| 1. |
- Abbaszad Rafi, Abdolrahim, et al.
(author)
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A facile route for concurrent fabrication and surface selective functionalization of cellulose nanofibers by lactic acid mediated catalysis
- 2023
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In: Scientific Reports. - : Springer Nature. - 2045-2322 .- 2045-2322. ; 13:1
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Journal article (peer-reviewed)abstract
- Celulose nanofibers are lightweight, recycable, biodegradable, and renewable. Hence, there is a great interest of using them instead of fossil-based components in new materials and biocomposites. In this study, we disclose an environmentally benign (green) one-step reaction approach to fabricate lactic acid ester functionalized cellulose nanofibrils from wood-derived pulp fibers in high yields. This was accomplished by converting wood-derived pulp fibers to nanofibrillated “cellulose lactate” under mild conditions using lactic acid as both the reaction media and catalyst. Thus, in parallel to the cellulose nanofibril production, concurrent lactic acid-catalyzed esterification of lactic acid to the cellulose nanofibers surface occured. The direct lactic acid esterification, which is a surface selective functionalization and reversible (de-attaching the ester groups by cleavage of the ester bonds), of the cellulose nanofibrils was confirmed by low numbers of degree of substitution, and FT-IR analyses. Thus, autocatalytic esterification and cellulose hydrolysis occurred without the need of metal based or a harsh mineral acid catalysts, which has disadvantages such as acid corrosiveness and high recovery cost of acid. Moreover, adding a mineral acid as a co-catalyst significantly decreased the yield of the nanocellulose. The lactic acid media is successfully recycled in multiple reaction cycles producing the corresponding nanocellulose fibers in high yields. The disclosed green cellulose nanofibril production route is industrial relevant and gives direct access to nanocellulose for use in variety of applications such as sustainable filaments, composites, packaging and strengthening of recycled fibers.
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| 2. |
- Avella, Angelica, 1995
(author)
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Interface design of biodegradable polyester/nanocellulose biocomposites via reactive melt processing: tailoring of polyester matrix
- 2021
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Licentiate thesis (other academic/artistic)abstract
- Pushed by the societal awareness of plastic pollution, attempts are being made to find sustainable materials that can minimize the environmental impact of plastics. In this context, biocomposites based on biodegradable polymers and renewable lignocellulose are of interest. Nanosized cellulose has the potential to enhance the physical properties of biopolymers, but due to chemical differences between these components, compatibilization methods should be implemented to achieve the desired improvements. For this purpose, reactive melt processing (REx) can be employed as green, one-step cost-effective method for the simultaneous compatibilization and manufacture of biocomposites. Two REx routes for the tailoring of biodegradable poly(ε-caprolactone) (PCL) are here reported, where the interface with cellulose nanocrystals (CNC) is designed and controlled. The first route involves radical crosslinking simultaneously with CNC wet-feeding, with the aim of improving the rheological properties of the biocomposites and promoting CNC dispersion. The second route uses PCL aminolysis to produce shorter and more hydrophilic PCL chains that can migrate to the interface with CNC and form an interphase region. To verify the process feasibility and tune the processing conditions, biocomposites were reacted in a batch mixer. The materials produced were compared to the unreacted references and structural, thermomechanical and rheological properties were assessed. PCL structure achieved showed the feasibility of both water-assisted crosslinking and aminolysis during REx. Dynamic rheology and creep tests proved that crosslinking was successful for enhancing the rheological properties of biocomposites. Biocomposites produced with aminolysed PCL showed a greater thermal stability and higher stiffness than the unreacted references. The water-assisted crosslinking strategy appears to be the most promising for the large-scale manufacture of biocomposites via REx. It also provides materials which shrink when heated, from which shape-memory features could be developed, thus expanding the applications of sustainable biocomposites manufactured by green methods.
