Amorphous Constituents Research Articles

Influence of Alkali Treatment and Maleated Polypropylene (MAPP) Compatibilizer on the Dry‐Sliding Wear and Frictional Behavior of Borassus Fruit Fine Fiber (BFF)/Polypropylene (PP) Polymer Composites for Various Engineering Applications

Tribological properties of the novel Borassus fruit fine fiber‐ (BFF‐) reinforced polypropylene (PP) composites with respect to fiber matrix surface modifications have been described. Composites were fabricated by an injection molding process using Borassus fruit fine fiber (BFF) of 5 wt.% as reinforcement and polypropylene (PP) as a matrix component. Fibers were treated with alkali (T) to remove the residual lignin (if present) and to enhance the interfacial adhesion between the fiber/matrix interface. Alkali treatment reveals additional reactive functional groups here on the surface of the Borassus fiber, allowing effective interaction bonding with the polypropylene matrix. Borassus fibers are primarily treated with an alkali solution to extract weaker unstructured amorphous constituents so that the fibers retain crystallized components, thereby strengthening the fiber’s strength. A 5 wt.% of maleated polypropylene (MAPP) was used as a compatibilizer to improve the interfacial adhesion between fiber and the polymer matrix. The wear and frictional behavior of BFF/PP composites with respect to the modifications were evaluated by steel counterface utilizing pin‐on‐disc test contraption under dry‐sliding conditions. The sliding velocity, applied load, and sliding distance were maintained as 2.198 m/s, 9.81–29.43 N, and 4000 m, respectively. The results demonstrate that the reinforcement of BFF to polypropylene matrix and the modifications improved the wear properties of the neat polymer matrix. Findings concluded that the abrasive wear resistance of T + PP + MAPP composite showed better interfacial adhesion and bonding, thus resulting in better tribological performance as compared to the other three compositions under different loading conditions. The effective substantial improvement of the coefficient of friction has been observed in alkali‐treated fiber and polypropylene matrix with MAPP compatibilizer (T + PP + MAPP) composites due to the presence of MAPP compatibilizer and alkali‐treated fibers. The frictional coefficient of T + PP + MAPP possesses better interfacial bonding strength upon NaOH treatment, and coupling agent, which results in enhancement of effective contact surface area and good surface friction characteristics, has been observed under different loading conditions. The fracture mechanism of worn‐out portions of BFF/PP composites was studied using high‐resolution scanning electron microscopy to analyze various imperfections like debonding, splits, fiber cracks, and wreckage or fragments formation.

Weathering of tephra and the formation of pedogenic minerals in young Andosols, South East Iceland

Frequent tephra deposition and a steady influx of aeolian material of multiple origins, dominate soil formation in Iceland. Little is known about the weathering behaviour, mineral formation and alteration of tephra and Icelandic Andosols after tephra deposition.Two sampling sites in the volcanically active area south of Vatnajökull in South East Iceland were selected according to the presence of two distinctive tephra layers; a light coloured, rhyolitic, tephra from the Öræfajökull eruption in 1362 CE and a black, basaltic, Veiðivötn tephra from 1477 CE. Through a combination of physical, chemical and mineralogical analyses, the present research improves the understanding of changes in properties, weathering processes and mineralogy in Andosols after the deposition of tephra and aeolian material. It adds significant knowledge about the impact of explosive volcanic eruptions and consequences of heavy tephra fall and erosion on soil development in Iceland in particular, but may have wide-ranging influence on the management of volcanic soils worldwide.Both pedons can be classified as Andosols, showing silandic and vitric soil properties. The soils were acidic and dominated by sand. Feo/Fed ratios above 0.75 in all soils indicated a low degree of soil development. The major portion of the clay size particles mainly derived from poorly crystalline and amorphous constituents (e.g. allophane and ferrihydrite). In spite of the low soil age (less than 650 years) and the prevailing cool climatic conditions, we observed signs of pedogenesis and the presence of secondary clay minerals in both, soils and tephra. It was mainly secondary chlorite, which could be verified. Usually it takes more time under given environmental conditions for clay minerals to form and alter. The phyllosilicates we found are supposedly attributed to aeolian influx of material from older, more weathered, more developed eroded surfaces of unknown origin and chemical composition, maybe from sources outside Iceland. This and the particular local site conditions (e.g. moisture, soil temperature, SOM), rather than the primary composition of the parent material, are the driving factors in the development of the investigated Andosols and the alteration of minerals. Additionally, the high volcanic activity in Iceland constantly provides new tephra to the soils.

