Analysis of Reactive Injection Compression Molding by Numerical Simulations and Experiments

Injection compression molding is an injection molding process with the addition of a compression stage after the injection. This process is useful for the injection molding of precision parts. A stable and controlled manufacturing process is needed to guarantee reliability of complex products, and usually process optimization is achieved by experimental and time consuming approaches. However, for being competitive a minimal market time is a very important requirement and computer simulations can help to optimize the process at the only expense of computational time. This paper reports and discusses for the first time the results of a 3D finite element simulation of reactive injection compression molding (RICM) by commercial software for the production of rubber diaphragms. In particular, the stages of mold filling dynamics and material curing are analyzed and the results verified with experimental tests. To get an accurate representation of the process, the rheological behavior, thermal properties, and kinetic behavior during curing of the real rubber compound were described by mathematical models. A differential scanning calorimeter (DSC) and a capillary rheometer are employed to characterize the rubber material in order to achieve an appropriate curing reaction and viscosity models, respectively. The computations are found to be in good agreement with the experimental results, indicating that reliable information on material viscosity and curing kinetics can play a key role in making well-founded predictions and avoiding trial and error methods

Developments in dynamic testing of rubber compounds: assessment of non-linear effects

Abstract In the present work, a test method to characterize the dynamic behaviour of rubber compounds by electrodynamic shaker (ES) in the frequency range of 10–1000 Hz was developed. Data of dynamic moduli of two different rubber compounds were determined through the analysis of the transmissibility of a suitably designed test system. The results were compared with those of dynamic moduli master curves obtained through frequency–temperature reduction of data measured by a commercial dynamic mechanical thermal analyser (DMTA), by scanning temperature at various frequencies in the range 0.3–30 Hz. Very good agreement of the data obtained by the two different aproaches were found, in spite of the different range of frequency explored by the two instruments, ES and DMTA, respectively. For one of the material examined, non-linear effects at low strain amplitudes were investigated by the two experimental methods considered

Polysaccharides on gelatin-based hydrogels differently affect chondrogenic differentiation of human mesenchymal stromal cells

Selection of feasible hybrid-hydrogels for best chondrogenic differentiation of human mesenchymal stromal cells (hMSCs) represents an important challenge in cartilage regeneration. In this study, three-dimensional hybrid hydrogels obtained by chemical crosslinking of poly (ethylene glycol) diglycidyl ether (PEGDGE), gelatin (G) without or with chitosan (Ch) or dextran (Dx) polysaccharides were developed. The hydrogels, namely G-PEG, G-PEG-Ch and G-PEG-Dx, were prepared with an innovative, versatile and cell-friendly technique that involves two preparation steps specifically chosen to increase the degree of crosslinking and the physical-mechanical stability of the product: a first homogeneous phase reaction followed by directional freezing, freeze-drying and post-curing. Chondrogenic differentiation of human bone marrow mesenchymal stromal cells (hBM-MSC) was tested on these hydrogels to ascertain whether the presence of different polysaccharides could favor the formation of the native cartilage structure. We demonstrated that the hydrogels exhibited an open pore porous morphology with high interconnectivity and the incorporation of Ch and Dx into the G-PEG common backbone determined a slightly reduced stiffness compared to that of G-PEG hydrogels. We demonstrated that G-PEG-Dx showed a significant increase of its anisotropic characteristic and G-PEG-Ch exhibited higher and faster stress relaxation behavior than the other hydrogels. These characteristics were associated to absence of chondrogenic differentiation on G-PEG-Dx scaffold and good chondrogenic differentiation on G-PEG and G-PEG-Ch. Furthermore, G-PEG-Ch induced the minor collagen proteins and the formation of collagen fibrils with a diameter like native cartilage. This study demonstrated that both anisotropic and stress relaxation characteristics of the hybrid hydrogels were important features directly influencing the chondrogenic differentiation potentiality of hBM-MSC

Anticamera smontabile per l’isolamento di patogeni in ambienti di strutture sanitarie

È descritta una struttura componibile, e smontabile, posizionabile tra due ambienti di una struttura ospedaliera per realizzare una zona cuscinetto. La struttura è provvista di pareti accoppiabili, che insieme definiscono e delimitano un’anticamera per la vestizione e la svestizione del personale sanitario. La struttura permette di erigere in poco tempo un’anticamera altrimenti non prevista nella struttura ospedaliera, ogniqualvolta si presenta la necessità di disporre di anticamere per la vestizione/svestizione del personale sanitario anche in quei reparti sprovvisti in origine di anticamere adibite a questo scopo, ad esempio reparti per la lunga degenza, oppure per la dialisi. La struttura secondo la presente invenzione è utilizzabile e riutilizzabile nel tempo anche in assenza di una pandemia, o prima che un virus inizi a diffondersi, per formare il personale sanitario non abituato a trattare con patogeni che richiedono una sanificazione completa di vestiti ed equipaggiamenti

Application of T-peel testing for the evaluation of the tearnig resistance of natural rubber / layered silicate nanocomposites

In the present work, the applicability of a fracture mechanics approach based on T-Peel tearing methodology to determine the tearing energy, Gc, of natural rubber/organo-modified montmorillonite nanocomposites was investigated. T-peel tests were performed by loading in tension the arms of the test-pieces at constant cross-head rates and the tearing energy was evaluated from the peel force. The effect of specimen geometry, with particular reference to thickness, on the tearing energy value was analysed. The peel-Test were use to characterize the fracture behaviour of NR organoclay samples with varying the clay content. For each sample the rate dependence of the peelresistance was also explored. A qualitative fracture surface analysis was performed on the tested samples