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Artificial Bristles from Proteins
T . L . M C M E E K I N , T . S . R E I D , R . C . W A R N E R , AND R . W . J A C K S O N E a s te r n R e g io n a l R e s e a r c h L a b o r a to r y , U. S . D e p a r tm e n t o f A g r ic u ltu r e , P h ila d e lp h ia , P a.
ET H O D S for th e con
version of am orphous proteins into fibers have long been kftown. In 1898 M illar (3) prepared protein fibers by extruding heated protein- w ater m ixtures into air.
A few years late r T o d ten h au p t (6) m ade casein fibers by ex
tru d in g an alkaline solution of casein in to an acid b ath . R ecent im provem ents in th e la tte r process have resulted in th e com
m ercial developm ent of a textile fiber from casein. E arly in th e developm ent of p rotein fibers, it was found th a t the du rab ility of th e fiber was m arkedly increased by trea tm e n t w ith form aldehyde an d o th er tanning agents. These substances decrease w ater ab
sorption an d bacterial decom position of pro tein fibers an d make th em m ore flexible. W ater absorption of th e treated protein fiber is no t completely elim inated, however, an d loss in stren g th and shape of th e fibers in th e presence of w ater lim its th eir use.
T he present shortage of pig bristles an d o th er coarse anim al hair, such as horsehair, suggested th e developm ent of a protein fiber having th e size and properties of these n a tu ra l hairs. In th e following m ethod for preparing such fiber, heated isoelectric pro
tein m ixed w ith .w ater is ex tru d ed in to air; it is th en stretched and hardened, under tension, w ith quinone alone or quinone fol
lowed by form aldehyde.
q uality of th e casein, however, is of im portance for m aking fiber. To be suitable for th e production of fiber, a casein should be free from lactose and o th er whey constituents, be soluble in borax solution, and yield an aqueous ex tract having a pH near th e iso-electric point of 4.7.
In m aking casein fiber, 40-100 m esh commercial acid-precip
ita te d casein containing approxim ately 9 % m oisture is mixed w ith 70% of its weight of w ater, an d th e m ixture is allowed to stan d for an hour. T he h y d rated casein is placed in a discontinu
ous press of th e cylinder ty p e w ith a volume of 370 cc. (Figures 1 and 2) and heated slowly to ab o u t 95° C. to remove air and form a plastic mass. F ibers are form ed by forcing th e heated casein- w ater m ixture through a die w ith holes of a suitable diam eter, usually from 0.3 to 0.6 mm. A finely woven stainless steel screen or breaker p late is placed in back of th e die to assist in th e rem oval of a ir and foreign m aterial from th e casein before th e fiber is formed. To m inimize sticking, th e fibers are passed rapidly by m eans of ro tatin g drum s through a solution, a t a pH of ab o u t 4.7, containing 2% form aldehyde, 0.1% naphthalene sulfonate, and 10% sodium sulfate. T he fibers are collected on a suitable reel, A m e th o d is d escrib ed for p rod u cin g coarse fibers from
ca sein by ex tru d in g a h e a te d m ix tu re o f ca se in a n d w ater th r o u g h a su ita b le d ie. W h en th e fiber is str e tc h e d an d h a rd en ed , u n d er te n sio n , w ith q u in o n e , a b r istle m a teria l is o b ta in e d , w h ic h is b ein g te ste d in cer ta in ty p es o f b ru sh es.
P R E P A R A T I O N O F F I B E R S
A num ber of proteins, including casein, soybean, gelatin, zein, edestin, arachin, an d glutenin, have been converted into fibers by extrusion. However, casein was used entirely in th e developm ent of fibers suitable for bristle m aterial as described in th is report.
Several commercial acid-precipitated caseins were found to be suitable for fiber extrusion. Purification of th e b e tte r commercial caseins did no t m aterially im prove th e q u ality of th e fiber. The
F ig u re 1 (B elo w ). P ress a n d A ccessory E q u ip m e n t for S p in n in g C asein F ib ers
F ig u re 2 (R ig h t) . C lo se-u p View o f F ib er F orm ed by E x tru sio n o f H eated C a sein -W ater M ixtu re th r o u g h th e
F o u r-H o le D ie in to Air
I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 37, No. 7
F ig u r e 3. M o to r-D riv e n M a c h in e f o r S t r e tc h i n g S k e in C a s e in F ib e r d u r in g H a r d e n in g w ith Q u in o n e
as show n in F ig u re 1. F ib er can also be m ade b y ex tru d in g casein m ixed w ith only 37% of its w eight of w ater. I n th is case sticking is so m uch reduced t h a t th e fibers are ex tru d ed d irectly in air w ith o u t th e b ath .
