The Study Of The β-transcrystallization Interface In The Acid Corroded Glass Fiber (GF)/isotactic Polypropylene (iPP)Composite

The application of the fiber reinforced isotactic polypropylene composites depends on their mechanical and physical properties. Particularly, the interface of the fiber/iPP composites is the key factor affacting their properties. Therefore, the control of the interface between fiber and iPP matrix is always the hot issue. For the glass fiber (GF) reinforced iPP composite, the compatibility between GF and iPP is very poor. So the effective methods to enhance the interface strength have drawn intense interests in the past decades. In our previous study, it was interesting to find that acid-corroded GF can induce iPP to form a-ringed nuclei in the early stage of crystallization and subsequent β-transcrystallization developed from these nuclei under isothermal conditions. However, the questions which should be understood are (i) the reason why the acid-corroded GF can induce iPP to form β-transcrystallization and (ii) whether such acid-corroded GF still has the ability to induce P-transcrystallization towards iPP under practical processing conditions (such as injection molding). So the main work in this paper is to explain the reason for the β-transcrystallization induced by acid-corroded GF and investigate the micromorphology and properties of the injection molded GF/iPP composites by wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), polarized optical microscope (POM), scanning electron microscopy (SEM) and so on. The main results are as follows:(1) The chemical component, chemical group and surface morphology of the GF exhibit no change after acid-corroding. So these factors are not the reasons to induce P-transcrystallization.(2) The acid-corroded GF can preserve the stress effect derived from the sample preparation. During isothermal conditions, the stress effect induces the oriented lamellae, that is a-ringed nuclei, perpendicular to the fiber axis. Thereafter, the β-transcrystallization can be finally developed from these nuclei.(3) The neat iPP, the virgin GF(0-GF)/iPP and acid-corroded glass fiber (4-GF)/iPP samples were injection molded by mixing-injection molding (MIM). At a given position of the samples,4-GF/iPP has the highest β-form crystallinity (Xβ), followed by the0-GF/iPP and neat iPP. Furthermore, the core regions of all the samples have higher content of Xβ, which is different from other studies.(4) Higher content of β-form in core region of neat iPP molded by MIM is observed. Moreover, the mechanism of β-form crystals developed in core region is suggested:in the process of MIM, precursors can be brought by the pre-shear during mixing-plasticization in the barrel via the rotating screw. Once the melt containing precursors was injected into the mold cavity, the precursors might partially survive and lead to the β-form crystals in the core region.(5) A few β-transcrystallization formed in the injection molded0-GF/iPP is attributed to the local shear caused by the relative flow rate of the iPP melt and rigid GF during filling stage. Compared with0-GF/iPP, more β-transcrystallization can be induced in the injetion molded4-GF/iPP which is caused by the ability to preserve the stress effect of the4-GF.