Search Results (2,042)

This study investigates the effects of thermal treatment, high-humidity exposure, and tensile loading during heating on the mechanical properties of kenaf fiber bundles and kenaf fiber-reinforced polypropylene (kenaf-PP) composites. Kenaf fiber bundles were thermally treated at 140, 160, 180, and 200 °C for one hour, and their tensile properties were evaluated before and after exposure to a high-humidity environment. The crystallinity index (CrI) was determined by X-ray diffraction using Segal’s empirical method to investigate the relationship between cellulose crystallinity and the mechanical performance of the fibers. Heating at 140 °C increased the average tensile strength by approximately 11%, which coincided with the highest crystallinity index measured by X-ray diffraction, whereas higher treatment temperatures resulted in reduced mechanical performance, consistent with the onset of thermal degradation. The application of tensile loading during thermal treatment further enhanced the tensile strength of the kenaf fiber bundles, with the greatest improvement observed for fibers treated at 140 °C under a 48 N load. Microwave-assisted treatment (600 W) under tensile loading provided comparable improvements in tensile properties while reducing the treatment time from one hour to 60 s. Kenaf-PP composite sheets reinforced with thermally treated fibers exhibited enhanced flexural performance, with fibers treated at 140 °C producing the best overall results, including increases of approximately 15% in specific flexural strength and 31% in specific flexural modulus. These findings demonstrate that moderate thermal treatment, particularly when combined with tensile loading, is an effective strategy for improving the mechanical performance of kenaf fibers and kenaf-PP composites. Furthermore, microwave-assisted heating represents a promising alternative to conventional thermal treatment by significantly reducing processing time while maintaining the mechanical benefits. Full article

This study investigates the fire behaviour of hybrid fibre reinforced concrete (HFRC) incorporating steel fibres combined with coir, polypropylene (PP), ramie, and sisal fibres under the ISO 834 standard fire curve. Concrete specimens were exposed to fire for 15, 30, and 60 min, and their residual compressive, split tensile, and flexural strengths were evaluated. Mass loss and a Thermal Performance Index (TPI) were determined to quantify fire-induced deterioration, while thermogravimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were performed to characterize the thermal, phase, and microstructural changes after fire exposure. The results showed that all concrete mixtures experienced progressive reductions in mechanical properties with increasing fire exposure duration. After 60 min of fire exposure, the compressive strength reductions were 45.9%, 42.9%, 37.9%, 45.1%, and 43.8% for CC, SPP, SCO, SSI, and SRA, respectively. The SCO mixture retained 62.1% of its compressive strength, exhibited the lowest mass loss (8.2%), and achieved the highest Thermal Performance Index (7.57). The TGA, XRD, and SEM analyses indicated lower thermal and microstructural deterioration in the hybrid fibre reinforced mixtures than in the control concrete. The findings demonstrate that hybrid fibre reinforcement improves the residual performance of concrete subjected to standard fire exposure. Full article

Polypropylene (PP) is a promising feedstock for extrusion-based additive manufacturing due to its low density and chemical resistance; however, its semicrystalline nature induces shrinkage and warpage during printing. This study investigates how hybrid carbon nanotube (CNT)–graphene oxide (GO) architectures influence the mechanical, thermal, melt flow, and dimensional behavior of PP during material extrusion (MEX) and fused granule fabrication (FGF). Neat PP, single-filler controls, and hybrid CNT–GO formulations (total filler ≤ 2 wt.%) were prepared via solvent-assisted dispersion and characterized by tensile/flexural testing, thermal analysis, spectroscopy, microscopy, melt flow index, and warpage measurements. CNT–GO incorporation increased tensile and flexural modulus and strength by up to 55%/57% and 71%/71%, respectively, while reducing ductility. Thermal stability and crystallinity improved, consistent with heterogeneous nucleation. Network development reduced melt flow index, increased apparent flow activation energy, and reduced warpage by up to 58% for the balanced 1:1 CNT: GO formulation. These formulation-dependent trends establish a common material-level link between reinforcement and printability. MEX and FGF showed broadly similar performance under the investigated conditions, with no statistically significant route effect detected for most properties; the balanced hybrid formulation provided the best overall balance between mechanical properties and dimensional stability. Full article

