Alberta Latteri

Composites Based on Natural Fibre Fabrics

In the latest years industry is attempting to decrease the dependence on petroleum based fuels and products due to the increased environmental consciousness. This is leading to the need to investigate environmentally friendly, sustainable materials to replace existing ones. The tremendous increase of production and use of plastics in every sector of our life lead to huge plastic wastes. Disposal problems, as well as strong regulations and criteria for cleaner and safer environment, have directed great part of the scientific research toward ecocomposite materials. Among the different types of eco-composites those which contain natural fibers (NF) and natural polymers have a key role. Since few years polymeric biodegradable matrices have appeared as commercial products, however their high price represents the main restriction to wide usage. Currently the most viable way toward ecofriendly composites is the use of natural fibres as reinforcement. Natural fibres represent a traditional class of renewable materials which, nowadays, are experiencing a great revival. In the latest years there have been many researches developed in the field of natural fibre reinforced plastics (Bledzki & Gassan, 1999). Most of them are based on the study of the mechanical properties of composites reinforced with short fibers. The components obtained therefore are mostly used to produce non-structural parts for the automotive industry such as covers, car doors panels and car roofs ( Magurno, 1999, John at al., 2008) (Fig.1,2).

Thermal and thermo-oxidative degradations of poly(2,6-dimethyl- 1,4-phenylene oxide) (PPO)/copoly(aryl ether sulfone) P(ESES-co-EES) block copolymers: a kinetic study

The thermal degradation of a series of three novel ABA block copolymers of different molar mass (Mn), were the block A is a poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), while the block B is a random copoly(aryl ether sulfone) P(ESES-co-EES), was studied in both inert (flowing nitrogen) and oxidative (static air) atmospheres, to investigate the effects of Mn of the central block on the thermal stability. Copolymers were synthesized with a two step method: in the first stage, a linking molecule is selectively attached as end group to the P(ESES-co-EES) which reacts in the second step with the phenolic hydroxyl group of PPO. Degradations were carried out into a thermobalance, in the scanning mode, at various heating rates, and the characteristic parameters of thermal stability, namely initial decomposition temperature (Ti) and the activation energy (Ea) of degradation, of the various copolymers were determined. Both Ti and degradation Ea values increased exponentially as a function of Mn of copolymers. The results were discussed and interpreted.

Thermal characterization of a series of lignin-based polypropylene blends

Polypropylene (PP), due to its chemical stability, is considered one of the main responsible of the increasing amount of plastic wastes on earth. To overcome this problem and to reduce the dependence of oil feedstocks, the use of lignocellulosics as fillers or reinforcements in thermoplastic materials has been increasing enormously in the last decades. In the present work, Liquid Wood (a mixture of cellulose, hemp, fax and lignin) was used to prepare, by mechanical mixing followed by thermal extrusion, blends of various PP/Liquid Wood ratios. Differential scanning calorimetry and thermogravimetric analysis experiments were performed in order to verify whether and how much the composition of the blends affects the thermal properties of the obtained compounds. Both calorimetric and thermogravimetric results indicate that the application of PP as a matrix does not limit the processing temperature of Liquid Wood, which may lead to a perfect marketable composite from these components. The addition of Liquid Wood also resulted in enhanced mechanical properties for the PP/Liquid Wood blends.

Dumbbell-shaped polyhedral oligomeric silsesquioxanes/polystyrene nanocomposites: The influence of the bridge rigidity on the resistance to thermal degradation

A comparative study concerning the resistance to the thermal degradation of polystyrene-based nanocomposites loaded with five novel aromatic dumbbell-shaped polyhedral oligomeric silsesquioxanes was carried out in dynamic heating conditions. The fillers were formed by two identical silicon cages R7(SiO1.5)8 (R = isobutyl) linked to several aromatic bridges (Ar, Ar–Ar, Ar–O–Ar, Ar–S–Ar and Ar–SO2–Ar) where Ar = p-C6H4. Nanocomposites were prepared by in situ polymerization of styrene in the presence of 5% of appropriate polyhedral oligomeric silsesquioxanes. The actual filler content in the products obtained, which was checked by 1H NMR spectroscopy, resulted in all cases slightly higher than that in starting mixtures. Glass transition temperature (Tg) was determined by differential scanning calorimetry. Thermogravimetric (TG) and differential thermogravimetric (DTG) analysis were carried out in both flowing nitrogen and static air atmosphere, and temperatures at 5% mass loss (T5%) were determined to investigate the resistance to the thermal degradation. The results obtained were compared with each other and discussed. The resistance to the thermal degradation showed modest increments in respect to neat polystyrene, differently from analogous nanocomposites containing as fillers aliphatic bridged polyhedral oligomeric silsesquioxanes, as supported by scanning electron microscopy measurements which evidenced polyhedral oligomeric silsesquioxanes auto-aggregation phenomena. This behaviour was interpreted as due to the rigidity of polyhedral oligomeric silsesquioxanes aromatic bridges, which leads to low miscibility between filler and polymeric matrix.

