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全球每年有1/3~1/2的能源以各种形式消耗在摩擦上,不仅造成了能源浪费与经济损失,甚至会引起生产事故[1−2]。使用合适的润滑剂可以在相互作用的摩擦表面上形成油膜,降低摩擦与磨损,减少能源的浪费,延长机械使用寿命。润滑脂是一种将稠化剂分散到基础油中进行增稠得到的半固态润滑剂产品,具有黏度大、耐压性强、密封性好以及减震降噪等优点,在钢铁、化工、采矿以及冶金等行业得到了广泛的应用[3−5]。现在市面上的润滑脂是以不可再生的石化资源为原料生产的。随着全球石化资源的日益枯竭以及开采和使用过程中带来的环境污染问题,以可再生的生物基材料为原料制备润滑脂近年来成为了研究热点[6−8]。润滑脂主要由基础油(65%~95%)、稠化剂(5%~35%)以及添加剂(0~10%)组成。目前,关于生物基润滑脂的相关研究尚处于起步阶段,主要在基础油的开发,通常的做法是以植物油代替矿物油制备生物基润滑脂。用于制备润滑脂的常见植物油包括蓖麻油[9−11],大豆油[12−14]和菜籽油[15−17]等。RAWAT等[18]以蓖麻油为基础油制备了锂基润滑脂,并用二硫化钼(MoS2)和氧化石墨烯纳米片作为添加剂,发现二维片状纳米材料可以显著改善蓖麻油基润滑脂的摩擦学性能。LIU等[13]以环氧大豆油为基础油,锂皂和三乙醇铵聚皂的混合物为稠化剂制备了润滑脂,发现聚皂结构中的交联可以提供润滑脂更高的抗变形能力,并且摩擦系数显著低于未添加聚皂的润滑脂。但目前关于润滑脂生物基稠化剂的研究还较少,且以金属皂和聚脲稠化剂为主[19−22]。金属皂和聚脲稠化剂的价格不稳定,限制了润滑脂行业的可持续发展。在“碳达峰”和“碳中和”的背景下,纤维素凭借可再生可降解、绿色环保以及储量丰富等优点受到了人们的青睐[23−25]。本研究以天然纤维素和二氧化硅(SiO2)为稠化剂,利用硅羟基与纤维素羟基通过氢键物理交联制备了一种新型生物基润滑脂,并对其理化性质、流变特性以及摩擦性能进行了测试,旨在对生物降解型润滑脂的发展进行补充和完善,实现环保型润滑脂的可持续发展。
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图1A~B为气相SiO2和纤维素的SEM照片,气相SiO2为纳米颗粒状,比表面积大,有利于与基础油的充分接触,具有良好的增稠作用。纤维素呈现微米级的短棒状,其表面的羟基可与SiO2的硅羟基形成氢键交联网络结构(图1C),改善润滑脂的胶体安定性,提升润滑脂的黏温性能和分油率。
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润滑脂锥入度、分油率以及滴点等相关理化性质见表1,3种润滑脂的外观如图2所示。纤维素/SiO2润滑脂的分油率仅为0.6%,较SiO2润滑脂的3.6%有显著下降(P<0.05)。微量的分油可以保持设备润滑,对润滑有利;但过度的分油则会使润滑脂变稠变硬,破坏胶体结构,使润滑脂失去润滑作用,不能满足润滑要求。分油率测试结果表明:纤维素与SiO2的氢键作用赋予了润滑脂优异的胶体安定性。此外,在滴点测试中,纤维素润滑脂和SiO2润滑脂没有滴点(即330 ℃下无滴点),而纤维素/SiO2润滑脂的滴点为327 ℃,这说明纤维素的引入改善了SiO2润滑脂在高温下易失去流动性的缺点。
表 1 润滑脂的理化性质
Table 1. Physicochemical properties of greases
样品 SiO2添加量/% 纤维素添加量/% 锥入度(0.1 mm) 稠度等级 分油率/% 滴点/℃ 纤维素润滑脂 0 41.3 290 ± 5 a 2# 0.0 ± 0.0 c − SiO2润滑脂 5.2 0 282 ± 2 a 2# 3.6 ± 0.4 a − 纤维素/SiO2润滑脂 2.4 26.2 284 ± 6 a 2# 0.6 ± 0.1 b 327 说明:锥入度和分油率数据为平均值±标准差。同列不同字母表示不同润滑脂间差异显著(P<0.05)。−表示无。 -
图3为3种润滑脂在剪切速率为300 s−1下的黏度-温度曲线。在0 ℃以下时,纤维素润滑脂的黏度出现了剧烈的抖动,其原因可能是纤维素润滑脂在此温度下发生了冻结,说明纯纤维素润滑脂的低温性能较差。其中,纯纤维素和SiO2润滑脂分别在80 和60 ℃发生黏度升高的现象,这是因为稠化剂与基础油发生了溶胶-凝胶转变,导致黏度升高。纤维素/SiO2润滑脂在温度扫描过程中,其黏度在90 ℃以内始终高于纯纤维素和纯SiO2润滑脂,显示出了优异的黏温性能。
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图4为3种润滑脂的应变扫描图。可以看出,应变值较小时,润滑脂的储能模量和损耗模量基本维持在一个恒定值,应变超过一定值时(A点),储能模量和损耗模量的线性规律不再保持,两者变化趋于相交。A点为润滑脂线性黏弹区和非线性黏弹区的临界点,其对应的应变为临界应变[26]。储能模量和损耗模量相交的B点称为润滑脂的流动点[27],此时润滑脂的储能模量和损耗模量相等。应变继续增加,损耗模量就开始大于储能模量,表示润滑脂黏性流动所消耗的能量大于弹性变形所存储的能量,呈流动状态[28]。从图4可以看出,纤维素/SiO2润滑脂的流动点所对应的应变值最大,表明润滑脂承受更大的应变时才能由固态转变为流动态。
