Alkali Resistance Properties Research Articles

PVC Dechlorination for Facilitating Plastic Chemical Recycling: A Systematic Literature Review of Technical Advances, Modeling and Assessment

Polyvinyl chloride (PVC) resins are widely used in modern society due to their acid and alkali resistance, low cost, and strong insulation properties. However, the high chlorine (Cl) content in PVC poses significant challenges for its recycling. This study reviews the treatment processes, model construction, and economic and environmental assessments to construct a methodological framework for the sustainable development of emerging dechlorination technologies. In terms of treatment processes, this study summarizes three types of processes, pretreatment, simultaneous dechlorination during chemical recycling, product purification, and emphasizes the necessity of dechlorination treatment from a systematic perspective. Additionally, the construction of models for dechlorination processes is investigated from the laboratory to the industrial production system to macro-scale material, in order to evaluate the potential inventory data and material metabolism behaviors. This review also summarized the methodology framework of Techno-Economic Analysis (TEA) and Life Cycle Assessment (LCA), which can be applied for evaluation of the economic and environmental performance of the dechlorination processes. Overall, this review provides readers with a comprehensive perspective on the state-of-the-art for PVC dechlorination technologies, meanwhile offering sustainable guidance for future research and industrial applications of chemical recycling of PVC waste.

Anti-fouling ampholytic polymer membrane with super-wetting surfaces for efficient oil-water emulsion separation

The development of highly efficient polymeric membranes with super-wetting surfaces (superhydrophilic/submerged superoleophobic) is one of the ideal options to achieve emulsified oily wastewater separation. However, this remains a challenging due to low fluxes and severe membrane contamination limitations. Here, we have demonstrated an ultra-hydrophilic, underwater super-oleophobic, highly anti-fouling and antibacterial (polydopamine/poly [2-(methacryloyloxy) ethyl] dimethyl- (3-sulfopropyl) ammonium hydroxide) PDA/PSBMA modified membrane by grafting amphoteric polymers via atom transfer radical polymerization (ATRP). Benefiting from PSBMA's superhydrophilicity and the unique adhesion of dopamine (DA), the PDA/PSBMA modified membrane shows superhydrophilic properties, superoleophobicity underwater, oil resistance, and fouling resistance. Meanwhile, PDA/PSBMA modified membrane reached a superb permeability to water as high as 5620 L·m−2·h−1·bar−1 and remarkable oil rejection rate of 98 % in separating diesel-in-water emulsions. Furthermore, the separating performance remained fairly constant over 10 emulsion filtration cycles. Besides, the PDA/PSBMA modified membranes have excellent acid and alkali resistance and antibacterial properties, showing its potential for oily wastewater purification. This work offers a simple and versatile strategy to fabricate superwetting efficient polymeric membranes to separate emulsified oily wastewater.

Effect of partial substitution of barium oxide by lanthanum oxide on the structure and properties of iron-based aluminosilicate glass

Silica-aluminum borates (SiO2-R2O3-R2O-RO-ZrO2 system) with La2O3 replacing BaO were preparing using the conventional melt quenching process. The impact of substituting BaO with La2O3 on the glass structure was examined using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman. The density, thermal properties, alkali resistance and dielectric properties of the glasses were measured and compared using Archimedes, Differential Scanning Circuit (DSC), Thermal Expansion Calorimetry (TEC), Weight Reduction and Impedance Spectroscopy. The viscosity of the glass system was calculated from the thermal properties and discussed in comparison with the wetting angle at 1000 °C. The results showed that the glass does not undergo precipitation. With the increase of La2O3 to BaO substitution, the Q4 in the glass network structure transforms to Q0+Q1 and Q2, causing depolymeriation of the glass structure. This results in an increase in the density of the glass, as well as an increase and subsequent decrease in the thermal expansion coefficient. Additionally, the glass transition temperature and glass softening temperature decrease and then increase, which was due to the high field strength of La3+. When substituting 5 wt% of BaO with La2O3, The glass displayed the lowest dielectric constant and dielectric loss, along with the best alkali resistance. Viscosity calculations showed that the viscosity gradually increases at 1000 °C with the increase of La2O3 substitution, which was consistent with the wettability results. The glass components in the 0-5 wt% weight range all satisfy the iron-sealed glass wetting angle requirements.

