【作者】 张玥；

【导师】 吴驰飞；

【作者基本信息】 华东理工大学 ， 材料科学与工程， 2011， 博士

【摘要】 本论文采用反应挤出法以回收聚对苯二甲酸乙二酯(R-PET)为基体,制备了R-PET与聚乙烯(PE)的增容超韧共混物。论文中探讨了PE的类型、PE与增容剂的相互作用以及增容剂在共混物中的分布对R-PET/PE共混物结构和性能的影响,并且通过改善加工工艺和后处理工艺等来消除共混物的内应力,对提高PET回料的使用价值、加快PET的工业化回收进程具有深远的意义。主要研究结果如下：(1)以甲基丙烯酸缩水甘油酯接枝乙烯-辛烯共聚物(POE-g-GMA)作增容剂,选择高密度聚乙烯(HDPE)、线性低密度聚乙烯(LLDPE)、低密度聚乙烯(LDPE)和极低密度聚乙烯(VLDPE)分别与R-PET共混。首先根据粘度匹配原则确定了最佳加工温度为245℃,这低于PET的熔点(Tm),有利于抑制PET回料在加工过程中的降解反应。组分的粘度和界面张力数据证明VLDPE和POE-g-GMA的相容性最好,而HDPE与POE-g-GMA的相容性最差。刻蚀后的共混物扫描电镜(SEM)显示R-PET/HDPE共混物中HDPE与POE-g-GMA独立分散,而R-PET/VLDPE共混物的断面很粗糙,表明共混时有大量的POE-g-GMA渗透到VLDPE相中。选择与POE-g-GMA相容性适中的LLDPE或LDPE与R-PET共混有利于提高POE-g-GMA的增容效果,共混物冲击强度和断裂伸长率较大。差示扫描量热分析(DSC)表明POE-g-GMA对PET有异相成核作用,提高PET的结晶温度(Tc)。动态热机械分析(DMA)表明POE-g-GMA与PET反应生成的共聚物是影响POE-g-GMA运动的主要因素,也就是说共混物中POE-g-GMA与PET的化学作用力大于POE-g-GMA与PE的物理缠结力。(2)为了增强POE-g-GMA与PE的相互作用,采用过氧化二异丙苯(DCP)作引发剂引发PE与POE-g-GMA的接枝反应。与LDPE相比,LLDPE有较多的叔碳和较短的支链,LLDPE与POE-g-GMA发生接枝反应的机率较大而交联副反应较少,所以选择LLDPE与POE-g-GMA反应制备LLDPE-g-(POE-g-GMA)共聚物。红外光谱(FTIR)和固体核磁共振(13C-NMR)分析证明,加入0.2%的DCP后,POE-g-GMA成功地接枝到LLDPE分子上。广角X射线衍射(WAXD)结果显示LLDPE与POE-g-GMA接枝后晶型结构不变,但是衍射峰的相对强度降低。LLDPE分子链的支化和扩链破坏了LLDPE链段的规整性的,Tm和Tc减小。SEM结果表明,LLDPE/POE-g-GMA共混物化学接枝改性后明显减小了POE-g-GMA的粒径,两相界面模糊,力学性能提高,但是当体系中形成微交联结构后,断裂伸长率减小。(3)以相同的原料配比,采用一步共混法、物理两步共混法、化学接枝两步共混法和化学交联两步共混法制备了四种以R-PET为基体的共混物。共混物刻蚀后的SEM结果表明,一步共混法制得的R-PET/LLDPE/POE-g-GMA共混物的相结构呈粘附型,而采用两步法共混的样品相结构都呈包覆型,表明两步法有利于POE-g-GMA与LLDPE形成核壳粒子。化学接枝两步法制备的共混物界面处有纤维状物质,证明体系中有R-PET-g-POE-g-LLDPE共聚物生成,相容性得到了明显的改善,分子间作用力增大。化学接枝两步法制备的共混物中R-PET的Tg最小,表明分散相的支化核壳结构有利于POE-g-GMA与R-PET的增容反应,而如果分散相形成了交联核壳结构,会阻碍POE-g-GMA向R-PET相表面的运动,降低体系的相容性。力学性能测试结果表明,化学接枝法制备的共混物冲击强度和断裂伸长率明显增大,拉伸强度、弯曲强度和弯曲模量也比其他共混物的高。(4)采用WAXD和DSC研究了以上四种共混物中PET的晶型结构、结晶熔融行为和非等温结晶动力学。结果显示化学接枝两步法制备的共混物WAXD图谱上出现了两个新的衍射峰,表明提高共混物的增容反应程度能促进POE-g-GMA对R-PET的异相成核作用,R-PET的Tc、Tm提高,t1/2减小。由于PET在结晶后期存在球晶碰撞及二次结晶,共混物的非等温结晶动力学符合Mo方程。(5)通过优化注塑工艺和热处理工艺,减少PET制品内应力,进一步提高化学接枝两步法制备的共混物的韧性。结果表明熔体温度对共混物冲击强度的影响最大。随着热处理温度和时间的增加,共混物链段缠结强度增加,刚性提高,韧性先增大后降低,溶剂沉浸测试结果表明,共混物在60℃热处理25 h后,材料内应力显著减小,与热焓松弛参数拟合结果一致。根据共混物老化活化能预测材料在室温的使用寿命为12.2年。更多还原

