Induction of Stereocomplex Crystallization in Poly(<scp>l</scp>‐lactide)/Poly(<scp>d</scp>‐lactide) Blends with High Molecular Weight by Halloysite Nanotubes

Wei, Yafei; Tian, Yang; Tian, Xiujuan; Fu, Zhenjiang; Zhao, Lifen

doi:10.1002/macp.202100356

Cited by 9 publications

(3 citation statements)

References 45 publications

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“…These include the synthesis of stereo-block PLLA- b -PDLA, − melt blending at a temperature between the melting points of SC and HC, , adding nucleating agents, , flow-induced crystallization, ,, high temperature annealing, , etc. In spite of all this effort, crystallization of pure SC still remains an unsolved challenge, especially in a high-molecular-weight (HMW) PLLA/PDLA racemate. − …”

Section: Introductionmentioning

confidence: 99%

Poisoning by Purity: What Stops Stereocomplex Crystallization in Polylactide Racemate?

et al. 2023

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Formation of stereocomplex crystals (SC) is an effective way to improve the heat resistance and mechanical performance of poly(lactic acid) products. However, at all but the slowest cooling rates, SC crystallization of a high-molecular-weight poly(l-lactic acid)/poly(d-lactic acid) (PLLA/PDLA) racemate stops at a high temperature or does not even start, leaving the remaining melt to crystallize into homochiral crystals (HC) or an SC–HC mixture on continuous cooling. To understand this intriguing phenomenon, we revisit the SC crystallization of both high- and low-molecular-weight PLLA/PDLA racemates. Based on differential scanning calorimetry (DSC), supplemented by optical microscopy and X-ray scattering, we concluded that what stops the growth of SC is the accumulation of the nearly pure enantiomer, either PDLA or PLLA, that is rejected from the SC ahead of its growth front. The excess enantiomer is a result of random compositional fluctuation present in the melt even if the average composition is 1:1. The situation is more favorable if the initial polymer is not fully molten or is brought up to just above the melting point where SC seeds remain, as proven by DSC and X-ray scattering. Moreover, we find that not only is SC growth poisoned by the locally pure enantiomer but also that at lower temperatures, the HC growth can be poisoned by the blend. This explains why SC growth, arrested at high temperatures, can resume at lower temperatures, along with the growth of HC. Furthermore, while some previous works attributed the incomplete SC crystallization to a problem of primary nucleation, we find that adding a specific SC-promoting nucleating agent does not help alleviate the problem of cessation of SC crystallization. This reinforces the conclusion that the main problem is in growth rather than in nucleation.

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Section: Introductionmentioning

confidence: 99%

Poisoning by Purity: What Stops Stereocomplex Crystallization in Polylactide Racemate?

et al. 2023

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“…Before use, the halloysite powder was chemically purified in our laboratory according to the reported methods. [25] The pristine HNTs were dispersed in 30% H 2 O 2 solution, ultrasonicated for 1 h, and then centrifuged from the liquid phase. The purified HNTs were obtained after drying in a vacuum oven at 60 C for 12 h.…”

Section: Methodsmentioning

confidence: 99%

Preparation of intercalating halloysite by in situ synthesized polymethyl methacrylate and its effects on the crystallization behaviors and mechanical properties of polylactic acid composites

et al. 2022

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Polylactic acid/halloysites (PLA/HNTs) composites with different nanotube contents were prepared by solution blending. Using unmodified HNTs and polymethyl methacrylate intercalated halloysites (PMMA-HNTs), their structures and properties were comparatively investigated. It is found that the glass transition temperature (T g ) of the composites is lower than that of pure PLA.In addition, both HNTs and PMMA-HNTs promoted the crystallization of PLA. However, due to the good dispersion of PMMA-HNTs in the matrix, the crystallinity of PMMA-HNTs-modified PLA is higher than that of HNTsmodified PLA loaded with the same nanoparticles. The study on the mechanical properties of PMMA-HNTs and HNTs-modified PLA composites suggested that when the content of PMMA-HNTs was not higher than 4 wt%, it could simultaneously improve the elongation at break and tensile strength. Thermal stability studies showed that the T 5% and T max of the two composites did not improve significantly, but the amount of carbon residues increased. This study provides a new strategy for modifying HNTs and preparing PLA composites with good comprehensive properties.

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“…As shown in Figure 3c, the diffraction peaks located at 2θ = 12.0 and 20.1 were attributed to the (110) and (300)/(030) reflections of SCs, respectively. 45,46 Of note, the diffraction peaks of SCs for the PLLA/g-CNCs/Scfibers annealed at 250 C were much more diffuse than that annealed at 200 C, which was related to crystal imperfection and usually attributed to lower molecular weight.…”

Section: Crystallization Behaviormentioning

confidence: 98%

Effect of electrospun stereocomplex PLA fibers and modified cellulose nanocrystals on crystallization of poly(L‐lactic acid)

Wan

Zhuang

et al. 2023

J of Applied Polymer Sci

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Poly(L-lactic acid) (PLLA) is a biodegradable polymer that has attracted increasing attention due to its fantastic properties. Nevertheless, the disadvantages of PLLA, such as low crystallization rate and brittleness, limit its wide commercial applications. In the present work, electrospun stereocomplex PLA fibers (Sc-fibers) and PLLA grafted cellulose nanocrystals (g-CNCs) are prepared as nano-fillers and then blended with PLLA matrix to prepare different nanocomposites. Both of nano-fillers would accelerate the crystallization rate of PLLA, and as expected, g-CNCs have much stronger nucleation ability towards PLLA than Sc-fibers. Nevertheless, the crystallization of PLLA will decrease to some extent in the presence of both nano-fillers of g-CNCs and Scfibers due to the preferential formation of stereocomplex crystals on the surfaces of CNCs. Moreover, the presence of nano-fillers would enhance the mechanical properties of PLLA, such as the elongation at break can increase by four times after incorporating both g-CNCs and Sc-fibers. This work provides a new consideration for designing different nano-fillers, especially for polymer matrices with low crystallization ability and brittleness.

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Induction of Stereocomplex Crystallization in Poly(l‐lactide)/Poly(d‐lactide) Blends with High Molecular Weight by Halloysite Nanotubes

Cited by 9 publications

References 45 publications

Poisoning by Purity: What Stops Stereocomplex Crystallization in Polylactide Racemate?

Poisoning by Purity: What Stops Stereocomplex Crystallization in Polylactide Racemate?

Preparation of intercalating halloysite by in situ synthesized polymethyl methacrylate and its effects on the crystallization behaviors and mechanical properties of polylactic acid composites

Effect of electrospun stereocomplex PLA fibers and modified cellulose nanocrystals on crystallization of poly(L‐lactic acid)

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