Induction Time Tests Research Articles

Natural weathering effects on white, green, and black HDPE textured GMs

This study investigates the degradation of textured High-Density Polyethene (HDPE) geomembranes (GMs) subjected to natural weathering for 8.5 to 10.5 years. The GMs, denoted as GM-W/B (white and black), GM-G (green) and GM-B (black), had a nominal thickness of 1.00 mm and were manufactured using a flat die process with texture on both surfaces. Standard Oxidation Induction Time (Std-OIT) tests and Thermogravimetric Analysis (TG/DTG) were performed to assess the antioxidant depletion and thermal decomposition. Additionally, degradation due to Ultraviolet (UV) radiation and environmental agents was assessed through retained physical and mechanical properties, including the Melt Flow Index (MFI) measured under various loading conditions. Antioxidant depletion and TG/DTG analyses indicated that environmental exposure compromised the thermal stability of these GMs. Among the tested GMs, GM-W/B exhibited the greatest reduction in both Std-OIT and MFI, followed by GM-G and GM-B, suggesting a direct correlation between these properties. While GM-B appeared to be still in the antioxidant depletion stage (Stage I), GM-W/B and GM-G showed signs of degradation beyond Stage I. This study provides insights into the degradation of textured HDPE GMs in the face of weathering exposure effects and the durability of colored HDPE GMs.

Influence of Different Types of Surfactants on the Flotation of Natural Quartz by Dodecylamine.

The synergistic effect among flotation agents is why combined flotation agents exhibit superior performance compared to single flotation agents. This research investigates the influence of three surfactants with different charges of polar groups, sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and octanol, combined with dodecylamine (DDA), on quartz flotation. Through the implementation of flotation tests, bubble-particle adhesion induction time testing, gas-liquid two-phase foam properties testing, and surface tension testing, it is revealed that substituting part of the DDA with these surfactants can either enhance or at least maintain the quartz recovery, affect the adhesion induction time, reduce the surface tension of the flotation system, and change the foaming performance and foam stability, depending on their mole ratio in the combined collector. Compared to DDA alone, combining CTAB or OCT with DDA can significantly increase quartz recovery, while SDS with DDA only yields an approximate recovery. Combining SDS or OCT with DDA can reduce the foam stability, while CTAB with DDA enhances the foam stability. The effect of the combination of surfactants and DDA on the adhesion induction time of quartz grains of different sizes with bubbles is the same; furthermore, there is a negative correlation between the adhesion induction time and the recovery, while the foaming properties and stability of foam are positively correlated with the recovery.

Investigation on the mechanism of air/condensate bubble flotation of emulsified oil droplet

Crude oil droplets in oilfield-produced water are highly emulsified, and the poor attachment between gas bubbles and oil droplets limits the effectiveness of oil-water separation during flotation processes. This paper proposes a new surface-functionalized bubble called a condensate bubble and evaluates its flotation performance based on surface properties and adhesion theory mechanism to address this issue. The surface chemical properties of the oil droplets were characterized using X-ray photoelectron spectroscopy (XPS), contact angle measurement, and zeta potential. Induction time and flotation tests were conducted to compare the attachment effects between air or condensate bubbles and emulsified oil droplets. The interaction forces were calculated using DLVO and extended DLVO theory. The experimental results showed that crude oil contains functional compounds containing oxygen that make it tough to float. However, the contact angle between the oil surface and condensate bubble was greater than 150°, demonstrating that the condensate liquid bubbles have better hydrophobicity than air bubbles. The micro-flotation experiments indicated that condensate bubbles have a strong collection capacity for emulsified oil droplets, which was confirmed by induction time tests. In 70 mM NaCl brine, the oil removal efficiency of condensate bubble flotation could reach 82%, which was a 30% improvement compared to air bubble flotation. However, DLVO theory failed to predict the flotation with a concentration higher than 10 mM NaCl. The extended DLVO theory accounted for hydrophobic interactions, which were observed due to similar solvent extraction and hydrophobicity of the condensate liquid film. As a result, the condensate bubble-oil droplet system exhibited stronger hydrophobic attraction, successfully confirming and illustrating the superiority of the condensate bubble in flotation.

