Multifunctional properties of 3D printed poly(lactic acid)/graphene nanocomposites by fused deposition modeling

In this work, three-dimensional (3D) printing system based on fused deposition modeling (FDM) is used for the fabrication of conductive polymer nanocomposites. This technology consists in the additive multilayer deposition of polymeric nanocomposite based on poly(lactic acid) (PLA) and graphene by means of a in house made low-cost commercial bench-top 3D printer. Further, 3D printed PLA/graphene nanocomposites containing 10 wt% graphene in PLA matrix were characterized for their mechanical, electrical and electromagnetic induction shielding properties of the nanocomposite. Furthermore X-ray computed micro-tomography analyses showed that printed samples have good dimensional accuracy and are significantly closer to the predefined design and the results of scanning electron microscopy (SEM) printed samples showed a uniform dispersion of graphene in PLA matrix The proposed material has uniquely advantageous when implemented in 3D printed structures, because incorporation of multifunctional graphene has been shown to substantially improve the properties of the resulting nanocomposite.     

Melt‐blending of unmodified and modified cellulose nanocrystals with reduced graphene oxide into PLA matrix for biomedical application

In this article, we successfully fabricated the bionanocomposites using cellulose nanocrystals (CNCs) and reduced graphene oxide (rGO) reinforced into biodegradable polylactic acid (PLA) matrix through melt‐mixing method. Due to the affinity difference between hydrophilic CNC and hydrophobic PLA, the surface modification of CNC was employed using quaternary ammonium salts (CTAB) as a surfactant. The nanocomposites were developed using different blend ratios of CNC/modified CNC (1, 2, and 3) wt% and (0.5 wt%) rGO into the polymer matrix. The morphology of CNC, q‐CNC (modified CNC), and nanocomposites were inspected by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). It is demonstrated from tensile tests that, the nanocomposite with 1 wt% CNC and rGO showed maximum tensile strength compared with PLA and its nanocomposites. Moreover, the nanocomposite with 1 wt% CNC and rGO was also having maximum thermal stability. From cytotoxicity evaluation, it is observed that all the nanocomposites are nontoxic and cytocompatible to HEK293 cells. In addition to this, the nanocomposite with q‐CNC showed enhanced barrier properties compared with PLA and PLA/CNC/rGO nanocomposite. The results obtained from different characterizations showed that the incorporation of surfactant onto CNC improved the dispersion in PLA but at the same time deteriorated the PLA matrix.     

Preparation and characterization of poly(propylene carbonate)/montmorillonite nanocomposites by solution intercalation

Poly(propylene carbonate) (PPC) is a new biodegradable aliphatic polycarbonate. However, the poor thermal stability and low glass transition temperatures (T_g) have limited its applications. To improve the thermal properties of PPC, organophilic montmorillonite (OMMT) was mixed with PPC by a solution intercalation method to produce nanocomposites. An intercalated-and-flocculated structure of PPC/OMMT nanocomposites was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal and mechanical properties of PPC/OMMT nanocomposites were investigated by thermal gravimetric analysis (TGA), differential scanning calorimetric (DSC), and electronic tensile tester. Due to the nanometer-sized dispersion of layered silicate in polymer matrix, PPC/OMMT nanocomposites exhibit improved thermal and mechanical properties than pure PPC. When the OMMT content is 4 wt%, the PPC/OMMT nanocomposite shows the best thermal and mechanical properties. These results indicate that nanocomposition is an efficient and convenient method to improve the properties of PPC.     

Preparation of PLA-based nanocomposites modified by nano-attapulgite with good toughness-strength balance

Polylactic acid (PLA) was modified by poly (butylene adipate-co-terephthalate) (PBAT) and nano-attapulgite (AT) using the melt blending technique. Ethylene-butyl acrylate-glycidyl methacrylate (E-BA-GMA) was used as a compatibilizer which can bond the AT nanoparticles with PLA/PBAT matrix by interaction between the epoxy and hydroxyl groups. The effects of the AT content on the mechanical properties, thermal properties, crystallinity and morphology of PLA/PBAT/ATT nanocomposites were investigated. The results showed that the tensile strength, elongation at break and impact strength of PLA/PBAT could be simultaneously increased by incorporating AT nanoparticles. PLA/PBAT/AT nanocomposites possessed higher thermal stability than pure PLA/PBAT. In the ternary composite system of PLA/PBAT/AT, AT acted as a heterogeneous nucleating agent and was able to increase the crystallization temperature. When the AT content was low (≤2.5 wt%), AT nanoparticles could uniformly disperse in the PLA/PBAT matrix. In general, AT was an effective filler to reinforce and toughen PLA/PBAT blend simultaneously, and the PLA/PBAT/AT nanocomposite with 2.5 wt% AT exhibited a good combination of strength and toughness.     

