Fabrizio Quadrini

Shape memory epoxy foams by solid-state foaming

Epoxy foams were produced by means of solid-state foaming and their shape memory properties were evaluated together with other physical properties. Solid-state foaming consists of pressing thermosetting resin powders to produce solid tablets, heating the tablets at high temperature to generate both the formation of pores inside the resin and the resin polymerization. A nanoclay was added to the resin powder before pressing it up to a maximum content of 5 wt%. Unfilled and composite foams were characterized by density measurements and thermal analyses. Subsequently, foam samples underwent up to two thermo-mechanical cycles: each cycle consisted of the storage of a compressed shape and the subsequent thermal recovery. Compression tests were used to measure the effect of the thermo-mechanical cycles on the foams mechanical performances and compressive toughness was extracted from the tests. It was observed that all the foams exhibited good shape memory properties also after cycling: nanoclay filler allows the foams to completely recover the initial shape and to increase the compressive and the specific compressive toughness.

Solid-State Foaming of Epoxy Resin:

A new foaming process has been developed for epoxy resins. Uncured epoxy tablets are fabricated by pressing commercial powders in a steel mold at room temperature and used as foam precursors. The tablets foam when heated in a muffle at high temperature. No blowing agent was added because the foaming mechanism depends on the uncured resin boiling point. The foaming temperature is set to be high enough to rapidly produce the resin boiling but not excessive to avoid the thermal degradation. During boiling, the epoxy resin polymerizes and the bubbles freeze in the final structure. Epoxy foams are obtained by heating the compacted tablets in cylindrical copper molds, having internal diameter equal to the tablet diameter. Several process parameters have been changed in the experiment to understand their correlation with the foaming efficiency. However, the foaming ratio (expressed in terms of the ratio between the final and the initial tablet height) is found to be mainly dependent on the initial tablet density. In optimal conditions, the foaming ratio can rise up to 6. Thermal tests have been performed to evaluate the epoxy powder behavior during the cure, whereas mechanical compression tests were used to evaluate the final performances of the foams.

Solid-state Foaming of Nano–Clay-Filled Thermoset Foams with Shape Memory Properties

A solid-state process was used to produce epoxy foams with different contents of nano-clay (up to 10%wt). The foam properties were studied by means of numerous tests: X-ray analysis, dynamic mechanical analysis, mechanical tests (compression, flexure, indentation, stress relaxation). The straightening effect of the nano-clay filler was investigated and related to the loading conditions and the intrinsic properties of the resin matrix. Small and large foam samples were produced by changing the number of solid precursors during foaming. In the end, shape recovery tests showed that composite foams exhibit remarkably shape memory properties, at least at low filler contents.

Shape Memory Foams of Microbial Polyester for Biomedical Applications

Foams of polycaprolactone (PCL) and microbial polyester (poly-hydroxybutyrate-hydroxyvalerate, PHBV with 10% mol PHV) were produced by particulate leaching in an urea preform and subsequent preform dissolution in distilled water. Films were also cast to compare mechanical and shape memory performances. SEM observations of foam sections showed that a homogenous microstructure was obtained with good replication of urea particles. Cylindrical PHBV samples (porosity about 90%) were used for shape memory tests in compression mode and a good behavior was observed. After training, 100% shape recovery can be achieved if a maximum 30% compression is applied.

Production of rubber parts by tyre recycling without using virgin materials

Abstract A new recycling technology (namely ‘direct powder moulding’) is proposed to produce large rubber parts from spent tyres without any addition of virgin materials or linking agents. Rubber pads were produced by compression moulding of rubber powder mixtures which were obtained by mechanical grinding of ground tyre rubbers. In this study, the effect of different powder mixtures on the final performances of the moulded parts was evaluated. Starting from three initial size distributions of the rubber powder, other binary and ternary blends were prepared, for a total of 15 different powder distributions. All these rubber mixtures were compression moulded to produce large pads. Differential scanning calorimetry of the rubber powders was carried out as well as tensile tests and dynamic mechanical analyses on samples extracted from the pads. It was found that the rubber powder distribution strongly affects the mechanical performances of the recycled rubber moulded products.

