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1、 高密度聚乙烯论文：碳纳米管改性不相容共混物HDPE/PA6的研究【中文摘要】高密度聚乙烯(High density polyethylene, HDPE)因其优良的韧性和防水性在工农业生产中得到了广泛的应用,但是较低的强度和不防油的特点限制了它的使用范围。将尼龙6 (Polyamide6, PA6)与HDPE共混既可以改善共混物的防油性能,也可以利用PA6的高强度提升共混物的强度。由于HDPE和PA6的分子链结构差别极大,因而两者的相容性较差,共混物表现出典型的两相结构以及较差的力学性能。得益于其超高的模量、强度和长径比,碳纳米管(Carbon nanotubes, CNTs)不仅可以起到增
2、强的效果,还能够通过桥接裂纹的方式阻止裂纹的引发和扩展,从而明显地增韧材料。基于此,本论文以HDPE和PA6的不相容共混物作为研究对象,利用碳纳米管作为改性填料,通过碳纳米管的官能化改性,选择性地控制碳纳米管在共混物中的分散位置和分散状态,从而获得了具有良好韧性、强度的纳米复合材料；并在此基础上进一步研究共混工艺、碳纳米管含量、界面张力等参数对碳纳米管复合材料的微观结构和宏观性能的影响。主要研究成果如下：1)利用HDPE为非极性聚合物而PA6为强极性聚合物,以及碳纳米管与极性相近的聚合物具有更大亲和力的特性,同时兼顾PA6分子链端的氨基能与羧基反应的特点,本次实验通过硝酸高温加热的方式,将碳纳
3、米管表面的五元、七元环氧化为具有较大极性的羧基,成功制得了改性多壁碳纳米管(Functionalized multiwalled carbon nanotubes, FMWCNTs),以期通过控制碳纳米管极性的方式以及加工工艺的选择实现碳纳米管在共混物中不同位置的选择性分布。2)采用不同的FMWCNTs加工工艺成功实现了FMWCNTs在HDPE/PA6不相容共混物中不同位置的选择性分散,并且对复合材料的力学性能产生了不同的影响。通过热力学计算可以发现FMWCNTs与PA6相的亲和力更好。所以,当使用FMWCNTs/PA6作为母料时,所有FWMCNTs都分布于PA6相当中；当使用FMWCNTs/
4、HDPE作为母料时,FWMCNTs会向PA6相迁移以求达到热力学意义上稳定状态。但由于粘度、共混时间等因素的影响,只有一部分FMWCNTs能够迁移到PA6相当中,其余的FMWCNTs则桥接于两相界面。由于桥接于两相界而的FMWCNTs可以抑制裂纹在界面的引发和扩展,所以使用FMWCNTs/HDPE作为母料的复合材料能够在更大的断裂伸长率下发生断裂。同时,桥接于两相界面的FMWCNTs可以阻止PA6分散相在共混过程中相互碰撞时发生的积聚,从而达到减小PA6分散相体积的效果,使得PA6分散相周围的应力场更容易发生叠加形成逾渗通道,进一步增加复合材料的韧性。3)通过同时引入增容剂马来酸酐接枝高密度聚
5、乙烯(Maleic anhydride grafted high density polyethylene, HDPE-MA)和FMWCNTs,进一步调控FMWCNTs在两相间的分散以及分散相形态,实现了HDPE-MA和FMWCNTs协同增强增韧HDPE/PA6的作用。研究表明,不同的FMWCNTs加入顺序能够对HDPE/HDPE-MA/PA6二元共混物的力学性能造成不同的影响。当使用FMWCNTs/HDPE/HDPE-MA作为母料时,复合材料表现出最好的韧性。因为在母料的配制过程中HDPE-MA能首先和FWMCNTs作用,从而在FMWCNTs的表面接枝上HDPE的分子链,减弱FMWCNTs向
6、PA6相迁移的趋势,使得的FWMCNTs分布在两相界面增加复合材料的界面结合力。同时,的FMWCNTs在界面的分布也更加有效地减小了共混物中PA6粒子的体积,进一步增加了复合材料的韧性。当使用FMWCNTs/PA6作为母料时,FMWCNTs全部分散在PA6颗粒当中并形成致密的FMWCNTs刚性网络结构,从而显著地改善PA6粒子的强度。同时,由于HDPE-MA的加入可以保证PA6粒子与基体材料间应力的有效传递,所以复合材料的整体强度能够随FMWCNTs网络在PA6粒子中的建立而明显增加。4)向HDPE/PA6(50/50)中加入不同含量的FMWCNTs可以诱发复合材料发生相反转。对HDPE/PA
7、6二元共混物来说,由于HDPE的粘度大大高于PA6的粘度,所以HDPE作为分散相分布于PA6基体当中。向共混物中加入少量FWMCNTs(2 wt%)时,FMWCNTs均匀地分散于PA6连续相当中,复合材料依然保持与二元共混物相似的海岛形态。随着FMWCNTs含量的进一步增加,复合材料中的HDPE相逐渐变为连续相,并在FMWCNTs含量达到5 wt%时表现出完全的双连续形态。通过测试复合材料的流变和结晶性能,发现FMWCNTs能够在含量大于2 wt%时以网络结构的方式存在。同时,由于FMWCNTs表面的羧基不仅能够和PA6分子链末端的氨基发生反应,还可以与PA6之间形成氢键,大大增强FMWCNT
8、s与PA6间的相互作用,所以FMWCNTs网络能够诱导PA6分布于其周围形成连续相并最终诱导复合材料呈现出双连续形态。当FMWCNTs增加为10wt%时,FMWCNTs不再以网络结构的形式存在,而是以球形团聚体的形式存在,并且诱导PA6分布于其团聚体周围,使得复合材料发生相反转。【英文摘要】High density polyethylene (HDPE) is widely used in our daily life due to its toughness and water-proof ability. However, its application is limited by its
