In this study, the electrical conductivity of melt spun composites consisting of PMMA containing both aligned carbon fibers (CF) and carbon black (CB) has been investigated. A broad range of ...composite compositions (up to 50 vol % CF and 20 vol % CB) was studied. The percolation thresholds of binary PMMA/CF and PMMA/CB composites were determined to 31.8 and 3.9 vol %, respectively. Experimental conductivity contour plots for PMMA/CF/CB ternary composites were presented for the first time. Additionally, based on a model for predicting the percolation threshold of ternary composites, a novel equation was proposed to predict the conductivity of ternary composites, showing results in agreement with corresponding experimental data. Finally, two mechanical contour plots for elastic modulus and tensile strength were presented, showing how the decreasing tensile strength and increasing E-modulus of the PMMA/CF/CB ternary composites was depending on the CB and CF filling fractions. The systematic measurements and novel equations presented in this work are especially valuable when designing ternary conductive polymer composites with two different fillers.
Novel High‐Speed Elongation Rheometer Bier, Alexander M.; Arne, Walter; Schubert, Dirk W.
Macromolecular materials and engineering,
July 2022, 2022-07-00, 20220701, Letnik:
307, Številka:
7
Journal Article
Recenzirano
Odprti dostop
The elongational viscosity of polymers can be determined by utilizing different devices such as extensional rheometer after Sentmanat (SER), oil bath rheometer after Meissner or tensile rheometer ...after Münstedt (MTR), with strain rates up to 10 s–1. Although these investigations are already complex, they do not depict real fiber spinning processes where higher elongation strain rates occur. Therefore, a novel method is developed to calculate the elongational viscosity of polymers during the fiber spinning process. To reduce the complexity of the system, two polymethylmethacrylates (PMMAs) with different molar masses are investigated using a capillary rheometer to exclude crystallization effects. The diameter of the polymeric strand is determined via a high‐speed camera from the die exit to the aspirator. In addition, simulations are carried out to describe the temperature profile of the polymeric strand along the spinline. It is possible to determine the elongational viscosity of the polymers in dependence of temperature and strain rates up to 100 s–1, by calibration of the force in an aerodynamic stretching device (aspirator).
This work reveals a novel method to determine the elongational viscosity during fiber spinning at elongation rates that are highly relevant to industrial processes. High‐speed camera recordings along the spinline as well as temperature simulations of the polymeric strand are performed. The elongational viscosity calculated from this is then mastered to interpret the results.
Alginate dialdehyde–gelatin (ADA–GEL) hydrogels have been reported to be suitable matrices for cell encapsulation. In general, application of ADA–GEL as bioink has been limited to planar structures ...due to its low viscosity. In this work, ring shaped constructs of ADA–GEL hydrogel were fabricated by casting the hydrogel into sacrificial molds which were 3D printed from 9% methylcellulose and 5% gelatin. Dissolution of the supporting structure was observed during the 1
st
week of sample incubation. In addition, the effect of different crosslinkers (Ba
2+
and Ca
2+
) on the physicochemical properties of ADA–GEL and on the behavior of encapsulated MG-63 cells was investigated. It was found that Ba
2+
crosslinked network had more than twice higher storage modulus, and mass decrease to 70% during incubation compared to 42% in case of hydrogels crosslinked with Ca
2+
. In addition, faster increase in cell viability during incubation and earlier cell network formation were observed after Ba
2+
crosslinking. No negative effects on cell activity due to the use of sacrificial materials were observed. The approach presented here could be further developed for cell-laden ADA–GEL bioink printing into complex 3D structures.
Clean water is one of the most important resources of the planet but human‐made contamination with diverse pollutants increases continuously. Microplastics (<5 mm diameter) which can have severe ...impacts on the environment, are present worldwide. Degradation processes lead to nanoplastics (<1 µm), which are potentially even more dangerous due to their increased bioavailability. State‐of‐the‐art wastewater treatment plants show a deficit in effectively eliminating micro‐ and nanoplastics (MNP) from water, particularly in the case of nanoplastics. In this work, the magnetic removal of three different MNP types across three orders of magnitude in size (100 nm–100 µm) is investigated systematically. Superparamagnetic iron oxide nanoparticles (SPIONs) tend to attract oppositely charged MNPs and form aggregates that can be easily collected by a magnet. It shows that especially the smallest fractions (100–300 nm) can be separated in ordinary high numbers (1013 mg−1 SPION) while the highest mass is removed for MNP between 2.5 and 5 µm. The universal trend for all three types of MNP can be fitted with a derived model, which can make predictions for optimizing SPIONs for specific size ranges in the future.
