The effects of the crystallinity and polymorphism of PLLA and PDLA–PLLA 50:50 blends on the free volume and transport properties have been studied. In the case of PDLA–PLLA 50:50 the increase on crystallinity promotes a process of densification and a reduction in free volume fraction and rigid amorphous fraction (RAF), contrary to PLLA in which the enlargement of a rigid amorphous fraction led to a dedensification. This result offers a unique opportunity to analyze separately the opposite influence in the transport properties of the crystallization and free volume associated with RAF. Overall, these findings provide a better understanding on the relationship between crystallinity and transport properties and would explain also the controversial data reported in the literature.

The electrocardiogram of diabetic patients shows a series of deviations from normal patterns, most of which involve the QT interval and the T wave. The QT interval is longer in patients with diabetes mellitus than in normal people [1]. Diabetic patients show a corrected QT interval (QTc), measured using Bazett's formula, longer than 0.44 s [2,3]. Using Holter ECG monitoring, the appearance of ventricular late potentials is more frequent in patients with Type I (insulin-dependent) diabetes mellitus than in healthy people, and even more frequent in patients with Type II (non-insulin-dependent) diabetes mellitus [4,5]. Nearly all these changes are related to repolarisation. The QRS complex lasts longer in diabetic patients than in control subjects, suggesting intracardiac conduction disorders, but this type of change has only been described in children [6].Various studies report a lengthening of the duration of the rat ventricular action potential (APD) stemming from diabetic cardiomyopathy as a possible cause of these changes [7±9]. None took into account, however, the regional variability in the duration of the action potential under control conditions [10,11]. Various reports pointed to a lowering of the transient outward current, I to [9,12,13] and, to a lesser extent, the delayed rectifying outward current, I K [9,12], as the main cause of the lengthening of APD. Initial studies did not take into account regional variations in the distribution of the repolarising outward Diabetologia (2000) Abstract Aims/hypothesis. To identify the possible causes of the lengthening of the action potential duration described in patients affected by diabetes mellitus. Methods. We studied the effects of streptozotocininduced diabetes on the current density of the repolarising potassium currents I to , I K , I ss and I K1 in enzymatically isolated myocytes from three different regions of rat heart: total right ventricle, subepicardium at the apex of the left ventricle and subendocardium at the base of the left ventricle. Results. No changes in I K1 were found due to diabetes, but there was a uniform decrease in I to (50 %) and I ss (40 %) current densities in the three regions.In contrast, I K diminished unevenly, with the greatest decrease in the subendocardium at the base of the left ventricle (48 %), followed by the subepicardium at the apex of the left ventricle (32 %) and right ventricle (10 %). Conclusion/interpretation. These findings suggest the existence of regional differences in ion channel expression associated with diabetes. The decrease of these repolarising currents could account for the lengthening of action potential and the consequent change in the Q-T interval of the ECG observed in diabetic rats. [Diabetologia (2000)

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The effectiveness of tributyl citrate (TbC) as a plasticizer for polylactide and polyhydroxybutyrate was analysed in order to improve the ductility of these polymers and make them good candidates for food packaging applications. Although the thermal and mechanical properties have been widely studied in the literature, the effect of the plasticizer on free volume and transport properties has not been deeply analysed. The free volume was characterized using positron annihilation lifetime spectroscopy observing its linear increase with TbC content. The permeability to water vapour, oxygen and carbon dioxide was determined and the obtained results were related to the changes in glass transition temperature, level of crystallinity of the samples and free volume. This work would allow a better understanding of the effect of the plasticizer on the barrier and mechanical properties of polymers allowing the development of competitive materials for packaging applications. © 2018 Society of Chemical Industry