【作者】 李忠；

【导师】 史铁钧；

【作者基本信息】 合肥工业大学 ， 材料学， 2010， 博士

【摘要】 本文开展了基于聚合物/无机物/生物质杂化复合材料及其陶瓷材料的探索研究,即利用天然木材独特的构造,制备了聚合物/SiO₂/木粉杂化复合材料及其陶瓷材料,并对这些材料的微观结构及性能进行了研究。1、通过系统的研究NaOH溶液浓度对杉木粉组成、结构和热性能的影响,结果发现,NaOH溶液使部分氢键被破坏,破坏了纤维素结晶结构,使更多的羟基能够参与反应,提高了木粉的可反应性。碱处理改善了杉木粉的微孔结构,使管胞与纹孔的多层次、规整有序的孔隙结构更清晰,有利于反应试剂在其中的渗透、扩散。2、采用溶胶凝胶-水热耦合的新方法,成功制备了具有互穿网络结构的无机/木粉杂化材料。在水热条件所提供的特殊物理化学环境中,前驱体ZrOCl2溶液进入到木粉的微孔结构中,水解产物的羟基与木粉的羟基发生缩合反应,形成了较强的Zr-O-C键,水解产物的自身的缩合反应生成了ZrO₂,填充在木粉的孔隙中,最终制得了具有无机氧化物凝胶纤维与木粉纤维质网络互穿结构的杂化材料。这种网络结构提高了杂化材料的耐热性能。在空气中800℃处理ZrO₂/木粉杂化材料制得了具有独特的、孔形规则的管状“网笼”结构的ZrO₂多孔陶瓷材料。以正硅酸乙酯（TEOS）为无机物前驱体,分别采用酸催化、非催化的溶胶凝胶-水热耦合法制备了具有无机物与木粉骨架互穿网络结构SiO₂/木粉杂化材料。傅立叶变换红外光谱（FTIR）、X-射线衍射（XRD）和热重（TG）分析结果表明,酸催化过程能形成更多的Si-O-C化学键结合,提高杂化材料的增重率和热性能。酸催化和非催化过程制得的SiO₂/木粉杂化材料的热分解起始温度分别为325℃和314℃,比木粉分别提高了50℃和39℃。在空气中1000℃热处理酸催化法制得的SiO₂/木粉杂化材料可制备具有木粉有序孔结构的SiO₂陶瓷材料,孔径主要分布在2⁴0nm之间。3、在苯酚:萘酚:甲醛的摩尔比为0.9:0.1:1.35,氨水作催化剂（pH=8⁹）,反应温度为90℃,反应时间为2.0h的最佳反应条件下,制备了以萘酚部分替代苯酚的高残碳热固性酚醛树脂。FTIR和TG分析结果表明,萘酚醛树脂具有较好的耐热性能,800℃时的残碳率为61.3%,是良好的碳/碳复合陶瓷材料树脂基体和粘合剂。以易于成型的SiO₂/木粉/萘酚醛树脂复合材料为陶瓷前驱体,在1550℃、氮气保护下发生碳热还原反应,得到了具有分级、有序孔结构的SiC陶瓷。FTIR、XRD的研究结果表明SiC多孔陶瓷的主要组成是β-SiC,场发射扫描电镜（FESEM）形态学研究表明陶瓷保留了木材组织分级、有序多孔结构。以SiO₂/木粉/萘酚醛树脂复合材料的高温裂解产物作为硅源和碳源,成功制备了具有独特的链珠状β-SiC长纤维。形态学研究结果表明,纤维的直径1²μm,长度可达几百微米,在长链上均匀的分布着直径为3⁵μm的微珠。实验的分析、检测结果表明,链珠状SiC纤维的生长过程为:碳热还原反应过程中,先按[111]方向外延性生长成直线型SiC晶须,而在（111）晶面内存在结构缺陷（堆垛层错）,再围绕SiC长链晶须表面的缺陷处生成新的SiC晶核,由此外延性生长形成包裹在长链上的SiC微珠,最后形成链珠状SiC纤维。4、以具有“韧”“硬”特性的SiO₂/木粉杂化材料作为填料、尼龙6（PA6）为高分子基体,采用双螺杆熔融挤出,成功制备了PA6/SiO₂/木粉杂化复合材料。XRD的研究结果表明,SiO₂/木粉杂化材料起着晶型转变剂的作用,促进了PA6的α晶型向γ晶型转变。DSC的研究结果表明,SiO₂/木粉杂化材料显著的提高了PA6的结晶温度和结晶速率。PA6/SiO₂/木粉杂化复合材料具有优良的力学性能。随着SiO₂/木粉杂化材料含量的增加,复合材料的拉伸、弯曲强度增大。与PA6相比,SiO₂/木粉杂化材料的含量为25 wt.%时,复合材料的拉伸强度由48.6MPa增加到59.7MPa,提高了23.3%;弯曲强度由55.0 MPa增大到87.9 MPa,提高了59.8%。KH550偶联剂、E-44环氧树脂的表面处理提高了SiO₂/木粉杂化材料与PA6基体的相容性,提高了复合材料的力学性能。5、采用混炼法分别制备了甲基乙烯基硅橡胶与木粉、SiO₂/木粉杂化材料的杂化复合材料,探讨了填料用量对复合材料力学性能的影响。实验结果表明,随着木粉、SiO₂/木粉杂化材料加入量的增大,复合材料的拉伸强度和拉断伸长率降低。撕裂强度先提高后降低,当木粉加入量为20phr时,达到最大值kN/M15.9和13.1kN/M最大值。木粉、SiO₂/木粉杂化材料的加入提高了硅橡胶的硬度。对木粉、SiO₂/木粉杂化材料表面改性的硅烷偶联剂KH570的用量分别为2和1 wt.%时,可以改善填料与硅橡胶的界面相容性,提高硅橡胶复合材料的综合力学性能。以可成型的甲基乙烯基硅橡胶/SiO₂/木粉杂化复合材料在氮气氛中、高温裂解原位生成SiO₂/SiC陶瓷。硅橡胶先裂解形成无定形的SiC_xO_y陶瓷,再发生结构重排生成SiO₂/SiC,而SiO₂/木粉杂化材料裂解生成C和SiO₂。1500℃高温下,复合材料的裂解产物发生碳热还原反应,生成了具有木材有序孔结构的SiC陶瓷,孔径为5²0μm。更多还原

【Abstract】 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.更多还原