Dynamic Mechanical Performances of Polyester–Clay Nanocomposite Thick Films

Dynamic mechanical properties of polyester—montmorillonite nanocomposite thick films, prepared by the in situ intercalative polymerization method, were evaluated in a tensile mode. A fast fabrication procedure was chosen to allow industrial applications. A total time less than 1 h was sufficient to obtain a thick film which could be cut for the specimen preparation. The final films had a thickness of 250 μm and a nano-clay content ranging from 0 to 10 wt%. A differential scanning calorimeter was used to investigate the effect of the clay content on the resin polymerization kinetics whereas tensile tests were performed to make a comparison with dynamic mechanical results. The maximum in the mechanical performances was obtained at the clay content of 1 wt% at which an increase of about 55% for the storage modulus was measured in comparison with the unfilled resin.

Process-efficiency prediction in high power diode laser forming

The present work is an experimental investigation on the laser forming process of aluminum alloy and stainless-steel thin sheets. A high-power diode laser (HPDL) with a nonsymmetric spot configuration was employed at medium and low scanning rates. The tests were performed at different operating conditions: scanning rate, laser spot orientation, and laser beam power. The experimental results revealed the great influence of the laser spot orientation on the total bending angle and the harmful effect of the surface melting during heating. Spot orientation significantly affects the treated area extension during laser scanning. Employing an analytical thermo-mechanical model, a dimensionless processing map can be presented that allows the prediction of the sheet bending angle depending on the material properties and machining parameters. Dimensional terms of the processing map can be associated to efficiency terms for heat transfer and bending.

Mechanical qualification of collagen membranes used in dentistry

AIM The aim of this work is the qualification of commercially available collagen membranes in a comparative manner. The natural origin of collagen makes standardization difficult. Nevertheless, through dimensional and mechanical measures it is possible to mechanically qualify collagen membranes, and compare them. METHODS Three commercially available collagen membranes used in Guided Bone Regeneration (GBR) and in Guided Tissue Regeneration (GTR) techniques, namely Bio-Gide, Collprotect and Jason, were chosen for the comparison. Quasi-static (tensile tests) and time-dependent (stress relaxation test) mechanical tests together with a functional test (tear test) were done to determine the responses of collagen membranes under different loading conditions. RESULTS The tested membranes exhibited different behaviours, different deformability values and thickness, Jason being the thinnest and Bio-Gide the thickest. Similar differences were also observed in terms of surface density. DISCUSSION Even though clinical observations were not within the aim of this study, our findings indicate that a better understanding of the correlation between mechanical properties and thickness could lead to a more rational design and use of these membranes in the face of specific clinical cases.

Forming of Shape Memory Composite Structures

A new forming procedure was developed to produce shape memory composite structures having structural composite skins over a shape memory polymer core. Core material was obtained by solid state foaming of an epoxy polyester resin with remarkably shape memory properties. The composite skin consisted of a two-layer unidirectional thermoplastic composite (glass filled polypropylene). Skins were joined to the foamed core by hot compression without any adhesive: a very good adhesion was obtained as experimental tests confirmed. The structure of the foam core was investigated by means of computer axial tomography. Final shape memory composite panels were mechanically tested by three point bending before and after a shape memory step. This step consisted of a compression to reduce the panel thickness up to 60%. At the end of the bending test the panel shape was recovered by heating and a new memory step was performed with a higher thickness reduction. Memory steps were performed at room temperature and 120 °C so as to test the foam core in the glassy and rubbery state, respectively. Shape memory tests revealed the ability of the shape memory composite structures to recover the initial shape also after severe damaging (i.e. after room temperature compression). Compressing the panel at a temperature higher than the foam resin glass transition temperature minimally affects composite stiffness.

Nd-YAG Laser Sculpture of WC Punches for Micro-Sheet Forming

A Q-switched Nd-YAG laser was used to sculpt a WC micro-punch in a sintered preform. A cylindrical punch was obtained with a nominal diameter of 400 μm and 80 μm in height. Laser machined surface was characterized both qualitatively and quantitatively by means of scanning surface topography instrument. A 20 μm thick aluminum sheet was micro-punched using a testing machine as a drive and a gasket material for support. The gasket followed the micro-punched disk during all the shearing process, collapsing under the punching load. This simple forming process was defined to reduce the micro-part distortion and to avoid the fabrication of a micro-die. Finally, optical microscopy showed that the punched part had a flat surface in the centre and some anomalies at the edges where the punch melted zones were reproduced.