Evaluation of thermal properties and crystallinity in PHB-based systems - a DoE approach

Complex formulations based on poly(hydroxybutyrate) (PHB) and poly(hydroxybutyrate-co-valerate) (PHBV) were studied to statistically assess the effect of formulation (i.e., hydroxyvalerate (HV) content, plasticiser chemistry and content, filler type and content) on their thermal properties and degree of crystallinity (Xc). In binary systems, thermal properties were mainly influenced by filler type rather than its content, while for plasticised systems the changes were dependent on both increasing plasticiser content and PHB-plasticiser compatibility. Variations in HV content affected the ability of the polymer chain to fold, leading to significant changes in both thermal properties and Xc. In ternary systems, presence of multiple additives and consequent changes in intermolecular interactions lead to multifaceted behaviours that were not easily predicted by results from binary systems alone. For example, melting temperature did not show dependence on filler presence in PHBV systems despite introducing variations in pure PHB systems. In general, thermal properties and Xc are affected by all parameters studied, with changes in system free volume (i.e. changes in HV content and plasticisation) playing the most significant role. These results expand the understanding of factors controlling crystallisation in complex polymer systems and can be used to control matrix properties in new generations of packaging materials

Polyhydroxybutyrate : a review of experimental and simulation studies on the effect of fillers on crystallinity and mechanical properties

Polyhydroxybutyrate (PHB) is a sustainable polymer that is a promising candidate for replacing petroleum-based plastics in food packaging. Fillers are used to improve the mechanical properties of PHB composites, simultaneously changing the crystallinity of the polymer matrix. However, it is not well understood how fillers affect crystallisation and microstructure, and thus the resulting mechanical properties of the composite. This review summarises simulation work on polymer nucleation and crystallisation and how nucleation is influenced by different types of polymer/filler interfaces. Experimental studies of PHB composites with a wide variety of fillers are reviewed to find trends between the filler type, crystallinity, and mechanical properties. It is clear that fillers act as nucleants that increase the number of spherulites while reducing spherulite size. This behaviour is apparent for almost all fillers regardless of filler chemistry or topology. However, the data obtained from literature does not seem to produce strong conclusions about the effect of degree of crystallinity on the tensile properties of PHB-filler composites, although there are some weak trends that indicate the importance of microstructure. In order to enable prediction and control of PHB composite properties, it is clear that further systematic studies are required to elucidate the effect of specific filler types and the connection between crystallinity, microstructure, and the mechanical properties

Running performance at high running velocities is impaired but V'O_{2max} and peripheral endothelial function are preserved in IL-6^{−/−} mice

It has been reported that IL-6 knockout mice (IL-6^{−/−}) possess lower endurance capacity than wild type mice (WT), however the underlying mechanism is poorly understood. The aim of the present work was to examine whether reduced endurance running capacity in IL-6^{−/−} mice is linked to impaired maximal oxygen uptake (V′O_{2max}), decreased glucose tolerance, endothelial dysfunction or other mechanisms. Maximal running velocity during incremental running to exhaustion was significantly lower in IL-6−/− mice than in WT mice (13.00±0.97 m.min^{-1} vs. 16.89±1.15 m.min^{-1}, P<0.02, respectively). Moreover, the time to exhaustion during running at 12 m.min^{-1} in IL-6^{−/−} mice was significantly shorter (P<0.05) than in WT mice. V′O_{2max} in IL-6^{−/−} (n = 20) amounting to 108.3±2.8 ml.kg^{-1}.min^{-1} was similar as in WT mice (n = 22) amounting to 113.0±1.8 ml.kg^{-1}.min^{-1}, (P = 0.16). No difference in maximal COX activity between the IL-6^{−/−} and WT mice in m. soleus and m. gastrocnemius was found. Moreover, no impairment of peripheral endothelial function or glucose tolerance was found in IL-6^{−/−} mice. Surprisingly, plasma lactate concentration during running at 8 m.min−1 as well at maximal running velocity in IL-6^{−/−} mice was significantly lower (P<0.01) than in WT mice. Interestingly, IL-6^{−/−} mice displayed important adaptive mechanisms including significantly lower oxygen cost of running at a given speed accompanied by lower expression of sarcoplasmic reticulum Ca^{2+}-ATPase and lower plasma lactate concentrations during running at submaximal and maximal running velocities. In conclusion, impaired endurance running capacity in IL-6^{−/−} mice could not be explained by reduced V′O_{2max}, endothelial dysfunction or impaired muscle oxidative capacity. Therefore, our results indicate that IL-6 cannot be regarded as a major regulator of exercise capacity but rather as a modulator of endurance performance. Furthermore, we identified important compensatory mechanism limiting reduced exercise performance in IL-6^{−/−} mice

