Examinando por Materia "ESPUMAS"

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  • Artículo de Publicación Periódica
    Compressive behavior of rigid polyurethane foams nanostructured with bacterial nanocellulose at low and intermediate strain rates
    (2019-05) Chiacchiarelli, Leonel Matías; Cerrutti, Patricia; Flores-Johnson, Emmanuel A.
    "Nanocellulose reinforced foams are lightweight with improved mechanical properties; however, the strain-rate effect on their mechanical response is not yet fully understood. In this work, rigid polyurethane foams (PUFs) nanostructured with bacterial nanocellulose at 0.2 wt % (BNCF) and without it (PUF) are synthesized and subjected to compression tests at different strain rates. The BNC acts as a nucleation agent, reducing the cell size but maintaining a similar apparent density of 40.4 3.3 kg m −3 Both BNCF and PUF exhibit strain-rate effect on yield stress and densification strain. The BNCF exhibits localized progressive crushing and reduced friability, causing a remarkable recovery in the transverse direction. Numerical simulations show that functionally graded foams subjected to impact could be designed using different layers of PUF and BNCF to vary energy absorption and acceleration rate. The results presented herein warrant further research of the mechanical properties of nanostructured foams for impact applications."
  • Artículo de Publicación Periódica
    Highly functional lactic acid ring-opened soybean polyols applied to rigid polyurethane foams
    (2019-10) Herrán, Rodrigo; Amalvy, Javier Ignacio; Chiacchiarelli, Leonel Matías
    "We synthesized polyols with high hydroxyl functionalities (FOHs), between 9.0 and 12.6, and characterized them with differential scanning calorimetry, thermogravimetric analysis, and size exclusion chromatography after we parametrically studied the ring-opening reaction of epoxidized soybean oil with lactic acid (LA) as a function of the reaction temperature and lactic acid equivalent frac-tion (fLA). An increase of only 20C in the reaction temperature (from 80 to 100C) caused changes in the hydroxyl number (+17.8%), FOH (–25%), viscosity (–14.0%), and oligomeric content (–24.1%). fLA mostly affected the ring-opening yield, and only for fLA values above 0.4 was possible to achieve values higher than 80%. Rigid polyurethane foams (rPUFs) were synthesized and characterized with scanning electron microscopy, dynamic mechanical analysis (DMA), and compressive mechanical tests. rPUFs with a very high specific compres-sive strength (7.8 kPa kg–1 m3) were synthesized solely with biobased soybean oil. DMA revealed a compromised relationship between the specific compressive strength and its temperature dependence. To increase the first one, the most relevant method was to increase FOH. Instead, to increase the latter one, the OH number had to be maximized."
  • Artículo de Publicación Periódica
    In-situ thermal aging of biobased and conventional rigid polyurethane foams nanostructured with bacterial nanocellulose
    (2021-11-02) Diaz, Tomás Joaquin; Cerrutti, Patricia; Chiacchiarelli, Leonel Matías
    "The incorporation of nanofillers and the use of biobased polyols might have a deleterious effect on the aging performance of rigid polyurethane foams (RPUFs) applied in the insulation and marine industries. To study this, RPUFs obtained from petroleum based (RPUF) and castor oil (RPUFRIC) polyols were nanostructured with bacterial nanocellulose (BNC) up to 0.3 wt%. Water immersion experiments revealed that the normalized water absorption (NWA) at the steady state was not affected by lower BNC contents (<0.2 wt%). Higher BNC contents caused a complex effect on post-cure and foaming, generating cell size expansion as well as shrinkage. In-situ DMA aging analysis revealed that the specific storage modulus (E'sp) under flexural conditions of the RPUFRIC and RPUF decreased by a maximum amount of 7.27% and 6.19%, respectively. The effect of BNC on the E'sp was negligible, expect for the case of the RPUF, where higher BNC concentrations (>0.2 wt%) caused a decrease of up to 13.69%. The previous results reinforce the hypothesis that the incorporation of BNC in both conventional and biobased polyurethane systems do not cause significant changes on the aging performance of the resulting foams, provided that low BNC concentrations are employed."
  • Artículo de Publicación Periódica
    Nanostructured rigid polyurethane foams with improved specific thermo-mechanical properties using bacterial nanocellulose as a hard Segment
    (2021-01) Chiacchiarelli, Leonel Matías; Benavides, Sara; Armanasco, Franco; Cerrutti, Patricia
    "Bacterial nanocellulose (BNC) was used to synthesize rigid polyurethane foams (RPUFs) based on its reaction with the isocyanate precursor (ISO route) and also by using the conventional procedure (POL route). The results indicated that at only 0.1 wt. % of BNC, drastic improvements of specific elastic compressive modulus (+244.2 %) and strength (+77.5 %) were found. The reaction of BNC with the precursor was corroborated through the measurement of isocyanate number and the BNC caused a significant nucleation effect, decreasing the cell size up to 39.7%. DSC analysis revealed that the BNC had a strong effect on post-cure enthalpy, decreasing its value when the ISO route was implemented. DMA analysis revealed that the RPUFs developed using the ISO route proved to have an improved damping factor, regardless of BNC concentration. These results emphasize the importance of using the ISO route to achieve foamed nanocomposites with improved specific mechanical properties."