Frans H. J. Maurer

Positronium formation at low temperatures: the role of trapped electrons

Abstract Measurements have been carried out of electron spin densities (by electron spin resonance technique) and positronium (Ps) formation probability as functions of Co-60 γ-irradiation dose in poly(methyl methacrylate) and linear poly(ethylene) at 77 K. We observe a linear relationship between the enhancement of the Ps formation and the density of trapped electrons in both polymers. This clear correlation strongly supports the previous suggestion by the authors that the increase in Ps formation with time (that has been observed at low temperatures for a number of polymers) can be explained as a reaction of free positrons with trapped electrons produced by the previously injected positrons.

Viscoelastic and Histologic Properties in Scarred Rabbit Vocal Folds After Mesenchymal Stem Cell Injection

Objective/Hypothesis: The aim of this study was to analyze the short‐term viscoelastic and histologic properties of scarred rabbit vocal folds after injection of human mesenchymal stem cells (MSC) as well as the degree of MSC survival. Because MSCs are antiinflammatory and regenerate mesenchymal tissues, can MSC injection reduce vocal fold scarring after injury?

Relation between free-volume quantities from PVT-EOS analysis and PALS

Abstract Unique information about the properties of free-volume sites in polymers is gained from positron annihilation lifetime spectroscopy (PALS). After calibration with the free-volume hole-fraction h PVT from pressure–volume–temperature and equation-of-state ( PVT –EOS) analysis using the Simha–Somcynsky theory, PALS data ( ortho -positronium ( o -Ps) lifetime τ 3 and o -Ps intensity I 3 ) may be used to calculate free-volume fractions h PALS from h PALS = C × V ( τ 3 )× I 3 , where V ( τ 3 ) is the subnanometer cavity hole-volume. The widespread use of this equation, in particular the correlation constant C , is given some attention, clarification and further improvement. From PVT data and PALS data, measured on chemically and physically identical amorphous poly(methyl methacrylate) samples, both below and above the glass transition temperature, we find improved relations: h B = B × V ( τ 3 ) and h PVT = k 1 + k 2 × V ( τ 3 ), where B , k 1 , and k 2 are correlation constants. We propose and show that the freezing fraction of polymer glasses can be calculated from the temperature coefficients of V ( τ 3 ), which further supports its close relation to h PVT .

Some remarks on the relation between free-volume fractions and ortho-positronium lifetimes in amorphous polymers

Unique information about the properties of free-volume sites in polymers is gained from Positron Annihilation Lifetime (PAL) measurements. After calibration with data from other techniques the method may be used to determine free-volume fractions. From pressure–volume–temperature (PVT) and PAL (ortho-Ps lifetime τ3) data, measured on identical amorphous poly(methyl methacrylate) (PMMA) samples with controlled thermal histories, we find a linear relationship between free-volume fractions, derived from PVT measurements, the Simha–Somcynsky equation-of-state theory and the mean subnanometer free-volume size both below and above the glass transition temperature.

Macroscopic pressure–volume–temperature properties versus free-volume characteristics of isotropic pressure-densified amorphous polymer glasses

We made a series of isotropic pressure-densified (0–200 MPa) amorphous homopolymer [atactic polystyrene (a-PS)] and copolymer [poly(styrene-co-acrylonitrile) (SAN) and poly(styreneco-maleic anhydride) (SMA)] glasses and studied their macroscopic pressure–volume–temperature (PVT) properties vs their free-volume characteristics from the Simha–Somcynsky equation-of-state (EOS) theory and from positron annihilation lifetime spectroscopy (PALS). The glass densities lie in the range of 1.0403–1.0535 g/cm3 (PS), 1.0573–1.0759 g/cm3 (SAN), and 1.0989–1.1196 g/cm3 (SMA). With increasing formation pressure, all pressure-densified glasses exhibit decreasing volume and free-volume characteristics such that the changes in specific volume (1.26%–1.85%) are <ortho-positronium (o-Ps) lifetime τ3 (5.5%–9.1%) <free-volume hole size V(τ3) (10.3%–17.1%) <free-volume fraction h (25.1%–30.5%). We find, furthermore, that the o-Ps formation probability I3 is independent of formation pressure. Likewise, the glasses’ thermal expan...

A new biological recovery approach for PHA using mealworm, Tenebrio molitor

Bacterial polyhydroxyalkanoates (PHA) are expensive partly due to the recovery and purification processes. Thus, many studies have been carried out in order to minimize the cost. Here we report on the use of mealworm, which is the larva of mealworm beetle (Tenebrio molitor) to recover PHA granules from Cupriavidus necator. Mealworms were shown to readily consume the freeze-dried C. necator cells and excrete the PHA granules in the form of whitish feces. Further purification using water, detergent and heat resulted in almost 100% pure PHA granules. Comparison with chloroform extraction showed no signs of reduction in the molecular weight and dispersion of the PHA molecules. Scanning electron microscopy and dynamic light scattering measurements revealed that the biologically recovered PHA granules retained their native spherical morphology. The PHA granules were subjected to a battery of tests to determine their purity and properties in comparison to the chloroform extracted PHA. This study has demonstrated the possibility of using mealworms as a biological agent to partially purify the PHA granules.

