Foamed Research Articles

Fabrication of Triblock Elastomer Foams and Gelation Studies for Oil Spill Remediation.

Polymeric foamed materials are among the most widely utilized technologies for oil spill accidents and releases of oil-contaminated wastewater oil due to their porosity to absorb and separate oil/water effectively. However, a major limitation of traditional polymeric foams is their reliance on an ad/absorption mechanism as the sole method of oil capture, leading to potential oil leakage once their saturation point is exceeded. Tri-block polymer styrene-ethylene-butylene-styrene (SEBS) is a fascinating absorbent material that can bypass this limitation by both capturing oil and providing a sealing mechanism via gelation to prevent oil leakage due to its unique chemical structure. SEBS foams are produced via simultaneous crosslinking and foaming that results in an impressive expansion ratio of up to 15.2 with over 93% porosity. Most importantly, the SEBS foams show great potential as oil absorbents in spill remediation, demonstrating rapid and efficient oil absorption coupled with superhydrophobic properties. Moreover, the unique interaction between the oil and SEBS enables the formation of a physical gel, acting as an effective barrier against oil leakage. These findings indicate the potential for commercializing SEBS foam as a viable option for geotextiles to mitigate oil spill concerns from infrastructures.

Determinants of Temperature Development during Dental Implant Surgery

Mechanical and thermal trauma during implant surgery may be reasons for initial peri-implant bone loss. Temperature development during drilling and implant insertion were quantified in this series of in vitro and animal experiments. Polyurethane foam material mimicking different classes of alveolar bone was used as a model material for simulating implant surgery. Using thermocouples, temperature development was determined in the model material at depths of 3 mm and 10 mm during site preparation and implant insertion. Additionally, an infrared camera allowed for measuring drill temperatures both in vitro and as part of an animal trial using an intraoral minipig model. Drill diameter and repeated usage of drills did not have a major effect on temperature generation. The addition of a diamond-like carbon coating, bone density, predrilling, and irrigation heavily affected intraosseous temperatures. In vivo, applying regular drill protocols, an intraosseous temperature rise of approximately 3 °K was determined. Implant geometry as well as the amount of undersizing of an osteotomy governed heat generation during implant insertion. Drill protocols and the amount of undersizing of an implant osteotomy constitute parameters by which clinicians can limit trauma during implant surgery.

E-VTOL Aircraft Assembling and Programming Using the Mission Planner Program

This study presents the design and programming of a modern new class of radio-controlled electric vertical takeoff and landing (E-VTOL) aircraft using lightweight polylactic acid (LW-PLA). Utilizing the LW-PLA cork foam material is crucial to lowering the aircraft's total weight and improving its mechanical characteristics at the same time. The type of LW-PLA utilized in this study was specific, and its fabrication process was made possible by a Creality Cr 10s pro-3D printer. In this study, a lightweight polylactic acid was used to demonstrate the design of an electric vertical takeoff and landing (E-VTOL) aircraft (LW-PLA). It is essential to use the LW-PLA cork foam material to reduce the overall weight of the airplane and enhance its mechanical properties simultaneously. The particular kind of LW-PLA used in this model was manufactured using a Creality Cr 10s pro-3D printer. Solid Work version 2021 was utilized in the development of the mathematical model. Since radio-controlled aircraft capable of vertical takeoff and landing can carry out both tasks, the goal of this study is to find the best way to utilize the features that both airplanes and drones have in common. Consequently, the suggested model represents a sophisticated enhancement of the aerodynamic characteristics of the many types of radio control aircraft that are capable of performing vertical takeoffs and landings.

Functional LSMO foams for magneto-caloric applications

The ferromagnetic La1-x\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{1-x}$$\\end{document}Srx\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{x}$$\\end{document}MnO3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_3$$\\end{document} (LSMO) manganites are ideal materials for magneto-caloric applications due to their high Curie temperature. Here, we prepare open-cell, porous LSMO foams starting from a commercial polyurethane (PU) foam and commercial LSMO powder with x=0.3.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$x = 0.3.$$\\end{document} The cut PU foams are then covered by a slurry of LSMO powder mixed with PVA and water, and then, the foams are subjected to a heat-treatment with two steps at 600 ∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\circ$$\\end{document}C (burn-off organic material) and 1200 ∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\circ$$\\end{document}C (sintering/compacting). The resulting ceramic LSMO foams are then characterized by X-ray, SEM, electron backscatter diffraction (EBSD) orientation mapping and magnetic measurements. The foam sample consists of randomly-oriented LSMO grains with an average grain size of 188 nm, being distinctly smaller than bulk samples of the same composition, but considerably larger than LSMO nanowires prepared by electrospinning. The magnetic data reveal a high Curie temperature like the bulk samples, and an entropy change, -ΔSM\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-\\Delta S_{\ ext{M}}$$\\end{document} slightly higher than that of the bulk samples, which points to a strong influence of the LSMO grain size. Thus, the resulting LSMO foam material is well suited for magneto-caloric applications at room temperature.

