可生物降解性聚合物-层状硅酸盐纳米复合材料的研究进展

可生物降解性聚合物一层状硅酸盐纳米复合材料比聚合物基体有更好的力学强度、热稳定性、热变形温度、气体阻隔特性和更快的降解速率，表现出剪切变稀、模量升高、似固体行为等流变特性。文中综述了可生物降解性聚合物纳米复合材料的制备方法、表征手段、性能测试及其应用等方面的研究进展。     

Ductile PLA nanocomposites with improved thermal stability

Polylactide (PLA) is used as a biomedical material because it is biodegradable, but the vast majority of biodegradable polymers in clinical use are composed of rather stiff materials that are unsuitable for use in numerous applications because they exhibit limited extendibility, weak mechanical strength, and poor thermal stability. We modified PLA with 2-methacryloyloxyethyl isocyanate (MOI) to prepare ductile PLA materials. By utilizing a novel sol–gel process, PLA nanocomposites were further prepared with improved mechanical properties and thermal stability. The 10% thermal decomposition temperature for PLA modified with 5% MOI and 5–10% silica was 21–32 °C higher than that of original pristine PLA. Elongation at break increased by 4–13 times when compared to neat PLA while the tensile strength was maintained at 30–40 MPa. These synthesized PLA nanocomposites can be applied as biomaterials with improved mechanical and thermal properties.     

Novel toughened polylactic acid nanocomposite: Mechanical,thermal and morphological properties

The objective of the study is to develop a novel toughened polylactic acid (PLA) nanocomposite. The effects of linear low density polyethylene (LLDPE) and organophilic modified montmorillonite (MMT) on mechanical, thermal and morphological properties of PLA were investigated. LLDPE toughened PLA nanocomposites consisting of PLA/LLDPE blends, of composition 100/0 and 90/10 with MMT content of 2 phr and 4 phr were prepared. The Young’s and flexural modulus improved with increasing content of MMT indicating that MMT is effective in increasing stiffness of LLDPE toughened PLA nanocomposite even at low content. LLDPE improved the impact strength of PLA nanocomposites with a sacrifice of tensile and flexural strength. The tensile and flexural strength also decreased with increasing content of MMT in PLA/LLDPE nanocomposites. The impact strength and elongation at break of LLDPE toughened PLA nanocomposites also declined steadily with increasing loadings of MMT. The crystallization temperature and glass transition temperature dropped gradually while the thermal stability of PLA improved with addition of MMT in PLA/LLDPE nanocomposites. The storage modulus of PLA/LLDPE nanocomposites below glass transition temperature increased with increasing content of MMT. X-ray diffraction and transmission electron microscope studies revealed that an intercalated LLDPE toughened PLA nanocomposite was successfully prepared at 2 phr MMT content.     

PLA/I.34TCN纳米复合材料的制备及其性能研究

将改性纳米黏土I.34TCN与聚乳酸(PLA)经过二次熔融混合制备了PLA/I.34TCN纳米复合材料。TEM表征结果显示,较高的黏土剥离程度提高了黏土在PLA中的分散性,使两相之间的界面作用力增强,同时可以使两相之间具有较大的界面增塑区;DSC表征结果显示,剥离型纳米黏土对纳米复合材料起到了结晶成核剂的作用,提高了纳米复合材料的结晶度。上述两方面的原因综合改善了纳米复合材料的力学性能,当黏土质量分数为2%时,PLA/I.34TCN纳米复合材料中黏土的剥离程度最高,使得该纳米复合材料的断裂伸长率显著提高,最多可提高101.00%,是纯PLA的18倍。TG表征结果发现,纳米复合材料的热稳定性能随I.34TCN含量的增加而逐渐增加。     

