Dispersion of Graphene Nanoplatelets in Polylactic Acid with the Aid of a Zwitterionic Surfactant: Evaluation of the Shape Memory Behavior

Developments in the dispersion of graphene nanoplatelets in polylactic acid were achieved with the aid of a zwitterionic surfactant. The graphene nanoplatelet surface modification was tracked by Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray diffraction, and elemental analysis. Different amounts of graphene nanoplatelets and surface-modified graphene nanoplatelets (3 and 6 phr) were used to prepare the polylactic acid nanocomposite through a solvent-mixing method. It was found that surface-modified graphene nanoplatelets were exfoliated and homogeneously dispersed in the polylactic acid matrix. Better dispersion of surface-modified graphene nanoplatelets compared with graphene nanoplatelets was due to enhancement of the polymer–graphene interaction induced by the zwitterionic surfactant. The shape memory properties of nanocomposites were evaluated using thermomechanical analysis. The obtained results revealed that the shape memory performance of nanocomposite samples was affected by the degree of dispersion. Higher shape recovery of nanocomposite samples in comparison with that of neat polylactic acid was obtained, which originated from their higher elastic glassy modulus. Up to 91% shape recovery was determined in nanocomposite samples containing surface-modified graphene nanoplatelets, which was attributed to the good dispersion of surface-modified graphene nanoplatelets in the polylactic acid matrix.     

Microwave responsive epoxy nanocomposites reinforced by carbon nanomaterials of different dimensions

This study fabricated nanocomposites consisting of epoxy‐based shape memory polymer (ESMP) matrix and carbon nanofillers. The nanofillers include zero‐dimensional carbon black, one‐dimensional multiwalled carbon nanotubes, two‐dimensional (2D) graphene nanoplatelets, and three‐dimensional (3D) functionalized graphene sheets, which are all efficient microwave‐absorbing materials that can transform microwaves into heat energy. As a result, the temperatures of the nanocomposites increased more rapidly than pristine ESMP in microwaves. The functionalized graphene sheets were found to transform the microwaves into heat more efficiently than the other nanofillers. Possible microwave propagation paths in the nanocomposites were proposed. Moreover, the nanocomposites displayed significantly higher mechanical strengths than pristine ESMP. The low cost and strong nanocomposites with fast microwave responses may be applied as actuators or deployable devices in medical treatments. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45676.     

Dielectric,mechanical and transport properties of bisphenol A polycarbonate/graphene nanocomposites prepared by melt blending

Nanocomposites based on polycarbonate (PC) and different amounts of untreated graphene nanoplatelets (GnP) (from 1 to 7 wt %) were prepared by melt blending. The nanocomposites were thoroughly characterized employing the following techniques: broad band dielectric spectroscopy, thermally stimulated depolarization currents, differential scanning calorimetry, tensile testing, dynamic mechanical thermal analysis, and water vapor, carbon dioxide and oxygen permeability measurements. The presence of a MWS relaxation mode indicated the accumulation of electrical charges trapped at the interfaces of the polycarbonate with graphene 2D platelets. The addition of GnP produced nanocomposite materials with enhanced mechanical and barrier properties. The melt mixed PC/graphene nanocomposites prepared here exhibit well‐balanced properties, even though unmodified graphene nanoplatelets were used. In addition, the nanocomposites were obtained by a single extrusion process, which is easily scalable for industrial applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44654.     

