Evaluation of residual cross-linking caused by self-heating effect in epoxy-based fibrous composites Rusing Raman spectroscopy

Mechaniczne obciążenia cykliczne struktur polimerowych wywołuje procesy dyssypacji energii mechanicznej, które prowadzą do powstania efektu samorozgrzania, tj. lokalnego wzrostu temperatury, odpowiadającemu gradientowi naprężeń. W szczególnych przypadkach obciążania zmęczeniowego, efekt samorozgrzania staje się procesem dominującym i nasila degradację strukturalną. Wcześniejsze badania w tym zakresie wykazują, że efekt samorozgrzania związany jest z sieciowaniem resztkowym grup epoksydowych (EP) w kompozytach włóknistych. Celem prezentowanych badań jest ocena stopnia sieciowania resztkowego oparta na analizie widm Ramana, profili temperaturowych oraz charakterystycznych temperatur w kompozytach poddawanych obciążeniom zmęczeniowym z występowaniem efektu samorozgrzania. Analizie poddano charakterystyczne pasma w widmach Ramana, a także charakterystyczne krzywe temperaturowe i ich zależność od częstotliwości wymuszenia. Uzyskane wyniki pozwalają na charakterystykę mechanizmów degradacji włóknistych kompozytów epoksydowych poddawanych zmęczeniu cieplnemu.Mechanical cyclic loading of polymeric structures causes dissipation processes, which introduce the self-heating effect, i.e. the local temperature increase equivalent to the stress gradient. In some specific cases of fatigue loading the self-heating effect dominates the process and intensifies the structural degradation. Previous studies in this area show that the heating-up is connected with residual cross-linking of epoxy groups (EP) in the fibrous composites. The purpose of the presented study is an evaluation of degree of residual cross-linking and an analysis of Raman spectra with temperature profiles and characteristic temperatures of EP-based fibrous composites subjected to the fatigue loading with occurrence of the self-heating effect. The characteristic bands in Raman spectra as well as characteristic temperature history curves and their dependence on the excitation frequency were investigated. Obtained results allow for the characterization of degradation mechanisms of EPbased fibrous composites under thermal fatigue

In situ self hardening bioactive composite for bone and dental surgery.

A new biomaterial is presented which consists of a cellulose derivative--silanised hydroxyethylcellulose (HEC-SIL) and biphasic calcium phosphate (BCP). Rheological properties of the polymer itself and its mixture with BCP are pH-dependent. At pH 10-12 HEC-SIL is liquid and undergoes quick gellation at pH < 9. Similarly, the paste of HEC-SIL and BCP is fluid and injectable at higher pH and solidifies in biological solutions. The rate of this solidification can be easily controlled by the degree of substitution of hydroxyethylcellulose with silicoalkoxy groups

Determination and Comparison of Ideal and Practical Selectivity Coefficients of Membranes Containing Different Conductive Polymers

In series of published works, usually, the ideal coefficients of selectivity is used as an indicator for separation performance of conducting polymer membranes. The main goal of the presented paper was to determine the relation between the ideal and practical selectivity coefficients of the investigated series of conductive polymer membranes, both layered and composite one, and assessed whether it is possible to rely only on the values of ideal selectivity coefficient for estimation of the membrane separation capacity. The results showed that high values of ideal membrane selectivity coefficients are necessary but not a sufficient indicator for evaluation of the real selectivity of membranes made from conducting polymers

Synthesis and characterization of chalcogenophene-based monomers with pyridine acceptor unit.

2,4,6-Trisubstituted pyridine derivatives with different electropolymerizable groups were investigated. It was shown that steric hindrance caused by bichalcogenophene substituents in the 2,6-positions of pyridine enables successful electropolymerization whereas previous studies on 3,5-substituted pyridines shown difficulties caused by the presence of the pyridine nitrogen lone electron pair. Cyclic voltammetry and differential pulse voltammetry techniques were used to determine the electronic properties of the studied compounds and obtained polymers. UV-Vis-NIR and EPR spectroelectrochemistry were used to determinate the behavior of the polymers in the doping-dedoping cycles. The polymers were found to have coloration efficiency up to 245 cm(2) C-1 and exhibit sufficient stability for application and highlighting their possible use as electroactive layers in electrochromic devices. (C) 2016 Elsevier Ltd. All rights reserved

Lipid pattern in middle-aged inhabitants of the Lower Silesian region of Poland. The PURE Poland sub-study

Introduction. A decreased serum high density lipoprotein-cholesterol (HDL-C) is a strong predictor of cardiovascular risk. However, total HDL is a very dynamic, changeable fraction, and does not perform the function of atherosclerosis markers. In the presented study, the pattern of serum lipids, including HDL-C subclasses (HDL2- and HDL3-cholesterol), in a middleaged Polish Lower Silesia population was defined. Materials and method. A group of 746 males and 1,298 females, aged 35–70, were investigated. All subjects were participants in the PURE study. Mean serum lipid levels were determined for groups selected on the basis of gender, age, cigarette smoking, drinking alcohol and place of residence (urban/rural area). The data were analyzed using STATISTICA 6.0 PL. Results. In multiple linear regression models, age was the most important independent and consistent predictor of total cholesterol (TC) and LDL cholesterol (LDL-C). The prevalence of low HDL-C (threshold 40 mg/dL in males, 50 mg/dL in females) was 16.5% for males and 22.6% for females. This gender-conditioned difference in the prevalence of low HDL-C was greater in rural (20.0% vs. 30.9%, respectively, in males and females) in comparison to urban (14.4% vs. 17.1%) areas. The lipid pattern was significantly worse in rural than in urban females. Female rural inhabitants showed higher triglycerides (TG) and lower HDL cholesterol (total and contained in subclasses HDL2 and HDL3). Simultaneously, a higher BMI, higher percent of smokers and drinkers and lower age of smoking female rural inhabitants in comparison to urban females were estimated. In the total population, cigarette smoking or drinking alcohol were associated with significant increases in TC, LDL-C and TG, also with decreased HDL-C (smoking) or HDL2-C (drinking). Two-way analysis of variance showed the existence of interaction between these risk factors in their influence on HDL-C and HDL3-C. Conclusion. In the middle-aged population of the Lower Silesian region in Poland the place of residence (urban/rural area) had a significant impact on the lipid pattern. This pattern is more atherogenic in rural women than in urban women