Effect of Nanoadditives on Bitumen Aging Resistance: A Critical Review

Starting from the eighties, the use of nanoadditives registered an increasing attention in the scientific and patent literature, especially for the case of polymeric nanocomposites. In the last decade, this involved bituminous materials, modified either with nanosized fillers or with polymeric nanocomposites. One of the expected benefits is an increased resistance of the binder to aging. After a short introduction underlining the uncertainties and risks of artefacts in aging tests, a review is given, focusing on the antiaging properties of layered silicates, which are by far the most important nanoadditives for bitumens. Together with layered silicates, other materials such as nanohydrated lime, nanosilica, and layered double hydroxides are mentioned. Preparation and characterization of the binary bitumen/layered silicate and ternary bitumen/layered silicate/polymer systems are described in order to individuate the aspects that influence the antiaging effect. Even if the available literature is quite abundant and unanimously confirms that nanoadditives may improve bitumen durability, there is a lack of studies clarifying the involved mechanisms. As it is for conventional fillers, it seems to be a combination of physical and chemical interactions. Nanoadditives with different chemistries, porosities, and interlayer spacings differently absorb the polar components from the bitumen, thus affecting their predisposition to oxidative aging

Azidated Ether-Butadiene-Ether Block Copolymers as Binders for Solid Propellants

Polymeric binders for solid propellants are usually based on hydroxyl-terminated polybutadiene (HTPB), which does not contribute to the overall energy output. Azidic polyethers represent an interesting alternative but may have poorer mechanical properties. Polybutadiene–polyether copolymers may combine the advantages of both. Four different ether-butadiene-ether triblock copolymers were prepared and azidated starting from halogenated and/or tosylated monomers using HTPB as initiator. The presence of the butadiene block complicates the azidation step and reduces the storage stability of the azidic polymer. Nevertheless, the procedure allows modifying the binder properties by varying the type and lengths of the energetic blocks

Crack growth behavior of SBR, NR and BR rubber compounds: comparison of Pure-Shear versus Strip Tensile test

Fatigue crack growth experiments on different carbon black–filled rubber compounds have been carried out to evaluate the influence of pure-shear and strip tensile testing mode by using sine and pulse as waveforms. In a previous set of experimental investigations regarding the influence of both waveform and tested material, it was found that the mode I of crack opening sometimes propagates too quickly to be properly monitored in tests involving strip-tensile specimens. An alternative test methodology based on pure-shear test mode has been investigated, optimizing both the shape of the specimen and the test equipment. Data obtained from the different compound formulations were consistent with the theoretical background and resulted in similar ranking of compound crack growth resistance for the two testing modes; in addition, pure-shear mode showed a higher sensitivity to formula variations

Homo- and copolymers of 3-tosyloxymethyl-3-methyl oxetane (TMMO) as precursors to energetic azido polymers

AbstractPoly(3-azidomethyl-3-methyloxetane) and its copolymers with 3,3- bis(azidomethyl)oxetane were synthesized by cationic polymerization from 3- tosyloxymethyl-3-methyl oxetane and 3,3-bis(bromomethyl)oxetane, using a polyol as initiator and boron trifluoride complex as catalyst, followed by azidation. The final objective is the synthesis of an energetic binder to be used for rocket propellants and therefore the effects of different initiator/catalyst systems on important properties, like, i.e., the molecular weight distribution and the functionality of the polymer, were investigated. It was found that, even though both the operating conditions and the catalytic system were chosen in order to grant the living character of the polymerization, the latter seems to be prevalently driven by an "active chain end" mechanism. In particular, this may lead to the undesired formation of a small quantity of oligomers and to the presence of non-hydroxylic chain-end functionalities. Nevertheless, the average number of OH groups can be strictly controlled when boron trifluoride tetrahydrofuranate is used as catalyst

Synthesis of GAP and PAMMO Homopolymers from Mesylate Polymeric Precursors

In azidic binders for solid propellants, the N3 functionality is introduced by substitution of a halogen or tosyl group, but recently the mesyl group has been suggested as an alternative. The mesylate group has two advantages, mainly related to its small dimensions and low cost. Poly(glycidyl azide) and poly 3-azidomethyl-3-methyl oxetane were prepared by using both tosylate and mesylate precursors. The azidation kinetics were studied at three different temperatures while keeping all other operating parameters the same. The results confirmed the good potential of the mesylate precursors for the production of azidic binders

