ScCO2-assisted fabrication and compressive property of poly (lactic acid) foam reinforced by in-situ polytetrafluoroethylene fibrils

Preparation of tomato peel pomace powder/polylactic acid foams under supercritical CO2 conditions: Improvements in cell structure and foaming behavior

Polylactic acid (PLA) is an eco-friendly material that can help address the problems of petroleum depletion and pollution. Blending renewable biomass materials with PLA to create composite foams with a tunable pore structure, superior performance, and low cost is a green technique for improving the pore structure and mechanical characteristics of single PLA foams. PLA/TP composites were created using melted tomato peel pomace powder (TP), which has a lamellar structure, as a reinforcing agent. Then, the relationship between the vesicle structure, morphology, and properties of the PLA/TP composite foams produced through supercritical CO2 intermittent foaming were investigated. The findings revealed that TP considerably enhanced the rheological characteristics and crystalline behavior of PLA. The PLA/TP composite foam had a better cell structure, compression characteristics, and wettability than pure PLA. The expansion ratio of the PLA/TP composite could reach 18.8, and its thermal conductivity decreased from 174.2 mW/m·K at 100 °C to 57.8 mW/m·K at 120 °C. Furthermore, annealing before foaming decreased the average composite foam blister size from 110.09 to 66.53 μm, and the annealing process also improved compression performance. This study contributes to solving environmental difficulties and creating PLA foams with controlled bubble structures, uniform bubble sizes, and outstanding overall performance.

Insights into heterogeneous surface induced bubble nucleation mechanisms in cellulose reinforced polylactic acid foams

As the most abundant natural homo-polymer, cellulose has the potential to enhance polymer properties reducing the cost of raw materials. In this work, the carboxylate cellulose nanofiber (CNF-C) was selected to modify polylactic acid (PLA) foams, and the density functional theory was constructed to help analyze the foaming mechanism quantitatively. The theoretical results showed that the ordered structure, the carboxyl and the hydroxyl of CNF-C were more conducive to providing much stronger CO2 adsorption for bubble nucleation, where the predicted critical bubble size decreased and the cell density increased with the addition of CNF-C. The experimental results revealed that the CNF-C promoted the rheological properties and crystallization behaviors of PLA samples, the PLA/CNF-C foams were characterized with uniform structures, the average cell size decreased from 21.39 μm to 0.19 μm, and the cell number density increased from 2.65×1010cell/cm3 to 2.30×1014cell/cm3. Those improvements resulted in an increase of 394.0 % for the compressive strength of the prepared foams. Generally, the high-performance PLA/CNF-C foams were fabricated successfully without compromising the properties of bio-based and biodegradable, the foaming mechanism was analyzed combining theoretical results with experimental data, and it was believed to provide a guide for cellulose reinforcing biodegradable polymer materials.

Super-tough poly(lactic acid)/silicone rubber thermoplastic vulcanizates: The organic and inorganic synergistic interfacial compatibilization

Polymer modification using silicone rubber represents a promising avenue for enhancing physico-mechanical properties. However, achieving optimal performance through direct blending is hindered by the poor interface compatibility between silicone rubber and the matrix. In this study, we prepared super-tough thermoplastic vulcanizates (TPVs) of polylactic acid/silicone rubber through dynamic vulcanization with PLA, methyl vinyl silicone rubber (MVQ), glycidyl methacrylate grafted MVQ (MVQ-g-GMA), and fumed silica nanoparticles (SiO2). The impact of the SiO2 addition in MVQ on the morphology, mechanical properties, crystallization, and thermal properties of the TPVs was investigated. The results showed that MVQ-g-GMA and SiO2 exhibited a synergistic compatibilization effect significantly improving the interfacial adhesion between PLA and MVQ. Therefore, the impact and tensile strength of the TPVs increased from 8.0 kJ/m2 and 22.2 MPa to 62.6 kJ/m2 and 36.7 MPa, respectively. Moreover, the TPVs also presented good low-temperature toughness with a maximum impact strength of 40.4 kJ/m2 at -20 °C. Additionally, improvements in thermal stability and crystallization rate were also observed. Overall, combining organic and inorganic synergistic compatibilization is a feasible and effective method to fabricate outstanding low-temperature toughness to PLA.

