The hydrothermal degradation of different polyolefins (virgin and recycled HDPE, recycled LLDPE, metallocene LLDPE, LDPE waste, virgin and recycled PP, PP waste) and their blends in different forms ...(granulate, foil) was investigated with supercritical water at 450 °C. The degradation of HDPE was investigated in a time range from 15 min to 240 min. The maximum yield of the oil phase was obtained at a degradation time of 60 min and was over 90 %, therefore all further experiments were carried out at a reaction time of 60 min. It was found that the composition of the oil obtained, and its calorific value depend on the type of material degraded. The oils obtained from PE materials contained between 65.3 % and 69.5 % saturated hydrocarbons, 11.4 %–17 % olefins and 8.9 %–20 % aromatics, while the oils from PP materials contained 40.8 %–45.9 % aromatics, 28.4 %–33.4 % saturated hydrocarbons and 10.6 % to 19.2% olefins. The main compounds in the oils from PP materials were the C9 compounds and from PE materials the C16 compounds. An exception were the oils from rLLDPE-1-g and LDPE-b, in which C8 compounds were most abundant and which contained the highest proportion of C17 – C31 hydrocarbons (approx. 17 %) compared to oils from other PE and PP materials (1.3 %–7.1 %). The HHV of the oils was between 29.4 and 45.7 MJ/kg and was highest for the oils where the gasoline/heavy oil ratio was less than 1, while the HHV of the gas phase was between 48.4 MJ/kg and 50.7 MJ/kg.
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•The hydrolysis process of xylan have been elaborated.•The hydrothermal degradation of d-xylose depended mainly on initial concentration.•Production of furfural could be effectively ...decrease by pH-regulation.•Production of formic acid could be effectively increase by pH-regulation.•Under alkaline conditions, d-xylose can degrade directly to formic acid.
One of the key issues in the development of biofuels using lignocellulosic feedstocks is to increase the yield of fermented sugar, and simultaneously decrease the generation of fermentation inhibitors. Therefore, it is essential to understand the degradation mechanism of xylan during hot-water pretreatment. We analyzed the hydrothermal degradation products of xylan and xylose under different conditions. Results showed that furfural and formic acid formed from xylose reached a maximum value of 32.56 % and 35.14 %, respectively. By increasing the initial pH of the xylan solution, the furfural concentration can be reduced effectively to 2% and the formation of formic acid was preferred under alkaline conditions. On this basis, we proposed a new hydrothermal degradation pathway of xylan in alkaline solution. The in-depth understanding of xlyan degradation during hot water pre-treatment will be beneficial for improving the efficiency of biofuel production.
•Char produced at 330°C has the largest surface area and the largest pore volume.•Crystalline structure of produced char is highly ordered with high hydrothermal temperature.•Char produced at higher ...hydrothermal temperature exhibited higher thermal-stability.•A possible mechanism was proposed for char structure evolution during lignin hydrothermal process.
Hydrothermal degradation of lignin was carried out at 280–365°C and the structure of solid char residue was extensively examined by means of scanning electron microscopy (SEM), nitrogen absorption/desorption, X-ray spectroscopy (XRD) and Fourier transform infrared spectroscopy (FTIR). The thermal stability of the produced char was estimated by Thermogravimetry–Fourier transform infrared spectroscopy (TG–FTIR). The char yield was 16.8% at 310°C, which then increased with the temperature and reached the maxima value of 26.77% at 365°C. SEM photo indicated that decomposition of lignin was enhanced with the increasing temperature, producing char with rough surface and few vesicles. The char at 330°C had the largest surface area (2.5936m2/g) and the largest pore volume (0.0189cm3/g). XRD spectrum revealed that the char prepared at higher temperature produced higher ordered crystalline structure. Most of functional groups in char identified by FTIR were eliminated at 350°C, except for the hydroxyl group. The char produced under high hydrothermal temperature exhibited high thermal-stability according to the right-shifted DTG curve against temperature. A mechanism was proposed to explain the possible steps for char structure evolution during lignin hydrothermal process in subcritical water, involving cleavage of the weak bonds at low temperature, and elimination of functional groups and carbonization at high temperature. The results would help improve the understanding of lignin degradation in subcritical water and optimize the hydrothermal process for producing value-added chemicals from lignin.
