混煉製程對於橡膠奈米複材之動態機械性質影響：奈米結構與輪胎應用之關聯

以二氧化矽取代碳黑作為輪胎填充料可以大幅的減低輪胎的滾動阻力(rolling resistance)進而節省油耗，增加濕地抓地力(wet traction)。但由於二氧化矽的親水性，如何使填充料良好分散於親油性的橡膠中因此成為一個重要的課題。本研究在不改變工業用配方的條件下，以不同的製程製作輪胎之胎面膠(tire tread)，希望能找到最理想的製程以達到濕抓與滾阻性值的最優化，並分析填充料結構如何影響填充料/橡膠複材之機械性質。在本研究中，胎面膠利用雙滾輪混煉機(benbury)製作，以相同的配方但不同的投料順序製程製作樣品。二氧化矽填充料之結構分析方面，胎面膠樣品後續經過冷凍切片處理，並利用原子力顯微鏡 (atomic force microscopy (AFM))之雙振幅(bimodal)模式進行樣品表面粒徑分析，配合穿透式電子顯微鏡 (transmission electron microscopy (TEM)) 觀察實際空間(direct space)的填充料結構。接著利用超小角X光散射 (ultra-small angle X-ray scattering (USAXS)) 分析x-ray動量空間(q-space)中，各階層之聚集結構(hierarchical aggregate structure)與前述實際空間結構之互補分析。最後利用動態機械分析儀 (dynamic mechanical analysis (DMA))進行1.非線性流變分析，確認填充料網絡狀態(Payne effect)以及2.線性流變分析，決定胎面膠之最終濕抓及滾阻性質。另外我們也探討說明混煉過程之混煉參數(如機器扭力、混煉溫度)對於混煉狀態及的影響之關連。以下內容不適合放在abstract。第一: 濕地抓地力性質測量標準為在0°C的能量耗損，在如此低溫下，由於接近填料表面之高分子鏈與填料之間吸附作用力影響，能夠藉由高分子鬆弛(relaxation)提供能量耗損貢獻之高分子為大尺寸結構(>60nm)，又稱為凝聚體(agglomerate)之外之高分子，此部分橡膠也被稱為自由橡膠(free rubber)。降低凝聚體之尺寸將有效的提升濕地抓地力性質。第二:滾動阻力性質測量標準為在60°C之能量耗損，在此高溫下鬆弛產生能量損耗的貢獻者為連接填料基本顆粒(primary particle)與顆粒間之少量高分子，也被稱為玻璃層(glassy layer)，基本顆粒藉由玻璃層連結填料網絡(network)進而形成聚集體(aggregate)。研究發現當聚集體的尺寸極小(<45nm)且緊密度(compacity)大時，推測將提升玻璃層之鬆弛溫度(relaxation temperature) (>60°C)，亦或是聚集體擁有大尺寸(>45nm)且緊密度小，將降低玻璃層之鬆弛溫度(<60°C)。上述兩種結構均能降低滾動阻力節省油耗。另外就工業用高含量填料胎面膠而言，填料結構若呈現區域團聚且良好分布，其性質會遠比整體良好分散與分布之樣品來的良好。製程方面發現油與填料的加入時間點大大影響著結構，其添加順序以及時間點與混煉機之剪切力增減息息相關，實驗發現在第一階段5分鐘的混煉當中，油的加入時間點定在2分鐘且與次要填料碳黑同時加入時，胎面膠會有良好的機械性質。以下歸納包含一次性進料以及分批進料之良好樣品之製程，製成差異在MB階段，其他包括NP、F以及後續熱壓均無不同，分批進料前之時間均為投料時間點: 一次性進料混煉5分鐘 (一次性進料之樣品混煉時間越久分散越佳) 分批進料: 0分鐘:橡膠→1分鐘:白煙、Si69→2.5分鐘:碳黑、氧化鋅、硬脂酸、油→5分鐘:出料。先進行白煙的粉碎及分布，白煙與碳黑分開加入以免耦合反應(coupling reaction)受影響，白煙的粉碎與分散時間長達1.5分鐘，油與碳黑同時加入以防止混煉時的油無法吃入以致打滑的情形。此製程有助於橡膠的大量滲入，樣品填料形貌呈現巨觀良好分布 0分鐘:橡膠→1分鐘:白煙、Si69→1.5分鐘:碳黑、氧化鋅、硬脂酸、油→5分鐘:出料。與前述製程不同的是，此製程白煙之混煉時間縮短至30秒，使得橡膠的少量滲入，樣品填料形貌呈現區域集中，此樣品性質會稍好於上述樣品。 0分鐘:橡膠→1分鐘:白煙、Si69→2分鐘:碳黑、氧化鋅、硬脂酸、油→5分鐘:出料。油的加入時間點做最適化後發現在2分鐘加入油與碳黑會有最好的性質。

