Low Temperature Impact
Strength of Cellulosic Plastics W.E. GLOOR Herrrcles P o w d e r C o m p a n y , F i l m i n g t o r i 99, D e l .
oi 600-gram \vi,iglit \vert' ni:tdr. Teat bars called for by A.S.T. 11. AIcthod D 256 were moldcil i n a laboratory transfer pot inlo I ' 2 X X 5 inch bat,.; and coiiilitionrd. These tcsts were rq)rb:iliz(l 0 1 1 a larger scalc, uiing 7 - to 10-pound batches of plastic mndi. l)y SOIL vent nicrhoils n-ith a 4.7-gallon stainless-clad 13aket,-l'c'I k i i i niisc.r ivitli kriu6eu hlaticj; later the plastic \vas rollcd to it sliclc>t and graiiulatcd,and the granules \vere dried. ntially the w i i ( result3 n-ere ohtaincd d i c n t h e e larger batchcs wi'w iii,iwlioiLX 5 invh tiars, notched, and tt,stcd. molded into ,'? X Ethyl cellulose hatchos were prepared in 3.3-pound balc.lic'. I J ~ hot niilling the flake antl separately premised plasticize1 o n :I 6 X 16 inch Thropp iiiill n-ith chrome-pl:Lted roll facos. 'l'hrcorrect n-eight of dry ethyl cellulose was weighed into l)i.:ilwr.;, and veighed portions of plasticizer, stabilizer, and I u ~ i r i r i i ~ i i , S T I : S S I F l E ~ I liiitc,rest in the pi.opei.tici. o f p l a 4 c s niaterialsat hcattd to 300-340" F., n-ere .qtirred into the mix by hand. Part sulizc~rotcnlpc'ratul'es ti loped during the n-ar as a result or' > on the turning roll, with surface- :it 280the 11er~1 aircraft p a n s and ordnance coniponc~iit-n-hich i v ( ~ ~ i l d of tlic inis ~ a placed 300" F., anti niilled into :I blanket, and the rcmaindor oi' t h i , l ) : ~ tr.11 function propclt.ly ovc'r a n-idr teniperature rangt~. This iiitcrcst, ddi:d as t h r nip {vas \vid?ntd A1kx)ui 25 minutes \vt'i'(' r('continucs into the pre,cnt peacetime period :ts a rcwlt of the rice& quircd t o i'(Jrii1 :I ~ v c l lcolloidcd shecxt. This \vas cooled, ~ I ' R I ~ U of product tlt+iers in the aiwrait, autnniotiv-c,, and rc.!'i,igclntor l:itetl, and dric,tl t o lex? than 0.4% volatili niaterial t w t o w tt'st industries in a(1apting the rol:~r and style possihilit iw of thc, rc.1hai.s 'war(, injection niolticvl. T h e ,stantlard ethyl(srlluloitLlest lulose plastic.; to the protlurtion of plasric part.< n-1iic.h \\-ill funrforniiila ivits 100 part.: c.tliylcc.llulosc plus plasticizc'r, 2 part i tion propell?- at lo\\- temperatures. Such peacetime uses ~voulcl m1~tliylplieno1,ctncl 0.73 part cwlcium atearatc,. be, for c ~ s a i n p l in ~ ~nircmii't , c Introl klI(Jb5 anti wiiidwrec~ns.autoFormulation of cc~llulowacetat(' plastic was csrricd out ii-iiip :t motivi. hard\vare, ~twi~ing-:vheelcovering. :md rcxfi,igc,i,ator standai,d plastim grad(. of flake niaterial (tSi.070 cornbineil awtic breakri,strips, trim, and panelling. acid content, 50-second Hercules viscosity, rquiv:ilent t i l 1.25 The purpos:" of this article is to 4ion- how tlic ha*ic. qualitici of intrinsic viscosity) with various coniniercial plasticicellulow tlixrivativ(xs and formulating ingrcdicnts can be chosen to t r k i c viicosity is defincd by Iiraemer (3):i.* follows : provide t h r moat suitable mechanical propcrtie. for plastic compountk entering w r h uses. -1s a simple criterion of suitahility [ V I = (!Z0 q..,/C the iniyxict strcmgth of the plastic materials ha. ticen selcctetl, since it is pc~liapsthv liest singli, nieawrc of thi, toughness ~vliich o > i t -of iiintr~ial.used i n tllir w i r k wa': i i i ~ ~ : i > u t ~ ~ ~ ~ I is soupkit i n ct~lluloncpla*tics and apprars to 1x3 rhe most criti(ma1 as follo\vy: Solutiolis ~l 0.1, 0.25, and 0.5 p~;rcent ~[~iic~tiii,:iii(iIis mechanical propt~i'tygivi~iiin the variour I.S.T.11. specification; ivrrc prcparcd, using awtone a s the jolvent for cc~llulo on rigid c t ~ l l u l o ~ i~noltling ci nxiterial?, such a:: D 706, D 707, anti and 8 : 2 tolucnc:alcolicil for cthylccllulosc viscosity, I ) ( I h i ~ s i * D 787. -411 plii~tirizcd thernioplastic compoqitiow sho\v con.