High-density polyethylene crystalline order

Thus, compared to other polymers, it is easier to obtain an extended and oriented chain structure in polyethylene. High density polyethylene (HDPE) is preferred to other types of polyethylene because HDPE has fewer branch points along its backbone and a high degree of crystallinity. These characteristics of linearity and crystallinity are important to obtain a high degree of orientational order and an extended chain structure in the final fiber. 

Polyethylene (PE). High-density polyethylene (HDPE) was introduced in the 1950s. Production is typically from metal oxide catalysis. HDPE is 90% crystalline with a Tm of 135°C. In 2001, the production for HDPE was 12,320 million lb in 2002, it was 13,600 million lb and, in 2006, 16,220 million lb. Historical growth has been on the order of 3.0-4.5% [4], Recent price data ranged from a high of 0.54 to a low of 0,315 per pound. 

The phase transition from disordered states of polymer melt or solutions to ordered crystals is called crystallization-, while the opposite process is called melting. Nowadays, more than two thirds of the global product volumes of synthetic polymer materials are crystallizable, mainly constituted by those large species, such as high density polyethylene (HOPE), isotactic polypropylene (iPP), linear low density polyethylene (LLDPE), PET and Nylon. Natural polymers such as cellulose, starch, silks and chitins are also semi-crystalUne materials. The crystalline state of polymers provides the necessary mechanical strength to the materials, and thus in nature it not only props up the towering trees, but also protects fragile lives. Therefore, polymer crystallization is a physical process of phase transition with important practical relevance. It controls the assembly of ordered crystalline structures from polymer chains, which determines the basic physical properties of crystalline polymer materials. 

Crystalline polymer a polymer with ordered structure, such as high-density polyethylene (HDPE) and cellulose. Semicrystalline polymers consist of regions of crystallinity or crystallites dispersed in amorphous regions. 

The polymer in this composite is high density polyethylene, which is semicrystalline with a crystallinity of about 75%. The crystalline melting point is about 130 C. This corresponds well to the abrupt increase in resistance observed in Figure 10a. The width of the polymer melting transition also corresponds well with the width of the abrupt increase in resistivity. The polymer melting is a second order phase transition, and shows hysteresis. When this composite is cooled from 180 to 20 C the polymer does not recrystallize at the same temperature at which it melted (130 C) it recrystallizes at a lower temperature. The resistance vs. temperature... 

High-density polyethylene is prepared at low pressure at about 10°C in the presence of a special catalyst (usually a titanium complex). The density is approximately 0.95 g/mL because of the higher degree of crystallinity and order in the polymer. 

The polyolefins, which contain relatively few double bonds are much more stable and their inherent oxidizability depends on the number of tertiary carbon atoms in the chain the order of oxidizability is therefore polypropylene (PP) > low density polyethylene (LDPE) > high density polyethylene (HOPE) [9]. However, HOPE and PP have a higher degree of crystallinity than LDPE and for the reasons discussed above, they undergo chemicrystallization and embrittlement more rapidly than LDPE. Electron-attracting groups in the polymer chain or pendant to the polymer chain increase oxidative stability, so... 

Fractional precipitation of crystalline polymers must be conducted above the melting point of the crystals to eliminate the effects of crystallinity on solubility. In addition, with polypropylene branching and tacticity differences can cause a reversal in the order of fractionation. In most cases polyolefins are fractionated from dilute solutions in poor solvents to eliminate these effects. However, the direct extraction of powdered high density polyethylene with solvents has been reported [94]. 

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