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Charles A Wilkie - One of the best experts on this subject based on the ideXlab platform.

  • preparation of graphene by pressurized oxidation and multiplex reduction and its polymer nanocomposites by masterbatch based Melt Blending
    Journal of Materials Chemistry, 2012
    Co-Authors: Chenlu Bao, Charles A Wilkie, Lei Song, Weiyi Xing, Bihe Yuan, Jianliu Huang, Yuqiang Guo
    Abstract:

    Graphene is prepared from graphite by pressurized oxidation and multiplex reduction. The pressurized oxidation is advantageous in easy operation and size-control, and the multiplex reduction, based on ammonia and hydrazine, produces single-atom-thick graphene (0.4–0.6 nm thick) which can be directly observed by atomic force microscopy. A masterbatch strategy, which is feasible in “soluble” thermoplastic polymers, is developed to disperse graphene into poly(lactic acid) by Melt Blending. The graphene is well dispersed and the obtained nanocomposites present markedly improved crystallinity, rate of crystallization, mechanical properties, electrical conductivity and fire resistance. The properties are dependent on the dispersion and loading content of graphene, showing percolation threshold at 0.08 wt%. Graphene reinforces the nanocomposites but cuts down the interactions among the polymer matrix, which leads to reduced mechanical properties. Competition of the reinforcing and the reducing causes inflexions around the percolation threshold. The roles of the heat barrier and mass barrier effects of graphene in the thermal degradation and combustion properties of the nanocomposites are discussed and clarified.

  • preparation and characterization of poly ethylene terephthalate clay nanocomposites by Melt Blending using thermally stable surfactants
    Polymers for Advanced Technologies, 2006
    Co-Authors: Marius C Costache, Evangelos Manias, Matthew Heidecker, Charles A Wilkie
    Abstract:

    Poly(ethylene terephthalate) (PET)/clay nanocomposites were prepared by Melt Blending and their morphologies and properties were investigated through X-ray diffraction, bright field transmission electron microscopy, thermogravimetric analysis and cone calorimetry. Three clays were comparatively studied—montmorillonite, hectorite and magadiite—all organically modified with thermally stable surfactants developed in this laboratory. Two such organic modifications were investigated, alkyl-quinolinium surfactants and vinylbenzyl-ammonium containing copolymers; both organic modifications combine high enough degradation temperature to allow for Melt processing with PET, and also favorable thermodynamics for nanocomposite formation with PET. All nanocomposites showed about the same value for the peak heat release rate (PHRR). The amount of char increases after nanocomposite formation and this could account for the PHRRs. Copyright © 2006 John Wiley & Sons, Ltd.

  • expandable graphite polyamide 6 nanocomposites
    Polymer Degradation and Stability, 2005
    Co-Authors: Fawn Marie Uhl, Hiroyoshi Nakajima, Evangelos Manias, Qiang Yao, Charles A Wilkie
    Abstract:

    Polyamide-6 (PA-6)/graphite nanocomposites were prepared by Melt Blending, using a variety of graphites, including virgin graphite, expandable graphites and expanded graphite. The resulting nanocomposites were characterized by X-ray diffraction, thermogravimetric analysis, cone calorimetry, and tensile mechanical analysis. Nanocomposite formation does occur, as denoted by the nanometre dispersion of graphite layers in the polymer matrix, and the dispersion depends on the graphite treatment. The material properties of the resulting composites are improved relative to the virgin/unfilled polymer; in particular, there is an enhancement of the thermal stability without any significant deterioration of the mechanical properties.

  • poly methyl methacrylate polypropylene and polyethylene nanocomposite formation by Melt Blending using novel polymerically modified clays
    Polymer Degradation and Stability, 2004
    Co-Authors: Shengpei Su, David D Jiang, Charles A Wilkie
    Abstract:

    Two new organically-modified clays that contain an oligomeric styrene or methacrylate have been prepared and used to produce nanocomposites of poly(methyl methacryate), polypropylene and polyethylene. Intercalated nanocomposites and, in some cases, exfoliated or mixed intercalated/exfoliated nanocomposites of all of these polymers have been produced by Melt Blending in a Brabender mixer. The use of the styrene-containing clay permits the direct Blending of the clay with polypropylene, without the usual need for maleation, to produce the nanocomposites. The systems have all been characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, cone calorimetry and the measurement of mechanical properties. These novel new clays open new opportunities for Melt Blending of polymers with clays to obtain nanocomposites with important properties.

