Degradation of Waste Tetra Pak Packaging with Hydrothermal Treatment in Sub-/Supercritical Water.

Tetra pak packaging is one of the most frequently used types of packaging in the food industry. The recycling of the tetra pak packaging waste presents a difficult task because of its multi-layered, multi-component structure. In this study, the degradation of tetra pak packaging in subcritical (SubCW) and supercritical (SCW) water was investigated. The experiments were carried out in one (SCW) or two stages (SubCW and SCW), whereby the influence of the reaction temperature and time on the yield and composition of the products obtained was investigated. The maximum oil phase yield achieved in a one-stage and a two-stage degradation process was 60.7% and 65.5%, respectively. The oil and gas phases were composed of different types of hydrocarbons. Higher temperature and longer time led to higher amounts of saturated aliphatic hydrocarbons in both the oil and gas phases. The aqueous phase contained sugars (glucose, fructose) and sugar derivatives (levulinic acid, glyceraldehyde, furfurals). Based on these results, the degradation pathway of waste tetra pak packaging in SubCW and SCW was proposed. The results of the study show that the degradation of waste tetra pak packaging with SubCW and SCW is a promising recycling process.

Influence of nanosecond laser surface patterning on dental 3Y-TZP: Effects on the topography, hydrothermal degradation and cell response.

OBJECTIVES: 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. METHODS: 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. RESULTS: 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. SIGNIFICANCE: The study suggests that linear microgrooves of 50 µm periodicity may help in promoting hMSC adhesion and alignment, while reducing bacterial cell attachment.

Evaluation of Feasibility on Dental Zirconia-Accelerated Aging Test by Chemical Immersion Method.

The aim of this study was to investigate the low-temperature degradation (LTD) kinetics of tetragonal zirconia with 3 mol% yttria (3Y-TZP) dental ceramic using two degradation methods: hydrothermal degradation and immersed degradation. To study transformation kinetics, we prepared 3Y-TZP powders. We pressed these powders uniaxially into a stainless mold at 100 MPa. We then sintered the compacted bodies at intervals of 50 °C between 1300 °C and 1550 °C and immersed the specimens at various temperatures from 60 °C to 80 °C in 4% acetic acid or from 110 °C to 140 °C for the hydrothermal method. We used a scanning electron microscope (SEM) to confirm crystalline grain size and used X-ray diffraction to analyze the zirconia phase. As the sintering temperature increased, the calculated crystalline grain size also increased. We confirmed this change with the SEM image. The higher sintering temperatures were associated with more phase transformation. According to the Mehl-Avrami-Johnson equation, the activation energies achieved using the hydrothermal method were 101 kJ/mol, 95 kJ/mol, and 86 kJ/mol at sintering temperatures of 1450 °C, 1500 °C, and 1550 °C, respectively. In addition, the activation energies of the specimens immersed in 4% acetic acid were 60 kJ/mol, 55 kJ/mol, 48 kJ/mol, and 35 kJ/mol, with sintered temperatures of 1400 °C, 1450 °C, 1500 °C, and 1550 °C, respectively. The results showed that a lower sintering temperature would restrain the phase transformation of zirconia because of the smaller crystalline grain size. As a result, the rate of LTD decreased.

Effect of Hydrothermal Factors on the Microhardness of Bulk-Fill and Nanohybrid Composites.

This study evaluates the effect of aging in artificial saliva and thermal shocks on the microhardness of the bulk-fill composite compared to the nanohybrid composite. Two commercial composites, Filtek Z550 (3M ESPE) (Z550) and Filtek Bulk-Fill (3M ESPE) (B-F), were tested. The samples were exposed to artificial saliva (AS) for one month (control group). Then, 50% of the samples from each composite were subjected to thermal cycling (temperature range: 5-55 °C, cycle time: 30 s, number of cycles: 10,000) and another 50% were put back into the laboratory incubator for another 25 months of aging in artificial saliva. The samples' microhardness was measured using the Knoop method after each stage of conditioning (after 1 month, after 10,000 thermocycles, after another 25 months of aging). The two composites in the control group differed considerably in hardness (HK = 89 for Z550, HK = 61 for B-F). After thermocycling, the microhardness decrease was for Z550 approximately 22-24% and for B-F approximately 12-15%. Hardness after 26 months of aging decreased for Z550 (approximately 3-5%) and B-F (15-17%). B-F had a significantly lower initial hardness than Z550, but it showed an approximately 10% lower relative reduction in hardness.

