【作者】 邵春光；

【导师】 洪时明； 李良彬；

【作者基本信息】 西南交通大学 ， 材料学， 2009， 博士

【摘要】 高分子物理主要由三个部分组成:第一方面是高分子的结构,包括单个分子的结构和聚集态的结构,高分子不同尺度的结构共同决定了材料的各种性能。第二方面是高分子材料的性能,区别于小分子材料,高分子材料具备特有的粘弹性。第三,高分子材料的结构与力学性能关系,高分子有很多尺度上的结构,这些结构的协同作用共同确定了高分子材料的性能。研究高分子材料在加工过程中的物理问题,可以获得材料的结构变化对其力学行性能的影响。同时,可以获得合适的加工方法,指导生产并为工业加工提供试验基础。本论文分为三个部分:第一部分是拉伸装置的设计及应用;第二部分为非晶硫(活性聚合物)的原位拉伸实验;第三个部分为间规聚丙烯sPP(晶体聚合物)的原位拉伸实验:(一)为了连接材料的微观结构和宏观力学性能,必须建立一套原位检测装置,可以同时获得材料形变过程中的微观结构变化和力学性能特性两个重要数据。为此,我们自行研制了一台微型精密拉伸装置,该装置具有拉伸速率可调、受测样品的温度可调等特性,配有高分辨率CCD摄像头,可以同时给出材料的工程应力-应变和真应力-应变曲线。配套有Labview处理程序,可以实时观测样品的宽度变化、控制电机的转速、控制样品温度。结合表征手段(X射线散射、红外光谱、小角激光散射等)可以同时给出材料形变过程中的结构变化信息。(二)拉伸诱导非晶硫的相转变以及微观结构变化对样品力学性能的影响。我们通过快速增压过程获得大块非晶硫(直径为20mm,厚度为3mm),非晶硫实际上是一种超分子材料,是由长链硫原子组成的高分子材料。高温情况下(温度高于140℃时),熔融状的硫是一种高分子熔体,具有高分子熔体的所有特征:比如粘度高、分子量大等特点。利用快速增压瞬间冻结单质硫熔体状态时的结构,可以得到大块的非晶单质硫。我们利用自制的精密拉伸装置与广角WAXD衍射仪联用,第一次原位在线观测到非晶高分子硫的结构变化,并指出了拉伸速率在其结构变化过程中的重要作用:(1)精密拉伸装置精确控制拉伸速率和拉伸长度,拉伸速度可变,可变范围为0.58—348μm/s。首次在一个很宽的拉伸速率范围里研究拉伸对材料结构变化的影响。该装置附有高精度力传感器,其精度为0.1N,可实时反馈材料的力学特性。(2)利用Mar 345广角X射线衍射仪,实时检测非晶硫的相变、结晶、晶体取向等微观结构变化情况,两者的联用给出材料的微观结构和力学性能的关系,得到不同拉伸速率对材料结构的影响。相同的实验温度下(25℃),以1.74—5.8μm/s的速率拉伸可以得到纤维硫,而1.74μm/s以下的拉伸速率下得到硫的单斜相,由此可以确定临界拉伸速率为1.74μm/s。(3)从外力场和温度场两个方面讨论加工方法对材料力学性能和结构的影响,得出的结论是:温度场和外力场的耦合作用会影响非晶硫聚合物的结构变化。在一定的温度下(室温25℃),力场的作用随着拉伸速率的提高越来越明显,当拉伸速率高于某一临界拉伸速率1.74μm/s时,外力场的作用占主导地位,可以得到纤维硫;当拉伸速率低于此临界值时,温度场起主要作用,得到单斜硫。(三)拉伸过程中sPP的结构变化,以及片晶厚度对其力学性能的影响。sPP是一种晶体聚合物,应用广泛。多用作制造薄膜、复合薄膜,有良好的透明性和表面光泽,能耐120℃的温度。与非晶聚合物(如:非晶硫)不同,晶体聚合物的结构更复杂,研究其结构与力学性能关系一直是人们关注的重要课题。我们的创新在于,通过不同的温度下等温结晶、淬火后高温回火等手段,得到具有不同片晶厚度的sPP材料。研究在单轴拉伸过程中,片晶厚度对其力学性能的影响,同时研究不同厚度的片晶在拉伸过程中的微观结构变化。我们以(200)晶面为研究对象,利用该晶面的X射线的衍射图谱的特征(包括峰位、衍射方位角、半峰全宽、衍射峰面积等参数)来分析材料的微观结构变化。同时我们把工程应力—应变曲线分为3个部分:完全弹性区、完全弹性区-屈服点的过渡区、屈服后。观察这些区域内晶体部分的微观结构变化,以及这些变化对材料力学性能的影响:比如结构变化和材料的弹性模量、屈服强度等等。本次实验是在相同的拉伸速率、相同的实验温度、初始样品结晶度基本相等的情况下进行,研究了拉伸过程中外部作用力在非晶区和晶区的加载情况,片晶厚度对sPP材料的力学性能的影响等。更多还原

