Polymer Crystallization

Journal Name	Impact Factor	CiteScore	Launched Year	First Decision (median)	APC
Crystals crystals	2.7	3.6	2011	10.6 Days	CHF 2600
Polymers polymers	5.0	6.6	2009	13.7 Days	CHF 2700
Reactions reactions	-	-	2020	18.3 Days	CHF 1000

4 pages, 183 KiB

Open AccessEditorial

Editorial on the Special Topic “Polymer Crystallization”

by Jun Xu, Günter Reiter and Rufina G. Alamo

Crystals 2022, 12(5), 618; https://doi.org/10.3390/cryst12050618 - 26 Apr 2022

Viewed by 1491

Abstract

Two thirds of polymer materials are crystalline [...] Full article

(This article belongs to the Topic Polymer Crystallization)

12 pages, 3074 KiB

Open AccessArticle

Substantially Enhanced Stereocomplex Crystallization of Poly(L-lactide)/Poly(D-lactide) Blends by the Formation of Multi-Arm Stereo-Block Copolymers

by Xingyuan Diao, Xiaonan Chen, Shihao Deng and Hongwei Bai

Crystals 2022, 12(2), 210; https://doi.org/10.3390/cryst12020210 - 30 Jan 2022

Cited by 8 | Viewed by 2594

Abstract

Stereocomplex-type polylactide (SC-PLA) created by alternate packing of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) chains in a crystalline state has emerged as a growingly popular engineering bioplastic that possesses excellent hydrolytic stability and thermomechanical properties. However, it is extremely difficult to acquire high-performance SC-PLA [...] Read more.

Stereocomplex-type polylactide (SC-PLA) created by alternate packing of poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) chains in a crystalline state has emerged as a growingly popular engineering bioplastic that possesses excellent hydrolytic stability and thermomechanical properties. However, it is extremely difficult to acquire high-performance SC-PLA products via melt-processing of high-molecular-weight PLLA/PDLA blends because both SC crystallites and homocrystallites (HCs) are competitively formed in the melt-crystallization. Herein, a facile yet powerful way was employed to boost SC formation by introducing trace amounts of some epoxy-functionalized small-molecule modifiers into the enantiomeric blends during reactive melt-blending. The results show that the SC formation is considerably enhanced with the in situ generation of multi-arm stereo-block PLA copolymers, based on the reaction between epoxy groups of the modifiers and hydroxyl end groups of PLAs. More impressively, it is intriguing to find that the introduction of only 0.5 wt% modifiers can induce exclusive SC formation in the blends upon isothermal and non-isothermal melt-crystallizations. The outstanding SC crystallizability might be attributed to the suppressing effect of such unique copolymers on the separation of the alternately arranged PLLA/PDLA chain segments in molten state as a compatibilizer. Furthermore, the generation of these copolymers does not result in a significant increase in melt viscosity of the blends. These findings suggest new opportunities for the high-throughput processing of SC-PLA materials into useful products. Full article

(This article belongs to the Topic Polymer Crystallization)

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16 pages, 2779 KiB

Open AccessArticle

Development of High Temperature Resistant Stereocomplex PLA for Injection Moulding

by Sebastian Körber, Kevin Moser and Jan Diemert

Polymers 2022, 14(3), 384; https://doi.org/10.3390/polym14030384 - 19 Jan 2022

Cited by 12 | Viewed by 2963

Abstract

In this study, the production of stereocomplex PLA formulations (sc-PLA) by compounding and subsequent injection moulding at different mould temperatures was investigated. Several selective nucleating agents were identified and compounded with different poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) ratios on a co-rotating twin screw extruder. The effect [...] Read more.