T h e ex tru d ed fiber, in th e form of a skein of continuous fila
m ents, is placed in th e stretch in g b a th (Figure 3) an d is passed th ro u g h tw o stirru p s. One of th ese is sta tio n a ry while th e o th er is g rad u ally pulled along th e length of th e ta n k by a m o to r m echa
nism . W hen a s a tu ra te d solution of quinone is em ployed a t room tem p eratu re, th e fiber is stretch ed a t th e ra te of 1 % of th e original len g th p er m in u te u n til th e original len g th has been doubled; th e tim e required is 1 h o u r an d 40 m inutes. W hen higher tem p eratu res are used, th e ra te of stretch in g m u st be in
creased. A fter stretch in g is com pleted, th e fiber rem ains under ten sio n in th e quinone b a th (room tem p eratu re) for a t least 24 h ours; fu rth e r hardening a n d a tte n d a n t reduction of w ater ab so rp tio n m ay be o b tain ed b y allowing it to sta n d u n d er ten sio n in a 2 % form aldehyde solution for a n o th e r 24 hours. H ardening h as been found to be b est n ear pH 4.7. F in ally th e fiber is re
m oved from th e b a th , w ashed, a n d dried a t room tem p eratu re u n d er sufficient tension to keep it straig h t.
T h e effect of v ariatio n s in degree of stretch in g on tensile stre n g th an d flexibility is show n in F igure 4. T h e testin g was done a t 65% relativ e h u m id ity an d 70° F . on a sta n d ard S co tt inclined-plane serigraph-2 testin g m achine. T h e tensile stren g th of a fiber w ith a loop tied in it w as em ployed as a m easure of flexibility (curve C). As th e degree of stretch in g is increased, tensile stre n g th increases. H ow ever, a po in t is reached w here an
Percent Stretch
F ig u r e 4. I n f lu e n c e o f D e g re e o f S tr e tc h in g o n P r o p e r t ie s o f F ib e r (300-1000.d e n ie r )
A an d 0 , dry te n sile stren g th ; C, te n s ile stren th o f fiber w ith a lo o p tie d in i t (flex ib ility ); D , w et te n sile stren th
increase in th e degree of stre tc h in g reduces flexibility. Conse
qu ently, stretch in g is n o t carried to th e g reatest possible extent in m ak in g bristlelike casein fibers. In s te a d th e fibers are stretched only to tw ice th eir original len g th in th e quinone b a th in order to o b tain th e highest stre n g th consisten t w ith g re atest flexibility S tretch in g also increases th e w et stre n g th a n d slig h tly decreases w ater absorption. T h is tre a tm e n t resu lts in a casein b ristle with a d ry stre n g th of 0 .7-0.8 g ram p er denier u n d er sta n d a rd condi
tio n s an d a w et stre n g th of 0 .3 -0 .4 gram p e r denier a fte r im m er
sion in w a ter for 4 hours a t 70° F . (T able I ) .
PRO PERTIES AND U SE S O F ARTIFICIAL BR IST L E S T h e stre tc h e d an d quinone-hardened casein fibers are cylin
d rical (Figure 5) a n d black. F ig u re 6 show s sam ples of experi
m en tal brushes m ade w ith casein b ristle fiber. T h e stiffness of the fiber varies w ith th e d iam eter. F ib ers w ith a d iam eter of 0.6 mm.
(3312 denier) are q u ite stiff; fibers w ith a d ian ie te r of 0.2 mm.
(368 denier) are so ft a n d pliable. E xperim en tal p a in t brushes m ade w ith th is fiber h av e been p rep ared in considerable num bers.
