Ultra-fast degradable PBAT/PBS foams of high performance in compression and thermal insulation made from environment-friendly supercritical foaming

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.

Characterization of Biodegradable Polymers for Porous Structure: Further Steps toward Sustainable Plastics

Plastic pollution poses a significant environmental challenge, necessitating the investigation of bioplastics with reduced end-of-life impact. This study systematically characterizes four promising bioplastics-polybutylene adipate terephthalate (PBAT), polybutylene succinate (PBS), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and polylactic acid (PLA). Through a comprehensive analysis of their chemical, thermal, and mechanical properties, we elucidate their structural intricacies, processing behaviors, and potential morphologies. Employing an environmentally friendly process utilizing supercritical carbon dioxide, we successfully produced porous materials with microcellular structures. PBAT, PBS, and PLA exhibit closed-cell morphologies, while PHBV presents open cells, reflecting their distinct overall properties. Notably, PBAT foam demonstrated an average porous area of 1030.86 μm2, PBS showed an average porous area of 673 μm2, PHBV displayed open pores with an average area of 116.6 μm2, and PLA exhibited an average porous area of 620 μm2. Despite the intricacies involved in correlating morphology with material properties, the observed variations in pore area sizes align with the findings from chemical, thermal, and mechanical characterization. This alignment enhances our understanding of the morphological characteristics of each sample. Therefore, here, we report an advancement and comprehensive research in bioplastics, offering deeper insights into their properties and potential morphologies with an easy sustainable foaming process. The alignment of the process with sustainability principles, coupled with the unique features of each polymer, positions them as environmentally conscious and versatile materials for a range of applications.

High-Strength Bio-Degradable Polymer Foams with Stable High Volume-Expansion Ratio Using Chain Extension and Green Supercritical Mixed-Gas Foaming

The preparation of biodegradable polymer foams with a stable high volume-expansion ratio (VER) is challenging. For example, poly (butylene adipate-co-terephthalate) (PBAT) foams have a low melt strength and high shrinkage. In this study, polylactic acid (PLA), which has a high VER and crystallinity, was added to PBAT to reduce shrinkage during the supercritical molded-bead foaming process. The epoxy chain extender ADR4368 was used both as a chain extender and a compatibilizer to mitigate the linear chain structure and incompatibility and improve the foamability of PBAT. The branched-chain structure increased the energy-storage modulus (G') and complex viscosity (η*), which are the key factors for the growth of cells, by 1-2 orders of magnitude. Subsequently, we innovatively used the CO₂ and N₂ composite gas method. The foam-shrinkage performance was further inhibited; the final foam had a VER of 23.39 and a stable cell was obtained. Finally, after steam forming, the results showed that the mechanical strength of the PBAT/PLA blended composite foam was considerably improved by the addition of PLA. The compressive strength (50%), bending strength, and fracture load by bending reached 270.23 kPa, 0.36 MPa, and 23.32 N, respectively. This study provides a potential strategy for the development of PBAT-based foam packaging materials with stable cell structure, high VER, and excellent mechanical strength.

Reinforcing a Thermoplastic Starch/Poly(butylene adipate-co-terephthalate) Composite Foam with Polyethylene Glycol under Supercritical Carbon Dioxide

Biodegradable foams are a potential substitute for most fossil-fuel-derived polymer foams currently used in the cushion furniture-making industry. Thermoplastic starch (TPS) and poly(butylene adipate-co-terephthalate) (PBAT) are biodegradable polymers, although their poor compatibility does not support the foam-forming process. In this study, we investigated the effect of polyethylene glycol (PEG) with or without silane A (SA) on the foam density, cell structure and tensile properties of TPS/PBAT blends. The challenges in foam forming were explored through various temperature and pressure values under supercritical carbon dioxide (CO₂) conditions. The obtained experimental results indicate that PEG and SA act as a plasticizer and compatibilizer, respectively. The 50% (TPS with SA + PEG)/50% PBAT blends generally produce foams that have a lower foam density and better cell structure than those of 50% (TPS with PEG)/50% PBAT blends. The tensile property of each 50% (TPS with SA + PEG)/50% PBAT foam is generally better than that of each 50% (TPS with PEG)/50% PBAT foam.

The synergistic effect of polytetrafluoroethylene in-situ fibrillation and dibenzoyl sebacate hydrazide on the crystallization and foaming behavior of poly (lactic acid)

The fully degradable poly (lactic acid) foam with green environmental protection characteristics can alleviate the shortage of petroleum resources caused by the application of plastics. However, due to the inherent low melt strength and slow crystallization rate of linear PLA. It is difficult to obtain PLA microcellular foam with good morphology. In order to obtain PLA microcellular foam with ultra-high expansion ratio and small cell size, PTFE (polytetrafluoroethylene) nanofibers with excellent CO₂ adsorption rate were introduced. Self-assembled nucleator TMC-300(dibenzoyl sebacate hydrazide) was also introduced to blend with PLA to obtain small-sized cells. The results show that the PTFE entanglement network as a self-assembled template can effectively improve the early crystallization nucleation efficiency and increase the crystallinity of branched PLA (CBPLA)/TMC by 7 %. The microcellular foam with PTFE content of 0.5 wt% (CBPLA/TMC/PTFE 0.5) was successfully prepared by physical foaming agent, which had the lowest cell size (8.7 μm) And high expansion ratio (1200 %).