In this study, the production of stereocomplex PLA formulations (sc-PLA) by compounding and subsequent injection moulding at different mould temperatures was investigated. Several selective nucleating agents were identified and compounded with different poly(L-lactide)/poly(D-lactide) (PLLA/PDLA) ratios on a co-rotating twin screw extruder. The effect of nucleating agents (NA) on the crystallisation behaviour of the compound was systematically investigated by DSC analysis. The crystallisation behaviour of NA-21 (aluminium complex of a phosphoric ester), also in combination with talc, under cooling rates of up to 70 K/min was analysed. The wide-angle X-ray diffraction (WAXD) results showed a complete stereocomplex (sc) crystal formation on all specimens containing NA-21 even at the highest cooling rates. The thermo-mechanical testing of sc-PLA shows a Young’s modulus of approx. 3 GPa, yield stress of 30–40 MPa, elongation of 1%, and a heat deflection temperature (HDT-B) up to 180 °C. Processing sc-PLA exclusively via the processing route of compounding and injection moulding will open new areas of application for PLA at higher temperatures. Full article

(This article belongs to the Topic Polymer Crystallization)

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12 pages, 3211 KiB

Open AccessArticle

Dependence on Film Thickness of Guest-Induced c Perpendicular Orientation in PPO Films

by Baku Nagendra, Emanuele Vignola, Christophe Daniel, Paola Rizzo and Gaetano Guerra

Polymers 2021, 13(24), 4384; https://doi.org/10.3390/polym13244384 - 14 Dec 2021

Cited by 12 | Viewed by 2178

Abstract

For poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) films exhibiting nanoporous-crystalline (NC) phases, c_⊥ orientation (i.e., crystalline polymer chain axes being preferentially perpendicular to the film plane) is obtained by crystallization of amorphous films, as induced by sorption of suitable low-molecular-mass guest molecules. The occurrence of c [...] Read more.

For poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) films exhibiting nanoporous-crystalline (NC) phases, c_⊥ orientation (i.e., crystalline polymer chain axes being preferentially perpendicular to the film plane) is obtained by crystallization of amorphous films, as induced by sorption of suitable low-molecular-mass guest molecules. The occurrence of c_⊥ orientation is relevant for applications of NC PPO films because it markedly increases film transparency as well as guest diffusivity. Surprisingly, we show that the known crystallization procedures lead to c_⊥ oriented thick (50–300 μm) films and to unoriented thin (≤20 μm) films. This absence of crystalline phase orientation for thin films is rationalized by fast guest sorption kinetics, which avoid co-crystallization in confined spaces and hence inhibit formation of flat-on lamellae. For thick films exhibiting c_⊥ orientation, sigmoid kinetics of guest sorption and of thickening of PPO films are observed, with inflection points associated with guest-induced film plasticization. Corresponding crystallization kinetics are linear with time and show that co-crystal growth is poorly affected by film plasticization. An additional relevant result of this study is the linear relationship between WAXD crystallinity index and DSC melting enthalpy, which allows evaluation of melting enthalpy of the NC α form of PPO (ΔH_m^ο = 42 ± 2 J/g). Full article

(This article belongs to the Topic Polymer Crystallization)

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18 pages, 6500 KiB

Open AccessArticle

Composite Micro-Nanoarchitectonics of MMT-SiO₂: Space Charge Characteristics under Tensile State

by Hongtao Jiang, Junguo Gao, Xiaohong Zhang and Ning Guo

Polymers 2021, 13(24), 4354; https://doi.org/10.3390/polym13244354 - 13 Dec 2021

Cited by 9 | Viewed by 1851

Abstract

Low density polyethylene (LDPE) is a good insulating material which is widely used in cable materials due to its excellent insulation and processability. However, in the DC high voltage environment, pure polyethylene materials still face many problems, the most serious of which is [...] Read more.

Low density polyethylene (LDPE) is a good insulating material which is widely used in cable materials due to its excellent insulation and processability. However, in the DC high voltage environment, pure polyethylene materials still face many problems, the most serious of which is space charge accumulation. The cable will inevitably be subjected to tensile stress during production, installation and operation. Therefore, it is of great significance to study the effect of stretching on the microstructure and space charge characteristics for polymers and their composites. In this paper, MMT/LDPE micro-composites, SiO₂/LDPE nano-composites and MMT-SiO₂/LDPE micro-nano-composites were prepared by melt blending. Mechanical stretching was carried out on pure LDPE materials and the above three kinds of composite materials. Each material was stretched according to four stretching ratios, which are 0%, 5%, 10% and 20%. The crystal morphology was observed by polarizing microscope (PLM), the crystallization perfection was tested by differential scanning calorimetry (DSC), and the space charge distribution inside each sample was measured by pulsed electro-acoustic (PEA) method. At the same time, the average charge density and apparent charge mobility for samples during depolarization were calculated and analyzed. The experimental results show that when the pure low density polyethylene sample is not stretched, its crystal structure is loose. Tensile stress can make the loose molecular chains align in LDPE and improve its crystalline structure, which is helpful to restrain the accumulation of space charge inside the sample. For MMT/LDPE, SiO₂/LDPE and MMT-SiO₂/LDPE composites, their internal crystal structure is compact. Stretching will destroy their original crystal structure at first, and then disorder molecular chains inside the three composite materials. With the increase of stretching ratio, the molecular chains begin to orient along the direction of force, the crystallization tends to be perfect gradually, and the space charge accumulation in samples also decreases. From the calculation results of apparent charge mobility for each sample, with the increase of stretching ratio, the trap depth and trap density inside samples firstly increased and then decreased. Full article

