| 1. |
- Xu, Huan, et al.
(författare)
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Structural Basis for Unique Hierarchical Cylindrites Induced by Ultrahigh Shear Gradient in Single Natural Fiber Reinforced Poly(lactic acid) Green Composites
- 2014
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 15:5, s. 1676-1686
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Tidskriftsartikel (refereegranskat)abstract
- A local shear flow field was feasibly generated by pulling the ramie fiber in single fiber reinforced poly(lactic acid) (PLA) composites. This was featured by an ultrahigh shear gradient with a maximum shear rate up to 1500 s(-1), a level comparable to that frequently occurring during the practical polymer processing. To distinguish shear-induced self-nucleation and ramie fiber-induced heterogeneous nucleation, the shear history was classified by pulling the fiber for 5 s (pulled sample) and pulling out the fiber during 10 s (pulled-out sample), while the static fiber-induced crystallization was carried out as the counterpart. As a result of the ultrahigh shear gradient, the combination of primary shear-induced nucleation in the central region and secondary nucleation in the outer layer assembled the unique hierarchical superstructures. By comparing the architectural configurations of interphases formed in the static, pulled, and pulled-out samples, it was shown that the hierarchical cylindrites underwent the process of self-nucleation driven by the applied shear flow, very different from the formation of fiber-induced transcrystallinity (TC) triggered by the heterogeneous nucleating sites at the static fiber surface. The twisting of transcrystallized lamellae may take place due to the spatial hindrance induced by the incredibly dense nuclei under the intense shearing flow, as observed in the synchrotron X-ray diffraction patterns. The influence of chain characteristics on the crystalline morphology was further explored by adding a small amount of poly(ethylene glycol) (PEG) to enhance the molecular mobility of PLA. It was of interest to find that the existence of PEG not only facilitated the growth rates of TC and cylindrites but also improved the preferential orientation of PLA chains and thus expanded the ordered regions. We unearthed lamellar units that were composed of rich fibrillar extended chain crystals (diameter of 50-80 nm). These results are of importance to shed light on tailoring crystalline morphology for natural fibers reinforced green composite materials. Of immense practical significance, too, is the crystalline evolution that has been tracked in the simple model penetrated with an ultrahigh shear gradient, which researchers have so far been unable to replicate during the practical melt processing, such as extrusion and injection molding.
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| 2. |
- Adolfsson, Karin H., et al.
(författare)
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Scavenging of DPPH by Persistent Free Radicals in Carbonized Particles
- 2023
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Ingår i: Advanced Sustainable Systems. - : Wiley. - 2366-7486. ; 7:3
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Tidskriftsartikel (refereegranskat)abstract
- Persistent free radicals (PFR) in carbonized particles may play a role in degradation of environmental compounds. The influence of PFR is evaluated in various carbonized particles on their radical scavenging efficiency upon the common radical indicator 2-2-diphenyl-1-picrylhydrazyl (DPPH). Carbonized particles are derived by hydrothermal carbonization of glucose (C-W) or glucose and urea (NC-W) and ionothermal carbonization of glucose and urea ionic liquid (IL) (NC-IL). The carbonized materials contain OH/COOH, C=C, and C-O functionalities. The addition of urea introduces NH/NH2 functionalities. The content of polar surface groups is lower in IL-processed NC-IL. The scavenging ability, measured as DPPH UV–vis absorption decline, increases with concentration and time for all particles, while the efficiency changes are in the order of C-W > NC-W > NC-IL. Electron paramagnetic resonance analysis reveals similar radical concentration in all carbonized materials studied. The difference in efficiency is, thus, not directly related to the PFR concentration but rather to the type of PFR, surface functionalities and/or scavenging mechanism. According to the g-values, radicals in these particles are carbon-centered. The minor variation in g-values suggests interactions between the radicals and their environmental functional groups. This provides insights into the influence of PFR in carbonized materials on their radical scavenging efficiency.
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| 3. |
- Aminlashgari, Nina, et al.