Preparation and energy absorption of flexible polyurethane foam with hollow glass microsphere

This paper presents the preparation of a partially open-cell and partially closed-cell flexible polyurethane foam material (flex-PUF), which exhibits improved cushioning performance compared to conventional protective materials. Hollow Glass Microspheres (HGM) were used as a filling material to enhance the compressibility of the material. In order to investigate the effects of HGM on the multi-impact protection and vibration damping performance of flex-PUF with different thicknesses, flex-PUF samples filled with varying volume fractions of HGM were subjected to multi-impact testing and dynamic viscoelasticity experiments. The destructive mechanism of HGM under impact was observed using scanning electron microscopy (SEM). The experimental results revealed that, under the same impact energy conditions, filling flex-PUF with HGM reduced the maximum impact displacement while enhancing energy absorption, although at the expense of cushioning performance. As the number of impact increases, the stiffness of flex-PUF decreased. In the vibration experiments, as the frequency increased, the proportion of flex-PUF’s viscous damping energy dissipation decreases.

Upcycling Humins via Esterification Reactions of Hydroxyl Groups: From Functional Powders to PLA Foams and Compatibilized Blends.

The valorization of humins side streams from bio-refineries holds significant economic and sustainability potential. One plausible strategy involves using them as building blocks to create new materials. However, humins pose conceptual challenges in their natural state due to their high viscosity, processing difficulties, and temperature sensitivity. This article presents a synthetic strategy for modifying humins properties to make them thermally stable and processable. Employing a sequence of esterification reactions and varying the reagent steric length, we showcase the selective transformation of humins into thermally-stable fine powders and low-viscosity liquids. We extend this approach by reacting humins with polyesters such as polylactic acids and polycaprolactone. In particular, we detail a one-pot single-step synthesis of micro-phase separated compatibilized blends of polylactic acid and humins capped with the polylactic acid arms. Processed via solution-casting, the obtained materials behave as high-strength thermoplastic elastomers having uniform foam morphologies and material characteristics superior to the pure polylactic acid. By varying the content of D-enantiomers, we demonstrate an additional possibility of manipulating the cellular structures of the foams. Finally, we provide a solution to product circularity by reporting a dissolution recycling method.

A Simulation-Free Replacement Solution for Radiation Therapy Immobilization Devices Using Computer Numerical Control (CNC) -Milled Polystyrene Molds

In radiation therapy (RT), if an immobilization device is lost or damaged, the patient may need to be brought back for resimulation, device fabrication, and treatment planning, causing additional imaging radiation exposure, inconvenience, cost, and delay. We describe a simulation-free method for replacing lost or damaged RT immobilization devices. Replacement immobilization devices were fabricated using existing simulation scans as design templates by computer numerical control (CNC) milling of molds made from extruded polystyrene (XPS). XPS material attenuation and bolusing properties were evaluated, a standard workflow was established, and 12 patients were treated. Setup reproducibility was analyzed postfacto using Dice similarity coefficient (DSC) and mean distance to agreement (MDA) calculations comparing onboard treatment imaging with computed tomography (CT) simulations. Results showed that XPS foam material had less dosimetric impact (attenuation and bolusing) than materials used for our standard immobilization devices. The average direct cost to produce each replacement mold was $242.17, compared with over $2000 for standard resimulation. Hands-on time to manufacture was 86.3 minutes, whereas molds were delivered in as little as 4 hours and mostly within 24 hours, compared with a week or more required for standard resimulation. Each mold was optically scanned after production and was measured to be within 2-mm tolerance (pointwise displacement) of design input. All patients were successfully treated using the CNC-milled foam mold replacements, and pretreatment imaging verified satisfactory clinical setup reproduction for each case. The external body contours from the setup cone beam CT and the original CT simulation with matching superior-inferior extent were compared by calculating the DSC and MDA. DSC average was 0.966 (SD, 0.011), and MDA average was 2.694 mm (SD, 0.986). CNC milling of XPS foam is a quicker and more convenient solution than traditional resimulation for replacing lost or damaged RT immobilization devices. Satisfactory patient immobilization, low dosimetric impact compared with standard immobilization devices, and strong correlation of onboard contours with CT simulations are shown. We share our clinical experience, workflow, and manufacturing guide to help other clinicians who may want to adopt this solution.

