A high-performance electromagnetic interference shielding composite based on reduced graphene oxide (rGO) and polystyrene (PS) is realized via high-pressure solid-phase compression molding. Superior shielding effectiveness of 45.1 dB, the highest value among rGO based polymer composite, is achieved with only 3.47 vol% rGO loading owning to multi-facet segregated architecture with rGO selectively located on the boundaries among PS multi-facets. This special architecture not only provides many interfaces to absorb the electromagnetic waves, but also dramatically reduces the loading of rGO by confining the rGO at the interfaces. Moreover, the mechanical strength of the segregated composite is dramatically enhanced using high pressure at 350 MPa, overcoming the major disadvantage of the composite made by conventional-pressure (5 MPa). The composite prepared by the higher pressure shows 94% and 40% increment in compressive strength and compressive modulus, respectively. These results demonstrate a promising method to fabricate an economical, robust, and highly efficient EMI shielding material.

Evolution of molecular conformation in uniaxially deformed isotactic polypropylene (iPP) as a function of temperature is investigated by time-resolved polarized Fourier-transform infrared spectroscopy. It is observed that oriented crystals (microfibrils) induced by deformation possess better thermal stability compared with isotropic spherulites. 2D correlation analysis reveals that the relaxation process of ordered helices in deformed iPP could be divided into two regions referring to the melting of different crystalline structures. No obvious sequential change of ordering conformations observed in low temperature region is attributed to melting of defective or destructed crystals. However, notable sequential changes of helices occur in the high temperature region; interestingly, long helices are more thermally stable than short helices. The central region of microfibrils is suggested to consist of a large amount of long helical bundles, and the short ordering segments are primarily located in the outer lateral surfaces. A physical picture of the conformational distribution in deformation-induced microfibrils is thus gained. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 673–684

Dodecyl amine (DA) functionalized graphene oxide(DA-GO) and dodecyl amine functionalized reduced graphene oxide (DA-RGO) were produced by using amidation reaction and chemical reduction, then two kinds of well dispersed DA-GO/high-density polyethylene (HDPE) and DA-RGO/HDPE nanocomposites were prepared by solution mixing method and hot-pressing process. Thermogravimetric, X-ray photoelectron spectroscopy, Fourier transforms infrared spectroscopy, X-ray diffractions, and Raman spectroscopy analyses showed that DA was successfully grafted onto the graphene oxide surface by uncleophilic substitution and the amidation reaction, which increased the intragallery spacing of graphite oxide, resulting in the uniform dispersion of DA-GO and DA-RGO in the nonpolar xylene solvent. Morphological analysis of nanocomposites showed that both DA-GO and DA-RGO were homogeneously dispersed in HDPE matrix and formed strong interfacial interaction. Although the crystallinity, dynamic mechanical, gas barrier, and thermal stability properties of HDPE were significantly improved by addition of small amount of DA-GO or DA-RGO, the performance comparison of DA-GO/HDPE and DA-RGO/HDPE nanocomposites indicated that the reduction of DA-GO was not necessary because the interfacial adhesion and aspect ratio of graphene sheets had hardly changed after reduction, which resulting in almost the same properties between DA-GO/HDPE and DA-RGO/HDPE nanocomposites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39803.

In this study, we performed the crystallization of carbon nanotube (CNT)/isotactic polypropylene (iPP) and graphene nanosheet (GNS)/iPP composites with very high nanofiller loadings; these are frequently used in polymer composites for electromagnetic interference shielding and thermal conductivity. Rheology testing indicated that both the high-loading CNTs and GNSs formed dense networks in the iPP matrix, and transmission electron microscopy showed that their connection types were completely different: the CNTs contacted one another in a dot-to-dot manner, whereas the GNSs linked reciprocally in a plane-to-plane manner. The carbon nanofiller networks brought about two opposite effects on iPP crystallization: a nucleation effect and a confinement effect. The CNT network showed a stronger nucleation effect; however, the CNT network also revealed a more powerful confinement effect because the CNT network was denser than the GNS network. With increasing content of the carbon nanofillers, the crystallization rates of both the CNT and GNS composites first increased, then decreased, and showed a very high saturation concentration at 50 wt %; this resulted from the competitive relationship between the nucleation effect and confinement effect. The crystallization was facilitated when the carbon nanofiller concentration was below saturation, where the nucleation effect invariably played a dominant role. Although the crystallization was depressed when the carbon nanofiller concentration was above saturation, the nucleation effect was subdued, and the confinement effect was extensive. Compared to the GNS/iPP composites, the CNT/iPP composites showed a more depressed crystallization. The suppression mechanism is discussed with consideration of the local topological structure constructed by those two carbon nanofillers. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 39505.

