Molecular density molding

M, molecular weight per cross-linked unit MDA molecular density molding... 

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. 

A routine method for determining relative crystallinity based on the amorphous bands in the spectrum has proved more rapid and precise than the x-ray method. In practice, the ratio of the 778 cm-1 (12.85 ft) and 2367 cm-1 (4.22 ft) band intensities is measured. Use of a ratio eliminates the thickness measurement and increases precision to about 1% at 50% crystallinity and considerably better at higher levels. A density measurement and an infrared crystallinity determination when combined give an estimate of the fraction of microvoids which can occur in molded specimens of polytetrafluoroethylene. The density of a sample is predicted on the basis of its crystallinity as measured by the infrared method and the difference between this density and the actual density measured by displacement in water is a measure of the microvoid content. This determination is precise to about 0,2% voids by volume. By the use of confirmatory infrared measurements, it is possible to check the possibility that the presence of a substantial percentage of voids may have led to erroneous indications of the molecular weight in the standard specific gravity test discussed earlier. 

Products SCLAIRTECH process can produce PE products with density range of 0.905-0.965 kg/m3, melt index (Ml) from 0.2 to in excess of 150, and narrow to broad molecular weight distribution (MWD). This allows producers to participate in the majority of the polyethylene market segments including among low-, medium- and high-density films, rotational, injection and blow molding applications. 

Products A wide range of bimodal and unimodal products, with a full control of comonomer distribution, can be produced, with densities ranging from 918 to 970 kg/m3 and melt flowrate from less than 0.1 to over 100. The molecular weight distribution can be controlled from narrow to broad. Advanced properties are tailor-made applications such as pipe strength, film bubble stability as well as high ESCR and stiffness in blow molding. Other special applications include extrusion coating and wire cable. 

Products Polymer density is easily controlled from 0.915 to 0.970 g/cm. Depending on catalyst type, molecular weight distribution is either narrow or broad. Melt index maybe varied from less than 0.1 to greater than 200. Grades suitable for film, blow-molding, pipe, roto-molding and extrusion applications are produced. 

The density and melting points of the original material are high and decrease with molding steps and in samples with lower molecular weights (Table 4). 

The linear polyethylene produced by the Ziegler-Natta process, called hi li-clensity polyethylene, is a highly ctystalline polymer with 4000 to 7000 ethylene units per chain and molecular weights in the range 100,000 to 200,000 amu. High-density polyethylene has greater strength and heat resistance than the branched product of radical-induced polymerization, called low-density polyethylene, and is used to produce plastic squeeze bottles and molded housewares. 

Dowlex [Dow]. TM for a hybrid polyethylene of both low and high density, i.e., it has both linear and branched molecular structure. It can be used for both containers and bags. Forms available are film, injection molding, and extrusion. 

Wang, W.Q. Kontopoulou, M. Effect of molecular structure on the rotational molding characteristics of ultra-low-density-ethylene-a-olefin copolymers. Polym. Eng. Sci. 2004, 44 (3), 496-508. 

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