【作者】 欧宝立；

【导师】 李笃信；

【作者基本信息】 中南大学 ， 材料学， 2009， 博士

【摘要】 采用纳米TiO₂改性聚丙烯/聚酰胺6（PP/PA6）共混物既可提升基体材料力学性能,又能赋予基体材料抗菌等功能。为提高纳米TiO₂与基体聚合物的相容性并防止其团聚采用了含不同官能团的硅烷偶联剂和甲苯-2,4-二异氰酸酯（TDI）对纳米TiO₂进行表面修饰,通过润湿性测试对表面修饰效果进行了评价分析,发现采用TDI表面修饰效果最好。在此基础上系统研究了投料比、反应温度和反应时间等因素对TDI与纳米TiO₂表面羟基（—OH）间化学反应的影响;结果表明,在投料比[TDI[/[—OH]=6:1（mol/mol）,反应温度为95℃,反应时间为6 h时,纳米TiO₂表面—OH反应程度达92.31 mol%。利用红外光谱（FTIR）和热失重分析（TGA）对表面修饰纳米TiO₂进行测试分析表明,TDI以化学键形式连接在纳米TiO₂表面;此外,还利用透射电镜（TEM）对TDI修饰纳米TiO₂观察发现,纳米TiO₂能均匀分散在甲苯中并保持原始尺寸。通过熔融共混法利用表面修饰纳米TiO₂表面—NCO与PA6的端氨基（—NH₂）和羧基（—COOH）间的化学反应以增强纳米TiO₂与PP/PA6间的界面作用制备了PP/PA6/TiO₂纳米复合材料。对PP/PA6/TiO₂纳米复合材料静态力学和动态力学性能测试发现,少量纳米TiO₂能显著提高基体材料力学性能;填充5份大分子增容剂PP-g-MAH和3份表面修饰纳米TiO₂能使PP/PA6/TiO₂纳米复合材料综合性能达到最优;相对PP/PA6共混物其拉伸强度、缺口冲击强度和弯曲强度分别提高了50.55%、71.84%和52.58%。采用扫描电镜（SEM）和透射电镜（TEM）等测试技术对PP/PA6/TiO₂复合材料的形态结构以及纳米TiO₂的分散状况进行了研究,发现PA6以分散相均匀分散在连续相PP中,纳米TiO₂主要分散在PA6相以及PP与PA6界面区域。此外,还发现纳米TiO₂和PP-g-MAH加入到PP/PA6共混物中能使分散相PA6相尺寸减小,说明纳米TiO₂对共混物具有良好的增容作用;在添加纳米TiO₂的基础上继续添加PP-g-MAH能进一步提升基体材料的力学性能。采用DSC方法系统研究了PP/PA6/TiO₂纳米复合材料等温和非等温结晶动力学及其熔融行为。用Avrami方法对等温结晶动力学分析发现,对非增容复合材料,纳米TiO₂加快了PP和PA6相的等温结晶速率。结晶成核理论计算结果表明纳米TiO₂促进了PP和PA6相的成核。对增容复合材料而言,对PP相等温结晶性能的影响不大,但纳米TiO₂能显著影响PA6相的等温结晶行为,由于部分PA6分子链接枝了纳米TiO₂使其运动受到阻碍,使结晶速率下降,等温结晶活化能增大。对等温结晶熔融行为研究发现,所有的PP/PA6/TiO₂纳米复合材料中PP相基本上是呈熔融单峰;PA6相呈现多重熔融峰,较高结晶温度下表现为双重熔融峰,较低温度下表现为三重熔融峰。纳米TiO₂使熔融峰Ⅰ和Ⅱ的温度升高,这是因为纳米TiO₂对PA6具有成核作用,生成更为完善的晶体。熔融峰Ⅲ是更稳定晶体熔融的结果,熔融温度基本上不随结晶温度而变化。多重熔融峰是由不同尺寸或不同完善程度的晶体在升温过程中再结晶和再熔融引起的。非等温结晶动力学研究发现,纳米TiO₂对PP和PA6相起到异相成核作用,使结晶在较高温度下开始;但纳米TiO₂的存在又阻碍了结晶增长使其结晶速率减慢。低含量时,纳米TiO₂能降低非等温结晶活化能;随着纳米TiO₂含量的提高,增容体系中PA6相的活化能有所提高。纳米TiO₂的存在使结晶度下降,而结晶度随着冷却速率的提高呈先增加后下降的变化趋势。这是因为纳米TiO₂对聚合物的结晶具有两方面的影响,一方面对聚合物起到成核作用,另一方面,纳米TiO₂与聚合物间的相互作用又阻碍了大分子链的自由运动。这两种作用相互竞争,导致结晶度的这种变化。非等温结晶熔融行为发现PA6相也出现了多重熔融峰,随降温速率不同表现为单熔融峰或双重熔融行为。对PP/PA6/TiO₂纳米复合材料稳态流变和动态流变性能测试发现,少量纳米TiO₂能使PP/PA6/TiO₂纳米复合材料熔体黏度下降;在增容体系中添加一定量的纳米TiO₂使其流动指数（非牛顿指数）n值增大,但纳米TiO₂量超过一定量时,流动指数n反而又会减小,使PP/PA6/TiO₂纳米复合材料的假塑性增强;少量纳米TiO₂使流活化能降低,熔体黏度对温度的敏感性下降,这是由于纳米TiO₂在基体聚合物中分散均匀,对基体聚合物良好的润滑作用所引起的。动态流变性能研究发现,少量纳米TiO₂使PP/PA6/TiO₂纳米复合材料的剪切储能模量G′,损耗模量G″和复数黏度η^*都有所提高,由此表明纳米TiO₂能同时赋予基体材料以良好的弹性和黏性。抗菌实验表明,在2h内,PP/PA6/TiO₂纳米复合材料对枯草芽孢杆菌、金黄色葡萄球菌和大肠杆菌的抗菌率达90%以上。热稳定性能研究表明,纳米TiO₂能明显提高PP/PA6基体材料的热稳定性;此外,从热失重数据可知理论失重率和实际失重率在误差范围内相等,说明纳米TiO₂在PP/PA6基体中分散均匀。更多还原

【Abstract】 Incorporation of titanium dioxide（TiO₂） nanoparticles into polypropylene/polyamide 6（PP/PA6） blends may give the matrix materials excellent mechanical properties and strong antibacterial and sterilization function.In order to improve the compatibility of TiO₂ nanoparticle and polymer and to hinder them aggregate together,silane coupling agents with different function groups and toluene-2,4-diisocyanate（TDI） were used to functionalize TiO₂ nanoparticle.It was found that TDI was the best modifier to functionalize TiO₂ nanoparticles.The main effecting factors on the reaction of TDI with the hydroxyl at the surface of TiO₂ nanoparticles had been investigated by determining the reaction extent of hydroxyl group.It was found that the reaction maintained at 95℃for 6 hours with the fixed mole ratio of[TDI]/[—OH]of 6:1,the reaction extent of hydroxyl reached 92.31 mol%.Fourier transform infrared spectrum（FTIR） spectroscopy and thermogravimetric analysis（TGA） were employed to characterize the TDI-functionalized TiO₂ and the results show the TDI molecules were