聚乳酸/氧化锌柱撑皂石纳米复合材料制备与性能及结构表征

通过微波水解法制备了ZnO柱撑皂石,并以其为加工助剂制备了聚乳酸(PLA)/ZnO柱撑皂石纳米复合材料.通过X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、对ZnO柱撑皂石及PLA/ZnO柱撑皂石纳米复合材料的结构进行了表征,并对其力学性能和热稳定性能进行了测试.微观结构分析表明,ZnO柱撑皂石呈现剥离状,并均匀分散在PLA基质中.力学性能研究表明0.3%ZnO柱撑皂石的加入有助于改善PLA复合材料的断裂伸长率.SEM分析表明PLA复合材料的断面发生明显改变,表现良好韧性;DSC结果显示纳米ZnO柱撑皂石可以降低复合材料的玻璃化转变温度、结晶温度,有助于提高PLA复合材料的结晶度,与XRD分析相吻合;热重分析表明ZnO柱撑皂石可以提高PLA复合材料的热稳定性.测试结果表明,ZnO柱撑皂石在PLA基质中起到了异相成核的作用,促进了PLA基质的结晶.     

Influence of chemical surface modification of cellulose nanowhiskers on thermal,mechanical, and barrier properties of poly(lactide) based bionanocomposites

In the aim of producing fully organic bionanocomposite based on poly(lactide) (PLA), cellulose nanowhiskers (CNW) were grafted by n-octadecyl-isocyanate (CNW-ICN) applying an in situ surface grafting method. The compatibilizing effect of the long aliphatic grafted chain was investigated by thermal, mechanical and permeability analysis of solvent cast nanocomposite films. The grafted CNW-ICN could be successfully dispersed in the polymer matrix. The gained compatibility brought about a nucleating effect, decreasing the half time of isothermal crystallization from 25 min for the neat PLA to 8.4 min for the nanocomposite including 2.5 wt% CNW-ICN, e.g., tensile strength was improved by 10 MPa for the same 2.5 wt% CNW-ICN/PLA composite. Mechanical reinforcement was also effective in the rubbery state of PLA and increased the tensile modulus of the rubbery plateau providing thereby thermal resistance to the polymer. Oxygen barrier properties did not change significantly upon the inclusion of CNW-ICN, even when the quantity of CNW-ICN was increased to 15 wt%. More interestingly, the water vapour permeability of the CNW-ICN nanocomposite was always lower than the one of ungrafted CNW composites, which led to the conclusion that the hydrophobic surface graft and improved compatibility could counteract the effect of inclusion of hydrophilic structures in the matrix on water vapour transport. In conclusion, the surface grafting of CNW with isocyanates might be an easy and versatile tool for designing fully organic bionanocomposites with tailored properties.     

Impact of in situ polymer coating on particle dispersion into solid laser-generated nanocomposites

The crucial step in the production of solid nanocomposites is the uniform embedding of nanoparticles into the polymer matrix, since the colloidal properties or specific physical properties are very sensitive to particle dispersion within the nanocomposite. Therefore, we studied a laser-based generation method of a nanocomposite which enables us to control the agglomeration of nanoparticles and to increase the single particle dispersion within polyurethane. For this purpose, we ablated targets of silver and copper inside a polymer-doped solution of tetrahydrofuran by a picosecond laser (using a pulse energy of 125 μJ at 33.3 kHz repetition rate) and hardened the resulting colloids into solid polymers. Electron microscopy of these nanocomposites revealed that primary particle size, agglomerate size and particle dispersion strongly depend on concentration of the polyurethane added before laser ablation. 0.3 wt% polyurethane is the optimal polymer concentration to produce nanocomposites with improved particle dispersion and adequate productivity. Lower polyurethane concentration results in agglomeration whereas higher concentration reduces the production rate significantly. The following evaporation step did not change the distribution of the nanocomposite inside the polyurethane matrix. Hence, the in situ coating of nanoparticles with polyurethane during laser ablation enables simple integration into the structural analogue polymer matrix without additives. Furthermore, it was possible to injection mold these in situ-stabilized nanocomposites without affecting particle dispersion. This clarifies that sufficient in situ stabilization during laser ablation in polymer solution is able to prevent agglomeration even in a hot polymer melt.     