Effects of magnesium carbonate concentration and lignin presence on properties of natural cellulosic Cissus quadrangularis fiber composites

Cissus quadrangularis biodegradable natural cellulosic fibers comprehensively characterized to assess their potential as reinforcing materials in polymer composites. Initially, the Cissus quadrangularis fibers were chemically treated with 5% Sodium hydroxide (NaOH) and 5% magnesium carbonate (MgCO3) to improvise the properties of the fiber. The mechanical test result shows that chemically treated 5% MgCO3 fiber show that 4% and 24% improved tensile strength compared to NaOH and untreated ones. The cellulose crystallinity of the treated fiber got increased as the amorphous constituents removed. Further, 5% MgCO3 treatment removed a larger amount of amorphous hemicellulose, lignin, and other impurities present on the fiber surface. Secondly, the composites were fabricated at different combination of MgCO3 (5%, 10%, 15%), plasticizer (5%, 7.5%, 10%), and fiber volume (20%, 25% and 30%) with L9 Taguchi orthogonal array approach. Based on the results, 5% MgCO3, 5% plasticizer, and 30% fiber volume showed significant improvement in Young's modulus, tensile, and flexural strength of 8%, 27%, and 16% respectively. Moreover, there was no notable improvement observed on impact strength for both treated (15.91 KJ/m2) and untreated (13.98 KJ/m2) fiber. The scanning electron microscopy (SEM) micrographs used to examine the interface bonding between fiber and the matrix.

Effect of alkali treatment on performance characterization of Ziziphus mauritiana fiber and its epoxy composites

This study aims to investigate the natural cellulosic fibers extracted from novel Ziziphus Mauritiana plants. The fibers were treated with alkali solution and epoxy composites were developed for both untreated and chemically modified fibers through hand lay-up process. Physico-chemical and thermomechanical characterization were carried for both untreated and alkali treated Ziziphus Mauritiana fibers through physical analysis, chemical analysis, Thermogravimetric analysis, Fourier transform infrared spectroscopy, X-Ray diffraction test and single fiber tensile test. The alkali treatment facilitates to remove amorphous constituents and improves the crystalline index by 1.31 times, thermal stability by 1.15 times and fiber strength by 1.44 times, which is supported by chemical analysis and Fourier transform infrared spectroscopy analysis. Later, developed Ziziphus Mauritiana composites were analyzed as per ASTM for its mechanical and sound absorption characteristics. The reduction in amorphous constituents after chemical treatment improved the surface roughness in alkali-treated Ziziphus Mauritiana fibers which influenced the bonding behavior. Also it improved the ultimate tensile strength by 2.12 times, flexural strength by 1.38 times and sound absorption coefficient by 1.15 times. Thus, the Ziziphus Mauritiana fibers are potentially suitable for use in lightweight structures.

Changes in topsoil characteristics with climate and island age in the agricultural zones of the Galápagos

The flora and fauna of the Galápagos Islands have long been subject to scientific inquiry, but the soils have remained largely ignored until recently. The objective of this study was to assess the differences in main soil characteristics and nutrient reserves within and among the agricultural zones of islands Isabela, Santa Cruz and San Cristóbal to provide background information for informed agricultural decision making and a baseline against which future changes may be assessed. Aqua regia-extractable Al and Fe showed a general trend of accumulation with island age and increasing moisture levels within the agricultural zone, while base cations Ca, K, Mg and Na tended to decrease along the same gradients, with some variation likely due to agricultural inputs. Concentrations of silicon, aluminum and iron associated with amorphous constituents (Sio, Alo, Feo) tended to decrease with island age while iron in crystalline and non-crystalline hydrous oxides (Fed) showed a slight increase. Aluminum and iron in non-crystalline and organic complexes were more abundant in areas with higher precipitation. Electrical conductivity, pH in water, pH in sodium fluoride, phosphate retention, organic carbon content and particle size tended to decrease with island age while bulk density increased. Andic properties were expressed in all the soils of the youngest island studied, Isabela, and in higher-elevation soils of the intermediate-age Santa Cruz Island, while the soils of the oldest island studied, San Cristóbal, did not show andic properties and were dominated by crystalline clays and iron oxides. The wide range of soil development across the three islands requires soil management recommendations be tailored to each island and even within each island to ensure appropriate stewardship of this important natural resource.