Influence of annealing-induced phase separation on the shape memory effect of graphene-based thermoplastic polyurethane nanocomposites

Thermoplastic polyurethane (TPU) is a multiblock copolymer that exhibits an attractive shape memory effect (SME). Its morphology consists of a soft segment (SS), which corresponds to the polyol or a long-chain diol, while the hard segment involves the intercalation of a diisocyanate and a chain extender. Due to the distinct thermodynamic parameters of each monomer, these segments are not miscible with each other, resulting in a phase-separated structure in their morphology. This structure is characterized by the formation of soft and hard domains (SD and HD), respectively. When incorporating 0.1 wt% of graphene nanoplatelets (GNP) or 0.1 wt% of multilayer graphene oxide (mGO) into the TPU matrix using solution casting process, a contribution to the phase separation of these domains is observed. This phenomenon becomes even more pronounced when graphene-based nanocomposites are subjected to annealing at 110°C for 24 hours, indicating a good interaction between the GO and GNP with the HD and SS, respectively. After annealing, the nanocomposites (TPU + GNP and TPU + mGO) exhibit improved performance in SME, as evidenced by an approximately 9% increase in the shape recovery ratio compared to the nonannealed TPU. Additionally, all nanocomposites maintained a high strain during SME programming, surpassing that of pure TPU, both before and after annealing. This suggests a direct influence of the graphene-based nanoparticles on the shape memory effect.     

Physical properties and shape memory behavior of thermoplastic polyurethane/poly(ethylene-<Emphasis Type="Italic">alt</Emphasis>-maleic anhydride) blends and graphene nanoplatelet composite

A new thermoplastic polyurethane (TPU) was prepared from polylactide-b-poly(ethylene glycol)-b-polylactide (soft segment) and 2,4-toluene diisocyanate (hard segment). Then, TPU in various proportions (i.e., 50, 70, and 90 wt%) was blended with poly(ethylene-alt-maleic anhydride) (PEMA) to form samples coded as TPU/PEMA50, TPU/PEMA70, and TPU/PEMA90. The TPU and PEMA blend at ratio of 50:50 was reinforced by various graphene nanoplatelets (GNPs) contents. Three novel strategies were opted in this research, including design of novel thermoplastic polyurethane, blend of TPU with poly(ethylene-alt-maleic anhydride), and fabrication of graphene nanoplatelet-based nanocomposites. Hydrogen bonding between blend component and GNPs directed the formation of regular nanostructure. Consequently, unique self-assembled flower-shaped morphology was observed in blends as well as hybrid materials using the scanning electron microscopy technique. Physical interlinking between blend components and nanofiller was also responsible for rise in tensile modulus (39.3 MPa) and Young’s modulus (4.04 GPa) of the TPU/PEMA/GNP 5 hybrid compared with the neat blend. The crystallization property was studied by the X-ray diffraction analysis and differential scanning calorimetry. The melting temperature of about 70 °C was preferred for the shape recovery studies. The results from heat-induced shape recovery were compared with those of electroactive shape memory effects. Electrical conductivity was increased to 0.18 S cm^?1 using 5 wt% GNP nanofiller, which was dependent on the applied temperature, as well. The original shape of TPU/PEMA/GNP 5 sample was almost 95 % recovered using heat-induced shape memory effect, while 98 % recovery was observed in an electric field of 40 V. Electroactive shape memory results were found to be better than those induced by heat stimulation effect.     

The aspect ratio of epoxy matrix nanocomposites reinforced with graphene stacks

The improvement of physical and mechanical properties of nanofilled matrices significantly depends on the average size of dispersed fillers. In particular, the aspect ratio of lamellar nanofillers, such as graphene stacks, results from a combination of both filler morphology and processing techniques. In this study, nanocomposites were obtained dispersing three different graphene precursors in an epoxy resin: expanded graphite, commercial graphene nanoplatelets, and natural graphite. Epoxy matrix nanocomposites reinforced with graphene stacks, ranging from 1 wt% to 3 wt% were prepared and characterized. The structural, mechanical, and thermal properties of expanded graphite‐based nanocomposites, as well as the rheological properties of liquid resin/filler suspensions, were studied and compared with those of the unfilled epoxy matrix and of the matrix filled with natural graphite and commercial nanoplatelets. The comparison of mechanical and rheological properties with simple mathematical models indicated that the aspect ratio of expanded graphite is in the order of 1000, i.e., a dispersion of nanoscale graphene stacks was obtained. This result suggests that the measurement of engineering properties of nanocomposites not only represents an objective but can also provide information about the average degree of dispersion. POLYM. ENG. SCI. 2013. © 2012 Society of Plastics Engineers     