(författare)
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Nanocomposites as novel surfaces for laser desorption ionization mass spectrometry
- 2011
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Ingår i: Analytical Methods. - : Royal Society of Chemistry (RSC). - 1759-9660 .- 1759-9679. ; 3:1, s. 192-197
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Tidskriftsartikel (refereegranskat)abstract
- The possibility to utilize nanocomposite films as easy-to-handle surfaces for surface assisted laser desorption ionization-mass spectrometry (SALDI-MS) of small molecules, such as pharmaceutical compounds, was evaluated. The signal-to-noise values of acebutolol, propranolol and carbamazepine obtained on the nanocomposite surfaces were higher than the values obtained on plain PLA surface showing that the nanoparticles participate in the ionization/desorption process even when they are immobilized in the polymer matrix. The advantages of nanocomposite films compared to the free nanoparticles used in earlier studies are the ease of handling and reduction of instrument contamination since the particles are immobilized into the polymer matrix. Eight inorganic nanoparticles, titanium dioxide, silicon dioxide, magnesium oxide, hydroxyapatite, montmorillonite nanoclay, halloysite nanoclay, silicon nitride and graphitized carbon black at different concentrations were solution casted to films with polylactide (PLA). There were large differences in signal intensities depending on the type of drug, type of nanoparticle and the concentration of nanoparticles. Polylactide with 10% titanium oxide or 10% silicon nitride functioned best as SALDI-MS surfaces. The limit of detection (LOD) for the study was ranging from 1.7 ppm up to 56.3 ppm and the signal to noise relative standard deviations for the surface containing 10% silicon nitride was approximately 20-30%. Scanning electron microscopy demonstrated in most cases a good distribution of the nanoparticles in the polymer matrix and contact angle measurements showed increasing hydrophobicity when the nanoparticle concentration was increased, which could influence the desorption and ionization. Overall, the results show that nanocomposite films have potential as surfaces for SALDI-MS analysis of small molecules.
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| 4. |
- Aminlashgari, Nina, 1986-
(författare)
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SALDI-MS Method Development for Analysis of Pharmaceuticals and Polymer Degradation Products
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Surface assisted laser desorption ionization-mass spectrometry (SALDI-MS) was evaluated as a new tool for analysis of polymer degradation products. A SALDI method was developed enabling rapid analysis of low molecular mass polyesters and their degradation products. In addition, the possibility to utilize nanocomposite films as easy-to-handle surfaces for analysis of pharmaceutical compounds was investigated. Poly(ε-caprolactone) was used as a model compound for SALDI-MS method development. The signal-to-noise values obtained by SALDI-MS were 20 times higher compared to traditional matrix assisted laser desorption ionization-mass spectrometry (MALDI-MS) of the same samples with 2,5-dihydroxybenzoic acid as a matrix. Halloysite nanoclay and magnesium oxide showed best potential as surfaces and clean backgrounds in the low mass range were observed. The SALDI-MS method for the analysis of polyester degradation products was also verified by electrospray ionization-mass spectrometry (ESI-MS). An advantage over ESI-MS is the possibility to directly analyze degradation products in buffer solutions. Compared to gas chromatography-mass spectrometry (GC-MS) it is possible to analyze polar compounds and larger molecular mass ranges at the same time as complicated extraction steps are avoided. The possibility to use nanocomposite films as surfaces instead of free nanoparticles was evaluated by solution casting of poly(lactide) (PLA) films with eight inorganic nanoparticles. The S/N values of the pharmaceutical compounds, acebutolol, propranolol and carbamazepine, analyzed on the nanocomposite surfaces were higher than the values obtained on the surface of plain PLA showing that the nanoparticles participated in the ionization/desorption process even when they are immobilized. Beside the ease of handling, the risk for instrument contamination is reduced when nanocomposites are used instead of free nanoparticles. The signal intensities depended on the type of drug, type and concentration of nanoparticle. PLA with 10 % titanium oxide or 10 % silicon nitride functioned best as SALDI-MS surfaces.
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| 5. |
- Aminlashgari, Nina, et al.
