【作者】 施庆锋；

【导师】 郭卫红；

【作者基本信息】 华东理工大学 ， 材料科学与工程， 2011， 博士

【摘要】 聚乳酸(PLA)是一种高强度的生物可降解高分子材料,目前可被应用于医药、包装等行业,但由于聚乳酸的一些致命缺陷——脆性高、耐热性差、抗冲击性低、结晶速率过慢,严重限制了其在更多领域的应用。本论文在保持聚乳酸及其复合材料生物降解性的基础上,加入各种生物可降解填料,改善聚乳酸及其复合材料的力学、耐热等性能,扩大聚乳酸的应用范围。本文采用天然竹纤维(BF)和滑石粉(Talc)作为聚乳酸的填料,通过熔融共混和成型后热处理等方式得到PLA/BF/Talc复合材料。经过热处理后,PLA复合材料的耐热性能(HDT)得到大幅提高,PLA/20 wt%BF/20 wt%Talc复合材料提高了将近40℃；而单独加入竹纤维或滑石粉,PLA复合材料的HDT提高幅度不大；在PLA/20 wt%BF/ 20 wt%Talc复合材料热处理前后通过热变形温度仪(HDT)、差示扫描量热(DSC)、偏光显微镜(POM)、动态机械性能(DMA)、广角X-射线衍射(WAXD)等测试表征,发现PLA基体内并未发生键合、氢键等化学反应,而是在竹纤维、滑石粉同时存在下,基体中出现了横晶结晶现象；研究了在不同温度、时间、组份下PLA复合材料的横晶现象,并提出了形成横晶的机理；同时还发现,横晶结晶的形成在一定程度、一定填料含量内,提高了PLA/BF/Talc复合材料的力学性能。接着利用解偏振光法考察了PLA/BF/Talc复合材料的等温结晶动力学,结果表明只有在较低温度下结晶才基本符合等温结晶动力学Avrami方程,滑石粉促进基体结晶过程中的成核、竹纤维促进晶体生长；用Jeziorny法、Ozawa方程和综合法研究了PLA/BF/Talc复合材料的非等温结晶动力学,Ozawa方程可以描述纯PLA的非等温结晶动力学但不适用于PLA复合材料；综合法则可以很好地描述PLA和PLA复合材料的结晶动力学；另外,通过不同降温速率和升温速率得到的DSC熔融双峰,提出了形成熔融双峰的机理和示意图；在降温和升温过程中,竹纤维结构中的大量缺陷使得重结晶在熔融和重结晶竞争中的确立了优势,与此同时,由于滑石粉促使PLA形成细小晶体,从而使含有滑石粉的PLA复合材料熔融峰在较低温度。采用淀粉和甘油共混制备了热塑性淀粉(TPS),加入甲基丙烯酸缩水甘油酯接枝的POE (GPOE)作为增塑、增韧剂改性PLA,得到PLA/TPS/GPOE复合材料。PLA/TPS/ GPOE复合材料力学性能优异,当同时加入20 wt%TPS和10 wt%GPOE时,断裂伸长率可达到200%左右,冲击强度10 kJ/m2左右,同时拉伸、弯曲强度均保持较高值；通过热力学测试(DSC、DMA)、SEM观察、FT-IR分析和TGA降解温度的提高,证实了三元PLA复合材料中的各组分间相互作用、发生了反应(微交联),并提出了TPS在基体中分布和其结构模型,得到了可能的反应示意图；最后用堆肥法和TGA法研究了PLA/TPS/GPOE的降解性能,表明PLA复合材料保持了优异的生物降解性能,在热降解过程中发现,三元的PLA复合材料热降解性能比纯PLA或二元的PLA复合材料优异。最后,成功制备天然纳米纤维素(NC)和马来酸酐改性聚乳酸(MPLA),用静电纺丝制备的MPLA/NC无纺布纤维直径远远小于PLA/NC无纺布纤维直径,MPLA/5wt%NC体系的纤维直径仅为132 nm；详细研究了无纺布膜与普通薄膜的拉伸原理和过程,从力学性能中显示,PLA/NC和MPLA/NC无纺布膜体系在NC含量为5 wt%时性能最优；而在热力学性能中,当NC含量较低时,MPLA/NC无纺布膜性能较好；采用体外降解实验研究了PLA和MPLA无纺布膜的降解性能,并展望了该无纺布膜的应用前景。更多还原

