微波辅助原位聚合法制备聚乳酸/蛭石纳米复合材料

对蛭石(VMT)有机改性后,以丙交酯为单体,在催化剂存在的条件下采用微波辅助原位聚合法制备聚乳酸/蛭石(PLA/VMT)纳米复合材料。利用广角X射线粉末衍射法(WAXD)、傅立叶红外光谱法(FT-IR)以及差示扫描量热法(DSC)对材料进行了表征。对蛭石的添加量对材料的插层效果以及材料性能的影响进行了讨论。结果表明,在反应时间很短的情况下,蛭石即可以纳米尺寸分布在PLA中。随蛭石含量的不同,分别得到了剥离型和插层性PLA/VMT纳米复合材料。     

微波辅助原位聚合法制备聚乳酸/蛭石纳米复合材料EI北大核心

对蛭石(VMT)有机改性后,以丙交酯为单体,在催化剂存在的条件下采用微波辅助原位聚合法制备聚乳酸/蛭石(PLA/VMT)纳米复合材料。利用广角X射线粉末衍射法(WAXD)、傅立叶红外光谱法(FT-IR)以及差示扫描量热法(DSC)对材料进行了表征。对蛭石的添加量对材料的插层效果以及材料性能的影响进行了讨论。结果表明,在反应时间很短的情况下,蛭石即可以纳米尺寸分布在PLA中。随蛭石含量的不同,分别得到了剥离型和插层性PLA/VMT纳米复合材料。     

聚乳酸/蒙脱土纳米复合材料的原位聚合及表征

从乳酸出发,在乳酸脱水结束后、缩聚开始之前将蒙脱土和催化剂一起加入反应体系,通过原位熔融直接缩聚法制得较高分子量聚乳酸/蒙脱土纳米复合材料.XRD和TEM结果表明:蒙脱土(MMT)添加量为0.5%(质量分数,下同)时制得剥离型纳米复合材料,添加量为1%时产物剥离与插层结构并存.力学性能研究表明:MMT含量为0.5%和1...     

原位聚合法制备纳米凹凸棒土/聚乳酸复合材料

将凹凸棒土（AT）进行提纯和有机改性后, 采用原位聚合法制备了OAT质量分数为1%、 3%、 5%的纳米凹凸棒土/聚乳酸复合材料（OAT/PLA-x）。采用红外、 扫描电镜、 X射线衍射等对复合材料进行了表征, SEM结果表明, 凹凸棒土粒子在复合材料中实现了均匀稳定分散。复合材料的力学性能和综合热性能测试表明: OAT/PLA-3复合材料的拉伸强度、 弹性模量分别比纯PLA增加98.6%和130.0%; 复合材料的热稳定性明显提高。同时, 复合材料的溶液降解速率也明显加快。      

纳米TiO2/聚乳酸复合材料的制备和表征

采用原位聚合的方法制备了有机化处理过的纳米 TiO 2粒子质量分数分别为 1 wt %、3 wt %、5 wt %和10 wt %的 4种纳米 TiO 2/聚乳酸复合材料。SEM结果表明 , 当纳米 TiO 2粒子质量分数较低时 , 纳米 TiO 2在聚乳酸基体中呈现均匀稳定分散 , 而质量分数较高时则发生团聚。通过力学和热学等性能测试发现复合材料的最大热分解温度、 玻璃化转变温度和力学性能相对于聚乳酸有较大幅度提高 , 其中纳米 TiO 2的质量分数为 3 wt %时改善效果最明显 , 其最大热分解温度、 玻璃化转变温度分别比聚乳酸提高了 25. 3℃和 4. 9℃, 拉伸强度、 断裂伸长率和弹性模量分别提高了 83. 6 %、 6. 73 %和 129. 4 %。     

DSC法研究原位聚合聚乙烯/凹凸棒石纳米复合材料的结晶行为

用DSC热力学分析手段着重对原位配位聚合法制备的聚乙烯／凹凸棒石纳米复合材料(IPC)进行研究，并与同组分的熔体机械共混法制备的聚乙烯／凹凸棒石复合材料(MBC)进行对比。结果表明，无机相的引入对纳米复合材料中的基体聚乙烯的结晶有很大影响；从Avrami等温结晶理论出发，得出IPC比MBC具有较强的结晶能力，结晶机理也不相同的结论。     