Pulverized expandable graphite (pEG) and melamine − formaldehyde (MF) resin core − shell structure particles (pEG@MF) as specific flame retardants for rigid polyurethane foam (RPUF) were synthesized by encapsulating pEG particles with a layer of MF resin via in situ polycondensation. The initial feed weight ratio of pEG and MF prepolymer was found to be the key factor affecting the shell forming process, and the shell growth can be regarded as a combination of ‘raspberry-like’ and conventional ‘core–shell’ formation mechanisms. With the encapsulation of a well formed MF shell, the expandability of pEG particles was significantly enhanced from 42 mL g^–1 to 76 mL g^–1 and thus the pEG@MF particles showed good flame-retardant performance in RPUF. The RPUF/pEG@MF composites passed the V-0 rate and the limiting oxygen index was remarkably increased from 21 to 28 vol% by adding only 10 wt% pEG@MF particles; both the expandability and available expandable graphite content played an important role in controlling the flame-retardant performance of pEG@MF particles. With a loading of fine sized pEG@MF particles, desirable mechanical and thermal insulation properties of RPUF/pEG@MF composites were achieved by preserving the complete cell structure of RPUF and screening the high thermal conductivity of the pEG particles with the thermally inert MF resin shell. The exciting application of the novel pEG@MF particles indicates that the core–shell structure design of expandable graphite can serve as promising solution for fabricating halogen-free flame-retardant RPUF composites with high performance. © 2013 Society of Chemical Industry

A novel processing technique, i.e. high-pressure compression molding/salt leaching, was developed to fabricate ultraporous poly(lactic acid) (PLA) scaffolds. The optimized composition was studied in relation to the porosity, pore morphology, thermal property, and mechanical performance of the PLA scaffolds. At a porogen (CaCO₃) content of 90 wt %, the scaffolds have an interconnected open pore structure and a porosity above 80%. It was truly interesting that the structural stability of high-pressure molded scaffolds was remarkably improved based on the fact that its glass transition temperature (83.5°C) increased about 20°C, as compared to that of the conventional compression-molded PLA (60°C), which is not far from physiological temperature (∼37°C) at the risk of structural relaxation or physical aging. More importantly, the mechanical performance of PLA scaffolds was drastically enhanced under optimized processing conditions. At pressure and temperature of 1000 MPa and 190°C, the porous PLA scaffolds attained a storage modulus of 283.7 MPa, comparable to the high-end value of trabecular bone (250 MPa) ever reported. In addition, our prepared PLA scaffolds showed excellent cellular compatibility and biocompatibility in vitro tests, further suggesting that the high-pressure molded PLA scaffolds have high potential for bone tissue engineering applications. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3509–3520, 2013

The structure evolution of the oriented layer (skin) and unoriented layer (core) from injection-molded isotactic polypropylene samples upon uniaxial drawing is probed by in situ synchrotron X-ray scattering. The X-ray data analysis approach, called “halo method”, is used to semiquantitatively identify the transformation process of crystal phase upon uniaxial drawing. The results verify the validation of the stress-induced crystal fragmentation and recrystallization process in the deformation of the injection-molded samples under different temperatures. Furthermore, the end of strain softening region in the engineering stress-strain curves explicitly corresponds to the transition point from the stress-induced crystal fragmentation to recrystallization process. Basically, the skin and core layers of the injection-molded parts share the similar deformation mechanism as aforementioned. The stretching temperature which dramatically affects the relative strength between the entanglement-induced tie chains and the adjacent crystalline lamellae determines the crystal structural evolution upon drawing. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1618–1631

