The role of nucleating agents in high-pressure-induced gamma crystallization in isotactic polypropylene

Abstract

Nucleation of the γ-form in isotactic polypropylene (PP) under high pressure was investigated. Three nucleating agents were used to nucleate crystallization of PP under atmospheric pressure: commercial Hyperform HPN-20E from Milliken Chemical, poly(tetrafluoroethylene) particles nucleating the α-form, and calcium pimelate nucleating the β-form. Crystallization of neat PP and PP with addition of 0.2 wt% of the nucleating agents was studied. Specimens were either kept at 200 °C under pressure of 200 MPa for time ranging from 2 min to 4 h or for 15 min under pressure ranging from 1.3 to 300 MPa. After cooling to ambient temperature and releasing the pressure, the specimens were analyzed by DSC, WAXD, and PLM to have an insight into the structure and to determine a crystallinity level and contents of crystallographic forms. Both α-nucleating agents strongly nucleated crystallization of PP under high pressure in the γ-form, whereas the β-nucleating agent had only a slight effect. The results show the possibility to use nucleating agents to nucleate the γ-form of PP under high pressure.

High-Pressure Crystallization of iPP Nucleated with 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol

“…PLM micrographs of thin sections of neat PP and PP/M02 crystallized according to protocol II are shown in Figure 8 . In neat PP, rather large polycrystalline aggregates, which obviously started to grow at 200 °C, are accompanied by smaller ones, which grew during cooling, as described previously [ 41 ]. Obviously, the crystallization was not completed at 200 °C and continued during cooling.…”

“…Melt flow index, determined according to ISO 1133 under 230 °C/2.16 kg, was equal to 25 g/10 min. The same polymer was used in our previous studies [ 41 , 42 , 43 ]. DMDBS Millad 3988i from Milliken Chemical (Spartanburg, SC, USA) was used to nucleate PP.…”

“…Our previous works revealed that high pressure γ-form of iPP was nucleated on heterogeneities, which under P atm nucleated the usual α-form [ 40 ]. Moreover, it was found that the nucleating agents, which nucleated the common α-form under P atm , efficiently nucleated the crystallization in the γ-form under high P [ 40 , 41 , 42 , 43 ]. Three nucleants were tested: particles of poly(tetrafluoroethylene), which is known to nucleate the α-form [ 44 , 45 ], and two commercial α-form nucleants: Hyperform HPN-20E (Milliken Chemical), containing calcium salt of cis-1,2-cyclohexanedicarboxylic acid, and ADK Stab NA-11UH (Adeka Palmarole) containing sodium 2,2′-methylene-bis-(4,6-di-t-butylphenyl) phosphate.…”

Synergistic Effect of Pressurization Rate and β-Form Nucleating Agent on the Multi-Phase Crystallization of iPP

“…Different kinds of NAs could promote the formation of the corresponding crystal phase according to the epitaxy theory, but this seems different in some circumstances, such as the crystallization under high pressure. Sowinski et al have shown that under high pressure, iPP can be efficiently nucleated in the γ-form by poly(tetrafluoroethylene) and Hyperform HPN-20E, both of which are known to nucleate the strong crystallization of iPP in the α-form at atmospheric pressure [19]. Zapala et al demonstrated that under high pressure, the γ-iPP could be promoted by active heterogeneities, which were able to nucleate in α-form [20].…”

“…When NAs and pressure treatment take effect simultaneously, an effective approach may be developed to improve iPP polymorphic crystallization [12,19,31]. However, as mentioned above, till now most of the research focuses on iPP mixed with α-NAs, but few reports have devoted to the effects of pressure on crystallization of iPP containing β-NAs.…”