Development and characterization of alkali-treated and untreated Dactyloctenium aegyptium fibers based epoxy composites

Natural fibers are widely used as they are ecofriendly and abundant in nature. The performance of the natural fibers is enhanced by chemical treatment. The current study deals with the extraction of Dactyloctenium aegyptium (DA) fibers, commonly known as “Crowfoot grass” using a conventional retting process. The obtained fibers were subjected to alkali treatment using NaOH followed by distilled cleaning to remove traces. This was followed by drying in sunlight and in a hot air oven. The obtained alkali-treated Dactyloctenium aegyptium fibers were mixed with an epoxy-hardener mixture in the ratio (60% matrix and 40% fibers) to form laminates using conventional hand lay-up process in comparison with untreated fibers. The final composite laminates were subjected to mechanical behavior namely tensile, flexural, impact as per ASTM. Test results showed that alkali-treated Dactyloctenium aegyptium fiber based epoxy composites had better mechanical properties with an ultimate tensile strength of 57 MPa compared to those untreated (45 MPa) due to the removal of amorphous constituents from the fiber leading to better interlocking properties with the matrix. These results prove that Dactyloctenium aegyptium fiber based epoxy composites can be used for lightweight and medium load applications.

Survey on chemical, physical, and thermal prediction behaviors for sequential chemical treatments used to obtain cellulose from Imperata Brasiliensis

The effects of chemical treatment sequences on the chemical, physical, and mainly the thermal properties of Imperata Brasiliensis grass in the process used to obtain cellulose fibers were analyzed. The thermal properties were extensively investigated by a thermogravimetric analysis, and a thermal behavior prediction was carried out using kinetic parameters and simulation. Thermal simulations using statistical tools enable thermal predictions for any material under different conditions. However, they are currently not widely reported in the literature for untreated and treated natural fibers. We used an alkaline treatment and alkaline treatment followed by one, two, or three bleaching steps with hydrogen peroxide (H2O2) (24% v/v). After each chemical treatment, changes in chemical composition due to the removal of amorphous constituents were observed and confirmed by the analysis of properties such as coloration, density, porosity, crystallinity, and thermal decomposition. The alkaline treatment followed by one step of bleaching was the most effective and viable chemical treatment sequence to obtain cellulose. The changes in coloration from dark brown to light yellow were accompanied by increases in real density (65%), crystallinity (69%), and thermal stability (27.4%) upon one step of bleaching. In general, the subsequent bleaching steps provided similar values. The predicted thermal degradation profiles were compared with experimental data in order to validate the proposed degradation mechanisms and models. The obtained kinetic parameters adequately described the mass loss histories of the studied natural fibers, even when extremely simplified kinetic schemes were used. The degradation mechanisms consisted of diffusion followed by autocatalytic reactions for all studied fibers.

Overcoming yard waste recalcitrance through four different liquid hot water pretreatment techniques – Structural evolution, biogas production and energy balance

Liquid hot water (LHW) pretreatment is considered as a key step in reducing biomass recalcitrance and improving its accessibility to microorganisms during anaerobic digestion. In the present study, a comprehensive comparison among hot air oven, hot water bath, autoclave and microwave (MW) pretreated yard waste (YW) was conducted. The effect of treatment temperature and duration for all the four LHW pretreatment techniques were optimized with respect to the organic matter solubilisation. The results showed that all four LHW pretreatment techniques have a positive effect on organic matter solubilisation. The highest organic matter solubilisation was found in case of MW pretreatment for a treatment duration of 100 s at a temperature of 140 °C. Therefore, batch biochemical methane potential (BMP) of untreated and MW pre-treated YW was carried out for this treatment condition. The BMP of MW pretreated YW resulted in an improvement in methane yield to 364.5 ± 11 mL/g VS on 26th day of anaerobic digestion, which was 1.1 times higher than that of untreated (328.9 ± 15 mL/g VS on 45th day of anaerobic digestion). The FTIR and XRD analysis confirmed that LHW pretreatment technique removed amorphous constituents due to the polymerization of polysaccharides present in YW. In addition, SEM analysis confirmed that the LHW pretreatment led irregular and distorted structure of biomass which improved cellulose accessibility to anaerobic bacteria. A positive energy balance confirmed the possible applicability of MW pretreatment in real life projects.

