【作者】 栾立醒；

【导师】 吴唯；

【作者基本信息】 华东理工大学 ， 材料科学与工程， 2011， 博士

【摘要】 本论文以聚丙烯(PP)为基体树脂、以天然海藻纤维(SW)为增强材料,制备了全新的聚丙烯/天然海藻纤维(PP/SW)复合材料。基于对“熔融加工-注塑成型”工艺参数的优化,在普通热塑性复合材料成型设备中成功制备了PP/SW复合材料,并对其力学性能、热机械性能、结晶性能、动态流变特性、热稳定性及燃烧性能进行了详细表征。本论文提出了PP/SW复合材料内部相结构的转变模型,并发现SW纤维对PP树脂的固相阻燃剂功效。首先探讨PP/SW复合材料的可加工性,比较了SW纤维添加量、螺杆挤出机类型对复合材料熔融过程的影响。实验结果表明,双螺杆挤出机可有效对PP/SW复合材料进行熔融加工,能在保证SW纤维热稳定性的同时实现其在PP树脂中良好的分散性。TPU可作为高效熔融助剂消除熔体破裂现象。然而SW纤维添加量不应超过50wt%,以保证足够的熔体流动性能；熔融温度不应超过185℃,螺杆转速不应超过60rpm,以避免SW纤维剧烈热降解的发生。同时,PP/SW复合材料可通过注塑成型工艺制备,最佳注塑成型参数为：注塑温度=180℃,螺杆转速=60rpm,注塑压力=保压压力=60bar,模具温度=60℃,冷却时间=45s。通过力学性能表征衡量了SW纤维对PP树脂的增强效果。研究表明,表面碱处理能去除杂质从而提高SW纤维强度。然而PP树脂与SW纤维之间的弱相容性导致复合材料低劣的力学强度,因此必须使用界面相容剂。本论文将界面相容剂作用机理区分为“内相容机理”及“外相容机理”。结果表明“外相容剂”MAPP及“内相容剂”CESA均能有效提高PP/SW复合材料的力学强度；热机械测试中储能模量及损耗模量的提高同样证明了SW纤维对PP树脂的增强作用。然而损耗因子的不同改变趋势证明两种相容剂不同的作用机理；MAPP提高了PP/SW复合材料的刚性而CESA提高了柔性。SW纤维能加快PP树脂的结晶过程,但降低了相对结晶度。MAPP及CESA均能提高PP树脂的相对结晶度,充分发挥SW纤维的异相成核作用。动态流变学测试给出界面相容剂对PP/SW复合材料相结构改变的信息。SW纤维能有效的增强PP树脂,末端区“牛顿平台”的出现说明PP树脂与SW纤维物理交联网络的形成；同时PP/SW复合材料较宽的线性粘弹区域证明了成型加工工艺的可行性。CESA通过对相结构的改变,从本质上提高了PP树脂与SW纤维之间物理交联网络的表观屈服应力；而MAPP对末端区特性改变不明显。通过“时-温等效原理”分析,CESA将PP/SW复合材料从非均相体系转变为均相体系,从而提高了相结构的稳定性。在测试温度范围内,CESA避免了PP/SW复合材料内部相分离情况的发生。本论文还系统研究了PP/SW复合材料的热降解及燃烧性能。SW凭借自身良好热稳定性,能有效推迟PP树脂的热降解过程。SW纤维同时能发挥固相阻燃功效,显著降低PP树脂的燃烧参数。稳定的相结构有利于充分发挥SW纤维阻燃效应,最终实现其热释放总量及热释放速率峰值分别下降25%和75%,达到普通应用标准。然而,SW纤维没有改变PP树脂的可燃性。研究表明,PP/SW复合材料具有理想的加工性能,其基本性能达到使用要求；同时PP/SW复合材料的耐热、耐燃烧性能明显优于PP树脂,具有耐热复合材料的应用前景。本论文的研究丰富了PP/NVF复合材料中的界面相容剂作用理论,并为此类复合材料研究提出新的思路。更多还原