Facile fabrication of fluorine-free waterproof and breathable nanofiber membranes with UV-resistant and acid-alkali resistant performances

Membranes with good waterproofness and breathability are desired for the preparation of outdoor sports garments. However, current waterproof and breathable membranes use environmentally hazardous fluorine-containing raw materials and suffer from many problems such as complicated preparation processes and single function. Therefore, it is a great challenge to select environmentally friendly raw materials to prepare multi-functional membranes with waterproof-breathable performance by simple preparation method. In this paper, fluorine-free poly(styrene-b-butadiene-b-styrene) (SBS), polyurethane (PU), and 2-hydroxy-4-n-octyloxy benzophenone (UV531) were selected to prepare multi-functional nanofiber membranes by convenient one-step electrospinning. The properties of the environmentally friendly multi-functional SBS/PU/UV531 nanofiber membranes were systematically optimized by adjusting the concentration of UV531 in the nanofiber membranes. The ultimately obtained multi-functional SBS/PU/UV531–2 nanofiber membrane shows excellent waterproofness (hydrostatic pressure: 58.8 kPa), high breathability (WVT rate: 5.2 kg m−2 d−1), good mechanical properties (breaking strength: 7.26 MPa, breaking elongation: 327.9%), excellent UV resistance (UPF: 238.23), and strong acid and alkali resistance properties. This multi-functional nanofiber membrane has broad application prospects in a variety of fields such as outdoor protective clothing, extreme environment materials, and military products.

Large-Scale Fabrication of Tunable Sandwich-Structured Silver Nanowires and Aramid Nanofiber Films for Exceptional Electromagnetic Interference (EMI) Shielding.

The recent advancements in communication technology have facilitated the widespread deployment of electronic communication equipment globally, resulting in the pervasive presence of electromagnetic pollution. Consequently, there is an urgent necessity to develop a thin, lightweight, efficient, and durable electromagnetic interference (EMI) shielding material capable of withstanding severe environmental conditions. In this paper, we propose an innovative and scalable method for preparing EMI shielding films with a tunable sandwich structure. The film possesses a nylon mesh (NM) backbone, with AgNWs serving as the shielding coating and aramid nanofibers (ANFs) acting as the cladding layer. The prepared film was thin and flexible, with a thickness of only 0.13 mm. AgNWs can easily form a conductive network structure, and when the minimum addition amount was 0.2 mg/cm2, the EMI SE value reached 28.7 dB, effectively shielding 99.884% of electromagnetic waves and thereby meeting the commercial shielding requirement of 20 dB. With an increase in dosage up to 1.0 mg/cm2, the EMI SE value further improved to reach 50.6 dB. The NAAANF film demonstrated remarkable robustness in the face of complex usage environments as a result of the outstanding thermal, acid, and alkali resistance properties of aramid fibers. Such a thin, efficient, and environmentally resistant EMI shielding film provided new ideas for the broad EMI shielding market.

Construction of Oxygen Vacancies of Zr-Doped CeO2 with Enhanced Dye Adsorption Performance

Congo red (CR), a highly pigmented anionic dye, is highly toxic and resistant to degradation. The discharge of CR wastewater into the natural environment can lead to ecological destruction and harm to human health. CeO2 as an adsorbent possesses the advantages of excellent acid and alkali resistance, biocompatibility, stable physical and chemical properties, and nontoxic by-products. The impact of Zr doping on the adsorption performance of nano-CeO2 was investigated. XPS and Raman characterisation revealed that Zr doping effectively enhanced the oxygen vacancy ratio at the active sites for CR adsorption on the surface of nano-CeO2. When the doping amount of Zr was 3%, the nanoparticles with the best adsorption properties were obtained, and the adsorption amount of CR at room temperature was as high as 3642.05 mg/g, which was approximately three times the adsorption amount of undoped CeO2. This excellent adsorption property shows good prospects for the removal of anionic dyes from wastewater.