Graphene triggered enhancement in visible-light active photocatalysis as well as in energy storage capacity of (CFO)1-x(GNPs)x nanocomposites

Cobalt ferrite-graphene nanoplatelets ((CFO)_1-x(GNPs)_x) nanocomposites are promising for efficient photocatalysis and high-performance supercapacitors. Multifunctional (CFO)_1-x(GNPs)_x nanocomposites prepared via facile chemical method have been investigated for their physio-chemical characteristics like crystal structure, morphology, chemical composition, optical properties, infrared vibrational modes, photocatalytic and supercapacitor applications. Interestingly, the photocatalytic activity of CFO nanostructures has been improved significantly from 38.3% to 98.7% with the addition of graphene which can be attributed to control over recombination of charge carriers. It is also found that the specific capacitance of the prepared (CFO)_1-x(GNPs)_x nanocomposite electrode at 0.5 Ag^-1 is three times higher than that of only CFO based electrode which could be due to the conducting nature of graphene nanoplatelets (GNPs). The enhanced photocatalytic and improved electrochemical characteristics suggest the effective use of prepared nanocomposites in water purification and supercapacitor nanodevices.     

High‐performance antistatic ethylene–vinyl acetate copolymer/high‐density polyethylene composites with graphene nanoplatelets coated by polyaniline

Graphene nanoplatelets coated by polyaniline (GNP@PANI) and ethylene–vinyl acetate (EVA) copolymer–high‐density polyethylene (HDPE) were used for the first time to prepare high‐performance antistatic composites through an effective method that combined solution mixing and melt blending. GNP@PANI nanocomposites were fabricated by in situ polymerization to improve the dispersion of graphene nanoplatelets (GNPs) in the EVA–HDPE matrix and the compatibility between the GNPs and the EVA–HDPE matrix. The GNP@PANI nanocomposites and EVA were first prepared as a premix through solution mixing, and then, the premix and HDPE were prepared as highly antistatic composites through melt blending. The dispersion of the GNPs in the EVA–HDPE matrix and the compatibility between the GNPs and the EVA–HDPE matrix were confirmed by field emission scanning electron microscopy and transmission electron microscopy observations. The GNP@PANI–EVA–HDPE composites met the requirements for antistatic materials when the content of the GNP@PANI nanocomposites was 5 wt % with only about 1 wt % GNPs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45303.     

Latex co‐coagulation approach to fabrication of polyurethane/graphene nanocomposites with improved electrical conductivity,thermal conductivity,and barrier property

This study describes a simple and effective method of synthesis of a polyurethane/graphene nanocomposite. Cationic waterborne polyurethane (CWPU) was used as the polymer matrix, and graphene oxide (GO) as a starting nanofiller. The CWPU/GO nanocomposite was prepared by first mixing a CWPU emulsion with a GO colloidal dispersion. The positively charged CWPU latex particles were assembled on the surfaces of the negatively charged GO nanoplatelets through electrostatic interactions. Then, the CWPU/chemically reduced GO (RGO) was obtained by treating the CWPU/GO with hydrazine hydrate in DMF. The results of X‐ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Raman analysis showed that the RGO nanoplatelets were well dispersed and exfoliated in the CWPU matrix. The electrical conductivity of the CWPU/RGO nanocomposite could reach 0.28 S m^?1, and the thermal conductivity was as high as 1.71 W m^?1 K^?1. The oxygen transmission rate (OTR) of the CWPU/RGO‐coated PET film was significantly decreased to 0.6 cm³ m^?2 day^?1, indicating a high oxygen barrier property. This remarkable improvement in the electrical and thermal conductivity and barrier property of the CWPU/RGO nanocomposite is attributed to the electrostatic interactions and the molecular‐level dispersion of RGO nanoplatelets in the CWPU matrix. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43117.     