Antioxidant-stabilizer depletion of 4 HDPE geomembranes with high HP-OIT in MSW leachate

The antioxidant-stabilizer depletion of four 1.5-mm HDPE geomembranes from the same manufacturer each with a different resin and additive package is examined in air and a synthetic municipal solid waste leachate at a range of temperatures (40–95°C) for 7.5 years. Two were formulated for high temperatures and used polyethylene of raised temperature resistance (PE-RT) resins while two used more conventional HDPE geomembrane formulations. The depletion of protective antioxidants and stabilizers was monitored using standard and high-pressure oxidative induction time (OIT) tests and the notably different depletion times for both OIT tests implied they were detecting different groups of AO-S. Although both PE-RT GMBs showed significantly slower AO-S depletion at 85°C in air compared to the conventional PE GMBs, only one PE-RT GMB maintained this status in 85°C leachate, highlighting the limitation of air aging tests (and importance of fluid immersion tests). The importance of running immersion tests long enough to reveal the residual HP-OIT value is stressed. The roles of stabilizer mobility and solubility in polyethylene and their suspected involvement in residual HP-OIT behavior are also illustrated.

Fabrication of a novel chitosan‐based macromolecular antioxidant and its effects on the anti‐aging properties of styrene‐butadiene rubber/silica composites

AbstractIn this work, a novel chitosan‐based macromolecular rubber antioxidant (denoted as COS‐AO) was successfully synthesized by using chitosan (COS) and 3‐(3,5‐di‐tert‐butyl4‐hydroxyphenyl) propionic acid (antioxidant, AO) via esterification reaction. The FTIR, 1H NMR, 13C NMR, and elemental analysis measurements were used to confirm the structure of COS‐AO. The performance of COS‐AO as a macromolecular antioxidant for styrene‐butadiene rubber (SBR)/silica composites were examined by oxidation induction time (OIT) test, methanol extraction experiments, accelerated thermo‐oxidative aging tests as well as thermogravimetric (TG) test. The results indicated that the macromolecular antioxidant COS‐AO presented better extraction resistance and migration resistance in SBR/silica composites compared to the small molecular antioxidant AO. Moreover, COS‐AO significantly improved the thermal stability as well as the value of the oxidation induction time of SBR/silica composites, exhibiting superior thermo‐oxidative aging resistance. In addition, the potential antioxidative mechanism of COS‐AO in SBR/silica composites was also discussed.

Adhesion between nanobubbles and fine cassiterite particles

Adhesion is an important process of particle-bubble interaction in fine particle (−10 μm) flotation. This paper studied the adhesion process and mechanism between nanobubbles and fine cassiterite particles by using a high-speed camera, atomic force microscope (AFM), adsorption capacity tests, and induction time tests. After being pretreated with nanobubbles (NBs) water, fine cassiterite particles flotation tests were carried out using caprylhydroxamic acid (CHA) as a collector. The results showed that NBs can improve the recovery and flotation rate of fine cassiterite while decreasing the collector dosage. The adsorption capacity test indicated that the cassiterite treated with NBs had lower demand for collector concentration. The AFM imaging results further demonstrate that NBs could reduce the adsorption of CHA on the surface of minerals. Since NBs played a part of the role of collector, it can improve the flotation effect while reducing the amount of collector. The induction time test and the high-speed camera observation test showed that NBs promoted the attachment between bubbles and cassiterite particles. On the other hand, NBs agglomerate cassiterite particles, increasing the probability of particles colliding with bubbles.