【Abstract】 In this thesis, seaweed fibre (SW) is adopted as reinforcing fibre for polypropylene matrix (PP) for the first time, the novel polypropylene/seaweed fibre (PP/SW) composites is prepared. After optimization of the parameters during "melt extrusion-injection moulding", PP/SW composites are successfully prepared by traditional processing equipments. The mechanical, thermal dynamical, crystallization, dynamic rheological properities as well as thermal decomposition and combustion progressions are well characterized. The model for phase structure transition of PP/SW composites is proposed as well as the solid-phase flame retardancy of SW fibre for PP matrix.Taking consideration of the influence of SW content and type of extruder on the compounding, the processability of PP/SW composites is well evaluated. Based on the results, PP/SW composites are successfully prepared in a twin-screw extruder, which maintain the thermal stability of SW fibre as well as realize fine dispersion within PP matrix. TPU could act as efficient PPA (Polymer Processing Aid) in compounding that eliminates melt-fracture phenomena in PP/SW melt. However, SW content should below 50wt% in order to keep enough melt flow rate. Compounding temperature and rotation speed of screw should be strictly controlled below 185℃and 60rpm to avoid fierce thermal decomposition of SW fibre during extrusion. PP/SW composites could be easlier moulded in-mjection maschine, the ideal moulding parameters in this thesis are:injection temperature=180℃, rotation speed of screw=60rpm, injection pressure=moulding pressure=60bar, moulding temperature=60℃and cooling time=45s.The reinforcing effect of SW fibre for PP matrix is evaluated by mechanical characterization. According to the properties, surface alkalization is could remove impurities from SW fibre thus improve its stiffness. However, the poor adhesion between PP matrix and SW fibre limits the properties of PP/SW composites; compatibilization and lubricating are of necessity. The lubricating effects are classified into "inner effect" and "outter effect" in this thesis. Based on the results, MAPP as "inner lubricant" and CESA as "outter lubricant" can both enhance the mechanical properties of PP/SW composites, which is in agreement to the raing of storage modulus and loss modulus from DMA test. Diversed effects on the damping factor state their difference in lubricating mechanisms, the stiffness is raised by MAPP while CESA improved the elasticity of PP/SW composites.SW fibre accelerates the process of crystallization of PP matrix, but reduces its degree of crystallization. With either MAPP or CESA, the degree of crystallization is improved which proves the heterogeneous nucleation effect of SW fibre for PP matrix.Dynamic rheological characterizations provide important information on the transition of phase structure for PP/SW composites. The wide linear viscoelastic region signifies fine dispersion of SW fibre, as well as feasibility of compounding and moulding process. A formation of "Newton Plateau" indicates the establishment of physical network between PP matrix and SW fibre. CESA remarkably changes the phase structure of PP/SW composites, and achieve a higher apparent yield stress; while MAPP leads to slight influence on the rheological properties. With "time-temperature superposition principle", it can be concluded that CESA transforms PP/SW composites from heterogeneous system into homogeneous system. Within studied temperature region, no evidence for phase-separation is traced after the addition of CESA.Moreover, the thermal decomposition and combustion behaviour of PP/SW composites are well studied in this thesis. With high thermal stability, SW fibre could delay the thermal decomposition of matrix. SW fibre also acts as a solid-phase flame retardant in the composite, remarkably reduces the combustion parameters of PP matrix. Higher uniformity in the composite is beneficial for SW fibre’s retarding effect, the total heat release and peak heat release rate are declined by 25% and 75%, respectively. However, SW fibre hardly reduces the flammability of PP matrix.To conclude, PP/SW composites possess favourable processability with satisfying mechanical properties for normal usage. The heat and flame resistance of PP/SW composites is greatly higher in comparsion to PP matrix, thus promises its potential in applications. The lubricating mechanism for PP/NVF composites and SW fibre’s interesting flame retarding effect found in this thesis could promote related research.更多还原