Foaming Ratio Research Articles

Preparing Polypropylene Auxetic Foam by a One‐Pot CO2Foaming Process

At present, the direct preparation of polymer foam with negative Poisson ratio (auxetic foam) from nonpolar polymer resins is still a challenge. Herein, a one‐pot CO2foaming method is established to directly prepare closed‐cell auxetic foams with different cellular structures (bimodal cell structure and homogeneous cell structure) from polypropylene (PP) resin by introducing hydrophilic additives (NaCl) into PP and regulating foaming conditions. The effects of foaming temperature, saturation time, and size of added NaCl on Poisson's ratio are studied. The comparison with PP/talc composites shows that the presence of NaCl plays a crucial role in the formation of the negative Poisson ratio of foam. Furthermore, the regulation of the size of negative Poisson ratio is achieved by controlling the amount of NaCl in PP/NaCl composites. This study has important reference significance for the preparation of nonpolar polymer auxetic foams.

A novel systematic multi-objective optimization to achieve high-efficiency and low-emission waste polymeric foam gasification using response surface methodology and TOPSIS method

Gasification is one of the most important thermochemical processes to convert a solid fuel to energy carriers of a gaseous product called syngas. This process has been well addressed in the literature for biomass and several valuable researches have been performed on plastic waste gasification. However, it is the first effort for a systematic comprehensive investigation and multi-objective optimization of gasification process for waste polymeric foams using response surface methodology and TOPSIS (Technique for Order Performance by Similarity to Ideal Solution) approach. Air and steam waste rigid polyurethane foam gasifications were modeled using coupled method of Gibbs minimization free energy and Lagrange method of undetermined multipliers, and then, validated. Effects of key features consisting gasification temperature and moisture content in both air and steam gasification types and equivalence ratio in air and steam to waste foam ratio in steam types were thoroughly studied on gas composition and energy and hydrogen efficiencies. Analysis of variance was employed for recognizing the most effective parameters on air and steam gasification performances. The results revealed that hydrogen and energy efficiencies of air gasification at multi-objective optimum conditions were 42.68 % and 89.58 %, respectively, and these values were 64.02 % and 96.52 % for steam gasification type. Air gasification of waste rigid polyurethane foam produced 3.13 g of CO2 emission at optimum state; however, its value was 10.02 g for steam gasification type. A multi-criteria decision analysis based on TOPSIS method was utilized for selecting the best gasification type in different scenarios and the findings indicated that air gasification had better performance compared to steam type due to its low emissions.

Aqueous polyvinyl alcohol solution foaming at different molecular masses

Objectives. Investigation of aqueous polyvinyl alcohol (PVA) foaming process and the influence of its water solution structure, when possessed of different molecular weights and concentrations, on foaming multiplicity.Methods. Solution foaming analysis was performed on the data of dynamic light scattering obtained on the Zetasizer Nano particle analyzer.Results. In this work, the foaming ability and foaming multiplicity of aqueous PVA solutions (as a main component for obtaining special-purpose foams) have been studied. It is shown that PVA solutions in water are colloidal dispersed systems consisting of different-sized associates (from 4.8 to 68.1 nm), depending on the molecular weight of PVA. Dependencies of aqueous PVA solution foaming multiplicities on the concentration, molecular weight, and solution temperature were given. Optimal values of concentration and molecular PVA weight, as well as optimal foaming process conditions from aqueous PVA solutions, were established.Conclusions. Increasing PVA concentrations in aqueous solutions cause foaming multiplicity to decrease for all molecular weights by 1.5 times, and increasing molecular weight increases foaming multiplicity by 2 times. The foaming ratio of aqueous PVA solutions with different concentrations and molecular weights (depending on a solution temperature characterized by a maximum of 30 °C) is associated with decreased viscosity and surface tension.

Modification of Asphalt Binder with Waste Expanded Polystyrene (EPS) Foam

Waste polymers are widely used in asphalt modification, especially, in order to reduce their detrimental effect on the environment. This study discusses the usability of waste expanded polystyrene (EPS) foam in asphalt modification. In this respect, the EPS foam, which produces waste in both production and use stages, was mixed with bitumen by weight at the ratios of 2%, 4%, 6%, and 8%, and dry modification method was employed. The penetration, ductility, softening point, flash point, and specific gravity values of virgin bitumen were compared with waste EPS foam modified bitumen. The comparison was made by both graphical and statistical methods. A strong correlation between the physical properties of modified asphalt and the ratio of EPS foam was observed. A drop was observed in penetration and ductility values. Besides, it was found by statistical analyses that 2% of the increase in the additive ratio is not sufficient to make a significant difference in the physical properties of bitumen, therefore, the increase should be at least 4%. Overall, it is concluded that EPS foam additive can be used in bitumen modification for hot regions where low penetration is required.

