Resins linear low-density polyethylene

Figure 1 Plot of density as a function of branch content for compression-molded density and linear low density polyethylene resins. (From Refs. 2 and 103.)...

Rotationally molded products have walls of uniform thickness that are free of orientation and weld lines. As such they are resistant to environmental stress cracking and are therefore suitable for use in large-scale chemical containment uses. Linear low density polyethylene resins excel in such applications. Storage tanks of up to several thousand gallons capacity are used in agricultural, domestic (septic systems), and industrial applications. On a smaller scale, rotationally molded fuel tanks (chemically treated to reduce diffusion) are used on tractors, cars, and small gasoline-powered appliances. 

Figure 2 Schematic diagram showing the viscosity versus shear rate eharaeteristics of conventional and metallocene linear low density polyethylene resins.

The mechanical properties of metallocene-type linear low density polyethylene resins are better than conventional resins in many respects, but there are also deficiencies in certain areas. On the positive side, the impact strength, puncture resistance, and tensile strength of metallocene-type linear low density polyethylene films are all improved by a considerable margin over those of conventional resins—300%, 50%, and 40%, respectively, according to one resin manufacturer... 

On the downside, metallocene-type linear low density polyethylene films have lower tear strengths than their conventional counterparts. When tear strength is not a crucial factor, the use of metallocene-type linear low density polyethylene resins permits downgauging, which is always attractive to film converters. 

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