Special Issue "Honor the Achievements of Prof. Alejandro J. Müller in Polymer Crystallization"

A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Analysis and Characterization".

Deadline for manuscript submissions: closed (30 April 2021).

Special Issue Editors

Prof. Dr. Dario Cavallo
E-Mail Website
Guest Editor
Department of Chemistry and Industrial Chemistry, University of Genoa, Via Dodecaneso 31, 16146 Genova, Italy
Interests: structuring processes of semicrystalline polymers
Prof. Dr. Guoming Liu
E-Mail Website
Guest Editor
Institute of Chemistry, Chinese Academy of Sciecnes, Beijing 100049, China
Interests: polymer structure & property relationship; polymer crystallization and relaxation in confined spaces; characterization of solid material structure by X-ray scattering

Special Issue Information

Dear Colleagues,

We are pleased to announce an honorary Special Issue of Polymers on the great contributions of Prof. Dr. Alejandro J. Müller on polymer crystallization.

Prof. A.J. Müller is an IKERBASQUE (Basque Foundation for Science) Research Professor at POLYMAT and the Polymer Science and Technology Department, Faculty of Chemistry, University of the Basque Country UPV/EHU in Donostia-San Sebastián, Spain. He is also an Editor for POLYMER (Elsevier), IF (2019): 4.231 (Q1), in the joint areas of Polymer Physics and Physical Chemistry. He is a Corresponding Member of the “Academia Nacional de la Ingeniería y del Hábitat de Venezuela (ANIH)" or Venezuelan National Academy of Engineering and Habitat.

He has co-authored more than 500 publications, which have been cited over 12000 times, with a H-index of 61. He has tutored 90 B.Sc. theses, 57 M.Sc., and 22 Ph.D. theses. He has won several awards in Venezuela, including the Lorenzo Mendoza Fleury, Polar Prize for basic science. In 2011, he received the international "Paul J. Flory Polymer Research Prize." Prof. Müller has given more than 85 keynotes, plenary, and invited lectures in more than 25 countries.

Prof. Müller has devoted many years of his research to the understanding of polymer crystallization. Among his most significant contributions, the following can be mentioned:

1) Understanding fractionated crystallization in polymer blends. The group of Prof. Müller was among the first to demonstrate that the fractionated crystallization of dispersed polymer micro-droplets was due to the lack of highly active heterogeneities (such as those in the bulk polymer) using self-nucleation and other nuclei injection approaches. They systematically study the effect of dispersion, droplet sizes, and the use of compatibilizers.

2) The first topic above led to the study of confined micro-domains in block copolymers. The group led by Müller was one of the first to study the nucleation and crystallization of confined block copolymers. They first studied strongly segregated block copolymers and worked on how confinement affected the crystallization kinetics recognizing the impact of nucleation on the Avrami index and the possible nucleating modalities: fractionated crystallization, surface-induced nucleation, and homogeneous nucleation.

3) Confinement and fractionated crystallization studies were also extended to polymer infiltration within anode aluminum oxide (AAO) nanoporous templates, where he and collaborators found that the origin of fractionated crystallization was the percolation of residual material on the surface. The crystallization kinetics of infiltrated materials (with well-cleaned template surfaces) transformed into nucleation-dominated kinetics.

4) Prof. Müller’s group was also one of the first to study the crystallization of double crystalline diblock copolymers and terpolymers both strongly segregated and weakly segregated. His group was able to show examples of “templated” crystallization leading to double crystalline and triple crystalline spherulites and their inter-lamellar assembly.

5) In the field of nanocomposites, he coined the term “super-nucleation” to describe the efficiency of certain nucleating agents (such as carbon nanotubes) that can be more efficient that the polymer self-nuclei.

6) He developed, with his group, the thermal fractionation technique successive self-nucleation and annealing (SSA). This technique has found a large number of applications for the characterization of any polymer whose linear crystallizable sequence is interrupted by branches, comonomers, stereo-defects, etc.