Head Roll-Tilt Subjective Visual Vertical Test in the Diagnosis of Persistent Postural-Perceptual Dizziness.

Objective:To examine the validity of head roll-tilt subjective visual vertical (HT-SVV) in diagnosing persistent postural-perceptual dizziness (PPPD).Study Design:Retrospective review.Setting:Tertiary referral center.Patients:Sixty-one patients with PPPD, 10 with unilateral vestibular hypofunction (UVH), and 11 with psychogenic dizziness (PD), showing chronic vestibular symptoms for >3 months.Interventions:Head-tilt perception gain (HTPG, i.e., mean perceptual gain [perceived/actual tilt angle]) during right or left head tilt of approximately 30° (HT-SVV) and conventional head-upright SVV (UP-SVV) were measured. Bithermal caloric testing, cervical and ocular vestibular-evoked myogenic potentials (cVEMP and oVEMP), and posturography were conducted.Main Outcome Measures:Multiple comparisons were performed for the HT-SVV and other vestibular tests among the disease groups. A receiver operating characteristic curve was created to predict PPPD using HTPG.Results:HTPG was significantly greater in the PPPD group than in the UVH and PD groups. There were no significant differences in UP-SVV, cVEMP, oVEMP, and posturography (foam ratio and Romberg ratio on foam) among the disease groups, while the UVH group had the highest canal paresis compared to the other two groups. The area under the curve of the receiver operating characteristic curve for predicting PPPD was 0.764, and the HTPG value of 1.202 had a specificity of 95.2% for diagnosing PPPD.Conclusions:While conventional vestibular tests including UP-SVV, VEMPs, and posturography did not show abnormalities in PPPD, high HTPG in the HT-SVV test, an excessive perception of head tilt, can be a specific marker for discriminating PPPD from other chronic vestibular diseases.

Preparation of Microcellular Foams by Supercritical Carbon Dioxide: A Case Study of Thermoplastic Polyurethane 70A

In this study, a case study to produce microcellular foam of a commercial thermoplastic polyurethane (TPU) through the supercritical carbon dioxide (CO2) foaming process is presented. To explore the feasibility of TPU in medical device and biomedical application, a soft TPU with Shore hardness value of 70A was selected as the model compound. The effects of saturation temperature and saturation pressure ranging from 90 to 140 °C and 90 to 110 bar on the expansion ratio, cell size and cell density of the TPU foam were compared and discussed. Regarding the expansion ratio, the effect of saturation temperature was considerable and an intermediate saturation temperature of 100 °C was favorable to produce TPU microcellular foam with a high expansion ratio. On the other hand, the mean pore size and cell density of TPU foam can be efficiently manipulated by adjusting the saturation pressure. A high saturation pressure was beneficial to obtain TPU foam with small mean pore size and high cell density. This case study shows that the expansion ratio of TPU microcellular foam could be designed as high as 4.4. The cell size and cell density could be controlled within 12–40 μm and 5.0 × 107–1.3 × 109 cells/cm3, respectively.

Performance of Polyvinyl Alcohol/Bagasse Fibre Foamed Composites as Cushion Packaging Materials

This work was designed to determine the mechanical properties and static cushioning performance of polyvinyl alcohol (PVA)/bagasse fibre foam composites with a multiple-factor experiment. Scanning electron microscopy (SEM) analysis and static cushioning tests were performed on the foamed composites and the results were compared with those of commonly used expanded polystyrene (EPS). The results were as follows: the materials had a mainly open cell structure, and bagasse fibre had good compatibility with PVA foam. With increasing PVA content, the mechanical properties of the system improved. The mechanical properties and static cushioning properties of the foam composite almost approached those of EPS. In addition, a small amount of sodium tetraborate obviously regulated the foaming ratio of foamed composites. With increasing sodium tetraborate content, the mechanical properties of foamed composites were enhanced. The yield strength and Young’s modulus of the material prepared by reducing the water content to 80.19 wt% were too high and not suitable for cushioned packaging of light and fragile products.

