Polymer最新文献

Two stereocomplexes (SCs) with different molecular weights in poly(L-lactide) (PLLA-49k and PLLA-163k) were prepared by mixing equal amounts of poly(D-lactide) (PDLA) and PLLA via the solution method. The exclusive formation of SCs was achieved in SC-PLLA-49k, whereas both homocrystallites (HCs) and SCs were observed in SC-PLLA-163k. Two blends were subjected to further processing via the ultrasonic microinjection molding technique at varying mold temperatures, yielding amorphous samples. As the samples were heated, the heating induced structural reorganization occurs with the concurrent SCs and HCs for all samples at ca. 80 °C. The degree of crystallinity for HCs X_HC exhibits a positive correlation with the mold temperature, whereas the degree of crystallinity for SCs X_SC shows a negative dependence on mold temperature for both systems. This behavior can be tentatively explained as follows. Firstly, the demixing of enantiomeric PLA chains occurs in the melt state as evidenced by twice heating measurements of blends. The degree of chain segregation is expected to increase with the increase in mold temperature due to lower supercooling, resulting in a decrease of PLLA/PDLA clusters (SC nuclei). Secondly, a high mold temperature is beneficial for the formation of HC nuclei as the chain mobility is improved. The reformulation of SC nuclei is difficult because of a longer diffusion distance required for PLA molecules. The coexistence of SC and HC nuclei causes the simultaneous appearance of SCs and HCs during heating of samples. As HCs start to melt, a transition from HCs to SCs occurs accompanied by a continuous increase in X_SC. For both systems, a maximum of X_SC is reached when SCs begin to melt followed by a mold temperature independent evolution of X_SC upon further heating. Such a maximum is larger in the low molar mass system because it is less entangled. The reservation of SC nuclei is demonstrated by a comparison of the structural evolution and isothermal cold crystallization behavior between the two blends and their ultrasonic microinjection molded samples.

Electrospinning is a unique technology based on the fabrication of polymer fibers from the solution under an applied electric field. Electrospun membranes are applied in various fields, starting from filter technologies to tissue engineering. Polyalyletherketones (PAEK) is a family of synthetic bioinert polymers characterized by outstanding mechanical performance, high chemical stability, and biocompatibility. In the present study, the effect of electrospinning parameters (collector-to-tip distance, applied voltage, spinning solution flow rate and polymer concentration in the spinning solution) on the morphology of the fabricated polyetherketoneketone (PEKK) membranes as well as their crystal structure, chemical stability and biocompatibility was investigated. Based on 108 combinations of the electrospinning parameters, it was found that minimum concentration of PEKK in the spinning solution in 1,1,1,3,3,3-hexafluoropropan-2-ol (HFP) required for the fibers’ formation is 4 wt %, while the applied voltage providing fibers without defects was found at 20 kV. It was demonstrated that the tested electrospinning regimes allow to fabricate the membranes with average fiber diameter from 0.76 ± 0.29 to 1.46 ± 0.60 μm and porosity from 87 ± 1 to 92 ± 1 %. It was found that electrospinning process has no effect on the chemical structure of PEKK macromolecules. Electrospinning parameters had no effect on crystal structure of PEKK in the fabricated membranes, which was found to be amorphous. The fabricated membranes demonstrated high Young modulus (above 150 MPa) and elongation over 170 %, were stable in strong alkali and acid solutions and biocompatible towards mouse embryonic fibroblasts.

In this work hybrid magnetite (Fe₃O₄)/poly(3,4-ethylenedioxythiophene) (PEDOT) core-shell particles are used to produce electro-responsive self-standing polycaprolactone (PCL) membranes with many potential applications. For this purpose, Fe₃O₄/PEDOT core-shell particles with different magnetite contents are prepared by combining chemical precipitation and emulsion polymerization. After chemical, morphological and physical characterization, the electrochemical response of the hybrid particles is analyzed and compared with that of PEDOT nanoparticles. In all cases, Fe₃O₄/PEDOT core-shell particles are more electroactive than PEDOT particles, with the electrochemical response of the former increasing with the content of magnetite. Composite membranes were prepared by spin-coating a mixture of polycaprolactone (PCL) and Fe₃O₄/PEDOT particles. The resulting Fe₃O₄/PEDOT-PCL membranes, which maintained the magnetic behavior, were transformed into electro-responsive by incorporating a PEDOT surface layer through anodic polymerization, which was possible thanks to the role of Fe₃O₄/PEDOT particles as polymerization nuclei. One of the potential applications of self-supported electro-responsive Fe₃O₄/PEDOT-PCL/PEDOT membranes was illustrated through a proof-of-concept. Specifically, a wide-spectrum antibiotic, chloramphenicol, was loaded into the membranes during the anodic polymerization step promoted by the hybrid Fe₃O₄/PEDOT particles and, subsequently, completely released by electrical stimulation. Overall, Fe₃O₄/PEDOT core-shell particles allowed us to obtain self-standing membranes with electric and magnetic properties, as promising candidates for many technological applications.

