| Polyolefins are the most widely used synthetic polymer materials at present. The study on solubilities of olefins in various polyolefins is important to the polyolefin industry, such as synthesis process, removal of residual monomers, and post-reactor modification.A experimental apparatus was established to measure the solubility and swelling volume data of propylene the propylene in semi-crystalline polyofins including isotactic polypropylene (i-PP), high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE) using a pressure-decay method. The experiments were carried out over wide temperature (75, 85,95 and 110 ℃) and pressure range (0-9MPa).The results were corrected with polymer swelling volume, and correlated with the Sanchez-Lacombe equation of state (SL EoS) with a temperature dependent binary interaction parameters k12. The results showed that the SL EoS could well predict the solubility of propylene in polyolefins, where the average deviation between experimental data and calculated results were within 4%. The relationship between k12 and temperature was provided. Therefore, the solubility of propylene in semi-crystalline polyolefins can be estimated under various conditions.The results demonstrated that solubilities of propylene in polyolefins were increased with elevated pressure and decreased with increased temperature. Meanwhile, it was found that the solubility of propylene in different polyolefins decreased in the order i-PP> LDPE> LLDPE, although the crystallinity of these polyolefin samples were similar. Moreover, propylene had higher solubility in i-PP than HDPE when the crystallinity of i-PP (59.9%) and HDPE (61.0%) were nearly the same. These suggested that the molecular structure of polyolefins and the dagree of long and short chain branching have significant influences in propylene solubilities.The interaction between the propylene solubility and the crystallinity of i-PP was also studied. The results showed that the crystallinity would influence the solubilities of propylene in the amorphous phase of i-PP. The higher crystallinity of i-PP would cause lower solubility of propylene. The relationship between k12 and crystallinity was provided. Therefore, the solubility of propylene in other semi-crystalline polypropylene with various crystallinity can be estimated.This work also found that the process of propylene dissolution could affect the crystallinity degree of i-PP. Moreover, the crystallinity degree, equilibrium time, equilibrium temperature and pressure could affect the induced crystallization. Low crystallinity degree of raw polymer sample, long equilibrium time, high temperature (below the metal point of i-PP) and high pressure could promote the process of induced crystallization. |
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