Based on auxetic foam: A novel type of seismic metamaterial for Lamb waves

Seismic metamaterial (SM) has lately received significant attention in the field of vibration isolation and damping due to its wave manipulation and bandgap properties. However, the limitations of unit cell size and the difference of the material parameters of each component have made it challenging to generate an ultra-low frequency bandgap. In order to overcome this challenge, a novel type of 2D SM composed of auxetic foam and steel is proposed to attenuate seismic waves at ultra-low frequencies. Firstly, the band structure of the SMs and the vibration modes of the upper and lower bounds of the first complete bandgap are calculated and analyzed by using the finite element method, and the mechanism of the bandgap generation is clarified. The transmission spectrum under the Lamb wave incident on the SM is investigated. It is validated that Lamb waves have a good attenuation effect in the frequency range below 10 Hz. Secondly, a parametric study of the SM with auxetic foam-coated hollow steel columns is carried out. The numerical results show that the shape and height of the unit cell, the elastic modulus, density and Poisson’s ratio of the auxetic foam play important roles in the formation of the bandgap. Finally, the numerical simulation verifies that adding through holes in the matrix which reduces the equivalent mass density of the matrix could widen the bandgap and enhance the effective attenuation of seismic waves. Based on theoretical model and combined with the exceptional material characteristics of auxetic foam, the focus of the study is to achieve a wide bandgap coverage for the seismic peak spectrum of 2 Hz which causes the principal damage of surface buildings.

A Graphical Interpretation Technique to Evaluate Strength and Stability of Foam in Porous Media Based on Mobile-Trapped Foam Ratio

A Graphical Interpretation Technique to Evaluate Strength and Stability of Foam in Porous Media Based on Mobile-Trapped Foam Ratio

Influence of the Poisson's ratio on the efficiency of viscoelastic damping treatments

An efficient way of mitigating noise and vibration is to embed viscoelastic patches into the host structure. Viscoelastic properties are of significant importance in determining the performance of the passive damping treatment. The behaviour of homogeneous isotropic materials is described by two elastic constants (generally the Young modulus and the Poisson ratio, or the shear and bulk moduli), which are frequency- and temperature-dependent in the case of viscoelastic materials. In practice, the Poisson's ratio is often considered as independent of temperature and frequency. One goal of this work is to numerically evaluate the validity of this assumption and its limitations (frequency range, thickness of the viscoelastic layer). To this end, a thermo-mechanical characterization of a viscoelastic material is carried out by dynamic measurements of the complex shear and bulk moduli, allowing the indirect measurement of the frequency- and temperature-dependent Poisson's ratio. Moreover, the measurements of the Poisson's ratio (direct or indirect) can lead to considerable uncertainties. For instance, large discrepancies have been observed when characterizing the Poisson's ratio of polymer foams. Another goal of this work is to investigate the influence of those uncertainties on the dynamic response of a damped structure.

Mechanical Properties Analysis on a Novel Negative Poisson's Ratio Voronoi Foam‐Filled Corrugated Tube Under Impact Loading

A novel negative Poisson's ratio (NPR) foam‐filled corrugated tube, made up of a corrugated tube and NPR isotropic foam core, is established by the finite element method. The 3D NPR isotropic foam core is achieved by using the triaxial compression method on a cubic Voronoi model, which is created based on the Voronoi tessellation technique. The triaxial compression ratio is defined as η. The Poisson's ratio of Voronoi foam decreases sharply and then increases gradually with an increasing η. A minimum Poisson's ratio, −0.076, is obtained when η = 0.2. Moreover, the Voronoi foam‐filled corrugated tube with minimum Poisson's ratio foam core exhibits the highest energy absorption capacity, which is 10.8% higher than that of the Voronoi foam‐filled corrugated tubes with uncompressed foam core.

Effect of acetylated cellulose nanocrystals on solid‐state foaming behaviors of chain‐extended poly(butylene adipate‐co‐terephthalate)

AbstractFully biodegradable chain‐extended poly(butylene adipate‐co‐terephthalate) (CPBAT)/acetylated cellulose nanocrystals (ACNCs) nanocomposites were prepared by the melt compounding process. The dispersibility of CNCs in deionized water was improved through the surface acetylation, which was observed by atomic force microscope and transmission electron microscope. The chain extender was added to the PBAT matrix to improve the melt strength and viscoelasticity of PBAT. The ACNC nanoparticles which served as bionano‐reinforcing fillers were introduced into CPBAT to further improve the crystallization behaviors and rheological properties of CPBAT/ACNCs nanocomposites. Finally, the CPBAT/ACNCs nanocomposite foams were prepared via batch supercritical CO2foaming process. The cell structure and morphology of various CPBAT/ACNCs foams were investigated by scanning electron microscope. It was found that the introduction of ACNC nanoparticles led to a reduction of cell size, an increase in cell density and in the uniform cell distribution owing to the heterogeneous cell nucleation effect of ACNCs. Meanwhile, the volume expansion ratio (VER) of CPBAT foams reached to 9.21 times, the highest VER reported for PBAT foam in the current literature. Also, the thermal conductive properties of nanocomposites and foams also were studied by a laser thermal conductivity analyzer.

