Model of Crystallization Behavior of Isotactic Polypropylene: The Role of Defects

Abstract

The crystallization behavior of propene–ethylene (iPPC2), propene–butene (iPPC4), propene–pentene (iPPC5), and propene–hexene (iPPC6) isotactic copolymers, prepared with single center metallocene catalysis, is described. Thanks to the perfectly random distribution of comonomers along the macromolecules, these copolymers can be considered as model for the crystallization behavior of isotactic polypropylene (iPP) that is mainly defined by the average length of the regular propene sequences. A model of the crystallization behavior of iPP is described based on the definition of a double effect of defects (stereodefects and comonomers), the interruption effect of defects excluded from the crystals that shortens the length of the crystallizable propene sequences inducing crystallization of the γ form, and the effect of inclusion of defects in the crystals of α form, γ form or δ form that induces the crystallization of the form whose lattice is less disturbed by the defect.

Self-Nucleation in Stereodefective Isotactic Polypropylene: The Impact of Stereodefects on the Melt Memory

“…It is apparent that almost identical values of f γ (max) are achieved in the two different crystallization conditions. As discussed above, the γ form is favored in stereodefective iPPs and tends to crystallize up to obtain a pure γ form in the very slow crystallizations at high isothermal crystallization temperatures, ,,,,,− whereas the α form is generally kinetically favored (as also indicated by Figures S3 and S4) and tend to crystallize at low isothermal crystallization temperatures or high cooling rates from the melt. ,, Therefore, the results of Figure B indicate that in rather fast crystallization from the melt by cooling at 10 °C/min that usually favors crystallization of the α form even in samples with high concentrations of stereodefects, high amount of γ form, similar to that achieved in slow isothermal crystallizations, can be obtained through self-nucleation when the melt is cooled from temperatures at which melt-memory is left.…”

Melt memory in propene–pentene isotactic copolymers: the case of defects hosted in the crystals

“…9 reminds us of analogous literature plots of the amount of the γ form that crystallizes in the same iPPC5 copolymers in isothermal crystallizations from the melt at different crystallization temperatures, 37 and in other copolymers of iPP with different comonomers. 38,52,53,55–60 These literature data demonstrate that iPPC5 copolymers crystallize in isothermal crystallization from the melt in mixtures of α and γ forms and the amount of the γ form increases with increasing crystallization temperature and for different samples, a maximum amount of the γ form is obtained at different crystallization temperatures. 37 The maximum amount of the γ form that crystallizes in isothermal crystallizations is different for different samples of copolymers and increases with increasing pentene concentration up to 6–7 mol% of pentene; then, it decreases for higher pentene content because of the favored crystallization of the δ form.…”

High-purity polypropylene from disposable face masks via solvent-targeted recovery and precipitation

“…The peaks were assigned according to the literatures. [17][18][19][20] The chemical shifts of both 1 H spectrum and 13 C spectrum were calibrated with the 1,1,2,2-tetrachloroethane-d 2 solvent peak: 6.00 ppm for 1 H spectrum and 74.0 ppm for 13 C spectrum. 21 High performance liquid chromatography (HPLC) was measured by a Waters 2695 separation module equipped with a Luna C18 (Phenomenex, part no.…”

“…S4b, † three major signals at δ 46.0, 28.4, 21.4 ppm in 13 C spectra of virgin PP corresponded to the carbon of methylene, methine, and methyl groups in the PP chain. 19 The peak at δ 21.1 ppm was the methyl group of toluene. 20 In the decolored PP spectrum, the integrated ratio of methylene, methine and methyl groups was 1 : 1 : 1, indicating the typical characteristics of PP.…”

“…The global pandemic of coronavirus disease 2019 (COVID- 19) has increased the use of disposable face masks with an estimated monthly consumption of 129 billion masks, which weigh 0.39-0.52 million tons. [1][2][3] Disposable face masks typically contain five components: outer layer, middle layer, inner layer, ear loop, and nose support.…”