Melting and crystallization behaviour of elastoplastic semicrystalline copolymers: poly(ether ester)

The melting and crystallization behaviour of an elastoplastic semi-crystalline poly(etherester) has been studied by differential scanning calorimetry. The shape of the melting endotherm is strongly dependent on heating rate and annealing time and results from the sum of simultaneous melting and crystallization phenomena. Samples prepared by different techniques, i.e. by solvent evaporation or by melt extrusion, behave very differently owing to specific crystal morphologies. By applying the Hoffman-Weeks plot, the equilibrium melting temperature has been extrapolated. The Avrami treatment allows the calculation of the index n and of the rate constant K from the isothermal kinetic data.     

Blends of polyamide 6 with bisphenol-A polycarbonate. I. Thermal properties and compatibility aspects

Blends of polyamide 6 (PA6) and polycarbonate (PC) have been investigated, over a full range of composition, to check interactions between them. SEM observations show that the mixtures are characterized by domains of clearly segregated homophases and voids between the two polymers. DSC and DMTA data indicate the presence of two T_g' s, corresponding to two separate phases, with the T_g of the PC phase decreasing on increasing the PA6 amount. Moreover, the crystallization kinetics of PA6 is slightly showed down by the PC. Chemical reactions between the two polymers are supposed to give rise to low molar mass compounds, as shown by GPC; these species plasticize the PC and partially dissolve into the molten polyamide, causing decrease of PC T_g and reduction of overall crystallization rate of PA6. Apparent influence of PC on melting temperature and enthalpy of PA6 is also discussed.     

Blends of polyamide 6 and bisphenol-A polycarbonate. Effects of interchange reactions on morphology and mechanical properties

Blends of polyamide 6 (PA6) and polycarbonate (PC) were prepared in a Brabender mixer, at 240°C, applying long mixing time, for 45 min. It was observed that the morphology and the mechanical properties tend to resemble those of a homogeneous material as the mixing time and PA6 concentration increase. This is attributed to chemical reactions taking place between the two homopolymers. Acidolysis, amidolysis, and aminolysis, catalyzed by the terminals and the amide groups of the polyamide, should in principle be possible. Our results indicate that the aminolysis is the main process, inducing simultaneously scission of PC chains and formation of PC-PA6 copolymer chains. The latter act as interfacial agents between incompatible PA6 and PC, improving the mechanical properties of PA6-rich blends, in agreement with the predictions of some theoretical models assuming good phase interpenetration. © 1992 John Wiley & Sons, Inc.     

Numerical Analysis on a Latent Thermal Energy Storage System with Phase Change Materials and Aluminum Foam

Abstract

A latent heat thermal energy storage system with phase change material (PCM) is numerically studied. To enhance the heat transfer inside the system, a highly conductive metal foam is employed with ceramic nanoparticles. The latter method of enhancement leads to a new class of material called Nano-PCM. The system under investigation is a 70-L tank filled up with pure PCM or Nano-PCM and several pipes are situated where the heat transfer fluid (HTF) flows. The pipe surfaces are assumed at constant temperature above the PCM melting temperature to simulate the heat transfer from the HTF. The enthalpy-porosity theory is applied to simulate the PCM phase change, while the porous media formulation is assumed to describe the metal foam behavior. The nano-PCM is modeled with single-phase model where the properties are the weighted-average between the fluid base and the nanoparticles. The simulations are accomplished for charging-discharging process at different porosities and nanoparticle concentration. The results are given in term of average melting fraction evolution, average temperature as function of time, average stored energy. The metal foam significantly improves the heat transfer between PCM and HTF respect to the addition of nanoparticles, reducing the charging and discharging time more than one order of magnitude.     

Synthesis and Structure Determination of the Adducts of Dibenzo[a,l]pyrene Diol Epoxides and Deoxyadenosine or Deoxyguanosine

Abstract

(±)?Syn?dibenzo[a,l]pyrene diol epoxide (DB[a,l]PDE) and (±)?anti?DB[a,l]PDE were reacted with deoxyadenosine (dA) or deoxyguanosine (dG) in dimethylformamide at 100 °C for 30 min. The crude products were purified by reverse phase HPLC under gradient and isocratic conditions. The structure of each adduct was assigned by 1D and 2D NMR spectra and by fast atom bombardment mass spectrometry. Five adducts were isolated from the reaction of (±)?syn?DB[a,l]PDE and dA: syn?DB[a,l]PDE?N⁶dA?1, syn?DB[a,l]PDE?N⁶dA?2, syn?DB[a,l]PDE?N⁶dA?3, syn?DB[a,l]PDE?N⁶dA?4 and syn?DB[a,l]PDE?N7Ade. Four adducts were isolated from the reaction of (±)?anti?DB[a,l]PDE and dA: anti?DB[a,l]PDE?N⁶dA?1, anti?DB[a,l]PDE?N⁶dA?2, anti?DB[a,l]PDE?N⁶dA?3 and anti?DB[a,l]PDE?N⁶dA?4. Two adducts were isolated from the reaction of (±)?syn?DB[a,l]PDE and dG: (±)?11,12,13?trihydroxy?tetrahydroDB[a,l]P?14?N²dG and (±)?11,12,13?trihydroxy?tetrahydroDB[a,l]P?14?N7Gua. Two adducts were isolated from the reaction of (±)?anti?DB[a,l]PDE and dG: (±)?11,12,13?trihydroxy?tetrahydroDB[a,l]P?14?N²dG and (±)?11,12,13?trihydroxy?tetrahydroDB[a,l]P?14?N7Gua.     

