Extrusion of self-reinforced thermoplastic composites illustrated by high density polyethylene

J of Applied Polymer Sci

1988

SynopsisA polytheylene composite was prepared and tested. It consisted of a high-density polyethylene (HDPE) matrix and uniaxial gel-spun high-modulus PE fiber. Aided by the similarity between matrix and fiber, transcrystallization of HDPE melt on the PE fiber surface was generated. Nucleating agents were not employed. The transcrystalline growth of HDPE on the PE fiber surface was found to consist of an inner and an outer zone. The inner zone, 2-3 pm thick, is composed of HDPE crystals nucleated on the PE fiber surface. Photomicrographs showed a well-defined region of row-nucleated HDPE on the surface of PE fiber. This means the fibrils of HDPE were found to grow out from the PE fiber axis and HDPE crystallites are oriented in planes perpendicular to the PE fiber axis. The fiber in the composite induced the transcrystalline growth of HDPE on the PE fiber surface at higher temperature than on cooling the melt. For 36 wt% fiber, the increase was 2.5"C, also resulting in -10% more crystals. Crystallization of a composite with 50 wt% fiber at 124°C involved two steps: The first a fast transcrystallization of HDPE on the PE fiber surface followed by the bulk crystallization of the HDPE.

Melt transcrystallization of polyethylene on high modulus polyethylene fibers

J of Applied Polymer Sci

1988

Solid‐state coextrusion of high‐density polyethylene. I. Effects of geometric factors

Kanamoto

Zachariades

J. Polym. Sci. Polym. Phys. Ed.

1979

The solid (crystalline) state coextrusion of two high‐density polyethylenes (HDPE) having weight‐average molecular weights (Mw) of 59,000 and 200,000 have been studied as a function of the geometrical arrangement and the volume fraction of the components. The extrusion rate increased nonlinearly with the volume fraction of the low‐Mw, component. The rate was faster when the low‐Mw, component was the core rather than the sheath in the initial cylindrical concentric billet. Thus the slow extrusion rate of high‐Mw HDPE alone was increased up to ten times by coextrusion with a small fraction of the low‐Mw, HDPE component in its center. Generally, the deformation flow profile changed gradually from a parabolic to a W‐shaped pattern as the volume fraction of the high‐Mw, component increased. However, the geometric arrangement of the two different Mw components also had a pronounced effect on the deformation. The deformation patterns showed that upon coextrusion the low‐ and high‐Mw HDPE's were extruded at the same rate and extrusion draw ratio. The geometrical arrangement had no substantial effects on the tensile modulus and strength of the extrudates; i.e., they increased linearly with volume fraction of the high‐Mw HDPE.

Solid‐State coextrusion of high‐density polyethylene. II. Effect of molecular weight and molecular weight distribution

Zachariades

Kanamoto

J. Polym. Sci. Polym. Phys. Ed.

1980

Self Cite

The recently developed technique of solid‐state coextrusion for ultradrawing semicrystalline thermoplastics has been applied in the preparation of self‐reinforced high‐density polyethylene extrudates. The extrudates consist of definite core and sheath phases composed of different molecular weights (Mw) in the range of 60,000–250,000 and different molecular weight distributions (Mw/Mn = 3.0–20). Concentric billets of two different phases were prepared for extrusion by in serting a polyethylene rod within a tubular billet of a different high‐density polyethylene followed by melting the two phases to obtain bonding between them. The billet was then split longitudinally to increase extrusion speed and extruded at 120°C, 0.23 GPa through a conical die of extrusion draw ratio 25. Extrudates of high tensile modulus (38 GPa) and strength (0.50 GPa) could be produced in a steady state process at a rate near 0.25 cm/min. The tensile properties of the extrudates from either the single or concentric billets increased with average molecular weight and were insensitive to the molecular weight distribution of the constituent phases. Thermal analysis indicated a high deformation efficiency for the sheath and core phases of the extrudates by the coextrusion technique.