PROCESS FOR ELIMINATING THE TRADITIONAL "RUBBER SMELL" FROM PROCESSED RAW NATURAL RUBBER
Field of Invention
This invention relates to the treatment of raw natural rubber from latex or cup lumps to remove malodour or the conventional rubber odour from the dry rubbers exported by natural producers. In particular this invention attempts to remove the adverse influences of non-rubbers which is basically absent in synthetic rubbers thus improving the competitive position of natural rubber versus synthetic rubber.
Background of the Invention
Natural rubber latex constitute the polymer cis, 4 polyisoprene nearly 98% and a whole host of non-rubbers which include significant quantities of proteins. Latex is generally collected in the liquid form stabilised with a small quantity of anticoagulant preservative with bacteriacidal properties such as ammonia. The industry also collects and processes the after flow which is collected as cup lumps. The cup lumps are the result of autocoagulation of the latex through bacterial action. While the latex collected in the field with field autocoagulants are subject to coagulation in the processing factory by the control addition of a volatile fatty acid such as formic acid, the cup lump which autocoagulates in the cups do so through bacterial action which generates the full range of volatile fatty acids including propionic and butyric acids all of which produces a foul smell.
The controlled coagulation of latex with formic acids in the factory produces high quality rubber with the conventional rubber smell which cannot be really considered unacceptable to individuals involved in the rubber manufacturing process. However the acceptable natural rubber smell will not be essentially like synthetic rubber derived from the petrochemical industry. The removal of even the acceptable rubber odour would be desirable.
In the case of cup lumps, the situation is very different. The collection, the storage in heaps, the resulting fermentation etc all of which take place prior to processing and drying results in rubber that can be considered malodorous. This

arises from the breakdown of proteins and the sulphur containing amino acids. The smell is entrapped in the rubber through comminution, washing and drying.
The tyre manufacturing sector shows a disproportionate preference for the lower grades of the technically specified grades such as TSR 10 and TSR 20 on perhaps purely economic reasons and these grades emanate from cup lumps with the accompanying smell problem. The tyre and transportation sector consume more than 50% of world production of dry natural rubber. The natural rubber industry is basically the small holder industry in South East Asia, Sri Lanka and India. This also applies in the rubber growing areas of the African continent. This is therefore a disproportionate production of cup lumps as against disciplined collection of latex and controlled coagulation, processing and drying other latex grade rubbers.
Collection of latex as fluid from the trees is confined to the production of centrifuged latex concentrates and the like production of specialist and modified forms of dry latex grade rubbers such as Constant Viscous (CV), epoxidised, very light colorized rubbers, pale crepes superior processing rubbers etc. The bulk of the latex collected in fluid form essentially ends up as latex concentrates used in the dipped goods manufacturing sector.
Thus there is a pressing need for dry rubbers from latex and essentially cup lumps or autocoagufated polybag rubber to be free from the malodour of protein putrefaction, fermentation during storage etc.
Objects and Summary of Invention
The present invention overcomes this malodour deficiency of deliberately coagulated or autocoagulated rubbers from natural rubber latex derived from Hevea brasiliensls. The process essentially deodorise and reodorise the rubbers resulting in natural rubbers that are essentially equivalents if not better than synthetic rubbers in the area of odour.
Essentially the invention achieves the removal of hydrolysed proteins, sulphur bearing amino acids and the foul smelling volatile fatty acids trapped in

the autocoagulated rubbers. The deliberately coagulated or autocoagulated rubbers are treated with hydroxides of alkali metals before the drying process. The treatment can be done during the storage of the lumps or during the form of wet comminuted crumbs or it can be done in both forms. The concentration of the hydroxide of alkali metals ranges from 0.5% to 10%, and preferably ranges from 1% to 5%. The treated rubbers are subsequently subjected to a spray of antioxidant such as phosphoric or oxalic acid to maintain plasticity retention index levels. The crumbs are finally subject to a spray of any commercially available antibacterial detergent, preferably with an attractive smell.
Detailed Description of the Invention
The process is essentially the removal of the results of proteolysis by
removing the remnants of these non-rubbers from the surface of the comminuted
crumbs during processing. This can be effectively achieved by immersing the wet
comminuted rubber crumbs in the solution of hydroxides of alkaline metals such
as sodium or potassium. The concentration of the hydroxide solution may vary
from 0.5 to 10% and the period of contact could be adjusted from 5 minutes to 2
hours depending on the size of the crumbs and the like surface area exposed.
The concentration of the hydroxide solution preferably varies from 1% to 5%.
After immersion in the alkaline hydroxides, the crumbs could be washed, sprayed
with antioxidants such as phosphoric or oxalic acids to maintain plasticity retention
index levels and subsequently a spray of any other nice smelling antibacterial
detergent available in the market to prevent other defeterious activity from taking
place during the drying process.
In the case of controlled coagulation of latex, the resulting rubber subjected to the same process results in the rubbers that have essentially no conventional or traditional rubber smell as the following examples illustrate.
Example 1.
Old and fresh cup lumps labelled A and B were subject to the usual method of processing into comminuted rubbers. Half the rubbers were dried as controls and the other half were treated for 2 hours in a 5% solution of sodium hydroxide, then washed and treated with a 0.7% spray of phosphoric acid and 0.1% spray of

commercial antibacterial detergent. The dry rubbers were then subject to odour testing using the Olfactor Odour Meter. Results are given in Table 1.
(Table 1 Removed)
Table 1.
Example 2.
Fresh latex collected from the field was deliberately coagulated with formic acid in the traditional way and comminuted. Half the rubber crumbs were dried as control and the other half was immersed for 2 hours in 5% sodium hydroxide, washed, immersed in 0.5% phosphoric acid for 30 minutes, then sprayed with 0.2% detergent and then dried. Both samples were then tested for odour using the Olfactor Odour Meter. Results are in Table 2.
Table 2.
(Table 2 Removed)
The time of contact with the alkaline hydroxides was reduced to 30 minutes and the results were encouraging even with the most foul smelling cup lumps stored in heaps over weeks or months. While sodium hydroxide was the most effective at low concentrations, potassium hydroxide and calcium hydroxides performed satisfactorily. The addition of phosphoric or oxalic acid is dictated by Plasticity Retention Index (PR!) requirements. The spray of antibacterial detergents may be added to ensure no other deleterious activity takes place during the drying period of 3 to 4 hours.

Claims
What is claimed is:
1. A-method of improving or removing the malodour from natural rubbers of
Hevea brasiliensis by treatment of the wet rubbers using hydroxides of
alkali metals before the drying process.
2. A method according to claim 1, wherein the rubbers so treated include
deliberately coagulated latex rubber, autocoagulated polybag rubber and
the traditional cup jumps arising from the after flow of latex.
3. A method according to any of the claim 1 to 2 in which the concentration of
the hydroxide of alkali metals ranges from 0.5 to 10%.
4. A method according to claim 3 in which the preferred concentration of the
hydroxide of alkali metals ranges from 1% to 5%.
5. A method according to claim 1 where the treatment with the alkaline
hydroxides is done during storage of the lumps.
6. A method according to claim 1 wherein treatment with the alkaline
hydroxides is done when the natural rubber is in the form of wet comminuted crumbs.
7. A method according to any of the claim 1 to 6 where the treated rubbers are
subsequently subject to a spray of antioxidants such as phosphoric or
oxalic acid to maintain plasticity retention index levels.
8. A method according to any of the claim 1 to 7 where the crumbs are finally
subject to a spray of any commercially available antibacterial detergent
preferably with an attractive smell.
9. All rubbers treated in the methods described and claimed under cJaifn1 to 8.