-olutioii \viis nic~asurcdat 25 ' C. uqing an Ost\valtl visc.omc~ter. sidwil)l(x variatioris i n mechanical propct,tie, xvith tmipcrature; and data \r.c>recixti,apolatid to zero cmncentration tiy uying tlic thcx chcirigc~in impact strength, in addition t o showing a largc PO.itr graph IJC v . ~C. 2's. conwiitration. The ratio of cellulo centxge c.h:tngc, with teniperaturc, is an rwil!- measured! i~ccpror r a n g d so that all formihtion. lint1 t I(' s:iiii(' . ducihlc. iiitlicatirin of these variations. It is linon-n that as the harclnws i~egctrrll~~ss of t h e pla5tirizi.r used. Thus, thc lo\v t cnia n i h w t tenipc,raturc cliwcase?, the impact strc,rigth- of thc, cplpc'raturi' impact strc~ngth; c o u l ~ lt w ronip;trcd for f o r ~ n u l : ~ t i o ~ i ~ lulosc~phstics alyo tlec1,e:w ( 7 ) . H o w v c r , for niost civilinri uses the Ion-cxst tcnipcrature to Tvhich plastic; article.: are likc.1)- to be Data are shoim in T a h k I. This pcrniiti ed t,he choicca Iii phi+ espo-rd !vi11 not fall belon- -40" F. Hence the twt ivorlc TT:~,. Ion- tempclrature impact, propcrt iw, and designid to rsamine the Ion- tenilxrnturc imp:ict propcrticv r)i' pii u d i n formulations t(i csploi,c, t IN. thesuc plastics at -20" or -40" F. tTffvct o n Ion- tt.inpc~i'aturcimpact caused by Anlw or x w i t L f l viucosities and arc~tvlation. E iitially the sanw p r o c e t ~ u i ~~c v~ : i ~ i'OllOW(Y1 f O l ('1 h ~ ~ ~ ~ ~ ~ ~ l ies, l ~ Comiul;ttion> O i ; l ~ I~xiiiggivc,ii i i i TEST SAMPLES Table 11. Basic raw nintcrials for the teats were coniniercial gIadw of ;it thc tinu, the plasticizer ~c~lvction work \vas done wit 11 celeellulose acetate and ethyl cellulose produced by Hewules I'o\\--dcr til, t h c a conditioning procedures arid I o n tenipc~t~uturt~ Company. To crtend t h c range of observation in mine of t h c tehting procedures of .l.S,T.lI. had not hern fully stantia~~tlizcd. tests, srniiplaiit batchci of tliesc materials. nicetin:: commercinl These tests \\-err nintle by conditioning tmt bars at 70" F. and SOY, requiremtmts of quality arid having unusually high viscosity, a l w relative, humidit?- for 24 hours prior to low tcniper:rturc rontiitionwere includcd. Commercially available plasticizers were used. ing a t -20" F. These bars were conditiooud a t least 2 l i ~ t l ar t~ Cellulose acetate batchcs Tvcrc prepared by a solvent process the low temperature, then put into the Charpy machine which similar to that ustld by Gilbert and Gloor ( 2 ) ,escept that batches was a t 70" F., and teeted within 15 seconds All other tests w r c
Elploration of the effec~cof plasticizers, degree of cubstitution, and intrinsic \iscosit> of eth>lcelluloses and r~elluloseacetate< used i n plastics show ed that both choice of pla aid in producing materials of iniproted l o w temperature impact strength. I*to plaqticizers, the cwefficieritc of \ i w o s i t > change with teniperature, aiitl the ani011tits of loosel) boitnd pla5ticiLer beem significant. I qe of eth>Ic*rllulo~e with a n intrinsic \iscosity aho\c. 1.3 and of vellulose acetate approaching a n intrinsic \ iicosit! of 2 also enhance- *uhzero impact propertiec.
