1,721,041 research outputs found
Plasticization of dialcohol cellulose and effect on the thermomechanical properties [Elektronisk resurs]
Get PDFCellulosic materials are considered good alternatives to conventional plastics in packaging applications, as they are renewable, bio-based and biodegradable, having good mechanical properties at relatively low densities. However, when considering production methods, cellulose has limitations. The possibility of exploiting the production methods of conventional plastics, such as melt processing, is precluded because cellulose decomposes before reaching melting. Lowering the glass transition, partial modification of cellulose pulp to dialcohol cellulose (DAC) fibres enabled a melt processability window between the glass transition and decomposition temperatures. Water was successfully used as an aid for DAC melt processing, but the final material properties are strongly influenced by the residual moisture content, which varies depending on the environmental conditions (temperature and relative humidity). This work aims to explore the addition of glycerol, a less volatile green plasticizer, to control the processability and physical properties of DAC-based materials. Materials containing different moisture and glycerol contents were melt compounded and the effect on the melt processability was evaluated by the in-line melt viscosity during the process. The effect of different initial moisture and glycerol contents on thermal decomposition, thermal transitions, thermomechanical and mechanical properties and surface morphology has been investigated. The addition of glycerol allows for improved melt processability, decreased elasticity and enhanced deformability up to a maximum glycerol content. An excess of glycerol leads instead to a neat fall in mechanical properties and thermal stability. The possibility of post-industrial mechanical recycling was also demonstrated and the effect on the thermal decomposition and mechanical properties assessed
Tunable Thermosetting Epoxies Based on Fractionated and Well-Characterized Lignins
No full textHere we report the synthesis of thermosetting
resins from low molar
mass Kraft lignin fractions of high functionality, refined by solvent
extraction. Such fractions were fully characterized by 31P NMR, 2D-HSQC NMR, SEC, and DSC in order to obtain a detailed description
of the structures. Reactive oxirane moieties were introduced on the
lignin backbone under mild reaction conditions and quantified by simple 1H NMR analysis. The modified fractions were chemically cross-linked
with a flexible polyether diamine (Mn ≈
2000), in order to obtain epoxy thermosets. Epoxies from different
lignin fractions, studied by DSC, DMA, tensile tests, and SEM, demonstrated
substantial differences in terms of thermo-mechanical properties.
For the first time, strong relationships between lignin structures
and epoxy properties could be demonstrated. The suggested approach
provides unprecedented possibilities to tune network structure and
properties of thermosets based on real lignin fractions, rather than
model compounds
Chemical-free Reactive Melt Processing of Biosourced Poly(butylene-succinate-adipate) for Improved Mechanical Properties and Recyclability
Get PDF: Biosourced and biodegradable polyesters like poly(butylene succinate-co-butylene adipate) (PBSA) are gaining traction as promising alternatives to oil-based thermoplastics for single-use applications. However, the mechanical and rheological properties of PBSA are affected by its thermomechanical sensitivity during its melt processing, also hindering PBSA mechanical recycling. Traditional reactive melt processing (RP) methods use chemical additives to counteract these drawbacks, compromising sustainability. This study proposes a green reactive method during melt compounding for PBSA based on a comprehensive understanding of its thermomechanical degradative behavior. Under the hypothesis that controlled degradative paths during melt processing can promote branching/recombination reactions without the addition of chemical additives, we aim to enhance PBSA rheological and mechanical performance. An in-depth investigation of the in-line rheological behavior of PBSA was conducted using an internal batch mixer, exploring parameters such as temperature, screw rotation speed, and residence time. Their influence on PBSA chain scissions, branching/recombination, and cross-linking reactions were evaluated to identify optimal conditions for effective RP. Results demonstrate that specific processing conditions, for example, twelve minutes processing time, 200 °C temperature, and 60 rpm screw