Publicação
Development of innovative luminescent optical markers for the traceability of polymeric composites
| Resumo: | Counterfeiting of polymeric products and packages has become a significant global problem not only in commercial and industrial fields but also in our daily lives. The urgent need for information security and inhibiting counterfeiting has triggered the rapid development of anti-counterfeiting technologies, which have evolved a long way from simple watermarks to more advanced holograms. Over the last few years, a booming development of luminescent composite materials has been observed, using a combination of diverse synthesis techniques and nanomaterials. The powerful capability to respond to external chemical or physical stimuli in various manners makes these composites particularly attractive in anti-counterfeiting technologies. In this context, luminescent materials are distinguished by their highly desirable properties, including unique optical signatures, well-defined emission intensities, and characteristic decay times. These features enable the generation of diverse outputs and the development of multiple encrypted codes that are inherently difficult to replicate. This work has a main goal the introduction of organic (carbon dots (CDs)) and inorganic particles (lanthanides in metal organic frameworks (LnMOFs) as fillers in different polymeric matrices, to produce luminescent composites for traceability and security of polymer-based products and goods. At first approach, the introduction of LnMOFs into polylactic acid (PLA) was performed using a thermal mixer. In this work, LnMOFs with europium (EuMOF) and terbium (TbMOF) were used. The preparation of the composites included the use of different LnMOFs loads, individually or mixed, to evaluate the best combination of color and intensity for the intended application. The composites’ chemical, structural, and morphological characterization was assessed via Fourier transform infrared absorption (FTIR), Raman spectroscopy, X-ray diffraction (XRD); Differential scanning calorimetry (DSC), and scanning/transmission electron microscopy (SEM, TEM/STEM). The optical characterization was carried out by photoluminescence (PL) and photoluminescence excitation (PLE). The as-obtained composites exhibited an excellent response to selective excitation with well-defined intraionic lines for trivalent terbium (TbMOF) @ 542 nm (5D4→7F5) and for trivalent europium (EuMOF) @ 615 nm (5D0→7F2). This selective response of the prepared composites is highly relevant, as it enables the creation of encrypted codes that remain hidden from the average user. As proof of concept, the luminescent composites were subsequently employed in 3D printing of QR codes for their application in anti-counterfeiting techniques. Moreover, to increase the codification complexity, different lanthanide MOFs based on dysprosium (DyMOF) and praseodymium (PrMOF), both individually and in combination with EuMOF and TbMOF, were incorporated into PLA. The as-obtained composites exhibited an excellent response to selective excitation with well-defined intraionic lines for trivalent DyMOF @ 570 nm (4F9/2→6H13/2), whereas for PrMOF intraionic auto-absorption lines from 3H4→3PJ levels were identified in the interval range of 445 to 485 nm. Additionally, excitation wavelength- and temperature-dependent PL measurements of selected hybrid samples were performed to assess the color tuning of the ion’s emission, adding an extra layer of safety to the development of these composite materials as traceable tags, serving as high-level optical markers for anti-counterfeiting applications. Following a second approach, CDs were introduced into high density polyethylene (HDPE) as optical markers. Several composites with different CDs loadings were made using a combination of processing techniques, including thermal mixing and injection molding. The luminescent properties of the different prepared composites were studied in detail, revealing a quenching of blue phosphorescence of the polymer host, which is highly dependent on the CDs content. Additionally, a decrease was also observed after each mechanical recycling cycle. Importantly, the composite with 0.1 wt.% of CDs exhibited luminescence that varied with the number of recycling cycles, enabling easy traceability and sorting using a standard mobile phone camera and a UV light. It is important to note that the mechanical properties of the polymer were not adversely affected by the addition of CDs. In fact, for the composite containing 0.5 wt.% of CDs, a 17% increase in tensile strength was observed after recycling, with a maximum strain of 9%. These new luminescent LnMOFs composite materials demonstrated strong potential for use as traceable tags for a wide range of polymeric products, serving as high-security optical markers for anti-counterfeiting applications. The CDs-based composite with 0.1 wt.% showed significant potential for tracking the recycling stage of a polymer, enabling its automated sorting. |
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| Autores principais: | Simões, Raúl |
| Assunto: | Carbon dots Lanthanide metal-organic frameworks Luminescent polymeric composites Recycled polymers 3D printing Traceability Security |
