Is it possible to mechanical recycle the materials of the disposable filtering masks?

In a singular period, such as during a pandemic, the use of personal protective masks can become mandatory for all citizens in many places worldwide. The most used device is the disposable mask that, inevitably, generates a substantial waste flow to send to incineration or landfill. The article examines the most diffused type of disposable face mask and identifies the characteristic of the constituent materials through morphological, chemical, physical, and thermal analyses. Based on these investigations, a mechanical recycling protocol with different approaches is proposed. Advantages and disadvantages of the different recycling solutions are discussed with considerations on necessary separation processes and other treatments. The four solutions investigated lead to a recycling index from 78 to 91% of the starting disposable mask weight. The rheological, mechanical, and thermo-mechanical properties of the final materials obtained from the different recycling approaches are compared with each other and with solutions present on the market resulting in materials potentially industrially exploitable

Thermal and UV aging of polypropylene stabilized by wine seeds wastes and their extracts

A commercial tannin wine seed extract powder (T), a seed polyphenol extract (Sext) and virgin wine seeds wastes (Se) have been mixed with polypropylene (PP) and tested as long-term stabilizers. Their stabilizing activity has been compared with that of a synthetic antioxidant commonly used within PP (Irganox 1010). Each sample has been subject to both UV and thermal aging. The PP-based films photo-oxidation has been followed through the C=O formation over the aging time by FT-IR. The PP-based tensile specimens have been oven aged and the mechanical properties loss has been investigated monitoring the variation of the elongation at break. Melt Flow Index (MFI) measures and Different Scanning Calorimetry analysis have been conducted on thermally aged samples. At the same time, wine derived additives have been characterized in terms of total polyphenol content, FT-IR and UV/VIS spectra meanwhile catechin and gallic acid have been quantified by LC-MS. Experimental results have evidenced the ability of all the wine derived additives to withstand both to thermal and UV long-term degradation. In particular, wine seeds extracts exhibit the best results in terms of stabilization (even better than Irganox 1010) without compromising the PP mechanical, thermal, morphological and rheological properties

Properties of graphene-related materials controlling the thermal conductivity of their polymer nanocomposites

Different types of graphene-related materials (GRM) are industrially available and have been exploited for thermal conductivity enhancement in polymers. These include materials with very different features, in terms of thickness, lateral size and composition, especially concerning the oxygen to carbon ratio and the possible presence of surface functionalization. Due to the variability of GRM properties, the differences in polymer nanocomposites preparation methods and the microstructures obtained, a large scatter of thermal conductivity performance is found in literature. However, detailed correlations between GRM-based nanocomposites features, including nanoplatelets thickness and size, defectiveness, composition and dispersion, with their thermal conductivity remain mostly undefined. In the present paper, the thermal conductivity of GRM-based polymer nanocomposites, prepared by melt polymerization of cyclic polybutylene terephtalate oligomers and exploiting 13 different GRM grades, was investigated. The selected GRM, covering a wide range of specific surface area, size and defectiveness, secure a sound basis for the understanding of the effect of GRM properties on the thermal conductivity of their relevant polymer nanocomposites. Indeed, the obtained thermal conductivity appeares to depend on the interplay between the above GRM feature. In particular, the combination of low GRM defectiveness and high filler percolation density was found to maximize the thermal conductivity of nanocomposites

Recycled PP for 3D Printing: Material and Processing Optimization through Design of Experiment

In this work, blends that were based on first use PP added with talc (PPt) and recycled polypropylene (r-PP) were designed and formulated, aiming at producing filaments that are suitable for 3D printing fused filament fabrication (FFF) processes. A preliminary characterization of PPt/r-PP blends at different weight ratios allowed selecting two systems showing adequate rheological behavior for FFF. The selected blends were melt compounded in a twin-screw extruder, optimizing the processing conditions through a design of experiments approach, involving the use of Taguchi's method. The materials that were prepared with the optimized processing conditions, hence showing the best performance in terms of rheological behavior and thermal characteristics, were then selected for the production of the filament and for the subsequent FFF processing. Finally, the morphology of the filament and the mechanical properties of 3D-printed samples were assessed, demonstrating the achievement of satisfactory results in terms of performances. In general, the obtained results clearly demonstrated that a proper optimization of both material and processing conditions offers the possibility of using recycled PP-based formulations for additive manufacturing processes, hence allowing a remarkable valorization of a low added-value material through its utilization for an innovative and sustainable manufacturing approach