A green route to sustainable alkali-activated materials by heat and chemical activation of lithium slag

Lithium slag (LS) is a potential new resource for fabricating alkali-activated materials, however, few works have reported the utilization of LS in alkaline activation area. Herein, the mineral composition of LS was evaluated by Rietveld quantitative analysis and the mechanical properties of alkali-activated LS (AALS) were systematically investigated. Based on the above studies, a method of heat incorporating with chemical activation was carried out to further improve the reaction activity of LS. The results indicated that pre-heating facilitated the improvement of reaction activity of LS and the active amorphous constituents in LS dramatically increased from 17.3 wt% to 50.7 wt% after heat activation at 700 °C. Furthermore, we also found that more active constituents in LS enhanced the rate and degree of reaction and resulted in the increase of mechanical strength of AALS. The compressive strength of specimens (aged for 1d) increased from 12.8 MPa to 47.7 MPa because a denser microstructure was observed in specimens prepared by heat-activated LS resource. In addition, the mechanism of heat activation for LS was also investigated by thermogravimetric analysis (TGA) and in-situ X-ray diffraction (XRD) at different temperature step. The results illustrated that the defective crystals in LS tended to transform into glassy phases between 300 and 800 °C. And the transformation was more significant as the temperature rising.

Biological and mineralogical controls over cycling of low molecular weight organic compounds along a soil chronosequence

Low molecular weight organic compounds (LMWOC) represent a small but critical component of soil organic matter (SOM) for microbial growth and metabolism. The fate of these compounds is largely under microbial control, yet outside the cell, intrinsic soil properties can also significantly influence their turnover and retention. Using a chronosequence representing 1200 ka of pedogenic development, we compared physicochemical vs biological controls on the turnover and retention of fast-cycling carbon (C), e.g. glucose (GLU) and p-hydroxybenzoic acid (PHBA). Along the chronosequence, we observed mineralogical gradients whereby amorphous constituents were greatest in intermediate-aged sites, while older sites demonstrated soils with more ordered and less reactive mineralogy. Soil microbial community composition varied along the soil chronosequence and we observed reductions in total biomass and fungal biomass from younger to older sites, but this did not affect the turnover of LMWOC. Microbial utilization of LMWOC was substrate- and soil-dependent; amorphous Fe and Al oxides reduced the respiration of PHBA but respiration from glucose remained less affected. Variation in soil mineralogy did not significantly alter recovery of PHBA within microbial biomass or fungal vs. bacterial biomarkers, suggesting that reduced respiration of the phenolic resulted from direct mineral interaction with ionizable functional groups rather than changes to microbial allocation of PHBA. We conclude patterns of soil carbon storage observed across chronosequences are moderated by mineralogical effects on microbial access to LMWOC, independent of variation in microbial community composition.

Resistance to Helium Bubble Formation in Amorphous SiOC/Crystalline Fe Nanocomposite.

The management of radiation defects and insoluble He atoms represent key challenges for structural materials in existing fission reactors and advanced reactor systems. To examine how crystalline/amorphous interface, together with the amorphous constituents affects radiation tolerance and He management, we studied helium bubble formation in helium ion implanted amorphous silicon oxycarbide (SiOC) and crystalline Fe composites by transmission electron microscopy (TEM). The SiOC/Fe composites were grown via magnetron sputtering with controlled length scale on a surface oxidized Si (100) substrate. These composites were subjected to 50 keV He+ implantation with ion doses chosen to produce a 5 at% peak He concentration. TEM characterization shows no sign of helium bubbles in SiOC layers nor an indication of secondary phase formation after irradiation. Compared to pure Fe films, helium bubble density in Fe layers of SiOC/Fe composite is less and it decreases as the amorphous/crystalline SiOC/Fe interface density increases. Our findings suggest that the crystalline/amorphous interface can help to mitigate helium defect generated during implantation, and therefore enhance the resistance to helium bubble formation.

