Low-Temperature Rheology and Thermoanalytical Investigation of Lubricating Greases: Influence of Thickener Type and Concentration on Melting, Crystallization and Glass Transition
This study investigates crystallization, melting and glass transition of Li- and Ca-12-hydroxystearate greases in relation to the pour point of the corresponding oils. The base oils for the greases are mineral oil, polyalphaolefin, alkylated naphthalene, propylene glycol, and trimellitate. For the m...
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| Format: | Article |
| Language: | English |
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MDPI AG
2021-12-01
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| Series: | Lubricants |
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| Online Access: | https://www.mdpi.com/2075-4442/10/1/1 |
| _version_ | 1818061117024370688 |
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| author | Andreas Conrad Annika Hodapp Bernhard Hochstein Norbert Willenbacher Karl-Heinz Jacob |
| author_facet | Andreas Conrad Annika Hodapp Bernhard Hochstein Norbert Willenbacher Karl-Heinz Jacob |
| author_sort | Andreas Conrad |
| collection | DOAJ |
| description | This study investigates crystallization, melting and glass transition of Li- and Ca-12-hydroxystearate greases in relation to the pour point of the corresponding oils. The base oils for the greases are mineral oil, polyalphaolefin, alkylated naphthalene, propylene glycol, and trimellitate. For the mineral oil-based greases the crystallization temperature <i>T</i><sub>c</sub> increases and the melting temperature <i>T</i><sub>m</sub> decreases upon addition of thickener. The pour point of the mineral oil then is 3 K below <i>T</i><sub>c</sub> and does not properly define the lowest application temperature for mineral oil (MO) based greases. Both thickeners induce a small increase of the glass transition temperature (1–3 K) of the synthetic oils polyalphaolefin, alkylated naphthalene, propylene glycol. The pour point of the base oils correlates well with the onset of the glass transition in the corresponding grease indicated by a sharp increase in grease viscosity. Pure trimellitate with unbranched alkyl chains does not crystallize upon cooling but shows noticeable supercooling and cold crystallization. As the percentage of thickener in corresponding greases increases, more oil crystallizes upon cooling 20 K above the crystallization temperature of the trimellitate without thickener (−44 °C). Here, the thickener changes the crystallization behavior from homogeneous to heterogeneous and thus acts as a crystallization nucleus. The pour point of the base oil does not provide information on the temperature below which the greases stiffen significantly due to crystallization. |
| first_indexed | 2024-12-10T13:43:12Z |
| format | Article |
| id | doaj.art-4e3e67f620a84902bec7cb4e168a5f01 |
| institution | Directory Open Access Journal |
| issn | 2075-4442 |
| language | English |
| last_indexed | 2024-12-10T13:43:12Z |
| publishDate | 2021-12-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Lubricants |
| spelling | doaj.art-4e3e67f620a84902bec7cb4e168a5f012022-12-22T01:46:34ZengMDPI AGLubricants2075-44422021-12-01101110.3390/lubricants10010001Low-Temperature Rheology and Thermoanalytical Investigation of Lubricating Greases: Influence of Thickener Type and Concentration on Melting, Crystallization and Glass TransitionAndreas Conrad0Annika Hodapp1Bernhard Hochstein2Norbert Willenbacher3Karl-Heinz Jacob4Applied Chemistry, Nuremberg Institute of Technology Georg Simon Ohm, 90489 Nuremberg, GermanyInstitute of Mechanical Process Engineering and Mechanics, Karlsruhe Institute of Technology, 76131 Karlsruhe, GermanyInstitute of Mechanical Process Engineering and Mechanics, Karlsruhe Institute of Technology, 76131 Karlsruhe, GermanyInstitute of Mechanical Process Engineering and Mechanics, Karlsruhe Institute of Technology, 76131 Karlsruhe, GermanyApplied Chemistry, Nuremberg Institute of Technology Georg Simon Ohm, 90489 Nuremberg, GermanyThis study investigates crystallization, melting and glass transition of Li- and Ca-12-hydroxystearate greases in relation to the pour point of the corresponding oils. The base oils for the greases are mineral oil, polyalphaolefin, alkylated naphthalene, propylene glycol, and trimellitate. For the mineral oil-based greases the crystallization temperature <i>T</i><sub>c</sub> increases and the melting temperature <i>T</i><sub>m</sub> decreases upon addition of thickener. The pour point of the mineral oil then is 3 K below <i>T</i><sub>c</sub> and does not properly define the lowest application temperature for mineral oil (MO) based greases. Both thickeners induce a small increase of the glass transition temperature (1–3 K) of the synthetic oils polyalphaolefin, alkylated naphthalene, propylene glycol. The pour point of the base oils correlates well with the onset of the glass transition in the corresponding grease indicated by a sharp increase in grease viscosity. Pure trimellitate with unbranched alkyl chains does not crystallize upon cooling but shows noticeable supercooling and cold crystallization. As the percentage of thickener in corresponding greases increases, more oil crystallizes upon cooling 20 K above the crystallization temperature of the trimellitate without thickener (−44 °C). Here, the thickener changes the crystallization behavior from homogeneous to heterogeneous and thus acts as a crystallization nucleus. The pour point of the base oil does not provide information on the temperature below which the greases stiffen significantly due to crystallization.https://www.mdpi.com/2075-4442/10/1/1lubricating greaseheterogeneous crystallizationglass transitionrheologydifferential scanning calorimetry (DSC) |
| spellingShingle | Andreas Conrad Annika Hodapp Bernhard Hochstein Norbert Willenbacher Karl-Heinz Jacob Low-Temperature Rheology and Thermoanalytical Investigation of Lubricating Greases: Influence of Thickener Type and Concentration on Melting, Crystallization and Glass Transition Lubricants lubricating grease heterogeneous crystallization glass transition rheology differential scanning calorimetry (DSC) |
| title | Low-Temperature Rheology and Thermoanalytical Investigation of Lubricating Greases: Influence of Thickener Type and Concentration on Melting, Crystallization and Glass Transition |
| title_full | Low-Temperature Rheology and Thermoanalytical Investigation of Lubricating Greases: Influence of Thickener Type and Concentration on Melting, Crystallization and Glass Transition |
| title_fullStr | Low-Temperature Rheology and Thermoanalytical Investigation of Lubricating Greases: Influence of Thickener Type and Concentration on Melting, Crystallization and Glass Transition |
| title_full_unstemmed | Low-Temperature Rheology and Thermoanalytical Investigation of Lubricating Greases: Influence of Thickener Type and Concentration on Melting, Crystallization and Glass Transition |
| title_short | Low-Temperature Rheology and Thermoanalytical Investigation of Lubricating Greases: Influence of Thickener Type and Concentration on Melting, Crystallization and Glass Transition |
| title_sort | low temperature rheology and thermoanalytical investigation of lubricating greases influence of thickener type and concentration on melting crystallization and glass transition |
| topic | lubricating grease heterogeneous crystallization glass transition rheology differential scanning calorimetry (DSC) |
| url | https://www.mdpi.com/2075-4442/10/1/1 |
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