Ground Tire Rubber Content Research Articles

Sustainable thermoplastic elastomers based on thermoplastic polyurethane and ground tire rubber

AbstractIn this research, blends are prepared of thermoplastic polyurethane (TPU), ground tire rubber (GTR) and its devulcanized version (dGTR). The primary objective is to produce thermoplastic elastomers wherein TPU is partially substituted by GTR or dGTR obtained from used tires, thereby forming a blend with a favorable cost/value ratio and a smaller environmental footprint. Throughout the experiment, the rubber content of the blends is varied between 0 and 50 wt% and the effect on mechanical properties is investigated. The blends are compounded with a twin‐screw extruder, after which sheet samples are produced by injection molding. With a view to a possible future industrial application, it is important that both the compounding and the injection molding of the specimens are easy to perform, even with a 50 wt% filler content. Increasing the amount of rubber phase reduce the tensile strength and elongation at break of the blends. Unfortunately, devulcanization did not significantly improve the properties of the blends. Overall, even at a (d)GTR content of 50 wt%, an elongation at break of 300% is achieved, which allows the use of the blends as thermoplastic elastomers. In addition, dynamic tests show that the rubber phase increases the damping capacity of the samples.

Assessment of Ground Tyre Rubber Impact on Stiffness Modulus and Cracking Resistance of Bituminous Mixtures

Abstract The objective of this study was to evaluate and characterize the performance of ground tire rubber (GTR) modified dense graded asphalt mixtures to recommend a suitable GTR content to produce a mix that provides superior pavement performance characteristics. The research effort encompassed investigation of stiffness and cracking resistance of six dense graded asphalt mixtures, including one conventional and five modified mixes covering 42 samples. Addition of GTR using wet process showed decrease in stiffness during loading. Cracking resistance of GTR modified mixtures increased with higher levels of dosages regardless of the base binder. An increase in the GTR dosage from 0 to 10% did not result in a significant change in fracture energy but a further increment to 25% increased the fracture energy. The laboratory Results indicated that 10% GTR was showed as the optimal content for the stiffness modulus and 25 % GTR as better content that provides better cracking resistance.

Evaluation and Correlation Analysis of the Rheological Properties of Ground Tire Rubber and Styrene Butadiene Styrene Compound-Modified Asphalt.

With the increase in highway traffic volume, many waste tires are being produced, which puts serious pressure on the global ecological environment. Processing waste tires into powder and adding them to asphalt is an important and effective way to solve this noticeable environmental challenge. In this paper, to produce ground tire rubber (GTR) and styrene-butadiene-styrene (SBS) compound-modified asphalt, GTR was put into SBS-modified asphalt (GTRSA). Subsequently, some ordinary property tests, frequency sweep tests, and multiple stress creep recovery tests were conducted to investigate the conventional properties and rheological properties of GTRSA. Moreover, the 2S2P1D (two springs, two parabolic elements, and one dashpot) model was adopted to analyze the consequences of adding GTR content on the rheological properties of GTRSA. Finally, the Pearson correlation coefficient was employed to reveal the connection between the conventional properties and the rheological properties. The results show that GTR has a great impact on improving the rutting resistance, thermo-sensitive performance, shear resistance capability, stress sensitivity, and creep recovery performance of GTRSA. Adding 20% GTR can improve the creep recovery rate to 80.8%. The 5 °C ductility index suggests that GTR makes a difference to the low-temperature properties. The rheological properties and conventional properties had a strong linear link.

Elastocaloric Waste/Natural Rubber Materials with Various Crosslink Densities.

The characterization of the mechanical behavior of elastocaloric materials is essential to identify their viability in heating/cooling devices. Natural rubber (NR) is a promising elastocaloric (eC) polymer as it requires low external stress to induce a wide temperature span, ΔT. Nonetheless, solutions are needed to further improve DT, especially when targeting cooling applications. To this aim, we designed NR-based materials and optimized the specimen thickness, the density of their chemical crosslinks, and the quantity of ground tire rubber (GTR) used as reinforcing fillers. The eC properties under a single and cyclic loading conditions of the resulting vulcanized rubber composites were investigated via the measure of the heat exchange at the specimen surface using infrared thermography. The highest eC performance was found with the specimen geometry with the lowest thickness (0.6 mm) and a GTR content of 30 wt.%. The maximum temperature span under single interrupted cycle and multiple continuous cycles were equal to 12 °C and 4 °C, respectively. These results were assumed to be related to more homogeneous curing in these materials and to a higher crosslink density and GTR content which both act as nucleating elements for the strain-induced crystallization at the origin of the eC effect. This investigation would be of interest for the design of eC rubber-based composites in eco-friendly heating/cooling devices.