(författare)
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Surface Assisted Laser Desorption Ionization-Mass Spectrometry (SALDI-MS) for Analysis of Polyester Degradation Products
- 2012
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Ingår i: Journal of the American Society for Mass Spectrometry. - : American Chemical Society (ACS). - 1044-0305 .- 1879-1123. ; 23:6, s. 1071-1076
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Tidskriftsartikel (refereegranskat)abstract
- Novel surface assisted laser desorption ionization-mass spectrometry (SALDI-MS) method was developed for rapid analysis of low molecular mass polyesters and their degradation products by laser desorption ionization-mass spectrometry. Three polycaprolactone materials were analyzed by the developed method before and after hydrolytic degradation. The signal-to-noise values obtained by SALDI-MS were 20-100 times higher compared with the ones obtained by using traditional MALDI-MS matrices. A clean background at low mass range and higher resolution was obtained by SALDI-MS. Different nanoparticle, cationizing agent, and solvent combinations were evaluated. Halloysite nanoclay and magnesium hydroxide showed the best potential as SALDI surfaces. The SALDI-MS spectrum of the polyester hydrolysis products was verified by ESI-MS. The developed SALDI-MS method possesses several advantages over existing methods for similar analyses.
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| 6. |
- Subramaniyan, Sathiyaraj, et al.
(författare)
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Designed for Circularity : Chemically Recyclable and Enzymatically Degradable Biorenewable Schiff Base Polyester-Imines
- 2023
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Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 11:8, s. 3451-3465
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Tidskriftsartikel (refereegranskat)abstract
- Bio-based plastics potentially have several positive impacts on the environment; however, in order to make a real difference, they need to have managed and sustainable end of life. This means they should from the start be designed for chemical, mechanical, and/or organic (biological) recycling. Development of energy-efficient and selective chemical recycling processes is a necessary part in reaching truly circular plastic flows. Polyesters are generally well suited for chemical recycling due to the presence of reversible ester bonds. Utilization of dynamic covalent chemistry to include a second, even more easily reversed bond, such as Schiff base (SB, imine bond), could further facilitate chemical recycling, enabling depolymerization back to monomeric products under mild conditions. Here, we present the synthesis of three vanillin-derived SB monomers SBM1, SBM2, and SBM3 and the corresponding polymers SBP3a-b, SBP4a-b, and SBP5a-b. Three different diamines and two potentially bio-sourced diesters were utilized to yield altogether six different polyester-imines with different aliphatic/aromatic contents. All the obtained SB-based polyesters were thermally stable at ∼290-330 °C and had a high char yield during the pyrolysis, which may indicate inherent flame resistance. All the polyesters were amorphous with glass transition temperatures from 36 to 76 °C. The chemical recyclability and hydrolytic degradation of the synthesized polyesters was evaluated by using real-time 1H NMR spectroscopy. Finally, the susceptibility of the synthesized polyester-imines to enzymatic degradation by PETase was demonstrated. The experimental results were further supported by induced-fit docking experiments to theoretically evaluate the potential productive binding of the produced polyester-imines and intermediates thereof to the active site of PETase.
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| 7. |
- Xu, Huan, et al.
(författare)
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Graphene Oxide-Driven Design of Strong and Flexible Biopolymer Barrier Films : From Smart Crystallization Control to Affordable Engineering
- 2016
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Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 4:1, s. 334-349
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Tidskriftsartikel (refereegranskat)abstract
- Development of multifunctional, versatile biobased polymers can greatly benefit from the discovery and application of 2D sheet-like materials. For instance, the hybrid system integrating graphene oxide (GO) nanosheets with enantiomeric poly(lactic acid) (PLA) showcases several key properties that can address emerging multifunction needs such as good gas barrier and high thermal resistance. Here we revealed that large specific surface area and homogeneous dispersion of GO conferred the construction of interconnected networks in PLA even with relatively low GO contents (0.1 and 0.5 wt %). These well-extended GO nanosheets were ready to provide enormous and active platforms to nucleate preferentially the neighboring stereocomplex chains, prompting the prevailing development of stereocomplex crystals (SCs). The notable scenario associated with the GO distribution was imaged by 2D Fourier transform infrared spectroscopy, and was further elucidated by dynamic crystallization. More importantly, the nanosheets decorated with ordered PLA lamellae, in turn, contributed to the impressive enhancement in barrier and mechanical properties and chemical resistance. For example, a distinct decrease of 98.5% in oxygen permeability coefficient was observed for the composite films containing 0.5 wt % GO (6.264 × 10-17 cm3 cm cm-2 s-1 Pa-1) compared to the control sample crystallized at 150 °C (4.214 × 10-15 cm3 cm cm-2 s-1 Pa-1). The performance distinction was accompanied by the unusual combination of high tensile strength (73.5 MPa) and high elongation (13.6%), displaying an increase of 31.7% and 183.3% compared to the counterpart, respectively. This may provide a broader context for exploiting 2D nanosheets as robust cells to advance the function and property of PLA, which helps to outline the roadmap for fashioning high-performance, affordable bioplastics.