7) He and his collaborators have recently made important contributions to long-standing problems in polymer crystallization, such as isodimorphic copolyesters and crystalline memory effects.

All submissions in polymer science are welcome and not limited to the polymer crystallization field.

Prof. Dr. Dario Cavallo
Prof. Dr. Guoming Liu
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Polymers is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2200 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Polymer crystallization
  • Block copolymers
  • Nucleation
  • Confined crystallization
  • Morphology
  • Crystallization kinetics
  • Thermal analysis
  • Random copolymers
  • Polymer blends
  • Nucleating agents
  • Nanocomposites
  • Self-assembly
  • AAO templates

Published Papers (15 papers)

Order results
Result details
Select all
Export citation of selected articles as:

Research

Jump to: Review

Communication
Surface Crystal Nucleation and Growth in Poly (ε-caprolactone): Atomic Force Microscopy Combined with Fast Scanning Chip Calorimetry
Polymers 2021, 13(12), 2008; https://doi.org/10.3390/polym13122008 - 19 Jun 2021
Cited by 1 | Viewed by 444
Abstract
By using an atomic force microscope (AFM) coupled to a fast scanning chip calorimeter (FSC), AFM-tip induced crystal nucleation/crystallization in poly (ε-caprolactone) (PCL) has been studied at low melt-supercooling, that is, at a temperature typically not assessable for melt-crystallization studies. Nanogram-sized PCL was [...] Read more.
By using an atomic force microscope (AFM) coupled to a fast scanning chip calorimeter (FSC), AFM-tip induced crystal nucleation/crystallization in poly (ε-caprolactone) (PCL) has been studied at low melt-supercooling, that is, at a temperature typically not assessable for melt-crystallization studies. Nanogram-sized PCL was placed on the active/heatable area of the FSC chip, melted, and then rapidly cooled to 330 K, which is 13 K below the equilibrium melting temperature. Subsequent isothermal crystallization at this temperature was initiated by a soft-tapping AFM-tip nucleation event. Crystallization starting at such surface nucleus led to formation of a single spherulite within the FSC sample, as concluded from the radial symmetry of the observed morphology. The observed growth rate in the sub-micron thin FSC sample, nucleated at its surface, was found being much higher than in the case of bulk crystallization, emphasizing a different growth mechanism. Moreover, distinct banding/ring-like structures are observed, with the band period being less than 1 µm. After crystallization, the sample was melted for gaining information about the achieved crystallinity and the temperature range of melting, both being similar compared to much slower bulk crystallization at the same temperature but for a much longer time. Full article
Show Figures

Graphical abstract

Article
Crystallization of Long-Spaced Precision Polyacetals III: Polymorphism and Crystallization Kinetics of Even Polyacetals Spaced by 6 to 26 Methylenes
Polymers 2021, 13(10), 1560; https://doi.org/10.3390/polym13101560 - 13 May 2021
Cited by 1 | Viewed by 585
Abstract
In this paper we extend the study of polymorphism and crystallization kinetics of aliphatic polyacetals to include shorter (PA-6) and longer (PA-26) methylene lengths in a series of even long-spaced systems. On a deep quenching to 0 °C, the longest even polyacetals, PA-18 [...] Read more.
In this paper we extend the study of polymorphism and crystallization kinetics of aliphatic polyacetals to include shorter (PA-6) and longer (PA-26) methylene lengths in a series of even long-spaced systems. On a deep quenching to 0 °C, the longest even polyacetals, PA-18 and PA-26, develop mesomorphic-like disordered structures which, on heating, transform progressively to hexagonal, Form I, and Form II crystallites. Shorter polyacetals, such as PA-6 and PA-12 cannot bypass the formation of Form I. In these systems a mixture of this form and disordered structures develops even under fast deep quenching. A prediction from melting points that Form II will not develop in polyacetals with eight or fewer methylene groups between consecutive acetals was further corroborated with data for PA-6. The temperature coefficient of the overall crystallization rate of the two highest temperature polymorphs, Form I and Form II, was analyzed from the differential scanning calorimetry (DSC) peak crystallization times. The crystallization rate of Form II shows a deep inversion at temperatures approaching the polymorphic transition region from above. The new data on PA-26 confirm that at the minimum rate the heat of fusion is so low that crystallization becomes basically extinguished. The rate inversion and dramatic drop in the heat of fusion irrespective of crystallization time are associated with a competition in nucleation between Forms I and II. The latter is due to large differences in nucleation barriers between these two phases. As PA-6 does not develop Form II, the rate data of this polyacetal display a continuous temperature gradient. The data of the extended polyacetal series demonstrate the important role of methylene sequence length on polymorphism and crystallization kinetics. Full article
Show Figures