Reuse and Valorisation of Hemp Fibres and Rice Husk Particles for Fire Resistant Fibreboards and Particleboards

The present manuscript deals with the reuse and valorisation of agricultural wastes and by-products (namely, hemp fibres and rice husk particles) to produce fire retardant fibreboards and particleboards for applications in biobuilding. Since fire retardancy is one of the most important challenges, a detailed study on the thermal and flame retardant properties of the above materials assembled using starch as the binder and different ammonium dihydrogen phosphate contents as fire retardant agents, is proposed. The combustion properties have been investigated in developing fire conditions, employing a radiating heat flux of 35 kW/m2generated by a cone calorimeter. An optimised formulation able to make both fibreboards and particleboards not ignitable has been found and is predicted to be \u201cA2/B\u201d class in the European fire classification for building products. The resultant materials have proven to undergo pyrolysis and not to burn, favouring the formation of a dense and consistent final residue

All Natural High-Density Fiber- and Particleboards from Hemp Fibers or Rice Husk Particles

In the present study, long hemp fibers and rice husk particles have been used for producing all natural-based boards for building, automotive and in-door furniture, employing a simple and economic transformation process (namely, compression molding). In order to have the required consistence and mechanical strength, cornstarch was employed as binder. By this way, fiber- and particleboards have been prepared and characterized in terms of morphology, mechanical properties (flexural modulus and strength). The influence of different relative humidity levels on composite storage modulus and heat deflection temperatures has been investigated, as well. Long fibers turned out to be capable of sustaining approximately three times the load with respect to particles in standard conditions. Thermal, hygro- and photo stability of the above materials have been investigated under three ageing conditions: namely, (i) high temperature (thermal ageing), (ii) humidity plus high temperature (hygro-thermal ageing) and (iii) UV radiations (photo ageing). Regardless of the experimental ageing conditions adopted, fiberboards have shown good mechanical stability with a modest decrease of storage modulus (<20%) with respect to the values before exposure

Towards heart tissue regeneration: a piezoelectric patch with smart nanocarriers for on-demand drug release

45% of death in Europe are ascribed to cardiac diseases and myocardial infarction (MI) weighs a large part of them. After an MI, a portion of the myocardium tissue is lost, substituted by fibrous tissue with minimal physiological functions: this can lead to severe heart dysfunction. Available therapies cannot successfully address the problem, therefore there is an urgent clinical need for new solutions. The Horizon Europe REBORN project (https://www.rebornproject.eu/project/) tackles this issue by designing a piezoelectric patch that can stimulate the restoration of healthy tissue by the piezoelectric fibre nanoarchitecture and on-demand drug release by nanocarriers (Fig. 1). The modulation of drug delivery can be triggered with different stimuli: within the REBORN project, ultrasounds will be used to control in-situ release. Among the various biofabrication techniques, electrospinning (ESP) is the most suitable to produce matrices with properties matching the ones of the cardiac extracellular matrix: aligned nanofibers with high interconnected porosity [1]. Furthermore, ESP provides high flexibility in terms of polymeric formulation that can be used, and it allows the incorporation of drug nanocarriers inside the fibres. The present work aims to exploit ESP with a rotating drum collector for the fabrication of polyvinylidene fluoride (PVDF) piezoelectric polymeric matrices with aligned fibres and the preliminary incorporation of mesoporous silica nanoparticles (MSN) as drug carriers. PVDF is a renowned piezoelectric biocompatible polymer largely used for electrospun devices for medical applications [2], and it was chosen to achieve electromechanical coupling with the myocardium. At first, non-toxic solvents to obtain PVDF spinnable solutions, acetone (ACE) and dimethyl sulfoxide (DMSO), were selected from the literature, to avoid possible cytotoxicity of the patch [3]. The effects of different formulations (PVDF concentration, ACE/DMSO ratio) and the ESP process parameters (voltage, flow rate, distance, drum speed) were investigated. The obtained membranes have been thoroughly characterized in terms of morphology, alignment, crystallinity, crystalline phases, mechanical properties, and wettability. By tuning the parameters, it was possible to obtain well-defined fibres, with a diameter of around 300 nm, and a good alignment. The piezoelectricity of PVDF depends on the amount of crystalline β phase, which was evaluated through FTIR spectroscopy along with the α and γ phases. The selected working conditions allow for obtaining high β phase content, about 94%. Furthermore, the overall crystallinity of the polymeric membranes, obtained by DSC, is also high, around 70%. The ESP process of PVDF is stable, allowing fibres deposition to last several hours, and to obtain various membrane thicknesses, from about 90 to 250 μm. The mechanical properties of the obtained membranes are comparable to the ones of other synthetic materials employed for cardiovascular surgery, with Young’s modulus of about 40 MPa and tensile strength of around 8.4 MPa, considering membranes thick about 100 μm. The contact angle is around 115°, as expected by a hydrophobic polymer. In preliminary trials for the incorporation of MSN, 5 %vol of MSNs was added to the PVDF solution. The nanoparticles were successfully embedded into the fibres, which showed smaller diameters with respect to fibres without MSNs due to the increased viscosity of the hybrid formulation. The PVDF+MSN membrane is a promising platform for the development of the REBORN patch and the treatment of heart failure due to MI. Future work will focus on the optimization of the ESP parameter and the investigation of drug release upon ultrasound stimulation. References [1] M.R. Gomes, F. Castelo Ferreira, P. Sanjuan-Alberte, Biomater. Adv. 137 (2022) 212808. [2] B. Azimi, M. Milazzo, A. Lazzeri, S. Berrettini, M.J. Uddin, Z. Qin, M.J. Buehler, S. Danti, Adv. Healthc. Mater. 9 (2020) 1901287. [3] J. Khao-iam, A. Salea, S. Chaipo, C. Putson, J. Phys. Conf. Ser. 2431 (2023) 012003

