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Fibre–reinforced concrete cannot replace the ordinary reinforced concrete. However, there are areas of use in which fibre–reinforced concrete can be used alternatively or in addition to the ordinary reinforced concrete, offering several advantages, some of that being presented in this study. The basic idea is that reinforcements create a multi–directional “mesh” within the cementitious matrix that will make concrete stronger. In fact, adding the fibrous material to concrete will increase the strength. In this sense, the micro–fibres primarily work to prevent micro– or shrinkage cracking, which mostly occurs during the initial curing process of the concrete, or those critical first 28 days. By contrast, the macro–fibres provide load–bearing strength after the concrete cracks. But, in fact, the subject is more complex. The types and size of fibres, their distribution and orientation are a hugely complex topic. Fibres, of whatever nature, have been found to improve the properties of concrete. Fibre–reinforced concrete provides an alternative to conventional reinforcement, with the advantage of time and reduced costs of performing maintenance work. The complexity of various fibre use presents challenges for the construction sectors that may be beyond current levels of expertise. In this study, particularities of concrete reinforced with polymer fibres are presented. Also, a comparative study is presented, based on our previous works in area of the concrete reinforcing with recycled polyethylene terephthalate (PET).

In this study, carboxymethyl cellulose (CMC) was synthesized from the cellulose of cassava peel using alkalization and etherification reaction, and it was subsequently characterized with various techniques. Microcellulose was obtained by hydrolyzing á-cellulose from cassava peel using H2SO4 with concentrations of 45%, 47%, and 49%. The experimental results indicate that the varying concentrations of acid affect the particle size of the cellulose, with 49% H2SO4 solution producing a cellulose with particle size of around 0.45-2.42 µm and relative percentage of 11.3% according to PSA analysis. Other analyses conducted included determination of substitution degrees, DTG/DTA/TGA, FTIR, SEM, and XRD. The value of the substitution degree was determined at 0.27. TGA decomposition thermograms at a temperature of 150oC-320oC of 19.60 % indicate CMC compounds. DTA thermograms show that these CMC compounds have endothermic properties at 140oC and exothermic properties at 260oC. FTIR spectra show the presence of absorption band at wave number 1605 cm-1, which is a characteristic absorption of carbonyl group bound to cellulose. The results of SEM analysis indicate that the CMC has a tenuous surface morphology, and the XRD diffractograms are marked by the presence of weak peak at 2è = 20o, implying the existence of CMC as mostly amorphous.

In the context of the COVID-19 pandemic and the lack of protective equipment worldwide, we aimed to study the literature for finding guidelines in the 3D manufacture of respiratory masks. We have searched for papers in CI-EXPANDED, SSCI, A&HCI, CPCI-S, CPCI-SSH, BKCI-S, BKCI-SSH, ESCI, CCR-EXPANDED, IC, using `3D printing materials sterilization` and `3D printing materials disinfection` keywords. From 80 results in databases, after refining, we selected six papers. We have also searched for manufacturers` information regarding 3D printing materials sterilization or disinfection. We have found seven materials that are suitable for 3D printing and sterilization, with regards to multiple utilizations. Analyzing the properties and recommendations for sterilization of elements obtained by 3D printing, a thorough filaments structures/behavior research for most of the 3D models for printing is needed regarding synthetic polymers suitable for 3D printing; also, to establish the physical and chemical properties resulted after the reactions with sterilizing substances. In the context of the COVID-19 pandemic, the authors want to help and find guidelines in the 3D manufacture for producing respiratory masks.

The paper presents the application of 3D printing in the forensic field in order to perform facial reconstruction on a 3D printed replica of the victim’s skull. Firstly, imagine data from a computed tomography of a skull was converted into a 3D model. Then, the 3D skull model was sliced and printed in different positions in order to optimize the 3D printing configuration. Since the quality of the 3D printing process depends on the thermal and rheological properties of the 3D printing filaments, the rheological behavior of the ABS was investigated using melt flow rate and capillary rheometry. Lastly, an accurate skull replica was achieved using the optimal printing parameters. The 3D printed skull was used to perform the facial reconstruction of the victim by the forensic team. Based on the results of the present research, the 3D printing technology is a feasible solution to obtain anatomically accurate skull replicas.

In the endeavor to explore more and more materials, this work is focused on the study of the potential applicability of a chelating sorbent based on an acrylic copolymer functionalized with amidoethylenamine groups in Cu(II) removal from wastewaters in batch and dynamic conditions. The proposed sorbent was synthesized by the chemical transformation reaction of ethylacrylate (EA): acrylonitrile (AN):2% divinylbenzene (DVB) copolymer with ethylenediamine (EDA). Batch sorption results pointed out that the Cu(II) retention by the acrylic copolymer functionalized with amidoethylen-amine groups was dependent on the initial solution pH, initial metal concentration and contact time. The sorption of Cu (II) on the tested chelating copolymer obeyed both Langmuir and Freundlich isotherms. The Langmuir maximum sorption capacity was 65.21mg Cu (II)/g of polymer. The kinetic experimental data fitted well with the pseudo - second order model. The dynamic behavior of a fixed bed column filled with the acrylic copolymer functionalized with amidoethylenamine groups has been studied in terms of breakthrough curve. The experimental breakthrough data have been well described by Thomas model. The tested chelating copolymer is suitable for multiple processes of Cu(II) sorption-desorption. The column studies with real wastewater sample presented a removal efficiency of 100% for Cu (II) and a significant improvement of the wastewater quality. The acrylic copolymer functionalized with amidoethyleneamine groups can be successfuly applied for the Cu (II) removal - recovery - recycling.

