Plastic Foam Research Articles

Organophosphate Esters and Polybrominated Diphenyl Ethers in Vehicle Dust: Concentrations, Sources, and Health Risk Assessment

Background: The primary flame retardants in vehicles, organophosphates (OPEs) and polybrominated diphenyl ethers (PBDEs), volatilize and accumulate in the enclosed vehicle environment, posing potential health risks. Amidst the rising number of vehicles, the scrutiny of persistent organic pollutants like OPEs and PBDEs in vehicles is increasing. This study investigates occupational and nonoccupational population exposure to specific OPEs (TnBP, TBOEP, TEHP, TCEP, TCiPP, TDCiPP, TPhP, EHDPP) and PBDEs (BDE-28, BDE-47, BDE-99, BDE-100, BDE-153, BDE-154, BDE-183, BDE-209) in vehicle dust. Methods: Data on OPEs and PBDEs in vehicle dust were sourced from PubMed and Web of Science. We applied PCA and PMF to identify pollutant sources and assessed health risks using the hazard index (HI) and carcinogenic risk (CR) methods. Monte Carlo simulations were conducted for uncertainty analysis, evaluating variable contributions to the results. Results: The predominant OPE in dust samples was TDCiPP (mean value: 4.34 × 104 ng g−1), and the main PBDE was BDE-209 (mean value: 1.52 × 104 ng g−1). Potential sources of OPEs in vehicle dust include polyvinyl chloride (PVC) upholstery, polyurethane foam (PUF) seats, electronics, carpet wear, hydraulic oil, and plastic wear in the brake system. PBDE sources likely include automotive parts, PVC upholstery, seats, carpets, and electronics. The 90th percentile HI and CR values for occupational and nonoccupational populations exposed to OPEs and PBDEs indicate that the noncarcinogenic and carcinogenic risks are relatively low. A sensitivity analysis showed that the pollutant concentration, time in the vehicle, exposure frequency, and duration significantly influence health risks. Conclusions: The health risks to both occupational and nonoccupational populations from exposure to OPEs and PBDEs in vehicle dust are relatively low.

The Flammability and Thermal Stability of Filling Epoxy Foam Plastics for Construction Purposes

An effective type of polymer heat-insulating material (foams) based on reactive oligomers is casting epoxy foams with high technological and operational parameters. However, polyepoxide foams are highly flammable, which significantly restrains their application in the construction industry. The aim of this work was to develop effective methods for reducing the flammability of filling epoxy foams. In order to achieve the objective, the following objectives were addressed: determining the influence of the chemical nature and content of additive and reactive bromine- and phosphorus-containing compounds on the thermal stability, flammability and operational properties of filling epoxy foams, and the development of polyepoxy foams of reduced flammability with high-quality physical and mechanical characteristics. When estimating the flammability of epoxy foams, we used both state-approved methods and the methods described in scientific and technical literature. The thermal properties of epoxy foams were studied with the help of multimodular thermoanalytical complex DuPont-9900. The data on the influence of the apparent density of foams and oxygen concentration in the oxidant flow on the flame propagation speed on the horizontal surface of polyepoxy foams are presented. It was revealed that the chemical nature of amine hardeners does not affect the thermal stability and flammability of epoxy foams. It was established that phosphate plasticizers are ineffective flame retardants of foamed epoxy resin, and the chemical structure of additive organobromic flame retardants insignificantly affects their efficiency. It was shown that microencapsulated flame retardants are inferior in flame retardant efficiency to additive flame retardants. It was found that effective flame retardants for casting polyepoxy foams are phosphorus-containing oligoether methacrylate and epoxidized waste from the production of tetrabromodiphenylpropane. The results of this research will form the basis for the production of an experimental industrial batch of samples of pouring epoxy foams of reduced flammability.

