碳纳米纤维增强聚甲醛复合材料制备及性能

通过纳米碳纤维(CNFs)在聚甲醛(POM)基体中的均匀分散以及取向,制备了具有优异力学性能和热性能的POM/CNFs复合材料。利用扫描电子显微镜、透射电子显微镜、拉伸性能测试、热重分析、动态热机械分析测试表征了POM/CNFs复合材料的结构和力学、热学性能。结果表明,CNFs与POM分子链形成氢键相互作用,促进了CNFs在POM基体内分散,同时使POM/CNFs复合材料的结晶度显著提高。随着CNFs含量增加,POM/CNFs复合材料的拉伸强度、储能模量和损耗模量均得到提高。当添加0.5%的CNFs时,拉伸强度、储能模量及损耗模量分别提高了20.5%,127%和58%。进一步研究了高温拉伸对POM/CNFs复合材料性能的影响。结果表明,CNFs沿拉伸方向定向排列,同时复合材料拉伸后结晶度提高,拉伸强度显著增加。     

PP/CNFs复合材料非等温结晶动力学研究

采用聚丙烯蜡乳液(PP-wax)改性纤维素纳米微纤(CNFs),再通过HAKKE转矩流变仪熔融混合制备了聚丙烯(PP)/CNFs复合材料。利用差示扫描量热仪(DSC)研究了改性CNFs对PP非等温结晶行为的影响,并分别用Jeziorny、Ozawa和Mo模型对数据进行了处理。结果表明:改性CNFs对PP结晶的影响主要由改性剂PP-wax决定。一方面,低分子量PP-wax降低了PP基体的规整性,抑制了PP的成核,使得PP结晶温度下降;另一方面,PP-wax提升了基体PP分子链的运动能力,使PP晶体的生长速度加快,进而提高了PP基体的结晶速率。另外,Kissinger公式计算结果表明,CNFs的引入降低了PP结晶的活化能。     

TPS/LDPE/纳米SiO_2材料结构与性能

以天然高分子木薯淀粉为研究对象,低密度聚乙烯(LDPE)和纳米二氧化硅(SiO_2)为改性材料,甘油为增塑剂,通过熔融法制备了热塑性木薯淀粉(TPS)/LDPE/纳米SiO_2复合材料,研究了复合材料的塑化性能、力学性能、结晶性能、热稳定性和微观结构。结果表明:纳米SiO_2能提高TPS/LDPE复合材料塑化性能,更容易进行加工;随着纳米SiO_2用量的增加,复合材料的拉伸强度降低、断裂应变增加,复合材料的熔融焓、结晶度减小,热降解温度提高;纳米SiO_2的加入使得复合材料的球晶变得更细密,改变了复合材料的晶型;当纳米SiO_2用量为2份(质量份)时在复合材料中分散较好,但随着纳米SiO_2用量的增加会发生团聚现象。     

PEG/CNFs相变储能材料非等温结晶动力学研究

通过溶液浇铸法制备了聚乙二醇/纤维素纳米微纤(PEG/CNFs)复合相变储能材料,采用差示扫描量热仪(DSC)研究了CNFs含量对该PEG/CNFs复合材料中PEG结晶行为的影响,并利用Jeziorny、Ozawa和Mo模型对DSC结果进行了非等温结晶动力学分析。结果表明:加入CNFs后,复合材料中PEG的半结晶时间(t1/2)与Avrami指数(n)下降,表明CNFs充当了PEG的成核剂;另外,CNFs含量的增加抑制了PEG晶体的生长,PEG的结晶焓(ΔHPEG)显著下降。     

Bi2S3/CNFs复合材料制备及其光催化性能

采用水热法制备硫化铋(Bi2S3)和活性纳米碳纤维掺杂硫化铋复合材料(Bi2S3/CNFs),以降解水溶液中甲硝唑(MTZ)抗生素.通过XRD、SEM、TEM、FTIR、XPS、UV-Vis和PL等对样品的晶型、形貌、结构、元素组成、表面官能团、光学性质进行了表征.结果表明,活性纳米碳纤维(CNFs)引入Bi2S3中,可降低光生电子-空穴对的复合速率,提高其光催化活性.在可见光照射下,考察了Bi2S3/CNFs复合材料光催化降解MTZ的活性,发现CNFs掺量为47％(以Bi2S3质量计,下同)、MTZ质量浓度为10 mg/L,复合材料用量为60 mg时,Bi2S3/CNFs复合材料光催化性能优异,在3 h内,MTZ的降解率为92％.Bi2S3/CNFs复合材料在3次循环后也表现出良好的稳定性和可回收性.活性基团捕获实验表明,羟基自由基(?OH)、光生空穴(h+)和超氧自由基(?O2–)参与了Bi2S3/CNFs对MTZ的降解,而?OH和h+是该体系的主要活性组分,并在此基础上初步探讨了光催化反应机理.     

