Synthesis Of Nylon 66/amino-modified SiO₂ Nanocomposites By In-situ Polymerization And Their Structure-Property Studies

Nylon 66 (Polyamide 66 or PA66) was a widely used as engineering plastics with excellent properties. Many studies focused on the modification of PA66 to enhance its performance. This thesis describes the synthesis of amino-modified silica nanoparticles (AMS) using 3-aminpropyltriethoxysilane as a silica nanoparticle surface-modification agent. Under nitrogen atmosphere, the aqueous solution of AMS and nylon-66 salt precursor was condensed under heat to achieve PA66/SiO2 nanocomposites. As contrast, PA66/unmodified SiO2 nanocomposites were prepared through in-situ polymerization. The structure and property of two kinds of namocomposites were compared. The results indicate that amino-modified silica nanoparticles were prepared succesfully. The amino groups at AMS surface react with the matrix PA66, thus some PA66 chains were loaded on AMS surface. This improves the interfacial adhesion strength between AMS and PA66. However, the hydroxyl groups at UMS surface interact with PA66 by hydrogen bonding, the interfacial adhesion strength was low. In PA66/AMS composites, AMS act as good nucleating agents, leading to the reduced activation energy of crystallization, and rapid crystallization process and high overall crystallinity of these nanocomposites. As contrast, the nucleating effect of USM was less significant than AMS, leading to a slow crystallization rate and low crystallinity of these nanocomposites. In PA66/AMS nanocomposites, AMS homogeneously dispersed in the PA66 matrix, and the high interfacial adhesion strength between AMS and PA66 facilitates the stress transfer. These lead to the increase of tensile strength. Meanwhile, the AMS acted as stress concentration points under the load outside, which induce more local deformation and absorb more energy. This increases the toughness of the PA66 matrix. As contrast, the low interfacial adhesion strength between UMS and PA66 matrix leads to the aggregation of UMS nanoparticles, which caused the stress concentration and large cracks, so that the improvement to the tensile strength was limited and the toughness decreased. The toughing mechanism of AMS to the PA66/AMS composites was cavitation-micro crack mechanism.