以界面活性劑取代矽烷耦合劑對二氧化矽填充胎面膠性質影響之研究

Abstract

現代的汽車對輪胎性能的要求越來越高，也對節省能源及環境保護非常重視。目前小客車輪胎胎面多以加入二氧化矽奈米顆粒來提升性能，但是親水性的二氧化矽在疏水性的橡膠中會傾向聚集，會導致填充二氧化矽的效益變差，因此會加入矽烷耦合劑作為界面改性劑來降低二氧化矽的親水性。由於矽烷耦合劑價格較高，且使用時容易對環境造成汙染，所以本研究參考矽烷耦合劑的結構與功能使用同樣具有親水性與疏水性結構，且較便宜與環保的界面活性劑取代矽烷耦合劑作為界面改性劑。本研究使用了三種常見的非離子性界面活性劑，Triton X、Tween與Span。本研究主要探討改變胎面膠填充之二氧化矽的界面改性劑對二氧化矽顆粒之分散以及胎面膠動態機械性能的影響。輪胎的性能主要探討濕地抓地力(wet grip)、滾動阻力(rolling resistance)及剛性(stiffness)。並利用小角度X光散射(SAXS)以及潘恩效應(payne effect)分析胎面膠內二氧化矽的分散聚集結構對動態機械性能的關聯。 我們先使用了Triton X系列來確認界面活性劑對胎面膠的動態機械性能的提升確實有效。我們發現添加界面活性劑能有效分散二氧化矽。我們認為這是因為界面活性劑的親水基會與二氧化矽表面的矽烷醇基形成氫鍵，另一端的疏水基與橡膠親和力高，所以在受到應力時界面活性劑會與二氧化矽及橡膠產生摩擦損耗，因此提高濕地抓地力。而且界面活性劑還有阻擋玻璃態橡膠產生的效果，因此能降低滾動阻力。界面活性劑對二氧化矽的分散效果不如Si69，因此添加界面活性劑的胎面膠剛性高於添加Si69之胎面膠。本研究亦利用Triton X系列的界面活性劑，研究疏水基的數量對胎面膠的動態機械性質的影響，實驗結果顯示，界面活性劑疏水基越多摩擦損耗越多，濕地抓地力上升。對二氧化矽的分散效果也越好，因此剛性越低。以及阻擋玻璃態橡膠產生效果也越強，因此滾動阻力越低。 本研究亦利用Tween與Span來研究界面活性劑親水基與疏水基造成的影響。實驗結果顯示，界面活性劑疏水基越長分散效果越好，阻擋玻璃態橡膠產生效果也越好，能有效提高濕地抓地力與降低滾動阻力。界面活性劑疏水基上若具有雙鍵時，能夠與彼此產生交聯，提高二氧化矽間作用力，並能有效提升胎面膠的剛性並降低滾阻，同時擁有較好的化學穩定性，但同時也降低濕地抓地力。若界面活性劑親水基上可產生氫鍵數量較多，受到應力時產生的摩擦損耗較大，同時阻擋玻璃態橡膠效果也越好，因此提高濕地抓地力與降低滾動阻力。 最後根據本研究的結果，我們認為選擇界面活性劑作為二氧化矽界面改性劑的原則，應選擇親水基可產生氫鍵數量較多且立體障礙較小的結構，以及疏水基較長的界面活性劑，可以同時提升濕地抓地力、剛性及降低滾動阻力，提升車輛行駛時的安全性及提高能源使用效率，並達到降低成本以及保護環境的目標。

Modern automobiles increasingly demand higher performance from tires, with a strong emphasis on energy saving and environmental protection. Currently, nano-sized silica particles are often added to passenger car tire tread to enhance its performance. However, hydrophilic silica tends to aggregate in hydrophobic rubber, reducing the effectiveness of silica filling. Therefore, silane coupling agents are added as interfacial modifiers to reduce the hydrophilicity of silica. Due to the high cost of silane coupling agents and their potential environmental pollution, this study explores the use of surfactants that are cheaper and more environmental friendly as replacements for silane coupling agents. This research uses three common nonionic surfactants: Triton X, Tween, and Span. The main focus is on the effect of changing the interfacial modifier for silica-filled tread on the dispersion of silica particles and the dynamic mechanical properties of the tread rubber. Tire performance of the tread is evaluated in terms of wet grip, rolling resistance, and stiffness. Small-angle X-ray scattering (SAXS) are used to analyze the dispersion and aggregation structure of silica within the tread rubber and its dynamic mechanical properties. We first used the Triton X series to confirm the effectiveness of surfactants in improving the dynamic mechanical properties of tread rubber. We found that adding surfactants effectively helps silica dispersion. We believe this is because the hydrophilic groups of the surfactant form hydrogen bonds with the silanol groups on the silica surface, while the hydrophobic groups have a high affinity with rubber. Therefore, under stress, the surfactant generates frictional losses with both silica and rubber, increasing wet grip. Additionally, surfactants prevent the formation of glassy rubber between silica nanoparticles, reducing rolling resistance of the tread. The dispersion effect of surfactants on silica is not as good as that of Si69, the most popular silane coupling agent used for tread. However, stiffness of tread with added surfactants is higher than that with Si69. This study also explores the effect of the number of hydrophobic groups in Triton X series surfactants on the dynamic mechanical properties of tread rubber. The results show that the more hydrophobic groups a surfactant has, the more frictional losses it generates, increasing wet grip. The better dispersion of silica also results in less glassy rubber, further reducing rolling resistance. This study also examines the effects of hydrophilic and hydrophobic groups in Tween and Span surfactants. The results show that longer hydrophobic groups improve silica dispersion and reduce glassy rubber formation, effectively increasing wet grip and reducing rolling resistance. If the hydrophobic groups of surfactants have double bonds, they may crosslink with each other, increasing the interactions between silica particles. This can effectively enhence the stiffness of the tread rubber and reduce rolling resistance, while also providing better chemical stability. However, this also reduces wet grip. If the hydrophilic groups of surfactants can form more hydrogen bonds with silica, they generate greater frictional losses under stress and better prevent glassy rubber formation, thus increasing wet grip and reducing rolling resistance. Finally, based on the results of this study, we suggest that selecting surfactants as interfacial modifiers for silica reinforced tread should prioritize structures with hydrophilic groups capable of forming more hydrophilic bonds with silica nanoparticles, along with longer hydrophobic groups. This can simultaneously enhance wet grip, stiffness, and reduce rolling resistance, improving vehicle safety and energy efficiency while achieving cost reduction and environmental protection goals.