Super protective effect, ultra-high juice absorption and long-term antibacterial of Ag-2MI@Chitosan biodegradable sponge for fruit preservation and transportation

Plastic foam packaging is often used for the transportation to avoid mechanical damage to the fruit, but it lacks antibacterial properties, water absorption and is non-degradable, leading to fruit decay and safety risks as well as serious environmental pollution. Herein, Ag-2-Methylimidazole@Chitosan (Ag-2MI@CS) was successfully synthesized by in situ synthesis at normal temperature and pressure, and improved the antibacterial performance of Ag-2MI@CS by using green solvent ethanol to adjust the solvent polarity. The results showed that the long-lasting inhibitory performance of Ag-2MI@CS was significantly improved, the long-lasting antibacterial time has been extended from 24 h to 96 h. Furthermore, Ag-2MI@CS can significantly protect fruits and reduce the damage of fruits, even when falling from a height of 60 cm or under extreme transportation conditions. Besides, Ag-2MI@CS had extremely high absorption rates of water and fruit juice, 1447.69 % and 1356.59 %, respectively, which was conducive to absorbing water generated by respiration and juice generated by damage during transportation, so as to avoid the growth of bacteria caused by water and fruit juice. Ag-2MI@CS can achieve fruit preservation in both indoor static and transportation dynamic conditions. This study offers novel insights into new biodegradable packaging material in fruit transportation.

Fabrication of PBAT/lignin composite foam materials with excellent foaming performance and mechanical properties via grafting esterification and twin-screw melting free radical polymerization

As one of the mainstream biodegradable materials, poly(butylene adipate-co-terephthalate) (PBAT) foams offer a sustainable alternative to traditional plastic foams, effectively reducing environmental pollution. However, the high cost and poor mechanical performance of PBAT foams impede their practical application. Herein, the glycidyl methacrylate-grafted biomass lignin (GML) was used to produce a PBAT/GML composite foam with good foaming performance and mechanical properties at high lignin-filling amounts by twin-screw melting free radical polymerization and supercritical CO2 foaming process. The compatibility of GML in the PBAT matrix was improved due to the formation of ester bonds in modified lignin, endowing the PBAT/GML (PGML) composite foam with exceptional foaming performance. Additionally, the mechanical properties of PGML composite foam were remarkably enhanced due to the introduction of the abundant aromatic structures of GML and the construction of a stable covalent crosslinking network. The compressive strengths and compression modulus of the PGML foam were improved by 2.53 times and 2.47 times, while its bending strength and bending modulus were improved by 1.27 times and 3.92 times compared to the neat PBAT. This research affords a new strategy for developing low-cost biodegradable biomass PBAT/lignin composite foam materials with good foaming performance and mechanical properties.Graphical abstract

Investigation of ultrasonic propagation in high attenuation porous materials

This research examines ultrasonic wave propagation in air-saturated plastic foams used for noise pollution reduction, questioning the effectiveness of current models such as the well known Johnson-Champoux-Allard model at high frequencies. These foams present a challenge for existing models to accurately depict visco-inertial and thermal interactions within their pores. The study highlights the model's failure to align experimental results with theoretical predictions. It introduces novel parameters denoted as Σ and V for viscous effects, and Σ′ and V ′ for thermal effects, to improve the representation of fluid-sturcture interactions. These parameters suggest a more significant boundary layer effect within the pores than previously considered. This approach aims to provide additional physical context for the principles governing the behavior of highly attenuating porous media and to explore new avenues for material characterization that surpass the limitations of existing models.

Characteristics of natural corn starch/waste paper fiber composite foams treated by organic-inorganic hybrid hydrophobic coating technology.

With the growing global awareness of environmental protection, the demand for biodegradable materials to replace traditional plastic foam has become increasingly urgent. Starch-based foam, with its abundant availability, low cost, and biodegradability, has shown great potential as an alternative to plastic foam. However, its inherent high hydrophilicity and relatively low mechanical performance limit its widespread application. The aim of this study is to modify corn starch (NCS) and waste paper fiber (WPF) using citric acid (CA) and stearic acid (SA), and to develop an efficient hydrophobic coating through an organic-inorganic hybrid approach. This successfully resulted in the preparation of hydrophobic corn starch/waste paper fiber composite foam materials. Experimental results showed that the foam materials treated with a palmitic acid (PA)-modified nano-SiO2 coating (MCF@PA) exhibited excellent hydrophobic performance, with a water contact angle reaching as high as 138°, and a significant reduction in moisture absorption to 3.1%. In water immersion tests, the material maintained buoyancy and shape stability, demonstrating excellent self-cleaning properties. Additionally, the coating significantly enhanced the material's compressive strength, increasing by 90kPa, while also retaining thermal stability. However, the coating prepared by this method increased the material's hardness and reduced its biodegradability, which poses challenges for environmental sustainability. This study provides a new approach for preparing high-strength foam materials with excellent hydrophobicity and mechanical performance, paving an economical and efficient pathway for industrial production.