Graphical abstract

Article
Strain-Induced Form Transition and Crystallization Behavior of the Transparent Polyamide
Polymers 2021, 13(7), 1028; https://doi.org/10.3390/polym13071028 - 26 Mar 2021
Viewed by 513
Abstract
A transparent polyamide, poly(4,4′-aminocyclohexyl methylene dodecanedicarboxylamide) (PAPACM12), was studied and characterized by in situ wide-angle X-ray diffraction (WAXD) to establish the relationship between its crystallization behavior, crystalline form transition under external fields, and macroscopic properties. During the heating process, cold crystallization occurred and [...] Read more.
A transparent polyamide, poly(4,4′-aminocyclohexyl methylene dodecanedicarboxylamide) (PAPACM12), was studied and characterized by in situ wide-angle X-ray diffraction (WAXD) to establish the relationship between its crystallization behavior, crystalline form transition under external fields, and macroscopic properties. During the heating process, cold crystallization occurred and increased, and there was no form transition below the melting point. During the isothermal process, PAPACM12 exhibited the same crystalline structure as that during the heating process. The crystalline structure of PAPACM12 was attributed to α-form crystal, which is the stable form, according to the WAXD diffraction peaks of the conventional AABB-type polyamides. During stretching deformation, the crystal transition from α-form to γ-form and strain-induced crystallization were observed to contribute to the PAPACM12 with higher breaking strength and elongation. This study firstly determine the crystalline structure of transparent polyamides, and then the controlled strain-induced crystallization and transformation are demonstrated to be effective preparation methods for polyamides with high properties. Full article
Show Figures

Figure 1

Article
Matching Rheology, Conductivity and Joule Effect in PU/CNT Nanocomposites
Polymers 2021, 13(6), 950; https://doi.org/10.3390/polym13060950 - 19 Mar 2021
Viewed by 474
Abstract
We investigated polyurethane (PU)–carbon nanotube (CNT) nanocomposites (PU/CNT) in a range of concentrations from 1 to 8 wt% CNT as hot melt adhesives. We studied the thermal properties of the nanocomposites, which is relevant from an applied point of view. The phase angle [...] Read more.
We investigated polyurethane (PU)–carbon nanotube (CNT) nanocomposites (PU/CNT) in a range of concentrations from 1 to 8 wt% CNT as hot melt adhesives. We studied the thermal properties of the nanocomposites, which is relevant from an applied point of view. The phase angle plots versus complex modulus results revealed the existence of a maximum above a given CNT concentration. The intensity of the peak and associated relaxation time was analyzed with percolation theory, leading to a new method to determine the rheological percolation threshold. A lower threshold value was obtained from the electrical conductivity data, which was justified recalling that the hopping/tunnelling effect takes place in the nanocomposite, as stated by previous studies in the literature. Joule effect studies indicated that the heating effect was very significant, reaching temperature increases, ΔT, of 60 °C for low voltages. For the first time, the percolation equation was applied to the ΔT to obtain the corresponding threshold. Stimulus-responsive systems were conceived considering the correlation between the ΔT and the conductivity. The case of PU/CNT nanocomposites acting as hot melt adhesives that are welded/unglued by applying/removing an electrical voltage is presented. Full article
Show Figures