Dissipative Dynamics of Polymer Phononic Materials

Phononic materials are artificial composites with unprecedented abilities to control acoustic waves in solids. Their performance is mainly governed by their architecture, determining frequency ranges in which wave propagation is inhibited. However, the dynamics of phononic materials also depends on the mechanical and material properties of their constituents. In the case of viscoelastic constituents, such as most polymers, it is challenging to correctly predict the actual dynamic behavior of real phononic structures. Existing studies on this topic either lack experimental evidence or are limited to specific materials and architectures in restricted frequency ranges. A general framework is developed and employed to characterize the dynamics of polymer phononic materials with different architectures made of both thermoset and thermoplastic polymers, presenting qualitatively different viscoelastic behaviors. Through a comparison of experimental results with numerical predictions, the reliability of commonly used elastic and viscoelastic material models is evaluated in broad frequency ranges. Correlations between viscous effects and the two main band-gap formation mechanisms in phononic materials are revealed, and experimentally verified guidelines on how to correctly predict their dissipative response are proposed in a computationally efficient way. Overall, this work provides comprehensive guidelines for the extension of phononics modeling to applications involving dissipative viscoelastic materials.</p

Efect of maleated anhydride on mechanical properties of rice husk filler reinforced PLA Matrix Polymer Composite

Polylactic acid (PLA) formulated from corn starch has a bright potential to replace the non-renewable petroleum-based plastics. The combination of PLA and natural fbre has gained interest due to its unique performance, as reported in many researches and industries. Meanwhile, rice husk produced as the by-product of rice milling can be utilised, unless it is turned completely into waste. Therefore, in the present study, the rice husk powder (RHP) was used as a fller in the PLA, so to determine the infuence of the fller loading on the mechanical properties of the PLA composite. A coupling agent was selected for treatment from two options, i.e., maleic anhydride polypropylene (MAPP) and maleic anhydride polyethylene (MAPE), by applying the agents with various loading contents, such as 2, 4 and 6 wt%. The composite was fabricated by using the hot compression machine. Both the treated and untreated RHP–PLA composites were characterised via the tensile, fexural and impact strength tests. The increase in the RHP loading content led to the decrease in the tensile and fexural strengths. The applications of the coupling agents (MAPE and MAPP) did not improve the tensile and impact strengths, but the fexural strength was enhanced