Cushioning Performance of a Novel Polyurethane Foam Material Applied in Fragile Packaging

Cushioning Performance of a Novel Polyurethane Foam Material Applied in Fragile Packaging

Improving the mechanical performance of foam material based on bioinspiration

Inspired from foam-like biological construction, artificial foam, which is typically an ultralight and multifunctional material, has been developed for engineering applications. However, the presence of constructed porous materials leads to an extremely weakened load-bearing capacity. Therefore, we propose encasing the outside of bare foam with high-strength fabric to enhance the foam’s mechanical properties. A series of three-point bending tests are conducted to examine the enhancement in bending resistance generated by a high-strength composite fabric. A comparison between bare and encased foams shows that encasing bare foam with high-strength fabric significantly increases the foam’s load-bearing capacity, especially in terms of its bending resistance while retaining its intrinsic lightweight advantages.

Preparation and properties of PP/SEBS foam materials

In this study, styrene-ethylene-butene-styrene block copolymer (SEBS) is blended with polypropylene (PP) to improve the melt strength of PP. Azodicarbonamide (AC) is used as a chemical foaming agent to prepare PP foaming materials with good mechanical properties by moulding foaming. The melt strength of the material, the content of the nucleating agent and the concentration of the foaming agent will affect the foaming effect of the material. Orthogonal optimization experiments are designed for these three factors to explore the best ratio of foaming materials. The results show that when PP:SEBS = 85:15, the addition amount of nano-SiO2 is 3%, and the content of AC foaming agent is 5%, the cell structure of the foaming material is the best. The cell structure is observed by SEM,the average cell diameter is reduced to 45.73 μm, and the cell density is increased to 4.12 × 106 cells cm−3. The apparent density of the material is measured to be 0.62 g cm−3, which is 32% lower than that of pure PP (0.91 g·cm−3). The tensile strength of PP/SEBS foamed composites is lower than that of pure PP and pure PP foamed materials, but its elongation at break is 124.3% higher than that of pure PP, and 238.8% higher than that of pure PP foamed materials. The bending strength of PP/SEBS foamed material is lower than that of pure PP and pure PP foamed material. The impact strength of PP/SEBS is only 8.4 % lower than that of pure PP, and 60.8 % higher than that of pure PP foamed material.

Large-scale and facile fabrication of phenyl-containing silicone foam materials with lightweight, wide-temperature flexibility and tunable pore structure for exceptional thermal insulation

Silicone foam materials with unique inorganic/organic molecular networks and porous structures are widely used in many emerging fields from aerospace to new energy fields. However, current silicone foam materials still show some limitations, such as the relatively high-density values of >200 mg cm−3, complex fabricating process and difficulty in tailoring pore structure. Herein, we report a large-scale and facile fabricating strategy to prepare phenyl-containing silicone foam materials (PhSiRF) with ultra-lightweight feature, tunable pore structure, and excellent wide-temperature mechanical flexibility. Interestingly, the presence of phenyl groups onto the Si–O–Si backbone tailors the chemical foaming rate probably due to the steric hindrance effect, thus producing tunable pore size distributions in the range of 180–500 μm. Typically, the PhSiRF with 50 % phenyl groups not only shows a very low density of ∼100 mg cm−3, superior to previous silicone foams and composites, but also exhibits wide-temperature flexibility (stable compressive strain of 80 % from −90 to 210 °C) and excellent thermal insulation performance, which outperforms those of conventional polymer foams including polyurethane, polyethylene and melamine foams. Based on the structure observation and theory analysis, the influence of different pore morphological structures on the thermal insulation performance is discussed and demonstrated. Clearly, this work provides a new yet simple method for developing high-performance silicone rubber foam materials for promising thermal insulation applications.