Preparation and characteristics of sustained-release microcapsule-based inhibitory foam with high foaming ratio

To reduce the effect of conventional halogen salt inhibitors on the performance of foaming solutions and extend the fire prevention and suppression time of water-based foams, herein, microencapsulation technology has been used in the preparation of inhibitors. Calcium chloride sustained-release microcapsule with ethyl cellulose as wall material was successfully prepared by solvent evaporation method. The microcapsule complied with Higuchi release kinetics equation. The experiment showed that the foaming solution added with 20 g microcapsules had almost the same foaming capacity as the pure foaming solution, and the foaming multiple could reach 14 times, and the half-life of the foam could reach 123 min. The foaming multiple was much higher than the foaming multiple of calcium chloride foam (0 times). Compared with calcium chloride foam, the new type of foam prepared in this paper has better inhibition ability, and the inhibition rate is as high as 83.8%. Ethyl cellulose used as wall material in microcapsules can soften covered coal in the process of heating up, isolate coal and oxygen, and thus inhibit coal and oxygen binding. The experimental results show that the temperature of T1 (84.6℃), T3 (338.2℃) and the cross-point temperatures of the coal sample treated with the new type of foam are higher than that of the coal sample treated with the calcium chloride foam. At the same time, the new type of foam can significantly inhibit the oxidation rate of methyl and methylene. It can be seen that the microencapsulation technology can improve the ability of the inhibitor foam.

Characteristics of Microcellular Foamed Ceramic Urethane.

Ceramics are non-metallic inorganic materials fabricated from natural or high-purity raw materials through heating and cooling processes. Urethane is a three-dimensional plastic with both elasticity and chemical resistance; moreover, it is used as a rubber substitute. The use of both materials in various applications is gradually increasing. However, as ceramics and urethane have distinctly different properties, this prompted questions regarding the properties of a material that is fabricated using both materials. Therefore, we studied the characteristics of a composite material fabricated through physical foaming using a batch process. The process was conducted with gas saturation, foaming, cooling, and curing. When a specimen of 2 mm thickness was saturated in 5 MPa of CO2 for 2 h, the solubility was 6.43%; when foaming was carried out at a temperature of 150 °C in boiled glycerin, the foaming ratio, cell size, cell density, and void fraction were found to be 43.62%, 24.40 µm, 9.1 × 10⁷ cells/cm2, and 22.11%, respectively. Furthermore, the volume increased by 102.96%, color changed from dark to light gray, hardness decreased by 24%, thermal diffusivity increased by 0.046 mm2/s at 175 °C, and friction coefficient decreased to 0.203. Thus, the microcellular foamed ceramic urethane exhibits a larger volume, lighter weight, and improved thermal conductivity and friction coefficient.

Solid-State Foaming Process Optimization for the Production of Shape Memory Polymer Composite Foam

This research examined the optimization of the sustainable manufacturing process for polyester-based polymers/Fe3O4 nanocomposite foaming. The foamed structure was achieved by using a solid-state foaming process, where the prepared foams were tested in order to ascertain the optimum foaming parameters with the highest foaming ratios and the lowest foaming densities. The foaming parameters used in this research were the polymer type, nanoparticle percentage, packing pressure, holding time, foaming temperature, and foaming time. Two levels were selected for each factor, and a Taguchi plan was designed to determine the number of experiments required to reach a conclusion. Further characterization techniques, namely, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) were used with the original samples to gain a better understanding of their structure and chemical composition. The data analysis showed that regardless of the parameters used, a high foaming ratio resulted in a low density. The introduction of nanoparticles (NPs) to the polymer structure resulted in higher foaming ratios. This increment in foaming ratio was noticeable on Corro-Coat PE Series 7® (CC) polymer more than Jotun Super Durable 2903® (JSD). The optimum parameters to prepare the highest foaming ratios were as follows: CC polymer with 2% NPs, compressed under a pressure of 10 K lbs. for a 3 min holding time and foamed at 290 °C for 15 min in the oven.

