WO2005007703A1

WO2005007703A1 - Method of producing deproteinised natural rubber in solid and latex form

Info

Publication number: WO2005007703A1
Application number: PCT/SG2003/000174
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: AU2003256224A1

Abstract

The method of the present invention involves clustering of field latex particles using a latex-creaming agent and centrifuged to obtain a dry rubber content (DRC) concentrations of 60% to 65%, and skim with below 2% DRC. By combining the process of improved centrifugation process in our co-pending Malaysian Patent Application PI 20014729 with the effect of alkalis such as sodium hydroxide or potassium hydroxide as a pre-treatment for field latex prior to centrifugation, dry natural rubber products may be produced with nitrogen levels below 0.1%. With the process of the present invention, improved deproteinised latex concentrates enable dipped latex products containing non-detectable levels of proteins to be economically produced with no detriment to the technological characteristics of the product.

Description

METHOD OF PRODUCING DEPROTEINISED NATURAL RUBBER IN SOLID AND LATEX FORM

Field of Invention

This invention is an improvement and addition to our co- pending Malaysian Patent Application No. PI 20014729 which discloses improvements in or relating to the concentration of natural rubber latex by centrifugation using commercially available centrifuge machines . The present invention relates to the method of producing rubber latex concentrate by centrifugation to produce deproteinised natural rubber latex concentrate .

Background of Invention

The centrifugation process for the concentration of natural rubber latex is very well known and widely practiced in all natural rubber-producing countries . In our co-pending Malaysian Patent Application No. PI 20014729, a method was described by which the efficiency of cream separation can be increased from the conventional range of 85% - 89% to more than 95%, thereby significantly improving productivity, reducing costs and diminishing the quantum of low market value skim rubber.

Natural rubber latex contains proteins dissolved in the serum and adsorbed at the surface of latex particles . Both centrifuged and latex concentrates contain a proportion of these proteins with the skim latex function having a significantly greater proportion of the dissolved protein. In the case of products such as gloves, catheters, latex threads, condoms, etc. which is made from dipping formers of such products in latex concentrate, it is now well- established that some of the proteins retained by tne dipped products may cause allergic reactions in certain individuals . As a result, the concern over latex protein allergy has now become a serious problem with sections of the population who are in constant or continuous contact with such products, such as surgeons, health workers etc., particularly when they are atopic or susceptible to allergies or cross allergies .

Apart from causing allergic reactions, there is also another reason for preferring none or very low levels of protein in natural rubber content. This includes certain engineering applications using natural rubber where the property of creep is important. Creep is influenced by the level of non- rubbers, particularly protein. Therefore, certain applications of natural rubber in solid or concentrate latex form require protein levels to be reduced drastically or removed to below detectable levels .

In the normal coagulation process, further quantities of proteins are removed through dilution, creping, sheeting, crumbing and washing, prior to drying of the product. In the case of latex concentrates, these are used to make dipped, foamed or extruded products all of which undergo some form of washing resulting in significant reduction of protein from levels detected in total solid films. However, in the case of skim rubber with very low dry rubber content on coagulation, washing and drying still retains abnormal proportion of proteins and non-rubbers and is therefore considered a low grade and discounted in market price. Nitrogen content of natural rubber is largely derived from proteins; hence analysis of protein content of rubber is often based on nitrogen content. Purified NR with Nitrogen levels below 0.1% commands a market premium. However, existing methods producing such rubbers are cumbersome, expensive and complicated; hence, there is a need for economically attractive methods of deproteinising rubber.

Objects and Summary of the Invention

There is a real need therefore for technology in producing natural rubber products with low levels of nitrogen or producing latex concentrates which will enable latex dipped products such as gloves with protein levels at non-detectable levels using the most accurate analytical procedure available. Such non-detectable protein level products have been shown to be totally free from allergic reactions.

Accordingly, the present invention provides for a process of preparing improved latex concentrates which will enable the reduction of proteins to below the accuracy levels of available protein assay, including non-detectable levels, in latex dipped products comprising effecting the removal of proteins of the latex particles prior to centrifugation using an effective alkali.

Preferably, the process for preparing improved latex concentrates which when diluted and coagulated produces natural rubber with nitrogen contents below 0.1%. In one preferred embodiment, field latex is treated with 1% to 3% of an alkali followed by 0.08% to 0.25% of a creaming agent on latex, kept standing for 2 to 24 hours prior to centrifugation with commercially available centrifuge. Preferably, the alkali is any one or combination of sodium hydroxide (NaOH) and potassium hydroxide (KOH) , and that the creaming agent is any one or combination of alginates or tamarind powder.