Within-tree variability of internal stress generated during drying of rubberwood lumber

The generation of drying stress within the lumber from the trunk of a rubber tree prepared from different locations (radial distance up to 110 mm and height up to 4 m) has been investigated in real-time by using a restoring force measurement on half-split specimens. Drying was performed at constant dry-bulb and wet-bulb temperatures of 90 and 60 °C, respectively. The entire restoring force profiles do not vary significantly with height. In addition, before and after the reversal of stress, the force profiles are largely similar and the maximum negative and positive forces are approximately equal regardless of wood locations within the tree trunk. However in the radial direction, the process of stress reversal consisting of two negative force maxima appears to proceed slower in the inner juvenile wood than in the outer mature wood. Upon water immersion of the specimens for 4 months, the second negative force maximum gradually disappears and the force profiles with a shorter stress reversal period become less sensitive to the wood locations. An examination of the drying curves in the second stage of drying during stress reversal also indicates a slower migration of bound water out of the lumber in the juvenile wood compared to that in the mature wood. The drying is also faster in the water-immersed specimens. It is concluded that variability of the internal stress within the trunk of a rubber tree originated from the role of cell wall amorphous constituents and cell wall extractives on creep property and the movement of bound water within the wood cell wall during drying.

Manufacturing and Characterization of High Impact Polystyrene (HIPS) Reinforced with Treated Sugarcane Bagasse

Natural fibers obtained from sugarcane bagasse were used as reinforcement for high impact polystyrene (HIPS) composites. Fibers were chemically treated with an alkaline solution and then bleached with sodium chlorite and acetic acid, in order to remove amorphous constituents and improve adhesion with polimeric matrix.The alkali-treated and bleached fibers over a range of 10-30 wt% were mixed with HIPS and placed in an injector chamber in order to obtain tensile and flexural test specimens. Chemical treatment effects on composites properties were evaluated through mechanical tests and thermal and microscopy analysis. Experimental results show that composites with 30 wt% of alkali-treated fibers present an improvement in the tensile strength (17%), tensile modulus (96%) and flexural modulus (34%) with a consequent decrease in the ductility and in the thermal properties in comparisson to pure HIPS. An huge increase of 191% in the flexural modulus for composites with 30 wt% of bleached fibers was obtained compared to pure HIPS.

Chemical treatment and characterization of soybean straw and soybean protein isolate/straw composite films

This work investigated changes in the chemical composition and structure of soybean straw (SS) treated with alkali (NaOH 5% and 17.5%) and bleached with hydrogen peroxide (H2O2) or sodium hypochlorite (NaOCl). Removal of the amorphous constituents increased the degree of crystallinity and the content of cellulose fibers particularly after reaction with high concentrations of alkali. Treatment with NaOH 17.5% contributed to the allomorph transition from cellulose I to II regardless of the bleaching agent, but H2O2 as bleaching agent promoted more effective delignification. This work also evaluated the potential use of treated and non-treated SS as reinforcement filler in soy protein isolate film (SPI). Films added with treated SS presented higher mechanical resistance, lower elongation at break, and lower solubility in water. Addition of non-treated SS did not affect the properties of the SPI film significantly. The low solubility and the reasonable water vapor permeability of the composite films make them suitable packaging materials for fresh fruit and vegetables.

Influence of Engine Age on Morphology and Chemistry of Diesel Soot Extracted from Crankcase Oil

In this study, the role of engine age on the structure and chemistry of crankcase soot was studied using X-ray diffraction, high-resolution transmission electron microscopy, energy-dispersive spectroscopy, and Raman spectroscopy. Results indicate that the basic structure of the carbonaceous species remains the same in all cases and is composed of turbostratic carbon. However, there are some very subtle changes in the structure of the soot as the age of the engine increases. Older engines have a greater proportion of non-crystalline amorphous carbonaceous constituents in the soot relative to newer engines. In addition, the wear-induced debris increase with the age of the engine, with a larger proportion of phosphates of Ca and Zn as well as sulfates of Ca in the soot of older engines. The presence of these wear debris particles incorporated in the soot extracted from the crankcase indicates that they arise from three-body abrasive wear between the soot and the tribofilms formed within the engine.