Mechanical and performance properties of re-vulcanized blends of GTR/NR

The effect of natural rubber (NR) on the mechanical and performance properties of ground tire rubber (GTR) has been investigated. The mechanical properties of vulcanized GTR/NR blends were determined in a universal testing machine. It was found a decreasing in the mechanical properties of the GTR/NR blends as the number of re-vulcanization processes increases. This behavior was attributed to the decrease in the concentration on GTR in the vulcanized GTR/NR blend with respect to the next one, and to a structural net degradation into the re-vulcanized GTR/NR blend due to the reversion process (over vulcanization). In the loss modulus charts was observed that the peaks of the curves got smaller and wide as the re-vulcanization process increased, due to the mechanical loses and elastic gains of the GTR/NR re-vulcanized blends. On the other hand, in the performance results was found that the cut growth values of Flexion Ross were more affected by the thickness of the plaque of vulcanized rubber than for the number of re-vulcanization processes of the GTR/NR blend. In addition, as the re-vulcanization processes increased, the structural degradation of the tridimensional cross-linked net, increased as well, more severely from the fourth re-vulcanization process. It could be concluded that the GTR/NR blends with high GTR content, could be used in the sole shoe fabrication, taking care that the thickness is ≤ 4.5 mm, and that the GTR/NR blends have not been subjected to more than two re-vulcanization processes.

Comprehensive Enhancement of Prepolymer-Based Flexible Polyurethane Foams' Performance by Introduction of Cost-Effective Waste-Based Ground Tire Rubber Particles.

Material innovations in polyurethane (PU) foams should ideally combine performance enhancement, environmental impact limitation, and cost reduction. These goals can be achieved by applying recycled or waste-based materials without broader industrial applications, implicating their low price. Herein, from 5 to 20 parts by weight of ground tire rubber (GTR) particles originated from the recycling of postconsumer car tires were incorporated into a flexible foamed PU matrix as a cost-effective waste-based filler. A two-step prepolymer method of foams manufacturing was applied to maximize the potential of applied formulation changes. The impact of the GTR content on the foams’ processing, chemical, and cellular structure, as well as static and dynamic mechanical properties, thermal stability, sound suppression ability, and thermal insulation performance, was investigated. The introduction of GTR caused a beneficial reduction in the average cell diameter, from 263.1 µm to 144.8–188.5 µm, implicating a 1.0–4.3% decrease in the thermal conductivity coefficient. Moreover, due to the excellent mechanical performance of the car tires—the primary application of GTR—the tensile performance of the foams was enhanced despite the disruption of the cellular structure resulting from the competitiveness between the hydroxyl groups of the applied polyols and on the surface of the GTR particles. The tensile strength and elongation at break were increased by 10 and 8% for 20 parts by weight GTR addition. Generally, the presented work indicates that GTR can be efficiently applied as a filler for flexible PU foams, which could simultaneously enhance their performance, reduce costs, and limit environmental impacts due to the application of waste-based material.

Compatibilized thermoplastic elastomers based on highly filled polyethylene with ground tire rubber

AbstractThermoplastic elastomers (TPE) based on ground tire rubber (GTR) are good strategies for the circular economy and sustainable development of waste tire rubber recycling. However, several parameters must be optimized to produce valuable TPE. The most important ones are GTR concentration and dispersion, as well as crosslinking degree, combined with interfacial interactions between the GTR and the thermoplastic matrix. In this work, TPE based on highly filled linear low‐density polyethylene (LLDPE) with GTR (50%–90%) was prepared via dynamic vulcanization. In particular, different reclaimed GTR (RR) was used alone or with a compatibilizer (maleic anhydride grafted polyethylene, PE‐g‐MAH) to prepare compatibilized TPE. The interactions between the rubber and plastic were quantified by a series of characterizations including mechanical tests, rheological measurements, differential scanning calorimetry, dynamic mechanical analysis and scanning electron microscopy. The results showed that the mechanical properties and processability decreased with increasing GTR content. Although the interfacial compatibility was improved with a higher GTR reclamation degree, the TPE mechanical properties were still gradually decreasing. To improve on these results, PE‐g‐MAH was added to increase the GTR‐LLDPE interfacial interactions. The results showed improvement in terms of mechanical properties and processability, especially for compatibilized TPE based on RR (tensile strength increased from 3.34 to 4.82 MPa and elongation at break from 91% to 101%).