(This article belongs to the Topic Polymer Crystallization)

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14 pages, 4700 KiB

Open AccessArticle

Microstructure and Lamellae Phase of Raw Natural Rubber via Spontaneous Coagulation Assisted by Sugars

by Wanna Bai, Jie Guan, Huan Liu, Shihong Cheng, Fuchun Zhao and Shuangquan Liao

Polymers 2021, 13(24), 4306; https://doi.org/10.3390/polym13244306 - 09 Dec 2021

Cited by 3 | Viewed by 2548

Abstract

Natural rubber (NR) as a renewable biopolymer is often produced by acid coagulation of fresh natural latex collected from Hevea brasiliensis. However, this traditional process is facing a huge economic and environmental challenge. Compared with the acid coagulation, spontaneous or microorganism coagulation [...] Read more.

Natural rubber (NR) as a renewable biopolymer is often produced by acid coagulation of fresh natural latex collected from Hevea brasiliensis. However, this traditional process is facing a huge economic and environmental challenge. Compared with the acid coagulation, spontaneous or microorganism coagulation is an ecofriendly way to obtain NR with excellent performance. To clarify the influence of different sugars on NR quality, several sugars were used to assist the coagulation process. Influence of different sugars on microstructure and cold crystallization were examined by ¹H NMR, DSC, etc. The results indicated that sugars exhibit different biological activity on terminal components of fresh field latex and can influence the resultant molecular structure and basic properties. Brown sugar exhibits higher metabolic activity and is inclined to decompose the protein and phospholipids crosslinking compared with other sugars. The larger molecular weight of sugar molecule is beneficial for the formation of the stable α lamellae phase and higher overall degree of crystallization. Full article

(This article belongs to the Topic Polymer Crystallization)

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12 pages, 4274 KiB

Open AccessArticle

Dependence of Crystallization Behavior of Interacting Telechelic Poly(butylene succinate) Oligomer on Molecular Weight

by Cong Chen, Xue-Wen Zhang and Hai-Mu Ye

Crystals 2021, 11(12), 1530; https://doi.org/10.3390/cryst11121530 - 08 Dec 2021

Cited by 4 | Viewed by 2047

Abstract

A large spherulite structure deteriorates the mechanical properties of crystalline polymers, and therefore various methods have been explored to increase primary nucleation density. Recently, chain-end modification has been proposed as an effective approach for regulating polymer crystal nucleation. However, the relevant nucleation mechanism [...] Read more.

A large spherulite structure deteriorates the mechanical properties of crystalline polymers, and therefore various methods have been explored to increase primary nucleation density. Recently, chain-end modification has been proposed as an effective approach for regulating polymer crystal nucleation. However, the relevant nucleation mechanism still requires investigation. Therefore, in this work, 2-ureido-4[1H]-pyrimidinone (UPy) units, which can form stacks via quadruple hydrogen bonds with each other, are introduced as end groups for the preparation of interacting telechelic poly(butylene succinate) (PBS-UPy) oligomers with different molecular weights (M_ns). The crystallization, especially the nucleation behavior of PBS-UPy, is studied in detail by comparing with the corresponding pre-polymer, the hydroxyl-terminal PBS (PBS-OH). The thermal properties of PBS-UPy exhibit similar M_n-dependent tendency to those of PBS-OH, but with weaker total crystallization rate. The spherulite growth rate is significantly reduced, whereas the primary nucleation density is highly promoted, after introducing UPy groups. Further investigation reveals that the mechanism of UPy stacks’ influence on nucleation ability changes from inhibition to promotion with respect to M_n. Even under an inhibition of nucleation ability, the final nucleation density is obviously increased because of a significant decline of the growth rate. In addition, the change in the impact of UPy stacks on nucleation ability is speculated to originate from the memory expression feasibility of ordered conformation in the melt during crystallization. Full article

