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Rivera P, Torres A, Romero J, Alarcón Á, Martínez S, Arrieta MP, Rodríguez-Mercado F, Galotto MJ. Effect of Operational Variables on Supercritical Foaming of Caffeic Acid-Loaded Poly(lactic acid)/Poly(butylene adipate-co-terephthalate) Blends for the Development of Sustainable Materials. Polymers (Basel) 2024; 16:948. [PMID: 38611209 PMCID: PMC11013249 DOI: 10.3390/polym16070948] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2024] [Revised: 03/03/2024] [Accepted: 03/25/2024] [Indexed: 04/14/2024] Open
Abstract
Expanded polystyrene will account for 5.3% of total global plastic production in 2021 and is widely used for food packaging due to its excellent moisture resistance and thermal insulation. However, some of these packages are often used only once before being discarded, generating large amounts of environmentally harmful plastic waste. A very attractive alternative to the conventional methods used for polymer processing is the use of supercritical carbon dioxide (scCO2) since it has mass-transfer properties adapted to the foam morphology, generating different path lengths for the diffusion of active compounds within its structure and can dissolve a wide range of organic molecules under supercritical conditions. The objective of this research was to evaluate the effect of operational variables on the process of caffeic acid (CA) impregnation and subsequent foaming of polylactic acid (PLA) as well as two PLA/poly(butylene-co-terephthalate-adipate) (PBAT) blends using scCO2. The results showed an increase in the degree of crystallinity of the CA-impregnated samples due to the nucleation effect of the active compound. On the other hand, SEM micrographs of both films and foams showed significant differences due to the presence of PBAT and its low miscibility with PLA. Finally, the results obtained in this work contribute to the knowledge of the important parameters to consider for the implementation of the impregnation and foaming process of PLA and PLA/PBAT blends with potential use in food packaging.
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Affiliation(s)
- Patricia Rivera
- Packaging Innovation Center (LABEN), Technology Faculty, Center for the Development of Nanoscience and Nanotechnology CEDENNA, University of Santiago de Chile (USACH), Santiago 9170201, Chile; (P.R.); (Á.A.); (S.M.); (F.R.-M.); (M.J.G.)
- Laboratory of Membrane Separation Processes (LabProSeM), Department of Chemical Engineering, Engineering Faculty, University of Santiago de Chile, Santiago 9170201, Chile;
| | - Alejandra Torres
- Packaging Innovation Center (LABEN), Technology Faculty, Center for the Development of Nanoscience and Nanotechnology CEDENNA, University of Santiago de Chile (USACH), Santiago 9170201, Chile; (P.R.); (Á.A.); (S.M.); (F.R.-M.); (M.J.G.)
| | - Julio Romero
- Laboratory of Membrane Separation Processes (LabProSeM), Department of Chemical Engineering, Engineering Faculty, University of Santiago de Chile, Santiago 9170201, Chile;
| | - Álvaro Alarcón
- Packaging Innovation Center (LABEN), Technology Faculty, Center for the Development of Nanoscience and Nanotechnology CEDENNA, University of Santiago de Chile (USACH), Santiago 9170201, Chile; (P.R.); (Á.A.); (S.M.); (F.R.-M.); (M.J.G.)
- Laboratory of Membrane Separation Processes (LabProSeM), Department of Chemical Engineering, Engineering Faculty, University of Santiago de Chile, Santiago 9170201, Chile;
| | - Sara Martínez
- Packaging Innovation Center (LABEN), Technology Faculty, Center for the Development of Nanoscience and Nanotechnology CEDENNA, University of Santiago de Chile (USACH), Santiago 9170201, Chile; (P.R.); (Á.A.); (S.M.); (F.R.-M.); (M.J.G.)
