Prediction of the tensile impact behavior of injection molded samples from quasi-static data

A methodology for predicting the mechanical behavior of injection molded semi-crystalline thermoplastics, within a wide range of strain rates and temperatures, is proposed in this work. This method is based on data obtained at isothermal low velocity tensile tests and on a phenomenological constitutive equation that describes the stress as a function of independent and multiplicative terms of the strain, strain rate and temperature. The effect of the processing conditions on the coefficients of this equation is considered by evaluating their dependence on thermo-mechanical indices, calculated from melt flow simulations. Using a finite element code that has this equation built-in, it is possible to predict the mechanical behavior of samples injected with different molding conditions. The extrapolation of the impact properties requires the consideration of the dependence of the material consistency on the strain rate, which is affected by the sample skin-core structure. So, any constitutive equation used to describe the mechanical behavior of the injection molded samples must consider the distinct contributions of the main microstructural layers.     

Polymerization and adhesion behavior of experimental dental bonding materials with different initiator systems

The use of alternative photoinitiators has been reported as a way to improve physical-mechanical characteristics of dental adhesive systems. In this way, the aim of this study was to evaluate the degree of conversion (DC) and dentin bond strength in dentin cavities of experimental simplified adhesive systems formulated with alternative photoinitiators and diphenyliodonium hexafluorophosphate (DPIHFP). A model simplified adhesive system was formulated by mixing a similar blend of monomers with different photoinitiator systems: camphorquinone (CQ), phenylpropanedione (PPD), bis-alkyl phosphine oxide (BAPO), CQ/PPD, and CQ/BAPO; with or without the addition of DPIHFP. DC was measured using Fourier Transform Infrared Spectroscopy. Bond strength was evaluated in bovine dentin cavities. DPIHFP increased DC for the CQ-based system, but did not affect the dentin bond strength. The PPD system showed the highest DC. All photoinitiator systems provided similar dentin bond strength. DPIHFP seems to increase the DC of CQ-based system, but it had no influence on PPD or BAPO systems. PPD was the most effective for to increase DC without improving bond strength of adhesive systems. Therefore, it is recommended that new adhesive systems to be formulated with phenylpropanedione to increase the DC of tooth restorations caused by traditional camphorquinone-based adhesive systems.     

Thermo-oxidative aging of acrylonitrile-butadiene rubber gaskets with real geometry used in plate heat exchangers

This study investigates the effects of aging on the physical and mechanical properties of commercially available acrylonitrile-butadiene rubber (NBR) gaskets while maintaining their original geometry. Thermo-oxidative cycles with 10 and 70 mm in length specimens were conducted from 80 to 170°C up to 180 days. The samples were analyzed employing compression set (CS), hardness, indentation modulus, cross-link density, total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and thermogravimetry. The results showed that longer specimens presented better resistance to thermo-oxidative aging. Indentation results indicated regular oxygen permeability into the entire samples up to 110°C, while at higher temperatures, limited diffusion oxidation (DLO) effects promoted non-uniform aging. Time–temperature superposition (TTS) and Arrhenius methods were applied to predict the specimens' lifetime using CS as a failure criterion. Activation energies for 10 and 70 mm samples were 68.74 and 43.63 kJ mol⁻¹, respectively. Thus, the 70 mm specimen's lifetime was greater than 10 mm. For temperatures below ≈38°C, the response to the thermo-oxidative aging is independent of specimen length. Therefore, in determining the lifetime of gaskets with complex geometry, longer specimens are recommended to provide more reliable results than those suggested by the standards.     

Green Nanoarchitectonics of Silver Nanoparticles for Antimicrobial Activity Against Resistant Pathogens

Journal of Inorganic and Organometallic Polymers and Materials - Antimicrobial resistance represents a serious concern to public health, being responsible for hospital infections, affecting mainly...     

A Proposed Approach for Provenance Data Gathering

Mobile Networks and Applications - Data provenance focuses on the source of the data and on the identification of data sources and their transformations undergone over time. This paper proposes a...     

Further evidence against the alleged failure of the classical nucleation theory below the glass transition range

We collected a plethora of new data to test the hypothesis that the failure of the Classical Nucleation Theory (CNT) below the glass transition range is just an experimental artifact. Since reaching the steady-state nucleation regime takes a significant time for treatments below the glass transition temperature, data collected in this temperature range tend not to have reached a steady state. Because of this potential problem, we examined the CNT using new experimental data for three stoichiometric silicate glasses: Li₂Si₂O₅, BaSi₂O₅, and Na₄CaSi₃O₉. We also measured the equilibrium viscosity for the studied glass batches and used it as a proxy for the effective diffusion coefficient. The analysis was conducted by applying a steady-state criterion and evaluating the error propagation throughout all calculations. Using this rigorous procedure, we have not observed the alleged CNT failure. Our comprehensive results support recent studies questioning this possible CNT failure helping solve a longstanding problem in glass science.