Molecular migration in complex industrial formulations

Understanding migration of small molecules within polymer matrices (either additives already in the matrix or those infiltrating from adjacent media) is a challenge in many industrial systems. Migration can lead to undesirable changes in product properties, reduced shelf-lives and increased material wastage that is harmful for the environment. Herein, this challenge is addressed by studying the migration characteristics of model additives (surfactants of various head group chemistry, plasticiser, and fluorophore) in poly(vinyl alcohol) (PVA) films that are widely used in single unit detergent applications. The aim of this project is to investigate how lateral migration (x,y-migration) and vertical migration (z-migration) of small molecules affect film behaviour, establishing the mechanisms that influence this phenomenon, the molecular interactions associated, and their timescales. To fully address the complex, multi-component nature of PVA-based films, complexity was introduced stepwise into the system. First, the migration mechanisms of a model additive (rhodamine B, RhB) were tracked through aqueous solutions of PVA, glycerol (a plasticiser) and surfactants of various head group chemistry (cationic, nonionic, and anionic) using fluorescence correlation spectroscopy. Specific intermolecular interactions and steric effects were revealed to be the primary factors influencing migration in formulations containing ionic surfactants and nonionic surfactants, respectively. Presence of the plasticiser was shown to decrease the diffusivity of the tracer, chiefly due to increased viscosity in the system. These solutions were then spin-coated, and RhB diffusion through the resultant films was tracked using fluorescence recovery after photobleaching. In films, an additional mechanism of migration was identified – compatibility of the components in the system, with phase separation of glycerol from the PVA matrix lowering the overall tracer diffusivity; again, intermolecular interactions and steric effects controlled tracer diffusivity in the surfactant-doped systems. Third, the mechanism of surfactant migration was studied as films were aged under various environmental conditions (primarily relative humidity, RH). The plasticising effect of atmospheric water was demonstrated, with films restructuring to reach equilibrium molecular conformation. The nature and speed of the restructuring was dependent on surfactant concentration and its compatibility with the other components of the system. The properties of the PVA-based matrix were then measured upon exposing it to elevated temperature, with system compatibility overall increasing as the glass transition temperature was exceeded. A significant dependence on compatibility was observed while changing the properties of the matrix (increased degree of hydrolysis (DH) and molecular weight (Mw) of the polymer) as well as introducing a second surfactant to the system. However, the molecular arrangement of surfactant within the polymer matrix remained the same independent of polymer DH and Mw. Overall, observed changes could be explained by the compatibility of the four components with one another, their hydrogen bonding, and other intermolecular interactions in the system. Finally, wetting of PVA-based film by water, dodecane, or aqueous surfactant solutions of various head group chemistry were examined. Variations in solvophilic behaviour were observed upon changing the polymer crystallinity, crystallite size, size of the free volume cavities, and polymer entanglement, regardless of liquid medium. Further, matrix hydrophilicity was identified as an important factor controlling infiltration of surfactant solutions into the polymer matrix. Through this work, importance of environmental conditions and chemical environment on molecular migration is highlighted, providing a set of variables that need to be controlled while designing migration in industrially relevant systems as well as future directions for further investigations

Evaluation of spherulite growth in PHB‐based systems – a DoE approach

Formulations based on poly(hydroxybutyrate) (PHB) and poly(hydroxybutyrate‐co‐valerate) were studied to statistically assess the importance of process parameters (temperature) and chemistry in filled and/or plasticized PHB‐based formulations on spherulite growth rate (SGR) and nucleation density (ND). It was found that in binary systems, addition of a plasticizer results in shift of the maximum SGR towards lower temperatures, with the value of the shift dependent on polymer‐plasticizer compatibility. The presence of the filler does not significantly influence SGR, instead resulting in ND changes dependent on filler chemistry, with Cloisite Ca++ showing the strongest nucleating action in all formulations among fillers studied. In ternary systems, statistical analysis shows that SGR strongly depends on the crystallization temperature (Tc), plasticizer type and concentration, and hydroxyvalerate content in the polymer chain while being independent of the presence and chemistry of the filler in the system. ND has, however, proven to be dependent on all investigated parameters, including both filler type and its concentration, with Tc being the most important factor. These results expand the understanding of factors controlling crystallization in polymer systems and provide an initial set of design tools that can be used to control mechanical properties in new generations of packaging materials