The effect of triethyl citrate on the dispersibility and water vapor sorption behavior of polylactic acid/zeolite composites

The aim of this study was to investigate the water vapor adsorption behavior and mechanical properties of poly (lactic acid) (PLA)/zeolite (5, 10, or 15 phr) composites prepared with triethyl citrate (TEC; 20 phr) via a melting process. TEC was used to improve the flexibility of the PLA and the dispersibility of the zeolite in TEC-zeolite suspensions that were ultra-sonicated. It was found that zeolite was uniformly dispersed in the PLA matrix, and the interfacial adhesion between the PLA matrix and zeolite was enhanced by TEC. In addition, the tensile strengths and Young's modulus of the composites improved with increasing zeolite content. The PLA/zeolite composites prepared with TEC had increased water vapor permeability and contact angles compared to neat PLA and standard PLA/zeolite due to the presence of TEC. In particular, TEC accelerated the hydrolysis of the PLA surface in a high humidity environment, resulting in an improvement in water vapor sorption capacity. At the same zeolite content of 15 phr, the equilibrium moisture content (EMC) values of PLA/zeolite films prepared with TEC increased by up to 39.25 mg/g whereas those prepared without TEC only increased by up to 24.33 mg/g. The results suggest the possibility of applying PLA/zeolite films prepared with TEC as a flexible active packaging material.     

Compatibilized polyethylene—thermally reduced graphene nanocomposites: Interfacial interactions and hyperspectral mapping for component distribution

Ethylene-co-acrylic acid (EAA) and ethylene-co-methacrylic acid ionomer (EMAZ) copolymers were used as compatibilizers for polyethylene-graphene nanocomposites generated by melt mixing. At 5 wt% content, the EAA compatibilizer enhanced the tensile modulus of PE by 40 % and shear modulus by >300 % (1 rad/s) due to efficient dispersion of graphene platelets which helped in effective stress transfer. These also resulted in enhanced thermal stability for PE-EAA-G nanocomposite as compared to nanocomposite with EMAZ. The properties of the nanocomposites were significantly better than the conventional nanocomposites based on layered silicate materials. Mapping of the component distribution in the nanocomposites was demonstrated by using hyperspectral imaging. The nanocomposite with EAA exhibited higher extent of spectral signal mixing due to better mixing of filler and compatibilizer in PE matrix. On the other hand, nanocomposite with EMAZ had no spectral mixing as the components did not mix optimally with each other. The DSC thermogram for this nanocomposite also exhibited a small shoulder at low temperature probably due to immiscibility of the compatibilizer with the matrix polymer. The hyperspectral imaging and mapping was thus demonstrated to be a useful method for determination of component distribution in complex nanocomposite systems.     

Effect of sepiolite nanoparticles on the properties of novel poly(sulfone ether imide)

A new poly(sulfone ether imide) was prepared, and related nanocomposites were produced through introduction of sepiolite nanoparticles into the matrix of polymer. Inherent viscosity, thermal and mechanical features of pristine poly(sulfone ether imide), and nanocomposite samples were evaluated and compared. The crystallinity was also investigated. Dispersion and distribution behaviors of nanocomposite samples and cross‐sectional morphology of nanocomposite films were also studied. Also, the optimized amounts of sepiolite nanoparticles in the matrix of polymer were determined by microscopic techniques (scanning electron microscope and transmission electron microscope). By introduction of 3 wt% of sepiolite, superior thermal and mechanical properties were observed. Copyright © 2016 John Wiley & Sons, Ltd.     

Polylactide/exfoliated graphite nanocomposites with enhanced thermal stability,mechanical modulus,and electrical conductivity

We have prepared a series of polylactide/exfoliated graphite (PLA/EG) nanocomposites by melt‐compounding and investigated their morphology, structures, thermal stability, mechanical, and electrical properties. For PLA/EG nanocomposites, EG was prepared by the acid treatment and following rapid thermal expansion of micron‐sized crystalline natural graphite (NG), and it was characterized to be composed of disordered graphite nanoplatelets. It was revealed that graphite nanoplatelets of PLA/EG nanocomposites were dispersed homogeneously in the PLA matrix without forming the crystalline aggregates, unlike PLA/NG composites. Thermal degradation temperatures of PLA/EG nanocomposites increased substantially with the increment of EG content up to ～3 wt %, whereas those of PLA/NG composites remained constant regardless of the NG content. For instance, thermal degradation temperature of PLA/EG nanocomposite with only 0.5 wt % EG was improved by ～10 K over PLA homopolymer. Young's moduli of PLA/EG nanocomposites increased noticeably with the increment of EG content up to ～3 wt %, compared with PLA/NG composites. The percolation threshold for electrical conduction of PLA/EG nanocomposites was found to be at 3–5 wt % EG, which is far lower graphite content than that (10–15 wt % NG) of PLA/NG composites. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 850–858, 2010     