| | - Marina P. Arrieta
- Departamento de Ingeniería Química Industrial y del Medio Ambiente, Escuela Técnica Superior de Ingenieros Industriales, Universidad Politécnica de Madrid (ETSII-UPM), Calle José Gutiérrez Abascal 2, 28006 Madrid, Spain;
- Grupo de Investigación, Polímeros, Caracterización y Aplicaciones (POLCA), 28006 Madrid, Spain
| | - Francisco Rodríguez-Mercado
- Packaging Innovation Center (LABEN), Technology Faculty, Center for the Development of Nanoscience and Nanotechnology CEDENNA, University of Santiago de Chile (USACH), Santiago 9170201, Chile; (P.R.); (Á.A.); (S.M.); (F.R.-M.); (M.J.G.)
| | - María José Galotto
- Packaging Innovation Center (LABEN), Technology Faculty, Center for the Development of Nanoscience and Nanotechnology CEDENNA, University of Santiago de Chile (USACH), Santiago 9170201, Chile; (P.R.); (Á.A.); (S.M.); (F.R.-M.); (M.J.G.)
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2
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Eselem Bungu PS, Luetzow K, Lettau O, Schulz M, Neffe AT, Pasch H. Stereochemical Heterogeneity Analysis of Polylactides by Multidimensional Liquid Chromatography. Anal Chem 2024; 96:4716-4725. [PMID: 38465448 PMCID: PMC10955512 DOI: 10.1021/acs.analchem.4c00336] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2024] [Revised: 02/23/2024] [Accepted: 02/27/2024] [Indexed: 03/12/2024]
Abstract
A new and robust high-performance liquid chromatography (HPLC) method that separates poly(lactic acid) (PLA) according to its stereochemical composition is presented. Using this method, poly(l-lactide) incorporating trace amounts of meso-lactide resulting from the racemization is separated from the pristine polymer. To prove this aspect in more detail, a representative poly(l-lactic acid) standard, assumed to be highly homogeneous, was separated using this method. The result showed that this was not the case as a fraction incorporating meso-lactide due to racemization occurring during the synthesis is separated. Employing two-dimensional liquid chromatography (2D-LC), the molar mass differences of the separated species were investigated, and fractions with similar molecular sizes were detected, confirming that the LC separation is solely based on stereochemical heterogeneity. The sample was further fractionated by preparative HPLC, followed by an in-depth analysis of the fractions using homonuclear decoupling in proton nuclear magnetic resonance (1H NMR). Convincing results that unveiled significant differences in the stereochemistry of the isolated PLA fractions were obtained. Subsequent analysis by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) also confirmed oligomer series with different end group structures, indicating that the applied HPLC method is very sensitive to minor variations in stereochemistry and end groups. This integrated approach offers detailed insight into the structural characteristics of PLA polymers, contributing to a better understanding of their composition and potential applications.
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Affiliation(s)
- Paul S. Eselem Bungu
- Department
of Multidimensional Polymer Characterization, Institute of Active Polymers, Helmholtz-Center Hereon, Kantstrasse 55, Teltow 14513, Germany
| | - Karola Luetzow
- Department
of Multidimensional Polymer Characterization, Institute of Active Polymers, Helmholtz-Center Hereon, Kantstrasse 55, Teltow 14513, Germany
| | - Olaf Lettau
- Department
of Multidimensional Polymer Characterization, Institute of Active Polymers, Helmholtz-Center Hereon, Kantstrasse 55, Teltow 14513, Germany
| | - Matthias Schulz
- PSS
Polymer Standards Service GmbH (Now Part of Agilent Technology), In der Dalheimer Wiese 5, Mainz 55120, Germany
| | - Axel T. Neffe
- Department
of Multidimensional Polymer Characterization, Institute of Active Polymers, Helmholtz-Center Hereon, Kantstrasse 55, Teltow 14513, Germany
| | - Harald Pasch
- Department
of Multidimensional Polymer Characterization, Institute of Active Polymers, Helmholtz-Center Hereon, Kantstrasse 55, Teltow 14513, Germany
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Zhu Z, Bian Y, Zhang X, Zeng R, Yang B. Study on the crystallization behavior and conformation adjustment scale of poly(lactic acid) in the terahertz frequency range. Phys Chem Chem Phys 2023; 25:8472-8481. [PMID: 36883295 DOI: 10.1039/d3cp00208j] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/09/2023]