Nanogels-based ink prepared using electron beam-synthesized poly(vinyl pyrrolidone) nanogels as pigment dispersing and stabilizing agent

Dispersion and stabilization of water-insoluble organic pigment particles using nanogels in water-based inks (e.g., inkjet, offset) is a progress opportunity for organic printing ink technology. This work proposes poly(vinyl pyrrolidone) (PVP) nanogels as a nano-structured particle “bumper” for dispersing, wetting, and stabilizing the pigment particles to protect them from flocculation. The expected satisfactory dispersion and stabilization reflects not only quality of formulated ink, but also the finished printed object. The PVP nanogels were prepared in pure water using electron beam-induced chemical reactions, particularly cross-linking, governing particles formation, as well as their final size. Influence of absorbed dose of radiation (2–10 kGy) as well as different molecular weights (MW) of the polymer (PVP-1, ca. 10 kDa and PVP-2, ca. 1400 kDa) on the nanogels formation was studied. The hydrodynamic diameter (Dh) of the PVP nanogels is in the range of around 15–340 nm, depending on the MW of PVP and the absorbed dose. AFM micrographs support the finding of nanoscopic structure of PVP nanogels. The water-insoluble organic pigment (Yellow 12) was used to formulate a water-based nanogels ink. The PVP nanogels in ink play an important role in pigment dispersion/stabilization, reduction of the pigment size, increase of hiding power, and improvement of lightfastness, as well as thermal, water, soap, alkali, and acid resistance properties. This work provides a promising advancement in printing ink and coating technologies due to employing the polymeric nanogels as dispersing, wetting, and stabilizing nanoplatform.

Supercritical CO2 as a potential tool for the eco-friendly printing of meta-aramid

Large degree of orientation, crystallinity, and high glass transition temperature of aramid make the fibers exhibit ultra-high strength, high modulus, high temperature resistance, acid and alkali resistance, light weight and other excellent properties. However, the resulting poor dyeability and water pollution problems of aramid greatly limits its application in protective areas. An eco-friendly supercritical CO2 assisted printing strategy for meta-aramid was developed firstly in this study. The effects of treatment temperature, time, pressure and dye concentration on the printing properties were investigated. The obtained results showed that the K/S values of the printed meta-aramid increased with the enhancing of CO2 temperature, treatment time and CO2 pressure. Compared to tradition printing, higher color depth can be obtained by supercritical CO2 assisted printing with 40% sodium carboxymethyl cellulose and 20% guar gum as original paste. The K/S values of the meta-aramid with Cationic Pink X-FG in supercritical CO2 was 12.18 while that of the samples with Cationic Yellow 5GL was 5.42. Washing and rubbing colorfastness rated above 4 were reached at 180 °C for Cationic Pink X-FG and at 160 °C for Cationic Yellow 5GL in supercritical CO2. In addition, up to 99% outline sharpness and acceptable stiffness, air permeability and mechanical properties was obtained, which demonstrated that the meta-aramid fabrics with supercritical assisted printing could better meet the wearability requirements.

Preparation and properties of polyvinyl alcohol (PVA)/amino-modified mesoporous silica (AMMS) composite membranes for diffusion dialysis

It is a plaguing problem of obtaining high ion flux while maintaining high selectivity during the diffusion dialysis (DD) process. However, functionalized mesoporous silica-based composite membrane is considered to be one of the effective candidates to solve it. Here, we report amino-modified mesoporous silica (AMMS) blended with pre-crosslinked polyvinyl alcohol (PVA) solution, after which a series of composite membranes were obtained to maintain high ion flux and selectivity. The fundamental properties of as-prepared membranes were tested, including water uptake (WR), alkali resistance, mechanical and thermal properties. The results of WR (181.7%–289.7%), alkali resistance (with swelling degree in the range of 250%–471% and mass loss in the range of 27.6%–35.3%), mechanical (with tensile strength (TS) in the range of 29.9–41.8 MPa and elongation at break (Eb) in the range of 135.3%–180.4%), and thermal (degradation temperature was higher than 200 °C) properties demonstrated that the as-prepared membranes possess higher water uptake and moderate alkali resistance and can be potentially applied in alkaline DD process. Further, microscopic morphologies of as-prepared membranes confirmed well dispersion of AMMS in PVA matrix and good compatibility between the two phases, which could be attributed to the hydrogen bonding between –NH2 of AMMS and –OH of PVA molecular. NaOH/Na2WO4 system was introduced to evaluate separation performance of as-prepared membranes via DD process and the effect of AMMS was detected preliminarily. The results indicated that amino-modified mesoporous silica (AMMS) blended with pre-crosslinked polyvinyl alcohol (PVA) membrane possessed high ion flux and selectivity simultaneously, and had strong practical application prospects. The mesopores and –NH2 groups of AMMS promoted the transport of OH− via hydrogen bonds synergistically.