原位聚合制备不饱和聚酯树脂/高岭土纳米复合材料及性能表征

利用超声法制备了高岭土-DMSO插层复合物前驱体,采取二步取代,原位聚合制备了不饱和聚酯树脂/高岭土纳米复合材料,并用XRD、FT-IR等手段对材料结构进行了表征,研究了纳米复合材料的阻燃性能。结果表明:当DMSO分子插入到高岭土层间时,d(001)值由0.717 nm增大到1.12 nm,插层率为91%,而不饱和聚酯树脂取代DMSO进入高岭土层间后,表征层状结构的d(001)特征衍射峰完全消失,高岭土内表面羟基吸收特征峰(3651 cm-1)和DMSO两个甲基的对称和反对称伸缩振动的吸收特征峰消失。燃烧实验表明这种材料相比纯树脂具有更好的阻燃性能。     

原位聚合法制备PMMA/膨胀石墨纳米复合材料

通过原位聚合将甲基丙烯酸甲酯(MMA)单体插入膨胀石墨层间,制备出以石墨层片为纳米分散相的导电复合材料.用红外光谱和X-射线衍射分析证实复合材料的合成,并讨论了石墨含量对复合材料的力学性能和导电性能的影响.     

原位聚合合成纳米胶囊

含有羧酸盐亲水基团,端基为可水解缩合的硅氧烷基的预聚体作为疏水物质如甲苯的分散剂获得内含疏水物质,聚聚体为壳层的纳米胶囊,预聚体壳层中的硅氧烷烃水解缩合形成交联,气相色谱测定水解醇深度证明水解缩合在常温24h内完成,透射电子显微镜（TEM）表征了纳米胶囊的形态。     

原位聚合法制备PA6/SiO2纳米复合材料

以正硅酸乙酯(TEO S)为前驱体,环氧丙基三乙氧基硅烷(W D-60)为改性剂,经原位聚合制备PA 6/S iO2纳米复合材料。利用端基滴定、力学性能测试、DSC、SEM、AFM等手段对材料的结构和性能进行研究。结果表明,经原位改性的S iO2纳米粒子在PA 6基体中分散均匀;与纯PA 6相比,复合材料的平均分子量下降,结晶速度明显加快,结晶度略有降低,材料的力学性能随S iO2加入量的增加而有一定的提高。     

Polyacrylamide/metakaolinite nanocomposites by in-situ intercalative polymerization

ABSTRACT

A series of polyacrylamide (PAM) organoclay nanocomposites were synthesized by in-situ intercalative polymerization using acrylic amide, sodium hydrogen sulfite, and ammonium peroxydisulfate in the presence of various contents of metakaolinite (MK) modified with potassium acetate (KAc). Both x-ray diffraction data and atomic force microscopy images of PAM/MK nanocomposites indicate that the MK was homogeneously dispersed on the nanoscale into the polymer matrix. Infrared and Raman spectroscopy indicated the formation of hydrogen-bonding interactions between PAM and MK and the distortion of the Si–O tetrahedron and Al–O polyhedron in the polymerization process. In addition, DSC results revealed that when the nanocomposites with MK modified with KAc were less than 10%, they have higher decomposition temperature and better thermal stability in comparison with the pure PAM.     

Nanodiamond/poly (lactic acid) nanocomposites: Effect of nanodiamond on structure and properties of poly (lactic acid)

Nanodiamond (ND)/poly (lactic acid) (PLA) nanocomposites with potential for biological and biomedical applications were prepared by using melting compound methods. By means of transmission electron microscopy (TEM), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Thermogravimetric analyses (TGA), Dynamic mechanical analyses (DMA), Differential scanning calorimetry (DSC) and Tensile test, the ND/PLA nanocomposites were investigated, and thus the effect of ND on the structural, thermal and mechanical properties of polymer matrix was demonstrated for the first time. Experimental results showed that the mechanical properties and thermal stability of PLA matrix were significantly improved, as ND was incorporated into the PLA matrix. For example, the storage modulus (E′) of 3 wt% ND/PLA nanocomposites was 0.7 GPa at 130 °C which was 75% higher than that of neat PLA, and the initial thermal decomposition was delayed 10.1 °C for 1 wt% ND/PLA nanocomposites compared with the neat PLA. These improvements could be ascribed to the outstanding physical properties of ND, homogeneous dispersion of ND nanoclusters, unique ND bridge morphology and good adhesion between PLA matrix and ND in the ND/PLA nanocomposites.     