Ground tire rubber/polyamide 6 thermoplastic elastomers produced by dry blending and compression molding

This study investigates the addition of ground tire rubber (GTR) into virgin polyamide 6 (PA6) to produce thermoplastic elastomer (TPE) blends. In particular, a wide range of GTR concentration (0–100% wt.) was possible by using a simple dry blending technique of the materials in a powder form followed by compression molding. The molded samples were characterized in terms of morphological (scanning electron microscopy), physical (density and hardness) and mechanical (tension, flexion and impact) properties. The results showed a decrease in tensile and flexural moduli and strengths with GTR due to its elastomeric nature. However, significant increases were observed on the tensile elongation at break (up to 167%) and impact strength (up to 131%) compared to the neat PA6 matrix. Based on the results obtained, an optimum GTR content around 75% wt. was observed which represents a balance between high recycled rubber content and a sufficient amount of matrix to recover all the particles. These results represent a first step showing that a simple processing method can be used to produce low cost PA6/GTR compounds with a wide range of physical and mechanical properties.

Ground tire rubber filled low-density polyethylene: The effect of particle size

In the present study, we investigated the possibility of value-added recycling of ultrafine ground tire rubber (uGTR) produced from water jet milling, with an average particle size of a few tens of microns. Our goal was to compare the properties of blends with different uGTR and conventional fine ground tire rubber (fGTR) contents prepared by blending with low-density polyethylene (LDPE). We also aimed to explore the property changes caused by the larger specific surface area due to the size effect. Samples were prepared with a hydraulic press after internal mixing. In the case of ground tire rubber (GTR) filled mixtures, the tensile properties showed rubber-like characteristics: with a significant decrease in modulus, elongation at break remained high, and tensile strength slightly decreased. The fracture surfaces of the samples were analyzed by scanning electron microscopy (SEM), wherein the case of materials made with uGTR showed better adhesion between the phases. In order to investigate the interfacial adhesion between the GTR and LDPE, we performed dynamic mechanical thermal analysis (DMTA). The glass transition peak of the uGTR shifted to a higher temperature and the storage modulus was higher than in the case of samples containing fGTR. Finally, we determined the Shore D hardness of the materials, which decreased with increasing GTR content, but hardness was greater in the case of uGTR samples. The better mechanical properties of blends containing uGTR were explained by better interfacial adhesion between the two phases due to the significantly higher specific surface area compared to fGTR.

Effect of Ground Tire Rubber (GTR) Particle Size and Content on the Morphological and Mechanical Properties of Recycled High-Density Polyethylene (rHDPE)/GTR Blends

This work investigates the effect of ground rubber tire (GRT) particle size and their concentration on the morphological, mechanical, physical, and thermal properties of thermoplastic elastomer (TPE) blends based on recycled high-density polyethylene (rHDPE). In our methodology, samples are prepared via melt blending (twin-screw extrusion followed by compression molding) to prepare different series of blends using GTR with three different particle sizes (0–250 μm, 250–500 μm, and 500–850 μm) for different GTR concentrations (0, 20, 35, 50, and 65 wt.%). The thermal properties are characterized by differential scanning calorimeter (DSC), and the morphology of the blends is studied by scanning electron microscopy (SEM). The mechanical and physical properties of the blends are investigated by quasi-static tensile and flexural tests, combined with impact strength and dynamic mechanical analysis (DMA). The SEM observations indicate some incompatibility and inhomogeneity in the blends, due to low interfacial adhesion between rHDPE and GTR (especially for GTR > 50 wt.%). Increasing the GTR content up to 65 wt.% leads to poor interphase (high interfacial tension) and agglomeration, resulting in the formation of voids around GTR particles and increasing defects/cracks in the matrix. However, introducing fine GTR particles (0–250 μm) with higher specific surface area leads to a more homogenous structure and uniform particle dispersion, due to improved physical/interfacial interactions. The results also show that for a fixed composition, smaller GTR particles (0–250 μm) gives lower melt flow index (MFI), but higher tensile strength/modulus/elongation at break and toughness compared to larger GTR particles (250–500 μm and 500–850 μm).

