J.R.R.I.M, Communication 236 SOFTENINE TH RUBBEF GO R
PART I ADDITIOE TH SOAPF N O SOFTENER D SAN LATEO ST X
BY
. WlvNTWORTH . V H
Summary
This paper reports preliminary investigations into the softening of rubber by pre-coagulation treatment of latex. Plasticity results are given which show the effect of the addition of emulsions of fatty acid soapd indicatd an s an s e drastith e c effect f coppero s e th , superiority of zinc soaps as softeners and the use of alkali soaps as emulsifiers in tests of softening agents. The incorporation of pine tar into latex up to 40 per cent on the dry rubber has been found possible and comparative plasticity a numbedat n o a f conventionao r l softener e reportedar se Th . possibility of master-batch preparation of softeners in plantation practice is suggested.
Introduction
Crude raw rubber as received by manufacturers has to be reduce y heatinb d d mechanicaan g l workin a sof o tt g plastic conditio o permit n t incorporatio e essentiath f o n l compounding ingredients. These operations consume time and power and it is therefore pertinent to enquire whether this consumption could be reduced by modifying the method of preparation of the rubber e plantationoth n . That thera deman a rubbes i e r fo d r softer thae plantationth n supplw no se facs showi yth t y thab n t plant is in operation using the Ungar-Schidrowitz process (1, 2, 3, 4, 5), n whici h rubbe s crumbedi r , washed, drie n vacuoi d , alloweo t d oxidis finalld an e y milled into slabs. e factoryth e n preliminarI th , y workin r masticatioo g s i n usually r morfollowe o e additioe th e on y liqui b f do n r solio d d softening agents which promote further softening and ease of processing e choicth , e being governe e methoth y f manub do d - facture and nature of the final product. A class of softening agents has lately become available which brings about a pro- nounced peptisatio r disaggregatioo n e rubbeth f no r when milled into it, effecting a reduction in power consumption and permitting of modifications to formulae (6, 7, 8). It is sometimes recom- mended thae rubberth t n removao , l fro e milmth l shoul e heldb d n elevatea t a d temperature.
90 91
e presene th objecTh f o t t o t investigatwor s i k e th e possibilities of methods of softening rubber which might be used in estate practice with the minimum of expenditure on additional appliances. Previous wor f thio k s nature include a a dtes f o t proprietary softening oil which was carried out in 1934 but proved it to be insufficiently effective (9). It was also shown that excessive dilutio f lateo n x before coagulatio t appreciablno d di n y influence the softness of the product (10) nor were the advantages obtained by autoclaving latex sufficient to warrant the ex- pense (11). A promising line of attack is the treatment of latex prior to coagulation with substances which will bring about softening in the e coursnormath f o e l smokin d dryinan g g process o forT .m a basi f comparisoo s n with these newer type f peptisero s s wa t i s considered desirabl o t examine e effectth ef o conventionas l softeners and allied materials used in this way. This paper covers only tha e investigatiot th par f o t d shoulan n e reab dn coni d - junction wite pape th hy Hasting b r s which follow t i (Pars t II).
Experimental THK ADDITION OP FATTY ACIDS AND THI^IR SOAPS TO LATKX In the first place it was decided to obtain data concerning the plasticity of rubber prepared from latex to which the common fatty acids and their soaps had been added prior to coagulation. Apart from their s possibla softeners e us e , som f o these e substances migh e useb s temulsifyin a d g agent n preparini s g dispersion f otheo s r materials. Blo d Garnewan r (12) examined e effectth f fatto s y acid softener y rubbe dr d usen i an sr d three r cent pe f softene o e ,rubber th n o r . This proportio s adoptenwa d and used but no adjustments of quantities to compensate for different equivalent weight e metale soapth th f n o ssi s were made in this work. e solublTh e soaps wer ee a for e late addeth f th m o n i xo t d e insolublsolutioth t bu ne soap e d fattb an s o yt acidd ha s incorporated in the form of an emulsion. This was prepared by dispersin e soa gth r aci po benzen n di d passinan e e dispersiogth n through a hand emulsifier simultaneously with ammoniacal water. orden I obtaio t r n satisfactory emulsion s necessarwa t i s varo yt y e amounth f benzeneo t alsd an o, exercis ee manipulatio carth n ei n of the emulsifier, which contributed largely to the success or failure of the operation. Tests had shown that the addition to the latex of emulsified benzene had no effect on the hardness of resultane th rubbee tth rubbern i r estimation h witA as . h e th f no and without addition of potassium oleate showed that less than 92
hale soath f p remaine e drieth d n i d e amount rubbeth t i bu ro s soluble soaps added wer t increaseno e n thio d s accounte Th . insoluble soaps appeared to be completely absorbed. The addition of the solutions or emulsions to fresh field latex reducey rubbedr e rth d conten r ceno 2t 5pe t t whic s furthehwa r reduce o about d 0 pe 2 e tcoagulantr th s cenfoun y wa b t dt I . impossible to obtain smooth coagulation with formic acid, immediate clotting taking place on addition of its solutions. It is of interest to note that a patent claiming the acceleration of acid coagulation by addition of a soap has been filed (13). Smooth coagulation was, however, obtained by the use of 0.3 per cent sodium silicofluoride solution. The quantities used were adjusted o product e rapid coagulatio d lesse an ne possibilit th n f pooo y r distributio e emulsionth n f o shoul y san d ten o breat d k after addition to the latex. The coagula were passed through a sheeting battery and dried in air at 120°F. for four days. Plasticity measurements befor d aftean e r masticatioe th f o n samples were mad Williama n ei s plastometer. The e recordeyar d
s 1Ja 30 valuethicknese th r o s whico t s pelleha t weighin grain4 g0. s is compresse minute0 3 n di stemperaa undet a . weigha rkg -5 f o t tur f 100°Co e . (14)n economA . n timys i effecte wa e y usinb d g
a modified procedure whereby the D3(; value was obtained from f correction o a D e 9, us readine th s y givegb n Tablni (15)1 e .
