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 e f 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 e rubbetth 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 ! -<•- <co C-M- Sa 33c ; E-I^Co O _^ '3 . S.MS o ' .' v <D -w i 0) <E «H "-' -». fi OJ Ci— , Q) •*-* O> «fi W : j gfi «pg C5|S; S ' °C.S : Sag CScSl =o S.sfi s~ •_ «£^.tf 5t t5" ' C.S **-t & Si - i-nS." ai % 1&£ b-Cfi " j -IS °bS | o-cfi ! bo 2Q '"""'•^ CQ bn ^ ' 02 ~" s '&* j i • ^^ ! | 1 | Fre e. .. Aci1.51d 1.19 7.4 9.9 1.48 1.22 9.2 7.6 1.51 ! 1.4 1 1.289. 0 i 4 7. 1.17 9.2 11.4 Ammoniu . .. 1.5m5 1.23 4.9 6.8 1.47 1.23 9.8 6.8 __ — — - 1.47 1.13 9.8 14.4 Sodium ... 1 1.41 1.21 13.5 8.3 1.46 1.22 10.4 7.6 1.47 1.15 9.8 12.9 __ _ i _ Potassium ..