9、 relatively low strength and permeability to oil. Since PA6 characterizes high strength and is oil-proof, blending HDPE with PA6 is an ideal route to obtain new material with multiple properties. Nevertheless, the blend of HDPE and PA6 displays two-phase morphology and inferior mechanical property,
10、because the difference between the chain structure of HDPE and PA6 is so large that they are immiscible of each other. Due to its high modulus, strength and aspect ratio, carbon nanotubes (CNTs) are used not only to strengthen the material but also significantly toughen the material by inhibiting th
11、e initiation and propagation of cracks. So, in this thesis, we firstly functionalized carbon nanotubes and then controled the localization and dispersion of these carbon nanotubes to obtain nanocomposites with excellent toughness and strength. Furthermore, the effects of blending protocols, CNTs con
12、tents and interfacial tension on the microscopic morphology and macroscopic properties are also analyzed. The main results obtained in this work are listed as follows:1) HDPE is a non-polar material while PA6 characterizes high polarity. Considering the fact that the amidogen groups of PA6 chains ca
13、n react with carboxyl group and the fact that materials with similar plarity have better affinity, the CNTs are modified to achieve better affinity with PA6. Thus the pristine carbon nanotubes are refluxed in concentrated nitic acid to obtain functionalized multiwalled carbon nanotubes (FMWCNTs) by
14、oxidizing the defects on the outer surface of mlutiwalled carbon nanotubes into carboxyl groups.2) Different blending protocols are applied to selectively disperse FMWCNTs in different locations of the nanocomposites, and subsequently leading to different mechanical properties of the nanocomposites.
15、 It is found that when all the FMWCNTs are pre-dispersed in PA6, they tend to remain in PA6 phase of the nanocomposites. When all the FMWCNTs are pre-dispersed in HDPE, they tend to migrate to PA6 to achieve thermodynamic equilibrium. However, due to various factors such as, viscosity and blending t
16、ime, only some of the FMWCNTs migrate into PA6 phase, leaving the other FMWCNTs on the interphase. The localization of FMWCNTs can exert “bridging effect” on the interphase and effectively inhibit the initiation and propagation of cracks along the interphase. In the mean time, the interfacial localization of FMWCNTs can prevent the coalescence of dispersed PA6 phase as well, leading to smaller PA6 particles and easier percolat