Green Composites Based on Blends of Polypropylene with Liquid Wood Reinforced with Hemp Fibers: Thermomechanical Properties and the Effect of Recycling Cycles

Green composites from polypropylene and lignin-based natural material were manufactured using a melt extrusion process. The lignin-based material used was the so called “liquid wood”. The PP/“Liquid Wood” blends were extruded with “liquid wood” content varying from 20 wt % to 80 wt %. The blends were thoroughly characterized by flexural, impact, and dynamic mechanical testing. The addition of the Liquid Wood resulted in a great improvement in terms of both the flexural modulus and strength but, on the other hand, a reduction of the impact strength was observed. For one blend composition, the composites reinforced with hemp fibers were also studied. The addition of hemp allowed us to further improve the mechanical properties. The composite with 20 wt % of hemp, subjected to up to three recycling cycles, showed good mechanical property retention and thermal stability after recycling.

Engineering thermoplastics for additive manufacturing: a critical perspective with experimental evidence to support functional applications

Background Among additive manufacturing techniques, the filament-based technique involves what is referred to as fused deposition modeling (FDM). FDM materials are currently limited to a selected number of polymers. The present study focused on investigating the potential of using high-end engineering polymers in FDM. In addition, a critical review of the materials available on the market compared with those studied here was completed. Methods Different engineering thermoplastics, ranging from industrial grade polycarbonates to novel polyetheretherketones (PEEKs), were processed by FDM. Prior to this, for innovative filaments based on PEEK, extrusion processing was carried out. Mechanical properties (i.e., tensile and flexural) were investigated for each extruded material. An industrial-type FDM machine (Stratasys Fortus® 400 mc) was used to fully characterize the effect of printing parameters on the mechanical properties of polycarbonate. The obtained properties were compared with samples obtained by injection molding. Finally, FDM samples made of PEEK were also characterized and compared with those obtained by injection molding. Results The effect of raster to raster air gap and raster angle on tensile and flexural properties of printed PC was evidenced; the potential of PEEK filaments, as novel FDM material, was highlighted in comparison to state of the art materials. Conclusions Comparison with injection molded parts allowed to better understand FDM potential for functional applications. The study discussed pros and cons of the different materials. Finally, the development of novel PEEK filaments achieved important results offering a novel solution to the market when high mechanical and thermal properties are required.

PES/POSS Soluble Veils as Advanced Modifiers for Multifunctional Fiber Reinforced Composites

Novel polyhedral oligomeric silsesquioxanes (POSS)-filled thermoplastic electrospun veils were used to tailor the properties of the interlaminar region of epoxy-based composites. The veils were designed to be soluble upon curing in the epoxy matrix, so that POSS could be released within the interlaminar region. Three different POSS contents, varying from 1 to 10 wt %, were tested while the percentage of coPolyethersulphone (coPES) dissolved in the epoxy resin was kept to a fixed value of 10 wt %. Good quality veils could be obtained at up to 10 wt % of POSS addition, with the nanofibers’ diameters varying from 861 nm for the coPES to 428 nm upon POSS addition. The feasibility of the soluble veils to disperse POSS in the interlaminar region was proved, and the effect of POSS on phase morphology and viscoelastic properties studied. POSS was demonstrated to significantly affect the morphology and viscoelastic properties of epoxy composites, especially for the percentages 1% and 5%, which enabled the composites to avoid POSS segregates occurring. A dynamic mechanical analysis showed a significant improvement to the storage modulus, and a shift of more than 30 °C due to the POSS cages hindering the motion of the molecular chains and network junctions.

