高分子纳米复合材料拉伸及压缩的分子动力学模拟

利用高分子-纳米粒子粗粒化模型,对高分子纳米复合材料(polymer nano-composites,PNC)的拉伸、压缩及平衡态过程进行分子动力学模拟研究.通过模拟PNC的拉伸及压缩过程,研究纳米粒子大小、质量分数对PNC力学性能的影响及拉伸、压缩过程中PNC体系微观交联网络的变化.在纳米粒子表面积或质量分数相同的情况下,小尺寸纳米粒子对PNC的力学性能增强效果更显著.对于含有质量分数不同的小尺寸纳米粒子的PNC体系,随纳米粒子质量分数增加,其力学性能增强,但增强程度逐渐减弱,且对于拉伸过程的材料增强效应,纳米粒子的质量分数存在最优值.在PNC体系中存在高分子-高分子(polymer-polymer)、高分子-纳米粒子(polymer-NP)2种微观交联网络,拉伸及压缩过程中PNC体系中2种微观交联网络的变化趋势不同,PNC拉伸及压缩产生应力的微观机制也相应有所不同.此外,对含质量分数不同的小尺寸纳米粒子的PNC平衡态过程的模拟研究表明,PNC体系中2种微观交联网络的比例直接影响其力学性能的变化,而纳米粒子的聚集则会降低PNC的力学性能增强效果.     

高分子量聚乙烯醇增强冰的研究

以本体光聚合法制备的高分子量聚乙烯醇(HMWPVA)为增强剂,考察了增强冰的力学性能.当HMWPVA的浓度为3%(质量分数)时,增强冰的拉伸强度、断裂伸长率、压缩强度和压缩模量分别为普通冰的11.7,3.5,2.3和2.1倍.对比试验发现PVA分子量对冰的拉伸性能影响较大,对冰的压缩性能影响较小.此外,在室温29℃时纯冰的融化时间为5 min,而4%HMWPVA增强冰的融化时间长达240 min.     

聚酰胺PACM12-PA66共聚物的制备及其性能研究

以4,4'-二胺基二环己基甲烷、十二碳二酸、己二酸己二胺盐为反应单体制备了(亚氨基-1,4-亚环己基亚甲基-1,4-亚环己基亚氨基十二碳二酰)-co-(亚氨基亚己基亚氨基己二酰)共聚物材料(PACM12-PA66),并研究了其光学性能和力学性能.光学性能研究表明,当PACM12含量高于40%时,为可见光(400~800 nm)透光度良好的高分子材料,其透光度与纯PA PACM12材料相当;共聚物材料的折光指数随PACM12含量的降低而略微增加.XRD结果分析表明,随PACM12含量的降低共聚物材料的晶粒尺寸变大,这是透光度降低的原因.力学性能研究表明,共聚物材料拉伸强度和冲击强度随PACM12含量的降低而增加.当PACM12含量为40%时,共聚物材料拉伸强度值(64.28 MPa)和冲击强度值(14 kJ/m2)分别比纯PACM12材料提高了16%和33%.     

高强度PAM/PVP半互穿网络凝胶制备及力学性能

以过硫酸铵为引发剂通过一步溶液聚合制备了由化学交联的聚丙烯酰胺(PAM)与聚乙烯吡咯烷酮(PVP)贯穿形成的PAM/PVP半互穿网络(semi-IPN)凝胶,着重研究了凝胶的机械性能。红外光谱、热重分析及拉伸实验分析可知PAM与PVP之间存在氢键作用。拉伸实验表明:在PAM中引入PVP,凝胶拉伸强度明显提高,m(PVP)/m(AM)=7.51%时制备的PAM/PVP semi-IPN凝胶拉伸强度比单纯化学交联的PAM增大64.67%;当AM=6mol/L,n(MBA)/n(AM)=1.67×10-4,m(PVP)/m(AM)=7.51%时,制备的凝胶机械性能较好,拉伸强度达到1.84MPa,断裂伸长率可达3322%;随着含水率增加,凝胶拉伸强度及断裂伸长率均有所降低。     

