340 



THE AGRICULTURAL NEWS, 



NOVEKBEE 3, 1917. 



THE QUALITY OP PLANTATION RUBBER. 



The cause of variability or lack of uniformity in the 

 quality of Para rubber [Hevea hraailiensis) has beci the 

 subject of very much discussion and investigation from time 

 to time in years past, and considerable work has been done 

 during recent years (see Agricultural News, Vol. XIV, No. 

 338, p. 125 ; No. 348, p. 283 ; Xo. 349, p. 29-5) by experi- 

 ment station workers in the larger rubber-growing countries, 

 acting on their own initiative, or conducted by the Depart- 

 ments of Agriculture of those countries themselves. Lat- 

 terly, as leaders are probably aware, this work has been 

 of the nature of experiments in vulcanization, the speed 

 of vulcanization (rate of cure) being the quality in Plantation 

 rubber which is most liable to variation ; and in a paper 

 which appeared in the Agricultural Bulletin of the Feder- 

 ated Malay States, ior July 1916, describing what were 

 then the latest results in the investigation of the 

 question of lack of uniformity, new and important 

 results, a summary of which was published in the Agricul- 

 tural News, Vol. XV, No. 382, p. 415, seemed to have 

 been obtaii ed regarding the cause of differences in vul- 

 canizability, and showing where these differences lie — 

 difference in qualitj' which is very trying to the manu- 

 facturer, and has bred a certain amount of distrust in 

 Plantation rubber. 



The results of further experimentation on a more exten- 

 sive and elaborate scale, which has been in progress during 

 the last three years, have since come to hand, in which 

 most valuable and important conclusions appear to have been 

 reached. These are published in the Bulletin oj the Imperial 

 Institute, Vol. XIV, No. 4. October-December 1916, and 

 are presented in the form of summaries prepared from a 

 selection of Reports made by the Directors of the Impe- 

 rial Institute, to the Colonial, Indian, and other 

 Governments concerned, of investigations of the quality of 

 Plantation rubber conducted under the Ceylon rubber 

 research scheme. This is a scheme of rubber research 

 arranged by the Government of Ceylon in conjunction with 

 some of the principal planting companies in the island and 

 with the Imperial Ii stitute. and has been in progress during 

 the last three years. The object of the scheme is to provide 

 for a continuous and systematic investigution of the special 

 problems which arise in the production of Plantation rubber, 

 with particular reference to tlae suitabilities of the rubber for 

 manufacturing purposes. A fair conception of the extensive 

 nature of the experiments undertaken, and of the very 

 considerable amount of w .rk involved, may be gained when it 

 is mentioned that these summaries occupy no fewer than 

 seventy pages of the total number of 185 of which the 

 Bulletin is comprised. 



The investigations recorded deal with the effect upon 

 the mechanical properties of the vulcanized rubber of 

 (1) different methods of coagulation; (2) the addition of various 

 substances to the latex in order to retard coagulation: (3) the 

 form of the rubber: (4) the method of drying: (5) 'over- 

 working' freshly coagul ited rubber in the washing machine; 

 (6) various methods of s^moking; (7) drying sheet rubber under 

 tension; (8) rolling up wet and dry sheet rubber with and 

 without tension; (9) the conversion of wet and dry crepe 

 rubber into block, and (10) separating the rubber from the 

 latex in successive portions. 



Tabulated results of chemical analyses, and of vulcani- 

 zation and mechenical tests Are given, and in the general 

 discussion of the results it is staled that these show that 

 it is in respect of the time required for correct vulcaniza- 

 tion that Plantation Para rubbers, prepared by different 

 methods, exhibit the greatest variation — thus confirming 

 results previously obtained. 



The more important conclusions which have been reached 

 during the course of the present inquiry are summarized at 

 the end of the article under reference. Reproduced below 

 will be found such of these as are applicable to conditions in 

 the West Indies and should prove instructive and of value 

 to rubber growers and others interested in the development 

 in the rubber industry in these colonies. 



GENEE.iL CONCLtrSIONS. 



Spontaneous coagulation of the latex usually yields 

 rubber of good quality which cures quickly, but the method 

 is scarcely suitable for practical use. 



Scrap from the trees has invariably given a low tensile 

 strength after vulcanization. 



Acetic acid is quite satisfactory as a coagulant, and, so 

 far as the vulcanizing and mechanical properties of the 

 rubber are concerned, there would appear to be no advantage 

 in using any other acid in place of it. Further, excess of 

 acetic aoid is less likely to affect the. rubber adversely than 

 excess of some acids, such as sulphuric acid. 



Plain unsmoked sheet rubber is usually of excellent 

 quality, the vulcanized product having as a rule a tensile 

 strength of 2,300 to 2,400 lb. per square inch. The rubber 

 also vulcanizes fairly rapidly, the average time under the 

 conditions of the present series of tests being about seventy 

 minutes. 



Crepe rubber invariably takes a much longer time to vul- 

 canize (105 to 130 minutes) than the corresponding plain sheet 

 from the same latex, and this effect is brought about even if 

 the freshly coagulated rubber is only passed through the 

 rough rollers four limes. The mechanical properties of 

 crepe rubber after vulcanization are very frequently inferior 

 to those of the corresponding plain sheet. 



The 'over- working' of the freshly coagulated rubber in 

 the preparaiion of crepe (up to seventy times through the 

 rough rollers) has very little effect on the mechanical 

 properties of the vulcanized rubber, and only slightly 

 increases the time of vulcanization compared with that of 

 crepe made by passing through the rough rollers only five or 

 seven times. 



Thick crepe rubber, made by rolling together several 

 pieces of thin cr^pe, does not differ from the latter in time of 

 vulcanization, and the differences in tensile strength are not 

 very marked or constant. Thick crepe, made by rolling out 

 the coagulum to the requited thickness, usually vulcanizes in 

 a shorter time than the corresponding thin crepe. 



Different methods of drying (air-drying at the ordinary 

 temperature, drying in hot air, and in vacuo) have very 

 little effect on the time of vulcanization or the tensile 

 strength of the rubber. 



The smoking of sheet rubber increases the time of 

 vulcanization very considerably, and in some cases appears 

 to affect adversely the mechanical properties of the vulcan- 

 ized product. 



The addition of an alkaline solution of creosote to the 

 latex before coagulation does not affect in any way the 

 properties of the dry sheet rubber. 



Pressing the dry rubber into block or rolling it up wth 

 or without tension has very little effect on the time of 

 vulcanization or on the mechanical properties. 



There is no marked difference in the time of vulcani- 

 zation or physical properties between the rubbers obtained 

 bj' coagulating latex in two or three fractions. 



Rubber which is allowed to remain in a wet condition 

 after coagulation (creosote having been added as a preserva- 

 tive) appears to have invariably a short time of vulcani- 

 zation, and to give very good mechanical results aft«r 

 vulcanization. Such rubber loses some proteins on washing. 