Investigation of hot mixture asphalt with high ground tire rubber content

Stockpiles of waste tires pose concerns of potential contamination of local groundwater, and fire risk from the large amounts of tires. To sustainably use the waste tires, Ground Tire Rubber (GTR) that produced from waste tires has been used in the pavement industry for decades. The typical GTR content is approximately 1–3% by weight of the asphalt mixture. To utilize more waste tires, there is an increasing demanding of using higher amount of GTR in recent years. The objective of this study was to determine the high GTR content that can be used in the asphalt pavement without sacrificing performance. In this study, gap-graded mixtures modified with differing GTR contents were designed. These GTR contents were 2.6%, 3.4%, 3.7%, 4.1% and 4.5% by weight of the mixture. Statistical analysis was conducted to determine the influence of GTR content on the mixture performance. It was found that the fracture energy of the GTR modified mixture was two to three times higher than that of the control mixture. All of the mixtures seemed to provide adequate rutting resistance for low-volume traffic, signifying that after 5000 wheel passes, the rutting depth did not exceed the 12.5-mm. The GTR modified gap-graded mixtures had high resistance to low-temperature cracking and high-temperature rutting. This can partly be attributed to the addition of GTR and the skeleton structure from gap gradation. The result of multiple comparisons suggested that even though the addition of GTR in dense-graded mixtures did not significantly improve the high-temperature performance, the addition of GTR in asphalt mixtures significantly improved the low-temperature performance.

Effect of Plastic and Tire Wastes on Marshall Properties, Density and Water Absorption of Polymer Pavement

The amount of plastic wastes and tire wastes were continuously increasing. The old tires and polymer which was low-density polyethylene (LDPE) were used to create polymer-modified pavement to get rid of plastic wastes and tire wastes replacing asphalt road. LDPE of 15 wt% was the main matrix material of the modified road pavement instead of asphalt; moreover, ground tire rubber (GTR) at various concentration of 3, 5, 7 and 10 phr was used as the additive mixed with mineral aggregates of 85 wt%. In this study, the Marshall method was used to prepare the sample. The properties of Marshall stability, Marshall flow, bulk specific gravity and voids of the polymer-modified pavement were studied for comparing to commercial asphalts. The results showed that the strength of the modified pavement increased which was higher than commercial asphalts although void concentration increased. The bulk specific gravity decreased as increasing amount of GTR. The percentage of water absorption increased as addition of GTR content. This study might be benefits in reduction of waste and valuable resources as bitumen, and also recovery an environment

Laboratory Evaluation of SBS Modified Asphalt Binder Containing GTR, SIS, and PE

Performance properties of polymer modified asphalt (PMA) binders with Styrene‐isoprene‐styrene (SIS), petroleum resin (PE), and ground tire rubber (GTR) were evaluated at high, intermediate, and low temperatures. Styrene‐butadiene‐styrene (SBS) PMA binder of PG 76‐22 was used as a base binder. The PG76 SBS PMA binders were blended with SIS, PE, and three different GTR contents (0, 5, and 10%). The binders were artificially short‐term and long‐term aged using rolling thin film oven (RTFO) and pressure aging vessel (PAV) procedures. Superpave binder tests were conducted on the binders through rotational viscometer (RV), dynamic shear rheometer (DSR), and bending beam rheometer (BBR). Multiple stress creep recovery (MSCR) test was also performed to evaluate the rutting property. The results of this study indicated that (1) the addition of PE can decrease the binder viscosity, (2) although the incorporation of GTR and SIS significantly improve the rutting resistance of the binders, the effect of PE is found to be insignificant, (3) PE is observed to have positive effect on the cracking properties of control PG76 SBS PMA binder blended with SIS and GTR, and (4) incorporation of PE might be an useful option to improve the workability of high performance PMA binder in lieu with maintaining good rutting and cracking resistance.