Effect of the surface finish on the mechanical properties and cellular adhesion in (Ce,Y)-TZP/Al2O3 ceramic composites for denture implants.

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.

Deep hydration of an Li7-3xLa3Zr2MIIIxO12 solid-state electrolyte material: a case study on Al- and Ga-stabilized LLZO.

Single crystals of an Li-stuffed, Al- and Ga-stabilized garnet-type solid-state electrolyte material, Li7La3Zr2O12 (LLZO), have been analysed using single-crystal X-ray diffraction to determine the pristine structural state immediately after synthesis via ceramic sintering techniques. Hydrothermal treatment at 150 °C for 28 d induces a phase transition in the Al-stabilized compound from the commonly observed cubic Ia-3d structure to the acentric I-43d subtype. LiI ions at the interstitial octahedrally (4 + 2-fold) coordinated 48e site are most easily extracted and AlIII ions order onto the tetrahedral 12a site. Deep hydration induces a distinct depletion of LiI at this site, while the second tetrahedral site, 12b, suffers only minor LiI loss. Charge balance is maintained by the incorporation of HI, which is bonded to an O atom. Hydration of Ga-stabilized LLZO induces similar effects, with complete depletion of LiI at the 48e site. The LiI/HI exchange not only leads to a distinct increase in the unit-cell size, but also alters some bonding topology, which is discussed here.

Mechanical properties of ceramic composites based on ZrO2 co-stabilized by Y2O3-CeO2 reinforced with Al2O3 platelets for dental implants.

OBJECTIVES: The objective of this work was the development and characterization of a ceramic composite based on (Ce,Y)-TZP/Al2O3 aiming an application on dental implants, comparing it with conventional monolithic 3Y-TZP ceramics, currently used for the same type of application. METHODS: Ceramic samples, 3Y-TZP (n = 40) and (Ce,Y)-TZP/Al2O3 (n = 40), were sintered at 1500 °C - 2h and characterized by relative density, X-Ray diffraction (XRD) and microstructure. Then, the samples of both materials were divided into two groups: 1) samples with original (as sintered) surfaces; 2) samples with conditioned, polished, surfaces. All samples were submitted to hydrothermal degradation tests, on an autoclave (134 °C - 2 bar), for 10 h in artificial saliva. The degraded samples were characterized by XRD and the polished group were also characterized by their elastic moduli, Vickers hardness and fracture toughness (Vickers indentation method). Both groups were also submitted to a flexural strength test, 3B-P testing, for which the data were interpreted using Weibull statistics. RESULTS: All sintered specimens presented nearly full densification. After the hydrothermal degradation tests, 3Y-TZP samples presented 16.4% of monoclinic (m)-ZrO2 phase while the composite samples withheld 100% of tetragonal (t)-ZrO2 phase. Both materials presented equiaxial ZrO2 grains with an average size of 0.48 ± 0.17 µm and 0.75 ± 0.22 µm, respectively, for the monolithic and composite ceramics. In the composites, is observed the presence of well distributed Al2O3 grains on the ZrO2 matrix, in two distinct morphologies: equiaxial grains and platelets. The composites (Ce,Y)-TZP/Al2O3 presented average values of elastic moduli, Vickers hardness and fracture toughness of 228.3 ± 6.5 GPa, 1427 ± 46 HV e 11.3 ± 0.4 MPa m1/2, respectively. An inversely proportional relationship is observed between the roughness and the bending strength, since the 3Y-TZP samples presented a average strength of 860.7 ± 81 MPa (as-sintered) and 965.4 ± 93 MPa (polished) while the (Ce,Y)-TZP/Al2O3 composites presented average strength of 810.6 ± 147 MPa (as-sintered) and 952.6 ± 88 MPa (polished). CONCLUSIONS: The composites (Ce,Y)-TZP/Al2O3 showed high resistance to degradation in saliva and adequate properties for use as dental implants. Values of flexural strength (>950 MPa) and Weibull modulus (m > 10) were similar to the conventional 3Y-TZP ceramics. Moreover, its hardness, elastic modulus and fracture toughness were higher than those obtained for 3Y-TZP. The expressive values of KIC obtained for (Ce,Y)-TZP/Al2O3 composites are results of association of different toughening mechanisms acting simultaneously in the material.

