【作者】 高华；

【导师】 王清文； 谢延军；

【作者基本信息】 东北林业大学 ， 生物材料工程， 2011， 博士

【摘要】 木塑复合材料是由木质纤维材料与热塑性塑料熔融复合形成的一类高性能、高附加值的新型环保材料,它的广泛应用为废旧塑料和木质纤维资源的高效利用提供了一条重要途径。然而,废旧塑料往往是由性质各异的几种非极性聚合物组成的混合物,塑料组分之间、塑料与木质纤维材料之间的相容性差,导致木塑复合材料的力学性能较低。本文以组成为80%PP-20%HDPE和80%HDPE-20%PP的聚烯烃混合物模拟聚烯烃类废旧塑料,马来酸酐(MAH)作为功能性接枝单体,过氧化二异丙苯(DCP)为引发剂,在双螺杆挤出机中熔融共混的同时进行接枝改性。考察了工艺参数及MAH用量对熔融指数和接枝率的影响,给出了每种接枝体系的最佳接枝条件。(1)聚烯烃共混物经马来酸酐接枝改性后,其拉伸强度和冲击强度得到提高；对于不同的共混物体系,MAH用量存在着不同的最佳值。(2)利用FTIR和SEM对共混接枝物进行表征,结果表明,通过接枝改性,在聚烯烃共混物中引入了极性酸酐基团,共混体系中PP和HDPE的相容性得到改善。(3)利用旋转流变仪对共混物流变性能的研究表明,80%PP-20%HDPE共混物接枝后更容易发生熔体结构破坏；随着MAH用量增加,共混物的分子量分布变宽；80%PP-20%HDPE共混物在低频区域出现“肩状倾向”、弹性增加和“拖尾”现象；80%HDPE-20%PP共混物随着MAH用量增加弹性特征越来越显著。(4)流变研究和挤出试验结果显示,与单一聚烯烃接枝物相比,共混接枝物的加工性能获得改善。以接枝改性的聚烯烃共混物作为基体,采用两步挤出法制备了木塑复合材料。研究了MAH用量、木粉填充量和木粉目数对复合材料的力学性能和尺寸稳定性的影响,结果表明, (1)聚烯烃共混物经过接枝改性后,木塑复合材料的力学性能得到显著提高,80%PP-20%HDPE基和80%HDPE-20%PP基木塑复合材料分别在MAH用量为1.0%和0.1%时综合力学性能最佳。(2)木粉填充量为70%时,复合材料的综合力学性能最好；当木粉目数为30-50时,复合材料的拉伸和弯曲性能最好,而冲击强度在60-80目时最佳。(3)聚烯烃共混物经过接枝改性后,木塑复合材料的吸水率和吸水厚度膨胀率显著降低,吸水速率下降。80%PP-20%HDPE基和80%HDPE-20%PP基木塑复合材料的24小时吸水率和吸水厚度膨胀率分别在MAH用量为1.0%和0.1%时最低。木塑复合材料的吸水率和厚度膨胀率都随着木粉含量增加而增加,随着木粉目数的增大而降低。(4)通过SEM观察断面形态,发现聚烯烃共混物经过接枝改性后,木粉与基体之间的界面结合得到改善。(5)利用共混与马来酸酐接枝相结合的方法对混合废旧塑料进行改性,木粉/混合废旧塑料复合材料的力学性能和尺寸稳定性都得到显著改善。运用旋转流变仪对木塑复合材料的流变性能和蠕变行为进行了研究,分析了MAH用量、木粉填充量和木粉目数对复合材料的性能的影响。结果表明, (1)聚烯烃共混物经过接枝改性后,复合材料的"Payne"效应不显著,说明界面结合增强；增加木粉含量和木粉目数,都会使复合材料的“Payne”效应变显著。(2)木塑复合材料的黏弹性行为偏离于聚烯烃共混物体系,表现出“似固体行为”；基体经过接枝改性后,木塑复合材料的储能模量、损耗模量和复数黏度都降低,频率对储能模量和损耗模量的影响增加,体系表现出强烈的剪切变稀行为。(3)随着木粉含量的增加,复合材料的储能模量和复数黏度都显著升高,似固体行为越来越显著；随着木粉目数的增加,复合材料的储能模量和复数黏度略有下降。(4)木塑复合材料的蠕变变形随着温度的升高而增加；基体经过接枝改性后,复合材料的蠕变变形显著降低,变形速率减慢,卸载后的残余应变也大大降低；随着木粉填充量的增加和木粉目数的减小,复合材料的蠕变变形降低,但填充量过多会因弱界面结合问题而导致变形增大。综上所述,利用熔融接枝法在聚烯烃共混物中引入极性酸酐基团,不但改善了聚烯烃共混物中PP和HDPE的相容性,而且提高了木粉与聚烯烃共混物之间的界面结合强度。这表明共混接枝改性的方法是利用混合废旧塑料制备高性能木塑复合材料的一种可行的方法。更多还原