Polypropylene random copolymer (PPR) is in high demand for pipelines due to its comprehensively brittle-ductile balance. It is a multiphase polymer composed of crystalline phases and rubbery phases in which improving the quantities of ductile β-crystals can effectively toughen PPR. However, the influence of β-crystallization on the aggregation of rubbery phases and their collaboration for toughening are still not well elucidated. In this work, the toughening mechanism of PPR/iPP/β-NA composites were illustrated by manipulating the crystallization and phase separation behaviors using different molecular weight of isotactic polypropylene (iPP) and β-nucleating agent (β-NA). A high relative β-crystal content (K_β) was obtained in PPR/iPP/β-NA composites and the influence of molecular weight of iPP on crystal structures of PPR/iPP/β-NA composites was investigated via differential scanning calorimetry (DSC) and x-ray diffraction (XRD). The phase separation behaviors were then studied using rheological measurements and scanning electron microscope (SEM). The impact behaviors of PPR/iPP/β-NA composites with similar crystal structures but different size of rubbery particles were demonstrated. It was found that crystallization of PPR into β-crystal promoted the phase separation process and the resulting rubbery particle size. The deformation of large rubbery particles induced small wavy cracks at the fracture surface other than layered cracks for small rubbery particles. This work basically introduces the toughening mechanism from collaboration of β-crystals and rubbery phases in polypropylene random copolymers and provides a new method for fabricating high toughness PPR pipe.

The use of ethyl cinnamate, an ester of cinnamic acid present in many fruits and plants, as a bio-based plasticizer for polyvinyl chloride (PVC) plastisols has been investigated. Different temperatures (180, 190, and 200 °C) and curing times (8, 11.5, and 15 min) have been evaluated for PVC plasticized with 70 phr (parts by weight of plasticizer per one hundred weight parts of PVC resin) of ethyl cinnamate in order to optimize the curing conditions of the material, as these play a fundamental role in determining the final properties. Optimization of curing conditions has been carried out by analyzing the effect of temperature and curing time on the tensile mechanical properties, thermal stability, morphological, color changes, and migration tendency for the different plasticized materials. It has been observed that the optimal curing conditions for PVC plasticized with ethyl cinnamate are achieved at a curing temperature of 190 °C and a curing time of 11.5 min. Under these conditions, a material with high tensile strength, around 6.4 MPa, and a high elongation at break, close to 570 %, is obtained which is comparable or even superior to materials cured in the presence of other conventional plasticizers used in the PVC industry. Additionally, through field emission scanning electron microscopy (FESEM), it has been observed that for these conditions, the curing process is complete, resulting in the complete fusion of PVC microcrystals. A material with high cohesion and very low migration loss, around 2.4 %, is obtained. The effectiveness of these curing conditions has also been demonstrated using thermogravimetry. An increase in the PVC dehydrochlorination temperature has been observed due to optimum plasticizer absorption and gelation.

Introduction

The increasing prevalence of severe bone diseases, such as osteoporosis and critical bone defects, necessitates the development of more effective bone substitutes. This study addresses this need by investigating 3D-printed bone scaffolds composed of sodium alginate and tricalcium phosphate, enhanced with three distinct types of hydroxyapatite (HA): bovine-derived HA, commercially available HA, and HA enriched with probiotic bacteria. We aim to evaluate the performance of these scaffolds in terms of mechanical strength, biocompatibility, and their ability to support bone regeneration.

Methods

The scaffolds were analyzed through various tests, including X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Differential Scanning Calorimetry (DSC) to characterization. Scanning Electron Microscopy (SEM) was used to examine pore structure, while swelling and degradation tests evaluated the scaffold's stability. Compression testing determined mechanical strength, and in vitro cell culture assays assessed cell proliferation, osteogenic differentiation, and biomineralization.

Results

SEM results indicated that 3D scaffolds with probiotic bacterial HA had the desired 472 μm pore size. These scaffolds demonstrated a strain of 29.26 % and a compressive strength of 10 MPa, meeting the mechanical standards of human trabecular bone. Cell culture studies revealed enhanced cell proliferation by 50 %, osteogenic differentiation with 15.3 U/mg ALP activity, and 1.22-fold biomineralization, suggesting they are highly biocompatible and promote bone growth.

