September 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
1149
the (lialkj-I hc~nzcnc~i, the ortho compounds have the smallest rcfractions. Thi. values for meta and para isomers are practically the sani(1. 1Ieta rompounds with fewer than twenty carbon atonii 1i:ivc~,-!iglitly lower refractions than the corresponding para structurw; atmvc. ) i = 30 the reverse is true. -inat tcniiit WL.- iii:atle t o ilc~tc~rmiiic: the eficct of branching and of pwition a n d tylie of urisatur:ttion i l l citle chains on molal refractioii, \)ut thc- tlatn n-ei'e too [I>\\- and too iriconaistent to permit . I n general, tile effect of structuw on molal :iplicw,- tu be more pronounced aillong rnorionucle~ar i~c~fi~ac~tiij-i. :iroimit ic.3 111:iii anioiig t h e :iliph:iti r 1iytiror:irl 1011i.
Effect of Humidity on Properties
of Plasticized Ethylcellulose J
W.P. JIOELLER
.&KD S . T.4YLOR
Celanese Corporntioii o f . d m e r i m . \eictrrk.
T h e purpo>e of tlii. in\estigation was to study the effect of Tarying humidities on the properties of plasticized eth? Icellnlose. ucing a typical nonsol\ eiit and a t? pica1
sol\ent modifier. Standard i.S.T.\I. procedures \$ere used for -uch properties as Izod impact, flexural and tensile strengths. a- \$ ell as Roe1.w ell hardness and heat distortion. Compari-on of the effect of humidity with that of plasticizer content show 5 that the absorbed moisture changes all but one of the properties in the sanie direction. The siniilarit? itifhe charipes of properties of the two t)pes of modifiers v ith increasing nioiqtnre content is discussed, as the reaiilts indicate the nece-iity for a re\iew of the method for defining plasticize- u.ed in eth? lcellulose.
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S 11.1SY plaQtic; t h \-ariation iri cliniatic conditions affects the properties of tile material to a considerable extent. The quantitative amount is of importance to the engineer and chemist
making use of'the plastic. It is Itnorm t h a t temperature affects the properties of plastics to a considerable extent (4,5, 6 , 14, f5, 18). Published information on the effect of humidity on physical properties of cellulosic plastic materials with various plasticizers has only recently appeared (18, 20). The purpose of this investigat'ion was to evaluate the effect of humidity on the different
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propertiea ~i erli~-l~.c.!luloic, iv1111~1i p l a ~icizetl t
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net ion I J ~plusticiziLrs frcquently t i i f f ~ , i ~ c ~ i i t i u ti(,t\vcen lt. t\vo t)-pc:s ( 1 1 , li)--nanicly, the Sl3lVCJil t y1r1115,\vlii(,li a r e yi~iic~rally considercd t u Iiavo n tlt~fiiite cffect o n t lit, polynic~r,and noiisolvent type>, ivhicli do not sliow a sii1v11'iitc,fi'c,c.t o i ' , w t nioit, only a clight ,welling artion :it levatcd ti'lli~,cl'utlll't..;. T~i-orc~pi'e~c'iitat ive plasticizers i w r e srlected--butyl stc'arate (solwiit type ) and ii mineral oil (non?olvcnt type). Thi~method ntl 3Ieyer ( 7 ) was used in this ,-.valuationfor dextermining solvcnt csffect on the resin. -1 10-gram sample of the polynier ia placed in 100 cc. of the test plasticizer and heatid for one hour a t 1SO' C. I t the end of this period the test tube is removed from the bath and the contents examined. The chemical is considered to be of the solvent type if a completely clear solution is obtained. If large globules or masses of undissolved portions of the plastic remain, the plasticizer is a nonsolvent. Gradations between these tn-o limits are noted and considered as semisolvent type or seminonsolvent in activity. I n this test at 180 a C. the ethylcellulose is substantially dissolved by the butyl st,earate, n-hile the mineral oil does not dissolve any noticeable portion of the polymer.
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1NDUS.TRIAL A N D ENGINEERING CHEMISTRY
1150 I 3.0
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Figure 1
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T E N S I L E ST.,MINERAL O I L 1 T E N S I L E ST.,BUTYL S T E A R A T E 2 FLEXURAL ST.,BUTYL STEARATE- 3 FLEXURAL ST.,MINERAL O I L 4
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Vol. 39, No. 9
rotary grinder, using a screen opening of 6 l l 6 inch. The plastic materials were dried for 30 minutes under inlrartstl 1anip;i to remove all residual moist u r e and moltled on a 1-ounce injection molding maciiinc into .LS.T.I\I. test bars. The niarliirie, drsc.ril)c,tl by 13x11, Le , and LIelnycliuk (Z), is similar in tlc-igii to the two-piston hydraulicall>. oprrat c d i i n i t i uied in h injection molding irio bar c.al-itic+ duytry. The niold contain-: t ~ test of poli~lwrlstcd q5 X X inch in size. I n iiioldiiig tiic t w t conipositions all v:i~iaCltescept tlic cylintli~rrmiperaturea m r e kept constant. Thc cycle !\-as Iii.jt1 at 30 seconds and tliv niold temperature a t 120 F. The piston pressui't. and $peed did not change during the collection of samples. I n each composition the lon-est injection molding temperature t o fill the mold COIIIpletely with p l a d c Fyas determined under thc above eonditioria. -in operating tcrnperaturc of 50' F. higher on borh the front and back cglindcrs was then used ior producing samples. This procedure gives reproducible operating conditions and is necessary in order t o make a valid comparison of the physical properties of plastic compositions ' ' of different formulation. according to Ball, Leyes, and Ilelnychuk (2). The .1.8.T.lI. trnsile test pieces were molded on a 2-ounce injection molding machine (Reed Prentice Coi,poration, model loa). A cycle of 45 seconds was used, and all other variables were held constant except temperature. The temperature was determined as above for this machine and a tno-cavity tensile bar die. The molding temperature for producing specimens was 50' F. above the lowest value found to give a complete molding. Sufficient samples were molded t o obtain all properties at the various conditions tested. and random selection Tyas used in taking pieces foi. any given test and con&tion.
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Figure 2
Other methods, such as casting f i l m containing the plasticizer used to evaluate its effect on polymers ( 8 ) ,also show the difference in the action of butyl stearate and mineral oil on ethylcellulose. FORMULATIONS
The experimental compositions were prepared t o contain 100 parts (86.2%) ethylcellulose, 15 parts (12.897,) plasticizer, and 1 part (0.9%) stabilizer. The ethylcellulose had an ethosyl content of 46.3YGand a viscosity of 103 centipoises. The vixosity (8) was determined by drying the flake for 30 minutt,s a t 100" C. and then making a 57; by weight solution, the solrcnts being a 70: 30 mixture of toluene and ethyl alcohol (8jC; 2B dcnatured). The ethosyl content is obtained by a semimicromethod in a motiified Zeisel apparatus (19). The plasticizers were of standard commercial quality, the mineral oil being mainly aliphatic iii nature and meeting the specifications of 0.860-0.SiO specific gravity at 60" F., a Saybolt viscosity at 100" F. of 125-135, and a pour point of 10 F. The plasticizers with the flake were processed in a small laboratory Banbury miser. The material, after thorough mastication for 5 minutes a t 300" F., was removed from the mixer, sheeted on a small two-roll mill: and ground into pox\-der through a standard
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