Characterizing Deep Brain Stimulation effects in computationally efficient neural network models

Background Recent studies on the medical treatment of Parkinsons disease (PD) led to the introduction of the so called Deep Brain Stimulation (DBS) technique. This particular therapy allows to contrast actively the pathological activity of various Deep Brain structures, responsible for the well known PD symptoms. This technique, frequently joined to dopaminergic drugs administration, replaces the surgical interventions implemented to contrast the activity of specific brain nuclei, called Basal Ganglia (BG). This clinical protocol gave the possibility to analyse and inspect signals measured from the electrodes implanted into the deep brain regions. The analysis of these signals led to the possibility to study the PD as a specific case of dynamical synchronization in biological neural networks, with the advantage to apply the theoretical analysis developed in such scientific field to find efficient treatments to face with this important disease. Experimental results in fact show that the PD neurological diseases are characterized by a pathological signal synchronization in BG. Parkinsonian tremor, for example, is ascribed to be caused by neuron populations of the Thalamic and Striatal structures that undergo an abnormal synchronization. On the contrary, in normal conditions, the activity of the same neuron populations do not appear to be correlated and synchronized. Results To study in details the effect of the stimulation signal on a pathological neural medium, efficient models of these neural structures were built, which are able to show, without any external input, the intrinsic properties of a pathological neural tissue, mimicking the BG synchronized dynamics. We start considering a model already introduced in the literature to investigate the effects of electrical stimulation on pathologically synchronized clusters of neurons. This model used Morris Lecar type neurons. This neuron model, although having a high level of biological plausibility, requires a large computational effort to simulate large scale networks. For this reason we considered a reduced order model, the Izhikevich one, which is computationally much lighter. The comparison between neural lattices built using both neuron models provided comparable results, both without traditional stimulation and in presence of all the stimulation protocols. This was a first result toward the study and simulation of the large scale neural networks involved in pathological dynamics. Using the reduced order model an inspection on the activity of two neural lattices was also carried out at the aim to analyze how the stimulation in one area could affect the dynamics in another area, like the usual medical treatment protocols require. The study of population dynamics that was carried out allowed us to investigate, through simulations, the positive effects of the stimulation signals in terms of desynchronization of the neural dynamics. Conclusions The results obtained constitute a significant added value to the analysis of synchronization and desynchronization effects due to neural stimulation. This work gives the opportunity to more efficiently study the effect of stimulation in large scale yet computationally efficient neural networks. Results were compared both with the other mathematical models, using Morris Lecar and Izhikevich neurons, and with simulated Local Field Potentials (LFP).

Environmental benefits of using ground tyre rubber in new pneumatic formulations: A life cycle assessment approach

Life cycle assessment methodology was applied as a tool to evaluate the real environmental benefit of using recycled waste tyres in mixture with virgin rubber. Styrene–isoprene–styrene rubber was mixed with different amounts of ground tyre rubber and vulcanised. Thermomechanical analysis (i.e. differential scanning calorimetry and thermogravimetric analysis) and dynamic mechanical thermal analysis were carried out in order to evaluate the compatibility of the rubber mixture and the chemical–physical properties of the vulcanised products. Experimental analysis results show that the addition of ground tyre rubber up to 50 phr does not sensibly affect the vulcanisation reaction, the wet skid resistance and the rolling resistance. Life cycle assessment results show that the main environmental impacts of the ground tyre rubber are associated to the use of virgin rubber (47.1%) and carbon black (34.3%) while the tyre grinding process contributes only for 4%. Because ground tyre rubber contains carbon black in its formulation, the substitution of virgin rubber with ground tyre rubber has double environmental benefits: to reduce the need of both amounts of virgin rubber and fresh carbon black in the new formulation.

Thermoplastic veils as advanced modifiers for multifunctional fiber reinforced composites

The present paper is focused on the development of a novel technique to obtain multifunctional fiber reinforced composites. The technique is based on the use of thermoplastic veils composed of nano and micro thermoplastic fibers which preferentially dissolve upon curing in the epoxy matrix. The technique allows to control the phase morphology in the inter- and intra-laminar region of the laminates. Moreover, the selective dissolution of the fibers allow to achieve tailored dispersion of different types of nanofillers in the composites to obtain a functional graded material.