Biodegradable blends of amorphous poly(lactic acid) (aPLA) and polycaprolactone (PCL) and nanocomposites of these blends were developed by melt blending. A morphological study of the bioblends was ...carried out by means of WAXS and SEM showing immiscible behavior. The nanocomposites were also characterized morphologically by WAXS, TEM and SEM, revealing high degree of interaction of the nanoclays with the aPLA. Mechanical, thermal and gas barrier properties of the different blends and nanocomposites were studied and the effect of blending and clay addition on the above‐mentioned properties was evaluated.
The miscibility of poly(d l-lactide) and poly(ε-caprolactone) (PDLLA/PCL) blends in a wide composition range was studied by the thermally stimulated depolarization currents technique by following the ...local and segmental dielectric relaxations changes as the blend composition is varied. The PCL primary relaxation is slightly shifted to higher temperatures as the PDLLA content increases, thus demonstrating the existence of a rich PCL phase and partial miscibility with PDLLA. Wide-angle X-ray scattering showed that neat PDLLA was amorphous, as expected for a sample with 12 mol % d-lactide isomer; nevertheless, the presence of 3D order was detected in the PDLLA that was melt blended with PCL. Differential scanning calorimetry also evidenced chain interaction by the decrease in the melting and crystallization temperatures as well as in the PCL crystallization kinetics which becomes slower in the presence of increasing amounts of PDLLA.
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► Important differences between abiotic and bio-degradation of PDLLA, PCL and blend. ► Possible prediction of degradation trend of miscible PDLLA/PCL blends. ► Dependence of ...environment and polymer phase content on PDLLA/PCL blend degradation.
Important differences between the biotic and abiotic hydrolysis of neat poly(dl-lactide) (PDLLA), poly(ε-caprolactone) (PCL) and a partially miscible PDLLA/PCL blend were found in this work. In abiotic conditions, the degradation process of all the studied specimens mainly proceeded by a bulk degradation mechanism and the diffusion rate of degradation products into the medium was relatively slow after 18weeks. The hydrophobic and semi-crystalline nature of PCL matrix made this polymer very stable against abiotic hydrolysis, whereas the degradation of PDLLA proceeded much faster due to its amorphous structure. In the first stages of degradation, PDLLA/PCL blend showed that its rich continuous PDLLA phase catalyzed the hydrolysis of the PCL phase, while the low content of PCL molecules partially delayed hydrolysis of PDLLA matrix. In compost, higher levels of degradation were found for all the studied systems during the first 12weeks of degradation, indicating an important effect of enzymes from microbes in compost on the degradation of PDLLA and PCL. Neat PDLLA and PDLLA/PCL blend seemed to degrade mainly by a bulk degradation mechanism, at least during the first 12weeks, such as previously observed in abiotic conditions, whereas PCL was preferentially degraded by a surface mechanism due to a very strong catalytic effect of microorganisms on its degradation. Contrary to the abiotic degradation, it was observed that the presence of a low content of PCL molecules in the rich-PDLLA blend did not interfere with the degradation trend of PDLLA in compost, and that the continuous PDLLA phase could partially suppress the biotic degradation of PCL molecules.
In general, abiotic and biotic hydrolysis of PDLLA/PCL blends seems to be a complex phenomenon depending not only on the mixing ratio of both polymers but also on their crystallinity, miscibility level of polymer phases and the preferential degradation mechanism of each polymer component. If blends of PDLLA/PCL present a similar level of miscibility, it would be possible to estimate if the presence of the PDLLA or PCL phase could have a general catalytic or delaying role in the blend during the initial degradation stages, depending on which environment they are subjected to and the content of each polymer phase in the blend.
An effective hydrolytic degradation of PDLLA, PCL and their blends in a phosphate-buffered solution of pH 4.0 at 37 °C for 18 weeks was achieved, observing a considerably faster degradation of PDLLA ...as compared to PCL due to the hydrophobic and semicrystalline nature of PCL matrix, able to partially prevent water diffusion into the bulk specimen.
DSC and FTIR results indicated that PCL phase, in compositions rich in PCL, was very stable against hydrolysis, but the presence of PDLLA in the PDLLA/PCL blends seemed to catalyze the hydrolytic degradation of the PCL phase, probably associated to easier diffusion of water into the PCL domains by the presence of PDLLA amorphous regions. This last trend was proportional to the content of PDLLA in the blends, excepting for the composition 64%PDLLA/36%PCL. It was confirmed that PCL molecules partially delayed hydrolysis of PDLLA molecules, according to FTIR analysis, and the water diffusion prevention level was proportional to the content of PCL in the blends, except for the system 64%PDLLA/36%PCL, which presented a lower extent of degradation than neat PDLLA but higher than the blend 80%PDLLA/20%PCL. This indicated that PCL molecules did not significantly impede hydrolysis of PDLLA molecules in this blend, possibly due to the achievement of a particular structure of the PDLLA/PCL interphase in this blend. In general, hydrolysis of PDLLA/PCL blends was found to be a complex phenomenon depending not only on the content of both polymer phases, but also on the polymer phase crystallinity and morphology.