Exercise Training Decreases Nitrite Concentration in the Heart and Locomotory Muscles of Rats Without Changing the Muscle Nitrate Content

Background Skeletal muscles are postulated to be a potent regulator of systemic nitric oxide homeostasis. In this study, we aimed to evaluate the impact of physical training on the heart and skeletal muscle nitric oxide bioavailability (judged on the basis of intramuscular nitrite and nitrate) in rats. Methods and Results Rats were trained on a treadmill for 8 weeks, performing mainly endurance running sessions with some sprinting runs. Muscle nitrite (NO2−) and nitrate (NO3−) concentrations were measured using a high‐performance liquid chromatography–based method, while amino acids, pyruvate, lactate, and reduced and oxidized glutathione were determined using a liquid chromatography coupled with tandem mass spectrometry technique. The content of muscle nitrite reductases (electron transport chain proteins, myoglobin, and xanthine oxidase) was assessed by western immunoblotting. We found that 8 weeks of endurance training decreased basal NO2− in the locomotory muscles and in the heart, without changes in the basal NO3−. In the slow‐twitch oxidative soleus muscle, the decrease in NO2− was already present after the first week of training, and the content of nitrite reductases remained unchanged throughout the entire period of training, except for the electron transport chain protein content, which increased no sooner than after 8 weeks of training. Conclusions Muscle NO2− level, opposed to NO3−, decreases in the time course of training. This effect is rapid and already visible in the slow‐oxidative soleus after the first week of training. The underlying mechanisms of training‐induced muscle NO2− decrease may involve an increase in the oxidative stress, as well as metabolite changes related to an increased muscle anaerobic glycolytic activity contributing to (1) direct chemical reduction of NO2− or (2) activation of muscle nitrite reductases

Skeletal muscle response to endurance training in IL-6^{-/-} mice

We examined effects of moderate-intensity endurance training on muscle COX/CS activities and V’O2max in control WT and IL-6−/− mice. Animals were exercised for 10 weeks on treadmill for 1 h, 5 days a week at velocity of 6 m·min−1 which was increased by 0.5 m·min−1 every 2 weeks up to 8 m·min−1 . Training triggered an increase of enzyme activities in soleus muscle of WT mice (COX: 480.3±8.9 U·g−1 in sedentary group vs. 773.3±62.6 U·g−1 in trained group, P&lt;0.05 and CS: 374.0±6.0 U·g−1 in sedentary group vs. 534.2±20.5 U·g−1 in trained group, P&lt;0.01, respectively) whereas no changes were observed in soleus of IL6−/− mice. Moreover, in mixed gastrocnemius muscle of trained IL-6−/− mice enzyme activities tended to be lower (COX: 410.7±48.4 U·g−1 for sedentary vs. 277.0±36.5 U·g−1 for trained group and CS: 343.8±24.6 U·g−1 for sedentary vs. 251.7±27.1 U·g−1 for trained group). No changes in V’O2max were observed in WT and IL-6−/− mice after training. Concluding, moderate-velocity endurance training-induced increase in COX and CS activities in muscles of WT mice only which suggests that IL-6 regulates training-induced skeletal muscle responses to exercise. Copyright © 2015, Georg Thieme Verlag KG. All rights reserved

The blood count and plasma lipid profile of WT control and IL-6^−/− mice.

<p>WBC (white blood cells: LYM% (% of lymphocytes), MON% (% of monocytes), GRA% (% of granulocytes)), RBC (red blood cells), HGB (hemoglobin), HCT (hematocrit), MCV ((red cell) mean corpuscular volume), MCH ((red cell) mean corpuscular hemoglobin), MCHC ((red cell) mean corpuscular hemoglobin concentration), RDW (red cell distribution width), PLT (platelets), MPV (mean platelets volume), LDL (low-density lipoprotein), HDL (high-density lipoprotein), TC (total cholesterol), TG (triglicerydes). Data are presented as means ± SEM.</p