Greener Nanocomposite Polyurethane Foam Based on Sustainable Polyol and Natural Fillers: Investigation of Chemico-Physical and Mechanical Properties

Nowadays, the chemical industry is looking for sustainable chemicals to synthesize nanocomposite bio-based polyurethane foams, PUs, with the aim to replace the conventional petrochemical precursors. Some possibilities to increase the environmental sustainability in the synthesis of nanocomposite PUs include the use of chemicals and additives derived from renewable sources (such as vegetable oils or biomass wastes), which comprise increasingly wider base raw materials. Generally, sustainable PUs exhibit chemico-physical, mechanical and functional properties, which are not comparable with those of PUs produced from petrochemical precursors. In order to enhance the performances, as well as the bio-based aspect, the addition in the polyurethane formulation of renewable or natural fillers can be considered. Among these, walnut shells and cellulose are very popular wood-based waste, and due to their chemical composition, carbohydrate, protein and/or fatty acid, can be used as reactive fillers in the synthesis of Pus. Diatomite, as a natural inorganic nanoporous filler, can also be evaluated to improve mechanical and thermal insulation properties of rigid PUs. In this respect, sustainable nanocomposite rigid PU foams are synthesized by using a cardanol-based Mannich polyol, MDI (Methylene diphenyl isocyanate) as an isocyanate source, catalysts and surfactant to regulate the polymerization and blowing reactions, H2O as a sustainable blowing agent and a suitable amount (5 wt%) of ultramilled walnut shell, cellulose and diatomite as filler. The effect of these fillers on the chemico-physical, morphological, mechanical and functional performances on PU foams has been analyze

Insight into bubble nucleation at high-pressure drop rate

This paper presents insight in bubble nucleation in polymer foaming with physical blowing agent using a batch foaming technique. In our experiments the bubble nucleation is triggered by a sudden pressure drop that causes the supersaturation in the polymer gas solution. In fact, the pressure drop rate is an important process variable since it plays a role in both bubble nucleation and growth. Herein, we investigated very high pressure drop rates, and confirmed the great importance of the pressure drop rate as foaming process variable. The results show that the number of nucleated bubbles increases of one order of magnitude and the foam density is reduced if the pressure drop rate is increased from 50 to 500 MPa/s. Interestingly, the number of nucleated bubble increases linearly in a bi-logarithmic scale as function of pressure drop rate at all the investigated temperatures. Moreover, in the current paper, it is discussed how talc used as nucleating agent plays a role in cooperation with pressure drop rate on bubble nucleation at different foaming temperatures

Graded biomimetic osteochondral scaffold prepared via CO2 foaming and micronized NaCl leaching

This study reports for the first time the design and fabrication of an osteochondral biomimetic poly(E-caprolactone) (PCL) and nano-metric hydroxyapatite (HA) scaffold for tissue engineering via CO2 foaming and micronized NaCl particles leaching. The control of the NaCl concentration, in the range from 30 to 80 wt.%, and the foaming temperature, in the range from 25 to 40 degrees C, allowed for the design and fabrication of PCL foams with different combinations of morphology, porosity and mean pore size. Furthermore, by creating concentration gradients of NaCl micro-particles and HA nano-crystals, we fabricated a novel graded biomimetic PCL-HA scaffold with biochemical and biophysical properties suitable for osteochondral tissue engineering

Polystyrene Foaming at High Pressure Drop Rates

We studied the foaming of polystyrene with CO2 as the physical blowing agent at large pressure drop rates (PDRs) and at different foaming temperatures, with a novel batch foaming apparatus, capable of reaching PDRs as high as 500 MPa/s (in the underlying literature, the maximum so far achieved is 100 MPa/s). Results show that, at each foaming temperature, the number of nucleated bubbles per unit initial volume (N) linearly increases with PDR in a bilogarithmic scale, with slopes increasing with the temperature. The effect of talc as the nucleating agent was also investigated. Furthermore, a phenomenological model was developed and utilized to predict N at PDRs not experimentally accessible. The approach was validated and a good agreement with the experimental data was obtained

Electrical Characterization and Modeling of a Gelatin/Graphene System

A gelatin/graphene composite has been analyzed by means of current density-voltage and the electrical impedance measurements. The DC electrical behavior has been interpreted in terms of an equivalent Thévenin model taking into account the open circuit voltage and the series resistance. A model based on the effect of the electrical double layer and on the diffusion of the charge carriers is used for the analysis of the experimental data, obtained in the frequency domain. The model reveals for any applied voltages a marked diffusion process at low frequencies. In particular, where the charge transfer mechanism is dominant, the time distribution of the reaction rates reveals that several multiple step reactions occur in the materials, especially at high values of the applied forward bias voltages

Effect of basalt fiber hybridization on the impact behavior under low impact velocity of glass/basalt woven fabric/epoxy resin composites

The low velocity impact behavior of E-glass/basalt reinforced hybrid laminates, manufactured by resin transfer moulding technique, was investigated. Specimens prepared with different stacking sequences were tested at three different impact energies, namely 5 J, 12.5 J and 25 J. Residual post-impact mechanical properties of the different configurations were characterized by quasi static four point bending tests. Post-impact flexural tests have been also monitored using acoustic emission in order to get further information on failure mechanisms. Results showed that basalt and hybrid laminates with an intercalated configuration exhibited higher impact energy absorption capacity than glass laminates, and enhanced damage tolerance capability. Conversely, the most favorable flexural behavior was shown by laminates with symmetrical sandwich-like configuration (E-glass fiber fabrics as core and basalt fiber fabrics as skins). © 2012 Elsevier Ltd. All rights reserved