生物可降解聚乳酸/层状硅酸盐纳米复合材料的研究进展

生物可降解聚乳酸是一种具有广泛应用前景的环境友好型的生物高分子材料,但是其力学性能、热稳定性能不稳定.利用层状硅酸盐的特殊结构,以各种有机改性的层状硅酸盐为添加物,通过原位插层聚合、溶液插层、熔融插层和剥离.吸附等方法制备生物可降解聚乳酸/层状硅酸盐纳米复合材料,其力学性能、热稳定性、生物降解性等均有显著提高,其展现出极其广阔的应用前景.本文概述了近年来生物可降解聚乳酸/层状硅酸盐纳米复合材料的制备、结构、性能和应用等方面的研究进展,并且对各种制备方法进行了分析比较.     

New polylactide-layered silicate nanocomposites. 2. Concurrent improvements of material properties, biodegradability and melt rheology

Our continuing research on the preparation, characterization, materials properties, and biodegradability of polylactide (PLA)-layered silicate nanocomposites has yielded results for PLA-montmorillonite nanocomposites. Montmorillonite modified with trimethyl octadecylammonium cation was used as an organically modified layered silicate for the nanocomposites preparation. The internal structure of the nanocomposites in the nanometer range has been established by using wide-angle X-ray diffraction and transmission electron microscope analyses. All the nanocomposites exhibited superior improvement of practical materials properties such as storage modulus, flexural modulus, flexural strength, heat distortion temperature, and gas barrier property as compared to that of neat PLA. The biodegradability of neat PLA and a representative nanocomposite was also studied under compost, and the rate of biodegradation of neat PLA significantly increased after nanocomposites preparation. The melt rheology of neat PLA and various PLACNs was also studied.     

Control of Biodegradability of Polylactide via Nanocomposite Technology

Polymer/layered silicate nanocomposite technology is not only suitable for the significant improvement of mechanical and various other materials properties of virgin polymers, it is also suitable to enhance the rate of biodegradation of biodegradable polymers such as polylactide. The biodegradability of polylactide in nanocomposites completely depends upon both the nature of pristine layered silicates and surfactants used for the modification of layered silicate, and we can control the biodegradability of polylactide via judicious choice of organically modified layered silicate.

Biodegradation of neat PLA and various PLA/OMLS nanocomposites recovered from compost with time.     

Fabrication and characterization of biodegradable poly(lactic acid)/layered silicate nanocomposites

In this study biocompatible/biodegradable poly(lactic acid) (PLA)/layered silicate nanocomposites (PLSNs) were successfully prepared by the intercalation of PLA polymer into organically modified layered silicate through the solution mixing process. Both X‐ray diffraction data and transmission electron microscopy images of PLSNs indicate most of the swellable silicate layers were disorderedly intercalated into the PLA matrix. Mechanical properties of the 0.1 wt% silicate‐containing fabricated nanocomposites performed by dynamic mechanical analysis have significant improvements in the storage modulus when compared to that of neat PLA matrix. Adding more layered silicates into PLA matrix induced a decrease in the mechanical properties of PLSNs, probably due to the presence of a large dimension of porosity in the fabricated nanocomposites. POLYM. ENG. SCI., 45:1615–1621, 2005. © 2005 Society of Plastics Engineers     

Influence of processing parameters on the structure of melt blended polyethylene/organoclay nanocomposites produced by a masterbatch route

Melt compounding is one of the most used methods to produce thermoplastic‐based nanocomposites. The aim of this study is the assessment of the effects of processing set‐up and conditions on the structure and properties of low‐density polyethylene/organically modifies layered silicate (OMLS) nanocomposites obtained by a two‐step process by concentrate masterbatch route. Concentrate masterbatch formulation and dilution have been investigated to correlate processing parameters with final nanocomposites structure by means of morphological and physical characterization. Even if a good dispersion/intercalation occurred regarding concentrate masterbatch, the probability of a further OMLS dispersion during the masterbatch dilution process depends remarkably on the extruder mixing capacity, with important consequences for the industrial application of masterbatch technology in net shape forming processes. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Effect of organoclay chemistry and morphology on properties of poly(lactic acid) nanocomposites

Poly(lactic acid) (PLA) nanocomposites with different layered organoclays (variation in the surface treatment of silicate) and one special nanofiller (mixed mineral thixotrope) were melt-compounded using a semi-industrial co-rotating twin-screw extruder. Effects of the silicate surface treatment and shape on the structure as well on processing and utility properties in PLA matrix were investigated. The structural changes in polymer matrix were evaluated from dynamic experiments in the shear flow using low-amplitude oscillatory measurements. Moreover, new approach for morphological investigation of nanocomposites using small-angle X-ray scattering was presented. Concerning utility properties, tests of mechanical and barrier properties were performed to compare enhancement of PLA matrix due to incorporation of different nanoparticles. Surprisingly, filling the PLA matrix with mixed mineral thixotrope resulted into very high material performance (in particular, significant improvement in barrier properties) compared to filling with commercial layered silicates. In this way, new type of nanofiller for PLA applications has been successfully tested.     