TABLE I
Amoun subtraco t t o t t I>9i measured obtain D3i>
51 — 60 14 61 — 70 IS 71 — 80 16 81 — 90 17 91 — 100 18 101 — 110 19 111 — 120 20 121 — 130 21 13 oved 1 an r 22
It was felt that a test of initial plasticity should be supple- mente a masticatio y b d n test whereb y additionaan y l softening e presenc th e adde duth o t ef do e material woul e indicatedb d .
A D.jC valu s thereforwa e e determined after passin 5 gram1 a g s sample ten times through a cold 12-inch mill of roll diameter 6 inches f .01o , 0p differentia ni e incheffec a Th n o .d t an l 4 11. : TABLI I E
Effect on Plasticity of the addition to Latex of 3 per cent, on the dry Rubber, of Soaps and Fatty Acids 1 | STEARATES OLEATES PALMITATES LINOLEATES
y i 0 ? t« .u 60 'ia'-w o -^ &JD -^ 'i bH 'Sc"-^j 6fl 4 J! O &5^D. OD jJ M i ba U-u i 'BO S» a~c 'G..MC - SM_ cPc a i* Me c HO "* ctf o; •dOS5>: -«S t<-5co 'S-rto •S'3 § ^ Irt TC ' S -IH £ r a2.SS £co ! -<•-
Plasticity of control rubber D30 1.63
Plasticity controlof rubber aftergrindings,10 D 1.32 x 94
crude rubber was a softening of approximately 20 per cent, as show t thi Tabln bu ni s , varieIV e d considerably between different samples of rubber and consequently a control test was always necessary. e plasticitTabln I th I I e y result e recordear s r foufo dr fatty f theio 6 r2 acid soapsd an s , together wit percentage hth e softening, initiall d -aftee masticatioan yth r n e testcalculationTh . e ar s e plasticit baseth e contro th n o df o yl rubber befor d aftean e r mastication, softening being calculated as a percentage change
in D30. From the results shown it appears that the free acids do not exert pronounced softening effects whic r practicafo h l purposes e identicalar , whil e soapth e s generall e morar y e effective than the acids. e threOth f e soluble alkali soaps sodium soaps appeae b o t r slightly better but the quantities required to stabilise emulsions of other substances would have littl ee plasticit th effec n o tf o y the resultant rubber. Apart from copper oleate, which would not be considered as a compounding ingredient in normal manufacture, the lowest initial plasticity is associated with nickel oleate. After mastica- tion, however, it is little better than zinc oleate and inferior to zinc stearate. Nickel would probable th f o e regarde b ye on s a d dangerous metal o associatt s e with rubbe e know vien th i r f wo n effects of cobalt to which Stevens has drawn attention (16,17). e hardeninTh g produce n oleatti s bee y ha deb n confirmed, the metal evidently displaying some of the affinity which is used in e procesth f cyclisatioo s n produced under other conditions (18). e zinTh c soap f steario s d oleian c c acidsi have- mosre o t t commend the s softenersma . Although initiall t ysofte theno o nyd rubber to the same extent as nickel oleate, their effectiveness is much enhanced by the subsequent mastication. They are materials of proved safety in rubber compounding and not subject to the doubts associated with a metal such as nickel, apart from the question of cost.
