Determination Of The Surface Functional Groups And The Application In Nylon-6 Of Surface Modified Nanosilica

As a kind of catalyst and novel functional materials, surface-modified nanosilica withγ-aminopropyltriethoxysilane (APS) andγ-glycidoxypropyltrimethoxysilane (GPS), coded as AMNS and GMNS, have been widely applied in the fields of life science, analytical chemistry and optics etc. At present, focus is being placed on modifying and integrating processes in terms of the preparation technology for AMNS and GMNS. And researches on the application of AMNS and GMNS are also begining to attract attention. However, current studies in relation to the applications of AMNS and GMNS are largely limited to exploration of experiences in labs, mainly due to insufficient understanding of the states and concentrations of the functional groups (i.e., amino and epoxy groups) on the surface of AMNS and GMNS, where the concentrations of the functional groups play a more critical role on the application. Besides, efforts are urgently needed to promote the application and development of AMNS in engineering. Therefore, the following three parts of research are to be highlighted in this dissertation:Part I: Determination of Amino Concentration on AMNSMethods such as hydrochloric acid-ethanol non-aqueous titration, perchloric acid-acetic acid non-aqueous titration, spectrophotometry and cyclic voltammetry (using glassy carbon electrode modified with p-aminobenzoic acid) were established for determining amino group on AMNS. The effects of various experimental conditions on the results of measurement were studied in detail. The main factors that affect the accuracy of measurement were investigated. The advantages and disadvantages of each method are discussed, and the main causes leading to differences from the measurement results by various methods are explored. Based on the above-mentioned studies, the analysis and test platforms have been established in relation to the synthesis and application of this type of nanomaterials. Results indicate that all the proposed methods could be well used to determine the amino concentration on AMNS with a good accuracy. For the both titration methods, treating the samples with ultrasonic vibration near the end point is favorable to shortening the titration process. For the perchloric acid-acetic acid method, the addition of 2-ethylhexanol as a dispersant could improve the inter-solubility of the titration system and decrease the system's freezing point, leading to broadening the application scope of the method. For spectrophotometry method, it was of great sensitivity, and pH value had the most important role in affecting the results of measurement. In terms of the cyclic voltammetry, the effects of the adsorption of indicator by nanoparticles and the light reflectance by the nanoparticles were eliminated, helping to reaching good accuracy. Besides, higher the results of measurement was obtained along with Kjeldahl Method, mainly because Kjeldahl Method was used to determine the total nitrogen in AMNS while the other methods were applied to determine only amino nitrogen in AMNS.Part II: Determination of Epoxy Concentration on GMNSVarious methods including non-aqueous titration with hydrochloric acid-butanone and perchloric acid-acetic acid, ultraviolet (UV) and fluorescence spectrophotometry, osciliopolarography and potential titration (using an electrode chemically modified with poly(p-nitro aniline)) were established to determine the content of GPS and the concentration of epoxy group on GMNS. The influences of various experimental conditions on the measurement results and the major factors significantly affecting the accuracy of measurement were investigated in detail. The characteristics of each method and its applicable scopes were discussed. And the analysis and test platforms in relation to the synthesis and application on this kind of nanomaterials were established. Results indicate that every established method could be well used to determine epoxy on GMNS accurately, showing insignificant difference in terms of the measurement results. For non-aqueous titration with hydrochloric acid-butanone and perchloric acid-acetic acid, the confirmation of the end point was the key factor to guarantee the accuracy of measurement. UV and fluorescence spectrophotometry methods had good sensitivity. Osciliopolarography method, without the interference by nanoparticles, had better accuracy and reproducibility than the other methods. Besides, potential titration, based on hydrochloric acid-butanone method and using an electrode modified with poly(p-nitro aniline) as the indicator electrode, had effectively increased accuracy.Part III: Structure and Properties of AMNS/Nylon 6 CompositesBased on the accurate determination of amino group on AMNS, the structures of AMNS/nylon 6 nanocomposites prepared by melt blending were analyzed. A model was established to illustrate the interfacial interactions between AMNS with different concentrations of amino group and nylon 6 matrixes. A concept of critical concentration of amino group was put forward. The optimized concentration of AMNS added in nylon 6 matrixes was determined. And the effect of amino group concentration of AMNS on the mechanical properties of AMNS/nylon 6 nanocomposites was explored. Results are obtained as follows:①The amino groups on AMNS surface reacted with the end carboxyl groups and acylamino groups of nylon 6, forming interfacial structures based on hydrogen bonding and covalent bonding. There might exist an optimum concentration of the functional groups in AMNS, at which maximum interfacial interactions between nanosilica as the filler and nylon 6 matrix would be realized, hence acquiring effectively improved mechanical properties of the filled nylon 6 composites.②The introduction of AMNS resulted in improvement of the mechanical properties of nylon 6. When the amino concentration was 2.86 mmol·g-1, the tensile strength, tensile modulous, flexural strength, flexural modulus, and notched impact strength of the nanocomposite were increased by 19.02%, 47.16%, 27.11%, 38.69%, and 17.11%, respectively, as compared with that of nylon 6 matrix.③The thermal stability of nylon 6 increased with the increase of amino concentration of AMNS. Compared with nylon 6, the temperature at which AMNS/nylon 6 composites showed weight loss of 10% was increased by 6~10 oC as compared with the nylon 6 matrix.④Increasing the amino concentration on AMNS favored the growth of nylon 6 along the (002)/(202) planes. The crystallization temperature of the nanocomposites decreased with the increase of amino concentration on AMNS, while the crystallinity of nylon 6 matrix kept also unchanged.