Spotting ignition of plastic foam by a fast-moving hot metal particle

Spotting ignition involves dynamic interaction between fuel bed and hot particles, but the scientific understanding of the ignition by a fast-moving hot particle is still limited. Herein, a hot steel particle with various horizontal velocities, temperatures, and sizes is shot to ignite vertically oriented low-density expandable polystyrene foam. A high-speed particle can directly get embedded into the foam to achieve flash-point, fire-point, or no ignition, while a low-speed particle bounces away from the foam without ignition. Results show that for a particle of 1150 °C, its minimum velocity for embedding is 12.00 m/s. Such a critical velocity for hot-particle embedded or ignition slightly decreases as particle temperature increases. Minimum ignition temperature of these high-speed particles is 200 °C higher than that of near-static or with a low free-fall velocity, due to the shorter residence time and insufficient to produce a flammable mixture. Moreover, when the particle is neither too slow to bounce away nor too fast to get embedded, it will be partially embedded on the sample surface to burnout the fuel, posing the biggest fire hazard. It deepens our knowledge of the complex interaction between hot moving particles and insulation foam to reduce spotting fire risk for building façade.

A flexible, thermal-insulating, and fire‐resistant bagasse-derived cellulose aerogel prepared via a refrigerator freezing combined ambient pressure drying technique

Cellulose aerogel is a most promising alternative to the plastic foam owing to its low thermal conductivity, eco-friendliness and renewability, which however suffers from the complex preparation process, poor mechanical property and flammability. Herein, we develop a flexible, thermal-insulating, and fire-resistant cellulose aerogel by a facile refrigerator freezing and ambient pressure drying process, using bagasse and inorganic minerals as the main raw materials. The as-obtained bagasse-derived cellulose (BC) aerogel exhibited a high porosity of 92 %, an acceptable thermal conductivity of 51.5 mW/(m·K) and an excellent compressible cyclability. Furthermore, an inorganic mineral-reinforced bagasse-derived cellulose aerogel (IMr-BC) with improved fire-resistant property was prepared via the same method. The inorganic minerals endowed the original BC aerogel with a superior flame retardancy, which was able to withstand a continuous burning of butane gun at 1300 °C for over 20 min, and its thermal insulation application could be extended to a temperature as high as 1100 °C. These aerogels prepared in this work are expected to be used for thermal management applications in harsh environments.

Discussion on the product model technology of XPS foam plastic

Discussion on the product model technology of XPS foam plastic

Foam density mapping via THz imaging

Plastic foams, near-ubiquitous in everyday life and industry, show properties that depend primarily on density. Density measurement, although straightforward in principle, is not always easy. As such, while several methods are available, plastic foam industry is not yet supported with a standard technique that effectively enables to control density maps. To overcome this issue, this paper proposes Terahertz (THz) time-of-flight imaging using normal reflection measurements as a fast, relatively cheap, contactless, non-destructive and non-dangerous way to map plastic foam density, based on the expected relationship between density and refractive index. The approach is demonstrated in the case of polypropylene foams. First, the relationship between the estimated effective refractive index and the polypropylene foam density is derived by characterizing a set of carefully crafted samples having uniform density in the range 70–900 kg/m3. The obtained calibration curve subtends a linear relationship between the density and the refractive index in the range of interest. This relationship is validated against a set of test samples, whose estimated average densities are consistent with the nominal ones, with an absolute error lower than 10 kg/m3 and a percentage error on the estimate of 5%. Exploiting the calibration curve, it is possible to build quantitative images depicting the spatial distribution of the sample density. THz images are able to reveal the non-uniform density distribution of some samples, which cannot be appreciated from visual inspection. Finally, the complex spatial density pattern of a graded foam sample is characterized and quantitatively compared with the density map obtained via X-ray microscopy. The comparison confirms that the proposed THz approach successfully determines the density pattern with an accuracy and a spatial scale variability compliant with those commonly required for plastic foam density estimate.

Biodegradable and Ultra-High Expansion Ratio PPC-P Foams Achieved by Microcellular Foaming Using CO2 as Blowing Agent.

