Shear-induced nonisothermal crystallization of two grades of PLA

Bojda, Joanna; Piórkowska, Ewa

doi:10.1016/j.polymertesting.2016.01.006

Cited by 39 publications

(20 citation statements)

References 27 publications

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“…For that purpose, selective etching of the injection‐molded substrates was carried out to emphasize the crystalline structure of the material under the overlying amorphous polymer. Etching was performed according to the modified method of He et al ., as described by Bojda and Piorkowska . The substrate was first dipped in a solution consisting in 1 mg of Trizma base (Sigma‐Aldrich) and 4 mg of proteinase K (Sigma‐Aldrich) diluted in 5 mL of distilled water at 37 °C and pH 8.0 to provide the enzyme with the conditions of highest activity.…”

Section: Methodsmentioning

confidence: 99%

“…The talc morphology before and after chemical modification was analyzed by a field emission gun/scanning electron microscope (Leo Supra 35, Cambridge, United Kingdom). Similarly, the morphology of the talc-PLA biocomposites was also analyzed by the field emission gun/scanning electron microscope (Leo Supra 35). For that purpose, selective etching of the injection-molded substrates was carried out to emphasize the crystalline structure of the material under the overlying amorphous polymer.…”

Section: Characterizationmentioning

confidence: 99%

“…On the microscale, shear stresses during melt processing can orientate the amorphous phase of the polymer, which can arrange consistently with the reinforcing/nucleating filler . In addition, strong shear stresses can create peculiar crystalline structures in the polymeric material known as shish kebabs , which feature their own specific thermal behavior.…”

Section: Introductionmentioning

confidence: 99%

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Thermal behavior of extruded and injection‐molded poly(lactic acid)–talc engineered biocomposites: Effects of material design, thermal history, and shear stresses during melt processing

Barletta

Pizzi

Puopolo

et al. 2017

J of Applied Polymer Sci

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Reinforced biocomposites were compounded by the reactive extrusion of poly(lactic acid) (PLA) and chemically modified microlamellar talcs. Talc was functionalized by the hydrolysis and condensation reaction of its surface hydroxyl groups with different kinds of organosilanes, namely, 3‐aminopropyl triethoxysilane and (3‐glycidoxypropyl)trimethoxysilane, and commercially available tri‐isocyanates, namely, Bayhydur 3100 and Desmodur 3900, which feature hydrophilic and hydrophobic behaviors, respectively. PLA–talc biocomposites were also compounded by the addition of two types of reactive biodegradable compatibilizing agents, namely, maleic anhydride and glycidyl methacrylate modified PLA. The resulting compounds were melt‐processed by injection molding to get flat substrates with different formulations. The thermal responses of the extruded compounds and injection‐molded items, specifically the first and second thermal transitions, were analyzed by differential scanning calorimetry. In particular, the influence of the different material formulations, their thermal history, and/or shear stress in single‐ or multiple‐stage heating and/or melt processing on the glass transition, crystallinity, and melting behavior of the biocomposites was investigated. The experimental findings revealed that the macroscopic thermal response of the compounds (i.e., extruded pellets) and substrates (i.e., injection‐molded flat slabs) manufactured by the melt processing of the available formulations was controlled and significantly improved by the fine‐tuning of the chemical (i.e., reaction mechanisms, chemical bonds) and physical interactions (i.e., steric hindrances, physical bonds) among the modified talc, PLA, and compatibilizing agents. These results are of great practical importance and open up broader scenarios for the industrial application of biopolymers and biocomposites, specifically in all of those consumer goods where thermal stability and the preservation of mechanical performance at moderate and high temperatures of the materials are pivotal. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45179.