Optimization of Actuation Load and Shape Recovery Speed of Polyester-Based/Fe3O4 Composite Foams.

In this research, polyester-based polymers/Fe3O4 nanocomposite foams were prepared in order to study their performance; namely shape recovery speed and actuation load. A foamed structure was obtained through a solid-state foaming process, which was studied and optimized in previous research. The optimum foaming parameters were applied in an attempt to achieve the highest foaming ratio possible. A Taguchi Map was then designed to determine the number of experiments to be conducted. The experimental results showed that the maximum actuation load obtained was 3.35 N, while optimal (fastest) recovery speed was 6.36 mm/min. Furthermore, temperature had no impact on the actuation load as long as a temperature above the Tg was applied. Moreover, the addition of nanoparticles reduced shape recovery speed due to discontinuity within the polymer matrix.

Effect of Compressive Strain Rate on Auxetic Foam

Auxetic foams have previously been shown to have benefits including higher indentation resistance than their conventional counterparts, due to their negative Poisson’s ratio, making them better at resisting penetration by concentrated loads. The Poisson’s ratio and Young’s modulus of auxetic open cell foams have rarely been measured at the high compressive strain rates typical during impacts of energy absorbing material in sporting protective equipment. Auxetic closed cell foams are less common than their open cell counterparts, and only their quasi-static characteristics have been previously reported. It is, therefore, unclear how the Poisson’s ratio of auxetic foam, and associated benefits such as increased indentation resistance shown at low strain rates, would transfer to the high strain rates expected under impact. The aim of this study was to measure the effect of strain rate on the stiffness and Poisson’s ratio of auxetic and conventional foam. Auxetic open cell and closed cell polymer foams were fabricated, then compression tested to ~80% strain at applied rates up to 200 s−1, with Poisson’s ratios obtained from optical full-field strain mapping. Open cell foam quasi-static Poisson’s ratios ranged from −2.0 to 0.4, with a narrower range of −0.1 to 0.3 for closed cell foam. Poisson’s ratios of auxetic foams approximately halved in magnitude between the minimum and maximum strain rates. Open cell foam quasi-static Young’s moduli were between 0.02 and 0.09 MPa, whereas closed cell foams Young’s moduli were ~1 MPa, which is like foam in protective equipment. The Young’s moduli of the auxetic foams approximately doubled at the highest applied strain rate of 200 s−1.

Reversing Poisson’s Ratio of Biomass Foam to Be Negative to Achieve Super Mechanical Properties via Viscoelastic Compression

We proposed a strategy to transform a cell shape from convex to concave via viscoelastic compression in order to reverse the Poisson’s ratio of biomass foam to be negative and improve its propertie...

Retraction: A versatile strategy for alternately arranging the foam ratio layers of multilayer graphene/thermoplastic polyurethane composite foams towards lightweight and broadband electromagnetic wave absorption

Retraction of ‘A versatile strategy for alternately arranging the foam ratio layers of multilayer graphene/thermoplastic polyurethane composite foams towards lightweight and broadband electromagnetic wave absorption’ by Chaozhi Wang et al., RSC Adv., 2019, 9, 23843–23855, DOI: 10.1039/C9RA04405A.

Effect of steam conversion on the cellular structure, Young’s modulus and negative Poisson’s ratio of closed-cell foam

Open-cell auxetic foams have shown potential for use in sporting and other protective equipment. Previous conversion methods for auxetic closed-cell foam used a bespoke pressure vessel. This work expands upon a recent method, using steam absorption followed by cooling and condensation, to change the cell shape of closed-cell foam to impart a negative Poisson’s ratio. Aiming to present a simple, repeatable conversion method, foam samples (20 × 10 × 100 mm) floating in water-filled (∼20 °C), covered ceramic containers (300 × 200 × 100 mm) were heated in an oven at 105 °C for between 1 and 6.5 hrs. Based on the results for these smaller samples, a larger sample of foam (30 × 100 × 100 mm) was also converted, with a steaming time of 8 hrs. The final volume ratio (original/final volume) increased with heating time, up to a maximum of 4.6. The amount and angle of re-entrant (inward-folding) cell walls increased with the final volume ratio as cells contracted further, as evidenced by micro-computed tomography. Poisson’s ratios, measured using digital image correlation, were as low as −0.3 in tension and −1.1 in compression. The tensile Young’s modulus increased from ∼2 up to ∼6 MPa with the final volume ratio and the compressive Young’s modulus reduced from ∼1.5 MPa for low values of the final volume ratio between one and three and then remained close to 1.5 MPa.