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| 8. |
- Yang, Xi, et al.
(författare)
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Two step extrusion process : From thermal recycling of PHB to plasticized PLA by reactive extrusion grafting of PHB degradation products onto PLA chains
- 2015
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 48:8, s. 2509-2518
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Tidskriftsartikel (refereegranskat)abstract
- A green and industrially viable two-step process was demonstrated for toughening polylactide (PLA) without compromising the biobased and biodegradable nature. First, poly(3-hydroxybutyrate) (PHB) biopolymer was thermally degraded in an extruder to create PHB oligomers (dPHB) with functional end-groups suitable for further reactions. Second, a reactive extrusion process was developed to covalently anchor dPHB onto the main chain of PLA. PLA with 20% (w/w) grafted dPHB demonstrated an impressive elongation at break of 538%, 66 times higher than that of pure PLA and significantly higher than the elongation at break of the corresponding physical blend. At the same time WAXD measurements illustrated that grafting significantly increased the crystallization ability of PLA. We present a viable recycling route for PHB and a highly promising approach for fully biobased toughened PLA with covalently anchored PHB plasticizers.
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| 9. |
- Noè, C., et al.
(författare)
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Frontal-Photopolymerization of Fully Biobased Epoxy Composites
- 2022
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Ingår i: Macromolecular materials and engineering. - : Wiley. - 1438-7492 .- 1439-2054. ; 307:6, s. 2100864-
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Tidskriftsartikel (refereegranskat)abstract
- The radical-induced cationic frontal photopolymerization (RICFP) of fully biobased epoxy composites is successfully demonstrated. This curing strategy considerably reduces the curing time and improves the efficiency of the composite fabrication. Two different natural fiber fabrics made of cellulose and flax fibers are embedded in two epoxy matrices, one derived from vanillin (diglycidylether of vanillyl alcohol-DGEVA) and the other from petroleum (3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate-CE). After RICFP the composites are characterized by means of dynamic mechanical thermal analysis and tensile tests. The mechanical properties improved with increasing fiber content, confirming a strong adhesion between the matrix and the reinforcing fiber fabrics, which is further evidenced by scanning electron microscopy analyses of the fracture surfaces. Furthermore, these fully bio-based composites possess comparable or even higher mechanical strength compared with the corresponding epoxy composites fabricated with conventional CE resin. A promising facile route to high-performing natural fiber-biobased epoxy resin composites is presented.
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| 10. |
- Bianchi, F., et al.
(författare)
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Novel sample-substrates for the determination of new psychoactive substances in oral fluid by desorption electrospray ionization-high resolution mass spectrometry
- 2019
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Ingår i: Talanta. - : Elsevier B.V.. - 0039-9140 .- 1873-3573. ; 202, s. 136-144
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Tidskriftsartikel (refereegranskat)abstract
- A reliable screening and non invasive method based on the use of microextraction by packed sorbent coupled with desorption electrospray ionization-high resolution mass spectrometry was developed and validated for the detection of new psychoactive substances in oral fluid. The role of different sample substrates in enhancing signal intensity and stability was evaluated by testing the performances of two polylactide-based materials, i.e. non-functionalized and functionalized with carbon nanoparticles, and a silica-based material compared to commercially available polytetrafluorethylene supports. The best results were achieved by using the non-functionalized polylactide substrates to efficiently ionize compounds in positive ionization mode, whereas the silica coating proved to be the best choice for operating in negative ionization mode. LLOQs in the low μg/L, a good precision with CV% always lower than 16% and RR% in the 83(±4)-120(±2)% range, proved the suitability of the developed method for the determination of the analytes in oral fluid. Finally, the method was applied for screening oral fluid samples for the presence of psychoactive substances during private parties, revealing mephedrone in only one sample out of 40 submitted to analysis.
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