開發適用於電動車之綠色輪胎：探討二氧化矽的層次聚集結構及新型添加劑提升動態性能之研究

Abstract

在環保及節能減碳日益重要的現今，電動車(electric vehicle或簡稱EV)的發展已成為全球交通運輸之重要趨勢。然而電動車對於輪胎的性能需求更高，因此，本研究為開發更高性能適用於電動車之二氧化矽填充胎面膠(tread)複合材料。 本研究主要分為兩個部分：(1)藉由分析立安東公司所生產之高比表面積與中比表面積二氧化矽顆粒粉末及懸浮水溶液樣品之多層次結構(hierarchical structure)，以了解二氧化矽自然狀態之開放結構與其混鍊於橡膠樣品中之關聯性，並分析開放結構對於輪胎動態機械性能的影響。(2)利用實驗室級小型混鍊機(0.2L)，將橡膠材料與二氧化矽進行混合，並且加入具備有親水性PEO (poly ethylene oxide)高分子做為新型界面改質劑，並分析改質後之二氧化矽對於多層次結構的影響與其機械性能的變化。 本研究的第一部分主要是分析多層次二氧化矽顆粒粉末及懸浮水溶液樣品之結構，並且觀察二氧化矽在橡膠系統中結構與其機械性能。我們是以新竹同步輻射研究中心(NSRRC-TPS25A1)之超小角度X光散射(USAXS)進行實驗，從散射數據中獲得二氧化矽粉末與懸浮液之基本顆粒大小(primary particle size)以及碎型維度(fractal dimension, Df)，此外我們亦可以從散射數據中獲得二氧化矽顆粒在橡膠系統中之階級性結構：基本顆粒大小(primary particle size)、碎型維度(fractal dimension, Df)以及二氧化矽聚集體大小(cluster size)。並且藉由碎型維度的大小可以告訴我們二氧化矽顆粒在自然狀態下的開放結構，若Df越接近3為越緊密，反之，若Df越接近1則越鬆散。而胎面橡膠之機械性能我們是以動態機械分析儀(dynamic mechanical analysis)測量所得之tanδ、儲存模數(storage modulus, G’)及損失模數(loss modulus, G”)以預測胎面橡膠之抓地力(wet grip, WG)，滾動阻力(rolling resistance, RR)以及剛性(stiffness, S)。 從實驗結果我們發現高比表面積二氧化矽粉末之碎型維度(~1.5)比中比表面積(~1.7)來的小，因此其聚集結構屬於較為鬆散之結構，也因為較鬆散之結構使其在混鍊的過程中更容易使橡膠高分子與二氧化矽聚集體之內部進行接觸，進而得到分散較好，顆粒較小之結果，而較小之聚集體會得到更少量之圍困橡膠(occluded rubber)進而提升抓地力(WG)，也會減少玻璃態橡膠(confined glassy rubber)的形成進而降低滾動阻力(RR)。 而本研究的第二部分主要是分析加入PEG2000作為介面改質劑之胎面橡膠並且比較加入傳統矽烷偶合劑(silane coupling agent)-Si69 (bis(triethoxysilylpropyl) tetrasulfide或簡稱TESPT)之胎面膠之輪胎性質差異。我們是以新竹同步輻射研究中心(NSRRC-TPS25A1)之超小角度X光散射(USAXS)進行實驗，從中我們可以獲取二氧化矽顆粒在橡膠系統中之階級性結構：基本顆粒大小(primary particle size)、碎型維度(fractal dimension, Df)、二氧化矽聚集體大小(cluster size)以及二氧化矽聚集體之平均距離(static correlation length)，並結合穿透式電子顯微鏡(transmission electron microscope, TEM)以了解其碎型結構。而胎面橡膠之機械性能我們是以動態機械分析儀(dynamic mechanical analysis)測量所得之tanδ、儲存模數及損失模數以預測胎面橡膠之抓地力(WG)，滾動阻力(RR)以及剛性(S)。除此之外，我們也會測量胎面橡膠之潘恩效應(Payne Effect)以了解二氧化矽與橡膠間之相互作用力。 從實驗結果我們發現隨著PEG2000的量增加二氧化矽聚集體會變大，因為EO鏈段會與silica本身之silanol group 形成氫鍵，幫助二氧化矽更加聚集形成較大之聚集體。而因PEG2000形成較大之聚集體會形成較多量之圍困橡膠(occluded rubber)使玻璃轉移溫度(Tg)上升而提升抓地力(WG)之效能，除此之外，也因為聚集體是因氫鍵聚集而成，在給予作用力時會因氫鍵而產生”滑動”使儲存模數下降、損失模數上升，而提升抓地力(WG)。也因為PEG2000會附著在二氧化矽表面，阻礙小尺度(~1nm)下之玻璃態橡膠的形成以降低失模數，因而使滾動阻力(RR)下降。PEG2000改質過後之二氧化矽胎面橡膠之性能皆高於傳統市面上的輪胎配方，且大幅降低輪胎之製造成本，相信本實驗方向與結果會影響輪胎產業使其往更好的方向邁進。

In today's world, with a focus on environmental protection and energy efficiency, the development of electric vehicles (EVs) has become an important trend in global transportation. To meet the higher performance requirements of EVs, this study aims to develop high-performance silica-filled tread rubber compounds suitable for electric vehicles. The research is divided into two parts. The first part examines the connection between the aggregation structure of silica and the performance of the corresponding silica-filled tread compounds. This is done by analyzing the structures of silica powders with either high or medium specific surface areas (SSA) produced by OSC Company and their aqueous suspension solution. In the second part, lab-scale internal mixers are used to prepare silica-filled tread compounds. Additionally, a hydrophilic polyethylene glycol (PEG) polymer is introduced as a new interface modifier. The effect of the modified silica addition on the hierarchical filler structure on the dynamic performance of the tread compounds is then analyzed. Ultra-small-angle X-ray scattering (USAXS) experiments are conducted to obtain the primary particle size, fractal dimension, and cluster size of silica in the tread compounds. The fractal dimension reflects the openness of silica particles, with a value close to 3 indicating a compact structure and a value close to 1 indicating an open structure. Dynamic mechanical analysis is used to measure tanδ, storage modulus (G'), and loss modulus (G") to predict the wet grip (WG), rolling resistance (RR), and stiffness (S) of the tread rubber. The experimental results show that silica powder with a high SSA has a smaller fractal dimension (Df ~ 1.5) compared with higher Df (Df ~ 1.7) for medium SSA silica, indicating a more open structure (loosed-branched). This open structure facilitates the good dispersion of rubber polymer with silica, resulting in smaller cluster size and reduced occluded rubber and confined glassy rubber, thereby improving wet grip (WG) and reducing rolling resistance (RR). On the other hand, by adding PEG2000 as a modifier, the silica aggregates become larger compared to the traditional silane coupling agent (Si69). Since PEG2000 can induce "sliding effect" between silica particles, it reduces the storage modulus (G') while the clusters become larger and hinders the formation of glassy rubber, thereby improving wet grip (WG) and reducing rolling resistance (RR). In summary, the experimental results of this study demonstrate that high specific surface area silica powder with an open structure, as well as silica-filled tread rubber incorporating a hydrophilic interface modifier, can provide excellent wet grip (WG) and reduced rolling resistance (RR), making them suitable for high-performance applications such as electric vehicles.