| Ano: | 2026 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Aveiro |
| Idioma: | inglês |
| Origem: | RIA - Repositório Institucional da Universidade de Aveiro |
| Resumo: | Counterfeiting of polymeric products and packages has become a significant global problem not only in commercial and industrial fields but also in our daily lives. The urgent need for information security and inhibiting counterfeiting has triggered the rapid development of anti-counterfeiting technologies, which have evolved a long way from simple watermarks to more advanced holograms. Over the last few years, a booming development of luminescent composite materials has been observed, using a combination of diverse synthesis techniques and nanomaterials. The powerful capability to respond to external chemical or physical stimuli in various manners makes these composites particularly attractive in anti-counterfeiting technologies. In this context, luminescent materials are distinguished by their highly desirable properties, including unique optical signatures, well-defined emission intensities, and characteristic decay times. These features enable the generation of diverse outputs and the development of multiple encrypted codes that are inherently difficult to replicate. This work has a main goal the introduction of organic (carbon dots (CDs)) and inorganic particles (lanthanides in metal organic frameworks (LnMOFs) as fillers in different polymeric matrices, to produce luminescent composites for traceability and security of polymer-based products and goods. At first approach, the introduction of LnMOFs into polylactic acid (PLA) was performed using a thermal mixer. In this work, LnMOFs with europium (EuMOF) and terbium (TbMOF) were used. The preparation of the composites included the use of different LnMOFs loads, individually or mixed, to evaluate the best combination of color and intensity for the intended application. The composites’ chemical, structural, and morphological characterization was assessed via Fourier transform infrared absorption (FTIR), Raman spectroscopy, X-ray diffraction (XRD); Differential scanning calorimetry (DSC), and scanning/transmission electron microscopy (SEM, TEM/STEM). The optical characterization was carried out by photoluminescence (PL) and photoluminescence excitation (PLE). The as-obtained composites exhibited an excellent response to selective excitation with well-defined intraionic lines for trivalent terbium (TbMOF) @ 542 nm (5D4→7F5) and for trivalent europium (EuMOF) @ 615 nm (5D0→7F2). This selective response of the prepared composites is highly relevant, as it enables the creation of encrypted codes that remain hidden from the average user. As proof of concept, the luminescent composites were subsequently employed in 3D printing of QR codes for their application in anti-counterfeiting techniques. Moreover, to increase the codification complexity, different lanthanide MOFs based on dysprosium (DyMOF) and praseodymium (PrMOF), both individually and in combination with EuMOF and TbMOF, were incorporated into PLA. The as-obtained composites exhibited an excellent response to selective excitation with well-defined intraionic lines for trivalent DyMOF @ 570 nm (4F9/2→6H13/2), whereas for PrMOF intraionic auto-absorption lines from 3H4→3PJ levels were identified in the interval range of 445 to 485 nm. Additionally, excitation wavelength- and temperature-dependent PL measurements of selected hybrid samples were performed to assess the color tuning of the ion’s emission, adding an extra layer of safety to the development of these composite materials as traceable tags, serving as high-level optical markers for anti-counterfeiting applications. Following a second approach, CDs were introduced into high density polyethylene (HDPE) as optical markers. Several composites with different CDs loadings were made using a combination of processing techniques, including thermal mixing and injection molding. The luminescent properties of the different prepared composites were studied in detail, revealing a quenching of blue phosphorescence of the polymer host, which is highly dependent on the CDs content. Additionally, a decrease was also observed after each mechanical recycling cycle. Importantly, the composite with 0.1 wt.% of CDs exhibited luminescence that varied with the number of recycling cycles, enabling easy traceability and sorting using a standard mobile phone camera and a UV light. It is important to note that the mechanical properties of the polymer were not adversely affected by the addition of CDs. In fact, for the composite containing 0.5 wt.% of CDs, a 17% increase in tensile strength was observed after recycling, with a maximum strain of 9%. These new luminescent LnMOFs composite materials demonstrated strong potential for use as traceable tags for a wide range of polymeric products, serving as high-security optical markers for anti-counterfeiting applications. The CDs-based composite with 0.1 wt.% showed significant potential for tracking the recycling stage of a polymer, enabling its automated sorting. |
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