【Abstract】 Super-toughened recycled poly (ethylene terephthalate) (R-PET)/polyethylene (PE) compatibilized blend was prepared by reaction extrusion. The effects of the type of PE, the miscibility between PE and compatibilizer, and the dispersion of compatibilizer on the morphology and properties of the blends were discussed. Processing and post-processing techniques were also investigated to remove the internal stress and further improve the toughness of the blend, which is meaningful to the industrial recovery of PET. The main results were presented as follows:(1) High density polyethylene (HDPE), linear low density polyethylene (LLDPE), low density polyethylene (LDPE) and very low density polyethylene (VLDPE) were chosen to blend with R-PET. Glycidyl methacrylate grafted poly(ethylene-octene) (POE-g-GMA) was used as compatibilizer. The optimum processing temperature of 245℃was confirmed by viscosity match principle, which is lower than the melting temperature (Tm) of PET, thus the degradation of R-PET was inhibited. The component viscosity and interfacial tension test showed the miscibility was best between VLDPE and POE-g-GMA and worst between HDPE and POE-g-GMA. The etched surface of the blend with VLDPE was very rough, indicating that a large amount of POE-g-GMA was migrated into VLDPE phase, while HDPE and POE-g-GMA dispersed in the matrix independently with wider distribution. It is clear that the proper miscibility of PE with POE-g-GMA is beneficial to improve the compatibilization effect of POE-g-GMA. Therefore, the impact strength and elongation at break of the blend with LLDPE or LDPE were higher than those of other two blends. Differential scanning calorimeter (DSC) results showed that POE-g-GMA has heterogeneous nucleating effect on PET and increased the Tc of R-PET. Dynamic mechanical analysis (DMA) results showed that the formation of PET-g-POE was the major factor in hindering the POE-g-GMA movement, in other words, the intermolecular forces between PE and POE-g-GMA are weaker than the intramolecular forces of PET-g-POE.(2) Dicumyl peroxide (DCP) was used as initiator to initiate the grafting reaction between PE and POE-g-GMA to improve the compatibilization effect. Compared with LDPE. LLDPE contains more tertiary carbon atoms and shorter branched chains. Therefore, it shows higher grafting reaction and lower crosslinking side reaction probability than LDPE and was finally selected to prepared graft copolymer PE-g-(POE-g-GMA). Fourier transform infrared ray and nuclear magnetic resonance analysis proved POE-g-GMA was grafted onto LLDPE by the initiation of 0.2% DCP. Wide angle X-ray diffraction (WAXD) and DSC measurements showed the integrity of LLDPE chains was destroyed after grafting reaction, leading to smaller diffraction peak intensities as well as lower Tm and Tc, but the crystalline structure of LLDPE wasn’t changed. LLDPE-g-(POE-g-GMA) graft copolymer displayed finer distribution of POE-g-GMA and better mechanical properties.(3) Four R-PET-based blends were respectively prepared by one-step blending, two-step physical blending, two-step chemical graft blending and two-step chemical crosslink blending. The etched surface showed the dispersed phase of one-step blend exhibited adhesion structure while the two-step blends all exhibited encapsulating structure, indicating two-step blending is favorable to the formation of core-shell structure of the dispersed phase in the blend. Moreover, fibrils can be seen at the interface of the two-step chemical graft blend, which improved the compatibility of the blend and increased the mechanical properties remarkably. However, the two-step chemical crosslink blend showed worse compatibility due to the crosslinked core-shell structure obstructed the movement of POE-g-GMA towards R-PET phase.(4) The crystal structure, crystallization and melting behavior and nonisothermal crystallization kinetics of these R-PET based blends were studied by WAXD and DSC, respectively. The WAXD patterns of the two-step chemical grafting blend showed two new diffraction peaks. It indicated that the improvement of compatibility of the blend promoted the heterogeneous nucleating effect of POE-g-GMA, consequently the Tc, Tm of PET increased and t1/2 decreased.(5) In order to improve the toughness of the two-step chemical grafting blend, the injection techniques were optimized. The results showed the melt temperature was the most influential factor on the impact strength of the blend. The rigidity increased and the toughness increased firstly and then decreased with the increase of annealing temperature and time. The solvent immersion test showed the internal stress decreased significantly of the blend annealed at 60℃for longer than 25 h, according with the result of enthalpy relaxation parameters fitting. The estimated service life of the blend was 12.2 year based on the annealing activation energy.更多还原