【Abstract】 Poly(lactide) (PLA) is a biodegradable aliphatic polyester, which derived from renewable resources, and it has good mechanical properties and biocompatibility, thus being a promising polymer either for biomedical applications or to replace petrol based polymers in medical, packaging and other fields. Unfortunately, with the inherent brittleness, low heat resistant, slow crystallization rate, and poor impact properties, PLA is restricted to apply in more fileds. In this thesis, the major goal is to improve the heat resistant and toughness of PLA by physical blending. Moreover, the novel PLA composite remain its excellent biodegradable with adding biodegraded fillers.PLA/ Bamboo Fiber (BF)/ Talc composites have been gained by mixing in Haake mixture and their properties have been investigated by heat-resistant testing (HDT), differential scanning calorimetry (DSC), polarized optical microscope (POM), dynamics mechanical analysis (DMA) and wide X-ray (WAXD). The effect of bamboo fiber and talc on heat resistant and crystallization of PLA have been studied carefully. Great high HDT value of PLA hybrid bio-composites was obtained which was loading BF and talc simultaneously after heat treatment. However, there was little improvement in HDT of PLA bio-composites which has only BF or talc loaded. With 20 wt% BF and 20 wt% talc loading; the HDT of PLA composites increased about 40℃. This is due to the hybrid and synergism of BF and talc in PLA composites. Transcrystallization was observed in PLA composite which has BF and talc simultaneously loaded and no similar phenomenon in other kinds of PLA composite. Improvement in HDT of PLA composite was not due to the effect of crystallinity. Furthermore, the formation of transcrystallization was the main effect in HDT of PLA composites and mechanism of forming transcrystallization was proposed. Transcrystallization improves the mechanical properties of PLA/ BF/ Talc in certain content of fillers and heat treatment.By DSC, polarized light method and XRD, the isothermal and non-isothermal crystallized kinetics of PLA/ BF/ Talc composites have been researched, and the influences of cooling rate or heating rate on thermal properties of PLA composites are also studied. Isothermal kenetic of PLA/ BF/ Talc composites could fit the Avrami equation in only low temperature. The non-isothermal kinetic of PLA/ BF/ Talc composites has been also investigated by Jeziorny, Ozawa and Synthesis methods. The non-isothermal kinetic of Pure PLA fits the Ozawa equation and non-isothermal of all composites fit the Synthesis equation. With different cooling rates and heating rates, the double-melting peak has been gained and the mechanism of forming double-melting peak has been proposed. The defects of BF structure promoted the recrystallization in the melting process and the talc promoted forming small crystals. With this reason, the main melting peak temperature was at a low temperature.PLA/TPS/GPOE composites have been gained by mixing of PLA, thermal starch (TPS, prepared by starch and glycerol) and glycidyl methacrylate grafted POE (GPOE). The mechanical, dynamic mechanical, phase structures, degradation properties and toughness mechanism of PLA/TPS/GPOE have been investigated in details. Important improvements in the elongation at break and impact properties of PLA with the addition of TPS and GPOE are reported here. For 10 wt% GPOE, the ternary blends (with 20 wt% TPS content) have improved mechanical properties. The blends have nearly 200% elongation at break and more than 10 kJ/m2 in impact strength. GPOE reduces the size of the TPS phase and improves the compatibility of the PLA blends as shown in the SEM images. The binary and ternary blends have excellent biodegradation by using composting method. In thermal decomposition, ternary blends have higher decomposition temperatures than pure PLA due to glycerol plasticization. A possible reaction mechanism and schematic diagram has also been proposed. The mechanism of reactions has been proved by many characterized methods.At the end, the natural nano-fiber (NC) was prepared by simply method and the PLA/NC non-woven mats have been prepared by electrospun method. We have researched the mechanical, thermal properties and appearance structures of PLA non-woven mats with different testing ways. Natural nano-fiber and maleic anhydride (MAH) grafted PLA (MPLA) have been prepared before mixing PLA and natural fiber in the solvent. Also, the PLA/NC or MPLA/NC non-woven mats have been gained by electrospun and the diameter of MPLA non-woven mats were smaller than that of PLA non-woven mats. The diameter of MPLA/5 wt% NC is only about 132 nm. The tensile mechanism and processing of non-woven mats and normal films have been studied carefully. From the results of mechanical and thermal properties, the PLA/5 wt% NC and MPLA/5 wt% NC non-woven mat has the best mechanical property and the MPLA/NC non-woven mat with lower NC content has the better thermal property in MPLA/NC mats. The degradation properties of PLA and MPLA nanocomposites were studied carefully through in vitro degradation method and SEM.更多还原