Microcellular foaming behaviors of chain extended poly (butylene succinate)/polyhedral oligomeric silsesquioxane composite induced by isothermal crystallization

Mechanical, Crystallization, Rheological, and Supercritical CO2 Foaming Properties of Polybutylene Succinate Nanocomposites: Impact of Carbon Nanofiber Content

As a substitute for conventional polymers for the preparation of biodegradable microcellular polymeric foams, polybutylene succinate (PBS) presents one of the most promising alternatives. However, the low melt strength of PBS makes it difficult to produce high-performance microcellular foams. This study aimed to improve the melt strength of PBS and explore the mechanical, thermal, crystalline, rheological, and supercritical CO2 foaming properties of PBS nanocomposites by using carbon nanofibers (CNFs). This study found that nanocomposites containing 7 wt% CNF exhibited the highest tensile strength, Young's modulus, and bending strength. Moreover, the CNF nanofillers were well dispersed in the PBS matrix without significant agglomeration, even at high filler concentrations. Furthermore, the nanocomposites demonstrated improved melting temperature and crystallinity compared with pure PBS. The rheological analysis showed that the addition of CNFs significantly increased PBS viscosity at low frequencies due to the interaction between the PBS molecular chains and CNFs and the entanglement of CNFs, resulting in a more complete physical network formation when the CNF content reached above 3 wt%. During the supercritical CO2 foaming process, the addition of CNFs resulted in increased cell density, smaller cells, and thicker cell walls, with good laps formed between the fibers on the cell walls of nanocomposite foams. Moreover, the electrical conductivity and electromagnetic interference (EMI) shielding properties of the foamed material were studied, and a nanocomposite foam containing 7 wt% CNF showed good electrical conductivity (4.5 × 10-3 S/m) and specific EMI shielding effectiveness (EMI SE) (34.7 dB/g·cm-1). Additionally, the nanocomposite foam with 7 wt% CNF also exhibited good compression properties (21.7 MPa). Overall, this work has successfully developed a high-performance, multifunctional PBS-based nanocomposite foam, making it suitable for applications in various fields.

Facile fabrication of PBS/CNTs nanocomposite foam for electromagnetic interference shielding

In order to reduce the pollutants of environment and electromagnetic waves, environment friendly polymer foams with outstanding electromagnetic interference shielding are imminently required. In this paper, a kind of electromagnetic shielding, biodegradable nanocomposite foam was fabricated by blending PBS with carbon nanotubes (CNTs) followed by foaming with supercritical CO2. The crystallization temperature and melting temperature of PBS/CNTs nanocomposites with 4 wt % of CNTs increased remarkably by 6 °C and 3.1 °C compared with that of pure PBS and a double crystal melting peak of various PBS samples appeared in DSC curves. Clearly, an increase of approximately 3 orders of magnitude was improved for storage modulus and near 9 orders of magnitude was enhanced for electrical properties with CNTs content from 0 to 4 wt %. Furthermore, CNTs endowed PBS nanocomposite foam with adjustable electromagnetic interference (EMI) shielding property, giving a specific EMI shielding effectiveness of 28.5 dB cm3/g. This study provided a promising methodology for preparing biodegradable, lightweight PBS/CNTs foam with outstanding electromagnetic shielding properties.

Influence of Polylactide (PLA) Stereocomplexation on the Microstructure of PLA/PBS Blends and the Cell Morphology of Their Microcellular Foams

Polylactide foaming materials with promising biocompatibility balance the lightweight and mechanical properties well, and thus they can be desirable candidates for biological scaffolds used in tissue engineering. However, the cells are likely to coalesce and collapse during the foaming process of polylactide (PLA) due to its intrinsic low melt strength. This work introduces a unique PLA stereocomplexation into the microcellular foaming of poly (l-lactide)/poly (butylene succinate) (PLLA/PBS) based on supercritical carbon dioxide. The rheological properties of PLA/PBS with 5 wt% or 10 wt% poly (d-lactide) (PDLA) present enhanced melt strength owing to the formation of PLA stereocomplex crystals (sc-PLA), which act as physical pseudo-cross-link points in the molten blends by virtue of the strong intermolecular interaction between PLLA and the added PDLA. Notably, the introduction of either PBS or PDLA into the PLLA matrix could enhance its crystallization, while introducing both in the blend triggers a decreasing trend in the PLA crystallinity, which it is believed occurs due to the constrained molecular chain mobility by formed sc-PLA. Nevertheless, the enhanced melt strength and decreased crystallinity of PLA/PBS/PDLA blends are favorable for the microcellular foaming behavior, which enhanced the cell stability and provided amorphous regions for gas adsorption and homogeneous nucleation of PLLA cells, respectively. Furthermore, although the microstructure of PLA/PBS presents immiscible sea-island morphology, the miscibility was improved while the PBS domains were also refined by the introduction of PDLA. Overall, with the addition of PDLA into PLA/10PBS blends, the microcellular average cell size decreased from 3.21 to 0.66 μm with highest cell density of 2.23 × 10¹⁰ cells cm⁻³ achieved, confirming a stable growth of cells was achieved and more cell nucleation sites were initiated on the heterogeneous interface.