Assessment of properties of bamboo fiber and EPDM reinforced polypropylene microcellular foam composites

Plant fiber reinforced composite has broad industrial application prospects, and has the trend of gradually replacing traditional materials, but there are also problems such as not obvious advantages of lightweight and poor toughness. In this paper, alkali modified bamboo fiber reinforced polypropylene (BF/PP) composite was prepared by supercritical foam injection molding. The effect of fiber content on the formability of BF/PP composite was studied. Furthermore, the strength and toughness of BF/PP composites were balanced by blending Ethylene Propylene Diene Monomer (EPDM) elastomers with different content under the optimal fiber content of 20 %. The physical and mechanical properties of BF/PP composites were studied. The results showed that the addition of bamboo fiber improved the structure of the cell and significantly enhanced the mechanical properties of the composite. The addition of elastomer EPDM effectively alleviates the problem of poor toughness and brittle fracture of bamboo fiber composites. The foam material density decreased by about 15 %, the addition of bamboo fiber brought the maximum 57.37 % tensile strength and 79.96 % flexural strength improvement to the polypropylene matrix. When the EPDM content was 10 %, the foaming effect of the material was the best, and the impact toughness increased by 34.42 % compared with pure polypropylene. This study expands the application prospect of the bamboo fiber reinforced polypropylene microcellular foam materials.

On thermal and strain-rate dependences of polymethacrylimide (PMI) foam materials

Polymethacrylimide (PMI) foams exhibit great potentials in engineering applications thanks to its outstanding lightweight and superior mechanical properties. However, the temperature and loading rate can greatly affect its mechanical behaviors, which are the key factors in analysis and design of the PMI foam structures for practical applications. Unfortunately, there is lack of fundamental data and constitutive models available concerning the elastic-plastic properties of the PMI foam in various stress states at different ambient temperatures and different strain rates. Therefore, this study aims to fill this knowledge gap by generating basic experimental data and providing a generic modeling solution for PMI foam materials and structures. To better reflect the actual service conditions in practice, different stress states are considered under different temperatures and strain rates. The cyclic loads are applied to characterize the actual mechanical responses of the PMI foam where the initial and subsequent yield surfaces were calibrated and analyzed. Following the experimental results, the elasticity, plasticity, viscosity and damage of the PMI foam are investigated thoroughly, especially for the initial and subsequent yielding behaviors. Further, the thermal and strain rate dependent constitutive models are established and calibrated based on the in-house experimental data for finite element (FE) modeling. A novel damage model is proposed to replicate the phenomenon of the stiffness degradation in compression. It is found that accurate predictions on the mechanical responses of PMI foam can be achieved under different temperatures and different strain rates. This study is anticipated to provide fundamental experimental data and effective constitutive models of PMI foams for real engineering applications, such as lightweight design of sandwich structures under some harsh conditions.

A numerical investigation of energy dissipation mechanism of visco-hyperelastic bimaterials subjected to low-velocity impact

Impact protection equipment typically relies on the material failure mechanism and is frequently discarded after the impact. A promising alternative emerges utilizing a foam-infilled lattice bimaterial with shape recovery trait and customizable impact protection capability. This study employs a numerical approach to elucidate the energy dissipation mechanism exhibited by the bimaterial under low-velocity impact condition. The experiment-based inverse method is used to characterize visco-hyperelastic models for two base materials. The investigation reveals that the interaction between the two base materials significantly amplifies the foam’s energy dissipation capability, resulting in an overall higher energy dissipation for the bimaterial. Besides, the study establishes a close correlation between the bimaterial’s effective viscoelastic properties and the enhancement in energy dissipation. Furthermore, the numerical design of experiments (DOE) analysis of base material properties indicates that there is an optimal region for selecting the critical foam material constants for a significant improvement of bimaterial energy dissipation. The results reveal that the combination effect of material interaction and material viscoelastic properties constitutes the fundamental elements of bimaterial energy dissipation mechanism. The insight derived from this study can inform the future design and material selection of a more complicated bimaterial across a wide range of impact protection applications.