Since h eatin g h ardened casein fibers above 100° C. for several h o u rs produces brittlen ess, o rd in ary m eth o d s of se ttin g natural bristles such as th a t involving th e v u lcan izatio n of ru b b er for several h o u rs a t 140° are u n su ited for artificial bristles made from casein. T h is difficulty has been overcom e b y vulcanizing w ith ru b b er a t low er tem p eratu res an d also by using a settin g
ma-July, 1945 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 687
F igu re 6. C asein B ristle a n d E x p erim en ta l B ru sh es M ade from A rtificial F ib er
terial, m ade of urea-form aldehyde an d alkyd ty p es of synthetic resin, th a t hardens a t 80° C. These p a in t brushes, although m ade of untapered bristles, have good pain t-carry in g capacity, m ake sm ooth films, an d have good w ear resistance. T h e bristles are resistant to oils and fa t solvents, b u t soften when allowed to stand in w ater.
A lthough th e d ry tensile stren g th of the casein bristles is no t so great as th a t of n atu ral bristles, th e stren g th is adeq u ate for m ost brushes n o t subject to w etting w ith w ater. I n w ater th e casein bristles absorb ab o u t 18% w ater, become soft, an d have a tensile strength of only ab o u t half th eir d ry tensile stren g th ; this m akes them unsuited for use in w ater. T able I I compares casein bristles w ith n atu ral bristles.
C asein bristles are stable in a ir under ordinary conditions and have been k ep t for tw o years w ith o u t deterioration. E ven a fter long h eating a t 60° C., th e physical properties of th e fiber were changed only slightly w hen subsequently conditioned a t room tem perature.
Ta b l e II. Co m p a r i s o n o f Ca s e i n Br i s t l e s w i t h Na t u r a l Br i s t l e s
Ten sile S tre n g th , G ./D e n ie r M a te ria l
C asein b ristle P ig b ristle H o rse h air
70 r.h .,F. Single k n o t 4 h r. in w ater 0 . 7 - 0 . 8
1.0-1. 2 I . 2 - 1 . 4
0 . 6 - 0 . 6 5 0.8-0.9 0 . 9 - 1 . 0
0 . 3 5 - 0 . 4 5 0 . 9 - 1 . 2 1.0-1.3
% W a te r afte r 24 Hr,
in W a te r (22-25° C.)
1 8 .5 2120
DISCUSSION
T he batch process described for th e production of casein bristles is adeq u ate for m any purposes. F o r large-scale economic pro
duction, however, a continuous process w ould be highly advan
tageous, and it has been found th a t th e fiber can be extruded with a comm ercially available screw -type extruder. T he process de
scribed here, involving hardening for 24 hours a t room tem pera
tu re, produces a fiber containing approxim ately 10% quinone.
T his am o u n t of quinone is required to m ake th e fiber durable and resistan t to w ater. T h e influence of tem p eratu re on th e ra te of u p tak e of quinone is show n in Figure 7. I n order to o b tain ap
proxim ately 10% quinone in th e fiber in 10 m inutes, it is necessary to use a tem perature of 60° C.
Ta b l eI. St r e n g t ho f St a n d a r d Ca s e i n Br i s t l e s St r e t c h e d t o Tw i c e Th e i r Or i g i n a l Le n g t h
Tensile S tr e n g th , G ./D e n ie r “ E x p t. N o. D enier 6 5 % r.h ., 70° F. 4 h o u rs in w ater
40 214 0 .8 4 0 .3 6
0 .7 8 0 . 4 8
0 .3 3
67 470 0 .8 5 0 .4 4
0 . 7 6 - 0 .4 2
0 .7 6 0 .3 7
104 425 0 .7 1 0 .4 7
0 .7 9 0 .4 0
0 .8 6 0 .4 5
388 507 0 .7 1
0 .7 1 0 .7 3
443 421 0 .7 3
0 .8 0 0 .8 2
° G ram s p e r denier ca n be co n v e rted t o p o u n d s p er s q u a r e inch b y m u lti
p lying b y th e fac to r 16,630 since th e fiber h a s a d e n s ity of a b o u t 1.3. [Sie
miński, M.A ., R ayon Textile M onthly, 24, 63 (1943)]. D enier = weight in g ram s of 9000 m eters of fiber.