I
1125
INDUSTRIAL AND ENGINEERING CHEMISTRY
1128
Vol. 39, No. 9 UlSCUSSION
~ PLASTICIZERS USED TABLE 111. VISCOSITYD A T .FROM
Dierhylene glycol diproiiionnteC Diethyl phthalatec Dimethyl phthalateC Tripropionin TriacetinC Triethyl citrateC Dibutyl ta>tra:eC 3Ietliyl phthalyl ethyl glycolateC I l e t h y l Cellosol\-e stearated Butyl Cellosolre stearated Dibutyl phthalate llineral oil
6 3 12.5 21.2 56.5
2.3 3.7 3.9 3.3 4.3 G.6 13.0
0.G63 0.45 0.39 0.50 0.34 0.31 0.23
73.4
14.4
0 20
3.26
3 7 8.8 10.8 7.0 13.4 0;) 7 39.5
7.8 12.6 13 3 10.8 11.8 22.5 44.2
7 8 ,,G Solid 11.2 14.7 81.3 8.8
49.0
14.2
,... 10 5 13.7 76.0 8 2
20 9
23.8
19.G
9 8
14.6
49 9 1 tricresyl phosphate: 1 16 2 methyl Cellosolve stearated 695.1 Castor oil, XAA grade
16.4
17.3 18.5 71.8
$indo1
~iscosity-temperature coefficient C [-sed with cellulo-e acetate. d L-sed w i t h ethylcellulose. e Calculated from niixrure data. f hbsolute r i s c o s i t y In centipoises.
b
,...
0.6Re 0 ,,515 0 39 0 28
5.9 5.4
21.1 4.9
0 60
8.16
0.41
9 2
5.0
0.5.3
39.9
4G.F
11 7
0 9.5
20 8
13 1
7 1
0 4; 0.19
408.3
=
8 10 1
1201
6.50;
Considering the foregoing esperinielital findings, it appears that choice of the proper plasticizer arid a cellulose derivative of intrinsic 1.5will in general give the beet iiiechanical properties to cellulose-derivative hot-moldirig plastic:, at low temperatures. T h e steepness of the viscosit>--temperature curve of the plasticizer may he related to the subzero impact strengili of the plastic made with i t ; this finding i j i i i accortl \\-itli the esperience of Tyorkers in the viiiyl field, ,such as Reed ( 5 ) and Leilich (4). This shc~uld offer a relatively easy way t o evaluate nvtv plasticizers lr-hich may be suggested for thi? purpose. Hon-ever, othcr criteria may be equally useful i i i iimkiiig thi- selection. For in:raiice. if the i l a t n of Ford>-ce arid Meyer (1) cm the niasinluni amount of plasticizer hcbld iii c.ellulo. havirig viscoeitytemperature coefficielits shown in Figure 6, i t will be fourid that tlicj .smaller the amount of plasticizer n hicli is pcrinaiicntly t~outicl to the f l a k , the better \\-ill he the 1017 tcmperaturc. impact alrengtlr
reiati\-e kinelnntic risco-ity a t 50" C relnri,.e killell,ntlc v l l c o z i t y a t 250
c.
TABLE Iv. COMP.%RIsOS O F I S J E C T I O S - L I O L D E D PL.4STICS FROM CELLULOSE .~CET.ITC OF CSUAI, ASD HIGHISTRISSIC VISCOSITIES Formulations L-sua1 ceiluiose acetate, 53.0C; roniblned acetic nrid content, 1.23 intrinbic \-i=co.itr High viscosity cellulose nre!xte, 54 0 ' ; con.blned aretic ncid content, 1.88 intrin-lc v i - r o i i t y Diethyl p h t h a l n t e Dlnierhyl p1ithaI:ite
.1
13
.. .
-.I I -
72 1'
21
4 36
4.29
..
,
7.29 (1 5 4
0 50 158 2 60
VISCOSITY-TEMPERATURE C O E F F I C I E N T OF P L A S T I C I Z E R Figure 6 . Kelatiori o f \ arioii- I'lafticiLera and Subzero Impact 3trenctll of
0.20 N o l d i n p conditiunP Indirnted temp , 1'. I'runt cylinder Rear cylinder Cycle. t o t d . sec. Gnge pre-.ure. 1b.isq. in. l I u l d ten111 , 'I-. Duration u f higii-rate punip impulse, sec.
450
440
4:u
451, :i:i 9x0 17(1 4
3:1 S5i) 170 4. i 3
of tlic, t1at:i obtairietl iii this x o r k iiidicates that n placticizcr coiiibiiiwtioii consisting largely of diethyl phtlialatc would give the lxlst subzcro impact strength anlong those r o m niei,cid pla-ticizclr> most highly regarded fur pcrmancnce a n d general utilitj.. 1-sing niisrui,t+ i l i 3 p i r t s diethyl phthalate to 1 part of tliincthyl phtlittlntc~'i: pia-ticizer, csploration of a seiies of Conatant vi,+ co,qit,ysitiiiplvs of cellulose acetate, made \\-it11 acetylations from 53 tco 55': combined acetic acid content, slio\\-ed that the subzero inipact sti,eiigtli varied but little n-ith acetyl:ition. Hoivevcr, thi: i r i t i ~ i i i ~ ivi,*cwity c of cellulose acetatc can be a11 iniportaiit factor in iiiipri>vi~igthe lun- temperature inipact properties of plastics made from this ccllulose ester (Figure 7 ) . By raising the intrinsic viscositv of the flake used in coniDouiiding froin the usual lcvels of 1.2-1.4 t o a 1cvc:l approaching 2, impact strength a t -40" F. niny be improved at least 50%. Such plastics are readily injection molded arid slion- other properties well in line with those given b conventiolial cdlulo.?.e acetate plastics, as shorn by Table I\-.