關鍵字

胎面膠；雙滾輪混煉機；二氧化矽；小角X光散射；雙振幅原子力顯微鏡；穿透式電子顯微鏡；動態機械分析儀

並列摘要

Tire compounds which use silica as the main property improvement fillers hold the key to enhance fuel efficiency of motor vehicles. The improvement of filler dispersion of carbon black and silica in rubber blends for reducing rolling-resistance (RR) and increasing wet-traction (WT) has been studied for decades. The hierarchical aggregate structure of the reinforcing nanoparticles takes an important role in the final performance of tire tread. Therefore, a series of experiments featuring with different mixing sequences to add the compound fillers in rubbers was conducted in order to study its effects on the filler morphology and mechanical property of the nanocomposites, and provide a fundamental correlation between them. In our present work, the hierarchical filler structure was characterized with a combination of atomic force microscope (AFM), transmission electron microscope (TEM) and small-angle x-ray scattering (SAXS). We used bimodal AFM to derive more precise phase contrast between rubber and filler. Subsequently, from the phase image we conducted a particle analysis method to measure the average size of fillers. By TEM and SAXS measurements, the local filler structure details could be presented. The mechanical properties of the rubber/filler system were evaluated with dynamic mechanical analysis (DMA). The results show that the property of wet traction is related to the large-scale filler morphology (>60nm). To improve property of WT, the mechanism of re-agglomeration by aggregates should be avoided to generate the trapped rubber. However, the property of rolling resistance depends on the relative small-scale filler structure (<60nm), that is the morphology within the aggregates. The thickness of joint rubber shell between primary beads should be either small to construct rigid filler network by nearly direct contact mode which cannot be break down and generate hysteresis loss, or far to form soft filler network which is also unbreakable by cyclic deformation. For tire tread with high filler loadings, the filler morphology characterized with high compacity, which mean the volume fraction of filler within an aggregate, aggregates will be better than the one with low compacity aggregates on the tire performance.For effect of adding sequences, the time spot of filler and oil addition is a crucial point due to the impact on the shear force given by machine and then affect filler morphology. Results show that in the 5 minutes first mixing stage, oil addition time at 2 minutes and with minor filler which is carbon black will give the better mechanical properties of tire tread samples.

並列關鍵字

tire tread ； twin-screw brabender ； silica filled rubber ； small angle X-ray scattering ； transmission electron microscopy

參考文獻

1. Mouri, H. and K. Akutagawa, Improved tire wet traction through the use of mineral fillers. Rubber chemistry and technology, 1999. 72(5): p. 960-968.

2. Krejsa, M. and J. Koenig, A review of sulfur crosslinking fundamentals for accelerated and unaccelerated vulcanization. Rubber chemistry and technology, 1993. 66(3): p. 376-410.

3. Medalia, A., Effect of carbon black on dynamic properties of rubber vulcanizates. Rubber chemistry and Technology, 1978. 51(3): p. 437-523.

5. Medalia, A.I., Heat generation in elastomer compounds: causes and effects. Rubber chemistry and technology, 1991. 64(3): p. 481-492.

6. Futamura, S., Deformation Index—Concept for Hysteretic Energy-Loss Process. Rubber chemistry and technology, 1991. 64(1): p. 57-64.

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混煉製程對於橡膠奈米複材之動態機械性質影響：奈米結構與輪胎應用之關聯

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