An innovative approach for the passive cooling of batteries: An empirical investigation of copper deposition on polyurethane foam for the enhancement of phase change material

A proof-of-concept utilising Copper-Plated Polyurethane Foam (CPPF) and Phase Change Material (PCM) for passive thermal management of lithium-ion batteries is demonstrated in this study. The aim of this research is to assess the effectiveness of CPPF when utilised as a constituent substance in PCM/Foam composites. Six distinct configurations of PCM/Foam composites are presented in this work using 10-pore-per-inch foam. A total of four deposition foam samples were produced. Of these, three were created by gradually increasing the immersion time in an electroless copper plating solution. For the fourth sample, an electroless plating technique was utilised for 80 min, followed by an electroplating procedure to deposit an additional layer of copper. The evaluation entails examining each plated sample in comparison to a copper foam that is commercially available with a purity level of 99.99 %. The findings reveal that the electroless-plated specimens exhibit improved effectiveness after being subjected to a prolonged plating period of 80 min. The electroplated sample exhibited the greatest degree of effectiveness, as evidenced by a 64.4 % reduction in battery cell surface temperature(10.98 °C), which is almost identical to the 64.5 % decrease in temperature (11.03 °C) observed with commercial foam but coupled with 88.1 % decrease in mass. The results suggest that the CPPF-PCM composites offer effective passive cooling properties for batteries.

Analyzing the Thermal Characteristics of Three Lining Materials for Plantar Orthotics.

The choice of materials for covering plantar orthoses or wearable insoles is often based on their hardness, breathability, and moisture absorption capacity, although more due to professional preference than clear scientific criteria. An analysis of the thermal response to the use of these materials would provide information about their behavior; hence, the objective of this study was to assess the temperature of three lining materials with different characteristics. The temperature of three materials for covering plantar orthoses was analyzed in a sample of 36 subjects (15 men and 21 women, aged 24.6 ± 8.2 years, mass 67.1 ± 13.6 kg, and height 1.7 ± 0.09 m). Temperature was measured before and after 3 h of use in clinical activities, using a polyethylene foam copolymer (PE), ethylene vinyl acetate (EVA), and PE-EVA copolymer foam insole with the use of a FLIR E60BX thermal camera. In the PE copolymer (material 1), temperature increases between 1.07 and 1.85 °C were found after activity, with these differences being statistically significant in all regions of interest (p < 0.001), except for the first toe (0.36 °C, p = 0.170). In the EVA foam (material 2) and the expansive foam of the PE-EVA copolymer (material 3), the temperatures were also significantly higher in all analyzed areas (p < 0.001), ranging between 1.49 and 2.73 °C for EVA and 0.58 and 2.16 °C for PE-EVA. The PE copolymer experienced lower overall overheating, and the area of the fifth metatarsal head underwent the greatest temperature increase, regardless of the material analyzed. PE foam lining materials, with lower density or an open-cell structure, would be preferred for controlling temperature rise in the lining/footbed interface and providing better thermal comfort for users. The area of the first toe was found to be the least overheated, while the fifth metatarsal head increased the most in temperature. This should be considered in the design of new wearables to avoid excessive temperatures due to the lining materials.

Effects of carboxymethyl cellulose concentration on mechanical, viscoelastic properties, and thermal properties of starch/plant fiber foaming tableware materials with foam structure

In this study, a novel bio-based composite of starch/plant fiber foaming tableware material was prepared by the hot-pressing foaming method. The influence of the content of carboxymethyl cellulos (CMC) as a new type of film-forming agent filler on the properties of foam materials was systematically investigated. The results showed that the foam material with 10 wt% CMC had excellent cell morphology and uniform cell size (the average cell size reached the minimum value of 465.7 μm), relatively high porosity (57.01%), and excellent thermal insulation properties (thermal conductivity: 0.0541 W/m·K). The tensile strength of foam increased from 4.289 MPa for 0 wt% CMC to 5.714 MPa for 10 wt% CMC loading. Similarly, the flexural strength also increased from 11.609 MPa to 15.719 MPa for the foam material with 10 wt% CMC. The thermal stability and viscoelastic properties of the foam material reached the highest after adding 10 wt% CMC. In addition, the increase of CMC content is beneficial to improve the oil resistance and biodegradability of the material. The research shows that CMC is an effective filler to improve the properties of starch/plant fiber foaming tableware materials, which can greatly promote the development of bio-based polymer foam materials.

Forefront Research of Foaming Strategies on Biodegradable Polymers and Their Composites by Thermal or Melt-Based Processing Technologies: Advances and Perspectives.