Cross‐linked and uncross‐linked biodegradable nanocomposites. I. Nonisothermal crystallization kinetics and gas permeability

Various nanocomposites of poly(butylene succinates) (PBS) with different ratios of organically modified layered silicates (OMLS) were prepared. Moreover, such PBS nanocomposites cross‐linked by dicumyl peroxide (DCP) were also prepared in this work. Effects of cross‐linking and OMLS on nonisothermal crystallization kinetics and the gas permeability of PBS samples were investigated further. WAXD indicates that the layers of clay were intercalated by the modifiers, and that the interlayer distance of OMLS in the nanocomposites could be expanded to about 2.96 nm. The results of DSC analysis revealed that the crystallization temperatures of nanocomposites shifted to the lower temperature with the increase of OMLS content. With the addition of OMLS, crystallinity was decreased, whereas the half‐life of crystallization was increased. On the other hand, even the cross‐linked effects also increased the half‐life of crystallization of the materials, but did not necessarily decrease crystallinity in all cases. Moreover, the PBS/OMLS nanocomposites showed a 23.87–46.64% decrease in permeability of oxygen when compared with the pristine PBS sample. Yet, the cross‐linked nanocomposites exhibited decrements of 6.38–39.53%. This indicates that the gas permeability of PBS was more effectively depressed by the addition of OMLS than by the cross‐linking reaction. The cross‐linked structure of polymer seemed not to be very effective in decreasing the gas permeability of PBS. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Recent advances in bionanocomposites: Preparation,properties, and applications

The authors report recent advances in the research and development of bionanocomposites based on four types of nanofillers, namely organically modified layered silicate (OMLS), cellulose nanofibers (CNs), carbon nanotubes (CNTs), and halloysite nanotubes (HNTs). These composite materials have received significant attention from academia and industries due to their unique advantages such as excellent biodegradability, availability, cost effectiveness, and eco-friendliness. The preparation and properties of bionanocomposites have been reviewed in detail together with their current and potential applications in the fields of electronics and sensors, tissue engineering, drug delivery, gene therapy, and cosmetics, as well as packaging.     

Enzymatic degradation kinetics of poly(butylene succinate) nanocomposites

In this work, poly(butylene succinates) (PBS)/organically modified layered silicates (OMLS) composites were prepared by solution blending. The degradability of PBS, PBS/layered silicates and PBS/OMLS nanocomposites have been investigated using enzymatic degradation method. Effects of layered silicates and OMLS contents on the degradation behavior of PBS were explored. The results reveal that the degradability of the composites was both enhanced by the addition of layered silicates or OMLS as compared to the pristine PBS sample. The calculated data based on the autocatalytic model show that the degradation kinetics of PBS/layered silicates composites is the chain scission process with the following autocatalytic reactions, which is very similar to that of pure PBS matrix. On the other hand, the surface-catalyzed reaction model may be more suitable to describe the degradation behavior of the PBS/OMLS nanocomposite. Moreover, the results show that rate-controlling step of the degradation reaction for PBS/OMLS nanocomposite is more probable to be the desorption step.     

层状硅酸盐黏土/硅橡胶纳米复合材料的研究进展

层状硅酸盐黏土因其独特的纳米层状结构在改性硅橡胶高分子材料性能上具有明显的理论优势,其资源丰富、成本低和绿色无污染等特点在实际应用中受到广泛关注.本文综述了近年来层状硅酸盐黏土包括2:1型结构如蒙脱石、凹凸棒石和1:1型结构如高岭石、埃洛石等在改性硅橡胶高分子材料机理和性能方面的国内外最新研究进展,指出目前研究的重点主...     

