RUBBER

Rotorua Morning Post, Volume 2, Issue 392, 29 November 1932, Page 6

RUBBER

ITS GROWTH, COLLECTION MANUFACTURE AND USE ADDRESS TO ROTARY A very interesting address on rubber was given before the Rotorua Rotary Club at the weekly luncheon yesterday by Mr. G. C. W. Reed. He gave a comprehensive review of the rubber' industry covering the collection of the latex, or juice, from the trees to the completion of the manufactured article- In opening he pointed out that many years ago rubber was obtained from quite a large number of botanical sources, but since the successful starting of plantations in such countries as Ceylon, Java, Sumatra, Straits Settlements and Malay Peninsula, there has been a growing tendency to employ the latex, or rubber milk from trees, the most popular being the Hevea Brasiliensis. This tree, growing to a height of 60ft., was found in Brazil and was, and still is, responsible for the fine Para rubber. The output of wild rubber was, of course, uncertain, but with plantations there were about 100 trees left to the acre. The yearly yield of dry rubber~from a plantation was 3001b. to the acre. It cost about £60 to bring an acre into production. A tree came into bearing after four to six years, but did not reach its maximum output until ten years old. The latex is placed in enamel buclcets and a : small quantity of acetic acid addedCoagulation follows and the rubber is then washed and smoked. In technical practiee a very large number of minerals and organic substances are added to rubber in addition to sulphur. These compounds are added to g-ive special qualities to the rubber. For . instanee, zinc oxide and carbon black are added to the rubber used for tyres to increase their toughness and tensile strength and give better abrasive wear on the roads- A tyre tread of pure rubber would be useless. Times and temperatures for vulcanisation had to be chosen carefully for different lcinds of goods. There were different methods of vulcanising or curing — the "wrapped cure" used for hose and tubing; the "open cure" employed for things like water bags; "dry heat eurc," for rubberised fabric. These three methods, together with the use of hydraulic presses and vulcanising boilers, all depend on the presence of sulphur in the mixture. The 'cold cure" is totally different and is applied to all dipped goods, silk, etc., which will not stand the heat.