On the Use of Biobased Waxes to Tune Thermal and Mechanical Properties of Polyhydroxyalkanoates–Bran Biocomposites

In this work, processability and mechanical performances of bio-composites based on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) containing 5, 10, and 15 wt % of bran fibers, untreated and treated with natural carnauba and bee waxes were evaluated. Wheat bran, the main byproduct of flour milling, was used as filler to reduce the final cost of the PHBV-based composites and, in the same time, to find a potential valorization to this agro-food by-product, widely available at low cost. The results showed that the wheat bran powder did not act as reinforcement, but as filler for PHBV, due to an unfavorable aspect ratio of the particles and poor adhesion with the polymeric matrix, with consequent moderate loss in mechanical properties (tensile strength and elongation at break). The surface treatment of the wheat bran particles with waxes, and in particular with beeswax, was found to improve the mechanical performance in terms of tensile properties and impact resistance of the composites, enhancing the adhesion between the PHBV-based polymeric matrix and the bran fibers, as confirmed by predictive analytic models and dynamic mechanical analysis results

Microstructure and rheological response of laboratory-aged SBS-modified bitumens

Polymer additives are widely used to improve the performance of road bitumens including their resistance to hardening during oxidation, although their oxidative inhibitor effect has not been well documented. This study aims to investigate the effect of laboratory-simulated ageing on the microstructure, and rheological properties of Polymer Modified Bitumens (PMBs) prepared with a Styrene-Butadiene-Styrene (SBS) copolymer and sulphur as a cross-linker. The laboratory ageing was conducted through the Rolling Thin Film Oven (RTFO) and the Pressure Aging Vessel (PAV) procedures. The unaged and aged binders were characterised using the Multiple Stress Creep and Recovery (MSCR) test, Gel Permeation Chromatography (GPC) and fluorescence microscopy. The MSCR test showed that the cross-linked polymer had a higher capability of mitigating the effect of bitumen hardening on the rheological response, while for the PMBs without cross-linking, the polymer effects decreased significantly after RTFOT ageing. The GPC results showed that the aromatics, resins and asphaltenes fractions of the unmodified bitumens shifted towards heavier molecules after one cycle of PAV ageing but showed limited variation with further ageing. Similar behaviour was observed for the uncross-linked polymer binders, while for the cross-linked polymer binder, the behaviour depended on the polymer concentration

Applicability of time-temperature superposition for laboratory-aged neat and SBS-modified bitumens

© 2020 Elsevier Ltd The applicability of the time–temperature superposition principle (TTSP) can breakdown in the case of highly oxidized bitumens and polymer-modified bitumens (PMBs). This study investigates such problem in Styrene Butadiene Styrene (SBS) modified bitumens subjected to high oxidative laboratory-aging levels. The effects of aging were investigated by gel permeation chromatography (GPC), fluorescence microscopy (FM), and linear viscoelastic rheological characterization. As expected, the GPC and FM showed, respectively, an increase in the heavy fractions of bitumen and the degradation of the polymer morphology. Both the phenomena affected the rheological response provided in the form of black diagrams and isochrones of the loss tangent. Neat bitumens demonstrated thermorheologically simple behavior with some very slight symptoms of TTSP breakdown only at very high levels of aging. On the other hand, the applicability of TTSP to PMBs depends on the polymer content and the aging level. Low-medium and medium–high polymer contents PMBs produce minor concerns for TTSP irrespective of the aging level. However, high polymer contents may induce a TTSP breakdown mainly in unaged PMBs with the degradation of the polymer backbone due to oxidative aging progressively restoring a thermorheological simple configuration

"Galileo Galilei" (GG) a small satellite to test the equivalence principle of Galileo, Newton and Einstein

"Galileo Galilei" (GG) is a small satellite designed to fly in low Earth orbit with the goal of testing the Equivalence Principle-which is at the basis of the General Theory of Relativity-to 1 part in 1017. If successful, it would improve current laboratory results by 4 orders of magnitude. A confirmation would strongly constrain theories; proof of violation is believed to lead to a scientific revolution. The experiment design allows it to be carried out at ambient temperature inside a small 1-axis stabilized satellite (250 kg total mass). GG is under investigation at Phase A-2 level by ASI (Agenzia Spaziale Italiana) at Thales Alenia Space in Torino, while a laboratory prototype (known as GGG) is operational at INFN laboratories in Pisa, supported by INFN (Istituto Nazionale di fisica Nucleare) and ASI. A final study report will be published in 2009