Poly(propylene carbonate-co-phthalate) (PPC-P) is an amorphous copolymer of aliphatic polycarbonate and aromatic polyester; it possesses good biodegradability, superior mechanical performances, high thermal properties, and excellent affinity with CO2. Hence, we fabricate PPC-P foams in an autoclave by using subcritical CO2 as a physical blowing agent. Both saturation pressure and foaming temperature affect the foaming behaviors of PPC-P, including CO2 adsorption and desorption performance, foaming ratio, cell size, porosity, cell density, and nucleation density, which are investigated in this research. Moreover, the low-cost PPC-P/nano-CaCO3 and PPC-P/starch composites are prepared and foamed using the same procedure. The obtained PPC-P-based foams show ultra-high expansion ratio and refined microcellular structures simultaneously. Besides, nano-CaCO3 can effectively improve PPC-P's rheological properties and foamability. In addition, the introduction of starch into PPC-P can lead to a large number of open cells. Beyond all doubt, this work can certainly provide both a kind of new biodegradable PPC-P-based foam materials and an economic methodology to make biodegradable plastic foams. These foams are potentially applicable in the packaging, transportation, and food industry.

Bird-nest inspired cellulose-based biofoam with excellent performance enabled by gas–liquid interface co-assembly and thermal welding for plastic replacement

Traditional plastic foam, typically derived from fossil fuel-based polymers that are resistant to natural degradation, faces environmental challenges. As an alternative, cellulose, a biodegradable polymer, shows promise in the production of eco-friendly foam. Nonetheless, its reliance on hydrogen bonding between fibers poses limitations for practical applications. Here, drawing inspiration from bird nest structures, a straightforward and scalable method (co-assembly and thermal welding) has been developed for creating cellulose-PLA biofoam. The resulting biofoam displays advantageous properties such as low density (12.9 ∼ 27.1 kg/m3), high compression strength (modulus of 12.1 MPa·cm3·g−1), good thermal stability, and water stability (maintaining structural integrity in water). Moreover, it exhibits exceptional degradation rates (significant degradation within 40 days) and recyclability. Thus, this biofoam holds promise as a sustainable alternative to standard plastic foams, mitigating “white pollution.”

Green fabrication for ultra-lightweight polyethersulfone/epoxy foam with excellent thermal insulation

High-performance polymers find extensive applications in heat-resisting materials, aerospace, and automobile manufacturing industry. However, due to their challenging processability, achieving low-density high-performance polymer foams for thermal insulation materials remains a big challenge. Furthermore, the preparation of lightweight special engineering plastic foams has garnered substantial attention in current research. Herein, we have developed polyethersulfone (PES)/bisphenol A epoxy resin (EP) blend foams with ultra-low density and good thermal insulation properties using a facile and environmentally friendly supercritical CO2 (ScCO2) foaming approach. The inherent compatibility between PES and EP resin enhanced the free volume of molecular chain in the matrix, subsequently improving the solubility and diffusion rate of carbon dioxide within the PES matrix. Consequently, in contrast to the maximum expansion ratio of 5.5 observed in pure PES, the PES/EP blend foams achieved an expansion ratio of up to 26 times, along with an improvement of the cell structure of PES and increasing cell density from 2.55 × 109 to 2.96 × 1010 cells/cm3. Furthermore, the thermal conductivity of PES-based foams notably decreased from 0.0667 to 0.0348 W/(m·K) with the addition of EP, possibly resulting from the low density (0.05 g/cm3) and high open-cell content (79.9%) of PES/EP blend foam. Our work presents a novel strategy for producing special engineering plastic foams with ultra-low density for thermal insulation, thereby expanding the potential application of special engineering plastic foam in areas such as biological scaffolds, absorbent material applications, and automotive interior industry.

Pleated stainless steel net supported polystyrene/zinc oxide sorbent stir bar for inspection of residual fipronil and its degradation products in chicken eggs

Residual fipronil and its degradation products in chicken eggs are crucial issues in food safety. A stir bar sorptive extractor was developed by employing a pleated stainless steel (SS) net covered with hydrothermal synthesized zinc oxide (ZnO) nanostructure and dip-coated polystyrene (PS) from plastic foam waste. The combination of a PS/ZnO/SS stir bar extraction followed by gas chromatography detection with an electron capture detector yields a highly feasible process for the inspection of residual fipronils in chicken eggs with a linear range of 0.10–150 μg kg−1 and detection limit of 0.07–0.41 μg kg−1 with high recoveries (87.0 ± 2.4 to 95.2 ± 2.5%) and good precision (2.1–9.6% RSDs). The developed PS/ZnO/SS stir bar could be reused up to nine times. Its main advantages are simplicity of preparation, low-cost materials, and efficient utilization of PS waste.

