【作者】 张阳；

【导师】 隋国鑫；

【作者基本信息】 中国科学技术大学 ， 材料学， 2021， 博士

【摘要】 石油基合成高分子材料在人们生产和使用过程中带来严重的环境问题,加大可持续的环境友好型高分子材料的研究和开发至关重要。选择天然可持续高分子逐步代替部分石油基合成高分子是可行的方案。因此,本文围绕可再生、可生物降解并且来源广泛、地球上最丰富的天然高分子纤维素作为基本原料,同时在纤维素表面原位生成功能性纳米四氧化三铁,制备出了微、纳米结构的纤维素原位纳米四氧化三铁复合材料(Cellulose@Fe3O4)。基于此结构,设计了不同的功能性复合材料。第一部分工作,通过共沉淀法,在纤维素表面原位生成纳米四氧化三铁(Fe3O4)粒子,并调控了纤维素表面纳米四氧化三铁的含量和分布。基于氢键的叠加性、协同性以及纤维素链物理纠缠相互作用,无需任何粘合剂,仅仅通过高温热压的方式就可以把Cellulose@Fe3O4压缩成全生物质、高机械强度、结构紧密的块状材料(BCFCs)。当纤维素表面纳米四氧化三铁含量为20 wt%时,块状材料的密度为1.7 g/cm3,压缩强度为213.6 MPa,并具有优异的生物降解能力。同时,本部分工作也证明以原位生成的填料的方式比机械共混的方式在增强复合材料方面更有优势。这种全新的生物质表面功能化策略不只适用于纤维素粉末,也可以扩展到其他的生物质材料,制备出一系列的可持续生物质材料。第二部分工作,通过共沉淀法在纤维素表面原位生成纳米四氧化三铁、纳米铁黄(FeOOH)及纳米普鲁士蓝粒子(PB),并制备出了红(Cellulose@Fe3O4)、黄(Cellulose@FeOOH)、蓝(Cellulose@PB)三原色复合材料(三原色粒子分别为纤维素含量的10 wt%)。通过调控纤维素表面三原色粒子的含量来调节复合材料的饱和度。基于三原色基本原理,三原色之间都是独立的,自然界的任何光都是由三种光色按不同比例混合而成的。把三原色复合材料加入到聚合物基体中就可以实现可见光任意颜色的调配。为了证明这种着色策略的普适性,分别选择了环氧树脂(Epoxy)、聚醋酸乙烯酯(PVAc)以及聚苯乙烯(PS)作为聚合物基体,加入三原色复合材料后调配出了一系列不同的颜色。制备出的聚合物复合材料还具有优异的紫外吸收能力。这种着色方法,具有一定的普适性,制备出的聚合物复合材料具有优异的耐候性、着色持久、颜色可任意调节,为聚合物着色提供了新的可借鉴方法。第三部分工作,通过共沉淀法,在纤维素表面原位生成纳米四氧化三铁(10 wt%)。利用碱/尿素/水体系低温条件,快速溶解了木质素、Cellulose@Fe3O4,在形成的均匀的溶液中加入钙离子以及环氧氯丙烷交联剂,基于化学交联和物理交联的双网络互穿策略,制备了磁性生物质水凝胶。制备出的磁性Cellulose@Fe3O4/Lignin-Ca2+水凝胶具有优异的弹性,且压缩强度高达300 kPa(70%应变下)、优异的耐火性能以及紫外吸收性能(100%)。更重要的是,基于Fe3O4纳米粒子的光热效应,在近红外光(波长为808 nm)的照射下,磁性水凝胶可以实现表面光刻和切割,也可以在水下和狭小空间内等透近红外光材料中实现精准的光刻。因此,制备出的磁性水凝胶在光学、电子和传感器领域具有良好的应用前景。第四部分工作,以第三部分的工作内容为基础,在碱/尿素体系低温溶解Cellulose@Fe3O4复合材料,加入环氧氯丙烷交联剂,通过控制交联时间实现自增稠、自增强、3D打印墨水的制备。运用3D打印技术和真空冷冻技术制备出了网状结构的磁性Cellulose@Fe3O4气凝胶。磁性纤维素基气凝胶是吸附和去除水中有机污染物的理想吸附剂。磁性气凝胶中的Fe3O4纳米粒子作为磁性吸附有机物的捕捉剂和载体,提供了较大的活性中心,使有机污染物快速、稳定的结合在它的表面。磁性气凝胶对亚甲基蓝(MB)的吸附效果取决于溶液pH值,磁性气凝胶对MB(5.6 mg/L,pH9)的去除效率为88.5%,在室温下几乎瞬间发生。此外,收集到的气凝胶-MB杂化物可以通过酸洗(pH3)重新活化磁性气凝胶,而气凝胶的吸附性能没有显著变化。磁性气凝胶能够快速、有效、循环地吸附有机物,为水质的修复工作提供了一种低成本、可循环的方法。更多还原