Graphical abstract

Article
Fast-Scanning Chip-Calorimetry Measurement of Crystallization Kinetics of Poly(Glycolic Acid)
Polymers 2021, 13(6), 891; https://doi.org/10.3390/polym13060891 - 14 Mar 2021
Cited by 1 | Viewed by 643
Abstract
We report fast-scanning chip-calorimetry measurement of isothermal crystallization kinetics of poly(glycolic acid) (PGA) in a broad temperature range. We observed that PGA crystallization could be suppressed by cooling rates beyond −100 K s−1 and, after fast cooling, by heating rates beyond 50 [...] Read more.
We report fast-scanning chip-calorimetry measurement of isothermal crystallization kinetics of poly(glycolic acid) (PGA) in a broad temperature range. We observed that PGA crystallization could be suppressed by cooling rates beyond −100 K s−1 and, after fast cooling, by heating rates beyond 50 K s−1. In addition, the parabolic curve of crystallization half-time versus crystallization temperature shows that PGA crystallizes the fastest at 130 °C with the minimum crystallization half-time of 4.28 s. We compared our results to those of poly(L-lactic acid) (PLLA) with nearby molecular weights previously reported by Androsch et al. We found that PGA crystallizes generally more quickly than PLLA. In comparison to PLLA, PGA has a much smaller hydrogen side group than the methyl side group in PLLA; therefore, crystal nucleation is favored by the higher molecular mobility of PGA in the low temperature region as well as by the denser molecular packing of PGA in the high temperature region, and the two factors together decide the higher crystallization rates of PGA in the whole temperature range. Full article
Show Figures

Graphical abstract

Article
Isothermal Crystallization Kinetics of Poly(ethylene oxide)/Poly(ethylene glycol)-g-silica Nanocomposites
Polymers 2021, 13(4), 648; https://doi.org/10.3390/polym13040648 - 22 Feb 2021
Viewed by 559
Abstract
In this work, the crystallization kinetics of poly(ethylene oxide) (PEO) matrix included with poly(ethylene glycol) (PEG) grafted silica (PEG-g-SiO2) nanoparticles and bare SiO2 were systematically investigated by differential scanning calorimetry (DSC) and polarized light optical microscopy (PLOM) method. [...] Read more.
In this work, the crystallization kinetics of poly(ethylene oxide) (PEO) matrix included with poly(ethylene glycol) (PEG) grafted silica (PEG-g-SiO2) nanoparticles and bare SiO2 were systematically investigated by differential scanning calorimetry (DSC) and polarized light optical microscopy (PLOM) method. PEG-g-SiO2 can significantly increase the crystallinity and crystallization temperature of PEO matrix under the non-isothermal crystallization process. Pronounced effects of PEG-g-SiO2 on the crystalline morphology and crystallization rate of PEO were further characterized by employing spherulitic morphological observation and isothermal crystallization kinetics analysis. In contrast to the bare SiO2, PEG-g-SiO2 can be well dispersed in PEO matrix at low P/N (P: Molecular weight of matrix chains, N: Molecular weight of grafted chains), which is a key factor to enhance the primary nucleation rate. In particular, we found that the addition of PEG-g-SiO2 slows the spherulitic growth fronts compared to the neat PEO. It is speculated that the interfacial structure of the grafted PEG plays a key role in the formation of nuclei sites, thus ultimately determines the crystallization behavior of PEO PNCs and enhances the overall crystallization rate of the PEO nanocomposites. Full article
Show Figures

