the overall domestic consumption in the country with a total of 30,341 mt (86.7%)

Biodegradability of Rubber

Manufacturer: We manufacture a range of moulded rubber products using both synthetic and natural rubbers. How biodegradable are these products? Would appreciate some brief notes from you.
 
John Woon (Senior Latex Consultant): It has been documented that degradation and assimilation of organic polymers by living organisms (i.e. bacteria and fungi) is possible and that natural rubber is more biodegradable than synthetic rubbers. Also, such degradation is facilitated by hydrolytic and oxidation breakdown of the polymers.

Microbiological degradation is favoured by high humidity, adequate minerals, sources of available carbon and absence of light. Past researches had indicated that Actinomyces such as Nocardia and Steptomyces are microorganisms responsible for the degradation of Natural Rubber products.

Thin products such as medical gloves made from natural rubber have been shown to degrade at quite a rapid rate after about 2 weeks of exposure to Nocardia, some experiencing a weight loss of more than 70%.

You could conduct your own test using ASTM D5988 - 03