Crystallization, Melting, and Branching of Polyethylenes

The melting temperature of PE varies over a broad range with the equilibrium melting temperature as the upper limit for LPE. The melting temperature varies with lamella 

Linear polyethylene (LPE or HOPE) has been blended with LLDPE with varying branch distributions. The critical branch content for phase separation was lower for mPE, where the branches were more evenly distributed, than for Ziegler-Natta LLDPE, where the branches are heterogeneously distributed. Where cocrystallization occurred, the unit cell of the crystals showed marked expansion (4). Crystallization conditions were shown to be important for the cocrystallization of blends of linear and branched polyethylenes, low isothermal temperatures promote cocrystallization as did quench cooling (5). 

ULDPE do not overlap, so it can be assumed that the branching distributions do not overlap making it unlikely that any components from each polymer would be dissolved in the other. 

Within a BPE with a distribution of branches, there will be a distribution of lamella thickness. This will result in a broad melting range. BPE with a bimodal distribution of branches will have a bimodal distribution of lamella thickness and a corresponding melting temperature range. When two polyethylenes are blended, assuming they are miscible, they will cocrystallize only where they have common MSL. Some molecular segments in each BPE will crystallize independently of 

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