Abstract
The observed properties of crystalline polymers are determined by their internal structure, which in turn is the result of their different crystallization behaviors. Here, we investigate the crystallization behavior of poly(lactic acid) (PLA) by terahertz time-domain spectroscopy (THz-TDS) at varied temperatures. We find that the changes in the chain packing and conformation of PLA are characterized by THz spectroscopy. Combining X-ray diffraction (XRD) and infrared spectroscopy (IR), we attributed the blue-shift of the THz peak to the tightness of the chain packing, while its absorption enhancement is caused by the conformation transition. The effects of chain packing and chain conformation on the characteristic peak are phased. Furthermore, absorption discontinuities of the characteristic peaks of PLA crystallized at different temperatures are observed, which originated from differences in the degree of conformational transition caused by different thermal energies. We find that the crystallization temperature at which the absorption mutation of PLA occurs corresponds to the temperature at which the motion of the segment and molecular chain is excited, respectively. At these two temperatures, PLA exhibits different scales of conformational transitions leading to stronger absorption and larger absorption changes at higher crystallization temperatures. The results demonstrate that the driving force of PLA crystallization is indeed from changes in chain packing and chain conformation, and the molecular motion scale can also be characterized by THz spectroscopy.
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Affiliation(s)
- Zhenqi Zhu
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou, 310018, P. R. China.
| | - Yujing Bian
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou, 310018, P. R. China.
| | - Xun Zhang
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou, 310018, P. R. China.
| | - Ruonan Zeng
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou, 310018, P. R. China.
| | - Bin Yang
- College of Textile Science and Engineering (International Institute of Silk), Zhejiang Sci-Tech University, Hangzhou, 310018, P. R. China.
- Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Ministry of Education, Zhejiang Sci-Tech University, Hangzhou, 310018, P. R. China
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Safandowska M, Rozanski A, Galeski A. Plasticization of Polylactide after Solidification: An Effectiveness and Utilization for Correct Interpretation of Thermal Properties. Polymers (Basel) 2020; 12:polym12030561. [PMID: 32143346 PMCID: PMC7182837 DOI: 10.3390/polym12030561] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2020] [Revised: 02/27/2020] [Accepted: 02/29/2020] [Indexed: 11/16/2022] Open
Abstract
Polylactide/triethyl citrate (PLA/TEC) systems were prepared in two ways by introducing TEC to solidified polymer matrix (SS) and by blending in a molten state (MS) to investigate the effectiveness of the plasticization process after solidification of polylactide. The plasticization processes, independently of way of introducing the TEC into PLA matrix, leads to systems characterized by similar stability, morphology and properties. Some differences in mechanical properties between MS and SS systems result primarily from the difference in the degree of crystallinity/crystal thickness of the PLA matrix itself. Based on the presented results, it was concluded that the plasticization process after solidification of polylactide is an alternative to the conventional method of modification-blending in a molten state. Then, this new approach to plasticization process was utilized for interpretation of thermal properties of PLA and PLA/TEC systems. It turned out that double melting peak observed at DSC thermograms does not result from the melting of a double population of crystals with different lamellar thickness, or the melting of both the α' and α crystalline phase (commonly used explanations in literature), but is associated with the improvement of perfection of crystalline structure of PLA during heating process.
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Affiliation(s)
- Marta Safandowska
- Correspondence: (M.S.); (A.R.); Tel.: +48-42-680-3236 (M.S.); +48-42-680-3228 (A.R.)
| | - Artur Rozanski
- Correspondence: (M.S.); (A.R.); Tel.: +48-42-680-3236 (M.S.); +48-42-680-3228 (A.R.)
