Search

Thermodynamic behaviour of the low­-temperature proton exchange membrane fuel cell (PEM FC) was under investigation. Different types of behaviour were observed depending on the thermal treatment of the FC. In the case of the relatively slow heating of reactant gases, the thermodynamic behaviour of the FC resembles the behaviour of the reversible FC, with an inverse proportionality between the open­-circuit voltage and temperature during the heating­-cooling cycle. In contrast, heating of the whole FC frame leads to predominantly direct proportionality during the heating­-cooling cycle and, in addition, to hysteresis.

The sustainable processing of recycled products requires veritable testing during quality control for commercial application. In this research work, mechanical (ASTM D3039), compression (ASTM D5467) and impact (ASTM A370) are utilized to observe the usability, diversity, and suitability of the developed polypropylene-postconsumer cotton fibers (PP-PCCF) composites for industrial applications. The cotton waste was ground using a grinding machine. The ground fibers were introduced to manufacture composites from 0 to 40% fiber loading variations. The fine cotton fibers and synthesized composites were characterized by scanning electron microscope before and after mechanical testing. The fiber length, diameter and area were in the range of 2.5 mm–5.5 mm, 12.5 μm–22 μm and 200.15 μm2–250.50 μm2, respectively. The engineering and design values were tensile strength (31.16 MPa–22.77 MPa), breaking strength (26.69 MPa–22.77 MPa), modulus of elasticity (2223.79 MPa–2770.77 MPa), and extension (17.48–3.21). Similarly, flexural strength, modulus, energy, and fracture force are also enhanced with an increase in fiber loading. The impact energies of pure polypropylene and PP-PCCF composites (with 10, 30, and 40% PCCF contents) were 50 kJ/m2, 48 kJ/m2, 43 kJ/m2, and 58 kJ/m2. The micrographs of PP-PCCF composites prove that the density of voids is enhanced with an increase in fiber contents. The PP-PCCF composites with 0%–30% fiber loadings showed minimum defects and were observed to be suitable for structural applications. On the other hand, the PP-PCCF composites with 30%–40% fiber loading are acceptable for environmental applications.

The circular economy (CE) is facing a problem of industrial implementation. The models are proposed for natural types of polymers and CE. The current work reports the technical strategies and paradigms for sustainable close-loop manufacturing. The post-consumer cotton polymer is used for optimization of functions like cost analysis, material evaluation, recycling technique selection, and quality control. The presentation of the results is advanced by break-even analysis, mechanical testing, tribological investigations, and polymer surface evaluations to select a reasonable processing technique. The current experimental and theoretical approaches could be used functionally for the adaption of the circular economy in polymer industries. The article also highlights the possible procedure for sustainable production of polymer products from natural and artificial wastes.

The circular economy is emerging as green technology solution for polymer and composite industries. However, the use of circular economy as an industrial practice is still a global challenge. In this article, polypropylene-cotton hybrid composite was developed using different amounts of cotton fibre waste (0, 10, 30, 40 wt%). Scanning electron microscope (SEM), tribometer, Rockwell hardness tester and binocular microscope were used for investigations of composite surface, hardness and coefficient of friction (COF). The mean coefficient of friction values was 0.64, 0.75, 0.88 and 0.94 for pure propylene, 10, 30 and 40% of cotton reinforced composites, respectively. The scanning electron microscopy characterization of hybrid composite revealed the voids, porosity and asperities due to random fibres orientation. The Rockwell hardness value of composites was increased due to rise of fibre fraction. Based on the COF values, hardness and surface characterization, polypropylene-cotton reinforced hybrid composite could be used functionally for thermal and sound applications.

Circular economy is still a theoretical field. In this research, alumina ceramic material was used to measure the coefficient of friction (COF) of cotton fabric with the objective of supporting the circular economy of textile industries. A scanning electron microscope (SEM), optical profilometer, mechanical profilometer and tribometer were used for evaluations of the cotton fabric surface and the coefficient of friction (COF). The cotton fabric surface was detected rough and damaged while the ceramic balls displayed smoothness along with high microhardness. The dynamic COF values were 0.12 to 0.15 in warp and 0.11 to 0.17 in weft directions. Based on the COF values, deformation, wear and morphologies evaluations, alumina ceramic materials could be used operationally for surface alterations of textile machinery parts. The results could also enhance the quality and performance of textile products.