Water contamination with pollutants like micro‐ and nanoplastics is continuously increasing with drastic consequences for flora and fauna. Surface modified superparamagnetic iron oxide nanoparticles (SPIONs) can trigger the formation of magnetically collectable agglomerates of diverse polymers of different sizes (100 nm–100 µm). A derived model may help to tailor the SPIONs in future toward a specific plastic size.
Five different poly (ethylene terephthalate) (PET) materials (two recycled and three virgin ones) were melt-spun into fibres using a capillary rheometer and aerodynamic stretching. In order to cover ...a wide range of processing parameters, two temperatures in combination with six different take-up pressures were used during the melt spinning process. The surface smoothness, diameter and mechanical properties of the PET fibres were investigated. Compared with other studies, this study provides comprehensive research on melt-spun PET fibres. One recycled PET and one virgin PET in this study showed acceptable tenacity, outstanding elongation at break and desirable fibre fineness in denier. The molecular and rheological properties of these materials were studied further and presented minor differences in weight-average molar mass and molar mass distribution as well as in their viscosity, which resulted in their similar processing behaviour. This study proved the possibility to make a fibre from bottle-grade recycled co-polymer PET with similar properties to the fibre-grade virgin homo-polymer PET.
•Two recycled and three virgin PET materials were investigated to be melt-spun into fibres.•A wide range of processing parameters was covered during the melt spinning process.•rPET-B and vPET-1 showed acceptable tenacity, outstanding elongation at break and a desirable fibre fineness.•It was possible to make a fibre from bottle-grade recycled co-polymer PET with similar properties to the fibre-grade virgin homo-polymer PET.•The similar mechanical properties of fibres were related to a higher crystallinity for vPET-1 but to a higher molecular orientation for rPET-B.
Multiple system atrophy (MSA) is a rare and rapidly progressive atypical parkinsonian disorder characterized by oligodendroglial cytoplasmic inclusions containing α‐synuclein (α‐syn), demyelination, ...inflammation and neuronal loss. To date, no disease‐modifying therapy is available. Targeting α‐syn‐driven oligodendroglial dysfunction and demyelination presents a potential therapeutic approach for restricting axonal dysfunction, neuronal loss and disease progression. The present study investigated the promyelinogenic potential of sobetirome, a blood–brain barrier permeable and central nervous system selective thyromimetic in the context of an in vitro MSA model. Oligodendrocyte precursor cells (OPCs) were obtained from transgenic mice overexpressing human α‐syn specifically in oligodendrocytes (MBP29 mouse line), a well‐described MSA model, and non‐transgenic littermates. mRNA and protein expression analyses revealed a substantial rescue effect of sobetirome on myelin‐specific proteins in control and α‐syn overexpressing oligodendrocytes. Furthermore, myelination analysis using nanofibres confirmed that sobetirome increases both the length and number of myelinated segments per oligodendrocyte in primary murine α‐syn overexpressing oligodendrocytes and their respective control. These results suggest that sobetirome may be a promising thyromimetic compound targeting an important neuropathological hallmark of MSA.
Sobetirome induces myelin markers in α‐syn overexpressing oligodendrocytes, increases length and number of myelinated nanofibres and is a potential rescue of α‐syn‐driven oligodendrocyte dysfunction.
The creep behavior is one of the most important properties and should be characterized to evaluate long-term durability and reliability of polymeric materials. An alteration of the crystalline ...structure and morphology in the semicrystalline polymer leads to a change in the creep behavior as well. In this work, in order to understand the creep behavior of different morphologies, a modified injection molding technology with twice melt filling (M2) was used to prepare isotactic polypropylene (iPP) samples with controllable skin-core structure. The different shear layer thicknesses were obtained by adjusting the time intervals of the twice melt filling. Compared with the conventional injection-molded samples (M1), M2 samples present better efficiencies in reducing the creep and recovery response, and the response was strongly influenced by the shear layer thicknesses. For example, the thickness of skin layer of M2 sample with a time interval of 9 s increased approximately 42% and its creep deformation reduced to 52% at 80 °C. It was also found that the creep and recovery strain reduced with decreased temperature or with applied stress. In addition, several theoretical models were used to describe the creep and recovery behavior of M2 samples for a better understanding of the mechanisms.