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| 3. |
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| 4. |
- Avella, Angelica, 1995
(author)
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Reactive extrusion of lignocellulose-polyester biocomposites
- 2024
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Doctoral thesis (other academic/artistic)abstract
- The development of biodegradable and recyclable composites based on renewable resources can mitigate the effects of plastic pollution and the depletion of fossil fuels. A biocomposite consists of a matrix strengthened with fibres, and in this work, biodegradable polyesters have been blended with lignocellulosic derivatives, and reactive processing strategies have been developed to tackle the drawbacks of poor lignocellulose dispersion and poor adhesion of the lignocellulose to the polymer matrix. Reactive melt processing combines melt compounding with chemical reactions, and herein it has been explored to tune the interface of biocomposites and improve their performance. Three different ways of strengthening the polymer-lignocellulose interface have been investigated involving (a) modification of the polymer matrix, (b) modification of the lignocellulose, and (c) the addition of a third component. The first approach was a peroxide-initiated branching/crosslinking carried out with water-assisted feeding of the lignocellulose. Crosslinking led to the formation of a uniform hybrid polymer-lignocellulose network that developed creep resistance and heat-shrinkage in the matrix. The mechanical recycling and industrial composting of crosslinked poly(butylene adipate-co-terephthalate) (PBAT)-pulp fibre biocomposites were successfully verified. In the second category, the grafting of epoxidized bio-sourced oils onto industrial lignin was investigated as a way to plasticize the lignin and promote its miscibility with polyesters. Deformable and tough PBAT-modified lignin blends were prepared and shaped by film-blowing, to be subsequently mechanically recycled or industrially composted. The cellulose was also modified by in-situ polymerization of bio-sourced ethylene brassylate to graft the polymer from the cellulose surface. Ring-opening polymerization was achieved by organic and enzymatic catalysis, which showed that grafting from is an effective method of achieving nanocellulose dispersion and consequent stress transfer with the matrix. In the third approach, amphiphilic diblock copolymers with two different tail lengths were designed to mediate the interface between cellulose nanofibrils and PBAT. In an aquatic environment, the cationic anchor block was effectively adsorbed onto the negatively charged nanofibrils, promoting their dispersion, while the longer tail block favoured entanglement with the matrix and deformation of the biocomposites. This thesis contributes to the understanding of biocomposite interfaces, paving the way for future investigations, and proposes sustainable alternatives for the industrial replacement of commodity plastics.
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| 5. |
- Avella, Angelica, 1995, et al.
(author)
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Reactive melt crosslinking of cellulose nanocrystals/poly(ε-caprolactone) for heat-shrinkable network
- 2022
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In: Composites Part A: Applied Science and Manufacturing. - : Elsevier BV. - 1359-835X. ; 163
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Journal article (peer-reviewed)abstract
- Focusing on the challenge of non-biodegradable plastics replacement, we propose a design for peroxide-initiated crosslinking of biodegradable poly(ε-caprolactone) (PCL) and renewable cellulose nanocrystals (CNCs) bionanocomposites. An industrially scalable water-assisted reactive melt-processing (REx) is studied to explore the hypothesis of synergy between simultaneous effects of water on improving CNC dispersion and boosting PCL branching/crosslinking. We demonstrate that the melt processing control enables the preparation of targeted thermoplastic/thermoset bionanocomposites with gel content up to ≈ 40 %, identified as the limit of their melt-processability. Structural characterization reveals that ≈ 70 wt% of the initial CNC content is irreversibly incorporated in a percolating network, enhancing the crosslinked bionanocomposites properties. The bionanocomposites' complex viscosity and elastic character increase with the gel content, thus improving PCL melt performance. Furthermore, the irreversible entrapment of CNCs in the 3D percolating network provides heat-shrinkability, indicating a potential of the reacted bionanocomposites for heat-triggered shape-memory.
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| 6. |
- Avella, Angelica, 1995, et al.