The presence of microplastics (MPs) in food products has become a concern, underscoring the need for reliable methods of isolation and analysis. There is no specific regulatory framework for monitoring MPs in food. A challenge is the lack of standardized and validated methods for the isolation and determination of MPs in food matrices. This study aimed to evaluate the effects of chemical digestion conditions used to isolate MPs from food matrices on the stability of polyethylene (PE) and polypropylene (PP) particles. The effects were evaluated using nitric acid, hydrochloric acid, hydrogen peroxide, potassium hydroxide, ethanol, and Milli-Q water at selected temperatures and reagent concentrations. Changes in particle surface morphology were assessed by scanning electron microscopy (SEM), while spectroscopic alterations were evaluated by Fourier transform infrared microspectroscopy (µ-FTIR). The SEM and µ-FTIR findings suggested that PE MPs were less affected than PP MPs under the tested treatment conditions. Less intensive treatment combinations were generally associated with fewer morphological and spectroscopic alterations for both polymers. The results showed that heating in Milli-Q water and treatment with acidic, oxidative, and alkaline reagents were associated with changes in selected recovery and spectroscopic parameters of PE and PP MPs under the tested experimental conditions. Full article

This study clarifies the mechanical recovery and structural retention of damaged glass fiber-reinforced polypropylene (PP/GF) composites subjected to repetitive sub-melting thermal annealing at 160 °C. Initial thermal annealing increased matrix crystallinity from 0.30 to 0.37 (+23.3%), thereby elevating flexural strength from 103 MPa to 122 MPa (+18.4%). Following one repair cycle, flexural strength was completely restored to 103–105 MPa (100% recovery rate). However, after three repair cycles, short-duration annealing (120 s) resulted in severe mechanical degradation down to 30 MPa (−70.9%), whereas long-duration annealing (1800 s) retained a strength of 59 MPa (−42.7%, preserving 57.3% of initial strength). Concurrently, the crystallinity index increased to 0.49 (+63.3%) for 1800 s. These results establish that extended dwell time at sub-melting temperatures is essential for promoting molecular chain re-entanglement while suppressing void growth. These findings present an engineering guideline for low-energy, structure-preserving repair of thermoplastic composites. Full article

Gravimetric mass loss in polymer–biogenic filler systems is often reported as polymer biodegradation without establishing which phase of the material is lost. This study proposes and applies an analytical framework that combines FTIR identification of the starting material, a phase balance ceiling, and removable inventory kinetics to assess such claims. Post-consumer cup plastic was blended with pyroconverted cassava (Manihot esculenta) peel dextrin in four matrix/dextrin/turpentine formulations (70/10/20 to 30/50/20% w/w) and exposed for 30 days to Aspergillus niger and A. fumigatus in Rivalier moist chambers with Sabouraud dextrose broth. FTIR revealed that the material sold as polypropylene contained polystyrene: the matrix ranged from essentially polystyrene (formulation B) to polypropylene-rich (C and D), as shown by the aromatic 755/697 ${\mathrm{cm}}^{-1}$ doublet and a PS/PP spectral index spanning more than one order of magnitude. Mass loss profiles followed a first-order removable inventory model with rate constants $\kappa$ of $9.9\times {10}^{-3}$ to $67.8\times {10}^{-3}$${\mathrm{d}}^{-1}$ (nominal residual solvent scenario) and inventory half-lives of 10–70 d. The removal rate increased with dextrin content ($\rho =0.80$ for both species) with a reproducible reversal between 30 and 40% dextrin that survives explicit bounding of the specimen surface-to-volume covariate. Five of the eight conditions remained below the removable fraction ceiling even on a dry basis; the other three required residual solvent fractions of only 1.2, 1.9, and 11.9% w/w, below the 20% nominal loading, so that no observation requires degradation of the PP/PS matrix. A greenness assessment of the framework with AGREE (0.62), MoGAPI (77%), and AGSA (66.7%) places it above the confirmatory methods it is intended to gate (respirometry, high-temperature GPC), with low throughput, manual operation, and the biosafety of the fungal assay as its main remaining limitations. The framework provides a reproducible, low-burden basis for separating selective removal of biodegradable or volatile phases from evidence that can legitimately support polymer biodegradation claims. Full article

