Preparation of composite material BCP/DLPLG with a different content of ceramic and polymer component

Using a new approach of synthesis, homogenisation of DLPLG polymer powder and BCP gel, BCP/DLPLG composite material has been obtained with morphological and structural characteristics making it potentially very suitable for practical application in certain fields of the reconstructive medicine. The composite material has been synthesised with different ratios of ceramics and polymer BCP/DLPLG; 65/35w/w, 10/90 w/w, 5/95 w/w and 2/98w/w. The samples were characterized by Differential Scanning Calorimetry (DSC) and Scanning Electron Microscopy (SEM).Physical chemistry 2006 : 8th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 26-29 September 200

Properties of Isotactic Polypropylene Irradiated in Various Atmospheres

In this paper, changes in structure and physical properties of stabilized isotactic polypropylene (iPP) were created by gamma irradiation, up to a dose of 700 kGy, in different media: air, deionized distilled (DD) water and acetylene. Two main effects occur when polyolefins, such as iPP, are subjected to ionizing radiation: crosslinking and scission of macromolecules. The domination of one or the other of these competitive processes is determined by both the structural peculiarities of the polymers and the experimental irradiation conditions. Gel and infrared (IR) spectroscopy measurements were used to determine the changes in the degree of network formation and oxidative degradation, respectively. Sol gel analysis was studied in detail using the Charlesby-Pinner (C-P) equation. The radiation-induced changes in the structure and evolution of oxygen-containing species were also studied through dielectric loss (tan delta) analysis in a wide temperature and/or frequency range. Evolution of low temperature dielectric relaxations with gamma irradiation was investigated. The results showed that degradation was the major reaction in the initial step of irradiation, no matter what the atmosphere was. The C-P equation seemed applicable when stabilized iPP was irradiated within a certain dose range in various atmospheres. The iPP irradiated in acetylene/air had the lowest/highest values for oxidation level, dielectric losses, D(g) and G(s)/G(x) values. The calculated D(g) values are 1.5 and 5 times larger for the irradiation in DD water and air than for the acetylene. Furthermore, our data confirm that oxidation strongly affects the gel point but has a much lower effect on the G(s)/G(x) ratio. In the case of dielectric relaxation measurements, the connection between the oxidative degradation and dielectric properties is well established and is in good agreement with IR spectroscopy measurements. The amount of carbonyl, hydroperoxide and other polar groups is much higher for the irradiation in air than in other media, leading to higher dielectric losses. Disappearance of low temperature (delta and gamma) relaxations with gamma radiation confirmed great sensitivity of iPP structure to radiation-induced changes. Complete vanishing of the gamma relaxation in iPP samples irradiated in air is connected with a large radiation-induced oxidative degradation in this medium. Similar crosslinking, oxidation and dielectric behaviour was observed for the samples irradiated in water and acetylene, indicating DD water as a good crosslinking medium

On the enthalpy of melting of poly(l-lactide)

Poly(l-lactide) (PLLA) is an extensively employed biodegradable semicrystalline polymer with usage from implantable medical devices and drug release matrices to environmentally friendly packaging materials. Since the morphology and crystallinity considerably determine the application field, PLLA samples with a large variation in crystallinity (going from below 20% to over 70%) were prepared by different procedures. Subsequent differences in morphology, crystallinity and thermal properties were followed by scanning electron microscopy (SEM), wide angle X-ray diffraction (WAXD) measurements and differential scanning calorimetry (DSC). The value of the enthalpy of melting of a perfectly (100%) crystalline PLLA was determined (ΔH f = 115.7 J/g). © 2019, © 2019 Taylor & Francis Group, LLC

The influence of the preparation conditions and filler content on thermal properties of poly-L-lactide and hydroxyapatite/poly-L-lactide nanocomposite