(author)
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Reusable, Recyclable, and Biodegradable Heat-Shrinkable Melt Cross-Linked Poly(butylene adipate-co-terephthalate)/Pulp Biocomposites for Polyvinyl Chloride Replacement
- 2024
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In: ACS Sustainable Chemistry & Engineering. - 2168-0485. ; 12:13, s. 5251-5262
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Journal article (peer-reviewed)abstract
- Heat-shrinkable films are widely used as disposable secondary packaging but are conventionally made from fossil-based and nonbiodegradable polyvinyl chloride or polyethylene. To lower the environmental impact of such products, this work reports the development of recyclable, biodegradable, and partially biosourced heat-shrinkable biocomposites that are cost-competitive with existing shrink wraps. Poly(butylene adipate-co-terephthalate), a growing biodegradable thermoplastic, was simultaneously reinforced with pulp fibers and partially cross-linked in a single-step reactive melt processing. The designed peroxide-initiated reaction led to a 55 wt % cocontinuous insoluble gel incorporating all the pulp fibers into a cross-linked polymer network. In the solid state, the cross-linked biocomposite shows 60% elongation at break with a 200% increase in Young’s modulus, while the only addition of pulp fibers stiffens and embrittles the matrix. Creep tests in the melt state indicated that the cross-linked network induces homogeneous shrinking even during the loading phase, demonstrating the potential use of the biocomposites as heat-shrinkable films. The shrinking also promotes the shape-memory of the biocomposite, which retains its dimensions after four cycles. The circularity of the materials was assessed by mechanical recycling and industrial composting, which have proven feasible end-of-life options for heat-shrinkable biocomposites.
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| 7. |
- Avella, Angelica, 1995, et al.
(author)
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Substantial effect of water on radical melt crosslinking and rheological properties of poly(ε-caprolactone)
- 2021
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In: Polymers. - : MDPI AG. - 2073-4360. ; 13:4, s. 1-16
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Journal article (peer-reviewed)abstract
- One-step reactive melt processing (REx) via radical reactions was evaluated with the aim of improving the rheological properties of poly(ε-caprolactone) (PCL). In particular, a waterassisted REx was designed under the hypothesis of increasing crosslinking efficiency with water as a low viscous medium in comparison with a slower PCL macroradicals diffusion in the melt state. To assess the effect of dry vs. water-assisted REx on PCL, its structural, thermo-mechanical and rheological properties were investigated. Water-assisted REx resulted in increased PCL gel fraction compared to dry REx (from 1–34%), proving the rationale under the formulated hypothesis. From dynamic mechanical analysis and tensile tests, the crosslink did not significantly affect the PCL mechanical performance. Dynamic rheological measurements showed that higher PCL viscosity was reached with increasing branching/crosslinking and the typical PCL Newtonian behavior was shifting towards a progressively more pronounced shear thinning. A complete transition from viscous-to solid-like PCL melt behavior was recorded, demonstrating that higher melt elasticity can be obtained as a function of gel content by controlled REx. Improvement in rheological properties offers the possibility of broadening PCL melt processability without hindering its recycling by melt processing.
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| 8. |
- Venkatesh, Abhijit, 1989, et al.
(author)
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Water-assisted melt processing of cellulose biocomposites with poly(ε-caprolactone) or poly(ethylene-acrylic acid) for the production of carton screw caps
- 2022
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In: Journal of Applied Polymer Science. - : Wiley. - 1097-4628 .- 0021-8995. ; 139:6
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Journal article (peer-reviewed)abstract
- Composites in 25 kg batches were compounded of cellulose nanocrystals (CNC) and thermomechanical pulp (TMP) and shaped into caps at industrial facilities on a pilot-plant scale. Some of the material was also injection molded into plaques to compare the effect of laboratory-scale and pilot-scale compounding of poly(ethylene-co-acrylic acid) (EAA7) and poly(caprolactone) composites reinforced with 10 wt% CNC and TMP. The materials compounded under laboratory-scale conditions showed a different morphology, improved mechanical properties, and a higher viscosity, than the materials compounded on a pilot-scale. In some cases, the rheological properties of the melts indicated the presence of a relatively strong percolating cellulosic network, and the interphase region between the cellulose and the matrix appears to be important for the mechanical performance of the composites. After the compounding on a pilot scale, both the length and width of the pulp fibers was reduced. The TMP provided better reinforcement than the CNC possibly due to the higher aspect ratio.
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