The last few decades have witnessed significant advances in the development of polymeric-based foam materials. These materials find several practical applications in our daily lives due to their characteristic properties such as low density, thermal insulation, and porosity, which are important in packaging, in building construction, and in biomedical applications, respectively. The first foams with practical applications used polymeric materials of petrochemical origin. However, due to growing environmental concerns, considerable efforts have been made to replace some of these materials with biodegradable polymers. Foam processing has evolved greatly in recent years due to improvements in existing techniques, such as the use of supercritical fluids in extrusion foaming and foam injection moulding, as well as the advent or adaptation of existing techniques to produce foams, as in the case of the combination between additive manufacturing and foam technology. The use of supercritical CO2 is especially advantageous in the production of porous structures for biomedical applications, as CO2 is chemically inert and non-toxic; in addition, it allows for an easy tailoring of the pore structure through processing conditions. Biodegradable polymeric materials, despite their enormous advantages over petroleum-based materials, present some difficulties regarding their potential use in foaming, such as poor melt strength, slow crystallization rate, poor processability, low service temperature, low toughness, and high brittleness, which limits their field of application. Several strategies were developed to improve the melt strength, including the change in monomer composition and the use of chemical modifiers and chain extenders to extend the chain length or create a branched molecular structure, to increase the molecular weight and the viscosity of the polymer. The use of additives or fillers is also commonly used, as fillers can improve crystallization kinetics by acting as crystal-nucleating agents. Alternatively, biodegradable polymers can be blended with other biodegradable polymers to combine certain properties and to counteract certain limitations. This work therefore aims to provide the latest advances regarding the foaming of biodegradable polymers. It covers the main foaming techniques and their advances and reviews the uses of biodegradable polymers in foaming, focusing on the chemical changes of polymers that improve their foaming ability. Finally, the challenges as well as the main opportunities presented reinforce the market potential of the biodegradable polymer foam materials.

Study on Dynamic Mechanical Properties of Sandwich Beam with Stepwise Gradient Polymethacrylimide (PMI) Foam Core under Low-Velocity Impact.

Different PMI foam materials of 52, 110, and 200 kg/m3 were used to design stepwise gradient cores to improve the impact resistance of the sandwich beam. The stepwise gradient core consists of three layers arranged in positive gradient, negative gradient, and sandwich-core (e.g., 200/52/200). These sandwich beams were subjected to the impact of a steel projectile under impact momentum of 10 to 20 kg·m/s, corresponding to impact energy in the range of 12.5 to 50 J. During the test, the impact force was recorded by an accelerometer, and the different failure modes were also obtained. Subsequently, the influence of the layer arrangement on the energy absorption and load transfer mechanism between the different layers was analyzed. The results showed that the top layer with a large density can improve the impact force, but the middle/bottom layer with a low density promoted specific energy absorption. Thus, based on these two points, the negative gradient core (200/110/52) had an excellent specific energy absorption because it can transfer and expand the area to bear the load layer by layer, which improved the energy absorption in each layer. Combined with the failure modes, the load transfer and deformation mechanisms between the layers were also discussed. The present work provided a valuable method to design an efficient lightweight sandwich structure in the protection field.

Facile Preparation of Lightweight Natural Rubber Nanocomposite Foams with High Wear Resistance.

The light weight and excellent mechanical properties of rubber foam means that it is widely applied in the aerospace, automobile, and military industries. However, its poor wear resistance contributes directly to a short service life and a waste of resources. Therefore, the design and development of high-wear-resistance rubber foam are of great importance. In this work, some nanoclay/rubber composite foams were prepared by blending NR/EPDM with different kinds of nanoclays containing layered double hydroxide (LDH), montmorillonite (MMT), and attapulgite (ATP) to indicate the effects of the kinds of nanoclays on the wear resistance and mechanical properties of nanoclay/rubber composite foams. The kinds of nanoclay/rubber composite foams were investigated by Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction. The results showed that nanoclay has heterogeneous nucleation in composite foamed materials. The wear resistance of the composite foam materials with added nanoclay was significantly improved, and the MMT of the lamellar structure (increased by 43.35%) and LDH (increased by 38.57%) were significantly higher than the ATP of the rod-like structure (increased by 13.04%). The improvement in the wear resistance of the matrix was even higher. Compared with other foams, the wear resistance of the OMMT-NR/EPDM foam (increased by 58.89%) with a lamellar structure had the best wear resistance. Due to the increase in the lamellar spacing of the modified OMMT, the exfoliation of worn rubber molecular chains has little effect on the adjacent molecular chains, which prevents the occurrence of crimp wear and further improves the wear resistance of composite foaming materials. Therefore, this work lays the foundation for the manufacturing of rubber foams for wear-resistant applications.