Thermomechanical and morphological properties of poly(ethylene terephthalate)/anhydrous calcium terephthalate nanocomposites

Calcium terephthalate anhydrous salts (CATAS), synthetized by reaction of terephthalic acid with metal (Ca) oxide were incorporated at dierent weight contents (0-30 wt. %) in recycled Poly(ethylene terephthalate) (rPET) by melt processing. Their structure, morphology, thermal and mechanical properties (tensile and flexural behavior) were investigated. Results of tensile strength of the dierent formulations showed that when the CATAS content increased from 0.1 to 0.4 wt. %, tangible changes were observed (variation of tensile strength from 65.5 to 69.4 MPa, increasing value for E from 2887 up to 3131 MPa, respectively for neat rPET and rPET_0.4CATAS). A threshold weight amount (0.4 wt. %) of CATAS was also found, by formation at low loading, of a rigid amorphous fraction at the rPET/CATAS interface, due to the aromatic interactions (π-π conjugation) between the matrix and the filler. Above the threshold, a restriction of rPET/CATAS molecular chains mobility was detected, due to the formation of hybrid mechanical percolation networks. Additionally, enhanced thermal stability of CATAS filled rPET was registered at high content (Tmax shift from 426 to 441 offiC, respectively, for rPET and rPET_30CATAS), essentially due to chemical compatibility between terephthalate salts and polymer molecules, rich in stable aromatic rings. The singularity of a cold crystallization event, identified at the same loading level, confirmed the presence of an equilibrium state between nucleation and blocking eect of amorphous phase, basically related to the characteristic common terephthalate structure of synthetized Ca-Metal Organic Framework and the rPET matrix

Basalt/polypropylene composites: The effects of mechanical reprocessing on their morphological, thermal, rheological and mechanical behavior

Considering the increasing spread of basalt fibers on the market as bio-based alternative to glass and the massive use of polypropylene (PP) in the automotive sector, the end-of-life of PP/basalt composites through mechanical reprocessing was addressed. Their thermal, rheological and mechanical properties were investigated up to seven reprocessing cycles and the main relationship between their changes and composites fibers length reduction was disclosed. The composites displayed a parabolic increase in their melt volume rate for increasing reprocessing cycles and were characterized by an improved flowability compared to the neat matrix at the fifth cycle, i.e., 89.3 against 74.8 cm3/10min, due to the intimate contact between the fibers and the matrix which causes a stronger degradation in PP molecular weight. Concerning the mechanical response, the logarithmic decrease in stiffness and strength was not directly proportional to fibers length reduction due to a progressive better orientation of the fibers along the injection direction. Finally, the comparison of the mechanical results obtained with the data available for PP composites reinforced with vegetable fibers allowed to conclude that PP/basalt composites are competitive with this type of composites up to the fifth cycle, displaying a tensile modulus of 3.5 GPa and tensile strength of 38 MPa

Development of thermoplastic starch (TPS) including leather waste fragments

A thermoplastic starch (TPS) material is developed, based on corn starch plasticized with glycerol and citric acid in a 9:3:1 ratio and further bonded with isinglass and mono-and diglycerides of fatty acids (E471). In TPS, leather fragments, in the amount of 7.5 15 or 22.5 g/100 g of dry matter, were also introduced. The mixture was heated at a maximum temperature of 80 °C, then cast in an open mold to obtain films with thickness in the range 300 ± 50 microns. The leather fragments used were based on collagen obtained from production waste from shoemaking and tanned with tannins obtained from smoketree (Rhus cotinus), therefore free from chromium. Thermogravimetric (TGA) tests suggested that material degradation started at a temperature around 285 °C, revealing that the presence of leather fragments did not influence the occurrence of this process in TPS. Tensile tests indicated an increase in tensile properties (strength and Young's modulus) with increasing leather content, albeit coupled, especially at 22.5 wt%, with a more pronounced brittle behavior. Leather waste provided a sound interface with the bulk of the composite, as observed under scanning electron microscopy. The production process indicated a very limited degradation of the material after exposure to UV radiation for eight days, as demonstrated by the slight attenuation of amide I (collagen) and polysaccharide FTIR peaks. Reheating at 80 °C resulted in a weight loss not exceeding 3%

