Evaluation of Small Amounts of Synthetic Rubber * c
his paper describes methods for compoundi . . and testing small dmOUnk of rubbers. mixing, small mill is used for mixing the batche&nd det
T
mining the processing characteristics of the rubb The properties of the vulcanizates are detepin from small molded specimens. With 9 grams of rubber the following properties can be determined: general processingcharacteristics, stress-strain cutves for three cures, durometer hardness for two cures, Schopper rebound for two cures, compression set for two cures, freezing with respect to loss of snap, becoming stiff, and becoming brittle, and change in volume in Rve solvents.
B. S. Garvey, Jr.
Y
8. F. Goodrich Company, Akron, Ohio
ce and s a k e weighing8 to the closeat milligram. For eighings a triplebeam bdance accurate to 0.1 gram ctory. The guide is the accuracy required to avoid cant e&gea in the recipe due to errors in weighing. soften may be dissolved in a solvent and measured etricaUy, allowing the solvent to evaporate before use. nb may be kept in cellophane envelopes. Softeners, ur accelerators, etc., may he kept in small aluminum ea or m bottle caps. (Sea Figure 1.) These small batchas are mixed on special mills with rolls 4 inchea in diameter. The first mill used was made in the Goodrich shops and is shown in Figure 2; the distance between the guides is 2,5 The seoond mil, was the National Rubber Machinery Company (Figure 3), and the dintance between the guides can be varied from 1 to 4 inches. Both mills ere connected with s t m u and cold water. The gear ratios for the rolls are 1.47. The speeds of the dow roll are 10.5 r. p. m. or a surface speed of 11 feet per minute. The milling procedure and mill temperature will depend on the tYPe of rubber tested.
* g’.
N RESEARCH on rubber syntheais, as in any broad program of chemical research, it is a distinct advantage to he able to do all the work on a normal laboratory or test tube scale. With rubber, however, the standard laboratory teating methods require from 200 to 500 grams of rubber for each batch. Hence it was obvious that, if the advantagea of small-
I
.
scale work in the preparational stages were to be realized, a new technique of rubber testing would have to be developed. The use of entirely new and unrelated procedures has two definite objections. In the first place the new procedures must be thoroughly tested and compared with the older methods of testing or with the processing and we requirements of the new rubbers. In the second place the significance of the results of such new tests can be conveyed, even to experienced rubber technologists, only after considerable interpretation of the methods. It seemed best, therefore, to modiry standard rubber testing methods 80 tht they could be applied to very small amounts of synthetic rubber. More recently the shortage of natural rubber has made n e c q a reduction in the amount of rubber used for testing. Poor this purpose the eame small-scale, procedures are highly advantageous. While some idea of the quality of a sample of natural or synthetic rubber can be obtained from examination of the crude rubber itself, it is much better to know the physical properties of the vulcsnized product. This meana that one or more balanced compounds must be mixed and tested. The purpose of t h i paper is to describe a technique which has been developed in the Goodrich laboratoriea whereby, with as little as 5 grams of rubber, the straas-cltrain characteristics may be determined and with 9 grams of rubber a fairly compehensive evaluation can be made. This method has been used to evaluate polymers made on the 10-gram scale by Frylisg (3). Compounding and Mixing For weighing some of the ingredients of a 10-gram batch (in this paper the batch &e is given as the number of grsms of crude rubber in the batch), it is necesssry to use an analytical 1320
Figure 1. Two Completed Batches
November, 1947.
***
Figure
9.
IE;
Goodrich
AL A N D ENGINEERING CHEMISTRY
Mill
Evaluetlon of k i n g Propwtio
Processing propertha are evaluated on bohh the crude synthetic rubber and on the mixedbatoh. Ron $he crude material the eane with which a mootb band is fowted on the roll, the extent of the breakdown, and the time requiredfor b d d o w n are signi6cant. In addition, the B B B ~of adding.the various components, the degrea of dispersion, and the total batch time are signi6cant for the mixed batoh. MILLINGB-VIOR. The general appesrsncs and feel of the stock on the mill are good indications of ita milling behavior. Agoodstockgipesasmpotbshbybandonthemill mU and can be pulled eaaily inta long strings. Other bat&= may b d short when pulled out. They m y be rsgged and cracked at the edge of band. They may be duU or rough in aptxarana. They may crack acm the wbole band and became lncy. In eatreme 08888 thestoctfsl$off the mb. The thiclrness of the band on the roll may be important. Some stocks mill wall on a tight mill, bat become maoked and lacy on a loose mill. The batoh is ugulls mixed with a rolling bank, and to evaluate milling behavior, the appearance is noted at this stage and slao with t h e mopmed until the bank slmoet dieapwam. Temperature is li&viae an important musideration in
Figure
******
1321
I I 3. National Machinery Company Mill
stock temperatures, it is possible to malw a fairly acmuate prediction as ta the way a StWL will behavein factoryopem tiOnS.
