基于石墨纳米片的聚乳酸复合材料的结构与性能研究

发布时间：2018-06-24 13:20

本文选题：聚乳酸 + 石墨纳米片　；参考：《扬州大学》2015年硕士论文

【摘要】：石墨是一种最常见的碳材料,其原料来源广泛、价格实惠。组成石墨的最基本单元是石墨烯,一种碳的二维晶体材料,其以独特的结构和优异的性能而备受关注。广大科研工作者就石墨烯展开了广泛的研究,其中包括石墨烯的制备和其复合材料。石墨烯的制备方法很多,但是往往能制得单片层的石墨烯量很少,得到更多的是厚度不一的石墨纳米片。将其与聚合物复合能够极大的改善基体的性能,而聚乳酸(PLA)是一种综合性能较好的生物可降解脂肪族聚酯,但其质脆、易弯曲变形等缺陷限制了其应用,填充改性是提高PLA综合性能的有效方法。PLA与石墨纳米片复合制备复合材料的研究才刚起步,深入研究其结构与性能之间的关系可以对制备出满足不同需求的复合材料具有指导意义。本文首先以天然鳞片石墨为原料,采用改进的Hummers法制备氧化石墨(GO)。然后采用溶液共混的方法制备出了不同种类及不同含量的石墨纳米片的PLA复合材料,然后通过形貌表征、结构流变学以及蠕变与应力松弛等手段详细研究了复合材料的结构与性能,并通过粘弹性理论、结晶动力学模型、力学模型等描述了PLA/石墨纳米片复合材料的结构与性能之间的关系。(1)利用改进的Hummers方法成功制得了GO,通过X射线衍射(XRD)对GO及其它石墨纳米片的进行表征发现,石墨经氧化后,石墨的特征峰消失,而在11.6。附近出现一个衍射峰,表明氧化过程使片层间的间距加大。不同厚度的石墨纳米片的石墨特征峰随着石墨纳米片厚度的减少而减弱,当减小到一定厚度时,在10～20。之间也出现了一个馒头峰,这也说明随着石墨纳米片厚度减小,其长程有序结构被破坏。这一结果也通过Raman光谱得到进一步证明。(2) 复合体系流变学的研究表明,随着石墨纳米片含量的增加,体系的储能模量、损耗模量、复数粘度都增加,但是由于石墨纳米片在基体中的分散性影响,即使在10wt%石墨纳米片,PLAgCs体系也未出现明显的逾渗行为。在相同的石墨纳米片填充的情况下,GO填充的复合体系具有更高的储能模量,这是由于GO与基体之间具有良好的亲和力。通过对所得到的数据进行分析发现,石墨纳米片的加入有效的抑制了内部分子链团的松弛行为。(3) 石墨纳米片加入PLA中后,对PLA结晶后形成的晶体结构不产生任何影响；无论是在等温冷结晶还是在非等温结晶过程中,石墨纳米片都具有明显的促进PLA基钵晶核形成的异性成核作用。但是随着石墨纳米片含量的增加、纳米片厚度的降低,结晶活化能均增加,这是由于具有较大填充体积的填料能够有效阻碍分子链的扩散,石墨纳米片的成核作用占据结晶动力学的主导地位,都导致结晶速率增加。(4) 石墨纳米片的加入提高了复合材料的拉伸强度。在填充量相同的情况下,层数少的石墨烯对PLA力学性能的改善效果较好,这是由于层数少的石墨纳米片具有较大的填充体积所致。进一步在小应力或小应变的作用下对复合体系的粘弹行为的研究发现复合体系的蠕变和应力松弛都对温度以及外加应力或应变具有依赖性。石墨纳米片的加入能够有效抑制复合体系的蠕变和应力松弛行为。随着石墨纳米片含量的增加,蠕变应变减小,松弛模量增大,即石墨纳米片能有效抑制分子链的运动。在石墨纳米片添加量相同时,体系的蠕变量、松弛模量均随着石墨纳米片厚度的减少而增加,这是由于厚度减少的石墨烯纳米片具有更大的填充体积,能更好的抑制链段的运动所致。粘弹模型可以较好地用于描述材料的蠕变和应力松弛行为,并得到复合材料粘弹行为与结构有关的信息。
[Abstract]:Graphite is one of the most common carbon materials, with a wide range of raw materials and good price. The most basic unit of graphite is graphene, a two-dimensional crystal of carbon, which has attracted much attention with its unique structure and excellent properties. There are a lot of preparation methods of graphene, but often the amount of graphene in a single layer is very small, and more graphite nanoscale is obtained. It can greatly improve the properties of the matrix, and PLA is a kind of biodegradable aliphatic polyester with better comprehensive properties, but its quality is brittle and easy. Defects such as bending and deformation restrict its application. Filling modification is an effective method to improve the comprehensive properties of PLA. The study of composite materials prepared by.PLA and graphite nanoscale has just started. The study of the relationship between structure and properties can be of guiding significance for the preparation of composite materials with different needs. Graphite oxide (GO) was prepared by improved Hummers method. Then the PLA composites of different types and different content of graphite nanoscale were prepared by solution blending. Then the structure and properties of the composites were studied in detail by means of morphology, structural rheology, creep and stress relaxation. The relationship between the structure and properties of PLA/ Graphite Nanocomposite was described by viscoelastic theory, crystallization kinetics model and mechanical model. (1) GO was successfully made by the improved Hummers method. The characterization of GO and other graphite nanoscale by X ray diffraction (XRD) was found, and the characteristic peak of graphite after the graphite was oxidized. A diffraction peak near 11.6. shows that the oxidation process increases the interval