Correlation Between the Structure and Compressive Property of PMMA Microcellular Foams Fabricated by Supercritical CO2 Foaming Method

The role of pore size and mechanical properties on the accumulation, retention and distribution of F98 glioblastoma cells in macroporous hydrogels

Glioblastoma (GBM) accounts for half of all central nervous system tumors. Once the tumor is removed, many GBM cells remain present near the surgical cavity and infiltrate the brain up to a distance of 20-30 mm, resulting in recurrence a few months later. GBM remains incurable due to the limited efficiency of current treatments, a result of the blood-brain barrier and sensitivity of healthy brain tissues to chemotherapy and radiation. A new therapeutic paradigm under development to treat GBM is to attract and accumulate GBM cells in a cancer cell trap inserted in the surgical cavity after tumor resection. In this work, porous gels were prepared using porous polylactide molds obtained from melt-processed co-continuous polymer blends of polystyrene and polylactide, with an average pore size ranging from 5 μm to over 500 μm. In order to efficiently accumulate and retain GBM brain cancer cells within a macroporous sodium alginate-based hydrogel trap, the pores must have an average diameter superior to 100 μm, with the best results obtained at 225 μm. In that case, the accumulation and retention of F98 GBM cells were more homogeneous, especially when functionalized with RGD adhesion peptides. At an alginate concentration of 1% w/v, the compression modulus reaches 15 kPa, close to the average value of 1-2 kPa reported for brain tissues, while adhesion and retention were also superior compared to 2% w/v gels. Overall, 1% w/v gels with 225 μm pores functionalized with the RGD peptide display the best performances.

Valorization of Agricultural Rice Straw as a Sustainable Feedstock for Rigid Polyurethane/Polyisocyanurate Foam Production

Agricultural rice straw (RS), often discarded as waste in farmlands, represents a vast and underutilized resource. This study explores the valorization of RS as a potential feedstock for rigid polyurethane/polyisocyanurate foam (RPUF) production. The process begins with the liquefaction of RS to create an RS-based polyol, which is then used in a modified foam formulation to prepare RPUFs. The resulting RPUF samples were comprehensively characterized according to their physical, mechanical, and thermal properties. The results demonstrated that up to 50% by weight of petroleum-based polyol can be substituted with RS-based polyol to produce a highly functional RPUF. The obtained foams exhibited a notably low apparent density of 18-24 kg/m3, exceptional thermal conductivity ranging from 0.031-0.041 W/m-K, and a high compressive strength exceeding 250 kPa. This study underlines the potential of the undervalued agricultural RS as a green alternative to petroleum-based feedstocks to produce a high-value RPUF. Additionally, the findings contribute to the sustainable utilization of abundant agricultural waste while offering an eco-friendly option for various applications, including construction materials and insulation.

Preparation of Bio-Foam Material from Steam-Exploded Corn Straw by In Situ Esterification Modification

In this work, we engineered a corn-straw-based bio-foam material under the inspiration of the intrinsic morphology of the corn stem. The explosion pretreatment was applied to obtain a fibrillated cellulose starting material rich in lignin. The in situ esterification of cellulose was adopted to improve the cross-linking network of the as-developed foam bio-material. The esterification of lignin was observed in the same procedure, which provides a better cross-linking interaction. The esterified corn-straw-derived bio-foam material showed excellent elastic resilience performance with an elastic recovery ratio of 83% and an elastic modulus of 20 kPa. Meanwhile, with surface modification by hexachlorocyclotriphosphazene-functionalized lignin as the flame retardant (Lig-HCCP), the as-obtained bio-foam material demonstrated quite a good flame retardancy (with 27.3% of the LOI), as well as a heat insulation property. The corn-straw-derived bio-foam material is prospected to be a potential substitution packaging material for widely used petroleum-derived products. This work provides a new value-added application of the abundant agricultural straw biomass resources.

Production and Application of Polymer Foams Employing Supercritical Carbon Dioxide

Polymeric foams have characteristics that make them attractive for different applications. However, some foaming methods rely on chemicals that are not environmentally friendly. One of the possibilities to tackle the environmental issue is to utilize supercritical carbon dioxide ScCO2 since it is a “green” solvent, thus facilitating a sustainable method of producing foams. ScCO2 is nontoxic, chemically inert, and soluble in molten plastic. It can act as a plasticizer, decreasing the viscosity of polymers according to temperature and pressure. Most foam processes can benefit from ScCO2 since the methods rely on nucleation, growth, and expansion mechanisms. Process considerations such as pretreatment, temperature, pressure, pressure drop, and diffusion time are relevant parameters for foaming. Other variables such as additives, fillers, and chain extenders also play a role in the foaming process. This review highlights the morphology, performance, and features of the foam produced with ScCO2, considering relevant aspects of replacing or introducing a novel foam. Recent findings related to foaming assisted by ScCO2 and how processing parameters influence the foam product are addressed. In addition, we discuss possible applications where foams have significant benefits. This review shows the recent progress and possibilities of ScCO2 in processing polymer foams.