纳米CaCO3及偶联剂对小本体PP结晶的影响

采用熔融共混法制备了小本体聚丙烯/纳米CaCO3复合材料(SBPP/纳米CaCO3),研究了经铝钛复合偶联剂处理前后的纳米CaCO3粒子对SBPP结晶性能的影响.结果表明纳米粒子能够诱导β晶的形成,提高SBPP的结晶度,降低SBPP球晶尺寸,使得球晶均匀程度增加,并且纳米CaCO3经偶联剂处理后以上几种效果更为显著;纳米CaCO3可以提高材料的结晶温度和结晶速率,但经偶联剂处理的纳米粒子的结晶速率却小于未经偶联剂处理的材料的结晶速率,说明偶联剂的加入在一定程度上抑制了纳米CaCO3对SBPP/纳米CaCO3复合材料的结晶过程.     

PP-g-MAH对PP/纳米SiO_2复合材料性能的影响

采用熔融共混法制备了聚丙烯(PP)/纳米SiO2复合材料,研究了相容剂马来酸酐接枝聚丙烯(PP-g-MAH)对复合材料力学性能、结晶性能及界面作用的影响。结果表明:PP-g-MAH能有效地增强纳米SiO2与PP基体间的界面作用,提高复合材料的力学性能;同时,PP-g-MAH增强了纳米SiO2的成核活性,使PP的结晶温度升高,球晶细化。     

表面改性对LDPE/nano-ATH复合材料性能的影响

采用熔融共混法制备了低密度聚乙烯(LDPE)/纳米氢氧化铝(nano-ATH)复合材料,研究了nano-ATH表面改性前后对复合材料力学性能和阻燃性能的影响;利用扫描电镜(SEM)分析了nano-ATH表面改性前后在LDPE基体中的分散性。结果表明:表面改性nano-ATH使复合材料具有较高的拉伸强度和断裂伸长率;nano-ATH用量较少时,其表面改性与否对复合材料的阻燃性能基本没有影响;加入量较大时,表面改性nano-ATH使复合材料具有较好的阻燃性能,其在LDPE基体中的分散性也得到改善。     

纤维素纳米纤维对聚乳酸结晶、流变和拉伸性能的影响

采用熔融共混⁃注射成型制备了聚乳酸（PLA）/纤维素纳米纤维（CNFs）可生物降解纳米复合材料,利用差示扫描量热仪、流变测试、拉伸性能测试等手段,考察了CNFs含量对PLA/CNFs复合材料结晶行为、流变特性和力学性能的影响规律。结果表明,少量的CNFs能均匀分散在PLA基体中,CNFs可作为PLA的异相成核剂,提高结晶速率常数,缩短半结晶时间,CNFs的含量为5 %（质量分数,下同）时,半结晶时间由纯PLA的10.4 min缩短至2.9 min;CNFs体现出润滑作用,使PLA/CNFs复合材料的储能模量和损耗模量均低于纯PLA;CNFs的含量为3 %时,复合材料的断裂伸长率较纯PLA提高了41.2 %。     

动态保压注射成型HDPE/Nano-OMMT复合材料的结构与性能

聚合物/黏土纳米复合材料是近几年聚合物材料改性的热点。为了进一步理解复合材料性能与结构的关系,利用自行研制的动态保压装置,借助WAXD、DSC、SEM等测试方法,研究了高密度聚乙烯(HDPE)/纳米有机蒙脱土(nano-OMMT)复合材料的结构与性能。结果表明,动态保压使OMMT纳米粒子在基体中的分散性提高,并形成插层结构。与此同时,动态剪切力场使HDPE/nano-OMMT复合材料的HDPE基体结构形态亦发生变化,试样中生成串晶结构,相比常规注塑试样,动态保压试样结晶度最大提高15%,结晶形态的变化和结晶度的提高均有利于HDPE/nano-OMMT复合材料强度的提高。力学性能试验显示,拉伸强度和冲击强度同时得到提高,HDPE/nano-OMMT复合试样的拉伸强度最大提高了119%,冲击强度最大提高430%。     

Effects of carbon nanofibers on crystalline structures and properties of ultrahigh molecular weight polyethylene blend fabricated using twin‐screw extrusion

