【作者】 张帆；

【导师】 徐伟箭；

【作者基本信息】 湖南大学 ， 化学工程与技术， 2008， 博士

【摘要】 高流动性尼龙通常可用于薄壁或精密器件的制作,近几十年来,如何提高尼龙的流动性引起了大量研究者的关注。大量文献显示,往尼龙中加入少量的有机、无机分子或低聚体,通过共混的方式,均能得到高流动性尼龙,但力学性能往往不易得到保证。从上世纪80年代以来,树枝状聚酰胺-胺(即PAMAM)的出现,引起了越来越多的研究者的兴趣。PAMAM因外围含有大量的活性官能团,具有独特的三维结构、低粘度、高溶解能力及高反应活性。近年来,在催化,药物或基因载体,螯合剂,自组装等方面的应用和研究引起人们广泛关注,但在塑料工程领域的应用并不多见。本工作采用一个新的策略合成了一种高流动性尼龙6,即利用1.0代、2.0代和3.0代聚酰胺-胺(PAMAM),分别与对苯二甲酸等当量反应,制得含树枝状结构单元的母盐溶液;适量的母盐溶液、封端剂、己内酰胺投入到高压反应釜中,利用原位聚合法,制得高流动性尼龙6。红外光谱显示,与纯尼龙6比较,高流动性尼龙6的N-H峰(γN-H和2δN-H)发生了蓝移。当尼龙6基体中含较少量的PAMAM树枝单元时,新型尼龙6的流动性得到了显著的改善(熔融流动指数增加了70-90%)。力学性能测试显示,拉伸强度没有下降,断裂伸长率降低了20-35%,各种高流动性尼龙6的缺口冲击强度均有不同程度的增强。用扫描电镜(SEM)对经过缺口冲击实验的断面进行分析,发现高流动性尼龙具有脆性断裂行为。用差示扫描量热分析仪(DSC)对高流动性尼龙6的非等温结晶过程进行了初步分析,结果发现高流动性尼龙6具有比纯尼龙6更宽的结晶峰。利用DSC,以Avrami方程为基础研究了高流动性尼龙6的等温结晶动力学。结果显示,同纯尼龙6相比较,高流动性尼龙6具有较低的结晶速率。高流动性尼龙6的结晶速率随着尼龙6基体中PAMAM树枝单元的代数而变化,并且随着基体中PAMAM树枝单元含量的增加有轻微的增加。传统分析显示,与由DSC结晶曲线直接得出的实际的最大结晶时间相比较,通过半结晶法得到的最大结晶时间比由Avrami曲线拟合得到的Avrami参数所求取的最大结晶时间更接近实际的最大结晶时间。这意味着由半结晶法得到的Avrami参数比由Avrami曲线直接拟合得到的参数更符合实际的结晶机理。同时发现,由DSC结晶曲线直接得出的实际最大结晶时间和半结晶法得到的最大结晶时间随着尼龙6基体中PAMAM树枝单元代数的增加和结晶温度的降低而越来越相一致。为了更准确地描述高流动性尼龙6的结晶机理,本论文设计了局部连续拟合法,得到了Avrami参数随结晶时间的变化规律。Avrami参数对结晶时间的关系图显示,高流动性尼龙6的结晶是分三段完成的。对Avrami参数对结晶时间的关系曲线求积分,得到Avrami参数的积分平均值nav和Kav,再由nav和Kav求得另外一套最大结晶时间。通过对比得知,这一套最大结晶时间tmaxav比用半结晶法求得的最大结晶时间更接近实际的最大结晶时间。这个结果意味着由局部连续拟合法和积分平均值法得到的Avrami参数比由半结晶法求得的Avrami参数更接近实际的结晶机理。高流动性尼龙6的Avrami指数n在2.1和2.4之间,这意味着高流动性尼龙6结晶成核和生长方式是二维的生长方式。作者利用Arrhenius方程求得了各样品的结晶活化能,结果显示:高流动性尼龙6的结晶活化能随尼龙6基体中PAMAM树枝单元的代数的增加而减小;同时高流动性尼龙6的结晶活化能还随尼龙6基体中PAMAM树枝单元的含量的增加而轻微减小。同样利用DSC,采用Ozawa法和建立在Ozawa与Avrami方程基础上的莫志深复合法对高流动性尼龙6的非等温结晶过程进行了研究。按照Ozawa法,得到lg[-ln(1-X(T))]～lgФ的双对数曲线,发现该曲线的线性关系很差。当按照不同的降温速率将曲线分成三个部分,再对每条线段进行线性拟合,得到了在不同结晶温度下的Ozawa指数m及冷却函数lgF(T)值。结果显示,高流动性尼龙6样品和纯尼龙6样品的Ozawa指数m及lgF(T)值随着温度的变化有着很显著的不同。对所有样品而言,Ozawa指数m是随着结晶温度的升高而增大的,这意味着随着结晶温度的升高聚合物的结晶越来越复杂;同时也反映出传统的Ozawa法通过新的解析方法得到了与实际结晶机理更相一致的结论。研究结果显示,高流动性尼龙6的Ozawa指数m与lgF(T)值随冷却速率的增加而增大,但它们也随结晶温度的降低和尼龙6基体中PAMAM树枝单元的代数的增加而减小。同时,结果还显示,高流动性尼龙6的Ozawa指数m和lgF(T)值对尼龙6基体中PAMAM树枝单元的含量比较敏感。总体而言,高流动性尼龙6比纯尼龙6具有更加复杂的结晶机理和较慢的结晶速率。利用莫志深复合法研究发现,每个样品的lgФ-lgt曲线均有很好的线性关系;这表示,建立在Avrami方程和Ozawa方程基础上的复合方法能很好地解析高流动性尼龙6和纯尼龙6的结晶动力学。结果显示,高流动性尼龙6的结晶速率比纯尼龙6慢,并且在基体中随着PAMAM树枝单元含量的增加其结晶速率明显减慢;高流动性尼龙6的结晶速率与尼龙6基体中PAMAM树枝单元的代数也有关系;较高代数的PAMAM树枝单元在结晶过程中起到了成核作用。利用Kissinger方程求取了各个样品在非等温结晶过程的结晶活化能。与纯尼龙6相比,高流动性尼龙6的结晶活化能都要低些;同时,在高流动性尼龙6基体中PAMAM树枝单元的代数和含量对其活化能也均有明显的影响。本论文还以PAMAM为原料,对多壁碳纳米管(MWNTs)进行修饰改性,用原位聚合法得到了另外一种新型的功能化MWNTs/PA6复合材料。首先多壁碳纳米管经过混酸(硫酸和硝酸)氧化,再与亚硫酰氯反应;得到的MWNTs-COCl分别与过量的1.0代和2.0代聚酰胺-胺(G1 PAMAM和G2 PAMAM)反应。红外光谱FTIR和热失重分析TGA证明了MWNTs已成功实现了功能化。MWNTs-G1 PAMAM和MWNTs-G2 PAMAM分别与适量的己内酰胺,蒸馏水和封端剂进行原位聚合反应,得到新型功能化碳纳米管复合材料: MWNTs-G1/PA6和MWNTs-G2/PA6。为了对比,在相同条件下,未处理的MWNTs也与适量的己内酰胺等原料进行反应,得到了MWNTs/PA6复合材料。与纯尼龙6相比,MWNTs-G1/PA6和MWNTs-G2/PA6复合材料具有更加优越的抗弯曲强度和冲击强度。扫描电镜SEM分析显示,在尼龙6基体中,MWNTs-G1 PAMAM比MWNTs-G2 PAMAM及原始的MWNTs要分散均匀些。DSC曲线显示,原始的和PAMAM功能化的MWNTs均起到不同程度的成核作用。更多还原