Xylan and xylose decomposition during hot water pre-extraction: A pH-regulated hydrolysis.

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.

Bacterial cellulose production from terylene ammonia hydrolysate by Taonella mepensis WT-6.

Hydrothermal degradation was used to pretreat terylene with an aim of noticeably improving the yield of fermentable monomers: terephthalic acid (TPA), mono (2- hydroxyethyl) terephthalic acid (MHET), bis-hydroxyethyl terephthalate (BHET), and ethylene glycol (EG). After 0.5 h of reaction time at 180 °C, hydrothermal degradation with ammonia led to almost complete conversion of the terylene to TPA, MHET, BHET and EG, which were then transformed by Taonella mepensis WT-6 to bacterial cellulose (BC). Furthermore, the optimum fermentation conditions with the maximum BC yield were 5.0 g/L yeast extract, 30.0 °C, pH 9.0, 8.0% inoculum, and hydrolysate TOC (5.02 g/L). Additionally, mechanical and thermal analysis revealed that the properties of BC produced from TAH medium were similar to those of BC produced with HS medium. Considering the substantial amount of global terylene waste being produced, this study provides an alternative solution for the biosynthesis of BC.

An experimental study on hydrothermal degradation of cubic-containing translucent zirconia.

PURPOSE: The aims of this study were to investigate mechanical properties and hydrothermal degradation behaviour of the cubic-containing translucent yttrium oxide stabilized tetragonal zirconia polycrystal (Y-TZP). MATERIALS AND METHODS: Four groups of Y-TZP (T, ST, XT, and P), containing different amount of cubic crystal, were examined. Specimens were aged by autoclaving at 122℃ under 2 bar pressure for 8 h. Phase transformation was analyzed using X-ray diffraction (XRD) to measure phase transformation (t→m). Kruskal-Wallis test was used to determine the difference. Surface hardness, biaxial flexural strength, and fracture toughness in values among the experimental groups and verified with Wilcoxon matched pairs test for hardness values and Mann Whitney U for flexural strength and fracture toughness. RESULTS: XRD analysis showed no monoclinic phase in XT and P after aging. Only Group T showed statistically significant decreases in hardness after aging. Hydrothermal aging showed a significant decrease in flexural strength and fracture toughness in group T and ST, while group XT and P showed no effect of aging on fractural strength and fracture toughness with P<.05. CONCLUSION: Hydrothermal aging caused reduction in mechanical properties such as surface hardness, biaxial flexural strength, and fracture toughness of Y-TZP zirconia. However, cubic-containing zirconia (more than 30% by volume of cubic crystal) was assumed to have high resistance to hydrothermal degradation. Clinical significance: Cubic-containing zirconia could withstand the intraoral aging condition. It could be suggested to use as a material for fabrication of esthetic dental restoration.

Effect of hydrothermal aging on the properties of zirconia with different levels of translucency.

OBJECTIVES: The aim of this study was to evaluate the effect of hydrothermal aging on the mechanical properties and translucency of dental zirconia with different levels of translucency. METHODS: Three different types of dental yttria-stabilized zirconia were used: 3Y-TZP (ZrO2 - 3 mol.% Y2O3) of medium opacity (designated Z3OP), 3Y-TZP of medium translucency (Z3MT), and 5Y-PSZ (ZrO2 - 5 mol.% Y2O3) of high translucency (Z5HT). A total of 120 specimens were sintered (n = 40 specimens/group). The control group (sintered→polished→heat-treated) and the aged group (sintered→polished→heat-treated→hydrothermally degraded at 134 °C, 2 bar, 5h) were characterized by relative density, quantitative phase analysis by X-ray diffraction using the Rietveld method, microstructural analysis by scanning electron microscopy, surface roughness and translucency. All groups were submitted to a biaxial flexural strength test. Data analysis using Kruskal-Wallis, Nemenyi (p-value = 0.05), and Weibull statistics were used. RESULTS: All sintered specimens presented full densification. After aging, an increase of the m-ZrO2 phase content was observed for the Z3OP group. On the other hand, Z3MT and Z5HT did not show any m-ZrO2 phase, indicating resistance to the hydrothermal degradation. Smaller grains were observed in the Z3MT group in relation to Z3OP group and the Z5HT group presented a bimodal grain distribution, where the largest grains were associated to cubic ZrO2. Z3OP exhibited a slight increase in roughness as a function of degradation, while the roughness remained statistically stable in the other groups. Translucency was little influenced by degradation, but considerably affected by increasing thickness. The Z5HT samples were the group with the highest translucency among the control groups. Z3OP exhibited the highest flexural strength, while being the most susceptible to hydrothermal degradation. The lowest values were presented by Z5HT in all groups, due to the high concentration of c-ZrO2 grains. CONCLUSION: Hydrothermal aging is less critical to the flexural strength of zirconia-based materials than the materials' composition and microstructure. Z5HT zirconia showed the highest translucency, however the measured difference is not visually perceptible. Z5HT was considered the most resistant to hydrothermal degradation.