Effects of coating amount and particle concentration on the impact toughness of polypropylene/CaCO3 nanocomposites

The effects of the coating amount of surfactant and the particle concentration on the impact strength of polypropylene (PP)/CaCO₃ nanocomposites were investigated. Nanocomposites prepared with monolayer-coated CaCO₃ nanoparticles had the best mechanical properties, including Young’s modulus, tensile yield stress and impact strength because of the good dispersion of the nanoparticles in the polymer matrix. In addition, the good dispersibility of the monolayer-coated nanoparticles allowed us to study the effects of particle concentration on the impact strength of the nanocomposites. H-PP and E-PP, which were the low and high molecular weight PPs, respectively, were used as polymer matrices. Critical particle concentrations of 10 and 25 wt% corresponding to an abrupt increase in the impact toughness were determined for the E-PP and H-PP nanocomposites, respectively. Good particle dispersion in a polymer matrix is the prerequisite for the calculation of the critical ligament thickness using the critical particle concentration. We propose that the observed critical ligament thickness actually corresponds to the critical thickness at which the plane-strain to plane-stress transition occurs. In addition, the critical ligament thickness of a nanocomposite depends on the properties of the polymer matrix, such as molecular weight, even for a given type of polymer.     

The effect of halloysite nanotubes and N,N'- ethylenebis (stearamide) on the properties of polylactide nanocomposites with amorphous matrix

Amorphous polylactide/halloysite nanotube (PLA/HNT) nanocomposites were prepared and examined. Neat HNT and HNT treated with N,N'- ethylenebis(stearamide) (EBS) were used as nanofillers. The role of HNT and/or EBS content on the cold crystallization of amorphous PLA matrix, HNT dispersion, as well as on the dynamic mechanical and optical properties of the materials was determined.The PLA/HNT-based nanocomposites contained well-distributed nanotubes and occasionally micron-sized aggregates, especially at high loading. HNT, EBS treated HNT and EBS influenced the cold crystallization of PLA, therefore the formation of the disorder α′ and the order α crystallographic forms of PLA.The nanocomposites exhibited increased stiffness and decreased transparency compared to the neat PLA. Due to the reinforcing effect and additional specific features of HNT, the addition of the nanofiller allows tuning of the properties of the nanocomposites with amorphous PLA matrix.     

Nanoperlite effect on thermal,rheological, surface and cellular properties of poly lactic acid/nanoperlite nanocomposites for multipurpose applications

In this study, poly lactic acid (PLA) based nanocomposites containing perlite nanoparticles were prepared by melt mixing method. Various characterization techniques were employed to evaluate the performance PLA/nanoperlite nanocomposites. The nanocomposites were characterized via FTIR to investigate the functional groups and chemical structure of the nanocomposites. Thermal properties of the nanocomposites, examined by DSC, showed that the increase of nano-perlite content in the PLA matrix reduces the crystallinity and melting temperature of the nanocomposites. The rheological studies indicated that both of storage and loss modulus are increased when the nanoperlite is added up to 5 wt%. However, the modulus is reduced in samples containing more than 5 wt% nanoparticle due to their agglomeration. The in-vitro degradation studies of the nanocomposites at elevated and normal temperatures showed hydrolytic degradation around 13–15 months. The surface behavior results implied that the water contact angle values exhibit a reducing trend when the nanoperlite content increases up to 3 wt%, which can be related to the decreased crystallinity of PLA and also to the hydrophilic nature of perlite. Moreover, the adhesion of osteoblast cells and their viability on an electrospun scaffold, made of optimized sample, showed the initial implications of potential applications of the nanocomposites in bone regeneration and biomedical applications. These multipurpose nanocomposites can also be used for packaging applications.     