Effect of TiO2 on preparation condition, mechanical properties and alkali resistance of continuous basalt fibers

The low alkali resistance of basalt fiber limits its utilization in the strong alkaline environment such as cement and concrete as the reinforcing material. Adding additive in the basalt rocks is the feasible method to enhance the alkali resistance. However, it is necessary to develop the efficient additive for basalt fiber. In this work, the effect of TiO2 on the preparation condition, alkali resistance and mechanical properties of basalt fiber was investigated. The preparation conditions were studied by DSC, XRD and high-temperature rotational viscometer. Then the corrosion behavior of TiO2-basalt fibers in NaOH solution was studied via SEM/EDX, FIB/SEM and FTIR. The results indicated that the viscosity of basalt melt decreased significantly with the increasing TiO2 content from 0% to 2%, but the crystallization tendency was not changed with TiO2 below 2%, the upper limit for TiO2 addition. The tensile strength increased by 20–60% because Ti4+ promoted Al3+ into the network structure and intensify the polymerization by entering the network structure as network precursor in the form of [TiO4]. Meanwhile, TiO2 in the basalt fibers formed insoluble titanium hydroxide, so the weight loss of TiO2-basalt fibers in NaOH solution was reduced up to 50%. Through FIB/SEM/EDX, the corrosion of basalt fiber in alkali condition is controlled by ion diffusion. The outward diffusion of Fe, Mg and Ti to the surface of fiber formed the insoluble layer, so the rate of substitution reaction between the OH− and basalt fibers was slowed down, but it also leaded to the non-uniform corrosion.

Effect of quartz sand on the properties and alkali resistance of refractory aluminosilicate castables

This study investigated the effect of ground quartz sand (0, 2.5%, 5.0%, and 7.5%) on the alkali resistance, physical and mechanical properties, porosity, and thermal shock resistance of castables containing different amounts of calcium aluminate cement (conventional cement content, medium cement content, and low cement content). It was found that the addition of ground quartz sand (d50 was approximately 8 µm) increased the alkali resistance by a factor>5, decreased the total porosity, and increased the strength of the castable (up to 5%), irrespective of the amount of calcium aluminate cement in the composition. The analysis of the EDS results after the alkali attack tests shows that the thickness of the formed protective barrier, depending on the type of castable is 650–1100 µm. However, over 2.5% of ground quartz sand significantly (>20%) decreased the thermal shock resistance of concrete owing to the polymorphic transformation of quartz.

A novel hydrophobically associating water-soluble polymer used as constant rheology agent for cement slurry.

During the process of well cementing in deep water, the cement slurry experiences a wide range of temperature variation from low temperature at seabed to high temperature in downhole. The elevated temperature affects the rheology of cement slurry. The change of rheology of cement slurry could influence the safety of cementing operation. The aim of this paper is to develop a new kind of hydrophobically associating water-soluble polymer (NHAWP) as an additive to prepare a constant rheology oil well cement slurry, which can be used at temperature range from 4°C to 90°C. The acrylamide, 2-acrylamide-2-methylpropionic acid and stearyl methylacrylate were applied to synthesize the NHAWP by the inverse microemulsion polymerization. Test results indicate that the critical association temperature of NHAWP is 45°C. The critical association temperature is independent of NHAWP concentration, salt concentration and alkalinity of solution. When the temperature is below 45°C, NHAWP shows little influence on the viscosity of solution. When the temperature is above 45°C, the NHAWP forms spatial network structure by intermolecular hydrophobic association and thus increases the viscosity of solution significantly. The NHAWP also displays good thermal stability and excellent salt and alkali resistance properties. In addition, the NHAWP shows nearly no negative influence on the basic properties of cement slurry, which indicates that the NHAWP can be used as a constant rheology agent to prepare a cement slurry with constant rheology in the temperature range of 4°C to 90°C.

