【作者】 徐亚娟；

【导师】 蹇锡高；

【作者基本信息】 大连理工大学 ， 高分子材料， 2009， 博士

【摘要】 环氧树脂由于在强度、模量、热稳定性及耐湿热、耐化学性、加工工艺性等方面的突出优点作为高性能树脂基复合材料的主要基体树脂,被广泛应用于航空航天等领域。但因其固化后质脆、耐冲击和应力性能差等缺点,在很大程度上限制了它在某些高技术领域的应用。因此,对环氧树脂的增韧改性具有十分重要的理论价值和实际意义,也是先进复合材料树脂基体研究的主要方向之一。含二氮杂萘酮联苯结构高性能聚芳醚树脂具有耐高温、可溶解、综合性能优异等特点,有望在提高环氧树脂韧性的同时不降低其耐热性。因此,本文在综述了目前国内外热塑性树脂改性环氧树脂的研究基础上,提出了采用杂萘联苯聚芳醚树脂改性环氧树脂的研究方法和思路。采用热熔法制备了一系列杂萘联苯聚芳醚树脂(PPAEs)改性环氧树脂(DGEBA)的共混物,重点考察了不同的固化条件下PPAEs主链结构及含量对共混物的结构和性能的影响,旨在优化固化工艺的基础上筛选最佳的改性树脂及其含量,制备出兼具优异韧性和耐热性的共混物。主要研究内容和结果如下:首先采用示差扫描量热法(DSC)对DGEBA/PPAEs共混体系的固化动力学进行了研究,其固化反应基本上都从150℃开始,反应活化能变化不大,都在60 KJ/mol左右,表明不同结构和含量的PPAEs均不影响环氧树脂的固化反应条件。对杂萘联苯聚醚酮(PPEK)改性环氧树脂体系的结构和性能进行了研究,从DSC和热失重(TG)测试结果来看,共混物的玻璃化温度(T_g)有所升高,而热稳定性略有降低,但降低不明显;不同的固化工艺下体系的冲击韧性和断裂韧性提高都不明显,扫描电镜(SEM)证实DGEBA/PPEK体系形成了均相结构,缺少能量吸收过程,而且断裂面的裂纹之间没有约束,界面结合力弱,因此韧性没有增加。选用带有极性侧基的杂萘联苯聚醚腈酮(PPENK)来改性环氧树脂,以提高两相间的界面结合力,改善增韧效果。DGEBA/PPENK体系的玻璃化温度有所升高,且热稳定性没有降低,在390℃以下不分解。尽管共混物形成了均相结构,但氰侧基的偶极作用使其与环氧树脂的界面结合力增强,共混物的韧性得到一定程度的提高,其冲击强度可达3.26 KJ/m~2,较未改性的环氧树脂提高了44%。采用杂萘联苯聚醚砜酮(PPESK)来改性环氧树脂,共混体系出现两个明显的玻璃化转变,且两相的玻璃化温度均大幅上升。体系的热稳定性同时得到了很好的保持,在390℃以下不降解。添加15 phr PPESK时,共混物形成了PPESK精细颗粒分布于连续的环氧基质中的相结构,此时韧性最大。断裂面的扫描电镜(SEM)结果证明裂纹形成了明显的偏转和歧化,吸收能量,使得韧性得到较大的提高。最后我们又选择了含有联苯结构的杂萘联苯共聚芳醚砜(PPBES)来改性环氧树脂。改性后的环氧树脂共混物的耐热性得到提高,同时热稳定性不降低,在395℃以下不分解。共混体系形成两相结构,引入了能量吸收过程,韧性提高较为明显,在150℃/3h+180℃/3h+200℃/2h工艺条件下添加15份PPBES时形成了反转相,冲击强度和断裂韧性均得到明显提高,其中冲击强度取得最大值3.76 KJ/m~2,增加幅度为65%。以上研究结果表明,在环氧树脂/PPAEs共混体系中,杂萘联苯聚芳醚热塑性树脂对增韧的贡献起着主导作用,其增韧机理主要归结为以下几点:(1)裂纹偏转,裂纹偏离原来的方向并引发大量微裂纹的产生,增加了裂纹的表面积从而增加了裂纹扩展的能量,提高了韧性;(2)基体的局部塑性变形,热塑性树脂颗粒充当应力集中点引发环氧树脂的局部塑性变形。所以,在杂萘联苯聚芳醚树脂改性环氧树脂体系中,局部的热塑性变形、裂纹路径的偏转以及热塑性树脂的延性撕裂等共同作用提高了共混体系的韧性。更多还原

