1,721,013 research outputs found
Use of fiberglass/epoxy and hemp/bioepoxy in a structural component: an assessment
No full textBiocomposite materials are often considered in substitution of fiberglass reinforced (FGR) polymers, especially thanks to the lower costs and environmental impact of the natural fibers. In this work, beams with the function of wing spar, for small aeronautic structure, have been chosen to compare both performance and manufacturing issues characteristics of the two different kind of laminates. After a preliminary analysis of the materials, four spars were manufactured and were subjected to static and to failure mechanical tests. The microstructure of the composite spars was analyzed by scanning electron microscopy. The most relevant differences resulted related to the resin retention, which is higher in the case of the hemp fibers, and to the fiber-resin interactions, affecting the failure modes
Gamma-irradiation effects on polyethylene terephthalate studied by positron annihilation lifetime spectroscopy
No full text
Autonomic Self-Healing in Epoxidized Natural Rubber
No full textThe development of polymers that can repair damage autonomously would be
useful to improve the lifetime of polymeric materials. To date, limited attention
has been dedicated to developing elastomers with autonomic self-healing ability,
which can recover damages without need for an external or internal source of
healing agents. This work investigates the self-healing behavior of epoxidized
natural rubber (ENR) with two different epoxidation levels (25 and 50 mol %
epoxidation) and of the corresponding unfunctionalized rubber, cis-1,4-
polyisoprene (PISP). A self-adhesion assisted self-healing behavior was revealed
by T-peel tests on slightly vulcanized rubbers. A higher epoxidation level was
found to enhance self-healing. Self-healing of rubbers following ballistic damages
was also investigated. A pressurized air flow test setup was used to evaluate the
self-healing of ballistic damages in rubbers. Microscope (OM, SEM, and TEM)
analyses were carried out to provide further evidence of healing in the impact
zones. Self-healing of ballistic damages was observed only in ENR with 50 mol %
epoxidation and it was found to be influenced significantly by the cross-link
density. Finally, self-healing of ballistic damages was also observed in
ENR50/PISP blends only when the content of the healing component (i.e., ENR50) was at least 25 wt %. From an analysis of the results, it was concluded that a
synergistic effect between interdiffusion and interaction among polar groups leads
to self-healing in ENR
Compatibility of Statistical Aromatic Copolycarbonates in Polystyrene and Poly(carbonate of Bisphenol A) Blends
No full textIn this work the compatibility of aromatic copolycarbonates containing
bisphenol A (BPA) and tetramethyl bisphenol A (TMBPA) with polystyrene (PS) was
investigated. Miscibility prediction data were used to select copolycarbonates of
potential interest for developing highly compatible blends. Statistical
copolycarbonates (CPCs) containing different BPA/TMBPA molar ratios were
synthesized by polycondensation reaction and the effect of copolymer composition
on the PS/CPC miscibility was studied. The blends were prepared by casting from
chloroform solutions and/or melt mixing. The compatibility was evaluated by
optical microscopy (OM), calorimetric (DSC), and dynamic-mechanical thermal (DMTA)
analyses. Two glass transition temperatures were found for all the prepared PS/CPC
blends, but an improvement of compatibility was obtained increasing TMBPA content
in CPC copolymer. On the other hand, blends of polycarbonate of bisphenol A (PCPA)
and CPCs were characterized by a single glass transition temperature and
transesterification reaction was noticed. Finally, a compatibilization effect of
CPCs and polycarbonate of tetramethyl-bisphenol A (PCTMP) was highlighted in
PS/PCPA/CPCs and PS/PCPA/PCTMP three components blends
Printability of recycled feedstock for extrusion additive manufacturing
Full text linkThe 3D printability of several thermoplastic feedstocks, recycled from post-industrial or post-consumer waste and the properties of printed items are presented and discussed. A preliminary investigation has been conducted with post-industrial scraps of PETG and PLA recycled into printable filaments. A comparison with samples produced with corresponding virgin materials showed similar mechanical characteristics. The printability of virgin, recycled and recycled/UVA exposed ABS pellets from extruded scraps is also compared. Recycled pellets were aged by exposure to UVA light up to 400 hours. The results of mechanical tests of 3D printed specimens indicate that the printability of recycled and artificially aged ABS pellets is still acceptable. Furthermore, nylon fibres recycled from clothing were used as feedstock for 3D printing. A simple and inexpensive recycling process is proposed to recover extruded pellets from nylon t-shirts. On the other hand, 3D printing tests showed that the recycled nylon has some prospects for 3D printing, but only if mixed at low percentage with virgin polymer
Extrusion of metal powder-polymer mixtures: Melt rheology and process stability
Full text linkThe mixture of metal powder and a viscous polymeric binder (often referred to as feedstock) is commonly used for Metal Injection Moulding (MIM) applications. Recently, the interest towards the extrudability of metal/binder feedstocks is increasing, especially because of the growth of additive manufacturing techniques based on the vertical extrusion and layered deposition of filaments. In this experimental work, a feedstock prepared as a mixture of stainless steel 316 L powder with water-soluble binder was tested. The rheological behaviour of different mixtures (with powder loading between 50 and 63% in volume) was assessed using a capillary rheometer. The theoretical window of optimal extrudability was determined, in terms of temperature, shear rate and powder loading. Then, a specially designed CNC controlled extrusion system was used for performing vertical extrusion tests. The analysis of extrusion pressure profiles and the dimensional variability of the filaments was used to correlate the theoretical extrudability predicted by the rheological model with the actual extrusion tests. All results indicate that the conditions which yield better stability of the extrusion process are those that allow higher viscosity of the mixtures
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