Abstract
This research utilized nano-materials such as colloidal silica(0-D) and carbon nanotube (1-D) and clay (2-D) to reinforce waterborne polyurethane (3-D) to prepare nanocomposite. In order to improve the dispersion of reinforcements and good interfacial bonding between the nanomaterials and waterborne polyurethane matrix, some surface modifications was proceeded. Characterization and physical properties of nanocomposites were also investigated. In the first part of this research, a novel clay / waterborne polyurethane (WPU) nanocomposite was synthesized from polyurethane and saponite organoclay. The clay was organically modified with various swelling agents. The effect of various swelling agents has been investigated. The nanocomposite was characterized using Fourier transform infrared (FT-IR). The d-spacing of clay was determined by X-ray diffraction (XRD) and confirmed by transmission electronic microscopy (TEM). XRD and TEM analyses indicated that clay retains a layered structure in the clay / waterborne polyurethane nanocomposite. Consequently, these materials are an intercalated nanocomposite with a d-spacing around 4 to 5 nm. FT-IR revealed that adding clay does not affect the synthesis of the waterborne polyurethane. Hydrogen bonding between organic and inorganic materials was characterized using FT-IR. Results implied that hydrogen bonding increased by adding organo-clay. GPC results indicated that molecular weight decreased as the clay content increased. TGA results showed that adding clay increased the temperature of thermal degradation. Tensile properties revealed that introducing clay into waterborne polyurethane will enhance the Young’s modulus(from 56 MPa increased to 126 MPa)、maximum stress (from 3.9 MPa to 7.6MPa)and elongation at break (from 27.7% to 58.7%) of the nanocomposite. Another novel clay / waterborne polyurethane (WPU) nanocomposite was synthesized from polyurethane and montmorillonite clay. The clay was acid-modified with hydrochloric acid. XRD analyses indicated that clay was disorderly exfoliated in the clay / waterborne polyurethane nanocomposite as the clay content is low and retains a layered structure in the clay / waterborne polyurethane nanocomposite as the clay content is more than 2phr(part per hundred parts of polyurethane resin).The molecular motion of nanocomposites was investigated using high resolution solid state 13C NMR technique. Adding clay can decrease the molecular mobility of waterborne polyurethane. TGA Results showed that adding clay increased the temperature of thermal degradation by 30℃. Thermal stability of nanocomposites prepared by this method is higher than that prepared by organic swelling agent. Two-leg trousers studies revealed that introducing clay into waterborne polyurethane enhance the tearing toughness of the nanocomposite by 58.6% . In the second part of this research, a colloid silica / waterborne polyurethane nanocomposite was successfully synthesized. FT-IR and GPC have been used to characterize the nanocomposite. SEM microphotograph and Si-mapping of colloid silica / waterborne polyurethane nanocomposite indicated that colloid silica was well dispersed in waterborne polyurethane. TEM microphotography revealed that the size of colloid silica remained in waterborne polyurethane nanocomposite was about 100nm, that is, nano-dispersed in nanocomposites. Thermal properties of the nanocomposite measured by TGA indicated that adding colloid silica increased the temperature of thermal degradation by 30℃. Mechanic property tests showed that adding colloid silica improved the wear resistance of colloid silica / waterborne polyurethane nanocomposite. In the third part of this research, a novel nanocomposite consists of multiwall carbon nanotube / waterborne polyurethane nanocomposite has been successfully prepared. Carbon nanotube was modified, to compatibilize with waterborne polyurethane via covalent bonding or ionic bonding. Thermal properties show that adding carbon nanotube enhanced the thermal stability by 26ºC (from 315ºC to 341ºC) when carbon nanotube content was 2.5 phr. After the surface modification, carbon nanotube can be dispersed effectively, and improve the interfacial strength between CNT and waterborne polyurethane matrix. Consequently, the physical properties of nanocomposite are enhanced, especially in the covalent bonding system. Mechanical property tests show that adding multiwall carbon nanotubes improve the tensile properties very significantly (370% in tensile strength). SEM microphotographs prove that carbon nanotube can be effectively dispersed in waterborne polyurethane matrix. Rheological tests show that carbon nanotube can increase the melt viscosity and reduce the variation of processing viscosity. In the final part of this research, the Taguchi method was utilized to analyze the synergetic effect of various nano-materials in the waterborne polyurethane matrix. Results showed that the synthesis time dominate the molecular weight and inter- and intra- molecule hydrogen bonding of nanocomposites. Increasing the carbon nanotube content can enhance the thermal stability and tensile property of nanocomposites. From the results of confirm tests, the nanocomposite with a small amount of clay(0.5 phr), colloidal silica(0.5 phr) and 2phr CNT have larger tensile strength than that of 4phr CNT nanocomposite.