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Jain S, Fuoco T, Yassin MA, Mustafa K, Finne-Wistrand A. Printability and Critical Insight into Polymer Properties during Direct-Extrusion Based 3D Printing of Medical Grade Polylactide and Copolyesters. Biomacromolecules 2019; 21:388-396. [DOI: 10.1021/acs.biomac.9b01112] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Shubham Jain
- Department of Fibre and Polymer Technology, KTH Royal Institute of Technology, Teknikringen, 56-58, SE 10044 Stockholm, Sweden
| | - Tiziana Fuoco
- Department of Fibre and Polymer Technology, KTH Royal Institute of Technology, Teknikringen, 56-58, SE 10044 Stockholm, Sweden
| | - Mohammed A. Yassin
- Tissue Engineering Group, Department of Clinical Dentistry, Faculty of Medicine, University of Bergen, Norway, Årstadveien 19, 5009 Bergen, Norway
| | - Kamal Mustafa
- Tissue Engineering Group, Department of Clinical Dentistry, Faculty of Medicine, University of Bergen, Norway, Årstadveien 19, 5009 Bergen, Norway
| | - Anna Finne-Wistrand
- Department of Fibre and Polymer Technology, KTH Royal Institute of Technology, Teknikringen, 56-58, SE 10044 Stockholm, Sweden
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Li X, Jia W, Dong B, Yuan H, Su F, Wang Z, Wang Y, Liu C, Shen C, Shao C. Structure and Mechanical Properties of Multi-Walled Carbon Nanotubes-Filled Isotactic Polypropylene Composites Treated by Pressurization at Different Rates. Polymers (Basel) 2019; 11:polym11081294. [PMID: 31382397 PMCID: PMC6723393 DOI: 10.3390/polym11081294] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2019] [Revised: 07/12/2019] [Accepted: 07/15/2019] [Indexed: 11/24/2022] Open
Abstract
Isotactic polypropylene filled with 1 wt.% multi-walled carbon nanotubes (iPP/MWCNTs) were prepared, and their crystallization behavior induced by pressurizing to 2.0 GPa with adjustable rates from 2.5 to 1.3 × 104 MPa/s was studied. The obtained samples were characterized by combining wide angle X-ray diffraction, small angle X-ray scattering, differential scanning calorimetry, transmission electron microscopy and atomic force microscopy techniques. It was found that pressurization is a simple way to prepare iPP/MWCNTs composites in mesophase, γ-phase, or their blends. Two threshold pressurization rates marked as R1 and R2 were identified, while R1 corresponds to the onset of mesomorphic iPP formation. When the pressurization rate is lower than R1 only γ-phase generates, with its increasing mesophase begins to generate and coexist with γ-phase, and if it exceeds R2 only mesophase can generate. When iPP/MWCNTs crystallized in γ-phase, compared with the neat iPP, the existence of MWCNTs can promote the nucleation of γ-phase, leading to the formation of γ-crystal with thicker lamellae. If iPP/MWCNTs solidified in mesophase, MWCNTs can decrease the growth rate of the nodular structure, leading to the formation of mesophase with smaller nodular domains (about 9.4 nm). Mechanical tests reveal that, γ-iPP/MWCNTs composites prepared by slow pressurization display high Young’s modulus, high yield strength and high elongation at break, and meso-iPP/MWCNTs samples have excellent deformability because of the existence of nodular morphology. In this sense, the pressurization method is proved to be an efficient approach to regulate the crystalline structure and the properties of iPP/MWCNTs composites.