Synthesis,characterization, and thermal aging behavior of HCl‐doped polyaniline/TRGO nanocomposites

In this article polyaniline (PANI) nanocomposites containing thermally reduced graphene oxide (TRGO) were synthesized and characterized before and after thermal aging. The nanocomposites were prepared through in situ oxidative polymerization of aniline in the presence of TRGO nanoplatelets. FTIR and Raman spectroscopies, XRD, FESEM, and electrical conductivity measurements were used to characterize synthesized materials. PANI/TRGO nanocomposites showed considerably higher electrical conductivity when compared to pure PANI, which was associated with the higher electrical conductivity of TRGO and increased crystallinity of PANI in the presence of TRGO. Pure PANI and PANI/TRGO nanocomposites were thermally aged at 70, 80, 90, and 100 °C. The results showed that the characteristic time of thermal aging process is higher for PANI/TRGO nanocomposites and increases with TRGO loading, which indicates better stability of conductivity during thermal aging process. On the other hand, the characteristic time of thermal aging reduced with aging temperature and a fast decrease was observed from 80 to 90 °C. Improved resistance over thermal aging can be attributed to the barrier effect of TRGO nanoplatelets to the dopant molecules, which retards conductivity degradation in the thermal aging process. Furthermore, TRGO increases PANI crystallinity and it can also prevent crystallinity reduction during thermal aging process. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44635.     

Processing–morphology–property relationships of polypropylene–graphene nanoplatelets nanocomposites

Polypropylene (PP) nanocomposites reinforced with graphene nanoplatelets (GNPs) were prepared via melt extrusion. A special sheet die containing with two shunt plates was designed. The relationships among the flow field of the special die, exfoliation, and dispersion morphology of the GNPs in PP and the macroscopic properties of the nanocomposites were analyzed. Flow field simulation results show that the die with shunt plates provided a high shear stress, high pressure, and high velocity. The differential scanning calorimetry, X‐ray scattering, and electron microscopy results reveal that the nanocomposites prepared by the die with the shunt plates had higher crystallinity values and higher exfoliation degrees of GNPs. The orientation of the GNPs parallel with the extrusion direction was also observed. The nanocomposites prepared by the die with shunt plates showed a higher electrical volume conductivity, thermal conductivity, and tensile properties. This indicated that the high shear stress exfoliated the GNPs effectively to a thinner layer and then enhanced the electrical, thermal, and mechanical properties. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44486.     

Effect of the molecular chains grafted on graphene nanosheets on the properties of poly(l‐lactic acid) nanocomposites

We prepared thermally reduced graphene oxide (TRG) grafted with polymethyl methacrylate (PMMA) and polyvinyl acetate (PVAc) (TRG‐g‐PMMA and TRG‐g‐PVAc) by γ‐ray irradiation‐induced graft polymerization and studied their effects on poly(l ‐lactic acid) (PLLA) nanocomposites. PMMA and PVAc chains were proved to be grafted on the TRG surface successfully. TRG‐g‐PMMA and TRG‐g‐PVAc was found to restrict the crystallization behavior of PLLA compared with TRG. Moreover, tensile‐test results showed that TRG‐g‐PMMA and TRG‐g‐PVAc could enhance the elongation at break of PLLA nanocomposites without reducing the tensile strength and modulus compared with TRG, which indicated that the grafting of PMMA and PVAc chains on TRG could improve the toughness of PLLA nanocomposites. POLYM. COMPOS., 38:5–12, 2017. © 2015 Society of Plastics Engineers     

Functional nanocomposites with graphene-DNA hybrid fillers: Synthesis and surface properties under UV irradiation