Fabrication of branching poly (butylene succinate)/cellulose nanocrystal foams with exceptional thermal insulation

Branching poly (butylene succinate) (BPBS) nanocomposite foams incorporated with cellulose nanocrystals (CNCs) were prepared by supercritical CO₂. Surface modification of CNCs by acetylation was achieved through replacing hydrophilic hydroxyl groups with hydrophobic acetyl groups, which improved the dispersibility of CNCs significantly. The crystallite sizes of CNCs and acetylated CNCs were calculated by Scherrer's formula as 25 and 19 nm, respectively. The initial crystallization temperature of diverse poly (butylene succinate) (PBS) specimens, a crucial factor for regulating cell nucleation type, increased remarkably by 11.8 °C as well as their storage modulus increased by 2 orders of magnitudes, due to branching reaction and bio-filler addition. BPBS/CNCs foam possessed a high volume expansion ratio as 37.1 times and displayed an exceptional thermal conductivity as 0.021 W(m K)^-1. This study provided a promising potential strategy to develop exceptional thermal-insulation polymer foams for composite structures, energy conservation and environment protection.

Rheological and Crystallization Properties of ABS/PA6-Compatibilized Blends via In Situ Reactive Extrusion

ABS/PA6-compatibilized blends were prepared by in situ reactive extrusion method. The main objective was to evaluate the influences of the morphology and blend composition on the rheological and nonisothermal crystallization properties. The morphology of submicron-sized ABS droplets evenly dispersed in PA6 led to dilatant fluid behavior and a transition from elastic to viscous behavior in the low-frequency region. The crystallization results indicated that reactive blends had elevated crystallization temperatures and crystallization rates, which were due to the heterogeneous nucleation of the submicron-sized ABS particles. In addition, it was observed that the theory by Mo suitably described the nonisothermal crystallization process. The activation energy slightly decreased for ABS contents of 5 and 15 wt % and then increased for a content of 25 wt %, indicating that the ABS promoted the crystallization of the blends at appropriate contents.

Crystallization-induced microcellular foaming behaviors of chain-extended polyethylene terephthalate

The microcellular foaming of chain-extended polyethylene terephthalate (CPET) by crystallization induction method was reported in this article. The crystallization behaviors of various polyethylene terephthalate (PET) samples which were affected by the combined effect of pyromellitic dianhydride, Surlyn, and CO2 were investigated. After Surlyn was added to CPET, the crystal nucleation of various CPET samples was improved, and numerous but small spherulites were generated. Two kinds of CPET samples with the content of 0 phr and 1 phr Surlyn were foamed at various temperature by batch foaming method. Changing the saturation temperature could adjust the appearance of high-temperature melting crystals which would affect the final cellular structures in various CPET foams. With the decrease of saturation temperature, the cell size decreased while cell density increased. At the saturation temperature of 265°C and 250°C, the cell density of CPET foam with Surlyn was one magnitude larger than CPET foam without Surlyn. At the saturation temperature of 247°C, the microcellular PET foams with the cell density of 109 cells cm−3 and the cell size less than 10 µm had been developed successfully.

Fabrication of fibrillated and interconnected porous poly(ε-caprolactone) vascular tissue engineering scaffolds by microcellular foaming and polymer leaching

This paper provides a method combining eco-friendly supercritical CO₂ microcellular foaming and polymer leaching to fabricate small-diameter vascular tissue engineering scaffolds.

Polyimide foams with outstanding flame resistance and mechanical properties by the incorporation of noncovalent bond modified graphene oxide

PI composite foams were in situ generated by incorporating modified GO to further improve flame resistance, thermal stability and mechanical properties.

Morphological evaluation of ultralow density microcellular foamed composites developed through CO2-induced solid-state batch foaming technique utilizing water as co-blowing agent

In this work, microcellular acrylonitrile-butadiene-styrene foams were developed with utilization of water as a co-blowing agent and CO2 as the primary blowing agent through the solid-state batch foaming process. The effect of saturation parameters with the content of the co-blowing agent has been studied extensively for various foaming attributes. The co-blowing agent enhanced the average cell size and the expansion ratio which are useful for better thermal insulation. The maximum expansion ratio of 29.9 obtained from the effect of saturation temperature and co-blowing agent, 23.6 from the effect of saturation pressure and co-blowing agent, and 22.4 from the effect of saturation time and co-blowing agent. The co-blowing agent significantly affects the cell morphology of polymeric foam with saturation parameters.