between layers. The graphite characteristic peak of different thickness of graphite nanoscale decreases with the decrease of the thickness of graphite nanoscale. When the thickness is reduced to a certain thickness, a steamed bun peak is found between 10 and 20., which also indicates that the thickness of the graphite nanoscale is also with the thickness of the graphite nanoscale. The result is further proved by the Raman spectrum. (2) the study of the rheology of the composite system shows that the energy storage modulus, the loss modulus and the complex viscosity of the system increase with the increase of the content of the graphite nanoscale, but the effect of the dispersion of graphite nanoscale in the matrix is even in the 10wt%. There is no obvious percolation in the graphite nanoscale and PLAgCs system. In the case of the same graphite nanoscale, the GO filled composite system has a higher energy storage modulus, which is due to the good affinity between the GO and the matrix. By analyzing the data obtained, it is found that the graphite nanoparticles are effectively suppressed. The relaxation behavior of the internal molecular chain groups. (3) graphite nanoscale has no effect on the crystal structure formed by the crystallization of PLA after adding PLA to the crystal structure. In the process of isothermal cold crystallization or in the non isothermal crystallization process, graphite nanoscale has a significant effect on the nucleation of the PLA base. The increase of the content of the film, the decrease of the thickness of the nanoscale and the increase of the activation energy of the crystal, this is because the filler with a larger filling volume can effectively impede the diffusion of the molecular chain. The nucleation of the graphite nanoscale occupies the dominant position of the crystallization kinetics and leads to the increase of the crystallization rate. (4) the addition of graphite nanoscale increases the composite material. Tensile strength. In the case of the same filling amount, the less number of graphene has better effect on the mechanical properties of PLA, which is due to the larger filling volume of the graphite nanoscale with few layers. Further study on the viscoelastic behavior of the composite system under the action of small stress or small strain found the creep and stress of the composite system. The addition of graphite nanoscale can effectively inhibit the creep and stress relaxation of the composite system. With the increase of the content of the graphite nanoscale, the creep strain decreases and the relaxation modulus increases. That is, graphite nanoscale can effectively inhibit the movement of the molecular chain. At the same time, the creep and relaxation moduli of the system increase with the decrease of the thickness of the graphite nanoscale, which is due to the larger filling volume of the graphene nanoscale with the decrease of thickness, which can better inhibit the movement of the chain segments. The viscoelastic model can be used to describe the creep and stress relaxation behavior of the material well, and the composite can be used to get the composite. The information related to the structure of the viscoelastic behavior of the material.
【学位授予单位】：扬州大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB332

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