The nanostructured (8 wt%) yttria stabilized zirconia coatings (n-YSZ) were deposited by atmospheric plasma spraying (APS) to study the effect of moisture degradation on the properties of n-YSZ ...coatings. Variations in phase composition, microstructure and mechanical properties were comprehensively characterized. The single-edge notched beam method used for fracture toughness testing is sufficiently reliable for evaluating the integral properties of the coatings in this study. Results indicated that the microstructure of the n-YSZ coatings was significantly affected by hydrothermal degradation. Hydrothermal degradation resulted in substantial defects, such as pores and cracks, which severely decreased the mechanical properties of the n-YSZ coatings. In addition, the ceramic coat was in a state of compressive stress, and the stress initially increased and then decreased with increasing degradation time. The variations in the stress of the n-YSZ coatings are closely related to the transformation of tetragonal to monoclinic phase, which is induced by hydrothermal degradation. Additionally, several major mechanical properties of the n-YSZ coatings decreased significantly with the hydrothermal degradation, including fracture toughness from 1.28 ± 0.05 to 0.08 ± 0.01 MPa m1/2, flexural strength from 60.51 ± 2.98 to 4.54 ± 0.14 MPa, and Young's modulus from 21.98 ± 0.96 to 1.46 ± 0.33 GPa.
The changes in mechanical properties, hydrothermal degradation and cell adhesion were studied in 3Y-TZP under two different superficial modification patterns (uni- and multidirectional) with a ...surface roughness ranging from 16 to 603 nm. In this sense, mechanical properties (i.e. hardness, indentation fracture toughness and scratch) and accelerated tests in water steam were measured to evaluate the influence of the surface treatments on the superficially modified layer. Moreover, a detailed characterization through micro-Raman spectroscopy and X-Ray diffraction was performed. Finally, SaOS-2 osteoblasts were used for the evaluation of the cell adhesion behaviour on the surfaces. Overall, ground/polished specimens increased the mechanical properties and ageing resistance of mirror-like polished specimens, although resistance to degradation was maximum at intermediate conditions (Sa ≈ 40−180 nm). The studied surfaces allowed cell attachment, but promoted contact guidance (i.e. cell alignment) only on unidirectionally ground surfaces above Sa = 150 nm.
The aim of this study was to systematically review the literature to assess if low-temperature degradation (LTD) simulation in autoclave promotes deleterious impact on the mechanical properties and ...superficial characteristics of Y-TZP ceramics compared to the non-aged protocol. The MEDLINE via PubMed electronic database was searched with included peer-reviewed publications in English language and with no publication year limit. From 413 potentially eligible studies, 49 were selected for full-text analysis, 19 were included in the systematic review with 12 considered in the meta-analysis. Two reviewers independently selected the studies, extracted the data, and assessed the risk of bias. Statistical analysis was performed using RevMan 5.1, with random effects model, at a significance level of p<0.05. Descriptive analysis of monoclinic phase content data showed that aging in autoclave promotes an increase in m-phase content (ranging from 0% up to 13.4% before and 2.13% up to 81.4% after aging) with intensity associated to the material susceptibility and to the aging parameters (time, pressure and temperature). Risk of bias analysis showed that only 1 study presented high risk, while the majority showed medium risk. Five meta-analyzes (factor: aging×control) were performed considering global and subgroups analyzes (pressure, time, temperature and m-phase % content) for flexural strength data. In the global analysis a significant difference (p<0.05) was observed between conditions, favoring non-aging group. Subgroup analysis revealed statistical difference (p<0.05) favoring non-aging, for aging time >20h. However, for shorter aging times (≤20h), there was no difference between groups. Pressure subgroup analysis presented a statistical difference (p<0.05) only when a pressure ≥2bar was employed, favoring non-aging group. Temperature subgroup analysis showed a statistical difference (p<0.05) only when temperature=134°C was used, favoring the non-aging group. M-phase % content analysis presented statistical difference (p<0.05) when more than 50% of m-phase content was observed, favoring non-aging group. High heterogeneity was found in some comparisons. Aging in autoclave promoted low-temperature degradation, impacting deleteriously on mechanical properties of Y-TZP ceramics. However, the effect of LTD depends on some methodological parameters indicating that aging time higher than 20h; pressure ≥2bar and temperature of 134°C are ideal parameters to promote LTD effects, and that those effect are only observed when more than 50% m-phase content is observed.
•Subcritical water extraction of sunflower oil- and water-soluble phase is proposed.•We examined degree of hydrothermal degradation of both phases.•Hydrothermal degradation did not affect oil ...quality, only water soluble extract.•Antioxidant capacity of oil increases drastically at temperatures >100°C.•Hydrothermal degradation of proteins occurs to a lesser degree than carbohydrates.
In this study, the subcritical water extraction is proposed as an alternative and greener processing method for simultaneous removal of oil- and water-soluble phase from sunflower seeds. Extraction kinetics were studied at different temperatures and material/solvent ratios in a batch extractor. Degree of hydrothermal degradation of oils was observed by analysing amount of formed free fatty acids and their antioxidant capacities. Results were compared to oils obtained by conventional methods. Water soluble extracts were analysed for total proteins, carbohydrates and phenolics and some single products of hydrothermal degradation.
