scholarly journals Shear-Induced Crystallization of Star and Linear Poly(L-lactide)s

Molecules ◽  
2021 ◽  
Vol 26 (21) ◽  
pp. 6601
Author(s):  
Joanna Bojda ◽  
Ewa Piorkowska ◽  
Grzegorz Lapienis ◽  
Adam Michalski
Keyword(s):  
Cooling Rate ◽  
Crystallization Temperature ◽  
Molar Mass ◽  
Star Polymers ◽  
Linear Analog ◽  
Linear Poly ◽  
Macromolecular Architecture ◽  
Light Depolarization ◽  
Induced Crystallization

The influence of macromolecular architecture on shear-induced crystallization of poly(L-lactide) (PLLA) was studied. To this aim, three star PLLAs, 6-arm with Mw of 120 and 245 kg/mol, 4-arm with Mw of 123 kg/mol, and three linear PLLAs with Mw of 121, 240 and 339 kg/mol, were synthesized and examined. The PLLAs were sheared at 170 and 150 °C, at 5/s, 10/s and 20/s for 20 s, 10 s and 5 s, respectively, and then cooled at 10 or 30 °C/min. Shear-induced crystallization during cooling was followed by a light depolarization method, whereas the crystallized specimens were examined by DSC, 2D-WAXS, 2D-SAXS and SEM. The effect of shear depended on the shearing conditions, cooling rate and polymer molar mass but it was also affected by the macromolecular architecture. The shear-induced crystallization of linear PLLA with Mw of 240 kg/mol was more intense than that of the 6-arm polymer with similar Mw, most possibly due to its higher Mz. However, the influence of shear on the crystallization of the star polymers with Mw close to 120 kg/mol was stronger than on that of their linear analog. This was reflected in higher crystallization temperature, as well as crystallinity achieved during cooling.

The effect of cooling rate on crystallization behavior and tensile properties of CF/PEEK composites

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Guangming Dai ◽  
Lihua Zhan ◽  
Chenglong Guan ◽  
Minghui Huang
Keyword(s):  
Cooling Rate ◽  
Crystallization Temperature ◽  
Crystallization Behavior ◽  
Crystalline Polymer ◽  
Scanning Calorimetry ◽  
Nonisothermal Crystallization ◽  
Cooling Rates ◽  
Control Range ◽  
Temperature Range ◽  
Transverse Tensile

Abstract In this study, the differential scanning calorimetry (DSC) tests were performed to measure the nonisothermal crystallization behavior of carbon fiber reinforced polyether ether ketone (CF/PEEK) composites under different cooling rates. The characteristic parameters of crystallization were obtained, and the nonisothermal crystallization model was established. The crystallization temperature range of the material at different cooling rates was predicted by the model. The unidirectional laminates were fabricated at different cooling rates in the crystallization temperature range. The results showed that the crystallization temperature range shifted to a lower temperature with the increase of cooling rate, the established nonisothermal crystallization model was consistent with the DSC test results. It is feasible to shorten the cooling control range from the whole process to the crystallization range. The crystallinity and transverse tensile strength declined significantly with the increase of the cooling rate in the crystallization temperature range. The research results provided theoretical support for the selection of cooling conditions and temperature control range, which could be applied to the thermoforming process of semi-crystalline polymer matrixed composites to improve the manufacturing efficiency.

scholarly journals Индий-индуцированная кристаллизация тонких пленок аморфного субоксида кремния

2020 ◽  
Vol 46 (12) ◽  
pp. 14
Author(s):  
А.О. Замчий ◽  
Е.А. Баранов ◽  
И.Е. Меркулова ◽  
Н.А. Лунев ◽  
В.А. Володин ◽  
...  
Keyword(s):  
Crystallization Temperature ◽  
Polycrystalline Silicon ◽  
Crystalline Silicon ◽  
Solid Phase ◽  
High Vacuum ◽  
Stoichiometric Coefficient ◽  
Free Standing ◽  
Solid Phase Crystallization ◽  
Silicon Suboxide ◽  
Induced Crystallization

A novel fabrication method of polycrystalline silicon by indium-induced crystallization (InIC) of amorphous silicon suboxide thin films with a stoichiometric coefficient of 0.5 (a-SiO0.5) is proposed. It was shown that the use of indium in the annealing process of a SiO0.5 allowed to decrease the crystallization temperature to 600°С which was significantly lower than the solid-phase crystallization temperature of the material - 850°С. As a result of the high-vacuum InIC of a-SiO0.5, the formation of free-standing micron-sized crystalline silicon particles took place.

Pressure induced crystallization and in situ simultaneous SAXS/WAXS investigations on structure transitions

CrystEngComm ◽  
2020 ◽  
Vol 22 (28) ◽  
pp. 4748-4757 ◽  
Author(s):  
Shaoyong Huang ◽  
Hongfei Li ◽  
Shichun Jiang
Keyword(s):  
Phase Diagram ◽  
Crystal Structures ◽  
Crystallization Temperature ◽  
Induced Crystallization

A phase diagram of PLLA crystal structures as a function of crystallization temperature (Tc) and pressure (Pc).