Thermal and mechanical properties of syndiotactic polystyrene/organoclay nanocomposites with different microstructures

The fabrication of syndiotactic polystyrene (sPS)/organoclay nanocomposite was conducted via a stepwise mixing process with poly(styrene‐co‐vinyloxazolin) (OPS), that is, melt intercalation of OPS into organoclay followed by blending with sPS. The microstructure of nanocomposite mainly depended on the arrangement type of the organic modifier in clay gallery. When organoclays that have a lateral bilayer arrangement were used, an exfoliated structure was obtained, whereas an intercalated structure was obtained when organoclay with a paraffinic monolayer arrangement were used. The thermal and mechanical properties of sPS nanocomposites were investigated in relation to their microstructures. From the thermograms of nonisothermal crystallization and melting, nanocomposites exhibited an enhanced overall crystallization rate but had less reduced crystallinity than a matrix polymer. Clay layers dispersed in a matrix polymer may serve as a nucleating agent and hinder the crystal growth of polymer chains. As a comparison of the two nanocomposites with different microstructures, because of the high degree of dispersion of its clay layer the exfoliated nanocomposite exhibited a faster crystallization rate and a lower degree of crystallinity than the intercalated one. Nanocomposites exhibited higher mechanical properties, such as strength and stiffness, than the matrix polymer as observed in the dynamic mechanical analysis and tensile tests. Exfoliated nanocomposites showed more enhanced mechanical properties than intercalated ones because of the uniformly dispersed clay layers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1685–1693, 2004     

Functionalized graphene/thermoplastic polyester elastomer nanocomposites by reactive extrusion‐based masterbatch: preparation and properties reinforcement

A reactive extrusion process was developed to fabricate polymer/graphene nanocomposites with good dispersion of graphene sheets in the polymer matrix. The functionalized graphene nanosheet (f‐GNS) activated by diphenylmethane diisocyanate was incorporated in thermoplastic polyester elastomer (TPEE) by reactive extrusion process to produce the TPEE/f‐GNS masterbatch. And then, the TPEE/f‐GNS nanocomposites in different ratios were prepared by masterbatch‐based melt blending. The structure and morphology of functionalized graphene were characterized by Fourier transform infrared, X‐ray photoelectron spectroscopy, X‐ray diffraction and transmission electron microscopy (TEM). The incorporation of f‐GNS significantly improved the mechanical, thermal and crystallization properties of TPEE. With the incorporation of only 0.1 wt% f‐GNS, the tensile strength and elongation at break of nanocomposites were increased by 47.6% and 30.8%, respectively, compared with those of pristine TPEE. Moreover, the degradation temperature for 10 wt% mass loss, storage modulus at ?70°C and crystallization peak temperature (T_cp) of TPEE nanocomposites were consistently improved by 17°C, 7.5% and 36°C. The remarkable reinforcements in mechanical and thermal properties were attributed to the homogeneous dispersion and strong interfacial adhesion of f‐GNS in the TPEE matrix. The functionalization of graphene was beneficial to the improvement of mechanical properties because of the relatively well dispersion of graphene sheets in TPEE matrix, as suggested in the TEM images. This simple and effective approach consisting of chemical functionalization of graphene, reactive extrusion and masterbatch‐based melt blending process is believed to offer possibilities for broadening the graphene applications in the field of polymer processing. Copyright © 2014 John Wiley & Sons, Ltd.     

PLA-ZnO nanocomposite films: Water vapor barrier properties and specific end-use characteristics

PLA nanocomposite films with multifunctional characteristics such as mechanical, anti-UV, antibacterial, electrical, gas barrier properties are potentially of high interest as packaging biomaterials. Occasionally, desired and beneficial effects obtained by addition nanofillers come along with some drawbacks, leading to the sharp drop in the molecular weights of the polyester chains, and consequently an important loss of mechanical and thermal properties. Novel PLA-ZnO nanocomposite films were produced by melt-compounding PLA with 0.5–3% ZnO rod-like nanoparticles. The surface treatment of nanofiller by silanization (with triethoxy caprylylsilane) was necessary to obtain a better dispersion and to limit the decrease of molecular mass of PLA. The morphology, molecular, thermo-mechanical and transport properties to water vapor of PLA-ZnO films were analyzed with respect to the neat PLA. According to DSC and to XRD, the produced films were essentially amorphous. The changes in PLA permeation properties were strongly dependent on temperature and nanofiller loading. The well dispersed ZnO nanoparticles within the polyester matrix were effective in increasing the tortuosity of the diffusive path of the penetrant molecules. The activation energy remained similar for PLA and PLA-1% ZnO, but was found greater at higher loading of ZnO (3%), confirming the increased difficulty of travelling molecules to diffuse through PLA. In comparison to the neat PLA (presenting no antimicrobial efficacy), the nanocomposites were active against both Gram-positive and Gram-negative bacteria, stronger antibacterial activity being evidenced after 7 days elapsed time. By considering the multifunctional properties of PLA-ZnO nanocomposites, the films produced by extrusion can be considered a promising alternative as environmental-friendly packaging materials.     