Enhancing flotation removal of unburned carbon from fly ash by coal tar-based collector: Experiment and simulation

The unburned carbon (UC) in fly ash is a vital parameter that governs the further utilization of fly ash in mortar and concrete industry. Flotation is an effective methodology for removing the UC from fly ash. However, the specific physicochemical properties of the UC particle surface make them difficult to float. In this study, a coal tar-based (CTB) collector was used to remove the UC from fly ash through flotation process. The adsorption mechanism of the CTB collector and diesel on the UC particle surface was characterized by scanning electron microscopy-energy dispersive spectrometry (SEM-EDS), fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), molecular dynamics (MD) simulation, and induction time tests. The levels of oxygen-containing functional groups and aromatic ring compounds present in the CTB collector were considerably higher than those in diesel. The oxygen-containing functional group contents on the untreated UC surface, the diesel-treated UC surface, and the CTB collector-treated UC surface decreased in that order. The MD simulation results indicated that the aromatic compounds (dibenzofuran and naphthalene, etc.) in the CTB collector interacted strongly and adsorbed at deep locations with the UC surface compared to the alkanes (dodecane, diesel, etc.). The alkanes are indispensable as the collector in the fly ash flotation process and synergize with aromatic compounds to improve the mobility of water molecules on the UC surface. The CTB collector significantly enhanced the floatability of the UC particle and hence improved the flotation removal of UC from fly ash.

Natural antioxidant from bamboo leaves for the processing stability of polypropylene

The antioxidant of bamboo leaves (AOB) was used firstly to stabilize polypropylene (PP). Thermogravimetric analysis, oxidation onset temperature and oxidation induction time tests were carried out to test the thermal and thermo-oxidative stability of samples. The melt flow rate and yellowness index were used to characterize the processing stability and color of samples. Field emission scanning electron microscopy was used to determine the distribution of additives. Results showed that AOB improved the thermo-oxidative stability and processing stability of PP. The efficacy of AOB was comparable with that of Irganox 1010 in protecting PP. However, due to the dark yellow color of AOB, the problem of the discoloration of the polymer matrix was not solved.

The Influence of the Accelerated Aging Conditions on the Properties of Polyolefin Geogrids Used for Landfill Slope Reinforcement.

Polyolefin geosynthetics are susceptible to oxidative degradation, which in turn leads to diminished mechanical properties in geotechnical constructions. When using these materials, it is extremely important to determine their durability over time in particularly aggressive conditions. In order to prolong the life of a geosynthetic material, antioxidants are added during the manufacturing process. The function of antioxidants is to prevent polymer oxidation reaction in time. As the antioxidant content is depleted, the polymer becomes less protected towards oxidative attacks. This article describes the aging process of uniaxial (high density polyethylene) HDPE geogrids under the influence of chemical and environmental factors. Evaluations of accelerated aging test of the uniaxial HDPE geogrids were incubated in simulated landfill conditions for a period of 12 months. Three temperatures (25 °C, 45 °C, and 75 °C) were selected for carrying out the aging experiments in aqueous solutions mimicking landfill conditions. The changes observed by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and melt flow index (MFI) correlate with the mechanical properties of the aged geogrid. No significant changes in the FTIR and MFI were observed over the 12 months of accelerated aging tests at none of the three different temperatures. The oxidation induction time (OIT) test showed no antioxidant remaining in the geogrid following eight months of aging test at 75 °C. No significant changes in the influence of accelerated aging tests on the average relative elongation at 25 °C and 45 °C of the tested material were observed. Accelerated aging tests at 75 °C showed that the mean elongation of 12.12% for the sample not subjected to accelerated aging tests (new sample) increased to 19.32% (after 12 months of incubation).

Comparison of flotation performances of low-rank coal with lower ash content using air and oily bubbles

The attachment interaction in a flotation process is critical because it controls the recovery of mineral particles and is dominated by the interaction energy barrier between bubbles and solid particles. In this investigation, the surface properties of coal particles and oily bubbles were evaluated via the X-ray photoelectron spectroscopy (XPS) analysis, zeta potential measurement and induction time tests. The results proved that the classical Derjagin–Landau–Verwey–Overbeek (DLVO) theory did not adequately predict the flotation performances of oily bubble flotation. The attractive interaction or hydrophobic force induced by the hydrophobic force should be considered in the extended DLVO (EDLVO) theory. Throughout this paper, therefore, it is significant to consider the attractive interaction or hydrophobic force between low-rank coal particles and oily bubbles when comparing the advantages of the flotation response using air and oily bubbles.