covalently bonded at the nanoparticle surface.In addition,transmission electron microscope（TEM） images showed that the functionalized-TiO₂ can be well dispersed in toluene with the pristine size.PP/PA6 based nanocomposites were prepared via melt blending.The mechanical properties were analyzed by static mechanical test and dynamic mechanical thermal analyzer（DMTA） and the results indicated that the mechanic properties can be significantly increased with the addition of functionalized-TiO₂.The comprehensive properties of the PP/PA6/TiO₂ nanocomposites will achieve their maximum with 3 phr functionalized-TiO₂ and 5 phr compatibilizer of PP-g-MAH.Compared with the uncompatibilized PP/PA6 blends,the tensile strength,notched impact strength and flexural strength of the PP-g-MAH compatibilized PP/PA6 blends with 3 phr of TDI-functionalized TiO₂ have increased 50.55%、71.84%and 52.58%,respectively.Scanning electron microscopy （SEM） and TEM were used to assess fracture surface morphology and dispersion of the TDI-functionalized TiO₂,respectively.Owing to the isocyanate（—NCO） at the TDI-functionalized TiO₂ surface can react with the—NH₂ or carboxyl groups of PA6 during melting blend,i.e.there are portions of PA6 will be grafted onto the nanoparticle surface,SEM and TEM micrographs showing that PA6 particles are uniformly distributed in the continuous PP phase and the functionalized-TiO₂ are preferentially located in the PA6 phase and the interface of PP and PA6 phase.In addition,it was found that the PA6 domain size would decrease with the incorporation of functionalized-TiO₂ and PP-g-MAH,which indicated they have strong compatibilizing effect on the immiscible PP/PA6 blends.In the presence of PP-g-MAH,the mechanical properties of PP/PA6 based nanocomposites filled with functionalized-TiO₂ will be further improved.The isothermal and non-isothermal crystallization and melting behavior of PP/PA6 based nanocomposites were investigated by differential scanning calorimetry（DSC）.The Avrami equation was used to describe the isothermal crystallization kinetics.It was found the TiO₂ nanoparticles act as effective nucleating agents,the crystallization rate of PP and PA6 in the uncompatibilized PP/PA6 based nanocomposites is increased.The TiO₂ nanoparticles have less influence on the isothermal crystallization of PP phase in PP-g-MAH compatibilized nanocomposites. However the TiO₂ nanoparticles play an important role in the isothermal crystallization behavior of PA6 phase.Owing to portions of PA6 chains were grafted at the TiO₂ surface,which hinder the motion of PA6 chains, incorporation of TiO₂ nanoparticles result in higher isothermal crystallization activation energies phase and lower crystallization rate of PA6.All PP phases exhibit single melting endotherms in the as-prepared nanocomposites isothermally crystallized,however PA6 phases exhibit double melting endotherms at higher crystallization temperature and triple melting endotherms at lower crystallization temperature.The increased melting temperatures forⅠandⅡpeaks of PA6 phase can be attributed to the nucleation of TiO₂,which resulted in perfect PA6 crystal. Melting temperature forⅢpeak did not change with the variable isothermal crystallization temperature,which can be attributed to melting