F ig u re 7. In flu en ce o f T em p era tu re o n U p ta k e o f Q u in o n e (F ib er D ia m e ter 0.3—0.5 M m . or 828-2301
D en ier)
T he sim ultaneous stretching an d hardening of th e fiber in a relatively sh o rt period requires fu rth er investigation. T o increase the tensile stren g th of th e fibers, th e stretch m u st be applied a t a definite tim e during hardening. Considerable stretch can be ap
plied to th e fiber as it emerges from th e orifice of th e extruder while it is in th e air and still a t an elevated tem perature. How
ever, no added stren g th is given th e fiber by th e m axim um stre tc h th a t can be applied in th is m anner. I t is necessary to have a certain m inim um degree of hardening in order to increase th e stren g th by stretching. If the hardening has progressed too far, however, th e fiber can be stretch ed com paratively little before
Ti m e in M i n u t e s
688 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y Vol. 37, No. 1
i t breaks. T h ere is th u s a n o ptim um am o u n t of h ard en in g for p e rm ittin g th e m axim um effective stre tc h to be applied. T his was show n b y an ex perim ent in w hich th e m axim um degree of stre tc h t h a t could be applied to th e fibers w as d eterm ined a t 5- m in u te in terv als a fte r im m ersion in a quinone solution u n d er v a r
ious conditions. T h e m axim um extension of ab o u t 300% was a tta in e d in 30 to 45 m inutes a t 22°, 15 to 35 m in u tes a t 35°, an d 10 m inutes a t 50° C. in 1% quinone, b u t it w as a tta in e d in less th a n 5 m in u tes a t 50° in 2 % quinone. S tre tc h should be applied u n d er an y of these com binations of tem p e ratu re an d tim e to be of m ost benefit. I f th e fiber is to be stretch ed n o t m ore th a n 100% , however, th ere is considerable latitu d e in th e tim e a t w hich stre tc h m ay be applied.
T he reactio n of quinone w ith casein appears to be irreversible in n eu tral solutions. C asein fiber h ardened w ith quinone is su
perior to form aldehyde-hardened fiber w ith respect to b rittleness an d resistance to w ater. Quinone hardening was m ost effective n ear th e isoelectric po in t of casein. A lthough th e n a tu re of th e reactions is still unknow n, quinone has been found to re ac t w ith proteins an d m any am ino com pounds (1, 2); m ost of these reac
tions proceed readily in aqueous solution a t room tem p eratu re.
I t has been found (4, 5) th a t deam inized collagen (hide powder) fixes ab o u t 60% of th e am o u n t of quinone fixed by u n tre a te d col
lagen in 24 hours. I t is th u s probable th a t th e «-a’nino groups of
lysine are available in pro tein s for reactions of th is ty p e, b u t th a t th ey account for only p a rt of th e reaction.
T he m odification of casein b y acety latio n , deam in atio n , or es- terification, as well as th e ad d itio n of sm all q u a n titie s of quinone or form aldehyde, m arkedly decreases th e a b ility of casein to form fibers in th e presence of w ater.
A C K N O W L E D G M E N T
T h e a u th o rs are g reatly in d eb ted to R . H ellbach an d N . J . H ipp of th is lab o rato ry for designing an d con stru ctin g th e eq u ip m en t used in th is developm ent. Also th e y wish to record th e ir grati
tu d e to Alice W olferd, H elen D earden, an d E d ith Polis for valu
able aid.
L I T E R A T U R E C I T E D (1) F ischer, E., an d Schrader, H., Ber., 43, 525 (1910).
(2) M eunier, L ., an d Seyew etz, A., Compt. rend., 146, 987 (1908).
(3) M illar, A., J . Soc. Chem. Ind., 18, 16 (1899).
(4) T hom as, A. W ., a n d F o ster, S. B ., J . A m . Chem. Soc., 48, 489 (1926).
(5) T hom as, A. W ., a n d K elly, M . W ., In d. En g. Ch e m., 16, 925 (1924).
(6) T o d te n h a u p t, F ., G erm an P a te n t 170,051 (1904).
Pb e s e n t e d a t a m e e tin g sp o n so re d b y t h e A m e r ic a n S o cie ty fo r T e s tin g M a- te rials, P h ila d e lp h ia D is tr ic t C o m m itte e , S e p te m b e r , 1943.