HDPE extrudates

Fig. 12.17 Scanning electron micrograph of HDPE extruded at a shear rate slightly lower than the oscillation region, showing sharkskin. [Reprinted by permission from N. Bergem, Visualization Studies of Polymer Melt Flow Anomalies in Extruders, Proceedings of the Seventh International Congress on Rheology, Gothenberg, Sweden, 1976, p. 50.]...

Figure 4. Effects of EDR on the DSC thermogram for the lower MW HDPE extrudates prepared at 90°C.

Figure 5. Melting peak temperature as a function of heating rate for the sample portions, a-c, of a high MW HDPE extruded at 110°C to EDR 12 and 25.

Table II. Melting Peak Temperatures and Heats of Fusion at Different Deformation Components for HDPE Extrudates Prepared at 110<>C. (Heating rate=10°C/min).

It has been reported (8,13) and confirmed here, that the DSC "T and AHf of HDPE extrudates became insensitive to draw at higher EOR. However, as shown in Table I and II, and Figures 4 and 5 there are... 

It has been shown that the elastic recovery in drawn HDPE can be a sensitive measure for the efficiency of draw (11,12). The correlations between this property and morphology (14) and tensile modulus (11) have been discussed. Thus, we measured thermally induced elastic recovery for each sample portion separated from the characteristic deformation components in the low and the high MW HDPE extruded at 90 and 110°C to EDR 12 and 25. When a drawn specimen was immersed and freely floated in a silicon oil bath kept at 160 C, the elastic shrinkage quickly occurred and completed within a few seconds. The shrinkage was evaluated in terms of % recovery (R) and molecular draw ratio (MDR) defined previously (11,12). 

Table III. Elastic Recovery Data for Different Deformation Components in HDPE Extrudates Prepared at 110°C.

All the results of DSC, elastic recovery, and x-ray measurements on the sample portions formed under characteristic deformation flow components indicate that the complex stress strain field in an extrusion die produces markedly different deformation flow profiles on crystalline-state extrusion of HDPE, but results in no significant effect on the morphology and properties of the extrudates prepared under the conditions used in this work. It is remembered, however, that an earlier electron microscopy study found marked morphological variations across the radius of HDPE extrudates prepared at higher temperatures (134 to 137°C) under the combined effects of chain orientation and pressure (4). The T, of the undeformed isotropic... 

Optical analysis of pure iPP and HDPE extrudates shows that the two semicristalline polymers exhibit spherulitic and microsphe-rulitic structure respectively (Figs. 8 and 9). It is to be noted that the HDPE microspherulites are oriented along telescopic decentralized patterns. Such circular orientations may be ascribed to the sudden air quenching of the molten material at the die exit. 

Prime HDPE, Extruded polyethylene sheet, Primex Plastics Cotp. 

Reference has been made to injection moulding, which is a fair market for HDPE. Extruded pipe from HDPE and a tougher variant of lower density is widely used for natural gas distribution, particularly in cold climates where some failures of PVC (Chapter 8) have been encountered. HDPE has also been formed into mudguards for commercial vehicles, where the non-corroding... 

FIGURE 7.9 HDPE extrudates obtained from a capillary at different apparent shear rates, yy from left to right the values of are 75, 75, 2250 s while the corresponding values of are 0.20, 0.27, 0.33 MPa. (Data from Moynihan, 1990.)... 

FIGURE 7.13 Effect of the method of measurement on the magnitude of die swell for HDPE extruded from a capillary at 180 °C at various wall shear rates, kr curve 1, isothermal curve 2, annealed curve 3, ambient air. (Data from White and Roman, 1976.)... 

Because of the excellent gas barrier properties, EVOH is of interest as a packaging material. However, because of its high water absorption it is usually used as an internal layer in a co-extruded film, sheet, bottle or tube. For example, the system HDPE-EVOH-EVA may be used as a barrier film for packaging cereals, and the system polystyrene-EVOH-polystyrene for packaging coffee and cream, whilst the system polystyrene-EVOH-polyethylene has the additional advantage of heat scalability. 

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. 

The rigid plastic milk bottles are made in the dairy processing plant using blow molding. In this process, HDPE pellets are fed from a hopper into an extruder where they are heated by shear and heat to soften them. 

Fig. 10. Scanning electron micrograph of a fracture surface parallel to the direction of extrusion of an extrudate of a 45 55 PS-HDPE blend with a viscosity ratio p 1. Fibrous PS is shown at different stages of breakup the diameter of the largest fiber is about 1 pm (Meijer el til., 1988).

High density extruded planks, 23 404 High density lipoproteins (HDLs), 5 135-137 10 829 niacin and, 25 798 High density polyethylene (HDPE), 10 596-595 11 225 16 21 17 724 20 149-179 24 267, 268. See also HDPE entries analysis of, 19 566 as barrier polymer, 3 377 bimodal reactor technology for, 20 170 blow molding of, 20 171-172 blown film applications, 20 173-174 catalysts used for, 20 152-155 chemical resistance of, 20 166 commercial applications of,... 

Single-screw extruders, 23 398, 16 723 Single-site catalyst, 16 82, 26 545 in HDPE production, 20 154-155 Single-site polyethylene catalyst systems, 17 725... 

Grooved bore extruders are common on European extruders up to barrel diameters of about 120 mm and on some applications up to 150 mm diameter [44]. For a 60 mm diameter machine, the maximum feed channel depth for a PP resin application is about 5 mm and 6 mm for HDPE resin applications channel depths are not much larger than this for larger diameter machines. Ingen Housz and Meijer [44]... 

In order to illustrate the utility of model parameter interpretation, a data set containing NIR transmission spectra of a series of polymer films will be used [85]. In this example, films were extruded from seven different polymer blends, each of which was formulated using a different ratio of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) where the blend compositions were 0, 2.5, 5,10, 25, 50 and 100% HDPE. NIR spectra were then obtained for four or five replicate film samples at each blend composition. Figure 12.18 shows the NIR spectra that were obtained. 

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