•Samples with controllable skin-core structure was prepared by a modified injection molding technology.•Different shear layer thicknesses were obtained by adjusting the time interval of the twice melt fillings.•Samples present better efficiencies in reducing the creep and recovery response.•Creep and recovery strain reduced with decreased temperature or with applied stress.
•Steady state viscosity obtained from both experimental modes is good agreement.•A well linear relationship between activation energy and molar mass was found.•Well overlapped master curves were ...obtained from modulus and compliances.
The influence of molar mass and temperature on the rheological properties of polymethylmethacrylate (PMMA) melts was investigated by dynamical mechanical and creep-recovery experiments. The results shown that the steady state viscosities obtained from both experimental modes were in good agreement, and a well linear relationship between the activation energy and molar mass was obtained. The creep compliance of PMMA increased with the molar mass increased or temperature decreased, while the linear steady state recoverable compliance was found to be independent of the molar mass and temperature. Moreover, it was found that the master curves followed the time-temperature superposition principle well in the whole frequency range or time scale.
The crystallinity of polymers is usually determined via Differential Scanning Calorimetry (DSC), X-ray diffraction (XRD) or density measurements. Even though DSC is an easy and fast way to determine ...crystallinity, it suffers of several disadvantages in the case of fibers and nonwovens. In DSC studies, the sample preparation of fiber material may be difficult, results are not calibration free and heat is introduced in the measuring process, which might lead to transitions in instable crystal structures in the polymer. XRD is able to overcome these problems but is also time consuming and complicated in terms of sample preparation and evaluation of the measurements. Furthermore, it is not possible to determine surface crystallinity or crystallinity gradients inside the specimen with both methods.
Based on approaches found in literature, a method was developed which is capable of measuring the degree of crystallinity in the bulk and at the surface of Polypropylene via Fourier transformed infrared spectroscopy. A broad set of calibration samples with a wide range of degrees of crystallinity but without a crystallinity gradient was produced by cooling samples with cooling rates from 1 to 3500 K min−1. The degree of crystallinity was then determined from the ratio of the maximum peak height at 974 cm−1 and the maximum peak height at 998 cm−1 multiplied by 61.4%.
Consecutively, the transferability of the method to the measurement of fibers and nonwovens is demonstrated and verified via procedures which are already well described in literature. This method has an excellent reproducibility, spatial resolution and is capable of determining the degree of crystallinity in less than 5 min. Furthermore, this method is easy to implement and does not require further sample preparation.
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•Development of a method, which is able to measure surface and bulk crystallinity of Polypropylene.•Method is capable of measuring surface and bulk crystallinity of fibers in a non-destructive, location-sensitive and fast way.•Surface and bulk crystallinity of fibers and nonwovens produced under different processing conditions is determined.•Influence of the calendaring process on bonding points and fibers spun from the melt is shown.•Influence of storage time and temperature on fiber crystallinity and post-crystallization is revealed.
Electrospinning of biopolymer and inorganic substances is one of the efficient ways to combine various advantageous properties in one single fibrous structure with potential for tissue engineering ...applications. In the present study, to integrate the high stiffness of polyhydroxybutyrate (PHB), the flexibility of poly(ε-caprolactone) (PCL) and the bioactivity of 58S bioactive glass, PHB/PCL/58S sol–gel bioactive glass hybrid scaffolds were fabricated using combined electrospinning and sol–gel method. Physical features such as fiber diameter distribution, mechanical strength and Young’s modulus were characterized thoroughly. FTIR analysis demonstrated the successful incorporation of 58S bioactive glass into the blend polymers, which greatly improved the hydrophilicity of PHB/PCL fibermats. The primary biological response of MG-63 osteoblast-like cells on the prepared fibrous scaffolds was evaluated, proving that the 58S glass sol containing hybrid scaffold were not only favorable to MG-63 cell adhesion but also slightly enhanced cell viability and significantly increased alkaline phosphate activity .
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