【Abstract】 Polymer Physics concerns three main aspects: the first is the structure of the polymer, including the individual elements of the structure and aggregation of the structure of the polymer, while micro-structure directly determines the mechanical properties of materials. The second aspect is the performance of polymer materials, whose viscoelastic properties are the unique performance beyond the other materials. And the third is the relationship between structure and mechanical properties. There are a lot of scales in polymer structure, and the synergies of these structures determine the material properties. Research of the physical problems during the polymer processing can access to material changes influenced by the mechanical properties, while it also provides an experimental basis for the processing industry. This paper is divided into two parts: the supermolecular surphor for Supramolecular amorphous sulfur （amorphous polymer） in situ tensile test, and syndiotactic polypropylene sPP （crystal polymer） in situ tensile test.1) Homemade Miniature Mechanical TesterWe made a miniature mechanical tester, which can change the drawing rate and the sample temperature. With hi-precision CCD camera, it’s able to get the Engineering stress-strain and the true Engineering stress-strain curve. Based on the Labview software, we can process the change of the sample’s width, control the motor’s rotation rate and the drawing rate. Furthermore, the homemade miniature mechanical tester is applicable for various light sources and different temperatures. After the installation onto the equipment measuring the micro-structure, it’s easy to observe the material structure change online during drawing and compressing.2) Deformation Induced Linear Chain-Ring Transition and Crystallization of Living Polymer SulfurThe large bulk amorphous sulfur with a diameter of 18 mm and a thickness of 1 mm was obtained by a rapid high-pressure jump apparatus, which has a pressing rate of 100 GPa/s. The large bulk amorphous sulfur was cut into small strips with a length and a width of 12 and 1.5 mm respectively. Amorphous sulfur was studied as the representative living polymer. At high-temperature melt or amorphous state, element sulfur is in a high-molecular-weight （HMW） linear chain configuration, while sulfur crystals generally contain low-molecular-weight （LMW） rings. This is the first time to study the structure changes of the amorphous sulfur under uni-axial deformation with in-situ WAXD: （1） Drawing experiments were carried out under room temperature （25℃）. Samples were mounted between two clamps of a homemade miniature mechanical tester. The mechanical error of the apparatus is less than 0.02 mm with a displacement of 100 mm. The drawing speed can be varied from 0.58 to 348μm/s with a step of 0.58μm/s. The error of the force sensor is about 0.1 N. （2） WAXS measurements were performed on a setup with Mar 345 image plate as detector and Mo KR as the source （wavelength is 0.07107 nm）. The information such as changes of crystallinity, phase transition, orientation of the crysal can be extracted form the WAXD image. Corresponding to the mechanical properties of the amorphous sulfur, the conclustion is that both thermal and drawing can induce chain scission and reforming, which leads to the transition between linear chain and rings. With the large drawing rates from 1.74 to 5.8μm/s, deformation-induced chain scission dominates, which results into fibrous phase composing of HMW linear chains and LMW cyclosulfur phases (S₁₈ and S₈). Under the low deformation rates （below 1.74μm/s）, the thermal effect takes over and leads to the formation of S8 phases which is similar to that under quiescent condition. 3) Streching of sPP and effect of lamellar thickness on structure evolutionsPP is one kind of the important semicrystal polymer, with many excellent properties such as transparency, surface gloss and special mechanical properties. It has been the most popular thermoplastics, used widly for the food industry, film engineering etc.As an important semi-crystalline polymer, the effect of sPP’s structure on its mechanical properties should be an interesting region. Compared with amorphous polymers, crystalline polymers are complicated systems, with an amorphous phase interlaying crystalline lamellae. The strength and toughness of crystalline system are interdependent due to crystalinity, lamellae thickness, molecular orientation etc. In this investigation, sPP samples with different lamellae thickness were obtained from different prepared method: isothermally crystallization and annealed crystallization. To correlate the structure changes and the mechanical properties, the engineering force curves were divded into three regions: part （1） Complete elastic region, part （2） Plastic region （from the first yield point to the second yield point） and part （3） after necking. The （200） crysal planes were chosen to study the structure changes of the crysal lattice under deformation. The most astonishing finding is the average d-spacing changes of （200） crystal planes. Since Havard and Thackay model was insufficient to explain our experiment, we established another model, in which the changes of the grain’s micro-strain agree well with that of average d-spacing.更多还原