HDPE melt

HDPE melts at about 135°C, is over 90% crystalline, and is quite linear, with more than 100 ethylene units per side chain. It is harder and more rigid than low density polyethylene and has a higher melting point, tensile strength, and heat-defiection temperature. The molecular weight distribution can be varied considerably with consequent changes in properties. Typically, polymers of high density polyethylene are more difficult to process than those of low density polyethylene. 

The thermal, mechanical, and morphological behaviors of two binary blends, HDPE-E-plastomer (Engage 8200) and iPP-E-plastomer (Engage 8200) have been investigated to compare the compatibility and molecular mechanistic properties of the blends. Both systems are thermodynamically immiscible but mechanically compatible. Thermal studies indicate that both blends exhibit two distinct melting peaks and there is depression of the HDPE melting peak in the blend with high... 

About 50% of all the ethylene produced is used to make polyethylene. There are two main types high density or HDPE and low density or LDPE. HDPE melts higher and is stiffer and harder than LDPE. It is also opaque, while LDPE is flexible and transparent. HDPE is used for molding bottles, housewares, toys, and for extruding pipe and conduit. LDPE is used mainly for packaging film. HDPE is made by a catalytic polymerization at relatively low pressure while LDPE is made by polymerization at very high pressure using a different catalyst. 

HDPE melt, 20 160 Head-area meters, 77 664-666 Headboxes, in paper manufacture, 73 106 Header design, 73 271-276 Head group/substrate interaction, 24 139 Headspace analysis, 77 518... 

Fig. 13. Measured scattering intensity of HDPE melt. Intensity corrections for air scattering, polarization, absorption, sample geometry and Compton scattering have beat performed...

Fig. 14. Experimental RDDF from HDPE melt at T = 153 °C. The finite resolution in r-space results from the finite q-range...

Most high density polyethylene processing technologies require the melting of HDPE. Typical HDPE melt viscosities are between 1,000 and 100,000 Pa s( 10,000 10 P) the melt viscosity of HDPE strongly... 

Most real cases of polymer melting (and solidification) involve complex geometries and shapes, temperature-dependent properties, and a phase change. The rigorous treatment for such problems involve numerical solutions (12-15) using finite difference (FDM) or FEMs. Figure 5.9 presents calculated temperature profiles using the Crank-Nicolson FDM (16) for the solidification of a HDPE melt inside a flat-sheet injection-mold cavity. The HDPE melt that has filled the cavity is considered to be initially isothermal at 300°F, and the mold wall temperature is 100°F. 

Example 9.2 The Design of a HDPE Pelletizing Extruder Design an 18,000-lb/hr pelletizing extruder for high-density polyethylene (HDPE) melt at 450°F to generate 2500 psi head pressure. Assume a constant channel depth extruder with an axial length of 60 in. The melt density is 54 lb/ft3, the viscosity is 0.15 lbfs/in2, and the specific heat is 0.717 Btu/lb°F. 

Fig. 10.48 Numerical simulation results of nonisothermal flow of HDPE, Melt Flow Index MFI = 0.1 melt obeying the Carreau-Yagoda model for a typical FCM model wedge of e/h — 3 and =15. (a) Velocity (b) shear rate and (c) temperature profiles [Reprinted by permission from E. L. Canedo and L. N. Valsamis, Non Newtonian and Non-isothermal Flow between Non-parallel Plate - Applications to Mixer Design, SPE ANTEC Tech. Papers, 36, 164 (1990).]...

The HDPE melt used has the rheological and thermomechanical parameters listed in Table 10.4. The boundary conditions employed are listed in Table 10.5. There was no... 

The site of the sharkskin distortion is again the die exit, and so is the screw thread pattern. The site of, and the mechanism for the gross extrudate distortion are problems that have no clear answers. The work of White and Ballenger, Oyanagi, den Otter, and Bergem clearly demonstrates that some instability in the entrance flow patterns is involved in HDPE melt fracture. Clear evidence for this can be found in Fig. 12.18. Slip at the capillary wall, to quote den Otter, does not appear to be essential for the instability region, although it may occasionally accompany it. ... 

Figure 3.67. Viscosity and first normal-stress difference versus shear rate for a HDPE melt. Adapted from Figure 6.3.4 (Macosko, 1994). Copyright (1994). Reprinted with permission of John Wiley and Sons, Inc.

Source of HDPE Melt index (g/10 min) Density (g/cm ) Tensile strength (psi) Secant modulus (psi)... 

Figure 17.2 Dependence of the apparent shear viscosity on the shear rate for HDPE (melt index 0.5 g/10 min).

Steady Shear Viscosity and Dynamic Viscosity Data Neat HDPE rheology data fairly well correspond to each other when obtained by both capillary and rotational rheometers. This actually means that HDPE melt obeys the Cox-Merz rule [26]. The... 

Nadkami and Jog (1986), Nadkami et al. (1987), and Jog et al. (1993) investigated the crystallization in blends of PPS with three types of HOPE, having a different melt flow index. In contrast to the PPS/PET blends, PPS crystallizes now in a superheated HOPE melt environment. Erom the dynamic cooling experiments, it was found that the presence of the HDPE melt suppresses the crystallization of PPS. The crystal growth rate, G, of PPS was found to remain unchanged, but its nucleation density was reduced as the concentration of HDPE in the blend increased or when the melt viscosity of the HDPE phase decreased. As a consequence, the overall crystallization rate of PPS was found to be retarded. 

Synthesized oligoketones were researched as HOPE modifiers. To evaluating the effectiveness of putting the oligomers into the HDPE melt, their 0,1% (at mass) concentration was studied. 

Figure 12.13. Laser-Doppler velocity profiles for a HDPE melt at the high and low parts of the cycle. Reprinted with permission from Munstedt et al., /. RheoL, 44, 413 (2000).

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