IAN873, Dongfang93114 and Reyan73397, created through vegetative propagation for their high yield and excellent cold resistance, are major clones planted in China. In this work, latexes with rubber ...particles of the same size from these clones are separated from fresh natural rubber latex, and corresponding rubber films are prepared from each latex. The structure and components of each film are measured. This indicates that the characteristics of the rubbers obtained from latexes with similar particle sizes show some resembling trends among different clones, while for specific samples, those characteristics vary depending on the clone. The molecular weight is generally highest in IAN873 and lowest in Reyan73397. Rubber chains in small rubber particles are longer, and large rubber particles show a wider molecular weight distribution. The gel content of every sample from Reyan73397 is lower than the other two clones. The nitrogen content increases with the size of rubber particles in all clones. The ester content of small rubber particles in IAN873 and Reyan73397 is almost zero. Large rubber particles have more branching points formed via esters. This study provides a new perspective on the influence of clones on the relationship between characteristics of natural rubber and the size of rubber particles in natural rubber latex.
The design of hierarchical structures from biomass has become one of the hottest subjects in the field of microwave absorption due to its low cost, vast availability and sustainability. A ...kapok-fiber-derived carbon microtube was prepared by facile carbonization, and the relation between the structure and properties of the carbonized kapok fiber (CKF) was systematically investigated. The hollow tubular structures afford the resulting CKF composites with excellent microwave-absorbing performance. The sample with a 30 wt.% loading of CKF in paraffin demonstrates the strongest microwave attenuation capacity, with a minimum reflection loss of −49.46 dB at 16.48 GHz and 2.3 mm, and an optimized effective absorption bandwidth of 7.12 GHz (10.64–17.76 GHz, 2.3 mm) that covers 34% of the X-band and 96% of the Ku-band. Further, more than 90% of the incident electromagnetic wave in the frequency from 4.48 GHz to 18.00 GHz can be attenuated via tuning the thickness of the CKF-based absorber. This study outlines a foundation for the development of lightweight and sustainable microwave absorbers with a high absorption capacity and broad effective absorption bandwidth.
High humidity and high dust concentration in deep coal mines may severely challenge the performance of respirators worn by coal miners. This paper aims at quantitatively evaluating the respirators ...used in deep coal mines and providing scientific guidance for the respiratory protection of miners. Based on the self-designed in-situ PM2.5 collector, controllable PM2.5 generator, human breathing simulator, and respirator simulation testing system, under the simulated deep mine working condition, this study investigated the effects of dust loading, wearing time, and dust concentration on the filtration efficiency, breathing resistance, and quality factor of N95 elastomeric respirators. With the increase of dust loading, the respirator filtration efficiency firstly decreased, then increased (minimum value 97.5%). The breathing resistance increased exponentially from 120 to 180 to 1020–1530 Pa, and the quality factor decreased logarithmically from 0.051 to 0.076 to 0.0058–0.0085 Pa−1. As the PM2.5 coal dust concentration increased from 5 to 50 mg/m3, the wearing time for the respirator breathing resistance to exceed 300 Pa reduced from 7 h to less than 1 h. One N95 elastomeric respirator is not able to perform an 8-h work shift. To avoid the excessive breathing resistance caused by dust loading, more filter cartridges are needed for coal miners.
Wet dedusting is the main coal dust suppression technique in coal mines, and coal wettability is the main factor affecting dust suppression efficiency. To investigate the main factors affecting the ...coal wettability and improve it, the coal–water contact angle was used as an index to characterize the coal wettability, and the wettability of six coal samples with different metamorphic degree was studied by analyzing the relationship between the physicochemical properties and the contact angle. To improve the coal wettability, the nonionic surfactant alkyl polyglycoside (APG), anionic surfactant sodium dodecyl benzene sulfonate (SDBS), and polymer surfactant polyacrylamide (PAM) were applied to the coal samples. The results show that SDBS is the most effective surfactant to improve the coal wettability, followed by APG, while the application of PAM would lead to more hydrophobic coal. It is also found that the coal wettability shows a high–low–high trend with the increase in the metamorphic degree. The wettability of long flame coal is the strongest and that of gas coal is the weakest. Moisture is the main hydrophilic factor of coal, while 1,4-dimethylbenzene is the main hydrophobic factor. The main factors affecting the treatment effect of APG, SDBS, and PAM on wettability are the aromatic methylbenzene, hydroxyl, and hydroxyl content of coal, respectively. Therefore, according to the content of hydroxyl in different coals, an SDBS solution can be prepared to improve the coal wettability. For coal with a low hydroxyl content, a higher concentration SDBS solution could be needed.
Constructing hierarchical structures is indispensable to tuning the electromagnetic properties of carbon-based materials. Here, carbon microtubes with nanometer wall thickness and micrometer diameter ...were fabricated by a feasible approach with economical and sustainable kapok fiber. The carbonized kapok fiber (CKF) exhibits microscale pores from the inherent porous templates as well as pyrolysis-induced nanopores inside the wall, affording the hierarchical carbon microtube with excellent microwave absorbing performance over broad frequency. Particularly, CKF-650 exhibits an optimized reflection loss (RL) of −62.46 dB (10.32 GHz, 2.2 mm), while CKF-600 demonstrates an effective absorption bandwidth (RL < −10 dB) of 6.80 GHz (11.20−18.00 GHz, 2.8 mm). Moreover, more than 90% of the incident electromagnetic wave ranging from 2.88 GHz to 18.00 GHz can be dissipated by simply controlling the carbonization temperature of KF and/or the thickness of the carbon-microtube-based absorber. These encouraging findings provide a facile alternative route to fabricate microwave absorbers with broadband attenuation capacity by utilizing sustainable biomass.