Rough, damaged, and distorted post-consumer natural and synthetic polymers cause wear and damage to textile machinery parts, presenting a major obstacle to the quality of recycled products. In this research, TiAlN coatings were used to measure the coefficient of friction (COF) for tribological properties. The scanning electron microscope (SEM) studies of cotton textiles revealed surface damage, distortions, and loose fibres produced on the fabric surface. SEM morphology of TiAlN coatings was found smooth and uniform. Additionally, Contour GT-K 3D optical microscope and mechanical profilometer (Mahr Perthometer) were used for coating surface analysis. The average coating surface roughness parameters were Rmax (0.30 µm), Rz (0.26 µm), and Rp (0.17 µm). The microhardness value was 35 GPa on the HV scale. The lower surface roughness and higher hardness values are an indication of reasonable quality and performance of textile fabrics during recycling. The dynamic COF values were obtained from 0.47 to 0.30 in warp and from 0.35 to 0.23 in weft directions. Higher COF values occurred in the warp direction due to lower thread densities, rough surface, preferred fibre orientation, randomly oriented fibres, and a plain-woven structure. Based on the COF values, permanent deformation, and morphology evaluations, TiAlN coatings could be used optimistically for surface modification of shredding, cutting, and textile machinery parts. The TiAlN coatings applications in industries could also enhance the quality and performance of recycled textile products.

The paper investigates the variation of friction force (Fx) during reciprocating sliding tests on nanocrystalline diamond (NCD) films. The analysis of the friction behavior during the run-in period is the focus of the study. The NCD films were grown using microwave plasma-enhanced chemical vapor deposition (MW-PECVD) on single-crystalline diamond SCD(110) substrates. Reciprocating sliding tests were conducted under 500 and 2000 g of normal load using Si3N4 balls as a counter body. The friction force permanently varies during the test, namely Fx value can locally increase or decrease in each cycle of sliding. The distribution of friction force drops (dFx) was extracted from the experimental data using a specially developed program. The analysis revealed a power-law distribution f-µ of dFx for the early stage of the run-in with the exponent value (µ) in the range from 0.6 to 2.9. In addition, the frequency power spectrum of Fx time series follows power-law distribution f-α with α value in the range of 1.0−2.0, with the highest values (1.6−2.0) for the initial stage of the run-in. No power-law distribution of dFx was found for the later stage of the run-in and the steady-state periods of sliding with the exception for periods where a relatively extended decrease of coefficient of friction (COF) was observed. The asperity interlocking leads to the stick-slip like sliding at the early stage of the run-in. This tribological behavior can be related to the self-organized criticality (SOC). The emergence of dissipative structures at the later stages of the run-in, namely the formation of ripples, carbonaceous tribolayer, etc., can be associated with the self-organization (SO).

The study deals with tribological properties of diamond films that were tested under reciprocal sliding conditions against Si3N4 balls. Adhesive and abrasive wear are explained in terms of nonequilibrium thermodynamic model of friction and wear. Surface roughness alteration and film deformation induce instabilities in the tribological system, therefore self-organization can occur. Instabilities can lead to an increase of the real contact area between the ball and film, resulting in the seizure between the sliding counterparts (degenerative case of self-organization). However, the material cannot withstand the stress and collapses due to high friction forces, thus this regime of sliding corresponds to the adhesive wear. In contrast, a decrease of the real contact area leads to the decrease of the coefficient of friction (constructive self-organization). However, it results in a contact pressure increase on the top of asperities within the contact zone, followed by material collapse, i.e., abrasive wear. Mentioned wear mechanisms should be distinguished from the self-lubricating properties of diamond due to the formation of a carbonaceous layer.