Study On Preparation And Properties Of Nylon6/SiO₂-COOH And Nylon6/Ethylene Bis-Stearamide/carboxylic Silica Composites

Nylon6’s （PA6） toughness, low coefficient of friction and good abrasion resistancemake it an ideal replacement for metals and rubber in many applications. However, asthe structure of nylon6was linear, there was entanglement between the chainsresulting in poor flowability in spite of its good mechanical properties. This leads torestricting the application in molded products of small parts with thin walls orprecision parts. Thus, it is necessary to design and develop nylon6systems with highflowability and obtaining its original mechanical properties.In this paper, according to the problems mentioned above, carboxylic-functiongroups on the silica surface （SiO₂-COOH） nanoparticles were added to the nylon6system to react with the amino terminal groups of nylon6. It can improve thecompatibility in the interface between the SiO₂-COOH nanoparticles and nylon6matrix to improve the mechanical properties of nylon6. On the basis of the abovediscussion, Ethylene bis-Stearamide （EBS）, as a plasticizer, was added to the nylon6matrix based on the problems. EBS within a certain range can not only improve theflowability of PA6but also maintain the original mechanical properties of PA6.Consequently, we added EBS and SiO₂-COOH together, a simultaneous increase in theflow and mechanical properties was hoped for.Nylon6/carboxylic acid-functionalized silica nanoparticles （SiO₂-COOH）nanocomposites by in situ polymerization of caprolactam in this paper. The aim of thiswork was to study the effect of carboxylic silica on the properties of the nylon6through the interfacial interactions between the SiO₂-COOH nanoparticles and thenylon6matrix. For comparison, pure nylon6, nylon6/SiO₂（unmodified） and nylon6/amino-functionalized SiO₂（SiO₂-NH2） were also prepared via the same method.Fourier transform infrared spectrometer （FTIR） spectroscopy was used to evaluate thestructure of SiO₂-COOH and nylon6/SiO₂-COOH. The results from thermalgravimetric analysis （TGA） indicated that decomposition temperatures of nylon6/SiO₂-COOH nanocomposites at the5wt%of the total weight loss were higher thanthe pure nylon6. Differential scanning calorimeter （DSC） studies showed that themelting point （Tm）, crystallization temperatures （Tc） and degree of crystallinity （Xc）of nylon6/SiO₂-COOH were lower than the pure nylon6. Mechanical propertiesresults of the nanocomposites showed that nylon6with incorporation of SiO₂-COOHhad better mechanical properties than that of pure nylon6, nylon6/SiO₂, and nylon6/SiO₂-NH2. The morphology of SiO₂, SiO₂-NH2, and SiO₂-COOH nanoparticles in nylon6matrix was observed using SEM measurements.Nylon6/EBS/SiO₂-COOH composites were prepared by in situ polymerization ofcaprolactam. For comparison, the pure PA6and PA6/EBS composites were alsoprepared via the same method. The PA6/EBS/SiO₂-COOH composites with low contentof EBS and SiO₂-COOH had greater melt-flow index （MFI）（the value of MFIincreased by50–80%） than the pure PA6. The results of mechanical properties showedalmost no decrease in the tensile strength of PA6/EBS/SiO₂-COOH composites, withthe bending strength decreasing by17-21%. However, the Izod impact strength of thePA6/EBS/SiO₂-COOH composites was greatly improved compared with pure PA6. Themorphology of Izod impacted fractured surfaces of PA6/EBS/SiO₂-COOH wasobserved by scanning electron microscopy （SEM）. The results from differentialscanning calorimetry （DSC） indicated that the melting point （Tm）, degree ofcrystallinity （Xc） and crystallization temperatures （Tc） of PA6/EBS/SiO₂-COOHcomposites were lower than the pure PA6.