Approaches to Recycling of Engine Air Filters

AbstractIt is becoming increasingly important to be able to recycle mass‐produced products such as engine air filters. Different processes were tested to investigate whether it is possible to recycle the composite material. Thereby, comminution with cutting stress is particularly suitable for disintegration. Next on, the filter medium could be separated very well with the help of a zig‐zag separator. The sorting of polyurethan foam and polypropylene hard plastic could be achieved with a dense media separation. It became clear that the pretreatment, which is intended to liberate the material, has a significant influence on the sorting result and the purity of the products.

Cellulose fiber-based and engineered capillary foam toward a sustainable, recyclable, and high-performance cushioning structural material

Foam materials have been widely used in cushioning packaging to ensure the integrity of products inside by absorbing energy and preventing collision. However, the extensive use of petroleum-based plastic foams may exacerbate environmental pollution and consume large amounts of energy. Therefore, there has been an increasing focus on producing high-performance and environmentally friendly foams in recent years. In this study, we developed a simple approach for manufacturing cellulose fiber-based capillary foams featuring superior stability and three-dimensional (3D) backbone network cross-linking structure composed of polyvinyl alcohol (PVA) and cationic starch (CS). The resultant capillary foam showed low density (0.154 g/cm3), superior mechanical properties (elastic modulus ranging from 77 to 501 kPa), high energy absorbing efficiency (32.8 %), and low cushioning coefficient (3.0). Besides, the end-of-life cellulose fiber-based capillary foam can be easily recycled for use, showing an attractive closed-loop cycle process. This study presents a unique option for creating affordable, eco-friendly, and malleable foams, demonstrating the potential to substitute the currently used petroleum-based foams in the packaging, food, and transport industries.

Secondary roughness effect of surface microstructures on secondary electron emission and multipactor threshold for PTFE-filled and PI-filled single ridge waveguides

Secondary electron yield (SEY) is a dominant factor in determining the multipactor threshold. In this study, we analyzed the secondary roughness effect of surface microstructures for plastic dielectric on SEY reduction and multipactor mitigation. A single ridge waveguide (SRW) operating in Ku-band, filled with polytetrafluoroethylene (PTFE) or polyimide (PI), was designed with a dielectric–metal multipactor gap. By employing a femtosecond laser, periodic microstructures were fabricated on PTFE and PI surfaces to suppress SEY. The SEY peak values of PTFE and PI decreased from 2.05 to 1.40 and 1.37 to 1.07 by the porous surface. The surface morphologies and cross-sectional images of the porous PTFE and PI demonstrated the existence of secondary roughness structures. Via simulation, we obtained multipactor thresholds of 8496 W, 12 374 W, and 9397 W for the SRWs filled with untreated PTFE surface, ideal porous surface (without secondary roughness), and real porous surface (with secondary roughness). Similar works were implemented for the PI-filled SRWs, resulting in simulated multipactor thresholds of 7640 W, 11 327 W, and 9433 W. The results indicate that the multipactor effect may not be effectively suppressed under the influence of secondary roughness structures such as plastic velvet and foam. Besides, simulation works indicated that the radio frequency electric field could extract secondary electrons from the microstructures, weakening the mitigation effect of microstructures on multipactor. The impact of surface charging on electron motion was also analyzed by considering energy distribution. It was suggested that the surface microstructures of plastic dielectrics lead to a decrease in the surface charge density and the electrostatic field strength, weakening the self-extinguishing effect and lowering the multipactor threshold. This study provides an in-depth analysis of the effect of secondary roughness on SEY and multipactor for organic dielectrics, which makes significant sense for the further investigation of dielectric multipactor.

Effect of Starch and Paperboard Reinforcing Structures on Insulative Fiber Foam Composites.