Dry reciprocating sliding wear behavior and mechanisms of bulk metallic glass composites

The dry sliding wear behavior and mechanisms in a bulk metallic glass composite, Ti48Zr20V12Cu5Be15, composed of in situ crystalline dendrites in an amorphous matrix, was studied in reciprocating mode against a WC counterface loaded at 5N and 10N. The composite showed higher wear rates but lower coefficient of friction compared to a monolithic fully amorphous glass. Nanomechanical characterization was done to map the hardness and modulus of the crystalline and amorphous constituents of the composite. Nano-scratch test was done on each phase to evaluate the coefficient of friction. The observed hardness values scale according to Archard’s relationship for sliding wear behavior. No tribolayer formation was seen for the composite in sharp contrast to that of the monolithic metallic glass.

Sub-amorphous thermal conductivity in amorphous heterogeneous nanocomposites

Here, we use equilibrium molecular dynamics to show that an amorphous SiGe nanocomposite can possess thermal conductivity substantially lower than those of the amorphous Si and Ge constituents.

Effect of fiber chemical treatment of nonwoven coconut fiber/epoxy composites adhesion obtained by RTM process

In this work untreated and alkali treated nonwoven coconut fiber mats/epoxy resin composites were manufactured using the resin transfer molding process. The alkaline solution removes some impurities present on fibers superficial layers and the effect regarding fiber/matrix adhesion were investigated by thermogravimetric analysis, dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), ultrasonic C‐scan, and quasi‐static flexural test. Results show a removing of some amorphous fibers constituents, mainly waxes, extractives, and hemicellulose, revealing the fiber roughness surface but no initial degradation temperature changing. Regarding the composites, a similar interfacial adhesion was observed in both one through the results of SEM, DMA and quasi‐static flexural tests. The conclusion is that chemical treatment conditions applied on the fiber surface was been suitable to improve fiber roughness but did not the adhesion between coconut fibers mat and epoxy resin. POLYM. COMPOS., 38:2518–2527, 2017. © 2015 Society of Plastics Engineers

Synthesis of Nano-Crystalline Materials in Open-Air Laboratory: A Case Study of Tobacco.

The work deals with synthesis of nano-crystalline materials in open-air laboratory and in-depth investigation of the tobacco sample of one branded cigarette and its ash using high-resolution transmission electron microscopy and associated techniques. It exhibits the presence of nanocrystals and nanorods of various oxides in cigarette ash. The structure, shape, size and composition of these nanocrystals and nanorods are explored. The energy dispersive X-ray spectra from different regions of the tobacco sample and its ash using high-angle annular dark field scanning/transmission electron microscopy mode are utilized to obtain elemental composition and their relative abundances. For a detailed distribution of different elements in the nanorods, elemental mapping using energy-filtered transmission electron microscopy is also presented. The results highlight the conversion of amorphous constituents of tobacco to nanomaterials on combustion at low temperatures, thus mixing up in the atmosphere.

Polymer Biocomposites and Nanobiocomposites Obtained from Mango Seeds

SummaryThe objective of this work is to obtain thermoplastic starch, polymer biocomposites and nanobiocomposites using agro‐industrial waste generated in mango processing, and characterize the obtained materials. The starch extraction from the kernels of mango pits showed a good yield and the obtained starch had high purity.The results obtained characterizing the fibers and cellulose nanowhiskers, from the husk of the mango seed, proved the effectiveness of chemical treatment removing the amorphous constituents (hemicellulose and lignin).The polymer biocomposites and nanobiocomposites were obtained and the TPS mango starch showed satisfactory results of mechanical and thermal properties, when compared with TPS corn starch materials with the same composition. It is concluded that the waste generated in the agro‐industrial processing of mangos showed a potential source for biodegradable materials production.