A Novel Surface Treatment of p-Aramid Fiber using Supercritical Fluid for Reinforcing Materials in Composites

在聚对苯二甲酸乙二酯(PPTA)纤维中，纤维与树脂之间的界面强度太弱，不能作为增强纤维应用于复合材料的整体性能。在这项研究中，我们提出了一种新的处理PPT的方法，包括硅烷偶联剂和成膜剂。在表面处理中，PPT纤维并不是正常的，而是在纤维纺丝过程中被改性，使纤维结构中的微晶之间有更大的间隙。我们称之为开放式结构PPT纤维。在表面处理中，超临界二氧化碳流体可以很容易地将大小分子渗透到PPT纤维的开口间隙中(第一步)。在穿透后，将纤维加热以闭合缝隙，即转变为普通型PPT纤维(第二步)。处理后的纤维增强复合材料的界面剪切强度和力学性能。结果，这种处理被发现改善了这些特性。为了阐明PPT纤维这种独特处理的界面增强机理，用X射线衍射法、IR-ATR法和杯针法对每一步进行了分析，并用X射线衍射仪研究了混合剂处理后的开放结构PPT的微晶尺寸和纤维结晶情况。结果是，处理使微晶尺寸增加到与正常PPT纤维一样大。这种效应会导致纤维强度的保持。用IR-ATR分析了混合剂在纤维中的浸渍情况。最终，微晶之间的开口促使试剂渗透到纤维的内部位置。杯针技术表明，成膜剂只有在加热下与硅烷混合才能硬化。这些结果支持上述机理。

In poly (p-phenylene terephthalamide)(PPTA) fiber, the interfacial strength between the fiber and resins is too weak to raise total performance as a reinforcing fiber in application to composites. In this study, we have proposed a novel treatment of PPT with normal sizes including silane coupling agents and film formers. In the surface treatment, PPT fiber is not normal, but is modified during fiber spinning to have larger gaps between crystallites in fiber structure. We call it open-structured PPT fiber.In the surface treatment, supercritical carbon dioxide fluid was used to easily penetrate molecules of the sizes into open gap in PPT fiber (the first step). After the penetration, the fiber was heated to close the gap, that is, to change into normal type of PPT fiber (the second step). After the treatment, the interfacial shear strength and the mechanical properties of composite reinforced with the treated fiber. As a result, this treatment was found to improve those properties. This treatment also keeps the fiber strength.In order to clarify the mechanism of interfacial reinforcement by this unique treatment of PPT fiber, each step have been examined using X-ray diffraction, IR-ATR, and cup-and-pin method.X-ray diffraction has been applied to know the size of crystallites and the crystallization of fiber for open-structured PPT treated with the mixed agents. As a result, the treatment enhances the size of crystallite as large as in normal PPT fiber. This effect leads to the maintenance of fiber strength. IR-ATR analysis has been used to know the impregnation of the mixed agents into fiber. Eventually, open slit between crystallites prompts the permeation of the agent into the inner site of fiber. Cup-and-pin technique shows the hardening of film former only by mixing with silane under heat. These results support the mechanism describe above.