Enhanced interfacial activity of multi-arm poly(ethylene oxide) star polymers relative to linear poly(ethylene oxide) at fluid interfaces

2017 ◽  
Vol 19 (35) ◽  
pp. 23854-23868 ◽  
Author(s):  
Yun-Ru Huang ◽  
Melissa Lamson ◽  
Krzysztof Matyjaszewski ◽  
Robert D. Tilton
Keyword(s):  
Molecular Weight ◽  
Ethylene Oxide ◽  
Interfacial Tension ◽  
Star Polymers ◽  
Fluid Interfaces ◽  
Tension Reduction ◽  
Interfacial Activity ◽  
Linear Poly ◽  
Poly Ethylene Oxide ◽  
Poly Ethylene

Interfacial tension reduction, dynamic dilatational elasticity and extent of adsorption were investigated for linear poly(ethylene oxide) (PEO) chains of varying molecular weight and for PEO star polymers with an average of 64 arms per star at air/water, xylene/water, and cyclohexane/water interfaces.

scholarly journals Non-Isothermal Crystallization Kinetics of Poly(4-Hydroxybutyrate) Biopolymer

Molecules ◽  
2019 ◽  
Vol 24 (15) ◽  
pp. 2840 ◽  
Author(s):  
Ina Keridou ◽  
Luis J. del Valle ◽  
Lutz Funk ◽  
Pau Turon ◽  
Lourdes Franco ◽  
...  
Keyword(s):  
Growth Rate ◽  
Cooling Rate ◽  
Crystallization Temperature ◽  
Isothermal Crystallization ◽  
Secondary Nucleation ◽  
Scanning Calorimetry ◽  
Limited Region ◽  
First Case ◽  
Biodegradable Poly ◽  
Insertion Mechanism

The non-isothermal crystallization of the biodegradable poly(4-hydroxybutyrate) (P4HB) has been studied by means of differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). In the first case, Avrami, Ozawa, Mo, Cazé, and Friedman methodologies were applied. The isoconversional approach developed by Vyazovkin allowed also the determination of a secondary nucleation parameter of 2.10 × 105 K2 and estimating a temperature close to 10 °C for the maximum crystal growth rate. Similar values (i.e., 2.22 × 105 K2 and 9 °C) were evaluated from non-isothermal Avrami parameters. All experimental data corresponded to a limited region where the polymer crystallized according to a single regime. Negative and ringed spherulites were always obtained from the non-isothermal crystallization of P4HB from the melt. The texture of spherulites was dependent on the crystallization temperature, and specifically, the interring spacing decreased with the decrease of the crystallization temperature (Tc). Synchrotron data indicated that the thickness of the constitutive lamellae varied with the cooling rate, being deduced as a lamellar insertion mechanism that became more relevant when the cooling rate increased. POM non-isothermal measurements were also consistent with a single crystallization regime and provided direct measurements of the crystallization growth rate (G). Analysis of the POM data gave a secondary nucleation constant and a bell-shaped G-Tc dependence that was in relative agreement with DSC analysis. All non-isothermal data were finally compared with information derived from previous isothermal analyses.

Crystallization and Separation of Potassium Vanadate in Highly Concentrated Potassium Hydroxide Solution

2011 ◽  
Vol 396-398 ◽  
pp. 655-662 ◽  
Author(s):  
Na Yang ◽  
Shi Li Zheng ◽  
Shao Na Wang ◽  
Ya Ling Qin ◽  
Wan Li Xie ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Cooling Rate ◽  
Crystallization Temperature ◽  
Potassium Hydroxide ◽  
Crystallization Behavior ◽  
Potassium Hydroxide Solution ◽  
Optimal Conditions ◽  
Mass Ratio ◽  
Experimental Conditions ◽  
Seed Addition

The crystallization behavior of potassium vanadate from highly concentrated potassium hydroxide aqueous solution was investigated. The effect of various parameters including KOH concentration, V2O5concentration, final crystallization temperature, cooling rate, stirring speed and additive amount of seed were examined. The optimal experimental conditions for K3VO4crystallization were obtained as follows: KOH concentration 800850 g/L, KOH-to-V2O5mass ratio 8~9, stirring speed 200 r/min, crystallization temperature from 80°C to 40°C with natural cooling, and seed addition 2% wt. Under optimal conditions, the K3VO4crystallization yield of 87% was obtained, and the purity of crystals was about 90%.

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

Crystals ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1138
Author(s):  
Yvonne Spoerer ◽  
Regine Boldt ◽  
René Androsch ◽  
Ines Kuehnert
Keyword(s):  
Injection Molding ◽  
Cooling Rate ◽  
Crystallization Kinetics ◽  
Crystallization Temperature ◽  
Random Copolymer ◽  
Shift Factor ◽  
Temperature Dependent ◽  
Chip Calorimetry ◽  
The Relationship ◽  
Kinetics Of

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.

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