Thermal properties of polyethylene/montmorillonite nanocomposites prepared by intercalative polymerization

A comparative study of thermal and thermal-oxidative degradation processes for polyethylene/organically modified montmorillonite (PE-MMT) nanocomposites, prepared by the ethylene intercalative polymerization in situ with or without subsequent addition of an antioxidant is reported. The results of TGA and time/temperature-dependent FTIR spectroscopy experiments have provided evidence for an accelerated formation and decomposition of hydroperoxides during the thermal oxidative degradation tests of PE-MMT nanocomposites in the range of 170–200 °C as compared to the unfilled PE, thus indicating to a catalytic action of MMT. It has been shown that effective formation of intermolecular chemical cross-links in the PE-MMT nanocomposite has ensued above 200 °C as the result of recombination reactions involving the radical products of hydroperoxides decomposition. Apparently, this process is induced by the oxygen deficiency in PE-MMT nanocomposite due to its lowered oxygen permeability. It is shown that the intermolecular cross-linking and dehydrogenation reactions followed by the shear carbonization lead to appreciable increase of thermal-oxidative stability of PE nanocomposite, as compared to that of pristine PE. Notably, the TGA traces for the antioxidant-stabilized PE-MMT nanocomposites recorded in air were quite similar to those obtainable for the non-stabilized PE-MMT nanocomposites in argon. The results of treatment of the experimentally acquired TGA data in frames of an advanced model kinetic analysis are reported and discussed.     

Novel lightweight sandwich-structured bio-fiber-reinforced poly(lactic acid) composites

Novel bio-based lightweight sandwich-structured composites with both skin and core materials made from biofiber and poly(lactic acid) (PLA) matrix were developed. The composites contained 48 wt% cellulose fiber and 52 wt% PLA matrix. The fabrication process was simple and required no adhesive for the skin–core bonding. The effects of fiber weight fraction and density on the core compressive properties were evaluated experimentally. Fifty percent of fibers gave the best results among the three fiber weight fractions studied and was used in preparing cores for subsequent fabrication of the sandwich-structured composites. The flexural properties and failure modes of the sandwich-structured composites were assessed. The flexural properties of the composites met the published deflection requirements for automotive load floor applications. Since these biocomposites were made using natural renewable materials that are fully biodegradable and recyclable, they show potential to be used as environmentally friendly alternatives to the existing products.     

Thermoelectric behaviour of melt processed carbon nanotube/graphite/poly(lactic acid) conductive biopolymer nanocomposites (CPC)

The aim of the study was to examine the possible use of conductive polymer composites (CPC) as thermoelectrical material for energy harvesting from temperature gradient. Their ease of processing, low cost and environmental impact compared to typical thermoelectric semiconductor materials were found to be strong advantages for large scale production. Our results show that eGR-CNT hybrid fillers are the most effective to enhance the CPC electrical conductivity up to σ = 4123 S.m^− 1, but that eGR is more effective to improve both thermal conductivity (λ_c = 5.5 W.m^− 1.K^− 1) and seebeck coefficient (S = 17 μV.K^− 1), whereas finally CNT give the best compromise to reach the highest ZT = 7 × 10^− 5 at room temperature. This finding is attributed to the ability of CNT network to allow electron circulation by tunnelling, when junctions are separated by an insulating polymer film (even of some nm thick), whereas phonon scattering at nanointerfaces will prevent their effective transmission through the CPC. Although the intrinsic individual physical properties obtained (σ, λ_c, S) with the different kinds of carbon filler were good, it was not possible to completely uncouple them to maximise ZT. We believe that this value of ZT, too low for commercial application, can be enhanced by increasing the confinement of conducting fillers with exclusion volumes and by decreasing the thermal conductivity of the matrix with voids.     