Poly-L-lactide (PLLA) and hydroxyapatite/poly-L-lactide (HAp/PLLA) are two widely used biomaterials for three-dimensional scaffolds, drug release matrices and implantable medical devices for reparation of bone tissue; diversity in the initial preparation and filler content has a significant influence on different properties such as morphology and crystallinity, thus playing a considerable role in most of these applications. For this reason, PLLA and HAp/PLLA samples with a large difference in crystallinity (from below 20% to over 70%) and filler content (up to 86 wt% of HAp nanoparticles with an average diameter of 80 nm) were prepared and consequent dissimilarities in morphology, crystallinity and thermal properties were investigated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) measurements and Fourier transform infrared (FTIR) spectroscopy. Special attention was devoted to analyzing data obtained from thermal measurements. A three-phase model was employed in order to describe the heat capacity step decline in the nanocomposite; the evolution in different polymer fractions, the crystalline fraction and the mobile and rigid amorphous fractions, with filler content was determined. (c) 2017 Society of Chemical Industr

The resistance of poly-(l-lactide) to gamma radiation: effect of initial preparation and crystallinity

In order to investigate the resistance of poly-(l-lactide) (PLLA) to high-energy radiation, two varieties of samples with substantial differences in microstructure and crystallinity are prepared and exposed to the gamma radiation to various absorbed doses (up to 300 kGy). Since the PLLA morphology is sensitive to preparation conditions and radiation, surface microstructures are analyzed by scanning electronic microscopy. The chain scission degradation is followed using a gel permeation chromatography, while the additional characterization is conducted by differential scanning calorimetry, wide-angle X-ray diffraction method and IR spectroscopy. Presented results show that the quenched samples are more susceptible to radiation than initially high crystalline ones. Furthermore, the radiation leads to two considerably dissimilar recrystallization dynamics, connected with initial structural differences and the presence/absence of taut-tie chains. Radiation-induced increase in the crystallinity (more than 25% of initial value) for the quenched samples is noticeable at low radiation doses. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature

The influence of gamma radiation on the dielectric relaxation behaviour of isotactic polypropylene: The alpha relaxation

The high-temperature a relaxation in gamma irradiated isotactic polypropylene (iPP) was studied over the temperature (298-406 K), frequency (10(3)-10(6) Hz) and absorbed dose (0-700 kGy) ranges by means of dielectric spectroscopy. The multiple a relaxation was resolved from the 0 relaxation by curve fitting and its parameters were determined. Its position, intensity and activation energy were found to be strongly dependent on the changes in the structural and morphological parameters attributed to the exposure of the samples to radiation. Wide angle X-ray diffraction (WAXD) was used to investigate radiation-induced changes in the crystalline structure and degree of crystallinity, since this relaxation is connected with the crystal phase. Infrared (IR) spectroscopy and gel measurements were used to determine the changes in the oxidative degradation and the degree of network formation, respectively; the polar (carbonyl and/or hydroperoxide) groups that were introduced by irradiation were considered as tracer groups. Conclusions derived according to different methods were compared. The results reveal uncommon a relaxation behaviour with gamma radiation and confirm the multiple nature of this process, together with high dielectric and/or relaxation sensitivity of iPP to the radiation-induced changes. (C) 2009 Elsevier Ltd. All rights reserved

Hyperbolic propagation of a thermal signal in an inhomogeneous medium

A numerical procedure for the calculation of space distribution of the thermal field in thermally inhomogeneous solids with thermal memory induced by a harmonically modulated surface heat source is presented. The procedure is based on the division of the complex hyperbolic heat conduction equation into four real first-order differential equations, followed by employment of the Bulirsch-Stoer method with adoptive stepsize. The applicability of the procedure is then demonstrated in few issues, important for the understanding of thermal signal distribution.Current Research in Advanced Materials and Processes, 6th Conference of the Yugoslav-Materials-Research-Society, Sep 13-17, 2004, Herceg Novi, Montenegr

The influence of the initial preparation and crystallinity on the free radical evolution in gamma irradiated PLLA