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。     

Polylactide based nanostructured biomaterials and their applications

Polylactide (PLA) is one of the most innovative materials being actively investigated for a wide range of industrial applications. The polymer is a linear aliphatic thermoplastic polyester which is biodegradable as well as biocompatible, which makes it highly versatile and attractive to various commodities and medical applications. A large variety of nanoparticles of different nature and size can be blended with PLA, therefore, generating a new class of nanostructured biomaterials or nanocomposites with interesting physical properties and applications. PLA based nanostructured biomaterials are the focus of this review article, throwing light on their preparation techniques, physical properties, and industrial applications. Structural characteristics and morphological features of PLA based nanocomposites have been explained on the basis of X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Depending upon the nature and characteristics of the nanoparticles, the ultimate properties of the resulting nanocomposite materials can be tailored. Biocompatible materials such as carbon nanotubes, cellulose nanowhiskers, hydroxyapitite, etc. could be incorporated into the PLA matrix, which increase the potential of PLA for biomedical applications. Applications of PLA based nanostructured materials in different areas have been summarized.     

Isothermal crystallization behavior and mechanical properties of polylactide/carbon nanotube nanocomposites

Carbon nanotube (CNT)–reinforced polylactide (PLA) nanocomposites were prepared using a melt compounding process employing a twin-screw extruder. The isothermal crystallization kinetics of PLA/CNT nanocomposites according to Avrami’s theory were analyzed using differential scanning calorimetry in the temperature range 90–120 °C. There was a significant dependence of CNT on the crystallization behavior of the PLA matrix. The incorporation of CNT improved effectively the crystallization rate of PLA/CNT nanocomposites through heterogeneous nucleation. The nucleating effect of CNTs which increased the number of nucleation sites and decreased the average spherulite size was confirmed using polarized optical microscopy. The rheological properties of the PLA/CNT nanocomposites were also investigated. Changes in the microstructure of the PLA/CNT nanocomposites occurred by incorporating CNT. Furthermore, the tensile strength/modulus and thermal stability of PLA/CNT nanocomposites were enhanced when a very small quantity of CNT was added. This research accounts for the effect of CNTs, which significantly influenced the isothermal behavior, thermal stability, mechanical, and rheological properties of the PLA/CNT nanocomposites, providing a design guide for PLA/CNT nanocomposites in industrial fields.     

PLA、PGA及其共聚物在包装领域应用研究进展

目的 综述聚乳酸(PLA)、聚乙交酯(PGA)、聚乙丙交酯(PLGA)及其改性材料在包装领域的研究进展,对改性材料及制备工艺进行展望,为PLA、PGA以及PLGA的改性与制备提供参考。方法 简介PLA、PGA以及PLGA的制备方法、基本性能,并总结近几年改性材料的种类及其制备工艺。结果 对PLA、PGA以及PLGA进行改性,再通过溶液铸膜、吹塑制膜等工艺制备薄膜,制备的薄膜具有优异的抗紫外性能、阻隔性能以及抗菌性能。结论 PLA、PGA以及PLGA具有优异的生物降解性能,通过改性后制备的薄膜性能更加均衡,在包装领域具有极大的应用前景,对聚合物的改性方法还需进行深入研究,制备出性能更加优异的改性材料。     

Dispersion characteristics and properties of poly(methyl methacrylate)/multi-walled carbon nanotubes nanocomposites

The preparation, characterization, and properties of poly(methyl methacrylate) (PMMA)/multi-walled carbon nanotubes (MWCNTs) nanocomposites are described. Nanocomposites have been prepared by melt-blending in a batch mixer. Both unmodified and surface modified MWCNTs have been used for the nanocomposites preparation. Using both unmodified and modified MWCNTs, the effect of surface modification in nanocomposites is investigated by focusing on three major aspects: dispersion characteristics, mechanical properties, and electrical conductivity measurements. Dispersion of the MWCNTs in the PMMA matrix is examined by scanning and transmission electron microscopy that revealed a homogeneous distribution-dispersion of MWCNTs in the PMMA matrix for both unmodified and modified MWCNTs. Thermomechanical behavior is studied by dynamic mechanical analyzer and results showed a substantial improvement in the mechanical properties of PMMA in conjunction to an increase in the elastic behavior. The tensile properties of neat PMMA moderately improved after nanocomposites preparation with both modified and unmodified MWCNTs, however, electrical conductivity of neat PMMA significantly improved after nanocomposites preparation with 2 wt% unmodified MWCNTs. For example, the through plane conductivity increased from 3.6 x 10(-12) S x cm(-1) for neat PMMA to 3.6 x 10(-9) S x cm(-1) for nanocomposite. The various property measurements have been conducted and results have shown that, in overall, surface modifications have very little or no effect on final properties of neat PMMA.     