Bond properties of bimetallic steel bar in seawater sea-sand concrete at different ages

The bimetallic steel bar (BSB) consisting of stainless steel (cladding) and carbon steel (substrate) exhibits outstanding mechanical properties and high corrosion resistance and has a wide application in reinforced concrete (RC) structures with seawater sea-sand concrete (SWSSC). A metallurgical bonding layer exists between the cladding and substrate. The bond properties between the BSB and SWSSC with different concrete ages and c/d ratios were investigated experimentally. Polyoxymethylene (POM) fibre, which has exceptional alkali resistance and tensile properties, was selected to improve the bond properties. The effects of the concrete age, POM fibre, and c/d ratio on the failure mode of bond test specimens are discussed. The scanning electron microscope (SEM) method was selected to clarify the connection between the POM fibre and SWSSC. After the bond test, there was no crack or broken area in the stainless-steel cladding of the BSB. Based on the test results, the variation trends of the key parameters of bond properties between the BSB and SWSSC are discussed. A time-varying bond–slip model is suggested to quantify the bond properties between the BSB and SWSSC effectively. A comparison of the peak bond stress τu variation trend between SWSSC and ordinary concrete specimens was conducted. The variation trend of τu,t/τu,28 of the test specimens without POM fibre was similar to that of ordinary concrete specimens. The test results indicated that the POM fibre had an adverse effect on the growth rate of bond properties between the BSB and SWSSC.

Transparent, flame‐retarded, self‐healable, mechanically strong polyurethane elastomers: Enabled by the synthesis of phosphorus/nitrogen‐containing oxime chain‐extender

AbstractPolyurethane (PU) elastomer has been widely used due to its excellent mechanics, acid and alkali resistance, abrasion resistance, and other properties. However, obtaining simultaneous mechanically strong, flame‐retarded, transparent, and efficient self‐heal ability of PU elastomer is of great challenge due to the structural design. Here, a phosphorus/nitrogen‐containing Oxime chain extender (PSK‐2) was introduced into the synthesis of PU elastomers to obtain a transparent, flame‐retarded, self‐healable, mechanically strong PU elastomers. The PU elastomers exhibited high tensile strength of ~23.3 MPa, breaking strain of ~1693%, good flame retardancy with high LOI of ~29.2%, and UL‐94 V1 rating with the addition of 4.67 mmol (mass fraction 1.37 wt%) PSK2. Furthermore, the PUPSK2 elastomer material also had good healing ability up to 60% at room temperature and good transparency of 83.7% at 350–800 nm visible.

Zr-rich basalt continuous fibers with increased alkali resistant properties

Zirconium-rich basalt continuous fibers with zirconium oxide content from 5.1 to 8.1 wt% with the addition of 1% lanthanum oxide were obtained in a laboratory facility. The production temperature range were measured. It was shown that lanthanum oxide addition allows to decrease production temperature by 50° and to make wider the production temperature range by 10°. Weight loss and tensile strength loss of fibers after refluxing in alkali solution were determined. The weight loss after boiling in 1 M NaOH and 0.5 M Na2CO3 solution is comparable to the weight loss of zirconium-rich glass fibers (AR glass). The addition of lanthanum oxide leads to an increase in the tensile strength of Zr-rich basalt continuous fibers by 15–20%. Based on the obtained data, it can be concluded that the presented approach will not only improve the alkali resistance of basalt continuous fibers for reinforcing cements and concretes, but also significantly reduce their cost.

Facile synthesis of hollow nanotube MnCoOx catalyst with superior resistance to SO2 and alkali metal poisons for NH3-SCR removal of NOx

A bottleneck of catalyst application to industrial flue gas denitrification is that the toxicity of SO2 and alkali metals in flue gas will result in the deactivation of active sites on the catalyst surface. In this work, in order to retain the active sites and minimize the catalyst deactivation by SO2 and alkali metals, we designed a hollow nanotube structured MnCoOx catalyst (MnCoOx-HNT) with surface anchoring function via a simple, easy to scale up and template free synthesis approach. The formation of hollow nanotube structure could be achieved easily by simply adjusting the metal salt precursor without any template or complicated equipment aids. More importantly, the hollow nanotube structured catalyst achieved excellent catalytic performance (80.1% NOx reduction) at 150 °C even when simultaneously exposed to the synthetic flue gas with coexistence of H2O, SO2 and alkali metals reaction feeds. The outstanding poisoning-resistant property of MnCoOx-HNT could be attributed to its unique hollow nanotube structure effectively protecting the active sites on the inner surface from being poisoned by SO2 or alkali metals. In addition, the abundant OH groups acted as sacrificial sites anchoring SO2 and alkali metals on the catalyst surface, resulting in the formation of sulfate species mainly in the form of surface sulfate rather than bulk sulfate. OH groups also had preference to combine with alkali metals, which delayed the combination of alkali metals with the Mn-Co active sites and consequently the poisoning process. The above excellent performance makes it possible for the MnCoOx-HNT to be applied to denitrification under extreme flue gas, and also provides a new idea for the design of functional materials with satisfactory SO2 and alkali resistance properties.