【Abstract】 Nylon with high flowability was often used in molded products of small parts with thin walls or precision parts, which has attracted a great deal of interest over several decades. Lots of work showed that high flow polyamides were almost prepared by melting blend and the flow behavior was improved by feeding low content of organic, inorganic or oligomer components and so on, unfortunately, however it might be hard to maintain their mechanical properties.Since 1980s, polyamidoamine (PAMAM) dendrimers have been paid more and more attentions due to their unique features such as three-dimensional architecture, low intrinsic viscosity, good solubility and high reactivity because of the presence of large amount of terminal functional groups. PAMAM dendrimers have attracted much more attention for their many potential applications, including nanoscale catalysts, drug or gene carriers, chelating agent, building blocks for assembly nanoconjugates and so forth. But few applications have been found in plastic engineering area.A new synthetic strategy for high flow nylon 6 was developed in this article. Generation 1, 2, 3 (G1, G2, G3) PAMAM dendrimers reacted with p-phthalic acid by equimolar terminal groups in water solution respectively,mother salt solution was then prepared. The high flow nylon 6 was prepared with suitable quantity of mother salt solution, end capping agent andε-caprolactam by in situ polymerization. Blue shifts are found for the peaks of NH (γN-H and 2δN-H) of the high flow nylon 6 compared with pure nylon 6 in the IR spectra. Comparing with the pure nylon 6, the high flow nylon 6 containing low content of PAMAM units, has high flow property and almost the same mechanical property. The high flow nylon 6 with low content of PAMAM units has greater melt-flow index (MFI) (the value of MFI increased by 70-90%). Hardly any decrease in the tensile strength is observed with the elongation at break decreasing by 20-35%. But the izod impact strength of the high flow nylon 6 increases. The SEM images show that the high flow nylon 6 presents brittle fracture with conglomeration-like structure while pure nylon 6 exhibits plastic fracture with island-like structure. DSC thermograms of non-isothermal crystallization exhibit that the peak of high flow nylon 6 broadens comparing with the pure nylon 6 and the broader peak means the wider processing temperature. The isothermal crystallization kinetics was investigated by differential scanning calorimetry for high-flow nylon 6. The Avrami equation has been adopted to study the crystallization kinetics. Comparing with pure nylon 6, the high-flow nylon 6 has lower crystallization rate, which varies with the generation and content of PAMAM units in nylon 6 matrix. The traditional analysis indicates that the values of Avrami parameters calculated from the half time of crystallization might be more in agreement with the actual crystallization mechanism than the parameters determined from