LLDPE Particals

process

Both LDPE and LLDPE Particals have excellent rheological or melt flow properties.LLDPE has less shear sensitivity because it has a narrow molecular weight distribution and short branched chains. LLDPE maintains greater viscosity during shear and is therefore more difficult to process than LDPE with the same melt index. In extrusion, the lower shear sensitivity of LLDPE results in faster stress relaxation of the polymer molecular chains, and the resulting physical properties are less sensitive to changes in blow-up ratio. In melt extension, LLDPE generally has a lower viscosity at all strain rates. This means that it will not strain harden in tension as LDPE does.

As the rate of deformation of the polyethylene increases, LDPE shows a surprising increase in viscosity, which is caused by entanglement of the molecular chains. This phenomenon is not observed in LLDPE, where the lack of long branched chains keeps the polymer from tangling. This property is extremely important for film applications, and LLDPE films are easier to make thinner films while maintaining high strength and toughness.

The rheological properties of LLDPE Particals can be summarized as "rigid in shear" and "soft in extension". When replacing LDPE with LLDPE, film extrusion equipment and conditions must be modified. the high viscosity of LLDPE requires higher power extruders. The high viscosity of LLDPE requires the extruder to have more power and provide higher melt temperatures and pressures. The die gap must be widened to avoid lower output due to high backpressure and melt breakage, and the typical die gap sizes for LDPE and LLDPE are 0.024 to 0.040 and 0.060 to 0.10, respectively.

LLDPE's "soft on elongation" characteristic is a disadvantage in the blown film process, and LLDPE Particals blown film bubbles are not as stabilized as LDPE's. A typical single-lip air ring is sufficient for LDPE stabilization. A typical single-lip air ring is adequate for LDPE stabilization, but the unique bubble of LLDPE requires a more sophisticated double-lip air ring for stabilization. Cooling the internal bubble with a double-lip air ring increases bubble stabilization while increasing film production capacity at high production rates.For LLDPE or LLDPE-rich blends with LDPE, the use of a typical LDPE extruder requires improved equipment. Depending on the life of the extruder, improvements may be required in the form of wider die gaps, but processing conditions need to be optimized. The rotomolding process requires the LLDPE to be ground into uniform pellets (35 mesh). The process consists of filling the mold with powdered LLDPE, heating and rotating the mold biaxially to distribute the LLDPE. After cooling the product is removed from the mold.