The preparation of polyether polyols from waste rigid polyurethane foam has been achieved by chemical degradation of ethylene glycol and diethylene glycol as the degradation agent. Then, the modified rigid polyurethane foam was prepared by polyether polyols and glass fiber. To detect the characteristic of rigid polyurethane foam, the density, water absorption, compressive strength, thermal conductivity, infrared spectrum, morphology structure had been tested. Finally, the best degradation formula was explored, and the modified rigid polyurethane foam had been prepared from the recycled polyol.

Posterior endodontically treated teeth are exposed to risk fracture due to the great masticatory forces developed in the area. Fiberglass posts are considered a practical solution for such situations, but their main disadvantage yet remains the poor adhesion to the remaining tooth structures. The purpose of the present study was to evaluate a material that could replace the use of fiberglass posts on posterior teeth. 32 premolars were selected and divided into 4 groups (n=8): the first group was considered the control group; the second group was composed of endodontically treated teeth that were filled with gutta-percha, but without any coronal restoration; the third group was composed of teeth that received the same endodontic treatment as in the second group but were restored with a fibreglass post and a light cured microfilled hybrid composite material; the fourth group was similar to the third one, except teeth were restored with a short-fibre-reinforced composite (EverX Posterior, GC Europe N.V., Leuven, Belgium) and a microfilled hybrid composite over it. The fracture resistance of all the teeth was tested using a universal testing device. One-way ANOVA and the Tukey post-hoc variation tests for multiple comparisons were used to analyze the results. The short-fibre-reinforced composite material increased the fracture resistance of endodontically treated teeth (1159.42 N), twice as much as that obtained by using fiberglass posts (522.35 N)). Within the limitations of the present study, EverX Posterior represents a better alternative compared to fiberglass posts in the crown and root reconstruction of posterior endodontically treated teeth.

Despite the advantages of the non-flammable, good performance and low price, poly (vinyl chloride) (PVC) still suffer from poor thermal stability, restricting its melting process and applications. Although addition of some heat stabilizers can be used to improve the low thermal stability, so far, they normally compromise the environmental issues and smoke density of PVC during combustion. In this work, a series of La doping Mg-Al layered double hydroxides (LaLDHs) with different molar ratio of La3+ / Al3+ were successfully synthesized by coprecipitation-hydrothermal method and characterized by X-ray diffraction (XRD), Fourier transform infrared spectrum (FT-IR), Scanning Electron Microscopy (SEM) and Transmission electron microscopy (TEM). The results showed that the as-prepared LaLDHs exhibit plate-like morphology with a lateral size around 100-180 nm. The different as-prepared LaLDHs were introduced into PVC as heat stabilizer to prepare PVC nanocomposites. The thermal stability and smoke suppression of PVC nanocomposites were investigated by TGA, thermal aging, Congo red and smoke density rating test (SDR), respectively. All the results demonstrated that PVC-LaLDHs2 nanocomposites containing 2% LaLDHs2 (the molar ratio of La3+ / Al3+ is 1 / 3) were optimized, which achieved the maximal T50% value of 337.2 oC, minimal SDR value of 45.6%, and prolonged the thermal aging time from less than 10mins to 90mins, respectively thermal stability time from 1242s to 2751s. In addition, the tensile strength and elastic modulus of PVC-LaLDHs2 respectively increased by 84.4% (56.6 MPa) and 75.5% (1019.4 MPa) with little affecting elongation at break of PVC. LDHs (layered double hydroxides); rare earth ions; thermal stability; smoke suppression; poly (vinyl chloride)

Hybrid composites of in-situ microfibrillar recycled polyethylene terephthalate (rPET)/glass fiber (GF)/polypropylene (PP) were developed as an economical and environmentally friendly alternative to glass fiber reinforced thermoplastic PP composites. The effect of replacing glass fibers with in-situ formed polymer microfibrils on mechanical and viscoelastic properties of the composites was investigated with tensile, flexural, and dynamic mechanical tests. Characterization results showed that mechanical and viscoelastic performance of 34% glass fiber reinforced PP can be obtained with 24% glass fiber, 10% microfibrillar rPET composites. Compatibilization effect of the maleic anhydride grafted PP (MA-g-PP) was studied using Fourier transform infrared (FTIR) spectroscopy. The scanning electron microscopy (SEM) images confirmed the formation of the rPET microfibrils in the hybrid matrix. Besides, composites with MA-g-PP compatibilizers showed significantly improved fiber-matrix interfacial adhesion on the SEM images.

The study performed the biomechanical testing of polymethylmethacrylate (PMMA) specimens with unreinforced progressive antibiotic loading, compared to samples reinforced with Kirschner wires, by subjecting these specimens to mechanical compression forces. A difference was observed in the yield of the reinforced specimens with Kirschner wires, in which an antibiotic concentration that exceeded the usual amount was used. In this antibiotic combination of vancomycin powder and liquid gentamicin, the spacer seemed to have a superior structure compared to using only the antibiotic in liquid form. These results are superior to the usually loaded specimens (not exceeding the threshold of 4 g of antibiotic per 40 g of cement), the maximum force recorded being of 20.98 kN and the minimum of 11.54 kN. The reinforced specimens indicated higher values of force, registering differences that varied between 10 kN and approximately 19 kN, thus considering that through the reinforcement with Kirschner wires, the biomechanical qualities of the cement spacers considerably improved.