Graphical abstract

Article
In Situ Synthesis of Poly(butyl methacrylate) in Anodic Aluminum Oxide Nanoreactors by Radical Polymerization: A Comparative Kinetics Analysis by Differential Scanning Calorimetry and 1H-NMR
Polymers 2021, 13(4), 602; https://doi.org/10.3390/polym13040602 - 17 Feb 2021
Cited by 2 | Viewed by 708
Abstract
In this work, we explore the ability to generate well-defined poly(butyl methacrylate) (PBMA) nanostructures by “in situ” polymerization of butyl methacrylate monomer (BMA). PBMA nanostructures of high and low aspect ratios have been successfully obtained through the free radical polymerization (FRP) of a [...] Read more.
In this work, we explore the ability to generate well-defined poly(butyl methacrylate) (PBMA) nanostructures by “in situ” polymerization of butyl methacrylate monomer (BMA). PBMA nanostructures of high and low aspect ratios have been successfully obtained through the free radical polymerization (FRP) of a BMA monomer in anodic aluminum oxide (AAO) nanoreactors of suitable size. A polymerization kinetics process has been followed by differential scanning calorimetry (DSC) and proton Nuclear Magnetic Resonance spectroscopy (1H-NMR).The determination of the kinetics of polymerization through DSC is based on a quick and direct analysis of the exothermic polymerization process, whereas the analysis through 1H-NMR also allows the unambiguous chemical analysis of the resulting polymer. When compared to bulk polymerization, both techniques demonstrate confinement effects. Moreover, DSC and 1H-NMR analysis give the same kinetics results and show a gel-effect in all the cases. The number average molecular weight (Mn) of the PBMA obtained in AAO of 60–300 nm are between 30·103–175·103 g/mol. Even if the Mn value is lower with respect to that obtained in bulk polymerization, it is high enough to maintain the polymer properties. As determined by SEM morphological characterization, once extracted from the AAO nanoreactor, the polymer nanostructures show controlled homogeneous aspect/size all throughout the length of nanopillar over a surface area of few cm2. The Young’s modulus of low aspect ratio PBMA nanopillars determined by AFM gives a value of 3.1 ± 1.1 MPa. In this work, a 100% of PBMA polymer nanostructures are obtained from a BMA monomer in AAO templates through a quick double process: 30 min of monomer immersion at room temperature and 90 min of polymerization reaction at 60 °C. While the same nanostructures are obtained by polymer infiltration of PBMA at 200 °C in about 6 h, polymerization conditions are much softer than those corresponding to the polymer infiltration process. Furthermore, the 1H-NMR technique has been consolidated as a tool for studying the kinetics of the copolymerization reactions in confinement and the determination of monomer reactivity ratios. Full article
Show Figures

Graphical abstract

Article
Insights into the Bead Fusion Mechanism of Expanded Polybutylene Terephthalate (E-PBT)
Polymers 2021, 13(4), 582; https://doi.org/10.3390/polym13040582 - 15 Feb 2021
Cited by 1 | Viewed by 603
Abstract
Expandable polystyrene (EPS) and expanded polypropylene (EPP) dominate the bead foam market. As the low thermal performance of EPS and EPP limits application at elevated temperatures novel solutions such as expanded polybutylene terephthalate (E-PBT) are gaining importance. To produce parts, individual beads are [...] Read more.
Expandable polystyrene (EPS) and expanded polypropylene (EPP) dominate the bead foam market. As the low thermal performance of EPS and EPP limits application at elevated temperatures novel solutions such as expanded polybutylene terephthalate (E-PBT) are gaining importance. To produce parts, individual beads are typically molded by hot steam. While molding of EPP is well-understood and related to two distinct melting temperatures, the mechanisms of E-PBT are different. E-PBT shows only one melting peak and can surprisingly only be molded when adding chain extender (CE). This publication therefore aims to understand the impact of thermal properties of E-PBT on its molding behavior. Detailed differential scanning calorimetry was performed on neat and chain extended E-PBT. The crystallinity of the outer layer and center of the bead was similar. Thus, a former hypothesis that a completely amorphous bead layer enables molding, was discarded. However, the incorporation of CE remarkably reduces the crystallization and re-crystallization rate. As a consequence, the time available for interdiffusion of chains across neighboring beads increases and facilitates crystallization across the bead interface. For E-PBT bead foams, it is concluded that sufficient time for polymer interdiffusion during molding is crucial and requires adjusted crystallization kinetics. Full article
Show Figures