Using maleic anhydride grafted poly(lactic acid) as a compatibilizer in poly(lactic acid)/layered‐silicate nanocomposites

The goal of this work was to prepare exfoliated poly(lactic acid) (PLA)/layered‐silicate nanocomposites with maleic anhydride grafted poly(lactic acid) (PLA–MA) as a compatibilizer. Two different layered silicates were used in the study: bentonite and hectorite. The nanocomposites were prepared by the incorporation of each layered silicate (5 wt %) into PLA via solution casting. X‐ray diffraction of the prepared nanocomposites indicated exfoliation of the silicates. However, micrographs from transmission electron microscopy showed the presence of intercalated and partially exfoliated areas. Tensile testing showed improvements in both the tensile modulus and yield strength for all the prepared nanocomposites. The results from the dynamic mechanical thermal analysis showed an improvement in the storage modulus over the entire temperature range for both layered silicates together with a shift in the tan δ peak to higher temperatures. The effect of using PLA–MA differed between the two layered silicates because of a difference in the organic treatment. The bentonite layered silicate showed a more distinct improvement in exfoliation and an increase in the mechanical properties because of the addition of PLA–MA in comparison with the hectorite layered silicate. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1852–1862, 2006     

Mechanical and rheological properties of the maleated polypropylene–layered silicate nanocomposites with different morphology

Three types of maleated polypropylene–layered silicate nanocomposites with different dispersion states of layered silicate (deintercalated, intercalated, and exfoliated states) are prepared from two kinds of polypropylenes with different molecular weights, organically modified layered silicate and pristine montmorillonite to investigate the effect of the final morphology of the nanocomposite on the rheological and mechanical properties. Maleated polypropylene with high molecular weight intercalates slowly and the other with low molecular weight exfoliates fast into the organophilic layered silicates. Rheological properties such as oscillatory storage modulus, nonterminal behavior, and relative viscosity has close relationship with the dispersion state of layered silicates. The exfoliated nanocomposite shows the largest increase and the deintercalated nanocomposite shows almost no change in relative shear and complex viscosities with the clay content. The exfoliated nanocomposite shows the largest drop in complex viscosity due to shear alignment of clay layers in the shear flow. In addition, the final dispersion state of layered silicates intimately relates to the mechanical property. The dynamic storage moduli of nanocomposites show the same behavior as the relative shear and complex viscosities. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1526–1535, 2003     

Effect of modified clay on the morphology and electric properties of PC/ABS‐MWCNT composites

Composites of MWCNTs and an organically modified partially synthetic layered silicate (OMLS) with PC/ABS were prepared by melt blending and the relationship between morphology and electric properties as a function of composite composition examined. The concept of double percolation was investigated and confirmed, as a consequence of CNT preferential segregation within one polymer phase (PC). A role of OMLS in hindering the formation of an effective electrically conductive network was observed above a certain clay loading, resulting in a shifting of electrical percolation threshold towards higher values. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Poly(butylene sucinate-co-adipate)/montmorillonite nanocomposites: effect of organic modifier miscibility on structure, properties, and viscoelasticity

Poly(butylene succinate-co-adipate) (PBSA)/layered silicate nanocomposites were prepared by melt extrusion of PBSA and three different types of commercially available organically modified montmorillonite (OMMT). Using three types of OMMT modified with three different kinds of surfactants, the effect of organic modification on nanocomposites was investigated by focusing of three major aspects: morphological study, property measurements, and melt rheological behavior under both small and large deformation flows. X-ray diffraction (XRD) patterns revealed that increasing the level of interactions (miscibility) between the organic modifier and PBSA matrix increases the tendency of the silicate layers to delaminate and distributed nicely within the PBSA matrix. Transmission electron micrographic (TEM) observations showed that the ordering of silicate layers in PBSA matrix is well matched with the XRD patterns. Thermal analysis revealed that extent of crystallinity of PBSA matrix is directly related to the extent of exfoliation of silicate layers in the nanocomposites. Dynamic mechanical analysis and tensile property measurements showed concurrent improvement in mechanical properties when compared to the neat PBSA and the extent of improvement is directly related to the extent of delamination of silicate layers in the PBSA matrix. The same tendency was also observed in melt rheological measurements.     

Study of the biodegradable poly(ε‐caprolactone)/clay nanocomposite foams

In this article, biodegradable poly(ε‐caprolactone)/layered silicate nanocomposites were prepared and characterized. The dispersion state of modified clay in PCL matrix and its effect on thermal, rheological and mechanical properties of PCL were studied. The PCL/clay nanocomposites were then foamed using chemical foaming method. Cellular parameters such as mean cell size, cell wall thickness and cell densities of nanocomposite foams with different clay loading were collected. Effect of layered silicate on the structure and mechanical properties of PCL foams were evaluated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

聚合物/层状硅酸盐纳米复合材料

目前,聚合物／层状硅酸盐纳米复合材料是重要的工程材料之一。由于层状硅酸盐的特殊结构,聚合物层状硅酸盐纳米复合材料的各项性能得到较大改善。聚合物／层状硅酸盐纳米材料的制备、表征、结构与性能的研究取得了重要进展。本文简要概述了聚合物／层状硅酸盐的结构及其有机改性机理,研究表明,插层剂和离子交换容量是插层的重要因素。最后,讨论了聚合物／层状硅酸盐纳米复合材料的制备方法和性能。     

