High density polyethylene characteristic

The majority of spunbonded fabrics are based on isotactic polypropylene and polyester (Table 1). Small quantities are made from nylon-6,6 and a growing percentage from high density polyethylene. Table 3 illustrates the basic characteristics of fibers made from different base polymers. Although some interest has been seen in the use of linear low density polyethylene (LLDPE) as a base polymer, largely because of potential increases in the softness of the final fabric (9), economic factors continue to favor polypropylene (see OlefinPOLYMERS, POLYPROPYLENE). 

The homopolymer finds a variety of uses, as an adhesive component, as a base for chewing gum, in caulking compounds, as a tackifier for greases, in tank linings, as a motor oil additive to provide suitable viscosity characteristics and to improve the environmental stress-cracking resistance of polyethylene. It has been incorporated in quantities of up to 30% in high-density polyethylene to improve the impact strength of heavy duty sacks. 

Polyethylene has low density when polymerized at pressures 9,000 - 45,000 psi and high density when made with special catalysts at 250 - 500 psi. Low-density polyethylene softens 68 F lower than high-density polyethylene, which is more crystalline and stiffer. The rigidity characteristics and surface of high-density polyethylene are comparable with polystyrene. It feels like nylon, has a bursting strength three times that of low-density polyethylene, and withstands repeated exposure to 250 F, hence, it can be sterilized. 

The physical characteristics of polyethylene resins vary widely as a function of their density. The density of polyethylene is highest when it has very few branches to impede the crystallization process. A 3 mm thick plaque of high density polyethylene is an opaque white solid that can... 

What characteristics of high density polyethylene make it suitable for the manufacture of rigid pipe What limitations would there be in the use of this pipe ... 

A major characteristic of the Phillips process chain polymerisation of ethylene is that it leads to very limited branching. The resulting polymer is thus highly linear and can reach high levels of crystallinity, hence high densities approaching 0.96-0.97. Such a polyethylene is known as HDPE for "High-density polyethylene". 

The effects of ionizing radiation on a low and a high density polyethylene and an ionomer indicate that similar networks are formed in the ionomer and in the low density polyethylene. The former crosslinks about 1.5 times as readily as the latter. In the high density resin, the network characteristics, and hence, presumably, the type and distribution of links, differ considerably from those in the other two resins. As a result, crosslinking rates in the high and low density polyethylenes cannot be directly compared. 

Ethylene Polymers. Depending on the polymerization conditions, three major types of polyethylene are manufactured low-density polyethylene (LDPE) by free-radical polymerization, linear low-density polyethylene (LLDPE) by copolymerization of ethylene with terminal olefins, and high-density polyethylene (HDPE) by coordination polymerization. The processes yield polymers with different characteristics (molecular weight, molecular weight distribution, melt index, strength, crystallinity, density, processability). 

Much work has been done within the framework of the international programme JUPAC by 14 laboratories of different companies to reveal a characteristic of polymer material correlating with specific features of its molding into sleeve film67). The studies were conducted with two samples of low-density polyethylene and two samples of high-density polyethylene. The samples had minor differences in molecular-weight distribution and ramification characterized by the content of different side branches. 

In 102,103) we have also studied rheological characteristics of the flow of molten polymers and compositions under conditions of acoustic treatment. Experiments indicate that the flow-rate of polymers through channels can be increased significantly with the help of acoustic treatment of molten polymers. Figures 21 gives the relative increase in the flow rate of high-density polyethylene versus amplitude of acoustic treatment. 

Fig. 7.18 (a) Characteristic morphologies of an incompatible blend of high density polyethylene... 

An additive system was developed for poly(vinyl chloride) for medical applications. The additives include primary stabilisers (Ca-Zn stearate and Zn stearate), secondary stabilisers (epoxides) and lubricants (ethylene bisamide and high density polyethylene), to improve melt processing and heat stability. The use of the stabilisers resulted in reduced equipment down-time, increased the level of recycled material which could be incorporated, and enhanced the product characteristics, including colour, clarity, blush, aqueous extractables and particle generation. 5 refs. 

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. 

The polymers mostly used in pharmaceutical packaging are polyethylene, polypropylene, PVC, polyamide, polystyrol, nylon, cellulose acetate, polyethylene terephthtalate, and blends thereof. Copolymers and rubbers are also used. The DSC melting curve of polyethylene used for packaging purposes is characteristic. Low- and high-density polyethylene are differentiated by their melting points. " Melting point and density of polyethylene are linearily correlated. " Crystallinity may be determined as described above for amorphous state. 

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