Conclusion

Probiotic bacterial HA scaffolds exhibit ideal properties and biocompatibility, enhancing bone regeneration and serving as an ideal alternative to chemical types.

Fumasep FAA-3-PK-130 is considered the state-of-the-art among the different commercially available Anion Exchange Membranes (AEMs). It is produced by Fumatech GmbH as a cost-effective blend of polyetheretherketone (PEEK) and poly (phenylene oxide) (PPO) characterized by high hydroxyl ions conductivity, high thermal and chemical resistance, and high dimensional stability. Nevertheless, the chemical structure of the anion exchange sites and their contents were unknown so far.

In this paper, we report a detailed structural characterization of Fumasep FAA-3-PK-130 to identify the material phase composition, the nature of the conducting moieties and their interactions with the adsorbed water molecules. A complete phase segregation between PPO and PEEK was found on a micrometric scale from ¹H spin-lattice relaxation times and micro-ATR analysis. Multinuclear (¹H, ¹³C, ¹⁹F) Solid-State NMR spectra, combined with nuclear spin relaxation measurements, allowed us to identify the anion exchange moiety with benzyl-ethyl-dimethylammonium. This is present as functionalizing group of PPO monomers with a functionalization degree of about 40 %. Moreover, the mobility of water absorbed in the membrane was studied by ²H Solid-State NMR on samples hydrated with deuterated water under controlled relative humidity: at low relative moisture, two different types of environments were found for water molecules, compatible with two types of water-ion clusters, one of which contains water molecules with a restricted mobility, limited to C₂ jumps, due to strong interactions with ions.

Constructing a three-dimensional (3D) filler network in polymer thermal interface materials (TIMs) is crucial for enhancing thermal conductivity and mechanical properties. However, the discontinuous and loose network of fillers are one of the main reasons hindering the joint improvement of thermal conductivity and mechanical properties. The construction of a regular and dense 3D continuous filler network remains a significant challenge. In this study, an innovative bidirectional freezing technique was designed to create a polyvinyl alcohol (PVA)/boron nitride (BN) composite with a tree-ring-like 3D network. This technique promotes the formation of 3D network consisting of long-range lamellar BN layers with a tree-ring-like structure by controlling the nucleation and growth of ice crystals along the bidirectional temperature gradient induced by a polytetrafluoroethylene (PTFE) cone. The resulting PVA/BN composite exhibits high thermal conductivity (6.25 W/m·K) due to the lower interfacial thermal resistance between fillers (1.271 × 10⁻⁷ K m²/W), and an enhanced tensile strength of 41.71 MPa, which is attributed to the regular and dense BN network. This study presents a feasible strategy for constructing a 3D continuous network structure in polymer-based TIMs, paving the way for advancements in thermal management solutions.

To explore novel approaches facilitating the structural evolution of high-entanglement ultrahigh molecular weight polyethylene (UHMWPE) films, this study precisely controlled the temperature during compression molding to successfully prepare high-entanglement UHMWPE films with different shish contents. Using in-situ small-angle X-ray scattering (SAXS)/ultra-small-angle X-ray scattering (USAXS)/wide-angle X-ray diffraction (WAXD) alongside ex-situ scanning electron microscopy (SEM) and differential scanning calorimetry (DSC), we investigated the influence of shish contents on the structural evolution of high-entanglement UHMWPE films during hot stretching. The results indicate that increasing shish content in high-entanglement UHMWPE films reduces the accumulation of inclined lamellar crystals caused by high entanglement, promoting the transformation of inclined lamellar crystals into shish-kebab crystals and facilitating the formation of more shish-kebab crystals. In high-entanglement UHMWPE films with high shish content, eventually, all inclined lamellar crystals even transform into shish-kebab crystals.

Polydimethylsiloxane (PDMS) exhibits exceptional thermal stability and processability, however, limited adhesion and carbonization performance hinders its applications as flexible thermal protection materials. Herein, a phenolic epoxy modified silicone rubber (KFAP@PDMS) was synthesized, and the microscopic morphology, macroscopic mechanical properties, adhesive properties, thermal properties and ablative properties were systematically investigated. Compared to pure PDMS, the modified material exhibits a maximum tensile strength increase of 170 %, maximum elongation at break increases of 141 %, maximum adhesion strength increases of 209 %, and linear ablation rate decrease 84.9 %, respectively. Thermal degradation analysis indicates that the introducing of KFAP increases crosslink density while the degradation products mainly consist of D₃, D₄, and toluene compounds. Ablation analysis reveals that the inclusion of KFAP promotes an in-situ carbon-silicon multiphase ceramization reaction, resulting in densification of the carbon layer and significant improvement of the ablation performance.