In the present work, we have studied the effect of the piezoelectricity of elastically deformed cortical bone collagen on surface using a biomimetic approach. The mineralization process induced as a ...consequence of the piezoelectricity effect was evaluated using scanning electron microscopy (SEM), thermally stimulated depolarization current (TSDC), and differential scanning calorimetry (DSC). SEM micrographs showed that mineralization occured predominantly over the compressed side of bone collagen, due to the effect of piezoelectricity, when the sample was immersed in the simulated body fluid (SBF) in a cell-free system. The TSDC method was used to examine the complex collagen dielectric response. The dielectric spectra of deformed and undeformed collagen samples with different hydration levels were compared and correlated with the mineralization process followed by SEM. The dielectric measurements showed that the mineralization induced significant changes in the dielectric spectra of the deformed sample. DSC and TSDC results demonstrated a reduction of the collagen glass transition as the mineralization process advanced. The combined use of SEM, TSDC, and DSC showed that, even without osteoblasts present, the piezoelectric dipoles produced by deformed collagen can produce the precipitation of hydroxyapatite by electrochemical means, without a catalytic converter as occurs in classical biomimetic deposition.
In this work the thermal behaviour of crosslinked low density polyethylene (XLPE) used as an insulator for commercial underground high tension (15 kV) cables was studied. Three types of materials ...were selected: an uncrosslinked low density polyethylene (NXLPE) used as a control sample, an XLPE and an aged XLPE sample. The ageing conditions involved the application of multiple stresses: temperature, voltage and voltage impulses during 60 d under time and temperature cycles that are the most representative load of daily operation in Caracas, Venezuela. The effect of morphology segregation or thermal fractionation under multiple stresses conditions was analysed by measuring the percentage of crosslinking before and after the ageing tests were performed, and by investigating the thermal response of the material by conventional DSC and by the application of the successive self‐nucleation and annealing (SSA) thermal fractionation technique. The degree of crosslinking was found to vary in the material depending on the distance from the conductor because a thermal gradient is generated radially during the curing reaction. Such differences did not significantly affect the usual DSC heating scans of the samples. However, when SSA was applied, a difference in the distribution of thermal fractions was detected as a function of the distance towards the conductor that could be correlated to the variations in the crosslinking degree. After the accelerated ageing the thermal response of XLPE changes as evidenced by the presence of multiple melting peaks in subsequent DSC heating scans. This multiple melting was interpreted, as a first approximation, as arising from thermal fractionation during ageing (ignoring the possible effects of the other stresses applied) and SSA was able to simulate a similar fractionation that was very accurate in the prediction of the exact temperatures of the melting peaks produced.
We investigate the effects of clay proportion and nanoscale dispersion in the dielectric response of poly(vinyl alcohol)-bentonite nanocomposites. The dielectric study was performed using the ...thermally stimulated depolarization current technique, covering the temperature range of the secondary and high-temperature relaxation processes. Important changes in the secondary relaxations are observed at low clay contents in comparison with neat poly(vinyl alcohol) (PVA). The high-temperature processes show a complex peak, which is a combination of the glass-rubber transition and the space-charge relaxations. The analysis of these processes shows the existence of two segmental relaxations for the nanocomposites. Dielectric results were complemented by calorimetric experiments using differential scanning calorimetry. Morphologic characterization was performed by x-ray diffraction (XRD) and transmission electron microscopy (TEM). TEM and XRD results show a mixture of intercalated and exfoliated clay dispersion in a trend that promotes the exfoliated phase as the bentonite content diminishes. Dielectric and morphological results indicate the existence of polymer-clay interactions through the formation of hydrogen bounds and promoted by the exfoliated dispersion of the clay. These interactions affect not only the segmental dynamics, but also the secondary local dynamics of PVA.
To asses if telemedicine with telemonitoring is a clinically useful and secure tool in the tracking of patients with COVID-19.
A prospective observational study of patients with COVID-19 diagnosis by ...positive PCR considered high-risk tracked with telemedicine and telemonitoring was conducted in the sanitary area of Lugo between March 17th and April 17th, 2020. Two groups of patients were included: Outpatient Tracing from the beginning and after discharge. Every patient sent a daily clinical questionnaire with temperature and oxygen saturation 3 times a day. Proactive monitoring was done by getting in touch with every patient at least 11a day.
313 patients (52.4% female) with a total average age of 60.9 (DE 15.9) years were included. Additionally, 2 patients refused to join the program. Since the beginning, 224 were traced outpatient and 89 after being discharged. Among the first category, 38 (16.90%) were referred to Emergency department on 43 occasions; 18 were hospitalized (8.03%), and 2 deceased. Neither deaths nor a matter of vital emergency occurred at home. When including patients after admissions monitoring was done in 304 cases. One patient re-entered (0.32%) to the hospital, and another one left the program (0.32%). The average time of monitoring was 11.64 (SD 3.58) days, and 224 (73.68%) patients were discharged during the 30 days of study.
Our study suggests that telemedicine with home telemonitoring, used proactively, allows for monitoring high-risk patients with COVID-19 in a clinically useful and secure way.
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