Comprehensive Enhancement of Prepolymer-Based Flexible Polyurethane Foams' Performance by Introduction of Cost-Effective Waste-Based Ground Tire Rubber Particles

Material innovations in polyurethane (PU) foams should ideally combine performance enhancement, environmental impact limitation, and cost reduction. These goals can be achieved by applying recycled or waste-based materials without broader industrial applications, implicating their low price. Herein, from 5 to 20 parts by weight of ground tire rubber (GTR) particles originated from the recycling of postconsumer car tires were incorporated into a flexible foamed PU matrix as a cost-effective waste-based filler. A two-step prepolymer method of foams manufacturing was applied to maximize the potential of applied formulation changes. The impact of the GTR content on the foams' processing, chemical, and cellular structure, as well as static and dynamic mechanical properties, thermal stability, sound suppression ability, and thermal insulation performance, was investigated. The introduction of GTR caused a beneficial reduction in the average cell diameter, from 263.1 µm to 144.8-188.5 µm, implicating a 1.0-4.3% decrease in the thermal conductivity coefficient. Moreover, due to the excellent mechanical performance of the car tires-the primary application of GTR-the tensile performance of the foams was enhanced despite the disruption of the cellular structure resulting from the competitiveness between the hydroxyl groups of the applied polyols and on the surface of the GTR particles. The tensile strength and elongation at break were increased by 10 and 8% for 20 parts by weight GTR addition. Generally, the presented work indicates that GTR can be efficiently applied as a filler for flexible PU foams, which could simultaneously enhance their performance, reduce costs, and limit environmental impacts due to the application of waste-based material.

A Review on Mechanical Models for Cellular Media: Investigation on Material Characterization and Numerical Simulation

Cellular media materials are used for automobiles, aircrafts, energy-efficient buildings, transportation, and other fields due to their light weight, designability, and good impact resistance. To devise a buffer structure reasonably and avoid resource and economic loss, it is necessary to completely comprehend the constitutive relationship of the buffer structure. This paper introduces the progress on research of the mechanical properties characterization, constitutive equations, and numerical simulation of porous structures. Currently, various methods can be used to construct cellular media mechanical models including simplified phenomenological constitutive models, homogenization algorithm models, single cell models, and multi-cell models. This paper reviews current key mechanical models for cellular media, attempting to track their evolution from their inception to their latest development. These models are categorized in terms of their mechanical modeling methods. This paper focuses on the importance of constitutive relationships and microstructure models in studying mechanical properties and optimizing structural design. The key issues concerning this topic and future directions for research are also discussed.

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.

Structural Changes and Their Implications in Foamed Flexible Polyurethane Composites Filled with Rapeseed Oil-Treated Ground Tire Rubber

The utilization of post-consumer car tires is an essential issue from an ecological and economic point of view. One of the simplest and the least harmful methods is their material recycling resulting in ground tire rubber (GTR), which can be further applied as fillers for polymer-based composites. Nevertheless, insufficient interfacial interactions implicate the necessity of GTR modification before introduction into polymer matrices. In this study, we investigated the influence of rapeseed oil-assisted thermo-mechanical treatment of GTR using a reactive extrusion process on the processing, structure, and performance of flexible polyurethane/GTR composite foams. Applied modifications affected the processing of polyurethane systems. They caused a noticeable reduction in the average cell size of foams, which was attributed to the potential nucleating activity of solid particles and changes in surface tension caused by the presence of oil. Such an effect was especially pronounced for the waste rapeseed oil, which resulted in the highest content of closed cells. Structural changes caused by GTR modification implicated the enhancement of foams’ strength. Mechanical performance was significantly affected by the applied modifications due to the changes in glass transition temperature. Moreover, the incorporation of waste GTR particles into the polyurethane matrix noticeably improved its thermal stability.

Microstructure and Properties of Glass Fiber-Reinforced Polyamide/Nylon Microcellular Foamed Composites

The automobile and aerospace industries require lightweight and high-strength structural parts. Nylon-based microcellular foamed composites have the characteristics of high strength and the advantages of being lightweight as well as having a low production cost and high product dimensional accuracy. In this work, the glass fiber-reinforced nylon foams were prepared through microcellular injection molding with supercritical fluid as the blowing agent. The tensile strength and weight loss ratio of microcellular foaming composites with various injection rates, temperatures, and volumes were investigated through orthogonal experiments. Moreover, the correlations between dielectric constant and injection volume were also studied. The results showed that the "slow-fast" injection rate, increased temperature, and injection volume were beneficial to improving the tensile strength and strength/weight ratios. Meanwhile, the dielectric constant can be decreased by building the microcellular structure in nylon, which is associated with the weight loss ratio extent closely.