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.
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Thursday, June 25, 2015
Sunday, June 14, 2015
Latex Stability Problem Due to Addition of Filler
John Woon (Senior Latex Consultant): You did not tell me your stabilizing system and how much stabilizer you are using. The problem you encountered is due to the fact that the stabilizers of the rubber particles are being "robbed" by the filler.
As a general rule, the level of the stabilizer (i.e.surfactant) added should be proportional to the quantity of filler added. Also, the level of stabilizer added in the form of a aqueous dispersion (or slurry) is lesser compared to the case when the filler is added as dry powder.
You should also take note that the lower the particle size of the filler, the higher is the level of the surfactant required.
Sometimes a blend of more than one surfactants works better than when only a single surfactant is used.
Saturday, June 13, 2015
Latex Thread Manufacturing - General Advise
John Woon (Senior Latex Consultant): "A general comment" is far from adequate as the latex thread extrusion is a complex process.
Anyway, here's my general advise:
1) The particle size of your compounding chemicals should be free from coarse particles especially for thread of smaller diameters. It should be below 3 micron.
2) The latex compound must be well matured at room temperature for a number of days depending on your cure recipe. This must then be followed by high pressure homogenizing, deaeration under vacuum and filtered before use.
3) Dry and cure at between 15 to 20 minutes at 125°C to 130°C. You can also try a shorter cure at higher temperature followed by post curing at lower temperature at about 70°C.
If you need my full report on the "Manufacturing of Latex Thread", please let me know.
Saturday, May 23, 2015
Transparent Rubber Shoe Soles
John Woon (Senior Latex Consultant): You should start with pale crepe as your base rubber. To have reasonable abrasion resistance, a good choice of filler is precipitated silica since you cannot use carbon black. For better processibility and molding in terms of rheology, magnesium carbonate could help. Light coloured mineral oil would also improve the transparency.
Wednesday, May 20, 2015
Rough Surface of Extruded Staioners' Rubber Bands
John Woon (Senior Latex Consultant): Thanks for sending me your formulations which helped me in my diagnosis of your problem.
You can easily overcome the problem by either switching your SMR to SP 20 of blending both.
SP means "Superior Processing Rubber" made form mixing vulcansied latex with normal latex at different ratios before the latex blend is coagulated to obtain the dry rubber. It has superior processing characteristics and good dimension stability which are ideal for calendering and extrusion processes. The extrudates would also show a smoother surface.
SP 20 indicates that 20% of the latex blend is vulcanised latex.
Poor Flocking Quality of Household Gloves
John Woon (Senior Latex Consultant): Your latex formulation for the adhesive layer should be designed to ensure the latex does not flow excessively and also there is a good latex-pick up to receive the flocks and hence the addition of a thickener is necessary. Also your surfactant system much be designed to ensure that there is no premature gelation of the latex otherwise the adhesion of the flocks to the latex is poor.
Friday, May 08, 2015
Governments to Construct Rubberised Roads
Saturday, April 25, 2015
Other Roles Played by the Detack Powder in Coagulant
John Woon (Senior Latex Consultant): Powder in the coagulant dip tank could help to minimize the the coagulant flow on the former which might result in thin patches. This is because as the water evaporates, the powder increases the viscosity of the coagulant on the former. The powder also causes the surface of the former to have a degree of roughness which in turns would also slow down the flow of the coagulant.
Other means of controlling the coagulant flow without using the detack powder have been sent to you separately as per your request.
Wednesday, March 25, 2015
How to Achieve Maximum Transparency in Latex Coagulant Dipped Products
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
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
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
John Woon (Senior Latex Consultant):
Monday, January 26, 2015
Why Is It Important to Remove Coagulant from 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
Sunday, December 28, 2014
Wet Tack and Dry Tack of Latex Based Adhesives
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
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
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
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
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
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
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.
Thursday, September 11, 2014
"Clastogenicity", "Mutagenicity" and "Teratogenicity" of Rubber Chemicals
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
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?
John Woon (Senior Latex Consultant): Please check out my earlier post titled
Friday, July 25, 2014
At What Temperatures Should Natural Rubber Latex be Stored?
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'
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
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
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.