Most of the acid fluids used in the existing acidfrac process have the shortcomings of plugging pores, polluting formation and poor effect. The method of adding nitric acid in a specific proportion ...to conventional acid can avoid the above problems to a certain extent. A mixture of HCl: HF: HNO3 (3:1:1) was used to acidize the shale of the Longmaxi Formation in Sichuan and the Piyuancun Formation in Jiangxi for 24 h. The mineral fractions and pore structures of the samples were then analyzed using scanning electron microscopy-energy dispersive spectrometry, X-ray diffraction, low-pressure nitrogen adsorption, and nuclear magnetic resonance. The results showed that by reducing the mineral constituents of shale, the 2–15-nm sized pores decreased, 1–10-μm sized pores increased, and fractal dimensions decreased. The mixed acid solution caused cross-scale porosity expansion in the shale and increased gas circulation within the matrix. The process of acid mixing in the shale pore structure was divided into four stages: surface dissolution, macroporous dissolution, meso–microporous dissolution, and feedback dissolution.
Coalbed methane (CBM) is an important resource of energy. For CBM recovery, sorption‐induced coal deformation can cause significant reservoir permeability change. Moisture content and coal pore ...morphology affect the gas adsorption capacity and can alter the coal deformation of the coal seam. Therefore, it is crucial to establish a coal gas moisture‐coupled model for CBM production prediction. However, there are currently insufficient data available for quantitative analyses. In this paper, a series of typical sorption‐induced strain experiments were carried out during methane adsorption and desorption on coal samples with different metamorphic degrees and moisture content. The pore morphology and adsorption capacity of coals were measured to analyze the reason for different deformation of coals with various pore structures and moisture. Results show that the adsorption capacity and deformation is corresponding to the specific surface area of micropore, which first decreases and then increases with coal ranks. The deformation and adsorption gas content of dried coals is greater than that of natural moisture coals, which means that moisture can reduce the sorption capacity of coals, resulting in the decrease of gas adsorption‐induced coal deformation. There is also residual deformation of coal samples after gas desorption caused by the residual adsorbed gas in coals. This paper quantitatively investigates the effects of pore characteristics and moisture on coal deformation and the internal mechanism. This work will provide essential information for building out a fully cross‐coupled model of coal gas‐moisture relationships for CBM production prediction.
In this paper, a series of typical sorption‐induced strain experiments were carried out on coal samples with different metamorphic degrees and moisture content during methane adsorption and desorption. The pore morphology and adsorption capacity of coals were measured. This paper quantitatively investigates the effects of pore characteristics and moisture on coal deformation and the internal mechanism, which is of great significance for coal permeability evolution quantification and CBM production prediction.
•Clarified that micropores were the main adsorption sites.•Functional groups indirectly affected the adsorption capacity by affecting micropores evolution.•The adsorption of CO2 and CH4 in low-rank ...coal showed the maximum adsorption difference.
By conducting research on the microscopic mechanisms of CH4 and CO2 adsorption in different rank coals, the CO2-enhanced coal bed methane recovery (CO2-ECBM) technique can be further developed. In this paper, low-pressure N2 adsorption (LPGA-N2), low-pressure CO2 adsorption (LPGA-CO2), isothermal adsorption, Fourier transform infrared (FTIR) experiments, and molecular simulations were applied to analyze the mechanisms. The results demonstrated that the pore volume and specific surface area (SSA) of coal showed a U-shaped trend with the increase of metamorphic. The volume and SSA of the micropore were positively correlated with the ultimate adsorption volume, indicating that micropores were the main sites for adsorption. With the increased metamorphic degree, the aliphatic chains and oxygenated functional groups shed, and the aromatic rings polymerized. These changes in chemical functional groups directly affected the adsorption capacity of coal and indirectly affected the adsorption capacity by affecting micropore evolution. Compared with the CH4 molecule, the CO2 molecule had a smaller structure and a stronger intermolecular force, shown as the larger adsorption energy and closer distance to the coal molecule in the molecular simulation. These findings can provide the data and theoretical basis for the CO2-ECBM technique, coal bed methane extraction, and effect evaluation of extraction.
The structures and properties of natural rubber (NR) obtained from latex with small and large rubber particles (SRP and LRP) are obviously different, while carbon black (CB)/SRP or CB/LRP composites ...have rarely been reported. In this work, SRP and LRP are separated from natural rubber latex (NRL). The properties of obtained NR/CB composites are systematically investigated as a function of SRP and LRP mass ratios. It shows that the nitrogen content of SRP (1.32%) is much higher than that of LRP (0.10%). Mechanical properties increase with the increase of LRP content because plenty of agglomerates exist in SRP/CB composite whereas LRP/CB composite shows a homogeneous dispersion. Furthermore, a possible model is proposed to illustrate the transformations of agglomerates during stretching and dynamic compressing process. This study provides a new perspective for the design of NR materials through the selection of rubber particles in NRL.
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•The cure characteristics of carbon black filled natural rubber vulcanizates increase with the increase of SRP content.•LRP composite shows highest tensile properties and fatigue life as well as lowest compression set and temperature rise.•The carbon black in LRP composite shows homogeneous distribution, while SRP composite contains lots of agglomerates.•The agglomerates in SRP composite form stress and heat concentration during tensile and dynamic compressing process.
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