The use of composite edible films made from biopolymers has attracted interest as a way to reduce pollution and recycling problems; however, the relation between barrier, mechanical and structural ...properties of the films have been scarcely studied. The aim of this work was to evaluate composite zein–chitosan edible films by applying common nanotechnology tools and to relate the results to zein concentration and film structural changes. Rougher, more elastic, and less hard film structures with better water vapour barrier properties were obtained using larger zein concentrations. Raman spectroscopy exhibited unexpected interactions, as indicated by the disappearance of the thiol groups of cysteine in the zein films and the appearance of OSO and COS groups in the blended materials in conjunction with the disappearance of zein ɛ-amino and NH2 functional groups in the zein film samples, thereby confirming changes in the blended film structure. Zein concentration presented linear correlations with water vapour permeability (R=−0.978) and film roughness (R=0.929). The composite films presented better barrier and mechanical properties than single ingredient films. This information shows the benefit of using protein–polysaccharide blends to prepare edible films.
•A nitriding pretreatment increases the adhesion of AlCrN coating on 4140 steel.•The adhesive failure mode of AlCrN is changed to cohesive by the nitrides layer.•The COF of AlCrN is reduced to 50% ...due to the nitriding pretreatment.•The specific wear rate of AlCrN is greatly reduced by the nitriding pretreatment.
In this work, a gas nitriding pretreatment (iron nitrides layer) formed on the surface of 4140 steel is proposed to improve the adhesion and wear resistance of the AlCrN coatings deposited by arc cathodic PVD. AlCrN, FexN and AlCrN/FexN (duplex) systems were formed with total thicknesses of 3, 10 and 13 µm, respectively. Using spherical instrumented indentation, hardness more than 22 GPa were determined for the AlCrN-based coatings, meanwhile 10 GPa for the iron nitrides. The adhesion of the coatings were evaluated by progressive load scratch tests (PLST) where the duplex coating reduced the CoF and changed the failure mode from adhesive to cohesive for the AlCrN coating. The AlCrN/FexN coating exhibited the lowest specific wear rate and the severity of damage was reduced in multipass scratch wear tests (MPST). The duplex system presented the best adhesion and wear resistance.
Titanium nitride (TiN) coatings with a Cr metallic interlayer were deposited on AISI 316L stainless steel substrates using D. C. unbalanced magnetron sputtering, changing substrate temperature and ...gas mixture. The effect of the sliding motion in wear tests was studied, comparing multipass (unidirectional) and reciprocating (bidirectional) sliding modes. In addition, microstructure, mechanical properties and adhesion were analyzed. The structural characterization was performed by scanning electronic microscopy (SEM) and grazing incidence X-ray diffraction (GIXRD). Moreover, hardness of the coating was measured by spherical nanoindentation, and thermal residual stresses were estimated. The scratch tests were conducted using a steel ball of 1 mm of diameter. To study the effect of sliding motion, the wear tests were carried out with an alumina ball of 3 mm of diameter, in both sliding modes the same linear test geometry, a stroke length of 3 mm and loads of 0.5 and 1 N were used. TiN coatings thicknesses ranged from 1.1 to 1.8 μm, growing in preferred orientations (200) and (111). It was found that increasing the nitrogen content during the deposition cause a decrease in the adhesion of the coating. In the sliding wear tests, the coefficient of friction (COF) values ranged from 0.12 and 0.22. The effect of sliding motion in COF was more evident in the tests performed with 0.5 N load, reciprocating exhibited higher values than multipass. The specific wear coefficients k varied from 6.9 × 10−4 to 1.88 × 10−3 mm3 · N−1m−1 for all tests, the highest value was obtained in a reciprocating test.
•Thermal residual stresses from −0.11 to −0.29 GPa were estimated.•Adhesion decreased by increasing nitrogen content.•Tribological behavior is studied by multipass and reciprocating sliding motion.•With 0.5 N test, lower COF was obtained in multipass than in reciprocating.
•Boriding reduced friction by up to 30% compared to heat-treatment in dry tests.•In dry tests, the borided steel showed mild wear and the heat-treated steel showed severe wear.•Grease lubrication ...reduced friction similarly in the borided and heat-treated steel.•The wear resistance of the borided steel improved by about 10 times using grease.
