Melt strengthening of polylactic acid and its blends: Shear and elongation rheological investigations of the forming process

Mapping Intimacies ◽

10.25518/esaform21.748 ◽

2021 ◽

Author(s):

Abderrahim Maazouz ◽

Khalid Lamnawar

Keyword(s):

Polylactic Acid ◽

Blow Up ◽

Good Alternative ◽

Thermomechanical Properties ◽

Chain Extension ◽

Nucleating Agents ◽

Forming Process ◽

Exclusion Chromatography ◽

Stability Maps ◽

The Stability

Polylactic acid (PLA) can be a good alternative to petroleum-based polymers thanks to its organic origin and its biodegradability. This study introduces some promising routes for enhancing the processability of PLA, which presents several challenges due mainly to the poor shear and elongation properties of this biopolymer. To our knowledge, this is the first paper dedicated to an investigation of foaming and/or blown extrusion of PLA that focuses on structural, rheological and thermomechanical properties. Two main routes were selected: (i) the modification of its structural, rheological and thermomechanical properties and (ii) blending the PLA with another ductile, thermoplastic biopolymer such as poly (butylene adipate-co-terephthalate) (PBAT) or polyamide (PA11). Various formulations of PLA with multifunctionalized epoxy, nucleating agents and plasticizer were prepared and characterized on the basis of their linear viscoelasticity and extensional properties. The balance of chain extension and branching was also investigated using solution viscosimetry, steric exclusion chromatography (SEC) and rheology (shear and elongation rheology). On one hand, a batch foaming process assisted by supercritical CO2 was carried out. The influence of the foaming parameters, the extent of chain modification and the contribution of crystallization to cell morphology were all evaluated. Based on these parameters, structures ranging from micro to macro-cellular-cell were obtained. On the other hand, the stability maps of blown extrusion for neat and modified PLA were established at different die temperatures. We succeeded in greatly enhancing the blown extrusion windows of PLA, achieving high blow-up ratio (BUR) and take-up ratio (TUR) values. We were able to demonstrate that faster kinetics of crystallization can also be reached for chain-extended and branched PLA formulated with adequate amounts of nucleating agents and plasticizers. Through this work, blown films with intriguing thermomechanical and mechanical properties were produced using an optimal formulation for PLA.

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Compounding and Melt Strengthening of Poly(Lactic Acid): Shear and Elongation Rheological Investigations for Forming Process

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.554-557.1751 ◽

2013 ◽

Vol 554-557 ◽

pp. 1751-1756 ◽

Cited By ~ 8

Author(s):

Benoit Mallet ◽

Khalid Lamnawar ◽

Abderrahim Maazouz

Keyword(s):

