Small-Angle X-ray Scattering Experiment In Situ in Melt Spinning of High-Density Polyethylene The effect of flow on the structure formation in polymeric melt under non-isothermal conditions has been attracting attention in both academic and industrial points of view. Fiber spinning is a process that primarily imposes extensional deformation on polymeric melt at the spinline during rapid cooling. In the industrial point of view, it is very important to elucidate the structure formation in the spinning process because the structure has a large effect on the properties of the obtained fibers. The structure formation in the spinning process is very complex because many phenomena (crystallization, phase separation, glass transition and so forth) occur in the process. An in situ experiment on the spinning process will provide fruitful information on the structure formation ; however, the intensity of the X -ray beam of a conventional laboratory source is very wea k for the experiment because the diameter of the spinning fiber is very thin ; in the order of tens of microns. Therefore, synchrotron radiation is useful for a small sample such as a spinning fiber. An in situ X -ray scattering experiment on spinning process by synchrotron radiation [1] was carried out at H A SYL A B , H amburg, by J apanese and G erman researchers for the first time : although, this type of in situ experiment has not been carried out in J apan. W e attempted an in situ small-angle X -ray scattering ( S A XS ) on the melt- spinning at SP ring- 8 and this may be the first trial of such an experiment in synchrotron facilities in J apan. Fig. 1. Schematic representation of the spinning apparatus for in situ small-angle X-ray scattering in BL40B2. H igh density polyethylene ( HDPE ) was used as a sample in this experiment. The X -ray scattering experiments were carried out at beamline BL40B2 . The custom-made spinning apparatus used in the in situ X -ray experiment is shown in Fig. 1 . The apparatus has a vertical movement system that ad j usts the position of the spinning fiber to the X -ray beam with an accuracy higher than 10 μ m. M oreover, the distance from the nozzle to the incident X -ray beam can be changed along the spinline. A melt polymer was extruded from a small hole and drawn with ta k e-up rollers. The energy of the incident X -ray was 8 k e V (wavelength λ = 0 . 155 nm) and the scattered X -ray from the fiber was recorded on an imaging plate system. Figure 2 shows the series of S A XS patterns obtained at different positions in the spinline. The distance L from the nozzle to the incident X -ray beam is depicted on the left top of each S A XS pattern. As L increased, the scattered intensity parallel to the fiber increased at first ( L = 100 mm) and subse q uently decreased ( L = 300 mm). M oreover, the scattering angle dependence of the scattered intensity parallel to the fiber changed with L . W e analyzed the scattered intensity as a function of the scattering vector q using a scattering theory [2] of a paracrystal model for oriented lamellar microdomains and obtained a model for the structure formed in the spinline. H ighly oriented lamellar crystals were grown in the direction Side view End view Cylinder Plunger Take-up rollers Imaging plate X-ray Fiber Nozzle Horizontal movement system Vertical movement system Optical bench of BL40B2 Spinning apparatus Fiber 110 References [1] Y. Hirahata et al . : Polyme r 23 ( 1 996) 5 1 3 1. [ 2 ] S . S a ku rai et al . : J . Appl . C r ys ta l . 24 ( 1 99 1 ) 679 . Fig. 2. In situ SAXS patterns obtained in the spinline. L is the distance from the nozzle to the incident X-ray beam. SAXS patterns inserted in this figure are taken at L = 50, 100 and 300 mm. A structure model derived from the analysis of the q dependence of scattered intensity parallel to the fiber is depicted on the right side of each SAXS pattern. fo r th e s tr uc t u r e fo r med i n th e sp i nl i ne . Hi g h ly o ri en t ed l a mell ar c r ys ta ls we r e g r own i n th e d ir ec ti on p ara llel t o th e f i be r. T h e a ve ra ge thi ckness of th e l a mell ar c r ys ta ls a nd th e a ve ra ge f r equency of dens it y fluc t u ati ons conce r n i ng th e l a mell ar c r ys ta ls a nd a mo r p h ous r eg i ons ar e dep i c t ed i n th e f i gu r e . Mo r eove r we s h ould no t e th e o th e r fe at u r e of th e sc att e ri ng p att e r n i nd i c at ed by a n arr ow “S . ” T hi s i s a “s tr e a k” p att e r n i nd i c ati ng th e fo r m ati on of a s tr uc t u r e o ri en t ed p ara llel t o th e f i be r. Vo i ds o r ex t ended c hai n c r ys ta ls c a n be attri bu t ed t o th e s tr uc t u r e g i v i ng ri se t o th e s tr e a k p att e r n; h oweve r , we c a nno t f i x e ith e r of th em f r om th e SAXS r esul t s . I t s h ould be no t e that th e i n t ens it y of th e s tr e a k p att e r n bec a me we a k f r om L = 1 00 mm t o 300 mm . T hi s sugges t s that th e s tr uc t u r e g i v i ng ri se t o th e s t e a k p att e r n w a s sme ar ed by th e l a mell ar s tr uc t u r e . We ar e go i ng t o eluc i d at e th e s tr uc t u r e fo r m ati on i n th e sp i nl i ne by mo r e de tai led a n a lys i s of th e sc att e r ed i n t ens it y a nd by elec tr on m i c r oscopy of th e f i be r ob tai ned i n th e in situ expe ri men t i n SP ri ng-8 . Hir ok i Mu ra se a , M a s ar u Ko t e ra b a nd K at su hi ko N a k a m a e b ( a ) TO Y OBO Rese ar c h Cen t e r Co . , L t d . (b) SP ri ng-8 / JASRI E-m ai l: hir ok i _mu ra se@k t.t oyobo . co . jp Polyethylene Nozzle Take-up roller Incident X-ray 12 nm 50 nm 22 nm 15 nm 50 nm L L = 50 mm L = 100 mm L = 300mm SAXS Model amorphous crystal S q = 0.2 nm -1 111
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