Blends of Short and Long Branched Polyethylenes

Kyu et al. (2) and Ree et al. (3,5) studied blends of LLDPE-B (114,000 M , 4.50 PDI, and 18 ethyl branches per 1000 backbone carbons) and LDPE (286,000 M, 15.98 PDI, and 26 short and 1.6 long branches per 1000 backbone carbons) using in situ small-angle light scattering (SALS) and DSC and found that these blends are miscible across the whole composition range. Similar miscibihty results were reported for LDPE blends with LLDPE-B and LLDPE-O polymers by other research groups. The DSC and DMTA analysis of Lee et al. (43) confirmed that the blends of LLDPEs (LLDPE-B 89,300 M, 3.8 PDI, and 15-16 branches per 1000 backbone carbons LLDPE-O 93,100 M, 3.6 PDI, and 15-16 branches per 1000 backbone carbons) and LDPEs (73,000-98,000 and 8.7-9.2 PDI 32-34 branches per 1000 

Lee and Denn (44), however, reported somewhat different results on LLDPE/ LDPE blends. They investigated blends of LDPE (388,440 M, 10.0 PDI, and 32 branches per 1000 backbone carbons) with LLDPE polymers (68,300-134,000 and 3.2-3.S PDI 10-16 short branches per 1000 backbone carbons) at 160°C using 

Contrary to the reports discussed above, Liu et al. (60) reported rheological results indicating that the LLDPE-B (45,700 M, 2.1 PDI, and 13.5 ethyl branches per 1000 backbone carbons) and LDPE (102,000 M , 6.8 PDI, and 27.5 branches per 1000 backbone carbons) blend is an immiscible system. 

As reviewed above, there is still no consensus on the miscibility of LLDPE/ LDPE blends, or the effects of short and long branches on the miscibility. Furthermore, the lack of detailed SANS analysis on LLDPE/LDPE blends is surprising, although the miscibility specifications of these blends are highly demanded, particularly in relation to their various applications in the polymer industry. 

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