Graphical abstract

Article
Poly(butylene succinate-co-butylene acetylenedicarboxylate): Copolyester with Novel Nucleation Behavior
Polymers 2021, 13(3), 365; https://doi.org/10.3390/polym13030365 - 24 Jan 2021
Viewed by 650
Abstract
Big spherulite structure and high crystallinity are the two main drawbacks of poly(butylene succinate) (PBS) and hinder its application. In this work, a new type of copolyester poly(butylene succinate-co-butylene acetylenedicarboxylate) (PBSAD) is synthesized. With the incorporation of acetylenedicarboxylate (AD) units into [...] Read more.
Big spherulite structure and high crystallinity are the two main drawbacks of poly(butylene succinate) (PBS) and hinder its application. In this work, a new type of copolyester poly(butylene succinate-co-butylene acetylenedicarboxylate) (PBSAD) is synthesized. With the incorporation of acetylenedicarboxylate (AD) units into PBS chains, the crystallization temperature and crystallinity are depressed by excluding AD units to the amorphous region. In contrast, the primary nucleation capability is significantly strengthened, without changing the crystal modification or crystallization kinetics, leading to the recovery of total crystallization rate of PBSAD under the same supercooling condition. The existence of specific interaction among AD units is found to be crucial. Although it is too weak to contribute to the melt memory effect at elevated temperature, the interaction continuously strengthens as the temperature falls down, and the heterogeneous aggregation of AD units keeps growing. When the aggregating process reaches a certain extent, it will induce the formation of a significant amount of crystal nuclei. The unveiled nucleation mechanism helps to design PBS copolymer with good performance. Full article
Show Figures

Graphical abstract

Article
Temperature-Modulated Scanning Calorimetry of Melting–Recrystallization of Poly(butylene terephthalate)
Polymers 2021, 13(1), 152; https://doi.org/10.3390/polym13010152 - 01 Jan 2021
Cited by 2 | Viewed by 834
Abstract
The melting and recrystallization behaviors of poly(butylene terephthalate) (PBT) were investigated using temperature-modulated scanning calorimetry in both fast- and conventional slow-scan modes. With this method, the response of multiple transition kinetics, such as melting and recrystallization, can be differentiated by utilizing the difference [...] Read more.
The melting and recrystallization behaviors of poly(butylene terephthalate) (PBT) were investigated using temperature-modulated scanning calorimetry in both fast- and conventional slow-scan modes. With this method, the response of multiple transition kinetics, such as melting and recrystallization, can be differentiated by utilizing the difference in the time constants of the kinetics. In addition to the previous result of temperature-modulated fast-scan calorimetry of polyethylene terephthalate (PET), the supporting evidence of another aromatic polyester, PBT, confirmed the behavior of the exothermic process of recrystallization, which proceeds simultaneously with melting on heating scan in the temperature range of double melting peaks starting just above the crystallization temperature up to the main melting peak. Because the crystallization of PBT is much more pronounced than that of PET, similar behavior of recrystallization was obtained by the conventional temperature-modulated differential scanning calorimetry at a slow-scan rate. Full article
Show Figures