静电纺丝法制备PAN/HNTs混杂纤维增强热塑性聚氨酯复合材料

静电纺丝方法制备了聚丙烯腈/埃洛石纳米管(PAN/HNTs)混杂纤维增强体,通过改变接收装置、热拉伸处理得到5种不同的PAN/HNTs混杂纤维增强体。采用浸渍法将5种增强体用于改性热塑性聚氨酯,得到PAN/HNTs/TPU复合材料。结果表明,PAN/HNTs混杂纤维增强体可显著提高复合材料的力学性能。将平板接收制备的PAN/HNTs混杂纤维增强体以及另外两种由1050r/m滚筒接收制备的PAN/HNTs混杂纤维增强体(前者不采用热拉伸,后者采用热拉伸),三者制成PAN/HNTs/TPU复合材料。与通过平板接收制备的复合材料相比,通过由1050r/m滚筒接收制备的两种复合材料性能要优于前者,相较于前者,其复合材料的拉伸强度分别增加了19%和43%,弹性模量分别增加了44%和122%,断裂伸长率分别增加了19%和24%。当定向接收的PAN/HNTs纤维膜的含量为5.6%时所得到的PAN/HNTs/TPU复合材料力学性能为最佳;通过热拉伸处理PAN/HNTs纤维膜,当含量为4.5%时,复合材料的力学性能为最佳。这种力学增强的主要原因是PAN/HNTs纤维与热塑性聚氨酯材料之间的相容性得到了改...     

不同石墨烯-碳纳米管杂化体系对热塑性聚氨酯复合材料力学和自修复性能的增强机制

采用溶液共混法,设计不同的杂化方案,制备了3种具有不同复合程度的石墨烯(G)和碳纳米管(CNT)三维空间结构材料,并对G-CNT填充的热塑性聚氨酯(TPU)复合材料的力学性能及在微波诱导下的裂纹自修复特性进行了研究.结果表明,G-CNT复合结构能改善增强相与基体间的界面结合及载荷传递,且复合程度越高其对TPU力学增强效果越显著.当采用预复合方法时G-CNT复合程度最高,此时TPU复合材料的拉伸强度比纯TPU提高了37.6%,比G/TPU提高了27.1%.TPU复合材料在微波场的诱导下可实现损伤裂纹的快速修复,然而其修复效率并未随着G-CNT复合程度的增加而升高,当采用超声复合时,G-CNT的复合程度低于预复合法的复合程度,但其修复率却达到最高值(138%).该自修复特性和G-CNT的空间构型及其异质界面与微波之间的耦合机制密切相关.     

复合改性竹纤维/聚丙烯复合材料的制备与性能研究北大核心CSCD

为改善竹纤维(BF)与聚丙烯(PP)的界面结合,采用碱(NaOH)和异氰酸酯偶联剂(TDI)复合改性竹纤维,制备BF/PP复合材料。分析了竹纤维改性前后主要化学成分、热行为及化学结构变化,考察了竹纤维改性对复合材料维卡软化点(VSP)和动态热力学性能影响,用扫描电镜对复合材料断面进行了观察,最后探讨了改性竹纤维添加量对复合材料力学性能的影响。结果表明:BF经复合改性后,表面形成了氨酯键结构,竹纤维素晶体尺寸和结晶度增大,竹纤维的最快热降解温度和复合材料的VSP分别提高了20℃和4.5℃。SEM、DMA分析显示,竹纤维复合改性改善了两相界面结合,利于力学性能提高。拉伸实验表明,在复合改性竹纤维添加比例为40%时,复合材料综合性能最佳,其冲击强度、拉伸强度和弯曲强度分别增加了21.6%、23.3%和27.8%,拉伸模量和弯曲模量分别增加了24.2%和30.4%。     