THB EFFECT SAMMTJOE OBTH ' N OF PINR KTA f tho ee moson s i Pint r effectiveta e softener common i s e nus f intereso s o examinewa t ant t i d s effecit 1 t when incorporated into rubbe additioy b r latexo t n .r pe Amount 0 4 o t f froo e s mon y rubbedr e rth cen wern o t e added. A number of emulsions were prepared by first warming the waten i pin r ta re containing potassium oleate t 70°C A e pin. th . e r n stirrinbroko ta p u e g into small globule formed an s a partiad l emulsion. This was then passed through a hand emulsiner three times together with a further quantity of water, such that the final volumes of the emulsions of different concentrations were all the same. These emulsions were adde o frest d h field lated an x the mixtures, which then had D.R.Cs. of approximately 12 per cent, were coagulated overnigh r cenpe tt 5 witsolutio0. a h f o n sodium silicofluoride. The coagula were passed through a sheeting battery and dried in air at 120°K. for four days. TABLE HI Plasticity of Rubber from Latex containing PineTar
Concentration , ...... After o r» • i Softening of Pine Tar Initiamll AD» iiun gnnding^HnHinffss {softenin(Tnitiallg : (.altef afterr on dry rubber ' P,V n ; Ds» (HI B grinding) r centPe . m tig. i; in Fig j) P(.r cent Per cent i i ; 0 1.57 | 1.28 — — 1 'i 1.56 1.25 | 0.6 | 2.3 i 2 1.57 1.22 0.0 | 4.7 i 3 i 1.50 1.19 4.5 7.0 j 4 1.46 1.18 7.0 | 7.8 1 | 5 1.41 1.14 10.2 | 10.9 1 • 10 | 1.26 0.97 19.7 24.2 20 0.98 0.80 37.6 37.5 30 0.81 0.62 48.4 51.6 40 0.67 0.54 57.3 57.8 TABLE IV Mastication of Crude Rubber from Latex used Preparationin of Samples in Table III
Numbe f o milr l , grindings D» Softening Fign i ) 1 .V (I r centPe . frf .010 inch i 0 1.57 _ 5 1.41 10.2 10 1.25 20.4 15 1.15 26.8 20 1.08 31.2 30 0.89 43.3 50 0.64 59.2 70 0.49 68.8 100 i 0.38 75.8 96
I I I I I I I FIGURE I. 1-5 COMPARISON OF PLASTICITY CHANCES DUE TO PIWE TAR AMD MASTICATION.
1-3
I'D
in 4J =1 6
IDA BUBBER CONTAIWIWC; PIN& TAR. INITIAL PLASTICITY , » rub - ». PLASTICITY AFTER. CBIWDIKJ TIMESO GI . E SAME RUBBER WITHOUT PIN&TAB. PLASTICITY AFTER VARIOUS CEIWDIWG5.
IO 2O 3O 4O 50 PEECEWT PIW& TAR. 10 20 30 4o so 60 TO so qo 100 CRIWDIWC5 (CUUVE IV) 97
The effect on plasticity is shown in Table III, while Table IV shows-the relative effect f variouo s s amounts f milo l grindinn go rubber prepared from the same latex. The results are plotted in Figure 1.
In Figure 1, curve IIIA gives the initial D values of samples 0
containing different amounts of pine tar whils3 t IIIB gives their plasticities after the standard mastication. Curve IV shows the effect on plasticity of different amounts of mastication of crude rubber from the same latex. It will be observed that relatively large proportions of pine tar produce a comparatively small degree of softening. e plasticitTh y which different manufacturers consider desirable varies considerably but D30 values of 0.8 and 0.7 are representative of some requirements. The different treatments which will
produce these! plasticities from crude rubbe f Do r3 0 e b 1.5 n 7ca obtained from the curves and are as follows:—
Rubber of D30 0.7 is obtained by:— (a) Inclusion of 37 per cent Pine Tar. 0>) „ „ 25 „ „ „ „ followed by 10 mill grinding t .01a s 0 inch. mil4 (c4 )l grinding t .01a s 0 inch.
Rubbe s obtainei f D8 o r3 0. 0 d by:— (a) Inclusion of 30 per cent Pine Tar. (b) „ „ 19 „ „ „ „ followed by 10 mill grindings at .010 inch. mil4 4 l ) grinding(c t .01a s 0 inch. Rubber containin e higheth g rs wa proportion r ta f o s surprisingly firm. That containing 40 per cent showed only a small tendency to plastic flow but the sample containing 30 per t exhibino cend di t t this tendenc s appearancit t d no an y d di e suggest that the rubber was diluted with such a high proportion r cen f pe pineoo ftr o ta liquid e incorporatiotw d Th .an e on f o n gave products which, although air-dried, had the appearance of medium and over-smoked sheet.