  • preparation and flammability properties of polyethylene clay nanocomposites
    Polymer Degradation and Stability, 2003
    Co-Authors: Jinguo Zhang, Charles A Wilkie
    Abstract:

    Abstract Polyethylene (PE)–clay nanocomposites have been prepared using Melt Blending in a Brabrender mixer. X-ray diffraction and transmission electron microscopy were used to characterize the nano-structure of these composites while the thermal stability was evaluated from thermogravimetric analysis and the flammability parameters using cone calorimetry. It is found that the PE–clay nanocomposites have a mixed immiscible-intercalated structure and there is better intercalation when maleic anhydride is combined with the polymer and clay to be Melt blended. The reduction in peak heat release rate is 30–40%.

Qin Zhang - One of the best experts on this subject based on the ideXlab platform.

  • toward supertough and heat resistant stereocomplex type polylactide elastomer blends with impressive Melt stability via in situ formation of graft copolymer during one pot reactive Melt Blending
    Macromolecules, 2019
    Co-Authors: Shihao Deng, Hongwei Bai, Zhenwei Liu, Qin Zhang
    Abstract:

    Stereocomplexation of enantiomeric poly(l-lactide)/poly(d-lactide) (PLLA/PDLA) chains opens up a great opportunity toward sustainable PLA engineering plastic with exceptional heat resistance and durability. However, the processing and applications of stereocomplex-type PLA (SC-PLA) are significantly blocked by its inferior Melt stability (i.e., the weak Melt memory effect in triggering complete SC crystallization, which makes it hard to obtain exclusive formation of SC crystallites in Melt-processed products) and inherent brittleness. In this contribution, we demonstrate an unprecedented strategy to address these obstacles by one-pot reactive Melt Blending of the equimolar PLLA/PDLA blend with reactive poly(ethylene–methyl acrylate–glycidyl methacrylate) (E-MA-GMA) in the presence of catalyst, where both the stereocomplexation and the grafting of some PLLA/PDLA chains onto E-MA-GMA backbones take place simultaneously and competitively. Intriguingly, the E-MA-graft-PLA copolymer in situ formed can substant...

  • Toward Supertough and Heat-Resistant Stereocomplex-Type Polylactide/Elastomer Blends with Impressive Melt Stability via in Situ Formation of Graft Copolymer during One-Pot Reactive Melt Blending
    2019
    Co-Authors: Shihao Deng, Hongwei Bai, Zhenwei Liu, Qin Zhang
    Abstract:

    Stereocomplexation of enantiomeric poly­(l-lactide)/poly­(d-lactide) (PLLA/PDLA) chains opens up a great opportunity toward sustainable PLA engineering plastic with exceptional heat resistance and durability. However, the processing and applications of stereocomplex-type PLA (SC-PLA) are significantly blocked by its inferior Melt stability (i.e., the weak Melt memory effect in triggering complete SC crystallization, which makes it hard to obtain exclusive formation of SC crystallites in Melt-processed products) and inherent brittleness. In this contribution, we demonstrate an unprecedented strategy to address these obstacles by one-pot reactive Melt Blending of the equimolar PLLA/PDLA blend with reactive poly­(ethylene–methyl acrylate–glycidyl methacrylate) (E-MA-GMA) in the presence of catalyst, where both the stereocomplexation and the grafting of some PLLA/PDLA chains onto E-MA-GMA backbones take place simultaneously and competitively. Intriguingly, the E-MA-graft-PLA copolymer in situ formed can substantially improve the Melt stability of SC-PLA matrix as compatibilizer, and thus highly crystalline SC-PLA/E-MA-GMA blend products with exclusive SC crystallites can be readily obtained by injection molding. Moreover, some E-MA-graft-PLA can also strengthen the blend interface as interfacial enhancer, which gives rise to an increase in the toughening efficiency. As a result, the obtained SC-PLA/E-MA-GMA blends exhibits impressive heat resistance (the Vicat softening temperature and heat deflection temperature are as high as 201 and 174 °C, respectively) and impact toughness (the notched Izod impact strength is close to 65 kJ/m2). Notably, their comprehensive performance is superior to some commercial petroleum-derived engineering plastics. Overall, the one-pot syntheses of copolymer by in situ grafting could open up a new horizon for creating super-robust SC-PLA-based engineering plastic using industrial Melt-processing technologies