【Abstract】 Petroleum based synthetic polymer materials bring seriously environmental problems during processing and under application.It is very important for us to study and develop sustainable,environmental-friendly polymer materials.It is feasible to choose natural sustainable polymer to replace some fossil based polymer step by step.As a result,the cellulose is choosen as the basic raw material in terms of renewable,biodegradable and the most widely available polymer on earth.The Cellulose@Fe3O4 composite is prepared based on the micro-nanostructure,in which the functional Fe3O4 nanoparticles(NPs)are in-situ formed on the surface of cellulose.Functional composites are designed based on as-prepared Cellulose@Fe3O4 composite.In the first part of the work,the reactive cores(Fe3O4 NPs)are anchored onto the cellulose chains by co-precipitation method.And the content and distribution of Fe3O4 NPs on surface of cellulose are easily regulated.Due to the additivity and cooperativity of hydrogen bonds as well as physical entanglement from cellulose chains,the biomass bulk materials(BCFCs)are prepared via in-situ formation of Fe3O4 NPs on the cellulose chains followed by hot-pressing without adhesion agent,leading to high density(1.7 g/cm3)magnetic medium,high compressive strength(CS)(213.6 MPa ±3.5 MPa)and excellent biodegradable property.This novel approach has a comprehensive effect on most of cellulose-based composites which indicates in-situ generating fillers are more efficient than blend fillers.This new strategy of biomass surface is not only suitable for cellulose powder,but also can be extended to other biomass materials.A series of green sustainable structural materials are prepared based on the new strategy.In the second part of the work,the Fe3O4,FeOOH and PB NPs are in-situ generated on the surface of cellulose by co-precipitation method,respectively.Three primary color composites(red Cellulose@Fe3O4,yellow Cellulose@FeOOH and blue Cellulose@PB)are prepared(the content of three primary color NPs is 10 wt%,respectively).The degree of saturation of the composites can be adjusted by regulating content of the three primary color nanoparticles on the surface of cellulose.Based on basic trichromatic principle,the three primary colors are independent,and any color can be mixed by three primary colors in different proportions.Arbitrary colors over the whole visible spectra can be prepared by mixing the three primary color composites at different ratios in the polymer field.To prove the universality of the coloring strategy,epoxy resin,polyvinyl acetate(PVAc)and polystyrene(PS)are selected as polymer matrix.Consequently,the prepared polymer composites have excellent UV absorption ability,durability and scalable colors,providing a new method in the polymer coloring field.In the third part of the work,the Fe3O4 NPs(10 wt%)are in-situ grown on the surface of cellulose by co-precipitation method.The lignin and Cellulose@Fe3O4 composites are quickly dissolved under alkali/urea/water system(-12℃).A novel Cellulose@Fe3O4/lignin-Ca2+hydrogel is prepared based on chemical and physical crosslinking networks by adding calcium ions and crosslinking agent(epichlorohydrin)into the formed homogeneous solution.The magnetic hydrogel displays excellent compressive strength(up to 300 kPa)and its elasticity is well-maintained under the temperature(-25～100℃).In addition,the magnetic hydrogel displays the outstanding fire resistance and UV absorption(100%)properties.Interestingly,the magnetic hydrogel exhibits controllable photoetching patterns based on the photothermal effect of Fe3O4 NPs under near-infrared(NIR)irradiation(808 nm),especially in the different circumstances including enclosed space and underwater condition.The photoetching magnetic cellulose-based hydrogel has great potential toward environmentally-friendly devices and applications in optics,electronics.In the fourth part of the work,drawing lessons from the third part of the work,the magnetic Cellulose@Fe3O4 hydrogel is prepared by adding the crosslinking agent(epichlorohydrin)in the alkali/urea/water system(-12℃).The self-thickening and self-strengthening hydrogel ink is achieved by regulating crosslinking time.The 3D printing of cellulose-based aerogel is achieved by direct ink writing with moderate rheology,and freezing drying.The magnetic cellulose-based aerogels are ideal adsorbers for adsorbing and removing organic pollutants from water.As catchers and carriers for magnetic removal,the Fe3O4 NPs of aerogel provide large active sites,where organic pollution enables fast and stable covalent binding on the surface.The adsorption effect of methylene blue(MB)is dependent on pH and the removal efficiency of MB(5.6 mg L-1,pH9)is 88.5%for magnetic aerogel,which occurs almost instantaneously at room temperature.In addition,the collected aerogel-MB hybrid can be reactivated by acid-washing(pH3),without significant changes in the adsorption performance of magnetic aerogel.The magnetic aerogel exhibits a fast,efficient and sustainable removal of organic pollutants,which provides an inexpensive and recyclable way for water remediation.更多还原