Evaluation of bioremediation and detoxification potentiality for papermaking black liquor by a new isolated thermophilic and alkali-tolerant Serratia sp. AXJ-M

There is a great need for efficiently treating papermaking black liquor because it can seriously pollute both soil and water ecosystems. In this study, the Plackett–Burman (PB) experimental design combined with response surface methodology (RSM) was used for improving the biodegradation efficiency of lignin by a new isolated thermophilic and alkali-tolerant strain Serratia sp. AXJ-M, and the results showed that a biodegradation efficiency of 70.5% was achieved under optimal culture conditions. The bacterium with ligninolytic activities significantly decreased target the parameters (color 80%, lignin 60%, phenol 95%, BOD 80% and COD 80%). The control and treated samples were analyzed by gas chromatography-mass spectrometer (GC-MS), which showed that the concentrations of a majority of low-molecular-weight compounds were decreased after biological treatment. Furthermore, toxicological, genotoxicity and phytotoxicity studies have supported the detoxification by the bacterium of black liquor. Finally, the genome sequence of the thermophilic, alkali-tolerant and lignin-degrading bacterium AXJ-M was completed, and the genetic basis of the thermophilic and alkali-resistant properties of AXJ-M was preliminarily revealed. The dyp-type peroxidase was first reported to have the potential to catalyze lignin degradation structurally. These findings suggest that Serratia sp. AXJ-M may be potentially useful for bioremediation applications for papermaking black liquor.

Selection of basalt fiber with resistance to concrete alkaline environment

Due to a growing interest in basalt fibers as a reinforcing material for concrete, it becomes necessary to study behavior of such fibers and their interaction with the concrete matrix. Basalt fibers have prospective mechanical and processability properties, as well as good cost-effectiveness when used as concrete reinforcement. However, alkali resistance properties of basalt fiber are rather weak. Three types of basalt fibers from various manufacturers are presented, which were produced from different basalt raw materials and with distinct production technologies. All presented basalt fiber types were studied before mixing with concrete and after it has cured. Size and morphology, young’s modulus, tensile strength, bending modulus and flexural properties as well as chemical analysis tests were carried out on the types of basalt fibers under consideration. One type of basalt fibers showed better alkali resistance properties due to the special selection of raw materials for the basalt fibers production.

Fabrication of superhydrophobic Eucalyptus wood surface with self-cleaning performance in air and oil environment and high durability

In this study, a simple and cost-effective method was developed to fabricate superhydrophobic coating on wood surface. The prepared superhydrophobic coating had a large water contact angle (159°), less water slide angle (6°), good durability, abrasion resistance property, excellent thermal stability, and good acid and alkali resistance property. Notably, the coatings had self-cleaning properties in air or oil environment. The superhydrophobic coating was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and Fourier transform infrared (FTIR) spectroscopy. We prepared the classical micro/nanostructured SiO2 on the wood surface on which the low surface free energy substance 1H,1H,2H,2H-perfluoroalkyltrichlorosilane (PFDS) was successfully modified. Furthermore, the treated wood had significantly better physical properties including water uptake and dimensional stability. The developed superhydrophobic coating is easy to fabricate and has great significance for the functional modification of wood.

Особенности распределения различных изоформ гемоглобина в эритроцитах крыс

The six fractions of cells that differ in the content and ratio of different isoforms of hemoglobin can be isolated using fractional centrifugation of peripheral blood erythrocytes in intact rats. The distribution of hemoglobin in red blood cells is characterized by the fact that if six protein isoforms are determined in whole blood, then only two in the cells of each individual fraction. Red blood cells with isoforms of lower molecular weight contain a lower percentage of hemoglobins with acid-and alkali-resistant properties.