Evaluation of Radiation Resistance of Polystyrene Using Molecular Dynamics Simulation

The scission rates of polystyrene and fluorinated polystyrene irradiated in an irradiation facility with Co-60 γ-rays were determined using molecular dynamics simulation and gel permeation chromatography (GPC) molecular weight distributions. The prediction was based on the assumption that γ-ray energy is transferred to the initial velocity of the primary knock-on atom. We employed a molecular dynamics simulation procedure to compute the changes in bond length between the connections for selected values of the absorbed dose and compared the calculated values with measurements made on the irradiated samples. The samples were exposed to four different absorbed doses of 25, 50, 75, and 100 kGy. The scission process and scission ratio were simulated with LAMMPS with ReaxFF potential for each bond, and we compared the simulation results with the experimental data especially measuring average molecular weight to evaluate the effect of fluorination on radiation enhancement.

Diblock dialternating terpolymers by one-step/one-pot highly selective organocatalytic multimonomer polymerization

The synthesis of well-defined block copolymers from a mixture of monomers without additional actions (“one-pot/one-step”) is an ideal and industrially valuable method. In addition, the presence of controlled alternating sequences in one or both blocks increases the structural diversity of polymeric materials, but, at the same time, the synthetic difficulty. Here we show that the “one-pot/one-step” ring-opening terpolymerization of a mixture of three monomers (N-sulfonyl aziridines; cyclic anhydrides and epoxides), with tert-butylimino-tris(dimethylamino)phosphorene (t-BuP1) as a catalyst, results in perfect diblock dialternating terpolymers having a sharp junction between the two blocks, with highly-controllable molecular weights and narrow molecular weight distributions (Ð < 1.08). The organocatalyst switches between two distinct polymerization cycles without any external stimulus, showing high monomer selectivity and kinetic control. The proposed mechanism is based on NMR, in-situ FTIR, SEC, MALDI-ToF, reactivity ratios, and kinetics studies.

Apparent Molecular Weight Distributions for Investigating Aging in Polymer-Modified Bitumen

The oxidative aging of bituminous binders affects the performance and durability of pavements. In the case of polymer-modified binders, aging involves both bitumen and polymers and has a strong impact on the whole architecture of the material. Rheology may help in understanding these structural changes, and interesting information may be obtained by analysing the evolution of apparent molecular weight distributions. This was demonstrated with a bituminous binder modified with a poly(styrene-butadiene) block copolymer and subjected to prolonged artificial aging. Isothermal frequency sweep tests were used to construct master curves of the phase angle and magnitude of the complex modulus. The master curves were then used to calculate relaxation spectra and apparent molecular weight distributions of the binders, as well as simulated temperature sweep tests. A comparison of the behaviour of the base and modified bitumen highlighted the role of the polymer in aging. Polymer degradation significantly damages the elastomeric network, yet the residual polymer chains still interact with the bitumen molecules and reduce their oxidative aging. The apparent molecular weight distributions were deconvoluted to create an aging index specifically developed for polymer-modified bitumen.

Use of Linear Viscoelastic Functions to Estimate the Aging Resistance and Internal Structure of Bituminous Binders

Rheology is the most widely used technique to evaluate the performance and aging of bituminous binders. Since there are many available rheological tests, there is also a wide range of aging indexes and it is not easy to choose the most appropriate one, because a single value may hardly be adequate for different properties or operating conditions. In order to generalize the usefulness of an index, a good starting point is deriving it from a set of data, such as the master curves of linear viscoelastic functions. Then, the problem is the quantification of aging in a single numerical value from continuous curves, covering a wide range of frequencies/temperatures. In this work, a summary of the aging indexes derived from the master curves is reported and discussed. The indexes are applied to a bituminous binder either with or without the addition of an organo-modified layered silicate. The apparent molecular weight distributions and relaxation spectra were also calculated from the master curves and used to characterize the effect of aging on the binder properties and structure. In this way, an interesting parallelism was observed between the SARA fractions and the populations derived from a deconvolution analysis of the apparent molecular weight distributions.

Isolation of Keratin from Waste Wool Using Hydrothermal Processes

The subcritical water (SubCW) extractions of waste wool to produce keratin were performed at temperatures of 150 °C to 250 °C and at different reaction times between 5 min to 75 min. The resulting proteins in the obtained products were confirmed with Fourier-transform infrared spectroscopy (FTIR). The molecular weight of the protein extracts was determined by using two different methods: with a polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate (SDS-PAGE) and by using a gel permeation chromatography. The results show, that by using SubCW, keratin can be isolated from waste wool in very high yields, much higher than by other chemical methods. Maximal yield was achieved at 180 °C and 60 min and it was 90.3%. The molecular weight distributions of extracted proteins, which were generated from waste wool were between 14 kDa and 4 kDa, what is comparable to the results obtained by other chemical methods.

Characterizations of Gelatin from the Skin of American Bullfrog (Rana catesbeiana) as Affected by Extraction Temperature

We investigated the effect of extraction temperature on the gel properties of gelatin from the skin of the American bullfrog (Rana catesbeiana) and the mechanisms. The textural and rheological properties of bullfrog gelatin extracted at 45 °C (G45), 55 °C (G55), and 65 °C (G65) were measured. The molecular weight distributions, microstructures, and amino acid compositions of the bullfrog gelatins were also determined. G45, G55, and G65 had gel strengths of 272.1, 225.6, and 205.8 g and hardness values of 28.1, 24.0, and 22.5 N, respectively. The gelling temperatures ranged from 19.3 to 23.9 °C, and the melting temperatures ranged from 28.9 to 31.5 °C. All the results were compared with those of commercial porcine gelatin. We propose that the higher gel strength of G45 with a higher band intensity of α2-chains compared with G55 and G65 was more likely to form ordered and strong cross-links. The gelatin extracted at a lower temperature (G45) had a finer gel structure, suggesting that it would be more difficult to disrupt by applied force. Gelatin extracted at a lower temperature demonstrated better properties with α2-chains and a fine gel structure. These results provide basic information on the extraction of American bullfrog skin gelatin for industrial applications.