Revisiting the Single Cell Protein Application of Cupriavidus necator H16 and Recovering Bioplastic Granules Simultaneously

Cupriavidus necator H16 (formerly known as Hydrogenomonas eutropha) was famous as a potential single cell protein (SCP) in the 1970s. The drawback however was the undesirably efficient accumulation of non-nutritive polyhydroxybutyrate (PHB) storage compound in the cytoplasm of this bacterium. Eventually, competition from soy-based protein resulted in SCP not receiving much attention. Nevertheless, C. necator H16 remained in the limelight as a producer of PHB, which is a material that resembles commodity plastics such as polypropylene. PHB is a 100% biobased and biodegradable polyester. Although tremendous achievements have been attained in the past 3 decades in the efficient production of PHB, this bioplastic is still costly. One of the main problems has been the recovery of PHB from the cell cytoplasm. In this study, we showed for the first time that kilogram quantities of PHB can be easily recovered in the laboratory without the use of any solvents and chemicals, just by using the cells as SCP. In addition, the present study also demonstrated the safety and tolerability of animal model used, Sprague Dawley given lyophilized cells of C. necator H16. The test animals readily produced fecal pellets that were whitish in color, as would be expected of PHB granules. The pellets were determined to contain about 82-97 wt% PHB and possessed molecular mass of around 930 kg/mol. The PHB granules recovered biologically possessed similar molecular mass compared to chloroform extracted PHB [950 kg/mol]. This method now allows the production and purification of substantial quantities of PHB for various experimental trials. The method reported here is easy, does not require expensive instrumentation, scalable and does not involve extensive use of solvents and strong chemicals.

Free volume and mechanical properties of Palacos R bone cement.

The free volume and the mechanical properties of Palacos® R bone cement were determined from positron annihilation lifetime spectroscopy (PALS) and from dynamic mechanical thermal analysis (DMA) in the temperature ranges 24–220 °C and 30–120 °C, respectively. The heating of bone cement caused an appreciable reduction of the free volume, measured as a decrease in the ortho-positronium lifetime τ3 from 2.04 to 1.91 ns, as well as a clear increase in the storage modulus from 2.3 to 3.0 GPa. The changes in free volume and storage modulus after the heat treatment were interpreted as an effect of elimination of residual monomer from the bone cement. The free volume of the bulk-polymerized phase of bone cement was estimated from a simple difference method, suggesting that the residual monomer was eliminated from the bone cement between 60 and 90 °C, thus implying a glass transition temperature of only 60 °C for the bulk-polymerized phase. The spherical free volume cavity size estimated from the ortho-positronium lifetime V(τ3), and the storage modulus E′storage from DMA measurements were found to correlate by a linear relationship throughout the studied temperature range, and the correlation appeared to be independent of the presence of residual monomer.

Vibration and Acoustic Damping of Flexible Polyurethane Foams Modified with a Hyperbranched Polymer

The dynamic mechanical properties and acoustic damping of polyurethane (PU) foams loaded with a hyperbranched polymer (HBP) have been studied. The results show a significant modulus enhancement parallel to an increased vibration damping in the low frequency range of ~1 Hz with increased amount of HBP. Furthermore, an increased acoustic damping in the frequency interval of 500—1600 Hz is observed with increasing amount of HBP. The origin of these property enhancements are sought in the morphology and the chemical composition of the PU foam. It has been found that no visible differences in cell sizes and strut thicknesses exist among the foams. However, FTIR reveals significant differences in chemical composition between the foams of different HBP content, indicating increased crosslinking.

Tensile properties and interfacial interactions of bimodal hard/soft latex blends

In this work, the effect of composition, particle size and particle size ratio on the tensile properties of well-characterized hard/soft latex blends was investigated. Four blends of hard/soft latices, with varying particle sizes (either small or large), and volume fractions of 100/0, 80/20, 60/40, 50/50, 40/60, 20/80 and 0/100 were studied. The stress at break increased and the strain at break decreased as the amount of hard particles in the blend increased. A simple model, introduced by Pukanszky for filled polymers and polymer blends, proved to be a very useful tool for evaluating the tensile properties of the latex blends. Parameter B of the model could be related to the specific surface of the dispersed hard particles and the particle size ratio. Increasing the specific surface of the dispersed hard particles resulted in an increase in parameter B. The influence of particle size ratio on parameter B was shown to depend on the formation of aggregates.