Graphical abstract

Article
High-Pressure Crystallization of iPP Nucleated with 1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol
Polymers 2021, 13(1), 145; https://doi.org/10.3390/polym13010145 - 01 Jan 2021
Viewed by 723
Abstract
1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (DMDBS) is highly effective in nucleation of the α- form of isotactic polypropylene (iPP). However, its role in high-pressure crystallization of iPP, facilitating the formation of the γ- polymorph, has not been explored. The present paper focuses on the influence of DMDBS [...] Read more.
1,3:2,4-bis(3,4-dimethylbenzylidene)sorbitol (DMDBS) is highly effective in nucleation of the α- form of isotactic polypropylene (iPP). However, its role in high-pressure crystallization of iPP, facilitating the formation of the γ- polymorph, has not been explored. The present paper focuses on the influence of DMDBS on nucleation of high-pressure crystallization of iPP. iPP with 0.2–1.0 wt.% of the DMDBS was crystallized under elevated pressure, up to 300 MPa, in various thermal conditions, and then analyzed by PLM, WAXD, SEM, and DSC. During cooling, crystallization temperatures (Tc) were determined. It was found that under high-pressure DMDBS nucleated crystallization of iPP in the orthorhombic γ- form. As a consequence, Tc and the γ- form content increased for the nucleated iPP, while the size of polycrystalline aggregates decreased, although the effects depended on DMDBS content. The significant increase of Tc and the decrease of grain size under high pressure of 200–300 MPa required higher content of DMDBS than the nucleation of the α-form under lower pressure, possibly due to the effect of pressure on crystallization of DMDBS itself, which is a prerequisite for its nucleating activity. Full article
Show Figures

Figure 1

Article
Microstructural Origin of the Double Yield Points of the Metallocene Linear Low-Density Polyethylene (mLLDPE) Precursor Film under Uniaxial Tensile Deformation
Polymers 2021, 13(1), 126; https://doi.org/10.3390/polym13010126 - 30 Dec 2020
Cited by 1 | Viewed by 817
Abstract
The microstructural origin of the double yield points of metallocene linear low-density polyethylene (mLLDPE) precursor films has been studied with the assistance of the synchrotron radiation small- and wide-angle X-ray scattering (SAXS/WAXS). It has been shown that the microstructural origin of the double [...] Read more.
The microstructural origin of the double yield points of metallocene linear low-density polyethylene (mLLDPE) precursor films has been studied with the assistance of the synchrotron radiation small- and wide-angle X-ray scattering (SAXS/WAXS). It has been shown that the microstructural origin of the double yield points is highly related to the initial orientation of the original precursor film. For less oriented mLLDPE precursor films, the rearrangement of lamellae and the appearance of the monoclinic phase are the microstructural origins of the first yield point. In comparison, for the highly-oriented mLLDPE precursor film, only the orthorhombic-monoclinic phase transition appears at the first yield point. The melting-recrystallization and the formation of the fibrillary structure happen beyond the second yield point for all studied mLLDPE precursor films. Finally, the detailed microstructural evolution roadmaps of mLLDPE precursor films under uniaxial tensile deformation have been established, which might serve as a guide for processing high-performance polymer films by post-stretching. Full article
Show Figures

Graphical abstract

Article
Fused Deposition Modeling of Polyamides: Crystallization and Weld Formation
Polymers 2020, 12(12), 2980; https://doi.org/10.3390/polym12122980 - 14 Dec 2020
Cited by 3 | Viewed by 887
Abstract
International newspapers and experts have called 3D printing the industrial revolution of this century. Among all its available variants, the fused deposition modeling (FDM) technique is of greater interest since its application is possible using simple desktop printers. FDM is a complex process, [...] Read more.
International newspapers and experts have called 3D printing the industrial revolution of this century. Among all its available variants, the fused deposition modeling (FDM) technique is of greater interest since its application is possible using simple desktop printers. FDM is a complex process, characterized by a large number of parameters that influence the quality and final properties of the product. In particular, in the case of semicrystalline polymers, which afford better mechanical properties than amorphous ones, it is necessary to understand the crystallization kinetics as the processing conditions vary, in order to be able to develop models that allow having a better control over the process and consequently on the final properties of the material. In this work it was proposed to study the crystallization kinetics of two different polyamides used for FDM 3D printing and to link it to the microstructure and properties obtained during FDM. The kinetics are studied both in isothermal and fast cooling conditions, thanks to a home-built device which allows mimicking the quenching experienced during filament deposition. The temperature history of a single filament is then determined by mean of a micro-thermocouple and the final crystallinity of the sample printed in a variety of conditions is assessed by differential scanning calorimetry. It is found that the applied processing conditions always allowed for the achievement of the maximum crystallinity, although in one condition the polyamide mesomorphic phase possibly develops. Despite the degree of crystallinity is not a strong function of printing variables, the weld strength of adjacent layers shows remarkable variations. In particular, a decrease of its value with printing speed is observed, linked to the probable development of molecular anisotropy under the more extreme printing conditions. Full article
Show Figures