(This article belongs to the Topic Polymer Crystallization)

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15 pages, 8685 KiB

Open AccessArticle

Evaporation-Induced Crystal Nucleation and Morphology of Dried Poly(Vinylidene Fluoride) Droplets

by Yongri Liang and Susu Wang

Crystals 2021, 11(12), 1442; https://doi.org/10.3390/cryst11121442 - 23 Nov 2021

Cited by 3 | Viewed by 2233

Abstract

The evaporation of a polymer solution droplet is important in solution-based polymer film fabrications, such as inkjet printing, spray coatings, and droplet casting, etc. In this work, we investigated the effect of droplet size, solvent evaporation rate, and concentration on the “coffee-ring” effect, [...] Read more.

The evaporation of a polymer solution droplet is important in solution-based polymer film fabrications, such as inkjet printing, spray coatings, and droplet casting, etc. In this work, we investigated the effect of droplet size, solvent evaporation rate, and concentration on the “coffee-ring” effect, crystal nucleation, polymorphism, and morphology of dried poly(vinylidene fluoride) (PVDF) solution droplets with the atomic force microscopy (AFM) and two-dimensional grazing incidence wide angle X-ray scattering (2D GIWAXS) method. We found that the crystal structure, morphology and crystal distribution in the center and edge regions of dried PVDF droplets were different due to the “coffee-ring” effect. The “coffee-ring” effect of dried PVDF droplets was mainly composited of accumulated crystals at the edge region of a droplet, which was mainly made by the crystallization of migrated chains. The interplay between the migration of chains and the crystallization and solidification of PVDF droplets significantly influenced the formation of the “coffee-ring”. In addition, our results showed that the decrease in droplet size and the controlling solvent evaporation rate were effective ways to improve the electroactive crystalline phases (β and γ-phases) nucleation and decrease the crystal size. Full article

(This article belongs to the Topic Polymer Crystallization)

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11 pages, 3484 KiB

Open AccessArticle

Design of Novel PLA/OMMT Films with Improved Gas Barrier and Mechanical Properties by Intercalating OMMT Interlayer with High Gas Barrier Polymers

by Abdul Shakoor Shar, Caili Zhang, Xieqing Song, Yunxuan Weng and Qiuyue Du

Polymers 2021, 13(22), 3962; https://doi.org/10.3390/polym13223962 - 16 Nov 2021

Cited by 6 | Viewed by 1827

Abstract

Polymer/clay composites are an innovative class of materials. In this study, we present a facile method for the preparation of biodegradable and robust PLA/organomodified montmorillonite (OMMT) composite films with excellent gas barrier performance. When the design of PLA/OMMT composite films, in addition to [...] Read more.

Polymer/clay composites are an innovative class of materials. In this study, we present a facile method for the preparation of biodegradable and robust PLA/organomodified montmorillonite (OMMT) composite films with excellent gas barrier performance. When the design of PLA/OMMT composite films, in addition to making OMMT have good intercalation effect in the matrix, the compatibility of intercalating polymer and matrix should also be considered. In this work, two polymers with high gas barrier properties, namely poly(vinyl alcohol) (PVA) and ethylene vinyl alcohol copolymer (EVOH), were selected to intercalate OMMT. The morphology and microstructures of the prepared PLA/PVA/OMMT and PLA/EVOH/OMMT composites were characterized by the X-ray diffraction measurement, scanning electron microscopy, and differential scanning calorimetry. It was shown that the good dispersibility of PVA in the PLA matrix, rather than the intercalation effect, was responsible for the improved gas barrier and mechanical properties of PLA/PVA/OMMT composite. The elongation at break increases from 4.5% to 22.7% when 1 wt % PVA is added to PLA/OMMT. Moreover, gas barrier of PLA/PVA1/OMMT measured as O₂ permeability is 52.8% higher than that of neat PLA. This work provides a route to intercalate OMMT interlayer with high gas barrier polymers and thus can be a useful reference to fabricate PLA/OMMT composites with improved gas barrier and mechanical properties. A comparison of oxygen permeabilities with existing commercial packaging films indicates that the biodegradable PLA/PVA/OMMT may serve as a viable substitute for packaging film applications. Full article