P L a a n m . With such dbatohea stsndsrd spedmem for determiniog pldioity cannot be obtained. It bas been found, however, that molded hardnass peuets can be used,
,intheGoodriohplastometea. If the batch and the peuet molded plaeticities~~cloaeto those of the milled batoh. TACK.There to ba no quantitative measure of building tsck,and its evaluation in one of feel and expience. It is &bated merely by sticking pima of the rubber together, on and offthe mill, and pulling them. Chmmm& It is obvious that muoh of this ofpmasslngc' ' a is neither objeative ti- but dem& to a lane measure on the &ill and iqmrience of the &$&nS. Its-sucoaesfnl use' in tilie laboratmy has been,due iB hrge measure to tM consniemtiouS care and Obeervati
D.E.%user, W.B. in this typa of work the eame
er and -to we certain words to describe a s at debita stsgee.
f T.ct S p c i m w
temperature is m e a n d by a spwial assembled by P. R. Tarr of the Goodrich Laboratory. By obsening the milling
. ForStmMhin 4 in& low, 0-.
ta the ted
and 0.026 mved in a polished, chromium-plated identifying markera are of 0.001-inch
alUminum,Bheet, with the lettepins,made without the ribbon. The bat& at& is% at the desired thi&n€sa ,sndplbyed u+ ~ b n u t h a l f s n h o u r b e f o r e t h e ~ . a r e Stripm6alwayn ~t. ~twiththegrsinofthestool. : . ' h m % %R m O u N D , c MSET. Thesethree, JJwsummenta are made m ? z z z e 8pecimem which in a ianall diak or pellet, I/, inch in dismeter and inch thick. They are pEepased by rolling the stock on the mill.ta the neoeaesrg diameter and cutting oiT cylindea,wbich &.,d in a -plate mold. The teat speoimens are shown in Fi$lue 5. 'Rapn, H~etrsmsrs.. For these testa speoial cyUnt$em am molded in the name manner'w the hardnese peU&'.. .The. cylinders are 0.7 inch in diamter and 1 inch thick. TIm AND TxxPmi,iTwQ or CUTm. The test-spacimems ing, the. OOBare oured at my time apd hpmuttgn aompatible with the stsnt deaeotion aompoundd: ;.
.
~
,
T d n e Vduniz.d Specimens
.. For Uae w%h the d ' t e n s i l e strips, a @%with a '/rinCh &mow section waa dp.igned by Z. E?.&giwm (1). Thpse spedmema are &.from the strips with die. In ea& cam the strip is out on a heah surto a m :Gb I n n c l u possible cut. traio meewvements am made on a Scott $&le Bheets; with the adjusted for the narrow '
-
dhbball.
h-. 'Durometer hardness is m e 5 e . d
04
the hard-
pellet.
&BOUXD. For megsuring rehound a metel block, inch thick with a suitsble hole in the middle, is placed in a Schop per rebound w h i n e . The hardnea6 pellet is placed in the
Figure 4.
Mold for Curing Specimens
rubber. ~ E Z I N QTEms. The broken ends of the dumbbells, trimmed to 1 X 0.5 inch, are ueed for determining freezing temperatwe?. Fsy.qqmyn@a are made w the temperature of a methanol bath is.lowerad in increments of 5" starting at '7.59 C. At each t e m p t u r e the specimen is either good or bad. the^ tanperatum halfway between the last good (+) temperatwe and the 5mt bad (-1 temperature is reportedaa thefreesing temperature with respect 6 that kid. A is the tpst for freesing with reepect to spontaneous recovery. The specimen is bent double in a clamp. The clamp i9 mdddy opened, and ifthespeoimen O p m B up 80 that it does not fall out, it ie good. If it reonains folded and fallsout, itisbad. Bin flexibility under a dead weight of 50 grams. A rod of thin weight is rested on the end of the speeimen which is held horixontelly in a rack. II the ssmple bends it is flexible. C is the flexibility under a load of 250 grams. The prowdun, is the asrm aa for B. Din the brittle temperature. The rod 18reuted on the end of the opeaimen which is hard enough to hold it mthout bending, ainOe it is not flexible in the C test. The top of the rod ia then tapped with a hsmmer. If the specimen craeke it is brittle. b m FLIX Bmmsrs. The special pellet hae the dimensions qf the standard apeoimen usad in the Goodrich Flexometer (a). The test is run by the standard pmaedure. COh a L U A T I O N OF 9 GRAM8 OB RUBBEE. With 9 gmna of rubber, using a tread-type reoipe, the batch is mixed. B d d o w n , e s e and time of mixing, tack, and b haviok on the mill at 1W0,1 W , and 180' F. are noted. One strip in cured a0 minutea, two strips are cud 30 minutes, and three strip are d45 minutee, wnming an optimum m a t 80 minutes m d e h t OW^ at 45 minutes. Hardnem pellets a r e c u d a0 and 45minutes. Bbreesetrain meanwanenta are made on all atrip except m e of tlwa cured 46 minutes. EIdnees, rebnund, and c o m p d o n set are measwed on eaoh pellet. The extra strip
N
d
, 1%
b used to determine swell in hexane, bemane, wtone, and alcohol at mom temperature and in Circo lightpmopss oil at 180’ F. Freering charact8riatiea are determined on the en& of the broken dumbbellsfor the 30- and &minute OUIPB. With this information it is possible to tell wbther or not the product b worth further development. In f a d it b possible to make a fairly good estimate of ita commercial poesibilities. Advantegr and Disadvantages ot the kdun DIUDVANTAQES. The moat obviow disadvantage of this pmedure ie the repeated we of single test 6pechem. Kth a single specimen them is no chance to check d t a , and socidentd dafecte may spoil the test. The UBB of the asme mimen for measuring hardnw, rebound, and wmprpssiovl set may alter the results somewha& Another objedion is the probable presemce of calender grain in the tensile stripe. F’mbably the greatest objection, particularly in ita application to natural rubber, is the e x k v e breakdown obtained in the milling of d batches. h w e synthetic rubbers do not break down to the extent that natural rubber does this hss not bean a &ow problem, provided it WBB remgaiped. With natural rubber it in to we a warm mill and mix the batch rapidly. It haa been W b l e to adoptthe d mill p r o d u r e to the we of natural rubber batdm containing Bomewhere between 10 and 50 grams of rubber.
