High-density polyethylene, molecular

Branching occurs to some extent and can be controlled. Minimum branching results in a high-density polyethylene because of its closely packed molecular chains. More branching gives a less compact solid known as low-density polyethylene. 

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. 

Fig. 19a, b. Curves of isometric heating a reference sample (curve 1) and sample obtained if molecular orientation exists and containing a spatial framework (curve 2) (schematic representation) b data for high density polyethylene (—A----------ordinary fiber, —O-------fiber obtained by... 

Fig. 20. Stress(er)-strain (ai) dependence for high density polyethylene samples. 1 reference sample, 2 sample obtained if molecular orientation exists, 3 super high tenacity fiber-fibril. Asterisks denote the points of fiber failure...

High density polyethylene, shown in Fig. 18.2 a), consists primarily of linear hydrocarbon chains of the type shown in Fig. 18.1. We commonly abbreviate its name to HDPE. As with all other polymers, high density polyethylenes contain a distribution of molecular weights. The molecules have few, if any, branches. 

A small number of companies use metal oxide catalysts, such as the example shown in Fig. 18.6, to make high density polyethylene. The polyethylene made with this catalyst generally has a narrower molecular weight distribution than high density polyethylene made with Ziegler-Natta catalysts. 

Morpholine chromate, molecular formula, properties, and uses, 6 562t Morphology. See also Structure of carbon fibers, 26 737-739 of high density polyethylene, 20 162 of polymer blends, 20 356 of polymer colloid, 20 386-388 of PVC particles, 25 658-661, 661-663, 664-665... 

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