Fabrication of bio-based biodegradable poly(lactic acid) (PLA) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) composite foams for highly efficient oil-water separation

The open-cell bio-based biodegradable polymer foams show good application prospect in dealing with the serious environmental issue caused by oil spill and organic solvents spills, while the cell structures and hydrophobic properties of the foams limit their performance. In this work, the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was selected to help prepare bio-based biodegradable poly(lactic acid) (PLA) foams. Based on a two-step foaming method, the crystallization ability of different samples was regulated by the "original crystals" together with PHBV in the foaming process, where skeleton structures were provided to facilitate the open-cell structures and promote their mechanical property. As illustrated, PHBV facilitated the formation of open-cell PLA foams, where the foams displayed superior oil-water separation capacity. The maximum volume expansion ratio of the foams was 80.08, the contact angle of deionized water reached to 134.5°, the adsorption capacity for oil or organic solvents was 10.8 g/g-51.8 g/g, and the adsorption capacity for CCl4 can still maintained 83.5 % of the initial value after 10 adsorption-desorption cycles. This work not only clarified the foaming mechanism of open-cell foams, but also provided a green and simple method for preparing bio-based biodegradable foams possessing excellent oil-water separation performance.

High-expansion-ratio PLLA/PDLA/HNT composite foams with good thermally insulating property and enhanced compression performance via supercritical CO2

It has been a great challenge to prepare high-expansion-ratio polylactide (PLA) foam with eminent thermal insulation and compression performance in packaging field. Herein, a naturally formed nanofiller halloysite nanotube (HNT) and stereocomplex (SC) crystallites were introduced into PLA with a supercritical CO₂ foaming method to improve foaming behavior and physical properties. The compressive performance and thermal insulation properties of the obtained poly(L-lactic acid) (PLLA)/poly(D-lactic acid) (PDLA)/HNT composite foams were successfully investigated. At a HNT content of 1 wt%, the PLLA/PDLA/HNT blend foam with an expansion ratio of 36.7 folds showed a thermal conductivity as low as 30.60 mW/(m·K). Meanwhile, the compressive modulus of PLLA/PDLA/HNT foam was 115% higher than that of PLLA/PDLA foam without HNT. Moreover, the crystallinity of PLLA/PDLA/HNT foam was dramatically improved after annealing, thus the results showed that compressive modulus of the annealed foam increased by as high as 72%, while it still maintained good heat insulation with the thermal conductivity of 32.63 mW/(m·K). This work provides a green method for the preparation of biodegradable PLA foams with admirable heat resistance and mechanical performance.

Hydrophobic and oleophilic open-cell foams from in-situ microfibrillation blends of poly(lactic acid) and polytetrafluoroethylene: Selective oil-adsorption behaviors

Confronted with severe water contamination induced by the spillage of oils, seeking oil-selective adsorbent to recover oil from oily wastewater is extremely urgent. In particular, the functionalized polymer foams with open-cell structures are highly promising oil-selective adsorbent. Herein, a simple, effective and green method was presented to prepare open-cell poly(lactic acid) (PLA)/polytetrafluoroethylene (PTFE) foams with selective oil-adsorption behaviors via melt blending and supercritical CO₂ batch foaming technique. The introduction of PTFE had a distinct positive influence on the melt viscoelasticity and crystallization performances of various PLA specimens. The resulted PLA/PTFE4 foam with a volume expansion ratio of 10.17 ± 0.93 and a cell density of 1.58 × 10⁸ cells/cm³ possessed the highest open-cell content of 90.81 ± 0.78 %. Meanwhile, PLA/PTFE4 foam revealed oil/water selective adsorption capacity of 1.2-6.1 g/g for various organic solvents and oils. The adsorption capacity of PLA/PTFE4 foam for CCl₄ exhibited no significant decrement during ten adsorption-desorption cycles. This research offered a guideline for the manufacture of green environmental open-cell polymer foams for oil-selective adsorption.