In this work, nanocomposites containing assemblies of graphene nanoplatelets (GNP) and double-stranded DNA are investigated as UV-sensitive materials, as they show good electrical properties combined with the chemical sensitivity of DNA to UV radiation, particularly to the more energetic UV-C band. Nanocomposite films were prepared by drop-casting technique after embedding the graphene-DNA fillers in a flexible polydimethylsiloxane (PDMS) matrix using a suitable solvent. The synthesis was optimized in order to improve the dispersion of the graphene-DNA elements in the polymer matrix, as the sensing properties of the nanocomposite materials are highly affected by the amount and homogeneity of the filler dispersion. The electrical and thermal properties of the GNP-DNA/PDMS films, as well as their surface morphology and wettability, were investigated before and after exposure to UV-C radiation using complementary techniques. Results give information on the potential applications of these novel functional nanocomposites for radiation monitoring in environments that are characterized by high levels of biologically-damaging UV radiation.     

Templated growth of polyaniline on exfoliated graphene nanoplatelets (GNP) and its thermoelectric properties

Polyaniline (PANi)/exfoliated graphene nanoplatelets (GNP) nanocomposites were prepared by in situ polymerization of aniline monomer in the presence of GNP for thermoelectric applications. PANi has a strong affinity for GNP due to π electron interactions, forming a uniform nanofibril coating. A paper-like nanocomposite was prepared by controlled vacuum filtration of an aqueous dispersion of PANi decorated GNP. The Seebeck coefficient of the resulting nanocomposite changes with initial concentration of aniline in the solution as well as the protonation of PANi, reaching as high as 33 μV/K for nanocomposites containing approximately 40 wt% of PANi and with a protonation ratio of 0.2. The presence of GNP improved the electrical conductivity of the nanocomposites to 59 S/cm. As a result, thermoelectric figure of merit ZT of the nanocomposites is 2 orders of magnitude higher than either of the constituents, exhibiting a significant synergistic effect.     

Novel electroactive polyamide 12 based nanocomposites filled with reduced graphene oxide

Novel electroactive nanocomposites were prepared by adding to a polyamide 12 (PA12) matrix different amounts (from 1 to 8 wt%) of reduced graphene oxide (rGO), and the thermo‐electrical behavior of the prepared bulk materials was compared with that of the corresponding fibers. FESEM micrographs on bulk materials highlighted an evident aggregation of the rGO lamellae, proportional to the filler concentration. The presence of rGO stacks was responsible of a heavy embrittlement of the samples, with a strong reduction of the elongation at break, and of the limited electrical conductivity of the samples (about 10⁵ Ω·cm with a rGO amount of 4 wt%). Moreover, nanofiller addition determined an improvement of the thermal degradation resistance, associated to a slight drop of the glass transition temperature (about 7°C with a nanofiller concentration of 4 wt%) and of the crystallinity degree (up to 9% for an rGO loading of 4 wt%). The extrusion process adopted to prepare nanocomposite fibers caused a partial breakage of rGO aggregates and their progressive alignment along the drawing direction, determining thus an electrical resistivity increase with respect to the bulk samples. Therefore, the surface heating of the prepared fibers through Joule effect was possible only at elevated rGO amounts (i.e., 8 wt%). POLYM. ENG. SCI., 59:198–205, 2019. © 2018 Society of Plastics Engineers     

Effects of ultrasound vibration on the structure and properties of polypropylene/graphene nanoplatelets composites

An ultrasound‐assisted extrusion system was added to melt extrusion process to prepare polypropylene (PP) nanocomposites reinforced with graphene nanoplatelets (GNPs). The relationships among the ultrasound vibration, exfoliation, and dispersion morphology of GNPs in PP matrix, the crystallinity, and the macroscopic properties of nanocomposites were investigated. The properties measurement results showed that the present of ultrasound vibrations increased the conductive properties, decreased the apparent viscosity and crystallinity of PP/GNPs nanocomposites. FESEM results revealed that the ultrasound vibration increased the exfoliation and dispersion of GNPs in PP matrix. This morphology was benefit for forming electrical and thermal network, therefore the electrical conductivity and thermal conductivity of PP/GNP nanocomposites were increased. But the powerful vibration that provided by 300 W ultrasound power would reduce the diameter of GNPs, then reduce its conductive properties. FTIR and TGA results showed that ultrasound vibration had less effect on the chemical bond and the degradation of PP/GNPs nanocomposites. POLYM. ENG. SCI., 58:377–386, 2018. © 2017 Society of Plastics Engineers     