This work presents new results about the dry and grease-lubricated wear resistance of borided AISI 52100 steel. Boriding was conducted at 850 °C for 1 h. The reciprocating wear tests were conducted with an alumina ball of 6 mm of diameter, with normal load of 20 N and sliding distances of 100, 150 and 200 m; a lithium grease was employed for lubrication. In comparison with heat-treated AISI 52100 steel, boriding reduced the coefficient of friction by 15–30% in dry conditions, although both stabilized similarly in grease-lubricated tests. In addition, the results showed that, for the longer sliding distance, boriding increased the wear resistance up to 8 times in dry conditions and up to 10 times using grease for lubrication. The implementation of boriding significantly improved the tribological performance of AISI 52100 steel in both tests conditions.
In this work, an experimental-numerical evaluation of the standing contact fatigue testing of a nitrided AISI 316L steel was developed. The nitride layers were formed at the surface of an AISI 316L ...steel by a salt bath nitriding process at a temperature of 580 °C for 1, 3 and 5 h of exposure time, obtaining three different layer thicknesses. In order to know the mechanical response and the different mechanisms of damage associated with the standing contact fatigue test, Hertzian tests were performed on a MTS machine by cyclic loading of a sphere on a flat surface formed by the layer/substrate system. The standing contact fatigue test was developed through two main stages. First, the critical loads for each treatment condition were determined by monotonic tests, where the appearance of circular cracks was considered as the failure criterion. Subsequently, cyclic subcritical loads were applied at a frequency of 5 Hz. A numerical model based on the finite element method was developed to evaluate the stress field generated in the system by cyclic contact loads. The results indicate that the thinnest thickness of nitride layer exhibits better resistance to standing contact fatigue.
•Nitride layers were evaluated through standing contact fatigue.•The stress field associated with contact damage modes in the nitride layers was obtained by the finite element method.•Cohesive damage was a function of both the range of the maximum principal stress and the amplitude of the radial distance.
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•Optimal conditions of oil extraction by thermosonication were found by RSM.•Thermosonication extraction improved oil yield and its quality was preserved.•Amplitude increase cause ...microstructural changes and reduce the crystallinity index•Structural changes in the residual cake caused by thermosonication were evidenced.
The seed of Ricinus communis L. is a source of oil that can be used to produce biodiesel. In this study, the thermosonication (TS) extraction of castor oil is proposed and is compared with Soxhlet (S) extraction as the conventional method. The optimum conditions for the TS extraction of castor oil were determined by response surface methodology (RSM). The time at 25, 35, and 45 min and amplitudes of 25, 50, and 75% were independent variables, while the dependent variables were the oil yield, iodine index, peroxide index, saponification index, unsaponifiable matter, acidity index, and refraction index. The optimal conditions for the oil yield were an amplitude of 50%, 35 min, and a solid/liquid ratio of 1/10 g/mL; a yield of 61.12% was reached under these conditions; by S extraction, the yield was 57.3% after 8 h of extraction. The microstructure of the residual cake before and after extraction was evaluated by scanning electron microscopy and the cellulosic compounds, proteins, and lipids in the residual cake were identified and their distribution observed by means of confocal laser scanning microscopy. Microscopy techniques and image analysis were helpful in evaluating the changes in the microstructure that occur on the residual cake during the TS and S extraction and to understand the extraction mechanisms. The crystallinity index was calculated from X-ray diffraction spectra to interpret changes in the structure of the residual cake before and after use of the extraction methods. Therefore, the TS extraction improved the oil yield in shorter extraction time. Characterization of the residual cake opens the way to study a potentially usable material as a source of cellulosic compounds.
The objective of this study was to evaluate the effect of the presence of calcium oxalate (CaOx) crystals on the micromechanical properties of sclerenchyma tissue from the pecan nutshell (Carya ...illinoinensis). The microstructure of the cross-section nutshell was examined using light microscopy (LM) and atomic force microscopy (AFM). Using an instrumented indentation system, indentation tests with maximum loads of 500 mN were made on the biological material where the variables studied were the number of crystals present in the evaluated area and the size of individual crystals. Microscopic analysis revealed that the pecan nutshell consists of sclerenchyma tissue with multiple CaOx crystals randomly distributed throughout the material, exhibiting prismatic shapes and various sizes. The results of the indentation tests showed that the examined areas where there were crystals (1, 2 or up to 3) presented values of hardness and elastic modulus significantly higher (P < 0.05) compared to the sclerenchyma (without crystals). Likewise, there were no significant differences (P > 0.05) between the values of the micromechanical properties of the areas evaluated as a function of the number of crystals. On the other hand, it was observed that the size of the crystals did not show a direct correlation with the mechanical properties evaluated as expected. In conclusion, the biomineralization phenomenon is a successful strategy designed by nature to improve the rigidity of the pecan nutshell, where the CaOx crystals strengthen the structure by increasing the micromechanical properties.