rotation speed, promote the formation of the long chain branched structure in PBSA. These structural changes resulted in a notable enhancement of the reacted PBSA rheological and mechanical properties, exhibiting a 23% increase in elastic modulus, a 50% increase in yield strength, and an 80% increase in tensile strength. The RP strategy also improved PBSA mechanical recycling, thus making it a potential replacement for low-density polyethylene (LDPE). Ultimately, this study showcases how finely controlling the thermomechanical degradation during reactive melt processing can improve the material's properties, enabling reliable mechanical recycling, which can serve as a green approach for other biodegradable polymers
Biocomposite PBAT/lignin blown films with enhanced photo-stability
No full textLignin can be obtained as a byproduct during cellulose-rich pulp fibers production and it is habitually treated as waste or intended for low-value destinations. However, due to UV absorption and mechanical properties, lignin can contribute to the fabrication of biodegradable blown films with superior performances. In this study, it was established the suitability of lignin for manufacturing biocomposite PBAT blown films with higher stiffness and photo-oxidation resistance. The effect of the filler concentration on the melt rheological behavior in non-isothermal elongational flow was investigated. The results allowed us to choose the correct filler concentration for producing films through a film blowing operation. The PBAT/lignin blown film composites displayed an increase of the elastic modulus if compared to neat PBAT films without affecting their elongation at break. Furthermore, the filler delayed the photo-oxidative degradation of PBAT hence potentially allowing open-air applications
Advanced piezoresistive sensor achieved by amphiphilic nanointerfaces of graphene oxide and biodegradable polymer blends
No full textThis work focuses on the preparation of a piezoresistive sensor device, by exploiting an amphiphilic sample of graphene oxide (GO) as a compatibilizer for poly (lactic acid) (PLA)-Poly (ethylene-glycol) (PEG) blends. The presence of GO determined a high stiffening and strengthening effect, without affecting toughness, and allowed a good stability of mechanical properties up to 40 days. Moreover, GO endowed the materials with electrical properties highly sensitive to pressure and strain variations: the biodegradable pressure sensor showed a responsivity of 35 μA/MPa from 0.6 to 8.5 MPa, a responsivity around 19 μA/MPa from 8.5 to 25 MPa. For lower pressure values (around 0.16–0.45 MPa), instead, the responsivity increases up to 220 μA/MPa in terms of ΔI/ΔP (i.e. (ΔI/ΔI0)/P close to 1 kPa−1). Furthermore, this novel sensor is able to monitor submicrometric displacements with an impressive sensitivity (up to 25 μA/μm in terms of ΔI/ΔL, or 70 in terms of (ΔI/I0)/ε). We implemented a model able to predict pressure changes up to 25 MPa, by monitoring and measuring variations in electrical conductivity, thus paving the road to use these biodegradable, ecofriendly materials as low-cost sensors for a large pressure range
Impact of water plasticization on dialcohol cellulose fibres melt processing-structure-properties relationship
Get PDFCellulose and its derivatives are considered sustainable alternatives to non-biodegradable fossil-based plastics. Chemically modified cellulose fibres to dialcohol cellulose (DAC) fibres demonstrated a melt processing window between the glass transition and degradation temperatures which enabled their extrusion by using only water as a temporary plasticizer. With the aim of supporting an industrial upscale of DAC fibres, this study investigates the processing design and the feasibility of melt processing, minimizing the moisture. Melt processes-structure-properties relationships were studied by varying the sequence of primary and secondary melt processes, i.e., extrusion and injection moulding, and by changing the moisture content. The effect of moisture and processing design on the fibre structural properties, such as molecular weight, crystallinity, fibre morphology and fibre suspensions rheology, was assessed. Then, the thermomechanical behaviour of the 3D-shaped DAC injected materials was correlated with DAC fibres structural features obtained by the different processing design and moisture content. Our results identified the injection moulding as a milder process for achieving the preparation of 3D-shaped material with enhanced mechanical properties. Moreover, we disclosed the relevance of controlled moisture in the extrusion process for enabling a secondary shaping directly after compounding and the possibility of 3D-shaping DAC fibres after a rehydration step