复合改性竹纤维/聚丙烯复合材料的制备与性能研究

为改善竹纤维(BF)与聚丙烯(PP)的界面结合,采用碱(NaOH)和异氰酸酯偶联剂(TDI)复合改性竹纤维,制备BF/PP复合材料。分析了竹纤维改性前后主要化学成分、热行为及化学结构变化,考察了竹纤维改性对复合材料维卡软化点(VSP)和动态热力学性能影响,用扫描电镜对复合材料断面进行了观察,最后探讨了改性竹纤维添加量对复合材料力学性能的影响。结果表明:BF经复合改性后,表面形成了氨酯键结构,竹纤维素晶体尺寸和结晶度增大,竹纤维的最快热降解温度和复合材料的VSP分别提高了20℃和4.5℃。SEM、DMA分析显示,竹纤维复合改性改善了两相界面结合,利于力学性能提高。拉伸实验表明,在复合改性竹纤维添加比例为40%时,复合材料综合性能最佳,其冲击强度、拉伸强度和弯曲强度分别增加了21.6%、23.3%和27.8%,拉伸模量和弯曲模量分别增加了24.2%和30.4%。     

谷朊粉/淀粉/甘油混合体系的流变行为与力学性能

研究了甘油增塑谷朊粉/淀粉混合体系的动态流变行为与单轴拉伸力学性能,考察了淀粉与水含量的影响.研究结果表明,含水量10%的混合体系储能模量(G′)随淀粉含量增大而增大,并在100℃出现橡胶平台.增塑谷朊粉在30℃呈现凝胶特性,在80℃出现交联网络结构.淀粉粒子可与小麦蛋白质形成复杂相互作用,阻碍蛋白质链段运动,导致模量与强度增加,断裂伸长率降低.含水量为20%与25%时,水份在淀粉粒子与蛋白质网络间起稀释和润滑作用,拉伸强度与断裂伸长率随淀粉含量的增高而降低.     

低温水凝胶力学性能的研究

本文采用单向压缩和单向拉伸法测定了聚乙烯醇(PVA)低温水凝胶的力学性能。结果表明,其机械强度随凝胶浓度和冷冻时间的增加而增强。得到弹性模量与凝胶浓度的关系符合标度律。说明采用低温处理方法可使PVA水溶液凝胶化,制得含水量高、具有较高强度、类似于橡胶的弹性材料,认为其力学强度来自于物理交联网络的贡献。     

High reinforcing capability cellulose nanocrystals extracted from <Emphasis Type="Italic">Syngonanthus nitens</Emphasis> (Capim Dourado)

The chemical composition and morphology of Syngonanthus nitens (Capim Dourado) fibers were investigated. An unusual low lignin content and high holocellulose content have been observed. High aspect ratio cellulose whiskers were prepared from these lignocellulosic fibers by an acid hydrolysis treatment. The average diameter and length were 4.5 nm and 300 nm, respectively, giving rise to an aspect ratio around 67. Natural Rubber nanocomposite films reinforced with cellulose whiskers extracted from capim dourado were prepared by film casting. The mechanical properties of the ensuing nanocomposite films were investigated in both the linear and the non-linear range using dynamical mechanical analysis and tensile tests, respectively. The reinforcing effect observed above the glass transition temperature of the matrix was higher than the one observed for other polysaccharide nanocrystals and cellulose whiskers extracted from other sources.     

Comparative study of pineapple leaf microfiber and aramid fiber reinforced natural rubbers using dynamic mechanical analysis