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Section: Methodsmentioning

confidence: 99%

Section: Characterizationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Thermal behavior of extruded and injection‐molded poly(lactic acid)–talc engineered biocomposites: Effects of material design, thermal history, and shear stresses during melt processing

Barletta

Pizzi

Puopolo

et al. 2017

J of Applied Polymer Sci

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“…Shearing the melt of slowly crystallizing PLLAs containing 1.5% and 2.8% d ‐isomer co‐units revealed a large effect of the shearing temperature on predominant formation of point‐like nuclei. With decreasing shearing temperature, between 160°C and 146°C, and with increasing shear rate and time, the crystallization temperature during subsequent cooling increased, with a larger effect obtained for the sample containing 1.5% d ‐units . Also, the effect of shear on the α/α’‐crystal polymorphism was analyzed and it was demonstrated that development of the more stable α‐structure is enhanced on crystallization at around 100°C in presence of shear, that is, at a temperature at which typically α’‐crystals form .…”

Section: Introductionmentioning

confidence: 99%

“…With decreasing shearing temperature, between 160 C and 146 C, and with increasing shear rate and time, the crystallization temperature during subsequent cooling increased, with a larger effect obtained for the sample containing 1.5% D-units. [37] Also, the effect of shear on the α/α'-crystal polymorphism [38,39] was analyzed and it was demonstrated that development of the more stable α-structure is enhanced on crystallization at around 100 C in presence of shear, that is, at a temperature at which typically α'-crystals form. [40] Further studies of shear-induced crystallization of PLLA focused on the effects of presence of blend components, [41] or long-chain branches, [42] with the employed PLLA grades containing 2% and 4% D-isomers, respectively.…”

mentioning

confidence: 99%

Critical specific work of flow for shear‐induced formation of crystal nuclei in poly (l‐lactic acid)

Iqbal

Jariyavidyanont

Rhoades

et al. 2019

Polymer Crystallization

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Shear‐induced formation of crystal nuclei in the poly (l‐lactic acid) homopolymer was analyzed by shearing the supercooled melt in a plate‐plate rheometer followed by evaluation of the kinetics of isothermal crystallization via viscosity measurements. The data revealed that shearing the melt for 10 seconds at 135°C and 140°C causes shear‐induced formation of nuclei if the shear rate is higher than about 0.1 s−1. If the shear rate at these conditions is higher than about 1 s−1 then row‐nuclei, as detected by aligned spherulites, develop. Besides providing comprehensive data about the effects of rate and time of shear at 135°C and 140°C on the crystallization kinetics, the concept of specific work of flow was tested. Shear rate and time compensate each other to drive shear‐induced nuclei formation, and the critical specific work required to form shear‐induced crystal nuclei is around 20 to 50 kPa. Further conceptual work included the analysis of the microstructure along the radius of the sheared discs as it permits evaluation of the effect of a broad range of shear rates in a single experiment.

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Effect of the application of low shear rates on the crystallization kinetics of PLA

Volpe

Foglia

Pantani

2020

Polymer Crystallization

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Flow-induced crystallization can effectively increase the crystallinity content in poly (lactic acid) parts, and this can be extremely significant since an increase of crystallinity for this material dramatically enhances many properties among which the heat resistance. This work analyzes nucleation and growth rate of spherulites formed during crystallization process of PLA at different temperatures and shear rates. The application of a shear flow results in an enhancement of the nucleation phenomena, with the formation of a new population of nuclei, and an improvement of the crystals growth already at low values of shear rates. Furthermore, it is possible to find a dependence of the equilibrium melting temperature upon the Weissenberg number.

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Shear-induced nonisothermal crystallization of two grades of PLA

Cited by 39 publications

References 27 publications

Thermal behavior of extruded and injection‐molded poly(lactic acid)–talc engineered biocomposites: Effects of material design, thermal history, and shear stresses during melt processing

Thermal behavior of extruded and injection‐molded poly(lactic acid)–talc engineered biocomposites: Effects of material design, thermal history, and shear stresses during melt processing

Critical specific work of flow for shear‐induced formation of crystal nuclei in poly (l‐lactic acid)

Effect of the application of low shear rates on the crystallization kinetics of PLA

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