Thermoplastic lignin esters as polymeric plasticizers for bioplastics
No full textIn this thesis, a sustainable and scalable process for modifying the structure of technical lignin to make it suitable for mixing with common bioplastics is studied. More specifically, this project deals with the development of a method of grafting fatty acids onto lignin. First, an updated state of the art concerning the processes for lignin production and its esterification is introduced and thoroughly discussed. Next, the materials and methods used to perform one-pot synthesis on lignin are described. The grafting process is initially optimized using a model reaction; afterwards, these conditions are adapted to technical lignin. The resulting process is also scaled up, overcoming unexpected issues due to mass and energy transfer. The modified lignins have been characterized through various thermal and analytical analyses (such as DSC, TGA and NMR), to provide a detailed description of their properties and structures. Finally, modified lignin was used to produce blends with commercial PLA as a proof of concept. As a matter of fact, this thesis is leading the basis for the fabrication of new-concepts materials based on plasticized lignin, aiming to conjugate sustainable industrially scalable processes and material performances
Phenanthroline-functionalized MWCNTs as versatile platform for lanthanides complexation
No full textA multiwalled carbon nanotube (MWCNT) scaffold was covalently functionalized with phenanthroline moieties capable to chelate tris Eu(III) complexes, such as Eu(III) tris-(2-theonyl)-trifluoroacetonate ([EuL 3]), yielding a brightly luminescent hybrid (MWCNTs- Phen•[EuL3]). The material was thoroughly characterized by means of TGA, XPS, TEM and steady-state UV-Vis absorption and emission investigations. These studies demonstrated both the integrity of the luminescent Eu(III)-based complex in the hybrid, as well as its high loading. The versatility of the coordinating properties of phenanthroline allowed the anchoring of other lanthanides like Gd(III), producing functional hybrids with potential applicability as magnetic resonance agents. Finally, the developed hybrid revealed to be highly dispersible in biodegradable polymer matrices such as Poly(l-lactide) (PLLA), making it a promising luminophore for applications in biomaterial science. © 2013 Elsevier Ltd. All rights reserved
Extrusion strategies for bio-based and biodegradable poly(butylene succinate-co-adipate)/thermoplastic starch blends
No full textOver the past decades, economic growth led to an increase in the use of plastics. Reliance on plastics
continued to grow because they offer advantages such as durability, versatility, lightweight, and
cheapness. This led to a rapid accumulation of solid waste, which harms the environment due to their
resistance to biodegradation. Nonrenewable feedstocks are environmentally harmful and are
becoming more expensive, leading to questioning about their sustainability and thus motivating study
and development of renewable alternatives. In this setting, biodegradable and bio-based polymers
have received increased attention.
Starch, a fully biodegradable polysaccharide, is the most widely applied renewable resource in the
world. In the presence of heat, shear and a limited amount of water or other plasticizers, starch
undergoes spontaneous de-structuration, forming a homogeneous melt known as thermoplastic starch
(TPS). However, thermoplastic starch cannot be employed directly in several applications because of
its poor mechanical properties and high water sensitivity. Poly(butylene succinate adipate) (PBSA)
is an emerging biodegradable polyester with water and chemical resistance, good processability, and
flexibility, but relatively more expensive. Blending these two polymers represents a potential strategy
to overcome their intrinsic drawbacks.
This thesis aims to develop PBSA/TPS blends with improved performance maximizing the starch
content. More specifically, the purpose is to obtain a polymer blend with good processability suitable
for film-blowing, and design different processing approaches to make the production more efficient,
i.e. minimizing energy consumption.
Two-steps, a one-step and a reactive one-step extrusions were explored, and the performances of the
resulting blends were thermally, mechanically and morphologically characterized. Melt film blowing
has been performed on selected blends to validate their enhanced processability
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