Synthesis of Polyethylene‐Grafted Phosphite Antioxidant and Its Antioxidant Behavior in Polypropylene

AbstractA novel macromolecular auxiliary antioxidant with polyethylene (PE) as polymer skeleton and phosphites as side groups is prepared based on commercial ethylene‐vinyl acetate (EVA) copolymers and its potential as polyolefin stabilizers is studied in depth. The synthesis approach of this PE‐grafted antioxidant consists of a typical EVA hydrolysis reaction and a two‐step nucleophilic substitution reaction of PCl3, 2,4‐di‐tert‐butylphenol, and the hydrolysis product. Results of the thermogravimetric analysis show that the macromolecular structures endow the as‐synthesized antioxidant with much better thermal stability than that of the commercial antioxidant 168. In addition, antioxidant behaviors of the PE‐grafted antioxidants in polypropylene (PP) matrix are investigated in detail through characterization of the melt flow index of multiple‐extruded stabilized PP as well as the short‐term oxidation induction time test and the long‐term thermo‐oxidative aging test. Results show that even with extremely low content of the effective antioxidant groups, the as‐synthesized macromolecular antioxidant still has excellent antioxygenic properties.

Predicting the depletion of antioxidants in high density polyethylene (HDPE) under sunlight using the reciprocity law

Depletion of antioxidants in HDPE subjected to sunlight exposure was studied. Sunlight radiation was simulated using a laboratory xenon light weatherometer at three irradiation levels. Oxidative induction time (OIT) test was performed on different layers along the thickness of the test coupons to establish the antioxidant depletion throughout the exposure duration. The highest drop in OIT was obtained for the surface layer facing the radiation, followed by the backside layer which was exposed to indirect radiation reflected from the wall of the weatherometer. The core section showed a slower decrease under the same exposure conditions. Furthermore, the OIT depletion rate in the surface layer increased with radiation intensity. The study proved that the sunlight degradation of the tested polyethylene can be accelerated by increasing the irradiation intensity based on the reciprocity law.

Novel nanocomposite based on EVA/PHBV/[60]Fullerene with improved thermal properties

A novel nanocomposite was prepared from ethylene-co-vinyl acetate copolymer (EVA) and poly-3-hydroxy butyrate-co-valerate (PHBV) in combination with small amounts of [60]Fullerene (C60). The thermal degradation as well as the incorporation effect of C60 on the thermo-oxidative decomposition of EVA/PHBV/C60 nanocomposites was investigated using thermogravimetric analysis (TGA). In order to assess the level of stabilization of nanocomposites, the oxidation induction time test was also determined. The obtained results indicated that the dispersion of C60 even at low loading (0.3, 0.5 and 0.7 wt.%) exerts a significant increase on the thermal stability properties of nanocomposite. The oxidation induction time values of nanocomposites were remarkably increased with the increase of C60 amounts. Surprisingly, the oxidation induction time of EVA/PHBV/C60 (0.3 wt.%) is 1643 s higher than that of unfilled EVA/PHBV blend.The flammability properties investigated in pyrolysis combustion flow calorimetry (PCFC) showed that the addition of C60 could prolong the time to peak of Heat Release Rate (pHRR) of around 30 °C compared to EVA/PHBV blend. It was demonstrated that C60 is inhibitor of the thermal and thermo-oxidative degradation of EVA/PHBV blend.

Effects of pre-wetting time on surface topography and floatability of lignite particles

The laser particle size analyzer, NMR, SEM/EDS, induction time tests and surface roughness analysis were employed in the mechanism analysis of this investigation. The floatability of lignite was decreased with the pre-wetting increasing from 0 – 5min because the pores and fractures of lignite surface can be filled with water. However, the floatability of lignite was increased with the pre-wetting from 5 – 480min. NMR and SEM indicate that a long pre-wetting process (>5min) polished and rubbed the surface of lignite reducing the amount of macropores and fractures as well as the porosity. The rough lignite surface was also polished to be smooth. As the pre-wetting time increases, the topography of lignite surface, such as porosity, macropores, fractures and roughness decreased, which results in the decrease of water filling negative effects, and hence the floatability of lignite gradually increased with the pre-wetting time over 5min.