Highest amount of oil was obtained at 130°C at a material/solvent ratio of 1/20g/mL after 30min of extraction. For all obtained oils minimal degree of hydrothermal degradation could be identified. High antioxidant capacities of oil samples could be observed. Water soluble extracts were degraded at temperatures ⩾100°C, producing various products of hydrothermal degradation.
An accelerated hydrothermal degrading test was designed in order to analyse the synergic effect of water and temperature on PLA/sisal biocomposites with and without coupling agent. As well, the ...physico-chemical properties of biocomposites were monitored along the hydrothermal test by means of Scanning Electron Microscopy, Size Exclusion Chromatography and Differential Scanning Calorimetry. The addition of fibre induced higher water absorption capability and promoted physical degradation, as observed in the surface topography. During the processing of biocomposites and throughout the hydrothermal ageing, a reduction of molecular weight due to chain scission was found. As a consequence, a faster formation of crystalline domains in the PLA matrix occurred the higher the amount of fibre was, which acted as a nucleating agent. Higher crystallinity was considered as a barrier against the advance of penetrant and a reduction in the diffusion coefficient was shown. The addition of coupling agent presented a different influence depending on the composition, showing an inflection point around 20% of sisal fibre.
Ceramic composites based on (Ce, Y)-TZP/Al2O3 system have great potential for applications as dental implants due to their unusually great balance between good mechanical properties and resistance to ...hydrothermal degradation. Surface roughness plays an important role in controlling these properties, but few studies have investigated the relationship between cytocompatibility and surface roughness, at levels considered moderate and low, comparable to titanium implants. In this work, bending strength, hydrothermal degradation and biological evaluation of a ceramic composite based on (Ce,Y)-TZP/Al2O3 system were investigated as a function of surface roughness. Compacted samples were sintered at 1500 °C - 2h and then submitted to different surface treatments: Group 1 composed of samples with smooth surfaces, Group 2 and Group 3 composed of rough surfaces (grinded with 15 μm or 45 μm diamond sandpaper, respectively. Samples were characterized by X-ray diffraction, scanning electron microscopy, contact angle and optical profilometry and then subjected to hydrothermal degradation tests in autoclave (134 °C - 2 bar) using artificial saliva. The Piston-on-three-balls (P–3B) testing was used to determine flexural strength. To assess indirect cytotoxicity, samples were immersed in the culture medium for NIH-3T3 cells for 72 h. Furthermore, cell adhesion and proliferation were investigated using MG63 cells (human osteosarcoma) after 3, 7, 14, and 21 days of culture. Cytotoxicity, adhesion, and cell proliferation were examined by the Methyl Tetrazolium salt (MTS) and Alizarin Red, using a confocal laser microscope. The results indicated that the materials have high resistance to degradation. Furthermore, the (Ce,Y)-TZP/Al2O3 composites are not cytotoxic. The flexural strength of the composites was 913 ± 103 MPa in samples presenting original (smooth) surface, however, a reduction in the order of 17% was observed in samples containing rough surfaces. The rougher samples show the best cellular adhesion and proliferation, leading to the formation of a mineralized matrix after 21 days. These results clearly suggest that the new (Ce,Y)-TZP/Al2O3 brand is strong and highly biocompatible and warrants further study.
Laser surface micropatterning of dental-grade zirconia (3Y-TZP) was explored with the objective of providing defined linear patterns capable of guiding bone-cell response.
A nanosecond (ns-) laser ...was employed to fabricate microgrooves on the surface of 3Y-TZP discs, yielding three different groove periodicities (i.e., 30, 50 and 100 µm). The resulting topography and surface damage were characterized by confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). X-Ray diffraction (XRD) and Raman spectroscopy techniques were employed to assess the hydrothermal degradation resistance of the modified topographies. Preliminary biological studies were conducted to evaluate adhesion (6 h) of human mesenchymal stem cells (hMSC) to the patterns in terms of cell number and morphology. Finally, Staphylococcus aureus adhesion (4 h) to the microgrooves was investigated.
The surface analysis showed grooves of approximately 1.8 µm height that exhibited surface damage in the form of pile-up at the edge of the microgrooves, microcracks and cavities. Accelerated aging tests revealed a slight decrease of the hydrothermal degradation resistance after laser patterning, and the Raman mapping showed the presence of monoclinic phase heterogeneously distributed along the patterned surfaces. An increase of the hMSC area was identified on all the microgrooved surfaces, although only the 50 µm periodicity, which is closer to the cell size, significantly favored cell elongation and alignment along the grooves. A decrease in Staphylococcus aureus adhesion was observed on the investigated micropatterns.
The study suggests that linear microgrooves of 50 µm periodicity may help in promoting hMSC adhesion and alignment, while reducing bacterial cell attachment.
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