Papers by Keyword: Foams

Abstract: A pressure-induced autoclave foaming assisted by supercritical CO₂ of degradable polylactide (PLA) has been developed. A central composite design (CCD) of response surface methodology (RSM) is used to optimize three distinct process conditions: foaming temperature, pressure, and time. The mathematical model built for examining the effect of process conditions on the foam density and volume expansion ratio was verified and determined to be acceptable with an R-square value derived from the regression model of 0.930 and 0.934, respectively. The experimental and statistical results showed that of the three factors examined, the foaming pressure had the greatest impact on the density and volume expansion ratio of the PLA foams. The foaming temperature and time also had significant interaction impacts on both responses. It was observed that the following conditions are optimal for foaming of PLA, with a maximum VER of 10.107 and a minimum foam density of 0.123 g/cc: foaming temperature of 165.86 °C and foaming pressure of 152.4 bar for 2.38 h of foaming time.

Abstract: Rigid low-density closed-cell polyurethane (PU) foams are used primarily as a thermal insulation material. The foams have to possess a sufficient strength and stiffness in order to ensure their mechanical integrity and dimensional stability in service. The mechanical characteristics of foams are enhanced by adding cellulose nanofibers to the polyol system, which both modify the foaming process and act as a reinforcement of cell struts and walls. A model of composite foam strength is developed based on a regular unit cell and assuming the onset of strut failure as the foam fracture criterion. The load-bearing capacity of foam struts is estimated by the modified Fukuda and Chou model considering the orientation of nanofibers along the strut axis. The model developed is shown to provide a reasonably accurate prediction for the nanofiber loading effect on the strength of composite foams.

Abstract: Composite foams from PLA, natural rubber and modified coconut fibers was prepared employing a compression molding method, which is suitable for the fabrication of composites containing high fiber content. The results revealed that the incorporation of natural rubber into composite foams increases the compressive stress to 101.17 kN/m². Further, a 10% wt increase of modified coconut fiber added into composite foams resulted in an increase of compressive stress to 105.24 kN/m². The addition of modified coconut fibers in composite foams showed a slight decrease of the crystallization state, obtained by DSC results by about 1-3 oC. Thus, modified coconut fibers played a role as a nucleating agent. Moreover, the combination of modified coconut fibers in composite foams could lead to improved adhesion between the surface area of PLA matrix and the natural rubber phase.

Abstract: This research attempted to prepare composite foams of PLA/bagasse fiber with various fiber content at 0, 5, 10, 15, 20 wt% and a fixed foaming agent with extra added 2 wt% for all composites. The mechanical properties and morphology of neat PLA and PLA/bagasse fiber composite foams were investigated. The tensile strength showed that the highest fiber content of 7 wt% was 45.27 MPa, while neat PLA was 25.63 MPa. Impact strength showed a decreasing trend with increasing fiber content. SEM analysis was important to reveal the phase of fiber and matrix for support to discuss the results trend of PLA and composite properties.

Abstract: The investigation focused on the properties of composite foam obtained by a compression molding method. The results could clarify the interaction among PLA, silica nanoparticles and coconut fiber. The compressive properties, including the compressive force and modulus of composites, contained in coconut fiber were improved. The incorporation of silica nanoparticles was able to modify the compressive properties slightly, whereas the thermal properties were decreased explicitly. Hydrogen bonding between the carboxylic group of PLA and the silica bonded group affected the increment in mechanical properties of composites. However, the incorporation of coconut fibers in composites exhibited a rougher surface. In addition, beneficial distribution of silica nanoparticles and porosity in the nanocomposite foam, equivalent to neat PLA foam, could be obtained.

Abstract: Prussian Blue (PB, iron hexacyanoferrate) is an efficient micron-sized sorbent that can be encapsulated in a biopolymer matrix (chitin) for the treatment of Cs (I)-bearing solutions. Different conditionings have been designed for the treatment of Cs-contaminated effluents (with natural Cs (I) solutions, and with ¹³⁷Cs spiked solutions). The sorbents conditioned under the form of beads or discs can be used in columns while sponges can be used for the treatment of accidental discharge of effluents (contaminated water absorption by the sponge, metal ions sorption on the ion-exchanger, treated water removal by centrifugation, metal concentration in the composite material).

Abstract: The paper deals with crack bridging modelling in Bioglass® based scaffolds due the presence of a special polymer coating. This includes a careful identification of bridging mechanism by polymer ligaments, selection of a suitable bridging model and its implementation into the gradient elasticity model of crack.

Abstract: Epoxy-based shape memory (SM) foams have been produced by solid state foaming. According to this foaming technology, precursors are made by cold compaction of thermosetting powders. Subsequently, precursors foam by heating in an oven. In this study, the SM epoxy powder was mixed with multi-walled carbon nanotubes (MWCNTs) and graphene so as to produce SM composite foams. Two different filling contents were used (0.5 and 1 wt%). In order to study the effect of nano-fillers on SM properties of the epoxy foams, foam compressibility was measured at a temperature higher than the transition temperature of the SM epoxy foam (i.e. the glass transition temperature). Moreover, recovery load was measured after a 50% of memorized strain. Results show the positive effect of the fillers in functional and structural terms.

Abstract: This passage studied the synthetic process of melamine formaldehyde resin foam, analyzed the addition time of modifier of PVA, reaction temperature, PVA quantification and different degree of polymerization PVA. The results of experiments showed that it was better to add the PVA at 50min after the heating start. The temperature was 90-95°C. It showed that there was an obvious distinction of the foam with different degree of polymerization PVA. Decomposition temperature of the foam was 300°C and the residual of mass was about 80%.

Abstract: A series of experiments have been conducted to investigate the stress wave attenuation mechanism and the response of sandwich panels made of steel face sheets with foam cores under blast loading in close range. Quantitative results including shock wave pressure and face sheet deflection were obtained and the deformation/failure modes of specimens were identified and discussed systematically. Results show that the face sheet deflection was reduced by adopting a higher density core, however, performance of sandwich panels in blast wave attenuation degrade. Cell collapse type of the central region of the foam core is dominated by brittle crushing under close-range blasting loading. All front face sheets produce localized failure at the focal area and global deformation in the peripheral region.