Crystallization-Modulated Nanoporous Polymeric Materials with Hierarchical Patterned Surfaces and 3D Interpenetrated Internal Channels

et al. 2021

Polymers

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In miscible crystalline/amorphous polymer blends, the exclusion behaviors of the latter with various molecular weights during the crystallization of the former were investigated by the combination of SAXS and DSC by taking a PVDF/PMMA blend as an example. The ratio between internal crystallinity from SAXS and overall crystallinity of the entire blend from DSC was employed to characterize the exclusion of PMMA. Our results indicate that the molecular weight of the amorphous component produces a remarkable influence on the diffusion coefficient (D) and the crystal growth rate (G) of the crystalline component. There are both inter-lamellar and inter-fibrillar structures when PVDF blended with lower-molecular-weight PMMA. With increasing molecular weight of PMMA, the decrease in crystal growth rate (G) dominates the enhanced exclusion behaviors of PMMA, resulting in bigger pores after extraction. Our results are significant not only for the basic understanding of crystallization in polymer blends, but also for the fabrication and structure control of porous structures based on crystallization templates.

Section: Resultsmentioning

confidence: 99%

Effect of PMMA Molecular Weight on Its Localization during Crystallization of PVDF in Their Blends

Lin

et al. 2021

Polymers

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“…In our previous work, a novel strategy has been developed to fabricate porous structures according to the crystallization template with the help of extraction, which is not only a facile way to prepare porous membranes but also an efficient method to re‐construct the distribution of two components in their blend. [ 18–22 ] On the one hand, the localization of amorphous component in inter‐ or inner‐spherulitic regions leads to different mechanical performance of the resultant porous membranes. The increase in inter‐spherulites fraction corresponds to lower stress and elongation at break due to the poor connectivity among neighboring spherulites [ 23 ] ; on the other hand, the fraction of amorphous component in inner‐spherulitic regions can be assessed by means of long periods in SAXS.…”

Section: Introductionmentioning

confidence: 99%

Inter‐spherulitic/inner‐spherulitic localization of PBSU during crystallization of PVDF in PVDF/PBSU blend

Cao

Journal of Polymer Science

et al. 2020

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In this work, the miscibility effect on the localization of poly(butylene succinate) (PBSU) during the crystallization of PVDF in their blend has been investigated. After annealed at 200 °C and 240 °C, homogeneous and phase‐separated structures can be obtained respectively, which was followed by isothermal crystallization at 141 °C. In the case of 200°C, PBSU tends to enrich in inner‐spherulitic regions because of the excellent miscibility of the blend and the higher growth rate of PVDF crystals. When the specimen was annealed at 240 °C, phase separation produces PVDF and PBSU domains. Upon cooling to 141 °C, one part of PBSU is miscible with , while the other part of it remains as phase‐separated domains due to the high viscosity and slow relaxation of them. The former accounts for the distribution of PBSU in inner‐spherulitic regions. In the latter, however, phase‐separated structures depress the diffusion of PVDF during its crystallization, leading to the lower magnitude of growth rate of spherulites. Both of them contribute to the localization of PBSU in inter‐spherulitic regions. The distribution of PBSU among PVDF spherulites has been validated by long periods, pore size, and mechanical performance of the porous PVDF membranes.

“…Nevertheless, the kinetic parameter Z c does not keep a constant as suggested by Jeziorny et al [33] at different scanning rates. The half crystallization time ( t 1/2 ) defined as the time taken to complete half of the full crystallization can be calculated by Equation (6).…”

Section: Resultsmentioning

confidence: 98%

“…Qiu et al [31] also found that the crystallization rate of PLA domains could be enhanced by POM fragment crystals in the PLA/POM blends with a small amount of POM. Furthermore, Zhu et al [32] reported a parallel-stripe structure observed in PLA/POM blend films, and Ye et al [33] reported a crystallization-modulated nanoporous structure for PLA/POM blends with hierarchical patterned surfaces and 3D interpenetrated internal channels due to such a partially miscible behavior. Huan et al [34] reported an investigation on the morphology, crystallization, rheology, and mechanical properties of PLA/POM blends so as to improve the heat resistance of PLA.…”

Section: Introductionmentioning

confidence: 99%

Development of Polyoxymethylene/Polylactide Blends for a Potentially Biodegradable Material: Crystallization Kinetics, Lifespan Prediction, and Enzymatic Degradation Behavior

et al. 2019

Polymers

This paper reported the development of polyoxymethylene (POM)/polylactide (PLA) blends for a potentially biodegradable material. A series of POM/PLA blends at different weight ratios were prepared by melt extrusion with a twin-screw extruder, and their mechanical properties, crystallization behavior and kinetics, thermal degradation kinetics and stability, lifespan prediction and enzymatic degradation behavior were investigated extensively. POM and PLA were found to be partially miscible in the melt state at low temperature and become phase-separated at elevated temperatures, and their blends exhibited a typical lower critical solution temperature behavior. There were two distinct glass transition temperatures (Tg) observed for POM/PLA blends at any mass ratios when quenched from the homogeneous state, and both POM and PLA domains showed an apparent depression in their respective Tg’s in the blends. Owing to the partial miscibility between two domains, the tensile strength and impact toughness of POM/PLA blends gradually decreased with an increase of PLA content, but their flexural strength and modulus presented an increasing trend with PLA content. The studies on non-isothermal and isothermal crystallization behaviors of the blends indicated that the crystallization rates of the blends decreased continually with increasing the PLA content, confirming that the crystallization of POM domain was controlled by the molecular-confined mechanism. The introduction of PLA into POM not only led to a slight increase of thermal stability of POM domain at low PLA contents but also shortened the lifespan of the blends, favoring the natural degradation of the blends. The POM/PLA blends exhibited an improvement in partially biodegradable performance with an increase of PLA content and their mass loss reached up to 25.3 wt % at the end of 48-h enzymatic degradation when 50 wt % of PLA was incorporated.