(This article belongs to the Topic Polymer Crystallization)

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11 pages, 3652 KiB

Open AccessArticle

In-Situ Isothermal Crystallization of Poly(l-lactide)

by Zirui Huang, Meiling Zhong, Haibo Yang, Enqin Xu, Dehui Ji, Paul Joseph and Ri-Chao Zhang

Polymers 2021, 13(19), 3377; https://doi.org/10.3390/polym13193377 - 30 Sep 2021

Cited by 5 | Viewed by 1587

Abstract

The isothermal crystallization of poly(l-lactide) (PLLA) has been investigated by in-situ wide angle X-ray diffraction (WAXD) and polarized optical microscopes (POM) equipped with a hot-stage accessory. Results showed that the spherulites of PLLA were formed at high temperature, whereas irregular morphology [...] Read more.

The isothermal crystallization of poly(l-lactide) (PLLA) has been investigated by in-situ wide angle X-ray diffraction (WAXD) and polarized optical microscopes (POM) equipped with a hot-stage accessory. Results showed that the spherulites of PLLA were formed at high temperature, whereas irregular morphology was observed under a low temperature. This can be attributed to the varying rates of crystallization of PLLA at different temperatures. At low temperatures, the nucleation rate is fast and hence the chains diffuse very slow, resulting in the formation of imperfect crystals. On the other hand, at high temperatures, the nucleation rate is slow and the chains diffuse fast, leading to the formation of perfect crystals. The change in the value of the Avrami exponent with temperature further verifies the varying trend in the morphological feature of the crystals. Full article

(This article belongs to the Topic Polymer Crystallization)

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12 pages, 3151 KiB

Open AccessArticle

Monomeric and Dimeric Carboxylic Acid in Crystalline Cavities and Channels of Delta and Epsilon Forms of Syndiotactic Polystyrene

by Antonietta Cozzolino, Guglielmo Monaco, Christophe Daniel, Paola Rizzo and Gaetano Guerra

Polymers 2021, 13(19), 3330; https://doi.org/10.3390/polym13193330 - 29 Sep 2021

Cited by 10 | Viewed by 1472

Abstract

Delta (δ) and epsilon (ε) co-crystalline forms of syndiotactic polystyrene with a carboxylic acid guest were obtained by sorption of liquid hexanoic acid in syndiotactic polystyrene films exhibiting delta and epsilon nanoporous-crystalline forms. The characterization study is facilitated by axially stretched syndiotactic polystyrene [...] Read more.

Delta (δ) and epsilon (ε) co-crystalline forms of syndiotactic polystyrene with a carboxylic acid guest were obtained by sorption of liquid hexanoic acid in syndiotactic polystyrene films exhibiting delta and epsilon nanoporous-crystalline forms. The characterization study is facilitated by axially stretched syndiotactic polystyrene films, used both for polarized FTIR spectra and for WAXD fiber patterns. Particularly informative are two carbonyl-stretching FTIR peaks, attributed to monomeric and dimeric hexanoic acid. The dichroism of these carbonyl peaks indicates that both delta and epsilon phases are able to include hexanoic acid as isolated guest molecules, while only the epsilon phase is also able to include dimeric hexanoic acid molecules in its crystalline channels. The inclusion of both isolated and dimeric hexanoic acid species in the epsilon form crystalline channels produces extremely fast hexanoic acid uptakes by syndiotactic polystyrene epsilon form films. Full article

(This article belongs to the Topic Polymer Crystallization)

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16 pages, 3667 KiB

Open AccessArticle

Investigation on the α/δ Crystal Transition of Poly(l-lactic Acid) with Different Molecular Weights

by Lei Zhang, Guoqun Zhao and Guilong Wang

Polymers 2021, 13(19), 3280; https://doi.org/10.3390/polym13193280 - 26 Sep 2021

Cited by 8 | Viewed by 2469

Abstract

Poly(l-lactic acid) (PLLA) crystal possesses a complex polymorphism, and the formation mechanism of various crystal forms has been a hot research topic in the field of polymer condensate matter. In this research, five kinds of PLLA with different molecular weights were [...] Read more.