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触变环是剪切速率按先增大后减小的规律变化时所形成的剪切应力变化曲线围成的封闭环。表明润滑脂结构的破坏速度显著高于恢复能力,即润滑脂的可恢复性较差。反之,表明润滑脂结构被破坏后的可恢复性越好。图5为3种润滑脂在25 ℃下的触变环曲线。可以看到,纤维素/SiO2润滑脂的面积为17 636 Pa·s−1,小于纯纤维素润滑脂的72 250 Pa·s−1和SiO2润滑脂的21 998 Pa·s−1,表明纤维素与SiO2复配后,润滑脂受剪切作用后的结构恢复性能得到了提升。
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图6A为纤维素、SiO2以及纤维素/SiO2润滑脂黏度的剪切速率扫描图。随着剪切速率的增加,润滑脂的黏度下降,呈现出剪切变稀的特征,并且纤维素和纤维素/SiO2润滑脂的黏度高于SiO2润滑脂。图6B为3种润滑脂剪切应力随剪切速率的变化关系,3种润滑脂的剪切应力随着剪切速率的增加而增加,且纤维素/SiO2润滑脂的剪切应力在剪切过程中是始终高于纯SiO2润滑脂的,表明其能承受的剪切应力更大。
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由表2可见:纤维素/SiO2润滑脂的摩擦系数和摩擦力平均值为0.078和3.798 N,显著低于纯纤维素润滑脂的0.093和4.578 N以及SiO2润滑脂的0.095和4.664 N(P<0.05)。其可能的减摩机制如图7所示,相比于纯纤维素润滑脂和SiO2润滑脂,纤维素/SiO2润滑脂在摩擦过程中受剪切力作用,纤维素与SiO2颗粒之间发生相对移动,进而发挥了协效作用,提高了润滑脂的减摩性能。但纤维素/SiO2润滑脂的磨斑直径显著高于纤维素润滑脂和SiO2润滑脂(P<0.05),这可能是因为纤维素与SiO2在相对运动摩擦表面会两相分离,在摩擦副表面发生团聚,产生了更大的磨损体积。
表 2 润滑脂的摩擦性能表
Table 2. Friction performance of 3 types of greases
润滑脂样品 摩擦系数 摩擦力/N 磨斑直径/mm 纤维素 0.093 ±0.020 a 4.578 ± 0.200 a 0.633 ± 0.030 c SiO2 0.095 ±0.030 a 4.664 ± 0.300 a 0.744 ± 0.040 b 纤维素/SiO2 0.078 ±0.030 b 3.798 ± 0.200 b 0.848 ± 0.040 a 说明:数据为平均值±标准差。同列不同字母表示不同润滑脂间差异显著(P<0.05)。
Preparation and properties of cellulose/SiO2 grease
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摘要:
目的 旨在以可再生的天然纤维素为稠化剂制备可持续发展的环保型润滑脂产品。 方法 分别以纯纤维素、气相二氧化硅(SiO2)以及纤维素/SiO2为稠化剂制备了3组稠度等级为2#的润滑脂产品,并对其进行了锥入度测试、滴点测试、分油率测试、流变性能测试以及摩擦学性能测试。 结果 SiO2表面的硅羟基与纤维素羟基可以发生氢键作用,改善了润滑脂的理化性质、流变性能以及摩擦学性能。理化性质方面:相较于纤维素润滑脂和SiO2润滑脂,纤维素/SiO2润滑脂具有较低的分油率,胶体安定性得到提高,并且在327 ℃时出现了滴点,改善了SiO2润滑脂在高温下易失去流动性的缺点。流变特性方面:纤维素/SiO2润滑脂的黏温性能和抗剪切能力较SiO2润滑脂得到了提高,且剪切破坏后的结构恢复速度更快,结构体系更加稳定。摩擦学性能方面:纤维素/SiO2润滑脂相较于纤维素润滑脂和SiO2润滑脂,其减摩性能得到了提高,具有最低的摩擦系数和摩擦力。 结论 获得了具有实用前景的纤维素基润滑脂,符合国家低碳及可持续发展战略。图7表2参32 Abstract:Objective With the increasing depletion of petrochemical resources and the environmental pollution caused by the extraction and use process, sustainable and environmentally friendly lubricating grease products have been prepared using renewable natural cellulose as a thickener. Method Three sets of lubricating grease products with a viscosity grade of 2# were prepared using pure cellulose, gas-phase