RUBBER RECLAMATION

Bay of Plenty Beacon, Volume 05, Issue 91, 14 August 1942, Page 5

RUBBER RECLAMATION

ANSWERS TO QUERIES

USEFUL INFORMATION

The drive for rubber conservation? is now in full swing in Whakatane aiul in answer to many queries as to how this useful substance can be rejuvenated Me publish the following information:-— Rubber before vulcanisation can be worked up and played around! with just as plasticine or chewing gum. Aftei- a percentage of sulphur is incorporated and it has been subjected to the required amount of heat, it heroines vulcanised. From this stage it cannot be brought back to the condition of new rubber freshly riiade i'roi'n latex. Some laboratory" methods bring rubber rflrtrost baerk to Its. original state; but commercial methods of reclamation" do not aint as high. The four principal me hods used commercially are as tffidcr f 1. G round Rubber 2. Oil-steam Process '■1. Acid Reclaim 4'. Alkali Digester Process

1. Ground llubbert A fine grinding of scrap rubber: By this method: rubber, which is free front fabric, is ground Hi) by a special machine consisting of two-toothed discs. The rubber parses- through' the two' faces and emerges as fine powder, which should pass through a Sf) mesli sieve.Any rubber powder is rfcr-incorporat-ed in rubber compounds and serves as a useful filler. The rubber is still wholly elastic; retains its- vulcanised rubber properties, and cannot be used alone. It is most conraitmly used in proportions of 10 to» 20' per cent of the compound.

2. Oil Process: - This process, consists of grinding* scrap rubber (free from any cotton fabric) to a coarse granular form l and incorporating enough oil, often over 10 per cent, to enable some degree of plasticity to be obtained. The rubber oil mixture is heated'in'shallow traj*s in a steam vessel for 8 to 24 hours. Oil' reclaim can be used'in much greater percentages than ground rubber, and its plasticity is intermediate between ground rubber and fully plasticised alkali' reclaim. It is cheapto produce, and' where a cheap reclaim for the production of com!petitive priced moulded products is required, it lias this- definite advan* tage over alkali reclaim.

The disadvantages are that it cannot be used Avith rubber containing cotton or linen fibres, and it docs not remove the free sulphur that is always present in vulcanised rubber;

3. Acid Reclaim: This method is an improvement" on-, oil reclaim? in that the acid destroys or dissolves all cotton-or canvas fibres; but for this it'lias practi'eally no advantage over oil reclaim, as it'leaves the rubber in the same state and does not remove all traces of free sulphur.

4. Alkali Reclaim: Alkali reclaim is made from all types of rubber goods containing cither all-rubber, such as car tubes, or complete car tyres, other- Mian;, tile AviTe beads. In this process, Avith ear tyros for instance, the- Avhole of the tyre (fabric and all)/ is ground up to a condition resembling rolled oats. It is then' placed in a digester and submitted to high temperatures and a strong Avater solution of caustic soda* ilt destroys the cotton fibres; and en-» :ables them to be Avashed aAvay from ; the rubber at a later stage> and itdissolves all the free sulphur in the compound, effecting- a real devulcanisation process. This plasticines the ■ rubber and produces the smoothest tj-pe- of reclaim rubber obtainable. The alkali caustic has. a. plasticising. effect (not at present understood): on the doA*ulcanised rubber. Ninety per cent of all rubber reclaim plants use. the alkali process. The product is A*ery satisfactory iY>r many pupposes . It can be used entirely Avithout the addition of neAV rubber. Car tyres arc being made in Ame-' rica with alkali reclaim rubber Avith guaranteed mileage providing a . speed limit of 80 miles per hour is noli exceeded. Owing to the presence of residual caustic soda, the* com-'.; pound vulcanises quicker than ord- . inary rubber and is apt to scorch; or "set up" on mixing (tuiis..lt ileetlaskilli'u 1 - operation and ' careful mixing. The product, howcA'er, is much more durable, does not rapidly per-; ish, and has a much longer life than, compounds made Avith oil, or witty the' acid process, both of AvhicH i cause oA*er~vulcanist\tion Avhen. re- . claimed. Well-made alkali reclaim . can be reA T ~rted back Avith water latex, whirl) has many uses,