  • enhancing the Melt stability of polylactide stereocomplexes using a solid state cross linking strategy during a Melt Blending process
    Polymer Chemistry, 2014
    Co-Authors: Qin Zhang, Feng Chen, Hua Deng, Ke Wang, Qiang Fu
    Abstract:

    Stereocomplexation between poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) provides a feasible route for improving the performance of polylactide (PLA), including mechanical strength, thermal stability and hydrolysis resistance. In recent years, several effective methods have been developed to prepare polylactide stereocomplexes (sc-PLA) from commercially available, linear, high-molecular-weight PLLA and PDLA. However, it is still a big challenge to attain pure sc-PLA in the Melt-processed products because the prepared sc-PLA has a very poor Melt stability, that is the ability to trigger the reformulation of stereocomplex (sc) crystallites after complete Melting is significantly depressed, resulting in the formation of mixed homochiral (hc) and sc crystallites. Here we present a facile strategy to fabricate sc-PLA with good Melt stability by low-temperature (180 °C) Melt-Blending of equimolar PLLA and PDLA in the presence of a trace amount (0.1–0.5 wt%) of a cross-linker. During the Blending process, sc crystallites form rapidly, followed by a slight cross-linking of PLLA and PDLA chain couples in the mobile amorphous phase, whereas the chain couples in the crystalline phase hardly participate in the cross-linking reaction. The exclusive cross-linking of PLA chains in the amorphous phase not only allows for the introduction of abundant cross-linking points at the ends of the chain couples to prevent them from completely decoupling upon Melting but also retains large amounts of long crystallizable PLA segments existing in the initially formed sc crystallites to impart the resulting sc-PLA with an excellent recrystallization ability upon cooling. The formation or reformulation of sc crystallites in the continuous Melting and recrystallization process is found to be perfectly reversible, without any trace of hc crystallites.

Lisong Dong - One of the best experts on this subject based on the ideXlab platform.

  • improvement in toughness and crystallization of poly l lactic acid by Melt Blending with ethylene methyl acrylate glycidyl methacrylate terpolymer
    Polymer Engineering and Science, 2013
    Co-Authors: Xin Zhang, Changyu Han, Lijing Han, Chao Zhou, Mingyao Zhang, Lisong Dong
    Abstract:

    Melt Blending of poly(lactic acid) (PLA) and ethylene/methyl acrylate/glycidyl methacrylate terpolymer (EGA) containing relatively high-concentration epoxide groups (8 wt%) was performed to improve the toughness and crystallization of PLA. The results of nonisothermal and isothermal crystallization investigation showed that the addition of EGA accelerated the crystallization rate and increased the final crystallinity of PLA in the blends. Significant enhancement in toughness and flexibility of PLA were achieved by the incorporation of the EGA elastomer. When 20 wt% EGA added, the impact strength increased from 3.0 kJ m(-2) of neat PLA to 59.8 kJ m(-2) and the elongation at break increased from 4.9 to 232.0%. The failure mode changed from brittle fracture of neat PLA to ductile fracture of the blend. (c) 2013 Society of Plastics Engineers

  • improvement in toughness and crystallization of poly l lactic acid by Melt Blending with poly epichlorohydrin co ethylene oxide
    Polymer Engineering and Science, 2011
    Co-Authors: Kunyu Zhang, Xuemei Wang, Changyu Han, Lijing Han, Xianghai Ran, Xin Wen, Yugang Zhuang, Lisong Dong
    Abstract:

    Melt Blending of poly(lactic acid) (PLA) and poly(epichlorohydrin-co-ethylene oxide) copolymers (ECO) was performed to improve the toughness and crystallization of PLA. Thermal and scanning electron microscopy analysis indicated that PLA and ECO were not thermodynamically miscible but compatible to some extent. The addition of a small amount of ECO accelerated the crystallization rate and increased the final crystallinity of PLA in the blends. Significant enhancement in toughness and flexibility of PLA were achieved by the incorporation of the ECO elastomer. When 20 wt% ECO added, the impact strength increased from 5 kJ/m(2) of neat PLA to 63.9 kJ/m(2), and the elongation at break increased from 5% to above 160%. The failure mode changed from brittle fracture of neat PLA to ductile fracture of the blend. Rheological measurement showed that the Melt elasticity and viscosity of the blend increased with the concentration of ECO. POLYM. ENG. SCI., 51:2370-2380, 2011. (C) 2011 Society of Plastics Engineers

  • morphology crystallization and enzymatic hydrolysis of poly l lactide nucleated using layered metal phosphonates
    Polymer International, 2011
    Co-Authors: Shusheng Wang, Xuemei Wang, Junjia Bian, Lisong Dong
    Abstract:

    Poly(L-lactide) (PLLA) was prepared via Melt Blending and nucleated using three layered metal phosphonates, i.e. zinc phenylphosphonate (PPZn), calcium phenylphosphonate (PPCa) and barium phenylphosphonate (PPBa). The morphology, crystallization and enzymatic hydrolysis of PLLA nucleated using PPZn, PPCa and PPBa were investigated. The results of both wide-angle X-ray diffraction and transmission electron microscopy observations show that the layers of PPZn, PPCa or PPBa are barely exfoliated or intercalated by PLLA chains in the Melt-Blending process. PPZn, PPCa and PPBa serve as effective nucleating agents, accelerating both non-isothermal and isothermal crystallization and enzymatic hydrolysis of PLLA. An interesting aspect is that the nucleating ability of PLLA incorporating PPZn, PPCa and PPBa decreases in the order PPZn > PPCa > PPBa, whereas the enzymatic hydrolysis of PLLA incorporating PPZn, PPCa and PPBa decreases in the reverse order, which is due to the different dispersion and interfacial interactions of PPZn, PPCa and PPBa throughout the PLLA matrix. Copyright © 2010 Society of Chemical Industry

Liqun Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Environmentally Friendly Method To Prepare Thermo-Reversible, Self-Healable Biobased Elastomers by One-Step Melt Processing
    2019
    Co-Authors: Zhanbin Feng, Ming Tian, Hongchi Tian, Hongli Zuo, Nanying Ning, Liqun Zhang
    Abstract:

    Thermo-reversible elastomers (TRE) can be repeatedly processed and, thus, can reduce the dependence of the petroleum for synthetic rubber. The preparation of TRE is generally carried out in solution, and it requires a long reaction time. These disadvantages limit the large scale preparation of TRE. In the present work, we chose the epoxidized natural rubber (ENR) as the matrix and designed a new method to prepare thermo-reversible, self-healable ENR by a catalyzed ring-opening (RO) reaction of ENR followed by a Diels–Alder (DA) reaction through one-step Melt Blending for the first time. Furfurylamine (FA) was first grafted onto ENR (ENR–FA) by an RO reaction under the presence of catalyzer, and then bismaleimide (BMI) was added to induce the cross-linking of ENR–FA via DA reaction, which can be easily realized during Melt Blending. As the DA reaction is reversible at different temperatures, the mechanical properties of thermo-reversible ENR (TRENR) could be tailored by the ratio of FA to BMI. The TRENR is recyclable twice by compression molding, while retaining 90% of its mechanical properties after the first recycling. In addition, the as-prepared TRENR exhibits self-healing ability. The preparation of TRENR was carried out in a Haake rheomixer batch mixer with a short reaction time, and it requires no solvent and does not produce a stimulating smell. This new technique is promising in industry for rubber recycling and large-scale preparation of TRE in an environmentally friendly method

  • microstructure and properties of highly filled rubber clay nanocomposites prepared by Melt Blending
    Composites Science and Technology, 2007
    Co-Authors: Ming Tian, Liqun Zhang, Yiuwing Mai
    Abstract:

    A series of highly filled rubber/clay nanocomposites (RCNs) based on ethylene-propylene diene rubber (EPDM), styrene butadiene rubber (SBR) and epichlorohydrin rubber (ECO) were prepared by Melt Blending with traditional rubber processing technique. Wide-angle X-ray diffraction (WAXD) characterization shows that the highly filled RCNs (up to ∼60 wt%) have intercalated silicate structures. TEM observations reveal that the dispersion homogeneity of clay layers improves with increasing content of organically modified clay (OMC). It was shown by dynamic mechanical thermal analysis (DMTA) for the first time that the Melt-like thermal transition of alkyl chains of the surfactant of OMC still occurs in the intercalated OMC. Addition of large amount OMC to rubber greatly improves the modulus of material. Highly filled RCNs also possess outstanding gas barrier properties when compared to neat rubbers.

  • characterization of citric acid glycerol co plasticized thermoplastic starch prepared by Melt Blending
    Carbohydrate Polymers, 2007
    Co-Authors: Zizheng Zhang, Liqun Zhang, Dafu Chen, Wei Tian
    Abstract:

    Abstract A novel citric acid (CA)–glycerol co-plasticized thermoplastic starch (CGTPS) was prepared by Melt Blending. The CA content varies from 10% to 40 wt%. Result from Fourier Transform Infrared spectroscopy (FTIR) show that partial esterification occurred during Blending. The degrees of substitution and esterification increased as the CA content increased. Results from intrinsic viscosity measurement, laser light scattering (LLS), and FTIR demonstrate the molecular weight of starch decreased as the CA percentage increased. The weight average molecular weight ( M w ) of CGTPS with 20 wt% CA was only one-tenth of that without CA under the same processing conditions. Crystal type and crystallinity changes as a function of CA were recorded by X-ray diffraction (XRD). Thermal stability and the glass transition temperature ( T g ) were detected by thermogravimetric (TG) and differential scanning calorimeter (DSC). Compared to the traditional GTPS, the novel CGTPS exhibits the special characters of partial esterification, low molecular weight and stronger interaction between starch and plasticizers. These new properties can be expected to prevent retrogradation, promote compatibility with polyesters, improve the processing ability, and adjust the degradation properties.

  • crystallization and morphology study of polyhedral oligomeric silsesquioxane poss polysiloxane elastomer composites prepared by Melt Blending
    Polymer, 2007
    Co-Authors: Ling Liu, Ming Tian, Liqun Zhang, Wei Zhang, James E Mark
    Abstract:

    Abstract Composites of poly(methylvinylsiloxane) (“silicone”) elastomers with polyhedral oligomeric silsesquioxane (POSS) were prepared by Melt Blending. One goal was to establish conditions that would lead to morphologies different from that of a simple filler dispersed in a polymer matrix for the purposes of reinforcement. To this end, the study focused on the dispersion and state of POSS in silicone rubber blends as determined by X-ray diffraction (XRD), polarizing optical microscopy (POM), scanning electron microscopy (SEM), and analysis using a rubber processing analyzer (RPA). Of particular interest were the thermal stability of POSS macromers, and the effects of mixing temperature and subsequent vulcanization of the polysiloxane. The results showed that highly crystalline POSS macromers could undergo condensation reactions at 230 °C in air, leading to partially amorphous structures. Also, POSS crystals apparently dissolved in the polysiloxane at high temperatures and POSS crystals with hexahedral or flake-like structures recrystallized out upon cooling. Both crystallites and POSS molecules co-existed in these blends, with the amount of dispersed molecular POSS being increased at higher temperatures. The POSS molecules exhibited some physical interactions with the polysiloxane uncross-linked chains, but phase separation was induced by the process of cross-linking. In this curing process, POSS molecules could react with the polysiloxane, resulting in decreases in cross-link density. The original POSS crystals could also be dissolved in the polysiloxane during the initial curing stages, but recrystallization upon cooling gave regenerated crystals that were roughly spherical.

  • effects of characteristics of rubber mixing and vulcanization on the structure and properties of rubber clay nanocomposites by Melt Blending
    Macromolecular Materials and Engineering, 2004
    Co-Authors: Yiqing Wang, Liqun Zhang
    Abstract:

    Summary: Three rubber-based nanocomposites, natural rubber (NR), styrene-butadiene rubber (SBR), and ethylene-propylene-diene rubber (EPDM) matrixes, were prepared with octadecylamine modified fluorohectorite (OC) by Melt Blending. X-ray diffraction (XRD) revealed that the SBR/OC and EPDM/OC nanocomposites exhibited a well-ordered intercalated structure and a disordered intercalated structure, respectively. In the case of the NR/OC nanocomposite, it exhibited an intermediate intercalated and even exfoliated structure. These results were in good agreement with transmission electron microscopy (TEM) observations. Furthermore, in the NR/OC and SBR/OC systems, the mixing process played a predominant role in the formation of nanometer-scale dispersion structure, whereas the intercalated structure of EPDM/OC formed mainly during the vulcanization process. The tensile strength of SBR/OC and EPDM/OC nanocomposites loading 10 phr OC was 4–5 times higher than the value obtained for the corresponding pure rubber vulcanizate, which could be ascribed to the slippage of the rubber molecules and the orientation of the intercalated OC. For the strain-induced crystallization NR, the exfoliated OC efficiently improved the modulus of the NR/OC nanocomposite relative to the pure NR. However, its hindrance on NR crystallization during the tensile process may be the main reason for the decrease in tensile strength of NR/OC. XRD diffraction patterns of three nanocomposites containing 10 phr organoclay.

Philippe Dubois - One of the best experts on this subject based on the ideXlab platform.

  • polylactide cellulose nanocrystal nanocomposites efficient routes for nanofiber modification and effects of nanofiber chemistry on pla reinforcement
    Polymer, 2015
    Co-Authors: Youssef Habibi, Philippe Leclere, Jean-marie Raquez, Stephen Spinella, John R Dorgan, Giada Lo Re, Philippe Dubois, Richard A. Gross
    Abstract:

    Abstract To improve the Heat Deflection Temperature of polylactide (PLA), nanocomposites were prepared with modified cellulose nanocrystals (CNCs) by Melt Blending. The preparation of acetate and lactate modified CNCs (AA- and LA-CNCs) was performed by a green one-pot dual acid (organic acid and HCl) method such that acid hydrolysis and Fischer Esterification occur in tandem. The degree of substitution for AA-CNCs and LA-CNCs, determined by FTIR, are 0.12 and 0.13, respectively. Relative to unmodified CNCs, esterification of CNC surfaces with lactate and acetate moieties resulted in a 40 °C increase in thermal stability. At 5 wt% loading of CNCs, LA-CNCs gave superior reinforcement below and above the glass temperature of PLA, corresponding to a 31% and 450% increase in PLA's storage modulus compared to neat PLA. An increase in PLA's heat deflection temperature by 10 °C and 20 °C was achieved by Melt-Blending PLA with 5 and 20% LA-CNCs, respectively. The above studies provide indirect evidence that LA-CNCs were best dispersed (lowest tendency to aggregate) in the PLA matrix. This hypothesis was confirmed through direct visualization using AFM. Thus, a simple modification strategy for CNCs was devised that enables the formation of PLA nanocomposites with high extents of nanofiber dispersion within the matrix. Furthermore, the dispersion of CNCs in PLA matrices is profoundly influenced by relatively small changes in the modification chemistry, in this case, appending lactate vs. acetate groups.

  • structure transport property relationships within nanoclay filled polyurethane materials using polycaprolactone based masterbatches
    Composites Science and Technology, 2014
    Co-Authors: Samira Benali, Giuliana Gorrasi, Leila Bonnaud, Philippe Dubois
    Abstract:

    Abstract The lamellar structure of montmorillonite (MMT) clays exhibits an interesting potential to improve the barrier properties of thermoplastic polyurethanes (TPU). However direct Melt Blending of an ester-based TPU and functional organoclays, despite showing good filler dispersion, did not allowed for improving neither barrier properties (i.e., sorption and diffusion to water vapor) not mechanical performances with respect to the unfilled TPU. Therefore, two alternative strategies involving poly(e-caprolactone) (PCL)/organoclay masterbatches were explored to investigate the possibility to prepare materials with improved mechanical and barrier properties. In the first strategy, a PCL/organoclay masterbatch with high inorganic content was obtained by Melt-Blending (coined “free PCL” masterbatch), whereas in the second strategy PCL-grafted organoclay nanohybrids, also with high inorganic content were synthesized by in situ intercalative grafting/ring-opening polymerization of e-caprolactone (CL). Purposely, ROP of CL was initiated from hydroxyl groups available onto the MMT surface actually organo-modified by alkylammonium cations bearing hydroxyl functions (coined “nanohybrid PCL” masterbatch). These highly-filled PCL masterbatches (with ca. 25 wt% in inorganics) were then added into the ester-based TPU to prepare nanoclay/polyurethane nanocomposites by Melt-Blending. The morphology and dispersion of the resulting materials were characterized by X-ray diffraction and transmission electron microscopy. Improved sorption and diffusion properties towards water vapor as well as mechanical properties were measured. Herein, these results are discussed as a function of both clay dispersion and matrix/organoclay interaction.

  • supported coordination polymerization a unique way to potent polyolefin carbon nanotube nanocomposites
    Chemical Communications, 2005
    Co-Authors: Daniel Bonduel, Michael Mainil, Michael Alexandre, Fabien Monteverde, Philippe Dubois
    Abstract:

    Homogeneous surface coating of long carbon nanotubes is achieved by in situ polymerization of ethylene as catalyzed directly from the nanotube surface-treated by a highly active metallocene-based complex and allows for the break-up of the native nanotube bundles leading, upon further Melt Blending with HDPE, to high-performance polyolefinic nanocomposites.

  • vapor barrier properties of polycaprolactone montmorillonite nanocomposites effect of clay dispersion
    Polymer, 2003
    Co-Authors: Giuliana Gorrasi, Michael Alexandre, Mariarosaria Tortora, Vittoria Vittoria, Eric Pollet, Benedicte Lepoittevin, Philippe Dubois
    Abstract:

    Different compositions of poly(e-caprolactone) (PCL) and (organo-modified) montmorillonite were prepared by Melt Blending or catalyzed ring opening polymerization of e-caprolactone. Microphase composites were obtained by direct Melt Blending of PCL and sodium montmorillonite (MMT-Na+). Exfoliated nanocomposites were obtained by in situ ring opening polymerization of e-caprolactone with an organo-modified montmorillonite (MMT-(OH)2) by using dibutyltin dimethoxide as an initiator/catalyst. Intercalated nanocomposites were formed either by Melt Blending with organo-modified montmorillonite or in situ polymerization within sodium montmorillonite. The barrier properties were studied for water vapor and dichloromethane as an organic solvent. The sorption (S) and the zero concentration diffusion coefficient (D0) were evaluated for both vapors. The water sorption increases with increasing the MMT content, particularly for the microcomposites containing the unmodified MMT-Na+. The thermodynamic diffusion parameters, D0, were compared to the value of the parent PCL: both microcomposites and intercalated nanocomposites show diffusion parameters very near to PCL. At variance exfoliated nanocomposites show much lower values, even for small montmorillonite content. In the case of the organic vapor, the value of sorption at low relative pressure is mainly dominated by the amorphous fraction present in the samples, not showing any preferential adsorption on the inorganic component. At high relative pressure the isotherms showed an exponential increase of sorption, due to plasticization of the polyester matrix. The D0 parameters were also compared to those of the unfilled PCL; in this case, both the exfoliated and the intercalated samples showed lower values, due to a more tortuous path for the penetrant molecules.

  • polymer layered silicate nanocomposites by combined intercalative polymerization and Melt intercalation a masterbatch process
    Polymer, 2003
    Co-Authors: Benedicte Lepoittevin, Michael Alexandre, Nadege Pantoustier, Myriam Devalckenaere, Cedric Calberg, Robert Jerome, Catherine Henrist, A Rulmont, Philippe Dubois
    Abstract:

    Abstract Poly(e-caprolactone) (PCL) and poly(vinyl chloride) (PVC) layered silicate nanocomposites were prepared by combination of intercalative polymerization and Melt intercalation. In a first step, high clay content PCL nanocomposites were prepared by in situ polymerization of e-caprolactone intercalated between selected organo-modified silicate layers. The polymerization was catalyzed with dibutyltin dimethoxide in the presence of montmorillonites, the surface of which were previously exchanged with (functionalized) long alkyl chains ammonium cations. Then, these highly filled PCL nanocomposites were added as masterbatches in commercial PCL and PVC by Melt Blending. The intercalation of PCL chains within the silicate layers by in situ polymerization proved to be very efficient, leading to the formation of intercalated and/or exfoliated structures depending on the organo-clay. These masterbatches were readily dispersed into the molten PCL and PVC matrices yielding intercalated/exfoliated layered silicate nanocomposites which could not be obtained by Melt Blending the matrix directly with the same organo-modified clays. The formation of nanocomposites was assessed both by X-ray diffraction and transmission electronic microscopy. Interestingly, this so-called ‘masterbatch’ two-step process allowed for preparing PCL nanocomposites even with non-modified natural clay, i.e. sodium montmorillonite, which showed a material stiffness much higher than the corresponding microcomposites recovered by direct Melt intercalation. The thermal stability of PCL nanocomposites as a function of clay content was investigated by thermogravimetry (TGA).