Influence of the Polymer/Inorganic Filler Interface on the Mechanical, Thermal, and Flame Retardant Properties of Polypropylene/Magnesium Hydroxide Composites

Abstract

The relationship between the interface structure and the macroscopic properties of composites composed of isotactic polypropylene (iPP) and magnesium hydroxide (MH) was investigated with a focus on mechanical properties, thermal stability, and flame retardancy. Surface treatment of MH was carried out using dodecanoic acid (DA) and dodecylphosphate (DP), both of which interacted with MH to form submonolayer coverages. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) revealed that both organic reagents adhere to the MH surface via ionic interactions. Even low amounts of organic reagents on the MH surface were sufficient to improve the mechanical, thermal, and flame retardant properties of the composites. The incorporation of 1.8 wt% of DP in (70/30) iPP/MH-DP composite decreased the peak heat release rate (PkHRR) to 39% compared with that of neat iPP. Since the effects of DA with the same dodecyl chains were not significant, it is concluded that the phosphate groups in DP provide flame retardancy.

Keywords:

• composite
• flammability
• interface
• magnesium hydroxide
• mechanical property
• polypropylene

Acknowledgments

The authors thank to the Collaborative Interdisciplinary Research Team, National Institute of Advanced Industrial Science and Technology (AIST) in Japan and their financial support provided in the 2006–2008 fiscal years.

Notes

^aAverage of results obtained for five specimens in the tensile tests performed at a crosshead speed of 10 mm/min.

^bAverage of results obtained for five specimens in the tensile impact tests.

^aValues determined by TG in air performed at a heating rate of 5°C/min from RT to 650°C.

Figure 12 Decomposition behavior of (70/30) iPP/MH composites during heating in air monitored by TG analysis [- - -, neat iPP;– –, iPP/MH;- · -, iPP/MH-DA;—, iPP/MH-DP].

Figure 13 Change in HRR during combustion of (70/30) iPP/MH composites in air […, neat iPP;- · -, iPP/MH;- - -, iPP/MH-DA;—, iPP/MH-DP].

^bTemperature at which 5% weight loss was observed.

^cValues determined by cone calorimetry following the ISO 5660 procedure.