Graphical abstract

Article
Flow-Induced Crystallization in Polyethylene: Effect of Flow Time on Development of Shish-Kebab
Polymers 2020, 12(11), 2571; https://doi.org/10.3390/polym12112571 - 02 Nov 2020
Cited by 2 | Viewed by 701
Abstract
The flow-induced formation and relaxation of the representative oriented shish-kebab structure were studied with synchrotron small-angle X-ray scattering (SAXS) method. The flow duration was varied from 2 to 6 s at an identical strain rate to reveal the effect of flow time on [...] Read more.
The flow-induced formation and relaxation of the representative oriented shish-kebab structure were studied with synchrotron small-angle X-ray scattering (SAXS) method. The flow duration was varied from 2 to 6 s at an identical strain rate to reveal the effect of flow time on stability and dimension of formed shish. It was found that the short flow time of 2 s was able to generate shish during flow, which, however, relaxed during the isothermal process after cessation of flow. An increase in flow time can improve the shish stability and the long flow time of 6 s can generate the stable shish that nucleate the growth of kebab lamellae. In addition, the quantitative analysis of SAXS results showed that with increasing flow time from 2 to 6 s, the shish length increased from 242 to 574 nm, while the shish diameter remained around 34 nm. This detailed information of the formed shish-kebab structure can be used to shed light on their evolution that occurred during flow from 2 to 6 s, where shish grew at a longitudinal speed of around 80 nm/s, and there was an improvement in the stability and nucleation capability for kebab lamellae. Full article
Show Figures

Figure 1

Review

Jump to: Research

Review
Binary Green Blends of Poly(lactic acid) with Poly(butylene adipate-co-butylene terephthalate) and Poly(butylene succinate-co-butylene adipate) and Their Nanocomposites
Polymers 2021, 13(15), 2489; https://doi.org/10.3390/polym13152489 - 28 Jul 2021
Cited by 1 | Viewed by 547
Abstract
Poly(lactic acid) (PLA) is the most widely produced biobased, biodegradable and biocompatible polyester. Despite many of its properties are similar to those of common petroleum-based polymers, some drawbacks limit its utilization, especially high brittleness and low toughness. To overcome these problems and improve [...] Read more.
Poly(lactic acid) (PLA) is the most widely produced biobased, biodegradable and biocompatible polyester. Despite many of its properties are similar to those of common petroleum-based polymers, some drawbacks limit its utilization, especially high brittleness and low toughness. To overcome these problems and improve the ductility and the impact resistance, PLA is often blended with other biobased and biodegradable polymers. For this purpose, poly(butylene adipate-co-butylene terephthalate) (PBAT) and poly(butylene succinate-co-butylene adipate) (PBSA) are very advantageous copolymers, because their toughness and elongation at break are complementary to those of PLA. Similar to PLA, both these copolymers are biodegradable and can be produced from annual renewable resources. This literature review aims to collect results on the mechanical, thermal and morphological properties of PLA/PBAT and PLA/PBSA blends, as binary blends with and without addition of coupling agents. The effect of different compatibilizers on the PLA/PBAT and PLA/PBSA blends properties is here elucidated, to highlight how the PLA toughness and ductility can be improved and tuned by using appropriate additives. In addition, the incorporation of solid nanoparticles to the PLA/PBAT and PLA/PBSA blends is discussed in detail, to demonstrate how the nanofillers can act as morphology stabilizers, and so improve the properties of these PLA-based formulations, especially mechanical performance, thermal stability and gas/vapor barrier properties. Key points about the biodegradation of the blends and the nanocomposites are presented, together with current applications of these novel green materials. Full article
Show Figures

Figure 1

Back to TopTop