Conventional compatibilization of polypropylene (PP)/mineral composites primarily improves local filler–matrix adhesion and dispersion. This study provides evidence for an elastomer-mediated interparticle bridging mechanism in which maleic anhydride-grafted ethylene propylene diene monomer (EPDM-g-MA) extends talc-associated polymer regions and promotes long-range elastic connectivity between neighboring platelets. Composites containing 5–40 wt% talc and 2.5–20 wt% EPDM-g-MA were characterized by frequency sweep, stress relaxation, strain sweep, and scanning electron microscopy. PP-g-MA and hybrid PP-g-MA/EPDM systems served as controls to distinguish conventional MA-mediated adhesion, independent elastomer addition, and their integration within EPDM-g-MA. PP-g-MA improved local interfacial continuity without promoting early network formation, whereas the hybrid systems failed to reproduce the low-threshold response of EPDM-g-MA. The apparent rheological network threshold decreased from approximately 40 wt% talc in the uncompatibilized system to approximately 30 wt% at 2.5–5 wt% EPDM-g-MA, 20 wt% at 10 wt%, and ≤5 wt% at 20 wt%. Effective interaction-volume analysis provides a geometric basis for the observed threshold reduction, while the combined rheological and morphological results support the development of talc-associated polymer regions into stress-bearing elastomer-mediated coupling. These findings establish compatibilizer architecture as a powerful strategy for controlling low-threshold melt-state network formation in PP/talc composites. Full article

This study evaluates the feasibility of incorporating a specific batch of distilled paint waste into acry-lonitrile–butadiene–styrene (ABS), polypropylene (PP), and polystyrene (PS) matrices at nominal feed contents of 10, 20, and 30 wt.%. After drying and grinding, the waste was compounded by extrusion and specimens were produced by injection molding. Melt-flow behavior, density, impact and tensile properties, thermal stability, thermal transitions, and dynamic-mechanical response were investigated. The effect of waste addition was strongly matrix dependent. In PS, MFR increased from 9.52 to 24.85 g/10 min between neat PS and the 30 wt.% nominal formulation, while Tg decreased from 106.4 to 81.6 °C. TGA showed non-monotonic, matrix-dependent changes in thermal stability. Mechanical performance generally deteriorated with increasing nominal waste content; for ABS, tensile strength decreased from 42.21 to 26.17 MPa and impact strength from 17.51 to 0.23 kJ/m². DMA confirmed matrix-dependent changes in stiffness and relaxation behavior. The results show that the investigated waste batch can be processed with all three ther-moplastic matrices, but increasing waste addition involves clear mechanical and thermal trade-offs. Full article

The growing accumulation of plastic waste is a serious environmental problem, and converting this waste into useful materials is an attractive solution. In this work, waste polypropylene (PP) was converted into hard carbon anode materials for lithium-ion batteries. When heated, PP decomposes into volatile hydrocarbons and leaves almost no solid residue, so it cannot be carbonized on its own. The waste PP was therefore first treated with concentrated sulfuric acid, which cross-links the polymer chains into a rigid, infusible network. This suppresses volatilization and promotes the formation of a thermally stable carbonaceous residue. The cross-linked material was then carbonized under argon at 700, 800, 900 and 1000 °C, and 22 to 24% of the original PP mass was recovered as carbon powder, depending on the carbonization temperature. X-ray photoelectron spectroscopy showed that the carbon surfaces retain 6.3–7.5 at% oxygen but almost no sulfur (≤0.2 at%), so sulfur is essentially absent from the final carbons. The carbonization temperature influenced the structure of the carbon and its performance in a battery. Among all samples, PP-900 delivered the highest reversible capacity at 0.1 A g⁻¹, reaching 373.1 mAh g⁻¹ at the 100th cycle. The first-cycle Coulombic efficiency was low for all samples (30–47%) and represents the main limitation of these materials. These results show that acid cross-linking followed by carbonization is a feasible route for converting PP waste into carbon anode material, and identify the low first-cycle efficiency and the rate performance at high current density as the principal issues to be addressed in further work. Full article