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Affiliation(s)
- Xiaoting Li
- Key Laboratory of Materials Processing and Mold (Zhengzhou University), Ministry of Education, National Engineering Research Center for Advanced Polymer Processing Technology, Zhengzhou University, Zhengzhou 450002, China
| | - Wenxia Jia
- Key Laboratory of Materials Processing and Mold (Zhengzhou University), Ministry of Education, National Engineering Research Center for Advanced Polymer Processing Technology, Zhengzhou University, Zhengzhou 450002, China
| | - Beibei Dong
- Key Laboratory of Materials Processing and Mold (Zhengzhou University), Ministry of Education, National Engineering Research Center for Advanced Polymer Processing Technology, Zhengzhou University, Zhengzhou 450002, China
| | - Huan Yuan
- Key Laboratory of Materials Processing and Mold (Zhengzhou University), Ministry of Education, National Engineering Research Center for Advanced Polymer Processing Technology, Zhengzhou University, Zhengzhou 450002, China
| | - Fengmei Su
- Key Laboratory of Materials Processing and Mold (Zhengzhou University), Ministry of Education, National Engineering Research Center for Advanced Polymer Processing Technology, Zhengzhou University, Zhengzhou 450002, China
| | - Zhen Wang
- Key Laboratory of Materials Processing and Mold (Zhengzhou University), Ministry of Education, National Engineering Research Center for Advanced Polymer Processing Technology, Zhengzhou University, Zhengzhou 450002, China
| | - Yaming Wang
- Key Laboratory of Materials Processing and Mold (Zhengzhou University), Ministry of Education, National Engineering Research Center for Advanced Polymer Processing Technology, Zhengzhou University, Zhengzhou 450002, China
| | - Chuntai Liu
- Key Laboratory of Materials Processing and Mold (Zhengzhou University), Ministry of Education, National Engineering Research Center for Advanced Polymer Processing Technology, Zhengzhou University, Zhengzhou 450002, China
| | - Changyu Shen
- Key Laboratory of Materials Processing and Mold (Zhengzhou University), Ministry of Education, National Engineering Research Center for Advanced Polymer Processing Technology, Zhengzhou University, Zhengzhou 450002, China
| | - Chunguang Shao
- Key Laboratory of Materials Processing and Mold (Zhengzhou University), Ministry of Education, National Engineering Research Center for Advanced Polymer Processing Technology, Zhengzhou University, Zhengzhou 450002, China.
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7
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Yuan C, Xu Y, Yang K, Wang Y, Wang Z, Cheng X, Su L. Isothermally crystallization behavior of poly (L-lactide) from melt under high pressure. POLYM ADVAN TECHNOL 2018. [DOI: 10.1002/pat.4425] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Chaosheng Yuan
- The High Pressure Research Center of Science and Technology; Zhengzhou University of Light Industry; Zhengzhou 450002 China
| | - Ying Xu
- School of Mathematics and Statistics; Zhengzhou University; Zhengzhou 450001 China
| | - Kun Yang
- The High Pressure Research Center of Science and Technology; Zhengzhou University of Light Industry; Zhengzhou 450002 China
| | - Yongqiang Wang
- The High Pressure Research Center of Science and Technology; Zhengzhou University of Light Industry; Zhengzhou 450002 China
| | - Zheng Wang
- The High Pressure Research Center of Science and Technology; Zhengzhou University of Light Industry; Zhengzhou 450002 China
| | - Xuerui Cheng
- The High Pressure Research Center of Science and Technology; Zhengzhou University of Light Industry; Zhengzhou 450002 China
| | - Lei Su
- Key Laboratory of Photochemistry; Institute of Chemistry, Chinese Academy of Sciences; Beijing 100080 China
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Nanthananon P, Seadan M, Pivsa-Art S, Hamada H, Suttiruengwong S. Facile Preparation and Characterization of Short-Fiber and Talc Reinforced Poly(Lactic Acid) Hybrid Composite with In Situ Reactive Compatibilizers. MATERIALS 2018; 11:ma11071183. [PMID: 29996535 PMCID: PMC6073708 DOI: 10.3390/ma11071183] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/15/2018] [Revised: 07/01/2018] [Accepted: 07/04/2018] [Indexed: 11/16/2022]
Abstract
Hybrid composites of fillers and/or fibers reinforced polymer was generally produced by masterbatch dilution technique. In this work, the simplified preparation was introduced for the large volume production of 30 wt % short-fiber and talcum reinforced polymer hybrid composite by direct feeding into twin-screw extruder. Multifunctional epoxide-based terpolymer and/or maleic anhydride were selected as in situ reactive compatibilizers. The influence of fiber and talcum ratios and in situ reactive compatibilizers on mechanical, dynamic mechanical, morphological and thermal properties of hybrid composites were investigated. The morphological results showed the strong interfacial adhesion between fiber or talcum and Poly(lactic acid) (PLA) matrix due to a better compatibility by reaction of in situ compatibilizer. The reactive PLA hybrid composite showed the higher tensile strength and the elongation at break than non-compatibilized hybrid composite without sacrificing the tensile modulus. Upon increasing the talcum contents, the modulus and storage modulus of hybrid composites were also increased while the tensile strength and elongation at break were slightly decreased compared to PLA/fiber composite. Talcum was able to induce the crystallization of PLA hybrid composites.