The process preferably includes the step of centrifuging to achieve said latex concentrates and dry rubber which may be used to manufacture latex dipped goods with non-detectable levels proteins and purified natural rubber with very low levels of nitrogen.

Detailed description of the Invention

Nitrogen levels of total solid films of concentrates and creams amount to about 0.25% to 0.35%, while the nitrogen levels of skim films will be well over 1.2% to 1.5%. As this nitrogen is largely derived from proteins, a rule of thumb calculation to estimate the protein content is to multiply the nitrogen levels by a figure of 6.2.

Table I below provides the general level of nitrogen and consequently protein in total solid films of field latex, centrifuged concentrate and skim. Table I Nitrogen levels in total solid films of NR latices

Essentially the method of the present invention involves clustering of field latex particles using a latex-creaming agent and centrifuged to obtain a dry rubber content (DRC) concentrations of 60% to 65%, and skim with below 2% DRC.

By combining the process of improved centrifugation process in our co-pending Malaysian Patent Application PI 20014729 with the effect of alkalis such as sodium hydroxide or potassium hydroxide as a pre-treatment for field latex prior to centrifugation, dry natural rubber products may be produced with nitrogen levels below 0.1%.

With the process of the present invention, improved deproteinised latex concentrates enable dipped latex products containing non-detectable levels of proteins to be economically produced with no detriment to the technological characteristics of the product.

The extent of removal of proteins may be further enhanced by dilution of the first concentrate addition of soap and repeating the centrifugation process. The following examples illustrates the essential efficiency of our improved invention: Example-A-t-

(i) Natural rubber field latex with a normal ammonia concentration of 0.3% is further preserved with sodium hydroxide at a concentration of 2% on the water phase and left standing for 2 to 24 hours.

(ii) To the latex is added the clustering agent or creaming agent, for example 0.08% of ammonium alginate or 0.16% of tamarind seed powder.

(iii) The mixture is then treated with 0.1% of ammonium oleate. This is then left standing for 2 - 24 hours and then mechanically centrifuged in the usual manner.

(iv) The centrifuge cream may be coagulated after dilution or directly used to make dipped products such as gloves, which will contain no detectable levels of proteins .

Table II below shows the results achieved:

Table II Nitrogen level in natural rubber latices and dipped products

The accuracy of the protein analysis test is <20 μg/g

Excess alkali, if any, may be neutralised and removed from dipped products using very dilute hydrochloric acid. Improvements to oxidation resistance may be imparted to the products by using phosphoric acid - all of which are well- known processes .

It will be apparent to a person skilled in the art that the above-described process may be adapted for deproteinising other constitutions of natural rubber latices. It may also be possible to use other suitable compounds or compositions as creaming agents apart from ammonium alginate or tamarind seed powder described above. In fact, the clustering agents used can be any product commercially used in the natural rubber latex creaming process . These and other substitutes not specifically described herein are not to be considered as departures from the present invention and shall be considered as falling within the letter and spirit of the following claims.

Claims

CLAIMSWhat we claim is:

1. A process of preparing improved latex concentrates which will enable the reduction of proteins to below the accuracy levels of available protein assay, including non-detectable levels, in latex dipped products comprising effecting the removal of proteins of the latex particles prior to centrifugation using an effective alkali.

2. A process according to Claim 1 for preparing improved latex concentrates which when diluted and coagulated produces natural rubber with nitrogen contents below 0.1%.

3. A process according to any one of Claims 1 and 2 wherein field latex is treated with 1% to 3% of an alkali followed by 0.08% to 0.25% of a creaming agent on latex, kept standing for 2 to 24 hours prior to centrifugation with commercially available centrifuge.

4. A process according to Claim 3 wherein the alkali is any one or combination of sodium hydroxide (NaOH) and potassium hydroxide (KOH) .

5. A process according to Claim 3 wherein the creaming agent is any one or combination of alginates or tamarind powder.

6. A process according to any one of Claims 1 to 3 further including the step of centrifuging to achieve said latex concentrates and dry rubber.

7. A process according to any one of the preceding claims in the manufacture of latex dipped goods with non-detectable levels proteins and purified natural rubber with very low levels of nitrogen.

6. Latex concentrate prepared according to any one of Claims 1 to 3 for centrifugation.

7. Latex concentrate and dry rubber obtained according to Claim 4.

8. A rubber product obtained from any one of latex concentrate and dry rubber according to Claim 7.