of the more stable crystal of PA6.The multiple melting endotherms are mainly caused by the recrystallization of PA6 spherulites with different crystal sizes and perfection during heating.The non-isothermal crystallization and melting behavior of PP and PA6 phase were investigated by DSC.The results show the Avrami index is higher than two,which indicated the non-isothermal crystallization process is complex.Owing to heterogeneous nucleation of TiO₂,non-isothermal crystallization of PP and PA6 phase began at higher temperature. However,the TiO₂ nanoparticles hinder the growth of PP and PA6 crystals and then lead to low crystallization rate.The crystallization activation energies of PP and PA6 phase decrease in the presence of low TiO₂ content.However,the crystallization activation energies of PA6 in the PP-g-MAH compatibilized nanocomposites increased with the incorporation of TiO₂.Crystallinity of PP and PA6 is increased with the incorporation of TiO₂ nanoparticles;however,they increased at first and then decreased with increase of cooling rate.This phenomenon can be explained as follows:the TiO₂ nanoparticles have two effects on the PP and PA6 phase,i.e.they act as effective nucleating agents for PP and PA6 phase,on the other hand the existence of the TiO₂ and the interaction between the nanoparticle and blends hinder the motion of the polymer chains.The two effects lead to the observed change of crystallinity with the increase of cooling rate.The PA6 phase in the non-isothermally crystallized sample exhibits multiple melting endotherms,which can be attributed to the different crystalline structures.The additions of small amount of TiO₂ nanoparticles make melt viscosity of PP/PA6 based nanocomposites decrease and also make non-newtonian index（n） of the PP-g-MAH compatibilized nanocomposites increase,however the n will decrease with increase of TiO₂ content,which favors the enhancement of pseudoplastic property. Flow activation energy of the PP-g-MAH compatibilized nanocomposites decrease with the incorporation of small amount of TiO₂ nanoparticles and the sensitivity of melt viscosity to temperature decreases.Owing to the homogeneous dispersion of TiO₂ nanoparticles in polymer blends,the TiO₂ nanoparticles have lubricating effect on the matrix polymer,which was the reason of the observed phenomenon.The storage（G’） and loss moduli（G"） and complex viscosity（η^*） are resulted from the dynamic frequency.All parameters increased monotonically in the entire frequency range with the addition of TiO₂ nanoparticles into the PP/PA6 blend,which indicated that the TiO₂ nanoparticles give the matrix polymer good elastic and viscous.The as-prepared PP/PA6 based nanocomposites have strong antimicrobial abilities against bacillus subtilis,staphylococcus aureu and escherichia coli.The average efficiency of antibacterial properties is over 90%within 2.0 h.Thermal stability of the PP/PA6 based nanocomposites was investigated by TGA and the result showed the TiO₂ nanoparticles favor the enhancement of thermal stability.In addition,the theoretical weight loss rate of the PP/PA6 based nanocomposites is equal to the actual weight loss rate at the range of error,which indicated that the nanoparticles are uniformly dispersed in the polymer matrix.更多还原