【Abstract】 Thermosetting epoxies possess many desirable properties,such as high tensile strength and modulus,excellent chemical and solvent resistance,high dimensional and thermal stability,good adhesive properties and processability.These characteristics make them ideal candidates for many important applications,especially matrix for high-performance fiber-reinforced composites in aerospace.However,the epoxy resins are generally brittle due to their high cross-link density,which limits their further proliferation into other applications that requires more impact resistant or tougher materials.This drawback has prompted many studies devoted to increasing their fracture toughness without compromising their desirable attributes.Poly(aryl ether) s containing phthalazinone moiety(PPAEs),are a kind of novel high performance polymer.Their special structure endows them with excellent comprehensive properties,including outstanding thermal properties and good solubility.It is expected to toughen epoxy resins without decreaseing their thermal properties.Therefore,the research on the epoxy resins modification by PPAEs is proposed on the summarization of early study of thermoplastic modified epoxy resins.A series of DGEBA / PPAEs blends were prepared by mechanical mixing without any solvent.In order to produce the mixtures with toughness and thermal resistance,we focused on the effects of the kinds and content of PPEAs on the structure and properties of DGEBA/ PPAEs mixtures in different curing conditions.The main studies and results are in the following:First,the curing kinetics of different blends was measured by differential scanning calorimetry(DSC).All the curing reactions of the blends began at 150℃and the activation energy was about 60 KJ/mol,which suggested that the additions of PPAEs didn’t changt the curing conditions of epoxy resins.The structure and properties of DGEBA/PPEK blendings were investigated.The glass transition temperatures(T_g) increased but the thermal stabilities decreased lightly by the measurement of DSC and thermalgravimetry(TG) respectively.The impact strength and fracture toughness has not significantly increased in different curing conditions.The scanning electron microscope(SEM) proved that DGEBA/PPEK blends formed homogeneous phase, and the interface bonding was weak.Therefore,there was lack of the process of energy absorption to enhance the toughness of the blends. In order to increase the interface bonding of the thermoplastics with epoxy resins, PPENK,with the polar cyano pendant group,was used to modify DGEBA epoxy resins.The T_g of the blends increased by the addition of PPENK and the thermal stabilities were maintained.All the blends did not degrade under 390℃.Moreover,the toughness was enhanced to some degree.Although the DGEBA/PPENK blends form homogeneous phase, the dipole-dipole interaction between cyano pendant groups increased the interface bonding with epoxy resins to increase the toughness.On the foundation of those two studies,PPESK was choosen to toughen epoxy resins. There were two glass transitions in the DSC traces of DGEBA/PPESK blends.One was the epoxy rich phase,and the other was the PPESK rich phase.These two T_gs were all enhanced greatly,which perhaps because of the two phase interpenetrating to restrain the deformation of each other.Meanwhile,the thermal stabilities of the blends were maintained.None of the blends degrade under 390℃.The toughness obtained the maximum(3.42 KJ/m~2) by the addition of 15 phr PPESK.The fracture surfaces were rough and the cracks deviated their original ways to initiate deflection and disproportionation.So the toughness of DGEBA/PPESK blends was improved.Finally,PPBES,containing biphenyl in the chain,was used to modify DGEBA epoxy resins.There were also two glass transitions with 20 phr PPBES and the two T_gs were close to each other.The T_g of the epoxy resin increased and the DGEBA/PPBES blends did not degrade under 395℃.The toughness obtained the most significant enhancement in the PPAEs systems.The maximum of impact strength was 3.76 KJ/m~2 by the addition of 15 phr PPBES after cured in thel50℃/3h +180℃/3h + 200℃/2h conditions.The increment was 65%.From the above results,we can summarize that the PPAEs play the leading role in the toughness enhancement in the DGEBA/PPAEs blends.The toughness mechanisms of PPAEs modified epoxy resins are summarized in the following:(1) Crack deflection.The cracks deviated from their original plane to splite into some branches and initiate more ductile microcracks,which resulted the increasing surface area of the cracks,thereby increasing the toughness.(2) Local plastic deformation of the matrix.PPAEs,which diffused into epoxy resin,improved the plasticity of epoxy resin around the PPAEs dispersed phase.Thererfore, the fracture mechanisms such as crack deflection and branches,ductile microcracks,ductile tearing of the thermoplastics and local plastic deformation of the matrix are responsible for the increase in the fracture toughness of the DGEBA/PPAEs blends.更多还原