the Avrami plots. Meanwhile, the plots of parameters n or K versus time were also obtained by local linear fitting. The results imply the parameters n or K from local linear fitting approach the actual crystallization mechanism more precisely than the parameters calculated from the half time of crystallization. The n values of the high-flow nylon 6 range between 2.1 and 2.4, meaning the crystallization of the high-flow nylon 6 is a two-dimensional growth process. The activation energies were determined by Arrhenius’method. The activation energies decrease with the increase in the generation of PAMAM units, but decrease quite slowly with the increase in the content of PAMAM units in nylon 6 matrix.The crystallization kinetics of the high-flow nylon 6 containing PAMAM dendrimers units in nylon 6 matrix was investigated by differential scanning calorimetry. Ozawa and Mo equation were used to describe the crystallization kinetics under non-isothermal condition. The values of Avrami exponent m and the cooling crystallization function F(T) were determined from the Ozawa plots, which showed bad linearity and were divided into three sections depending on different cooling rates. The plots of the m and lgF(T) values versus crystallization temperatures were obtained, which indicated that the actual crystallization mechanisms might change with the crystallization temperatures. The high-flow nylon 6 has higher values of m and lgF(T) than pure nylon 6, which implied that the high-flow nylon 6 had more complicated crystallization mechanisms and slower crystallization rate than pure nylon 6. The good linearity of the Mo plots verified the success of this combined approach. The activation energies of the high-flow nylon 6 were determined by the Kissinger method. TheΔE values were lower than that of pure nylon 6, and meanwhile theΔE was affected by both the generation and the content of PAMAM units in the nylon 6 matrix.The crude MWNTs were oxidized using sulfuric and nitric acid solution, then reacted with thionyl chloride, resulting in MWNTs-COCl, which reacted respectively with an excess of G1 PAMAM and G2 PAMAM respectively. FTIR and TGA indicated the successful functionalization of MWNTs. The MWNTs-G1 PAMAM and MWNTs-G2 PAMAM were respectively put into an autoclave along withε-caprolactam, distilled water and acetic acid, and then MWNTs-G1/PA6 and MWNTs-G2/PA6 composites were obtained by in situ polymerization. For comparison, PA6 and crude MWNTs/PA6 were also prepared under the same condition. Compared with pure nylon 6, the bending strength and izod impact strength of MWNTs-G1/PA6 and MWNTs-G2/PA6 composites were significantly improved. The SEM images indicated that MWNTs-G1 PAMAM was more uniformly dispersed than MWNTs-G2 PAMAM and crude MWNTs in the PA6 matrix. DSC analysis showed the crude and functionalized MWNTs might act as heterogeneous crystal nuclei of the matrix.更多还原