Comparative study on the properties of poly(trimethylene terephthalate) ‐based nanocomposites containing multi‐walled carbon (MWCNT) and tungsten disulfide (INT‐WS2) nanotubes

Multi‐walled carbon (MWCNT) and tungsten disulfide (INT‐WS₂) nanotubes are materials with excellent mechanical properties, high electrical and thermal conductivity. These special properties make them excellent candidates for high strength and electrically conductive polymer nanocomposite applications. In this work, the possibility of the improvement of mechanical, thermal and electrical properties of poly(trimethylene terephthalate) (PTT) by the introduction of MWCNT and INT‐WS₂ nanotubes was investigated. The PTT nanocomposites with low loading of nanotubes were prepared by in situ polymerization method. Analysis of the nanocomposites' morphology carried out by SEM and TEM has confirmed that well‐dispersed nanotubes in the PTT matrix were obtained at low loading (<0.5 wt%). Thermal and thermo‐oxidative stability of nanocomposites was not affected by the presence of nanotubes in PTT matrix. Loading with INT‐WS₂ up to 0.5 wt% was insufficient to ensure electrical conductivity of PTT nanocomposite films. In the case of nanocomposites filled with MWCNT, it was found that nanotube incorporation leads to increase of electrical conductivity of PTT films by 10 orders of magnitude, approaching a value of 10^?3 S/cm at loading of 0.3 wt%. Tensile properties of amorphous and semicrystalline (annealed samples) nanocomposites were affected by the presence of nanotubes. Moreover, the increase in the brittleness of semicrystalline nanocomposites with the increase in MWCNT loading was observed, while the nanocomposites filled with INT‐WS₂ were less brittle than neat PTT. Copyright © 2016 John Wiley & Sons, Ltd.     

Poly(ether‐imide) and related sepiolite nanocomposites: investigation of physical,thermal, and mechanical properties

Novel poly(ether‐imide) and sepiolite nanocomposites were synthesized based on a unique diamine monomer with the aim of improving physical and mechanical properties of final polyimide films. The diamine was polycondensed with 4,4′‐(hexafluoroisopropylidene) diphthalic anhydride to produce related poly(ether amic acid) prepolymer. Pure poly(ether‐imide) and nanocomposite films were prepared via thermal imidization process of poly(ether amic acid). Coexistence of ether, pyridine, and phenylene functional groups in the diamine chemical structure resulted in flexible polyimide films with significant thermal, physical, and mechanical properties. Thermal stability, glass‐transition temperature, dimensional stability, and tensile properties of polymer and nanocomposites were studied and compared. Morphology of nanocomposites was also investigated using scanning and transmission electron microscopic methods to study the distribution and dispersion behavior of sepiolite nanofibers in the polyimide matrix. By introduction of sepiolite nanoparticles, overall improvement of properties was observed in respect to pure polyimides. Copyright © 2015 John Wiley & Sons, Ltd.     

In‐situ thermal reduction and effective reinforcement of graphene nanosheet/poly (ethylene glycol)/poly (lactic acid) nanocomposites

This study aims to achieve a molecule‐level dispersion of graphene nanosheets (GNSs) and a maximum interfacial interaction between GNSs and a polymer matrix. GNS‐reinforced poly (ethylene glycol) (PEG)/poly (lactic acid) (PLA) nanocomposites are obtained by a facile and environment‐friendly preparation method. Graphite oxide and GNSs are characterized by atomic force microscopy, Raman spectroscopy, and X‐ray diffraction. Scanning electron microscopy shows that the state of dispersion of the GNS in the PEG/PLA matrix is distribution. The tensile strength and Young's modulus increases by 45% and 188%, respectively, with the addition of 4.0 wt% GNSs. The thermal stability of the GNS‐based nanocomposites also improves. Differential scanning calorimetry indicates that GNSs have no remarkable effect on the crystallinity of the nanocomposites. The effective reinforcement of the nanocomposites is mainly attributed to the highly strong molecular‐level dispersion of the GNSs in the polymer matrix. Copyright © 2014 John Wiley & Sons, Ltd.