Abstract
This research utilized different environmental friendly reinforcements or fillers, such as cellulose, ammonium polyphosphate, and carbon nanotube, to reinforce the environmentally conscious polymer, such as linear low-density polyethylene and biodegradable polyester, forming the eco- and nano-composites. Wood flour (WF) reinforced linear low-density polyethylene (LLDPE) composites were prepared in the first part of this dissertation. Water-crosslinking technique was used to improve the physical properties of wood composite. Composites were compounded in a twin-screw extruder and treated with a coupling agent (vinyltrimethoxysilane, VTMOS), and then moisture-crosslinked in hot water. Composite after water-crosslinking treatment exhibited better mechanical properties than the non-crosslinked one because of the improved chemical bonding between the wood fiber and the polyolefin matrix. As the wood flour content reaches to 30wt% and after water-crosslinking for 4 hours, tensile strength and flexural strength are increased by 87%（from 14.7 to 27.5 MPa）and 137.5％（from 11.2 to 26.6 MPa）with respect to that of non-crosslinked ones. Photographs of Scanning Electron Microscopy (SEM) of the fracture surfaces of water-crosslinked composites showed superior interfacial strength existed between the wood fiber and the polyolefin matrix. Thermal analyses of water-crosslinked composites indicate that thermal degradation temperature and heat deflection temperature of composite increase with the increasing of water-crosslinking time. The heat deflection temperature of the composite can be raised from 55.7□C to 88.5□C. The preparation and characterization on the novel water-crosslinked cellulose reinforced poly (butylene succinate) composites have been conducted. Wood flour (raw cellulose) reinforced poly (butylene succinate) (PBS) composites have been prepared utilizing unique water-crosslinking technique to improve the physical properties of composites. The composites were treated with a coupling agent ( Vinyltrimethoxysilane ) and then were compounded in a twin screw extruder. The compound was moisture-crosslinked. 13C NMR, 1H NMR and FT-IR spectra were utilized to monitor and characterize the water-crosslinking reaction. Composites via water-crosslinking treatment exhibits improved mechanical properties due to the interfacial bonding between the wood fiber and the PBS matrix. SEM microphotographs of the fracture surfaces of water-crosslinked composites showed superior interfacial linkage existed between the wood fiber and the PBS matrix. Thermal analysis on the water-crosslinked composites indicated that thermal degradation temperature of composite increased with the increasing of water-crosslinking time. POM microphotographs revealed that the water-crosslinking reaction can increase the crystalline rate but decrease the spherulites size of PBS. Biodegradation tests showed that adding wood flour increased the biodegradability of composite; however, the water-crosslinking reaction may reduce the biodegradability of wood composite. The second part of this dissertation focuses on the effect of water-crosslinking reaction on the flame retardancy and non-dripping properties of ammonium polyphosphate / poly (butylene succinate) composites. Ammonium polyphosphate (APP) reinforced poly (butylene succinate) (PBS) composites have been prepared utilizing a unique water-crosslinking technique to improve the flame retardancy and non-dripping property of composites, meanwhile, maintain the main structure of composites. The composites were treated with a coupling agent ( Tetraethoxysilane, TEOS ) and then were compounded in a twin screw extruder. The compound was moisture-crosslinked. FT-IR spectra were used to monitor the water-crosslinking reaction. Composites via water-crosslinking treatment exhibits improved mechanical properties due to the interfacial bonding between the APP and the PBS matrix. Microphotographs of SEM of the fracture surfaces of water-crosslinked composites showed the void size was increased with the increasing of water-crosslinking time. Composite with 15wt% APP were classified as UL-94 V-2. However, the ones with only 0.5 hr water-crosslinking reaction were classified as UL-94 V-0. Thermal analysis on the water-crosslinked composites indicated that thermal degradation temperature of composite increased with the increasing of water-crosslinking time. DSC results revealed that the water-crosslinking reaction can limit the crystalline rate of PBS. The third part of this dissertation is the preparation of carbon nanotube / linear low density polyethylene composites by a water-crosslinking reaction. A novel method to prepare the multiwall carbon nanotube (MWCNT) / linear low density polyethylene composite is demonstrated. The combination of free radical reaction and water-crosslinking reaction to prepare the MWCNT/LLDPE composite was characterized by Raman and FT-IR. Mechanical properties and thermal stability of composite were significantly improved after silane modification and water-crosslinking reaction. The crosslinking network between LLDPE and carbon nanotube plays a vital role for the improvement of mechanical properties and thermal stability of composite. The tensile strength and impact strength of 0.5 phr VTMOS-g-MWCNT / LLDPE composites can increase 65.6% and 24.8%, respectively, comparing with pristine MWCNT /LLDPE composites. The heat deflection temperature of 4phr VTMOS-g-MWCNT / LLDPE composites (via 4 hr water-crosslinking reaction) was 79.7□C, which is much higher than pristine LLDPE (60.0□C). Thermal degradation temperature of composite can increase 42oC via silane modification and water-crosslinking reaction. The fourth part of this dissertation is to elucidate the mechanical, electrical and thermal characteristics of novel multi-wall carbon nanotubes / lowly and highly crystalline poly (lactic acid) nanocomposites. This work presents a new approach to prepare multi-wall carbon nanotubes / polylactide (PLA) nanocomposite. Comparisons of carbon nanotube-reinforced high-crystalline and low-crystalline PLA nanocomposites were discussed. High electrical conductivity of nanocomposite can be achieved at a low carbon nanotube loading. When only 0.5phr modified MWNT was added to LC-PLA, the surface resistance of the nanocomposite reduced from 5.46×1015 to 2.61 × 102 Ω/□ (by 1013 orders). Carbon nanotubes cause the mechanical characteristics of low-crystalline PLA to be better than those in high-crystalline PLA. Only 0.5 phr modified MWCNT induces crystallization, and improves the thermal properties of the nanocomposite. The extent of the dispersion of carbon nanotubes in low-crystalline PLA matrix can be used to control carbon nanotube-induced crystallization