聚醯胺/聚苯醚聚摻合物機械性質、破壞韌性及破壞機制之研究

Abstract

PA6/PPE聚摻合系統在實際應用上經常遭遇兩大問題：熱力學不相容性及耐衝擊強度低。嘗試加入不同種類的反應型相容劑來改善聚摻合物的相容問題，其中以SMA和TGDDM兩種的效果較佳。此兩者會於聚摻合的過程中，分別在相界面上形成PA6-g-SMA及PA6-co-TGDDM-co-PPE共聚物成為真正的相容劑，有效地降低聚摻合物的界面張力、減少分散相的凝集現象及減小分散相的粒徑大小，進而提升聚摻合物的機械性質。在SMA及TGDDM增容的PA6/PPE聚摻合系統中，加入不同種類的彈性體來改善其耐衝擊強度低的缺陷，其中以G1651的效果最好。整體而言，以PA6/PPE/SMA/G1651聚摻合系統具有最佳的熱變形溫度、機械性質及耐衝擊強度；而其韌-脆性轉移的臨界彈性體含量為15 phr且在破壞的過程中，能量消耗機制隨著彈性體含量增加而產生更大的作用，促使其耐衝擊強度大幅地提升。 PA6/PPE/SMA/G1651聚摻合系統的破壞行為模式大致可分為三大類：脆性、半韌性及韌性。在低應變速率及平面應變條件下，脆性或具有小規模降伏的聚摻合物，其KIC和GIC值隨著彈性體含量增加而增加，但不受試片厚度的影響。對於韌性聚摻合物而言，根據修正之ASTM E813-89標準方法、遲滯能量法及破壞基本功法所測得的JIC及we值來表示其破壞韌性，這些平面應力破壞韌性值彼此相當地接近且不受試片厚度的影響，因此這三種方法可應用於評估低應變速率下，韌性高分子聚摻合物的臨界破壞韌性。而ASTM E813標準方法中的Tm值及破壞基本功法中的bwp值皆可當作材料阻止裂縫成長能力的評估準則。在高應變速率及固定試片厚度條件下，PA6/PPE/SMA/G1651韌性聚摻合物的we值隨著測試溫度及彈性體含量增加而增加。對於符合破壞基本功法條件限制的聚摻合物，其塑化變形區的深度與繫帶長度成線性關係，因此證明破壞基本功法適用於韌性高分子聚摻合物的破壞韌性之特性評估。 藉由SEM觀察PA6/PPE/SMA/G1651聚摻合系統，其破壞行為主要由連續相剪切降伏及分散相拔出機制互相競爭所控制；韌性破壞行為是由剪切降伏所主導，脆性破壞行為是由拔出機制所主導。利用TEM觀察及拉伸膨脹測試得知，韌性聚摻合物的破壞機制順序為連續相和分散相首先產生小幅度的變形，接著包埋於分散相PPE中的G1651顆粒被拉伸變形；而當彈性體周圍的應力-應變狀態達到其臨界值時，彈性體會產生空腔現象，進而誘導材料大量剪切降伏作用而產生大規模的變形。

There exist two main problems in the applications of PA6/PPE blends, thermodynamic incompatibility and low impact strength. SMA and TGDDM have been demonstrated as effective and efficient compatibilizers in the PA6/PPE blends. Reduction of interfacial tension, coalescence and the dispersed phase domains by PA6-g-SMA or PA6-co-TGDDM-co-PPE formed at the interface that is able to function as true compatibilizer results in mechanical property improvement. In the SMA- and TGDDM-compatibilized PA6/PPE blending systems, G1651, SEBS elastomer, shows a great ability to improve the impact strength. To sum up, the PA6/PPE/SMA/G1651 blends have excellent thermal properties, mechanical properties and impact strength. There exists a critical elastomer content, 15phr G1651, for the ductile-brittle transition and energy dissipation increases with increasing elastomer content during the fracture process. The fracture behavior of the PA6/PPE/SMA/G1651 blends can divide into three categories : brittle, semi-ductile and ductile. Under slow strain rate, KIC and GIC values of brittle blends increase with increasing elastomer content, but independent of specimen thickness. Plane-stress fracture toughness, JIC and we, of ductile blends according to modified ASTM E813-89 method, hysteresis energy method and essential work of fracture method are comparable and invariant with specimen thickness. These three methods are acceptable to evaluate the critical fracture toughness for the toughened polymer blends. Moreover, Tm and we values can characterize the crack propagation resistance of polymer blends. Under high strain rate impact tests, we value increases with the increase of testing temperature and elastomer content. The depth of the plastic deformation zone increases linearly with the ligament length for those blends that exhibit ductile failure, hence supporting the essential work of fracture method for impact toughness characterization. Morphologically, there are two fracture mechanisms, PA6 matrix shear yielding and pullout of second phase dispersed particles of PPE, that compete against each other. Shear yielding is dominant for ductile failure and particle pullout is typical of brittle fracture. From TEM and tensile dilatometry results, the fracture sequence of the ductile failure is small-scale deformation of the matrix and the dispersed phase followed by G1651 particle deformation. Then, if the stress-strain around elastomer particle approaches to its critical value, cavitation of elastomer will happen to induce massive shear yielding.