Aging resistance, mechanical properties and translucency of different yttria-stabilized zirconia ceramics for monolithic dental crown applications.

OBJECTIVES: The dental market moves towards high-translucency monolithic zirconia dental crowns, which are usually placed either with - or without - a thin glaze layer. The microstructural features and the mechanical performances of these materials are still controversial, as well as their susceptibility to aging. This paper aims at studying these aspects in the current generation of zirconia dental crowns showing different degrees of translucency. METHODS: Four different commercial zirconia materials were investigated, including one standard 'full-strength' 3Y-TZP and three grades with improved translucency. The microstructural features (phase composition and assemblage, grain size) were carefully studied, as well as mechanical properties (biaxial bending strength and indentation toughness), translucency and aging behavior (in autoclave at 134°C). Aging was conducted on crowns with and without glaze to better represent clinical uses. RESULTS: Important differences are found in terms of microstructures among the materials in terms of cubic phase content and yttria in the tetragonal phase, leading to different optical, mechanical and aging resistance properties. We show that higher cubic phase content leads to better translucency and stability in water steam, but at the expense of strength and toughness. A compromise is always inevitable between translucency and aging resistance on one side and mechanical properties on the other side.

Effect of grinding and aging on subcritical crack growth of a Y-TZP ceramic

Abstract This study aimed to investigate slow crack growth (SCG) behavior of a zirconia ceramic after grinding and simulated aging with low-temperature degradation (LTD). Complementary analysis of hardness, surface topography, crystalline phase transformation, and roughness were also measured. Disc-shaped specimens (15 mm Ø × 1.2 mm thick, n = 42) of a full-contour Y-TZP ceramic (Zirlux FC, Amherst) were manufactured according to ISO:6872-2008, and then divided into: Ctrl - as-sintered condition; Ctrl LTD - as-sintered after aging in autoclave (134°C, 2 bar, 20 h); G - ground with coarse diamond bur (grit size 181 μm); G LTD - ground and aged. The SCG parameters were measured by a dynamic biaxial flexural test, which determines the tensile stress versus stress rate under four different rates: 100, 10, 1 and 0.1 MPa/s. LTD led to m-phase content increase, as well as grinding (m-phase content: Ctrl - 0%; G - 12.3%; G LTD - 59.9%; Ctrl LTD - 81%). Surface topography and roughness analyses showed that grinding created an irregular surface (increased roughness) and aging did not promote any relevant surface change. There was no statistical difference on surface hardness among different conditions. The control group presented the lowest strength values in all tested rates. Regarding SCG, ground conditions were less susceptible to SCG, delaying its occurrence. Aging (LTD) caused an increase in SCG susceptibility for the as-sintered condition (i.e. G < G LTD < Ctrl < Ctrl LTD).