Isotactic polypropylene (iPP) composite with two-scale reinforcement structure, i.e. nanoscale shish–kebab structure and micron-scale glass fiber (GF) with orientation, was fabricated by an oscillatory shear injection molding (OSIM) technology. The oscillatory shear flow provided by the OSIM gave rise to a high fraction of shish–kebab structures in the iPP composite, characterized by X-ray scattering technique. On the other hand, the oscillatory shear flow oriented GFs in the iPP composite, which was revealed by scanning electron microscopy measurement. The iPP composite with this two-scale reinforcement structure exhibited simultaneously remarkably enhanced tensile strength and impact strength. Fracture mechanism of this iPP composite was also proposed. Copyright © 2012 John Wiley & Sons, Ltd.

This article reports the organic liquid stimuli-response behaviors of carbon black (CB)-filled electrically conductive microfibrillar poly(ethylene terephthalate) (PET)/polyethylene (PE) composite (FCMC) with CB particles selectively localized at PET microfibrils' surfaces. It was found that FCMC's thickness and CB concentration affected its responsivity significantly, a thinner FCMC film with a high CB content exhibited higher responsivity and better signals. In immersion-drying tests, FCMC displayed high and stable responsivities after six immersion-drying runs, indicating that the solvent absorption/desorption equilibrium state was achieved. After long-term immersion, FCMC showed obviously different organic liquid stimuli-response behaviors with faster response rate in immersion and higher terminal resistivity platform in drying, compared with samples without immersion treatment. Conductive network's microstructural changes induced by the long-term immersion and evident capillary effect, which resulted in slow evaporation of remaining solvent in FCMC's interfaces, are the reasons for the phenomenon. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

This article reports the positive temperature coefficient (PTC) and negative temperature coefficient (NTC) effects of a carbon black (CB)-filled electrically conductive microfibrillar poly(ethylene terephthalate) (PET)/polyethylene (PE) composite (FCMC). The composite contains in situ polymer microfibrils in the matrix of another polymer with CB particles selectively localized at microfibrils' surfaces. Anomalous attenuations of PTC and NTC intensities (I_PTC and I_NTC) of FCMC were observed during heating–cooling runs (HCRs) and long-term isothermal treatments. Particularly, when the isothermal treatment time was 32 h, the I_PTC decreased from 5.5 in the original sample to only 0.5, showing a tremendous attenuation ratio of up to 91%, and the NTC effect was completely eliminated. On the contrary, attenuations of PTC and NTC effects in a common conductive polymer composite (CCPC) were so weak as to be negligible through the same thermal treatments. Microstructural changes of the conductive network by Brownian motion and large size of the conductive component-CB coated PET microfibrils are both responsible for the great reductions in I_PTC and I_NTC. The present results strongly suggest that thermal field induced microstructural transformation by Brownian motion helps to reveal the origin of PTC and NTC effects. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The poly(lactic acid) (PLA)/ramie fiber biocomposites were fabricated, which exhibited considerable reinforcement effect comparable to the glass fiber at the same loading. The attempts were made to understand the flow-induced morphology of ramie fibers and PLA crystals in the injection-molded PLA/ramie fiber biocomposites, thus revealing its relationship to biocomposite mechanical properties. The polarized optical microscopy (POM) and two-dimensional wide-angle X-ray diffraction (2D-WAXD) were for the first time used to determine the distribution of nature fibers, which interestingly showed the ramie fibers aligned well along the flow direction over the whole thickness of injection-molded parts, instead of skin-core structure. This easy alignment of ramie fibers during the common processing was ascribed to the intrinsically high flexibility of ramie fibers and strong interfacial interaction between PLA chains and cellulose molecules of ramie fibers. Both 2D-WAXD and differential scanning calorimeter (DSC) measurements suggested that the PLA matrix in its ramie biocomposites had rather high orientation degree and crystallinity, which was attributed to effective heterogeneous nucleation induced by ramie fibers and local shearing field in the vicinity of fiber surface. Remarkable improvement of mechanical and thermo-mechanical properties was achieved for PLA/ramie fiber biocomposites, without sacrifice of toughness and ductility. Addition of 30wt% ramie fibers increased the tensile strength and modulus of PLA/ramie fiber biocomposites from 65.6 and 1468 MPa for pure PLA to 91.3 and 2977 MPa, respectively. These superior mechanical properties were ascribed to easy alignment of ramie fibers, high crystallinity of PLA, and favorable interfacial adhesion as revealed by scanning electron microscopy (SEM) observation and theoretical analysis based on dynamic mechanical analysis (DMA) data. © 2012 Wiley Periodicals, Inc. Biopolymers 97: 825–839, 2012.