Melt mixing in an extruder with polymers is an effective approach for forming nanocomposites, allowing mass production applications. The intent of this study is to investigate carbon nanofiber composites with ultrahigh molecular weight polyethylene (UHMWPE) matrix using the twin‐screw extruder. To decrease the high viscosity of UHMWPE, a low density polyethylene (LDPE) was added into the UHMWPE. The effects of carbon nanofibers (CNFs) on the crystalline structures and properties of the nanocomposites were analyzed. The differential scanning calorimetry (DSC) and X‐ray diffraction (XRD) measurements showed the addition of CNFs decreases the degree of crystallinity, but does not impart significant effects on the crystalline structure of the UHMWPE/LDPE blend. Tensile test results showed that the nanocomposite with loading of 3 wt % CNFs had an increase of 38% in tensile strength and 15% in modulus. The thermal stability and thermal conductivity of UHMWPE/LDPE blends were also enhanced by the addition of CNFs. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effects of crystallization on dispersion of carbon nanofibers and electrical properties of polymer nanocomposites

Polymer nanocomposites filled with low volume fractions of carbon nanofibers (CNFs) were prepared by melt‐compounding. Three types of polymers with different crystallization behavior, i.e., weakly‐crystallized low density polyethylene (LDPE), strongly crystallized high density polyethylene (HDPE) and amorphous polystyrene (PS), were selected as matrices for the nanocomposites. The effects of polymer crystallization on the dispersion of CNFs were examined. Optical and electron microscopic examinations revealed that the dispersion of CNFs in the nanocomposite matrices was strongly depended on the crystallization behavior of polymer matrices. The CNFs were found to disperse uniformly in weakly crystallized LDPE and amorphous PS matrices, but agglomerated in HDPE due to its strong crystallization tendency. Such a distinct dispersion behavior of CNFs in polymers had a profound effect on the electrical properties of the nanocomposites investigated. The PS/CNF nanocomposites exhibited the lowest percolation threshold. The HDPE/CNF nanocomposites showed the largest percolation threshold due to the CNF agglomeration within the amorphous phase of HDPE. POLYM. ENG. SCI., 48:177–183, 2008. © 2007 Society of Plastics Engineers     

Crystallization behavior and mechanical properties of polypropylene/halloysite composites

In this work, halloysite nanotubes (HNTs), a new type of inexpensive filler, were used for the modification of polypropylene (PP). HNTs were first surface treated by methyl, tallow, bis-2-hydroxyethyl, quaternary ammonium, then melt mixed with PP. Scanning electron microscope (SEM) was used to examine the dispersion of HNTs in PP matrix. Differential scanning calorimetry (DSC), polarized light microscope (PLM), dynamic melt rheometry and wide angle X-ray diffraction (WAXD) were employed to investigate the crystallization behavior of the prepared PP/HNT composites. The mechanical properties were evaluated by Instron and impact tests. SEM results revealed that HNTs could be well-dispersed in PP matrix and had a good interfacial interaction with PP, even up to a high content of 10 wt%. DSC data indicated that HNTs could serve as a nucleation agent, resulting in an enhancement of the overall crystallization rate and the non-isothermal crystallization temperature of PP. PLM showed a constant spherulite growth rate and a decreased spherulite size at given isothermal crystallization temperature, suggesting that nucleation and growth of a spherulite are two independent processes. The result obtained by dynamic melt rheometry indicated that HNTs mainly promoted nucleation and had not much influence on the growth of PP crystallization. Nevertheless, by fast cooling the samples, almost constant spherulite size can be obtained for both pure PP and PP/HNT composites due to the limited nucleation effect of HNTs on PP crystallization. WAXD showed that HNTs mainly facilitated α-crystal form of PP. Though a good dispersion of HNTs in PP matrix was observed, out of our expectation, not much enhancement on mechanical properties of PP/HNT composites had been achieved, and this could be mainly ascribed to the constant crystallinity and spherulite size of PP as well as the small length/diameter ratio of HNTs.     