Poly-L-lactide (PLLA) is a well-known biodegradable and biocompatible semi-crystalline polymer, used in a wide variety of applications, from implantable medical devices and drug release matrices to environmentally friendly packaging materials: diversity in the initial preparation, morphology and crystallinity plays a significant role in most of these applications. On the other hand, gamma radiation, as a processing tool, has often been used for the sterilisation of sensitive polymeric materials. This study presents the influence of the initial preparation and crystallinity on the gamma radiation-induced evolution of free radicals in PLLA. For this purpose, PLLA samples with a large variation in crystallinity (below 20% and over 70%), prepared by two different procedures, were exposed to gamma radiation in air to absorbed doses of 25, 50 and 100 kGy. The annealing treatment was applied to part of the samples, too. The presence and evolution of free radicals were followed using electron spin resonance (ESR) spectroscopy for three weeks. Further characterisation was performed by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD) measurements. Presented results show that depending on the initial preparation conditions, the radiation-induced changes in structure and properties of PLLA, as well as the evolution of free radicals, can differ significantly. Furthermore, the annealing treatment substantially reduces the concentration of long-lived free radicals, but can also introduce significant crystallisation. (C) 2011 Elsevier Ltd. All rights reserved.12th Tihany Symposium on Radiation Chemistry, Aug 27-Sep 01, 2011, Zalakaros, Hungar

Uniaxially Oriented High Density Polyethylene

The molecular relaxation behavior of an ice-quenched high density polyethylene (HDPE) subjected to solid-state stretching at elevated temperature (100 degrees C) to various draw ratios (up to lambda=13.7) was examined by means of dielectric spectroscopy. All relaxation zones (alpha, beta and gamma, in order of decreasing temperature) between 25 K and melting temperature were studied in the frequency range from 1 kHz to 1 MHz. The changes observed in different dielectric relaxations were related to the orientation-induced modifications of the structural and morphological parameters. In order to investigate orientation-induced structural changes, optical microscopy (OM), scanning electron microscopy (SEM), wide angle X-ray scattering (WAXS), and differential scanning calorimetry (DSC) were employed. Hermans orientation function (f(c)) was used to quantify the degree of crystal orientation. Complete disappearance of the already weak beta relaxation with orientation is attributed to the increase in crystallinity, but the contribution due to a more restricted chain segment mobility in the interlamellar regions of oriented specimens should also be taken into account. Presented results also reveal two different orientation-induced dynamics in the evolution of the dielectric alpha and gamma relaxations connected with the main transformation stages in the drawing of crystalline polymers. The transformation of the initial isotropic into a fully oriented fibrillar structure introduces large changes in the dielectric relaxation spectra of HDPE, especially in the alpha relaxation zone; by contrast, with further increase in the draw ratio much smaller changes are observed due to the deformation of the fiber structure by longitudinal sliding motions of microfibrils and/or by fibrils slipping past each other

Uniaxially Oriented High Density Polyethylene

The molecular relaxation behavior of an ice-quenched high density polyethylene (HDPE) subjected to solid-state stretching at elevated temperature (100 degrees C) to various draw ratios (up to lambda=13.7) was examined by means of dielectric spectroscopy. All relaxation zones (alpha, beta and gamma, in order of decreasing temperature) between 25 K and melting temperature were studied in the frequency range from 1 kHz to 1 MHz. The changes observed in different dielectric relaxations were related to the orientation-induced modifications of the structural and morphological parameters. In order to investigate orientation-induced structural changes, optical microscopy (OM), scanning electron microscopy (SEM), wide angle X-ray scattering (WAXS), and differential scanning calorimetry (DSC) were employed. Hermans orientation function (f(c)) was used to quantify the degree of crystal orientation. Complete disappearance of the already weak beta relaxation with orientation is attributed to the increase in crystallinity, but the contribution due to a more restricted chain segment mobility in the interlamellar regions of oriented specimens should also be taken into account. Presented results also reveal two different orientation-induced dynamics in the evolution of the dielectric alpha and gamma relaxations connected with the main transformation stages in the drawing of crystalline polymers. The transformation of the initial isotropic into a fully oriented fibrillar structure introduces large changes in the dielectric relaxation spectra of HDPE, especially in the alpha relaxation zone; by contrast, with further increase in the draw ratio much smaller changes are observed due to the deformation of the fiber structure by longitudinal sliding motions of microfibrils and/or by fibrils slipping past each other