Oriented structure formation during polymer film extrusion

Abstract

An experimental technique is described for producing fiberreinforced polymer films by inserting needle‐like obstructions in a film‐extrusion die. The, needles act as nucleation sites, generating a highly extensional local flow field, which causes sufficient orientation to induce the formation of oriented fibrillar crystallites embedded in a much less oriented matrix. To study the effectiveness of the above technique, linear low density polyethylene (LLDPE) and blends of linear low density with high density polyethylene (HDPE) were extruded through a film die with converging walls, with one or five needles inserted parallel to the extrusion direction, Microscopy observations, birefringence, and differential scanning calorimetry (DSC) measurements performed on the produced films showed in all cases that the presence of the needle induced the formation of a more oriented phase, which in most cases had a birefringence at least an order of magnitude higher than the film matrix. The best results were obtained in the case when blends of HDPE and LLDPE were extruded. The oriented structures obtained in this case consisted of HDPE and exhibited not only high birefringence but melting point elevation as well, indicating their fibrous nature.

Solid-state relaxations in linear low-density (1-octene comonomer), low-density, and high-density polyethylene blends

“…Blends of LLDPE with other polyethylenes, greenhouse in Korea; thus, the grades in common use in the field are need to be investigated to supnamely, LLDPE/HDPE, 6,7 MDPE (medium-density polyethylene)/LLDPE, 8 LLDPE/LDPE, 8,9 port their uses. and LDPE/HDPE, 10 have been investigated by various researchers.…”

Formation of fibrous crystals in flowing blends of polyethylene melts

“…As seen, the Marlex 6001 shows power-law behavior over the range of shear stresses considered and has a much higher viscosity in the low stress region where This behavior is indicative of the influence of a very high molecular weight tail in the Marlex 6001 [14], therefore this material is more likely to remain immiscible in LLDPE over the time scale of the experiment than is Chemplex HDPE which is in fact almost entirely miscible [10]. This feature is also reflected in the much greater tendency of the Marlex to fibrillate and finally crystallize under flow.…”

“…The film extrusion die used in these studies was similar in design to that described earlier [10] and was fitted with circular windows to enable observation in the vicinity of the seed. Figure 1 shows a schematic drawing of the flow channel and seed placement.…”

“…Rheological characterization of these materials, as well as the Chemplex HDPE (M.I. = 1.3) used in our earlier study [10], was also carried out. A cone and plate apparatus (Rheometrics System IV) was used to generate data in the low shear rate region and slit or capillary dies were used for higher shear rates.…”

“…This occurs when the two phases have different melting points and the minor phase, with the higher melting point, is forced by the major phase to flow past the seed. In a recent study we described the use of such a technique in a converging flow film extrusion geometry [10] using a high density polyethylene (HDPE) and a linear low density polyethylene (LLDPE) flowing past a needle suspended along the central axis of the die. T h e extruded films contained a more oriented HDPE phase imbedded along the symmetry axis in the LLDPE matrix, however, the orientation of the HDPE phase, as evidenced by its birefringence and superheating, was low.…”