ADVANTAGES. The outatanding advanhgw of this p m cedure are the small mounta of material required and the speed with which the work can be done. Another advantage ia the accurate w n h l of mill and batoh temperatures. This make8 paesible the obssrvation of milling behavior at qmi6ed h p e r s t u ~ which ~ , is din predicting faatory proc&bhsrscteristies. A number of compsrisoIlshave shown that conclwiow b d on experimenta on the &inch mills agree well with those b d on eorperimente run on the standard 12-inch exp~aimentdmilla While the rapid adoption of a new material into fadory production depende primarily on the skill of the factory operstora, considerable wn6dence in this lOgram p d u r e haa been gained from the fadthat on more than one &on it haa bean possible to go frum 1Wam operations to factory production in a very short time. The predictions made from the small*ale evaluations have been in large meaBuTB ful6Ued in production.
Litemtun Cited (1) A. 8. T.M. Btandud. on Rubber produota, D412-41, Fig. 3-D (1941). (2) Ibid.. Das6-4(yT. Method B (1941). (a) hylink c. F.,~npubli.bed W X ~ (4) Garvey, B. E., A. 8. T. M.E&. 109, 18 (1941). 16) E.T..IND. ~mra.h. ANAL. . ED.. 9. 682 figan
w.
Unsatursaion of Synthetic * c * Rubberlike Materials * *
. Xeller-
La Verne E. Cneynoy The Goodyear Ti+%
Rubb
*
n,
+
Ohio4
*
he unsaturation of three ynthetj( butadiene Tpolymers hds been determined by a modified. tion of the Kemp-Wijs method. The reaction proceeds much more slowly than with rubber, 24 hours at 30” C. being required t o complete the addition reaction. The iodine values obtained vary somewhdt w i t h thesolvent employed, but in general are in the range of 85 t o 90 per cent of the theoretical values for straight linear polymers. The difference i s attributed to cross linkage.
HE quantitative determination of rubber unsaturation has concerned numerous investigators. The use of iodine chloride aa a reagent for this purpose (the well-known Wijs method) has achieved favor in recent years (S, 9, ld, 19, 16, 16, 26, 27). Under the proper experimental conditions, the addition has been shown to be quantitative, and substitution rmtions can be kept at a minimum (16,18). This procedure has likewise been rather extensively employed aa a measure
T
of the residual unsaturation of various rubber derivative (6, 7,8, SO,SI, Sd). This reagent docs not, however, add quantitatjvely to all unsaturated compounds, regardless of structure (16). The presence of a negative substituent on one or more of the unsaturated carbon a t o m inhibits the reaction; in fact, it may entirely prevent it, as in the cases of maleic or fumaric acids or dichloroethylene (9, 19). In other compounds extensive substitution may occur along with addition, aa in the case of the unsaturated terpenes ( 1 6 ) . The unsaturation of the polymerized d i o l e h should be of considerahle interest, especially in comparison with natural rubber. It should he of special interest to study the comparative reactions with iodine chloride, which has become practically a standard reagent for rubber. Kemp and Mueller (16) mention that polychloroprene, to which they erroneously refer as polyvinyl chloride, adds iodine chloride to only 30 per cent of theory. This could be due to two causes-the negative inhence of the chlorine attached to an unsaturated carbon, and/or possible cross linkage between chains (cyclization). It is well established that polychlorcprene is much less reactive chemically toward other reagents than is natural rubber (4). It is unfortunate that Kemp and Mueller did not state with more detail the history of the sample studied, as such a result might have shbwn some intereating correlation with the experiments reported in this paper. a m a s et 01. (5’4) report that the unsaturation of the class of materials known as butyl rubber is between 1 and 2 per