Mechanical recycling of polypropylene (PP)-based plastics from end-of-life vehicles (ELVs) is a key route to increase circularity in the automotive sector, but the practical use of ELV recyclates is limited by compositional variability and contamination, especially paint residues. In this study, a PP-based ELV bumper recyclate was compared to a virgin mineral-reinforced and elastomer-modified automotive PP compound and incorporated as a drop-in component at up to 35 wt.-%. Composition was assessed by differential scanning calorimetry, thermogravimetry, and CRYSTEX analysis, while contamination was quantified by computed tomography and related to tensile, impact, and instrumented puncture properties. Mineral and elastomer contents of the ELV recyclate were comparable to the virgin reference after re-stabilization, enabling blends with limited stiffness loss. However, ductility and toughness decreased with increasing recyclate content, especially at low temperature, due to the combined effects of elastomer degradation and rigid contaminant inclusions. Melt filtration of the recyclate substantially reduced the volume fraction of inclusions, removing particularly the largest particles greater than 100 µm, and thereby improved strain at break and puncture performance. Double filtration at 35 wt.-% recyclate loading achieved 50–85% of the virgin-reference ductility and toughness levels and nearly retained the stiffness. These results demonstrate that PP-based ELV recyclates can be used in high-impact automotive formulations at contents exceeding current long-term regulatory targets with recipe modification being limited to further stabilizer addition, provided that contaminant control and elastomer-phase quality are adequately managed. Full article

Softening impact-resistant polypropylene (PP) copolymers (ICPs) may be accompanied by reduced breakdown performance; coordinating mechanical and electrical properties is closely related to crystalline-framework and rubber-rich-phase organization. Homopolymer PP matrix HICP and random copolymer PP matrix RICP formed the primary comparison, with high-phase-continuity CICP as a reference, through composition, fractionation, crystalline structure, morphology, viscoelasticity, and charge analyses. Relative to HICP, RICP matrix randomization extended crystallizability distributions toward lower temperatures, refined the crystalline framework, and expanded interphase regions. Tensile and flexural moduli decreased by 38.8% and 38.7%, respectively, while Weibull characteristic breakdown strength increased from 226.2 to 310.8 kV/mm. CICP, containing 23.3 wt% ethylene, comprised a continuous low-crystallinity/rubber-rich phase with dispersed PP crystalline domains. Its tensile modulus was 89.4 ± 4.9 MPa; it retained partial break in notched impact testing at −20 °C and a characteristic breakdown strength of 384.4 kV/mm. Thermally stimulated depolarization current, conduction, and space-charge results indicated that local trapping environments and multiphase transport pathways jointly regulate charge migration and accumulation, providing a charge-behavior basis for maintaining high insulation performance as flexibility increases. The relationships linking molecular sequences, crystalline organization, phase connectivity, and mechanical–electrical responses provide a basis for designing multiphase PP-based DC cable insulation. Full article

To further enhance the mechanical performance and early-age crack resistance of engineered cementitious composites (ECC), an ECC-based multiscale hybrid-fiber system was investigated. The system used carbon nanotube-modified polyethylene (M-PE) fibers as the primary reinforcement together with polypropylene (PP) and basalt (BF) fibers. The effects of fiber hybridization on compressive strength, uniaxial tensile behavior, flexural performance, early-age crack resistance, and microstructure were systematically evaluated. Mixtures retaining at least 60% M-PE exhibited a clear post-cracking strain-hardening response, whereas lower M-PE fractions led to crack localization and loss of strain hardening. At 28 days, BF-0 (1.5 vol.% M-PE + 0.3 vol.% BF) reached compressive, tensile, and flexural strengths of 85.3, 7.35, and 36.38 MPa, respectively. A six-indicator entropy-weighted TOPSIS evaluation identified BF-0 as the best-balanced mixture among the investigated groups. Increasing PP or BF content improved early-age plate crack resistance; BF-5 (1.5 vol.% BF) achieved the highest crack reduction coefficient of 67.98%, with a nominal total crack area of 27.6 mm². Scanning electron microscopy (SEM) observations were used only as qualitative morphological evidence, whereas mercury intrusion porosimetry (MIP) revealed quantitative pore-structure trends and X-ray diffraction (XRD) indicated that fiber hybridization did not generate new detectable crystalline phases. The results reveal the performance trade-offs among strength, ductility, and early-age crack control in multiscale hybrid-fiber cementitious composites. Full article