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.     

The relationship between microstructure and mechanical properties of carbon nanotubes/polylactic acid nanocomposites prepared by twin-screw extrusion

Twin-screw extrusion was applied to prepare the carbon nanotubes/polylactic acid (CNT/PLA) nanocomposites. Five different extruded plates were produced under variation of CNT concentrations. The internal microstructures were also observed by optical microscope to examine the distribution and dispersion of CNT in the PLA. Besides, the crystallinity of the CNT/PLA nanocomposites was investigated by differential scanning calorimetry (DSC) and density method. The effects of the CNT concentrations on the mechanical and electrical properties of the nanocomposites were investigated. Scanning electron microscope (SEM) was performed to observe the CNT dispersion in the nano-scale. These results suggested that the crystallinity was increased with the increase of CNT concentrations, demonstrating that CNT played a role as a nucleating agent in PLA. Moreover, the mechanical and electrical properties of PLA have been improved by a proper incorporation of CNTs due to a good distribution and dispersion of the CNTs.     

Enhanced ductility and tensile properties of hybrid montmorillonite/cellulose nanowhiskers reinforced polylactic acid nanocomposites

Montmorillonite (MMT)/cellulose nanowhiskers (CNW) reinforced polylactic acid (PLA) hybrid nanocomposites were prepared by solution casting. CNW were isolated from microcrystalline cellulose using a chemical swelling method. An initial study showed that the optimum MMT content, for mechanical properties, in a PLA/MMT nanocomposite is five parts per hundred parts of polymer (phr). Various amounts of CNW were added to the optimum formulation of PLA/MMT to produce PLA/MMT/CNW hybrid nanocomposites. FT-IR analysis indicated the formation of some polar interactions, resulting in enhanced tensile properties of the hybrid nanocomposites. The highest tensile strength for the hybrid nanocomposites was obtained for a 1 phr CNW content. Young’s modulus was also found to increase with an increasing CNW content. Interestingly, the strain to failure (or ductility) of the hybrid nanocomposites increased significantly from ~10 to ~90 % with the addition of 1 phr CNW. This increase in ductility was proposed to be due to the nucleation of crazes and the formation of shear bands in the PLA.     

Preparation,structure and thermal properties of polylactide/sepiolite nanocomposites with and without organic modifiers

Polylactide-based nanocomposites containing unmodified and organic modified sepiolite were prepared through a solution casting method. The structure and properties of materials were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). From the results it can be concluded that the bundles of sepiolite have been dispersed into small aggregates containing several nanorods without destroying the crystal structure. Sepiolite nanofibers were well dispersed in the PLA matrix, exhibiting a randomly orientation with the contact among them in all cases. But the thermal stability of nanocomposites has been improved more by introducing unmodified sepiolite than that with organic modified sepiolite, which has also been confirmed by molecular dynamics simulation results that hydrophobic parts of organic modifiers could prevent the interaction between PLA molecules and sepiolite surface.     