【Abstract】 Wood plastic composites (WPC), usually made from wood fiber and thermoplastic, are environmentally friendly materials with good performance and high added value. The wide application of composites provides an alternative for effective utilization of waste plastic and natural fiber resources. However, the waste plastics are usually mixtures of various nonpolar polymers bearing the different properties. The compatibility between the compositions in the resulting WPC is weak thereby causing poor mechanical properties.The mixture of virgin PP and PE with varying proportions was compounded to simulate the mixed plastic wastes. Grafting maleic anhydride (MAH) onto 80%PP-20%HDPE and 80%HDPE-20%PP blends were performed in a twin screw extruder at the melt state in the presence of dicumyl peroxide (DCP) as initiator. The effects of extruding parameters and MAH content on melt flow index and grafting degree were investigaged and the optimized grafting conditions for each system were obtained. (1) Both the tensile strength and impact strength of grafted blends increased at the optimum MAH content; (2) Characterizing the grafted blends using FTIR and SEM techniques revealed that MAH can be grafted onto the PP/HDPE blends and the compatibility between PP and HDPE was improved. (3) The rheological analysis of PP/HDPE blends using the rotational rheometer showed that the melt structure of 80%PP-20%HDPE blends were easier to fail due to grafting and the blends exhibited a broader molecular distribution with increasing MAH content. A "shoulder shape tendency", increased elasticity, and trail phenomenon were observed at the low frequencies for 80%PP-20%HDPE blends. The elasticity of 80%HDPE-20%PP was obvious increased with the MAH content. (4) Rheological study and extrusion processes showed that the processibility of grafted blends was improved compared with the individually grafted polyolefin.The MAH grafted PP/HDPE blends were used as a polymer matrix to prepare the WPC by two-step extrusion. The effects of MAH and wood flour content, and particle size of wood flour on the mechanical properties and dimensional stability of WPC were respectively investigated. The results are summarized as below:(1) Mechanical properties of the resulting WPC were improved due to grafting. The optimum MAH contents were 1.0%and 0.1%for the 80%PP-20%HDPE based and 80%HDPE-20%PP based composites, respectively. (2) Addition of 70%wood flour provides the resulting WPC the good mechanical properties. The WPC obtained a highest tensile and flexural properties at the wood flour size of 30-50 meshes; however, is the size of 60-80 meshes was optimum for the impact strength of resulting WPC. (3) The water uptake and swelling of composites were significantly reduced due to grafting of matrix. For the 80%PP-20%HDPE based composites, the water uptake and swelling reach the lowest value after 24h immersion at 1.0%MAH level, while for 80%HDPE-20%PP based composites, the MAH content is 0.1%. The water uptake and swelling of composites increased with wood flour content and reduced with increase wood flour mesh. (4) The fractured WPC surfaces observed using SEM indicated an improved interfacial bonding between wood flour and matrix due to matrix grafting. (5) As using the mixed plastic wastes instead of origin PP/HDPE blends, the resulting WPCs exhibited a comparable improvement in the physical and mechanical properties.The rheological and creep behavior of WPC were investigated using the rotational rheometer at varying MAH content, wood flour content, and wood flour size. The results showed that, (1) Grafting the PP/HDPE blends eliminated the uPayne effect" of WPC, which confirmed the improved interfacial bonding. The "Payne effect" of WPC became observable with increasing wood flour content and wood flour mesh. (2) The WPC exhibited a solid-like behavior, which did not occur in the case of blends alone. The storage modulus, loss modulus and complex viscosity of WPC decreased due to MAH grafting. With increasing frequency, the storage modulus and loss modulus increased and the composites therefore exhibited a shear thinning behavior. (3) The storage modulus and complex viscosity of WPC elevated as increasing wood flour content suggesting that the "soild-like behavior" was more significant. The storage modulus and complex viscosity of WPC reduced with decreased wood particle size. (4) Increasing the environmental temperature resulted in an increased creep deformation of WPC. Grafting modification of PP/HDPE blends apparently reduced the creep of the resulting WPC. The creep deformation was generally reduced with increasing wood flour content and particle size of wood flour, except at the high wood concentrations due to the weak interfacial bonding.Summarily, incorporation of MAH into PP/HDPE blends via grafting reaction in the extruder faciliated the compatibility between the plastic compositions in the blends. The interfacial bonding between the grafted plastic blends and wood flour was also improved thereby. These results demonstrate that grafting blends with anhydride is a feasible approach to improve the properties of wood/plastic blend composites and provide an alternative strategy for utilizing the recycled waste plastics.更多还原