WO2005007704A1

WO2005007704A1 - Improvements to centrifugation of rubber latex

Info

Publication number: WO2005007704A1
Application number: PCT/SG2003/000172
Authority: WO
Inventors: Balachandra Chakkingal Sekhar
Original assignee: B.C. Sekhar Sdn Bhd; Nair, Sushil, Sukumaran
Priority date: 2003-07-21
Filing date: 2003-07-21
Publication date: 2005-01-27
Also published as: AU2003256222A1

Abstract

A process for improving the centrifugation efficiency of NR latex to more than 95% and reducing the DRC of the skim to less than 2%. The process comprises effecting the clustering of latex particles in the natural rubber latex which is to be separated by centrifugation. In particular the clustering of the latex particles is effected prior to centrifuging the latex. The clustering of the latex particles is achieved by adding a latex creaming agent such as alginates, tamarind seed powder, and polyvinyl alcohol. Preferably, the concentration of creaming agents added is in the range of 0.3% to 0.7% of DRC. Higher concentrations may be used without any particular advantage. In another preferred embodiment, the input field latex is diluted to a lower DRC and/or a detergent is added.

Description

IMPROVEMENTS TO CENTRIFUGATION OF RUBBER LATEX

Technical Field

This invention is or relates to a process for improving the efficiency of centrifugation of natural rubber (NR) latex. In particular, the invention relates to a process of increasing the efficiency of separation of NR latex cream by centrifugation.

Background Art

Natural rubber latex formulations in concentrated liquid form are extensively used to make foam rubber products, dipped goods such as gloves, extruded threads, balloons, bladders and in a whole host of applications. The consumption of natural rubber latex concentrates the world over amounts to about 900,000 tonnes dry rubber content (DRC) in the year 2000 and is increasing.

Any increase in concentrating efficiency and reduction of the accompanying skim rubber is of major economic and technical importance to the industry. It is an object of the present invention to achieve both of these desirable targets.

Presently, there are two categories of processes of concentrating the DRC of rubber latex, i.e. the centrifugation process and the creaming process.

The centrifugation process for concentration of natural rubber latex is very well known and widely practiced in all NR producing countries. The most efficient operation gives a separation efficiency of about 85 - 89% with the centrifuged cream component having about 60% DRC and the skim component at about 3 to 5% DRC. Improvements that have been effected through the years to impact on the efficiency and costs of centrifugation relate to machines used rather than the process itself.

An alternative method of concentrating the DRC of latex used in the industry is the creaming process. Creaming agents such as alginates, tamarind seed powder, polyvinyl alcohol, etc. are admixed with natural rubber field latex and allowed to cream up by standing through a period of several weeks. When the separation is complete, the aqueous serum phase is run off leaving the cream phase, which is stabilised appropriately with ammonia. The creaming process separates most of the latex rubber particles with no skim fraction, i.e. achieving a 97% to 98% separation efficiency. While the creaming process can attain a DRC of around 65%, the resultant latex concentrate has high viscosity.

Both systems of concentration, centrifuging and creaming have their respective attendant disadvantages . The former leaves a skim fraction with a DRC of 3 to 5%, which poses difficulties of coagulation. Moreover, because of the high non-rubber content, it gives a technologically inferior rubber composition, thus fetching a highly discounted market price.

The latter, i.e. the creaming process, is cumbersome and requires an inordinate period of time, i.e. 4 to 6 weeks of standing time. While it achieves a DRC of 65%, the latex has a high viscosity, which limits the use of the resultant concentrate in manufacturing operations, and the process is significantly costly. The creaming process has as a result all but disappeared from commercial operations .

Summary of Invention

According to the present invention therefore, there is provided a process which not only improves the centrifugation efficiency of NR latex to more than 95% but also reduces the DRC of the skim to less than 2%.

The process according to the present invention comprises effecting the clustering of latex particles in the natural rubber latex which is to be separated by centrifugation. In particular the clustering of the latex particles is effected prior to centrifuging the latex.

In a preferred embodiment, the clustering of the latex particles is achieved by adding a latex creaming agent. Preferably still, the creaming agent is chosen from any one of the following: alginates, tamarind seed powder, and polyvinyl alcohol.

In another preferred embodiment, the concentration of creaming agents added is in the range of 0.3% to 0.7% of DRC. Higher concentrations may be used without any particular advantage .

In yet another preferred embodiment, the input field latex is diluted to a lower DRC and/or a detergent is added. Detailed Description

The essence of our invention is to effect latex particle clustering prior to centrifugation. The clustering of latex particles must be achieved without destabilising the latex.

Latex particle clustering can be achieved by adding creaming agents . The clustering of latex particles is achieved within hours of the addition of the creaming agent and centrifugation subsequently enables the clustered small particles to join the larger particles to appear in the concentrate. The limitation of separation is only dictated by the increasing viscosity of the concentrate at DRC's higher than 60%. However, a compromise can be achieved by attaining centrifugation efficiency in excess of 95% and accepting some rubber in the skim fraction which can be as low as 1 to 2%.

The process of the present invention uses commercially available creaming agents at concentrations used and acceptable to the industry and centrifuged in any commercially available machines and used by the industry.

The following example illustrates the essential efficiency of the inventio : -

Field latex at DRC's ranging from 25-35% is a moniated to 0.3% and a creaming agent at the concentration of 0.5 to 0.7 on DRC is added. Higher concentrations can be tolerated but provide no particular advantage.

The latex is allowed to stand for 2-24 hours and then centrifuged in the usual manner. The separation of cream and skim with the former ammoniated to 0.7%, is highly efficient and the table below provides the comparison between the conventional centrifuging and creaming process and our novel process .

The process can be further enhanced and improved by adjustments of DRC of input latex, refinement of creaming agents, addition of soaps etc. However the essence of our invention is the prior clustering of latex particles before mechanical centrifugation.

Claims

CLAIMSWhat we claim is : -

1. A process for the improvement in the efficiency of NR latex centrifugation by effecting clustering of latex particles without destabilizing the latex.

2. A process according to claim 1 wherein the clustering of latex particles is effected prior to centrifuging the latex.

3. A process according to any one of claims 1 and 2 wherein the clustering of the latex particles is effected by adding a

NR latex creaming agent.

4. A process according to any one of claims 1 to 4 wherein the creaming agent is chosen from any one of: alginates, tamarind seed powder, and polyvinyl alcohol.

5. A process according to any one of claims 1 to 4 wherein the concentration of creaming agents added ranges from 0.3% to 0.7% on DRC.

6. A process according to any one of the .preceding claims wherein the latex to be processed is first diluted to a lower DRC.

7. A process according to any one of Claims 1 to 6 wherein the latex to be processed is first treated with the addition of a detergent.

8. A process according to any one of Claims 1 to 6 wherein the latex to be processed is first diluted to a lower DRC and a detergent is added.

9. A process of enhancing centrifugation efficiency and the reduction of skim rubber substantially as described.