Effect of several repair techniques on the bond strength between composite resin and degraded Y-TZP ceramic / Efeito de várias técnicas de reparo na resistência de união entre resina composta e zircônia degradada

Objective: To evaluate the bond strength of different repair treatments for composite resin to aged Y-TZP ceramics. Material and Methods: Zirconia blocks were cut into smaller specimens, sintered according to manufacturer's recommendations (final dimensions of 4×4×3 mm), and randomly allocated into nine groups (n=15) according to the surface treatment and presence/ absence of aging of the substrate (subjected to lowtemperature degradation - LTD), as follows: without LTD (Control: without treatment; TBS: tribochemical silica coating + silane + adhesive); with LTD (Control-LTD: without treatment; TBS-LTD: TBS with hydrothermal degradation; MoS-LTD: Monobond S + adhesive; MoPLTD: Monobond Plus + adhesive; MZP-LTD: Metal/ Zirconia Primer + adhesive; USB-LTD: Single Bond Universal; AP-LTD: Alloy primer + adhesive). LTD was simulated in an autoclave (134 °C, 2 bar, 5 h). The ceramic blocks were embedded in PVC cylinders with a self-curing acrylic resin; each surface treatment protocol was performed; a composite resin cylinder ( : 3.25 mm and height: 3 mm) was then build-up using split metallic matrices. All the specimens were aged (thermocycling + storage in water for 90 days) and subjected to the shear bond strength test using a universal testing machine (1 mm/min). The failure mode was classified into four types: adhesive, composite resin cohesive fracture, ceramic cohesive fracture, and mixed. The bond strength values were subjected to Mann­Whitney test. Results: Only air-abraded samples (TBS and TBS­LTD) survived thermocycling. More than 80% of the samples of the other groups presented pre-test failures. TBS groups presented higher values of bond strength (3.94) compared to TBSLTD (0.96). The predominant type of failure for the surviving samples were adhesive. Conclusion: Air particle abrasion is mandatory to improve the bond strength of the Y-TZP substrate; an aged substrate presents an even more unfavorable scenario for adhesion. (AU)

Objetivo: Avaliar a resistência de união ao cisalhamento gerada por diferentes técnicas de reparo em resina composta aderida em zircônia envelhecida (sujeita a degradação a baixa temperatura - LTD). Material e Métodos: blocos de zircônia foram seccionados em espécimes, sinterizados de acordo com o fabricante (dimensões finais de 4x4x3 mm), e aleatorizados em nove grupos (n=15) de acordo com o tratamento de superfície e presença/ausência de envelhecimento do substrato (LTD), conforme: sem LTD (Control: sem tratamento; TBS: tribosilicatização + silano + adesivo); com LTD (Control-LTD: Monobond S + adesivo; MoP-LTD: Monobond plus + adesivo; MZPLTD: Meta/Zirconia primer + adesivo). LTD foi simulada em autoclave (134 °C, 2 bar, 5 h). Os blocos de cerâmica foram embutidos em cilindros de PVC com resina acrílica autopolimerizável; cada tratamento de superfície foi realizado; um cilindro de resina composta ( : 3,25 mm 3 mm de altura) foi confeccionado usando matrizes metálicas bipartidas. Todos os espécimes foram envelhecidos (termociclagem + armazenagem em água por 90 dias) e sujeitos ao teste de cisalhamento usando um equipamento de teste universal (1 mm/ min). O modo de falha foi classificado em quatro grupos: adesivo, fratura coesiva em resina composta, fratura coesiva da cerâmica, e mista. Os valores de adesão foram sujeitos ao teste de Mann-Whitney. Resultados: somente as amostras jateadas (TBS e TBSLTD) sobreviveram a termociclagem. Mais que 80% dos espécimes dos outros grupos apresentaram falhas préteste. Os grupos TBS apresentaram os maiores valores de resistência ao cisalhamento (3,94) comparado com TBS-LTD (0,96). Os tipos predominantes de falha para os espécimes sobreviventes foi adesiva. Conclusão: o jateamento é recomendável para aumentar a resistência adesiva à zircônia; um substrato envelhecido apresenta um cenário mais desfavorável de adesão. (AU)

Surface micro-morphology, phase transformation, and mechanical reliability of ground and aged monolithic zirconia ceramic.