Poly(l-lactic acid) (PLLA) crystal possesses a complex polymorphism, and the formation mechanism of various crystal forms has been a hot research topic in the field of polymer condensate matter. In this research, five kinds of PLLA with different molecular weights were prepared by ring-opening polymerization with strict dehydration operations and multistep purification treatments. Then, thin film isothermal crystallization experiments were carried out to obtain crystallized samples. Previous research has proven that the PLLA α crystal form is usually formed at a temperature above 120 °C and the PLLA δ (or α’) crystal form is usually formed at a temperature below 120 °C. However, in this research, the characterization results indicated that the PLLA crystal changed from δ form to α form with the decrease of molecular weight at a temperature of 80 °C. Considering the molecular weight effect, the paper argued that the transitions of the α/δ crystal form are not only associated with temperature, but also related to entanglement state before crystallization. The small-angle X-ray scattering of the PLLA crystal and rheology analysis of the PLLA melt before crystallization further proved the significant role of entanglement. Finally, we tentatively proposed the entanglement effect mechanism on the transitions of the α/δ crystal form. Full article

(This article belongs to the Topic Polymer Crystallization)

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14 pages, 5489 KiB

Open AccessArticle

Pressure- and Temperature-Dependent Crystallization Kinetics of Isotactic Polypropylene under Process Relevant Conditions

by Yvonne Spoerer, Regine Boldt, René Androsch and Ines Kuehnert

Crystals 2021, 11(9), 1138; https://doi.org/10.3390/cryst11091138 - 18 Sep 2021

Cited by 4 | Viewed by 2586

Abstract

In this study, a non-nucleated homopolymer (HP) and random copolymer (RACO), as well as a nucleated HP and heterophasic copolymer (HECO) were investigated regarding their crystallization kinetics. Using pvT-measurements and fast scanning chip calorimetry (FSC), the crystallization behavior was analyzed as a function [...] Read more.

In this study, a non-nucleated homopolymer (HP) and random copolymer (RACO), as well as a nucleated HP and heterophasic copolymer (HECO) were investigated regarding their crystallization kinetics. Using pvT-measurements and fast scanning chip calorimetry (FSC), the crystallization behavior was analyzed as a function of pressure, cooling rate and temperature. It is shown that pressure and cooling rate have an opposite influence on the crystallization temperature of the materials. Furthermore, the addition of nucleating agents to the material has a significant effect on the maximum cooling rate at which the formation of α-crystals is still possible. The non-nucleated HP and RACO materials show significant differences that can be related to the sterically hindering effect of the comonomer units of RACO on crystallization, while the nucleated materials HP and HECO show similar crystallization kinetics despite their different structures. The pressure-dependent shift factor of the crystallization temperature is independent of the material. The results contribute to the description of the relationship between the crystallization kinetics of the material and the process parameters influencing the injection-molding induced morphology. This is required to realize process control in injection molding in order to produce pre-defined morphologies and to design material properties. Full article

(This article belongs to the Topic Polymer Crystallization)

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13 pages, 31239 KiB

Open AccessEditor’s ChoiceArticle

Heterogeneous Crystal Nucleation from the Melt in Polyethylene Oxide Droplets on Graphite: Kinetics and Microscopic Structure

by Muhammad Tariq, Thomas Thurn-Albrecht and Oleksandr Dolynchuk

Crystals 2021, 11(8), 924; https://doi.org/10.3390/cryst11080924 - 09 Aug 2021

Cited by 7 | Viewed by 2435

Abstract

It is well known that the crystallization of liquids often initiates at interfaces to foreign solid surfaces. In this study, using polarized light optical microscopy, atomic force microscopy (AFM), and wide-angle X-ray scattering (WAXS), we investigate the effect of substrate–material interactions on nucleation [...] Read more.

