Influence of Thermo-Oxidative Ageing on the Thermal and Dynamical Mechanical Properties of Long Glass Fibre-Reinforced Poly(Butylene Terephthalate) Composites Filled with DOPO.

Daohai Zhang,Jie Yu,Shuhao Qin,Ying Zhou,Min He,Weidi He

doi:10.3390/ma10050500

Abstract

In this work, the long glass fibre-reinforced poly(butylene terephthalate) (PBT) composites filled with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) were prepared by melt blending, and the influence of thermo-oxidative ageing on the static and dynamic mechanical properties, thermal behaviours and morphology of composites with different ageing time at 120 °C were investigated and analysed. The results showed that the mechanical properties decreased in the primary stage of ageing, while embrittlement occurs in the later period, and the crystallinity of PBT decreases first, and then recovers to some extent. The scanning electron microscopy (SEM) photos of the samples indicated that the obvious crack appeared on the sample surface and a deeper, broader crack occurred with a longer ageing time. The results of energy dispersive X-ray analysis (EDAX) proved the DOPO filler diffused to the sample surface by measuring the content of phosphorus. Thermal gravimetric analysis (TGA) curves showed that the thermal stabilities of composites increased with longer ageing time, as did the values of the limited oxygen index (LOI). Meanwhile, the results of dynamic mechanical analysis (DMA) indicated that the glass transition temperature shifted to a higher temperature after ageing due to the effect of crosslinking, and both the crosslinking and degradation of PBT molecular chains act as the main factors in the whole process of thermo-oxidative ageing.

Highlights

Poly(butylene terephthalate) (PBT) is a type of typical semi-crystalline polymer material with wide applications due to its properties, such as rigidity, a high rate of crystallization, and hardness [1,2].PBT has a relatively low mechanical strength, especially impact strength, which shows a sensitive effect to notches [3,4]
The notched izod impact strength of PBT/long glass fibre (LGF)/DOPO composites (60 days) is decreased by 43.56%, compared with that of unaged specimens. These results indicate that the mechanical properties decrease obviously in the early period of ageing by the effect of heat flow and oxidation
It has been reported that long glass fibre reinforcement other kinds of matrix, such as polypropylene and polyamide 6, in thermo-oxidative ageing both show a global decrease in mechanical strength, without recovery or post-cure [8,16]

Summary

Introduction

Poly(butylene terephthalate) (PBT) is a type of typical semi-crystalline polymer material with wide applications due to its properties, such as rigidity, a high rate of crystallization, and hardness [1,2].PBT has a relatively low mechanical strength, especially impact strength, which shows a sensitive effect to notches [3,4]. Poly(butylene terephthalate) (PBT) is a type of typical semi-crystalline polymer material with wide applications due to its properties, such as rigidity, a high rate of crystallization, and hardness [1,2]. There have been growing interest in long glass fibre (LGF)-reinforced polymer composites because of their light weight, high mechanical strength, and low cost, which have been applied in automobiles, construction, and aviation [5,6,7]. With these advantages, the LGF-reinforced PBT composites can become more suitable for highly demanding situations than original PBT materials. Traditional halogen flame retardants can act to Materials 2017, 10, 500; doi:10.3390/ma10050500 www.mdpi.com/journal/materials

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Conclusion