Thermal and Mechanical Properties of Amorphous and Semi-Crystalline Polyamide Blends

Thermoplastics are cost effective, corrosion resistant, and light weight alternatives to metallic materials. Polyamides are a class of thermoplastics with high toughness which are suitable for structural components under severe load conditions. A series of novel thermoplastic materials are being developed to improve mechanical, physical, and thermal properties. The focus of this study is finding a balance of properties when blending amorphous polyamides with semi-crystalline polyamides. Blending semi-crystalline and amorphous polyamides could result in improved mechanical properties compared to the mechanical properties of individual polymers. However, these blends could have mixed thermal characteristics, depending on the ratio of the amorphous polymer in the blend, molding conditions, property of interest, etc. In this study, we use PA66 and PA6I6T (67% 6I (isophthalic) and 33% 6T (Terephthalic)) which are semi-crystalline and amorphous, respectively. Both PA66 and PA6I6T have a great balance of mechanical, physical, and thermal properties, in dry as molded (DAM) condition. The addition of PA6I6T could improve a variety of properties, including glass transition temperature and mold stability of the compounds, while maintaining mechanical and physical properties, in DAM condition. However, because of the amorphous nature of PA6I6T, mechanical properties at elevated temperatures and thermal properties could be significantly different than those of the semi-crystalline polyamide (PA66). The heat deflection temperature (HDT) of a semi-crystalline polyamide is well above its glass transition temperature and could be as high as melt temperature. On the other hand, the HDT of an amorphous polyamide could be as low as Tg. In this study, we investigated the HDT trend of the amorphous and semi-crystalline blend at different mixing ratios. Additionally, we investigated the crystallization rate and ratio of amorphous and semi-crystalline polyamide blends to comprehend the impact of amorphous polyamide ratio on crystalline domains ratio, crystallization rate, and consequently the thermal performance at elevated temperatures.