Evaluation of High‐Performance Asphalt Binders Modified with SBS, SIS, and GTR

In this study, performance properties of polymer‐modified asphalt (PMA) binders are evaluated depending on ground tire rubber (GTR) and styrene‐isoprene‐styrene (SIS). Styrene‐butadiene‐styrene‐ (SBS‐) modified asphalt binder of PG 76‐22 is used as a base binder to manufacture the rubberized PMA binder. The rubberized PMA binders are blended using SIS modifier. The binders were artificially short‐term and long‐term aged using rolling thin‐film oven (RTFO) and pressure aging vessel (PAV) procedures. Superpave binder tests were conducted on the binders through rotational viscometer (RV), dynamic shear rheometer (DSR), and bending beam rheometer (BBR). Furthermore, multiple stress creep recovery (MSCR) test and atomic force microscopy (AFM) microstructural analysis were performed. The results of this study indicated that (1) the viscosity properties seem to be highly dependent on GTR and SIS contents, (2) the addition of SIS is observed to have a significant effect on improving the rutting performances of rubberized PMA binders, (3) the cracking properties are considered to be improved significantly through SIS modification, and (4) in general, the rubberized PMA binders with SIS showed the best performance for rutting and cracking among all the binders used in this study.

Polymer Foams Based on Low Density Polyethylene/Ethylene Vinyl Acetate/Ground Tire Rubber (LDPE/EVA/GTR): Influence of the GTR Particle Size and Content on the Cellular Morphology and Density of the Final Foamed Compounds

Addition of different contents of ground tire rubber (GTR) of different particles size in crosslinked-foamed compounds based on low density polyethylene (LDPE)/ethylene vinyl acetate (EVA) was studied. Compounds were made by melt mixing in an internal mixer at 100°C and 60 rpm. Trigonox 145-45B as crosslinking agent, azodicarbonamide (ADC) as chemical blowing agent (CBA) and ZnO/SiO2as foaming co-agents, were used. GTR of 149, 74, and 44 μm particle size was incorporated as “cell nucleating agent”, each particle size at 5, 10, and 20 phr. Morphological parameters such as average cell size (d), cell size distribution and cellular density (NC) were evaluated from images acquired by scanning electron microscopy (SEM). The results obtained from the SEM characterization show a significant reduction ofd, a significance increment onNC, up to 5.81*105to 3.62*107cells/cm3and a better homogenization of the cell size distribution in the foamed compounds with high GTR contents of the smaller particle size.

Production of Thermoplastic Elastomers Based on Recycled PE and Ground Tire Rubber: Morphology, Mechanical Properties and Effect of Compatibilizer Addition

AbstractConstant growth of waste polymers around the world leads to several environmental problems. This is why solutions to reuse these high amounts of materials available must be developed. In this work, highly filled (up to 90 wt.%) recycled polyethylene (R-PE)/ground tire rubber (GTR) thermoplastic elastomers were prepared by extrusion compounding and injection molding. To improve on processability and overall properties, two copolymers (Engage 8180 and Vestenamer 8012) were added as compatibilizers for comparison. SEM results showed that compatibilizer addition changed the blend morphology. In all cases, the mechanical properties in tension and flexion decreased with GTR addition. It was also observed that the addition of a copolymer improved on some properties (such as elongation at break), but Engage 8180 showed better compatibilization effect than Vestenamer 8012 which was confirmed from SEM analysis, while other properties (tensile strength, Young's and flexural modulus) were reduced due to lower GTR and compatibilizer moduli. For impact strength, negligible variation was observed below 40 wt.% GTR. However, the samples did not break for GTR contents above 60 wt.%. Density increased with GTR content, while Shore A and D hardness decreased. Overall, the addition of a compatibilizer mostly enabled to produce compounds at higher GTR contents (above 70 wt.%). From the result obtained, it can be concluded that recycled materials can be used to produce blends with reasonable quality for automotive, packaging and construction applications since the mechanical properties can be optimized via formulation over a very wide range of GTR (0–90 wt.%).

Rotomolding of Foamed and Unfoamed GTR-LLDPE Blends: Mechanical, Morphological and Physical Properties

In this work, a simple method is presented to produce ground tire rubber (GTR) -linear low density polyethylene (LLDPE) compounds and foams via rotational molding. In particular, different GTR concentrations (0 to 50% wt.) were dry-blended with different chemical blowing agent (CBA) content (0 to 1% wt.). From the samples produced, a complete set of characterization was performed in terms of mechanical properties (tensile, flexural and impact), density and morphological properties. The results show that increasing GTR content or CBA content not only decreased both tensile and flexural moduli, but decreased ultimate strength and strain at break. As expected, increasing blowing agent content decreased density. Besides, with respect to impact strength, the value of all samples decreased with the addition of GTR or CBA except for 0.2% wt. CBA of GTR-LLDPE composite foams, which nearly remain at the same level.