Processing and characterization of solid and microcellular poly(lactic acid)/polyhydroxybutyrate-valerate (PLA/PHBV) blends and PLA/PHBV/Clay nanocomposites

The morphology, microstructure, tensile properties, and dynamic mechanical properties of solid and microcellular poly(lactic acid) (PLA)/polyhydroxybutyrate-valerate (PHBV) blends, as well as PLA/PHBV/clay nanocomposites, together with the thermal and rheological properties of solid PLA/PHBV blends and PLA/PHBV/clay nanocomposites, were investigated. Conventional and microcellular injection-molding processes were used to produce solid and microcellular specimens in the form of ASTM tensile test bars. Nitrogen in the supercritical state was used as the physical blowing agent in the microcellular injection molding experiments. In terms of rheology, the PLA/PHBV blends exhibited a Newtonian fluid behavior, and their nanocomposite counterparts showed a strong shear-thinning behavior, over the full frequency range. An obvious pseudo-solid-like behavior over a wide range of frequencies in the PLA/PHBV/clay nanocomposites suggested a strong interaction between the PLA/PHBV blend and the nanoclay that restricted the relaxation of the polymer chains. PLA/PHBV/clay nanocomposites possess a higher modulus and greater melt strength than PLA/PHBV blends. The addition of nanoclay also decreased the average cell size and increased the cell density of microcellular PLA/PHBV specimens. As a crystalline nucleating agent, nanoclay significantly improved the crystallinity of PHBV in the blend, thus leading to a relatively high modulus for both solid and microcellular specimens. However, the addition of nanoclay had less of an effect on the tensile strength and strain-at-break.     

Effects of grafted chain length on mechanical and electrical properties of nanocomposites containing polylactide-grafted carbon nanotubes

We herein report the effects of interfacial reinforcement on mechanical and electrical properties of nanocomposites based on polylactide (PLA) and multi-walled carbon nanotube (MWCNT). For this purpose, a series of MWCNTs grafted with PLA chains of various lengths (MWCNT-g-PLAs) were prepared by ring-opening polymerization of l-lactide with carboxylic acid-functionalized MWCNT (MWCNT-COOH). MWCNT-g-PLAs were then mixed with commercial PLA to obtain PLA/MWCNT-g-PLA nanocomposites with 1.0 wt.% MWCNT content. It was revealed that morphological, mechanical, and electrical properties of PLA/MWCNT-g-PLA nanocomposites were strongly dependent on the PLA chain length of MWCNT-g-PLAs. FE-SEM images exhibited that the nanocomposites containing MWCNT-g-PLA with longer PLA chain length exhibited better dispersion of MWCNTs in the PLA matrix. Initial moduli and tensile strengths of PLA/MWCNT-g-PLA composites increased with the increment of chain length of PLA grafted on MWCNTs, which attributes to the improved interfacial adhesion between the grafted PLA chains of MWCNT-g-PLA and the PLA matrix. As a result, the experimental initial modulus (2775 ± 193 MPa) of the nanocomposite including MWCNT-g-PLA with PLA chains of average molecular weight of 530 g/mol was quite close to the theoretical value (2911 MPa) predicted for the nanocomposite with perfect interfacial adhesion. Unexpectedly, electrical resistivities of PLA/MWCNT-g-PLA nanocomposites were found to increase from ∼10⁴ to ∼10¹² Ω/sq with increasing the PLA chain length of MWCNT-g-PLA, which is due to the fact that the PLA chains grafted on MWCNTs prevent the formation of the electrical conduction path of MWCNTs in the PLA matrix.     

Poly(lactic acid)/graphene nanocomposites prepared via solution blending using chloroform as a mutual solvent

Poly(lactic acid) (PLA)/graphene nanocomposites were prepared by direct solution blending of PLA with graphene using chloroform as a mutual solvent. Graphene was prepared by a solution-phase processing followed by thermal reduction, which can be dispersed stably in chloroform for more than one month. Transmission electron microscopy (TEM) was used to examine the quality of the dispersion of graphene in the PLA matrix. The thermal properties and crystallization behavior of the nanocomposites were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and polar optical microscopy (POM). The results showed that the thermal stability of PLA was significantly improved with a very low loading of graphene and the addition of graphene had a great effect on spherulite morphology of PLA.     