Natural fiber is often considered inadequate for high performance reinforcement of polymer matrix composites. However, some natural fibers have relatively high mechanical properties with modulus close to that of high-performance synthetic fibers. Since the reinforcing efficiency of a short fiber is determined not only by the fiber modulus, but also by other physical properties such as the length to diameter ratio. Here it is shown, for the first time, that pineapple leaf fiber, whose modulus is somewhat lower than that of aramid fiber, can be used to reinforce natural rubber more effectively than aramid fiber. The situation was achieved by breaking down the fiber bundles into the constituent microfibers to gain very high aspect ratio. Comparisons were made at fiber contents of 2, 5 and 10 parts (by weight) per hundred of rubber (phr) using dynamic mechanical analysis over a range of temperature. The results reveals that at temperature below the glass transition of the matrix rubber and low fiber contents of 2 and 5 phrs, aramid fiber displays slightly better reinforcement efficiency. At high temperatures of 25 and 60 °C and high fiber content of 10 phr, pineapple leaf microfiber clearly displays higher reinforcement efficiency than does aramid fiber. Surface modification of the fiber by silane treatment provides a slight improvement in reinforcing efficiency.     

Effects of cellulose whiskers on properties of soy protein thermoplastics

Environmentally-friendly SPI/cellulose whisker composites were successfully prepared using a colloidal suspension of cellulose whiskers, to reinforce soy protein isolate (SPI) plastics. The cellulose whiskers, having an average length of 1.2 microm and diameter of 90 nm, respectively, were prepared from cotton linter pulp by hydrolyzing with sulfuric acid aqueous solution. The effects of the whisker content on the morphology and properties of the glycerol-plasticized SPI composites were investigated by scanning electron microscopy, dynamic mechanical thermal analysis, differential scanning calorimetry, ultraviolet-visible spectroscopy, water-resistivity testing and tensile testing. The results indicated that, with the addition of 0 to 30 wt.-% of cellulose whiskers, strong interactions occurred both between the whiskers and between the filler and the SPI matrix, reinforcing the composites and preserving their biodegradability. Both the tensile strength and Young's modulus of the SPI/cellulose whisker composites increased from 5.8 to 8.1 MPa and from 44.7 to 133.2 MPa, respectively, at a relative humidity of 43%, following an increase of the whisker content from 0 to 30 wt.-%. Furthermore, the incorporation of the cellulose whiskers into the SPI matrix led to an improvement in the water resistance for the SPI-based composites.     

环和纳米管径向呼吸振动模式的一个简单理论模型

用密度泛函方法在B3LYP/6-31G(d)基组下计算了(MgO)n和(BeO)n环(n=3-10)的径向呼吸振动. 大环的径向呼吸振动频率正比于环直径的倒数, 但键长的变化导致频率偏离了这种线性关系. 随着环直径的减小, 直径倒数的三次方和键长的变化将导致频率更大地偏离线性行为. 从化学键的角度出发利用一维谐振子及弹簧的串并联思想, 解释了这种线性关系和偏离现象. 这种模型还可以用于研究纳米管的径向呼吸振动频率.     

A fiber composite model of highly oriented polyethylene

A fiber composite model of highly drawn polyethylene is presented. Quantitative predictions and calculations are made using shear-lag theory. The drawing process is shown to occur in two stages, a neck and a postneck taper. It is shown that there is an empirical linear relationship, with a high correlation, between the parameter x in shear-lag theory (which involves the aspect ratio of the reinforcing elements and the square root of the ratio of matrix shear modulus to the Young's modulus of the reinforcing elements) and the 3/2 power of the taper draw ratio. It is concluded that crystalline fibrils (the reinforcing elements) deform homogeneously during the secondary, taper drawing process. The increase in aspect ratio resulting from this homogeneous deformation is held to be responsible for the increase in tensile modulus owing to the increased efficiency of the fibrils as reinforcing elements. The model is also used to explain the self-hardening process exhibited by these fibers and, using measurements of density of hardened fibers, to predict that immediately after the neck the aspect (length to diameter) ratio of the crystalline reinforcing elements is ca. 2 and that the shear modulus of the matrix material in as-drawn fibers is ～10³N/m² and does not change significantly during the taper-drawing process.     

