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

Uticaj starenja na morfološke i optičke karakteristike TPD tankih filmova

U ovom radu ispitivan je uticaj prirodnog starenja na morfološke i optičke karakteristike TPD (N, N’ – bis (3 – metilfenil – N, N’ difenilbenzidin) tankih filmova. Inicijalno, filmovi su pripremljeni fizičkom vakuumskom depozicijom pare, sa kosinusnom raspodelom debljine duž monokristalne SiO2 podloge. Morfologija tankih filmova proučavana je optičkom (OM) i „atomic force“ (AFM) mikroskopijom. Prostorno korelisana morfološka (AFM i OM) i optička (absorbanca i fotoluminescencija) merenja primenjena su za određivanje uzajamne veze optičkih osobina i različitih morfologija filma. Promene u absorpcionim i fotoluminescentnim spektrima čvrsto su povezane sa promenama u mikrostrukturi nastalim starenjem filmova

HAAR WAVELET OPERATIONAL MATRIX BASED NUMERICAL INVERSION OF LAPLACE TRANSFORM FOR IRRATIONAL AND TRANSCENDENTAL TRANSFER FUNCTIONS

Irrational and transcendental functions can often be seen in signal processing or physical phenomena analysis as consequences of fractional-order and distributed-order models that result in fractional or partial differential equations. In cases when finding solution in analytical form tends to be difficult or impossible, numerical calculations such as Haar wavelet operational matrix method can be used.  Haar wavelet establishes a direct procedure for transfer function inversion using the wavelet operational matrix for orthogonal function set integration. In this paper an inverse Laplace transform of irrational and transcendental transfer functions using Haar wavelet operational matrix is proposed. Results for a number inverse Laplace transforms are numerically solved and compared with the analytical solutions and solutions provided by commonly used Invlap and NILT algorithms. This approach is useful when the original cannot be represented by an analytical formula and validity of the obtained result needs to be crosschecked and error estimated

Bubrenje i termodinamička analiza temperaturno osetljivih 2- hidroksietil metakrilat/itakonska kiselina kopolimernih hidrogelova sintetisanih gama zračenjem

Sintetisani su kopolimerni hidrogelovi na bazi 2-hidroksietil metakrilata (HEMA) i itakonske kiseline (IA) polimerizacijom indukovanom gama zračenjem. Analizirani su proces bubrenja i termodinamičke osobine PHEMA i kopolimernih P(HEMA/IA) hidrogelova sa različitim sadržajem IA (2, 3.5 i 5 mol %) u širokom opsegu pH i temperature. Preliminarne analize gelova pokazuju interesantnu pH i temperatursku osetljivost u procesima bubrenja i otpuštanja lekova. Posebna pažnja posvećena je temperaturama u okolini fiziološke (37o C), gde male promene u temperaturi značajno utiču na stepen bubrenja i proces otpuštanaj lekova. Ispitivan je P(HEMA/IA) hidrogel sa 5mol% IA sa i bez antibiotika (gentamicin) na pH 7.40 i u temperaturskom intervalu 25- 42o C, u cilju praćenja mogućnosti njihovog korišćenja u medicini

Structure and characteristics of the hot pressed hydroxyapatite/poly-L-lactide composite

Hydroxyapatite/poly-L-lactide (HAp/PLL) composite biomaterial can be obtained by different processing methods. Three-dimensional blocks of HAp/PLLA composite biomaterial with mechanical characteristics close to the natural bone tissue can be obtained by hot pressing procedure. Effects of synthesis and compacting on the structure and characteristics of the HAp/PLLA composite biomaterial were studied in this work. Using wade angle X-ray structural analyses (WAXS), differentially scanning calorimetry (DSC), thermogravimetric analysis (TGA) and infrared (IR) spectroscopy, the changes occurring in the material during synthesis and hot pressing were monitored. Surface microstructure was analyzed by scanning electronic microscopy (SEM) coupled with electron-dispersion analysis (EDX). The results obtained indicate a possible decrease in the degree of crystallinity with hot pressing time increase. A block of HAp/PLLA composite biomaterial with 1.6 times lower crystallinity of the polymer phase was obtained by hot pressing in a given time interval with a maximum of 60 minutes. Results of TG analysis show that PLLA stability decreases with increasing hot pressing time, and vice versa. IR study proved that neither destructive changes in constituents nor formation of new phases occurred during hot pressing