The carbon nanotubes (CNTs)/rigid polyurethane (PU) foam composites with a low percolation threshold of ∼ 1.2 wt % were prepared by constructing effective conductive paths with homogeneous dispersion of the CNTs in both the cell walls and struts of the PU foam. The conductive foam presented excellent electrical stability under various temperature fields, highlighting the potential applications for a long-term use over a wide temperature range from 20 to 180°C. Compression measurements and dynamical mechanical analysis indicated 31% improvement in compression properties and 50% increase in storage modulus at room temperature in the presence of CNTs (2.0 wt %). Additionally, the incorporation of only 0.5 wt % CNTs induced remarkable thermal stabilization of the matrix, with the degradation temperature increasing from 450 to 499°C at the 50% weight loss. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

The carbon nanotubes/ultrahigh molecular weight polyethlene (CNTs/UHMWPE) conductive composite with a low percolation threshold had been successfully fabricated, and CNTs were only dispersed in the interface of matrix particles. Some factors, including CNTs concentration, processing temperature, and the time of isothermal treatment, which could exert influence on the positive temperature coefficient effect of the composite, were investigated. Similar with negative temperature coefficient effect, the resistivity decreased during isothermal treatment above the melting point of UHMWPE, which could be thought to be a relaxation process originated from movement of molecular chains. This relaxation, also a process of CNTs aggregating to reorganize the conductive network, was testified as a function of time, temperature, filler concentration, and heating rate. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Poly(L-lactide) (PLLA)/multiwall carbon nanotube (MWNT) composites were prepared by the solvent-ultrasonic-casting method. Only very low concentrations of MWNTs (<0.08 wt %) were added in the composites. Isothermal and nonisothermal crystalline measurements were carried out on PLLA/MWNT composites to investigate the effect of MWNTs on PLLA crystalline behavior. DSC results showed that the incorporation of MWNTs significantly shortened the crystalline induction time and increased the final crystallinity of the composite, which indicated MWNTs have a strong nucleation effect on PLLA even at very low concentrations. The nonisothermal crystallization measurements showed that the MWNTs greatly speed up crystallization during cooling. From isothermal crystallization results, both PLLA and PLLA/MWNT composites samples closely followed a relationship based on Lauritzen-Hoffman theory, with the regime II to III transition shifting to lower temperature with increasing MWNT concentration. A double melting peak appeared in both nonisothermal and isothermal measurements. The conditions under which it appeared were found to closely depend on the regime II-III transition temperature obtained from Lauritzen-Hoffman theory. From the magnitude and position of melting peaks, it is proposed that the double melting peak is caused by a disorder-order crystal phase transition. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2341–2352, 2009

The conductivity of an immiscible polymer blend system, microfibrillar conductive poly(ethylene terephthalate) (PET)/polyethylene (PE) composite (MCPC) containing carbon black (CB), was changed by the addition of insulating CaCO₃ nanoparticles. In MCPC, the PET forms microfibrils during processing and PE forms the matrix. The CB particles are selectively localized in the PET microfibrils. When the insulating CaCO₃ nanoparticles are added, they substitute for some of the conductive CB particles and obstruct the electron paths. As a result, the resistivity of the MCPC can be tailored depending on the insulating filler content. The resistivity-insulating filler content curve displays a sluggish postpercolation region (the region immediately following the percolation region and in front of the equilibrium flat of the resistivity-filler content curve), suggesting that the MCPC in the postpercolation region possesses an enhanced manufacturing reproducibility and a widened processing window. These features are of crucial importance in making sensor materials. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008.