Mechanical Properties ◽

Lactic Acid ◽

Supercritical Co2 ◽

Food Packaging ◽

Blow Up ◽

Good Alternative ◽

Chain Extension ◽

Poly Lactic Acid ◽

Forming Process ◽

Batch Foaming

The poly (lactic acid) (PLA), through its organic origin and its biodegradation properties, can be a good alternative to petroleum-based polymers. To this end, the forming process as well blown extrusion and foaming of PLA was investigated in this study as an alternative for the production of food packaging. Through this work, we present some promising routes to enhance its processing ability which presents several challenges mainly due to the poor shear and elongation properties of this biopolymer. To our knowledge, there is no paper dedicated to the investigation of foaming and/or blown extrusion of PLA that involves structural, rheological and thermo-mechanical properties. To achieve this objective, various formulations of PLA with multifunctionalized epoxy, nucleants and plasticizer were prepared and characterized on the basis of their linear viscoelasticity and extensional properties. The balance of chain extension and branching has been also investigated using solution viscosimetry, Steric exclusion chromatography (SEC) and rheology (relaxation spectrum, Van Gurp Palmen curves….). We pushed further by characterizing both the structure and thermo-mechanical properties of PLA formulations. On one hand, a batch foaming assisted with supercritical CO2 was achieved following a full characterization in physicochemical, rheological and thermal domain, The influence of the foaming parameters, the extent of chain modification as well as the contribution of crystallization on cell morphology was evaluated. Based on these parameters, structures ranging from micro to macro-cellular-cell were obtained. On the other hand, the stability maps of blown processing for neat and modified PLA were established at different die temperatures. We have achieved a great enhancement of the blown processing windows of PLA with high BUR (Blow Up Ratio) and TUR (Take Up Ratio) attained. We were able to demonstrate that a higher kinetic of crystallization can also be reached for chain-extended and branched PLA formulated with adequate amounts of nucleants and plasticizers. Induced crystallization during process was also demonstrated. Through this work, blown films with interesting thermo-mechanical and mechanical properties have been produced using an optimal formulation for PLA. References [1] A. Maazouz, K. Lamnawar, B. Mallet, Patent: C08L67/00; C08J5/10. FR2941702 (A1). (2010) [2] Y.-M. Corre, A. Maazouz, J. Duchet, J. Reignier, Batch foaming of chain extended PLA with supercritical CO2: Influence of the rheological properties and the process parameters on the cellular structure. J. of Supercritical Fluids,58 (2011) 177-188 [3] B. Mallet, K. Lamnawar, A. Maazouz, Compounding and processing of biodegradable materials based on PLA for packaging applications: In greening the 21st century material’s world, Frontiers in Science and Engineering, 1-2(2011) 1-44 [4] B. Mallet, K. Lamnawar, A. Maazouz, Improvement of blown extrusion processing of PLA: structure-processing-properties relashionships. Polymer engineering and Science (To appear in 2013).

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Analysis of the interaction of thermoacoustic modes with a Green’s function approach

International Journal of Spray and Combustion Dynamics ◽

10.1177/1756827718809570 ◽

2018 ◽

Vol 10 (4) ◽

pp. 326-336 ◽

Cited By ~ 2

Author(s):

Alessandra Bigongiari ◽

Maria Heckl

Keyword(s):

Green’S Function ◽

Green's Function ◽

Initial Perturbation ◽

Time History ◽

Function Approach ◽

Stability Maps ◽

Flame Describing Function ◽

The Stability ◽

Dynamics Simulations ◽

Fast Prediction

In this paper, we will present a fast prediction tool based on a one-dimensional Green's function approach that can be used to bypass numerically expensive computational fluid dynamics simulations. The Green’s function approach has the advantage of providing a clear picture of the physics behind the generation and evolution of combustion instabilities. In addition, the method allows us to perform a modal analysis; single acoustic modes can be treated in isolation or in combination with other modes. In this article, we will investigate the role of higher-order modes in determining the stability of the system. We will initially produce the stability maps for the first and second mode separately. Then the time history of the perturbation will be computed, where both the modes are present. The flame will be modelled by a generic Flame Describing Function, i.e. by an amplitude-dependent Flame Transfer Function. The time-history calculations show the evolution of the two modes resulting from an initial perturbation; both transient and limit-cycle oscillations are revealed. Our study represents a first step towards the modelling of nonlinearity and non-normality in combustion processes.

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Strain improvement of newly isolated Lactobacillus acidophilus MS1 for enhanced bacteriocin production

Turkish Journal of Biochemistry ◽

10.1515/tjb-2017-0075 ◽

2017 ◽

Vol 43 (3) ◽

pp. 323-332 ◽

Cited By ~ 1

Author(s):

Mahwish Salman ◽

Shazia Anwer Bukhari ◽

Muhammad Shahid ◽

Tanzila Sahar ◽

Shazia Naheed

Keyword(s):