It is well known that the crystallization of liquids often initiates at interfaces to foreign solid surfaces. In this study, using polarized light optical microscopy, atomic force microscopy (AFM), and wide-angle X-ray scattering (WAXS), we investigate the effect of substrate–material interactions on nucleation in an ensemble of polyethylene oxide (PEO) droplets on graphite and on amorphous polystyrene (PS). The optical microscopy measurements during cooling with a constant rate explicitly evidenced that the graphite substrate enhances the nucleation kinetics, as crystallization occurred at approximately an 11 °C higher temperature than on PS due to changes in the interactions at the solid interface. This observation allowed us to conclude that graphite induces heterogeneous nucleation in PEO. By employing the classical nucleation theory for analysis of the data with reference to the amorphous PS substrate, the obtained results indicated that the crystal nuclei with contact angles in the range of 100–117° were formed at the graphite interface. Furthermore, we show that heterogeneous nucleation led to a preferred orientation of PEO crystals on graphite, whereas PEO crystals on PS had isotropic orientation. The difference in crystal orientations on the two substrates was also confirmed with AFM, which showed only edge-on lamellae in PEO droplets on graphite compared to unoriented lamellae on PS. Full article

(This article belongs to the Topic Polymer Crystallization)

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13 pages, 6001 KiB

Open AccessArticle

UIO-66 as Nucleating Agent on the Crystallization Behavior and Properties of Poly(Ethylene Terephthalate)

by Yue Yin, Yuan Wang and Linghui Meng

Polymers 2021, 13(14), 2266; https://doi.org/10.3390/polym13142266 - 10 Jul 2021

Cited by 10 | Viewed by 2698

Abstract

In this study, not only was the similar terephthalate structure between UIO-66 and PET utilized to improve compatibility, but the Zr⁴⁺ exposed by defects of UIO-66 was also utilized to improve the interaction between PET and UIO-66. Furthermore, PET nanocomposites with different [...] Read more.

In this study, not only was the similar terephthalate structure between UIO-66 and PET utilized to improve compatibility, but the Zr⁴⁺ exposed by defects of UIO-66 was also utilized to improve the interaction between PET and UIO-66. Furthermore, PET nanocomposites with different contents of UIO-66 were also fabricated. Due to the high specific surface area and coordination of Zr⁴⁺, UIO-66 has high nucleation efficiency in the PET matrix. Compared with pure PET, the crystallization rate of PET/UIO-66 nanocomposite is significantly increased, and the crystallization temperature of PET-UIO66-1 is significantly increased from 194.3 °C to 211.6 °C. In addition, the tensile strength of nanocomposites has also been improved due to coordination. Full article

(This article belongs to the Topic Polymer Crystallization)

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19 pages, 2571 KiB

Open AccessReview

Concepts of Nucleation in Polymer Crystallization

by Jun Xu, Günter Reiter and Rufina G. Alamo

Crystals 2021, 11(3), 304; https://doi.org/10.3390/cryst11030304 - 19 Mar 2021

Cited by 38 | Viewed by 8201

Abstract

Nucleation plays a vital role in polymer crystallization, in which chain connectivity and thus the multiple length and time scales make crystal nucleation of polymer chains an interesting but complex subject. Though the topic has been intensively studied in the past decades, there [...] Read more.

Nucleation plays a vital role in polymer crystallization, in which chain connectivity and thus the multiple length and time scales make crystal nucleation of polymer chains an interesting but complex subject. Though the topic has been intensively studied in the past decades, there are still many open questions to answer. The final properties of semicrystalline polymer materials are affected by all of the following: the starting melt, paths of nucleation, organization of lamellar crystals and evolution of the final crystalline structures. In this viewpoint, we attempt to discuss some of the remaining open questions and corresponding concepts: non-equilibrated polymers, self-induced nucleation, microscopic kinetics of different processes, metastability of polymer lamellar crystals, hierarchical order and cooperativity involved in nucleation, etc. Addressing these open questions through a combination of novel concepts, new theories and advanced approaches provides a deeper understanding of the multifaceted process of crystal nucleation of polymers. Full article

(This article belongs to the Topic Polymer Crystallization)

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