This study aimed to determine the effects of grinding and low temperature aging on the biaxial flexural strength, structural reliability (Weibull analysis), surface topography, roughness analysis, and phase transformation (t→m) of an yttrium-stabilized tetragonal zirconia polycrystalline ceramic. Ceramic discs (15.0×1.2±0.2mm, VITA In-Ceram YZ) were prepared and randomly assigned into six groups according to 2 factors (n=30): 'grinding' (Ctrl - without treatment, as-sintered; Xfine - grinding with extra fine diamond bur - 30µm; Coarse - grinding by coarse diamond bur - 151µm), and 'aging' (without or with aging: CtrlLTD; XfineLTD; CoarseLTD). Grinding was performed in an oscillatory motion with a contra-angle handpiece under constant water-cooling. Low temperature degradation (LTD) was simulated in an autoclave at 134°C, under 2bar pressure, for 20h. The roughness (Ra and Rz parameters) significantly increased after grinding in accordance with bur grit-size (Coarse>Xfine>Ctrl), and aging promoted distinct effects (Ctrl=CtrlLTD; Xfine>XfineLTD; Coarse=CoarseLTD). Grinding increased the m-phase, and aging led to an increase in the m-phase in all groups. However, different susceptibilities to LTD were observed. Weibull analysis showed a significant increase in the characteristic strength after grinding (Coarse=Xfine>Ctrl), while aging did not lead to any deleterious impact. Neither grinding nor aging resulted in any deleterious impact on material reliability (no statistical decrease in the Weibull moduli). Thus, neither grinding nor aging led to a deleterious effect on the mechanical properties of the evaluated Y-TZP ceramic although a high m-phase content and roughness were observed.

Hydrothermal degradation of a 3Y-TZP translucent dental ceramic: A comparison of numerical predictions with experimental data after 2 years of aging.

OBJECTIVES: The purpose of the study was to assess the hydrothermal resistance of a translucent zirconia with two clinical relevant surface textures by means of accelerated tests (LTD) and to compare predicted monoclinic fractions with experimental values measured after two years aging at 37°C. METHODS: Polished (P) and ground (G) specimens were subjected to hydrothermal degradation by exposure to water steam at different temperatures and pressures. The t-m phase transformation was quantified by grazing incidence X-ray diffraction (GIXDR). The elastic modulus and hardness before- and after LTD were determined by nanoindentation. RESULTS: G specimens presented a better resistance to hydrothermal degradation than P samples. Activation energies of 89 and 98kJ/mol and b coefficients of 2.0×10(-5) and 1.8×10(-6) were calculated for P and G samples respectively. The coefficients were subsequently used to predict transformed monoclinic fractions at 37°C. A good correlation was found between the predicted values and the experimental data obtained after aging at 37°C during 2 years. Hydrothermal degradation led to a significant decrease of the elastic moduli and hardness in both groups. SIGNIFICANCE: The dependency of the t-m phase transformation rate on temperature must be determined to accurately predict the hydrothermal behavior of the zirconia ceramics at oral temperatures. The current prevailing assumption, that 5h aging at 134°C corresponds to 15-20 years at 37°C, will underestimate the transformed fraction of the translucent ceramic at 37°C. In this case, the mechanical surface treatment influences the ceramic's transformability. While mild grinding could potentially retard the hydrothermal transformation, polishing after occlusal adjustment is recommended to prevent wear of the antagonist teeth and maintain structural strength.

Low-temperature degradation of Y-TZP ceramics: A systematic review and meta-analysis.

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.

Simultaneous extraction of oil- and water-soluble phase from sunflower seeds with subcritical water.

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 1/20 g/mL after 30 min 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.

Chemo-selective high yield microwave assisted reaction turns cellulose to green chemicals.

Exceptionally high cellulose liquefaction yields, up to 87% as calculated from the amount of solid residue, were obtained under mild conditions by utilizing the synergistic effect of microwave radiation and acid catalysis. The effect of processing conditions on degradation products was fingerprinted by rapid laser desorption ionization-mass spectrometry (LDI-MS) method. The reaction was chemo-tunable, enabling production of glucose (Glc) or levulinic acid (LeA) at significantly high selectivity and yields, the relative molar yields being up to 50 and 69%, respectively. A turning point from pure depolymerization to glucose to further degradation to levulinic acid and formic acid was observed at approximately 50% liquefaction or above 140 °C. This was accompanied by the formation of small amounts of solid spherical carbonized residues. The reaction was monitored by multiple analytical techniques. The high yields were connected to the ability of the process to break the strong secondary interactions in cellulose. The developed method has great potential for future production of green platform chemicals.