Survival Rate ◽

Ethidium Bromide ◽

Lactobacillus Acidophilus ◽

Strain Improvement ◽

Bacteriocin Production ◽

Chemical Mutagenesis ◽

16S Rdna Sequence Analysis ◽

Wide Range ◽

Exclusion Chromatography ◽

The Stability

Abstract Background: Lactic acid bacteria (LAB) are considered as GRAS (generally recognized as safe) and being used extensively as bio-preservatives. Bacteriocins, the metabolites of LAB, belong to a diverse family of naturally synthesized antimicrobial peptides. Objective: Strain improvement for enhanced bacteriocin production by physical and chemical mutagenesis. Methods: The bacterial strain was identified by 16S rDNA sequence analysis and improved by ultraviolet and ethidium bromide mutation. The resultant bacteriocin was biochemically characterized, purified and analyzed for mass determination. Results: Among mutants of identified Lactobacillus acidophilus MS1, the UV6 (ultraviolet mutant) revealed 3400 AU bacteriocin activity with 42% survival rate and EB5 (ethidium bromide mutant) exhibited 4020 AU with 28% survival rate. Bacteriocin of 6.5 kDa was purified by cation exchange and gel exclusion chromatography. It was found to be thermally stable at 100°C for 30 min and maintained the stability up to 121°C. The activity was monitored in a wide range of pH (4–9). Conclusion: Being resistant to several biochemical parameters, the bacteriocins have an effective incorporation in food, forage and pharmacy. There is a need to engage more efforts to explore novel bacteriocins and multifarious applications.

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Thermomechanical properties of poly(1‐butene) synthesized by Ziegler–Natta catalyzed polymerization of 1‐butene in the presence of nucleating agents

Polymer International ◽

10.1002/pi.6067 ◽

2020 ◽

Vol 69 (12) ◽

pp. 1237-1242

Author(s):

Xiaopeng Cui ◽

Chuang Li ◽

Gaosheng Gu ◽

Yanfeng Gong ◽

Binyuan Liu ◽

...

Keyword(s):

Thermomechanical Properties ◽

Nucleating Agents ◽

Catalyzed Polymerization

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Chemical Preparation Routes and Lowering the Sintering Temperature of Ceramics

Ceramics ◽

10.3390/ceramics3030029 ◽

2020 ◽

Vol 3 (3) ◽

pp. 312-339

Author(s):

Philippe Colomban

Keyword(s):

Electrode Materials ◽

Sintering Temperature ◽

Microwave Sintering ◽

Sol Gel ◽

Transient Liquid Phase ◽

Ceramic Matrix Composites ◽

Thermomechanical Properties ◽

Matrix Composites ◽

Chemical Preparation ◽

The Stability

Chemically and thermally stable ceramics are required for many applications. Many characteristics (electrochemical stability, high thermomechanical properties, etc.) directly or indirectly imply the use of refractory materials. Many devices require the association of different materials with variable melting/decomposition temperatures, which requires their co-firing at a common temperature, far from being the most efficient for materials prepared by conventional routes (materials having the stability lowest temperature determines the maximal firing temperature). We review here the different strategies that can be implemented to lower the sintering temperature by means of chemical preparation routes of oxides, (oxy)carbides, and (oxy)nitrides: wet chemical and sol–gel process, metal-organic precursors, control of heterogeneity and composition, transient liquid phase at the grain boundaries, microwave sintering, etc. Examples are chosen from fibers and ceramic matrix composites (CMCs), (opto-)ferroelectric, electrolytes and electrode materials for energy storage and production devices (beta alumina, ferrites, zirconia, ceria, zirconates, phosphates, and Na superionic conductor (NASICON)) which have specific requirements due to multivalent composition and non-stoichiometry.