PEG链段对聚乙二醇接枝聚苯胺结构与性能的影响

将苯胺(An)与甲氧基聚乙二醇邻氨基苯基醚氧化共聚,制备了梳状接枝共聚物PAn-g-PEG.研究了梳状接枝共聚物的UV-Vis、微观结构、热稳定性和溶解成膜性等随侧链聚乙二醇(PEG)链段的变化规律.结果表明随PAn-g-PEG中PEG链段长度和含量的提高,共聚物的溶解性和成膜性能显著提高,电子导电率缓慢降低,热稳定性变差.共聚物具有微相分离结构,其形态随PEG链段的改变分别为“海-岛相”和“双连续相”;提高PEG链段长度和含量,PAn-g-PEG能形成稳定的水溶性分散体系,并能浇注成柔韧平整的导电高分子自支撑膜.     

Biocomposites based on poly(butylene succinate) and curaua: Mechanical and morphological properties

Biocomposites based on poly(butylene succinate) (PBS) and curaua fibers have been produced by compression molding, and investigated as a function of fiber length and amount. Mechanical tests, water uptake and morphology studies were carried out in order to assess the composite features according to the characteristics of the reinforcing agents. It turns out that the impact and flexural strengths increase with fiber content. Moreover, the fiber length, varying from 1 to 4 cm for the composite reinforced with 20 wt% of fiber, influences impact strength, which is higher for shorter than for longer fibers. However, flexural strength is not greatly influenced by the length of the fibers. Water uptake studies reveal a higher sensitivity of the material to fiber content rather than fiber size. Biocomposites, which are characterized by enhanced mechanical properties as compared to PBS, can have different applications, for example in rigid packaging or interior car parts.     

A Simple Theoretical Model for Ring and Nanotube Radial Breathing Mode

The radial breathing modes (RBMs) of (MgO)_n and (BeO)_n rings (n=3-10) were calculated using the density functional theory at B3LYP/6-31G(d) level. It was found that for large rings, the radial breathing mode (RBM) frequency was inversely proportional to the centre diameter, but the variation of bond length may lead to deviations from a linear behavior. The deviations caused by inverse cubic term of diameter and variation of bond length, became dramatic with the decrease of ring diameter. From the point of chemical bond view, using one-dimensional harmonic oscillator and the method of cascade and parallel connection of “springs”, the linear relation and deviations were explained. The model can be applied to nanotubes.     

Preparation of Long Glass Fiber Reinforced Poly(butylene terephthalate) Composites with Chemical Bonding Interphase

Long glass fiber reinforced poly(butylene terephthalate) composites (LGF/PBT) were prepared by a new process. PBT oligomers with low melt viscosity were impregnated into the reinforcing glass fiber and then grafted to the reinforcing glass fiber surface treated with a silane coupling agent during solid‐state polymerization. The reinforcing glass fiber, after removing ungrafted PBT from LGF/PBT, was investigated with the result showing the presence of a grafted PBT layer on the surface of treated glass fiber. The mechanical properties of the composites were significantly improved owing to the grafting of the PBT macromolecules. The fiber length distribution and fiber arrangement in the injection molded composites were also studied and the results showed that a small amount long glass fiber could be connected at junction points in the composites, which were of benefit to the mechanical properties of the composites.     

Preparation and characteristics of spinnable sol and continuous mullite fibers with nano silica addition

The spinning precursor sols for the continuous mullite-based fibers were prepared by adding nano-silica to substitute part of silica sol. The effect of SiO₂ nanoparticles on the particle evolution models, polymerization degree and solid content of the sol,and the spinning length and sintering behavior of the fibers was investigated. The results were shown that the addition of nano silica enhanced the polymerization degree and extended the spinnable range of the sol. The appropriate polymerization degree (B value) for this sol system was 1.885–2.145. The grain diameter decreased from 39.6 to 25.9 nm with increasing the nano-silica content to 20 %, and then, it increased to 41.2 nm with increasing the nano-silica content to 100 %. The appropriate content of nano-silica powders would reduce the grain diameter. However, it had no influence on the linear growth model, homogeneity and solid content of the precursor sol.