Biomass-based composites from poly(lactic acid) and wood flour by vapor-phase assisted surface polymerization

To prepare biomass-based composites in an environmentally benign manner, vapor-phase assisted surface polymerization (VASP) was applied to prepare the composites from wood flour and poly(l-lactic acid) (PLLA) without solvent. VASP of l,l-lactide successfully proceeded on the wood flour surfaces, resulting in surface coverage by newly generated PLLA. For obtained PLLA/wood flour composites, it was clarified that grafting of PLLA on wood flour surfaces had occurred to form covalently bonded composites, with the accumulated PLLA layers having crystallized in situ during VASP. Resulting PLLA layers showed very high crystallinity of 79.2% and a high melting point close to the equilibrium melting point. Moreover, thermal degradation behavior of the composites suggested a cooperative degradation manner of the components.     

Physico-chemical and mechanical properties of nanocomposites prepared using cellulose nanowhiskers and poly(lactic acid)

A range of nanocomposites were prepared using cellulose nanowhiskers (CNWs) and poly(lactic acid) (PLA) via a solvent casting process. Acid hydrolysis process was used to produce CNWs from bleached cotton. Structural morphology and surface topography of the CNWs and nanocomposites were examined using transmission (TEM) and scanning electron microscopy. TEM images revealed rod-like whiskers in the nano-scale region which were dispersed within the PLA matrix. The presence of the functional groups of CNWs and PLA were confirmed via FTIR analysis. Tensile tests were conducted on thin films and the nanocomposites containing 1 wt% CNWs showed a 34 and 31% increase in tensile strength and modulus, respectively, compared to pure PLA. The dynamic mechanical analysis showed that the tensile storage modulus also increased in the visco-elastic temperature region with increasing CNWs content in the nanocomposites. Thermogravimetric analysis showed that all the materials investigated were thermally stable from room temperature to 210 °C. A positive effect of CNWs on the crystal nucleation of PLA polymer in the nanocomposites was observed using differential scanning calorimetry and X-ray diffraction analysis. The degradation profiles of the nanocomposites in deionised water over 1 week revealed a mass loss of 1.5–5.6% at alternate temperatures (25, 37 and 50 °C) and at the same conditions the swelling ratio and water uptake were seen to increase with CNWs content in the nanocomposites, which was strongly influenced by the presence of crystalline CNWs.     

聚乳酸纤维的研究进展

聚乳酸是一种新型的生态环保型高分子材料.本文主要介绍了世界各国对聚乳酸纤维研究及生产的相关情况,对聚乳酸的生产工艺作了深入的探究,并介绍了聚乳酸的应用及发展前景.     

聚乳酸的聚合方法

本文探讨了聚乳酸的现有聚合方法 ,同时对聚乳酸的另一直接 -固相新聚合方法进行了研究 ,分析了聚乳酸固相聚合机理 ,通过实验验证了固相聚合方法的有效性     

Properties of poly(lactic acid)/montmorillonite/carbon nanotubes nanocomposites: determination of percolation threshold

Incorporation of rigid nanoparticles is the most effective means of improving polymer properties. Montmorillonite (MMT) and multi-walled carbon nanotubes (MWCNTs) are legendary in this field for their individual exceptional properties. A synergistic phenomenon is induced between these two particles when they are simultaneously incorporated into polymers. At a definite nanofillers concentration, called the percolation threshold, there is a sudden change in nanocomposite properties due to the formation of a 3D-structured network of the nanoparticles within the matrix. In this work, the properties of poly(lactic acid) (PLA) nanocomposites filled with different fractions of MMT/MWCNTs hybrid (0.5–2.0 wt%) were analyzed. In particular, the percolation threshold of the MMT/MWCNTs hybrid was uniquely identified by differential scanning calorimetry, thermogravimetric analysis and dynamic mechanical thermal analysis. The structural studies by X-ray diffraction and Fourier-transform infrared spectroscopy were also associated with the percolation threshold of MMT/MWCNTs in PLA. At 1.0 wt% MMT/MWCNTs concentration, the complete exfoliation of the particles was maintained, and the thermal characteristics such as glass transition, crystallization and melting temperatures reached their plateau at this hybrid concentration. Moreover, the thermal degradation and viscoelastic parameters showed their peak values at this critical point, which is correlated with the formation of the percolation threshold within the matrix. The morphological studies confirmed the homogeneous dispersion of MMT/MWCNTs in PLA up to a concentration of 1.0 wt%. At 2.0 wt% MMT/MWCNTs, few aggregations occurred in the PLA-based composite, confirming that the percolation threshold was formed at a lower concentration of MMT/MWCNTs nanoparticles.