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Affiliation(s)
- Phornwalan Nanthananon
- Department of Materials Science and Engineering, Faculty of Engineering and Industrial Technology, Silpakorn University, Nakhon Pathom 73000, Thailand.
| | - Manus Seadan
- Department of Physics, Faculty of Science, Silpakorn University, Nakhon Pathom 73000, Thailand.
| | - Sommai Pivsa-Art
- Department of Material and Metallurgical Engineering, Faculty of Engineering, Rajamangala University of Technology Thanyaburi, Pathumthani 12110, Thailand.
| | - Hiroyuki Hamada
- Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto City 606-8585, Japan.
| | - Supakij Suttiruengwong
- Department of Materials Science and Engineering, Faculty of Engineering and Industrial Technology, Silpakorn University, Nakhon Pathom 73000, Thailand.
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Baran A, Vrábel P, Olčák D, Chodák I. Solid state13C-NMR study of a plasticized PLA/PHB polymer blend. J Appl Polym Sci 2018. [DOI: 10.1002/app.46296] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Affiliation(s)
- Anton Baran
- Department of Physics, Faculty of Electrical Engineering and Informatics; Technical University of Košice, Park Komenského 2; Košice 042 00 Slovakia
| | - Peter Vrábel
- Department of Physics, Faculty of Electrical Engineering and Informatics; Technical University of Košice, Park Komenského 2; Košice 042 00 Slovakia
| | - Dušan Olčák
- Department of Physics, Faculty of Electrical Engineering and Informatics; Technical University of Košice, Park Komenského 2; Košice 042 00 Slovakia
| | - Ivan Chodák
- Polymer Institute, Slovak Academy of Sciences, Dúbravská Cesta 9; Bratislava 845 41 Slovakia
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10
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Koval'aková M, Olčák D, Hronský V, Vrábel P, Fričová O, Chodák I, Alexy P, Sučik G. Morphology and molecular mobility of plasticized polylactic acid studied using solid-state13C- and1H-NMR spectroscopy. J Appl Polym Sci 2016. [DOI: 10.1002/app.43517] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Mária Koval'aková
- Department of Physics; Faculty of Electrical Engineering and Informatics, Technical University of Košice; Park Komenského 2 042 00 Košice Slovakia
| | - Dušan Olčák
- Department of Physics; Faculty of Electrical Engineering and Informatics, Technical University of Košice; Park Komenského 2 042 00 Košice Slovakia
| | - Viktor Hronský
- Department of Physics; Faculty of Electrical Engineering and Informatics, Technical University of Košice; Park Komenského 2 042 00 Košice Slovakia
| | - Peter Vrábel
- Department of Physics; Faculty of Electrical Engineering and Informatics, Technical University of Košice; Park Komenského 2 042 00 Košice Slovakia
| | - Oľga Fričová
- Department of Physics; Faculty of Electrical Engineering and Informatics, Technical University of Košice; Park Komenského 2 042 00 Košice Slovakia
| | - Ivan Chodák
- Polymer Institute; Slovak Academy of Sciences; Dúbravská cesta 9 845 41 Bratislava Slovakia
| | - Pavel Alexy
- Institute of Natural and Synthetic Polymers; Slovak University of Technology; Radlinského 9 812 37 Bratislava Slovakia
| | - Gabriel Sučik
- Department of Ceramics; Faculty of Metallurgy, Technical University of Košice; Park Komenského 19 042 00 Košice Slovakia
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