Temperature responsive hydrogels based on ethylene glycol propylene glycol "block" units with VPTT close to human body temperature

New hydrogels based on different oligo(alkylene glycol) methacrylate (OAGMA) with inverse thermo-response and volume phase transition temperature (VPTT) close to human body temperature were investigated in this work. Synthesis was performed from monomer-solvent mixture by gamma radiation; four different OAGMA (EG6MA, EG6PG3MA, EG3PG6MA and PG5MA) were used. The main focus was made on hydrogels based on EGxPGy pendant chains with different number of ethylene glycol and propylene glycol units in “block” backbone since in the case of POPGMA and POEGMA homopolimers (e.g. hydrogels with pure PG and EG pedant chains) the VPTTs were observed far below and far above the human body temperature, respectively. Characterisation of the hydrogels was performed by swelling, UV-Vis, FTIR, SEM, DSC and in vitro biocompatibility investigations. Due to the possibility to combined VPTT close to human body temperature with good biocompatibility, new hydrogels based on EGPG “block” pedant chains show great potential for biomedical applications

Uticaj orijentacije na ponašanje radijaciono umreženih/oksidovanih polietilena

U ovom radu proučavan je uticaj orijentacije i strukturnih karakteristika na promene u različitim polietilenima (PE) izazvane radijacionom oksidacijom/umrežavanjem. Radi toga, polietilen niske gustine (LDPE), linearni polietilen niske gustine (LLDPE) i polietilen visoke gustine (HDPE) su orijentisani u čvrstom stanju istezanjem na povišenoj temperaturi. Orijentisani uzorci su ozračeni različitim dozama γ-zračenja (do 700 kGy) u vazduhu. Za ispitivanje morfoloških promena izazvanih orijentacijom i zračenjem, mikrostruktura površine je analizirana optičkom (OM) i skenirajućom elektronskom (SEM) mikroskopijom. Diferencijalna skenirajuća kalorimetrija (DSC), IR spektroskopija i određivanje gela su korišćeni za utvrđivanje promena u kristaliničnosti, oksidativnoj degradaciji i stepenu formiranja mreže, respektivn

Influence of the mechanochemical treatment on structural changes in hydroxyapatite/poly-l-lactide composite

Promena strukture i osobina biokompozitnog materijala HAp/PLLA tokom mehano­hemijskog tretmana predmet su analize u ovom radu. Smeša HAp/PLLA uparena je u vakuumu i zatim podvrgnuta suvom mlevenju u planetarnom mlinu do 480 minuta. Korišćene su rendgenostrukturna analiza (XRD), diferencijalna skanirajuća kalorimetrija (DSC), skenirajuća elektronska mikroskopija (SEM) transmisiona elektronska mikroskopija (TEM) i infracrvena spektroskopija (IR) za karakterizaciju dobijenog materijala. Na osnovu prime­njenih analiza utvđen je uticaj mehanohemijskog tretmana na promene kompozitnog biomaterijala. U najvećoj meri dolazi do smanjenja kristaliničnosti poli-L-laktida(PLLA) i smanjenja veličine kristalita hidroksiapatita (HAp). Sa povećanjem vremena mehano­hemijskog tretmana dobija se homogena raspodela faza.Mechanochemically treated hydroxyapatite/poly-L-lactide (HAp/PLLA) composite biomaterial undergoes significant changes in structure and properties. These were the subject of the analysis presented in this paper. HAp/PLLA mixture was evaporated in vacuum and then subjected to dry milling in a planetary ball mill for 480 minutes. Characterization of the material obtained was carried out using X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electronic microscopy (SEM), transmission electronic microscopy (TEM) and infrared spectroscopy (IR). These techniques confirmed that mechanochemical treatment induces changes in the composite biomaterial. The most significant changes are reduction of PLLA crystallinity and size of HAp crystalites. Homogeneous phase arrangenment is obtained by extending the duration of mechanochemical treatment