Study On Hybrid Polymer/Inorganic/Biomass Composite And Its Ceramic Material

In this work, hybrid polymer/Inorganic/biomass composite and its ceramic material were fabricated from natural wood with hierarchical structures. Furthermore, their microstructures and properties were studied.1. To increase the chemical reactive activity, fir flour was treated by NaOH solution, and the effects of alkali concentration on the component, structure and properties of fir flour were characterized by means of FTIR, XRD, FESEM and TG. The results showed that the hydrogen-bonds among celluloses have been broken partly and the degree of crystallinity of celluloses decreased during the high alkali concentration treatment, and the reaction activity of cellulose increased. Furthermore, the cross-porous network structure of the tracheid and the pit of wood appeared clearly, which made it easy for chemical penetration.2. Inorganic/wood flour hybrid materials with interpenetrating network were prepared using a novel Sol-gels hydrothermal couple method. Under hydrothermal condition, Zr precursor was infiltrated into the tracheid and the pit of wood flour, the hydroxyl groups from the hydrolysis of ZrOCl₂ reacted with the hydroxyl groups of the wood and interpenetrating network micro structure of the hybrid material was lastly formed. TG showed that the decomposition temperature increased from 275℃for wood flour to 298℃for the hybrid material. Polyporous ZrO2 ceramics were obtained after the hybrid material being treated under 800℃and the diameter of the pore was about 10²0μm.Using tetraethylorthosilicate (TEOS) as precursor, SiO₂/wood flour hybrid materials with interpenetrating network were fabricated by non-catalytic, acid catalytic Sol-gels hydrothermal couple method, respectively. Under hydrothermal condition, the precursor penetrated the cell wall, hydrolyzed and condensed with wood tissues, and SiO₂ formed in pores of fir flour resulting in formation of organic/inorganic interpenetrating network. The analysis of FTIR, XRD and TG revealed that acid catalytic process promoted the formation of Si-O-C bonds, and increased the thermal property. The decomposition temperature increased from 275℃for wood flour to 325, 314℃for the hybrid materials obtained acid catalytic, non-catalytic process, respectively. Polyporous SiO₂ ceramics were obtained after SiO₂/wood flour hybrid materials being treated under 1000℃. The final oxide products retained the ordered pores structure, and also showed unique pore size and distribution with hierarchy on nanoscale derived from the fir flour.3. Naphthol modified thermosetting phenolic resin (PF) with high char yield was synthesized. The factors influencing the synthesis, concentration of naphthol, amount of catalyst, condensation temperature and reaction time were discussed. The optimum conditions were determined as follows: the molar ratio of phenol, naphthol and formaldehyde is 0.9:0.1:1.35, ammonia as catalyst (pH value 8⁹), reaction temperature of 90℃and reaction time of 2.0h. The analysis results showed that naphthol has been actually grafted on the chain of PF, which had lower content of instability aether bonds. The decomposition temperature, the highest char yield of the modified PF was 460℃and 61.3%, respectively. Naphthol modified PF is suitable for use as the typical precursors used to fabricate carbon/carbon composite materials and ablative materials.The novel SiO₂/wood flour/phenolic composite was chosen to convert into SiC ceramic with hierarchically porous structures via the carbothermal reduction reaction. XRD, FTIR and FESEM were employed to characterize the phase identification and microstructural changes during the wood flour/SiO₂/phenolic composite to porous SiC ceramic conversion. The results showed that at 1550 0C the wood flour/SiO₂/phenolic composite converted into porous SiC ceramic with pore diameters of 10⁴0μm in a flowing ultra-high purity N2 atmosphere. The porous ceramic consisted ofβ-SiC located at the position of former wood cell walls.Long SiC micro-whiskers with necklace-like morphology have been successfully synthesized by carbothermal reduction process. In the process, the SiO₂/wood flour/phenolic composite was chosen as both silicon and carbon sources. The morphology and structure were investigated by X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). Studies found that the as-synthesized whiskers were grown as single crystallineβ-SiC along (111) direction with the length up to hundreds of micrometers. The every string with 1-2μm in diameter is regularly decorated with numerous equal-sized beads of 3-5μm diameters. On the basis of characterization results, a growth mechanism is proposed to clarify the formation of necklace-like whiskers. During the carbothermal reduction process, initially, the freshly formed carbon atoms and silicon atoms from the pyrolysis of wood flour/SiO₂/phenolic composite, which are not stable because of high-energy, react and create SiC nuclei. Then, the SiC strings along [111] direction, which has the lower energy than those of others inβ-SiC, grow fast by absorbing gas-phase carbon atoms and silicon atoms. The longer strings can be formed along with the consecutive growth of SiC. With the extension of the reaction time, SiC strings are circumvented by gas-phase carbon atoms and silicon atoms, which nucleate around the defects on the surface of strings in the nucleation process. With an increasing supply of carbon atoms and silicon atoms diffusing to the nucleation regimes, the spherical SiC beads are gradually created by an epitaxial growth process. The epitaxial orientation relationship is preserved to reduce the lattice mismatch energy. Further asymmetrical growth of the beads forms the necklace-like SiC micro-whisker. 4. The composites of polyamide-6 (PA6) reinforced with the SiO₂/wood flour hybrid materials were firstly prepared by melt-mixing in twin-screw extruder. Part of SiO₂/wood flour hybrid materials was treated withγ-aminopropyltriethyoxysilane or epoxy resin as compatibilizer, to improve its adhesion to PA6. XRD analysis results showed that the SiO₂/wood flour hybrid materials could induce PA6 to transit fromαtoγcrystal form. DSC analysis results indicated that the addition of the SiO₂/wood flour hybrid materials raised the crystallization temperature and increased the crystallization rate of PA6. The effects of SiO₂/wood flour hybrid materials content and the compatibilizer on mechanical properties of the composites were discussed. Tensile strength of the composites with 25 wt.% of the SiO₂/wood flour hybrid materials increased from 48.6 to 59.7 MPa representing 23.3% increase over pure PA6 , whereas 59.8% increase in flexural strength was observed. Two kinds of compatibilizer could enhance the interfacial adhesion between the SiO₂/wood flour hybrid materials and PA6, resulting in the impact strength of the composites efficiently increasing.5. Silicon rubbers (methyl vinyl siloxane rubber, MVS) composites reinforced with wood flour or the SiO₂/wood flour hybrid materials were prepared in a two-roll mill, and the properties of two series of composites such as tensile strength, tear strength, elongation at break and hardness were investigated. The experimental results showed that the rubber composites exhibited an increase in hardness, however, their tensile strength and tensile elongation at break decreased with increasing filler loading. Tear strength firstly increased and then decreased with increasing filler loading, and the maximum values are 15.9 kN/M at 20 phr of wood flour and 13.1kN/M at 10 phr of the SiO₂/wood flour hybrid materials, respectively. A silane coupling agent,γ-glycidoxypropyltrimethy- oxysilane (KH570) was used to modify filler surfaces, 2 wt.% for wood flour and 1 wt.% for the SiO₂/wood flour hybrid materials, respectively. It was found that the silane coupling agent improved the rubber matrix-filler interaction and consequently enhanced strength properties. Porous SiO₂/SiC ceramic was fabricated by carbonizing and sintering MVS/SiO₂/wood flour composites at high temperature. The fabrication process involved the following steps: (1) transforming the silicon rubbers by pyrolysis into silicon oxycarbide (SiOC), and (2) fabricating porous SiO₂/SiC ceramic by carbothermal reduction and subsequent sintering. The resulting porous ceramic exhibited hierarchical porous structures with pore diameters of 5²0μm.