LDPE及LDPE/TiO_2纳米复合材料的熔限及等温结晶研究

采用熔融共混法制备了LDPE／TiO2纳米复合材料,以膨胀计对LDPE及LDPE／TiO2复合材料的熔点、熔限及等温结晶进行了研究。结果表明：膨胀计可用于LDPE及LDPE／TiO2纳米复合材料熔点及熔限的测试：与LDPE相比,LDPE／TiO2复合体系的半结晶期及AVrami指数较小,表明TiO2粒子对LDPE的结晶具有明显的异相成核作用;而Avrrdmi指数为非整数,且Avrami作图直线的最后部分与实验点的偏离,则表明LDPE及LDPE／TiO2纳米复合材料的等温结晶过程比Avrami方程要复杂得多。     

Ultrasonic oscillations induced morphology and property development of polypropylene/montmorillonite nanocomposites

Polypropylene/montmorillonite nanocomposites (PPCNs) with 3% organophilic montmorillonite (OMMT) content were prepared via ultrasonic extrusion. The objective of present study was to investigate the effects of ultrasonic oscillations in processing on the morphology and property development of PPCNs. XRD and TEM results confirmed the intercalated structure of OMMT in conventional nanocomposite (without ultrasonic treatment) and ultrasonicated nanocomposite, but ultrasonic oscillations could make silicate layers finely dispersed and a little exfoliated. According to SEM, the OMMT particles were evenly and finely dispersed in the ultrasonicated nanocomposite via ultrasonic oscillations, and the aggregation size of clay particles was about 100 nm, which is less than that in conventional nanocomposite. The crystalline dimension, crystalline morphology and the growth rate of crystallization in PPCNs were investigated by DSC and PLM, it was found that the OMMT particles and ultrasonic oscillations played an important role in the nucleation rate, crystallization temperature and spherulite size of PP matrix in nanocomposites. Compared with conventional nanocomposite, the mechanical properties of the ultrasonicated nanocomposite increased due to the improved dispersion of OMMT and diminished spherulite size. The thermal stability and the rheological behavior of PP and its nanocomposites were both studied by thermogravimetry and high pressure rheometer, respectively.     

表面结构不同的纳米二氧化硅原位改性聚甲醛的研究

分别选用环氧基纳米二氧化硅（SiO2）(RNSE)和甲基纳米SiO2(DNS)为填料,通过原位聚合法制备了聚甲醛(POM)/纳米SiO2复合材料,采用场发射扫描电子显微镜、热重分析仪、差示扫描量热仪、偏光显微镜和X射线衍射仪对所得复合材料的结构、热稳定性和结晶行为进行了研究。结果表明,纳米SiO2的用量和表面结构不仅影响了其在复合材料中的分散性,而且对复合材料的热稳定性和结晶行为影响显著;当RNSE的用量少于1 %（质量分数,下同）时,其在POM基体中具有较好的分散性,且相对于DNS,RNSE的分散性更好;纳米SiO2加速了POM结晶,减小了球晶尺寸,提高了结晶度,而且RNSE比DNS对POM的结晶具有更显著的促进作用,但纳米SiO2没有改变POM的晶体结构;引入纳米SiO2降低了POM的热稳定性。     

Crystallization behavior of carbon nanofiber/linear low density polyethylene nanocomposites

Crystallization behavior of LLDPE nanocomposites is reported in the presence of three types of carbon nanofibers (CNFs) (MJ, PR‐19, and PR‐24). During nonisothermal crystallization studies, all three crystalline melting peaks for LLDPE matrix were observed in the presence of PR‐19 nanofibers (up to 15 wt % content), but only the high‐ and low‐temperature peaks were observed in the presence MJ nanofibers. The broad melting peak at low‐temperature became bigger, suggesting an increase in the relative content of thinner lamellae in the presence of MJ nanofibers. TEM results of nanocomposites revealed transcrystallinity of LLDPE on the surface of CNFs, and a slightly broader distribution of lamellar thickness. STEM studies revealed a rougher surface morphology of the MJ nanofibers relative to that of PR nanofibers. Also, BET studies confirmed a larger specific surface area of MJ nanofibers relative to that of PR nanofibers, suggesting that the larger and the rougher surface of MJ nanofibers contributes toward the different crystallization behavior of MJ/LLDPE nanocomposites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Spherulite nucleation in isotactic polypropylene based nanocomposites with montmorillonite under shear

The crystallization of nanocomposites of isotactic polypropylenes with organo modified montmorillonite compatibilized by maleic anhydride grafted polypropylene was studied by light microscopy in isothermal conditions in quiescent state and in shear. The isothermal and nonisothermal crystallization of the composites was also investigated by DSC method. Only weak nucleation activity of montmorillonite was observed during crystallization in static conditions. The clay nucleation activity was greatly enhanced in shear-induced crystallization and resulted in a drastic decrease of spherulite sizes. In nanocomposite films crystallized isothermally the intense nucleation of isotactic polypropylene spherulites was observed when the polymer was forced to flow to compensate the volume shrinkage due to crystallization. It was also found that the presence of a glass support enhances spherulite nucleation in nanocomposites which is caused possibly by shear due to a difference in thermal shrinkage of a polymer matrix and a glass support.