•The effect of CaOx crystals on the micromechanical properties of the sclerenchyma from the pecan nutshell were evaluated by indentation tests.•The CaOx crystals increased the hardness (≈20%) and elastic modulus (≈13%) of the sclerenchyma tissue locally.•There were no significant differences between the values of the micromechanical properties evaluated as a function of the number of crystals.•The size of the crystals did not show a direct correlation with the mechanical properties.•CaOx crystals strengthen the structure of the pecan nutshell, demonstrating that they fulfill a mechanical function.
•Microstructure of nopal spines was characterized by microscopy techniques.•Distribution of cellulose and lignin in nopal spines was evidenced by microscopy.•Micromechanical properties are influenced ...by the structural arrangement of spines.•Nopal spines are harder than wood materials.•Nopal spines could be an alternative source of cellulose and lignin.
The aim of this work was to study the microstructure and micromechanical properties of spines obtained from nopal waste. Spines were obtained by drying at 40 °C then sieving. Physical and chemical assays and microscopy techniques were used to determine the role of microstructural arrangement in local micromechanical properties. Transversal (TS) and longitudinal sections (LS) of the spines were studied by indentation and microscopy. Environmental scanning electron microscopy was helpful for characterizing the overall structure of spines. Confocal laser scanning microscopy was used for determining the distribution of cellulose and lignin in spines, which was associated with their micromechanical properties. Atomic force microscopy showed that TS is less rough (Ra = 3.08 ± 0.75 nm) and more hard (0.57 ± 0.31 GPa) than LS (Ra = 24.56 ± 1.60 nm, 0.57 ± 0.31 GPa). In accordance with these results, the elastic modulus of LS (8.65 ± 3.18 GPa) is lower than that of TS (14.94 ± 7.09 GPa). The hardness and elastic modulus of libriform fibers and sclerified epidermis are influenced by their microstructures and as well as the distribution of cellulose and lignin in the spines. The microstructural arrangement and the distribution of cellulose and lignin in the TS provide greater hardness values than those of woods. The current study presents a novel structural characterization of nopal spines and their local micromechanical properties. This waste product could be a cheap and non-wood alternative resource of cellulose with good mechanical properties useful for designing novel biomaterials with applications in the agricultural sector.
Atomic force microscopy (AFM) was used to evaluate the mechanical properties of apple tissue (Malus domestica var. Golden Delicious) and isolated cells. Young's modulus (E) obtained for the tissue ...was 0.86±0.81MPa, while for isolated cells an average value of 0.63±0.42MPa was found. The fractal dimension of the distribution of E (FDE) was estimated to be 1.81 for tissue and 2.47 for isolated cells, which indicates more anisotropic structures in single cell topography in comparison with the tissue. Finally, an image texture analysis was performed and different values were obtained; for roughness Ra=49.70±23 and 18.00±3, entropy Ent=5.26±0.66 and 5.70±0.23 and for the fractal dimension of the texture image FDT=2.55±0.02 and 2.62±0.03, for tissue and isolated cells respectively.
AFM is rarely used to evaluate the structural and mechanical properties of food materials. AFM studies could provide insight on food properties. For example, the nanoindentation of cells by AFM could be used to follow-up changes to the mechanical properties that occur during the processing and storage of fruits with industrial relevance such as apple. Study of the nanostructure and nanomechanical properties of vegetable cells could lead to a more in-depth understanding of the relationship structure–functionality in foodstuffs. This could be applied to address several issues, such as extending the storage life of climacteric fruits, verifying the structural modifications of the tissues when they are chemically treated and having a better control of mechanical and structural properties. Currently, fractal and image analysis is gaining attention in the food science industry. Their application allows one to obtain quantitative information from nanoindentation data and AFM images which can be related to structural modifications which occur during ripening and processing of climacteric fruits. This methodology could be extended to other food materials.
•Chemical isolation procedure of apple cells caused severe microstructural changes.•Young's modulus of the tissue was higher than for isolated cells and showed a wider variability.•The variability of the Young modulus distribution was characterized by fractal analysis.•Texture parameters of the AFM images can be linked with nanomechanical properties.
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