Electrically conductive polyethylene terephthalate/graphene nanocomposites prepared by melt compounding

Graphene nanosheets were prepared by complete oxidation of pristine graphite followed by thermal exfoliation and reduction. Polyethylene terephthalate (PET)/graphene nanocomposites were prepared by melt compounding. Transmission electron microscopy observation indicated that graphene nanosheets exhibited a uniform dispersion in PET matrix. The incorporation of graphene greatly improved the electrical conductivity of PET, resulting in a sharp transition from electrical insulator to semiconductor with a low percolation threshold of 0.47 vol.%. A high electrical conductivity of 2.11 S/m was achieved with only 3.0 vol.% of graphene. The low percolation threshold and superior electrical conductivity are attributed to the high aspect ratio, large specific surface area and uniform dispersion of the graphene nanosheets in PET matrix.     

Electroactive shape memory performance of polyurethane/graphene nanocomposites

A series of electroactive shape memory polyurethane (SMPU) nanocomposites were synthesized from poly(tetramethylene ether) glycol (PTMG), 4,4-methylenebis(phenyl isocyanate) (MDI) and 1,3-butandiol (1,3-BD) with the addition of various amounts of thermally reduced graphenes (TRG) which were chemically modified with allyl isocyanate (iTRG). The effects of iTRG on electroactive shape recovery behaviors as well as the conventional direct heat actuated SMPU material have been studied in terms of morphological, thermal, mechanical, electrical properties and thermomechanical cyclic behavior. It was found that significant increases in electrical conductivity and temperature were obtained high iTRG contents (>2%) to electrically actuate the nanocomposite, along with large increases in glass transition temperature (T_g) and initial modulus with a dramatic drop in elongation at break.     

Graphene Nanoplatelets as Novel Reinforcement Filler in Poly(lactic acid)/Epoxidized Palm Oil Green Nanocomposites: Mechanical Properties

Graphene nanoplatelet (xGnP) was investigated as a novel reinforcement filler in mechanical properties for poly(lactic acid) (PLA)/epoxidized palm oil (EPO) blend. PLA/EPO/xGnP green nanocomposites were successfully prepared by melt blending method. PLA/EPO reinforced with xGnP resulted in an increase of up to 26.5% and 60.6% in the tensile strength and elongation at break of the nanocomposites respectively, compared to PLA/EPO blend. XRD pattern showed the presence of peak around 26.5° in PLA/EPO nanocomposites which corresponds to characteristic peak of graphene nanoplatelets. However, incorporation of xGnP has no effect on the flexural strength and modulus. Impact strength of PLA/5 wt% EPO improved by 73.6% with the presence of 0.5 wt% xGnP loading. Mechanical properties of PLA were greatly improved by the addition of a small amount of graphene nanoplatelets (<1 wt%).     

Shape memory polyester-based nanomaterials: cutting-edge advancements

ABSTRACT

Shape memory polymers have gained immense importance across technical industries ranging from aerospace and electronics to biomedical fields. This article presents state-of-the-art overview of versatile shape memory polyesters and derived nanocomposites. Shape memory polyesters such as polylactic acid, polyhydroxyalkanoate, polycarbonate, and polyester blends have been identified. Shape memory polyesters have also been reinforced with nanoreinforcements including fullerene, graphene, carbon nanotube, and polyhedral oligomeric silsesquioxane (POSS). Consequently, different groups of stimuli-responsive polyester nanocomposites have been discussed such as polyester/graphene, polyester/carbon nanotube, polyester/fullerene, and polyester/POSS. Future development of shape memory polyesters may reveal superior electrical, mechanical, and thermal performance for technical applications.