Polymer layered silicate nanocomposites

Polymers filled with low amounts of layered silicate dispersed at nanoscale level are most promising materials characterized by a combination of chemical, physical and mechanical properties that cannot be obtained with macro‐ or microscopic dispersions of inorganic fillers. Polymer layered silicate nanocomposites can be obtained by insertion of polymer molecules in the galleries between the layers of phyllosilicate. Here, hydrated alkaline or alkaline earth metal cations are hosted which neutralize the negative charge resulting from isomorphous substitutions of Mg or Al cations within the silicate. Insertion of polymer molecules to prepare “intercalation hybrids” can be carried out by replacing the water hydration molecules in the galleries by polymers containing polar functional groups, using the so called ion‐dipole method. A more general technique involves compatibilization of the silicate by intercalation of an organic molecule, typically an organic alkylammonium salt, that replaces the cations in the interlayer galleries to form an organically modified layered silicate (OLS). The aliphatic chain of the OLS favors the intercalation of any type of polymer. Intercalated or delaminated polymer‐silicate hybrids are obtained depending on whether the stack organization of the silicate layers is preserved or is lost, with single sheets being distributed in the polymer matrix. The methods currently used for preparing polymer layered silicate (PLS) nanocomposites are: in situ polymerization, from polymer solution, or from polymer melt. Although PLS nanocomposites have been known for a long time, it is the possibility of preparing them by melt intercalation of OLS in processing that is boosting the present interest in these materials and their properties. So far PLS nanocomposites have been characterized by X‐ray diffractometry, transmission electron microscopy, differential scanning calorimetry, and NMR. Published results on PLS nanocomposites are reviewed concerning their characterization and properties with particular reference to fire retardant behavior.     

Combinatorial methods for polymer materials science: Phase behavior of nanocomposite blend films

Polymer materials are often mixed with inorganic materials in the bulk to enhance properties, including mechanical, electrical, thermal, and physical. Such property enhancements are induced not only by the physical presence of the filler but also significantly by the interaction of the polymer with the filler via altering the local properties of the polymer material. In this regard, recently layered silicate nanocomposites have been shown to be effective in modifying the polymer properties because of their high surface area of contact between the polymer and the high aspect ratio nanoparticle. Potential property enhancements should also occur in polymer nanocomposite thin films owing to nanoparticle orientation from film confinement effects. In this paper we investigate the effect of layered silicate nanoparticles on the phase behavior of a classic polymer blend using small angle neutron scattering and compare those results to phase diagrams obtained by high throughput combinatorial methods.     

New Polylactide/Layered Silicate Nanocomposites, 6

The measurement of rheological properties of any polymeric material under molten state is crucial to gain fundamental understanding of the processability of that material. In the case of polymer/layered silicate nanocomposites, the measurements of rheological properties are not only important to understand the knowledge of the processability of these materials, but is also helpful to find out the strength of polymer‐layered silicate interactions and the structure‐property relationship in nanocomposites. This is because rheological behaviors are strongly influenced by their nanoscale structure and interfacial characteristics. In order to get this knowledge in the case of polylactide/montmorillonite nanocomposites, we have studied melt rheological properties of these materials in detail. On the basis of rheological data, we have conducted foam processing of pure polylactide and one representative nanocomposite by a newly developed pressure cell technique using carbon dioxide as a physical‐blowing agent.

The time variation of the elongational viscosity of one of the intercalated polylactide/montmorillonite nanocomposites.     

Morphology and rheological behavior of polylactic acid/clay nanocomposites

The investigated rheological properties of polylactic acid (PLA)/clay nanocomposite are important to understand the effect of organically modified layered silicates (OMLS) (clay) on processing as well as the change in viscoelastic properties due to polymer filler interaction. The time sweep result revealed that the thermal stability improved with addition of nanoclay due to the formation of percolating network structure. It was also supported by multi wave ramp test. The frequency sweep analysis showed that the dynamic moduli increased with addition of nanoclay. Viscoelastic spectra (DMTA) showed an increase of the storage and loss moduli with the increase in the clay content. Wide angle X‐ray diffraction (WAXD) and transmission electron microscopy (TEM) were used to determine the degree of intercalation, or exfoliation and nanostructure level of clay dispersion on PLA nanocomposites. XRD data demonstrated complete exfoliation at lower nanoclay content. On increasing the nanoclay content, exfoliated and partially intercalated structures were obtained. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers