The role of crystalline phase in triblock copolymer PS-PEG-PS based gas sensing materials

To reveal the role of crystalline phase in the matrix polymer of gas sensing conductive polymer composite materials, a series of triblock copolymer polystyrene-b-poly(ethylene glycol)-b-polystyrene (PS-PEG-PS) was synthesized by atom transfer radical polymerization (ATRP). The copolymers have similar molecular weights but different fractions of the crystalline PEG segments. As a result, the ratio of the crystalline phase to the amorphous one can be tuned regardless of the molecular weight of the entire copolymer. The composites consisting of the copolymer and carbon black exhibit gas sensing ability as characterized by the drastic increase in the electrical resistance when meeting organic solvent vapors. It is found that matrix swelling, which provides the composites with gas sensitivity, results from the contribution of the amorphous phase. The crystalline portions prove to be unchanged in the vapors with respect to their microstructure within the time of interests. The appearance of the crystalline phase in the matrix polymer helps to push the conductive fillers into the amorphous regions, which increases the effective filler content and leads to higher responsivity to solvent vapors at lower filler loading.     

A novel sensor for organic solvent vapors based on conductive amorphous polymer composites: carbon black/poly(butyl methacrylate)

Summary Conductive composites from carbon black/poly(butyl methacrylate) (CBPBMA) are synthesized through polymerization filling. The experimental results indicate that relatively low percolation threshold (∼6wt%) is associated with the composites. When the composites are exposed to good solvent vapors of the matrix polymer, the electric resistance of the composites drastically increases by over lo⁴ times. In the case of poor solvent vapor, however, the electrical response of the composites is rather weak, demonstrating selective gas sensibility. In addition, environment temperature exerts great influence on the responsivity of the composites against organic vapors. The higher the temperature, the faster and the stronger the electrical response. It was also found that the response of electric resistance of the composites against good solvent vapors is provided with sufficient reproducibility and stability. It can thus be concluded that the CB/PBMA composites can be used as promising gas sensing materials in practice. Received: 2 December 2002/Revised version: 27 January 2003/ Accepted: 8 February 2003 Correspondence to Ming Qiu Zhang     

Electrical resistance response of poly(ethylene oxide)‐based conductive composites to organic vapors: Effect of filler content,vapor species,and temperature

In this work conductive composites consisting of carbon black (CB) and poly(ethylene oxide) were prepared by solution mixing. The composites' resistance drastically changes in organic vapors so that the composites can be used as candidates for gas‐sensing materials. Owing to the different conduction mechanisms and solvent/composites interactions, the electrical response behaviors of the composites exhibit specific dependences on CB content and environmental temperature, which were only reported previously in a few instances. In addition, the rate of response was also correlated with solvent polarity, solubility, etc. The findings would help to understand the micromechanism of response of the composites and to improve the sensing performance as well. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1517–1523, 2005     

聚乙二醇接枝炭黑纳米导电复合材料气敏性研究

以聚乙二醇接枝炭黑(PEG—g—CB)为导电粒子，不同相对分子质量的聚乙二醇(PEG)为基体，制备了PEG／PEG—g—CB纳米导电高分子复合材料，并研究了其气敏性能。结果发现，该复合材料在PEG极性溶剂蒸汽中电阻响应快，而在非极性溶剂蒸气中电阻几乎不改变；PEG的晶相结构以及CB的接枝与否对响应重复性有很大影响。     

Dynamic percolation phenomenon of poly(methyl methacrylate)/surface fluorinated carbon black composite

The electrical resistivity of polymer filled with conductive filler, such as carbon black (CB) particles, is greatly decreased by incorporating the conductive filler. This is called the percolation phenomenon and the critical CB concentration is called the percolation threshold concentration (Φ*). For CB particle–filled insulating polymer composite at lower than Φ*, the conductive CB network is constructed in the polymer matrix when the composite is maintained at a temperature higher than the glass‐transition temperature or the melting temperature of the polymer matrix. This phenomenon is called dynamic percolation and the time to reach the substantial decrease in resistivity is called percolation time (t_p). To investigate the relationship between the dynamic percolation process and the surface state of CB particles, we used three kinds of carbon black particles such as original carbon black (CB0) and fluorinated carbon black (FCB010 and FCB025)–filled poly(methyl methacrylate) (PMMA). It was observed that the dynamic percolation curves for CB0‐filled PMMA and FCB‐filled PMMA composites shifted to a shorter percolation time with increases in both the annealing temperature and the filler concentration. However, the dynamic percolation curves of FCB‐filled PMMA showed a gradually decreasing trend compared to that of CB0‐filled PMMA composites. The activation energy calculated from an Arrhenius plot of the t_p against the inverse of the annealing temperature was decreased by surface fluorine treatment. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1151–1155, 2003     

Gas sensitivity of carbon black/waterborne polyurethane composites

The synthesis of conductive composites consisting of waterborne polyurethane (WPU) and carbon black (CB) is reported. Besides the low percolation threshold (0.7-0.95 wt%), the composites are quite sensitive to organic solvent vapors regardless of their polarities as characterized by the drastic changes in conductivity. In the case of polar solvents, negative and positive vapor coefficient phenomena of the composites were successively observed with a rise in CB content. It was found that different mechanisms are responsible for the broad applicability of the composites as candidates for gas sensing materials owing to the different interactions among the matrix polymer, the filler particles and the solvent molecules.     

Electrical Response to Organic Vapor of Conductive Composites from Amorphous Polymer/Carbon Black Prepared by Polymerization Filling

In recent years, conductive polymer composites have found applications as gas sensors because of their sudden change in electric resistance of several orders of magnitude when the materials are exposed to certain solvent vapors. However, the composites having this function reported so far are mostly based on crystalline polymeric matrices, which factually sets a limit to materials selection. The present work prepares polystyrene/carbon black composites through polymerization filling and proves that the amorphous polymer composites can also serve as gas sensing materials. The composites' percolation threshold is much lower than that of the composites produced by dispersive mixing. In addition, high responsivity to some organic vapors coupled with sufficient reproducibility is acquired. The experimental data show that molecular weight and molecular weight distribution of the matrix polymer and conducting filler content exert great influence on the electrical response behavior of the composites. As a result, composites performance can be purposely tailored accordingly. Compared with the approaches of melt‐blending and solution‐blending, the current technique is characterized by many advantages, such as simplicity, low cost, and easy to be controlled.

Effect of different organic solvent vapors on the electric resistance of PS/CB composites (CB content = 10.35 vol.‐%).     

Poly(1,3‐butylene adipate) plasticized poly(lactic acid)/carbon black as electrical conductive polymer composites

Poly(1,3‐butylene adipate) (PBA) as the plasticizer for poly(lactic acid) (PLA) and carbon black (CB) as conductive filler, electrically conductive polymer composites (CPC) with different CB and PBA contents were prepared. Fourier transform infrared revealed that the interaction existed between PLA/PBA matrix and CB filler, and PBA could improve this interaction. The rheology showed that CB could obviously improve the apparent viscosity and decrease the fluidity of the composites, but just the reverse for PBA. PLA/PBA/CB composites exhibited the low electrical percolation thresholds of 0.516, 1.20, 2.46, and 2.74 vol% CB at 30, 20, 10, and 0 wt% PBA. The conductivity of the composite containing 3.98 vol% CB and 30 wt% PBA reached 1.67 S/cm. Scanning electron microscopy revealed that the addition of PBA facilitated the dispersion of PLA/CB composites. PBA could dramatically increase the elongation at break of plasticized PLA. But high‐PBA content caused the lowering of tensile strength. With the increasing of CB contents, the enforcement effect on the plasticized PLA became more obvious. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Partially miscible poly(lactic acid)‐ blend‐poly(propylene carbonate) filled with carbon black as conductive polymer composite

BACKGROUND: Conductive polymer composites (CPCs) can be obtained by filling polymer matrices with electrically conductive particles, and have a wide variety of potential applications. In the work reported, the biodegradable polymer poly(lactic acid) (PLA) as a partially miscible blend with poly(propylene carbonate) (PPC) was used as a polymer matrix. Carbon black (CB) was used as the conducting filler. RESULTS: Fourier transform infrared spectroscopy revealed interactions between matrix and CB filler; this interaction was stronger in PPC‐blend‐CB than in PLA‐blend‐CB composites. A rheology study showed that low‐viscosity PPC could improve the fluidity of the CPCs, but decrease that of CB. With increasing CB content, the enforcement effect, storage modulus and glass transition temperature increased, but the elongation at break decreased. CPCs exhibited the lowest electrical percolation thresholds of 1.39 vol.% CB when the content of PPC in PLA‐blend‐PPC was 40 wt%. The conductivity of CPCs containing 5.33 vol.% CB and 40 wt% PPC reached 1.57 S cm^?1. Scanning electron microscopy revealed that CB exhibits a preference for dispersion in the low‐viscosity phase (PPC) of the multiphase matrix. CONCLUSION: In the presence of CB, partially miscible PLA‐blend‐PPC could form multi‐percolation CPCs. Moreover, the combination of PLA and PPC with CB broadens novel application of both renewable polymers and CPCs. Copyright © 2008 Society of Chemical Industry     

VGCF填充PVDF/PMMA复合材料导电性能的研究

以气相生长碳纤维（VGCF）为导电填料,聚偏氟乙烯（PVDF）、聚甲基丙烯酸甲酯（PMMA）为基体制备复合型导电高分子材料。考察了填料用量、基体种类、配比以及PVDF结晶行为对复合材料导电性能的影响。结果表明,VGCF填充PMMA、PVDF、PVDF／PMMA（50／50）体系的渗滤阔值分别为5、4、3phr的填料用量。VGCF的加入会导致PVDF／PMMA体系发生微观相分离,而且VGCF会选择性富集在PVDF的非晶相中,所以PVDF／PMMA／VGCF体系的导电性呈现双重渗滤现象,该体系的体积电阻率不仅取决于富集相中VGCF的含量,而且还与PVDF相的连续性及其结晶行为密切相关。     

One pot synthesis of free standing highly conductive polymer nanocomposite films: Towards rapid BTX vapor sensor

In this work, we report the synthesis of robust, flexible, and free standing PMMA/NGP (nanographitic platlets) composite by one‐pot polymerization technique for sensing organic vapors. The synergy between the NGPs and PMMA matrix through strong interaction results in remarkable electrical and sensing properties of the composite system. The chemical structure and morphology of as‐prepared PMMA/NGP composites were investigated by using FTIR, XRD, and SEM techniques. The electrical conductivity of the prepared PMMA/NGP composites increases with increasing concentration of NGPs owing to the formation of conductive paths within the composite due to the quantum tunneling mechanism. The electrical conductivity of PMMA/NGP composites with different NGP concentration shows a percolation behavior with percolation threshold of ～1.2 wt%. The temperature dependent conductivity studies of the PMMA/NGPs were studied to understand the charge transport mechanism in the composite films by using Mott's Variable range hopping model. The PMMA/NGP composite have been evaluated for detection of benzene, toluene, and xylene vapors and were found to exhibit fast response, rapid recovery, and excellent repeatability. The sensitivity along with the flexibility of PMMA/NGP composite films opens up a new opportunity to fabricate the sensor in any shape as per the requirement of modern electronics. POLYM. ENG. SCI., 58:1074–1081, 2018. © 2017 Society of Plastics Engineers     

Effect of noncovalent chemical modification on the electrical conductivity and tensile properties of poly(methyl methacrylate)/carbon nanotube composites

Noncovalent chemical modification by initiated chemical vapor deposition technique is applied to carbon nanotubes (CNTs) to reduce average agglomerate size of the nanoparticles in the polymer matrix and to improve surface interaction between the composite constituents. CNT surfaces are coated conformally with thin poly(glycidyl methacrylate) (PGMA) polymer film and coated nanoparticles are incorporated in poly(methyl methacrylate) (PMMA) polymer matrix using solvent casting technique. Conformal PGMA coatings around individual nanotubes were identified by scanning electron microscopy analysis. Transmission electron microscopy and optical microscopy analyses show homogeneous composite morphology for composites prepared by using PGMA coated nanotubes. Fourier Transform Infrared and X‐ray photoelectron spectroscopy analyses show the successful deposition of polymer with high retention of epoxide functionality. PGMA coating of CNTs exhibits improvement in electrical conductivity and tensile properties of PGMA‐CNT/PMMA systems when compared with uncoated nanoparticles. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and characterization of genistein containing poly(ethylene glycol) microparticles

The purpose of this study was to prepare, characterize, and evaluate genistein‐containing microparticles with enhanced dissolution profile using poly(ethylene glycol) (PEG) as polymer matrix. Genistein loaded microparticles were prepared by a solvent evaporation process and their surface, thermal, chemical, and dissolution properties were analyzed by microscopy, differential scanning calorimetry, ATR‐FTIR spectroscopy, and USP dissolution apparatus II, respectively. The wettability index was also determined. Genistein exhibited an elongated crystal habit. However, the drug containing PEG microparticles were discrete and quasispherical. The ATR‐FTIR studies performed on the formulation suggested hydrogen bonding between the drug and the polymer matrix. Thermal analysis indicated a conversion of the crystalline form of the drug to an amorphous form. Genistein, exhibiting low solubility and high permeability, is a Class II drug of the Biopharmaceutical Classification Scheme. However, there was a ～9‐fold increase in the rate of dissolution of genistein in the case of all formulations as compared to native genistein. This study showed that genistein could be effectively encapsulated into PEG microparticles using an emulsion‐solvent evaporation technique, therefore avoiding the potential disadvantages of other solid dispersion techniques. This approach provided a significant enhancement in the drug dissolution profile. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2070–2078, 2006     

Morphology and electrical properties of carbon black/poly(ethylene terephthalate)/polypropylene composite

This work attempts to develop a carbon black (CB) filled conductive polymer composite based on poly(ethylene terephthalate) (PET) and polypropylene (PP). The process follows by localizing the CB particles in the minor phase (PET), and then the conductive masterbatch was elongated to form conductive microfibrils in PP matrix during melt extrusion process. After compression molding, a fine conductive three‐dimensional microfibrillar network is constructed. For comparison purpose, CB, PET, and PP are mixed using different pattern. The morphology and the volume resistivity of the obtained composites are evaluated. Electrical conductivity investigation shows that the percolation threshold and resistivity values are dependent on the CB concentration. The best morphological observation shows that the PET phases forms well‐defined microfibrils, and CB particles overwhelmingly localize in the surfaces of the PET microfibrils, which led to a very low percolation threshold, i.e., 4.5 phr, and a reasonable conductivity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Mass production of carbon nanotube reinforced poly(methyl methacrylate) nonwoven nanofiber mats

Forcespinning® technology was used to study large-scale production of conductive nonwoven nanofiber composite mats. Carboxyl functionalized multi-walled carbon nanotubes (CNT) were used to reinforce poly(methyl methacrylate) (PMMA). Composite nanofibers were developed with average diameters ranging from 370 nm to 800 nm depending on the selected processing parameters. It was found that the most influential processing parameters were viscosity of the solution and angular velocity used in the system. SEM revealed polymer wetted CNT aligned and oriented along the axis of the nanofibers. The mechanical and electrical properties of the composites were improved, compared to those of the pristine PMMA nanofibers. A 10 orders of magnitude drop in electrical resistivity and an electromagnetic shielding effectiveness of more than 20 db were obtained. Raman and Fourier transform infrared spectroscopy analyses indicated changes on the asymmetry of the polar bonds due to interactions between the CNTs and the matrix.     

In situ fast polymerization of graphene nanosheets‐filled poly(methyl methacrylate) nanocomposites

A series of graphene nanosheets‐filled poly(methyl methacrylate) nanocomposites (GNS/PMMA) is successfully prepared by an in situ fast polymerization method with graphene weight fractions from 0.1 to 2.0 wt %. In situ polymerization is effective in well dispersing of GNS in matrixes and suitable for both low and high content of GNS. The synthesis processes of polymer composites could be simplified and fast by using industrial grade graphene. The GNS fillers are found to disperse homogeneously in the PMMA matrix. The maximum electrical conductivity of the composites achieves 0.57 S m^?1, with an extremely low percolation threshold of 0.3 wt %. The electrical conductivities are further predicted by percolation theory and found to agree well with the experimental results. The results indicate that the microstructures, thermal, electrical, and mechanical properties of PMMA polymer are significantly improved by adding a low amount of graphene nanosheets. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43423.     

Electrical conductivity and electromagnetic interference shielding effectiveness of nano-structured carbon assisted poly(methyl methacrylate) nanocomposites

Nanostructured carbon-based polymeric nanocomposites are gaining research interest because of their cost-effectiveness, lightweight, and robust electromagnetic interference (EMI) shielding performance. Till now, it is a great challenge to design and fabricate highly scalable, cost-effective nanocomposites with superior EMI shielding performance. Herein, highly scalable EMI shielding material with tunable absorbing behaviors comprising of low-budget ketjen black (K-CB) reinforced poly(methyl methacrylate) (PMMA) nanocomposites have been prepared using simple solvent assisted solution mixing technique followed by hot compression technique. The morphological investigation revealed the homogeneous distribution of K-CB and strong interfacial interaction in PMMA matrix, which validated the strong reinforcement and other intriguing properties of the nanocomposites. The PMMA nanocomposites showed a low percolation threshold (2.79 wt%) and excellent electrical conductivity due to the formation of 3D conductive network like architecture within the polymer matrix. Specifically, the 10 wt% K-CB nanocomposite possessed a superior EMI shielding performance of about 28 dB for X-band frequency range. Further, a huge change in EMI shielding performance of PMMA nanocomposites is observed with varying thickness. The brand new K-CB decorated PMMA nanocomposites are expected to open the door for next-generation cost-effective EMI shielding materials for academic and industrial applications.     

Strain‐induced deformation mechanisms of polylactide plasticized with acrylated poly(ethylene glycol) obtained by reactive extrusion

This work aimed at identifying the tensile deformation mechanisms of an original grade of plasticized polylactide (pPLA) obtained by reactive extrusion. This material had a glass transition temperature of 32.6 °C and consisted of a polylactide (PLA) matrix grafted with poly(acryl‐poly(ethylene glycol)) (poly(Acryl‐PEG)) inclusions. pPLA behaved like a rubber‐toughened amorphous polymer at 20 °C, and its tensile behavior evolved toward a rubbery semicrystalline polymer with increasing temperature. The drawing of pPLA involved orientation of amorphous and crystalline chains, crystallization, and destruction of crystals. It was found that crystal formation and crystal destruction were in competition below 50 °C, resulting in a constant or slightly decreasing crystallinity with strain. Increasing temperature enhanced crystal formation and limited crystal destruction, resulting in an increased crystallinity with the strain level. Drawing yielded a transformation of the initial spherical poly(Acryl‐PEG) inclusions into ellipsoids oriented in the tensile direction. This mechanism may engender the formation of nanovoids within the inclusions due to a decreased density, assumed to be responsible for the whitening of the specimen. © 2015 Society of Chemical Industry     

Influence of wrapping on some properties of MWCNT–PMMA and MWCNT–PE composites

The melt processing technique was used to elaborate composites made with a polymer matrix [polymethylmethacrylate (PMMA) or polyethylene (PE)] and multiwall carbon nanotubes (MWCNT). Nanotubes were wrapped by amphiphilic block copolymer (PE–co-polyethylene oxide) in aqueous solution to facilitate the dispersion and the handling. Morphology and physical properties (thermal, mechanical, electrical, and rheological) of the resulting composites were investigated. The wrapping of MWCNT allowed a good dispersion of these nanoparticules in the polymer matrices. Physical properties such as thermal degradation, mechanical behavior, and conduction are improved. The use of wrapped MWCNT allows to reduce drastically the melt viscosity of the blends of crystalline PE composites whereas it is almost non efficient for amorphous PMMA ones.     

3D printing of copper particles and poly(methyl methacrylate) beads containing poly(lactic acid) composites for enhancing thermomechanical properties

Poly(lactic acid) (PLA) composite filaments with different copper (Cu) contents as high as 40 and 20 wt% of poly(methyl methacrylate) (PMMA) beads have been fabricated by twin-screw extruder for 3D printing. A fused-deposition modeling (FDM) 3D printing technology has been used to print the PLA composites containing hybrid fillers of Cu particles and PMMA beads. The morphology, mechanical, and thermal properties of the printed PLA composites were investigated. The tensile strength was slightly decreased, but storage modulus and thermal conductivity of PLA composites were significantly improved by adding Cu particles in the presence of PMMA beads. The PLA composites with hybrid fillers of 40 wt% of Cu particles and 20 wt% of PMMA beads resulted in thermal conductivity of 0.49 W m⁻¹ K⁻¹ which was three times higher than that of the bare PLA resin. The facilitation of the segregated network of high-thermally conductive Cu particles with the PMMA beads in PLA matrix provided thermally conductive pathways and resulted in a remarkable enhancement in thermal conductivity.