Key Engineering Materials Vol. 893

Abstract: Polyamines are water-soluble polyelectrolytes with the amino groups that can be used to attach the polymers onto functional surfaces of fibrous materials. In addition, polyamines can be readily modified by (super) nucleophilic groups such as (alkyl) aminopyridines that enhance the polymer’s ability to promote hydrolysis of organophosphorous chemical warfare agents. Furthermore, attachment of hydantoin moieties augments the number of the imide, amide, or amine groups on the polyamine’s chain, which provides oxidizing properties to the resulting modified polyamine after halogenation. We report on polyamines with side chains modified to contain both (4-aminopyridine, APy) and 5-(4-hydroxybenzylidene) hydantoin (HBH) functionalities with enhanced content of the active bromine. Virucidal activity of the APy-and HBH-modified polyallylamine against human coronavirus (type 229E) was tested both in solution and on nylon-cotton fabric. The polymers appeared to be effective in inactivation of the coronavirus, at both low concentrations and short exposure times.

Abstract: This work describes the study of the effect of thermal annealing on the properties of the ZnO:Ag thin film composites, which are the basis of sensors of heavy metal ions, as well as sensors of poisonous and explosive substances. Changes of the optical properties and morphology of the surfaces of composites with five different component ratios were analyzed. The studies performed have revealed significant changes in the properties of nanocomposites ZnO:Ag. This study may become the basis for future works on improving the sensitivity of sensors of poisonous and explosive substances.

Abstract: Chemical, biological, radiological and nuclear (CBRN) threats pose many challenges to address in terms of reconnaissance, detection, personnel protection and countermeasures comprising a common set of techniques and procedures that fit in the concept of “all hazard” approach. The scientific and technological developments that led to the use of unmanned aerial systems (UAS) in an ubiquitous manner, enables its integration in CBRN operations, as sensors platforms for detection. In this scope, the GammaEx project targets to validate the concepts of operation using a specifically developed UAS with ATmosphères EXplosives (ATEX) compliance, equipped with chemical and radiological sensors for detection in CBRN scenarios. This paper aims to review the main concepts and challenges involving the sensors integration in UAS for specific CBRN environments considering the ATEX compliance, followed by the GammaEx project description and the presentation of the preliminary results of the laboratory and field comparative assays concerning the specifically developed sensors for the project and the commercial of the shelf sensors, follow on activities and future trends.

Abstract: Spiders silks have extraordinary strength and toughness simultaneously, thus has become dreamed materials by scientists and industries. Although there have been tremendous attempts to prepare fibers from genetically manufacture spider silk proteins, however, it has been still a huge challenge because of tedious procedure and high cost. Here, a facile spider-silk-mimicking strategy is reported for preparing highly scratchable polymers and supertough fibers from chemical synthesis route. Polymer films with high extensibility (>1200%) and supertough fibers (~387 MJ m^-3) are achieved by introducing polypeptides with β-sheet and α-helical structure in polyureathane/urea polymers. Notabley,the toughness of the fiber is more than twice the reported value of a normal spider dragline silk, and comparable with the toughest spider silk, aciniform silk of Argiope trifasciata.

Abstract: This paper shows the possibility to thermally camouflage a human body in a beach environment, during the day and at night, through the use of two knitted fabric clothing prototypes. The conceptual design process applied was initially developed based on the need to firstly understand the behaviour of an individual dressed under the focus of a thermal imaging camera in the light of the infrared spectrum. The thermal tests undertaken to observe the model's thermal camouflage in certain positions/perspectives in both environments, enable simultaneously running of different solutions while introducing changes to the clothing. Printing with copper pigments and the patchwork using stitched structures in polyester knitted fabric played a decisive role to capture the thermal colours of the thermal image intended for the camouflage effect.

Abstract: In this work, natural-based and biodegradable nanofibers were produced by electrospinning for drug delivery and wound dressing applications, using gelatin (Gel), chitosan (CS), cellulose nanocrystals (CNC) and natural propolis extract. The polymeric formulations and electrospinning parameters were optimized, resulting in the development of Gel/CS nanofibers with mean diameters of 97 nm. CNC were successfully introduced into the optimized Gel/CS solution and the viscosity and conductivity values were recorded. The developed nanofibers were characterized using FESEM, ATR-FTIR, TGA and WCA. The incorporation of different CNC concentrations improved the solutions’ electrospinnability and the membranes’ physical integrity. Defect-free and uniform Gel/CS/CNC nanofibers were observed by FESEM images, and the fibers’ diameters slight increased. The hydrophilic character was maintained after the CNC incorporation. Finally, Gel/CS/CNC/Propolis nanofibers demonstrated antibacterial activity against both Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria.

Abstract: This work aims to develop safety shoes, with thermal regulation systems, namely innovative heating and cooling systems. Heating system was developed using printing techniques; and cooling system was developed using the integration of Peltier modules in the shoe structure. These materials are based on the Peltier effect, in which, when an electric current is applied, the heat moves from one face to the other, being subsequently removed using thermal dissipation methods. This effect allows an active cooling. Given the high technological challenge of integrating cooling systems into footwear, this paper will present only developments related to cooling system.

Abstract: The study of the impact energy and the composite behaviour plays a vital role in the efficient design of composite structures. Among the various categories of impact tests, it is essential to study low-velocity impact tests as the damage generated due to these loads is often not visible to the naked eye. The internal damages can reduce the strength of the composites and hence the impact behaviour must be addressed specifically for improving their applications in the transport industry. The main aim of this paper is to provide a comprehensive review of the work focusing on the assessment of biocomposites performance under low impact velocity, the different deformations, and damage mechanisms, as well the methods to improve the impact resistance.

Abstract: Reinforced concrete strategic structures for military purposes are often established in coastalor offshore areas, widely subjected to chemical attacks, mainly due to an aggressive saline and acidenvironments. Porosity of cementitious conglomerates favour penetration of chlorides, which tend tocorrode the internal metallic rebar. The reinforcement of structures with fibrous composite materialsis a viable solution to restore the initial requirements of the building, especially when it exerts defence purposes. Among synthetic fibres, polyphenylenebenzobisoxazole (PBO) is an organic fibre based on linked aromatic structures with high elastic modulus and tensile strength and highly dissipative attitudes. In this work, the assessment of durability of continuous fibrereinforced cementitious mortar (FRCM) composites is carried out comparing the mechanical performance of laminates subjected to uniaxial tensile tests. It is found that PBOFRCM presents high resistance against aggressive environments and specifically preserve its mechanical strength in the presence of saltwater, where other reinforcing materials undergo to a dramatic degradation process.