Long-term performance of a HDPE geomembrane stabilized with HALS in chlorinated water

A high density polyethylene geomembrane (GMB) stabilized with hindered amine (light) stabilizers (HALS or HAS) is immersed in four chlorinated water solutions with a simulated free chlorine concentration range of 0.5–5 ppm at five different temperatures (25, 40, 65, 75, and 85 °C) for 70 months. Standard and high pressure oxidative induction time (OIT) tests are performed to monitor antioxidants depletion while melt flow index, tensile, and stress crack resistance (SCR) tests are conducted to monitor degradation in physical and mechanical properties. Degradation in the GMB properties occurred shortly after immersion in chlorinated water at all temperatures except at 25 °C. Increasing the free chlorine concentration resulted in faster degradation of the tensile properties and SCR. The predicted time to nominal failure based on SCR ranges between 25 years at 40 °C and 5 years at 85 °C in chlorinated water (with 0.5 ppm free chlorine). A comparison between the degradation in SCR of this GMB and a GMB with a different resin and without HALS shows significant difference in their performance in chlorinated water but not in other incubation media.

Effects of ultrasonic pretreatment on particle size and surface topography of lignite and its relationship to flotation response

ABSTRACT The aim of this investigation was to study the effects of different ultrasonic powers and treatment times on particle size and surface topography of low ash fine lignite (<0.125 mm) combined with flotation, wet-screening, surface roughness, scanning electron microscopy (SEM), and induction time tests. Flotation results show the concentrate yield gradually decreased with the increase of ultrasonic power and treatment time except 18 W. The wet-screening results indicate that increasing ultrasonic power and treatment time had more significant crushing effect on lignite particles and produced more fine particles (<0.045 mm), which was harmful for the improvement flotation performance of lignite. SEM results show that crack was gradually expanded into a gap as well as some new cracks and cavities on the surface of lignite are produced with the increase of ultrasonic power. The generation of these gaps, new cracks, and cavities increases the roughness of lignite surface. The higher the ultrasonic power is, the rougher the lignite surface becomes, which promotes its surface to entrap more water during the flotation process resulting in a formation of thick hydration shell. The induction time increased as ultrasonic power and treatment time increased except 18 W. Hence, there will be a negative impact on lignite flotation if the lignite particles are treated by higher ultrasonic power for longer. The findings of this paper may provide some guidance to understand the effects of ultrasound on surface topography of lignite and makebetter use of ultrasound to assist coal flotation.

Intensification of interfacial adsorption of dodecylamine onto quartz by ultrasonic method

Besides being a versatile mineral resource, quartz is also a common gangue mineral in mineral separation. The separation and enrichment of quartz minerals are particularly important in industrial production. Cationic surfactants of dodecylamine (DDA) is mainly used as collector in the quartz flotation as it consists of hydrophilic amino group which attach to the quartz surface, and the hydrophobic carbon-chain groups which make the quartz hydrophobic. So the adsorption behaviour of DDA is vital to the quartz flotation. In this paper, we examine an ultrasonic method for enhancing the adsorption of DDA in the froth flotation of quartz. The adsorption mechanism of the DDA collector onto quartz is systematically investigated via Fourier transform infrared spectroscopy (FTIR) measurements, adsorption heat measurements, adsorption amount tests, contact angle analysis, and induction time tests, and X-ray photoelectron spectroscopy (XPS) analysis. Our results indicate that ultrasonication does not change the functional groups of the DDA, however, the adsorption intensity with an adsorption heat of −26.56 J/g between ultrasonically treated DDA and quartz is fairly large. The adsorption amount of DDA onto quartz significantly increases after ultrasonically treated without increasing its concentration, and the maximum contact angle of quartz particles after conditioning by the ultrasonically treated DDA increase from 53.07° (for untreated DDA) to 66.13° at the concentration of 8 × 10−5 mol/L. In bubble attachment tests, the induction time between quartz particles and a bubble is observed to decrease from 30 ms to 20 ms compared to that without ultrasonic treatment, and coupled with a greater attachment performance of the DDA solution with ultrasonic treatment. And the XPS analysis confirms the adsorption of ultrasonically treated DDA onto quartz surface. Further, we perform micro-flotation tests to verify the enhanced adsorption of the ultrasonically treated collector onto the quartz surface for different initial concentrations; the results indicate that ultrasonication of DDA significantly improves the flotation recovery of quartz, particularly at moderate collector concentrations. This study is beneficial for understanding the interfacial adsorption and the ultrasonic intensification of DDA onto quartz particles.