Cellulose i c e t a t e I'Ia$tic> C ~ l l u l o r ra c r t a t r usrd hncl i n t r i n s i c v i i c o s i ~ : of 1.35 and conlbined acrtic acid content of 53%
MOTOR- NOTCHED
x
/
-NOTCH ED
01 0
I
0.5
I
1.0
I
1.5
I
2.0
I
2.5
I N T R I N S I C VISCOSITY OF C E L L U L O S E ACETATE Figure 7 . Relation between Intri~isic \.iicoiity of Cellulose ,icetate and Subzero I m p a ( . t of I'ln-!icc:clluloar acetatrs
had co,nl,inrd 33.0 a n d 5 5 . 0 7 ~
aci,l
Vl,ntcntb
INDUSTRIAL AND ENGINEERING CHEMISTRY
September 1947
1127
temperatures first set forth by Leilich (4). This author stated that, in the polyvinyl chloride plastics, the best low temperature toughness was obtained by using a plasticizer which changed viscosity least with temperature, and further s h o w d that the logarithm of viscosity bore a lincar relation lvith temperature. Kinematic osity vias used as a criterion of this behavior, incc the actual niolecular friction uncorrected or liquid density appears to govern. l a b l c I11 yivm the results of kinematic viscosity mcasurenic.nl.z on the plasticizers used for these tests. i'e seem to he n wlation tietireen the osity-tcmperature eoofTiciont of plasticizers and the l o ~ rtemperature impact properties of
that the strength of the material a t low temperatures rises appreciably with the degree of etherification of the ethylcellulose, with all types showing iathcr good impact strength a t this low temperature. The effect of viscosity of the ethylcellulose used in a plast,ic is shown in Figure 5, It appears that, below an intrinsic viscosity of 1.2, t ~ h eimpact ,strength of molded ethylcellulose plastics at lo^ temperatures falls off, in the G-type material used in making this comparison. Most commercial ethylcellulose plastics, however, are made from material of intrinsic viscosity from 1.3 t o 1.7, :md in this range the mateiial s h o w good low temperature which increases as the viscosity of the flake inAIaterial in the high end of the coniiiiercial
0
Z L 2.00
ol2 0 z
45.3% ETHOXYL
) I,
"
, W
$ Z
u!?
S
A
x
43.9% ETHOXYL
%
I.0-
i-\
#Mo
0# ,o'o) %
-
xic u
$
O
"0
N Pl
U
-
1
rt'
I
I
I
I
I
I
I
-
- L L
44 1;igure
1.
45
46
47
48
49
*/e E T H O X Y L i N E T H Y L CELLULOSE I X e c t of Snhztitution 011 subzero Impact Strength of' Et1i~Ic*ellolo~r P1abtic.s
(.ompnrisona a t flow of 275' F. d r n o i r d by circle: at Rocktiell R hardness of 95 b y cross. A f e t h y l c d l O d O l V e fiLCaratr used as p l a a t i cizer; all ethylcellulosrfi h a d intrinsic viscosity between 1.5 and 1 . 7
S%YISCoSTTY20 40
0
1
INTRINSIC VlSCOSlTY
1.0
100 I
1
2.0
I
700 SEC. I
I
3.0
Figure 5 . Effect of Intrinsic Yisrosity of Flake on Suhzero Impact Streiigth of Ethj-lc*clltilosePlastics Plastic rompusitions contained rneth)l C e l l o s o I ~stearate ~ as plaatiriaer: a11 rtliylcelluloa-s wrr? of 11.8 to 45.570
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
September 1947
of the plastic niade using it. This criterion should not be overlooked iii tlie preliminary evaluation of plasticizers for this purpose, particularly since (in the case of ethylcelluiose) certain ne11 known plasticizers such a3 mineral oil, which promote lorvteinpcmture inipact strength, fall out of line if coefficient of viscosity chnngc, i i the only criterion applied. It wail founti that the use of a cellulose acetate a t a high level opity will produce a definite iniprovemerir in tlie lox tcmpc~rntureimpact strength of the resulting plastic; this is also pardlri - ( I other experience in the field of high polymers. that thc. brittlenesj temperature of hat is, its mechanical properties d-as the degree of polymerization or thP iriri I I I P I C Yiscosity of this polymer increaqed. Since%.among (itlirr facliii~~ Tiie . low teniper:tture iriipact strength of d l u l o v :ti'c,t:ite pl:irti,.>1i:i.s b w n coti.~iileredtoo lon- for wcli uiei: a; trail