Influence of graphene nanoplatelet incorporation and dispersion state on thermal,mechanical and electrical properties of biodegradable matrices

Graphene nanoplatelets (GNPs) were used as multifunctional nanofiller to enhance thermal and mechanical properties as well as electrical conductivity of two different biodegradable thermoplastics: poly lactide (PLA) and poly (butylene adipate-co-terephthalate) (PBAT). Morphological investigations showed different levels of GNP dispersion in the two matrices, and consequently physical properties of the two systems exhibited dissimilar behaviours with GNP incorporation. Crystallinity of PLA, determined from differential scanning calorimetry, was observed to increase markedly with addition of GNPs in contrast to the decrease in crystallinity of PBAT. Isothermal and non-isothermal thermogravimetric analyses also revealed a more significant delay in thermal decomposition of PLA upon addition of GNPs compared to that of PBAT. Furthermore, results showed that increasing GNP content of PLA and PBAT nanocomposites influenced their Young’s modulus and electrical conductivity in different ways. Modulus of PBAT increased continuously with increasing GNP loading while that of PLA reached a maximum at 9 wt% GNPs and then decreased. Moreover, despite the higher conductivity of pure PBAT compared to pure PLA, conductivity of PLA/GNP nanocomposites overtook that of PBAT/GNP nanocomposites above a certain GNP concentration. This demonstrated the determining effect of nanoplatelets dispersion state on the matrices properties.     

Plasticized polylactic acid nanocomposite films with cellulose and chitin nanocrystals prepared using extrusion and compression molding with two cooling rates: Effects on mechanical,thermal and optical properties

Triacetate citrate plasticized poly lactic acid and its nanocomposites based on cellulose nanocrystals (CNC) and chitin nanocrystals (ChNC) were prepared using a twin-screw extruder. The materials were compression molded to films using two different cooling rates. The cooling rates and the addition of nanocrystals (1 wt%) had an impact on the crystallinity as well as the optical, thermal and mechanical properties of the films. The fast cooling resulted in more amorphous materials, increased transparency and elongation to break, (approx. 300%) when compared with slow cooling. Chitin nanocomposites were more transparent than cellulose nanocomposites; however, microscopy study showed presence of agglomerations in both materials. The mechanical properties of the plasticized PLA were improved with the addition of a small amount of nanocrystals resulting in PLA nanocomposites, which will be further evaluated for film blowing and thus packaging applications.     

Nanocomposites of PLA and PCL based on montmorillonite and sepiolite

PLA and PCL nanocomposites prepared by adding two organically modified montmorillonites and one sepiolite were obtained by melt blending. Materials were characterized by Wide Angle X-ray analysis (WAXS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA) and Dynamic-Mechanical Thermal Analysis (DMTA).All clays showed a good dispersion level with both polymeric matrices, whilst the highest thermo-mechanical improvements were reached depending on type of clay. These improvements were considerably higher in the case of PLA based nanocomposites probably because of a higher polymer/filler compatibility.     

聚乳酸/石墨/多壁碳纳米管复合材料的制备及性能

通过共溶剂法制备了由石墨(GN)和多壁碳纳米管(MWCNTs)掺杂的聚乳酸(PLA)纳米复合材料,借助扫描电镜等手段,研究了MWCNTs用量对复合材料微观结构、热稳定性、导热和导热性能及介电性能的影响。结果显示,MWC-NTs和GN在PLA基体中形成了稳定的导电和导热网络结构,从而导致复合材料具有较低的导电和导热逾渗阈值,其值约为MWCNTs/GN=0.5/1。MWCNTs和GN均匀分散和协同增强效应促使复合材料热稳定性、导热和导电性能明显提高。与纯PLA相比,填料在逾渗阈值附近的复合材料的初始分解温度提高了近16℃,导热系数提高了1倍,体积电阻降低了109数量级。