1. INTRODUCTION. In many polymer processing operations, molten polymers. emerge from dies into a stress field which deforms the

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1 . NTRODUCTON. Histrical ntes f melt spinning prcess n many plymer prcessing peratins, mlten plymers emerge frm dies int a stress field which defrms the melt int a final fabricated shape. This is the case in melt spinning f fiber and in film extrusin. The melt spinning prcess invlves preparatin f a spinning fluid) extrusin f the melt thrugh spinneret int a cling atmsphere) and elngatin f the extruded melt. The resulting filaments are then subjected t drawing and anealing. Figure. shws a schematic diagram f these melt spinning prcesses. We have btained the fine and strng filament by these prcesses in melt spinning. The prcess f melt spinning dates frm the pineering effrts f Carthers and Hill l reprted in 932. t has been an imprtant manufacturing prcess, and a large fractin f all synthetic fiber is prduced via the melt spinning rute. At present time the melt spinning prcess is applied t the methd f fiber frmatin frm liquid-crystalline material;,3 the fabricatin methd f ultrafine fibers by using f cmpsite spinning; high speed melt spinning 5 methd, and s n. The filaments with many useful prperties have been develped by these new methds. The prperties f filaments are highly dependent n --

2 the spinning cnditins used in their prductin. This behavir is due t the effect f prcess variables n the structure f the spun filament. The frmatin f structure during melt spinning is cmplicated by the cmbined influences f melt structure, rhelgical factrs and nn-isthermal effects. Because f these cmplicatins, early wrk was little fundamental study f the rhelgical behavir untill the wrk f Ziabick and Kedzierska 6 in Preparatin Extrusin Elnga tin After treatment Figure. Scheme f melt spinning After their wrk, many studies n the elngatinal regin in Figure. have been carried ut; heat transfer f running filament;-9 kinematics and dynamics f defrmatin f the spinline,lo-5 mlecular rientatin -2-

3 fob accmpanylng er splnnlng,." 0-20 crysta"" lzatln beh avlr " t 2l - 24 h b d" d Th f 0 runnlng fol amen ave een stu le. e resu ts f these wrks have made pssible the frmulatin f a system f mathematical equatin describing the melt spinning prcess as a whle. These studies were reviewed in the bk f Ziabicki: 5 Hwever, there are several unreslved imprtant prblems. First, in spite f nn-newtnian viscsity f plymer melt having been knwn in the study f shear flw, the running filament in melt spinning has been assumed t be Newtnian fluid: three times the zer shear viscsity have been used as the viscsity f running filament. Cnsiderably less effrt has s far been invested in studying the nnnewtnian viscsityf elngatinal flw in melt spinning, althugh this is f cnsiderable significance. Anther prblem is the quantitative estimatin f crystallizatin prgress in running filament by using f the data f static isthermal crystallizatin experiments. A third prblem is assciated with the effects f prehistry in preparatin n elngatinal flw and crystallizatin behavir. -3-

4 .2 Elngatinal flw Elngatin is the dminant mde f defrmatin in many imprtant plymer prcesses. The imprtance f such flw in prcessing applicatins has been indicated by many authrs including Cgswell and Lamb, Dealy and Petrie. 28 Mrever, ther significant reasn fr cnsidering elngatinal flw is the fact that a knwledge f physical behavir in shear des nt generally suffice t characterise a material's respnse in ther type f defrmatin. Mst studies n plymer melt rhelgy have cncentrated 29-3 n shear flw, which were bserved in such flw gemetries as Piseuille flw and Cuette flw and in parallel plate and cne and plate trsin flws. Simple shear flw in the Cartesian cdinate can be visuallized by cnsidering a liquid between tw flat plates, ne statinaly and the ther mving. We assign labels t the pints using the spatial crdinates xi at time t and the bdy crdinates i at an arbitrary past time t' (Figure 2). We shall write the equatin characterizing the defrmatin in the frm x = x 2 = x 3 = X l + X 2 X 2 X 3. The Finger strain tensrs are calculated directly frm -4-

5 ,, ",,-", ~~:_---~~~~~----~,,, Ti'S t : X,,X X 3,X 3 Figure.2 Shear flw,,,..,..'' X' J ",-"0 Figure.3 Engatina flw.2 - n terms f physical cmpnents C ij, ne has - 5-

6 -e: -e:.3 Simple shear is accmpanied by the rtatin f flw unit, as fund by equatin (.) r by Figure.2. This causes a macrmlecular cil t rtate abut its center f gravity, and lessens the rientating effect f flw field. This mtin.f plymer mlecules is cnsidered as a cause 32 f nn-newtnian viscsity f plymer melt, which decreases with increasing strain rate. say x, n elngatin, the defrma~in in ne directin, is independent f psitin in the ther tw directin (Figure 3). The dimensinal change is given by x l = sx l x 2= s-/2 X2 x 3 = s-/2 X Where s is an elngatin rati. The cmpnent f C - is 2 s 0 0 a: - = 0 s s The rate f strain tensr e is als independent f psitin and is given by 0 0 e =

7 where y is the rate f strain, and if we cnsider elngatin a cylindrical specimen f length and crsssectin area A then, Ẏ = T(ff= dl.7 Upn integratin, we btain the fllwing expressin fr the time dependent length and crss-sectin area that must be created in rder t generate this flw. (t) = 0exp (yt) A(t)= AOexp(-yt).8 Thus, the needed elngatinal strain yt fr elngatinal flw is y = yt = n T = n s.9 n elngatinal flw, the velcity gradient develps in the same directin as the velcity itself rather than rthgnal t it as in shear flw, i.e. elngatinal flw is strain prcess free frm the rtatin f flw unit. This favrs a large elngatin f the lng chain mlecules frm the randm cil cnfrmatin and a stable rientatin f elngated mlecules in the directin f flw. The experiments f elngatinal flw was first studied by Trutn 33 in 906 fr pitch, tar and shemaker's wax descending under their wn weight. Trutn defined the engatina viscsity as - 7-

8 = F/A A dv/dx--.0 where F is applied axial frce and dv/dx velcity gradient in the axal directin. Nwwe cnsider the velcity V at a psitin x and V at an initial psitin, then the elngatinal strain at a psitin x is and V y=ln- V. dv dv y=v <T =ax Hence the Trutn's elngatinal viscsity is equal t..2 cr A = f.3 Trutn als shwed that the elngatinal viscsity was three times the shear viscsity fr Newtnian fluids: A=3n. Recently, the experiments f a cnstant elngatinal strain rate fr plymer melt have been studied by Ballman, 'Vingradv,35 Meissner. 36 On the ther hand, Cgswel 37 has emplyed a cnstant stress methd and btained the elngatinal viscsity. An alternative methd studing elngatinal flw is an isthermal melt spinning methd. The isthermal melt spinning has been examined by Aciern et.al. and Han and Lamnte. The elngatinal experiments fr plymer slutin have been als carried ut by using f a slutin spinning methd,40,4l the tubeless-syphn methd 42 and the triplet jet methd