A POSSIBLE; COMMERCIAL APPLICATION A general market for rubber containing pine tar or any other compounding ingredient is not at present visualised. But since e incorporatioth f largno e amount f pin o r sint ta e o rubber seems practicable e suggestioth , s madni e that master-batch preparation on estates might be worthy of consideration by rubber manu- 98
fa.cturers. After the addition of emulsified pine tar complying with the manufacturer's specification, latex could be treated by modifications of present estate methods. Modern large-scale production of pine tar and stearic acid master-batches involves disintegrating the rubber, dipping in the heated softener and batching on an apron-mill. By using the suggested process, cost reduction of equipment and processing appears possible, at the same time eliminating from the rubber works an undesirable series of operations, whilst also offering the advantages of master-batch compounding. Ther e obviouear s difficulties militating against suc hschema e t forwar pu beliee s th i suggesy n t fdi i ma s novethat i d t bu i tt an l possibilities making it worthy of closer consideration by the manufacturers concerned. THE EFFECTS OF OTHER SOFTENERS In order to obtain more data upon the softening obtainable with conventional softeners, seven others, of which two were pro- prietary, were teste n comparisoi d n with pine tarr thiFo . s purpose one concentration of softener was sufficient and 10 per cent was selected. The results are shown in Table V.
TABLE V Effect on Plasticity of the addition of various Softeners at a concentration of 10 per cent, on the Rubber
Softening After 10 Softening (After Description Initial grindings (Initial) Dao grinding) Dso r centPe . r centPe .
Rubber without softener 1.62 1.32 _ _ Pine Tar 1.30 1.02 19.8 22.7 Tackol 1.30 1.03 19.8 22.0 Rubberinl Ge e 1.2S 1.00 22.8 24.2 Rosin Oil 1.28 1.00 21.0 24.2 Stearic Acid 1.24 1.01 23.4 23.5 Lanolin 1.18 1.00 27.2 24.2 Petroleum Jelly 1.26 1.02 22.2 22.7 Coar Ta l 1.35 l.OS 16.7 20.5 99
No outstanding effects are indicated in the table. This was not unexpected, as the conventional types of softeners are more in the nature of diluents and lubricants rather than chemicals which bring about alteration n structurei s e indicationTh . e ar s e thapreviouth t s remarke subjecth n f o master-batcheo st s prepared from latex are applicable to other materials used in quantity, in particular stearic acid.
Acknowledgment
Thanks are due to the Singapore Rubber Works Ltd. for supplying the rubber grade chemicals used in this work. The practical assistance given by Lek Kay Tee and A. G. Lee is gratefully acknowledged.
Literature cited (1) B.P. 368,902. (2) " SOFTENED RUBBER " India-Rubber 6 (1933I.8 7 7 ) (3) CHOU?T . E . P , India-Rubber6 World, 91 (19352 )4 4 India-Rubber 9 (1935I.8 3 51 ) 42 ) McRoBERTS(4 . C . D , India-Rubber2 World, 95 0 7 d (1936an 2 5 ) (5) MARTIN, G., DAVEY, W. S. Fourth Quarterly Circular of AND BAKER, H. C. the Rubber Research Scheme, Ceylon (1933) 102 (6) RUBBER PEPTISING AGENT Du Pont Reports Nos. 193, 198 d supplemenan . 200No .o . t 3 t AN 2 . . D. No 1 No , No B.P. 480,178, B.P. 490,292 ) VULCAME(7 X (I.C.I.) B.R.M.R.A. Summary f o Cur- rent Literature 16 (1938) 658 (8) O.X.A.F. (U.S. RUBBER Co.) India-Rubber World 97, 4 (19389 5 ) ) MARTIN(9 , G., DAVEY. S J.R.R.I.M. . W , 5 (1934 7 30 ) D AN BAKER . C . H , RHODES. E , (10) MARTIN, G., DAVEY, W. S., Ibid 299 D AN BAKER. C . H , RHODES, E- 100
(11) MARTIN, G. AND RHODES, E. Ibid 302 (12) BLOW, C. M. AND Trans. Inst. Rubber Ind. X GARNUR . LT ,. (19356 44 ) (13) S.S.P. 1,717 Wingfoot Corp. (14) DE VRIKS . O , Archief Rubbercultuur 9 (1925 ) 223 (15) MARTTN . G , Private communication. (16) STKVENS . H . W , Trans. Inst. Rubber Ind.V (1930) 374 (17) STKVENS . . P ANH Trans.. . DH W , Inst. Rubber I Ind.X (1935) 185 (18) CHKMJSTRY AND TECHNOLOGY DAVIS, C. C. AND BLAKK, J. T. 661 ov RUBBER.
Kuala Lumpur 21st April, 1939