Single-use plastic foams are used extensively as interior packaging to insulate and protect items during shipment but have come under increasing scrutiny due to the volume sent to landfills and their negative impact on the environment. Insulative compression molded cellulose fiber foams could be a viable alternative, but they do not have the mechanical strength of plastic foams. To address this issue, a novel approach was used that combined the insulative properties of cellulose fiber foams, a binder (starch), and three different reinforcing paperboard elements (angular, cylindrical, and grid) to make low-density foam composites with excellent mechanical strength. Compression molded foams and composites had a consistent thickness and a smooth, flat finish. Respirometry tests showed the fiber foams mineralized in the range of 37 to 49% over a 46 d testing period. All of the samples had relatively low density (Dd) and thermal conductivity (TC). The Dd of samples ranged from 33.1 to 64.9 kg/m3, and TC ranged from 0.039 to 0.049 W/mk. The addition of starch to the fiber foam (FF+S) and composites not only increased Dd, drying time (Td), and TC by an average of 18%, 55%, and 5.5%, respectively, but also dramatically increased the mechanical strength. The FF+S foam and paperboard composites had 240% and 350% higher average flexural strength (σfM) and modulus (Ef), respectively, than the FF-S composites. The FF-S grid composite and all the FF+S foam and composite samples had equal or higher σfM than EPS foam. Additionally, FF+S foam and paperboard composites had 187% and 354% higher average compression strength (CS) and modulus (Ec), respectively, than the FF-S foam and composites. All the paperboard composites for both FF+S and FF-S samples had comparable or higher CS, but only the FF+S cylinder and grid samples had greater toughness (Ωc) than EPS foam. Fiber foams and foam composites are compatible with existing paper recycling streams and show promise as a biodegradable, insulative alternative to EPS foam internal packaging.

Multifunctional Bagasse Foam with Improved Thermal Insulation and Flame Retardancy by a Borax-Induced Self-Assembly and Ambient Pressure Drying Technique.

Cellulose foams are considered an effective alternative to plastic foam, because of their advantages of low density, high porosity, low thermal conductivity, and renewable nature. However, they still suffer from complex processing, poor mechanical properties, and flammability. As an agricultural waste, bagasse is rich in cellulose, which has attracted much attention. Inspired by the fact that borate ions can effectively enhance the strength of plant tissue by their cross-linking with polysaccharides, the present work designs and fabricates a series of multifunctional bagasse foams with robust strength and improved thermal insulation and flame retardancy via a unique borax-induced self-assembly and atmospheric pressure drying route using bagasse as a raw material, borate as a cross-linking agent, and chitosan as an additive. As a result, the optimized foam exhibits a high porosity (93.5%), a high hydrophobic water contact angle (150.4°), a low thermal conductivity (63.4 mW/(m·K) at 25 °C), and an outstanding flame retardancy. The present study provides a novel and inspiring idea for large-scale production of cellulose foams through an environmentally friendly and cost-effective approach.

Development of toughened and heat-resistant biodegradable injection-molded polylactide acid-based blend foams via enhancing interfacial bonding and PLA phase crystallization

Polylactic acid (PLA) foam is gaining increased attention as a biodegradable alternative to traditional petroleum-based plastic foams, which pose significant environmental pollution issues post-use. However, its potential application is greatly limited by inherent shortcomings such as brittleness and diminished heat resistance post-melting. Herein, high-performance biodegradable PLA/poly(butylene succinate) (PBS) blend foams with well-defined cell structure, high ductility, and enhanced heat resistance were fabricated using a core-back foam injection molding (FIM) process coupled with a straightforward annealing procedure. To enhance compatibility and tailor the dispersed phase morphology into a more fibrillar structure, an epoxy-functional chain extender (ADR) was incorporated. This addition resulted in a substantial increase in the notched impact strength, elevating it to 7.0 kJ/m2, compared to the mere 1.5 kJ/m2 of unmodified PLA foam. Moreover, with the inclusion of 1.0 phr ADR, the notched impact strength of the foam post-annealing soared to 20.7 kJ/m2, a 13.8-fold enhancement compared to pure PLA foam. The formation of a uniformly distributed and interlocked “shish-kebab" crystal structure in the blend facilitated effective stress transfer and distribution, leading to shear yield in the PLA matrix. Additionally, the heat deflection temperature of the annealed blend foam showed a significant increase significantly to 94.7 °C, in contrast to the mere 55.6 °C of pure PLA foam. This study demonstrates a viable and feasible strategy for preparing fully biodegradable PLA foams with high-toughness and heat resistance.