What should be your cure temperature and time for examination gloves?

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Manufacturer: Great knowing you from the Internet. I am an engineer in the field of constructing glove dipping line in Malaysia. I need your advice in following:

What will be the vulcanization energy per piece of 7.5g x 300mm long exam NR glove & Nitrile glove? And what should be the vulcanization and latex dwell time? Most the glove manufacturers requests for at least 15 minutes in the vulcanization oven.

--> John Woon (Senior Latex Consultant): 1) We don't go to the academic level to determine the energy required to vulcanise a piece of glove. It depends on whether you are using a pre-vulcanised latex or post-vulcanisable latex compound. With the former you don't require any heat for vulcanisation - any temperature used is solely for the purpose of drying the gloves. This is usually 90C to 110C.

As for post-vulcanisable latex compounds, the normal cure temperature ranges from 110C to 130C for an average cure time of 15 to 20 minutes. Actual cure temperature/time must be determined by lab trial based on a given latex curative recipe. Different recipes or formulations would require different cure parameters. Please take note the vulcanisation chemical reaction would commence immediately once the curatives are added into the latex even at ambient temperature. 

Air permeability of synthetic rubbers is different from that of natural rubber and this would also affect the choice of oven temperature and the drying time.

2) Latex dwell time must be determined in the lab as it depends on the latex TSC, coagulant strength, former temperature and the thickness of the gloves. However, generally for today's technology for examination gloves, a latex dwell time could be quite short.

You have to work closely with a latex technologist. Engineering know-how alone would not do.

If you require, a detailed report on the Dipping Technology can be made available for you and your team.

Factors affecting the quality of natural rubber latex

Manufacturer:We are natural rubber latex concentrate producer. We heard that the DRC (Dry Rubber Content)is influenced by the density of tapping, age of rubber trees and that the quality of the latex varies from the height of tapping. How true is this?
John Woon (Senior Latex Consultant): You heard right. When a rubber tree is first tapped, the DRC is usually very high. This yield would slowly drop until a stability is reached. The greater the density of tapping the faster is the drop in DRC. If the planter does his job properly, the latex yield should be quite constant in the first 5 years of tapping.

As regards the effect of height of tapping on latex composition and hence the quality, early research works have proved that the higher a rubber tree is tapped, the higher would be the quantity of non-rubbers which sometimes lead to poorer latex stability. However I do not think that such difference has any significant impact on the latex technology especially that for dipping - if the latices collected from different sources are well blended.

Having said that, I must stress that latex with higher level of non-rubbers, especially the ash content could lead to early clogging of your centrifuges resulting in lower efficiency.

Pink Glove Dance for Breast Cancer Awareness

Emily (MacInnes) Somers created, directed and choreographed this in Portland for her Medline glove division as a fundraiser for breast cancer awareness. This was also her idea to help promote their new pink gloves. One wonders how she got so many employees, doctors and patients of the hospital to participate, but it started to really catch on.

The participants put together this video to generate breast cancer awareness throughout the hospital system and had lots of fun putting this together and hope it inspires others to join in the cause.

When the video gets 1 million hits, Medline will be making a huge contribution to the hospital, as well as offering free mammograms for the community. Please check it out at:
http://www.youtube.com/watch?v=OEdVfyt-mLw

Polyvinyl acetate emulsion (latex) as stiffening agent

Manufacturer: We are manufacturer from Europe. Besides using latex (both natural and synthetic), we are also using Polyvinyl acetate (PVac) as a binding agent for textiles and felt etc. Our aim is to increase the body and stiffness of the textiles. Can use advise us on the choice of the right grade of PVac?

John Woon (Senior Latex Consultant): Some Polyvinyl acetate emulsions (or rather latex) are plasticized either externally or internally through copolymerization with one or more different monomers. For maximum stiffness you should select one that is not plasticized or only lightly plasticized. Also, emulsion with coarser particle size would have more stiffening effect than those with finer particle size.

For your application, usually a low solid content is required. Hence the emulsion you select should have good colloidal stability on addition of water.

It might interest you to know that PVac emulsion with coarser particle size also tend to have better freeze-thaw stability especially when the polymer has a relatively higher molecular weight while the plasticizer content is not too high.

Having said that, you could also consider using PVac as a stiffening and reinforcing agent for your natural rubber latex.

You are at the site for answers and solutions to all your problems in natural rubber latex processing and manufacturing of industrial, household and medical gloves, condoms, catheters, baby teats and baby pacifiers, toy balloons, latex foam products, latex threads etc.

How to keep tensile strength of gloves consistent?

Manufacturer: We are gloves manufacturer. We have had problem of getting consistent tensile strength of our gloves despite using a well maintained and calibrated tensiometer. Besides controlling the cure state of our latex compound and strict process control what else could we do?

John Woon (Senior Latex Consultant): It's very difficult to achieve 100% consistency in tensile properties as long as you are using a post-vulcanisable latex compound since the cure state increases with time with the corresponding increase in modulus and a drop in elongation and tensile strength. You should look into using prevulcanised latex.

Having said this, please ensure the following:

1) The cutter of your test pieces must be very sharp and free from any irregularity and damage to the cutting edges.

2) Gloves must be sufficiently dried and moisture content of the gloves must be consistent. Damp gloves would result in low tensile strength. Leaving the test pieces in a desiccator overnight would be helpful.

3) After drying, the gloves should be "well rested" before testing. The minimum time between vulcanisation and testing should be 16 hours. Depending on the formulation of the latex compound, some gloves continue to vulcanise even at room temperature while in storage.

4) Maintain and control the relative humidity and temperature in the testing room.

5) The gloves should be stored flat to prevent creasing while awaiting testing.

You are at the site for answers and solutions to all your problems in natural rubber latex processing and manufacturing of industrial, household and medical gloves, condoms, catheters, baby teats and baby pacifiers, toy balloons, latex foam products, latex threads etc.