Removing Inorganic Impurities from Polypropylene by Swelling-Complexation Process

To address the issue of residual inorganic impurities degrading the electrical properties of insulating materials， this study proposes a swelling-chelating deashing method for purifying polypropylene （PP）. Multiple complexing agents-including aliphatic alcohols， glycol diethers， tetramethylethylenediamine （TMEDA）， and acetylacetone etc. were employed in conjunction with polymer swelling to remove inorganic impurities （Mg， Al， Ti） from commercial PP. Among them， acetylacetone exhibited the highest removal rate， which can reduce the inorganic ash content of PP from 33.88 mg/L to 9.06 mg/L， with a removal rate of 73.3%. The ash content was further reduced to 3.63 mg/L by using a compound agent （acetic acid/acetylacetone）. For a high-impurity PP grade， ash content was reduced from 50.09 mg/L to 9.68 mg/L （80.7% removal）. Differential scanning calorimetry （DSC） and electrical tests confirmed that deashing enhanced crystallinity and insulation properties： breakdown strength increased by 29.1 and 50.5 kV/mm， while resistivity rose by 2.59×10¹³ and 4.34×10¹³ Ω·m for the two PP grades （PP1， PP2）， respectively. This work provides an effective strategy to advance PP′s application in high-performance cable insulation.