Hybrid metal/polymer filaments for fused filament fabrication (FFF) to print metal parts

The exploitation of mechanical properties and customization possibilities of 3D printed metal parts usually come at the cost of complex and expensive equipment. To address this issue, hybrid metal/polymer composite filaments have been studied allowing the printing of metal parts by using the standard Fused Filament Fabrication (FFF) approach. The resulting hybrid metal/polymer part, the so called “green”, can then be transformed into a dense metal part using debinding and sintering cycles. In this work, we investigated the manufacturing and characterization of green and sintered parts obtained by FFF of two commercial hybrid metal/polymer filaments, i.e., the Ultrafuse 316L by BASF and the 17-4 PH by Markforged. The Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectrometry (EDS) analyses of the mesostructure highlighted incomplete raster bonding and voids like those observed in conventional FFF-printed polymeric structures despite the sintering cycle. A significant role in the tensile properties was played by the building orientation, with samples printed flatwise featuring the highest mechanical properties, though lower than those achievable with standard metal additive manufacturing techniques

3D Printing of Low-Filled Basalt PA12 and PP Filaments for Automotive Components

Fused Deposition Modeling (FDM) enables many advantages compared to traditional manufacturing techniques, but the lower mechanical performance due to the higher porosity still hinders its industrial spread in key sectors like the automotive industry. PP and PA12 filaments filled with low amounts of basalt fibers were produced in the present work to improve the poor mechanical properties inherited from the additive manufacturing technique. For both matrices, the introduction of 5 wt.% of basalt fibers allows us to achieve stiffness values comparable to injection molding ones without modifying the final weight of the manufactured components. The increased filament density compared with the neat polymers, upon the introduction of basalt fibers, is counterbalanced by the intrinsic porosity of the manufacturing technique. In particular, the final components are characterized by a 0.88 g/cm3 density for PP and 1.01 g/cm3 for PA12 basalt-filled composites, which are comparable to the 0.91 g/cm3 and 1.01 g/cm3, respectively, of the related neat matrix used in injection molding. Some efforts are still needed to fill the gap of 15–28% for PP and of 26.5% for PA12 in tensile strength compared to injection-molded counterparts, but the improvement of the fiber/matrix interface by fiber surface modification or coupling agent employment could be a feasible solution

Hybrid cellulose–Basalt polypropylene composites with enhanced compatibility. The role of coupling agent

This study deals with the development and optimization of hybrid composites integrating microcrystalline cellulose and short basalt fibers in a polypropylene (PP) matrix to maximize the mechanical properties of resulting composites. To this aim, the effects of two different coupling agents, endowed with maleic anhydride (MA-g(grafted)-PP) and acrylic acid (AA-g-PP) functionalities, on the composite properties were investigated as a function of their amount. Tensile, flexural, impact and heat deflection temperature tests highlighted the lower reactivity and effectiveness of AA-g-PP, regardless of reinforcement type. Hybrid formulations with basalt/cellulose (15/15) and with 5 wt. % of MA-g-PP displayed remarkable increases in tensile strength and modulus, flexural strength and modulus, and notched Charpy impact strength, of 45% and 284%, 97% and 263%, and 13%, in comparison with neat PP, respectively. At the same time, the thermo-mechanical stability was enhanced by 65% compared to neat PP. The results of this study, if compared with the ones available in the literature, reveal the ability of such a combination of reinforcements to provide materials suitable for automotive applications with environmental benefits

Polylactic acid as biobased binder for the production of 3D printing filaments for Ti6Al4V alloy manufacturing via bound metal deposition