SiO2, and cellulose/SiO2 as thickeners, and their penetration, drop point, oil separation rate, rheological properties, and tribological properties were tested. Result The silicon hydroxyl groups on the surface of SiO2 can undergo hydrogen bonding crosslinking with the hydroxyl groups of cellulose, improving the physicochemical properties, rheological properties, and tribological properties of lubricating grease. In terms of physicochemical properties, compared to cellulose grease and SiO2 grease, cellulose/SiO2 grease has a lower oil separation rate and improved colloidal stability; And a drop point appeared at 327 ℃, which improved the fluidity at high temperatures of silicone grease. In terms of rheological properties, the viscosity temperature performance and shear resistance of cellulose/SiO2 lubricating grease have been improved, and the structural recovery speed is faster than that of silicone grease, and the structural system is more stable. In terms of tribological performance, compared to cellulose grease and SiO2 grease, cellulose/SiO2 grease has an improved friction reduction effect, with the lowest friction coefficient and friction force. Conclusion A cellulose based grease with practical prospects has been obtained, which is in line with the national low-carbon and sustainable development strategy. [Ch, 7 fig. 2 tab. 32 ref.] -
Key words:
- lubricating grease /
- cellulose /
- rheology /
- friction /
- modification
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表 1 润滑脂的理化性质
Table 1. Physicochemical properties of greases
样品 SiO2添加量/% 纤维素添加量/% 锥入度(0.1 mm) 稠度等级 分油率/% 滴点/℃ 纤维素润滑脂 0 41.3 290 ± 5 a 2# 0.0 ± 0.0 c − SiO2润滑脂 5.2 0 282 ± 2 a 2# 3.6 ± 0.4 a − 纤维素/SiO2润滑脂 2.4 26.2 284 ± 6 a 2# 0.6 ± 0.1 b 327 说明:锥入度和分油率数据为平均值±标准差。同列不同字母表示不同润滑脂间差异显著(P<0.05)。−表示无。 表 2 润滑脂的摩擦性能表
Table 2. Friction performance of 3 types of greases
润滑脂样品 摩擦系数 摩擦力/N 磨斑直径/mm 纤维素 0.093 ±0.020 a 4.578 ± 0.200 a 0.633 ± 0.030 c SiO2 0.095 ±0.030 a 4.664 ± 0.300 a 0.744 ± 0.040 b 纤维素/SiO2 0.078 ±0.030 b 3.798 ± 0.200 b 0.848 ± 0.040 a 说明:数据为平均值±标准差。同列不同字母表示不同润滑脂间差异显著(P<0.05)。 -
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https://zlxb.zafu.edu.cn/article/doi/10.11833/j.issn.2095-0756.20230492