Modification of thermal and rheological characteristics of bitumen by waste PET/GTR blends

Waste poly(ethylene terephthalate) (wPET)/ground tire rubber (GTR) blends with variable compositions were applied as low-cost modifiers into bitumen and their performance has been evaluated via morphological, thermal and rheological analyses. Depending on the weight ratio of wPET/GTR, dispersion of single/composite domains of waste polymers in the bitumen has promoted the interaction between bitumen and blend components. Fourier transform infrared spectroscopy confirmed an adequate physical interaction between bitumen and wPET/GTR blend, while morphological analyses suggested deterioration of interaction upon increase of GTR content, which can be ascribed to the cross-linked structure of GTR. Increasing wPET/GTR content led to an improved rheological properties and thermal stability of the bitumen, especially for wPET/GTR blends composed mainly of wPET due to its thermoplastic character. The present work indicates that rheological and thermal properties of bitumen can be satisfactorily modified varying composition and content of wPET/GTR in the bitumen matrix.

Effect of Coupling Agent and Ground Tire Rubber Content on the Properties of Natural Fiber Polymer Composites

AbstractIn this work, high density polyethylene (HDPE)/hemp fiber composites were produced by extrusion compounding followed by injection molding. In particular, the effect of ground tire rubber (GTR) and coupling agent (maleated polyethylene, MAPE) content was studied to modify the mechanical properties of these natural fiber composites (NFC). From the samples produced, a complete characterization was performed including morphology, density, hardness, as well as mechanical properties in tension, flexion, and impact. The results indicate that substantial improvement in NFC impact strength occurred after GTR addition, while tensile and flexural moduli/strengths decreased. On the other hand, the addition of a coupling agent was able to improve adhesion between each phase resulting in better composite properties. Overall, the final properties of the composites represent a balance between elasticity/toughness from GTR and rigidity/strength from hemp and MAPE. From the data obtained, a regression model for different properties is presented to design/control the final properties of these composites.

Investigation of moisture damage resistance of GTR-modified asphalt binder by static contact angle measurements

More than 300 million scrap tires are being generated every year in the United States and their proper disposal has been a major concern from environmental safety and economical point of views. Using these scrap tires as ground tire rubber (GTR) in asphalt mixes is becoming a common practice now a days. A number of research studies have been conducted to characterize the mechanistic properties of GTR modified asphalt. However, a very limited research has been conducted to evaluate their moisture susceptibility, particularly through fundamental science approaches. Moisture damage or stripping, the loss of strength and stiffness of asphalt mixes due to the existence of moisture, of asphalt pavements is one of the major concerns to the state and federal highway agencies for many years. The objective of this research was to evaluate moisture susceptibility of GTR modified asphalt binders through a surface science approach, in which surface free energy (SFF) components were estimated by following the sessile drop method. In the experimental plan, a commonly used performance grade (PG) binder (PG 64-22) modified with different dosages (0%, 10%, 15%, and 20%) of GTR were tested for static contact angles. Three different probe liquids, namely: water, formamide and ethylene glycol were used to determine contact angle with binder samples using an optical contact angle analyzer (OCA) device. The SFE of five different aggregates, namely: sandstone, gravel, granite, basalt and limestone, were used to evaluate the work of adhesion and compatibility ratio (CR). The SFE results of unmodified and modified binders showed that SFE increased due to the addition of GTR in binder. The work of adhesion of a binder aggregate system also increased with an increase of the GTR content when measured in the absence of water, but it decreased gradually in the presence of water. Granite and basalt showed lowest work of adhesion, whereas sandstone showed the highest work of adhesion. The CR data showed that granite and basalt were the most compatible aggregates with GTR modified binders. The CR value also had an increasing trend with an addition of higher GTR content, indicating an improved moisture resistance. The CR values of all asphalt aggregate systems were found to be greater than 1.5 with 20% GTR, indicating “good” moisture susceptibility.