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Improvements in Amperometric Detection of Sulfite in Food Matrixes

Journal of AOAC International ◽

10.1093/jaoac/80.6.1374 ◽

1997 ◽

Vol 80 (6) ◽

pp. 1374-1380 ◽

Cited By ~ 3

Author(s):

Michele B Wygant ◽

John A Statler ◽

Alan Henshall

Keyword(s):

Amperometric Detection ◽

Method Performance ◽

Pulsed Amperometric Detection ◽

Ion Exclusion Chromatography ◽

Working Electrode ◽

Ion Exclusion ◽

Before And After ◽

Exclusion Chromatography ◽

The Stability

Abstract Sulfite is added to foods as an antimicrobial, antibrowning agent, or antioxidant. It also can occur naturally, and is often used in the production of beer and wine. For years the standard methodology for determination of sulfite in foods has been the Monier–Williams method, which is a combination of acid distillation and titration. Recently, AOAC adopted a chromatographic method based on a method developed by Kim and Kim for the determination of sulfite. The method combines ion exclusion chromatography with direct-current (DC) amperometric detection to provide more convenient and accurate quantitation of sulfite. However, fouling of the platinum working electrode results in a rapid decrease in method sensitivity. As a result, standards must be injected before and after every sample, and the electrode must be polished frequently to maintain adequate detection limits. Pulsed amperometric detection overcomes electrode fouling problems by repeatedly and continuously applying cleaning potentials to the working electrode. Using this technique, a reproducible electrode surface can be maintained, and injection-to-injection repeatability is greatly improved. A comparison of method performance for both DC and pulsed amperometric detection is presented. Also investigated was the stability of sulfite samples at varying pH, and in the presence or absence of a preservative.

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Prediction of the Thermoacoustic Combustion Instabilities in Practical Annular Combustors

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4027067 ◽

2014 ◽

Vol 136 (9) ◽

Cited By ~ 33

Author(s):

Giovanni Campa ◽

Sergio Mario Camporeale

Keyword(s):

Combustion Chamber ◽

Three Dimensional ◽

Design Stage ◽

Combustion Instabilities ◽

Combustion Chambers ◽

Stability Maps ◽

Dimensional Finite Element ◽

Practical Tool ◽

The Stability ◽

Three Dimensional Finite Element

A three-dimensional finite element code is used for the eigenvalue analysis of the thermoacoustic combustion instabilities modeled through the Helmholtz equation. A full annular combustion chamber, equipped with several burners, is examined. Spatial distributions for the heat release intensity and for the time delay are used for the linear flame model. Burners, connecting the plenum and the chamber, are modeled by means of the transfer matrix method. The influence of the parameters characterizing the burners and the flame on the stability levels of each mode of the system is investigated. The obtained results show the influence of the 3D distribution of the flame on the modes. Additionally, the results show what types of modes are most likely to yield humming in an annular combustion chamber. The proposed methodology is intended to be a practical tool for the interpretation of the thermoacoustic phenomenon (in terms of modes, frequencies, and stability maps) both in the design stage and in the check stage of gas turbine combustion chambers.

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Stability Evaluation of Karst Foundation Based on Orthogonal Test

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.807-809.1725 ◽

2013 ◽

Vol 807-809 ◽

pp. 1725-1732

Author(s):

Yi Ping Wu ◽

Jian Hong Zhou ◽

Qiu Xia Zhang ◽

Zhong Jie Zhao

Keyword(s):

Simulation Method ◽

Orthogonal Test ◽

Ratio Method ◽

Stability Evaluation ◽

Rock Slide ◽

Factors Influencing ◽

Object Based ◽

Stability Maps ◽

The Stability ◽

Stability Results

Many State Grid projects of China are facing a series of natural disaster threats, such as landslide, collapse, mud-rock slide, etc. This article takes the Huangshi Daye Steel Substation as research object. Based on the orthogonal test which confirmed factors influencing the stability, it adopts the Numerical Simulation Method and the Roof Thickness-to-span Ratio Method to evaluate the stability of the Huangshi Daye Steel Substations karst foundation. By doing this, karst foundation stability maps of the substation are respectively obtained. Analyzing the stability results of the two methods, it has been found that the stability evaluation results measured by the two methods are the same. And orthogonal test has advantages such as comprehensiveness, speediness, reliability and accuracy. Meanwhile, according to the stability evaluation results, specific site operation suggestions are proposed.

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