Microplastic (MP) contamination of agricultural soils is an emerging environmental concern because MPs may alter soil physicochemical properties and nutrient dynamics. However, information on polymer- and soil-dependent responses in South Asian agricultural systems remains limited. This study investigated the temporal effects of polypropylene (PP) and polyethylene terephthalate (PET) microplastics (≤20 μm) on soil pH and dissolved ion concentrations in agricultural soils from Gazipur and Mymensingh, Bangladesh. Soil–MP composite systems were prepared with a 1% (w/w) MP loading and incubated under controlled laboratory conditions for 30 days, with measurements conducted on days 1, 15, and 30. Concentrations of NH₄⁺, Na⁺, SO₄²⁻, Cl⁻, and Br⁻ were determined by ion chromatography. The results showed substantial temporal and treatment-dependent variation in soil pH and ion concentrations. PP-containing systems showed pronounced changes in NH₄⁺, whereas PET-amended Mymensingh soil exhibited marked changes in SO₄²⁻ and Br⁻. Na⁺ generally declined during incubation, while Cl⁻ showed pronounced short-term variation. PCA identified distinct patterns among the measured ions, with three components explaining 91.471% of the total variance. These findings indicate that PP and PET microplastics can be associated with changes in nutrient and ion dynamics under controlled laboratory conditions, with responses varying according to polymer type, soil characteristics, and incubation time. However, the single MP concentration, short incubation period, limited polymer types, non-sterile experimental conditions, and incomplete nitrogen speciation limit direct extrapolation to field conditions. Further studies using environmentally realistic concentrations, longer incubation periods, diverse and aged polymers, complete nitrogen speciation, and soil–plant or field systems are needed to clarify the broader implications of MP contamination in agricultural soils. Full article

CO₂ gasification of biomass represents a promising pathway toward carbon neutrality. While current research predominantly focuses on biomass carbonization with plastics or CO₂ gasification of pure biochar, the critical relationship between physicochemical structures and gasification reactivity remains underexplored. The present work explores the CO₂ gasification behavior of biochar derived from maize cob-polypropylene (PP) blends. The experimental results demonstrate that PP blending significantly enhances the gasification reactivity of maize cob-derived biochar. Structural characterization revealed that increasing the PP mass ratio led to an enhancement in specific surface area, which was the primary factor of biochar reactivity improvement. The thermogravimetric data were analyzed using both the random pore model (RPM) and unreacted core model (URCM). Comparative analysis confirmed that the RPM provided the best fit for the gasification process, with activation energy decreasing from 219.3 kJ/mol to 162.2 kJ/mol as the PP content increased from 0% to 60%. Full article

In this study, it was aimed to determine the occurrence, concentration and polymer types of microplastics in the stomach, intestine and gill tissues of pelagic fish species including bonito (Sarda sarda), horse mackerel (Trachurus mediterraneus), and anchovy (Engraulis encrasicolus), as well as demersal fish species including red mullet (Mullus barbatus) and whiting (Merlangius merlangus) from the Black Sea. A total of 150 fish samples (30 individuals from each species) were analyzed. Stomach, intestine and gill tissues were collected and prepared for microplastic analysis, and polymer identification was performed using Fourier Transform Infrared Spectroscopy (FTIR). Microplastics were detected in a considerable proportion of the examined individuals. In pelagic fish species, the most common polymers identified were polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC). In stomach tissues, PE (29%) and PVC (29%) were the dominant polymer types. In intestinal tissues, PP (35%) and PE (27%) were most prevalent, while in gill tissues PP (24%) and PE (22%) were the most frequently detected polymers. In demersal fish species, the dominant microplastic polymers were also PP and PE. In stomach tissues, PP (22%) and PE (17%) were most common, while intestinal tissues contained PP (25%) and PE (21%). In gill tissues, PP (23%) and PE (21%) were the most abundant polymers detected. The results indicate that both pelagic and demersal fish species in the Black Sea are exposed to microplastic contamination, with notable differences in polymer composition among tissues. These findings highlight the widespread presence of microplastics in commercially important fish species and emphasize the potential ecological and food safety implications of microplastic pollution in the Black Sea ecosystem. Full article