Waste colza oil used as renewable collector for low rank coal flotation

The high cost of low rank coal flotation using diesel as the collector significantly restricts the improvement in economic efficiency of the coal plant. Waste colza oil (WCO) from the catering industry was used as a renewable and alternative collector for ultrafine low rank coal flotation in this investigation. Scanning electron microscopy (SEM) test was carried out to check the surface morphologies of the coal sample. Fourier-transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) tests were performed to examine the coal chemical compositions. The flotation yield using WCO was always higher than that of using diesel, especially at a high dosage. When 6 kg/t dosage was used, 35.68% yield was obtained with WCO, 5.54% higher than that with diesel. The mechanism of WCO used as an alternative collector was discussed based on the induction time, FTIR, and XPS tests. The induction time of the low rank coal after conditioning with 6 kg/t diesel and WCO were 200 ms and 100 ms, respectively, indicating that WCO was a more effective collector for improving the floatability of low rank coal compared with traditional diesel. XPS tests confirmed the adsorption of WCO on coal surface as the WCO has a large amount of CO groups according to FTIR results. The hydrogen bonding between oxygen-containing groups in WCO and low rank coal surface was responsible for the improvement of floatability and flotation recovery.

The flotation behavior of coal-pyrite in high-sulfur coal

ABSTRACTThe properties and flotation behavior of coal-pyrite were analyzed by the contact angle, induction time, and flotation tests. The results indicate that compared with coal, coal-pyrite has a smaller contact angle and longer induction time. The floatability of coal-pyrite is poor with dodecane as the collector. A part of fine liberated pyrite mixed with the clean coal in flotation. The linear relationship between the ash and liberated pyritic sulfur recoveries implies the same recovery mechanism, that is, mechanical entrainment. Molecular dynamics simulation also demonstrates that dodecane could not break through the hydrated film to be absorbed on the pyrite surface.

Optimization of Thermal Stability of High-Density Polyethylene Composite Using Antioxidant, Carbon Black and Nanoclay Addition by a Central Composite Design Method: X-ray Diffraction and Rheological Characterization

The thermal stability of high-density polyethylene, as characterized by an Oxidation Induction Time (OIT) test in the presence of the three additives, antioxidant, carbon black and nanoclay, was investigated. The twenty experiments used were designed by using the Central Composite Design (CCD) method, and the effects of the main parameters and their interactions were analyzed. The results of Analysis of Variance (ANOVA) showed that the antioxidant, nanoclay and carbon black contents, the antioxidant-nanoclay interaction and the antioxidant-carbon black interaction, had significant effects on the thermal stability. By optimization of the percent compositions used, the best composition was obtained, 0.26%, 2.21% and 4.69% for antioxidant, carbon black and nanoclay, respectively, to achieve thermal stability equal to the targeted value of 60 minutes. X-ray diffraction confirmed a weak polymer-nanocaly interaction in the optimal sample structure. The rheology frequency sweep test showed an increase in the elastic and viscous modulus in the optimal sample relative to the control samples. The Melt Flow Index (MFI) test for an optimum sample showed a pseudo-plastic structure with the lowest melt flow index of 0.2614 g/10 min, which was consistent with the results of the complex viscosity, with the optimal sample having the highest value (128500 Pa.s). The density test indicated the most crystalline structure for the optimized sample, with the highest value (0.976 g/cm3) compared to the control samples (0.962 and 0.957 g/cm3 for the polyethylene/nanoclay and the polyethylene/carbon black sample, respectively).