【作者】 宋娜；

【导师】 许鑫华；

【作者基本信息】 天津大学 ， 材料学， 2009， 博士

【摘要】 本文使用啮合同向双螺杆挤出机在不同加工条件下制备了不同共混组成的等规聚丙烯/聚乙烯-1-辛烯(PP/POE)共混物,利用在线小角激光背散射系统(in-line SALS)和扫描电子显微镜(SEM)研究了PP/POE在共混过程中的相分散和相归并过程,并研究了共混物的结晶性能和流变性能。使用in-line SALS和SEM对共混过程的瞬态分析表明PP/POE共混物在沿螺杆经加料斗-压缩输送-加热塑化-混合均质的挤出过程中,分散相粒子经历由最初的熔融混合,粒子尺寸较大,混合不均匀到分散混合细化,尺寸减小,分散均匀的过程。在共混过程中存在一个临界粒径尺寸,当粒径小于临界粒径尺寸时,会发生相的聚集,反之是相的分散过程。在本文所使用的原料及加工条件下,临界粒径尺寸为0.25μm(POE含量大于25wt-%时或POE含量20wt-%,转速小于84rpm时)。在沿螺杆距进料口1.33m的位置和口模处,随着分散相含量的增大,粒子间的碰撞聚集作用使分散相尺寸增大,分布宽度变大,分散呈不均匀状态;且当螺杆转速84rpm和共混温度范围210-220℃时,POE在PP中处于最佳分散状态。此外,对共混物的相归并过程进行了深入研究。实验结果表明在密炼机中当转子停止转动并降低PP/POE共混物温度时,在共混物发生结晶之前,没有相归并发生,在结晶过程中,有相归并行为;同时在结晶完善时相归并行为终止。且in-line SALS可以比较准确的反映本体系的共混过程。对于PP/POE(20/80),in-line SALS方法可灵敏的检测到PP的受限结晶,结晶温度较PP本体状态低30℃;广角X光衍射(WAXD)测试表明此时PP结晶形态仍为α晶。剪切诱导相归并时,认为PP/POE共混物形态演变应该是分成三段,这三段可以用不同的标度函数来刻画。研究了PP/POE共混物的结晶性能,探讨了共混组分对共混物热力学性能的影响。研究了POE的加入对PP等温结晶动力学的影响,结果表明Avrami方程能够较准确地描述共混物等温结晶初期过程;当POE作为分散相时,PP/POE共混物具有两个相对独立的结晶峰和熔融峰;等温结晶、熔融曲线及WAXD谱图分析表明POE的加入对PP的结晶起到了诱导结晶的作用,使得PP的晶粒尺寸变大。观察到当PP以小颗粒分散在POE中时会发生的受限结晶现象。通过TEM直接观察到了PP分散在POE中的形态,且随着PP含量的提高,颗粒形态粗化;相应的DSC及偏光分析表明以小颗粒分散在POE中的PP粒子发生了受限结晶。PP/POE体系的流变测试结果表明:温度是影响共混体系粘度的主要因素,温度越高,粘度越低;POE含量越高,体系粘度对温度的敏感性越弱;动态测试条件下,随着温度升高及POE含量的增加,体系的粘度降低,模量值也降低(POE含量10wt-%和20wt-%的组分例外)。动态频率扫描测试中,体系的动态剪切模量G ’和动态损耗模量G"随频率的升高而升高,复数粘度η*随频率的升高而降低。不同频率下模量和粘度与POE含量的关系都表明:当POE含量为10wt-%和20wt-%时,共混物的G ’和G "具有最高值;当温度为210℃和220℃时,POE含量10wt-%的共混物松弛时间最长。以上结果都说明POE含量为10wt-%或20wt-%的共混物分子链段的相互作用都强于其他组分的共混物,这一结果和PP/POE体系相形态有关。更多还原

【Abstract】 Isotactic polypropylene/ Poly(ethylene-1-octene) (PP/POE) blends with various blend ratios were prepared in an intermeshing co-rotating twin-screw extruder under different mixing conditions. The morphology development,thermal properties and rheology properties of PP/POE blends were investigated in details by Scanning Electron Microscopy (SEM), In-line Small Angle Laser Scattering (in-line SALS), Differential scanning calorimetry (DSC) and Rotational rheometer.The influences of blend composition and processing conditions (mixing time,rotor speed and mixing temperature) on phase morphology development of the blends were investigated by SEM. The experiment result showed the rule of phase morphology evolution of the blends, and the effect of viscoelastic rheological and thermodynamic properties on the rule are given.There are exist an critical particle size below which the phase colascene will be observed. Under the mixing conditions we chose, the critical particle size is 0.25μm. With the dipersed content incresing, the dispersed phase dimension is increased. The optimum mixing conditions is that 84rpm and 210-220℃.The solidification process of the blends in intrim mixer is investigated by SEM and in-line SALS. The result shows phase coalescence occurs in the normal cooling process and analysis the reason of it. The confinment crystallization behaviors of PP which the crystallization temperature is lowered than the bulk polymer was first obseverd during the solidification process. WAXD graph incidated that the crystallization structure is not chang. The syudy of shear induce phase coalescence of blends incidates that the morphology development should be composed of three parts. The three parts can be described by various scaling function.DSC was used to get the thermodynamic properties of PP/EOC blends. Melting, crystallization behaviors showed that the two components are partly miscible. When the POE dispersed as particles, melting curve and WAXD graph represents that the addition of POE do not affect the crystallizaiton structure of PP. The Avrami equation can be used to describe the isothermal crystallization of PP exactly. When the PP dispersed as particles in POE martix, the morphology of PP was obsevered by TEM in the solution directly. The corresponding DSC analysis indicates that the confinement crystallization is occur in the PP particles.The results of rheological measurement on PP/POE blends were list as follow. Temperature was a key factor in viscosity of the pure polymers and blends. The higher temperature the lower activation energy. It showed that viscosities of the blends were less sensitive to temperature. Under the condition of dynamic rheological measurements, viscosities and modulus decreased as temperature and addition of POE increased, except the blends with 10% and 20% POE. Under the condition of dynamic rheological measurement, the dynamic storage modulus, G’, and the dynamic loss modulus, G”increased as the frequency increased. The complex viscosity,η*decreased as the frequency increased. The relation between modulus , viscosity and addition of POE showed that blends with 10% or 20% POE had the highest value. The blends with 10% POE had the longest relaxation time,τx at the temperature 220℃and 230℃. The results all above showed that interaction between molecular chain in blends with 10% or 20% POE were stronger than other blends. This may be related to the brittle-tough transition.更多还原