The Primary Role of Apurinic Sites in Tumor Initiation

The profiles of DNA adducts determined for benzo[a]pyrene (BP), 7,12-dimethylbenz[a]anthracene (DMBA) and dibenzo[a,l]pyrene (DB[a,l]P) reveal that a majority of adducts are released from DNA by depurination. Papillomas were induced in mouse skin by several PAH, and mutations in the c-Harvey-ras oncogene were determined to investigate the relationship between DNA adducts and ras oncogene mutations. The pattern of mutations induced by each PAH correlated with the profile of depurinating adducts. DB[a,l]P and DMBA formed predominantly depurinating adenine adducts (78% and 79%, respectively) and consistently induced a CAA → CTA transversion in codon 61 of ras. In contrast, BP produced both guanine (46%) and adenine (25%) depurinating adducts and induced a GGC → GTC mutation in codon 13 of c-H-ras in 54% of tumors and a CAA → CTA mutation in codon 61 in 15% of tumors. These results support the hypothesis that mis-replication of unrepaired apurinic sites generated by loss of PAH-DNA adducts is responsible for transforming mutations leading to papillomas in mouse skin.     

Minisymposium on Endogenous Carcinogens: The Catechol Estrogen Pathway. An Introduction

Abstract

A major carcinogenic risk for many human cancers may be associated with endogenous procarcinogens that are precursors to carcinogens. If natural protective mechanisms become insufficient, these procarcinogens can be activated, giving rise to formation of endogenous carcinogens. Catechol estrogens (CE), which are metabolites of the estrogens estrone and 17β-estradiol are hypothesized to be such ubiquitous procarcinogens. Their oxidation to CE semiquinones and/or quinones can generate the DNA damage that leads to the tumor initiation process. In addition, redox cycling of CE semiquinones and quinones can generate free radicals that lead to enhancement of DNA damage. The minisymposium discussing this area of research was moderated by Pentti Siiteri and introduced by Ercole Cavalieri. It included presentations by Joachin Liehr, Judith Weisz, Cyrus Creveling and Herman Adlercreutz.     

How artificial intelligence and machine learning can help healthcare systems respond to COVID-19

Machine Learning - The COVID-19 global pandemic is a threat not only to the health of millions of individuals, but also to the stability of infrastructure and economies around the world. The...     

Recycling of waste glasses into partially crystallized glass foams

Waste soda-lime glass, alone or mixed with wastes from the manufacturing of glass fibers, was successfully converted into partially crystallized glass foams by a particularly simple and economic processing, consisting of a direct heating of glass powders at temperatures from 900 to 1050 °C. The foaming operated by the oxidation of SiC, inserted as powder additive, was found to depend on a complex combination of processing temperature, soaking time, tendency of the investigated glasses toward devitrification, and amount of MnO₂, acting as oxidation promoter. Selected combinations led to foams with a good microstructural homogeneity and mechanical strength, suitable for application as aggregates in lightweight concrete.     

Production and Immunochemical Characterization of a High-Affinity Monoclonal Antibody Specific for 7-(Benzo[a]pyren-6-yl)guanine (Bp-6-N7GUA), a Depurinating DNA Adduct of Benzo[a]pyrene

Molecular dosimetry of depurinating DNA adducts of benzo[a]pyrene (BP) offers a promising new approach to determining risk of PAH-induced cancer. Depurinating adducts are the predominant form of BP-induced DNA damage, are excreted in urine and, importantly, are linked to cancer initiation. We have produced a monoclonal antibody (MAb) with high specific affinity for BP-6-N7Gua, a major depurinating DNA adduct of BP, and have developed a sensitive and specific competitive enzyme-linked immunosorbent assay (ELISA). The I_50S (quantity producing 50% inhibition of MAb binding in the ELISA) of selected BP adducts and metabolites were determined. The results indicated 1) a high degree of discrimination between BP-6-N7Gua (I₅₀=750 fmol) and BP (I₅₀=900,000 fmol), 2) high affinity of the MAb for BP-6-N7Ade (I₅₀=1,500 fmol), another major depurinating DNA adduct, and 3) specific structural requirements for MAb-adduct binding. In addition, the competitive ELISA provided an accurate determination of BP-6-N7Gua added to normal human urine, at a sensitivity of 200 fmol.