In this paper, a biobased binder mainly composed of polylactic acid (PLA) was developed for the production of Ti6Al4V feedstock suitable for 3D printing via material extrusion. 3D printed samples were debound via solvent and thermal treatments and successfully sintered in reducing atmosphere obtaining dense metallic components. The designed and produced bio-binder is completely eliminated during the debinding processes leading to sintered samples showing a high densification (93–94%), with a microstructure composed of primary alpha phase with segregated beta phase at grain boundaries and having average grain size of 70 μm. 3D printed sintered samples show good mechanical properties (yield strength (σy) = 662 MPa, ultimate tensilte strength (UTS) = 743 MPa, elongation at break (εmax) = 12%, hardness = 5.15 GPa) influenced by the sintering parameters and the presence of some degree of micro-porosity in the final structure

Correlation between mechanical properties and processing conditions in rubber-toughened wood polymer composites

The use of wood fibers is a deeply investigated topic in current scientific research and one of their most common applications is as filler for thermoplastic polymers. The resulting material is a biocomposite, known as a Wood Polymer Composite (WPC). For increasing the sustainability and reducing the cost, it is convenient to increase the wood fiber content as much as possible, so that the polymeric fraction within the composite is thereby reduced. On the other hand, this is often thwarted by a sharp decrease in toughness and processability-a disadvantage that could be overcome by compounding the material with a toughening agent. This work deals with the mechanical properties in tension and impact of polypropylene filled with 50 wt.% wood flour, toughened with different amounts (0%, 10%, and 20%) of a polypropylene-based thermoplastic vulcanizate (TPV). Such properties are also investigated as a function of extrusion processing variables, such as the feeding mode (i.e., starve vs. flood feeding) and screw speed. It is found that the mechanical properties do depend on the processing conditions: the best properties are obtained either in starve feeding conditions, or in flood feeding conditions, but at a low screw speed. The toughening effect of TPV is significant when its content reaches 20 wt.%. For this percentage, the processing conditions are less relevant in governing the final properties of the composites in terms of the stiffness and strength

Assessment of agglomerated corks and PVC foams cores crashworthiness under multiple-impact events in different loading conditions

Thanks to the unique flexural properties, sandwich composites are considered as irreplaceable structures in many industrial fields, but their susceptibility to impact events is still a considerable drawback that undermines their structural integrity determining a reduction of their load-bearing capabilities. Considering that the core material plays the major role to distance the skins, the knowledge of its multiple-impacts response becomes a key design parameter in order to ensure a long-term stability to the structure. In view of this, the present work addresses the multiple-impacts behavior in dynamic compression and puncture impact conditions of bio-based agglomerated cork cores taking into account the effect of density and providing a meaningful comparison with more traditional petroleum-based foams. Despite the inherently higher mechanical properties of the PVC (polyvinyl chloride) foams, agglomerated cork demonstrated to provide a higher dimensional stability to the structure after repeated impacts thanks to its unique microstructure. With a reduction lower than 25% of its initial height after 10 impacts, agglomerated cork NL25 proved to be an exceptional alternative to the common HP130 foam, which undergoes a halving of its initial height after only 3 impacts, to obtain a more eco-friendly and performing sandwich composite

Finite-temperature relativistic Landau problem and the relativistic quantum Hall effect

This paper presents a study of the free energy and particle density of the relativistic Landau problem, and their relevance to the quantum Hall effect. We study first the zero temperature Casimir energy and fermion number for Dirac fields in a 2+1-dimensional Minkowski space-time, in the presence of a uniform magnetic field perpendicular to the spatial manifold. Then, we go to the finite-temperature problem, with a chemical potential, introduced as a uniform zero component of the gauge potential. By performing a Lorentz boost, we obtain Hall's conductivity in the case of crossed electric and magnetic fields.Comment: Final version, to appear in Journal of Physics A: Mathematical and Genera